Organobimetallic RuII–ReI4-ethynylpyridyl complexes: structures and non-linear optical properties

Abstract

A series of heterobimetallic complexes, [RuCp(CCpy-4)(P-P)][Re(CO)₃(N-N)]⁺ (P-P = dppf, N-N = bpy 5, Me₂bpy 6, ^tBu₂bpy 7, phen 8, tpy 9; P-P = 2PPh₃, N-N = bpy 10) have been obtained from Lewis addition between the metalloligands [RuCp(CCpy-4)(P-P)] (P-P = dppf 1; 2PPh₃2) and solvent-stabilised fac-[Re(CH₃CN)(CO)₃(N-N)]⁺. All new complexes 5–10, together with fac-[ReBr(CO)₃(tpy)] (3) and fac-[Re(CH₃CN)(CO)₃(tpy)][PF₆] (4), are characterized by solution spectroscopy; 3 and 5–9 are also characterized by single-crystal X-ray crystallography. The terpyridine ligands in 3 and 9 are in an unusual η²-bidentate coordination mode with a pendant pyridyl. Electrochemical studies showed successive metal-based oxidations and a ligand-centered reduction in 5–10. Significant oxidation changes are observed at the Ru(II) and Re(I) centers in 5–10 when compared with their respective monometallic components. Cubic nonlinearities of 5–10 determined by the Z-scan technique at 750 nm reveal two-photon absorption that increases significantly on progression from Ru(II) monomeric precursors to heterobimetallics, suggesting NLO enhancement upon heterometallic complex formation.