2‐Nitrophenylboronic acids serve as interesting starting materials for the construction of biphenyl‐ and terphenyl‐based amines if subjected to the Suzuki–Miyaura reaction. Unfortunately, these ...boronic acids suffer from low reactivity in Suzuki reactions, alongside their low stability in the presence of Pd. Herein, a general method for the construction of 2‐nitro‐substituted bi‐ and terphenyls is presented, with special emphasis on the synthesis of 2‐amino‐2'‐nitrobi‐ and terphenyls. Comparisons are made with other boronic acids that have some of the aforementioned issues. Finally, the application of the obtained 2‐amino‐2'‐nitrobi‐ and terphenyls as starting materials for the synthesis of bi‐ and terphenyl based di‐ and triamines is encountered for, with emphasis on the use of these amines as precursors for Schiff base ligands. In addition, the synthesis of some Zn complexes of these ligands is presented.
The Suzuki–Miyaura reaction is used as a key step for the synthesis of 2‐aminobiphenyls and 2,2'‐diaminobiphenyls, which in turn can be utilized to make Schiff base complexes of Zn. Special emphasis is on the cross‐coupling reaction between 2‐bromoanilines and a 2‐nitro‐substituted arylboronic acid, for which there is little existing precedence.
Herein, we report the discovery of a toroidal inorganic cluster of zirconium(IV) oxysulfate of unprecedented size with the formula Zr70(SO4)58(O/OH)146⋅x(H2O) (Zr70), which displays different packing ...of ring units and thus several polymorphic crystal structures. The ring measures over 3 nm across, has an inner cavity of 1 nm and displays a pseudo‐10‐fold rotational symmetry of Zr6 octahedra bridged by an additional Zr in the outer rim of the ring. Depending on the co‐crystallizing species, the rings form various crystalline phases in which the torus units are connected in extended chain and network structures. One phase, in which the ring units are arranged in layers and form one‐dimensional channels, displays high permanent porosity (BET surface area: 241 m2 g−1), and thus demonstrates a functional property for potential use in, for example, adsorption or heterogeneous catalysis.
A toroidal Zr(IV) oxysulfate cluster of unprecedented size with the formula Zr70(SO4)58(O/OH)146⋅x (H2O) (Zr70) was synthesized. Depending on the co‐crystallizing species, it displays different packing of the ring units. One of the phases contains one‐dimensional channels through the rings, showing high permanent porosity (surface area: 241 m2 g−1). The ring entity measures over 3 nm across and displays a pseudo‐10‐fold rotational symmetry.
Herein, we report the discovery of a toroidal inorganic cluster of zirconium(IV) oxysulfate of unprecedented size with the formula Zr
(SO
)
(O/OH)
⋅x(H
O) (Zr
), which displays different packing of ...ring units and thus several polymorphic crystal structures. The ring measures over 3 nm across, has an inner cavity of 1 nm and displays a pseudo-10-fold rotational symmetry of Zr
octahedra bridged by an additional Zr in the outer rim of the ring. Depending on the co-crystallizing species, the rings form various crystalline phases in which the torus units are connected in extended chain and network structures. One phase, in which the ring units are arranged in layers and form one-dimensional channels, displays high permanent porosity (BET surface area: 241 m
g
), and thus demonstrates a functional property for potential use in, for example, adsorption or heterogeneous catalysis.
Zn complexes of Schiff base ligands derived from 2,2'‐diaminobiphenyls and salicylaldehyde derivatives were synthesized and characterized by NMR and single‐crystal X‐ray diffraction analysis. The ...detailed NMR studies suggest that the Zn complexes have a complicated behavior in solution, which is strongly dependent on the donating ability of the solvent, the steric properties of the ligand, as well as the concentration of the complex in the solvent. All these factors are decisive for the determination of the coordination number of the complex in solution. Furthermore, pentacoordinated Zn complexes of the aforementioned type, ligated by a series of nitrogen bases, were synthesized. NMR studies of the different complexes at different concentrations and temperatures, revealed information about their conformational stability. The differences were further examined by single‐crystal X‐ray diffraction analysis. In addition to the studies conducted on Zn complexes, comparative studies were conducted on a series of Cd complexes.
Zn complexes of Schiff base ligands derived from 2,2'‐diaminobiphenyls were synthesized and studied by NMR. The complexes showed a complicated behavior in solution, strongly dependent on the nature of the solvent, the substitution pattern on the aromatic rings, and the concentration of the complexes. Similar behavior was observed in studies of the corresponding base‐ligated Zn complexes, obtained by reaction with different nitrogen bases.
A series of Cu(I) complexes of bidentate or tetradentate Schiff base ligands bearing either 1‐H‐imidazole or pyridine moieties were synthesized. The complexes were studied by a combination of NMR and ...X‐ray spectroscopic techniques. The differences between the imidazole‐ and pyridine‐based ligands were examined by 1H, 13C and 15N NMR spectroscopy. The magnitude of the 15Nimine coordination shifts was found to be strongly affected by the nature of the heterocycle in the complexes. These trends showed good correlation with the obtained Cu−Nimine bond lengths from single‐crystal X‐ray diffraction measurements. Variable‐temperature NMR experiments, in combination with diffusion ordered spectroscopy (DOSY) revealed that one of the complexes underwent a temperature‐dependent interconversion between a monomer, a dimer and a higher aggregate. The complexes bearing tetradentate imidazole ligands were further studied using Cu K‐edge XAS and VtC XES, where DFT‐assisted assignment of spectral features suggested that these complexes may form polynuclear oligomers in solid state. Additionally, the Cu(II) analogue of one of the complexes was incorporated into a metal‐organic framework (MOF) as a way to obtain discrete, mononuclear complexes in the solid state.
A series of N,N,N,N Cu(I) Schiff base complexes was studied by NMR and X‐ray spectroscopic techniques. In solution, the aggregation behaviour was investigated by DOSY and variable‐temperature NMR. 15N NMR studies shed light on the Cu−N interactions in the complexes. XAS and XES, supported by DFT calculations, highlighted the complexes’ tendencies to form polynuclear species in the solid state.
A range of N,C‐chelated, cyclometalated gold(III) complexes Au(ppyR)X2 have been prepared and characterized by spectroscopic, crystallographic, and computational means. Here, ppyH is 2‐phenylpyridine ...dicarboxylic acid (series 1), ppyEt is diethyl 2‐phenylpyridine dicarboxylate (series 2), and X is trifluoroacetate OAcF (a), Cl (b), Br (c), or I (d) anion. The dihalo complexes 1b‐d and 2b‐d are obtained when Au(ppyR)(OAcF)2 (1a and 2a) are treated with HNO3/HX mixtures (aqua regiaX). Good to high yields are obtained with short reaction times (< 30 min) and simple work‐up. Notably, the strongly acidic medium does not cause protolytic cleavage of the Au–C or Au–N bonds in the chelate, nor is ester hydrolysis of complexes 2b‐d seen. Ethylene inserts into an Au–O bond of 1a and 1b, and the resulting trifluoroacetoxyethyl–Au complexes can be further elaborated in aqua regia without cleavage of the two Au–C bonds in the molecule. Facile, mutual halide exchange reactions between complexes with different halides (1b and 1d, 1c and 1d) were observed and led to formation of mixed‐halide complexes Au(ppyH)(X)(Y). These exchange reactions occurred with complete stereoselectivity. The stereoisomer produced was the one expected based on the relative trans influence of the halides (I > Br > Cl), i.e. the highest trans influence halide was located trans to N which is the lowest trans influence end of the chelate. These thermodynamic preferences were also investigated by DFT computations.
Synthesis and characterization of N,C‐chelated, cyclometalated gold(III) complexes prepared by reaction of cyclometalated gold(III) bistrifluoroacetates with aqua regia solutions composed of mixtures of HNO3 and HCl, HBr, or HI. Mutual halide exchange reactions between complexes with different halides led to formation of mixed‐halide complexes Au(N^C)(X)(Y).
Symmetry of three-center, four-electron bonds Reiersølmoen, Ann Christin; Battaglia, Stefano; Øien-Ødegaard, Sigurd ...
Chemical science,
2020, Letnik:
11, Številka:
3
Journal Article
Recenzirano
Odprti dostop
Three-center, four-electron bonds provide unusually strong interactions; however, their nature remains ununderstood. Investigations of the strength, symmetry and the covalent
versus
electrostatic ...character of three-center hydrogen bonds have vastly contributed to the understanding of chemical bonding, whereas the assessments of the analogous three-center halogen, chalcogen, tetrel and metallic &z.sgcir;-type long bonding are still lagging behind. Herein, we disclose the X-ray crystallographic, NMR spectroscopic and computational investigation of three-center, four-electron D-X-D
+
bonding for a variety of cations (X
+
= H
+
, Li
+
, Na
+
, F
+
, Cl
+
, Br
+
, I
+
, Ag
+
and Au
+
) using a benchmark bidentate model system. Formation of a three-center bond, D-X-D
+
is accompanied by an at least 30% shortening of the D-X bonds. We introduce a numerical index that correlates symmetry to the ionic size and the electron affinity of the central cation, X
+
. Providing an improved understanding of the fundamental factors determining bond symmetry on a comprehensive level is expected to facilitate future developments and applications of secondary bonding and hypervalent chemistry.
The factors determining the symmetry and the fundamental nature of the three-center, four-electron bonds are assessed.
A highly asymmetric AuIII η3‐allyl complex has been generated by treating Au(η1‐allyl)Br(tpy) (tpy=2‐(p‐tolyl)pyridine) with AgNTf2. The resulting η3‐allyl complex has been characterized by NMR ...spectroscopy and X‐ray crystallography. DFT calculations and variable temperature 1H NMR suggest that the allyl ligand is highly fluxional.
Gold and dynamic: The π coordination of an allyl group at the cyclometalated (N,C coordinated) AuIII moiety induces high asymmetry in the allyl group. DFT calculations and variable temperature 1H NMR spectroscopy suggest that the allyl ligand is highly fluxional.
Catalytic Activity of trans-Bis(pyridine)gold Complexes Reiersølmoen, Ann Christin; Csókás, Dániel; Øien-Ødegaard, Sigurd ...
Journal of the American Chemical Society,
04/2020, Letnik:
142, Številka:
13
Journal Article
Recenzirano
Odprti dostop
Gold catalysis has become one of the fastest growing fields in chemistry, providing new organic transformations and offering excellent chemoselectivities under mild reaction conditions. ...Methodological developments have been driven by wide applicability in the synthesis of complex structures, whereas the mechanistic understanding of Au(III)-mediated processes remains scanty and have become the Achilles’ heel of methodology development. Herein, the systematic investigation of the reactivity of bis(pyridine)-ligated Au(III) complexes is presented, based on NMR spectroscopic, X-ray crystallographic, and DFT data. The electron density of pyridines modulates the catalytic activity of Au(III) complexes in propargyl ester cyclopropanation of styrene. To avoid strain induced by a ligand with a nonoptimal nitrogen–nitrogen distance, bidentate bis(pyridine)–Au(III) complexes convert into dimers. For the first time, bis(pyridine)Au(I) complexes are shown to be catalytically active, with their reactivity being modulated by strain.
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