| Abstract
| - Bicyclo[2.2.1]hepta-2,5-diene (2,5-norbornadiene) dimerizes in the presence of a catalytic amountof Ru(1-2:5-6-η-cyclooctadiene)(1-6-η-cyclooctatriene) (Ru(cod)(cot)) and an electron-deficient olefin suchas N,N-dimethylacrylamide, dimethyl fumarate, or dimethyl maleate in toluene or tetrahydrofuran (THF) togive a new compound, pentacyclo[6.6.0.02,6.03,13.010,14]tetradeca-4,11-diene (PCTD), in high yield along witha small amount of a known endo−endo dimer, heptacyclo[6.6.0.02,6.03,13.04,11.05,9.010,14]tetradecane (HCTD),which is a major product in the reaction in DMSO. Ru(cod)(cot)-dimethyl fumarate in THF was the mostefficient catalyst, and the yield of PCTD was 96% even at 40 °C. The structure of PCTD was determined byX-ray analysis of its derivative, [AgOTf(PCTD)]n. PCTD was found to be derived via endo−endo dimerizationof 2,5-norbornadiene. Formation of PCTD from two molecules of 2,5-norbornadiene involves the cleavage oftwo carbon−carbon bonds. Dimerization of 7-tert-butoxy-2,5-norbornadiene gave the corresponding exo- andendo-4,9-disubstituted PCTD derivatives. Ru(cod)(cot) reacts with dimethyl fumarate to give a novel complex,Ru(cot)(dmfm)2 (dmfm = dimethyl fumarate), in high yield. The structure of the complex was determined byX-ray analysis. At 40 °C in toluene, Ru(cot)(dmfm)2 itself catalyzes the dimerization of 2,5-norbornadiene togive PCTD in excellent yield in the absence of olefinic additives. The mechanisms of the formation of PCTDare discussed.
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