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1.
Phys Chem Chem Phys ; 21(31): 17221-17231, 2019 Aug 21.
Artigo em Inglês | MEDLINE | ID: mdl-31346590

RESUMO

Cubane-type Mo3S4 cluster hydrides decorated with phosphine ligands are active catalysts for the transfer hydrogenation of nitroarenes to aniline derivatives in the presence of formic acid (HCOOH) and triethylamine (Et3N). The process is highly selective and most of the cluster species involved in the catalytic cycle have been identified through reaction monitoring. Formation of a dihydrogen cluster intermediate has also been postulated based on previous kinetic and theoretical studies. However, the different steps involved in the transfer hydrogenation from the cluster to the nitroarene to finally produce aniline remain unclear. Herein, we report an in-depth computational investigation into this mechanism. Et3N reduces the activation barrier associated with the formation of Mo-HHOOCH dihydrogen species. The global catalytic process is highly exergonic and occurs in three consecutive steps with nitrosobenzene and N-phenylhydroxylamine as reaction intermediates. Our computational findings explain how hydrogen is transferred from these Mo-HHOOCH dihydrogen adducts to nitrobenzene with the concomitant formation of nitrosobenzene and the formate substituted cluster. Then, a ß-hydride elimination reaction accompanied by CO2 release regenerates the cluster hydride. Two additional steps are needed for hydrogen transfer from the dihydrogen cluster to nitrosobenzene and N-phenylhydroxylamine to finally produce aniline. Our results show that the three metal centres in the Mo3S4 unit act independently, so the cluster can exist in up to ten different forms that are capable of opening a wide range of reaction paths. This behaviour reveals the outstanding catalytic possibilities of this kind of cluster complexes, which work as highly efficient catalytic machines.

2.
Chem Sci ; 10(10): 3130-3142, 2019 Mar 14.
Artigo em Inglês | MEDLINE | ID: mdl-30996896

RESUMO

Nanolayered cobalt-molybdenum sulphide (Co-Mo-S) materials have been established as excellent catalysts for C-S bond construction. These catalysts allow for the preparation of a broad range of thioethers in good to excellent yields from structurally diverse thiols and readily available primary as well as secondary alcohols. Chemoselectivity in the presence of sensitive groups such as double bonds, nitriles, carboxylic esters and halogens has been demonstrated. It is also shown that the reaction takes place through a hydrogen-autotransfer (borrowing hydrogen) mechanism that involves Co-Mo-S-mediated dehydrogenation and hydrogenation reactions. A novel catalytic protocol based on the thioetherification of alcohols with hydrogen sulphide (H2S) to furnish symmetrical thioethers has also been developed using these earth-abundant metal-based sulphide catalysts.

3.
Chemistry ; 23(53): 13205-13212, 2017 Sep 21.
Artigo em Inglês | MEDLINE | ID: mdl-28767165

RESUMO

Herein, we report a straightforward protocol for the preparation of N,N-dimethylated amines from readily available nitro starting materials using formic acid as a renewable C1 source and silanes as reducing agents. This tandem process is efficiently accomplished in the presence of a cubane-type Mo3 PtS4 catalyst. For the preparation of the novel [Mo3 Pt(PPh3 )S4 Cl3 (dmen)3 ]+ (3+ ) (dmen: N,N'-dimethylethylenediamine) compound we have followed a [3+1] building block strategy starting from the trinuclear [Mo3 S4 Cl3 (dmen)3 ]+ (1+ ) and Pt(PPh3 )4 (2) complexes. The heterobimetallic 3+ cation preserves the main structural features of its 1+ cluster precursor. Interestingly, this catalytic protocol operates at room temperature with high chemoselectivity when the 3+ catalyst co-exists with its trinuclear 1+ precursor. N-heterocyclic arenes, double bonds, ketones, cyanides and ester functional groups are well retained after N-methylation of the corresponding functionalized nitroarenes. In addition, benzylic-type as well as aliphatic nitro compounds can also be methylated following this protocol.

4.
Angew Chem Int Ed Engl ; 55(1): 387-91, 2016 Jan 04.
Artigo em Inglês | MEDLINE | ID: mdl-26555216

RESUMO

Reported herein, for the first time, is the selective ruthenium-catalyzed reductive alkoxylation and amination of phthalimides/succinimides. Notably, this novel methodology avoids hydrogenation of the aromatic ring and allows methoxylation of substituted imides with good to excellent selectivity for one of the carbonyl groups. The reported method opens the door to the development of new processes for the selective synthesis of various functionalized N-heterocyclic compounds. As an example, intramolecular reductive couplings to afford tricyclic compounds are presented for the first time.

5.
J Am Chem Soc ; 137(42): 13580-7, 2015 Oct 28.
Artigo em Inglês | MEDLINE | ID: mdl-26484397

RESUMO

A convenient, practical and green N-alkylation of amines has been accomplished by applying readily available carboxylic acids in the presence of molecular hydrogen. Applying an in situ formed ruthenium/triphos complex and an organic acid as cocatalyst, a broad range of alkylated secondary and tertiary amines are obtained in good to excellent yields. This novel method is also successfully applied for the synthesis of unsymmetrically substituted N-methyl/alkyl anilines through a direct three-component coupling reaction of the corresponding amines, carboxylic acids, and CO2 as a C1 source.

6.
Chemistry ; 21(47): 16759-63, 2015 Nov 16.
Artigo em Inglês | MEDLINE | ID: mdl-26450368

RESUMO

Methylation of amines is a fundamental and commonly used reaction in organic synthesis. Many methods are known including various reductive methylations using formaldehyde, formic acid, or carbon dioxide in the presence of reductants. However, several of these methods suffer from limited substrate scope and chemoselectivity because of the different nucleophilicities of substrates. In this respect, the combination of carbonates and hydrosilanes is a valuable methylation source in the presence of Pt-based catalysts. This highly tunable method allows for methylation of both aromatic and aliphatic amines, and chemoselective methylation of aminoalcohols and diamines. Notably, the in situ-formed catalyst can also be used for the reduction of carbonates to methanol at room temperature. Mechanistic insights on intermediates formed during the reaction pathway were obtained by using ESI mass spectrometry.

8.
J Am Chem Soc ; 136(40): 14314-9, 2014 Oct 08.
Artigo em Inglês | MEDLINE | ID: mdl-25230096

RESUMO

A straightforward process for the N-alkylation of amines has been developed applying readily available carboxylic acids and silanes as the hydride source. Complementary to known reductive aminations, effective C-N bond construction proceeds under mild conditions and allows obtaining a broad range of alkylated secondary and tertiary amines, including fluoroalkyl-substituted anilines as well as the bioactive compound Cinacalcet HCl.


Assuntos
Aminas/química , Ácidos Carboxílicos/química , Nitrogênio/química , Alquilação , Catálise , Silanos/química
9.
Chemistry ; 20(26): 7878-83, 2014 Jun 23.
Artigo em Inglês | MEDLINE | ID: mdl-24889122

RESUMO

A general catalytic protocol for the methylation of amines has been developed applying, for the first time, formic acid as the C1 building block and silanes as reducing agents. A broad range of aromatic and aliphatic, both primary and secondary, amines has been converted to the corresponding tertiary amines including [N-(13)C]-labelled drugs in good to excellent yields under mild conditions.


Assuntos
Aminas/química , Formiatos/química , Catálise , Metilação , Estrutura Molecular
11.
Inorg Chem ; 51(20): 10512-21, 2012 Oct 15.
Artigo em Inglês | MEDLINE | ID: mdl-23009632

RESUMO

A general protocol to access Mo(3)FeS(4)(4+) clusters selectively modified at the Fe coordination site is presented starting from the all-chlorine Mo(3)(FeCl)S(4)(dmpe)(3)Cl(3) (1) [dmpe = 1,2-bis(dimethylphosphane-ethane)] cluster and tetrabutylammonium salts (n-Bu(4)NX) (X = CN(-), N(3)(-), and PhS(-)). Clusters Mo(3)(FeX)S(4)(dmpe)(3)Cl(3) [X = CN(-) (2), N(3)(-) (3), and PhS(-) (4)] are prepared in high yield, and comparison of geometric and redox features upon modification of the coordination environment at the Fe site at parity of ligands at the Mo sites is also presented. The existence of the cubane-type Mo(3)FeS(4)(4+,5+) redox couple is demonstrated by cyclic voltammetry and for compound 1 by cluster synthesis and X-ray structure determinations. Ground states for the 1/1(+) redox couple are evaluated on the basis of magnetic susceptibility measurements, electron paramagnetic resonance, and (57)Fe Mössbauer spectroscopy aimed at providing an input of experimental data for electronic structure determination based on density functional theory calculations.


Assuntos
Elétrons , Ferro/química , Molibdênio/química , Compostos Organometálicos/química , Fosfinas/química , Análise Espectral , Enxofre/química , Ligantes , Fenômenos Magnéticos , Modelos Moleculares , Conformação Molecular , Oxirredução , Teoria Quântica
12.
Angew Chem Int Ed Engl ; 51(31): 7794-8, 2012 Jul 27.
Artigo em Inglês | MEDLINE | ID: mdl-22711684

RESUMO

Chemoselective cubes: Cubane-type [Mo(3)S(4)X(3)(dmpe)(3)](+) clusters (dmpe = 1,2-(bis)dimethylphosphinoethane), in combination with an azeotropic 5:2 mixture of HCOOH and NEt(3) as the reducing agent, act as selective cluster catalysts (X = H) or precatalysts (X = Cl) for the transfer hydrogenation of functionalized nitroarenes, without the formation of hazardous hydroxylamines.


Assuntos
Compostos de Anilina/síntese química , Complexos de Coordenação/química , Nitrocompostos/química , Compostos de Anilina/química , Catálise , Complexos de Coordenação/síntese química , Hidrogenação , Estrutura Molecular
13.
J Am Chem Soc ; 133(32): 12875-9, 2011 Aug 17.
Artigo em Inglês | MEDLINE | ID: mdl-21740024

RESUMO

The first well-defined iron-based catalyst system for the reduction of nitroarenes to anilines has been developed applying formic acid as reducing agent. A broad range of substrates including other reducible functional groups were converted to the corresponding anilines in good to excellent yields at mild conditions. Notably, the process constitutes a rare example of base-free transfer hydrogenations.


Assuntos
Compostos de Anilina/química , Hidrocarbonetos Aromáticos/química , Ferro/química , Nitrocompostos/química , Catálise , Hidrogenação , Oxirredução
14.
Inorg Chem ; 49(13): 5935-42, 2010 Jul 05.
Artigo em Inglês | MEDLINE | ID: mdl-20515025

RESUMO

The molybdenum(IV) cluster hydrides of formula [Mo(3)S(4)H(3)(diphosphine)(3)](+) with diphosphine = 1,2-(bis)dimethylphosphinoethane (dmpe) or (+)-1,2-bis-(2R,5R)-2,5-(dimethylphospholan-1-yl)ethane ((R,R)-Me-BPE) have been isolated in moderate to high yields by reacting their halide precursors with borohydride. Complex [Mo(3)S(4)H(3)((R,R)-Me-BPE)(3)](+) as well as its tungsten analogue are obtained in optically pure forms. Reaction of the incomplete cuboidal [M(3)S(4)H(3)((R,R)-Me-BPE)(3)](+) (M = Mo, W) complex with acids in CH(2)Cl(2) solution shows kinetic features similar to those observed for the related incomplete cuboidal [W(3)S(4)H(3)(dmpe)(3)](+) cluster. However, there is a decrease in the value of the rate constants that is explained as a result of the higher steric effect of the diphosphine. The rate constants for the reaction of both clusters [M(3)S(4)H(3)((R,R)-Me-BPE)(3)](+) (M = Mo, W) with HCl have similar values, thus indicating a negligible effect of the metal center on the kinetics of reaction of the hydrides coordinated to any of both transition metals.


Assuntos
Molibdênio/química , Compostos Organometálicos/química , Fosfinas/química , Tungstênio/química , Dicroísmo Circular , Concentração de Íons de Hidrogênio , Cinética , Espectroscopia de Ressonância Magnética , Modelos Moleculares , Compostos Organometálicos/síntese química , Fosfinas/síntese química , Espectrometria de Massas por Ionização por Electrospray , Espectroscopia de Infravermelho com Transformada de Fourier , Estereoisomerismo , Difração de Raios X
15.
Dalton Trans ; 39(15): 3725-35, 2010 Apr 21.
Artigo em Inglês | MEDLINE | ID: mdl-20354625

RESUMO

The synthesis, crystal structure and solution characterization of the cubane-type [Mo(3)(FeCl)S(4)(dmpe)(3)Cl(3)] (1) (dmpe = 1,2-bis(dimethylphophane-ethane)) cluster are reported and the ligand substitution processes of chloride by thiophenolate investigated. The kinetics and the intimate mechanism of these substitutions reveal that compound 1 undergoes a number of Fe and Mo site specific ligand substitution reactions in acetonitrile solutions. In particular, PhS(-) coordination at the tetrahedral Fe site proceeds in a single resolved kinetic step whereas such substitutions at the Mo sites proceed more slowly. The effect of the presence of acids in the reaction media is also investigated and reveals that an acid excess hinders substitution reactions both at the Fe and Mo sites; however, an acid-promoted solvolysis of the Fe-Cl bonds is observed. Electrospray ionization (ESI) and tandem (ESI-MS/MS) mass spectrometry allow the identification of all the reaction intermediates proposed on the basis of stopped-flow measurements. The distinctive site specific reactivity made it possible to isolate two new clusters of the Mo(3)FeS(4)(4+) family featuring mixed chlorine/thiophenolate ligands, namely Mo(3)S(4)(FeSPh)(dmpe)(3)Cl(3) (2) and [Mo(3)S(4)(FeSPh)(dmpe)(3)(SPh)(3)] (3). A detailed computational study has also been carried out to understand the details of the mechanism of substitution at the M-Cl (M = Mo and Fe) bonds as well as the solvolysis at the Fe-Cl sites, with particular emphasis on the role of acids on the substitution process. The results of the calculations are in agreement with the experimental observations, thus justifying the non-existence of an accelerating effect of acids on the thiophenolate substitution reaction, which differs from previous proposals for the Fe(4)S(4) and MoFe(3)S(4) clusters and some related compounds.


Assuntos
Complexos de Coordenação/química , Ferro/química , Ligantes , Molibdênio/química , Complexos de Coordenação/síntese química , Complexos de Coordenação/isolamento & purificação , Cristalografia por Raios X , Cinética , Conformação Molecular , Espectrometria de Massas por Ionização por Electrospray , Espectrofotometria Ultravioleta
16.
Inorg Chem ; 49(4): 1894-904, 2010 Feb 15.
Artigo em Inglês | MEDLINE | ID: mdl-20085305

RESUMO

A two-step procedure for the preparation of hybrid complexes based on electroactive tetrathiafulvalene (TTF)- functionalized o-P(2) diphosphanes (o-P(2) = 3,4-dimethyl-3,4-bis(diphenylphosphino)tetrathiafulvalene) and inorganic C(3)-symmetrized Mo(3)Q(4) (Q = S, Se) clusters, namely, [Mo(3)S(4)Cl(3)(o-P(2))(3)]PF(6) ([1]PF(6)) and [Mo(3)Se(4)Cl(3)(o-P(2))(3)]PF(6) ([2]PF(6)), is reported. Their molecular and electronic structures are also described on the basis of X-ray diffraction experiments and density functional theory (DFT) calculations aimed at understanding the interactions established between both the organic and the inorganic parts. Cyclic voltammograms of compounds [1]PF(6) and [2]PF(6) display reduction features associated to the Mo(3)Q(4) core and oxidation characteristics due to the TTF skeleton. The oxidation chemistry of [1]PF(6) and [2]PF(6) in solution is also investigated by means of in situ electrospray ionization (ESI) mass spectrometry, UV-vis, and, electron paramagnetic resonance (EPR) measurements. Upon addition of increasing amounts of NOPF(6) (less than 3 equiv), the sequential formation of 1(n+) (n = 1-4) species was observed whereas addition of a 3-fold excess of NOPF(6) allows to access the three-electron oxidized [Mo(3)S(4)Cl(3)(o-P(2))(3)](4+) (1(4+)) and [Mo(3)Se(4)Cl(3)(o-P(2))(3)](4+) (2(4+)) cations. These 1(4+) and 2(4+) cations represent still rare examples of complexes with oxidized TTF-ligands that are remarkably stable either toward diphosphane dissociation or phosphane oxidation. Polycrystalline samples of compound [1](PF(6))(4) were obtained by oxidation of compound [1]PF(6) using NOPF(6) which were analyzed by solid state absorption, UV-vis, and Raman spectroscopies.


Assuntos
Compostos Heterocíclicos/química , Molibdênio/química , Selênio/química , Compostos de Sulfidrila/química , Eletroquímica/métodos , Estrutura Molecular , Espectrofotometria Infravermelho/métodos , Espectrofotometria Ultravioleta/métodos
17.
Inorg Chem ; 48(11): 4837-46, 2009 Jun 01.
Artigo em Inglês | MEDLINE | ID: mdl-19466804

RESUMO

The substitutional lability of Mo-Cl and Cu-Cl bonds in cubane-type Mo(3)CuS(4) and incomplete cubane-type Mo(3)S(4) clusters is exploited in an attempt to prepare cyanide-terminated complexes, namely [Mo(3)S(4)(CuCN)(dmpe)(3)Cl(3)]PF(6) ([2]PF(6)) and [Mo(3)S(4)(dmpe)(3)(CN)(3)]PF(6) ([5]PF(6)), and to subsequently use them as precursors in low-dimensional linking reactions. Mixed-metal assemblies formulated as [Mo(3)S(4)(Cu-muCN...Mo(CO)(5))(dmpe)(3)Cl(3)](+) ([3](+)) and [Mo(3)S(4)(dmpe)(3)(muCN...Mo(CO)(5))(3)](+) ([6](+)) are obtained by reaction of tetrahydrofuran solutions of [2]BPh(4) and [5]BPh(4) with the complex (THF)Mo(CO)(5). The intrinsic stability of the (M'-muCN...Mo(CO)(5)) linkages (M' = Cu in 3(+) and Mo in 6(+)) in solution and in the gas phase is investigated through a combination of variable-temperature (31)P NMR, IR, UV-vis spectroscopies, and electrospray ionization tandem mass spectrometry. The spectroscopic and electrochemical consequences of CN coordination as well as Mo(CO)(5) ligation either at the Cu or the Mo site in Mo(3)CuS(4) and Mo(3)S(4) clusters are reported. Replacement of Cl by CN or CN...Mo(CO)(5) at the Cu site does not affect the redox potentials, whereas analogous substitution at Mo sites exerts a profound anodic shift of 220 and 500 mV upon Cl to CN and Cl to CN...Mo(CO)(5) replacement, respectively.

18.
J Am Soc Mass Spectrom ; 18(10): 1863-72, 2007 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-17716910

RESUMO

Electrospray ionization mass spectrometry makes it possible to generate gas-phase bis-ethylenediamine nickel and copper dications, [M(en)(2)](2+) (M = Ni, 1; M = Cu, 2), as well as their {[M(en)(2)]@cuc[8]}(2+) inclusion complexes with the macrocyclic cavitand cucurbit[8]uril (cuc[8]). The unimolecular gas-phase reactivity of these species has been investigated by electrospray ionization tandem mass spectrometry with a quadrupole-time-of-flight configuration. Distinctive fragmentation pathways have been observed for the free and encapsulated [M(en)(2)](2+) (M = Ni, Cu) dications under collision-induced dissociation (CID) conditions. The dications [M(en)(2)](2+) (M = Ni, Cu) dissociate according to several competitive pathways that involve intra-complex hydrogen or electron-transfer processes. Most of these channels are suppressed after encapsulation inside the cucurbit[8]uril macrocycle and, as a consequence, a simplification of the {[M(en)(2)]@cuc[8]}(2+) fragmentation pattern is observed. The results obtained demonstrate that the encapsulation of a coordination complex inside a host molecule can be used to alter the nature of the product ions generated under CID conditions.

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