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An efficient method for the C–N cross-coupling of (hetero)aryl (pseudo)halides with optically pure α-amino acid esters employing a commercially available nickel catalyst and weak inorganic base was developed. This is the first example of Ni-catalyzed N-arylation of amino acid esters without the use of electrochemistry, which was shown to effectively couple a variety of amino acid tert-butyl esters with (hetero)aryl chlorides, bromides, and tosylates in high yields and excellent enantioretention. Base-mediated racemization was revealed during control experiments, but increasing the steric bulk of the amino acid ester group limited the amount of racemization of the product.

The present contribution describes the systematic structural diversification of the κ2-P,N DalPhos ligand family in an effort to improve catalytic efficiency in the monoarylation of ammonia and acetone. The study is focused primarily on modifying the backbone phenylene linker, while retaining the same bite angle and steric bulk as the Mor-DalPhos ligand through the use of P(1-Ad)2 and morpholine donors. Eight new variants of Mor-DalPhos were prepared; two of these feature a pyridine linker (L1, L2), and five others feature either electron-donating (L3, L4) or electron-withdrawing (L5–L7) substituents on the phenylene linker. Additionally, thiomorpholino substitution (L8) was performed to investigate the effects of a possible tridentate coordination mode. Precatalyst complexes of the general formula LPd(cinnamyl)Cl were prepared and characterized in both solution and solid state. Solution studies demonstrated a significant degree of lability in the Pd–N bond, whereby dynamic behavior is seen to be dependent on the nature of the ligand backbone. The utility of these new ligands in the palladium-catalyzed monoarylation of ammonia or acetone was then surveyed. Notably, pyridine-derived ligand variants (L1, L2) were observed to out-perform parent Mor-DalPhos in the latter transformations.

The competitive catalytic screening of 18 known and newly prepared Mor-DalPhos ligand variants in the palladium-catalyzed cross-coupling of chlorobenzene with aniline, octylamine, morpholine, indole, ammonia, or acetone is presented, including ligands derived from the new secondary phosphine HP(Me2Ad)2 (Me2Ad = 3,5-dimethyladamantyl). Although triarylphosphine ancillary ligand variants performed poorly in these test reactions, ligands featuring either PAd2 or P(Me2Ad)2 donors (Ad = 1-adamantyl) gave rise to superior catalytic performance. Multiple Mor-DalPhos variants proved effective in cross-couplings involving aniline, octylamine, or morpholine; conversely, only a smaller subset of ligands proved useful in related cross-couplings of indole, ammonia, or acetone. In the case of the N-arylation of indole, a Mor-DalPhos ligand variant featuring ortho-disposed PAd2 and dimethylmorpholino donor fragments (L13) proved superior to all other ligands surveyed, including the parent ligand Mor-DalPhos (L5). Conversely, L5 was found to be superior to all other ligands in the palladium-catalyzed monoarylation of ammonia. Ligand L6 (i.e., the P(Me2Ad)2 variant of L5) proved superior to all other ligands in the monoarylation of acetone and, with the exception of indole N-arylation, was the most broadly useful of the Mor-DalPhos ligands surveyed herein.

We report herein on our synthetic, structural, and catalytic investigations of new P,S-DalPhos ligands featuring pairings of phosphorus and sulfur donor groups as well as new sulfur-containing analogues of the previously reported P,N-ligands Me-DalPhos and Mor-DalPhos, featuring a 2,3-disubstituted thiophenyl backbone. In examining the catalytic performance of these new sulfur-containing ligands in the Buchwald–Hartwig amination of octylamine, aniline, or ammonia with 4-chlorotoluene, noteworthy differences in reactivity behavior relative to Me-DalPhos and Mor-DalPhos were observed.

The phosphino–phenolate complex (κ2-{2-i-Pr2PC6H4}O)Ir(COD) (COD = η4-1,5-cyclooctadiene; 1) is shown to be an effective precatalyst for the intramolecular hydroamination of unactivated alkenes with pendant secondary alkylamines, providing either pyrrolidine or piperidine heterocycles in high isolated yields. While monitoring the progress of a selected test reaction of this type, a significant induction period (~3 h) was observed; variable-temperature 1H and 31P NMR studies (25–100 °C) under catalytically relevant conditions revealed no new metal-containing species. In an effort to develop an enantiopure variant of 1, a synthetic route to the chiral (κ2-P,O)Ir(COD) complex (7), which features a 1-aryl-2,5-dialkylphospholane structure derived from (2S,5S)-2,5-hexanediol cyclic sulfate, was developed. The structure of 7 was confirmed by use of single-crystal X-ray diffraction techniques. While 7 failed to provide enantioselectivity in the intramolecular hydroamination of unactivated alkenes with pendant secondary alkylamines, the activity of 7 was found to be comparable to that of 1.

Treatment of trichlorovinylsilane with 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluoro-1-octanol (3 equiv.) in the presence of excess triethylamine produces the fluorous vinylsilane, 1, which can be isolated in 74% yield as an analytically pure oil. The addition of bis(pentafluorophenyl)borane to 1 produces the fluorous boranes, 2a–2b, as an analytically pure, isomeric mixture of anti-Markovnikov and Markovnikov hydroboration products in 38% isolated yield. Compounds 2a–2b are soluble in both arene solvents and perfluoro(methylcyclohexane). Treatment of 2a–2b with excess trimethylphosphine generates a mixture of products, including the Lewis adduct, 3, which can be isolated as an analytically pure oil in 15% yield. When exposed to either dimethylaminopyridine or piperidine at room temperature, the trimethylphosphine donor in 3 is cleanly displaced, based on in situ 31P NMR studies; under similar conditions, triethylamine does not react with 3. Addition of either dimethylaminopyridine or piperidine to 2a–2b, followed by purification and subsequent treatment with an excess of either hydrogen chloride or p-toluenesulfonic acid, results in cleavage of the Si–O linkages and the regeneration of 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluoro-1-octanol.Key words: fluorous, borane, silane, Lewis acid.

Reactions involving Fe(NO)2(CO)2 and the bis(phosphine) ligands bis(diphenylphosphino)methane (DPPM), bis(diphenylphosphino)acetylene (DPPA), 1,6-bis(diphenylphosphino)hexane (DPPH), and 1,4-bis(diphenyl phosphino)benzene (DPPB) have been examined. From these reactions, the mononuclear complex, Fe(κ1-DPPM)(NO)2(CO) 3, linear dinuclear species of the type Fe2(µ-L)(NO)4(CO)2 (L = Ph2PCH2PPh2 4, Ph2PC[Formula: see text]CPPh2 5, Ph2PCH2(CH3)4CH2PPh2 6, and Ph2P(p-C6H4)PPh2 7), and macrocyclic dinuclear species of the type Fe2(µ-L)2(NO)4 (L = Ph2PCH2PPh2 8 and Ph2PC[Formula: see text]CPPh2 9) were isolated and spectroscopically characterized. For 4, 5, 8, and 9, the solid-state molecular structures of the products were determined by use of single-crystal X-ray diffraction techniques. Key words: dinitrosyliron, iron nitrosyls, dinuclear macrocycles, bis(phosphine) complexes.