Palladacycles in Catalysis

Abstract

Palladium compounds containing a Pd‐C that are stabilized intramolecularly by at least one two‐electron donor group have numerous applications as pre‐catalysts. In particular, these compounds denominated palladacycles possess very attractive properties such as high thermal stability and low air sensitivity and they are ease to handle. These compounds are very active catalyst precursors in Heck coupling, Suzuki coupling, Buchwald–Hartwig amination and related coupling reactions under mild conditions, for instance at room temperature or in water. However, palladacycles serve as precursors to highly active palladium(0) species consist of soluble clusters or colloids, often stabilized by quaternary ammonium salts in highly dilute solutions or highly active low‐coordinate complexes of electron‐rich phosphines or carbenes. Moreover, chiral palladacycles are very important catalysts for enantioselective allylic rearrangements, allylic additions and aldol chemistry, since they act as Pd(II) Lewis acids and no redox process occurs

Gas-Phase Unimolecular Reactions of Pallada- and Nickelalactone Anions

“…First, CID of metal carboxylates to induce decarboxylation has been used as a straightforward method to create a range of elusive organometallic ions in the gas phase, including complexes of copper, 6 silver, 7 gold, 8 nickel, palladium, platinum, 9 magnesium, 10 calcium, strontium, and barium. 11 For example, the coinage metal dimethylmetallates have been "synthesized" via double decarboxylation (eqs 1 …”

“…They most commonly consist of a five-membered ring containing palladium bound on one side to carbon and on the other to a two-electron donor such as nitrogen, oxygen, sulfur, or phosphorus. While they are most commonly thought of as a controlled source of Pd(0) for catalytic C−C and C−X bond coupling reactions, 1 there are also numerous cases in which palladacycles have been reported to be directly involved in catalysis. 2 One subclass of palladacycles that has been largely overlooked thus far is the palladalactones.…”

Palladacycle-Catalyzed Carbonylative Suzuki–Miyaura Coupling with High Turnover Number and Turnover Frequency

“…The main drawbacks of these catalytic systems include high palladium loading, poor turnover numbers (TON’s) and turnover frequencies (TOF’s), and the need to handle air- and moisture-sensitive phosphine ligands. Palladacycles have been reported exhaustively for conventional cross-coupling reactions (Heck, Suzuki, Sonogashira, Buchwald–Hartwig) and have been shown to produce extremely high TON’s and TOF’s vis-à-vis conventional palladium sources . The fact that they are air- and moisture-stable is an added advantage.…”

Characterization and improvement of LTCC composite materials for application at elevated temperatures

“…The glass composition of this system was developed to exhibit an excellent RF behavior 10 and is more complex than the one of Du Pont 951. Instead of using a Si-O-network, DP 943 incorporates B 2 O 3 , Al 2 O 3 , and La 2 O 3 to build the glass network ( Table 3).…”