Synthesis and characterisation of mono-acetylide and unsymmetrical bis-acetylide complexes of ruthenium and osmium: X-ray structure determinations on[(dppe)(2)Ru(Cl)(C C-C6H4-p-NO2)], [(dppe)(2)Ru(Cl)(C C-C6H3-o-CH3-p-NO2)] and [(dppm)(2)Os(C C-C6H4-p-CH3)(C C-C6H4-p-NO2)]

The synthesis of a series of metal mono-acetylides trans-[(dppe)(2)Ru(Cl)(C =C-R)] (R = C6H4-p-C6H5, C6H4-p-CH3, C6H4-p-NO2, C6H3-o-CH3-p-NO2, dppe = P h2PCH2CH2PPh2), and unsymmetrical metal bis-acetylides trans-[(dppm)(2)M(C= C-R)(C=C-R)]; (M = Ru, Os; R = C6H4-p-NO2, R' = C6H5, C6H4-p-CH3; R = C6H5, R' = C6H4-p-CH3) using a variety of sigma-acetylide coupling reactions is reported. Three compounds have been structurally characterised, including t he unsymmetrical trans[(dppm)(2)Os(C=C-R)(C=C-R')] (R = C6H4-p-CH3, R' = C6 H4-p-NO2] which shows the 'rigid-rod' nature of the acetylide-metalacetylid e linkage. The electrochemistry of symmetrical and unsymmetrical Ru(II) com plexes demonstrates the role of the acetylide and the auxiliary ligands in determining the ease of oxidation at the metal centre whilst W-vis spectral changes illustrate the influence of electron-withdrawing and -donating lig ands. (C) 1999 Elsevier Science S.A. All rights reserved.