Alexandr Shafir

Perfluoro-tagged, phosphine-free palladium nanoparticles supported on silica gel: application to alkynylation of aryl halides, Suzuki–Miyaura cross-coupling, and Heck reactions under aerobic conditions

The utilization of perfluoro-tagged palladium nanoparticles immobilized on fluorous silica gel through fluorous–fluorous interactions (Pdnp–A/FSG) or through covalent bonding to silica gel (Pdnp–B) in the alkynylation of aryl halides, in the Suzuki–Miyaura cross-coupling, as well as in the Heck reaction between methyl acrylate and aryl iodides is described. The reactions are carried out under aerobic and phosphine-free conditions with excellent to quantitative product yields in each case. The catalysts are easily recovered and reused several times without significant loss of activity. The alkynylation of aryl halides (under copper-free conditions) and the Suzuki–Miyaura cross-coupling are carried out in water. The Heck reaction of methyl acrylate with aryl iodides is best performed in MeCN. The utilization of Pdnp–B in the synthesis of 2,3-disubstituted indoles from 2-(alkynyl)trifluoroacetanilides and aryl halides is also reported.

Palladium nanoparticles supported on an organic-inorganic fluorinated hybrid material. Application to microwave-based heck reaction.

Phosphine-free palladium nanoparticles were embedded in a fluorous organic-inorganic hybrid material 6b prepared by the sol-gel process. The use of Pdn.6b in the Heck coupling reaction under microwave irradiation has been investigated. Recycling studies have shown that the catalyst can be readily recovered and reused several times without significant loss of activity. Reactions and recovery of the solid-supported palladium catalyst system can be carried out in the presence of air, without any particular precaution.

The Heck Reaction of Allylic Alcohols Catalyzed by Palladium Nanoparticles in Water: Chemoenzymatic Synthesis of (R)‐(−)‐Rhododendrol

The use of phosphine‐free perfluoro‐tagged palladium nanoparticles immobilized on fluorous silica gel (FSG), either through fluorous–fluorous interactions or covalent bonding, in the Heck reaction of aryl iodides with allylic alcohols under aerobic conditions in water is described. 4‐(4‐Methoxyphenyl)‐butan‐2‐one, an important fine chemical, is readily accessed by this procedure. A two‐step one‐pot process, involving a Heck reaction followed by an enantioselective enzyme‐catalyzed reduction, to form chiral alcohols is applied to the synthesis of (R)‐(−)‐rhododendrol. The palladium catalysts can be recycled several times, both in the Heck reaction and in the one‐pot chemoenzymatic process.

Reactions of N,N′,N″-trimethyl-1,4,7-triazacyclononane with butyllithium reagents

Treatment of N,N′,N″-trimethyl-1,4,7-triazacyclononane (Me3tacn) with a range of alkyllithiums led to metallation of the N-methyl groups and, in the case of tBuLi, to the formation of an unusual μ-tBu complex; the latter undergoes clean transmetallation with toluene to form a Me3tacn complex of benzyllithium.

An Alternative to the Classical α‐Arylation: The Transfer of an Intact 2‐Iodoaryl from ArI(O2CCF3)2

The α-arylation of carbonyl compounds is generally accomplished under basic conditions, both under metal catalysis and via aryl transfer from the diaryl λ(3)-iodanes. Here, we describe an alternative metal-free α-arylation using ArI(O2CCF3)2 as the source of a 2-iodoaryl group. The reaction is applicable to activated ketones, such as α-cyanoketones, and works with substituted aryliodanes. This formal C-H functionalization reaction is thought to proceed through a [3,3] rearrangement of an iodonium enolate. The final α-(2-iodoaryl)ketones are versatile synthetic building blocks.

Alkynylation of aryl halides with perfluoro-tagged palladium nanoparticles immobilized on silica gel under aerobic, copper- and phosphine-free conditions in water

The utilization of perfluoro-tagged palladium nanoparticles immobilized on fluorous silica gel through fluorous-fluorous interactions (Pd(np)-/FSG) or linked to silica gel by covalent bonds (Pd(np)-) in the alkynylation of terminal alkynes with aryl halides under aerobic, copper- and phosphine-free conditions in water, and their recovery and re-utilization, is described.

Zirconium complexes incorporating diaryldiamidoferrocene ligands: generation of cationic derivatives and polymerization activity towards ethylene and 1-hexene

Abstract Palladium-catalyzed coupling of ArX (ArX=MesBr, 2,6-dichloroiodobenzene and 9-bromonaphtalene) with 1,1′-diaminoferrocene afforded a series of substituted diamide ligands Fc(NHAr) 2 ( 1 ). A Zr-dibenzyl complex 2 of the mesityl-substituted ligand was synthesized using ZrBn 4 , and its ability to act as precatalyst for olefin polymerization was investigated. Abstraction of one benzyl group using B(C 6 F 5 ) 3 resulted in the zwitterionic species [LZrBn][BnB(C 6 F 5 ) 3 ] ( 3 ), which reacted slowly (approximately 30 min) with ethylene to afford the monoinsertion product [LZrCH 2 CH 2 CH 2 Ph][BnB(C 6 F 5 ) 3 ]. Further insertions of ethylene were slower and led, after 2 h, to the di- and tri-insertion products. Use of [Ph 3 C][B(C 6 F 5 ) 4 ] as an activator resulted in a competent 1-hexene polymerization catalyst affording high molecular weight poly-1-hexene with a PDI of 1.3–1.4.

Water-soluble metal nanoparticles with PEG-tagged 15-membered azamacrocycles as stabilizers

The synthesis of palladium, platinum and ruthenium nanoparticles stabilized by azamacrocycles bearing polyoxyethylenated chains has been achieved by decomposition of the corresponding organometallic precursors (Pd(dba)(2), Pt(2)(dba)(3) and Ru(COD)(COT)) under dihydrogen atmosphere, whereas gold and rhodium nanoparticles have been obtained in the presence of these ligands by reduction of HAuCl(4) and RhCl(3), respectively. The metal nanoparticles were characterized by several techniques including IR, NMR, UV-vis, HRTEM, ED, and elemental analysis. The Pd nanoparticles have been used as recoverable catalyst in Suzuki cross-coupling in aqueous medium.

Modulation by Amino Acids: Toward Superior Control in the Synthesis of Zirconium Metal-Organic Frameworks.

The synthesis of zirconium metal-organic frameworks (Zr MOFs) modulated by various amino acids, including l-proline, glycine, and l-phenylalanine, is shown to be a straightforward approach toward functional-group incorporation and particle-size control. High yields in Zr-MOF synthesis are achieved by employing 5 equivalents of the modulator at 120 °C. At lower temperatures, the method provides a series of Zr MOFs with increased particle size, including many suitable for single-crystal X-ray diffraction studies. Furthermore, amino acid modulators can be incorporated at defect sites in Zr MOFs with an amino acid/ligand ratio of up to 1:1, depending on the ligand structure and reaction conditions. The MOFs obtained through amino acid modulation exhibit an improved CO2 -capture capacity relative to nonfunctionalized materials.

Asymmetric synthesis of L-carbidopa based on a highly enantioselective α-amination.

A stereoselective synthesis of L-carbidopa in seven steps and 50% overall yield from commercial compounds is described. The key step involves a highly enantioselective α-amination reaction of an acyclic β-ketoester with di-tert-butyl azodicarboxylate induced by europium and (R,R)-diphenyl-pybox.