The hydroacylation of alkenes and alkynes represents a synthetically valuable method for the conversion of aldehyde substrates to ketone products. The first step of catalytic hydroacylation involves the C-H activation of aldehydes to generate acyl-rhodium(III)-hydrides. We hypothesized that decarbonylation, a common side reaction occurring from these acyl-rhodium(III)-hydride intermediates, could be suppressed by using complexes bearing pendant borane Lewis acids. Reaction of rhodium(I) complexes bearing a conformationally flexible 2-(9-borabicyclo[3.3.1]nonane)-ethyldiphenylphosphine ambiphilic ligand (P–B) with chelating aldehyde substrates, such as 8-quinolinecarbaldehyde, yielded stable, isolable rhodium(III)-metallacycles. Surprising, the use of a chelating aldehyde that does not form a optimal metallacycle, such as 2-pyridinecarboxaldehyde, exhibited rarely observed reactivity resulting in C(sp<sup>3</sup>)-H bond cleavage and C–C bond formation in the 9-borabicyclo[3.3.1]nonane Lewis acid ring. The resulting product was isolated and characterized. Mechanistic studies using a variety of electronically and sterically perturbed substituted 2-pyridinecarboxaldehyde substrates will be discussed.

Influence of a second coordination sphere borane on rhodium(I) oxidative addition of chelating aldehydes

2019 Spring National Meeting

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