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(4) For the use of earthꢀabundant transitionꢀmetals, such as Fe and
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B(C6F5)3] as the FLP precursor; however, A was confirmed as the sole
product. For details, see SI.
(5) (a) During the preparation of this manuscript, Soós et al. reꢀ
ported the B(2ꢀClꢀ6ꢀFꢀC6H3)(2,6ꢀCl2C6H3)2ꢀcatalyzed, FLPꢀmediated
reductive amination of carbonyls in toluene. This outstanding study
mainly focuses on the development and properties of organoboranes,
and the optimal catalyst system and applicable substrate scope (e.g.,
aliphatic and electronꢀrich aromatic amines) for the reductive aminaꢀ
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For recent examples, see: (a) Mahdi, T.; Stephan, D. W. Angew.
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(14) The reductive alkylation was examined under the optimized
conditions shown in Scheme 2 using a reaction mixture of 1a and 2a,
which was prepared in the presence of air and moisture (i.e., outside
the glove box), which resulted in a significant decrease of the yield of
3aa (<15%). The concomitant formation of unidentified products was
confirmed by 1H NMR analysis of the crude product mixture.
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(16) The condensation between 1h and 2a in the presence of 5
mol% of B(2,6ꢀCl2C6H3)(pꢀHC6F4)2 was also monitored, resulting to
the formation of N,Nꢀdimethylꢀ4ꢀ((phenylimino)methyl)aniline in
only 44% yield even after 30 min. The formation of the imine interꢀ
mediate should be thus unfavorable in the reaction between 1h and 2a
under the standard conditions (Scheme 2), and eventually the side
reaction proceeded to yield N,Nꢀdimethylꢀpꢀtoluidine via the FLPꢀ
catalyzed hydrogenation of 1h, followed by deoxygenation.
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(20) We were unable to monitor the reaction with 20 mol% B(2,6ꢀ
Cl2C6H3)(pꢀHC6F4)2 under 20 atm H2 due to its rapid completion.
Under the conditions shown in Figure 3c, MS are not necessary, as
only 5 equivalents of H2O are generated in situ. An FLP comprising
B(2,6ꢀCl2C6H3)(pꢀHC6F4)2 and THF has been reported to show activiꢀ
ty toward the heterolytic cleavage of H2 in the presence of less than
20 equivalents of H2O; for details, see: refs 9e.
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