Copper-NHC-Mediated Semihydrogenation and Hydroboration of Alkynes: Enhanced Catalytic Activity Using Ring-Expanded Carbenes

Abstract

A series of two-coordinate copper tert-butoxide complexes bearing five-, six-, and seven-membered ring N-heterocyclic carbenes, prepared by protonolysis of (NHC)CuMes with t BuOH, have been used as catalytic precursors in the semihydrogenation of alkynes with silanes/ t BuOH and the hydroboration of alkynes with HBPin. Both processes proceed with high regioselectivity and show enhancements with six-and seven-membered ring carbenes.

Twisting the arm: structural constraints in bicyclic expanded-ring N-heterocyclic carbenes

“…2,3 These effects are associated with a wider N-C-N angle that leads to a reduced s orbital contribution on the carbon 'lone pair' (electronic effect). The exosubstituents in ER-NHCs are thrust towards the metal centre (steric effect) which has repercussions on their coordination chemistry/catalytic application and can lead to improved per-formance over analogous complexes of 3e,4 Electronic product control in gold(I) catalysed cyclisations has been observed recently by Bielawski and coworkers 5 whereas Aldridge et al 2b have noted the unusual occurrence of backbone C-H activation in ER-NHC complexes of iridium. This latter activity has been attributed to the large size of the ligands which preclude coordination of more than one ER-NHC at a single metal centre.…”

The first ring-expanded NHC–copper(i) phosphides as catalysts in the highly selective hydrophosphination of isocyanates

“…[24][25][26] RE-NHCcopper(I) complexes such as copper(I) halides and copper(I) alkoxides have been established as having enhanced catalytic activity over their five-membered ring counterparts. [27][28][29] We thus set out to synthesise and characterise a range of low-coordinate copper phosphide species supported by both 5-and 6-membered NHCs in order to evaluate their potential as catalytic intermediates. Herein we report the rational synthesis of four (NHC)CuPPh 2 compounds (NHC = IPr, 6-Dipp, SIMes and 6-Mes), including the first examples of RE-NHC copper phosphides.…”

Sterically Demanding AgI and CuI N‐Heterocyclic Carbene Complexes: Synthesis, Structures, Steric Parameters, and Catalytic Activity

“…Spectroscopic characterization of Ag I erNHC complexes 2 – 7 by 13 C{ 1 H} NMR reveals the typical carbene carbon (C NHC ) signals of two doublets displaced in high chemical shifts with coupling constants of 1 J C 107 Ag =224–227 Hz, and 1 J C 109 Ag =260–263 Hz, in agreement with the spin–spin interaction between 107 Ag (spin , 51.8 %) and 109 Ag (spin , 48.2 %) isotopes with the singlet C NHC . The ratio of these constants reflects approximately the gyromagnetic ratio γ for the two silver nuclei involved that is γ( 109 Ag)/γ( 107 Ag)=1.15 …”

“…BF 4 − or PF 6 − ) rather than halides (e.g. Br − , Cl − , I − ), presumably due to the halide counter anion is being able to form an hydrogen bond with the C2‐H amidinium proton . Hence, the optimization experiments employing the erNHC salts of bulky ligands 9‐Dipp and 10‐Dipp were conducted (Table ).…”