Jeffrey L. Petersen

Triazole-Au(I) complexes: a new class of catalysts with improved thermal stability and reactivity for intermolecular alkyne hydroamination.

A series of 1,2,3-triazole-bound cationic Au(I) catalysts have been synthesized, and their structures have been characterized by X-ray crystallography. Variable-temperature NMR studies revealed dynamic triazole-Au cation coordination in solution. Reaction profiles clearly indicated that these new catalysts possess much better thermal stability than literature-reported Au catalysts, including IPrAu x NTf(2). By application of these catalysts, challenging intermolecular hydroaminations were achieved with less-reactive internal alkynes and unprotected aliphatic amines, giving excellent yields with low catalyst loading.

N,N-addition of frustrated Lewis pairs to nitric oxide: an easy entry to a unique family of aminoxyl radicals.

The intramolecular cyclohexylene-bridged P/B frustrated Lewis pair [Mes(2)P-C(6)H(10)-B(C(6)F(5))(2)] 1b reacts rapidly with NO to give the persistent FLP-NO aminoxyl radical 2b formed by P/B addition to the nitrogen atom of NO. This species was fully characterized by X-ray diffraction, EPR and UV/vis spectroscopies, C,H,N elemental analysis, and DFT calculations. The reactive oxygen-centered radical 2b undergoes a H-atom abstraction (HAA) reaction with 1,4-cyclohexadiene to give the diamagnetic FLP-NOH product 3b. FLP-NO 2b reacts with toluene at 70 °C in an HAA/radical capture sequence to give a 1:1 mixture of FLP-NOH 3b and FLP-NO-CH(2)Ph 4b, both characterized by X-ray diffraction. Structurally related FLPs [Mes(2)P-CHR(1)-CHR(2)-B(C(6)F(5))(2)] 1c, 1d, and 1e react analogously with NO to give the respective persistent FLP-NO radicals 2c, 2d, and 2e, respectively, which show similar HAA and O-functionalization reactions. The FLP-NO-CHMePh 6b derived from 1-bromoethylbenzene undergoes NO-C bond cleavage at 120 °C with an activation energy of E(a) = 35(2) kcal/mol. Species 6b induces the controlled nitroxide-mediated radical polymerization (NMP) of styrene at 130 °C to give polystyrene with a polydispersity index of 1.3. The FLP-NO systems represent a new family of aminoxyl radicals that are easily available by N,N-cycloaddition of C(2)-bridged intramolecular P/B frustrated Lewis pairs to nitric oxide.

Efficient Synthesis of N-2-Aryl-1,2,3-Triazole Fluorophores via Post-Triazole Arylation

Efficient post-triazole regioselective N-2 arylation was developed from C-4, C-5 disubstituted-1,2,3-NH-triazoles. Three different approaches had been investigated, including S(N)Ar, Cu(I) catalyzed aryl amidation and Cu(II) mediated boronic acid coupling. The N-2-aryl triazoles were successfully synthesized with excellent yields. The structures were characterized by X-ray crystallography and some N-2-triazole products gave strong fluorescence with various emission controlled by the C-5 groups.

Iron-Catalyzed C−O Bond Activation for the Synthesis of Propargyl-1,2,3-triazoles and 1,1-Bis-triazoles

The FeCl(3)-catalyzed triazole propargylation was developed. This transformation was suitable for a large scope of substituted propargyl alcohols, giving the corresponding propargyl triazoles in excellent yields (up to 96%). Further derivatization produced the 1,1-bis-triazoles in excellent yields and regioselectivity, which could be applied as potential transition metal ligands or new reagents.

Gold‐Catalyzed Intermolecular CS Bond Formation: Efficient Synthesis of α‐Substituted Vinyl Sulfones

A general method for the synthesis of α-substituted vinyl sulfones makes use of a combination of a triazole gold complex and gallium triflate. This efficient CS bond formation between simple terminal alkynes and sulfinic acids provides access to various α-substituted vinyl sulfones.

Enantioselective Intermolecular Crossed‐Conjugate Additions between Nitroalkenes and α,β‐Enals through a Dual Activation Strategy

Double the fun: The title reaction was developed by using a Lewis base/iminium activation strategy (see scheme). The reaction proceeded with excellent yields and ee values, and the products were additionally transformed into a single enantiomer of a substituted pyrrolidine with excellent retention of configuration.

Ligand-Assisted Gold-Catalyzed Cross-Coupling with Aryldiazonium Salts: Redox Gold Catalysis without an External Oxidant†

Gold-catalyzed C(sp)-C(sp(2)) and C(sp(2))-C(sp(2)) cross-coupling reactions are accomplished with aryldiazonium salts as the coupling partner. With the assistance of bpy ligand, gold(I) species were oxidized to gold(III) by diazonium without any external oxidants. Monitoring the reaction with NMR and ESI-MS provided strong evidence for the nitrogen extrusion followed by Au(III) reductive elimination as the key step.

1,2,3-Triazole: Unique Ligand in Promoting Iron-Catalyzed Propargyl Alcohol Dehydration

A 1,2,3-traizole-promoted iron(III)-catalyzed propargyl alcohol dehydration was developed for the synthesis of conjugated enynes. The desired conjugated enynes were prepared in good to excellent yields (up to 95%) with a large substrate scope and excellent stereoselectivity (only Z-isomers).

N-2-Aryl-1,2,3-triazoles: A Novel Class of UV/Blue-Light-Emitting Fluorophores with Tunable Optical Properties

The N-2-aryl-1,2,3-triazole derivatives (NATs) were developed as a new class of UV/blue-light-emitting fluorophores. Though both N-1-aryl-1,2,3-triazoles and N-2-aryl-1,2,3-triazoles gave strong photo absorption under excitation at 330 nm, only the N-2-analogous showed strong fluorescence emission in the UV/blue range with high efficiency in various solvents (quantum yield Φ around 0.3-0.5). Significant substituted group effects were observed, allowing tunable optical properties with emission (λ(max)) from 350-400 nm and Stokes shift from 38-93 nm. The computational studies along with X-ray crystal structures indicated the significance of the effective conjugation between triazole ring and aryl groups on the N-2 position. The planar intramolecular charge transfer (PICT) mechanism was proposed, which was supported by solvent effect studies. Simple derivatizations gave NAT-modified lysine and strong UV/blue emitting bis-NAT (Φ=0.76, λ(max)=390), which suggested the great potential of this new class of fluorophores in biological and material science research.

Remarkable coordination behavior of alkyl isocyanides toward unsaturated vicinal frustrated P/B Lewis pairs

The conjugated frustrated phosphane/borane Lewis pairs formed by 1,1-carboboration of a substituted diphenylphosphino acetylene, undergo a synergistic 1,1-addition reaction to n-butyl isocyanide with formation of new B–C and P–C bonds to the former isonitrile carbon atom. Using tert-butyl isocyanide dynamic behaviour between the isocyanide–[B] adduct and the 1,1-addition product formation was observed in solution. The different modes of isocyanide binding to the FLPs in the solid state were characterized using X-ray crystal structure analyses and comprehensive 11B and 31P solid-state magic-angle-spinning (MAS-) NMR experiments. The free FLP, the Lewis adduct at the borane group, and the cyclic product resulting from isocyanide addition to both reaction centers, can be differentiated via11B and 31P isotropic chemical shifts, 11B nuclear electric quadrupole coupling constants, isotropic indirect 11B–31P spin–spin coupling constants, and 11B⋯31P internuclear distances measured by rotational echo double resonance.