Stepwise assembly of linearly-aligned Ru–M–Ru (M = Pd, Pt) heterotrimetallic complexes with σ-4-ethynylpyridine spacer

Abstract

Two heterotrinuclear oligomeric complexes [trans-RuCl(CCpy-4)(dppm)₂]₂[MCl₂] (M = Pd 2; M = Pt 3) are prepared from the metalloligand trans-[RuCl(CCpy-4)(dppm)₂] (dppm = Ph₂PCH₂PPh₂, 1). The resultant linear alignment of the metals [Ru-M-Ru] is imposed by a combinative use of trans-directed spacers and planar metals with trans-juxtaposed donor sites. Ligand exchange of 1 with [Pd(CH₃CN)₄][PF₆]₂ gives trans-[Ru(CH₃CN)(CCpy-4)(dppm)₂][PF₆] (4). All complexes are characterized by single-crystal X-ray crystallography and solution spectroscopy. Acid–base titration on 1 suggested protonation of the pendant pyridyl. Complexes 2 and 3 also undergo protonation at the CC moiety under acid conditions. The inter-conversion of alkynyl and vinylidene functionality is described. The dual acid and base characters of 4 makes it a potential metalloligand towards basic and acidic fragments in multinuclear heterometallic assemblies.