Rhodium and Palladium Complexes of a 3,5-Lutidine-Based Phosphine Ligand

The chelating bis(phosphine) 3,5-bis((diphenylphosphino)methyl)pyridine (dppLH, 9) was synthesized from 3,5-lutidine by radical chlorination, followed by reaction with LiPPh₂. Compound 9 was used to prepare Rh and Pd complexes. The three complexes (dppL)RhL (L = PⁱPr₃ (11), PPh₃ (12), and CO (13)) are obtained from Rh₂Cl₂(COE)₄ (COE = cyclooctene) and HRh(PPh₃)₄. Compound 9 reacts with (PhCN)₂PdCl₂ to form the Pd(II) complex (dppL)PdCl (14). All complexes are fully characterized. The X-ray crystal structure of 11 has been determined. It crystallizes in the triclinic space group P1̄ (No. 2) with a = 12.242(3) Å, b = 14.384(3) Å, c = 11.653(2) Å, α = 98.61(2)°, β= 96.88(2)°, γ = 106.38(2)°, V = 2023.3(8) ų, Z = 2, R = 0.045, and R_w = 0.052. The Rh(I) center is in a square-planar coordination environment with the two phosphines of the dppL ligand framework being trans to each other. The pyridine nitrogen is unobstructed and available for binding to other metal centers. Compound 14 acts as a metalloligand toward Pd(II) centers to form the trinuclear complex {(dppL)PdCl}₂PdCl₂ (16). N-coordination of a metal moiety and of a Lewis acid influences the electronic properties on the Pd center.