Interaction of bis(trimethylsilyl)acetylene complex of titanocene with tris(pentafluorophenyl)borane.: Synthesis and structure of a new type of zwitterionic metallocene (η5-C5H5){η5-[C5H4B(C6F5)3]}Ti

In the interaction of the bis(trimethylsilyl)acetylene complex of titanocene Cp2Ti(Me2SiC2SiMe3) with an equimolar amount of B(C6F5)(3) in toluene at 20 degrees C, electrophilic substitution of a hydrogen atom in one of the eta(5)-C5H5 rings by a B(C6F5)(3) group takes place and the paramagnetic zwitterionic titanium complex (eta(5)-C5H5){eta(5)-[C5H4B(C6F5)(3)]} Ti (I) is produced. The formation of I is accompanied by liberation of molecular hydrogen. Bis(trimethylsilyl)acetylene and 1,2-bis(trimethylsilyl)ethane were found in organic products of the reaction. An X-ray diffraction study of complex I revealed the coordination of the ortho-fluorine atoms of two C6F5 groups with the positively charged titanium centre. In contrast to other known titanium. zirconium and hafnium zwitterionic metallocenes, complex I contains a metal in the +3 oxidation state and does not contain any sigma-bonded organic radicals at the metal atom. (C) 2000 Elsevier Science S.A. All rights reserved.