Copper(I) complexes of 1,2-bis(diphenylphosphino)benzene as efficient catalysts for alkyne hydroamination and azide-alkyne cycloaddition

Abstract

This paper reports the synthesis of a small group of three copper(I) complexes using 1,2-bis(diphenylphosphino)benzene, abbreviated as dppbz, and their utilization as catalyst for CN bond formation reactions. Reaction of dppbz has been carried out with three different copper(I) sources. While reaction with [Cu(CH3CN)4]ClO4 affords [CuI(dppbz)2]ClO4 (complex 1), that with CuI and CuSCN affords di-copper complexes [{CuI(dppbz)I}2] and [{CuI(dppbz)(SCN)}2] (complexes 2 and 3) respectively. Bulk characterization on the complexes has been done by elemental (C, H, N) analysis, magnetic susceptibility measurement, and spectroscopic (IR, NMR and UV–vis) methods. Crystal structures of all three complexes have been determined. In [CuI(dppbz)2]ClO4, copper(I) is having a highly distorted tetrahedral CuP4 core. In [{CuI(dppbz)I}2] and [{CuI(dppbz)(SCN)}2], the tetrahedral CuP2I2 and CuP2SN cores are relatively less distorted. These copper complexes have been found to serve as efficient catalyst precursors for two types of CN bond formation reactions, viz. hydroamination and click reaction. Hydroamination of aryl alkynes with aryl amines has afforded selectively imine products of a single type (Markownikov product) in good yields under relatively mild condition. However, similar hydroamination with benzyl amines or alkyl amines has afforded selectively anti-Markownikov imine products. Click reaction between aryl alkynes and aryl azides yielding the cycloaddition products has also been brought about successfully with remarkable catalytic efficiency.