Fourier-transform carbon-13 nuclear magnetic resonance study of (arene)tricarbonylchromium complexes

Abstract

13C nmr spectroscopy was employed to study the perturbations in bonding for monosubstituted benzene derivatives upon complexation with Cr(CO)3. An analysis of the C(4) 13C nmr chemical shifts of both free and complexed arenes implies that there is no significant change in the transmission of resonance substituent effects upon complexation. A similar analysis of the C(l) 13C nmr chemical shifts and the ' 3 * coupling constants indicates a net withdrawal of electron density by the Cr(CO)3 fragment from the a framework of the arene ring.

The Question of σ Participation in the Bonding of Fluorosubstituted Arenes to Chromium Tricarbonyl. A 19F Nuclear Magnetic Resonance Investigation

“…This remarkable constancy of the dominance of the resonance parameter in the transmission of substituent effects is most gratifying especially as a recent 13C n.m.r. study showed exactly comparable behavior (18). The correlation between the lgF chemical shifts in para-substituted fluorobenzenes and the 13C chemical shift of the C, carbon in the corresponding monosubstituted arenes is well established (25), and this relationship still holds in most cases when the arenes are complexed (see Fig.…”

Rh NMR studies of organometallic rhodium(I) derivatives

“…'J(RhP) is usually considered to reflect the strength of the u component of the b~nding.,~-~" The general trend for lJ(RhP) is an increase with the basicity of the p h~s p h i n e .~~ Nevertheless, the reverse behaviour, a decrease in ' J ( M P ) with increasing basicity of the phosphine ligand, has already been observed where M = Rh4', M = Pt.41 compounds [Rh.Cl.cod.PRJ (30)(31)(32)(33).…”

A 13C‐NMR. Study of naphthalene chromium complexes. Correlation with reactivity: Nucleophilic aromatic substitution reactions

“…Coordination of an arene to a transition metal causes large shifts to lower frequencies of the ring C-resonances in respect to the free arene [15]. The increase in shielding has been variously attributed to metal ligand bond anisotropy [ 16-181, changes in ring C-hybridization [19] and changes in electron density in the 0- [20] [21] and n- [22- interpretation of these shifts is not yet available [26] [27], however, a thorough study of the factors that influence the coordination shift concludes that changes in n-electron density and, particularly, metal to arene n*-backbonding play a dominant role in the observed shielding of coordinated arenes [23]. These conclusions receive support from the results of molecular orbital calculations [25] [28-301 and a He (I) photoelectron study [3 11.…”