The mechanisms for Ni(dppe)Cl(2)-catalyzed chain-growth polymerization of 4-bromo-2,5-bis(hexyloxy)phenylmagnesium chloride and 5-bromo-4-hexylthiophen-2-ylmagnesium chloride were investigated. Rate studies utilizing IR spectroscopy and gas chromatography revealed that both polymerizations exhibit a first-order dependence on the catalyst concentration but a zeroth-order dependence on the monomer concentration. (31)P NMR spectroscopic studies of the reactive organometallic intermediates suggest that the resting states are unsymmetrical Ni(II)-biaryl and Ni(II)-bithiophene complexes. In combination, the data implicate reductive elimination as the rate-determining step for both monomers. Additionally, LiCl was found to have no effect on the rate-determining step or molecular weight distribution in the arene polymerization.

A highly efficient and regioselective Pd-catalyzed method for the oxidative coupling of arylpyridine derivatives is reported. Remarkably, the reactions proceed at room temperature and are compatible with diverse functionalities, including aryl halides and thiophenes. Mechanistic studies suggest that these transformations proceed via a previously unprecedented mechanism involving two different pyridine-directed C-H activation reactions-one at a PdII center and one at PdIV.

The mechanisms for Ni(dppp)Cl2-catalyzed chain-growth polymerization of 4-bromo-2,5-bis(hexyloxy)phenylmagnesium chloride and 5-bromo-4-hexylthiophen-2-ylmagnesium chloride were investigated. A combination of rate and spectroscopic studies revealed that transmetalation is the rate-determining step of the catalytic cycle for both monomers. 31P NMR spectroscopic studies revealed that a Ni(II)−aryl halide and a Ni(II)−thienyl halide are the catalyst resting states. In addition, LiCl was found to alter the arene polymerization rates. These results are different than those previously obtained with an alternative catalyst (Ni(dppe)Cl2) and suggest that the ligand has a strong mechanistic influence on the polymerization.

Synthesis of Octapeptide 3Boc-Ser(Al)-OH 1 : NaH (2.44 g of a 60% oil dispersion, 1.46 g, 0.061 mol) was suspended in 20 mL of DMF and cooled to 0 °C in a flask fitted with a dropping funnel. Boc-Ser-OH (5.0 g, 0.024 mol) was dissolved in 40 mL of DMF and the resulting solution was transferred to the dropping funnel. This solution was added drop-wise to the NaH solution over a period of 30 minutes. Allyl bromide (2.0 mL, 0.024 mol) was added and the flask contents warmed to room temperature and stirring was continued for 3 hours. The reaction was quenched by the slow addition of 12 mL of water. The solvents were then removed on the rotary evaporator and the residue dissolved in water (40 mL), which was washed with two 20 mL portions of ethyl acetate. The aqueous phase was acidified to pH 2 with the addition of 6 M HCl and extracted with two 40 mL portions of ethyl acetate. The organic phases were combined and dried over anhydrous magnesium sulfate. After filtration, the solvent was evaporated to yield a viscous oil (4.8 g, 82%) which was found to be of sufficient purity to be used in subsequent reactions.1 H NMR (400 MHz, CDCl 3 ): δ 9.1 (1H br s), 5.85 (1H, m), 5.41 (1H, d, J = 8.4 Hz), 5.25 (1H, dq, J = 17.2, 1.5 Hz), 5.19 (1H, dq, J = 10.4, 1.5 Hz), 4.45 (1H, d, J = 8.5 Hz), 4.00 (2H, dt, J = 5.7, 1.5 Hz), 3.90 (1H, dd, J = 9.5, 3.0 Hz), 3.67 (1H, dd, J = 9.5, 3.6 Hz), 1.45 (9H, s).13 C NMR (100 MHz, CDCl 3 ): δ 175. 96, 156.15, 134.25, 118.21, 80.77, 72.80, 69.96, 54.16, 28.70

The role of ligand-based steric effects was investigated in the polymerization of 4-bromo-2,5-bis(hexyloxy)phenylmagnesium chloride. Three different Ni(L-L)Cl2 catalysts were synthesized using commercially available bis(dialkylphosphino)ethane ligands with varying steric properties. One of these catalysts (Ni(depe)Cl2) outperformed the others for this polymerization. The polymer characterization data were consistent with a chain-growth mechanism. Rate and spectroscopic studies revealed a rate-limiting reductive elimination for both initiation and propagation with Ni(depe)Cl2. In contrast, less hindered Ni(dmpe)Cl2 and more hindered Ni(dcpe)Cl2 were ineffective polymerization catalysts; NMR spectroscopic studies indicated that competing decomposition and uncontrolled pathways intervene. For other monomers, Ni(depe)Cl2 performed similar to the conventional catalysts. Copolymerization studies revealed that block copolymers could be effectively prepared. Overall, these studies indicate that altering the ligand-based steric properties can have a significant impact on the chain-growth polymerization.

A new LiI-promoted O- to N-alkyl migration has been developed for the conversion of O-alkylated 2-hydroxy pyridines, quinolines, and pyrimidines to the corresponding N-alkylated heterocycles in good to excellent yields (57-99%). This method serves as an efficient means for the preparation of N-benzyl pyridones, quinolones, and pyrimidones.

An efficient and inexpensive LiI-promoted O- to N-alkyl migration of 2-benzyloxy-, 2-allyloxy-, and 2-propargyloxypyridines and heterocycles is reported. The reaction produces the corresponding N-alkyl 2-pyridones and analogues under green, solvent-free conditions in good to excellent yields (30 examples, 20-97% yield). This method has been shown to be intermolecular and requires heat and lithium cation to occur.

2-Arylpyridines undergo palladium-catalyzed oxidative C-C coupling using Oxone as a terminal oxidant. Biphenyls (II) and bithienyl (IV) are obtained with complete regioselectivity under optimized conditions. Substrates (V) and (VIII) that contain meta-substituents form mixtures of regioisomers in a ratio close to 1:1. A previously unprecedented mechanism is suggested involving two sequential C-H activation reactions at Pd(II) and Pd(IV), respectively. -(HULL, K. L.; LANNI, E. L.; SANFORD*, M. S.; J.