Rhenium carbonyl complexes with monodentate-coordinated diphosphines: activation of terminal phosphino groups towards amine-oxide oxidation

Terminal phosphino groups of [Re2(CO)9(η1-P-P)] (P-P = diphosphines) are activated towards oxidation by Me3NO. The respective reactions of Me3NO with [Re2(CO)9{η1-P(o-anisyl)2(CH2)3PPh2}], [Re2(CO)9{η1-PPh2(CH2)3P(o-anisyl)2}] and [Re2(CO)9(η1-trans-PPh2CHdouble bond; length as m-dashCHPPh2)] were studied to investigate the mechanism of this oxidation. The results are consistent with an intramolecular pathway involving a cyclic intermediate, without exchange of the coordinated and terminal phosphino groups. A mechanism which involves an interaction of the terminal phosphino group with a carbonyl ligand is proposed. In sharp contrast to eq-[Re2(CO)9(η1-P-P)] (P-P = Ph2P(CH2)nPPh2, n = 1–6), eq-[Re2(CO)9(η1-trans-PPh2CHdouble bond; length as m-dashCHPPh2)] appears to be indefinitely stable towards equatorial → axial isomerization at room temperature, thus, allowing its crystal structure to be determined.