Reversible O-H Bond Activation by Tripodal tris(Nitroxide) Aluminum and Gallium Complexes.

Herein, we report the preparation and characterization of the Group 13 metal complexes of a tripodal tris(nitroxide)-based ligand, designated (TriNOx3-)M (M = Al (1), Ga (2), In (3)). Complexes 1 and 2 both activate the O-H bond of a range of alcohols spanning a ∼10 pKa unit range via an element-ligand cooperative pathway to afford the zwitterionic complexes (HTriNOx2-)M-OR. Structures of these alcohol adduct products are discussed. We demonstrate that the thermodynamic and kinetic aspects of the reactions are both influenced by the identity of the metal, with 1 having higher reaction equilibrium constants and proceeding at a faster rate relative to 2 for any given alcohol. These parameters are also influenced by the pKa of the alcohol, with more acidic alcohols reacting both to more completion and faster than their less acidic counterparts. Possible mechanistic pathways for the O-H activation are discussed.

Development of cross-service training and job performance criterion measures for the U.S. Military.

As part of an effort to provide standardized criterion measures across the Armed Services, the current research effort developed a set of service-wide criterion measures for first-term enlisted personnel using a recently developed model of cross-service job performance. Two concurrent work streams developed criterion measures which provide complete construct coverage of the cross-service performance model. Using existing service-specific instruments, methods for development of the Cross-Service Situational judgment Test (CSSJT), the Cross-Service Job Performance Ratings Scales (CSPRS), and two cross-service self-report measures (end of training and in unit surveys) are described and discussed.

Mars Oxygen ISRU Experiment (MOXIE)-Preparing for human Mars exploration.

MOXIE [Mars Oxygen In Situ Resource Utilization (ISRU) Experiment] is the first demonstration of ISRU on another planet, producing oxygen by solid oxide electrolysis of carbon dioxide in the martian atmosphere. A scaled-up MOXIE would contribute to sustainable human exploration of Mars by producing on-site the tens of tons of oxygen required for a rocket to transport astronauts off the surface of Mars, instead of having to launch hundreds of tons of material from Earth's surface to transport the required oxygen to Mars. MOXIE has produced oxygen seven times between landing in February 2021 and the end of 2021 and will continue to demonstrate oxygen production during night and day throughout all martian seasons. This paper reviews what MOXIE has accomplished and the implications for larger-scale oxygen-producing systems.

Synthesis and Characterization of Neutral Ligand α-Diimine Complexes of Aluminum with Tunable Redox Energetics.

The synthesis and full characterization of a series of neutral ligand α-diimine complexes of aluminum are reported. The compounds [Al(LAr)2Cl2)][AlCl4] [LAr = N, N'-bis(4-R-C6H4)-2,3-dimethyl-1,4-diazabutadiene] are structurally analogous, as determined by multinuclear NMR spectroscopy and solid-state X-ray diffraction, across a range of electron-donating [R = Me (2), tBu (3), OMe (4), and NMe2 (5)] and electron-withdrawing [R = Cl (6), CF3 (7), and NO2 (8)] substituents in the aryl side arm of the ligand. UV-vis absorption spectroscopy and electrochemistry were used to access the optical and electrochemical properties, respectively, of the complexes. Both sets of properties are shown to be dependent on the R substituent. Density functional theory calculations performed on the [Al(LPh)2Cl2)][AlCl4] complex (1) indicate primarily ligand-based frontier orbitals and were used to help support our discussion of both the spectral and electrochemical data. We also report the reaction of the LPh ligand with both AlBr3 and AlI3 and demonstrate a different reactivity profile for the heavier halide relative to the lighter members of the group.

Synthesis and Characterization of Aluminum Complexes of Redox-Active Pyridyl Nitroxide Ligands.

The aluminum complexes ((R)pyNO(-))2AlCl ((R)pyNO(-) = N-tert-butyl-N-(2-pyridyl)nitroxyl; R = H (1), CH3 (2), CF3 (3)) were prepared in 80-98% yield through the protonolysis reaction between the pyridyl hydroxylamine ligand precursors (R)pyNOH and dimethylaluminum chloride. Complex 1 was also prepared using a salt metathesis route in 92% yield. Complexes 1-3 were characterized using (1)H and (13)C NMR spectroscopies. Single-crystal X-ray diffraction analysis of the complexes revealed that 1-3 are isostructural, with the Al(III) cation in all cases being five coordinate with distorted square pyramidal geometries. The geometry of complex 1 was studied using DFT, which showed primarily ligand-based frontier molecular orbitals. Reaction of 1 with NaOt-Bu gave (pyNO(-))2AlOt-Bu (4), while reaction of 1 with AgBPh4 gave [(pyNO(-))2Al(THF)2][BPh4] (5) in 54% and 87% yields, respectively. Compounds 4 and 5 were both characterized using (1)H and (13)C NMR spectroscopies and compound 5 by X-ray diffraction. Complexes 1-5 were also characterized by UV-vis electronic absorption spectroscopy and electrochemistry. The cyclic voltammograms of the complexes show two separate oxidation process, the potentials of which are dependent on both the substitution pattern of the (R)pyNO(-) ligands and the anion that completes the aluminum coordination sphere. A correlation was determined between the chemical shift of the t-Bu of the (R)pyNO(-) ligand in the (1)H NMR spectroscopy and the potentials of the redox events for complexes 1-4.

Synthesis and Characterization of α-Diimine Complexes of Group 13 Metals and Their Catalytic Activity toward the Epoxidation of Alkenes.

Complexes of group 13 metal (Al, Ga, In) ions with neutral α-diimine ligands have been prepared and characterized. The Al(III) and Ga(III) [M(α-diimine)2Cl2][MCl4] complexes catalyze the epoxidation of alkenes by peracetic acid under ambient conditions. The two complexes display nearly identical reactivity, demonstrating that inexpensive and highly abundant aluminum is a viable catalytic metal for these reactions.

Synthesis and characterization of aluminum-α-diimine complexes over multiple redox states.

The aluminum complexes (LMes(2-))AlCl(THF) (3) and (LDipp(-))AlCl2 (4) (LMes = N,N'-bis[2,4,6-trimethylphenyl]-2,3-dimethyl-1,4-diazabutadiene, LDipp = N,N'-bis[2,6-diisopropylphenyl]-2,3-dimethyl-1,4-diazabutadiene) were prepared by direct reduction of the ligands with sodium metal followed by salt metathesis with AlCl3. The (LMes(-))AlCl2 (5) complex was prepared through one-electron oxidative functionalization of 3 with either AgCl or CuCl. Complex 3 was characterized using (1)H and (13)C NMR spectoscopies. Single-crystal X-ray diffraction analysis of the complexes revealed that 3-5 are all four-coordinate, with 3 exhibiting a trigonal pyramidal geometry, while 4 and 5 exist between trigonal pyramidal and tetrahedral. Notable in the LMes complexes 3 and 5 is a systematic lengthening of the C-Nimido bonds and shortening of the C-C bond in the N-C-C-N backbone with increased electron density on the ligand. The geometries of the complexes 3 and 5 were optimized using DFT, which showed primarily ligand-based frontier orbitals, supporting the analysis of the solid-state structural data. The complexes 3-5 were also characterized by electrochemistry. The cyclic voltamogram of complex 3 showed an oxidation processes at -0.94 and -0.03 V versus ferrocene, while complexes 4 and 5 exhibit both reduction (-1.37 and -1.34 V, respectively) and oxidation (-0.62 and -0.73 V, respectively) features.

Organometallic uranium(IV) fluoride complexes: preparation using protonolysis chemistry and reactivity with trimethylsilyl reagents.

Reaction of the uranium alkyl complex (C(5)Me(5))(2)UMe(2) (1) with Et(3)N.3HF in toluene in the presence of a donor ligand (pyridine or trimethylphosphine oxide) results in gas evolution and the formation of the uranium(IV) difluoride complexes (C(5)Me(5))(2)UF(2)(L) (L = NC(5)H(5) (2), Me(3)P=O (3)). Similarly, reaction of (C(5)Me(5))(2)U[kappa(2)-(C,N)-CH(2)Si(CH(3))(2)N(SiMe(3))] (5) with Et(3)N.3HF in toluene gives the uranium(IV) amide-fluoride complex (C(5)Me(5))(2)U[N(SiMe(3))(2)](F) (6). The fluoride complex (C(5)Me(5))(2)UF(2)(NC(5)H(5)) (2) shows versatile reaction chemistry with a variety of trimethylsilyl reagents and demonstrates that the U-F bond provides an attractive synthetic strategy for accessing new functional groups that are not available from alkoxide or chloride complexes.

Comparative study of f-element electronic structure across a series of multimetallic actinide and lanthanoid-actinide complexes possessing redox-active bridging ligands.

A comparative examination of the electronic interactions across a series of trimetallic actinide and mixed lanthanide-actinide and lanthanum-actinide complexes is presented. Using reduced, radical terpyridyl ligands as conduits in a bridging framework to promote intramolecular metal-metal communication, studies containing structural, electrochemical, and X-ray absorption spectroscopy are reported for (C(5)Me(5))(2)An[-N horizontal lineC(Bn)(tpy-M{C(5)Me(4)R}(2))](2) (where An = Th(IV), U(IV); Bn = CH(2)C(6)H(5); M = La(III), Sm(III), Yb(III), U(III); R = H, Me, Et) to reveal effects dependent on the identities of the metal ions and R-groups. The electrochemical results show differences in redox energetics at the peripheral "M" site between complexes and significant wave splitting of the metal- and ligand-based processes indicating substantial electronic interactions between multiple redox sites across the actinide-containing bridge. Most striking is the appearance of strong electronic coupling for the trimetallic Yb(III)-U(IV)-Yb(III), Sm(III)-U(IV)-Sm(III), and La(III)-U(IV)-La(III) complexes, [8](-), [9b](-), and [10b](-), respectively, whose calculated comproportionation constant K(c) is slightly larger than that reported for the benchmark Creutz-Taube ion. X-ray absorption studies for monometallic metallocene complexes of U(III), U(IV), and U(V) reveal small but detectable energy differences in the "white-line" feature of the uranium L(III)-edges consistent with these variations in nominal oxidation state. The sum of these data provides evidence of 5f/6d-orbital participation in bonding and electronic delocalization in these multimetallic f-element complexes. An improved, high-yielding synthesis of 4'-cyano-2,2':6',2''-terpyridine is also reported.

Pentavalent uranium chemistry: synthetic pursuit of a rare oxidation state.

This feature article presents a comprehensive overview of pentavalent uranium systems in non-aqueous solution with a focus on the various synthetic avenues employed to access this unusual and very important oxidation state. Selected characterization data and theoretical aspects are also included. The purpose is to provide a perspective on this rapidly evolving field and identify new possibilities for future developments in pentavalent uranium chemistry.

Selenate and tellurate complexes of pentavalent uranium.

Oxidation of (C(5)Me(5))(2)U([double bond, length as m-dash]N-2,6-(i)Pr(2)-C(6)H(3))(THF) with PhE-EPh yields the corresponding U(V)-chalcogenate complexes (C(5)Me(5))(2)U([double bond, length as m-dash]N-2,6-(i)Pr(2)-C(6)H(3))(EPh) (E = S, Se, Te) in excellent (>90%) isolated yields.

Challenging the metallocene dominance in actinide chemistry with a soft PNP pincer ligand: new uranium structures and reactivity patterns.

A soft embrace for U: Replacement of C(5)Me(5) by the soft PNP pincer ligand is a successful strategy to promote new reactivities and support new structures for the actinide series (see picture, py-O = pyridine-N-oxide). The specific electronic and steric properties of the PNP ligand enable access to previously unreported structures not available for the C(5)Me(5) ligand set and support not only low-valent uranium but also the high-valent uranium(VI) ion.

Probing the chemistry, electronic structure and redox energetics in organometallic pentavalent uranium complexes.

A series of organometallic pentavalent uranium complexes of the general formula (C(5)Me(5))(2)U(=N-2,6-(i)Pr(2)-C(6)H(3))(Y) (Y = monoanionic, non-halide ligand) have been prepared using a variety of routes. Utilizing the direct oxidation of (C(5)Me(5))(2)U(=N-2,6-(i)Pr(2)-C(6)H(3))(THF) (2) with the appropriate copper(I) salt yielded the triflate (Y = OTf (OSO(2)CF(3)), 11), thiolate (Y = SPh, 12), and acetylide (Y = C[triple bond]CPh, 13) complexes, while a salt metathesis route between the U(V)-imido (C(5)Me(5))(2)U(=N-2,6-(i)Pr(2)-C(6)H(3))(I) (10) and various alkali salts gave the diphenylamide (Y = NPh(2), 14), aryloxide (Y = OPh, 15), alkyl (Y = Me, 16), and aryl (Y = Ph, 17) complexes. Paired with 13, the isolation of 16 and 17 shows that U(V) can support the full range of carbon anions (sp, sp(2), and sp(3)), and these are, to the best of our knowledge, the first examples of pentavalent uranium complexes with anionic carbon moieties other than carbocyclic (C(5)R(5), C(7)H(7), C(8)H(8)) ligands. Finally, both protonolysis and insertion pathways afforded the U(V)-imido ketimide complex (C(5)Me(5))(2)U(=N-2,6-(i)Pr(2)-C(6)H(3))(N=CPh(2)) (18). The complexes have been isolated in good yield and characterized using various combinations of (1)H NMR spectroscopy, elemental analysis, mass spectrometry, single crystal X-ray diffraction, cyclic voltammetry, UV-visible-NIR absorption spectroscopy, and magnetic susceptibility measurements. All (C(5)Me(5))(2)U(=N-Ar)(X) (X = F, Cl, Br, I) and (C(5)Me(5))(2)U(=N-Ar)(Y) complexes exhibit U(VI)/U(V) and U(V)/U(IV) redox couples by voltammetry. The potential separation between these couples remains essentially constant at approximately 1.50 V, but both processes shift in tandem in potential by approximately 700 mV across the series of X/Y ligands. No significant differences between mu(eff) values or temperature dependencies in the magnetic susceptibility were observed for these complexes regardless of the identity of the ancillary X/Y ligand. However, an excellent linear correlation was observed between the chemical shift values of C(5)Me(5) ligand protons in the (1)H NMR spectra and the oxidation potentials of (C(5)Me(5))(2)U(=N-2,6-(i)Pr(2)-C(6)H(3))(X/Y), suggesting that there is a common origin, overall sigma-/pi-donation from the ancillary X/Y ligand to the metal, contributing to both observables. Combined, these data confer the following trend in increasing sigma/pi-donating ability of the X/Y ligand to the U(V) metal center: OTf < I < Br < Cl < SPh < C[triple bond]CPh < F < [OPh approximately Me approximately Ph] << NPh(2) < N=CPh(2). These (C(5)Me(5))(2)U(=N-2,6-(i)Pr(2)-C(6)H(3))(X/Y) complexes also show distinct hallmarks of a covalent bonding interaction between the metal and the imide ligand that is modulated to varying degrees by the interaction between the X/Y ancillary ligand and the U(V) metal center. These signatures of covalency include stabilization of multiple metal oxidations states [U(VI), U(V), and U(IV)] and enhanced intensities in the intraconfiguration (f-f) transitions. Of particular note in this regard is the more than 20-fold enhancement in the f-f intensities observed for Y = C[triple bond]CPh and N=CPh(2), which is a clear reflection of the covalent metal-ligand bonding interactions sustained by the acetylide and ketimide ligands in these pentavalent systems.

Evidence for the involvement of 5f orbitals in the bonding and reactivity of organometallic actinide compounds: thorium(IV) and uranium(IV) bis(hydrazonato) complexes.

Migratory insertion of diphenyldiazomethane into both metal-carbon bonds of the bis(alkyl) and bis(aryl) complexes (C(5)Me(5))(2)AnR(2) yields the first f-element bis(hydrazonato) complexes (C(5)Me(5))(2)An[eta(2)-(N,N')-R-N-N=CPh(2)](2) [An = Th, R = CH(3) (18), PhCH(2) (15), Ph (16); An = U, R = CH(3) (17), PhCH(2) (14)], which have been characterized by a combination of spectroscopy, electrochemistry, and X-ray crystallography. The two hydrazonato ligands adopt an eta(2)-coordination mode leading to 20-electron (for Th) and 22-electron (for U) complexes that have no transition-metal analogues. In fact, reaction of (C(5)H(5))(2)Zr(CH(3))(2) or (C(5)Me(5))(2)Hf(CH(3))(2) with diphenyldiazomethane is limited to the formation of the corresponding mono(hydrazonato) complex (C(5)R(5))(2)M[eta(2)-(N,N')-CH(3)-N-N=CPh(2)](CH(3)) (M = Zr, R = H or M = Hf, R = CH(3)). The difference in the reactivities of the group 4 metal complexes and the actinides was used as a unique platform for investigating in depth the role of 5f orbitals on the reactivity and bonding in actinide organometallic complexes. The electronic structure of the (C(5)H(5))(2)M[eta(2)-(N,N')-CH(3)-N-N=CH(2)](2) (M = Zr, Th, U) model complexes was studied using density functional theory (DFT) calculations and compared to experimental structural, electrochemical, and spectroscopic results. Whereas transition-metal bis(cyclopentadienyl) complexes are known to stabilize three ligands in the metallocene girdle to form saturated (C(5)H(5))(2)ML(3) species, in a bis(hydrazonato) system, a fourth ligand is coordinated to the metal center to give (C(5)H(5))(2)ML(4). DFT calculations have shown that 5f orbitals in the actinide complexes play a crucial role in stabilizing this fourth ligand by stabilizing both the sigma and pi electrons of the two eta(2)-coordinated hydrazonato ligands. In contrast, the stabilization of the hydrazonato ligands was found to be significantly less effective for the putative bis(hydrazonato) zirconium(IV) complex, yielding a higher energy structure. However, the difference in the reactivities of the group 4 metal and actinide complexes does not arise on thermodynamic grounds but is primarily of kinetic origin. Unfavorable steric factors have been ruled out as the sole influence to explain these different behaviors, and electronic factors were shown to govern the reactivity. For the actinides, both the C(5)H(5) and more realistic C(5)Me(5) ligands have been taken into account in computing the energy surface. The reaction profile for the C(5)Me(5) system differs from that with the C(5)H(5) ligand by a uniform shift of approximately 5 kcal/mol in the relative energies of the transition state and products. The insertion of a second diazoalkane molecule into the sole metal-carbon bond in the mono(hydrazonato) complexes involves a high energy barrier (approximately 20 kcal/mol) for the zirconium(IV) system, whereas the actinides can facilitate the approach of the diazoalkane by coordination (formation of an adduct) and its insertion into the An-C bond with a very low barrier on the potential energy surface.

1,4-dicyanobenzene as a scaffold for the preparation of bimetallic actinide complexes exhibiting metal-metal communication.

Reaction of two equivalents of [(C5Me4Et)2U(CH3)(Cl)] (6) or [(C5Me5)2Th(CH3)(Br)] (7) with 1,4-dicyanobenzene leads to the formation of the novel 1,4-phenylenediketimide-bridged bimetallic organoactinide complexes [((C5Me4Et)2(Cl)U)(2)(mu-(N=C(CH3)-C6H4-(CH3)C=N))] (8) and [((C5Me5)2(Br)Th)2(mu-(N=C(CH3)-C6H4- (CH3)C==N))] (9), respectively. These complexes were structurally characterized by single-crystal X-ray diffraction and NMR spectroscopy. Metal-metal interactions in these isovalent bimetallic systems were assessed by means of cyclic voltammetry, UV-visible/NIR absorption spectroscopy, and variable-temperature magnetic susceptibility. Although evidence for magnetic coupling between metal centers in the bimetallic U IV/U IV (5f2-5f2) complex is ambiguous, the complex displays appreciable electronic communication between the metal centers through the pi system of the dianionic diketimide bridging ligand, as judged by voltammetry. The transition intensities of the f-f bands for the bimetallic U IV/U IV system decrease substantially compared to the related monometallic ketimide chloride complex, [(C5Me5)2U(Cl)(-N=C(CH3)-(3,4,5-F(3)-C6H2))] (11). Also reported herein are new synthetic routes to the actinide starting materials [(C5Me4Et)(2)U(CH3)(Cl)] (6) and [(C5Me5)2Th(CH3)(Br)] (7) in addition to the syntheses and structures of the monometallic uranium complexes [(C5Me4Et)2UCl2] (3), [(C5Me4Et)2U(CH3)2] (4), [(C5Me4Et)2U(-N==C(CH3)-C6H4-C==N)2] (10), and 11.

Organometallic uranium(V)-imido halide complexes: from synthesis to electronic structure and bonding.

Reaction of (C5Me5)2U(=N-2,4,6-(t)Bu3-C6H2) or (C5Me5)2U(=N-2,6-(i)Pr2-C6H3)(THF) with 5 equiv of CuX(n) (n = 1, X = Cl, Br, I; n = 2, X = F) affords the corresponding uranium(V)-imido halide complexes, (C5Me5)2U(=N-Ar)(X) (where Ar = 2,4,6-(t)Bu3-C6H2 and X = F (3), Cl (4), Br (5), I (6); Ar = 2,6-(i)Pr2-C6H3 and X = F (7), Cl (8), Br (9), I (10)), in good isolated yields of 75-89%. These compounds have been characterized by a combination of single-crystal X-ray diffraction, (1)H NMR spectroscopy, elemental analysis, mass spectrometry, cyclic voltammetry, UV-visible-NIR absorption spectroscopy, and variable-temperature magnetic susceptibility. The uranium L(III)-edge X-ray absorption spectrum of (C5Me5)2U(=N-2,4,6-(t)Bu3-C6H2)(Cl) (4) was analyzed to obtain structural information, and the U=N imido (1.97(1) A), U-Cl (2.60(2) A), and U-C5Me5 (2.84(1) A) distances were consistent with those observed for compounds 3, 5, 6, 8-10, which were all characterized by single-crystal X-ray diffraction studies. All (C5Me5)2U(=N-Ar)(X) complexes exhibit U(V)/U(IV) and U(VI)/U(V) redox couples by voltammetry, with the potential separation between these metal-based couples remaining essentially constant at approximately 1.50 V. The electronic spectra are comprised of pi-->pi* and pi-->nb(5f) transitions involving electrons in the metal-imido bond, and metal-centered f-f bands illustrative of spin-orbit and crystal-field influences on the 5f(1) valence electron configuration. Two distinct sets of bands are attributed to transitions derived from this 5f(1) configuration, and the intensities in these bands increase dramatically over those found in spectra of classical 5f(1) actinide coordination complexes. Temperature-dependent magnetic susceptibilities are reported for all complexes with mu(eff) values ranging from 2.22 to 2.53 mu(B). The onset of quenching of orbital angular momentum by ligand fields is observed to occur at approximately 40 K in all cases. Density functional theory results for the model complexes (C5Me5)2U(=N-C6H5)(F) (11) and (C5Me5)2U(=N-C6H5)(I) (12) show good agreement with experimental structural and electrochemical data and provide a basis for assignment of spectroscopic bands. The bonding analysis describes multiple bonding between the uranium metal center and imido nitrogen which is comprised of one sigma and two pi interactions with variable participation of 5f and 6d orbitals from the uranium center.

A mechanistic investigation of the asymmetric Meerwein-Schmidt-Ponndorf-Verley reduction catalyzed by BINOL/AlMe(3)-structure, kinetics, and enantioselectivity.

The kinetics of the Al-catalyzed asymmetric Meerwein-Schmidt-Ponndorf-Verley (MSPV) reduction are presented. Structural identification of the catalytic precursor formed in situ between (S)-2,2'-dihydroxy-1,1'-binapthyl ((S)-BINOL), AlMe3, and 2-propanol was established through 1H and 27Al NMR spectroscopies, and APCIMS. All experimental evidence points toward the formation of a BINOL-chelated, pentacoordinate aluminum species in solution. Ligand-accelerated catalysis was confirmed for the phenolate/AlMe3/2-propanol system. The rate law for the catalytic reaction was determined to be nearly unimolecular dependent on aluminum, zero-order dependent on substrate, and inversely dependent on 2-propanol. At the low catalyst loading employed in the BINOL/AlMe3 system, the inherent reversibility of the MSPV reaction does not affect product yield or enantiomeric excess over time. Systematic ligand studies imply that while a tetrahedral geometry around the aluminum center may result in the most active MSPV reduction catalysts, the enantioselectivity of the reaction is enhanced when the aluminum center allows for a 2-point coordination of the substrate to achieve a pentacoordinate geometry with the fifth ligand weakly coordinated to the axial site of a pseudo square pyramid.

Efficient and selective Al-catalyzed alcohol oxidation via Oppenauer chemistry.

A highly active and selective Al-based catalytic Oppenauer (O) oxidation is reported. Quantitative and selective oxidations of a variety of benzylic, propargylic, allylic, and aliphatic primary and secondary alcohols were achieved using nitrobenzaldehyde derivatives as the oxidant and simple aluminum compounds as precatalysts.

Enantioselective MSPV reduction of ketimines using 2-propanol and (BINOL)Al(III).

[reaction: see text] A highly enantioselective Meerwein-Schmidt-Ponndorf-Verley (MSPV) reduction of N-phosphinoyl ketimines by (BINOL)Al(III)/2-propanol is reported. Yields ranging between 79 and 85% with high enantiomeric excesses (93-98%) are observed for a wide range of structurally diverse ketimines. A [2.0.4] bicyclic chelation model is proposed to account for this high selectivity.