SYNTHESIS, CHARACTERIZATION, AND REACTIVITY OF ALKOXO COMPLEXES CONTAINING CP-ASTERISK-M(NO) GROUPS (M=MO, W)

Stepwise treatment of CpM(NO)Cl2 [CP* = eta5-C5Me5;M = Mo,W] in THF a t low temperatures with 2 equiv of alkoxide anion affords first CpM(N O)(OR)CI complexes and then the bis(alkoxo) compounds CpM(NO)(OR)2 [M = Mo, R = CMe3; M = W, R = CMe3, Ph, CH2Ph], both types of complexes being isolable in reasonable yields. Alkoxo alkyl complexes are prepar able from the corresponding alkyl chloro precursors by similar metathe sis process. Single-crystal X-ray crystallographic analyses have been performed on Cp W (NO) (OCMe3)2 and Cp*W(NO)(OCH2Ph)2 as representati ve members of the bis(alkoxide) class of compounds. Crystal data for C pW(NO)(OCMe3)2 (2): a = 23.627(3) angstrom, b = 15.862(2) angstrom, c = 11.009(3) angstrom, V = 4125.7(11) angstrom3, Z = 8, space group Pb ca (No. 61); RF = 0.032, R(WF) = 0.035 for 2473 reflections with I gre ater-than-or-equal-to 3sigma(I). Crystal data for CpW(NO)(CH2Ph)2 (4) : a = 8.758(2) angstrom, b = 15.7617(13) angstrom, c = 16.352(2) angst rom, V = 2257.3(8) angstrom3, Z = 4, Space group Pnma (No. 62); R(F) = 0.031, R(wF) = 0.034 for 1807 reflections with I greater-than-or-equa l-to 3sigma(I). Complexes 2 and 4 both have normal three-legged piano- stool molecular structures whose intramolecular dimensions are consist ent with the existence of some degree of W-0 multiple bonding. The IR spectra and electrochemical properties of both types of alkoxide compl exes indicate that their metal centers are more electron-rich than tho se in comparable Cp'M(NO)R2 complexes [R = alkyl, aryl; Cp' = Cp(eta5- C5H5), Cp; M = Mo, W]. Representative reactions of selected complexes with O2, H2O, CNCMe3, and HCI are presented. The outcomes of these re actions establish the relative Lewis acidities of these complexes as w ell as the polarities of their M-R and M-OR linkages.