An Alternative Preparation of 1-(NN-Dimethylaminomethyl)-1′-(diphenylphosphanyl)ferrocene: Synthesis and Structural Characterization of AuI and PdII Complexes with this Hybrid Ligand

摘要

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 AgClO4 produced an ill-defined material formulated as Au(>1)ClO4. The uncoordinated amine substituent reacted with traces of hydrogen chloride formed by slow decomposition typically occurring in solution. In this manner, complexes [AuCl(Ph2PfcCH2NHMe2)]Cl (>3, fc=ferrocene-1,1′-diyl) and [AuCl(Ph2PfcCH2NHMe2)]ClO4 (>4) were isolated from crystallizations experiments with >2 and Au(>1)ClO4, respectively. On a larger scale, complex >3 was prepared easily from >2 and hydrogen chloride. The course of reactions between [PdCl2(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-[PdCl2(>1-κP)2] (>5), that of a Pd:P ratio 1:1 produced ligand-bridged dimer [(μ->1)PdCl2]2 (>6). With hydrogen chloride, complex >6 reacted to afford zwitterionic complex [PdCl3(>1H-κP)] (>7), which was also formed when ligand >1 and [PdCl₂(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⋅2CHCl₃ and >7⋅1.5CHCl₃ were determined by single-crystal X-ray diffraction analysis.