Structural Influence on the Photochromic Response of a Series of Ruthenium Mononitrosyl Complexes

In mononitrosyl complexes of transition metals two long-lived metastable states corresponding to linkage isomers of the nitrosyl ligand can be induced by irradiation with appropriate wavelengths. Upon irradiation, the N-bound nitrosyl ligand (ground state, GS) turns into two different conformations: isonitrosyl O bound for the metastable state 1 (MS1) and a side-on nitrosyl conformation for the metastable state 2 (MS2). Structural and spectroscopic investigations on [RuCl­(NO)­py₄]­(PF₆)₂·1/2H₂O (py = pyridine) reveal a nearly 100% conversion from GS to MS1. In order to identify the factors which lead to this outstanding photochromic response we study in this work the influence of counteranions, trans ligands to the NO and equatorial ligands on the conversion efficiency: [RuX­(NO)­py₄]­Y₂·<i>n</i>H₂O (X = Cl and Y = PF₆^– (<b>1</b>), BF₄^– (<b>2</b>), Br^–(<b>3</b>), Cl^– (<b>4</b>); X = Br and Y = PF₆^– (<b>5</b>), BF₄^– (<b>6</b>), Br^–(<b>7</b>)) and [RuCl­(NO)­bpy₂]­(PF₆)₂ (<b>8</b>), [RuCl₂(NO)­tpy]­(PF₆) (<b>9</b>), and [Ru­(H₂O)­(NO)­bpy₂]­(PF₆)₃ (<b>10</b>) (bpy = 2,2′-bipyridine; tpy = 2,2′:6′,2″-terpyridine). Structural and infrared spectroscopic investigations show that the shorter the distance between the counterion and the NO ligand the higher the population of the photoinduced metastable linkage isomers. DFT calculations have been performed to confirm the influence of the counterions. Additionally, we found that the lower the donating character of the ligand trans to NO the higher the photoconversion yield

CH Bond Activation of Unsaturated Hydrocarbons by a Niobium Methyl Cyclopropyl Precursor. Cyclopropyl Ring Opening and Alkyne Coupling Reaction

The transient intermediate η²-cyclopropene/bicyclobutane niobium complex [Tp^Me2Nb­(η²-<i>c</i>-C₃H₄)­(MeCCMe)] <b>A</b>, generated by an intramolecular β-H abstraction of methane from the methyl cyclopropyl complex [Tp^Me2NbMe­(<i>c</i>-C₃H₅)­(MeCCMe)] (<b>1</b>), is able to cleave the CH bond of a variety of unsaturated hydrocarbons RH in a selective manner to give the corresponding hydrocarbyl complexes [Tp^Me2NbR­(<i>c</i>-C₃H₅)­(MeCCMe)] (R = 2-furyl, 2-thienyl, 1-alkynyl, 1-cyclopentenyl, 1-ferrocenyl (Fc), pentafluorophenyl). The activation of the C–H bond occurs stereospecifically via a 1,3-CH addition across the Nb­(η²-cyclopropene) bond of <b>A</b>. Full characterization of several of these complexes includes multinuclear NMR spectroscopy, X-ray diffraction, UV/vis spectroscopy, and electrochemical data. A charge transfer between the ferrocenyl moiety and the niobium center is responsible for the characteristic purple color of the bimetallic complex [Tp^Me2NbFc­(<i>c</i>-C₃H₅)­(MeCCMe)]. The reactivity of these complexes with benzene follows qualitatively the strength and the p<i>K</i>_a of the CH bond that is cleaved. The pentafluorophenyl complex [Tp^Me2Nb­(C₆F₅)­(<i>c</i>-C₃H₅)­(MeCCMe)] undergoes cyclopropyl ring opening and alkyne coupling to give two isomeric η⁴-butadienyl complexes, with [Tp^Me2Nb­(C₆F₅)­(η⁴-CMeCMeCHCHMe)] as the major isomer

Structural Influence on the Photochromic Response of a Series of Ruthenium Mononitrosyl Complexes

In mononitrosyl complexes of transition metals two long-lived metastable states corresponding to linkage isomers of the nitrosyl ligand can be induced by irradiation with appropriate wavelengths. Upon irradiation, the N-bound nitrosyl ligand (ground state, GS) turns into two different conformations: isonitrosyl O bound for the metastable state 1 (MS1) and a side-on nitrosyl conformation for the metastable state 2 (MS2). Structural and spectroscopic investigations on [RuCl­(NO)­py₄]­(PF₆)₂·1/2H₂O (py = pyridine) reveal a nearly 100% conversion from GS to MS1. In order to identify the factors which lead to this outstanding photochromic response we study in this work the influence of counteranions, trans ligands to the NO and equatorial ligands on the conversion efficiency: [RuX­(NO)­py₄]­Y₂·<i>n</i>H₂O (X = Cl and Y = PF₆^– (<b>1</b>), BF₄^– (<b>2</b>), Br^–(<b>3</b>), Cl^– (<b>4</b>); X = Br and Y = PF₆^– (<b>5</b>), BF₄^– (<b>6</b>), Br^–(<b>7</b>)) and [RuCl­(NO)­bpy₂]­(PF₆)₂ (<b>8</b>), [RuCl₂(NO)­tpy]­(PF₆) (<b>9</b>), and [Ru­(H₂O)­(NO)­bpy₂]­(PF₆)₃ (<b>10</b>) (bpy = 2,2′-bipyridine; tpy = 2,2′:6′,2″-terpyridine). Structural and infrared spectroscopic investigations show that the shorter the distance between the counterion and the NO ligand the higher the population of the photoinduced metastable linkage isomers. DFT calculations have been performed to confirm the influence of the counterions. Additionally, we found that the lower the donating character of the ligand trans to NO the higher the photoconversion yield

Highly Fluorinated Aryl-Substituted Tris(indazolyl)borate Thallium Complexes: Diverse Regiochemistry at the B–N Bond

The synthesis and characterization (mainly by ¹⁹F NMR and X-ray diffraction) of highly fluorinated aryl-4,5,6,7-tetrafluoroindazoles and their corresponding thallium hydrotris­(indazolyl)­borate complexes are reported [aryl = phenyl, pentafluorophenyl, 3,5-dimethylphenyl, 3,5-bis­(trifluoromethyl)­phenyl]. Thanks to N–H···N hydrogen bonds, the indazoles crystallize as dimers that pack differently depending on the nature of the aryl group. The thallium hydrotris­(indazolyl)­borate complexes Tl­[Fn-Tp^4Bo,3aryl] resulting from the reaction of aryl-4,5,6,7-tetrafluoroindazoles [aryl = phenyl, 3,5-dimethylphenyl, 3,5-bis­(trifluoromethyl)­phenyl] with thallium borohydride adopt overall <i>C</i>_3<i>v</i> symmetry with the indazolyl groups bound to boron via their N-1 nitrogen in a conventional manner. When the perfluorinated pentaphenyl-4,5,6,7-tetrafluoroindazole is reacted with thallium borohydride, a single regioisomer of <i>C</i>_<i>s</i> symmetry having one indazolyl ring bound to boron via its N-2 nitrogen, TlHB­(3-pentafluorophenyl-4,5,6,7-tetrafluoroindazol-1-yl)₂(3-pentafluorophenyl-4,5,6,7-tetrafluoroindazol-2-yl) Tl­[F27-Tp^(4Bo,3C6F5)*], is obtained for the first time. Surprisingly, the perfluorinated dihydrobis­(indazolyl)­borate complex Tl­[F₁₈-Bp^3Bo,3C6F5], an intermediate on the way to the hydrotris­(indazolyl)­borate complex, has <i>C</i>_<i>s</i> symmetry with two indazolyl rings bound to boron via N-2. The distortion of the coordination sphere around Tl and the arrangement of the complexes in the crystal are discussed

Highly Fluorinated Aryl-Substituted Tris(indazolyl)borate Thallium Complexes: Diverse Regiochemistry at the B–N Bond

The synthesis and characterization (mainly by ¹⁹F NMR and X-ray diffraction) of highly fluorinated aryl-4,5,6,7-tetrafluoroindazoles and their corresponding thallium hydrotris­(indazolyl)­borate complexes are reported [aryl = phenyl, pentafluorophenyl, 3,5-dimethylphenyl, 3,5-bis­(trifluoromethyl)­phenyl]. Thanks to N–H···N hydrogen bonds, the indazoles crystallize as dimers that pack differently depending on the nature of the aryl group. The thallium hydrotris­(indazolyl)­borate complexes Tl­[Fn-Tp^4Bo,3aryl] resulting from the reaction of aryl-4,5,6,7-tetrafluoroindazoles [aryl = phenyl, 3,5-dimethylphenyl, 3,5-bis­(trifluoromethyl)­phenyl] with thallium borohydride adopt overall <i>C</i>_3<i>v</i> symmetry with the indazolyl groups bound to boron via their N-1 nitrogen in a conventional manner. When the perfluorinated pentaphenyl-4,5,6,7-tetrafluoroindazole is reacted with thallium borohydride, a single regioisomer of <i>C</i>_<i>s</i> symmetry having one indazolyl ring bound to boron via its N-2 nitrogen, TlHB­(3-pentafluorophenyl-4,5,6,7-tetrafluoroindazol-1-yl)₂(3-pentafluorophenyl-4,5,6,7-tetrafluoroindazol-2-yl) Tl­[F27-Tp^(4Bo,3C6F5)*], is obtained for the first time. Surprisingly, the perfluorinated dihydrobis­(indazolyl)­borate complex Tl­[F₁₈-Bp^3Bo,3C6F5], an intermediate on the way to the hydrotris­(indazolyl)­borate complex, has <i>C</i>_<i>s</i> symmetry with two indazolyl rings bound to boron via N-2. The distortion of the coordination sphere around Tl and the arrangement of the complexes in the crystal are discussed