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-pyridinecarboxald ehyde (2CHO-py) have been examined in protic (H2O, MeOH, EtOH) and aprotic (DMF, CH2Cl2) solvents. Compounds in which the pyridine ligand is N-coordin ated, either in the original aldehydic form or in a new form derived from a ddition of one or two protic molecules, have been isolated, namely: [Au(2CH O-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)C l-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 m etal ion and the ancillary ligands as well as of the total charge of the co mplexes on the relative stability of the addition products are discussed.