Unusual Reactions of Titanocene- and Zirconocene-Generating Complexes

All articles of this category The titanocene alkyne complex without any additional ligands Cp 2 Ti(Me 3 SiC≡CSiMe 3 ) 1 and the zirconocene alkyne complexes free from stabilizing phosphine ligands (Cp 2 Zr(L)(Me 3 SiC≡CSiMe 3 ) (L = THF 2 , pyridine 3 ) as well as the metallacyclic complex Cp 2 Zr-O-CMe 2 -C(SiMe 3 )=C(SiMe 3 ) 4 react with some substrates in an unusual manner depending on metals M, ligands L and the substituents R of the substrates. Also in some cases the competitive reaction of coupling of the complexed alkyne occurs. In this account all products without coupling of the silylalkyne are numbered, the data of detailed NMR studies and X-ray crystal structure analyses are given in the cited references. The reaction of ”Cp 2 Zr” with benzophenone gives the ligand stabilized metallocene η 2 -ketone complex 5 . With di( tert -butyl)acetylene-dicarboxylate a coupling of a C≡C- and a C=O-ester group to 6 and with bis(trimethylsilyl)acetylenedicarboxylate an unusual 1,3-migration of a SiMe 3 unit from an oxygen to a carbon atom yielding the dimeric complex 7 occurs. Ketimines react with metallocenes either to the ligand stabilized η 2 -complexes 8 or the derivatives bearing N-H functions to amido alkylideneamido complexes 9 and 10 by a hydrogen transfer reaction. Aldimines give the cyclic diamido complex 11 or in the case of a methyl group at the nitrogen under evolution of methane an unsaturated cyclic complex. Heterocyclic C=N systems, e.g. benzoxazoles or benzthiazoles, show a ring enlargement and a simultaneous coupling to 12 and 13 or, e.g. benzisoxazoles, yield without coupling the dimeric complex 14 . Depending on metals, ligands, substituents and used stoichiometry the generated metallocenes ”Cp 2 M” react with one equivalent of 1,4-disubstituted 1,3-butadiynes RC≡C-C≡CR’ to give five-membered metallacyclic cumulenes 15 and 16 or with a half equivalent of the diyne the bimetallic complexes 17-19 . Two diyne molecules are coupled by ”Cp 2 Ti” to yield a titanacyclopentadiene 20 in contrast to ”Cp 2 Zr”, which gives the seven-membered zirconacyclic cumulenes 21 and 22 . Titanocene - zirconocene - alkyne complexes - butadiynes - coupling reactions - metallacyclocumulenes - C-C and Si-H bond activations