REACTION OF A TETRAAZA[14]ANNULENE COBALT(III) COMPLEX WITH ACETYLENE - SYNTHESIS AND STRUCTURAL CHARACTERIZATION OF A NOVEL COBALT(III) COMPLEX CONTAINING A PENTADENTATE MACROCYCLIC LIGAND WITH A CARBON SIGMA-DONOR ATOM - [(7-(CIS-BETA-VINYLIDE)-7,16-DIHYDRO-6,8,15,17-TETRAMETHYLDIBENZO[B,I]-[1,4,8,11]TETRAAZACYCLOTETRADECINATO)PYRIDINECOBALT(III)] HEXAFLUOROPHOSPHATE MONOACETONITRILET

The cycloaddition reaction of acetylene with Co(III) complexes of the 7, 16-dihydro-6, 8, 15, 17-tetramethyldibenzo[b, i][1, 4, 8, 11]tetraazacyclotetradecinato ligand yields a novel, dianionic pentadentate macrocycle with four equatorial nitrogen donor atoms and a vinylide carbon a donor occupying one axial site. The Co(III) complex containing this ligand, [Co(C24H24N4)(C5H5N)]PF6•CH3CN, crystallizes in the monoclinic space group Pcwith cell parameters a = 10.644 (2) Å, b = 8.309 (2) Å, c = 18.614 (5) Å, β = 107.7 (1)° and Z = 2. The structure was refined by Fourier and least-squares techniques to conventional and weighted R values of 4.1 and 4.7%, respectively, based on 4490 unique data with |F0| ≥ 3σ|F0|. The acetylene has added across one six-membered 2, 4-pentanediiminato chelate ring bridging the cobalt atom and the methine carbon. The resultant macrocycle contains a bicyclic, tridentate chelate with pentane-2, 4-diimine-3-vinylide functionalities and an unmodified 2, 4-pentanediiminato chelate ring. The Co(III) atom lies in the N4donor atom plane with an average Co-N distance of 1.892 Å. The Co-C(vinylide) distance is 1.908 Å. The long Co-N(pyridine) distance of 2.098 Å is attributable to a combination of a trans effect and steric interactions. The importance of peripheral steric interactions within the ligand on the details of the macrocyclic ligand conformation and the role these play in the formation of the complex are discussed. Structural comparisons are made with other Co(III)-vinyl species and with Co(III) porphyrin complexes. © 1979, American Chemical Society. All rights reserved.