C-13 NMR SPECTROSCOPIC AND EHMO STUDY OF SLOWED TRIPODAL ROTATION IN [(BENZYL)CR(CO)3]+ AND (FULVENE)CR(CO)3 SYSTEMS - METAL-STABILIZED NONPLANAR CATIONS

The variable-temperature C-13 NMR spectra of a series of methyl- and methoxy-substituted (benzyl)Cr(CO)3 cations and neutral (fulvene)Cr(CO)3 complexes reveal that the metal carbonyl resonances are split at low temperature; the barriers to tripodal rotation are rationalized in terms of the degree of localization of charge at the aromatic or fulvene carbons. It is shown that primary benzyl cations require greater stabilization by the tricarbonylchromium fragment than do analogous secondary or tertiary benzyl cations. These experimental results are complemented by molecular orbital calculations at the extended Huckel level.