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Insertion of Isocyanide into Metal−Carbon Bonds of Alkylchloro(pentamethylcyclopentadienyl)niobium‐ and ‐tantalum Complexes − X‐ray Structure of [TaCp*Cl 2 (CH 2 CMe 2 Ph){η 2 ‐C(CH 2 CMe 2 Ph)=N(2,6‐Me 2 C 6 H 3 )}] and Unexpected Decomposition of Alkyldichloro(η 2 ‐iminoacyl) Complexes of Tantalum
Author(s) -
Castro Aurora,
Galakhov Mikhail V.,
Gómez Manuel,
GómezSal Pilar,
Martín Avelino,
Sánchez Fernando,
Velasco Patricia
Publication year - 2000
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/1099-0682(200009)2000:9<2047::aid-ejic2047>3.0.co;2-v
Subject(s) - chemistry , alkyl , tantalum , medicinal chemistry , stereochemistry , aryl , benzene , isocyanide , reagent , organic chemistry
Methylation of NbCp*Cl 2 Me 2 using excess ZnMe 2 gives NbCp*ClMe 3 ( 1 ) which has been found to exhibit a Berry pseudorotation process on the NMR time scale (log A = 12.2 ± 0.3, E a = 12.2 ± 0.4 kcal·mol −1 , Δ H ≠ = 11.6 ± 0.4 kcal·mol −1 , Δ S ≠ = −4.4 ± 1.3 e.u., Δ G ≠298K = 12.9 kcal·mol −1 ). Alternatively, lithium dimethylamide reacts with NbCp*Cl 2 Me 2 to form NbCp*Me 2 (NMe 2 ) 2 ( 2 ) which decomposes in solution under the elimination of methane to give the (dimethylamido)methylazaniobacyclopropane derivative NbCp*Me(NMe 2 )(η 2 ‐CH 2 NMe) ( 3 ). Reaction of NbCp*Cl 2 Me 2 with 1 equiv. of 2,6‐Me 2 C 6 H 3 NC results in a double methyl group migration to give the dichloroazaniobacyclopropane complex [NbCp*Cl 2 {η 2 ‐CMe 2 N(2,6‐Me 2 C 6 H 3 )}] ( 4 ). Dialkyldichloro complexes TaCp*Cl 2 R 2 [Cp* = η 5 ‐C 5 Me 5 ; R = CH 2 SiMe 3 ( 5 ), CH 2 CMe 2 Ph ( 6 ), CH 2 CMe 3 ( 7 ), CH 2 C 6 H 5 ( 8 )] were obtained by treating TaCp*Cl 4 with the requisite amounts of the appropriate alkylating agents. Reactions of the dialkyldichloro complexes TaCp*Cl 2 R 2 ( 5 − 8 ) with 1 equiv. of 2,6‐Me 2 C 6 H 3 NC resulted in migration of only one of the two alkyl groups to give (alkyl)dichloro(η 2 ‐iminoacyl) complexes [TaCp*Cl 2 R{η 2 ‐C(R)=NAr}] [Ar = 2,6‐Me 2 C 6 H 3 ; R = CH 2 SiMe 3 ( 9 ), CH 2 CMe 2 Ph ( 10 ), CH 2 CMe 3 ( 11 ), CH 2 C 6 H 5 ( 12 )]. The molecular structure of complex 10 has been determined by X‐ray diffraction analysis. The η 2 ‐iminoacyl complexes 9 − 12 decompose in [D 6 ]benzene or n ‐hexane solutions to give [TaCp*Cl 2 {N(2,6‐Me 2 C 6 H 3 )}] and the corresponding trans or cis olefins R′−CH=CH−CH 2 −R′ [R′ = SiMe 3 ( 9o ), CMe 2 Ph ( 10o ), CMe 3 ( 11o ), C 6 H 5 ( 12o )]. A mechanism for this reaction is proposed. All the new compounds have been characterized by IR spectrophotometry, 1 H‐ and 13 C{ 1 H}‐NMR spectroscopy, and elemental analysis.