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In the study presented herein, we explore the ability of copper complexes with coordinated pyridine-2-carboxaldehyde (pyca) or 2-acetylpyridine (acepy) ligands to promote the addition of amines (Schiff condensation) and other nucleophiles such as alcohols (hemiacetal formation). Distinct reactivity patterns are observed: unlike pyca complexes, acepy copper complexes can promote self-aldol addition. The introduction of a flexible chain via Schiff condensation with β-alanine allows the possibility of chelate ring ring-opening processes mediated by pH. Further derivatization of the complex [CuCl(py-2-C(H)[double bond, length as m-dash]NCH2CH2COO)] is possible by replacing its chloride ligand with different pseudohalogens (N3-, NCO- and NCS-). In addition to the change in their magnetism, which correlates with their solid-state structures, more unexpected effects in their cytotoxicity and relaxitivities are observed, which determines their possibility to be used as MRI contrast agents. The replacement of a chloride by another pseudohalogen, although a simple strategy, can be used to critically change the cytotoxicity of the Schiff base copper(ii) complex and its selectivity towards specific cell lines.

The systematic assembly of supramolecular arrangements is a persistent challenge in modern coordination chemistry, especially where further aspects of complexity are concerned, as in the case of large molecular mixed-metal arrangements. One targeted approach to such heterometallic complexes is to engineer metal-based donor ligands of the correct geometry to build 3D arrangements upon coordination to other metals. This simple idea has, however, only rarely been applied to main group metal-based ligand systems. Here, we show that the new, bench-stable tris(3-pyridyl)stannane ligand PhSn(3-Py) 3 (3-Py=3-pyridyl) provides simple access to a range of heterometallic Sn IV /transition metal complexes, and that the presence of weakly coordinating counter anions can be used to build discrete molecular arrangements involving anion encapsulation. This work therefore provides a building strategy in this area, which parallels that of supramolecular transition metal chemistry., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Complexes containing pyridine-2-carboxaldehyde (pyca) ligand acting as κ(2)-(N,O) chelates in [MX(CO)(3)(pyca)] (M = Mn, Re; X = Cl, Br), or [MoX(methallyl)(CO)(2)(pyca)] (X = Cl, Br), are good precursors for iminopyridine complexes derived from amino esters and peptides of formula [MX(CO)(3)(py-2-C(H)═NCHX-COOY)] or [MoX(methallyl)(CO)(2)(py-2-C(H)═NCHX-COOY)], via Schiff condensation of the aldehyde function of pyca with the terminal NH(2) group of the amino ester or peptide. X-ray determinations confirm the structures and show that in solid phase the peptide chains assemble through H-bonds adopting different patterns which depend on the geometry of the metal-ligand fragments. The H-bonding patterns have been analyzed in detail and described by using graph set methods. In most cases, Mo complexes show intramolecular arrangement involving the halogen (Cl or Br) and an NH group of the side chain. For the Mn and Re complexes, the peptide side arms form infinite chains, helices, and rings. In many cases, the terminal carboxylic O-H function is engaged in a "terminal" H-bond with a polar molecule of solvent (THF or acetone), instead of forming the usual head-to-head arrangement found in simple carboxylic acids. For the longer tripeptide Gly-Gly-Gly, a discrete, dimeric association is observed, in which the peptide chains show antiparallel arrangement with a complementary disposition of the internal N-H and C═O functions. DOSY experiments in solution show significant changes in the diffusion rates upon addition of OPBu(3), which indicate H-bonding interaction of OPBu(3) with the peptide hydrogens.