Dimolybdenum and Ditungsten Cyclopentadienyl Carbonyls with Electron-Rich Phosphido Bridges. Synthesis of the Hydrido Phosphido Complexes [M₂Cp₂(<i>μ</i>-H)(<i>μ</i>-PRR‘)(CO)₄] and Unsaturated Bis(phosphido) Complexes [M₂Cp₂(<i>μ</i>-PR₂)(<i>μ</i>-PR‘R‘ ‘)(CO)<i>_x</i>] (<i>x</i>= 1, 2; R, R‘, R‘ ‘ = Et, Cy,^tBu)

Abstract

New hydrido complexes of the type [M 2 Cp 2 ( μ -H)( μ -PRR‘)(CO) 4 ] (M = Mo, W) have been prepared through the thermal reaction of [Mo 2 Cp 2 (CO) 6 ] with HPCy 2, H 2 PCy, or HPEt 2 or the thermal reaction of [W 2 Cp 2 (CO) 4 ] with HPR 2 (R = Cy, Et, Ph). In contrast, UV irradiation of [M 2 Cp 2 (CO) 6 ] and HPRR‘ leads with good yield to the bis(phosphido) complexes [M 2 Cp 2 ( μ -PRR‘) 2 ( μ -CO)] (R = R‘ = Cy, Et, Ph; R = Cy, R‘ = H). Related complexes having different phosphido groups, [M 2 Cp 2 ( μ -PR 2 )( μ -PR‘R‘ ‘)( μ -CO)] (R = Cy, t Bu, Ph; R‘ = Cy, t Bu, Et; R‘ ‘ = Cy, t Bu, Et, H), can be prepared in high yield through the photochemical reaction of [M 2 Cp 2 ( μ -PR 2 )( μ -H)(CO) 4 ] and HPR‘R‘ ‘ or [M 2 Cp 2 ( μ -H)( μ -PR‘R‘ ‘)(CO) 4 ] and HPR 2 . All triply bonded compounds react easily with carbon monoxide at room temperature or under moderate heating to finally yield the corresponding trans -dicarbonyl complexes [M 2 Cp 2 ( μ -PRR‘) 2 (CO) 2 ] or [M 2 Cp 2 ( μ -PR 2 )( μ -PR‘R‘ ‘)(CO) 2 ]. Some of the intermediates in these carbonylation reactions have been identified, including the cis -dicarbonyl complex [Mo 2 Cp 2 ( μ -PPh 2 )( μ -P t Bu 2 )(CO) 2 ] and the tricarbonyl complex [Mo 2 Cp 2 ( μ -PEt 2 ) 2 (CO) 3 ]. The structures of the new complexes are analyzed on the basis of the corresponding IR and NMR ( 1 H, 31 P, 13 C) data, and the reaction pathways operative in these highly efficient syntheses of bis(phosphido) complexes is discussed on the basis of the available data and some cross-experiments.