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1.
Chem Commun (Camb) ; 56(57): 7893-7896, 2020 Jul 21.
Artigo em Inglês | MEDLINE | ID: mdl-32524101

RESUMO

The reaction of the bis(methoxy)-2-pyridyl-phosphine (MeO)2P(2-py) (1) with [Ni(MeCN)6](BF4)2 leads to the unexpected single-step reduction of NiII and the formation of a tetrahedral nickel(0) complex [{(MeO)2P(2-py-H)}2{(MeO)2P(2-py)}2Ni](BF4)2 (2). The redox activity is probably induced by the decomposition of the tetrafluoroborate anion; NMR spectroscopic studies point towards a fluoride-assisted oxidation of the 2-pyridyl-phosphine ligand, with associated reduction of the metal.

2.
Dalton Trans ; 2020 Apr 03.
Artigo em Inglês | MEDLINE | ID: mdl-32242884

RESUMO

The coordination characteristics and donor/acceptor properties of a series of 2-pyridyl substituted phosphine ligands have been investigated using structural, spectroscopic and DFT calculational studies. A range of different coordination modes are observed in Mo and W carbonyl complexes of tris-2-pyridyl-phosphine ligands of the type P(2-py') (2-py' = substituted or unsubstituted 2-pyridyl group), including an unprecedented example exhibiting N,N',µ2-π coordination. DFT calculations were used to assess the relative donor/acceptor properties of a range of related 2-pyridyl-phosphine ligands with respect to PPh3 and PtBu3.

3.
Chemistry ; 26(26): 5765-5769, 2020 May 07.
Artigo em Inglês | MEDLINE | ID: mdl-32048370

RESUMO

Tertiary phosphines are generally known to withstand inversion under moderate conditions. In this work, a remarkable racemization process of three P-chiral ferrocenyl phosphines is reported. Subjected to conventional column chromatography as highly enantioenriched compounds, they greatly experienced racemization when collected at the column outlet within minutes. Initially, attention was drawn to this unusual inversion behavior after observing that the superb enantiomeric excess of these ligands (>95 % ee in all cases) was almost lost in their corresponding ruthenium(II) complexes. Successively excluding possible racemization causes, these P-chiral ferrocenyl phosphines were found to undergo a significant, acid-catalyzed racemization process at room temperature within a few minutes. This process is mainly observed during standard column chromatography by using conventional silica or alumina, but can also be triggered deliberately by addition of certain acids. Therefore, the stereochemical preservation of P-chiral phosphines during their purification may per se not always be guaranteed, since column chromatography is the most frequently used technique for purifying such types of compounds.

4.
Chem Commun (Camb) ; 53(68): 9434-9437, 2017 Aug 22.
Artigo em Inglês | MEDLINE | ID: mdl-28792017

RESUMO

The reaction of the commercially available ammonium salt NH4BPh4 with a pyridine-activated pinacolborane species generates a boronium cation that facilitates the 1,4-selective hydroboration of pyridines in polar solvents. This catalytic reaction is amenable to a host of reactive functional groups and provides access to sterically bulky hydroboration products, previously inaccessible by metal-free routes. Further, the regioselectivity of this reaction can be altered by reducing the polarity of the reaction solvent, resulting in greater proportions of the 1,2-hydroboration product.

5.
Chem Commun (Camb) ; 53(7): 1225-1228, 2017 Jan 19.
Artigo em Inglês | MEDLINE | ID: mdl-27966697

RESUMO

Here we illustrate a new method for the rapid determination of ee's of chiral alcohols using the thermally-stable, non-chiral lithium aluminate reagent [EtAl(6-Me-2-py)3Li] (1). In situ reaction of the alcohols with 1 produces robust dimers in solution, present as diastereomeric pairs (SS/RR and RS) with distinct resonances in their 1H and 7Li NMR spectra. The ee can be calculated simply from integration of the 1H and/or 7Li NMR spectra.

6.
Dalton Trans ; 46(2): 578-585, 2017 Jan 03.
Artigo em Inglês | MEDLINE | ID: mdl-27981324

RESUMO

Metal-doped polyoxotitanate (M-POT) cages have been shown to be efficient single-source precursors to metal-doped titania [TiO2(M)] (state-of-the-art photocatalytic materials) as well as molecular models for the behaviour of dopant metal ions in bulk titania. Here we report the influence halide ions have on the optical and electronic properties of a series of halide-only, and cobalt halide-'doped' POT cages. In this combined experimental and computational study we show that halide ions can have several effects on the band gaps of halide-containing POT cages, influencing the dipole moment (hole-electron separation) and the structure of the valance band edge. Overall, the band gap behaviour stems from the effects of increasing orbital energy moving from F to I down Group 17, as well as crystal-field splitting of the d-orbitals, the potential effects of the Nephelauxetic influence of the halides and electron-electron repulsion.

7.
Dalton Trans ; 45(1): 276-83, 2016 Jan 07.
Artigo em Inglês | MEDLINE | ID: mdl-26599428

RESUMO

Introducing substituents into the 6-position of the 2-pyridyl rings of neutral tris-pyridyl phosphanes of the type P(2-py')3 (where 2-py' is a substituted 2-pyridyl ring), has a marked impact on their coordination of transition metal ions, as revealed in the current study. Whereas the unsubstituted phosphorus-bridged tris-pyridyl ligand P(2-py)3 (1) forms the sandwich cation [{P(py)3}2Fe](2+) (4) with iron(II), coordinating via all of the donor nitrogen atoms, the reaction of the methyl-substituted counterpart P(6-Me-2-py)3 (2) and FeCl2 results in the half-sandwich arrangement [{P(6-Me-2-py)3}FeCl2]·toluene (5·toluene), in which only two N-atoms of the ligand coordinate to the metal. A similar half-sandwich type complex, [{P(6-Me-2-py)3}FeCl(OTf)]·2THF (6·2THF), is obtained from reaction of 2 with Fe(OTf)2 in the presence of LiCl, only now with all three of the N-atoms of the ligand coordinated to Fe(II). The formation of a half-rather than full-sandwich complex 2 with suggests that steric clashing of the Me groups prevents the formation of sandwich-type arrangements. The reaction of [Cu(MeCN)4]PF6 with P(6-Me-2-py) (2) gives the complex [(MeCN)3Cu{P(6-Me-2-py)3}Cu(MeCN)](PF6)2 (7), in which two Cu(I) atoms are coordinated by the bridgehead P-atom and by the three N-atoms of the tris-pyridyl ligand (a unique coordination mode in this area). Overall, the results indicate that 6-Me substitution results in a promising 6-electron capping ligand for organometallic synthesis and catalysis.

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