Remarkable Stability of Copper(II)–N-Heterocyclic Carbene Complexes Void of an Anionic Tether
摘要:
A library of pyridyl- and picolyl-substituted imidazolium salts have been synthesized and coordinated to copper, via transmetalation from silver(I)-N-heterocyclic carbenes (NHCs), to prepare several copper(I)- and copper(II) Cu(NHC)Br, with the solid-state structures revealing a variety of coordination NHC complexes. The copper(I)-NHCs are complexes of the type environments around the copper centers. The stability of the copper(II) complexes is particularly unusual, given the absence of a "hard" anionic tethering group appended to the ligands. The stability has been attributed to the pyridyl substituent, with the complexes being extremely stable, while those with an appended anionic group tend to be more sensitive to air/moisture. The ligands and complexes have been examined in an Ullmann-type etherification reaction and exhibit improved activity in comparison to copper in the absence of a ligand or the common Cu(I)-NHC complexes Cu(IMes)Cl and [Cu(IMes)(2)]PF6, indicating stabilization of higher oxidation state species by the ligands during the catalytic cycle.
Solid-state structure, solution-state behaviour and catalytic activity of electronically divergent C,N-chelating palladium–N-heterocyclic carbene complexes
作者:Michael R. Chapman、Benjamin R. M. Lake、Christopher M. Pask、Bao N. Nguyen、Charlotte E. Willans
DOI:10.1039/c5dt02194d
日期:——
picolyl-substituted imidazoliumsalts have been prepared and coordinated to palladium in a single step, to deliver a variety of palladium(II)–N-heterocyclic carbene (NHC) complexes. Neutral Pd(NHC)X2, cationic [Pd(NHC)2X]X and dicationic [Pd(NHC)2]X2-type complexes have been isolated and fully characterised, with single-crystal X-ray analysis revealing a variety of coordination environments around the palladium centres
已经制备了一系列电子多样的吡啶基和吡啶基取代的咪唑鎓盐,并可以在单个步骤中与钯配位,以提供各种钯(II)–N-杂环卡宾(NHC)配合物。分离并充分表征了中性Pd(NHC)X 2,阳离子性[Pd(NHC)2 X] X和阳离子性[Pd(NHC)2 ] X 2型配合物,单晶X射线分析揭示了多种钯中心周围的协调环境。预先形成的络合物已用于Suzuki-Miyaura模型的交叉偶联反应中,从而产生空间拥挤的四邻位取代的联芳基产品,其营业额数字可与Pd-PEPPSI-IPr催化剂相比。