Photoredox catalysis has emerged as a powerful strategy for C—O cross-coupling reactions. We herein report a new class of tridentate pyridinophane ligands .sup.RN3 that allow for detailed mechanistic studies of the photocatalytic C—O coupling reaction. The derived (.sup.RN3)Ni complexes are active C—O cross-coupling photocatalysts under mild conditions and without an additional photocatalyst. We also utilized the .sup.RN3 ligands to study the essential but so far putative steps involving paramagnetic Ni species in a proposed catalytic cycle: the oxidative addition of an aryl bromide to a Ni(I) species, the ligand exchange at a Ni(III) center, and the C—O reductive elimination from a Ni(III) species.

Photoredox catalysis has emerged as a powerful strategy for C—O cross-coupling reactions. We herein report a new class of tridentate pyridinophane ligands .sup.RN3 that allow for detailed mechanistic studies of the photocatalytic C—O coupling reaction. The derived (.sup.RN3)Ni complexes are active C—O cross-coupling photocatalysts under mild conditions and without an additional photocatalyst. We also utilized the .sup.RN3 ligands to study the essential but so far putative steps involving paramagnetic Ni species in a proposed catalytic cycle: the oxidative addition of an aryl bromide to a Ni(I) species, the ligand exchange at a Ni(III) center, and the C—O reductive elimination from a Ni(III) species.

A nanoribbon includes a structure represented by a structural formula (8), where g, p, q, r, s, t, and u are mutually independent and are integers greater than or equal to 1, R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5, R.sup.6, R.sup.7, and R.sup.8 are mutually independent and are one of a hydrogen atom, a substituent, an alkyl moiety, a phenyl moiety, and a halogen atom, and A denotes a hydrogen atom or an aryl group.

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The present invention provides an improved process for preparation of L-threo-(2S,3R)-3-(3,4-dihydroxyphenyl)serine (I) (Droxidopa) and its salts; comprising (a) reaction of the aldehyde compound (III) (as described herein) with Metal complex (II) (as described herein), and (h) hydrolysis of the compound (IV) obtained from step (a) in presence of acid. The present invention also relates to a novel intermediates metal chiral complex (IV) for the preparation of Droxidopa.

Triaryl phosphine ligands, as shown in general formulae Ia and Ib, or a mixture thereof, and a preparation method therefor. The invention addresses the deficiencies of biaryl phosphine ligands invented by Buchwald et al. Also provided are a triaryl phosphine coordinated palladium complex, a system composed of triaryl phosphine ligand and a palladium salt or complex, and a use of the triaryl phosphine coordinated palladium complex in catalysing organic reactions, in particular a use in catalysis of coupling reactions involving (pseudo)halogenated aromatic hydrocarbon as substrate.

Triaryl phosphine ligands, as shown in general formulae Ia and Ib, or a mixture thereof, and a preparation method therefor. The invention addresses the deficiencies of biaryl phosphine ligands invented by Buchwald et al. Also provided are a triaryl phosphine coordinated palladium complex, a system composed of triaryl phosphine ligand and a palladium salt or complex, and a use of the triaryl phosphine coordinated palladium complex in catalysing organic reactions, in particular a use in catalysis of coupling reactions involving (pseudo)halogenated aromatic hydrocarbon as substrate.

The invention discloses a mixed Ni(II) complex containing bisoxazoline-derived nitrogen heterocyclic carbene ligand and phosphite ligand and application thereof; the chemical formula of the mixed Ni(II) complex is Ni(NHC)[P(OR).sub.3]X.sub.2, wherein R is ethyl or isopropyl, X is bromine or chlorine, and NHC is a bisoxazoline-derived nitrogen heterocyclic carbene ligand. In the presence of magnesium shavings, the mixed Ni(II) complex containing bisoxazoline-derived nitrogen heterocyclic carbene ligand and phosphite ligand of the present invention can catalyze low-activity chlorinated aromatic hydrocarbons and fluorinated aromatic hydrocarbons with chlorinated benzyl compounds, respectively, reductive cross-coupling reaction at a single temperature, generating a diarylmethane compound in one step, providing a new method for the synthesis of diarylmethane compounds.

The invention discloses a mixed Ni(II) complex containing bisoxazoline-derived nitrogen heterocyclic carbene ligand and phosphite ligand and application thereof; the chemical formula of the mixed Ni(II) complex is Ni(NHC)[P(OR).sub.3]X.sub.2, wherein R is ethyl or isopropyl, X is bromine or chlorine, and NHC is a bisoxazoline-derived nitrogen heterocyclic carbene ligand. In the presence of magnesium shavings, the mixed Ni(II) complex containing bisoxazoline-derived nitrogen heterocyclic carbene ligand and phosphite ligand of the present invention can catalyze low-activity chlorinated aromatic hydrocarbons and fluorinated aromatic hydrocarbons with chlorinated benzyl compounds, respectively, reductive cross-coupling reaction at a single temperature, generating a diarylmethane compound in one step, providing a new method for the synthesis of diarylmethane compounds.

Provided are triaryl phosphine ligands, as shown in general formulae Ia and Ib, or a mixture thereof, and a preparation method therefor. The invention addresses the deficiencies of biaryl phosphine ligands invented by Buchwald et al. Also provided are a triaryl phosphine coordinated palladium complex, a system composed of triaryl phosphine ligand and a palladium salt or complex, and a use of the triaryl phosphine coordinated palladium complex in catalysing organic reactions, in particular a use in catalysis of coupling reactions involving (pseudo)halogenated aromatic hydrocarbon as substrate.

Provided are triaryl phosphine ligands, as shown in general formulae Ia and Ib, or a mixture thereof, and a preparation method therefor. The invention addresses the deficiencies of biaryl phosphine ligands invented by Buchwald et al. Also provided are a triaryl phosphine coordinated palladium complex, a system composed of triaryl phosphine ligand and a palladium salt or complex, and a use of the triaryl phosphine coordinated palladium complex in catalysing organic reactions, in particular a use in catalysis of coupling reactions involving (pseudo)halogenated aromatic hydrocarbon as substrate.