PubMed Health⌕ Search

Biomedical subjects

Steven P Nolan

Publications and source records attributed to Steven P Nolan.

At least 19 recordsLinked to original sources
PubMed2007

Copper-carbene complexes as catalysts in the synthesis of functionalized styrenes and aliphatic alkenes.

(NHC)-Cu (NHC = N-heterocyclic carbene) complexes efficiently catalyzed the methylenation of a variety of aliphatic and aromatic aldehydes and ketones in the presence of trimethylsilyldiazomethane, triphenylphosphine, and 2-propanol. The copper catalysts are not only inexpensive compared to rhodium complexes, but they also exhibit better functional group compatibility with aromatic aldehydes and ketones. Indeed very high yields were obtained for the formation of styrenes containing nitro, trifluoromethyl, amino, and ester groups, as well as for pyridine-, pyrrole-, and indole-substituted alkenes.

Journal Article↗
PubMed2006

(NHC)Copper(I)-catalyzed [3+2] cycloaddition of azides and mono- or disubstituted alkynes.

A versatile and highly efficient catalyst for the Huisgen cycloaddition reaction has been developed. Previously isolated or in situ generated azides yielded 1,2,3-triazoles with differently substituted alkynes in the presence of a [(NHC)CuBr] complex (NHC = N-heterocyclic carbene). Extremely high reaction rates and excellent yields were obtained in all cases. This catalytic system fulfils the requirements of "click chemistry" with its mild and convenient conditions, notably in water or solvent free reactions and simple isolation with no purification step. Furthermore, for the first time, an internal alkyne was successfully used in this copper-catalyzed cycloaddition reaction. DFT calculations on this particular system allowed for the proposition of a new mechanistic pathway for disubstituted alkynes.

Journal Article↗
PubMed2006

Rapid room temperature Buchwald-Hartwig and Suzuki-Miyaura couplings of heteroaromatic compounds employing low catalyst loadings.

The use of second-generation [(NHC)Pd(R-allyl)Cl] complexes for Suzuki-Miyaura and Buchwald-Hartwig cross-coupling reactions involving heteroaromatic halides at room temperature is reported. The first examples of room temperature Suzuki-Miyaura cross-coupling of deactivated aryl chlorides with alkenyl boronic acids are also disclosed. Terminal substitution at the allyl moiety of the palladium complex facilitates its activation at room temperature leading to very active catalytic species enabling the present catalytic transformations to be performed rapidly using very mild reaction conditions. Catalyst loadings can be as low as 10 ppm for the Buchwald-Hartwig aryl amination and 50 ppm for the Suzuki-Miyaura reaction.

Boronic Acids↗
PubMed2006

(IPr)Pd(acac)Cl: an easily synthesized, efficient, and versatile precatalyst for C-N and C-C bond formation.

A very straightforward synthesis of (IPr)Pd(acac)Cl from two commercially available starting materials, Pd(acac)2 and IPr.HCl [acac = acetylacetonate; IPr = N,N'-bis(2,6-diisopropylphenyl)imidazol-2-ylidene], has been developed. The resulting complex, (IPr)Pd(acac)Cl (1), has proven to be a highly active PdII precatalyst in the Buchwald-Hartwig and the alpha-ketone arylation reactions. A wide range of substrates has been screened, including unactivated, sterically hindered, and heterocyclic aryl chlorides.

Journal Article↗
PubMed2006

Modified (NHC)Pd(allyl)Cl (NHC = N-heterocyclic carbene) complexes for room-temperature Suzuki-Miyaura and Buchwald-Hartwig reactions.

A series of (NHC)Pd(R-allyl)Cl complexes [NHC: IPr = N,N'-bis(2,6-diisopropylphenyl)imidazol-2-ylidene, SIPr = N,N'-bis(2,6-diisopropylphenyl)-4,5-dihydroimidazol-2-ylidene; R = H, Me, gem-Me2, Ph] have been synthesized and fully characterized. When compared to (NHC)Pd(allyl)Cl, substitution at the terminal position of the allyl scaffold favors a more facile activation step. This translates into higher catalytic activity in the Suzuki-Miyaura and Buchwald-Hartwig reactions, allowing for the coupling of unactivated aryl chlorides at room temperature in minutes. In the Suzuki-Miyaura reaction, aryl triflates, bromides, and chlorides react with boronic acids using very low catalyst loading. In the N-aryl amination reaction, a wide range of substrates has been coupled efficiently; primary-, secondary-, alkyl-, or aryl-amines react in high yields with unactivated, neutral, and activated aryl chlorides and bromides. In both reactions, extremely hindered substrates such as tri-ortho-substituted biaryls and tetra-ortho-substituted diarylamines can be produced without loss of activity. Finally, the present catalytic system has proven to be efficient with as low as 10 parts-per-million (ppm) of precatalyst in the Buchwald-Hartwig reaction and 50 ppm in the Suzuki-Miyaura reaction.

Journal Article↗
PubMed2006

Suzuki-Miyaura, alpha-ketone arylation and dehalogenation reactions catalyzed by a versatile N-heterocyclic carbene-palladacycle complex.

[reaction: see text] The activity of the complex (IPr)PdCl(eta2-N,C-C12H7NMe2), 1 [IPr = (N,N'-bis(2,6-diisopropylphenyl)imidazol)-2-ylidene], in the Suzuki-Miyaura cross-coupling reaction involving unactivated aryl chlorides and triflates with arylboronic acids at room temperature in technical grade 2-propanol is described. These conditions allow for the synthesis of di- and tri-ortho-substituted biaryls in very short reaction times. This complex also displays very high activity for alpha-ketone arylation and dehalogenation reactions of activated and unactivated aryl chlorides.

Journal Article↗
PubMed2005

A simple and efficient copper-catalyzed procedure for the hydrosilylation of hindered and functionalized ketones.

The catalytic hydrosilylation of highly hindered and functionalized ketones is described. The combination of inexpensive catalyst precursors, CuCl and NHC.HX (NHC = N-heterocyclic carbene), leads to a highly efficient reduction mediator for the preparation of silyl ethers from unfunctionalized and functionalized alkyl, cyclic, bicyclic, aromatic, and heteroaromatic ketones. A series of catalyst precursors have been structurally characterized and a catalyst-structure activity relationship is discussed.

Journal Article↗
PubMed2005

Interaction of a bulky N-heterocyclic carbene ligand with Rh(I) and Ir(I). Double C-H activation and isolation of bare 14-electron Rh(III) and Ir(III) complexes.

Reactivity and structural studies of unusual rhodium and iridium systems bearing two N-heterocyclic carbene (NHC) ligands are presented. These systems are capable of intramolecular C-H bond activation and lead to coordinatively unsaturated 16-electron complexes. The resulting complexes can be further unsaturated by simple halide abstraction, leading to 14-electron species bearing an all-carbon environment. Saturation of the vacant sites in the 16- and 14-electron complexes with carbon monoxide permits a structural comparison. DFT calculations show that these electrophilic metal centers are stabilized by pi-donation of the NHC ligands.

Journal Article↗
PubMed2005

Steric and electronic properties of N-heterocyclic carbenes (NHC): a detailed study on their interaction with Ni(CO)4.

N-heterocyclic carbene ligands IMes (1), SIMes (2), IPr (3), SIPr (4), and ICy (5) react with Ni(CO)(4) to give the saturated tricarbonyl complexes Ni(CO)(3)(IMes) (8), Ni(CO)(3)(SIMes) (9), Ni(CO)(3)(IPr) (10), Ni(CO)(3)(SIPr) (11), and Ni(CO)(3)(ICy) (12), respectively. The electronic properties of these complexes have been compared to their phosphine analogues of general formula Ni(CO)(3)(PR(3)) by recording their nu(CO) stretching frequencies. While all of these NHCs are better donors than tertiary phosphines, the differences in donor properties between ligands 1-5 are surprisingly small. Novel, unsaturated Ni(CO)(2)(IAd) (13) and Ni(CO)(2)(I(t)()Bu) (14) compounds are obtained from the reaction of Ni(CO)(4) with IAd (6) and I(t)()Bu (7). Complexes 13 and 14 are highly active toward substitution of the NHC as well as the carbonyl ligands. This has allowed the determination of Ni-C(NHC) bond dissociation energies and the synthesis of various unsaturated Ni(0) and Ni(II) complexes. Computational studies on compounds 8-14 are in line with the experimental findings and show that IAd (6) and I(t)()Bu (7) are more bulky than IMes (1), SIMes (2), IPr (3), SIPr (4), and ICy (5). Furthermore, a method based on %V(bur) values has been developed for the direct comparison of steric requirements of NHCs and tertiary phosphines. Complexes 8-14, as well as NiCl(C(3)H(5))(I(t)()Bu) (16) and NiBr(C(3)H(5))(I(t)()Bu) (17), have been characterized by X-ray crystallography.

Journal Article↗
PubMed2005

Olefin metathesis route to antiviral nucleosides.

The success of the early nucleoside agents, the toxicity and metabolic instability of many nucleoside analogues and the effects of viral pathogens on public health are driving the design, synthesis and evaluation of new nucleoside analogues. In this context, a powerful reaction has emerged over the past decade that has fundamentally changed the outlook on nucleoside chemistry: the olefin metathesis reaction. This review is designed to give an overview of the synthesis of some nucleosides of biological interest, according to their structural types (e.g., neplanocins and aristeromycin analogues, 2',3'-unsaturated nucleoside analogues, and acyclonucleosides), using metathesis reactions by employing either the alkoxy imido molybdenum catalyst developed by Schrock and various ruthenium carbene catalysts developed by Grubbs, Hoveyda-Grubbs and Nolan.

Alkenes↗