| Abstract
| - The title complexes[M2Cp2(CO)4(μ-tedip)](M = Mo, W; Cp = η5-C5H5;tedip = (EtO)2POP(OEt)2) have been synthesized in high yield from thereaction of tedip and thecorresponding species[M2Cp2(CO)4]. Thestructure of the ditungsten compound has beendetermined through a single-crystal X-ray study. Thermolyticdecarbonylation of thedimolybdenum complex gives the phosphido−phosphonate compound[Mo2Cp2{μ-OP(OEt)2}{μ-P(OEt)2}(CO)2] which results froma P−O bond oxidative addition of the backbone of thetedip ligand to the dimetal center. The latter compound reactsrapidly with CO at roomtemperature to give the tetracarbonyl species[Mo2Cp2{μ-OP(OEt)2}{μ-P(OEt)2}(CO)4],aprocess that can be reversed either thermal or photochemically.Additional experimentsshow that the above tetracarbonyl complex can be partially convertedinto[Mo2Cp2(CO)4(μ-tedip)], which means that the P−O cleavage of the tedip ligandis reversible. Theditungsten title complex behaves in a related way but gives at 140 °Ca mixture of di- andtetracarbonyl phosphido−phosphonate products. Photochemicaldecarbonylation of the titledimolybdenum compound showed low selectivity and under a variety ofexperimentalconditions gave a mixture of the phosphido−phosphonate complexes[Mo2Cp2{μ-OP(OEt)2}{μ-P(OEt)2}(CO)2] and[Mo2Cp2{μ-OP(OEt)2}{μ-P(OEt)2}(μ-CO)]and the triply-bonded [Mo2Cp2(CO)2(μ-tedip)], which could notbe isolated from the reaction mixtures. By contrast,photolysis of the ditungsten title compound at −15 °C gave as amajor product thehydridocyclopentadienylidene complex[W2(μ-η1,η5-C5H4)Cp(μ-H)(CO)3(μ-tedip)]along withsome[W2Cp2(CO)2(μ-tedip)].The cyclopentadienylidene complex decomposes rapidly atroomtemperature to give a mixture of the starting compound and[W2Cp2{μ-OP(OEt)2}{μ-P(OEt)2}(CO)2]. The underlying reaction pathways in thedecarbonylation of the title compoundsare discussed on the basis of the above data and several separateexperiments.
- Depending on the metal andexperimental conditions, decarbonylation of the title compounds caninduce either C−H bond cleavage in the cyclopentadienyl ligand orP−O bond cleavage in the backbone of the tetraethyl pyrophosphiteligand to give products as the ones shown in the figure. Both typeof processes have been found to be reversible under the appropriateconditions.
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