Palladium() complexes supported by PBP and POCOP pincer ligands: a comparison of their structure, properties and catalytic activity

A Pd( ii ) chloride complex supported by a Yamashita-Nozaki PBP pincer ligand, [C 6 H 4 -1,2-(NCH 2 P t Bu 2 ) 2 B]PdCl ( 1a ), was synthesized. The structure, properties and catalytic activity of complex 1a were compared with those of the corresponding POCOP pincer complex [C 6 H 3 -2,6-(OP t Bu 2 ) 2 ]PdCl ( 2a ). It was found that the Pd centre in complex 1a is more electron rich and easier to be oxidized than that in complex 2a ; complex 1a is a much better catalyst for Suzuki-Miyaura cross-coupling reactions than complex 2a . Starting from complexes 1a and 2a , two series of Pd( ii ) pincer complexes bearing a SH, BH 4 , N&cmb.b.line;CS, N&cmb.b.line;CSe or N 3 covalent ligand, [C 6 H 4 -1,2-(NCH 2 P t Bu 2 ) 2 B]PdY (Y = SH, 1b ; BH 4 ; 1c ; N&cmb.b.line;CS, 1d ; N&cmb.b.line;CSe, 1e ; and N 3 , 1f ) and [C 6 H 3 -2,6-(OP t Bu 2 ) 2 ]PdY (Y = SH, 2b ; BH 4 , 2c ; N&cmb.b.line;CS, 2d ; N&cmb.b.line;CSe, 2e ; and N 3 , 2f ), were synthesized and fully characterized. Single crystal X-ray diffraction analysis indicated that the Pd centre is less tightly chelated in PBP pincer complexes. The strong σ-donor ability of the PBP pincer ligand has little influence on the structure of the covalent ligand possessing both σ-donor and π-acceptor properties. However, the stretching vibrational frequencies of N&cmb.b.line;CS, N&cmb.b.line;CSe and N 3 ligands and the coordination mode of the BH 4 ligand are significantly different in these two types of palladium pincer complexes. The structure, properties and catalytic activity of two series of Pd( ii ) complexes supported by PBP and POCOP pincer ligands were investigated.