Cyclopropenylidene carbene ligands in palladium catalysed coupling reactions: carbene ligand rotation and application to the Stille reaction

Abstract

Reaction of [Pd(PPh(3))(4)] with 1,1-dichloro-2,3-diarylcyclopropenes gives complexes of the type cis-[PdCl(2)(PPh(3))(C(3)(Ar)(2))] (Ar = Ph 5, Mes 6). Reaction of [Pd(dba)(2)] with 1,1-dichloro-2,3-diarylcyclopropenes in benzene gave the corresponding binuclear palladium complexes trans-[PdCl(2)(C(3)(Ar)(2))](2) (Ar = Ph 7, p-(OMe)C(6)H(4)8, p-(F)C(6)H(4)9). Alternatively, when the reactions were performed in acetonitrile, the complexes trans-[PdCl(2)(NCMe)(C(3)(Ar)(2))] (Ar = Ph 10, p-(OMe)C(6)H(4)11 and p-(F)C(6)H(4)) 12) were isolated. Addition of phosphine ligands to the binuclear palladium complex 7 or acetonitrile adducts 11 and 12 gave complexes of the type cis-[PdCl(2)(PR(3))(C(3)(Ar)(2))] (Ar = Ph, R = Cy 13, Ar = p-(OMe)C(6)H(4), R = Ph 14, Ar = p-(F)C(6)H(4), R = Ph 15). Crystal structures of complexes 6·3.25CHCl(3), 10, 11·H(2)O and 12-15 are reported. DFT calculations of complexes 10-12 indicate the barrier to rotation about the carbene-palladium bond is very low, suggesting limited double bond character in these species. Complexes 5-9 were tested for catalytic activity in C-C coupling (Mizoroki-Heck, Suzuki-Miyaura and, for the first time, Stille reactions) and C-N coupling (Buchwald-Hartwig amination) showing excellent conversion with moderate to high selectivity.

Reactivity vs. Stability of Cyclopropenium Substituted Phosphonium Salts

“…To overcome the overly stabilizing effect of N i Pr 2 substituents on the cyclic structure, 1,2‐diarylcyclopropenes were then selected as alternative precursors . Treatment of 3,3‐dichloro‐1,2‐diphenylcyclopropene 3 with a stoichiometric amount of PPh 3 in CH 2 Cl 2 at room temperature afforded the corresponding 3‐triphenylphosphoniocyclopropene [ 5 ]Cl in 90 % yield (Schemeà).…”

M-CPOnes: Transition Metal Complexes with Cyclopropenone-Based Ligands for Light-Triggered Carbon Monoxide Release

“…[43][44][45][46][47][48] Cyclopropenones are appealing as prospective CORMs not only for their efficient photodecarbonylation but since they can be prepared via various synthetic methods (e.g. Friedel-Crafts reaction, [49][50][51][52][53] [2+1] cycloaddition and hydrolysis, 37,[54][55][56][57] Favorskii rearrangement 29,39,58,59 and substitution of cyclopropenone acetals [60][61][62][63] ). In addition, they are stable in aqueous media and cellular environments 45,47,64 and there is the potential to exploit multi-photon induced decarbonylation for carbon monoxide release at higher wavelengths (800-950 nm).…”

The synthesis of Nα-protected amino hydroxamic acids from Nα-protected amino acids employing versatile chlorinating agent CPI-Cl

“…CPI-Cl has been converted to cyclopropenylidene carbene complexe catalysts and employed for C-C bond formation reactions. 30,31 It was also used to chlorinate carboxylic acids 32 and alcohols. 33 It was found to catalyze Beckmann rearrangement to obtain amides/lactams from corresponding oximes.…”