Crystal structures of tribromo(η5-3,6-di-tert-butyl-9,10,11-trimethylbicyclo( 6.3.0)undeca-4-en-8,10-dienyl)titanium(IV), Ti(C22H35)Br3, and tribromo(η5-4,5-dibromo-3,6-di-tert-butyl-9,10,11-trimethylbicyclo( 6.3.0)undeca-8,10-dienyl)titanium(IV), Ti(C22H35Br2)Br3

Abstract

C22H35Br3Ti, triclinic, P1 (no. 2), a = 9.621(2) A, b = 11.796(2) A, c = 12.232(2) A, 4 = 102.23(3)°, 3 = 97.71(3)°, 2 = 112.32(3)°, V = 1219.2 A, Z = 2, Rgt(F) = 0.058, wRobs(F) = 0.134, T = 293 K. C22H35Br5Ti, monoclinic, P121/n1 (no. 14), a = 7.474(1) A, b = 18.458(4) A, c = 20.171(4) A, 3 = 100.28(3)°, V = 2738.0 A, Z = 4, Rgt(F) = 0.054, wRobs(F) = 0.119, T = 293 K. Source of material Dibromo-pentamethylcyclopentadienyl-trimethylcyclopentadienyl-cyclooctene-Ti(IV) [1] (1; 125 mg, 0.195 mmol) was dissolved in 20 ml of n-hexane under argon and treated with an excess (0.3ml) of bromine. Standing at room temperature for 20 h and concentration of the orange-red solution in vacuum to 2 ml gave a mixture of red crystals of complexes Cp*TiBr3, the title compounds (2 and 3) in a molar ratio of 35:35:30 as identified by NMR. Fractional recrystallization from n-hexane gave small amounts of individual complex 2 (20 mg) and complex 3 (30 mg) which were separated from the mother liquor, washed with cold n-hexane and dried in vacuum. Discussion For group 4 decamethyltitanocenes and -zirconocenes manifold C—H bond activations of methyl groups of pentamethylcyclopentadienyl ligands with coupling reactions with butadiynes RCC–CCR have been verified forM=Ti,R=Me, Ph, t-Bu and M = Zr, R = t-Bu [2-4]. This is a facile method for functionalizing metallocenes to obtain chiral and non-chiral complexes [1,5]. One example for this is a formal Ti(II) complexwith one pentamethylcyclopentadienyl and one anellated trimethylcyclopentadienylcyclooctyne ligand [1-5]. Hydrogenation of this complex yields a Ti(II) complex with one pentamethylcyclopentadienyl and one anellated trimethylcyclopentadienyl-cyclooctene ligand, which is easily oxidized by bromine to a Ti(IV) dibromide (1) with one pentamethylcyclopentadienyl and one anellated trimethylcyclopentadienylcyclooctene ligand [1]. In the crystal structures of the title compounds, the 1-coordinated Cp ligand and three bromine ligands form a ”piano-stool”-like coordination. As in the case of the starting complex 1 and their chloride congener the cyclooctene unit is oriented away from the metal. There is no hint for any interaction of the double bondwith the metal in 2. This was expected for the electronically saturated Ti(IV). The bromine substituents in 3 are in an anti conformation to each other. Z. Kristallogr. NCS 223 (2008) 57-60 / DOI 10.1524/ncrs.2008.0027 57 © by Oldenbourg Wissenschaftsverlag, Munchen