Half-sandwich complexes of Ir(iii), Rh(iii) and Ru(ii) with the MaxPhos ligand: metal centred chirality and cyclometallation

Abstract

The reaction of the acetylacetonates [(η⁵-C₅Me₅)M(acac)Cl] with (S_P)-[HMaxPhos][BF₄] afforded cationic complexes with the formula (S_M,R_P)-[(η⁵-C₅Me₅)MCl(MaxPhos)][BF₄] (M = Rh (1), Ir (2)). The reaction of (S_P)-MaxPhos with [RuCl(μ-Cl)(η⁶-p-MeC₆H₄ⁱPr)]₂ and NH₄X afforded (S_Ru,R_P)-[(η⁶-p-MeC₆H₄ⁱPr)RuCl(MaxPhos)][X] (X = BF₄ (3), PF₆ (3')). The complexes have been completely characterized by analytical and spectroscopic means, including the determination of the crystal structures of 1, 2 and 3'. Treatment of the iridium complex 2 with AgBF₄, at 253 K, resulted in the intramolecular cyclometallation of one of the tert-butyl substituents of the MaxPhos diphosphane ligand, affording a mixture of isomers of (S_Ir,R_P¹,S_P² and R_Ir,R_P¹,R_P²)-[(η⁵-C₅Me₅)Ir(MaxPhos)][BF₄] (4a and 4b). However, rhodium complex 1 and ruthenium complex 3 reacted with AgBF₄ forming the expected unsaturated intermediates "(ηⁿ-ring)M(MaxPhos)" which were trapped by MeCN, affording the cationic adducts (S_M,R_P)-[(ηⁿ-ring)M(MaxPhos)(MeCN)][BF₄]₂ (M = Rh (5), Ru (6)). Only one epimer at the metal was isolated in high yield for the complexes 1, 2, 3, 3', 5 and 6 and the metallation of 2 to give 4 occurs with high diastereoselectivity.