Synthesis, molecular structure, and reactivity of allenylideneosmium complexes of the half-sandwich-type

Abstract

The reaction of the areneosmium(II) compunds [Os(η6-arene)(L)X2] 2a–2e, 3, 4 with propargylic alcohols HCCCR2(OH) (where R = phenyl or p-tolyl) in the presence of AgPF6 leads to the formation of the cationic osmium allenylidenes [Os(η6-arene)(CCCR2)(L)X]PF65a–5h in good to excellent yields. Salt metathesis of 5a (L = PMe3) and 5b (L = PCy3) with NaB(ArF)4 gives [Os(η6-mes)(CCCPh2)(PR3)Cl]B(ArF)46a, 6b while treatment of 5b with KBr, NaI and CF3CO2Ag affords the corresponding bromo, iodo and trifluoracetato complexes [Os(η6-mes)(CCCPh2)(PCy3)X]PF67a–7c. Compound 5a reacts with MeOH and EtOH to give the Fischer-type osmium carbenes [Os(η6-mes){C(OR)CHCPh2}(PMe3)Cl]PF68a and 8b, of which 8a has been converted by treatment with NaH to the neutral allenyl complex [Os(η6-mes){C(OMe)CCPh2}(PMe3)Cl] 9. The reaction of 5a and 5b with tertiary phosphines PR′3 yields a mixture of [Os(η6-mes){C(PR′3)CCPh2}(PR3)Cl]PF610a–10c and [Os(η6-mes)(PR3)(PR′3)Cl]PF611a–11c, which could not be separated by analytical tools. The cationic bis(phosphine) compounds 11a–11c were prepared independently from 2a–2c and PMe3 in the presence of NH4PF6. The molecular structures of 5a and 8b were determined crystallographically.