FULL PAPER Neutral and Cationic [Bis(η 1 -amidosilyl)-η 5 -cyclopentadienyl]titanium and -zirconium Complexes: Synthesis, X-ray Molecular Structures and DFT Calculations Jesu ´ s Cano, [a] Pascual Royo,* [a] Heiko Jacobsen, [b][‡] Olivier Blacque, [b] Heinz Berke, [b] and Eberhardt Herdtweck [c] Keywords: Cations / Cyclopentadienyl ligands / Density functional calculations / Nitrogen ligands / Titanium / Zirconium Treatment of LiNHtBu with THF solutions of C 5 H 4 (SiMe 2 Cl) 2 gave C 5 H 4 (SiMe 2 NHtBu) 2 (1). Deprotonation of 1 with M(NMe 2 ) 4 (M = Ti, Zr) under different conditions provided the monocyclopentadienyl complexes [M{η 5 -C 5 H 3 - [SiMe 2 (NHtBu)] 2 }(NMe 2 ) 3 ] [M = Ti (2), Zr (3)] and the single (η-amidosilyl)cyclopentadienyl compounds [M{η 5 -C 5 H 3 [Si- Me 2 (NHtBu)][SiMe 2 (η 1 -NtBu)]}(NMe 2 ) 2 ] [M = Ti (4), Zr (5)]. The related dibenzyl compounds [M{η 5 -C 5 H 3 [SiMe 2 - (NHtBu)][SiMe 2 (η 1 -NtBu)]}(CH 2 Ph) 2 ] [M = Ti (6), Zr (7)] re- sulted from treatment of 1 with M(CH 2 C 6 H 5 ) 4 (M = Ti, Zr). Further deprotonation of the amido complexes 4 and 5 and the benzyl complexes 6 and 7 by heating in toluene solution gave the bis(η-amidosilyl)cyclopentadienyl complexes Introduction The group-4 metallocenes [MCp 2 X 2 ] [1] and cylopentadi- enylamido complexes [M(η 5 -C 5 R 4 -E-η 1 -NR')X 2 ] [2] are the two essential types of catalyst precursors for insertion poly- merization of olefins based on the use of cyclopentadienyl ligands. After alkyl abstraction by a Lewis acid {MAO, B(C 6 F 5 ) 3 , [CPh 3 ][B(C 6 F 5 ) 4 ]} the metallocene compounds generate the cationic, coordinatively unsaturated, 14-elec- tron d 0 [MCp 2 R] + species, [3] whereas the cyclopentadienyl- amido complexes provide the electronically more unsatu- rated 12-electron d 0 [M(η 5 -C 5 R 4 -E-η 1 -NR')R' ' ] + cations. [4] [a] Departamento de Quı ´mica Inorga ´nica, Facultad de Quı ´mica, Universidad de Alcala ´, Campus Universitario, 28871 Alcala ´ de Henares, Spain Fax: (internat.) + 34-91/8854683 E-mail: pascual.royo@uah.es [b] Anorganisch-chemisches Institut der Universität Zürich Winterthurerstrasse 190, 8057 Zürich, Switzerland Fax: (internat.) + 41-1/635-6802 E-mail: hberke@aci.unizh.ch [c] Anorganisch-chemisches Institut der Technischen Universität München Lichtenbergstrasse 4, 85747 Garching bei München, Germany [‡] Present address: KemKom, 1864 Burfield Ave., Ottawa, Ontario K1J 6T1, Canada, E-mail: jacobsen@kemkom.com Supporting information for this article is available on the WWW under http://www.eurjic.org or from the author. Eur. J. Inorg. Chem. 2003, 2463-2474 DOI: 10.1002/ejic.200200698  2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 2463 [M{η 5 -C 5 H 3 [SiMe 2 (η 1 -NtBu)] 2 }(NMe 2 )] [M = Ti (8), Zr (9)] and [M{η 5 -C 5 H 3 [SiMe 2 (η 1 -NtBu)] 2 }(CH 2 Ph)] [M = Ti (10), Zr (11)], respectively. Treatment of the monobenzyl complexes 10 and 11 with B(C 6 F 5 ) 3 yielded the cationic compounds [M{η 5 -C 5 H 3 [SiMe 2 (η 1 -NtBu)] 2 }] + as [(CH 2 Ph)B(C 6 F 5 ) 3 ] - [M = Ti (12), Zr (13)] salts. All new compounds were characterized by NMR spectroscopy, and the crystal structures of 10 and 13 were studied by diffraction methods. DFT calculations for the neutral and cationic species are described and provide an explanation for the unusual η 1 coordination of a phenyl ring to a group-4 metal cation. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) The technological applications [5] of these ‘‘constrained-ge- ometry’’ catalysts are based not only on their electronic un- saturation, but also on their sterically open reactive sites, combined with rigidity of the molecular framework and thermal stability. These features facilitate the coordination of bulkier olefins, allowing the synthesis of various copoly- mers of ethylene with 1-hexene, 1-octene, styrene and other larger olefins. Scheme 1. Types of metallocene and (cyclopentadienylsilyl)amido cations Amido ligands are π-donors and in this respect resemble Cp ligands. Even if π-electrons are included, however, the formal electron count of a single group never reaches that of the Cp moiety. Replacement of one Cp by an amido group, as demonstrated in structures I and II, establishes a 12-electron cyclopentadienylamido complex [6] on the basis