Boranes reaction with carbon dioxide

Reaction of the enantioenriched carbanions with carbon dioxide was ori-ginally employed by Ohashi and Imamoto and more recently by others to access P-stereogenic a-carboxyphosphine boranes and some reduced derivatives (Scheme 5.14). 

Many simple reactions of carbon dioxide require the presence of acid-base systems (bifunctional systems). Recently, CO2 was found to react easily with frustrated Lewis pairs [15, 16]. For instance, the components of the couple 2,2,6,6-tetramethylpiperidine (TMP)/tris(pentafluorophenyl)borane [B(C6p5)3] activate CO2, yielding boratocarbamate — TMPH ion pair (Scheme 2.4). CO2... 

Trialkylborane additives promote the reduction of carbon dioxide to formate, via bis(diphosphine) Ni(II) and Rh(III) hydride complexes. Late transition metal hydrides, which can be formed by the reaction with molecular H2, transfer hydride to CO2 to yield a formate-borane adduct. In order to drive this process, the borane must be of appropriate Lewis acidity hence, weaker... 

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