Aza-Claisen Rearrangement in the Cyclization Reactions of Nitrogen-Containing Enynes via Ruthenium Vinylidene Complexes

The cyclization reaction of several diallyl aromatic amine molecules, each containing an ethynyl group at the ortho position of the aromatic ring, is accompanied by an aza-Claisen rearrangement, causing an allyl group migration to give substituted indole compounds. This cyclization is catalyzed by ruthenium triphenylphosphine and diphenylphosphinoethane (dppe) complexes as well as gold complexes with silver reagent. The less sterically crowded dppe complex is a more efficient catalyst. The mechanism involving a vinylidene intermediate is proposed on the basis of isolation of several intermediates in the ruthenium-catalyzed system. Single crystals of a metal complex with the cyclized ligand were obtained, and the structure was determined by an X-ray diffraction analysis

Initiation Steps for the Polymerization of Vinyl Ethers Promoted by Cationic Palladium Aqua Complexes

Both deuterium-labeled experimental and NMR spectroscopic analyses of poly(vinyl ether) offer the mechanistic insight into the polymerization, indicating that the cationic palladium aqua imine−phosphine complexes [(P∼N)PdMe(H2O)]BF4 (P∼N = o-C6H4(PPh2)(NCHAr)) promote the reaction via proton-transfer initiation. Insertion of vinyl ether into the Pd−Me bond in [(P∼N)PdMe(H2O)]BF4 does not proceed, but the single insertion of the same substrate into the Pd−acetal bond of [(P∼N)PdCOCH3(L)]BF4 provides the stable inserted product [(P∼N)PdCH(OEt)CH2COCH3]BF4, which has been characterized by an X-ray structural determination. However, these palladium complexes do not catalyze the polymerization or copolymerization of vinyl ether and carbon monoxide

Initiation Steps for the Polymerization of Vinyl Ethers Promoted by Cationic Palladium Aqua Complexes

Both deuterium-labeled experimental and NMR spectroscopic analyses of poly(vinyl ether) offer the mechanistic insight into the polymerization, indicating that the cationic palladium aqua imine−phosphine complexes [(P∼N)PdMe(H2O)]BF4 (P∼N = o-C6H4(PPh2)(NCHAr)) promote the reaction via proton-transfer initiation. Insertion of vinyl ether into the Pd−Me bond in [(P∼N)PdMe(H2O)]BF4 does not proceed, but the single insertion of the same substrate into the Pd−acetal bond of [(P∼N)PdCOCH3(L)]BF4 provides the stable inserted product [(P∼N)PdCH(OEt)CH2COCH3]BF4, which has been characterized by an X-ray structural determination. However, these palladium complexes do not catalyze the polymerization or copolymerization of vinyl ether and carbon monoxide

N,N′-Dialkylation Catalyzed by Bimetallic Iridium Complexes Containing a Saturated Bis-N-Heterocyclic Carbene (NHC) Ligand

Reaction of the bis-aminophosphinimine [<i>m</i>-C₆H₄(HNCH₂CH₂NPPh₃)] with W­(CO)₆ afforded [<i>m</i>-C₆H₄{(CNCH₂CH₂NH)­W­(CO)₅}₂] (<b>2</b>), which underwent N-alkylation with benzyl bromide to yield [<i>m</i>-C₆H₄{(CNCH₂CH₂NCH₂Ph)­W­(CO)₅}₂] (<b>3</b>). A carbene transfer reaction from W(0) to Ir­(I) proceeded smoothly via the reaction of <b>3</b> with [Ir­(COD)­Cl]₂ under mild conditions to give the diiridium­(I) carbene complex [<i>m</i>-C₆H₄{(CNCH₂CH₂NH)­Ir­(CO)₂Cl}₂] (<b>4</b>). Ligand substitution of <b>4</b> with an excess of PPh₃ produced the phosphine complex <b>5</b>. All complexes have been characterized by spectroscopic and elemental analyses. Complexes <b>2</b> and <b>5</b> were further confirmed by X-ray diffraction studies. Complex <b>4</b> is an efficient catalyst for the reductive N,N′-dialkylation of phenylenediamines with alcohols. The mechanistic pathway of the catalysis involving the possible synergistic effect between two metal centers is discussed

N,N′-Dialkylation Catalyzed by Bimetallic Iridium Complexes Containing a Saturated Bis-N-Heterocyclic Carbene (NHC) Ligand

Reaction of the bis-aminophosphinimine [<i>m</i>-C₆H₄(HNCH₂CH₂NPPh₃)] with W­(CO)₆ afforded [<i>m</i>-C₆H₄{(CNCH₂CH₂NH)­W­(CO)₅}₂] (<b>2</b>), which underwent N-alkylation with benzyl bromide to yield [<i>m</i>-C₆H₄{(CNCH₂CH₂NCH₂Ph)­W­(CO)₅}₂] (<b>3</b>). A carbene transfer reaction from W(0) to Ir­(I) proceeded smoothly via the reaction of <b>3</b> with [Ir­(COD)­Cl]₂ under mild conditions to give the diiridium­(I) carbene complex [<i>m</i>-C₆H₄{(CNCH₂CH₂NH)­Ir­(CO)₂Cl}₂] (<b>4</b>). Ligand substitution of <b>4</b> with an excess of PPh₃ produced the phosphine complex <b>5</b>. All complexes have been characterized by spectroscopic and elemental analyses. Complexes <b>2</b> and <b>5</b> were further confirmed by X-ray diffraction studies. Complex <b>4</b> is an efficient catalyst for the reductive N,N′-dialkylation of phenylenediamines with alcohols. The mechanistic pathway of the catalysis involving the possible synergistic effect between two metal centers is discussed

Coupling Reactions of <i>N</i>‑Propargyl Semi-Salen Compounds Induced by Ruthenium Complex

The coupling reaction of N-propargyl semi-salen compound 1d on [Ru]-Cl ([Ru] = Cp­(PPh3)2Ru) generates the carbene complex 3d containing a substituted 2H-chromene unit in 7 d. The precursor vinylidene complex 2d is isolated from the reaction of the propargyl group of 1d with [Ru]-Cl in 12 h. Addition of an o-cresol moiety to Cα and Cβ of the vinylidene ligand of 2d takes place in a longer reaction time to yield 3d. Reactions of [Ru]-Cl with other analogous compounds 1a, 1b, and 1c, in excess, also afford carbene complexes 3a, 3b, and 3c, respectively, in 48 h via a similar coupling process. Their precursor vinylidene complexes 2a, 2b, and 2c are also observed in 12 h. Structures of 2 and 3 are determined on the basis of spectroscopic data. The solid state structure of the dppe analogue 3a′ is further confirmed by X-ray diffraction analysis. The added o-cresol part comes from compounds 1, instead of aldehyde which is confirmed by the cross-coupling reactions of 2 and 1 using mass spectrometry. For comparison, treatment of [Ru]Cl with the amine analogue 13b retaining the propargyl and phenol moieties yields no coupling product

Synthesis of Iridium Pyridinyl N-Heterocyclic Carbene Complexes and Their Catalytic Activities on Reduction of Nitroarenes

Coordination of iridium(I) metal ions with a pyridinyl imidazol-2-ylidene ligand (pyN∧C-R) [R = Me, mesityl(2,4,6-trimethylphenyl)] that processes bulky substituents has been investigated. The iridium carbene complexes [(C-pyN∧C-R)IrCl(COD)] (COD = 1,5-cyclooctadiene) are prepared via transmetalation from the corresponding silver carbene complexes. Upon the abstraction of chloride, the chelation of pyN∧C becomes feasible, resulting in the formation of [C,N-(pyN∧C-R)Ir(COD)](BF4) (4). The coordinated COD of complex 4 can be replaced by carbon monoxide to yield the corresponding carbonyl species [C,N-(pyN∧C-R)Ir(CO)2](BF4). The labile nature of the pyridinyl nitrogen donor is readily replaced by acetonitrile, as is evidenced by the NMR study. All iridium complexes show catalytic activity on the hydrogen-transfer reduction of carbonyl and nitro functionalities. By manipulation of the reaction conditions, the iridium-catalyzed reduction of nitroarenes can selectively provide aniline or azo compounds as the desired product

Coupling Reactions of <i>N</i>‑Propargyl Semi-Salen Compounds Induced by Ruthenium Complex

The coupling reaction of <i>N</i>-propargyl semi-salen compound <b>1d</b> on [Ru]-Cl ([Ru] = Cp­(PPh₃)₂Ru) generates the carbene complex <b>3d</b> containing a substituted 2<i>H</i>-chromene unit in 7 d. The precursor vinylidene complex <b>2d</b> is isolated from the reaction of the propargyl group of <b>1d</b> with [Ru]-Cl in 12 h. Addition of an <i>o</i>-cresol moiety to Cα and Cβ of the vinylidene ligand of <b>2d</b> takes place in a longer reaction time to yield <b>3d</b>. Reactions of [Ru]-Cl with other analogous compounds <b>1a</b>, <b>1b</b>, and <b>1c</b>, in excess, also afford carbene complexes <b>3a</b>, <b>3b</b>, and <b>3c</b>, respectively, in 48 h via a similar coupling process. Their precursor vinylidene complexes <b>2a</b>, <b>2b</b>, and <b>2c</b> are also observed in 12 h. Structures of <b>2</b> and <b>3</b> are determined on the basis of spectroscopic data. The solid state structure of the dppe analogue <b>3a′</b> is further confirmed by X-ray diffraction analysis. The added <i>o</i>-cresol part comes from compounds <b>1</b>, instead of aldehyde which is confirmed by the cross-coupling reactions of <b>2</b> and <b>1</b> using mass spectrometry. For comparison, treatment of [Ru]Cl with the amine analogue <b>13b</b> retaining the propargyl and phenol moieties yields no coupling product

Synthesis of Iridium Pyridinyl N-Heterocyclic Carbene Complexes and Their Catalytic Activities on Reduction of Nitroarenes

Coordination of iridium(I) metal ions with a pyridinyl imidazol-2-ylidene ligand (pyN∧C-R) [R = Me, mesityl(2,4,6-trimethylphenyl)] that processes bulky substituents has been investigated. The iridium carbene complexes [(C-pyN∧C-R)IrCl(COD)] (COD = 1,5-cyclooctadiene) are prepared via transmetalation from the corresponding silver carbene complexes. Upon the abstraction of chloride, the chelation of pyN∧C becomes feasible, resulting in the formation of [C,N-(pyN∧C-R)Ir(COD)](BF4) (4). The coordinated COD of complex 4 can be replaced by carbon monoxide to yield the corresponding carbonyl species [C,N-(pyN∧C-R)Ir(CO)2](BF4). The labile nature of the pyridinyl nitrogen donor is readily replaced by acetonitrile, as is evidenced by the NMR study. All iridium complexes show catalytic activity on the hydrogen-transfer reduction of carbonyl and nitro functionalities. By manipulation of the reaction conditions, the iridium-catalyzed reduction of nitroarenes can selectively provide aniline or azo compounds as the desired product

Synthesis of Iridium Pyridinyl N-Heterocyclic Carbene Complexes and Their Catalytic Activities on Reduction of Nitroarenes

Coordination of iridium(I) metal ions with a pyridinyl imidazol-2-ylidene ligand (pyN∧C-R) [R = Me, mesityl(2,4,6-trimethylphenyl)] that processes bulky substituents has been investigated. The iridium carbene complexes [(C-pyN∧C-R)IrCl(COD)] (COD = 1,5-cyclooctadiene) are prepared via transmetalation from the corresponding silver carbene complexes. Upon the abstraction of chloride, the chelation of pyN∧C becomes feasible, resulting in the formation of [C,N-(pyN∧C-R)Ir(COD)](BF4) (4). The coordinated COD of complex 4 can be replaced by carbon monoxide to yield the corresponding carbonyl species [C,N-(pyN∧C-R)Ir(CO)2](BF4). The labile nature of the pyridinyl nitrogen donor is readily replaced by acetonitrile, as is evidenced by the NMR study. All iridium complexes show catalytic activity on the hydrogen-transfer reduction of carbonyl and nitro functionalities. By manipulation of the reaction conditions, the iridium-catalyzed reduction of nitroarenes can selectively provide aniline or azo compounds as the desired product