X-ray crystallography and electrochemistry reveal electronic and steric effects of phosphine and phosphite ligands in complexes RuII(κ4-bda)(PR3)2 and RuII(κ3-bda)(PR3)3 (bda?=?2,2′-bipyridine-6,6′-dicarboxylato)

Article abstract of DOI:10.1016/j.poly.2018.12.033

We have examined coordination of PR₃ = triphenylphosphine, triethylphosphine, triisopropyl phosphite, trimethyl phosphite, and 1,3,5-triaza-7-phosphaadamantane (PTA) to the fragment Ru^II(bda) to better understand how different phosphine and phosphite ligands influence the electronic and structural properties of the Ru^II complexes. PTA and P(OMe)₃ afforded complexes with three phosphorus ligands bound to Ru, with the bda being tridentate (κ³-N,N,O) in complexes 4 and 5; for the other three phosphorus ligands, even in the presence of >2 equiv, only Ru^II(κ⁴-bda)(PR₃)₂ species 1–3 were seen. Both experimental and computational methods were used to study the complexes. Steric effects are the main factor determining whether bis- or tris(PR₃) complexes are formed. Cyclic voltammetry studies of the complexes revealed an increase in Ru^III/II potential upon having another phosphorus ligand in the equatorial position. Computational studies predict that the additional phosphine ligand in the equatorial plane of 4 engages in significant orbital mixing with the ruthenium center that results in lower energy bonding as compared to the axial phosphine ligands. This work provides the first evaluation of phosphorus ligand steric and electronic effects on the Ru^II(bda) fragment.