Syntheses of Cationic and Zwitterionic Cyclobutadiene Compounds of Cobalt(I). Crystal and Molecular Structure of Tricarbonyl(.eta.-1-methoxy-3-methyl-2-phenylcyclobutadiene)cobalt(1+) Hexafluorophosphate
American Chemical Society
The (r;3-cyclobutenonyl)cobalt complexes 1 react with trialkyloxonium salts to yield cationic cyclobutadiene compounds 2, which have been characterized by IR, XH NMR, and 13C NMR spectroscopy. Compounds 1 also react with BF3-OEt2 to afford the zwitterionic cyclobutadiene derivatives 4. Reactions of lb with PhCO+SbFe- or (CF3S02)20 produce 6 and 7, respectively. The CO ligands in 2a are displaced in refluxing benzene, affording the cationic sandwich complex 8, and the unstable zwitterion 4g can be trapped in refluxing benzene to give the zwitterionic sandwich complex 9. An X-ray crystallography investigation of 2i at -100 °C revealed a monoclinic crystal with space group P27/c (No. 14): a = 14.689 (5) A, b = 8.444 (2) A, c = 14.865 (5) A, (8 = 109.32 (3)°, Z = 4, R = 0.087, R„ = 0.051. The cyclobutadiene ring is planar, and substituent atoms bound to the ring are displaced away from the metal. The carbon-carbon distances within the cyclobutadiene ring are unequal, as are the cobalt-carbon distances.