Restricted rotation about arene–oxygen bonds in some 1,3-di-tert-butyl-2-methoxyarenedicarbonylphosphorus(III)chromium compounds

Abstract

, 2566 (1984).The 'H nrnr spectra of 1,3-di-tert-butyl-2-methoxybenzenedicarbonyltriphenylphosphinechromium (5) and some related compounds at low temperatures show the presence of two species which interconvert with free energy of activation near 50 W mol-'. The species differ in the orientation of the methoxy with respect to the chromium, since the same type of process is observed in a chelate complex in which a phosphinite ligand on chromium is also attached to the arene. Hindered rotation about the arene-chromium axis is not involved. The crystal structure of 5 shows the Ph3P anti to the methoxy and the 0-methyl group proximal to chromium.

Toward an Understanding of 1,5-Asymmetric Induction during Nucleophilic Addition to (Arene)chromium Tricarbonyl Complexes: Conformational Preference of the Chromium Tricarbonyl Tripod for Transmission of Chirality

“…The preference for a single conformation results from the significant barrier to arene−oxygen bond rotation. While π-symmetry interactions between the arene and the substituent are well-known in uncomplexed arenes, systematic studies of substituent effects in (arene)chromium tricarbonyl complexes also indicate significant double-bond character for the arene carbon−oxygen bond . From the X-ray crystal structures determined in the present work, the C2−O−arene carbon bond angles are measured to be 120.07, 124.32, 120.18, and 120.19° for complexes 3a , b , c(A) , c(B) , respectively, indicating sp 2 hybridization of oxygen, and thereby leading to significant π-interaction with the arene.…”

Synthesis and Characterization of BHT-Derived tert-Butyl Dendrons

“…The crude product was precipitated with MeOH/H 2 O (10:1) and the precipitate filtered. The crude yellow solid was recrystallized in hexanes to yield 3 as fluffy white crystals (21.9 g, 81% from 2 ): mp 99−101 °C (lit . mp 101−102 °C); 1 H NMR (200 MHz, CDCl 3 ) δ 7.25 (s, 2H), 4.62 (d, J = 5.6 Hz, 2H), 3.69 (s, 3H), 1.62 (t, J = 5.2 Hz, 3H), 1.43 (s, 18H); 13 C NMR (75.4 MHz, CDCl 3 ) δ 159.1, 143.8, 134.7, 125.6, 65.7, 64.2, 35.7, 32.0; MS (FAB + ) m / z 250.33 (C 16 H 26 O 2 requires 250.19).…”

“…°C (lit 11. mp 101-102 °C); 1 H NMR (200 MHz, CDCl3) δ 7.25 (s, 2H), 4.62 (d, J ) 5.6 Hz, 2H), 3.69 (s, 3H), 1.62 (t, J ) 5.2 Hz, 3H), 1.43 (s, 18H); 13 C NMR (75.4 MHz, CDCl3) δ 159.1, 143.8, 134.7, 125.6, 65.7, 64.2, 35.7, 32.0; MS (FAB + ) m/z 250.33 (C16H26O2 requires 250.19).…”