Regioselective reactions of isothiocyanates with the titanocene vinylidene fragment [Ti(=C=CH2)(h-C5Me5)2]. Crystal and molecular structure of [Ti{SC(=N(C6H11)C=CH2}(h-C5Me5)2]

R. Beckhaus, J. Sang, T. Wagner, U. Böhme 
J. Chem. Soc. Dalton Trans. 1997, 2249-2255

The titanocene vinylidene intermediate [Ti(=C=CH2)(h-C5Me5)] 1 formed by ethane or methane elimination from [Ti(CH2CH2C=CH2)(h-C5Me5) 2 or [Ti(CH=CH2)Me(h-C5Me5) 3 respectively, reacted with isothiocyanates RNCS (R = C6H11 a, Ph b or But c) by a [2 + 2] cycloaddition, to give the titanathietane complexes [Ti{SC(=NR)C=CH2}(h-C5Me5)2]. The crystal structure of the R = C6H11 complex has been dterminde. In all cases the regioisomer in which the sulfur atom is bonded to tinanium is observed as the primary product. Upon heating in the presence of pyridine a rearrangement to the regioisomeric titanacyclobutane derivative [Ti{C(=NR)SC=CH2}(h-C5Me5)2] 8 was observed. The regioselectivity of the formation of the complexes 5 and 7 is discussed on the basis of ab initio calculations at the Hartree-Fock level of theory, with an effective core potential basis set.

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