Reaction of B₂(o‐tol)₄ with CO and Isocyanides: Cleavage of the C≡O Triple Bond and Direct C−H Borylations

Abstract

The reaction of highly Lewis acidic tetra(o-tolyl)diborane(4) with CO afforded a mixture of boraindane and boroxine by the cleavage of the C≡O triple bond. C labeling experiments confirmed that the carbon atom in the boraindane stems from CO. Simultaneously, formation of boroxine 3 could be considered as borylene transfer to capture the oxygen atom from CO. The reaction of diborane(4) with Bu-NC afforded an azaallene, while the reaction with Xyl-NC furnished cyclic compounds by direct C-H borylations.

Functionalization of Carbon Monoxide and tert‐Butyl Nitrile by Intramolecular Proton Transfer in a Bis(Phosphido) Thorium Complex

“…[61,62] Throughout the Fischer-Tropsch reaction chemistry literature,w e cannot find any report in which ap roton is transferred directly to the carbon of CO without an external agent (Lewis acid or proton source) or beginning from ah ydride source. [71] Other examples involving Frustrated Lewis Pairs (FLPs) have been noted, [72][73][74] but we can find no prior reports of unassisted functionalization of CO (other than when hydride is part of the starting material). [71] Other examples involving Frustrated Lewis Pairs (FLPs) have been noted, [72][73][74] but we can find no prior reports of unassisted functionalization of CO (other than when hydride is part of the starting material).…”

“…Proton transfer reactions to CO or substrates isoelectronic with CO (such as isocyanides) are known in organometallic chemistry,t hese usually involve metal-hydride precursors, [63][64][65][66][67][68] addition of ap rotonic substrate, [69] electrophile addition, [70] or ligand degradation. [71] Other examples involving Frustrated Lewis Pairs (FLPs) have been noted, [72][73][74] but we can find no prior reports of unassisted functionalization of CO (other than when hydride is part of the starting material).…”

Metallomimetic Chemistry of Boron

“…186,187 Interestingly, 9 also reacts with carbon monoxide with initial insertion of CO into the B-B bond, followed by subsequent rearrangement. 188 Typical alkyl and arylboranes are usually relatively inert towards π-acceptor bases such as CO, because they lack the filled orbitals that allow TM complexes to effect backbonding. In this case, however, the electron density of the B-B bond appears to be accepted by CO, resulting in cleavage and metathesis to give a boroxine and a C-H insertion product.…”

Synthesis of Unsymmetrical Diboron(5) Compounds and Their Conversion to Diboron(5) Cations

“…Many modern routes to organoboranes use diboron(4) compounds, e.g. bis-pinacolatodiboron B2pin2, thus these reagents have received considerable interest -as have diboron (5) derivatives that possess two distinct boron moieties with one being four coordinate. 1 These unsymmetrical diboron (5) species can be easily accessed by adding a neutral or anionic Lewis base to a (RO)2B-B(OR)2 precursor, quaternizing one boron center.…”

“…bis-pinacolatodiboron B2pin2, thus these reagents have received considerable interest -as have diboron (5) derivatives that possess two distinct boron moieties with one being four coordinate. 1 These unsymmetrical diboron (5) species can be easily accessed by adding a neutral or anionic Lewis base to a (RO)2B-B(OR)2 precursor, quaternizing one boron center. Quaternization leads to polarization of the B-B σ bond and the resulting mixed sp 2 /sp 3 diborons then react as sources of nucleophilic boron, reacting with an array of carbon electrophiles even in the absence of precious metal catalysts, thus providing a powerful route for forming C-B bonds.…”