Transition Met Chem (2010) 35:89–93 DOI 10.1007/s11243-009-9299-4 Synthesis and structures of two ruthenium dibenzoylmethane triphenylphosphine mixed ligand complexes Hung Huy Nguyen • Nham Hoang Ulrich Abram • Received: 20 May 2009 / Accepted: 20 October 2009 / Published online: 12 November 2009 Ó Springer Science+Business Media B.V 2009 Abstract The reaction of dibenzoylmethane (HDBM) with [RuCl2(PPh3)3] in benzene in the presence of a supporting base (Et3N) under reflux gives two different complexes, the side product as a green-yellow Ru(III) compound of composition [RuIIICl2(DBM)(PPh3)2] (2) and the main product as a red Ru(II) complex of composition [RuII(DBM)2(PPh3)2] (3) The products were studied by spectroscopic methods, cyclic voltammetry and X-ray single crystal diffraction The molecular structure of shows a distorted octahedral environment around the Ru atom with two phosphine ligands in trans positions The octahedral complex shows a cis arrangement of two phosphine ligands Introduction To date, many ruthenium mixed-ligand complexes of b-diketones and phosphines have been synthesized and characterized [1–4] These complexes possess a diversity of coordination modes including different isomeric types and oligomeric compounds [5, 6] Some of them reveal good catalytic effects [7, 8] and remarkable biological activities [9, 10] However, in spite of extensive work, only a few fully structurally characterized ruthenium b-diketonate complexes containing phosphines have been published, so far [11–15] H H Nguyen (&) Á N Hoang Inorganic Chemistry Department, Hanoi University of Science, Le Thanh Tong 19, Hanoi, Vietnam e-mail: hunghuy@zedat.fu-berlin.de U Abram Institute of Chemistry and Biochemistry, Freie Universitaăt Berlin, Fabeckstraòe 34-36, 14195 Berlin, Germany e-mail: abram@chemie.fu-berlin.de In this paper, we report the synthesis, spectroscopic properties, electrochemistry and X-ray single crystal structures of two ruthenium b-diketonate triphenylphosphine mixed ligand complexes, [RuIIICl2(DBM)(PPh3)2] (2) and [RuII(DBM)2(PPh3)2] (3) (where DBM- is dibenzoylmethanate) The formation of compound has been reported before; however, its molecular structure was only deduced from spectroscopic evidence [16, 17] Compound is newly reported Experimental All reagents used in this study were reagent grade and used without further purification Solvents were dried and used freshly distilled unless otherwise stated For synthesis of the complexes, solvents were degassed with Ar for 30 before use [{RuCl2(PPh3)3}2] was synthesized following a standard procedure [18] Infrared spectra were measured as KBr pellets on a Shimadzu FTIR-spectrometer between 400 and 4,000 cm-1 FAB? mass spectra were recorded with a TSQ (Finnigan) instrument using a nitrobenzyl alcohol matrix Elemental analysis of carbon and hydrogen were determined using a Heraeus vario EL elemental analyzer NMR spectra were taken with a JEOL 400 MHz multinuclear spectrometer Cyclic voltammetry measurements were performed on a PCI4 (Gamry Instruments) using a conventional three electrode cell with working and counter platinum wire electrodes and an Ag wire pseudo electrode The measurements were carried out in CH2Cl2 solutions with a scan rate of 0.1 V/s at T = 293 K with [n-Bu4N][PF6] as the supporting electrolyte Potentials are quoted relative to the Fc/Fc? couple used as internal reference (E1/2 = 0.55 V vs SCE) 123 90 Transition Met Chem (2010) 35:89–93 X-ray structure determination The intensities for the X-ray structure determinations were collected on a STOE IPDS 2T instrument with Mo Ka ˚ ) The programs SHELXS97 [19] radiation (k = 0.71073 A and SHELXL97 [19] were used for the solution and refinement of the structures Details concerning crystal data and refinements are given in Table The structures were solved with direct methods and subsequently completed by difference Fourier recycling All the non-hydrogen atoms were refined anisotropically using full-matrix least-squares techniques The hydrogen atoms were calculated for idealized positions Comparably big voids between the large complex molecules in the solid state structures are not occupied with solvent molecules The highest peaks of electron density in ˚ for both structures the final Fourier maps are\1 e/A Synthesis of the complexes The reaction was carried out under Ar atmosphere A solution of [RuCl2(PPh3)3] (192 mg, 0.2 mmol), dibenzoylmethane (90 mg, 0.4 mmol) and Et3N (50 mg, 0.5 mmol) in degassed benzene (20 mL) was refluxed for h The resulting precipitate was filtered off The volume of clear red filtrate was reduced under vacuum to mL, and then n-hexane (20 mL) was added to precipitate a green–yellow solid of [RuCl2(DBM)(PPh3)2], which was separated by Table Crystal and refinement data for complexes and Data for [RuCl2(DBM)(PPh3)2] Yield: 5% (9 mg) Elemental Anal Found: C, 66.2; H, 4.1% Calcd for C51H41Cl2O2P2Ru: C, 66.6; H, 4.5% IR (cm-1): 3055 w (mCH), 1540 vs (mC=O), 1519 s (C=C), 1481 s (dCH), 1091 m (mRu–P), 745 s and 694 s (dCH phenyl), 516 w (mMO); FAB? MS (m/z): 919 [M]?, 884 [M–Cl]? Data for [Ru(DBM)2(PPh3)2] Yield: 61% (131 mg) For analysis, the compound was dried under vacuum for day Elemental Anal Found: C, 73.7 H, 4.8% Calcd for C66H52O4P2Ru: C, 73.9; H, 4.9% IR (cm-1): 3055 w (mCH), 1542 vs (mC=O), 1516 s (C=C), 1481 s (dCH), 1091 m (mRu–P), 740 s and 694 s (dCH phenyl), 520 m (mMO) 1H NMR (CDCl3; d, ppm): 6.16 (s, 2H, C–H), 6.8–7.4 (m, 50H, Car-H) 31P NMR (CDCl3; d, ppm): 53.17 FAB? MS (m/z): 1072 [M]? Results and discussion The reaction of HDBM and a common precursor for the synthesis of ruthenium(II) compounds, namely [RuCl2(PPh3)3], [RuCl2(DBM)(PPh3)2] (2) [Ru(DBM)2(PPh3)2] (3) Formula C51H41Cl2O2P2Ru C66H52O4P2Ru Mw 919.75 1072.09 Temperature/K 200(2) 200(2) Crystal system; Space group Triclinic; P-1 Triclinic; P-1 Unit cell ˚ a/A 12.797(17) 12.710(2) 12.890(9) 14.832(2) a/° 14.094(13) 76.87(6) 16.839(2) 75.983(10) b/° 74.49(8) 84.141(10) 69.48(8) 69.192(10) ˚ b/A ˚ c/A 123 filtration The final filtrate was then dried under vacuum, and the residue was recrystallized from MeOH/CH2Cl2 giving big red crystals of [Ru(DBM)2(PPh3)2] c/° ˚ 3; Z; Dcalc/g cm-3 V/A 2,075(4); 2; 1.472 2,878.6(7); 2; 1.237 Absorption coefficient/mm-1 0.626 0.374 Reflections collected 21,664 29,962 Independent reflections/Rint 11009/0.1814 15247/0.1596 Observed reflections [I [ 2r(I)] 4,600 5,042 Refined parameters 524 659 Goodness-of-fit on F2 0.861 0.856 R1(F)/wR2(F2) [I [ 2r(I)] 0.0790/0.1007 0.0880/0.1639 R1(F)/wR2(F2) (All data) 0.2056/0.1342 Largest diff peak and hole ˚3 0.810, -0.943 e/A 0.2297/0.2162 ˚3 0.950, -0.769 e/A Transition Met Chem (2010) 35:89–93 91 Scheme PPh3 O 0.2 PPh3 [RuCl2(PPh3)3] HDBM O - HCl O O2 C ,H l Cl Ru O H 2O - 0,5 Cl PPh3 PPh3 Ru Cl PPh3 HD BM -H Cl PPh3 PPh3 O Ru O O O in benzene in the presence of a supporting base (Et3N) gives two different complexes; a red complex of composition [RuII(DBM)2(PPh3)2] (3) as the main product and a small amount (about 5%) of a green-yellow complex of composition [RuIIICl2(DBM)(PPh3)2] (2) (Scheme 1) The formation of complex can be rationalized by the oxidation of the mono DBM Ru(II) intermediate complex by traces of oxygen (Scheme 1) The formation of complexes of type was previously reported in the reactions of [RuCl2(PPh3)3] and two equivalents of b-diketones in boiling benzene under aerobic conditions [17] The exchange of the second DBM ligand proceeds more slowly Theoretically, both cis and trans isomers should be formed However, due to its greater thermodynamic stability, the cis product [RuII(DBM)2(PPh3)2] (3) was exclusively obtained after extended reflux times Similar transformation of the trans isomer to the cis isomer was previously reported for trans [RuII(Acac)2(PPh3)2] where Acac- is acetylacetonate [5] The purity of two products was confirmed by elemental analysis, which gave good fits to the expected molecular formulas The infrared spectra of complexes and exhibit strong bands in the 1540 cm-1 region but no absorptions at 1634 cm-1 where the mC=O stretch is present in the spectrum of free HDBM This corresponds to a bathochromic shift of about 100 cm-1 and indicates chelate formation with a large degree of electron delocalization within the chelate rings [20] FAB? mass spectra of both complexes show intense peaks of the molecular ions with the expected isotopic distributions A fragment resulting from the loss of a chloro ligand appears in the spectrum of The 31P NMR spectrum of does not show any signal in the normal chemical shift range, as expected for a paramagnetic Ru(III) compound The 31P NMR spectrum of contains one singlet at 53.17 ppm, indicating that the two triphenylphosphine ligands are magnetically equivalent The 1H NMR spectrum of reveals one broad singlet for the methine proton at 6.16 ppm The aromatic protons appear in the range between 6.8 ppm and 7.4 ppm Figure is an ORTEP representation of Selected bond lengths and angles are given in Table In 2, the Ru atom, which is coordinated by an O,O-bidentate DBMligand, two chloro ligands and two triphenylphosphines exhibits a distorted octahedral geometry Two triphenylphosphine ligands are in mutually trans positions The Ru atom, two oxygen atoms of the DBM- ligand and two chloro ligands are placed almost in the same plane with a maximal deviation from the mean least-squares plane of ˚ for O1 The trans angles that are from 175.5 to 0.029(3) A 176.9 ° are only a little deviated from those of the ideal octahedral compound All the C–O and C–C distances in the chelate ring are between those expected for C–O, C–C single and double bonds, indicating delocalization of the p electrons Regarding this ligand arrangement, is only Fig ORTEP representation [21] of [RuCl2(DBM)(PPh3)2] (2) with 40% probability ellipsoids The hydrogen atoms are omitted for clarity 123 92 Transition Met Chem (2010) 35:89–93 ˚ ) and angles (°) for [RuCl2(DBM)Table Selected bond lengths (A (PPh3)2] (2) ˚) Bond lengths (A Ru–O(1) 2.003(5) Ru–P(2) 2.408(4) Ru–O(5) 2.023(5) O(1)–C(2) 1.295(7) Ru–Cl(1) 2.342(3) C(2)–C(3) 1.362(10) Ru–Cl(2) 2.347(3) C(3)–C(4) 1.398(9) Ru–P(1) 2.425(4) C(4)–O(5) 1.285(7) Angles (°) O(1)–Ru–O(5) 87.9(2) O(5)–Ru–P(2) 90.1(2) O(1)–Ru–Cl(1) 176.4(2) Cl(1)–Ru–Cl(2) 95.5(1) O(1)–Ru–Cl(2) 87.7(2) Cl(1)–Ru–P(1) 89.5(1) O(1)–Ru–P(1) O(1)–Ru–P(2) 92.1(2) 89.7(2) Cl(1)–Ru–P(2) Cl(2)–Ru–P(1) 88.6(1) 91.7(1) O(5)–Ru–Cl(1) 88.9(2) Cl(2)–Ru–P(2) 91.0(1) O(5)–Ru–Cl(2) 175.5(2) P(1)–Ru–P(2) 176.9(1) O(5)–Ru–P(1) 87.5(2) precedented by [RuIIICl2(HFA)(PPh3)2] where HFA is hexafluoroacetylacetone [22] All Ru–O, Ru–Cl and Ru–P bond distances of are also in the same region as those in [RuIIICl2(HFA)(PPh3)2] The compound is stable in the solid state as well as in solution In the air, at room temperature, no significant oxidation of can be detected by means of NMR for at least several days Single crystals of suitable for X-ray studies were obtained by slow evaporation of a CH2Cl2MeOH solution An ORTEP diagram of is illustrated in Fig 2, and selected bond lengths and angles are presented in Table The structure of shows that the Ru atom is coordinated by two bidenate O,O-monoanionic DBMligands and two PPh3 ligands The arrangement around the Ru atom is distorted octahedral; the trans angles fall in the range between 166.4 and 173.2 °, and two triphenylphosphine ligands are mutually cis In this arrangement, the two phosphine ligands are magnetically equivalent, which results in a singlet in the 31P NMR spectrum The average Ru–O bond distance in is slightly longer than that in 2, consistent with the respective Ru oxidation states of ?2 and ?3 Nevertheless, despite its lower oxidation state, has shorter average Ru–P bond distance than that in due to the trans effect of triphenylphosphine in the latter complex Crystal structures with the same overall geometry have been previously published for cisbis(acetylacetonato) bis(monodentate phosphine) ruthenium(II) complexes that were synthesized from cis[Ru(Acac)2(l2-C8H14)2] starting material [5] The redox behavior of these complexes revealed some interesting features in their electrochemistry In dry CH2Cl2 under argon, the cyclic voltammograms of the complexes show no reduction process from -1.2 V to 0.0 V However, 123 Fig ORTEP representation [21] of [Ru(DBM)2(PPh3)2] (3) with 30% probability ellipsoids The hydrogen atoms are omitted for clarity ˚ ) and angles (°) for [Ru(DBM)2Table Selected bond lengths (A (PPh3)2] (3) ˚) Bond lengths (A Ru–O(1) 2.037(5) C(2)–C(3) 1.427(9) Ru–O(11) 2.042(5) C(3)–C(4) 1.369(10) Ru–O(5) Ru–O(15) 2.087(5) 2.052(5) C(4)–O(5) O(11)–C(12) 1.301(8) 1.297(8) Ru–P(1) 2.319(2) C(12)–C(13) 1.376(10) Ru–P(2) 2.307(2) C(13)–C(14) 1.413(10) O(1)–C(2) 1.275(7) C(14)–O(15) 1.282(8) Angles (°) O(1)–Ru–O(5) 90.8(2) O(5)–Ru–P(2) 171.3(1) O(1)–Ru–O(11) 173.2(2) O(11)–Ru–O(15) 91.0(2) O(1)–Ru–O(15) 82.8(2) O(11)–Ru–P(1) 89.1(1) O(1)–Ru–P(1) 96.4(1) O(11)–Ru–P(2) 96.4(1) O(1)–Ru–P(2) 86.2(1) O(15)–Ru–P(1) 166.4(1) O(5)–Ru–O(11) 85.7(2) O(15)–Ru–P(2) 89.0(1) O(5)–Ru–O(15) 82.5(2) P(1)–Ru–P(2) 104.5(1) O(5)–Ru–P(1) 83.9(1) in the range between 0.0 V and 1.2 V, reversible oxidations at 0.182 V (DEp = 92 mV) for and 0.428 V (DEp = 88 mV) for 3, which are assigned to the oxidation of Ru(II) compounds to their corresponding Ru(III) species, are observed It is necessary to mention that at the same condition, the DEp value of the Fc/Fc? couple is 83 mV The high oxidative potential of is in good agreement with its stability in air By contrast, the low potential of the reduction process Transition Met Chem (2010) 35:89–93 93 Supporting information Crystallographic data for and have been deposited with the Cambridge Crystallographic Data Center as supplemental publication numbers CCDC 732758 and CCDC 732759 Copies of the data can be obtained free of charge via http://www.ccdc.cam.ac.uk Acknowledgments The authors would like to thank the Ministry of Science and Technology of Vietnam for financial support and Dr Adelheid Hagenbach (FU Berlin) for her kind help in the collection of the X-ray diffraction data References Fig Cyclic voltammograms with scan rate 100 mV/s in CH2Cl20.2 M (NBu4)[PF6] a [RuIIICl2(DBM)(PPh3)2] (2); 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