An experimental and theoretical study into the facile, homogenous (N-heterocyclic carbene)2-Pd(0) catalyzed diboration of internal and terminal alkynes

Melvyn B Ansell,Oscar Navarro,Vitor H Menezes Da Silva,John Spencer,Gabriel Heerdt,Ataualpa A C Braga

doi:10.1039/c6cy01266c

Melvyn B Ansell, Oscar Navarro + Show 4 more

Open Access

https://doi.org/10.1039/c6cy01266c

Copy DOI

Abstract

Pd(ITMe)2(PhCCPh) is a pre-catalyst in the unprecedented homogenous catalyzed diboration of terminal and internal alkynes.

Highlights

Scheme 1 Palladium catalyzed diboration of alkynes.Paper endothermic with a very low reverse activation barrier[16] and kinetically and thermodynamically unfavourable.We recently reported the synthesis of the N-heterocyclic carbene bearing[17] complex PdIJITMe)2(PhC CPh) (ITMe = 1,3,4,5-tetramethylimidazol-2-ylidene) (1) and its high catalytic reactivity in bis-silylation[18] and silaboration of internal and terminal alkynes.[19]
DFT calculations suggest that a similar reaction pathway to that proposed for platinum phosphine analogues is followed, and that destabilization of key intermediates by the NHCs is vital to the overall success for the palladium-catalyzed B–B addition to alkynes
Low catalyst loadings and temperatures were used for the 100% stereoselective synthesis of syn-1,2-diborylalkenes

Summary

Introduction

The bis-ligand complex is energetically preferred for both NHC and phosphine systems, in the oxidative addition of bisIJpinacolato)diboron to the Pd centre (see ESI† for more details on the free energy profile of reaction pathways).

Results

Conclusion