SHORT COMMUNICATION DOI: 10.1002/ejic.201200242 Different Inertness of Titanocene [Cp 2 Ti] and Decamethyltitanocene [Cp* 2 Ti] in Reactions with N,N-Bis(trimethylsilyl)sulfurdiimide – Elimination of Tetramethylfulvene and Formation of Half-Titanocene Complexes Katharina Kaleta, [a] Monty Kessler, [a] Torsten Beweries,* [a] Perdita Arndt, [a] Anke Spannenberg, [a] and Uwe Rosenthal* [a] Keywords: C–H activation / Metallacycles / Metallocenes / Titanium / Structure elucidation The reaction of the titanocene alkyne complex [Cp* 2 Ti(η 2 - Me 3 SiC 2 SiMe 3 )] (1) (Cp* = η 5 -pentamethylcyclopentadienyl) with N,N-bis(trimethylsilyl)sulfurdiimide (2) results in the formation of 1,2,3,4-tetramethylfulvene (3) as well as three titanium complexes 4, 5 and 6. During the reaction, formal elimination of one Cp* ligand induces a series of C–H and N–S bond activation steps, thus yielding the products. The Introduction Since the early days in titanocene [1] and zirconocene [2] chemistry the [Cp 2 M] complex fragment (Cp = cyclopen- tadienyl) was mostly considered to be relatively inert re- garding the dissociation of Cp ligands: “In most organo- metallic reactions of transition metal complexes, the η 5 -Cp ligand plays the role of a spectator that stays tightly bound in η 5 fashion to the metal centre throughout the course of the reactions.” [3] Nevertheless, there were some strong hints from Brintzinger’s results on the elimination of the η 5 -Cp ligands during reduction, which motivated his group to in- troduce the ansa-bridged rac-ebthi [ebthi = 1,2-ethylene- 1,1'-bis(η 5 -tetrahydroindenyl)] ligand to prevent the elimi- nation of Cp by the chelate effect. [4] Already in 1974, the photochemically induced exchange reaction of Cp ligands between different titanocene com- plexes was observed. [5] Numerous reactions of metallocene complexes involving the Cp ligand are known; examples in- clude C–H activation, coupling and ring opening reac- tions. [6] These “unexpected” activation processes influence synthetic [7] and catalytic [8] applications and should therefore be taken into account when using such metallocene com- plexes. In our studies of the metallocene alkyne complexes Cp' 2 M(L)(η 2 -Me 3 SiC 2 SiMe 3 ) (M = Ti, Zr, Hf; L = thf, pyridine; Cp' = substituted or unsubstituted η 5 -cyclopen- [a] Leibniz-Institut für Katalyse e.V. an der Universität Rostock, Albert-Einstein-Str. 29a, 18059 Rostock, Germany Fax: +49-381-1281-51104, -51176 E-mail: torsten.beweries@catalysis.de uwe.rosenthal@catalysis.de Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/ejic.201200242. © 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Eur. J. Inorg. Chem. 2012, 3388–3393 3388 molecular structures of complex 5 and of the free fulvene were determined by X-ray crystallographic analysis. Evi- dently, in these reactions [Cp* 2 Ti] is less stable than [Cp 2 Ti]; a possible reason was found to be the well-known intramo- lecular C–H activation yielding the tautomeric tetrameth- ylfulvene hydride species, from which 1,2,3,4-tetramethyl- fulvene (3) can dissociate. tadienyl), elimination or insertion reactions of the alkyne were the dominant reaction patterns. However, some exam- ples of the activation or elimination of the cyclopentadienyl ligand were observed. [9,10] For the parent fully methylated complex fragment [Cp* 2 M] (Cp* = pentamethylcyclopentadienyl), similar ex- amples for the loss of one Cp* group from the titanium centre are known. Very recently, in our group such formal ligand eliminations were found in the reaction of the titano- cene alkyne complex [Cp* 2 Ti(η 2 -Me 3 SiC 2 SiMe 3 )] (1) with azobenzene [11] or during the irradiation of the decamethyl- titanocene dihydroxido complex [Cp* 2 Ti(OH) 2 ], where eli- mination of a pentamethylcyclopentadienyl radical takes place. [12] Pentamethylcyclopentadienol and pentamethylcy- clopentadiene, formed by recombination of Cp* · with OH · and H · (which were also cleaved off during irradiation), respectively, were found to be the organic products in this bond activation reaction. The unsubstituted complex [Cp 2 Ti(η 2 -Me 3 SiC 2 SiMe 3 )] reacts with N,N-bis(trimethylsilyl)sulfurdiimide (2) with al- kyne substitution to give a four-membered Ti–N–S–N metallacycle (A) (Scheme 1). [13] In this earlier paper, we re- Scheme 1. Reaction of [Cp 2 Ti(η 2 -Me 3 SiC 2 SiMe 3 )] with Me 3 SiN=S=NSiMe 3 .