Phosphine-boronates R(2)P(o-C(6)H(4))B(OR')(2) have been evaluated as bifunctionalorganocatalysts for the Michaeladdition of malonate pronucleophiles to methylvinylketone. The presence of the Lewis acidic boron center adjacent to phosphorus significantly improves catalytic performance. Isolation and complete characterization of a key intermediate, namely a beta-phosphonium enolate, substantiate the