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1.
Inorg Chem ; 2020 Sep 18.
Artigo em Inglês | MEDLINE | ID: mdl-32945677

RESUMO

Pd-catalyzed C-H bond arylation applied to 2-(2,4-difluorophenyl)-5-(trifluoromethyl)pyridine (1) and 2-(3,5-difluorophenyl)-5-(trifluoromethyl)pyridine (5) allows the access to two families of Ir(III) complexes, charge-neutral and cationic species. The reaction is regioselective since only the C3- or C4-position of the fluorinated phenyl ring of 1 or 5 is readily functionalized - namely the C-H bond flanked by the two fluorine atoms which is the most acidic - which allows the electronic control of the reactive site. A range of electron-withdrawing (CN, CO2Et, C(O)Me) substituents on the aryl group has been incorporated leading to the pro-ligands (1, Ar-2,4-dFppy; 2, Ar = p-C6H4-CN; 3, Ar = p-C6H4-CO2Et; 4, Ar = p-C6H4-C(O)Me; 5, and Ar-3,5-dFppy; 6, Ar = p-C6H4-CO2Et). The unsubstituted complexes F1/G1 and F1/G5 featuring 1 and 5, respectively, as C^N ligands are used as reference complexes. The families of five charge-neutral [Ir(C^N)2(N^O)] complexes (C^N is 2-(5-aryl-(4,6-difluorophenyl)-5-(trifluoromethyl)pyridinato (F2-F4), and 2-(4-aryl-(3,5-difluorophenyl)-5-(trifluoromethyl)pyridinato (F5-F6), N^O = 2-picolinate) and five cationic [Ir(C^N)2(N^N)]PF6 complexes (N^N = dmbpy is 4,4'-dimethyl-2,2'-bipyridine) (G2-G6) were synthesized, and their structural and photophysical properties were studied with comparison to the unsubstituted analogues used as reference complexes. The appended aryl group provides large steric bulk as the biaryl fragment is twisted as shown by the X-ray crystal structures of F2, F5, F6, G3, and G5. These latter complexes display a wide variety of different Ir···Ir intermetallic distances in crystals, from 8.150 Å up to 15.034 Å. Moreover, the impact on the emission energy is negligible, as a result of the breaking of the conjugation between the two aryl groups. Charge-neutral complexes [Ir(C^N)2(N^O)] (N^O = 2-picolinate) show bright luminescence: F2-F4 (λem = 495-499 nm) are blue-green emitters, whereas F5 and F6 (λem = 537, 544 nm), where the fluorine substituents are located at the C3- and C5-positions, emit in the green region of the visible spectrum. In all cases, a unitary photoluminescence quantum yield is found. The improvement of Φ might be explained by an increase of the radiative rate constant due to a higher degree of rigidity of these congested molecules, compared to the unsubstituted complex F1. The same trends are observed for the family of complexes G. Complexes G1-G4 exhibit blue photoluminescence, and G5 and G6 lead to a red-shifted emission band, as also found for the related complexes F5 and F6 due to the similar fluorine substitution pattern. Their emission quantum yields are remarkably high for charged complexes in the CH2Cl2 solution. These results showed that Pd-catalyzed C-H bond arylation is a valuable synthetic approach for designing efficient emitters with tunable photophysical properties.

2.
Dalton Trans ; 2020 Sep 11.
Artigo em Inglês | MEDLINE | ID: mdl-32914818

RESUMO

The synthesis and structural features of several families of unsolvated molecular complexes of the heavy alkaline earths (Ae = calcium, strontium and barium) supported by bis(phenolate)s or bis(fluoroalkoxide)s are described. These dianionic, multidentate ligands are built around diaza-macrocycles that contain either five or six N- and O-heteroatoms. Several of these complexes have been characterised by X-ray diffraction crystallography. A list of comparative features was drawn upon close examination of the molecular structures of these complexes. It highlights the subtle influences of the identity of the central Ae metal, denticity and nature -fluoroalkoxide vs. phenolate- of the anionic tethers in the ligands. All complexes are seven- or eight-coordinate. It is observed in particular that a decrease of the number of heteroatoms in the macrocyclic backbone of the ligand will be compensated by the establishment of intramolecular AeF interactions (accounting for ca. 3.8-6.4% of the pertaining coordination spheres according to bond valence sum analysis), dimerisation of the complex, or, in one case, solvent (thf) retention. Attempts to gauge the Lewis acidity in these series of complexes were carried out by three independent methods (Childs, Gutmann-Beckett and global electrophilicity index). However, conflicting results were obtained and no clear trend can be delineated, even if on the whole, these measurements concur to suggest relatively low Lewis acidity.

3.
Dalton Trans ; 2020 Aug 18.
Artigo em Inglês | MEDLINE | ID: mdl-32807997

RESUMO

The tridentate ligand 1,8-bis-(2,6-diisopropylphenyl)imino-3,6-di-tert-butyl-carbazolate, {CarbDiPP}-, has been used to prepare a variety of complexes of the large alkaline earths (Ae) calcium, strontium and barium. A complex of their smaller congener, magnesium, has also been synthesised. The range of coligands that have been utilised include alkyls, amides, halides and tetrelides. All structurally characterised complexes presented herein are stable in solution and do not undergo ligand redistribution that is otherwise well-known to pollute the chemistry of the alkaline-earth metals. Detailed structural and spectroscopic data for these compounds are discussed. They provide compelling evidence that this nitrogen ligand allows for the kinetic stabilisation of Ae complexes through optimal steric encapsulation of the voluminous metal centres. Its ease of access combined to its evident versatility make {CarbDiPP}H stand out in the portfolio of proligands that have been devised for similar purposes in the past decade. Yet, it fell short in our attempts to synthesise heteroleptic Ae-hydrides upon action of PhSiH3 onto Ae-amides, as the crystallised products showed the imine groups were prone to hydride reduction and formal hydrosilylation.

4.
Org Biomol Chem ; 18(31): 6042-6046, 2020 Aug 12.
Artigo em Inglês | MEDLINE | ID: mdl-32729604

RESUMO

The asymmetric synthesis of the 3-allyl-3-hydroxyoxindole skeleton was accomplished in yields up to 99% via a metal-free and enantioselective allylation of isatins (90-96% ee) using BINOL derivatives as catalysts and an optimized allylboronate. This methodology was applied at a gram-scale to the synthesis of the natural product (R)-chimonamidine.

5.
Inorg Chem ; 2020 Mar 03.
Artigo em Inglês | MEDLINE | ID: mdl-32125834

RESUMO

The reactions of dimetallaoctaboranes(12) [(Cp*M)2B6H10] [M = Co (1) or Rh (2); Cp* = η5-C5Me5] with different chalcogen sources, such as Li[BH2E3] and Li[BH3EPh] (E = S, Se, or Te), led to two unique reaction outcomes. For example, the formation of 10-vertex nido-[(Cp*M)2B6E2H6] (3, M = Co, E = S; 4, M = Co, E = Se; 5, M = Co, E = Te; 6, M = Rh, E = Se) from compounds 1 and 2 is a typical representation of a cluster growth reaction, while the formation of arachno-[(Cp*Co)2B6H9(EPh)] [E = S (9), Se (10), or Te (11)] is a rare method that yielded arachno clusters, keeping the core geometry identical. The formation of arachno-9-11 is a unique method that converts disobedient cluster 1 to obedient clusters 9-11. Further, the reactivity of nido-4 with various metal carbonyls presented sequential cluster growth reactions, which afforded 11-vertex nido-[(Cp*Co)2B6Se2H6{Fe(CO)3}] (7) and 13-vertex fused closo-[(Cp*Co)2B6Se2H6{Ru3(CO)8}] (8). The core geometry of nido-7 is uncommon and very similar to that of [C2B9H11]2- with a unique open pentahapto-coordinating five-membered face.

6.
Artigo em Inglês | MEDLINE | ID: mdl-32091662

RESUMO

Reported here is a readily available bis(imino)carbazole-based proligand that constitutes a convenient entry point into the challenging synthetic molecular chemistry of barium. It enables the preparation of rare or even, up to now, unknown, solution-stable heteroleptic barium complexes. The syntheses and structural features for the first molecular barium fluoride and the first barium stannylide, with an unsupported Ba-Sn bond, are described, along with other carbazolate barium species: an amide (both a remarkably stable starting material and an excellent hydrophosphination precatalyst), iodide, and silanylide. DFT analysis of bonding patterns in the barium stannylide and barium silanylide highlights a prevailingly ionic barium-tetrelide bond with a small covalent contribution.

7.
Molecules ; 25(3)2020 Jan 23.
Artigo em Inglês | MEDLINE | ID: mdl-31979347

RESUMO

The reaction between the 2,2'-benzene-1,4-diylbis(6-hydroxy-4,7-di-tert-butyl-1,3-benzodithiol-2-ylium-5-olate triad (H2SQ) and the metallo-precursor [Yb(hfac)3]2H2O led to the formation of a dinuclear coordination complex of formula [Yb2(hfac)6(H2SQ)]0.5CH2Cl2 (H2SQ-Yb). After chemical oxidation of H2SQ in 2,2'-cyclohexa-2,5-diene-1,4-diylidenebis(4,7-di-tert-butyl-1,3-benzodithiole-5,6-dione (Q), the latter triad reacted with the [Yb(hfac)3]2H2O precursor to give the dinuclear complex of formula [Yb2(hfac)6(Q)] (Q-Yb). Both dinuclear compounds have been characterized by X-ray diffraction, DFT optimized structure and electronic absorption spectra. They behaved as field-induced Single-Molecule Magnets (SMMs) nevertheless the chemical oxidation of the semiquinone to quinone moieties accelerated by a factor of five the relaxation time of the magnetization of Q-Yb compared to the one for H2SQ-Yb. The H2SQ triad efficiently sensitized the YbIII luminescence while the chemical oxidation of H2SQ into Q induced strong modification of the absorption properties and thus a quenching of the YbIII luminescence for Q-Yb. In other words, both magnetic modulation and luminescence quenching are reached by the oxidation of the protonated semiquinone into quinone.

8.
Bioorg Chem ; 94: 103347, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31810757

RESUMO

Original 1-amino substituted thioxanthone derivatives were easily prepared from the bare heterocycle by a deprotometalation-iodolysis-copper-catalyzed CN bond formation sequence. This last reaction delivered mono- or/and diarylated products depending on the aniline involved. 1-Amino-9-thioxanthone was also prepared and reacted with 2-iodoheterocycles. Interestingly, while 1-(arylamino)-9-thioxanthones could be isolated, their subsequent cyclization was found to deliver original hexacyclic derivatives of helicoidal nature. Evaluation of their photophysical properties revealed high fluorescence in polar media, indicating potential applications for biological imaging. These compounds being able to inhibit PIM1 kinase, their putative binding mode was examined through molecular modeling experiments. Altogether, these results tend to suggest the discovery of a new family of fluorescent PIM inhibitors and pave the way for their future rational optimization.

9.
Angew Chem Int Ed Engl ; 59(2): 780-784, 2020 Jan 07.
Artigo em Inglês | MEDLINE | ID: mdl-31682058

RESUMO

We report a single-chain magnet (SCM) made of a terbium(III) building block and a nitronyl-nitroxide radical (NIT) functionalized with an aliphatic chain. This substitution is targeted to induce a long-range distortion of the polymeric chain and accordingly it gives rise to chains that are curled with almost 20 nm helical pitch. They self-organize as a chiral tubular superstructure made of 11 chains wound around each other. The supramolecular tubes have a 4.5 nm internal diameter. Overall, this forms a porous chiral network with almost 44 % porosity. Ab initio calculations highlight that each TbIII ion possesses high magnetic anisotropy. Indeed, notwithstanding the supramolecular arrangement each chain behaves as a SCM. Magnetic relaxation with both finite and infinite-size regimes is observed and confirms the validity of the Ising approximation. This is associated with quite strong coercive field and magnetic remanence (Hc =2400 Oe MR =2.09 µB at 0.5 K) for this class of compounds.

10.
J Am Chem Soc ; 142(1): 93-98, 2020 01 08.
Artigo em Inglês | MEDLINE | ID: mdl-31846302

RESUMO

Well-defined optically pure transition metal (TM) complexes bearing C1- and C2-symmetric N-heterocyclic carbene (NHC) ligands were prepared from prochiral NHC precursors. As predicted by DFT calculations, our strategy capitalizes on the formation of a metal-carbene bond which induces an axis of chirality. Configurationally stable atropisomers of various NHC-containing TM complexes were isolated by preparative HPLC on a chiral stationary phase in good yields and excellent optical purities (up to 99.5% ee). The carbene transfer from an optically pure Cu complex to a gold or palladium center reveals, for the first time, a full stereoretentivity, supporting the hypothesis of an associative mechanism for the transmetalation. The potential of these new chiral TM complexes was illustrated in asymmetric catalysis with up to 98% ee.

11.
Org Biomol Chem ; 17(42): 9352-9359, 2019 10 30.
Artigo em Inglês | MEDLINE | ID: mdl-31617544

RESUMO

In spite of the growing interest in fluorine-containing compounds, and the improvements in materials, optical and biological properties that can arise from substitution of a phenyl ring by ferrocene within a molecular scaffold, synthetic strategies that allow the efficient preparation of fluoroferrocene derivatives are scarce. Following conversion of ferrocene to fluoroferrocene, we have developed routes to fluorine-containing di-, tri-, tetra- and penta-substituted ferrocene derivatives to extend the available chemical space. Our approach is based on the identification of suitable reagents and conditions to achieve fluorine-directed deprotometalation, and exploitation of the halogen 'dance' rearrangement in the ferrocene series.

12.
Chemistry ; 25(71): 16236-16240, 2019 Dec 18.
Artigo em Inglês | MEDLINE | ID: mdl-31618479

RESUMO

Although PbII -siloxides have been known until now to decompose to oxoclusters, here [{ROF }PbOSi(SiMe3 )3 ] (ROF =fluoroalkoxide) and, most importantly, [Pb2 {OSi(SiMe3 )3 }{µ2 -OSi(SiMe3 )3 }3 ], are presented. The unusual bonding pattern in the latter thermally stable dinuclear complex was investigated by crystallographic and computational methods. Its stability is much higher than that of the simple, yet elusive "[Pb(OSiPh3 )2 ]", for which decomposition pathways towards [Pb4 (µ4 -O)(µ2 -OSiPh3 )6 ] have been clearly established.

13.
Chem Commun (Camb) ; 55(77): 11583-11586, 2019 Sep 24.
Artigo em Inglês | MEDLINE | ID: mdl-31495849

RESUMO

The activation of ruthenium-indenylidene complexes containing two unsymmetrical unsaturated N-heterocyclic carbenes (u2-NHCs) by a transmetalation process is reported. The use of copper(i) or gold(i) chlorides promotes the rapid trapping of one NHC ligand, which releases the catalytically active Ru-species. Impressive initiation rates with full-conversions are observed within one minute. This practical protocol demonstrates excellent catalytic performances in various ring-closing metathesis (RCM) and self-metathesis (SM) reactions.

14.
Angew Chem Int Ed Engl ; 58(43): 15244-15248, 2019 Oct 21.
Artigo em Inglês | MEDLINE | ID: mdl-31369186

RESUMO

An efficient visible light induced rhodium(I)-catalyzed regioselective borylation of aromatic C-H bonds is reported. The photocatalytic system is based on a single NHC-RhI complex capable of both harvesting visible light and enabling the bond breaking/forming at room temperature. The chelating nature of the NHC-carboxylate ligand was critical to ensure the stability of the RhI complex and to provide excellent photocatalytic activities. Experimental mechanistic studies evidenced a photooxidative ortho C-H bond addition upon irradiation with blue LEDs, leading to a cyclometalated RhIII -hydride intermediate.

15.
Chemistry ; 25(59): 13509-13513, 2019 Oct 22.
Artigo em Inglês | MEDLINE | ID: mdl-31411764

RESUMO

The first unsupported barium siloxide, the homoleptic dimer [Ba2 {µ2 -OSi(SiMe3 )3 }3 {OSi(SiMe3 )3 }], is presented, and its structural features are discussed in the light of DFT computations. This complex, together with the related [Ba{µ2 -OSi(SiMe3 )3 }{N(SiMe3 )2 }]2 and their parent [Ba{N(SiMe3 )2 }2 ]2 , mediates the formation of asymmetric siloxanes R3 Si-O-SiR'3 through the first case of main group metal-mediated dehydrocoupling of silanols and hydrosilanes. Early kinetic analysis highlights an unusual catalytic manifold.

16.
Angew Chem Int Ed Engl ; 58(42): 14940-14943, 2019 Oct 14.
Artigo em Inglês | MEDLINE | ID: mdl-31393659

RESUMO

A halogen-bond templated 1:1 macrocyclization in solution is reported. Tetra(iodoperfluorophenyl) ethers were used as halogen-bonded exotemplates in a substoichiometric amount (5 mol %). Pyridine-containing macrocyclic architectures were formed by ruthenium-catalyzed tandem metathesis/transfer hydrogenation sequence using sodium borohydride and methanol as non-dihydrogen hydrogen source. The halogen-bonded stabilization energies were analyzed relying on density functional theory.

17.
Dalton Trans ; 48(27): 9944-9948, 2019 Jul 21.
Artigo em Inglês | MEDLINE | ID: mdl-31231734

RESUMO

We report here on the utilisation of a readily available bidentate aminofluoroalkoxide in lead(ii) chemistry. Stable heteroleptic three-coordinate complexes can be produced in high yields, including a convenient amido synthetic precursor and a rare case of PbII-boryloxide.

18.
Dalton Trans ; 48(25): 9173-9180, 2019 Jun 25.
Artigo em Inglês | MEDLINE | ID: mdl-31149687

RESUMO

The detailed multistep syntheses of two nitrogen-based sterically congested iminoanilidine and amidine proligands bearing a tethered 15-member aza-ether-crown macrocycle, namely {I^Acrown}H and {Amcrown}H, are reported. These proligands react with [Ba{N(SiMe2H)2}2·(thf)n] to generate the heteroleptic barium complexes [{I^Acrown}BaN(SiMe2H)2] (5) and [{Amcrown}BaN(SiMe2H)2] (6) in high yields. These complexes exhibit high coordination numbers (resp. eight and seven) and are in addition stabilised by mild BaH-Si interactions. Unusually for oxophilic elements such as barium, the amidinate ligand in 6 is only η1-coordinated. Complexes 5 and 6 mediate the intermolecular hydrophosphination of styrene with primary (PhPH2) and secondary (HPPh2) phosphines. Their catalytic performance compares favourably with those of other barium precatalysts for these reactions. During the course of the hydrophosphination of styrene with HPPh2 catalysed by 5, the phosphide complex [{I^Acrown}BaPPh2] (7) could be intercepted and crystallographically characterised.

19.
Chem Commun (Camb) ; 55(43): 6058-6061, 2019 May 28.
Artigo em Inglês | MEDLINE | ID: mdl-31066386

RESUMO

The transmetalation reaction of a chiral-bidentate NHC-silver complex to racemic [Ir(µ-Cl)(ppy)2]2 operates with kinetic resolution leading to chiral octahedral NHC-iridium(iii) complexes and enantio-enriched bis-cyclometalated iridium(iii) complexes. The iridium(iii) complexes demonstrated efficient catalytic activities in intermolecular [2+2] photocycloaddition reactions and in asymmetric Friedel-Crafts alkylations, respectively.

20.
Chemistry ; 25(37): 8854-8864, 2019 Jul 02.
Artigo em Inglês | MEDLINE | ID: mdl-31026099

RESUMO

A set of calcium and barium complexes containing the fluoroarylamide N(C6 F5 )2 - is presented. These compounds illustrate the key role of stabilising M⋅⋅⋅F-C secondary interactions in the construction of low-coordinate alkaline earth complexes. The nature of Ca⋅⋅⋅F-C bonding in calcium complexes is examined in the light of structural data, bond valence sum (BVS) analysis and DFT computations. The molecular structures of [Ca{N(C6 F5 )2 }2 (Et2 O)2 ] (4'), [Ca{µ-N(SiMe3 )2 }{N(C6 F5 )2 }]2 (52 ), [Ba{µ-N(C6 F5 )2 }{N(C6 F5 )2 }⋅toluene]2 (62 ), [{BDIDiPP }CaN(C6 F5 )2 ]2 (72 ), [{N^NDiPP }CaN(C6 F5 )2 ]2 (82 ), and [Ca{µ-OB(CH(SiMe3 )2 )2 }{N(C6 F5 )2 }]2 (92 ), where {BDIDiPP }- and {N^NDiPP }- are the bidentate ligands CH[C(CH3 )NDipp]2 - and DippNC6 H4 CNDipp- (Dipp=2,6-iPr2 -C6 H3 ), are detailed. Complex 62 displays strong Ba⋅⋅⋅F-C contacts at around 2.85 Å. The calcium complexes feature also very short intramolecular Ca-F interatomic distances at around 2.50 Å. In addition, the three-coordinate complexes 72 and 82 form dinuclear structures due to intermolecular Ca⋅⋅⋅F-C contacts. BVS analysis shows that Ca⋅⋅⋅F-C interactions contribute to 15-20 % of the bonding pattern around calcium. Computations demonstrate that Ca⋅⋅⋅F-C bonding is mostly electrostatic, but also contains a non-negligible covalent contribution. They also suggest that Ca⋅⋅⋅F-C are the strongest amongst the range of weak Ca⋅⋅⋅X (X=F, H, Cπ ) secondary interactions, due to the high positive charge of Ca2+ which favours electrostatic interactions.

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