Oxidative additions of coordinated ligands at unsaturated molybdenum and tungsten diphosphine-bridged carbonyl dimers .1. Decarbonylation reactions of [W-2(eta(5)-C5H5)(2)(CO)(4)(mu-R(2)PCH(2)PR(2))] (R=Ph, Me)

The new complexes [W(2)Cp(2)(CO)(4)(mu-L(2))] (Cp = eta(5)-C5H5; L(2) = Ph(2)PCH(2)PPh(2) (dppm), Me(2)PCH(2)PMe(2) (dmpm)) have been prepared from [W(2)Cp(2)(CO)(4)] and the corresponding diphosphine at room temperature. Decarbonylation of the dppm complex in refluxing n-octane gives the triply bonded compound [W(2)Cp(2)(CO)(2)(mu-dppm)] as the major product, along with a small amount of the oxo complex [W(2)Cp(2)(mu-CH(2)PPh(2))(O)(mu-PPh(2))(CO)], which results from a P-C(sp(3)) cleavage in the dppm ligand. Both compounds (as their dibenzene and toluene solvates, respectively) have been characterized through single-crystal X-ray studies. The analysis of the dicarbonyl complex, carried out at 200 K, reveals the presence of linear semibridging carbonyls experiencing an incipient dynamic disorder that at higher temperatures might be observed as a fully developed disorder of each carbonyl between its two asymmetric dispositions. The latter is consistent with a structure determination carried out previously on the same compound at 291 K and with its dynamic behavior in solution. This air-sensitive complex adds oxygen readily to give the W(I)-W(V) oxo derivative [W(2)Cp(2)(O)(2)(CO)(2)(eta(1)-dppm)]. Photochemical decarbonylation of [W(2)Cp(2)(CO)(4)(mu-L(2))] proceeds via the hydride cyclopentadienylidene complexes [W-2(mu-eta(1):eta(5)-C5H4)Cp(mu-H)(CO)(3)(mu-L(2))] to finally give the corresponding dicarbonyls [W(2)Cp(2)(CO)(2)(mu-L(2))]. The latter react readily with (t)BuNC at room temperature or below to give [W(2)Cp(2)(mu-eta(1):eta(2)-CN(t)Bu)(CO)(2)(mu-L(2))], which, when L(2) = dppm, isomerizes at room temperature to give [W-2(mu-eta(1):eta(5)-C5H4)Cp(mu-H)(CN(t)Bu)(CO)(2)(mu-dppm)].