pi-arene complexes - 11. Site control affected by steric and electronic factors of ring substituents in sigma,pi-coordinated bimetallic complexes

Metallation of [Cr(eta(6)-C6H5NMe2)(CO)(3)] affords, after subsequent quenc hing with [Ti(eta(5)-C5H5)(2)Cl-2], the sigma,pi-bimetallic complex [Cr(eta (6)-C6H5NMe2{TiCp2Cl})(CO)(3)] in a ratio of 1:3 for the p(1):m(2) isomers. The isomers were separated and 2 crystallizes in the space group Pbca (No. 61), the lattice parameters being a = 14.233(2), b = 15.778(2), c = 17.974 (2) Angstrom and Z = 8. The substituents cause a decrease in the endocyclic angles within the benzene ring and the Ti-C(arene) and N-C(arene) bonds ar e 2.236(5) and 1.378(7) Angstrom, respectively which are indicative of elec tron donating groups. This is supported by the chemical shifts for the aren e resonances in the H-1 and C-13 NMR spectra. The cyclopentadienyl rings in 2 are diastereotopic due to the planar chirality of the pi-complex and the central chirality of the titanium. (C) 1999 Elsevier Science S.A. All righ ts reserved.