Addition of dimethylphenylphosphine to µ- and µ3-alkynyl and µ3- allenyl ligands in triosmium clusters: X-ray crystal structures of three zwitterionic adducts

Abstract

The µ₃-alkynyl complexes [Os₃H(CO)₉(CCR)](R = H, Me, Ph, or CMe₂OH), the µ-alkynyl complex [Os₃H(CO)₁₀(CCPh)], and the µ₃-allenyl complex [Os₃H(CO)₉(MeCCCH₂)] all form 1 :1 adducts with PMe₂Ph. The tertiary phosphine molecules add at carbon atoms to give zwitterionic complexes containing phosphonium centres and negative charges formally on the metal atoms. To confirm structures based on ¹H n.m.r. and i.r. data, single-crystal X-ray structures of three rather different adducts have been determined. Crystals of [Os₃H(CO)₉(HCCPMe₂Ph)] are monoclinic, space group P2₁/c, with a= 14.579(6), b= 8.301(3), c= 19.523(9)Å, β= 93.45(2)°, Z= 4, and final R= 0.053. Crystals of [Os₃H(CO)₉(MeCCCH₂PMe₂Ph)] are monoclinic, space group C_c with a= 15.990(5), b= 11.974(4), c= l3.480(4)Å, β= 98.11(2)°, Z= 4, and final R= 0.037. Crystals of [Os₃H(CO)₁₀(CCPhPMe₂Ph)] are triclinic, space group P, with a= 14.075(3), b= 12.210(3), c= 8.724(2)Å, α= 100.86(3), β= 95.41(2)γ= 101.5l(3)°, Z = 2, and final R= 0.040. The two nonacarbonyl complexes are structurally very similar, both containing µ₃-alkyne ligands with phosphonium centres positioned β and γ respectively to the metal atoms. The different relative positions of the phosphonium centres have no detectable effect on structural parameters but lead to different carbonyl-stretching frequencies. The fluxional behaviour of the µ₃-alkyne complexes is described. Whereas PMe₂Ph attack is at the 1-position of the µ₃-alkynyl ligands, it is at the 2-position of the µ-alkynyl ligand to give [Os₃H(CO)₁₀(CCPhPMe₂Ph)] which is structurally characterised as containing a µ-alkylidene ligand with a phosphonium substituent.