No abstract

Chiral 3,3'-bis(trisarylsilyl)-substituted binaphtholate rare earth metal complexes (R)-[Ln{Binol-SiAr3}(o-C6H4CH2NMe2)(Me2NCH2Ph)] (Ln = Sc, Lu, Y; Binol-SiAr3 = 3,3'-bis(trisarylsilyl)-2,2'-dihydroxy-1,1'-binaphthyl; Ar = Ph (2-Ln), 3,5-xylyl (3-Ln)) and (R)-[La{Binol-Si(3,5-xylyl)3}{E(SiMe3)2}(THF)2] (E = CH (4a), N (4b)) are accessible via facile arene, alkane, and amine elimination. They are efficient catalysts for the asymmetric hydroamination/cyclization of aminoalkenes, giving TOF of up to 840 h(-1) at 25 degrees C for 2,2-diphenyl-pent-4-enylamine (5c) using (R)-2-Y. Enantioselectivities of up to 95% ee were achieved in the cyclization of 5c with (R)-2-Sc. The reactions show apparently zero-order rate dependence on substrate concentration and first-order rate dependence on catalyst concentration, but rates depend on total amine concentrations. Activation parameters for the cyclization of pent-4-enylamine using (R)-2-Y (deltaH(S)(double dagger) = 57.4(0.8) kJ mol(-1) and deltaS(S)(double dagger) = -102(3) J K(-1) mol(-1); deltaH(R)(double dagger) = 61.5(0.7) kJ mol(-1) and deltaS(R)(double dagger) = -103(3) J K(-1) mol(-1)) indicate a highly organized transition state. The binaphtholate catalysts were also applied to the kinetic resolution of chiral alpha-substituted aminoalkenes with resolution factors f of up to 19. The 2,5-disubstituted aminopentenes were formed in 7:1 to > or = 50:1 trans diastereoselectivity, depending on the size of the alpha-substituent of the aminoalkene. Rate studies with (S)-1-phenyl-pent-4-enylamine ((S)-15e) gave the activation parameters for the matching (deltaH(double dagger) = 52.2(2.8) kJ mol(-1), deltaS(double dagger) = -127(8) J K(-1) mol(-1) using (S)-2-Y) and mismatching (deltaH(double dagger) = 57.7(1.3) kJ mol(-1), deltaS(double dagger) = -126(4) J K(-1) mol(-1) using (R)-2-Y) substrate/catalyst combination. The absolute configuration of the Mosher amide of (2S)-2-methyl-4,4-diphenyl-pyrrolidine and (2R)-methyl-(5S)-phenyl-pyrrolidinium chloride, prepared from (S)-15e, were determined by crystallographic analysis. Catalyst (R)-4a showed activity in the anti-Markovnikov addition of n-propylamine to styrene.

3 )(THF) can be prepared in high yields by a σ-bond metathesis reaction between Y(CH 2 SiMe 3 ) 3 (THF) 2 and amino-functionalized cyclopentadienes or indene. The structure of Y(η 5 :η 1 -C 5 Me 4 SiMe 2 NCMe 2 Et)(CH 2 SiMe 3 )(THF) was shown by single-crystal X-ray diffraction to be that of a three-legged piano stool. Reaction of Y(CH 2 -SiMe 3 ) 3 (THF) 2 with the tridentate linked amido-cyclopentadienyl ligands (C 5 Me 4 H)SiMe 2 -NHR (R ) CH 2 CH 2 OMe, CH 2 CH 2 NMe 2 , CH 2 CH 2 CH 2 OMe, CMe 2 CH 2 OMe), which contain an additional donor site, results in the cleavage of the silicon-cyclopentadienyl bond and the formation of the tetramethylcyclopentadienyl complexes Y(η 5 -C 5 Me 4 H){N(SiMe 2 CH 2are prepared in good yields by hydrogenolysis of the corresponding alkyl complexes. Variable-temperature 1 H, 13 C, 29 Si, and 89 Y NMR spectroscopic data show that the hydrido complexes retain their dimeric structure in solution on the NMR time scale but that they undergo fluxional processes which include THF dissociation and cis-trans isomerization. The presence of monomeric species is inferred from 1 H NMR spectroscopic detection of the crossover product [Y(η 5 :η 1 -C 5 Me 4 SiMe 2 NCMe 3 )(THF)(µ-H) 2 Y(η 5 :η 1 -C 5 Me 4 -SiMe 2 NCMe 2 Et)(THF)], which forms within minutes at 50 °C when [Y(η 5 :η 1 -C 5 Me 4 SiMe 2 -NCMe 2 R)(THF)(µ-H)] 2 with R ) Me and Et are mixed in C 6 D 6 . Ethylene is polymerized with moderate activity by the hydrido complexes, whereas styrene derivatives and 1-hexene are cleanly converted into the monoinsertion products. 1,5-Hexadiene reacts with the hydrido complexes to give the monomeric cyclopentylmethyl complex Y(η 5 :η 1 -C 5 Me 4 SiMe 2 NCMe 3 ){CH 2 -CH(CH 2 ) 4 }(THF). The 1-phenylethyl complexes Y(η 5 :η 1 -C 5 Me 4 SiMe 2 NCMe 3 ){CH(CH 3 )(C 6 H 3 -2-R-4-R′)}(THF) (R ) R′ ) H; R ) H, R′ ) OMe; R ) R′ ) Me), selectively formed by secondary insertion of the corresponding styrene derivatives, show fluxional η 3 -coordination in solution. A monomeric structure with a weak η 3 -interaction was confirmed by single-crystal X-ray diffraction of Y(η 5 :η 1 -C 5 Me 4 SiMe 2 NCMe 2 Et){CH(CH 3 )(C 6 H 4 -4-tBu)}(THF). The insertion product of 1-hexene is dimeric in solution, but partially loses THF under vacuum. This product initiates the polymerization of styrene to give atactic polystyrenes with narrow molecular weight distributions (M w /M n 1.10-1.23) and microstructures enriched in syndiotacticity (rr ≈ 70%).

The silicon-bridged [1]ferrocenophanes Fe(η-C5H4)2SiRR‘ [3 (R = Me, R‘ = Cl), 4 (R = R‘ = Cl)] with chlorine substituent(s) at silicon were prepared via the reaction of Fe(η-C5H4Li)2·TMEDA (TMEDA = tetramethylethylenediamine) with the chlorinated silanes MeSiCl3 and SiCl4, respectively. An X-ray diffraction study of 4 indicated that the cyclopentadienyl rings in this species are tilted by an angle of 19.2(4)°, typical of other structurally characterized silicon-bridged [1]ferrocenophanes. Thermal ring-opening polymerization (ROP) of 3 and 4 at 250 °C yielded the first high molecular weight poly(ferrocenylsilanes) with halogen substituents at silicon, [Fe(η-C5H4)2SiRR‘] n [7 (R = Me, R‘ = Cl), 8 (R = R‘ = Cl)]. Transition-metal-catalyzed polymerization of 3 and 4 with Pd and Pt catalysts also yielded polymers 7 and 8 in solution at room temperature. Polymer 7 was soluble in polar organic solvents and was characterized by 1H, 29Si, and 13C NMR and elemental analysis. In contrast, poly(ferrocenylsilane) 8 was found to be insoluble in organic solvents and this material was characterized by elemental analysis and derivatization. Substitution of the chlorine side groups in polymer 7 was achieved under mild conditions via reaction with the organolithium reagents MeLi, PhLi, and LiC⋮C(CH2)4H to afford the known polymers [Fe(η-C5H4)2SiMe2] n (2a) and [Fe(η-C5H4)2SiMePh] n (2d) and the new polymer [Fe(η-C5H4)2SiMeC⋮C(CH2)4H] n (9), respectively. The molecular weights for the completely halogen-substituted poly(ferrocenylsilanes) 2a, 2d, and 9 were estimated by gel permeation chromatography in THF to be in the range of M w = 7.4 × 104 to 1.7 × 105 and M n = 3.6 × 104 to 1.1 × 105 versus polystyrene standards. Substitution of the chlorine atoms in 8 was also demonstrated by reaction of the polymer with MeLi to give 2a.

Direct preparation of alkyl half‐sandwich complexes of the heavier rare earth elements (such as 1) is possible by alkane elimination from the corresponding cyclopentadiene derivative and the trialkyl complex [Y(CH2SiMe3)3(thf)2]. Hydrogenation of 1 gives the highly fluxional dimeric hydride complex 2. Both complexes catalyze the polymerization of the polar monomers tert‐butyl acrylate and acrylonitrile.

Monomeric diolate amido yttrium complexes [Y[diolate][N(SiHMe(2))(2)](thf)(2)] can be prepared in good yield by treating [Y[N(SiHMe(2))(2)](3)(thf)(2)] with either 3,3'-di-tert-butyl-5,5',6,6'-tetramethyl-1,1'-biphenyl-2,2'-diol (H(2)(Biphen)), 3,3'-bis(2,4,6-triisopropylphenyl)-2,2'-dihydroxy-1,1'-dinaphthyl (H(2)(Trip(2)BINO)) or 3,3'-bis(2,6-diisopropylphenyl)-2,2'-dihydroxy-1,1'-dinaphthyl (H(2)(Dip(2)BINO)) in racemic and enantiopure form. The racemic complex [Y(biphen)[N(SiHMe(2))(2)](thf)(2)] dimerizes upon heating to give the heterochiral complex (R,S)-[Y(biphen)[N(SiHMe(2))(2)](thf)](2). The corresponding dimeric heterochiral lanthanum complex was the sole product in the reaction of H(2)(Biphen) with [La[N(SiHMe(2))(2)](3)(thf)(2)]. Single-crystal X-ray diffraction of both dimeric complexes revealed that the two Ln(biphen)[N(SiHMe(2))(2)](thf) fragments are connected through bridging phenolate groups of the biphenolate ligands. The two different phenolate groups undergo an intramolecular exchange process in solution leading to their equivalence on the NMR timescale. All complexes were active catalysts for the hydroamination/cyclization of aminoalkynes and aminoalkenes at elevated temperature, with [Y((R)-dip(2)bino)[N(SiHMe(2))(2)](thf)(2)] being the most active one giving enantioselectivities of up to 57 % ee. Kinetic resolution of 2-aminohex-5-ene proceeded with this catalyst with 6.4:1 trans selectivity to give 2,5-dimethylpyrrolidine with a k(rel) of 2.6.

The development of efficient methods for the synthesis of nitrogen-containing compounds remains an important goal in contemporary catalysis research because of the central role of this class of compounds in biological systems and pharmaceutical applications.[1] The addition of an amine N À H bond to a carbon-carbon multiple bond, so-called hydroamination, [2] is a reaction with great synthetic potential, as it not only reduces the formation of waste owing to its atom economy, but it utilizes also very simple starting materials. The development of novel catalyst systems for hydroamination has seen significant progress in the last two decades, [2,3] but the intermolecular hydroamination of unactivated alkenes with simple amines remains very challenging. [4] Therefore, it is not too surprising that asymmetric hydroamination reactions [5] have been studied predominantly in intramolecular reactions. [6, 7] Intermolecular reactions have been reported only sporadically and all of these studies were limited to the reaction between aniline derivatives and activated alkenes, such as vinyl arenes, [8] 1,3-dienes, [9] and strained bicyclic alkenes.[10] The first enantioselective goldcatalyzed addition of cyclic ureas to unactivated alkenes in up to 78 % ee was reported recently by Widenhoefer and coworkers.[11] Herein we report the stereoselective addition of simple amines to unactivated alkenes utilizing chiral rareearth-metal-based catalysts.Catalyst systems based on rare-earth-metal complexes exhibit high catalytic activity, in particular in intramolecular hydroaminations, [2, 3f] whereas intermolecular hydroaminations are significantly more difficult to achieve as a result of the unfavorable competition between weakly coordinating alkenes and strongly coordinating amines. [4a,b, 6b, 12] We have previously reported on efficient biphenolate and binaphtholate rare-earth-metal catalysts, [6b, 13] which can catalyze the intramolecular hydroamination of aminoalkenes with high activity and up to 95 % ee. Preliminary studies with a corresponding binaphtholate lanthanum complex for the reactions of styrene [6b] and 1,3-cyclohexadiene [14] indicated the potential applicability of these systems in asymmetric intermolecular hydroaminations. As the lanthanum catalyst showed rather low selectivity [14] we decided to utilize the generally more selective yttrium and lutetium catalysts in our study. For the initial catalyst screening we chose the reaction of 1-heptene with benzylamine.

Two 3,3‘-dialkyl-5,5‘,6,6‘-tetramethyl-1,1‘-biphenyl-2,2‘-diols (where alkyl = t-Bu, adamantyl) were prepared in two steps and resolved as the menthol phosphate derivative. Addition of the dipotassium salt of each biphenolate to various Mo(N-Aryl)(CHR)(OTf)2(DME) complexes produced racemic and enantiopure compounds of the type Mo(N-aryl)(CHR)(biphenolate). X-ray crystallographic studies of syn-Mo(N-2,6-i-Pr2C6H3)(CHCMe2Ph)[(S)-Biphen] and syn-Mo(N-2-CF3C6H4)(CHCMe3)[(S)-Biad](pyridine) proved the absolute stereochemistry of the biphenolate ligands. Neophylidene and neopentylidene complexes were found to have predominantly the syn conformation in solution. The [syn]/[anti] equilibrium constant for Mo(N-Aryl)(CHR)[Biphen] complexes increased in magnitude with decreasing size of the arylimido ligand, and decreased upon reducing the steric bulk of the alkylidene substituent. The rates of exchange of syn and anti isomers, as determined by single-parameter line shape analysis and by spin saturation transfer, were found to be on the order of ∼1 s-1 at 22 °C.