A Valuable, Inexpensive Cu^I/N‐Heterocyclic Carbene Catalyst for the Selective Diboration of Styrene

Abstract

The complexes [Cu(NHC)(NCMe)]BF4 (NHC=N-heterocyclic ligand), with bis(catecholato)diboron (B2(cat)2) as the boron source, efficiently catalyze the diboration of styrene with very high degrees of conversion. With the appropriate NHC ligand, the reaction proceeds quantitatively toward the diborated derivative PhCH(Bcat)--CH2(Bcat). The [styrene]/[B2(cat)2] ratio also has a strong effect on the selectivity: the use of an excess of styrene allows modification of the selectivity toward the formation solely of the monoborated derivative, PhCH2--CH2(Bcat). DFT calculations suggest that no oxidative addition processes take place at copper, but that intermediates containing coordinated sigma-bonds are involved in the catalytic cycle.

Synthesis of Copper(I) Complexes of N‐Heterocyclic Carbene–Phenoxyimine/amine Ligands: Structures of Mononuclear Copper(II), Mixed‐Valence Copper(I)/(II), and Copper(II) Cluster Complexes

“…Silver NHC complexes have been of particular interest because of their wide use as ligandtransfer agents [3] to transition metals principally from groups 8-10 and also their biological activity as antimicrobial agents. [4] Copper NHC complexes have now been shown to act as precatalysts for a range of reactions, [5] including conjugate addition, [6] alkylation/arylation, [7] reduction, [8] cycloaddition, [9] carbonylation, [10] hydrosilylation, [11] and more recently boration, [12] aziridination [13] and hydroamination/hydrothiolation. [14] Since 2003 the in an ellipse motif.…”

Singular Metal Activation of Diboron Compounds

“…Fernández and Pérez studied the nature of the interaction between the unsaturated complex [Cu(NHC)(NCMe)] + and B 2 cat 2 through a theoretical DFT study with the B3LYP functional in order to understand the activation mode. 94 The results were conclusive, in favor of the [Cu(NHC)(σ-catB-Bcat)] + (18) description (Fig. 3 unbroken BdB bond coordinates Cu as a B-B sigma adduct.…”

Catalytic asymmetric boron–boron addition to unsaturated molecules

“…We studied the potential of several complexes containing the (NHC)Cu core as the catalyst for this reaction (Fig. 2) [31] given the success that Cu complexes have displayed in related catalytic transformations [32]. We found that the complexes [(NHC)Cu (NCMe)]BF 4 efficiently catalyze the diboration of styrene, when bis(catechol)diboron is used as the boryl source, with a very high degree of conversion.…”