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 prepar ed from [W(2)Cp(2)(CO)(4)] and the corresponding diphosphine at room t emperature. Decarbonylation of the dppm complex in refluxing n-octane gives the triply bonded compound [W(2)Cp(2)(CO)(2)(mu-dppm)] as the ma jor product, along with a small amount of the oxo complex [W(2)Cp(2)(m u-CH(2)PPh(2))(O)(mu-PPh(2))(CO)], which results from a P-C(sp(3)) cle avage in the dppm ligand. Both compounds (as their dibenzene and tolue ne solvates, respectively) have been characterized through single-crys tal X-ray studies. The analysis of the dicarbonyl complex, carried out at 200 K, reveals the presence of linear semibridging carbonyls exper iencing an incipient dynamic disorder that at higher temperatures migh t be observed as a fully developed disorder of each carbonyl between i ts two asymmetric dispositions. The latter is consistent with a struct ure 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 compl exes -2(mu-eta(1):eta(5)-C5H4)Cp(mu-H)(CO)(3)(mu-L(2))] to finally giv e the corresponding dicarbonyls [W(2)Cp(2)(CO)(2)(mu-L(2))]. The latte r react readily with (t)BuNC at room temperature or below to give )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 1):eta(5)-C5H4)Cp(mu-H)(CN(t) Bu)(CO)(2)(mu-dppm)].