Organometallics 1992,11, 2251-2262
2251
Nonlinear Substituent Interactions and the Electron Rlchness of Substituted (q'-Arene)Cr(CO), Complexes As Measured by I R and ''C NMR Spectroscopy and Cyclic Voltammetry: Role of r-Donor and r-Acceptor Interactions'** Allen D. Hunter;
Vivian Mozol, and Stanislaus D. Tsai
Department of Chemisfry, Univers& of Atbe-,
Edmonton, Alberta, Canada T6G 202
Received November 29, 199 1
The spectroecopiccharacterization and oxidative electrochemical behavior (stationaryPt-bead electrode, CH,C&., [n-Bu,NlPFB) of a series of 63 (&rene)Cr(CO), complexes having between zero and six Substituents on the arene ring &e. NEh, NMe2,NH2, OMe, F, C1, Me, SiMe3,C02Me, C(O)Me, CF,) with various substitutiongeometries are reported. The incremental effect of the substituents upon the electron richness of the complexes,as measured by the formal oxidation potentials,EO', the IR carbonyl stretching frequencies and force constants, KCO,and the 13C NMR chemical shifts of the carbonyl ligands, ace, is nonlinear and is found to be dependent upon both the electron richness of the chromium center and the substitution geometry about the arene ring. It is p r o w that the origin of thew nonlinearities lies principally in ?r-donor and ?r-acceptor interactionsbetween the substituents on each arene and between each of the substituents on the arene and the chromium center in each complex. Evidence is also provided that the stability of the radical cations of these complexes is dependent upon the electron richness of the metal centers. A valence bond rationale for these effects is provided, and the relationship between these results and the degree of arene planarity and Cr-CO and CrC-O bond lengths of these complexes is discussed.
Introduction The central goal of our work is the synthesis and characterization of low molecular weight complexes having structures similar to the repeat units of organometallic In this context, we have prepared and characterized a series of complexes, e.g. hi.? O < D > F p
bC 8
6
c
*o
