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(Ar_F)₄ gives [Os(η⁶-mes)(CCCPh₂)(PR₃)Cl]B(Ar_F)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.