Wide bite angle diphosphine rhodium complexes: Synthesis, structure, and catalytic 1,4-addition of arylboronic acids to enones

A rhodium complex [ClRh(CO)(L1)] featuring a wide bite angle diphosphine ligand (L1 = 1,3-bis(2-diphenylphosphinomethylphenyl)benzene) has been synthesized and structurally characterized. L1 supports a bite angle (P–M–P angle, β) of 171.4° in the trans-square planar complex. L1 was tested in Rh-catalyzed 1,4-addition reactions of arylboronic acids (six examples) to α,β-unsaturated ketones (five examples). In mixed aqueous/cyclohexane solution at 60 °C, addition reactions proceed in up to quantitative yield with a 1:1 arylboronic acid/enone ratio. Yields as high as 77% can be acquired even when one of the coupling partners is sterically encumbered 2,4,6-trimethylphenylboronic acid.