THE REACTION BETWEEN π-CYCLOPENTADIENYLDI-CARBONYLCOBALT AND PHENYLETHYNYLSILANE, AND AN X-RAY CRYSTALLOGRAPHIC INVESTIGATION OF ONE OF THE PRODUCTS, (π-CYCLOPENTADIENYL)-[trans-DIPHENYL-DI(TRIMETHYLSILYL)-CYCLOBUTADIENE]-COBALT

Abstract

Abstract This is a report of the broad range of reactions and products that occur in refluxing xylene when π-cyclopentadienylcobalt or (π-cyclopentadienyl)-dicarbonylcobalt react with either symmetric or unsymmetrical acetylenes, specially when one of the substituents of the acetylene is an aromatic moeity. Since these reactions produce a variety of products, several of which are cis- and trans- tetrasubstituted cyclobutadiene-cobalt isomers, mnr and mass spectral methods were used to distinguish between them. In order to obtain an independent and indisputable structure assignment for the structural isomers investigated by spectral techniques, the crystal structure of the title compound was investigated by x-ray crystallographic techniques. The compound crystallizes in space group Pbca with the following cell dimensions: a = 29.622(7), b = 9.967(2) and c = 17.140(3) Å; V = 5060.46 Å3; D(exp) = 1.23(2) gm-cm−3, D(calc) = 1.24 gm-cm−3 for Z = 8 molecules/unit cell. The intensity data were collected with MoKα radiation (Λ = 0.71069 Å) using a computer-controlled diffractometer equipped with a graphite monochromator. In all 6331 reflections were collected of which 3173 were independent and had F 0 2 ± 3[sgrave] (F 0 2). The data were corrected for absorption and the transmission coefficients ranged from 0.72 to 0.79. The (π-cyclopentadienyl) ring is planar and has normal Co–C and C–C distances which average 2.049(7) and 1.389(17) Å, respectively. The Co–(Cp ring centroid) distance is 1.67 Å and the ring librates about this axis to a small degree which is not, however, large enough to affect the C–C distances. The average value of the C–C–C angle in the π-cyclopentadienyl ring is 108° indicating that it is planar and, in fact, the largest deviation of any carbon from the least-squares plane is 0.006 Å. In the Co-cyclobutadiene moiety, the Co–C and C–C distances are 1.982(15) and 1.467(3) Å and the Co–(cyclobutadiene ring centroid) distance is 1.69 Å. The angle between the normals of the five- and four-membered rings is 1.6°. The phenyl rings and trimethylsilyl fragments have normal distances and angles and the phenyl rings are planar. The two silicon and two carbon atoms of the phenyl rings linked to the π-cyclobutadiene moeity are out of the mean plane of the ring and bend away from the Co atom. Finally, and most important, the four-membered ring is planar (the largest deviation from planarity is 0.003 Å) and the four C–C distances are the same length; however, the internal angles are not 90.0°. Instead, the two angles at carbons bonded to phenyl rings have values of 88.1(2)° and 88.4(2)° while those at carbon atoms bonded by silicons have values of 91.6(2)° and 91.8(2)°. The final discrepancy indices for this structural analysis were R 1 = 0.038 and R 2(F) = 0.044.