LOW OXIDATION DINUCLEAR TITANIUM COMPLEXES WITH THE BRIDGING MU-(DIMETHYLSILYL)BISCYCLOPENTADIENYL LIGAND - CRYSTAL-STRUCTURE OF I(ETA(5)-C5H5))(2)(MU-CL)(2)(MU-ME(2)SI(C5H4)(2))]

The chlorotitanium(III) derivative ta(5)-C5H5}](2){mu-Cl)(2)[mu-Me(2)S i(C5H4)(2)}](2) was synthesized in 85% yield by reduction of the titan ium(IV) derivative {[Ti(eta(5)-C5H5)Cl-2](2)[(2) mu-Me(2)Si(C5H4)(2)]} ) (1) with 2 equiv of sodium amalgam. The structure of 2 has been dete rmined by X-ray diffraction methods. Crystals are monoclinic, space gr oup P2(1)/n, with Z = 8, in a unit cell of dimensions a. = 28.262(10), b = 8.089(5), and c = 18.446(9) Angstrom, beta = 91.06(2)degrees. The structure has been solved from diffractometer data by direct and Four ier methods and refined by blocked full-matrix least-squares methods o n the basis of 3200 observed reflections to R and R(w) values of 0.056 8 and 0.0727, respectively. The [Me(2)Si(C5H4)(2)](2-) ligand, through the two cyclopentadienyl rings, acts as a bridge between the two Ti a toms, which are also involved in a double Cl bridge. Moreover, each Ti atom eta(5)-interacts with a cyclopentadienyl ring. If the cyclopenta dienyl centroids are considered as coordination sites, then the coordi nation geometry around each titanium is distorted tetrahedral. In the presence of oxygen, 2 is immediately transformed into the eta-oxo comp ound Ti(eta(5)-C5H5)Cl](2)(mu-O)[mu-Me(2)Si(C5H4)(2)]}. Reduction of 1 with sodium amalgam or HgCl2-activated magnesium in THF at room tempe rature in the presence of a stoichiometric amount of the appropriate l igand (L) gave the titanium(II) adducts {Ti(eta(5)-C5H5)L(2)}(2)[mu-Me (2)Si(C5H4)(2)] [L = CO (3); CN(2,6-C(5)H(3)Me(2)) (5)]. The same redu ction of 1 with sodium amalgam or HgCl2-activated magnesium in THF, in the presence of PMe(2)Ph, resulted in the loss of hydrogen and format ion of the diamagnetic complex u-eta(1)-eta(5)-C5H4)(2){mu-Me(2)Si(C5H 4)(2)}](6). The dicarbonyl derivative 3 was also obtained by reaction of [{Ti(eta(5)-C5H5)Me(2)}(2){mu-Me(2)Si(C5H4)(2)}] with CO. This reac tion enables us to identify the formation of the acetone-coordinated t itanium compound 4 as an intermediate species.