Oxidative Additions of Coordinated Ligands at Unsaturated Molybdenum and Tungsten Diphosphine-Bridged Carbonyl Dimers. 1. Decarbonylation Reactions of [W₂(η⁵-C₅H₅)₂(CO)₄(μ-R₂PCH₂PR₂)] (R = Ph, Me)^†

The new complexes [W₂Cp₂(CO)₄(μ-L₂)] (Cp = η⁵-C₅H₅; L₂ = Ph₂PCH₂PPh₂ (dppm), Me₂PCH₂PMe₂ (dmpm)) have been prepared from [W₂Cp₂(CO)₄] and the corresponding diphosphine at room temperature. Decarbonylation of the dppm complex in refluxing n-octane gives the triply bonded compound [W₂Cp₂(CO)₂(μ-dppm)] as the major product, along with a small amount of the oxo complex [W₂Cp₂(μ-CH₂PPh₂)(O)(μ-PPh₂)(CO)], which results from a P−C(sp³) 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 [W₂Cp₂(O)₂(CO)₂(η¹-dppm)]. Photochemical decarbonylation of [W₂Cp₂(CO)₄(μ-L₂)] proceeds via the hydrido cyclopentadienylidene complexes [W₂(μ-η¹:η⁵-C₅H₄)Cp(μ-H)(CO)₃(μ-L₂)] to finally give the corresponding dicarbonyls [W₂Cp₂(CO)₂(μ-L₂)]. The latter react readily with ^tBuNC at room temperature or below to give [W₂Cp₂(μ-η¹:η²-CN^tBu)(CO)₂(μ-L₂)], which, when L₂ = dppm, isomerizes at room temperature to give [W₂(μ-η¹:η⁵-C₅H₄)Cp(μ-H)(CN^tBu)(CO)₂(μ-dppm)].