The aryl−aryl interchange reaction of
ArPdL2I complex 1m was found to follow
pseudo-first-order kinetics.
A marked inhibition in the presence of excess phosphine and/or
excess iodide was observed, suggesting that a
dissociative pathway was involved, contrary to the analogous
alkyl−aryl interchange reaction studied previously.
Phosphine flooding experiments could not be performed due to a
competing phosphonium salt formation reaction
that occurred in the presence of excess phosphine. A deuterium
labeling experiment indicated that the interchange
reaction proceeded via the reductive elimination to form the
phosphonium salt, suggesting that excess phosphine
was acting as a trap for intermediate palladium(0) species
preventing the generation of the interchanged
palladium(II) complex. Substituent effect studies of the interchange
reaction indicated that it was inhibited by electron-withdrawing groups on both the phosphine and palladium-bound aryl groups
and by increased steric bulk on both
the phosphine and palladium-bound aryl groups. Under catalytic
conditions, the distribution of phosphines formed
from the aryl−aryl interchange during palladium-mediated
cross-coupling reactions could be modeled by statistics.
Various strategies for eliminating the formation of byproducts
caused by the interchange during cross-coupling reactions
were screened and optimized.
Suzuki aryl cross-couplings employing aryl bromides and aryl iodides proceed under mild conditions (65 °C) with high efficiency (substrate-to-catalyst ratios in excess of 500) in the presence of phosphine-free palladium catalysts derived from palladium acetate, Pd-KdbahOeHe (dba = dibenzylideneacetone), and [(?7* 123-C3H5)PdCl]2. Phosphine inhibition is shown to play a key role in limiting catalytic efficiency; qualitative comparison studies show that the phosphine-free systems are 1-2 orders of magnitude more active than phosphine-supported catalytic systems. Pd[P(Ph)3]4 proved to be the least active of the catalytic species screened. The phosphine-free methodology appears to be generally applicable; cross-couplings of aryl iodides yielding biaryls 6 and 7 proceed without noticeable steric or electronic effects. Cross-couplings employing aryl bromides are insensitive to electronic effects in the synthesis of 6 but are slowed by steric hindrance in the synthesis of 7. Acceleration of cross-coupling is observed in the presence of polar cosolvents and at high pH.
The 2007 International Technology Roadmap for Semiconductors (ITRS) 1 specifies Extreme Ultraviolet (EUV) lithography as one leading technology option for the 32nm half-pitch node, and significant world wide effort is being focused towards this goal. Readiness of EUV photoresists is one of the risk areas. In 2007, the ITRS modified performance targets for high-volume manufacturing EUV resists to better reflect fundamental resist materials challenges. For 32nm half-pitch patterning at EUV, a photospeed range from 5-30 mJ/cm 2 and low-frequency linewidth roughness target of 1.7nm (3σ) have been specified. Towards this goal, the joint INVENT activity (AMD, CNSE, IBM, Micron, and Qimonda) at Albany evaluated a broad range of EUV photoresists using the EUV MET at Lawrence Berkeley National Laboratories (LBNL), and the EUV interferometer at the Paul Scherrer Institut (PSI), Switzerland. Program goals targeted resist performance for 32nm and 22nm groundrule development activities, and included interim relaxation of ITRS resist performance targets. This presentation will give an updated review of the results. Progress is evident in all areas of EUV resist patterning, particularly contact/via and ultrathin resist film performance. We also describe a simplified figure-of-merit approach useful for more quantitative assessment of the strengths and weaknesses of current materials.
Soluble derivatives of poly(p-phenylene) of high molecular weight were synthesized via Suzuki coupling reactions catalyzed by palladium(0) precursors in the presence of either triphenylphosphine (TPP) or tri(o-tolyl)phosphine (TOTP). Syntheses involving the former ligand resulted in the formation of polymers in which the incorporation of phosphine was clearly observable by 31 P NMR. However, polymers formed utilizing the latter ligand in a hydrophobic solvent such as CH2Cl2 exhibited no signals in the 31 P NMR spectrum, even after 20 000 scans. Analyses by tandem GPC-light scattering and tandem GPC-light scattering-viscometry showed that polymers synthesized by utilizing a large amount of TPP-based catalyst (2%) possessed a considerably lower molecular weight than did the other samples and exhibited markedly different dependencies of the radius of gyration and intrinsic viscosity on molecular weight. From these studies, it does appear that the aryl-aryl interchange reaction known to occur in ArPdL2I complexes significantly affects the architecture of these polymers.
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