On the stability of Benzonorbornadienone and Tricarbonyl(benzonorbornadienone) chromium

Abstract

Benzonorbornadienone could not be isolated at 0°, nor detected at -45° in the hydrolysis of 7,7-dimethoxybenzonorbornadiene (9,9-dimethoxy- 1,4-dihydro-1,4-methanonaphthalene) (5). Reaction of (5) with chromium hexacarbonyl gave endo-tricarbonyl(7,7- dimethoxybenzonorbornadiene)chromium (14) (1 %) and a new type of alkene-ether complex of composition (7,7- dimethoxybenzonorbornadiene)-Cr(CO)₄ (36%). Hydrolysis of (14) gave-only tetracarbonyl(naphthal-ene)chromium (24), and naphthalene. Oxidation of exo- and endo- tricarbonyl(anti-7-benzonorbornadienol)chromium with silver carbonate on Celite at 40° gave mainly tricarbonyl(1-naphthaldehyde)chromium, accompanied by a small amount of (24). It is concluded that benzonorbornadienone and tricarbonyl(benzonorbornadienone)chromium are unstable at -45°, and 40°, respectively. The factors contributing to the instability of these ketones are briefly discussed.