Oxidative additions of coordinated ligands at unsaturated molybdenum and tungsten diphosphine-bridged carbonyl dimers .2. Decarbonylation reactions of [Mo-2(eta(5)-C(5)H(4)R)(2)(Co)(4)(mu-Ph(2)PCH(2)PPh(2))] (R=H,Me)

Decarbonylation of the dimolybdenum complexes [Mo-2(eta(5)-C(5)H(4)R)(2)(CO)(4)(mu-dppm)] (R = H, Me, dppm = Ph(2)PCH(2)PPh(2)) occurs readily upon heating in tetrahydrofuran or toluene solution to afford with good yield the phosphido complexes [Mo-2(eta(5)-C(5)H(4)R)(2)(mu-CH(2)PPh(2))(mu-PPh(2))(CO)(2)], which arise from an irreversible P-C(sp(3)) bond cleavage in the backbone of the dppm ligand. Other minor products in these reactions are the oxo complexes [Mo-2(eta(5)-C(5)H(4)R)(2)(mu-CH(2)PPh(2))(O)(mu-PPh(2))(CO)], which are formed by the action of oxygen on the former dicarbonyl compounds, and the triply-bonded complexes [Mo-2(eta(5)-C(5)H(4)R)(2)(CO)(2)(mu-dppm)], in which the dppm ligand remains intact. By contrast, photochemical decarbonylation of the parent tetracarbonyl complexes at 10 degrees C yields the triply-bonded dicarbonyls as major products, along with a small amount of the monocarbonyl complexes [Mo-2(eta(5)-C(5)H(4)R)(2)(mu-CH(2)PPh(2))(mu-PPh(2))(mu-CO)]. Separate experiments show that the latter compounds are formed from [Mo-2(eta(5)-C(5)H(4)R)(2)(mu-CH(2)PPh(2))(mu-PPh(2))(CO)(2)] under photolytic conditions, this reaction being reversible. Thus it is concluded that the P-C(sp(3)) cleavage of the dppm ligand is fairly well suppressed at ambient temperatures or below. The reactions of all the above unsaturated species with CN(t)Bu proceed rapidly at room temperature. In this way, the new isocyanide derivatives [Mo-2(eta(5)-C(5)H(4)Me)(2)(mu-CH(2)PPh(2))(mu-PPh(2))(CN(t)Bu)(mu-CO)(CO)], [Mo-2(eta(5)-C5H5)(2)(mu-CH(2)PPh(2))(mu-PPh(2))(CN(t)Bu)(CO)], and [Mo-2(eta(5)-C(5)H(4)R)(2)(mu-eta(1),eta(2)-(CNBU)-B-t)(CO)(2)(mu-dppm)] have been prepared. All of them are formed in good yields as single isomers but have a rather low stability. Reaction of the monocarbonyl derivative with atmospheric oxygen gives the oxo complex [Mo-2(eta(5)-C5H5)(2)(mu-CH(2)PPh(2))(mu-O)(mu-OPPh(2))(CN(t)Bu)(CO)], which is also obtained as a single isomer. In marked contrast to their ditungsten analogues, the isocyanide-bridged compounds [Mo-2(eta(5)-C(5)H(4)R)(2)(mu-eta(1),eta(2)-(CNBU)-B-t)(CO)(2)(mu-dppm)] do not experience C-H bond cleavages in their cyclopentadienylic rings to a significant-extent.