Effect of Ancillary Ligands on Ru(II) on Electronic Delocalization in Ruthenium(II) Bisferrocenylacetylide Complexes

Abstract

The synthesis and properties of [cis-Ru(dppm)2(C⋮CFc)2]CuI (dppm = Ph2PCH2PPh2, Fc = ferrocenyl) (1) and trans,trans,trans-Ru(PBu3)2(CO)(L)(C⋮CFc)2 (3, L = CO; 4, L = pyridine; 5, L = P(OMe)3) are reported. The ruthenium bisacetylide bridges in these complexes allow electronic interaction between the terminal ferrocenyl groups. The interaction is enhanced when the ancillary ligands on the ruthenium center are electron donors and lessened when the ligands are acceptors. Complex 1 was prepared in 70% yield by the coupling of FcC⋮CSn(n-Bu)3 and cis- or trans-RuCl2(dppm)2 in the presence of excess CuI and was crystallographically characterized. Removal of the coordinated CuI from 1 with excess P(OMe)3 yields trans-Ru(dppm)2(C⋮CFc)2 (2). Reaction of 2 with CuI yields 1. trans,trans,trans-Ru(PBu3)2(CO)2(C⋮CFc)2 (3) was synthesized from RuCl2(CO)2(PBu3)2 and FcC⋮CSn(n-Bu)3 using a CuI catalyst and was crystallographically characterized. Reaction of 3 with excess pyridine yields trans,trans,trans-Ru(PBu3)2(CO)(py)(C⋮CFc)2 (4). The reaction is reversible; 3 may be obtained by reacting 4 with excess carbon monoxide. Reaction of 4 with P(OMe)3 yields trans,trans,trans-Ru(PBu3)2(CO)(P(OMe)3)(C⋮CFc)2 (5). Dications of all the complexes were prepared by oxidation with 2 equiv of FcPF6, and monocations were prepared in solution by reaction of the neutral complexes with the dications. The difference between the first and second ferrocenyl oxidations (ΔE1/2) in the cyclic voltammograms of 1, 3, 4, and 5 are 0.14, 0.09, 0.13, and 0.15 V, respectively. Characterization of the complexes by visible, IR, and near-IR spectroscopy supports the conclusion that the ligand environment of the ruthenium center affects the extent of electronic delocalization between the ferrocenyl groups.