Synthesis and coordination behaviour of a protic phosphinoferrocene amidine

Abstract

A phosphinoferrocene amidine Ph₂PfcNCHNHiPr (1; fc = ferrocene-1,1′-diyl) has been synthesised and studied as a new P,N-hybrid donor in group 10 metal complexes. Thus, reactions with metal dichloride precursors produced tetrahedral and paramagnetic [NiCl₂(1-κ²P,N)] and square-planar diamagnetic [MCl₂(1-κ²P,N)] (M = Pd, Pt) and [PdCl(Me)(1-κ²P,N)]. The Pd(II) complex [MCl₂(1-κ²P,N)] was converted to chloride-bridged dimers [Pd₂(μ-Cl)₂(1-κ²P,N)₂][BARF]₂ and [(μ-Cl){PdCl(1-κ²P,N)}₂][BF₄] (BARF = tetrakis(3,5-bis(trifluoromethyl)phenyl)borate) through reactions with halide scavengers. In solution, the former compound exists in equilibrium with monopalladium species featuring an Fe–Pd bond, [PdCl(1-κ³Fe,P,N)][BARF]. The interaction of 1 with [Pd(MeCN)₄][BF₄] and triphenylphosphine produced analogous κ³ complexes [Pd(PPh₃)(1-κ³Fe,P,N)]X (X = BF₄ and, after anion exchange, also PF₆). Eventually, the compound family was expanded by a Pd(0) complex, [Pd(η²-ma)(1-κ²P,N)], containing a π-coordinated maleic anhydride (ma). With the exception of the nonisolable [PdCl(1-κ³Fe,P,N)][BARF], all reported compounds were fully characterised via a combination of elemental analysis, spectroscopic methods (ESI MS and NMR), and single-crystal X-ray diffraction analysis. Attempts to prepare complexes with a deprotonated terminal NH group failed. Nonetheless, the NH group plays the role of a structure-stabilising moiety, forming intramolecular NH⋯Cl hydrogen bonds with chloride ligands.