Asymmetric olefin hydroamination/cyclization is a promising method for the synthesis of optically active cyclic amines.[1] To date, the most selective catalysts are C 2 -symmetric rare earth and zirconium complexes. [2,3] These C 2 -symmetric catalysts contrast with seminal C 1 -symmetric ansa-lanthanidocenes that epimerize under catalytic conditions.[4] Despite advances, current asymmetric hydroamination/cyclization catalysts are highly sensitive to substrate substitution patterns.Two distinct pathways have been proposed for C À N bond formation in zirconium-catalyzed processes:[1b] olefin insertion into a M À NR 2 bond (Scheme 1, Mechanism A)[5] and aabstraction followed by [2p + 2p] cycloaddition (Mechanism B). [3,6] These two pathways can be difficult to distinguish because of conflicting observations, including large deuterium isotope effects and first-or second-order rate laws.Our research group has recently described an achiral catalyst [{PhB(C 5 H 4 )(Ox Me 2 ) 2 }Zr(NMe 2 ) 2 ] (1; Ox Me 2 = 4,4-dimethyl-2-oxazolinyl) that cyclizes aminoalkene compounds at room temperature. [7] This unusually high activity motivated the preparation of optically active oxazolinylborate analogues that might provide highly reactive, robust, and non-epimerizable complexes. Herein, we report a chiral catalyst that provides pyrrolidine derivatives with excellent enantiopurity. Our data, including a unique deuterium isotope effect on enantioselectivity, unambiguously rules out both pathways of Scheme 1.Precatalyst preparation is outlined in Equations (1) and (2).[8] Deprotonation of the oxazoline substrate 2 H-Ox iPr,Me 2 by nBuLi and subsequent treatment with 0.5 equivalents of PhBCl 2 provided chiral borane 2.[9] A crude sample of 2 was then treated with NaC 5 H 5 in THF and gave 3-H 2 as a mixture of C 5 H 5 isomers; one isomer is shown in Equation (1) A catalytic amount of 4 (2-10 mol %) and primary aminoalkenes 5 a-9 a rapidly yielded pyrrolidines 5 b-9 b with enantiomeric excesses ranging from 89 % to 98 % (see Table 1). Although the reaction rate is sensitive to catalyst and substrate concentration, the enantioselectivity is not. The catalyst can be recycled once without loss of activity or enantioselectivity. The secondary aminoalkene 5 a-NMe was not cyclized by 4, even upon heating for 12 hours at 80, 120, 140, or 170 8C. However, upon addition of nPrNH 2 , 20% conversion into 5 b was observed at room temperature.Significantly, the ee values obtained with 4 as the catalyst are the highest to date for unprotected pyrrolidines 5 b, 6 b,

In order to facilitate oxidative addition chemistry of fac-coordinated rhodium(I) and iridium(I) compounds, carbene−bis(oxazolinyl)phenylborate proligands have been synthesized and reacted with organometallic precursors. Two proligands, PhB(Ox Me2 ) 2 (Im tBu H) (H[1]; Ox Me2 = 4,4-dimethyl-2-oxazoline; Im tBu H = 1-tertbutylimidazole) and PhB(Ox Me2 ) 2 (Im Mes H) (H[2]; Im Mes H = 1-mesitylimidazole), are deprotonated with potassium benzyl to generate K[1] and K[2], and these potassium compounds serve as reagents for the synthesis of a series of rhodium and iridium complexes. Cyclooctadiene and dicarbonyl compounds {PhB(Ox Me2 ) 2 Im tBu }Rh(Mes }Ir(CO) 2 (7) are synthesized along with To M M(η 4 -C 8 H 12 ) (M = Rh (8); M = Ir (9); To M = tris(4,4-dimethyl-2-oxazolinyl)phenylborate). The spectroscopic and structural properties and reactivity of this series of compounds show electronic and steric effects of substituents on the imidazole (tert-butyl vs mesityl), effects of replacing an oxazoline in To M with a carbene donor, and the influence of the donor ligand (CO vs C 8 H 12 ). The reactions of K[2] and [M(μ-Cl)(η 2 -C 8 H 14 ) 2 ] 2 (M = Rh, Ir) provide {κ 4 -PhB(Ox Me2 ) 2 Im Mes ′ CH 2 }Rh(μ-H)(μ-Cl)Rh(η 2 -C 8 H 14 ) 2 (10) and {PhB(Ox Me2 ) 2 Im Mes }IrH(η 3 -C 8 H 13 ) (11). In the former compound, a spontaneous oxidative addition of a mesityl ortho-methyl to give a mixed-valent dirhodium species is observed, while the iridium compound forms a monometallic allyl hydride. Photochemical reactions of dicarbonyl compounds 5 and 7 result in C−H bond oxidative addition providing the compounds {κ 4 -PhB(Ox Me2 ) 2 Im Mes ′ CH 2 }RhH(CO) (12) and {PhB(Ox Me2 ) 2 Im Mes }IrH(Ph)CO (13). In 12, oxidative addition results in cyclometalation of the mesityl ortho-methyl similar to 10, whereas the iridium compound reacts with the benzene solvent to give a rare crystallographically characterized cis-[Ir](H)(Ph) complex. Alternatively, the rhodium carbonyl 5 or iridium isocyanide {PhB(Ox Me2 ) 2 Im Mes }Ir(CO)CN t Bu (15) reacts with PhSiH 3 in the dark to form the silyl compound {PhB(Ox Me2 ) 2 Im Mes }RhH(SiH 2 Ph)CO (14) or {PhB(Ox Me2 ) 2 Im Mes }IrH(SiH 2 Ph)CN t Bu (17). These examples demonstrate the enhanced thermal reactivity of {PhB(Ox Me2 ) 2 Im Mes }-supported iridium and rhodium carbonyl compounds in comparison to tris(oxazolinyl)borate, tris(pyrazolyl)borate, and cyclopentadienyl-supported compounds. ■ INTRODUCTIONOxidative addition is an essential part of the rich chemistry of low-valent rhodium and iridium compounds, playing a central role in C−H bond activation chemistry 1 and a large range of catalytic chemistry including hydrogenation, 2 hydrosilylation, 3 hydroformylation, 4 and hydroacylation. 5 Decarbonylation of aldehydes also involves oxidative addition of formyl C−H bonds. 6 Recently, we described a rhodium(I)-catalyzed alcohol and aldehyde decarbonylation reaction that involves oxidative addition of formyl C−H bonds. 7 The To M Rh(CO) 2 or To M Rh(H) 2 CO (To M = tris(4,4-dimethyl-2-oxazolinyl...

An electrophilic, coordinatively unsaturated rhodium complex supported by borate-linked oxazoline, oxazoline-coordinated silylene, and N-heterocyclic carbene donors [{κ(3)-N,Si,C-PhB(Ox(Me2))(Ox(Me2)SiHPh)Im(Mes)}Rh(H)CO][HB(C6F5)3] (, Ox(Me2) = 4,4-dimethyl-2-oxazoline; Im(Mes) = 1-mesitylimidazole) is synthesized from the neutral rhodium silyl {PhB(Ox(Me2))2Im(Mes)}RhH(SiH2Ph)CO () and B(C6F5)3. The unusual oxazoline-coordinated silylene structure in is proposed to form by rearrangement of an unobserved isomeric cationic rhodium silylene species [{PhB(Ox(Me2))2Im(Mes)}RhH(SiHPh)CO][HB(C6F5)3] generated by H abstraction. Complex catalyzes reductions of organic carbonyl compounds with silanes to give hydrosilylation products or deoxygenation products. The pathway to these reactions is primarily influenced by the degree of substitution of the organosilane. Reactions with primary silanes give deoxygenation of esters to ethers, amides to amines, and ketones and aldehydes to hydrocarbons, whereas tertiary silanes react to give 1,2-hydrosilylation of the carbonyl functionality. In contrast, the strong Lewis acid B(C6F5)3 catalyzes the complete deoxygenation of carbonyl compounds to hydrocarbons with PhSiH3 as the reducing agent.