Organometallic ligands : The preparation and properties of complexes of the ferrocenylphosphines

Abstract

Coordiantion complexes of ferrocenyldiphenylphosphine, diferrocenylphenylphosphine, and triferrocenylphosphine have been prepared. An examination of the CO stretching frequencies of the eight possible compounds of the series (Fc x Ph 3 -x P) M(CO) 5 (M = Mo, W) showed that the A 1 1 and E modes decreased in frequency as the number of ferrocyney groups increased. This has been interpreted as resulting from a concomitant increase in the σ donor ability of the ferrocenylposphine. 1H NMR studies of (Fc x Ph 3 -x P)Me +I − and methylbis(dimethylglyoximato)(ferrocenylphosphine)cobalt(III) demostrate the same trend, that is, the PMe or CoMe groups are increasingly shielded with increasing ferrocenyl group substitution. Although the σ donor ability of the phosphine increases with increasing ferrocenyl substitution, the steric requirements of the ligand also increase greatly. As evidence, no ligand exchange is observed in solutions of Fc 3P and methylbis(dimethylglyoximato)(pyridine)cobalt(III), nor is complexation observed between this same phosphine and bis(acetylacetonato)nickel(II); however, ligand exchange or complexation is observed for the other phosphines of the series. The contact shifted NMR spectra of FcPl 2P and Fc 2PhP show that spin may not be delocalized from the substituted π-C 5H 4 ring through the iron atom into the π-C 5H 5 ring and that more spin density may be delocalized into the phenyl groups than into the ferrocenyl groups; this latter result may be a manifestation of the fact that the phenyl group is less electron releasing than the ferrocenyl group. In a preliminary survey of the electrochemistry of these phosphine and their complexes, it was found that the ferrocenyl group of FcPh 2P and (FcPh 2P)Mo(CO) 5 underwent reversible, one-electron oxidation at +0.48 and +0.62 V vs. S.C.E., respectively. At more oxidizing potentials, more complex, irreversible processes occur.