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 alpha-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 a-hydroxyphosphonates. The calculated activation barriers (free energies) are ca. 20 kcal mol(-1).