1'-(DIPHENYLPHOSPHINO)FERROCENECARBOXYLIC ACID AND ITS P-OXIDE AND METHYL-ESTER - SYNTHESIS, CHARACTERIZATION, CRYSTAL-STRUCTURE, AND ELECTROCHEMISTRY

The ferrocene derivative (eta(5)-C(5)H(4)PPh(2))Fe(eta(5)-C5H4COOH) (3 ), a potential hybrid phosphine ligand with heteroannular soft and har d donor groups, was synthesized in 71% yield from 1-phenyl-1-phospha[1 ]ferrocenophane by ring opening with phenyllithium, followed by reacti on with carbon dioxide and acidification. Oxidation of 3 with hydrogen peroxide and its esterification with diazomethane provided the deriva tives, phosphine oxide 4 and methyl ester 5, respectively. The new com pounds were characterized by IR, UV/vis, MS, and NMR spectroscopy, the degenerate H-1 NMR spectra being assigned with the aid of selective H -1-{H-1} decoupling, H-1,H-1-COSY, C-13 HMQC, and (n)J(P,C) from APT. The solid-state structures of 3-5 were determined by single-crystal X- ray diffraction. Voltammetric measurements of 3-5 and related monosubs tituted derivatives in acetonitrile revealed that the phosphines are f irst oxidized to the corresponding ferrocenium derivatives which are t hen the subject of the intramolecular electron transfer from the phosp hine group to iron, the resulting species being immediately stabilized by further electrochemical and/or chemical oxidation to give phosphin e oxides. The second independent electrochemical process is the revers ible oxidation of these ferrocene/phosphine oxides to ferrocenium/phos phine oxides. There are further electrochemical processes associated w ith the irreversible oxidation of the carboxyl group.