Steric control over the formation of cis and trans bis-chelated palladium(ii) complexes using a new series of flexible N,P pyridyl–phosphine ligands
作者:Deborah A. Clarke、Philip W. Miller、Nicholas J. Long、Andrew J. P. White
DOI:10.1039/b709032c
日期:——
The deprotection of phosphonium chloride salts [PR2(CH2OH)2]+Clâ and subsequent condensation reaction with N-methyl-2-aminopyridine has been carried out to give a series of ligands of the form PR2CH2N(CH3)C5H4N (R = Ph 6, Cy 7, t-Bu 8) which have been fully characterised either as the pure ligand (6) or the air stable borane adducts (R = Cy 7a, t-Bu 8a). The 1 : 1 reactions of 6, 7 and 8 with PdCl2(COD) gave the N,P chelate complexes [PdPR2CH2N(CH3)C5H4N}Cl2]; the Cy (10) and t-Bu (11) complexes were characterised by X-ray crystallography. The bisligated species [PdPCy2CH2N(CH3)C5H4N}2Cl2] (12) was obtained when the reaction was carried out at higher temperatures and the ligands were found to be coordinated to the metal in a trans configuration through the phosphorus donors. Abstraction of the chlorides from the bis-ligated species 12, using silver salts, resulted in the coordination of the pyridine ring forming the bis-chelate complex [PdPCy2CH2N(CH3)C5H4N}2]2+13. In comparison, the palladium bis-chelate complex of ligand 5 [PdPPh2CH2N(CH3)C5H4N}2]2+ (14) was shown to form in a cis configuration and was fully characterised by X-ray crystallography.
去保护磷盐酸盐[PR2(CH2OH)2]+Cl¯并与N-甲基-2-氨基吡啶进行后续缩合反应,得到一系列形式为PR2CH2N(CH3)C5H4N的配体(R = Ph 6,Cy 7,t-Bu 8),这些配体要么作为纯配体(6)被完全表征,要么作为稳定的硼烃加合物(R = Cy 7a,t-Bu 8a)。配体6、7和8与PdCl2(COD)的1:1反应生成了N,P螯合物[PdPR2CH2N(CH3)C5H4N}Cl2];Cy (10)和t-Bu (11)配合物通过X射线晶体学进行表征。当在更高温度下进行反应时,得到的双配体物种[PdPCy2CH2N(CH3)C5H4N}2Cl2] (12),发现配体通过磷供体以反式构型与金属配位。使用银盐从双配位物种12中抽取氯离子,导致吡啶环的配位,形成双螯合物[PdPCy2CH2N(CH3)C5H4N}2]2+ (13)。相比之下,配体5的钯双螯合物[PdPPh2CH2N(CH3)C5H4N}2]2+ (14)显示为顺式构型,并通过X射线晶体学进行完全表征。