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

• Published in: Organometallics Vol. 18; no. 18; pp. 3579 - 3583
• Main Authors: Riley, Patrick N, Parker, Jennifer R, Fanwick, Phillip E, Rothwell, Ian P
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 30.08.1999; Amer Chemical Soc
• Subjects: Chemistry; Chemistry, Inorganic & Nuclear; Chemistry, Organic; Physical Sciences; Science & Technology; NIOBIUM; LIGANDS; ZIRCONIUM; ALKYL; MOLECULAR-STRUCTURE; REACTIVITY; SULFUR; DERIVATIVES
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/om990388a

The reaction of [Cp*TaCl4] with the potassium salt of carbazole (cbK, >3 equiv) in hydrocarbon solvents leads to the species [(C5Me4CH2)Ta(cb)2Cl] (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 LiCH2SiMe3 or PhCH2MgCl generates the corresponding monoalkyl derivatives [(C5Me4CH2)Ta(cb)2(R)] (7 or 8, respectively). Structural studies of 1, 7, and 8 support an η1:η5-CH2C5Me4 (σ:η5-CH2C5Me4) description for the metalated ligands, with significant slippage toward an η1:η3-CH2C5Me4 resonance form. To compare the extent of π-bonding between cb and dialkylamido ligands, the complex [(cb)2Ta(NMe2)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−NMe2 distances. An improved (safer) procedure for the synthesis of [Ta(NMe2)5] is presented.