Formation of Tantalum “Tuck-in” Complexes by Activation of Methyl C−H Bonds in Pentamethylcyclopentadiene Groups by Carbazole Ligation

Abstract

The reaction of [Cp*TaCl 4 ] with the potassium salt of carbazole (cbK, >3 equiv) in hydrocarbon solvents leads to the species [(C 5 Me 4 CH 2 )Ta(cb) 2 Cl] (1), in which one of the ring methyl C-H bonds of the Cp* ligand has been cleaved along with free cbH. Spectroscopic and structural studies of 1 show a lack of a plane of symmetry through the molecule with nonequivalent cb ligands. A minor component of the reaction mixture is believed to be the substitutional isomer 2, in which both carbazole ligands are equivalent. Alkylation of 1 with LiCH 2 SiMe 3 or PhCH 2 MgCl generates the corresponding monoalkyl derivatives [(C 5 Me 4 -CH 2 )Ta(cb) 2 (R)] (7 or 8, respectively). Structural studies of 1, 7, and 8 support an η 1 :η 5 -CH 2 C 5 Me 4 (σ:η 5 -CH 2 C 5 Me 4 ) description for the metalated ligands, with significant slippage toward an η 1 :η 3 -CH 2 C 5 Me 4 resonance form. To compare the extent of π-bonding between cb and dialkylamido ligands, the complex [(cb) 2 Ta(NMe 2 ) 3 ] (9) was synthesized and structurally characterized. The molecular structure of 9 consists of a tbp arrangement of nitrogen atoms with trans, axial cb ligands. The Ta-cb distances are 0.2 Å longer than the Ta-NMe 2 distances. An improved (safer) procedure for the synthesis of [Ta(NMe 2 ) 5 ] is presented.

Intramolecular C–H Activation in Alkaline‐Earth Metal Complexes

“…The deprotonation reaction described in Scheme can be classified as an intramolecular C–H activation or cyclometalation, a reaction type that is common for early transition‐metal complexes 15. The formation of “tuck‐in” complexes (Scheme ) are the best documented examples of intramolecular C–H activation and are well‐known for metal complexes of groups 3b (including the lanthanides),15c,d 4b,15e–g and 5b 15h. However, the reaction in Scheme can also be described as a directed metalation reaction.…”

Intramolekulare C‐H‐Aktivierung in Erdalkalimetall‐Komplexen

“…Die Deprotonierung in Schema könnte man als eine intramolekulare C‐H‐Aktivierung oder Cyclometallierung bezeichnen. Diese Reaktion ist typisch für die Chemie der frühen Übergangsmetalle:15 Die Bildung von “Tuck‐in”‐Komplexen (Schema ) ist wahrscheinlich das am besten erforschte Beispiel der intramolekularen C‐H‐Aktivierung und wurde bei metallorganischen Verbindungen der Gruppen 3 (inklusive der Lanthanoide),15c,d 415e–g und 5 beobachtet 15h. Andererseits könnte man die Reaktion in Schema auch als eine dirigierte Metallierung beschreiben.…”

trans-Dichloro-cis-bis(3,6-dimethylcarbazolyl)-cis-bis(tetrahydrofuran)zirconium(IV) benzene sesquisolvate

“…One of the major goals of inorganic chemistry has been attained with the application of the electronic properties of hard amide ligands, an area that has been reviewed recently (Cummins, 1998;Schrock, 1997a,b). In contrast, recent work by ourselves (Nygren et al, 2003(Nygren et al, , 2004 and others (Riley et al, 1998(Riley et al, , 1999(Riley et al, , 2001Tanski & Parkin, 2003) has been based on the exploration of the chemistry of amide ligands in which the % interaction is uncertain with respect to the donation to the metal center. These amides with a lower % basicity (Tanski & Parkin, 2003) form a class of non-innocent ligands in coordination chemistry that differ from the non-innocent ligands described by Gray et al (1967), in that the oxidation state is not uncertain, only the degree of electronic coupling between the %-donating ligating atom and the metal center.…”

“…Carbazolyl complexes of transition metals that are '-bound are rare (Lopez et al, 2002); most of the known examples (Riley et al, 1998(Riley et al, , 1999(Riley et al, , 2001) involve group 4B and 5B metals. A few biscarbazolyl structures are known for the group 4B metals (mostly containing titanium; Riley et al, 2001).…”