Bulky triarylarsines are effective ligands for palladium catalysed Heck olefination

Abstract

The four arsines, As{C6H3(o-CH3)(p-Z)}3{Z=H (2a) or OMe (2b)} and As{C6H3(o-CHMe2)(p-Z)}3{Z=H (2c) or OMe (2d)} react with [PdCl2(NCPh)2] or [PtCl2(NCBu(t))2] to give trans-[MCl2L2] or trans-[M2Cl2(mu-Cl)2L2]. The crystal structures of trans-[PdCl2(2a)2] and [PtCl2(2d)2] have been determined, the latter as its dichloromethane solvate. The structures show that in these complexes, the ligands adopt gga type conformations as do all analogous tri-o-tolyl- and tri-o-isopropylphenylphosphines in square-planar and octahedral complexes. The variable-temperature NMR behaviour of the complexes shows that they are fluxional due to restricted As-C bond rotation. The rate of the fluxionality is more rapid than in the analogous phosphine complexes and this is associated with longer As-C and As-M bonds allowing more free movement. The catalytic activity of the palladium complexes of the arsines and their phosphine analogues for the reaction of 4-bromoacetophenone and n-butyl acrylate has been screened. The results show that the arsines are generally superior to the phosphines as ligands for this catalysis. Tri(o-isopropylphenyl)phosphine and tri(o-isopropylphenyl)arsine are superior to tri-o-tolylphosphine as ligands for this Heck reaction and a p-methoxy substituent improves the arsine catalyst but not the phosphine catalyst. The phosphine catalysts are superior to the arsine catalysts for the reaction of 4-chloroacetophenone and n-butyl acrylate. These observations are discussed in the context of ligand stereoelectronic effects, as measured by the Tolman electronic parameter, nuCO of the [NiL(CO)3]{L=AsAr3 or PAr3}.

Bulky Monodentate Biphenylarsine Ligands: Synthesis and Evaluation of Their Structure Effects in the Palladium‐Catalyzed Heck Reaction

“…With the set of biphenyl‐based arsine ligands to hand, and in view of the high performances of bulky triarylarsine ligands in the Heck reaction,10,25 this coupling reaction was selected as a model system for evaluation of the catalytic activity of biphenylarsine ligands. To determine the performance of these ligands, the challenging Heck reaction between p ‐bromotoluene ( 5a ) and styrene ( 6a ) was chosen as the model reaction (Figure 1).…”

“…Arsines are known to have coordination modes similar to those of phosphines; however, they are recognized to be poorer σ‐donors than phosphines, and this leads to contrasting steric and electronic effects on coordination spheres different from those of phosphines. Pringle and co‐workers investigated the catalytic activity of Pd complexes of a series of bulky arsine ligands, exploring their stereoelectronic effects 25. They established that Pd‐arsine complexes were generally more active in the Heck reaction than analogous complexes resulting from phosphine.…”

Novel Enantioselective Synthesis of Functionalized Pyridylarsanes by a Chiral Palladium Template Promoted Asymmetric Hydroarsanation Reaction

“…Tertiary arsanes have been reported to be more appropriate ligands than phosphanes in a number of transition metal-catalyzed organic reactions, for example, Stille [1] and Heck reactions, [2] hydroformylation, [3] Suzuki-Miyaura coupling reaction, [4] carbonylation, [5] norbornene polymerization [6] and Wittig-type olefination of aldehydes. [7] Although several chiral arsane compounds have been used in asymmetric catalytic reactions, [8] these earlier studies have not involved optically active pyridylarsanes, which would provide a variety of applications in asymmetric catalysis as shown by their phosphorus analogues.…”

Synthesis of poly(vinylene‐arsine)s‐stabilized silver nanoparticles

“…Because 1 has arsenic atoms in the backbone, the transition metal can coordinate directly towards its backbone, and connection of transition metals can be expected. In some reports, organoarsenic compounds have been reported to be superior ligands 2–5. For example, osmium complexes with the arsenic ligands exhibited phosphorescence with greater quantum yields.…”