Synthesis, molecular structure and electrochemistry of gold(I) complexes with 1-(diphenylphosphino)-1'-[(diphenylphosphino)methyl]ferrocene
Abstract
Depending on the reaction stoichiometry, 1-(diphenylphosphino)-1'-[(diphenylphosphino) methyl]ferrocene (1) reacts with [AuCl(tht)] (tht = tetrahydrothiophene) to afford an insoluble polymer formulated as [AuCl(1)]n (2) or ligand-bridged digold(I) complex, [(mu-1)(AuCl)2] (3). The latter compound readily undergoes metathesis reactions with anionic reagents such as in situ generated acetylides, thiocyanate or N,N-diethyldithiocarbamate to give the corresponding digold(I) complexes [(mu-1)(AuY)2], where Y is CCPh (4), CCFc (5; Fc = ferrocenyl), SCN (6), and Et2NCS2 (7).
Similar reaction of 3 with a dithiolate formed from propane-1,3-dithiol and sodium methoxide affords a macrocyclic bis-chelate [(mu-1)(AuSCH2CH2CH2SAu)] (8). Compounds 2-8 have been characterized by spectroscopic methods (multinuclear NMR, ESI, MS, UV-vis and IR) and by elemental analysis, and the molecular structures of 3.1/2C2H4Cl2, 4.2CHCl3, 7.2CHCl3, and 8 have been determined by single-crystal X-ray diffraction analysis.
Cyclic voltammetric study revealed that ligand 1 undergoes a one-electron oxidation at the ferrocene unit, which is associated with some chemical complications resulting presumably from the presence of the lone electron pair at phosphorus. After coordination to Au(I)L fragments bearing simple auxiliary ligands (e. g., in 3, 4, and 6), the Fe-II/Fe-III redox process becomes reversible and appears shifted to more positive potentials owing to an electron density transfer from the diphosphine ligand to the coordinated metal centers.
For compounds 5 and 7, this redox change is accompanied by additional waves attributable to oxidation of ferrocenyl groups in the terminal ferrocenylethynyl groups and to redox changes occurring at the Au-bound carbamate ligands, respectively.