Simple, Efficient Catalyst System for the Palladium-Catalyzed Amination of Aryl Chlorides, Bromides, and Triflates

Palladium complexes supported by (o-biphenyl)P(t-Bu)_2 (3) or (o-biphenyl)PCy_2 (4) are efficient catalysts for the catalytic amination of a wide variety of aryl halides and triflates. Use of ligand 3 allows for the room-temperature catalytic amination of many aryl chloride, bromide, and triflate substrates, while ligand 4 is effective for the amination of functionalized substrates or reactions of acyclic secondary amines. The catalysts perform well for a large number of different substrate combinations at 80−110 °C, including chloropyridines and functionalized aryl halides and triflates using 0.5−1.0 mol % Pd; some reactions proceed efficiently at low catalyst levels (0.05 mol % Pd). These ligands are effective for almost all substrate combinations that have been previously reported with various other ligands, and they represent the most generally effective catalyst system reported to date. Ligands 3 and 4 are air-stable, crystalline solids that are commercially available. Their effectiveness is believed to be due to a combination of steric and electronic properties that promote oxidative addition, Pd−N bond formation, and reductive elimination

Arene C−H Bond Activation and Arene Oxidative Coupling by Cationic Palladium(II) Complexes

N,N‘-Diaryl-α-diimine-ligated Pd(II) dimethyl complexes (^(tBu)2^(Ar)DAB^(Me))PdMe_2 and {(CF_3)_2^(Ar)DAB^(Me)}PdMe_2 {^(tBu)2^(Ar)DAB^(Me): ArNC═(CH_3)−C(CH_3═NAr, Ar=3,5-di-tert-butylphenyl; (CF_3)_2^(Ar)DAB^(Me):Ar = 3,5-bis(trifluoromethyl)phenyl} undergo protonolysis with HBF_4(aq) in trifluoroethanol (TFE) to form cationic complexes [(α-diimine)Pd(CH_3)(H_2O)][BF_4]. The cations activate benzene C−H bonds at room temperature. Kinetic analyses reveal trends similar to those observed for the analogous platinum complexes:  the C−H activation step is rate-determining (KIE = 4.1 ± 0.5) and is inhibited by H_2O. The kinetic data are consistent with a mechanism in which benzene substitution proceeds by a solvent- (TFE-) assisted associative pathway. Following benzene C−H activation under 1 atm O_2, the products of the reaction are biphenyl and a dimeric μ-hydroxide complex, [(α-diimine)Pd(OH)]_2[BF_4]_2. The Pd(0) formed in the reaction is reoxidized by O_2 to the dimeric μ-hydroxide complex after the oxidative C−C bond formation. The regioselectivity of arene coupling was investigated with toluene and α,α,α-trifluorotoluene as substrates

Palladium catalysis in the synthesis of polyaniline-related materials

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 1999.Includes bibliographical references (leaves 182-197).The palladium-catalyzed aryl amination reaction, in conjunction with an orthogonal protective group scheme, forms the basis of two routes to oligoaniline precursors. One method consists of a bidirectional chain growth from a symmetric core piece, whereas the other involves a divergent-convergent synthesis of nonsymmetric fragments, followed by coupling to a symmetric core fragment. The oligoaniline precursors are soluble in a variety of common organic solvents, and are easily converted to the deprotected oligoanilines. The method allows the preparation of odd or even chain lengths, as long as a 24-mer, and the incorporation of a variety of functional groups. The effects of chain length and substitution upon oligomer behavior have been investigated by electronic absorption spectroscopy and cyclic voltammetry. Certain aspects of aryl amination methodology, arising from or applicable to the synthesis of polyaniline derivatives, are described. Commercially available benzophenone imine serves as a convenient ammonia equivalent in the palladiumcatalyzed amination of aryl halides and triflates. The chelating ligand bis[2-(diphenylphosphino) phenyl] ether (DPEphos), in combination with palladium acetate, forms a highly active catalyst system for the coupling of anilines with aryl bromides. A modification in the experimental procedure for aryl amination allows the use of palladium chloride, the least expensive compound of palladium, as the palladium source. A new copper-mediated method has been developed for the synthesis of 2- (di-tert-butylphosphino)biphenyl, a versatile ligand developed by Wolfe and Buchwald for palladium-catalyzed cross-coupling reactions, on multigram scale. The use cf this ligand in aryl amination reactions is described. The synthetic methods for the synthesis of oligoanilines have been modified to afford a wider variety of polyaniline-related materials. The preparation of ringsubstituted monomers for incorporation into internally functionalized oligoanilines is described. The synthesis of protected polyaniline derivatives by step-growth polymerization or copolymerization of suitable monomers has been achieved. A new analogue of polyaniline, a poly(aminophenothiazine), has also been synthesized by palladium catalysis.by Joseph P. Sadighi.Ph.D

A Trigold(I) Ketenylidene Cation

An (N-heterocyclic carbene)­gold­(I) acetate reacts with acetic anhydride and triethylamine to form a ketenylidene-bridged trigold­(I) cation as its dihydrogen triacetate salt. Ion exchange with tetrafluoroborate affords a more stable compound. The cation reacts with borohydride to form (NHC)gold hydride and with benzenethiol to form (NHC)­gold benzenethiolate and <i>S</i>-phenyl thioacetate

Synthesis and Reactivity of New Copper(I) Hydride Dimers

The expanded-ring N-heterocyclic carbenes 6Dipp and 7Dipp (6Dipp = 1,3-bis­(2,6-diisopropylphenyl)-3,4,5,6-tetrahydropyrimidin-2-ylidene and 7Dipp = 1,3-bis­(2,6-diisopropylphenyl)-4,5,6,7-tetrahydro-1,3-diazepin-2-ylidene) support isolable neutral copper hydride dimers. [(6Dipp)­CuH]₂ reacts with 1-hexene to give (6Dipp)­copper­(I) hexyl by 1,2-insertion and with benzyl isonitrile to afford an η¹-formimidoyl by 1,1-insertion

Stable Mono- and Dinuclear Organosilver Complexes

A series of mononuclear and dinuclear complexes of silver­(I), supported by an N-heterocyclic carbene and bound to sp³-, sp²-, and sp-hybridized carbanions, has been synthesized. Synthetic routes include transmetalation from organozinc, organomagnesium, and organosilicon reagents, as well as the deprotonation of a terminal alkyne. These complexes exhibit greater thermal stability than typical organosilver reagents, permitting spectroscopic and structural characterization. The carbanion-bridged disilver cations feature three-center, two-electron bonding with short Ag···Ag distances. A mononuclear vinylsilver complex releases organic homocoupling products upon thermal decomposition, while mononuclear alkylsilver complexes exhibit nucleophilic behavior, for example, inserting CO₂ to form silver carboxylates