910294-48-3Relevant academic research and scientific papers
M-P versus M=M bonds as protonation sites in the organophosphide-bridged complexes [M2Cp2(μ-PR2)(μ- PR′2)(CO)2], (M = Mo, W; R, R′ = Ph, Et, Cy)
Alvarez, M. Angeles,Garcia, M. Esther,Martinez, M. Eugenia,Ramos, Alberto,Ruiz, Miguel A.,Saez, David,Vaissermann, Jacqueline
, p. 6965 - 6978 (2008/10/09)
The unsaturated complexes [W2Cp2(μ-PR 2)(μ-PR′2)(CO)2] (Cp = η5-C5H5; R = R′ = Ph, Et; R = Et, R′ = Ph) react with HBF4·OEt2 at 243 K in dichloromethane solution to give the corresponding complexes [W 2Cp2(H)(μ-PR2)(μ-PR′2) (CO)2]BF4, which contain a terminal hydride ligand. The latter rearrange at room temperature to give [W2Cp 2(μ-H)(μ-PR2)(μ-PR′2)(CO) 2]BF4, which display a bridging hydride and carbonyl ligands arranged parallel to each other (W-W = 2.7589(8) A when R = R′ = Ph). This explains why the removal of a proton from the latter gives first the unstable isomer cis-[W2Cp2(μ-PPh 2)2(CO)2]. The molybdenum complex [Mo 2Cp2(μ-PPh2)2(CO)2] behaves similarly, and thus the thermally unstable new complexes [Mo 2Cp2(H)(μ-PPh2)2(CO) 2]BF4 and cis-[Mo2Cp2(μ-PPh 2)2-(CO)2] could be characterized. In contrast, related dimolybdenum complexes having electron-rich phosphide ligands behave differently. Thus, the complexes [Mo2Cp2(μ-PR 2)2(CO)2] (R = Cy, Et) react with HBF 4·OEt2 to give first the agostic type phosphine-bridged complexes [Mo2Cp2(μ-PR 2)(μ-κ2-HPR2)(CO)2]BF 4 (Mo-Mo = 2.748(4) A for R = Cy). These complexes experience intramolecular exchange of the agostic H atom between the two inequivalent P positions and at room-temperature reach a proton-catalyzed equilibrium with their hydride-bridged tautomers [ratio agostic/hydride = 10 (R = Cy), 30 (R = Et)]. The mixed-phosphide complex [Mo2Cp2(μ-PCy 2)(μ-PPh2)(CO)2] behaves similarly, except that protonation now occurs specifically at the dicyclohexylphosphide ligand [ratio agostic/ hydride = 0.5]. The reaction of the agostic complex [Mo 2Cp2(μ-PCy2)(μ-κ2- HPCy2)(CO)2]BF4 with CNtBu gave mono- or disubstituted hydride derivatives [Mo2Cp2(μ-H) (μ-PCy2)2(CO)2-x(CNtBu) x]BF4 (Mo-Mo = 2.7901(7) A for x = 1). The photochemical removal of a CO ligand from the agostic complex also gives a hydride derivative, the triply bonded complex [Mo2Cp 2(H)(μ-PCy2)2(CO)]BF4 (Mo-Mo = 2.537(2) A). Protonation of [Mo2Cp2(μ-PCy 2)2(μ-CO)] gives the hydroxycarbyne derivative [Mo 2Cp2(μ-COH)(μ-PCy2)2]BF 4, which does not transform into its hydride isomer.
