Molybdenum carbonyl complexes with pyridylimino acidato ligands

摘要

Reactions of [Mo(CO)_4(pip)_2] with pyridine-2-carbaldehyde and the appropriate amino ester or amino acid produce complexes with chelated pyridylimino ligands bearing,respectively,an ester (1) or carboxylate (2a,b,4,5a,b) pendant arm,the structures of which have been determined by X-ray crystallography.In the case of alpha-amino acids,the resulting imino carboxylate complexes are unstable towards decarboxylation,this being complete for (R)-2-phenylglycine.The products of decarboxylation 3a-c were isolated and characterized,including X-ray structure determinations for 3b and 3c.In contrast,the derivatives of beta-alanine (4) and 3-and 4-aminobenzoic acids (5a,b) are stable towards decarboxylation.The structure determinations show that the pyridyliminocarboxylate complexes crystallize as salts with piperidinium cations,forming hydrogen-bonded ion-pair dimers featuring twelve-or eight-membered rings.Protonation of carboxylate complexes with 2 M HCl in CH_2Cl_2/ water yields the corresponding neutral complexes 6a,b containing a free carboxylic acid functionality.