2 research outputs found
Synthesis, NMR, and X‑ray Studies of Iridium Dihydride C,N and N,P Ligand Complexes
No full textThe iridium(III) dihydride complexes
[Ir(H)<sub>2</sub>(L1)(6,6′-bi-2-picoline)]BAr<sub>F</sub> (<b>5</b>; L1 = (<i>S</i>)-1-[2-(2-adamantan-2-yl-4,5-dihydrooxazol-4-yl)-ethyl]-3-(2,6-diisopropylphenyl)-1,2-dihydroimidazol-2-ylidene,
BAr<sub>F</sub> = tetrakis[3,5-bis(trifluoromethyl)phenyl]borate)
and [Ir(H)<sub>2</sub>(L2)(6,6′-bi-2-picoline)]BAr<sub>F</sub> (<b>6</b>; L2 = (<i>R</i>)-2-((di-<i>tert</i>-butylphosphanyl)methyl)-4-phenyl-4,5-dihydrooxazole)
were prepared from the corresponding [Ir(COD)(L)]BAr<sub>F</sub> precursors by treatment with 6,6′-bi-2-picoline under H<sub>2</sub> and characterized by 2D NMR spectroscopy and X-ray diffraction.
In solution, the N,P complex <b>6</b> exists as two isomeric
dihydride species (<b>6a</b> and <b>6b</b>) that are in
rapid equilibrium at room temperature. Furthermore, the X-ray structures
for [Ir(COD)(L1)]BAr<sub>F</sub> (<b>1</b>) and [Ir(COD)(L2)]BAr<sub>F</sub> (<b>2</b>) are reported. The structural comparison
of the solid-state structures of the iridium(I) precursor <b>1</b> and the iridium(III) dihydride complex <b>5</b> revealed a
significant change in the backbone geometry of the C,N ligand. The
original U-shaped conformation of the ligand switches to an S-shaped
conformation, and therefore, the substituent in the oxazoline ring
occupies different quadrants in the iridium coordination sphere. Notable
in this context is the finding that a similar switch in the ligand
backbone was observed for the C,N iridium(III) dihydride olefin species <b>3</b> ([Ir(H)<sub>2</sub>[(<i>E</i>)-1-methyl-4-(1-phenylprop-1-en-2-yl)benzene-D<sub>5</sub>](L1)]BAr<sub>F</sub>), which represents a catalytically
competent intermediate
Characterization and Reactivity Studies of Dinuclear Iridium Hydride Complexes Prepared from Iridium Catalysts with N,P and C,N Ligands under Hydrogenation Conditions
No full textThe
dinuclear iridium hydride complexes [IrH(CH<sub>3</sub>CN)(L1)(μ-H)]<sub>2</sub>(BAr<sub>F</sub>)<sub>2</sub> (<b>7</b>; L1 =
(<i>S</i>)-2-(2-((diphenylphosphanyl)oxy)propan-2-yl)-4-isopropyl-4,5-dihydrooxazole,
BAr<sub>F</sub> = tetrakis[3,5-bis(trifluoromethyl)phenyl]borate),
[IrH(CH<sub>2</sub>Cl<sub>2</sub>)(L1)(μ-H)]<sub>2</sub>(BAr<sub>F</sub>)<sub>2</sub> (<b>8</b>), [IrH(L2)(μ-H)]<sub>2</sub>(BAr<sub>F</sub>)<sub>2</sub> (<b>9a</b>; L2 =
(<i>S</i>)-1-[2-(2-adamantan-2-yl-4,5-dihydrooxazol-4-yl)-ethyl]-3-(2,6-diisopropylphenyl)-1,2-dihydroimidazol-2-ylidene),
and [IrH(L3)(μ-H)]<sub>2</sub>(BAr<sub>F</sub>)<sub>2</sub> (<b>9b</b>; L3 = (<i>S</i>)-1-[2-(2-<i>tert</i>-butyl-4,5-dihydrooxazol-4-yl)-ethyl]-3-(2,6-diisopropylphenyl)-1,2-dihydroimidazol-2-ylidene)
were prepared from the corresponding mononuclear [Ir(COD)(L)]BAr<sub>F</sub> precursors by treatment with H<sub>2</sub> and characterized
by 2D NMR spectroscopy and X-ray diffraction. Conversion to a trinuclear
iridium hydride complex, which is usually observed for N,P iridium
hydride complexes, is inhibited by addition of 0.5 equiv of [H(OEt<sub>2</sub>)<sub>2</sub>]BAr<sub>F</sub> or acetonitrile. Reactions
with acetonitrile or 6,6′-bi-2-picoline afforded the mononuclear
iridium dihydride complexes [Ir(H)<sub>2</sub>(CH<sub>3</sub>CN)<sub>2</sub>(L1)]BAr<sub>F</sub> (<b>5</b>), [Ir(H)<sub>2</sub>(CH<sub>3</sub>CN)<sub>2</sub>(L3)]BAr<sub>F</sub> (<b>10</b>), or [Ir(H)<sub>2</sub>(6,6′-bi-2-picoline)(L3)]BAr<sub>F</sub> (<b>11</b>). The CH<sub>3</sub>CN complexes <b>7</b> and <b>10</b> are inactive as hydrogenation catalysts. In
contrast, the coordinatively unsaturated dinuclear complexes <b>9a</b> and <b>9b</b> are active catalysts for the hydrogenation
of (<i>E</i>)-1,2-diphenyl-1-propene at 50 bar hydrogen
pressure
