Ni(I)–Alkyl Complexes Bearing Phenanthroline Ligands: Experimental Evidence for CO₂Insertion at Ni(I) Centers

Abstract

Although the catalytic carboxylation of unactivated alkyl electrophiles has reached remarkable levels of sophistication, the intermediacy of (phenanthroline)Ni(I)–alkyl species—complexes proposed in numerous Ni-catalyzed reductive cross-coupling reactions—has been subject to speculation. Herein we report the synthesis of such elusive (phenanthroline)Ni(I) species and their reactivity with CO 2 , allowing us to address a long-standing question related to Ni-catalyzed carboxylation reactions.

Ni‐Catalyzed Direct Carboxylation of Aryl C−H Bonds in Benzamides with CO2

“…On the basis of our experimental results and previous studies, [11,15,16] a plausible mechanism via Ni(0)‐Ni(II)‐Ni(I) catalytic cycle is suggested (Scheme 6). Initially, the Ni(II) catalyst was reduced to catalytically active Ni(0) species by Mn dust in the presence of ligand.…”

Evaluating a dispersion of sodium in sodium chloride for the synthesis of low-valent nickel complexes

“…It does not appear to be nickel(0), otherwise η 2 -or η 6 coordination of a planar arene would be expected, such as in the case of all other unsupported nickel(0)-arene complexes found in the Cambridge Structural Database: 39 nickel complexes with a single NHC or phosphine ligand favour [Ni(η 6 -arene)(L)] geometries, 12,13 while complexes with two monodentate phosphine ligands or one bidentate phosphine ligand favour η 2coordination, 40 even with heteroarenes. 41 The structure in Figure 5 differs from [Ni(μ-κ 2 (N,N):η 2 -2,6-mes2phen)]n (n = 3,4), 23 where each nickel centre coordinates C5 and C6 in an η 2mode rather than C2,C3,C4 in an η 3 -mode as observed here.…”

“…16 In addition, there are relatively few examples of well-defined nickel (pre-)catalysts with bipyridine-type ligands. The developing mechanistic landscape of nickel catalysis continues to implicate nickel(I) complexes as either species that are offcycle and poorly active, 17,18 complexes that are competent for catalysis via a Ni I /Ni III manifold, 19 or the true active species in catalysis; [20][21][22][23] the exact role of nickel(I) in a particular reaction is not easy to determine, and is a function of ligand and substrate structure.…”

Ligand and solvent effects on CO2 insertion into group 10 metal alkyl bonds

“…It has traditionally been challenging to perform kinetics experiments on CO 2 insertion into group 10 alkyl complexes either because of the instability of the complexes 14 or the harsh conditions required for insertion. 16,17 In contrast, the insertion of CO 2 into ( t Bu PBP)Pd(CH 3 ) under mild conditions enables kinetics experiments to be performed.…”