Arene-metal complexes. VI. Hindered rotations in mono(tricarbonylchromium) complexes of diarylmethanes and related compounds

Abstract

Mono(tricarbonylchromium) complexes of dimesitylmethane (1), dimesityl ketone (2), 1,1-dimesitylethene (3), 2,6-dimethylphenyl mesityl ketone (with the mesityl ring complexed) (4), and dimesitylmethanol (5) are described. By nmr spectroscopy the barriers of rotation of the uncomplexed rings, complexes 1-5, were found to be (in kcal/mol) 14.3 at 18°, 19.6 at 118°, 14.2 at 14°, 19.4 at 115°, and 13.9 at 22°, respectively. The higher barriers for the ketone complexes are attributed to increased stabilization of the ground-state conformation of the ketone complexes by conjugation of the tt electrons of the uncomplexed ring with those of the carbonyl group. It is suggested that the approximately equal barrier for the methane (1) and ethene (3) complexes means that there is very little interaction berween the electrons of the uncomplexed ring and those of the carbon-carbon double bond. Also reported are the ir absorption bands for the carbonyl group of some aryl ketones and their tricarbony lchromium complexes. Results and DiscussionMono(tricarbonylchromium) complexes of dimesitylmethane (1), dimesityl ketone (2), 1,1-dimesitylethene

Synthesis, Structure, and Reactivity of Organo-Iron(II) Complexes with N-Heterocyclic Carbene Ligation

“…Though most were unsuccessful, its reactions with CO and Pr i NCNPr i did lead to the isolation of dimesityl ketone and [(IPr)Fe(Mes)(η 2 -Pr i NC(Mes)NPr i )] ( 5 ), respectively (Scheme ). Dimesityl ketone was characterized by 1 H and 13 C NMR and mass spectra that are consistent with the reported data . Its formation could be explained by a consecutive insertion−reductive elimination mechanism as proposed in other carbonylation reactions of iron alkyls. , Attempts to isolate the presumable iron-containing product (IPr)Fe(CO) 4 were unsuccessful.…”

Artificial Molecular Rotors

“…Trahanovsky, Kowalski, and Avery first investigated the dynamics of monochromium tricarbonyl complexes of diarylmethanes, diaryl ketones, diarylmethanols, and diarylethenes ( 57 ), and they suggested that the rotation of the complexed ring was correlated with that of the uncomplexed ring. Barriers for the uncomplexed ring were in the range of (Δ G ⧧ ) 14−20 kcal mol -1 .…”

Dichlorobis(pyridine)zinc(II) – a redetermination

“…1,3,3,5-TETRA METHY L -6-( 1 ', 2'-N A P H TH O) -BICYCLO[3,2,1 ] O CTENE sky, Kowalski & Avery, 1974;Thoennes, Wilkins & Trahanovsky, 1974). For example, the C(19) methyl proton n.m.r, shift data are, respectively, 6.=-0.38 and 3n=-0.08 [3(TMS)=0.00] for C20H24 and C23H24OaCr, indicating markedly increased proton shielding in the former.…”