Aminoalkenes are catalytically cyclized in the presence of cyclopentadienylbis(oxazolinyl)borato group 4 complexes {PhB(C5H4)(OxR)2}M(NMe2)2 (M = Ti, Zr, Hf; OxR = 4,4-dimethyl-2-oxazoline, 4S-isopropyl-5,5-dimethyl-2-oxazoline, 4S-tert-butyl-2-oxazoline) at room temperature and below, affording five-, six-, and seven-membered N-heterocyclic amines with enantiomeric excesses of >90% in many cases and up to 99%. Mechanistic investigations of this highly selective system employed synthetic tests, kinetics, and stereochemistry. Secondary aminopentene cyclizations require a primary amine (1-2 equiv vs catalyst). Aminoalkenes are unchanged in the presence of a zirconium monoamido complex {PhB(C5H4)(Ox4S-iPr,Me2)2}Zr(NMe2)Cl or a cyclopentadienylmono(oxazolinyl)borato zirconium diamide {Ph2B(C5H4)(Ox4S-iPr,Me2)}Zr(NMe2)2. Plots of initial rate versus [substrate] show a rate dependence that evolves from first-order at low concentration to zero-order at high concentration, and this is consistent with a reversible substrate-catalyst interaction preceding an irreversible step. Primary kinetic isotope effects from substrate conversion measurements (k′obs(H)/k′obs(D) = 3.3 ± 0.3) and from initial rate analysis (k2(H)/k2(D) = 2.3 ± 0.4) indicate that a N-H bond is broken in the turnover-limiting and irreversible step of the catalytic cycle. Asymmetric hydroamination/cyclization of N-deutero-aminoalkenes provides products with higher optical purities than obtained with N-proteo-aminoalkenes. Transition state theory, applied to the rate constant k2 that characterizes the irreversible step, provides activation parameters consistent with a highly organized transition state (ΔS⧧ = −43(7) cal·mol-1 K-1) and a remarkably low enthalpic barrier (ΔH⧧ = 6.7(2) kcal·mol-1). A six-centered, concerted transition state for C-N and C-H bond formation and N-H bond cleavage involving two amidoalkene ligands is proposed as most consistent with the current data. ABSTRACT: Aminoalkenes are catalytically cyclized in the presence of cyclopentadienylbis(oxazolinyl)borato group 4 complexes {PhB(C 5 H 4 )(Ox R ) 2 }M(NMe 2 ) 2 (M = Ti, Zr, Hf; Ox R = 4,4-dimethyl-2-oxazoline, 4S-isopropyl-5,5-dimethyl-2-oxazoline, 4S-tert-butyl-2-oxazoline) at room temperature and below, affording five-, six-, and seven-membered N-heterocyclic amines with enantiomeric excesses of >90% in many cases and up to 99%. Mechanistic investigations of this highly selective system employed synthetic tests, kinetics, and stereochemistry. Secondary aminopentene cyclizations require a primary amine (1−2 equiv vs catalyst). Aminoalkenes are unchanged in the presence of a zirconium monoamido complex {PhB(C 5 H 4 )(Ox 4S-iPr,Me 2 ) 2 }Zr(NMe 2 )Cl or a cyclopentadienylmono(oxazolinyl)borato zirconium diamide {Ph 2 B(C 5 H 4 )-(Ox 4S-iPr,Me 2 )}Zr(NMe 2 ) 2 . Plots of initial rate versus [substrate] show a rate dependence that evolves from first-order at low concentration to zero-order at high concentration, and this is consistent with a reversible substrate−catalyst interac...

The homoleptic organocerium complex Ce{C(SiHMe ) } (1) reacts with B(C F ) to produce the zwitterionic bis(alkyl) hydridoborato Ce{C(SiHMe ) } HB(C F ) (2). NMR and IR spectroscopy and X-ray crystallography indicate that each alkyl ligand contains two bridging Ce↼H-Si interactions in both 1 and 2. Compound 2 serves as a precatalyst for the hydrosilylation of acrylates to give α-silyl esters at room temperature with a turnover number of 2200.

The 1,2-FCl rearrangement reaction of a series of haloethanes is investigated by comparisons of the optimized ground- and transition-state geometries. Investigation of the effect of level of theory and basis set shows that the trends in threshold energies for rearrangement are reproduced across all levels of theory and basis set, and hence that a moderate level of theory and basis set is adequate for investigating the important trends in this reaction. Threshold barriers increase when a large number of fluorine atoms are attached to the carbon atom bearing the interchanging fluorine, suggesting that the C–F bonds prove difficult to distort to the transition geometry; the increase is smaller for fluorine substitution on the carbon atom bearing the interchanging hydrogen atom. By considering sets of isomeric reactions, the barrier height is shown to closely follow the thermodynamic stability of the alkane undergoing rearrangement; however there is a secondary effect owing to the relative stability of the transition geometry. This relative stability can be related to the thermodynamic stability of a series of isomeric alkenes that resemble the transition geometry without the rearranging atoms. This series of molecules constitute an unusual set owing to the ability to consider these three contributions to the activation barrier separately.

We report the synthesis of a new mixed oxazoline-carbene scorpionate ligand, bis(4,4-dimethyl-2-oxazolinyl)(1-mesitylimidazolyl)phenylborate (PhB(Ox(Me2))2Im(Mes)). Reactions of the protonated form PhB(Ox(Me2))2(Im(Mes)H) with dialkylzinc compounds provide four-coordinate zinc alkyl complexes, and X-ray diffraction studies of the {PhB(Ox(Me2))2Im(Mes)}ZnR (R = Me, Et) compounds show significant structural distortions involving the R groups shifting away from the carbene donor. The reaction of {PhB(Ox(Me2))2Im(Mes)}ZnEt (3) and O2 provides an isolable mononuclear zinc alkylperoxide {PhB(Ox(Me2))2Im(Mes)}ZnOOEt (4), which has been characterized by single crystal X-ray diffraction and (17)O NMR spectroscopy.