Addition of protic molecules to coordinated 2-pyridinecarboxaldehyde in gold(III), palladium(II), and platinum(II) complexes

The reactions of Au-III, Pt-II and Pd-II complexes with 2-pyridinecarboxaldehyde (2CHO-py) have been examined in protic (H2O, MeOH, EtOH) and aprotic (DMF, CH2Cl2) solvents. Compounds in which the pyridine ligand is N-coordinated, either in the original aldehydic form or in a new form derived from addition of one or two protic molecules, have been isolated, namely: [Au(2CHO-py . H2O)Cl-3], [Au(2CHO-py . MeOH)Cl-3], [Au(2CHO-py . 2EtOH)Cl-3], cis-[Pt(2CHO-py)(2)Cl-2], trans-[Pd(2CHO-py)(2)Cl-2], trans-[Pt(dmso)(2CHO-py)Cl-2], [Pt{C5H4N-(CH2SMe)}Cl(2CHO-py)](ClO4), [Pt(terpy)(2CHOpy)](ClO4)(2), [Pt(terpy)(2CHO-py . H2O)](ClO4)(2) (terpy = 2,2':6',2 "-terpyridine). H-1-n.m.r. experiments show that the addition of the protic molecule(s) to the Pt-II and Pd-II complexes is reversible. The effects of the nature of the metal ion and the ancillary ligands as well as of the total charge of the complexes on the relative stability of the addition products are discussed.