Kinetically Stabilized 1,1′-Bis[(E)-diphosphenyl]ferrocenes: Syntheses, Structures, Properties, and Reactivity

Abstract

Abstract Kinetically stabilized 1,1′-bis[(E)-diphosphenyl]ferrocenes were synthesized by taking advantage of extremely bulky substituents, 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl (denoted as Tbt) and 2,6-bis[bis(trimethylsilyl)methyl]-4-[tris(trimethylsilyl)methyl]phenyl (denoted as Bbt) groups, and characterized by the spectroscopic and X-ray crystallographic analyses. The electronic structures of the 1,1′-bis[(E)-diphosphenyl]ferrocenes were determined by analyzing electronic spectra, the transitions of which were reasonably assigned based on theoretical calculations. In the cyclic voltammograms, there were two well-defined reversible one-electron reduction couples corresponding to the intramolecular two diphosphene units. Furthermore, the 1,1′-bis[(E)-diphosphenyl]ferrocene was found to undergo ligand-exchange reactions with group 6 metal carbonyl complexes along with the E-to-Z isomerization of the diphosphene moieties, leading to the formation of the corresponding 1,1′-bis[(Z)-diphosphenyl]ferrocene group 6 metal tetracarbonyl complexes, [M(CO)4{(Z,Z)-(BbtP=PC5H4)2Fe}] (M=Cr, Mo, and W). The molecular structures of these complexes were determined by spectroscopic analyses (1H, 13C, and 31P NMR spectra, and UV–vis spectra), and that of the tungsten complex was determined by X-ray crystallographic analysis. Several types of d→π∗P=P electron transitions due to the iron and group 6 metals were detected by using UV–vis spectroscopy, and these results were supported by theoretical calculations.