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.
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The reaction of [Ta(NMe 2 ) 5 ] with the o- (2,3-dihydro-1-naphthyl)-, o-(1-naphthyl)-, and o-(inden-3-yl)phenols [HOC 6 H 2 Ar-2-Bu t 2 -4,6] (Ar ) C 10 H 9 (1), C 10 H 7 (Np; 2), C 9 H 7 (3)) has been investigated. In all three cases initial displacement of 1 equiv of dimethylamine occurs, yielding mono(aryloxides) [(ArO)Ta(NMe 2 ) 4 ]. Structural studies of the o-(2,3-dihydro-1naphthyl) and o-(1-naphthyl) compounds 4 and 5 show they both adopt geometries best described as square pyramidal with an apical dimethylamido ligand and basal aryloxide oxygen. The Ta-O-Ar angles are 162°in both compounds, with no metal interaction with the ortho substituents. Compound 4 reacts with 2,3,5,6-tetraphenylphenol to form the corresponding bis(aryloxide) 6. The intermediate o- (inden-3-yl)phenoxide [(ArO)Ta(NMe 2 ) 4 ] 7 thermally eliminates a further 1 equiv of HNMe 2 with formation of the tris(amido) compound [Ta(OC 6 H 2 {η 1 -Ind}-2-Bu t -4,6)(NMe 2 ) 3 ] 8. The coordination geometry about tantalum in 8 is best described as trigonal bipyramidal, with an oxygen and amido group in the axial positions: O-Ta-N ) 170°. The carbon atom of the indenyl ring bound directly to the phenoxide nucleus is metalated, leading to a five-membered metallacycle. Hence, both deprotonation (CH bond activation) and tautomerization of the original inden-3-yl ring has occurred. The Ta-C(121) distance of 2.285(9) Å is consistent with an η 1 -indenyl ring being present in 8. Replacement of the dimethylamido ligands in 8 by chloride groups was achieved by reaction with SiCl 4 . Structural analysis of the 4-phenylpyridine adduct [Ta(OC 6 H 2 {η 3 -Ind}-2-Bu t -4,6)(NC 5 H 4 Ph-4)Cl 3 ] 9 showed the presence of an η 3 -indenyl interaction with the tantalum metal center. The bonding parameters for the η 1 -and η 3 -indenyl rings are compared with those of related η 5 -cyclopentadienyl derivatives of niobium and tantalum.
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