David S. Glueck

Catalytic Asymmetric Synthesis of Chiral Phosphanes

Chiral phosphanes, important ligands for metal-catalyzed asymmetric syntheses, are often prepared with compounds from the chiral pool, by using stoichiometric chiral auxiliaries, or by resolution. In some cases, this class of valuable compounds can be prepared more efficiently by catalytic asymmetric synthesis. This Concepts article presents an overview of these synthetic methods, including recent advances in catalysis by metal complexes, biocatalysis, organocatalysis, and ligand-accelerated catalysis.

The electrochromic properties of chemically deposited tungsten oxide films

Abstract Thin films of tungsten oxide were prepared by deposition from a solution of tungsten chloride, and, for comparison, by the acidification of a solution of sodium tungstate. The electrochromic behavior of these films was investigated by studying their current-voltage behavior, absorbance spectra, response time, and the diffusion coefficient of lithium ions in the film.

Platinum-Catalyzed Enantioselective Tandem Alkylation/Arylation of Primary Phosphines. Asymmetric Synthesis of P-Stereogenic 1-Phosphaacenaphthenes

Enantioselective tandem alkylation/arylation of primary phosphines with 1-bromo-8-chloromethylnaphthalene catalyzed by Pt(DuPhos) complexes gave P-stereogenic 1-phosphaacenaphthenes (AcePhos) in up to 74% ee. Diastereoselective formation of four P-C bonds in one pot with bis(primary) phosphines gave C2-symmetric diphosphines, including the o-phenylene derivative DuAcePhos, for which the rac isomer was formed with high enantioselectivity. These reactions, which appear to proceed via an unusual metal-mediated nucleophilic aromatic substitution pathway, yield a new class of heterocycles with potential applications in asymmetric catalysis.

Substrate and Catalyst Screening in Platinum-Catalyzed Asymmetric Alkylation of Bis(secondary) Phosphines. Synthesis of an Enantiomerically Pure C2-Symmetric Diphosphine

Platinum-catalyzed asymmetric alkylation of bis(secondary) phosphines was investigated. The modular design of the catalyst precursor Pt(diphos*)(R′)(Cl) and the substrates, a bis(secondary) phosphine HRP∼PHR and a benzyl halide, along with an efficient 31P NMR screening method, enabled rapid evaluation of the rate and diastereoselectivity of these reactions. These experiments identified a selective catalyst, Pt(DuPhos)(Ph)(Cl), and showed that the alkylation of PhHP(CH2)3PHPh (2) was faster and more selective than that of PhHP(CH2)2PHPh (1), MesHP(CH2)3PHMes (3), or 1,1′-(C5H4PHPh)2Fe (4). Alkylation of 1 with o-CF3C6H4CH2Br using the base NaOSiMe3 and the catalyst precursor Pt((R,R)-i-Pr-DuPhos)(Ph)(Cl), or the analogous Me-DuPhos complex, gave the diphosphine Ph(CH2o-CF3C6H4)P(CH2)2P(CH2o-CF3C6H4)Ph (7), which was prepared on a multigram scale and isolated as a borane adduct (6). The rac and meso diastereomers of 6 were separated by recrystallization, and enantiomerically pure 6 was isolated. Both (R,R)...

Synthesis and structure of platinum and palladium complexes of dimesitylphosphine

Abstract Treatment of Pd(tmeda)Me2 with dimesitylphosphine (PMes2H, L) gave cis-PdL2Me2 (1). trans-ML2Cl2 (M=Pd (2), Pt (3)) were prepared from a variety of starting materials. The reaction of Pt(cod)Cl2 with L gave cis-PtL2Cl2 (4), which reacted with PPh3 to yield cis-Pt(L)(PPh3)Cl2 (5). cis-PtL2(Me)(Cl) (6) was prepared from L and Pt(cod)(Me)(Cl), while reaction of L with Pt(cod)(Et)(I) gave cis-PtL2(Et)(I) (7), which isomerized to trans-PtL2(Et)(I) (8). The phosphine–borane PMes2H·BH3 (9) was made by reaction of L with BH3·SMe2. Crystal structures of 2·2CH2Cl2, 4·CH2Cl2, 5·2CH2Cl2, 6, and 9 provided 7information on the steric bulk of L (cone angle ca. 149°). Restricted rotation about the PtP and PC bonds in complexes 4–8 was studied by variable temperature NMR spectroscopy.

Synthesis, reactivity, and resolution of a C2-symmetric, P-stereogenic benzodiphosphetane, a building block for chiral bis(phosphines).

Although the pyramidal inversion barriers in diphosphines (R(2)P-PR(2)) are similar to those in phosphines (PR(3)), P-stereogenic chiral diphosphines have rarely been exploited as building blocks in asymmetric synthesis. The synthesis, reactivity, and resolution of the benzodiphosphetane trans-1,2-(P(t-Bu))(2)C(6)H(4) are reported. Alkylation with MeOTf followed by addition of a nucleophile gave the useful C(2)-symmetric P-stereogenic ligand BenzP* and novel analogues.

Selectivity viacatalyst or substrate control in catalytic asymmetric transformations of bifunctional symmetrical substrates

Catalytic asymmetric transformations of bifunctional symmetrical substrates pose interesting problems in selectivity. In one extreme, catalyst control leads to identical selectivity at both sites, and amplification of chirality in the product. This improved enantiopurity comes at the expense of reduced yield; the undesired meso byproduct must be separated. Alternatively, substrate control may modify the inherent selectivity of the catalyst. The first transformation may change the substrate to make the second transformation less selective (negative cooperativity), while positive cooperativity can result in selectivity greater than that afforded by simple catalyst control. Similar behavior may occur in polyfunctional substrates with three or more identical reactive sites. Substrate vs. catalyst control and positive vs. negative cooperativity plausibly depends upon the structure of the substrate and the linker between the active sites, but has rarely been investigated systematically. This perspective presents several examples of structure–selectivity relationships with the eventual goal of designing substrates for positive cooperativity and enhanced selectivity in asymmetric catalysis.

Synthesis, Structure, and Luminescence of Copper(I) Halide Complexes of Chiral Bis(phosphines)

For investigation of structure-property relationships in copper phosphine halide complexes, treatment of copper(I) halides with chiral bis(phosphines) gave dinuclear [Cu((R,R)-i-Pr-DuPhos)(μ-X)]2 [X = I (1), Br (2), Cl (3)], [Cu(μ-((R,R)-Me-FerroLANE)(μ-I)]2 (5), and [Cu((S,S)-Et-FerroTANE)(I)]2 (6), pentanuclear cluster Cu5I5((S,S)-Et-FerroTANE)3 (7), and the monomeric Josiphos complexes Cu((R,S)-CyPF-t-Bu)(I) (8) and Cu((R,S)-PPF-t-Bu)(I) (9); 1-3, 5, and 7-9 were structurally characterized by X-ray crystallography. Treatment of iodide 1 with AgF gave [Cu((R,R)-i-Pr-DuPhos)(μ-F)]2 (4). DuPhos complexes 1-4 emitted yellow-green light upon UV irradiation at room temperature in the solid state. This process was studied by low-temperature emission spectroscopy and density functional theory (DFT) calculations, which assigned the luminescence to (M + X)LCT (Cu2X2 to DuPhos aryl) excited states. Including Grimmes dispersion corrections in the DFT calculations (B3LYP-D3) gave significantly shorter Cu-Cu distances than those obtained using B3LYP, with the nondispersion-corrected calculations better matching the crystallographic data; other intramolecular metrics are better reproduced using B3LYP-D3. A discussion of the factors leading to this unusual observation is presented.