Hydrogen-transfer reactions which generate new imine, imido, and trimethylenemethane complexes of tantalum

Journal Article · Wed May 04 00:00:00 EDT 1983 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00347a023· OSTI ID:5719722

Mayer, J M; Curtis, C J; Bercaw, J E

The reactions of Cp*TaMe/sub 3/Cl (Cp* = n/sup 5/-C/sub 5/Me/sub 5/) with a variety of alkali-metal alkoxide, alkylamide, and alkyl reagents have been examined. Reaction with LiNMe/sub 2/ produces Cp*Ta(NMe/sub 2/)Me/sub 3/, which decomposes at 25/sup 0/C to an imine (or metallaazirane) complex, Cp*Ta(CH/sub 2/NMe)Me/sub 2/. The decomposition is a first-order, unimolecular process with a large kinetic isotope effect (k/sub H//k/sub D/ = 9.7). Monoalkylamides (LiNHR) react with Cp*TaMe/sub 3/Cl to form imido complexes Cp*Ta(NR)Me/sub 2/. Reaction of Cp*TaMe/sub 3/Cl with lithium diisopropylamide forms a bridging methylene complex, Cp*Ta(..mu..-CH/sub 2/)(..mu..-H)/sub 2/TaMe/sub 2/Cp*. The alkoxide compounds Cp*Ta(OR)Me/sub 3/ (R = Me, CHMe/sub 2/, CMe/sub 3/) are very stable and decompose only over 100/sup 0/C. Alkyl complexes are stable only if the alkyl group does not have ..beta..-hydrogens. Treatment of Cp*TaMe/sub 3/Cl with (2-methylallyl)magnesium bromide affords an unstable tantalum 2-methylallyl compound, which decomposes cleanly to the trimethylenemethane complex Cp*TaMe/sub 2/)n/sup 4/-C(CH/sub 2/)/sub 3/). The rates of hydrogen abstraction or elimination processes in this system correlate with the nature of the atom bound to tantalum: for reactions involving a ..beta..-hydrogen transfer the order is C > N > O, while the facility of ..cap alpha..-hydrogen abstraction reactions appear to decrease in the reverse order N > C. These reactivity patterns appear to reflect the variance in Ta-C, Ta-N, and Ta-O bond energies in this series. Hydrogenation of the imido compounds (Cp*Ta(NR)Me/sub 2/) in the presence of phosphine ligands yields new examples of imido hydride complexes Cp*Ta(NR)H/sub 2/(L) (L = PMe/sub 3/, PMe/sub 2/(C/sub 6/H/sub 5/); R = CMe/sub 3/, CH/sub 2/CMe/sub 3/). A moderately stable alkyl hydride complex, Cp*Ta(CH/sub 2/NMe)Me(PMe/sub 3/)H, has also been prepared.

• Research Organization: California Inst. of Tech, Pasadena
• OSTI ID: 5719722
• Journal Information: J. Am. Chem. Soc.; (United States), Vol. 105:9
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
TANTALUM COMPLEXES
CHEMICAL REACTIONS
ALKYLATION
AMIDES
CHEMICAL BONDS
DECOMPOSITION
HYDROGEN TRANSFER
HYDROGENATION
IMIDES
IMINES
METHANE
ALKANES
COMPLEXES
HYDROCARBONS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
TRANSITION ELEMENT COMPLEXES
400102* - Chemical & Spectral Procedures