MoO2Cl2 as a Novel Catalyst for C−P Bond Formation and for Hydrophosphonylation of Aldehydes

This work reports the use of MoO2Cl2 as a novel catalyst for C−P bond formation, exemplified here by the hydrophosphonylation of aldehydes. A series of α-hydroxyphosphonates was prepared in excellent yields using the catalytic system HP(O)(OEt)2/MoO2Cl2 (5 mol %) under solvent-free conditions or at refluxing THF. DFT calculations indicate that the P═O bond coordinates to molybdenum while the P−H hydrogen is transferred to one Mo═O oxygen atom. The active species then reacts with the aldehyde to form the α-hydroxyphosphonates. The calculated activation barriers (free energies) are ca. 20 kcal mol−1.