C O M M U N I C A T I O N S
withdrawing group,9a,11 without deactivating the catalyst by forma-
tion of a stable chelate.
Table 3. Coupling of Substituted Anilines with 1-Octene
To gain insight into the identity of the tantalum complexes in
the catalytic system, we analyzed reactions of N-methyl-p-toluidine
1
by H NMR spectroscopy. After heating this substrate with Ta-
[N(CH3)2]5 and 1-octene in toluene at 160 °C for 3 h, the bis(anilide)
and tris(anilide) complexes [(p-tol)(CH3)N]2Ta[N(CH3)2]3 (1) and
[(p-tol)(CH3)N]3Ta[N(CH3)2]2 (2) (∼1:1 ratio) accounted for >75%
of the tantalum-amido species in solution (1H NMR analysis).17
Studies on the chemistry of these complexes relevant to this catalytic
process are ongoing.
In summary, we have described an efficient C-H bond func-
tionalization process that constitutes a hydroaminoalkylation of
alkenes. The selectivity of this reaction appears to be controlled
by the electronic properties of the amine, but this reaction does
not require functionality on nitrogen, such as a pyridyl, iminyl, or
carbamoyl groups, that directly coordinates to the metal.
a Isolated yield after purification by flash-column chromatography.
b Reaction conducted in neat 1-octene (2.50 equiv) using 8 mol % of
Ta(NMe2)5; relative stereochemistry not assigned. c 8 mol % of Ta(NMe2)5.
The selectivities of this process are notable. With the exception
of the alkylaniline products shown in entry 2, the branched
alkylation products were formed as the sole detectable regioisomer
and products arising from multiple alkylations were not observed.
Many reactions of R-olefins are complicated by competitive
isomerization processes. 1H NMR analysis of these crude hy-
droaminoalkylation reaction mixtures revealed that only 10-20%
of the unreacted olefin consisted of internal isomers. Finally, in
contrast to most C-H bond functionalizations that occur through
organometallic intermediates, the reactions occur preferentially at
sp3 C-H bonds over sp2 C-H bonds.
Acknowledgment. We thank the NIH (NRSA fellowship to
S.B.H. and NIGMS GM-55382 to J.F.H.) for support of this work.
Supporting Information Available: Detailed experimental pro-
cedures and spectral data of all new compounds. This material is
References
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