Anion exchange in [Ni(η5-C5H4R)(Cl)(NHC)]. Counterion effect on the structure and catalytic activity

Abstract

A series of novel complexes [Ni(η⁵-C₅H₄R)(L)(NHC)]⁺A⁻2a–2j and [Ni(η⁵-C₅H₅)(A)(NHC)] 3a–3c has been obtained by anion metathesis from the corresponding chlorides 1a–1d, depending on the anion binding properties and reaction conditions. Solid-state structures of two cationic complexes (2c, 2j) and two complexes with a coordinated anion (3a, 3c) have been determined by X-ray diffraction revealing a trigonal planar geometry in all cases. Unexpectedly, 3c displayed unprecedented for this type of compounds temperature-dependent NMR spectra that were interpreted in terms of spin equilibrium. The cationic complexes 2 were less efficient in styrene polymerization than the parent chlorides 1. However, the activity of 2 and 3 in Suzuki cross-coupling did not depend considerably on the counterion.