CYCLOPENTADIENYLCOBALT COORDINATION TO ALKENYLARENES - FROM 1,3-DIENECOORDINATION TO MU-ARENE CLUSTER COMPLEXES

Reaction of [CpCo(C2H4)(2)], 7, with a number of alkenylnaphthalene de rivatives C(10)H(7)R (R = 1-CH=CH2, 2-CH=CH2, 1-CH=CHMe, and 1-CH=CHPh ) gave the mononuclear [CpCo{eta(4)-(alkenyl)naphthalene}] complexes 1 5a,b, 16, and 17. In these complexes, two pi-electrons each of the nap hthalene nucleus and the olefinic side chain are involved in metal coo rdination. The crystal and molecular structure of the 1-vinyl derivati ve, 15a, has been determined. Relevant crystal parameters are as follo ws: orthorhombic, space group Pcab; Z = 8; a 8.206(1) Angstrom, b = 11 .372(3) Angstrom, c = 28.067(7) Angstrom; wR2 = 0.131 (based on 2308 u nique reflections), R = 0.050 (1374 reflections with I greater than or equal to 2 sigma(I)). The distribution of carbon-carbon bond lengths indicates considerable electronic localization within the metal-coordi nated part of the six-membered ring. Strong metal-to-ligand bonding is shown by equilibration of the carbon-carbon bonds within the 1,3-dien e system. From m- and p-distyrylbenzene and 7 the dinuclear complexes [(CpCo)(2)(eta(4):eta(4)-distyrylbenzene)] 18a,b were obtained. Here, coordination to each metal is in a 1,3-diene fashion via an olefinic d ouble bond and a localized double bond of the central arene (phenylene ) ring. In toluene, 18b partially decomposed to form 3)(mu(3)-eta(2):e ta(2):eta(2)-p-distyrylbenzene)], 19. Both 18b and 19 were also formed from p-distyrylbenzene and [CpCo(C(6)Me(6))], 8. Compound 19 is fluxi onal in solution; the barrier Delta G(double dagger) for arene rotatio n was estimated to 50 kJ mol(-1) at 250 K. From the reaction of alpha- methylstyrene, Cp(2)Co, and potassium, a minor amount of [CpCo{1-3,8,9 -eta-(1-Cp-3-Me-1-cobaltaindenyl)}] 20 was isolated. Compound 20 has b een characterised by X-ray crystallography. Crystal data: tetragonal, space group I (4) over bar; Z = 8; a = 18.150(12) Angstrom, c = 9.307( 5) Angstrom; wR2 = 0.100 (based on 1878 unique reflections), R = 0.045 (1373 reflections with I greater than or equal to 2 sigma(I)).