No abstract

A combination of Pd(2)(dba)(3) and SPhos (1:2 molar ratio) is an excellent precatalyst for the Negishi cross-coupling of the serine-derived organozinc reagent 2 with aryl halides, including previously difficult ortho-substituted examples. In the case of meta- and para-substituted aryl halides, Pd-loadings of 0.5 mol % give satisfactory results. Use of 2-iodoaniline as substrate gives the lactam 12 in good yield.

The structure of the alkylzinc-tetramethylethyl-enediamine (TMEDA) cluster cation 3 has been determined in the gas phase by a combination of tandem mass spectrometry, infrared multiphoton dissociation (IRMPD) spectroscopy, and DFT calculations. Both sets of experimental results establish the existence of a strongly stabilizing interaction of TMEDA with the zinc cation. High-level DFT calculations on the alkylzinc-TMEDA cluster cation 3 allowed the identification of two low energy conformers, each featuring a four-coordinate zinc atom with a bidentate TMEDA ligand, and internal coordination from the carbonyl group of the Boc group to zinc. The experimental IRMPD spectrum is reproduced with an appropriately weighted combination of the IR spectra of the two conformers identified by theory. DFT calculations on the structure of the alkylzinc halide 2 with coordinated TMEDA using the PCM model of water solvent suggest that TMEDA can promote ionization of the zinc-iodine bond in organozinc iodides under aqueous conditions, providing a credible explanation for the role of TMEDA in stabilizing the carbon-zinc bond. Reaction of the serine-derived iodide 1 with aryl iodides "on water", promoted by nano zinc in the presence of PdCl(2)(Amphos)(2) (5 mol %) and TMEDA, leads to the formation of protected phenylalanine derivatives 4 in reasonable yields. In the case of ortho-substituted aryl iodides and aryl iodides that are solids at room temperature, conducting the reaction at 65 °C gives improved results. In all cases, the product 5 of reductive dimerization of the iodide 1 is also isolated.

The gallium−chalcogen heterocubanes [Cp*Ga(μ3-E)]4, E = S (1) and Se (2), and [Cp†Ga(μ3-Se)]4 (3) have been synthesized by dehalosilylation reactions between E(SiMe3)2 (E = S, Se) and RGaCl2, R = Cp* (C5Me5) and Cp† (C5Me4Et), and are characterized by elemental analyses, NMR spectroscopy, and mass spectrometry. The use of compounds 1 and 2 as single-source MOCVD precursors for the low-temperature growth of Ga2E3 films at 290−310 °C is described. The as-deposited films were amorphous; however, upon thermal annealing (500 °C) the films crystallized to the thermodynamic cubic phases, while the corresponding tellurium analog decomposed in the solid state at 220 °C forming a gallium-rich product.