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

Abstract

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 (σ_p), suggesting appreciable 'communication' along the through-conjugate chain. Cyclic voltammety shows irreversible oxidative behaviour, at more anodic E_pa than in the respective alkynyl-chloride complexes, though apparently moderated by the remote substituent.