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C 2-Symmetric bis(oxazolinyl)pyridine (pybox)−Cu(II) complexes have been shown to catalyze enantioselective Mukaiyama aldol reactions between (benzyloxy)acetaldehyde and a variety of silylketene acetals. The aldol products are generated in high yields and in 92−99% enantiomeric excess using as little as 0.5 mol % of chiral catalyst [Cu((S,S)-Ph-pybox)](SbF6)2. With substituted silylketene acetals, syn reaction diastereoselection ranging from 95:5 to 97:3 and enantioselectivities ≥95% are observed. Investigation into the reaction mechanism utilizing doubly labeled silylketene acetals indicates that the silyl-transfer step is intermolecular. Further mechanistic studies revealed a significant positive nonlinear effect, proposed to arise from the selective formation of the [Cu((S,S)-Ph-pybox)((R,R)-Ph-pybox)](SbF6)2 2:1 ligand:metal complex. A stereochemical model is presented in which chelation of (benzyloxy)acetaldehyde to the metal center to form a square pyramidal copper intermediate accounts for the observed sense of induction. Support for this proposal has been obtained from double stereodifferentiating reactions, EPR spectroscopy, ESI spectrometry, and, ultimately, the X-ray crystal structure of the aldehyde bound to the catalyst. The C 2-symmetric bis(oxazolinyl)−Cu(II) complex [Cu((S,S)-tert-Bu-box)](OTf)2 is also an efficient catalyst for the aldol reaction, but the scope with this system is not as broad.

The structures and temperature-dependent photoluminescence properties of the one-dimensional compounds [(TPA)(2)Au][Au(CN)(2)], 1, and (TPA)AuCl, 2, are reported. An extended linear chain with weak Au.Au interactions along the c-axis is evident in the structure of 1, and a helical chain with a pitch of 3.271 A is seen for 2. The intrachain Au...Au separation is 3.457(1) and 3.396(2) A in 1 and 2, respectively. As a result of this weak Au...Au interaction, the physical properties of these compounds are anisotropic. Scanning electron microscopy (SEM) studies indicate that single crystals of both compounds are noninsulating. Single crystals of 1 do not luminesce visibly, but grinding the crystals finely initiates a strong green emission under UV irradiation at room temperature. Further interesting optical properties include the dependence of the emission profile of the powder on the exciting wavelength and luminescence thermochromism. When excited at wavelengths < 360 nm, the powder exhibits a blue emission at 425 nm while excitation with longer wavelengths leads to a green emission near 500 nm. While the green emission dominates at ambient temperature, cooling to cryogenic temperatures leads to the dominance of the blue emission. Fibers of 2 are luminescent at 78 K with an emission band centered at 580 nm. Compound 1 crystallizes in the orthorhombic space group Cccm (No. 66), with Z = 2, a = 6.011(1) A, b = 23.877(6) A, c = 6.914(1) A, V = 992.3(3) A(3), and R = 0.0337. Compound 2 crystallizes in the trigonal space group R3 (No. 148), with Z = 18, a = 22.587(2) A, b = 22.587(2) A, c = 9.814(2) A, V = 4336 A(3), and R = 0.0283.

No abstract

A five-coordinate chloride ion is believed to template the assembly of a pentadecanuclear lanthanide complex of europium(III). This cluster (see picture) has been prepared by coordination of europium(III) perchlorate with tyrosine at about pH 6. Single crystal X-ray analysis established an unprecedented structure in which 15 constituent europium(III) ions are organized into three parallel pentagonal layers.

A series of pentadecanuclear lanthanide-hydroxo complexes possessing a common core of the formula [Ln(15)(mu(3)-OH)(20)(mu(5)-X)](24+)(1, Ln = Eu, X = Cl(-); 2, Ln = Nd, X = Cl(-); 3, Ln = Gd, X = Cl(-); 4, Ln = Pr, X = Br(-); 5, Ln = Eu, X = Br(-)) were prepared by L-tyrosine-controlled hydrolysis of corresponding lanthanide perchlorates in the presence of added Cl(-) or Br(-). The cationic cluster core comprises five vertex-sharing cubane-like [Ln(4)(mu(3)-OH)(4)](8+) units centered on the halide template. In the case of templating I(-), dodecanuclear complexes were isolated instead. The core component, [Ln(12)(mu(3)-OH)(16)(I)(2)](18+) (6, Ln = Dy; 7, Ln = Er), consists of four vertex-sharing cubane-like [Ln(4)(mu(3)-OH)(4)](8+) units and exists as a square-shaped cyclic structure with one I(-) located on each side of the square plane. An analogous hydrolytic reaction involving Er(NO(3))(3), L-tyrosine, and NaOH affords the known hexanuclear complex [Er(6)(mu(6)-O)(mu(3)-OH)(8)(NO(3))(6)(H(2)O)(12)](NO(3))(2) whose core component is a face-capped octahedral [Er(6)(mu(6)-O)(mu(3)-OH)(8)](8+) cluster with an interstitial mu(6)-oxo group (Wang, R.; Carducci, M. D.; Zheng, Z. Inorg. Chem. 2000, 39, 1836-1837.). The efficient self-assembly of halide-encapsulating multicubane complexes (1-7) and the inability to produce an analogous nitrate-containing complex demonstrate the superior templating roles played by the halide ion(s). Further credence for the halide template effects was provided by the isolation of the cationic pentadecanuclear complex 3 as the sole product when tyrosine-supported hydrolysis of Gd(NO(3))(3) was carried out in the presence of competitive Cl(-). Magnetic moments of complexes 1-7 measured at room temperature by using Evans' method are in excellent agreement with those calculated by the Van Vleck equation, assuming magnetically noninteractive lanthanide ions.

Experiment and theory favour a model of C–H borylation where significant proton transfer character exists in the transition state.

Ir catalysts supported by bidentate silyl ligands that contain P- or N-donors are shown to effect ortho borylations for a range of substituted aromatics. The substrate scope is broad, and the modular ligand synthesis allows for flexible catalyst design.