Homo and heterometallic assemblies from lewis acidic and basic metallic precursors 3

Chapter Three Preparation of Dinuclear Complexes from Mononuclear Pincer [PCP] Pd(II) Complexes 90 Chapter Three: Preparation of Dinuclear Complexes from Mononuclear PCP Pincer Pd(II) Complexes Chapter Three Preparation of Dinuclear Complexes from Mononuclear Pincer [PCP] Pd(II) Complexes 3.1 Introduction It was mentioned in Chapter One that the pincer [PCP] complexes may serve as useful precursors to dinuclear complexes (Section 1.2). The dinuclear species were detected in the ESI-MS studies. One of these species viz. 2.18 was isolated and characterised. The results have been discussed in Chapter Two. In this chapter, the results on the synthesis of dinuclear complexes from complex 2.16a and other mononuclear complexes will be presented. The structures of the dinuclear complexes in both solution and solid states will be discussed. 3.2 Results and Discussion 3.2.1 Synthesis and Characterisation of the Ligand-bridged Complexes of Dppf and 4,4’-Bipyridine The triflato complex 2.16a readily reacted with neutral bidentate ligands to give the cationic dinuclear ligand bridged complexes [{Pd(PCP)}2(µ-L)][OTf]2 (L = dppf, 3.1a; 4,4’-bpy, 3.3b) (Scheme 3-1). Both complexes were characterised by NMR, elemental analysis and single-crystal X–ray diffraction. 91 Chapter Three: Preparation of Dinuclear Complexes from Mononuclear PCP Pincer Pd(II) Complexes PPh2 Ph2P PPh2 L = 4,4'-bpy, dppf Pd OTf Pd r.t L Pd 2+ OTf PPh2 Ph2P PPh2 L = dppf 3.1a; 4,4'-bpy 3.1b 2.16a Scheme 3-1: Preparation of the dinuclear complexes 3.1a and 3.1b from complex 2.16a. The 1H NMR spectrum of complex 3.1a showed that the protons of the Cp rings in the dppf ligand were upfield shifted (2.85 ppm and 3.00 ppm) compared to free dppf ligand (4.00 ppm and 4.25 ppm). The Cp protons are chemically shielded due to the ring current effect, imposed by the phenyl rings of both the bridging and chelating phosphines (Figure 3-1). The NMR data suggest close proximity of the phenyl rings and the Cp rings. Hβ PbPh2 Pd Hα Hβ Pa Hα Fe Pb Hα Pb Hα Hβ Pa Pd Ph2Pb Hβ Figure 3-1: An illustration of the ring current effect in complex 3.1a. (Pa refers to Pdppf; Pb refers to Ppincer). 31 P{1H} NMR analysis of complexes 3.1a and 3.2b gave a downfield shift of the chelating phosphines [δP(pincer) = 55.1 ppm (3.1a) and 49.8 ppm (3.1b)] 92 Chapter Three: Preparation of Dinuclear Complexes from Mononuclear PCP Pincer Pd(II) Complexes compared to 44.8 ppm in 2.16a. The downfield 31P signals suggests deshielding of Ppincer upon replacement of the triflato ligand by dppf and 4,4’-bipyridine. The 31 P{1H} spectrum of complex 3.1a showed two signals, consistent with the chemically inequivalent phosphines that are strongly coupled to each other [δP(dppf) = 6.6 ppm (t); δP(pincer) = 55.1 ppm (d)] (Figure 3-2). The 2JP-P is 44 Hz. This value is comparable to that of [Pd(Me)(PMe3)3][hfac] (hfac = hexafluoroacetylacetonate) (2JP-P = 43 Hz).127 In comparison to the known dppfbridged complexes [{(dppf)PdCl}2(µ-dppf)][ClO4 ]2 (δP(dppf) = 26.8 ppm)128 and [Pd2(C2,N-dmpa)2(µ-dppf)Cl2] (dmpa =N,N–dimethyl-1-phenethylamine) (δP(dppf) = 32.7 ppm),129 the observed chemical shift of the bridging dppf appears to be more shielded. A singlet peak 49.8 ppm was observed in the 31 P{1H} NMR spectrum of complex 3.1b is consistent with the presence of chemically equivalent phosphines in complex 3.1b. Pb = 55.1 ppm 2+ PbPh2 Ph2 Pd Pa Fe PbPh2 Ph2Pb Ph2 Pa Pd Pa = 6.6 ppm Ph2Pb 50 40 30 20 10 (ppm) Figure 3-2: 31P{1H} NMR spectrum of complex 3.1a in CDCl3. (Pa refers to Pdppf; Pb refers to Ppincer). 93 Chapter Three: Preparation of Dinuclear Complexes from Mononuclear PCP Pincer Pd(II) Complexes Moreover, the signal of the metallated carbon was observed in the 13C{1H} NMR spectrum of complex 3.1a at 79.3 ppm (dt). It is strongly coupled to the dppf ligand at the trans position (2JC-P(dppf) = 28 Hz) and is weakly coupled to the phosphines of the pincer ligand (2JC-P( pincer) = Hz) cis to it. The signal of the metallated carbon of complex 3.1b was observed at 60.2 ppm as a broad singlet peak. A 31P{1H} NMR study suggested that complexes 3.1a and 3.1b are stable in non-coordinating solvent (CDCl3) for two weeks. However, the complexes underwent dissociation in CD3CN. The 31 P{1H} NMR spectrum of complex 3.1a recorded in CD3CN gave a singlet at 51.3 ppm together with two small peaks at 49.5 ppm (s) and 55.1 ppm (s). The singlet at 51.3 ppm were assigned to the CD3CN-coordinated species [Pd(CD3CN)(PCP)][OTf] 3.2, this assignment was confirmed by comparing the 31 P{1H} NMR spectrum of complex 2.16a recorded in CD3CN. Observation of a clean 31 P{1H} NMR spectrum of complex 2.16a in CD3CN suggested a facile substitution of the triflato ligand by CD3CN. The small peaks of the spectrum have not been identified. A signal that is close the free dppf ligand (δP = -18.0 ppm) was also observed in the NMR spectrum of complex 3.1a, possibly due to the dangling phosphine of the monocationic species [Pd(PCP)(dppf)][OTf] 3.3 (Figure 3-3). This species was observed in the earlier ESI-MS study (See Section 2.2.2). The CH3CN-coordinated complexes of Pd(II) have been widely used as precursors to Pd(II) phosphine complexes.119 The reverse ligand displacement of a phosphine by an CH3CN ligand as in the case of complex 3.1a is not common. The ease of such displacement is likely due to the combination of several factors. 94 Chapter Three: Preparation of Dinuclear Complexes from Mononuclear PCP Pincer Pd(II) Complexes These factors include the lack of chelating effect from the bridging dppf ligand that is important in stabilising complex 3.1a, the high trans-effect of the metallated carbon causing the dppf ligand to become labile, and the steric crowding of the phenyl rings of both dppf and pincer moiety that helps in pushing the dppf ligand out from the pincer moiety. The trans-effect can be associated with the trans-influence, as suggested by the NMR and crystallographic data (an upfield 31 P signal of the bridging dppf ligand and a long Pd-C bond). The steric crowding between the dppf ligand and the pincer moiety are indicated by the upfield shift of the Cp protons and the highly distorted square-planar coordination geometry around the Pd(II) centre. 3.1a (Pb) PPh2 Pd NCCD3 OTf PPh2 3.1a (Pa) 3.2 PPh2 Pd Ph2 P PPh2 Fe OTf PPh2 3.3 * * 50 40 30 20 10 -10 -20 (ppm) Figure 3-3: 31P{1H} NMR spectrum of complex 3.1a in CD3CN. (* = unknown; Pa refers to Pdppf, Pb refers to Ppincer). 95 Chapter Three: Preparation of Dinuclear Complexes from Mononuclear PCP Pincer Pd(II) Complexes In the case of complex 3.1b, the above mentioned singlet peak at 51.3 ppm was observed as the main peak together with two small peaks at 49.5 ppm (s) and 55.5 ppm (s) when CD3CN was used as solvent. The 31 P{1H} NMR spectrum suggested a facile substitution of the 4,4’-bipyridine ligand by an CD3CN ligand. This result is however contradictory to the previous ESI-MS study. Although the molecular ion was not observed in the ESI mass spectrum, the monocationic species [Pd(PCP)(4,4’-bpy)]+ was detected (See Section 2.2.2). 3.2.2 Crystal Structures of Complexes 3.1a and 3.2b The crystal structure of complex 3.1a shows that the pincer moieties are bridged by a dppf ligand (Figure 3-4). The ferrocenyl moiety is surrounded by the phenyl rings of the P atoms in both dppf and the pincer ligands. This observation is in agreement with the upfield Cp protons shift in the 1H NMR spectrum of complex 3.1a. Lengthening of the Pd-C bond was observed from 2.071(2) Å in 2.16a to an average of 2.126(7) Å in 3.1a upon replacement of the triflato ligand by dppf indicating weakening of that bond. The Pd-P bonds trans to the metallated carbon [average bond length = 2.369(2) Å] are longer than those cis to the metallated carbon [average bond lengths = 2.313(2) Å]. This is due to the transinfluence of the metallated carbon and the steric crowding between the pincer moieties and the dppf ligand. The trans-influence and the steric effect also cause distortion of the coordination geometry around the two Pd(II) atoms. This can be seen from the C-Pd-Pdppf [C(1)– Pd(1)– P(5) = 166.9(2)°; C(6)-Pd(2)-P(6) = 167.9(2)°] and the P-Pd-P angles [P(1)-Pd(1)-P(2) = 159.7(7)° ; P(3) –Pd(2) – P(4) = 159.3(8)°] which are highly deviate from 180º, much more so than its 96 Chapter Three: Preparation of Dinuclear Complexes from Mononuclear PCP Pincer Pd(II) Complexes precursor complex 3.1a (L = OOTf) [C – Pd – O = 171.7(9)°; Ppincer-Pd- Ppincer = 166.2(2)°]. Figure 3-4: An ORTEP plot of complex 3.1a with 50% thermal ellipsoids. The OTf anions are omitted for clarity. Selected bond lengths (Å) and angles (º): Pd(1)-P(1) = 2.322(2), Pd(1)-P(2) = 2.317(2), Pd(2)-P(3) = 2.313(2), Pd(2)-P(4) = 2.303(2), Pd(1)-P(5) = 2.376(2), P(2)-P(6) = 2.363(2), Pd(1)-C(1) = 2.122(6), Pd(2)-C(6) = 2.130(7), C(1)-C(2) = 1.507(1), C(1)-C(4) = 1.526(9), C(6)-C(7) = 1.478(1), C(6)-C(9) = 1.533(1); C(1)Pd(1)-P(5) = 166.9(2), C(6)-Pd(2)-P(6) = 167.9(2), P(1)-Pd(1)-P(2) = 159.7(7), P(3)Pd(2)-P(4) = 159.3(8), P(1)-Pd(1)-C(1) = 81.2(2), P(2)-Pd(1)-C(1) = 80.9(2), P(3)-Pd(2)C(6) = 80.7(3), P(4)-Pd(2)-C(6) = 81.7(2), P(1)-Pd(1)-P(5) = 99.1(6), P(2)-Pd(1)-P(5) = 100.5(7), P(3)-Pd(2)-P(6) = 99.2(7), P(4)-Pd(2)-P(6) = 100.3(8), Pd(1)-C(1)-C(2) = 115.3(5), Pd(1)-C(1)-C(4) = 116.8(5), Pd(2)-C(6)-C(7) = 115.7(6), Pd(2)-C(6)-C(9) = 113.9(5), Pd(1)-P(5)-C(11) = 116.5(2), Pd(2)-P(6)-C(16) = 118.3(2). The crystal structure of complex 3.1b shows a dinuclear framework with a bipyridyl ligand bridging across the two square-planar Pd(II) pincers, as shown in Figure 3-5. The angle between the coordination plane and the pyridyl ring deviates significantly from 90º [P(1)-Pd(1)-P(2)-C(1)-N(1)/N(1)-C(6)-C(7)-C(8)C(9)-C(10) = 80.4º]. This value is smaller than those angles observed for the related square-planar d8 complexes [(Pt(pip2NCN))2(μ-L)]2+ (pip2NCN- = 1,397 Chapter Three: Preparation of Dinuclear Complexes from Mononuclear PCP Pincer Pd(II) Complexes bis(piperidylmethyl)phenyl; L = 4,4’-bipyridine, pyrazine or trans-1,2-bis(4pyridyl)ethylene) where the dihedral angles between the Pt(II) coordination planes and the pyridyl rings are in the range of 83.3º to 89.9˚.12b,12c The Pd-C bond length in 3.1b [Pd(1)-C(1) = 2.088(4) Å] is intermediate between that of the complex 2.1 [Pd(1)-C(1) = 2.111(7) Å] and 2.16a [Pd-C = 2.071(2) Å]. The Pd-N bond [Pd(1)-N(1) = 2.187(4) Å] in complex 3.1b is longer than those Pd-N(pyridyl) bonds in the metallomacrocyclic compounds [{Pd(dppm)(μ-L)}2][OTf]4 (dppm = bis(diphenylphosphino)methane; L = NC5H43-CH2NHCOCONHCH2-3-C5H4N or N,N’- bis(pyridine-4-yl)-pyridine-2,6- dicarboxamide) and the polymeric complex [{Pd(dppp)(μ-L)}x][OTf]2x (dppp = 1,3-bis(diphenylphosphino)propane ; L = N,N’- bis(pyridine-4-yl)-isophthalamide) where their Pd-N bond lengths fall in between 2.095(4) Å and 2.114(5) Å.130 The lengthening of Pd-N bond suggests a high trans-influence of the metallated carbon in 3.1b. 98 Chapter Three: Preparation of Dinuclear Complexes from Mononuclear PCP Pincer Pd(II) Complexes Figure 3-5: An ORTEP plot of complex 3.1b with 50% thermal ellipsoids. The OTf anions and (CH3)2CO molecule are omitted for clarity. Selected bond lengths (Å) and angles (º): Pd(1)-P(1) = 2.324(1), Pd(1)-P(2) = 2.317(1), Pd(1)-N(1) = 2.187(4), Pd(1)C(1) = 2.088(4), C(1)-C(2) = 1.499(7), C(1)-C(4) = 1.492(7), C(2)-C(3) = 1.453(8), C(4)C(5) = 1.486(8), C(8)-C(8)#1 = 1.511(8); P(1)-Pd(1)-P(2) = 164,4(5), P(1)-Pd(1)-N(1) = 99.0(1), P(2)-Pd(1)-N(1) = 96.4(1), P(1)-Pd(1)-C(1) = 82.5(1), P(2)-Pd(1)-C(1) = 82.0(1), N(1)-Pd(1)-C(1) = 176.8(2), Pd(1)-C(1)-C(2) = 113.8(3), Pd(1)-C(1)-C(4) = 113.2(3), C(2)-C(1)-C(4) = 115.2(5). Dihedral angle (º): P(1)-Pd(1)-P(2)-C(1)-N(1)/N(1)-C(6)C(7)-C(8)-C(9)-C(10) = 80.4. 3.2.3 Synthesis and Characterisation of the Pincer [PCP] Pd(II) 4-Pyridinethiolato Complexes The pyridinethiolato complexes have been reported as good building blocks to homo-,131 hetero-132 and mixed-valent133 complexes. Therefore, it would be interesting to find out whether the dinuclear complexes containing a pincer moiety and linked by a pyridinethiolato ligand could be prepared. ESI-MS studies of complex 2.1 with the pyridinethiolato complexes of Au(I), Hg(II) and Pt(II) 99 Chapter Three: Preparation of Dinuclear Complexes from Mononuclear PCP Pincer Pd(II) Complexes F:\nke150506\nke2\Pd2Spy 5/16/2006 10:44:29 AM dissolved in acetone, CT 150, CV20, TLO 15, MeOH/H2O (80:20) pd2Spy - + – Cl Pd2Spy #1 [2.1 RT: 0.02 AV:]1 NL: 4.60E7 T: + c Full ms [ 50.00-2000.00] 545.20 100 Pd + S PPh PPh2 Pd + PPh2 S Ph2 P N PPh2 Pd 90 Ph 2P N H 80 656.01 70 R e la ti v e A b u n d a n c e [3.5 - PF6- ]+ [3.4 + H+ ]+ 60 1199.98 50 40 585.66 30 20 10 779.87 833.57 423.32 400 600 800 1027.88 1166.72 1000 m/z 1200 1278.74 1409.80 1531.86 1400 Figure 3-8: Positive-ion ESI mass spectrum of 3.5, with CH3OH/H2O (80:20) as solvent. The crystal structure of 3.5 shows that the two pincer Pd(II) fragments are bridged by a pyridinethiolato ligand (Figure 3-9). The bent 4-pyridinethiolato ligand [Pd(1)-S(1)-C(13) = 104.1(1)°] allows coordination of the two bulky pincer moieties. This is illustrated in the molecular view along the C-Pd-S axis (Figure 39, bottom). The C-Pd-L [C(1)-Pd(1)-S(1) = 175.5(8)°; C(6)-Pd(2)-N(1) = 176.1(1)°] and Ppincer-Pd-Ppincer angles [P(1)-Pd(1)-P(2) = 163.4(3)°; P(3)-Pd(2)P(4) = 165.4(3)°] fall in the range of C-Pd-L [171.1(3)°- 177.4(8)°] and Ppincer-PdPpincer angles [155.3(3)° - 167.1(1)°] observed in other complexes.92 106 Chapter Three: Preparation of Dinuclear Complexes from Mononuclear PCP Pincer Pd(II) Complexes Figure 3-9: ORTEP plots of complex 3.5 showing the side view (top) and the view along C(1)-Pd(1)-S(1) (bottom). The PF6- anion is omitted for clarity. Selected bond lengths (Å) and bond angles (º): Pd(1)-P(1) = 2.290(8), Pd(1)-P(2) = 2.280(8), Pd(2)-P(3) = 2.304(9), Pd(2)-P(4) = 2.283(9), Pd(1)-S(1) = 2.430(8), Pd(2)-N(1) = 2.140(3), Pd(1)-C(1) = 2.099(3), Pd(2)-C(6) = 2.080(3), C(1)-C(2) = 1.520(4), C(1)-C(4) = 1.522(4), C(6)-C(7) = 1.530(5), C(6)-C(9) = 1.501(6); C(1)-Pd(1)-S(1) = 175.5(8), C(6)-Pd(2)-N(1) = 176.3(1), P(1)-Pd(1)-P(2) = 163.4(3), P(3)-Pd(2)-P(4) = 165.4(3), P(1)-Pd(1)-C(1) = 82.6(9), P(2)Pd(1)-C(1) = 83.0(9), P(3)-Pd(2)-C(6) = 82.9(1), P(4)-Pd(2)-C(6) = 82.6(1), P(1)-Pd(1)S(1) = 99.5(3), P(2)-Pd(1)-S(1) = 95.5(3), P(3)-Pd(2)-N(1) = 98.3(7), P(4)-Pd(2)-N(1) = 96.2(7), Pd(1)-C(1)-C(2) = 114.1(2), Pd(1)-C(1)-C(4) = 113.7(2), Pd(2)-C(6)-C(7) = 112.6(3), Pd(2)-C(6)-C(9) = 114.(2), Pd(1)-S(1)-C(13) = 104.1. 107 Chapter Three: Preparation of Dinuclear Complexes from Mononuclear PCP Pincer Pd(II) Complexes 3.2.4 Analyses of the 13 C and 31P NMR Data of the Pincer [PCP] Pd(II) Complexes It has been demonstrated that dinuclear pincer Pd(II) complexes can be easily prepared from either Lewis basic or acidic precursors. Both homofunctional and difunctional spacers were used as the bridging ligand. These successes have opened up more options in the di-pincer assemblies in terms of the choice of metals, spacers and geometries. NMR spectroscopy was a very useful tool for characterising the mononuclear and dinuclear pincer Pd(II) complexes. Changes in the chemical shift upon ligand substitution gave a strong indication of the formation of new products. Analyses of the 13 C and 31 P NMR data of a series of pincer [PCP] complexes were performed. These findings will be discussed in this section. The electronic interaction in transition metal complexes is known to influence their chemical reactivity.139 An understanding of this interaction enables chemists to carry out chemical experiments in a systematic way.140 NMR spectroscopy has been used as a tool to study the interaction between a metal and ligands in its coordination sphere.141 Studies of the chemical shifts of a series of related complexes allow prediction of the chemical shift of a complex when a modification is made. It may also lead to a better understanding of the metalligand interaction in those complexes. The chemical shifts of mononuclear complexes 2.1, 2.16, 2.17a, 3.4 and dinuclear complexes 3.1a and 3.1b were consolidated and analysed. The analogous tert-butyl92, 142 and the related aryl143 complexes were included for comparison. The structures of the pincer [PCP] complexes under study are shown in Figure 3-10.8 The solvent effect (CDCl3, 108 Chapter Three: Preparation of Dinuclear Complexes from Mononuclear PCP Pincer Pd(II) Complexes CD2Cl2 and C6D6) on chemical shifts of the nucleus under observation was small and would not be taken into consideration in the discussion. PR2 PR2 PR2 L Pd Pd L Pd PR2 L = Cl, [PdCl(PCarylP)] R = Ph, X = BF4, 2.17a R = tBu, X = BPh4, [Pd(OH2)(PCP -tBu)][BPh4] 2+ PR2 Pd X PR2 PR2 R = Ph, L = Cl, 2.1 R = Ph, L = OTf, 2.16a R = Ph, L = NO3, 2.16b R = Ph, L = 4-Spy, 3.4 R = tBu, L = Cl, [PdCl(PCP -tBu)] OH2 Ph2P PPh2 L X Pd PPh2 PR2 R = Ph, L = NH2Ph, X = BPh4, [Pd(NH2Ph)(PCarylP)][BPh4] R = tBu, L = H2O, X = BF4, [Pd(OH2)(PCarylP-tBu)][BF4] L Pd OTf Ph2P L = dppf, 3.1a; L = 4,4' -bpy, 3.1b Figure 3-10: Chemical structures of the pincer [PCP] Pd(II) complexes.8 The 13 C chemical shifts of the selected complexes are listed in Table 3-1. The use of phosphine ligands with different substituents (R = tert-butyl vs R = phenyl) and the overall charges of complexes (neutral vs cationic) did not cause any significant changes in the 13 C chemical shift of the metallated carbon (δCm). The chemical shift of the metallated carbon (Cm) increased with decreasing chemical hardness of donor atom (O < N < Cl < S < P) of L as a result of the trans-influence. The downfield shift observed for the 13 C chemical shift of the metallated carbon in complex 3.1a could be due to the positive charges of the molecule. 109 Chapter Three: Preparation of Dinuclear Complexes from Mononuclear PCP Pincer Pd(II) Complexes Table 3-1: 13C chemical shifts of the pincer [PCP] complexes L δCm (DAL) (ppm)a Phenyl Cl (Cl) 60.8 CH Phenyl OTf (O) 58.3 2.16b CH Phenyl NO3 (O) 56.0 2.17a CH Phenyl H2O (O) 58.6 3.1a CH Phenyl dppf (P) 79.3b 3.1b CH Phenyl 4,4’-bpy (N) 60.2 3.4 CH Phenyl 4-Spy (S) 65.3 [PdCl(PCP-tBu)] CH tert-butyl Cl (Cl) 62.1c, d [Pd(OH2)(PCP-tBu)][BPh4] CH tert-butyl H2O (O) 60.0b, e 10 [PdCl(PCarylP)] Phenyl Phenyl Cl (Cl) 159.0f 11 [Pd(NH2Ph)(PCarylP)][BF4] Phenyl Phenyl NH2Ph (N) 156.4g Entry Complexes Cm R 2.1 CH 2.16a a = recorded in CDCl3 unless otherwise stated. b = recorded in CD2Cl2. c = recorded in C6D6. d = reference 142. e = reference 92. f = reference 143b. g = reference 143c. Table 3-2 lists the 31 P chemical shifts of the selected pincer [PCP] complexes. A higher chemical shift was observed when ligand L is a soft ligand, as seen for complexes 3.1a, 3.1b and 3.4. This could be due to the π back-bonding of the soft ligand to the metal centre. The 31 P chemical shifts of the neutral mononuclear complexes 2.1, 2.16, and 3.4 suggest that the use of different ligands resulted in small changes in the 31P chemical shifts of these complexes (δP 3.4 - δP 2.1 ≈ ppm). A downfield shift was observed for the cationic complex 2.17a 110 Chapter Three: Preparation of Dinuclear Complexes from Mononuclear PCP Pincer Pd(II) Complexes (46.0 ppm) as compared to the neutral complexes 2.16 (44.8 ppm and 44.6 ppm). The downfield shift could have been caused by the positive charge of 2.17a. The 31P chemical shifts of the chelating phosphine were also dependent on both the hybridisation of the metallated carbon as well as the substituent groups on the P atoms. The data suggest that the chemical shifts follow the trend Cm = aliphatic, R = tert-butyl > Cm = aliphatic, R = Phenyl > Cm = aromatic, R = Phenyl. This was best demonstrated by comparing the 31 P chemical shifts of 2.1, [PdCl(PCP-tBu)] and [PdCl(PCarylP)] (Entries 1, and 8). When the pincer [PCP] ligand was PCP-tBu, the P atoms are exposed to a number of groups (CH-, tertbutyl, Cl) that remove electron density from the P atoms, and as a result they are deshielded and shifted to a higher frequency (inductive effect). When the substituents on the chelating phosphine ligand are replaced by the phenyl groups, the electrons from the phenyl substituents are delocalised into the P atoms (resonance effect). Therefore the P atoms are more shielded and the signal was observed at a lower frequency. The resonance effect is enhanced by replacing the aliphatic metallated carbon with an aromatic one. This replacement caused the 31P signal to shift further upfield. However, the change in 31 P chemical shift due to such enhancement was small (δ 2.1 - δ [PdCl(PCarylP)] ≈ ppm) compared to the changes of R (δ [PdCl(PCP-tBu)] - δ 2.1 ≈ 41 ppm). 111 Chapter Three: Preparation of Dinuclear Complexes from Mononuclear PCP Pincer Pd(II) Complexes Table 3-2: 31P chemical shifts of the pincer [PCP] complexes L δP (DAL) (ppm)a Phenyl Cl (Cl) 41.8 CH Phenyl OTf (O) 44.8 2.16b CH Phenyl NO3 (O) 44.6 2.17a CH Phenyl H2O (O) 46.0 3.1a CH Phenyl dppf (P) 55.1 3.1b CH Phenyl 4,4’-bpy (N) 49.8 3.4 CH Phenyl 4-Spy (S) 46.4 [PdCl(PCP-tBu)] CH tert-butyl Cl (Cl) 83.2b [Pd(OH2)(PCP-tBu)][BPh4] CH tert-butyl H2O (O) 87.1c,d 10 [PdCl(PCarylP)] Phenyl Phenyl Cl (Cl) 34.4e 11 [Pd(NH2Ph)(PCarylP)][BF4] Phenyl Phenyl NH2Ph (N) 41.2f Entry Complexes Cm R 2.1 CH 2.16a a = Recorded in CDCl3 unless otherwise stated. b = reference 142. c = recorded in CD2Cl2. d = reference 92. e = reference 143a. f = reference 143c. 3.3 Summary Complexes 3.1a and 3.1b were prepared from 2.16a. The dinuclear complexes have been characterised using multinuclear NMR spectroscopic technique, ESI-MS, elemental analysis and X-ray crystallography. An attempt to prepare a Pd/Ag heterometallic complex using the mononuclear 4-pyridinethiolato complex 3.4 as a precursor led to the isolation of the dinuclear 4-pyridinethiolato Pd(II) complex 3.5. Complex 3.5 has also been prepared from 3.4 and the aqua Pd(II) complex 2.17b. Both complexes 3.4 and 3.5 have been fully characterised. 112 Chapter Three: Preparation of Dinuclear Complexes from Mononuclear PCP Pincer Pd(II) Complexes Analyses of the NMR data of a series of related pincer [PCP] complexes suggest that the 13 C and 31 P chemical shifts change with the nature of the metallated carbon and the organic groups attached on the P arms (aliphatic vs aromatic), as well as ligand trans to the metallated carbon. 3.4 Experimental Section 3.4.1 General Procedures and Materials All solvents were freshly dried using 3Ǻ molecular sieves. All reagents were commercial products and were used as received. Elemental analyses were performed by the Chemical, Molecular and Materials Analysis Centre (CMMAC) NUS. 3.4.2 NMR Spectroscopy and Electrospray Ionisation Mass Spectrometry The 1H and 13C{1H}NMR spectra were recorded at 25oC on a Bruker ACF 300MHz FT-NMR spectrometer. Chemical shifts are reported relative to TMS where δ CHCl3 = 7.26 ppm (1H) or δ CDCl3 = 77.1 ppm (13C). The 31P{1H} NMR spectra were externally referenced to 85 % H3PO4 at 121.39 MHz. The 19 F{1H} NMR spectra were referenced to CF3COOH at 282.38 MHz. ESI mass spectra of the samples were recorded in positive ion mode using a Thermo Finningan LCQ spectrometer. The compounds were dissolved in CH2Cl2 and CH3OH was used as mobile phase. Peaks were assigned using methods and software123 described in Section 2.4.3. 113 Chapter Three: Preparation of Dinuclear Complexes from Mononuclear PCP Pincer Pd(II) Complexes 3.4.3 X-Ray Crystallography Analyses of crystals of clusters 3.1a, 3.1b, 3.4 and 3.5 were carried out using the instrument, softwares124-126 and methods as described in Section 2.4.4. The crystal of complex 3.1a is orthorhombic, space group Pbca. The asymmetric unit contains one tilted cation and two OTf anions. One of the OTf is disordered into two positions at a 40:60 occupancy ratio. The carbon, fluorine and oxygen atoms were not refined with anisotropic thermal parameters. After the final refinement cycles, there was one residual peak of 1.07 eA-3. This peak is 2.89Å away from oxygen atoms of one of the OTf anions. It is likely a water molecule with partial occupancy. Final R values for 2θ up to 50º are: R1 = 0.0675, wR2 = 0.178 which are good results for a poor data set with R(int) = 0.151. For complex 3.1b, the crystal is monoclinic, space group P21/c. The asymmetric unit contains half of the cation and one OTf anion. Final R values are: R1 = 0.0637 and wR2 = 0.1244. For complex 3.4, this crystal is monoclinic, space group C2/c. The asymmetric unit contains one titled molecule and half an acetone. The acetone is disordered and is situated at the two fold axis. Final R values are: R1 = 0.0418 and wR2 = 0.0918. The crystal of complex 3.5 is monoclinic, space group P21/c. The asymmetric unit contains one complex cation and one PF6- anion. Final R values are R1 = 0.0482 and wR2 = 0.1059. The data collection parameters of complexes 3.1a, 3.1b, 3.4 · 0.5(CH3)2CO and 3.5 are listed in Table 3-3. 114 Chapter Three: Preparation of Dinuclear Complexes from Mononuclear PCP Pincer Pd(II) Complexes Table 3-3: Data collection parameters of the pincer [PCP] Pd(II) complexes 3.1a, 3.1b, 3.4 · 0.5 (CH3)2CO and 3.5 Chemical formula FW, g mol-1 Crystal system Space group a, Å b, Å c, Å α, o β, o γ, o Volume, Å3 Z ρcalcd, Mg m-3 µ, mm-1 T (K) No of reflections collected No of independent reflections No of parameters GooF R1 and wR2 [I> sigma(I)] R1 and wR2 (all data) Large diff. peak and hole (e.Å-3) 3.1a C94H86F6FeO6P6Pd2S2 3.1b C70H66F6N2O6P4Pd2S2 1944.22 Orthorhombic Pbca 21.063(8) 21.651(8) 39.051(2) 90 90 90 17809.1(1) 1.450 0.780 223(2) 101270 1546.05 Monoclinic P21/c 10.004(1) 17.732(2) 18.719(3) 90 101.490(4) 90 3253.9(8) 1.578 0.788 223(2) 23012 15676 R(int) = 0.1513 7463 R(int) = 0.0692 1053 415 0.993 R1 = 0.0675, wR2 = 0.1508 R1 = 0.1336, wR2 = 0.1768 1.064 and -0.945 1.038 R1 = 0.0637, wR2 = 0.1244 R1 = 0.1025, wR2 = 0.1381 1.371 and -0.680 115 Chapter Three: Preparation of Dinuclear Complexes from Mononuclear PCP Pincer Pd(II) Complexes Table 3-3: Data collection parameters of the pincer [PCP] Pd(II) complexes 3.1a, 3.1b, 3.4 · 0.5 (CH3)2CO and 3.5 (continued) Chemical formula FW, g mol-1 Crystal system Space group a, Å b, Å c, Å α, o β, o γ, o Volume, Å3 Z ρcalcd, Mg m-3 µ, mm-1 T (K) No of reflections collected No of independent reflections No of parameters GooF R1 and wR2 [I> sigma(I)] R1 and wR2 (all data) Large diff. peak and hole (e.Å-3) 3.4 · 0.5 (CH3)2CO C35.50H36NO0.50P2PdS 685.05 Monoclinic C2/c 22.749(3) 9.417(1) 29.902(4) 90 97.231(3) 90 6355.2(1) 1.432 0.778 223(2) 40276 3.5 C63H62F6NP5Pd2S 1346.85 Monoclinic P21/c 12.947(5) 17.489(7) 26.595(1) 90 91.388(1) 90 6019.9(4) 1.486 0.824 223(2) 77929 7280 [R(int) = 0.0513] 388 1.149 R1 = 0.0418 wR2 = 0.0866 R1 = 0.0498 wR2 = 0.0897 0.746 and -0.601 13826 [R(int) = 0.0429] 703 1.182 R1 = 0.0482 wR2 = 0.1021 R1 = 0.0573 wR2 = 0.1058 0.928 and -0.455 3.4.4 Preparation of [{Pd(PCP)}2(μ-dppf)][OTf]2 3.1a The reaction and the crystallisation were carried out using degassed solvent. Complex 2.16a (0.10g, 0.14 mmol) and dppf (0.04g, 0.07 mmol) were mixed in CH2Cl2 (20 ml) and allowed to stir under a nitrogen atmosphere overnight. The solution was then pumped dried to give an orange powder and was washed with hexane (5 ml) and Et2O (5 ml). The solid was dissolved in CH2Cl2 (5 ml) and addition of Et2O (25 ml) gave an orange powder of complex 3.1a (0.09g, 66 %). Orange X-ray quality crystals were grown by diffusion of Et2O into a 116 Chapter Three: Preparation of Dinuclear Complexes from Mononuclear PCP Pincer Pd(II) Complexes concentrated CH2Cl2 solution of 3.1a under a nitrogen atmosphere. Analytical data for 3.1a: (Found: C, 58.24 H, 4.66. Anal. Calcd. for C94H86P6Pd2FeF6S2O6 : C, 58.09 H, 4.42). 1H NMR (CDCl3) (δ): 1.31 (m, 4H, PCH2CH2), 1.82 (m, 4H, PCH2CH2 overlapped with H2O peak), 2.28 (t, br, 4H, PCH2CH2), 2.43 (m, 4H, PCH2CH2), 2.85 (s, 4H, Cp), 3.00 (s, 4H, Cp), 3.66 (t, br, 2H, PdCH), 6.72-7.58 (m, 60H, Ph). 13C{1H} NMR (CD2Cl2) (δ): 35.4 (vt, PCH2CH2, 2JC-P(Pincer) = Hz), 35.9 (td, PCH2CH2, JC-P(Pincer) = 13 Hz, 3JC-P(dppf) = Hz), 72.3 (d, Cp, 3JC-P(dppf) = Hz), 73.3 (d, Cp, 2JC-P(dppf) = 12 Hz), 76.5 (dt, Cp, JC-P(dppf) = 82 Hz, 3JC-P(pincer) = Hz), 79.3 (dt, PdC, 2JC-P(dppf) = 28 Hz, 3JC-P(pincer) = 3.0 Hz), 121.4 (q, OTf-, JC-F = 322 Hz), 126.7 (vt, Ph, JC-P(pincer) = 22 Hz), 128.7 (vt, Ph, 3JC-P(pincer) = Hz), 128.8 (d, Ph, 3JC-P(pincer) = Hz), 129.3 (d, Ph, 3JC-P(pincer) = Hz), 130.1 (vt, Ph, JCP(pincer) = 22 Hz), 130.5 (s, Ph), 131.0 (d, Ph, JC-P(pincer) = 39 Hz), 131.4 (s, Ph), 132.0 (vt, Ph, 2JC-P(pincer) = Hz), 132.6 (s, Ph), 133.7 (d, Ph, 2JC-P(pincer) = 14 Hz), 135.1 (vt, Ph, 2JC-P(pincer) = Hz). 31P{1H} NMR (CDCl3) (δ): 6.6 (t, PPh2, 2JP-P = 44 Hz), 55.1 (d, PPh2, 2JP-P = 44 Hz). 19F{1H} NMR(CDCl3) (δ):-1.8 (s, OTf-). ESI-MS (m/z, %): [{Pd(PCP)}2(μ-dppf)]2+ (823, 100), [{Pd(PCP)}(μ-dppf)]+ (1099, 53), [Pd(PCP)]+ (545, 43). 3.4.5 Preparation of [{Pd(PCP)}2(μ-4,4’-bpy)][OTf]2 3.1b Complex 2.16a (0.10g, 0.14 mmol) and 4,4’-bipyridine (0.01g, 0.07 mmol) were mixed in degassed (CH3)2CO (20 ml). The solution was allowed to stir for hours at room temperature. The colourless solution was then filtered through Celite to remove a trace amount of solid. The solution was then pumped dry to give a white powder. The white powder was washed with hexane (3 ml), toluene (3 ml) and Et2O (3 ml). The solid was then dissolved in (CH3)2CO (5 ml) and 117 Chapter Three: Preparation of Dinuclear Complexes from Mononuclear PCP Pincer Pd(II) Complexes addition of Et2O (25 ml) gave a white powder of 3.1b (0.07g, 65 %). Colourless X-ray quality crystals of 3.1b were grown by layering of hexane to a concentrated CH2Cl2 solution of 3.1b. Signals corresponding to OTf - anions were not observed in the 13C{1H} NMR spectrum, probably due to its low intensity and overlapping with pyridyl signals. Analytical data for 3.1b: (Found: C, 54.40 H, 4.14 N, 1.89. Anal. Calcd. for C70H66P4Pd2N2F6S2O6 : C, 54.42 H, 4.27 N, 1.81). 1H NMR (CDCl3) (δ): 1.83 – 2.02 (m, 8H, PCH2CH2), 2.31 (t, br, 4H, PCH2CH2), 63 (m, 4H, PCH2CH2), 3.43 (t, br, 2H, PdCH), 7.15-7.52 (m, 40H, Ph), 7.71 (d, 4H, pyridyl), 8.14 (d, 4H, pyridyl). 13C{1H} NMR (CDCl3) (δ): 30.9 (vt, PCH2CH2, JCP = 13 Hz), 36.9 (vt, PCH2CH2, 2JC-P = Hz), 60.2 (s, br, PdC), 123.8 (s, br, pyridyl), 129.1 (vt, Ph, JC-P = 21 Hz), 129.5 (vt, Ph, 3JC-P = Hz), 129.8 (vt, Ph, JC-P = Hz), 130.2 (vt, Ph, JC-P = 20 Hz), 131.5 (s, Ph), 131.7 (vt, Ph, 2JC-P = Hz), 132.0 (s, Ph), 133.0 (vt, Ph, 2JC-P = Hz), 145.0 (s, br, pyridyl), 151.8 (s, br, pyridyl). 31 P{1H} NMR (CDCl3) (δ): 49.8 (s, PPh2). 19F{1H} NMR (CDCl3) (δ): - 2.0 (s, OTf-). ESI-MS (m/z, %): [Pd(PCP)]+ (545, 100); [Pd(PCP)(CH3CN)]+ (586, 28); [{Pd(PCP)}(μ-4, 4’-bpy)]+ (700, 37). 3.4.6 Preparation of [Pd(4-Spy)(PCP)] · 0.5 (CH3)2CO [3.4 · 0.5 (CH3)2CO] 4-Pyridinethiol (0.50g, 0.86 mmol) was dissolved in CH3OH (10 ml). To this solution was added KOH (0.07g, 1.29 mmol). The solution was allowed to stir for 15 minutes. The mixture was then added to a solution of 2.1 prepared by dissolving the complex (0.14g, 1.29 mmol) in CH2Cl2/(CH3)2CO mixture (1:1 v/v) (total volume = 20 ml). The yellow solution turned orange immediately after addition. The orange solution was allowed to stir overnight. The solution was then 118 Chapter Three: Preparation of Dinuclear Complexes from Mononuclear PCP Pincer Pd(II) Complexes filtered and pumped dry. The orange solid was dissolved in CH2Cl2 (20 ml) and extracted with H2O (10 ml) to remove excess ligand. The organic extract was dried using anhydrous MgSO4, filtered through Celite and concentrated to a small volume under reduced pressure. Addition of hexane (30 ml) followed by filtration gave a yellow powder of complex 3.4 (0.49g, 87 %). Orange X-ray quality crystals were grown by slow evaporation of a (CH3)2CO solution of 3.4. The presence of (CH3)2CO solvent in the complex was confirmed by elemental analysis, 1H and 13 C{1H} NMR spectroscopy. Analytical data for [3.4 · 0.5 (CH3)2CO]: (Found: C, 61.45 H, 5.32 N, 1.93 S, 4.56. Anal. Calcd. for C34H33P2PdNS · 0.5 (CH3)2CO: C, 61.55 H, 5.40 N, 2.08 S, 4.76). 1H NMR (CDCl3) (δ): 1.70 (m, 2H, PCH2CH2), 1.90 (m, 2H, PCH2CH2), 2.17 (s, 6H, CH3, acetone), 2.29 (t, br, 2H, PCH2CH2), 2.70 (m, 2H, PCH2CH2), 3.20 (t, br, 1H, PdCH), 6.94 (d, 2H, pyridyl), 7.21-7.78 (m, 22H, Ph + pyridyl). 13 C{1H} NMR (CDCl3) (δ): 30.9 (s, CH3, acetone), 32.3 (vt, PCH2CH2, JC-P =12 Hz), 36.4 (vt, PCH2CH2, 2JC-P = Hz), 65.3 (vt, br, PdC, 3JC-P = Hz ), 128.4 (s, br, pyridyl), 128.5 (vt, Ph, 3JC-P = 4.5 Hz), 128.8 (vt, Ph, 3JC-P = 4.5 Hz), 130.4 (s, Ph), 130.7 (s, Ph), 131.6 (vt, Ph, JC-P = 20.0 Hz), 132.3 (vt, Ph, 2JC-P = 6.0 Hz), 132.9 (vt, Ph, JCP = 21 Hz), 133.6 (vt, Ph, 2JC-P = Hz), 143.5 (s, pyridyl), 165.6 (s, pyridyl), 207.7 (s, CO, acetone). 31 P{1H} NMR (CDCl3) (δ): 46.4 (s, PPh2). ESI-MS (m/z, %): [Pd(PCP)(SpyH)]+ (656, 100). 3.4.7 Preparation of [{Pd(PCP)}2(μ-4-Spy)][PF6] 3.5 Complex 2.1 (0.05 g, 0.09 mmol) was dissolved in (CH3)2CO (15 ml). To this solution was then added an aqueous solution of AgPF6 (0.07 g, 0.26 mmol) in deionised H2O (5 ml). The solution mixture was allowed to stir for hour and 119 Chapter Three: Preparation of Dinuclear Complexes from Mononuclear PCP Pincer Pd(II) Complexes then filtered through Celite to remove AgCl formed. The filtrate was then pumped dry and washed with deionised water (3 x ml) followed by Et2O (2 x ml). The yellow-brown solid (complex 2.17b) obtained was then dissolved in CH2Cl2 and complex 3.5 (0.06g, 0.09 mmol) was added to the solution. After stirring at room temperature for hours, the solution was filtered. The yellow filtrate was concentrated and filtered. Diffusion with Et2O gave yellow crystals of complex 3.5 (0.02 g, 18 %). Analytical data for 3.5: (Found: C, 56.50 H, 4.94 N, 1.13 S, 1.99. Anal. Calcd. for C63H62P5Pd2SNPF6: C, 56.17 H, 4.65 N, 1.04 S, 2.38). 1H NMR (CDCl3) (δ): 1.51-2.38 (m, 12H, PCH2CH2, overlapped with H2O peak), 2.61 (m, 4H, PCH2CH2), 3.17 (t, br, 1H, PdCH), 3.32 (t, br, 1H, PdCH), 6.59-7.76 (m, 42H, Ph + pyridyl), 6.91 (d, 2H, pyridyl). 13 C{1H} NMR (CDCl3) (δ) : 30.9 (vt, PCH2CH2, JC-P =13 Hz), 31.9 (vt, PCH2CH2, JC-P =12 Hz), 36.1 (vt, PCH2CH2, JC-P = Hz), 36.6 (vt, PCH2CH2, 2JC-P = Hz), 59.5 (s, br, PdC), 66.3 (s, br, PdC), 128.1 (vt, Ph, 3JC-P = Hz), 128.8 (vt, Ph, 3JC-P = Hz), 129. (vt, Ph, 3JC-P = Hz), 129.3 (s, pyridyl), 129.6 (vt, Ph, 3JC-P = Hz), 129.8 (s, Ph), 130.3 (vt, Ph, JC-P = 20 Hz), 130.8 (s, Ph), 130.9 (s, Ph), 131.1(vt, Ph, JC-P = 20 Hz), 131.2 (vt, Ph, JC-P = 20 Hz), 131.7 (s, Ph), 132.0 (vt, Ph, 2JC-P = Hz, overlapped with upper face phenyl C2/C6 signal of Pd(II) moeity bonded to thiolate), 132.0 (vt, Ph, JC-P = Hz, overlapped with upper face phenyl C2/C6 signal of Pd(II) moeity bonded to pyridine), 132.9 (vt, Ph, JC-P = 20 Hz), 133.2 (vt, Ph, 2JC-P = Hz),133. (vt, Ph, 2JC-P = Hz), 146.3 (s, pyridyl), 168.2 (s, pyridyl). 31 P{1H} NMR (CDCl3) (δ): -143.5 (sep, PF6-, JF-P = 713 Hz), 47.1 (s, PPh2), 48.3 (s, PPh2). 19 F{1H} NMR(CDCl3) (δ): 2.6 (d, PF6-, JF-P = 712 Hz). ESI-MS (m/z, %): [Pd(PCP)]+ (545,100), [Pd(PCP)(CH3CN)]+ (586, 33), [Pd(PCP)(SpyH)]+ (656, 69), [{(Pd(PCP)}(μ-Spy)]+ (1200, 50). 120 Chapter Three: Preparation of Dinuclear Complexes from Mononuclear PCP Pincer Pd(II) Complexes 3.4.8 Preparation of [Pd(OH2)(PCP)][PF6] 2.17b Complex 2.17b was prepared similarly to 2.17a by using 2.1 (0.05g, 0.09 mmol) and AgPF6 (0.10g, 0.43 mmol). The yellow-brown powder obtained was washed with Et2O (2 x ml) to give complex 2.17b (0.02g, 39%). Signals corresponding to P-bound aryl carbon atoms were not observed in the 13 C{1H} NMR spectrum due to their low intensity. Analytical data for 2.17b: 13 C{1H} NMR (CDCl3) (δ): 29.2 (vt, PCH2CH2, JC-P =13 Hz), 36.9 (vt, PCH2CH2, 2JC-P = Hz), 59.2 (s, br, PdC), 129.3 (vt, Ph, 3JC-P = Hz), 129.5 (vt, Ph, 3JC-P = Hz), 131.2 (s, Ph), 131.7 (s, Ph), 132.0 (vt, Ph, 2JC-P = Hz), 133.5 (vt, Ph, 2JC-P = Hz). 31 P{1H} NMR (CDCl3) (δ): 46.5 (s, PPh2), -143.8 (sep, PF6-, JF-P = 713 Hz).19F{1H} NMR (CDCl3) (δ): 3.3 (d, PF6-, JF-P = 714 Hz). ESI-MS (m/z, %): [Pd(PCP)]+ (545, 100), [Pd(PCP)(CH3CN)]+ (586, 19). 121 [...]... Orthorhombic Pbca 21.0 63( 8) 21.651(8) 39 .051(2) 90 90 90 17809.1(1) 8 1.450 0.780 2 23( 2) 101270 1546.05 Monoclinic P21/c 10.004(1) 17. 732 (2) 18.719 (3) 90 101.490(4) 90 32 53. 9(8) 2 1.578 0.788 2 23( 2) 230 12 15676 R(int) = 0.15 13 74 63 R(int) = 0.0692 10 53 415 0.9 93 R1 = 0.0675, wR2 = 0.1508 R1 = 0. 133 6, wR2 = 0.1768 1.064 and -0.945 1. 038 R1 = 0.0 637 , wR2 = 0.1244 R1 = 0.1025, wR2 = 0. 138 1 1 .37 1 and -0.680 115... pyridyl) 13 C{1H} NMR (CDCl3) (δ): 30 .9 (s, CH3, acetone), 32 .3 (vt, PCH2CH2, JC-P =12 Hz), 36 .4 (vt, PCH2CH2, 2JC-P = 6 Hz), 65 .3 (vt, br, PdC, 3JC-P = 3 Hz ), 128.4 (s, br, pyridyl), 128.5 (vt, Ph, 3JC-P = 4.5 Hz), 128.8 (vt, Ph, 3JC-P = 4.5 Hz), 130 .4 (s, Ph), 130 .7 (s, Ph), 131 .6 (vt, Ph, JC-P = 20.0 Hz), 132 .3 (vt, Ph, 2JC-P = 6.0 Hz), 132 .9 (vt, Ph, JCP = 21 Hz), 133 .6 (vt, Ph, 2JC-P = 6 Hz), 1 43. 5... and wR2 [I> 2 sigma(I)] R1 and wR2 (all data) Large diff peak and hole (e.Å -3) 3. 4 · 0.5 (CH3)2CO C35.50H36NO0.50P2PdS 685.05 Monoclinic C2/c 22.749 (3) 9.417(1) 29.902(4) 90 97. 231 (3) 90 635 5.2(1) 8 1. 432 0.778 2 23( 2) 40276 3. 5 C63H62F6NP5Pd2S 134 6.85 Monoclinic P21/c 12.947(5) 17.489(7) 26.595(1) 90 91 .38 8(1) 90 6019.9(4) 4 1.486 0.824 2 23( 2) 77929 7280 [R(int) = 0.05 13] 38 8 1.149 R1 = 0.0418 wR2 =... 13 C{1H} NMR (CDCl3) (δ) : 30 .9 (vt, PCH2CH2, JC-P = 13 Hz), 31 .9 (vt, PCH2CH2, JC-P =12 Hz), 36 .1 (vt, PCH2CH2, 2 JC-P = 6 Hz), 36 .6 (vt, PCH2CH2, 2JC-P = 7 Hz), 59.5 (s, br, PdC), 66 .3 (s, br, PdC), 128.1 (vt, Ph, 3JC-P = 5 Hz), 128.8 (vt, Ph, 3JC-P = 5 Hz), 129 2 (vt, Ph, 3JC-P = 5 Hz), 129 .3 (s, pyridyl), 129.6 (vt, Ph, 3JC-P = 5 Hz), 129.8 (s, Ph), 130 .3 (vt, Ph, JC-P = 20 Hz), 130 .8 (s, Ph), 130 .9... = 13 Hz, 3JC-P(dppf) = 5 Hz), 72 .3 (d, Cp, 3JC-P(dppf) = 8 Hz), 73. 3 (d, Cp, 2JC-P(dppf) = 12 Hz), 76.5 (dt, Cp, JC-P(dppf) = 82 Hz, 3JC-P(pincer) = 5 Hz), 79 .3 (dt, PdC, 2JC-P(dppf) = 28 Hz, 3JC-P(pincer) = 3. 0 Hz), 121.4 (q, OTf-, JC-F = 32 2 Hz), 126.7 (vt, Ph, JC-P(pincer) = 22 Hz), 128.7 (vt, Ph, 3JC-P(pincer) = 5 Hz), 128.8 (d, Ph, 3JC-P(pincer) = 5 Hz), 129 .3 (d, Ph, 3JC-P(pincer) = 5 Hz), 130 .1... Pd(II) and Pt(II) pyridinethiolato complexes have been reported only recently 134 The metalloligand [Pd(4Spy)(PCP)] 3. 4 was prepared by a standard ligand replacement reaction 135 of complex 2.1 with 4-pyridinethiolate ligand The thiolato ligand was generated insitu from 4-pyridinethiol and KOH (Scheme 3- 2) CH2Cl2 /(CH3)2CO / CH3OH (1:1:1 v/v) RT N PPh2 Pd Cl + K+ -S KCl PPh2 2.1 PPh2 Pd S PPh2 N 3. 4 Scheme... pyridyl) 13C{1H} NMR (CDCl3) (δ): 30 .9 (vt, PCH2CH2, JCP = 13 Hz), 36 .9 (vt, PCH2CH2, 2JC-P = 6 Hz), 60.2 (s, br, PdC), 1 23. 8 (s, br, pyridyl), 129.1 (vt, Ph, JC-P = 21 Hz), 129.5 (vt, Ph, 3JC-P = 5 Hz), 129.8 (vt, Ph, 3 JC-P = 5 Hz), 130 .2 (vt, Ph, JC-P = 20 Hz), 131 .5 (s, Ph), 131 .7 (vt, Ph, 2JC-P = 7 Hz), 132 .0 (s, Ph), 133 .0 (vt, Ph, 2JC-P = 7 Hz), 145.0 (s, br, pyridyl), 151.8 (s, br, pyridyl) 31 P{1H}... = 6 Hz), 59.2 (s, br, PdC), 129 .3 (vt, Ph, 3JC-P = 4 Hz), 129.5 (vt, Ph, 3JC-P = 6 Hz), 131 .2 (s, Ph), 131 .7 (s, Ph), 132 .0 (vt, Ph, 2JC-P = 7 Hz), 133 .5 (vt, Ph, 2JC-P = 7 Hz) 31 P{1H} NMR (CDCl3) (δ): 46.5 (s, PPh2), -1 43. 8 (sep, PF6-, JF-P = 7 13 Hz).19F{1H} NMR (CDCl3) (δ): 3. 3 (d, PF6-, JF-P = 714 Hz) ESI-MS (m/z, %): [Pd(PCP)]+ (545, 100), [Pd(PCP)(CH3CN)]+ (586, 19) 121 ... observed Figure 3- 6: An ORTEP plot of complex 3. 4 · 0.5 (CH3)2CO with 50% thermal ellipsoids The (CH3)2CO molecule is omitted for clarity Selected bond lengths (Å) and angles (º): Pd(1)-P(1) = 2 .30 1(7), Pd(1)-P(2) = 2.282(8), Pd(1)-S(1) = 2.4 03( 8), Pd(1)-C(1) = 2.117 (3) , C(1)-C(2) = 1.528(4), C(1)-C(4) = 1.522(4); P(1)-Pd(1)-P(2) = 155 .3( 3), P(1)Pd(1)-S(1) = 96 .3( 3), P(2)-Pd(1)-S(1) = 100 .3( 3), P(1)-Pd(1)-C(1)... PCP Pincer Pd(II) Complexes PPh2 Pd ONO2 AgNO3 PPh2 2.16b PPh2 Pd S PPh2 3. 4 Ag S N PPh2 N n Pd S PPh2 1/2 AgPF6 Ph2 P N PF6 Pd Ph2P 3. 5 Scheme 3- 3: Reactions of complex 3. 4 with AgNO3 and AgPF6 Complex 3. 5 is presumably formed from a reaction between 3. 4 and 2.17a To support this, the complex was synthesised independently from 3. 4 and [Pd(H2O)(PCP)][PF6] 2.17b Complex 2.17b can be prepared in an analogous . AgPF 6 Pd PPh 2 PPh 2 ONO 2 2.16b AgS N n Pd S PPh 2 PPh 2 N 3 . 5 Pd Ph 2 P Ph 2 P PF 6 Scheme 3- 3: Reactions of complex 3. 4 with AgNO 3 and AgPF 6 . Complex 3. 5 is presumably formed from a reaction between 3. 4 and 2.17a. To. 2 .32 2(2), Pd(1)-P(2) = 2 .31 7(2), Pd(2)-P (3) = 2 .31 3(2), Pd(2)-P(4) = 2 .30 3(2), Pd(1)-P(5) = 2 .37 6(2), P(2)-P(6) = 2 .36 3(2), Pd(1)-C(1) = 2.122(6), Pd(2)-C(6) = 2. 130 (7), C(1)-C(2) = 1.507(1), C(1)-C(4). prepared from either Lewis basic or acidic precursors. Both homofunctional and difunctional spacers were used as the bridging ligand. These successes have opened up more options in the di-pincer assemblies