Coordination behaviour of a hybrid phosphinoguanidine ligand

Abstract

This contribution focuses on the coordination behaviour of 2-[2-(diphenylphosphino)phenyl]-1,3-diisopropylguanidine (1), which is a representative of the unique P,N-ligands combining phosphine moieties with strongly basic guanidinium substituents. This compound was prepared by the reaction of 2-(diphenylphosphino)aniline with 1,3-diisopropylcarbodiimide in the presence of diethylzinc (10 mol%). When mixed with [MCl₂L₂] (M = Pd, Pt; L = a weakly bonding ligand), ligand 1 gives rise to P,N-chelate complexes [MCl₂(1-κ²P,N)]. However, in the case of kinetically inert Pt(II), the products of partial substitution and chloride ionisation, [PtCl(1-κ²P,N)(L)]Cl, where L = Me₂SO or η²-cycloocta-1,5-diene, can be intercepted. Ionisation also occurs in the reaction with [PdCl(η³-C₃H₅)]₂, leading to [Pd(η³-C₃H₅)(1-κ²P,N)]Cl, while [Pd(MeCN)₄][BF₄]₂ produces the bis-chelate complex, cis-[Pd(1-κ²P,N)₂][BF₄]₂. In contrast, the corresponding hydrochloride (1H)Cl behaves as a simple phosphine, reacting with PdCl₂ surrogates to give the zwitterionic species [PdCl₃(1H-κP)] and the bis-phosphine complex trans-[PdCl₂(1H-κP)₂]Cl₂, depending on the metal-to-ligand ratio.