STRUCTURE AND BONDING OF (MU-DICARBIDO)HEXA-TERT-BUTOXYDITUNGSTEN, (T-BUO)3WC-CW(O-T-BU)3

The molecular structure of (t-BuO)3W = C-C = W(O-t-Bu)3 (1) has been determined by single-crystal X-ray crystallography at -171-degrees-C. The compound crystallizes with two toluene molecules in the triclinic system, space group P1BAR, with a = 10.926 (7) angstrom, b = 15.706 (12) angstrom, c = 9.674 (6) angstrom, alpha = 90.99 (5)-degrees, beta = 90.27 (4)-degrees, gamma = 82.59 (5)-degrees, V = 1646.1 angstrom 3, and Z = 1. The two W(O-t-Bu)3 groups are arranged in the staggered conformation. The C-C bond length of 1.34 (3) angstrom in the bridge W = C-C = W moiety parallels that in H-C = C-C = C-H (1.384 (2) angstrom). The W = C bond length of 1.819 (16) angstrom is somewhat longer than that in most tungsten alkylidyne complexes. The UV-visible spectrum of 1 in hexane shows five absorptions at 430 (2490 M-1 cm-1), 354 (7590 M-1 cm-1), 294 (11 300 M-1 cm-1), 254 (27 800 M-1 cm-1), and 246 (26 800 M-1 cm-1) nm. Cyclic voltammetry measurements in CH2Cl2 with n-Bu4NPF6 (n-Bu = CH3CH2CH2CH2) as the supporting electrolyte reveal two irreversible oxidations at 0.362 and 0.816 V vs a saturated calomel electrode (SCE) reference. A MO calculation employing the Fenske-Hall method on the model compound (HO)3WC2W(OH)3 indicates that the C2 ligand is both a strong pi-donor and strong pi-acceptor, which leads to an approach of the limiting valence bond description W = C-C = W for the central moiety. A comparison is made with the established chemistry of linear bridged dinitrogen complexes.