Studies of the reactions of tripodal pyridine-containing ligands with Re(CO)5Br leading to rheniumtricarbonyl complexes with potential biomedical applications

Abstract

The complexes formed from the reaction of N-acylated tris-(pyridin-2-yl)methylamine (LH) with [Re(CO)(5)Br] depend on the structure of the ligand and the reaction conditions. Thus, while N-[1,1,1-tris-(pyridin-2-yl)methyl]acetamide coordinates through the three pyridine nitrogens to give a stable cationic complex [LHRe(CO)(3)Br], the analogous N-benzoyl ligand reacts under similar conditions to give a neutral complex [LRe(CO)(3)] with coordination through two pyridine nitrogens and a deprotonated amide. To try to explain these different outcomes, the reactions of some structurally related N-acylated [1,1-bis(pyridin-2-yl)]methylamines (L'H) with [Re(CO)(5)Br] have been studied and the reaction pathways identified. These studies indicate that a neutral complex [L'HRe(CO)(3)Br] is initially formed in which the amide portion of the ligand is uncoordinated, but that this complex under appropriate conditions then rearranges to give a cationic complex [L'HRe(CO)(3)]Br in which the coordinated amide nitrogen either remains protonated or is present in its imidic acid tautomeric form. Elimination of HBr from these complexes either thermally or in the presence of base then gives stable neutral complexes [L'Re(CO)(3)]. The impact of the N-acyl group and any substituent at the apex of the tripodal ligands (L''H) on the relative stabilities of intermediate complexes on the reaction pathway helps provide an explanation for the observed difference in behaviour of the N-acylated tris(pyridin-2-yl)methylamines (LH).

Synthesis and coordination chemistry of 1,1,1-tris-(pyrid-2-yl)ethane

“…31 The dinuclear nature of the initial product of the transformation, 7a, has been confirmed crystallographically. However, we have also now shown that aqueous solutions of 7a react further, forming mononuclear copper/carbonato (8) and ligand disproportionation products (9).…”

“…Tris-( pyrid-2-yl)methane, tris-( pyrid-2-yl)amine, tris-( pyrid-2yl)phosphine and related compounds were first synthesised in the first half of the 20 th century, 1 and developed as tripodal ligands for transition ions in the 1960-1980s. [2][3][4] Despite this long-standing chemistry, they continue to find use as facial protecting groups in organometallic chemistry, [5][6][7] catalysis, 8 transition metal photochemistry, 9 molecular magnetism [10][11][12][13][14] and other aspects of coordination chemistry. 15 A number of such ligands py 3 X ( py = 2-pyridyl) have been prepared, with different bridgehead groups 'X' (Scheme 1).…”

fac-Re(CO)3 complexes of 2,6-bis(4-substituted-1,2,3-triazol-1-ylmethyl)pyridine “click” ligands: synthesis, characterisation and photophysical properties

“…1, 1) ligand families are the most commonly exploited tridentate scaffolds. However, ligands that contain thiazolyl, 6 pyridyl, 9,10 pyrazolyl, 11 imidazolyl, 10,12 Fig. 1 The ubiquitous biofunctionalised tridentate ligands, bis (2methylpyridyl)amine or 2-[bis (2-methylquinolinyl)]amine 1, and the related tridentate "click" ligand 2,6-bis(4-substituted-1,2,3-triazol-1ylmethyl)pyridine, 2. benzoimidazolyl, 7 and even "click" derived 1,2,3-triazoyl 12,13 heterocyclic units have all been synthesised and characterised.…”

Synthesis and bonding analysis of pentagonal bipyramidal rhenium carboxamide oxo complexes

“…1A). [1][2][3] The conjugate base carboxamidates can bind through oxygen or nitrogen as well (Fig. 1A).…”