449732-79-0Relevant academic research and scientific papers
Synthesis, stereochemistry and ligating properties of tetraalkyl-substituted ethanedithioamides - Evidence for the lowering of high-energy rotation barriers under the trans influence of Pt-σ-bonded aryl groups
Lanza, Santo,Nicolo, Francesco,Tresoldi, Giuseppe
, p. 1049 - 1055 (2007/10/03)
The structural and coordinating properties of five tetrasubstituted tetraalkyldithioxamides (R4DTO) have been studied: tetraethyldithioxamide (Et4DTO, 1), tetrabenzyldithioxamide (Bz4DTO, 2), (E,E)-N,N′-dibenzyl-N,N′-diethyldithioxamide [(E,E)-Bz2Et2DTO, 3], (E,Z)-N,N′-dibenzyl-N,N′-diethyldithioxamide [(E,Z)-Bz2Et2DTO, 4], (Z,Z)-N,N′-dibenzyl-N,N′-diethyldithioxamide [(Z,Z)-Bz2Et2DTO, 5]. The solid structure of 4, determined by single-crystal X-ray diffraction, is characterised by two planar thioamide groups positioned almost orthogonally to each other, connected by a C-C single bond. Each of these dithioxamides showed high-energy barriers to rotation around both the C-N and the central C-C bond. This latter is a chiral torsion, so that R4DTO species exist as pairs of enantiomers. Compounds 3, 4 and 5 slowly isomerised in solution to give equimolar mixtures of the three isomers; the activation enthalpy of the process was 30.0 kcal mol-1. The ligands 1-5 reacted with [Pt(Me2SO)2X2] (X = Cl, Br, Me, Ph) to give chiral chelate complexes [(R4DTO-κ-S,S′)PtX2], but 3 (and also 4 and 5) provided a mixture of three isomeric platinum chelates in which the S,S′-coordinated ligands showed the (E,E), (E,Z) and (Z,Z) conformations. Furthermore, the presence of small amounts of the platinum complexes cis-[Pt(Me2SO)2Ph2] or [(Et4DTO-κ-S,S′)PtPh2] caused the fast isomerisation of large quantities of a given isomerically pure ligand. We have explained the collapse of the R4DTO rotational barriers by assuming that a release of electrons from the metal atom to incoming ligands in the transition state twists these into a partially reduced, dithiolenic form. Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002.
