Baran Group Meeting 02/15/06 Platonic Hydrocarbons Ryan Shenvi Background The knowledge at which geometry aims is knowledge of the eternal, and not of aught perishing and transient My noble friend, geometry will draw the soul towards truth, and create the spirit of philosophy, and raise up that which is now unhappily allowed to fall down Nothing should be more sternly laid down than that the inhabitants of your fair city by all means learn geometry Platonic hydrocarbons are the corresponding carbogens, where each vertex is a carbon, each edge a bond, and each face a ring –Plato (ca 427-347 BC) “The Republic,” ca 370 BC en arch hn o logoz kai o logoz hn proz ton qeon kai qeon hn o logoz In the beginning was the word (logos) and the word was with God and the word was God –St John, (ca 10 AD-100 AD) “The Gospel of John,” ca 96 AD • Not all platonic solids translate to platonic hydrocarbons; limited by carbon valence, bonding angles, and strain Octahedrane and icosahedrane have not been prepared, nor has unsubstituted tetrahedrane • However, numerous inorganic molecules adopt these geometries: What are the 'platonic hydrocarbons'? Platonic Solids: • Regular solids, regular polyhedra: convex polyhedra whose faces are equivalent, convex regular polygons • Discovered 'first' by the neolithic Scots, ca 1300-1400 BC C2B10H12 carboranes • Described mathematically by Theaetetus (417 BC-369 BC), who proved the existance of and only regular solids; included in Euclid's Elements, Book X Polyhedron Tetrahedron Hexahedron Octahedron Dodecahedron Icosahedron Faces 12 20 Edges 12 12 30 30 Vertices 20 12 Symmetry Group Td Oh geometric duals Oh Ih Ih geometric duals • Included in Plato's Timaeus as part of his 'theory of everything,' which assigned the regular geometry of the solids to each of the elements: earth, water, air, fire, and ether (an element of order or logic added to the original elements described by Emedocles of Agrigentum, 495-435 BC) • In 1852, Schläfli proved the existance of exactly six regular polyhedra in four dimensions and three in all higher dimensions (some may be familiar with the hypercube, or tesseract, of A Wrinkle in Time fame) [Zr6Cl18]3– • Tetrahedrane and cubane have been called "super s-aromatic and super s-antiaromatic, respectively: Cyclopropane exhibits strong s-aromaticity as evidenced by its large diamgnetic susceptibility and anisotropy, upfield shifts of attached protons, shielding of protons above its ring and a stabilization of 11.3 kcal/mol (compare 33.2 kcal/mol for benzene) Cyclobutane exhibits strong s-antiaromaticity: similarity to cyclopropane's strain (27.5 vs 26.5 kcal/mol), abnormally low diamagnetic susceptibility, deshielded 1H and 13C shifts Planar cyclopropane, cyclobutane, tetrahedrane, and cubane dissected nucleus-independent chemical shift grids Red and green points denote positive and negative NICS values, respectively Baran Group Meeting 02/15/06 Platonic Hydrocarbons Ryan Shenvi Dodecahedrane DODECAHEDRANE O CO2Me Considerations: • tandem bond-forming events require proper alignment • severe entropic disadvantage in dimerization events • new bonds must form on the endo face O Late-stage reactions must all be able to take place from the exo-face KOH (aq.), MeOH; I2, NaHCO3 (94%) O O c) Zn/Cu, MeOH (78%) I O CO2Me CO2Me Ph heat, high pressure, irradiation, transition metals MeO2C O O CO2Me H2, Pd/C, EtOAc (100%) O (C10H10) + (C10H10) (C15) + (C5) (C16) + (C4) Eaton et al, JACS, 1972, 1014 FAILED Paquette et al, JACS, 1978, 1600 FAILED O MeO2C H HCl, MeOH OH OH Li/ NH3, BOMCl Cl F I 2, TH C ° –80 H CO2Me + MeO2C H H a) hn b) TsOH c) HN=NH OPh a) hn CO2Me OPh CO2Me (i-Bu)2AlH b) Li/ NH3 c) H3O+ MeO2C PCC H H H H H H CO2Me + CO2Me CO2Me (15-20%) : H H H O CHO H CO2Me + CO2Me CO2Me CO2Me CO2Me O (48%) CHO H Na CO2Me CO2Me O 950 °C CO2Me OPh Cl (62%) SUCCESS! Paquette, L A.; Ternansky, R J.; Balogh, D W JACS, 1982, 104, 4502 Ni (83%) first non-meso intermediate O O O b) P4O10, MsOH O CO2Me H (77%) O CO2Me NaBH4, MeOH (81%) S Ph a) H2O2, MeOH CO2Me Woodward et al, JACS, 1964, 3162 FAILED CO2Me a) NaOH, MeOH O I b) H2SO4, Na2Cr2O7 a) KOH, EtOH Pd/ C b) hn c) TsOH d)HN=NH 250 °C Baran Group Meeting 02/15/06 Prinzbach et al Angew Chem Int Ed Engl 1994, 2239 O Cl Cl Cl Cl Cl Cl O S Cl O Cl Cl A Cl Cl Cl TETRAHEDRANE • Numerous attmpts towards its synthesis O S Cl Cl Cl [–SO2] Cl Cl Cl Cl D Cl H Cl Cl Cl Cl D Li, t-BuOH c) Pd/C, 250 °C (35%) (95%) Cl O O O H TsLiN O • High-energy diradical-like intermediate can rapidly convert to its lower energy lumomer Cl nearly equal energies of activation Cl H H Cl Cl Cl HOMO-LUMO crossing through diradical bicyclobutane Cl Cl hn 'bonding' interaction between 'radicals, and s-conjugation ~126 O O O O O O Cu2O, bipy., H2O E ~22 PhH, D ~32 (kcal/ mol) a) B2H6•THF, quinoline, 150 °C (73%) b) NaOH, H2O2 c) CrO3, Me2CO O MeO2C N O " leaving as the only consolation the knowledge of how not to make tetrahedrane." -Henning Hopf • High-energy diradical-like intermediate can rapidly convert to its lower energy lumomer Cl Cl a) A, D b) Li, t-BuOH N H • O O H2 transfer NLiTs Cl Cl H H Cl Cl Cl Cl isodrin (30%) Platonic Hydrocarbons Ryan Shenvi Dodecahedrane CO2Me hn O N2 N2 O MeOH (95%) a) HCO2Me, NaH O b) TsN3, Et3N (83%) 'anti-bonding' interaction between 'radicals and through space interaction with central bond ~94 Schematic representation of the MERP (minimum energy reaction path) for conversion of tetrahedrane to cyclobutadiene • However, tetrahedrane (Estr= 126-140 kcal/mol) can be stabilized by 'corset effect.' a) OH– (76%) b) Pb(OAc)4, I2 CCl4, hn c) Na-K, THF; t-BuOH any movement away tetrahdral geometry increases tert-butyl steric interactions, imparting kinetic stability t-Bu E Pt/Re/Al2O3/H2 t-Bu t-Bu t-Bu H 'black box' DHf° 64.4 (Estr) (115.0) Pagodane: 14 pots 24% overeall (90%/step) 250 °C (3 - 8%) – 42.2 kcal/mol (–46.1) H 22.2 (68.9) H H decomposition products Rxn Coordinate • Originally proposed and utilized by G Maier et al in the first synthesis of a tetrahedrane Maier, G et al Angew Chem Int Ed Engl., 1978, 520 Baran Group Meeting 02/15/06 Platonic Hydrocarbons Ryan Shenvi Platonic Hydrocarbons Cubane (Hexahedrane) t-Bu O t-Bu t-Bu t-Bu hn O + t-Bu t-Bu H Eaton, P E et al JACS 1964, 962 Eaton, P E et al JACS 1964, 3157 H O hn O O t-Bu O O t-Bu t-Bu t-Bu t-Bu t-Bu t-BuLi, DME t-Bu t-Bu O 13C t-Bu t-Bu Br O 12% 8:3 t-hexane/ pentane (Rigisolve) –196 °C (35%) 50% KOH (aq.) (30%) 130 °C, cyclosilane DHf = 144-159 kcal/mol (calculated) 1H NMR: d = t-Bu t-Bu hn (300 nm), rt t-Bu t-BuO2 O CO2H t-BuO2H, HO C Py (prepared by Fluorochem in CA, and EniChem Synthesis in Milan on a multi-kilogram scale) O t-Bu t-Bu Br + Fe(CO)3 Br Br O hn, PhH CAN O (90%) Br O Br O O Br O hn CO2Me e– aromatic 6p cyclobutadiene t-Bu TMS TMS TMS CpCo(CO)2 TMS Co TMS 2Li Li, THF, rt TMS TMS R = Me, H (2.85 ppm) BrCH2CH2Br, THF (85%) TMS TMS TMS TMS TMS TMS Sekiguchi, A et al JACS, 2003, 12684 NC b) SOCl2, D (90%) CN HO2C O a) CH2Cl2, (COCl)2; THF, NH3, –78 °C N(i-Pr)2 NC TMS TMS TMS pentane, –100 °C (50%) CN TMS CO2 (90%) N(i-Pr)2 NC CN (77%) a) BrMgTMP, THF, –78 °C; CO2 (100%) b) KOH (aq), EtOH, D HO2C O TMS O BrMgTMP, THF, –78 °C; hn (254 nm), MeLi, THF, rt (67%) TMS N(i-Pr)2 CO2H a) CH2Cl2, (COCl)2; (99%) THF, NH3, –78 °C b) CHCl3, DMF, TMEDA (77%) SOCl2, –10 °C Eaton et al JACS, 1993, 10202 NC O N(i-Pr)2 –78 °C; CO2 NC (85%) TMS R Me2SO4, C6D6, rt OR N(i-Pr)2 TMS 2– O Mg(TMP)2, THF NC MeO2C TMS TMS O2t-Bu R Pettit and co-workers JACS 1966, 1328 hn t-Bu Li 100 °C t-Bu t-Bu t-Bu C6D6, rt SOCl2 diisopropylbenzene t-Bu t-Bu • + Br Br O H O t-Bu O t-Bu 6N KOH, 2d t-Bu (80%) O hn (254 nm), t-Bu O t-Bu NMR: d = 32.26, 28.33, 10.20 mp = 135 °C t-Bu t-Bu t-Bu Br O Br2, CCl4; –10 °C to rt 2d (22%) O hn, MeOH, HCl Et3N (40%) O O + t-Bu TMS NBS Br2/ Br– HO2C HO2C N(i-Pr)2 CO2H LAH, THF, D; Ac2O, (89%) AcO AcO OAc N(i-Pr)2 OAc DMDO, Me2CO; SOCl2; Barton's NaNHPT, DMAP; t-BuSH, hn, PhH (72%) AcO OAc AcO OAc Baran Group Meeting 02/15/06 AcO OAc AcO OAc Cubane 10% NaOH (aq.) KMnO4 HO2C (85%) HO2C SOCl2, MeCN; CH2Cl2, TMSN3; CO2H CO2H CHCl3, D; DMDO, Me2CO, H2O (30%) NO2 O2 N O2N NO2 equiv NHMDS, THF/MeTHF –78 °C; N2O4, –130 °C, (74%) i-pentane; H+, Et2O O2N O2N O2N O2N NO2 NO2 NO2 NO2 O3 (45-55%) DHf = 81-144 kcal/mol density ~ 1,9-2.2 g/cm 'leads to calculated detonation velocities and pressures much higher than that of TNT, 15-30% greater than HMX and perhaps even better than CL-20, the most powerful nonnuclear explosive known.' O2 N O2N O2N O2N NO2 NO LHMDS, CH2Cl2 NO2 NO2 –78 °C Me O2 N N O2N NO2 NO2 TNT NO2 NO2 O2N O2N O2N NO2 N N O2 N NO2 H O2N O2N NO2 N O2N N N NO2 HMX NO2 N N N N NO2 CL-20 NO2 Platonic Hydrocarbons Ryan Shenvi ... through space interaction with central bond ~94 Schematic representation of the MERP (minimum energy reaction path) for conversion of tetrahedrane to cyclobutadiene • However, tetrahedrane (Estr= 126-140... decomposition products Rxn Coordinate • Originally proposed and utilized by G Maier et al in the first synthesis of a tetrahedrane Maier, G et al Angew Chem Int Ed Engl., 1978, 520 Baran Group Meeting 02/15/06... (73%) b) NaOH, H2O2 c) CrO3, Me2CO O MeO2C N O " leaving as the only consolation the knowledge of how not to make tetrahedrane." -Henning Hopf • High-energy diradical-like intermediate can rapidly