Oxidative additions of coordinated ligands at unsaturated molybdenum and tungsten diphosphine-bridged carbonyl dimers .4. Decarbonylation reactions of [M-2(eta(5)-C5H5)(2)(Co)(4){mu-(EtO)(2)POP(OEt)(2)}] (M=Mo, W)

The title complexes [M2Cp2(CO)(4)(mu-tedip)] (M = Mo, W; Cp = eta(5)-C5H5; tedip = (EtO)(2)POP(OEt)(2)) have been synthesized in high yield from the reaction of tedip and the corresponding species [M2Cp2(CO)(4)] The structure of the ditungsten compound has been determined through a single-crystal X-ray study, Thermolytic decarbonylation of the dimolybdenum complex gives the phosphido-phosphonate compound [Mo2Cp2{mu-OP(OEt)(2)}{mu-P(OEt)(2)}(CO)(2)] which results from a P-O bond oxidative addition of the backbone of the tedip ligand to the dimetal center, The latter compound reacts rapidly with CO at room temperature to give the tetracarbonyl species [Mo2Cp2{mu-OP(OEt)(2)}{mu-P(OEt)(2)}(CO)(4)], a process that can be reversed either thermal or photochemically. Additional experiments show that the above tetracarbonyl complex can be partially converted into [Mo2Cp2(CO)(4)(mu-tedip)], which means that the P-O cleavage of the tedip ligand is reversible, The ditungsten title complex behaves in a related way but gives at 140 degrees C a mixture of di- and tetracarbonyl phosphido-phosphonate products. Photochemical decarbonylation of the title dimolybdenum compound showed low selectivity and under a variety of experimental conditions gave a mixture of the phosphido-phosphonate complexes [Mo2Cp2{mu-OP(OEt)(2)}{mu-P(OEt)(2)}(CO)(2)] and [Mo2Cp2{mu-OP(OEt)(2)}{mu-P(OEt)(2)}(mu-CO)] and the triply-bonded [Mo2Cp2(CO)(2)(mu-tedip)] which could not be isolated from the reaction mixtures, By contrast, photolysis of the ditungsten title compound at -15 degrees C gave as a major product the hydridocyclopentadienylidene complex [W-2(mu-eta(1),eta(5)-C5H4)Cp(mu-H)(CO)(3)(mu-tedip)] along with some [W2Cp2(CO)(2)(mu-tedip)]. The cyclopentadienylidene complex decomposes rapidly at room temperature to give a mixture of the starting compound and [W2Cp2{mu-OP(OEt)(2)}{mu-P(OEt)(2)}(CO)(2)]. The underlying reaction pathways in the decarbonylation of the title compounds are discussed on the basis of the above data and several separate experiments.