Steric and Electronic Effect of Cp-Substituents on the Structure of the Ruthenocene Based Pincer Palladium Borohydrides.

Ruthenocene-based PCP pincer ligands were used to synthesize novel pincer palladium chloride Rc[PCP]PdCl () and two novel palladium tetrahydroborates Rc[PCP]Pd(BH) () and Rc[PCP]Pd(BH) (), where Rc[PCP] = κ-{2,5-(tBuPCH)CH}Ru(Cp) (Cp = CMeCF), and Rc*[PCP] = κ-{2,5-(tBuPCH)CH}Ru(Cp*) (Cp* = CMe). These coordination compounds were characterized by X-ray, NMR and FTIR techniques. Analysis of the X-ray data shows that an increase of the steric bulk of non-metalated cyclopentadienyl ring in and relative to non-substituted Rc[PCP]Pd(BH) analogue (; where Rc[PCP] = κ-{2,5-(tBuPCH)CH}Ru(Cp), Cp = CH) pushes palladium atom from the middle plane of the metalated Cp ring in the direction opposite to the ruthenium atom. This displacement increases in the order < < following the order of the Cp-ring steric volume increase. The analysis of both X-ray and IR data suggests that BH ligand in both palladium tetrahydroborates and has the mixed coordination mode η. The strength of the BH bond with palladium atom increases in the order Rc[PCP]Pd(BH) < Rc*[PCP]Pd(BH) < Rc[PCP]Pd(BH) that appears to be affected by both steric and electronic properties of the ruthenocene moiety.