Structural and Energetical Characterization of Reactive Intermediates Derived from Toluene-Cr(CO)3

Abstract

In order to gain a deeper understanding of the specific reactivity of arene ± Cr(CO) 3 complexes, the structures and energies of the reactive intermediates formally generated by abstraction of a proton (H ), a hydride (H À ), or a hydrogen atom (H . ) from the methyl group of toluene ± Cr(CO) 3 (2) were computationally investigated by using density functional theory based quantum chemical techniques. The solid-state structure of the parent complex (2) was determined by low-temperature X-ray crystallography and this confirmed the high accuracy of the computational methods. Besides calculating the geometry of the lowest energy conformation, particular emphasis was laid on the rotational barrier of the Cr(CO) 3 group as well as on that of the exocyclic carbon ± carbon bond which exhibited a significant amount of double-bond character in all of the reactive intermediates investigated. The results are put into broader perspective by discussing their relevance for the rationalization and prediction of the selectivity of synthetically relevant reactions of arene chromium tricarbonyl complexes.

Carbocations in Superacid Systems

“…731 According to X-ray data, the 2-bornyl cation leans toward Mo in the mixed-metal Mo,Co complex. 735 An interesting feature of complex 414 is that the benzylic carbon bends down to coordinate to Co; that is, the contribution of resonance form 414b is significant. 732 Cr(CO) 3 is also known to strongly stabilize carbocations.…”

“…The synthesis and X-ray structure of a dicationic dimolybdenum complex was also reported. [735][736][737] Consequently, the complex may be better viewed as a pentadienyl cation with an exocyclic double bond. Theoretical studies for benzyl cations are abundant.…”

Synthesis of Polyarylated Methanes through Cross‐Coupling of Tricarbonylchromium‐Activated Benzyllithiums

“…[18][19][20] An alternative approach to attenuate the reactivity of benzylic nucleophiles is h 6 -coordination to a metal fragment such as {Cr(CO) 3 }. [21][22][23][24] Along these lines, Kalinin and co-workers generated [(h 6 -C 6 H 5 CH 2 Li)Cr(CO) 3 ], but were unable to effect palladiumcatalyzed cross-coupling reactions. After transmetalation to zinc the resulting [(h 6 -C 6 H 5 CH 2 ZnCl)Cr(CO) 3 ] underwent palladium catalyzed single coupling with aryl halides to furnish diarylmethanes in low yield (average 37 %).…”

Organometallic Radicals: Thermodynamics, Kinetics, and Reaction Mechanisms

“…16 Optimized geometries (bold) and natural charges of the staggered and the eclipsed structure of the C 6 H 5 --CH 2 .--Cr(CO) 3 complex and the transition state describing the rotation of the terminal CH 2 group. The charges of the hydrogen atoms are summed into the carbon atoms 156. The charges of the hydrogen atoms are summed into the carbon atoms 156.…”