Bulky <i>N</i>-Heterocyclic Carbene IPr* in Selected Organo- and Transition Metal-Mediated Catalytic Applications

A series of studies were conducted to probe the stability and reactivity of a very sterically encumbered N-heterocyclic carbene. The X-ray structure of the NHC IPr* (IPr* = 1,3-bis­(2,6-bis­(diphenylmethyl)-4-methylphenyl)­imidazol-2-ylidene) was determined. IPr* was used as an organocatalyst in transesterification reactions. Steric and electronic parameters characterizing IPr* were determined via the synthesis of a nickel-carbonyl complex, [Ni­(CO)3(IPr*)]. A related complex, [(Cp*)­Ru­(IPr*)­Cl] (Cp* = η5-C5Me5), was prepared and characterized by X-ray crystallography, and its catalytic performance in the racemization of chiral alcohols is reported. The catalytic performance of the NHC and of its transition metal derivatives permit establishing the standing of this uniquely bulky member among the NHC family.本系列研究旨在探究一款空间位阻极大的氮杂环卡宾（N-heterocyclic carbene, NHC）的稳定性与反应活性。研究人员测定了该NHC即IPr*（IPr* = 1,3-双(2,6-二(二苯甲基)-4-甲基苯基)咪唑-2-亚基）的X射线晶体结构。将IPr*作为有机催化剂应用于酯交换反应中。通过合成羰基镍配合物[Ni(CO)₃(IPr*)]，测定了IPr*的空间与电子参数。制备了相关配合物[(Cp*)Ru(IPr*)Cl]（其中Cp* = η⁵-五甲基环戊二烯基），并通过X射线衍射对其进行表征，同时报道了其在手性醇外消旋化反应中的催化性能。该NHC及其过渡金属衍生物的催化性能，有助于明确这款极具空间位阻的NHC成员在氮杂环卡宾家族中的定位。