Dedicated to Professor Manfred T. Reetz on the occasion of his 60th birthdayWhereas nickel-and palladium-catalyzed methods for crosscoupling aryl and vinyl halides and sulfonates with a range of organometallic reagents have reached a fairly high level of sophistication, [1] comparable progress has not yet been achieved for reactions of alkyl halides and sulfonates.[2]Recently, we and others have begun to address this shortcoming by describing catalysts for certain Suzuki, [3] Negishi, [4,5] Kumada, [6,7] Stille, [8] and Hiyama [9] couplings of primary alkyl electrophiles. With the exception of Suzuki's observation that [Pd(PPh 3 ) 4 ] effects cross-couplings of alkyl iodides with R-(9-BBN), [3a] the palladium-based catalysts that were reported for coupling alkyl electrophiles have all employed a hindered trialkylphosphane (PCy 3 or P(tBu) 2 Me) as the ligand.To increase the likelihood of expanding the still-limited scope of cross-couplings of alkyl electrophiles, we have been exploring the use of new classes of ligands for these processes. Herein, we establish that, in the presence of alkyldiaminophosphanes (PR(NR' 2 ) 2 ), we can accomplish palladiumcatalyzed Stille cross-couplings of alkyl bromides and iodides not only with vinyl stannanes, but also with aryl stannanes [Eq. (1)], a class of reaction partners that are not efficiently coupled by Pd/PR 3 (PR 3 = trialkylphosphane).As a consequence of the electron-richness and the ready accessibility of alkyldiaminophosphanes (PR(NR' 2 ) 2 ), [10] we

Dedicated to Professor Manfred T. Reetz on the occasion of his 60th birthdayWhereas nickel-and palladium-catalyzed methods for crosscoupling aryl and vinyl halides and sulfonates with a range of organometallic reagents have reached a fairly high level of sophistication, [1] comparable progress has not yet been achieved for reactions of alkyl halides and sulfonates.[2]Recently, we and others have begun to address this shortcoming by describing catalysts for certain Suzuki, [3] Negishi, [4,5] Kumada, [6,7] Stille, [8] and Hiyama [9] couplings of primary alkyl electrophiles. With the exception of Suzuki's observation that [Pd(PPh 3 ) 4 ] effects cross-couplings of alkyl iodides with R-(9-BBN), [3a] the palladium-based catalysts that were reported for coupling alkyl electrophiles have all employed a hindered trialkylphosphane (PCy 3 or P(tBu) 2 Me) as the ligand.To increase the likelihood of expanding the still-limited scope of cross-couplings of alkyl electrophiles, we have been exploring the use of new classes of ligands for these processes. Herein, we establish that, in the presence of alkyldiaminophosphanes (PR(NR' 2 ) 2 ), we can accomplish palladiumcatalyzed Stille cross-couplings of alkyl bromides and iodides not only with vinyl stannanes, but also with aryl stannanes [Eq. (1)], a class of reaction partners that are not efficiently coupled by Pd/PR 3 (PR 3 = trialkylphosphane).As a consequence of the electron-richness and the ready accessibility of alkyldiaminophosphanes (PR(NR' 2 ) 2 ), [10] we

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The cluster structure in the catalyst ink of a proton exchange membrane fuel cell determines its performance. The interaction among solvent, ionomer, and catalyst in ink determines the cluster structure and affects the microstructure and surface morphology of the catalyst layer, which is of great significance to improve the conductivity of the catalyst layer to protons, electrons, and water. First, the dissolved state of the main chain and the side chain of the ionomer in solvent was characterized. The results of relative viscosity, ζ-potential, effective proton fraction, and nuclear magnetic resonance (NMR) showed that the alcohol aqueous solution promoted the stretching electrolysis of the main chain and the side chain of the ionomer more than the pure aqueous solvent, making the ionomer clusters smaller. The rheological test of the ink shows that the pure water solvent ink has the largest cluster and the strongest network structure. Under the test conditions, the clusters in the ink can be reconstructed quickly after breakage through viscous shearing. The addition of alcohols will make the clusters in the ink smaller and the network structure brittle. After the clusters and the network structure are damaged, they will slowly recombine and the viscosity in the ink will gradually recover. Ethanol will minimize the clusters in the ink, and the network structure in the ink is the weakest. The effect of the network strength on the cluster structure is weakened by reducing the solid content in the ink. The amplitude scanning test shows that the network structure in the slurry is almost eliminated after reducing the solid content, the storage modulus of ink with water, 50 wt % isopropyl alcohol (IPA), 50 wt % n-propanol (NPA), and 50 wt % ethanol (ET) decreases in turn, as well as the liquid viscosity behavior increases and the cluster particle size in the ink decreases. In conclusion, more dispersed ionomers and alcohol molecules with smaller molecular structures are more conducive to the dispersion of clusters in the ink.

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