Reactions of N-aryl and N-alicyclic derivatives of aminophosphines with paraformaldehyde lead to methylene insertion into P-N bond followed by oxidation of phosphorus from the P(III) to P(V) state. When N-alkyl derivatives are reacted with paraformaldehyde, dimerization takes place to afford bis(phosphine oxide)s of the type Ph2P(O)CH2N(R)CH2P(O)Ph-2 (R = Me, Pr-n, Bu-n). Aminobis(phosphines) also undergo methylene insertion when treated with paraformaldehyde to give bis(phosphine oxides) Ph2P(O)CH2N(R)CH2P(O)Ph-2 (R = Me, Et, Pr-n, Pr-i, Bu-n) in good yield. The reaction of aminophosphines with aromatic aldehydes ArCHO leads to insertion of "ArCH" into the P-N bond to give Ph2P(O)CH(R)N(H)Ph (R = C6H5, furfuryl, o-C6H4OH), but with aliphatic aldehydes such as butanal, P-N bond cleavage takes place to afford alpha-hydroxy phosphine oxide. The reaction of aminobis(phosphines) with both aromatic and aliphatic aldehydes leads to the formation of alpha-hydroxy phosphine oxides through P-N bond cleavage whereas the reaction with furfural leads to the P-N bond insertion. The structure of the alpha-hydroxy derivative Ph2P(O)CR(H)(OH)Pr-n shows intermolecular hydrogen bonding between OH and P=O oxygen. The phosphine oxide derivatives act as bidentate ligands and form chelate complexes with Co(II), Mo(VI), Th(IV), and U(VI) derivatives. The crystal structure of the molybdenum complex, cis-[MoO2Cl2{(OPPh2CH2)(2)NEt-kappaO,kappaO}], shows the distorted octahedral geometry around Mo with two oxo groups cis to each other.