We were interested in electron deficient organotitanium complexes das potential Ziegler-Natta catalysts likely to show particularly interesting structural features and easily accessible low valent oxidation states and so we chose pentamethylcyclopentadienyltitanium trichloride as the starting product for our studiesThe research described here is included in Project PR-84-0407 financially sup­\ud ported by CAICYT and sponsored by Repsol Petr6leo. We are also indebted to S. Martinez \ud Carreras and S. Garcia Blanco of the Departamento de Cristalografia CSIC (Madrid), and \ud to Prof. A. Tiripicchio of the Centro di Studio per la Strutturistica \ud Diffrattometrica de!CNR de la Universita di Parma (Italy) for determination of the \ud X-ray structures. Our excellent co-workers J.C. Flores, F. Palacios and Dra. I. Saez \ud carried out some of the experimental work described here and their collaboration is warmly \ud acknowledged

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306ChemInform Abstract The OR1-bridged Os clusters (I) react with Me3NO in MeCN (II) to produce monoacetonitrile derivatives in which the acetonitrile ligand attaches to one of the bridgehead Os atoms and which form two isomers of the monophosphite derivatives (IV) on treatment with P(OMe)3 (III). The bis(phosphite) analogues (V) are prepared from reaction of (Ia), (Ib), (Id) with 2.2 equiv. of Me3NO in MeCN (II) followed by P(OMe)3 (III). The SR2-bridged Os clusters (VI) afford the isomeric monoacetonitrile derivatives (VIIa)-(VIIc) and (VIIIa)-(VIIIc) under analogous conditions. Their substitution reactions with P(OMe)3 (III) lead to only one isomer of the phosphite derivatives (VIId) and (VIIId). The acetonitrile complex (VIIc) reacts with the tert. phosphines L5 (IX) to give the monosubstitution products (VIIe), (VIIf). The structure of the title complex (VIIe) (space group P21/a, Z=4) is confirmed by X-ray analysis. All the products are characterized by IR and 1H NMR spectroscopy.

tert-Butyl isocyanide reacts with the m 3 -alkylidyne complex [{TiCp*(m-O)} 3 (m 3 -CH)] (1, Cp* h 5 -C 5 Me 5 ) to give a single insertion into a m 3 -carbon ± titanium bond and the formation of the new derivative [{TiCp* (m-O)} 3 (m 3

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