pH-Dependent C−C Coupling Reactions Catalyzed by Water-Soluble Palladacyclic Aqua Catalysts in Water

Abstract

The series of water-soluble palladacyclic aqua complexes [( t Bu-SCS)PdII(H2O)]+ ([1]+, t Bu-SCS = C6H3-2,6-(CH2S t Bu)2), [( i Pr-SCS)PdII(H2O)]+ ([2]+, i Pr-SCS = C6H3-2,6-(CH2S i Pr)2), [(PCP)PdII(H2O)]+ ([3]+, PCP = C6H3-2,6-(OP i Pr2)2), and [(PC)PdII(H2O)2]+ ([4]+, PC = 4-MeC6H3-2-(OP i Pr2)) have been synthesized from the reaction of the corresponding palladacyclic chloro complexes with silver salts in water to optimize the catalytic activity for pH-dependent C−C coupling reactions in water by changing the supporting ligands from S-supporting (SCS) to P-supporting (PCP) ligands and also from tridentate (PCP) to bidentate (PC) ligands. It was confirmed that there was no precipitation of palladium black under the present reaction conditions. The PC palladacyclic aqua complex [4]+ exhibits the highest catalytic activity among the water-soluble palladacyclic aqua complexes [1]+−[4]+ for the pH-dependent Suzuki−Miyaura, Mizoroki−Heck, and Stille coupling reactions in water. This is one of the highest catalytic activities ever reported for coupling reactions with water-soluble palladium catalysts in water. The catalytic ability of the palladacyclic aqua catalysts is drastically dependent on the pH of the solution and the structures of supporting ligands. The structures of palladacyclic aqua and chloro complexes were unequivocally determined by X-ray analysis.

Palladium‐Catalyzed Asymmetric Conjugate Addition of Arylboronic Acids to Heterocyclic Acceptors

“…The addition of mercury to a catalytic reaction is widely used to exclude catalysis by Pd-nanoparticles as the amalgation should only deactivate heterogenous metal particles. [12] For the conversion of chromone with phenylboronic acid in presence of 200 equiv of mercury, with respect to the catalyst, only a slight drop of the yield from 91% to 80% was observed, while the ee of 94% remained unaltered. Addition of mercury to the reaction of 3-Me-cyclohexenone and phenylboronic acid resulted in quantitative yield and a slightly reduced ee of 90% for addition product 2 , which is within error margins.…”

Suzuki–Miyaura cross-coupling reaction of aryl bromides catalyzed by palladium(II) pyridoxal hydrazone complexes

“…It is well established that palladium complexes containing triphenylphosphine group, which combine both good s-donor strength and a p-accepting capacity, always have a high catalytic activity in SuzukieMiyaura cross-coupling reactions [48,49]. Therefore we attempted to use one of our palladium(II) complex (3) as catalyst in SuzukieMiyaura reaction.…”

Triflyloxy-substituted carboranes as useful weakly coordinating anions

“…In at least one experiment, we observed production of Cs[HCB 11 Cl 9 (OTf) 2 ] as the dominant product with the triflyloxy (triflato) substituents apparently in the 35 7,12-positions as evidenced from an XRD study on a single crystal (Fig. 1).…”