Iron-borane catalyzed carbonyl hydroboration and isolation of an iron(I)-ketyl radical

TL;DR

A new iron-based catalyst efficiently performs hydroboration of various compounds under mild conditions.

Contribution

The discovery of a novel iron(0)-mediated hydride transfer mechanism and an iron(I)-ketyl radical with unique magnetic properties.

Findings

An iron metalloborane complex efficiently catalyzes hydroboration of ketones, cyclic esters, and CO2.

A direct iron(0)-mediated hydride transfer process was identified as the rate-determining step.

An iron(I)-benzophenone ketyl radical with an antiferromagnetic ground state was isolated and characterized.

Abstract

Hydroboration of carbonyl compounds has proven a pivotal route to access alcohols and other C1 moieties in recent years. Despite this, iron-based catalyst systems are somewhat limited with very little mechanistic understanding of these systems developed. Here we show that an iron metalloborane complex [{(iPrDPBPh)Fe}2(μ−1,2-N2)] (A) is an efficient pre-catalyst for hydroboration of ketones, cyclic esters and CO2 with mild conditions. Mechanistic insights reveal a previously unreported direct iron(0)-mediated ligand-to-ligand hydride transfer (LLHT) process is in operation with B–H bond breaking being rate determining, indicating the importance of mechanistic studies on well-known transformations. An iron(I)-benzophenone ketyl radical with a unique S = 1 antiferromagnetic ground state has been isolated and fully characterized.

Homogeneous catalytic hydroboration represents a valuable strategy for the synthesis of alcohols but reports which employ iron-based catalysts are somewhat limited. Here, the authors report an iron metalloborane complex as an efficient pre-catalyst for hydroboration of ketones, cyclic esters and CO2 with mild conditions.

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