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

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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 Cc 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.

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