Theoretical Study on the Mechanism of Ni‐Catalyzed Alkyl–Alkyl Suzuki Cross‐Coupling

Abstract

Ni-catalyzed cross-coupling of unactivated secondary alkyl halides with alkylboranes provides an efficient way to construct alkyl-alkyl bonds. The mechanism of this reaction with the Ni/L1 (L1=trans-N,N'-dimethyl-1,2-cyclohexanediamine) system was examined for the first time by using theoretical calculations. The feasible mechanism was found to involve a Ni(I)-Ni(III) catalytic cycle with three main steps: transmetalation of [Ni(I)(L1)X] (X=Cl, Br) with 9-borabicyclo[3.3.1]nonane (9-BBN)R(1) to produce [Ni(I)(L1)(R(1))], oxidative addition of R(2) X with [Ni(I)(L1)(R(1))] to produce [Ni(III)(L1)(R(1))(R(2))X] through a radical pathway, and C-C reductive elimination to generate the product and [Ni(I)(L1)X]. The transmetalation step is rate-determining for both primary and secondary alkyl bromides. KOiBu decreases the activation barrier of the transmetalation step by forming a potassium alkyl boronate salt with alkyl borane. Tertiary alkyl halides are not reactive because the activation barrier of reductive elimination is too high (+34.7 kcal mol(-1)). On the other hand, the cross-coupling of alkyl chlorides can be catalyzed by Ni/L2 (L2=trans-N,N'-dimethyl-1,2-diphenylethane-1,2-diamine) because the activation barrier of transmetalation with L2 is lower than that with L1. Importantly, the Ni(0)-Ni(II) catalytic cycle is not favored in the present systems because reductive elimination from both singlet and triplet [Ni(II)(L1)(R(1))(R(2))] is very difficult.

Computational Studies of Synthetically Relevant Homogeneous Organometallic Catalysis Involving Ni, Pd, Ir, and Rh: An Overview of Commonly Employed DFT Methods and Mechanistic Insights

“…302 Calculations at the PCM (dioxane) B3PW91/6-311+G(2d,p)(SDD)//B3PW91/D95 V 303 (LANL2DZ) level of theory suggested that a Ni(I)/Ni(III) catalytic cycle is operative as opposed to the usual Ni(0)/Ni(II) cycle ( Figure 17). …”

NiI Catalyzes the Regioselective Cross‐Coupling of Alkylzinc Halides and Propargyl Bromides to Allenes

“…[8,16] To probe the possible existence of intermediate radicals, enantiomerically enriched 1d (e.r. Thef ormation of Ni I appearst op roceed through the comproportionation of Ni II precursors andN i 0 complexes formed upon reduction of the precatalyst by the organometallic nucleophile.…”

Spin‐forbidden reactions: computational insight into mechanisms and kinetics

“…Going beyond such qualitative arguments, calculating the energy of MECPs can yield useful additional insight into reactivity. One example of this, illustrated in Figure , is a recent study of the mechanism of nickel‐catalyzed Suzuki coupling of alkyl halides with alkyl boranes . The nickel centre is coordinated with a diamine.…”