Crystal structure and dynamic behavior of [Ni{PhNHC(S)NP(S)(OPr i)2-S,S}2] complex in dichloromethane solution

Abstract

The crystal structure of the complex [Ni{PhNHC(S)NP(S)(OPr i)2-S,S}2] has been determined and its behavior in dichloromethane solution investigated by NMR 31P spectroscopy. The X-ray structural analysis shows the nickel atom at the symmetry center in a distorted square-planar arrangement with trans-disposition of the ligands. The six-membered cycle NiS(1)PNCS(2) has the form of the asymmetric boat. In dichloromethane solutions of the compound four signals have been detected by 31P-{1H} NMR method. These signals are related to three diamagnetic square-planar isomers with different dispositions and conformations of two ligands in anti-orientation: trans-chair-boat (A), cis-boat-boat (B), and trans-boat-boat (C). These isomers are in slow exchange equilibria. It was shown that all these forms are in rather fast chemical exchange with minor (unobserved) paramagnetic pseudo-tetrahedral isomers (AT, B T, and CT). The thermodynamic constants of equilibria between A, B, and C as well as rate constants and activation parameters for conversion of three square-planar to respective pseudo-tetrahedral forms were calculated from the 31P-{1H} NMR data. © 2005 Elsevier Ltd. All rights reserved.