CYCLOPENTOXYDITUNGSTEN COMPOUNDS AND CRYSTAL AND MOLECULAR-STRUCTURES AND DYNAMIC SOLUTION BEHAVIOR OF W2(MU-H)(O-C-C5H9)7(HNME2)

The reaction between W2(NMe2)6 and cyclopentanol (greater-than-or-equal-to 6 equiv) in hexane solvents initially forms the dimethylamine adduct W2(O-c-C5H9)6(HNMe2)2 but with time in the presence of cyclopentanol and dimethylamine the hydrido-bridged compound W2(mu-H)(O-c-C5H9)7(HNMe2) is formed and may be isolated as green crystals. Crystal data at -155-degrees-C: a = 13.057 (3) angstrom, b = 15.592 (4) angstrom, c = 10.376 (2) angstrom, alpha = 97.72 (1)-degrees, beta = 109.55 (1)-degrees, gamma = 94.22 (1)-degrees, Z = 2, d(calcd) = 1.738 g cm-3, and space group P1BAR. The bridging hydride was not located crystallographically but can be inferred to occupy a position trans to the HNMe2 ligand so as to complete a confacial bioctahedron. In solution, the molecule is fluxional and the dimethylamine is labile and has been replaced by PMe3. Variable-temperature H-1 and P-31 NMR studies reveal that the (RO)3W(mu-H)(mu-OR)2W(OR)2(L) molecules are in a temperature dependent equilibrium with the unligated molecule W2(mu-H)(OR)7 and the free ligand. At high temperature, rapid OR group scrambling generates two equivalent (time-averaged) W atoms, but at low temperature the NMR spectra are consistent with expectations based on the solid-state structure of W2(mu-H)(O-c-C5H9)7(HNMe2).