113567-79-6Relevant articles and documents
Intermolecular [2 + 2 + 2] cycloaddition reactions of alkynes and alkenes mediated by cobalt: X-ray crystal structures of two isomeric (η5-cyclopentadienyl)(η4-1,3-cyclohexadiene)cobalt complexes
Macomber, David W.,Verma, Akhilkumar G.,Rogers, Robin D.
, p. 1241 - 1253 (2008/10/08)
Treatment of bicyclic alkenes (norbornylene, endo-dicyclopentadiene) with alkynes (diphenylacetylene, dimethyl acetylenedicarboxylate) in the presence of CpCo(CO)2 produced CpCo(η4-1,3-cyclohexadiene) complexes (1, 2, 6, 7, 10, 11) in good yields. Oxidation of complexes 1, 2, 6, 7, 10, and 11 using CuCl2·2H2O afforded the free diene ligands 4, 8, and 13. Further oxidation of 4 and 8 using ceric ammonium nitrate produced the aromatic derivatives 5 and 9. The isomeric complexes 1 and 2, which were obtained from endo-dicyclopentadiene and diphenylacetylene, were characterized by two-dimensional NMR spectroscopic techniques as well as X-ray crystallography. Complex 1 isomerized to 2 at 154°C in a first-order process with an observed rate constant of (1.5 ± 0.1) × 10-5 s-1. Treatment of norbornylene with diphenylacetylene in the presence of (η5-C5H4CH3)Co(CO)2 produced two isomeric (η5-C5H4CH3)Co(η 4-1,3-cyclohexadiene) complexes (14, 15). A 1:1 mixture of 1 and 14 isomerized intramolecularly to 2 and 15 in xylene-d10 at 155°C. Both 1 and 2 are triclinic, P1; 1 has unit cell parameters a = 10.943 (2) A?, b = 11.439 (1) A?, c = 14.954 (6) A?, α = 71.94 (3)°, β = 87.00 (3)°, γ = 62.27 (1)°, and D(calcd) = 1.30 g cm-3 for Z = 2. These values for 2 are a = 10.752 (1) A?, b = 12.640 (3) A?, c = 13.754 (3) A?, α = 69.89 (3)°, β = 66.83 (1)°, γ = 68.38 (1)°, and D(calcd) = 1.31 g cm-3 for Z = 2. Both were refined via least-squares, 1 to a conventional R value of 0.041 based on 4605 independent observed reflections ([Fo ≥ 5σ(Fo)] and 2 to 0.041 utilizing 3530 reflections. Each cobalt atom is η5-coordinated to the cyclopentadienyl ligand (Co-Cp(av) = 2.09 (2) A? for 1 and 2.08 (3) A? for 2) and η4-bonded to the 1,3-cyclohexadiene ligand. The two exterior Co-C distances average 2.08 (3) A? in 1 and 2.07 (2) A? in 2, whereas the two interior Co-C values average 1.97 (1) and 1.984 (8) A?, respectively.
