UNUSUAL REACTIONS OF TITANOCENE-GENERATING AND ZIRCONOCENE-GENERATINGCOMPLEXES

The titanocene alkyne complex without any additional ligands Cp(2)Ti(M e(3)SiC=CSiMe(3)) 1 and the zirconocene alkyne complexes free from sta bilizing phosphine ligands Cp(2)Zr(L)(Me(3)SiC=CSiMe(3)) (L = THF 2, p yridine 3) as well as the metallacyclic complex Cp(2)Zr-O-CMe(2)-C(SiM e(3))=C(SiMe(3)) 4 react with some substrates in an unusual manner dep ending on metals M, ligands L and the substituents R of the substrates . Also in some cases the competitive reaction of coupling of the compl exed alkyne occurs. In this account all products without coupling of t he silylalkyne are numbered, the data of detailed NMR studies and X-ra y crystal structure analyses are given in the cited references. The re action of ''Cp(2)Zr'' with benzophenone gives the ligand stabilized me tallocene eta(2)-ketone complex 5. With di(tert-butyl)acetylenedicarbo xylate a coupling of a C=C- and a C=O-ester group to 6 and with bis(tr imethylsilyl)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 stabi lized eta(2)-complexes 8 or the derivatives bearing N-H functions to a mido alkylideneamido complexes 9 and 10 by a hydrogen transfer reactio n. Aldimines give the cyclic diamido complex 11 or in the case of a me thyl group at the nitrogen under evolution of methane an unsaturated c yclic complex. Heterocyclic C=N systems, e.g. benzoxazoles or benzthia zoles, show a ring enlargement and a simultaneous coupling to 12 and 1 3 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 metalla cyclic 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. Als o a novel cleavage of the central C-C single bond of the butadiynes by the metallocene occurs yielding the homobimetallic, doubly sigma,pi-a cetylide bridged complexes 23 - 26. The heterobimetallic complex 27 wa s obtained in the reactions of the metallacyclocumulens 15 with ''Cp(2 )Zr'' or 16 with ''Cp(2)Ti''. Complexes (Ph(3)P)(2)Ni(eta(2)-RC=C-C=CR ') gives with ''Cp(2)Ti'' the Ni(0) complexed titanacyclocumulene 28 o r with ''Cp(2)M'' the heterobimetallic sigma,pi-acatylide-bridged comp lexes 29 - 31. The metallocene units interact with one equivalent of a n alkynylsilane carrying SI-H groups (RC=CSiMe(2)H) to yield cans-coor dinated alkyne complexes with strong Si-H-M interactions like 32, whic h at low temperatures is in agreement with the description on the way to a novel hydride eta(3)-silaallenyl complex. Two molecules of the al kynylsilane are coupled to metallacyclopentadienes without Si-H-M inte ractions (e.g. 33).