Change of the coordination type for the phospholyl ligand under nucleophilic attack of H2O on phosphorus atom in 2,5-diphenylphosphacymantrene promoted by aliphatic amines

η5-2,5-Diphenylphosphacymantrene (1) in benzene or CH2Cl2 solution does not react with amines. However, with amines NHEt2, NEt3, NEt(i-Pr)2 in excess and in the presence of small amounts of water 1 reacts to form anionic complexes [(CO)3Mn(η4-Ph2H2C4P(O)H]− A+, where cation A = H 2 NEt 2 + (2a), HNEt 3 + (2b), HN(Et) ( Pr i ) 2 + (2c). Probably, first an unstable intermediate with Р–ОН bond is formed as a result of the attack by the activated H2O molecule at the P atom. Afterwards, the rapid rearrangement occurs with migration of H from O to P which leads to the ligand 2,5-diphenyl-1-Н-phosphol-1-oxide, Ph2H2C4P(O)H. Salts 2а–с have been characterized by 1H, 31P, 13C NMR- and IR-spectra and the structures of 2a and 2c established by single crystal X-ray diffraction analyses. The phosphoryl ligand in anions 2a and 2c has the “envelope” conformation and is η4-coordinated with Mn(CO)3. The phosphorus atom is not involved in the coordination with Mn because the Mn–P distances (2.7670(4) and 2.7732(8) Å) are greater than the sum of covalent radii of P and Mn.