Allylic C–H bond activation and functionalization mediated by tris(oxazolinyl)borato rhodium(i) and iridium(i) compounds

Dalton Transactions Pub Date: 2011-05-12 DOI: 10.1039/C1DT10249D

Abstract

Allylic C–H bond oxidative addition reactions, mediated by tris(oxazolinyl)borato rhodium(I) and iridium(I) species, provide the first step in a hydrocarbon functionalization sequence. The bond activation products ToMMH(η3-C8H13) (M = Rh (1), Ir (2)), ToMMH(η3-C3H5) (M = Rh (3), Ir (4)), and ToMRhH(η3-C3H4Ph) (5) (ToM = tris(4,4-dimethyl-2-oxazolinyl)phenylborate) are synthesized by reaction of Tl[ToM] and the corresponding metal olefin chloride dimers. Characterization of these group 9 allyl hydride complexes includes 1H-15N heteronuclear correlation NMR experiments that reveal through-metal magnetization transfer between metal hydride and the trans-coordinated oxazoline nitrogen. Furthermore, the oxazoline 15N NMR chemical shifts are affected by the trans ligand, with the resonances for the grouptrans to hydride typically downfield of those trans to η3-allyl and tosylamide. These group 9 oxazolinylborate compounds have been studied to develop approaches for allylic functionalization. However, this possibility is generally limited by the tendency of the allyl hydride compounds to undergo olefin reductive elimination. Reductive elimination products are formed upon addition of ligands such as CO and CNtBu. Also, ToMRhH(η3-C8H13) and acetic acid react to give ToMRhH(κ2-O2CMe) (8) and cyclooctene. In contrast, treatment of ToMRhH(η3-C3H5) with TsN3 (Ts = SO2C6H4Me) gives the complex ToMRh(η3-C3H5)NHTs (10). Interestingly, the reaction of ToMRhH(η3-C8H13) and TsN3 yields ToMRh(NHTs)(H)OH2 (11) and 1,3-cyclooctadieneviaβ-hydride elimination and Rh–H bond amination. Ligand-induced reductive elimination of ToMRh(η3-C3H5)NHTs provides HN(CH2CH[double bond, length as m-dash]CH2)Ts; these steps combine to give a propene C–H activation/functionalization sequence.

Graphical abstract: Allylic C–H bond activation and functionalization mediated by tris(oxazolinyl)borato rhodium(i) and iridium(i) compounds
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