Inductive and Polarizability Effects of an Exocyclic Diene-Iron Tricarbonyl Group. The acetolyses of exo- and endo-irontricarbonyl complexes of 5,6-dimethylidene-2-exo-norbornyl and 2,3-dimethylidene-7-anti-norbornyl parabromobenzenesulfonates
✍ Scribed by Charles Barras; Larry G. Bell; Raymond Roulet; Pierre Vogel
- Publisher
- John Wiley and Sons
- Year
- 1981
- Tongue
- German
- Weight
- 750 KB
- Volume
- 64
- Category
- Article
- ISSN
- 0018-019X
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✦ Synopsis
Abstract
The exo‐ and endo‐irontricarbonyl complexes of 5,6‐dimethylidene‐2‐exo‐norbornyl alcohols 10x, 10n, p‐bromobenzenesulfonates 11x, 11n, acetate 12x and of the 2,3‐dimethylidene‐7‐anti‐norbornyl alcohols 17x, 17n, p‐bromobenzenesulfonates 19x, 19n and acetates 20x, 20n have been prepared. The S~N~1 buffered acetolyses of 11x, 19x and 19n gave 12x, 20x and 20n, respectively (retention of configuration). The first‐order rate constants of the acetolyses have been evaluated and compared with those of the acetolyses of the uncomplexed 5,6‐dimethylidene‐2‐exo‐norbornyl (14) and 2,3‐dimethylidene‐7‐anti‐norbornyl p‐bromobenzenesulfonates (18). A rate retardation effect of ca. 1.5 · 10^5^ was measured for 11x → 12x (65°) compared with the acetolysis of 14. The retardation effect is larger (> 5 · 10^7^) with 11n. Contrastingly, the acetolysis 19x → 20x was slightly accelerated with respect to that of the uncomplexed p‐bromobenzenesulfonate 18. An unsignificant rate‐retardation effect was measured for the acetolysis 19n → 20n. The results are interpreted in terms of competitive inductive destabilization and charge‐induced dipole stabilizing interaction by the exocyclic diene‐iron tricarbonyl fragment. PMO. arguments give a rationale for the difference in polarizability between the diene‐Fe(CO)~3~ group in 19 and that in the endo‐7‐norbornadienyl‐iron tricarbonyl system.