DYNAMIC STEREOCHEMISTRY IN THE TITANOCENE SERIES WITH CENTRAL AND PLANAR CHIRALITY - X-RAY STRUCTURE AND RELATIVE CONFIGURATION OF THE RACEMIC FORM (MP 186-DEGREES-C) OF [(ETA(5)-1-ME-2-(PRC5H3)-PR-I)(ETA(5)-C5H5)TI(2,6-ME(2)C(6)H(3)O)CL]

The dynamic stereochemistry of two substitution reactions [(i) and (ii)] for the thiocyanate and isocyanate complexes of titanocene has been reinvestigated. [GRAPHICS] The metathesis reaction (ii) has been shown to be chemoselective and stereospecific with inversion of the configuration at the titanium for X = NCO and retention for X = NCS. This stereochemical behaviour contrasts with that proposed previously, i.e. inversion of configurations for both X = NCO and X = NCS. The present result is unambiguously supported by the crystallographic structure of the racemic compound 1c' (X = Cl, m.p. 186 degrees C), which was chosen as the starting stereochemical reference. The complex 1c' crystallizes in the monoclinic system, space group C-c. Two well-characterized quasi-eclipsed and staggered conformational forms of the complex 1c' are presented. According to Seebach's nomenclature, this structure corresponds to the u(Ti, p) configuration.