Creation of New Boron–Carbon Bonds by Dichlorocarbene Insertion into the Boron–Hydrogen Bond of Amine– and Phosphine–Boranes

Diamidocarbene Induced B–H Activation: A New Class of Initiator-Free Olefin Hydroboration Reagents

“…Although dichlorocarbene and select carbenoids have been shown to facilitate the 1,1-insertion of BH 3 complexes, the corresponding transformations were nonselective and did not proceed in a controlled manner. 7,8 In addition, such B−H bond activation processes typically result in multiple hydride additions and/or rearrangement. 7,8 As such, efforts have been directed toward the use of carbenes that are isolable and exhibit predictable reactivities as a means to realize organocatalyzed hydroborations.…”

“…7,8 In addition, such B−H bond activation processes typically result in multiple hydride additions and/or rearrangement. 7,8 As such, efforts have been directed toward the use of carbenes that are isolable and exhibit predictable reactivities as a means to realize organocatalyzed hydroborations. 9−12 Collectively, these efforts have demonstrated that most isolable carbenes, including the N-heterocyclic carbenes (NHCs) and the cyclic (alkyl)(amino)carbenes (CAACs), 13 result in the formation of Lewis acid−base adducts upon exposure to BH 3 (i.e., B−H activation is not observed, Scheme 1).…”

“…15−25 The paucity of examples of isolable carbenes that facilitate the 1,1-addition of BH 3 may be attributed to an energetically unfavorable double electron transfer process wherein the borane is required to act as both a π-acceptor and a σdonor. 7,8,17,26 For this reason, B−H activation requires a carbene with sufficient nucleophilicity to facilitate σ electron donation to the Lewis acidic borane as well as sufficient electrophilicity to enable π back-bonding from the resultant BH 3 complex. 7,8,17,26 Our group and others have previously demonstrated that the N,N′-diamidocarbenes (DACs) are ambiphilic and exhibit diminished nucleophilicity in comparison to the NHCs and CAACs.…”

Carbene B−H Insertion Reactions for C−B Bond Formation

“…[21] In addition to cyclic phosphine-boranes, Foucaud and Carboni respectively showed that the reaction of acyclic phosphine-boranes 10 with reactive dichlorocarbene intermediate afforded mixtures of monoinsertion 11 and diinsertion products 12 (Scheme 5). [20,22] In the same work, Carboni found that when amine-boranes 13 were used as substrates, for R 1 ¼ 6 H, a similar reaction result as acyclic phosphine-boranes was achieved, while for R 1 diinsertion products 17, triinsertion product 18 was also obtained (Scheme 6).…”

Uncommon carbene insertion reactions

“…Although the site selectivity of the reaction is poor, this reaction represents the pioneering attempt in B-H bond insertion reaction. Later in 1990s and 2000s, classical dichlorocarbene, 16,17 and methylenecarbene 18 species were found efficient to react with borane amine or phosphine adducts, affording various methyl borane derivatives (Scheme 1b). In 2003, Sierra et al 19 reported the reaction of alkynyl alkoxy pentacarbonylchromium carbene toward the B-H bond of NaCNBH 3 , which unambiguously proved However, the lack of effective catalytic protocols in B-H bond insertion reactions resulted in limited choice of carbene precursors, low efficiency and poor selectivity.…”