An Alternative Preparation of 1-(N,N-Dimethylaminomethyl)-1′-(diphenylphosphanyl)ferrocene: Synthesis and Structural Characterization of Au(I) and Pd(II) Complexes with this Hybrid Ligand

1-(N,N-Dimethylaminomethyl)-1′-(diphenylphosphanyl)ferrocene (1) was synthesized in good yield by lithiation of 1-bromo-1′-(diphenylphosphanyl)ferrocene and subsequent reaction with Eschenmoser's salt (dimethylmethylideneammonium iodide). Making use of an easily accessible, nontoxic starting material, this procedure represents a convenient alternative to the original synthetic protocol based on stepwise lithiation/functionalization of 1,1′-bis(tributylstannyl)ferrocene and reductive amination [M. E. Wright, Organometallics 1990, 9, 853–856]. Compound 1 has typical hybrid-donor properties. When reacted with [AuCl(tht)] (tht=tetrahydrothiophene), it afforded the expected Au(I) phosphane complex [AuCl(1-κP)] (2). An attempted removal of the chloride ligand from 2 with AgClO(4) produced an ill-defined material formulated as Au(1)ClO(4). The uncoordinated amine substituent reacted with traces of hydrogen chloride formed by slow decomposition typically occurring in solution. In this manner, complexes [AuCl(Ph(2)PfcCH(2)NHMe(2))]Cl (3, fc=ferrocene-1,1′-diyl) and [AuCl(Ph(2)PfcCH(2)NHMe(2))]ClO(4) (4) were isolated from crystallizations experiments with 2 and Au(1)ClO(4), respectively. On a larger scale, complex 3 was prepared easily from 2 and hydrogen chloride. The course of reactions between [PdCl(2)(cod)] (cod=cycloocta-1,5-diene) and 1 were found to depend on the ligand-to-metal ratio. Whereas the reaction with two equivalents of 1 afforded bis(phosphane) complex trans-[PdCl(2)(1-κP)(2)] (5), that of a Pd:P ratio 1:1 produced ligand-bridged dimer [(μ-1)PdCl(2)](2) (6). With hydrogen chloride, complex 6 reacted to afford zwitterionic complex [PdCl(3)(1H-κP)] (7), which was also formed when ligand 1 and [PdCl(2)(cod)] were allowed to react slowly by liquid-phase diffusion of their chloroform solutions. The compounds were characterized by spectroscopic methods (multinuclear NMR and ESI–MS), and the molecular structures of complex 2–4, 6⋅2CHCl(3) and 7⋅1.5CHCl(3) were determined by single-crystal X-ray diffraction analysis.