Cyaphide-alkynyl complexes: metal-ligand conjugation and the influence of remote substituents.

A homologous series of novel trans-cyaphide-alkynyl complexes, viz. trans-[Ru(dppe)2(C[triple bond, length as m-dash]P)(C[triple bond, length as m-dash]CC6H4R-p)] (R = Me, H, F, CO2Me, NO2) is prepared and comprehensively characterised, alongside their parent phosphaalkyne-complex cations trans-[Ru(dppe)2(η1-P[triple bond, length as m-dash]CSiMe3)(C[triple bond, length as m-dash]CC6H4R-p)]+. Structural data for trans-[Ru(dppe)2(C[triple bond, length as m-dash]P)(C[triple bond, length as m-dash]CC6H4R-p)] (R = Me, F) and trans-[Ru(dppe)2(η1-P[triple bond, length as m-dash]CSiMe3)(C[triple bond, length as m-dash]CC6H4R-p)]+ (R = F, CO2Me) are described, along with that for the previously reported trans-[Ru(dppe)2(C[triple bond, length as m-dash]P)(C[triple bond, length as m-dash]CCO2Me)]. NMR spectroscopic data indicate significant influence of the remote aromatic substituent over the properties of the cyaphide ligand, in line with the Hammett parameter (σp), suggesting appreciable 'communication' along the through-conjugate chain. Cyclic voltammety shows irreversible oxidative behaviour, at more anodic Epa than in the respective alkynyl-chloride complexes, though apparently moderated by the remote substituent.