Tin-catalyzed reductive coupling of amines with CO₂ and H₂

Abstract

Reductive coupling of amines with CO2 and H2 can be catalyzed by transition metals. However, functional group (FG) tolerance is improved when using auxiliary main group hydrides (instead of H2),...

Frustrated Lewis Pairs Catalyse the Solvent‐Assisted Synthesis of Azoles from ortho‐Substituted Anilines, CO2 and H2

“…The initial reaction conditions [o‐phenylenediamine (1 mmol), sulfolane (5 mL), 180 °C, CO 2 (4 bar) and H 2 (96 bar)] were selected based on published results for N‐formylation of aliphatic amines with R 3 SnX‐based FLPs [39] . In the absence of nucleophilic amines, which could act as primary N‐formylation target(s) and subsequently as transfer formylation reagents, the catalytic activity of R 3 SnX‐based FLPs for the synthesis of benzimidazole from o‐phenylenediamine was low (Table 1, entries 1–3 and Table S1, SI) in line with previous findings because R 3 SnX‐based FLPs do not N‐formylate aniline [39] …”

“…An additional base may also accelerate the N-formylation of o-phenylenediamine by its partial deprotonation, increasing the nucleophilicity and its associated reactivity with the formylation source, presumably R 3 SnOC(H)O. [39] Thus we hypothesized that including nucleophilic amines, acting as primary N-formylation target(s) and subsequently as transfer formylation reagents, could accelerate the reaction (Scheme 1C). Moreover, transfer formylations are catalysed by LAs [8,22] and hence should be compatible with and promoted by the FLP used here for CO 2 reduction to formate.…”

“…[28][29][30] Yet, despite considerable research efforts to study the N-formylation reaction with CO 2 and H 2 and to develop high-activity catalysts for N-formylation of aliphatic amines, [12,[31][32][33][34][35][36][37][38] only four systems are known to catalyse the two-step tandem synthesis of azoles from ortho-substituted anilines using CO 2 and H 2 . [28][29][30] This lack of catalysts may be due to difficulties with the N-formylation of anilines with CO 2 and H 2 [31,39] because anilines are less nucleophilic than aliphatic or benzylic amines.…”

“…Recently, Frustrated Lewis pairs (FLPs) demonstrated the ability to N‐formylate secondary aliphatic amines [39] . Since FLPs are composed of LAs, suitable for transfer formylation reactions, we hypothesized that a combined strategy of N‐formylation of nucleophilic amine(s) with CO 2 and H 2 followed by in‐situ formate transfer and simultaneous recycling of the amine (Scheme 1C) may prove effective with FLP catalysts.…”

Advances in CO2 activation by frustrated Lewis pairs: from stoichiometric to catalytic reactions

“…Hulla reported an application of tin-based FLPs in the form R 3 SnX/N-base (R = alkyl and X = OTf − or NTf 2 − ] which can catalyse the formation of azoles from ortho-substituted anilines via complete deoxygenation of CO 2 in the presence of H 2 . 138 Computational insights into group 13 and 14 Lewis acids in FLP catalysed CO 2 activation Grimme reported mechanistic insights, based on extensive DFT calculations, on all steps of the FLP catalysed reduction of CO 2 to boryl formate, H 2 CO, bis(boryl) acetal, and methoxyl borane products in 2020. 139 The work addressed three FLP catalysts that had been previously reported; (i) Fontaine's B/P intramolecular FLP reported in 2013, 55,56 (ii) Stephan's intermolecular FLP consisting of tBu 3 P and 9-BBN from 2014, 58 and (iii) Cantat's 2016 Si/N FLP with 9-BBN (Fig.…”