Structure And Catalytic Activity Of Ni,Pd,Pt Complexes Supported By PBP And POCOP Pincer Ligands

Transition metal pincer complexes play an extremely important role in the fields of metal organic chemistry and homogeneous catalysis.For this type of complexes,the pincer backbone framework can significantly affect the structure and properties of the complexes.Based on the previous work,a series of Yamashita-Nozaki PBP-type pincer nickel,palladium and platinum complexes were synthesized;the structure and catalytic performance of these complexes were systematically studied and compared with the corresponding POCOP-type nickel,palladium and platinum pincer complexes.The specific work is as follows:Firstly,two series of palladium(II)complexes supported by PBP and POCOP pincer ligands with SH^-,(?)CS^-,(?)CSe^-,N₃^-or OTf^-as the covalent ligand,[C₆H₄-1,2-(NCH₂P^tBu₂)₂B]Pd Y(Y=SH,NCSe,OTf)and[C₆H₃-2,6-(OP^tBu₂)₂]Pd Y(Y=NCS,NCSe,N₃,OTf),were prepared and fully characterized.The structure and properties of these two series of complexes were investigated.It was found that the palladium centre is less tightly chelated and more electron rich in the PBP system compared with that in the POCOP system.However,the strong?-donor ability of the boryl ligand has very little influence on the structures of the covalent ligands even for those possessing both?-donor and?-acceptor properties.Next,the reactivity of[C₆H₃-2,6-(OP^tBu₂)₂]Pd SY(Y=SH,SCH₂Ph)against BH₃�THF was explored and the coordination mode of BH₄^-in these complexes was studied in detail.Meanwhile a series of PBP boron-based pincer transition metal tetrahydroborate complex were synthesized and fully characterized by multinuclear NMR,FTIR,HRMS and single crystal X-ray analysis.X-ray crystallography and FTIR studies supported a?¹-HBH₃ monodentate coordination mode for the BH₄ligand in[C₆H₃-2,6-(OP^tBu₂)₂]Pd BH₄ and a?²-H₂BH₂ coordination mode in other complexes.Finally,the catalytic property of[C₆H₄-1,2-(NCH₂P^tBu₂)₂B]Pd Cl and[C₆H₃-2,6-(OP^tBu₂)₂]Pd Cl towards the Suzuki�Miyaura cross-coupling reaction was investigated.Complex[C₆H₄-1,2-(NCH₂P^tBu₂)₂B]Pd Cl is a much better catalyst for the Suzuki�Miyaura cross-coupling reaction compared with[C₆H₃-2,6-(OP^tBu₂)₂]Pd Cl.At 80?C,a maximum turnover frequency(TOF)of 30,000 h^-1was observed in toluene solution.The above results are of great significance for the development of the chemistry of transition metal piner complexes and homogeneous catalysis.