σ-Acetylide complexes of ruthenium and osmium containing alkynylsilane ligands

The use of the ligands, diethynyldiphenylsilane and 1,3-diethynyltetramethyldisiloxane, in the synthesis of Group 8 metal σ-acetylide mononuclear complexes is demonstrated. New complexes trans-[(dppm)2ClMCCSi(Ph)2CCH] (M=Ru 1; Os 2) and trans-[(dppm)2ClMCCSi(Me)2–O–Si(Me)2CCH] (M=Ru, 3; Os, 4) featuring different silyl units were prepared from a mixture of cis-[M(dppm)2Cl2] and HCCSi(Ph)2CCH or HCCSi(Me)2–O–Si(Me)2CCH in the presence of NaPF6 followed by deprotonation with 1,8-diazabicyclo[5.4.0]undec-7-ene. All the new complexes have been fully characterized by FTIR and NMR spectroscopies and fast atom bombardment mass spectrometry. Single-crystal X-ray structures of 1 and 2 confirm that the two diphosphines adopt a trans geometry at the metal centre and one of the terminal ethynyl groups remains intact. Complexes 1–4 show reversible redox chemistry and their half-wave potentials due to the metal centres are less anodic than those for the starting precursors cis-[M(dppm)2Cl2] (M=Ru, Os).