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to prevent undesired hydrosilylation of the aldehyde. Analogously, reaction of n-butanal and cyclohexanecarboxaldehydegave(1 b ) and (1 c) in 67 % and 37 % yields, respectively.In the case of cyclohexanecarboxaldehyde, the yield of ( 1 c ) was low because of the formation of diethyl(methy1)siloxymeth-

The latter compound contains a bridging isonitrile ligand of fluxionial behavior as proved by high temperature 'H NMR spectroscopy. The u + B bonded character of the isonitrile bridge was established by X-ray c~st~o~aphy.Much attention has been paid to the addition of small donor molecules to the formally unsaturated [C,H,Mo(CO), I2 [2]. Careful investigations have been carried out recently on the symmetrical addition of allenes [3]. In contrast, relatively little is known about the reaction with heteroallenes, X=C=Y. As a first example we showed that (C~R~)~M~(CO)~ (R = H, CH,) reacts with boiling S=C=S to give complexes of the type CSR,(CO),Mo-Mo(CO),(q'-CS,)C~R~, containing a nonbridging, terminal q2-CS, ligand [4]. Stimulated by this result, we are using other heteroallenes, e.g. isothiocyanates and carbodiimides. In this paper we report on the reaction of [C+Me,(CO),Mo], with CH,N=C=S. Ex~~mentaI sectionAll procedures were carried out under nitrogen with solvents freshly distilled under nitrogen from appropriate drying agents. I was prepared according to a published procedure [5], CH,NCS was obtained from Fluka.

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97. 34(3t [97.47(3t] at 300 K [120 K] with Z = 2. Even at 120 K the Si-O-Si fragment is found to be strictly linear due to crystallographically imposed symmetry. To explain the unusual electron distribution derived from the X-ray data collected, several types of possible disorders are discussed, none of which leads to a satisfying explanation. It was found that the lone pairs on the siloxane oxygen were tipped away from cylindrical symmetry. The tipping was directed toward the fluorine substituents on the silicon atoms and away from the CpFe(CO)2 units. A pertubational approach was utilized to rationalize this effect.