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1.
Artigo em Inglês | MEDLINE | ID: mdl-32048388

RESUMO

We report on the structures of three unprecedented heteroleptic Sb-centered radicals L(Cl)GaSb R (2-R, R = B[N(Dip)CH]22-B, 2,6-Mes2C6H32-C, N(SiMe3)Dip 2-N) stabilized by one electropositive metal fragment [L(Cl)Ga] (L = HC[C(Me)N(Dip)]2, Dip = 2,6-i-Pr2C6H3) and one bulky B- (2-B), C- (2-C), or N-based (2-N) substituent. Compounds 2-R are predominantly metal-centered radicals. Their electronic properties are largely influenced by the electronic nature of the ligands R , and significant delocalization of unpaired spin density onto the ligands was observed in 2-B and 2-N. Cyclic voltammetry (CV) studies showed that 2-B undergoes a quasi-reversible one-electron reduction, which was confirmed by the synthesis of [K([2.2.2]crypt)][L(Cl)GaSbB[N(Dip)CH]2] ([K([2.2.2]crypt)][2-B]) containing the stibanyl anion [2-B]-, which was shown to possess significant Sb-B multiple bonding character.

2.
Inorg Chem ; 2020 Jan 21.
Artigo em Inglês | MEDLINE | ID: mdl-31961137

RESUMO

We present the synthesis of a series of new lanthanide(III) complexes supported by a monoanionic bidentate anilidophosphine ligand (N-(2-(diisopropylphosphanyl)-4-methylphenyl)-2,4,6-trimethylanilide, short PN-). The work comprises the characterization of a variety of heteroleptic complexes containing either one or two PN ligands as well as a study on further functionalization possibilities. The new heteroleptic complexes cover selected examples over the whole lanthanide(III) series including lanthanum, cerium, neodymium, gadolinium, terbium, dysprosium, and lutetium. In case of the two diamagnetic metal cations lanthanum(III) and lutetium(III), we have furthermore studied the influence of the lanthanide ion (early vs. late) on the reactivity of these complexes. Thereby we found that the radius of the lanthanide ion has a major influence on the reactivity. Using sterically demanding, multidentate ligand systems, e.g., cyclopentadienide (Cp-), we found that the lanthanum complex La(PN)2Cl (1-La) reacts well to the corresponding cyclopentadienide complex, while for Lu(PN)2Cl (1-Lu) no reaction was observed under any conditions tested. On the contrary, employing monodentate ligands such as mesitolate, thiomesitolate, 2,4,6-trimethylanilide or 2,4,6-trimethylphenylphosphide, results in the clean formation of the desired complexes for both lanthanum and lutetium. All complexes have been studied by various techniques, including multi nuclear NMR spectroscopy and X-ray crystallography. 31P NMR spectroscopy was furthermore used to evaluate the presence of open coordination sites on the complexes using coordinating and noncoordinating solvents, and as a probe for estimating the Ce-P distance in the corresponding complexes. Additionally, we present cyclic voltammetry (CV) data for Ce(PN)2Cl (1-Ce), La(PN)2Cl (1-La), Ce(PN)(HMDS)2 (8-Ce) and La(PN)(HMDS)2 (8-La) (with HMDS = hexamethyldisilazide, (Me3Si)2N-) exploring the potential of the anilidophosphane ligand framework to stabilize a potential Ce(IV) ion.

3.
Chem Commun (Camb) ; 56(7): 1105-1108, 2020 Jan 23.
Artigo em Inglês | MEDLINE | ID: mdl-31894766

RESUMO

A series of hydrogen-bonded liquid crystals based on resveratrol and resveratrone is reported and investigated with respect to their photo-switchability (at 405 nm) and photo-cyclisation (at 300 nm).

4.
Dalton Trans ; 49(2): 375-387, 2020 Jan 02.
Artigo em Inglês | MEDLINE | ID: mdl-31829382

RESUMO

Four tetranuclear magnesium complexes were synthesized and fully characterized. They are excellent catalysts for the ring-opening polymerization (ROP) of bulk racemic-lactide (rac-LA) and ε-caprolactone (ε-CL) even with low catalyst loading under industrially relevant conditions without additional co-initiators, yielding polymers with high molecular weight (Mn) and moderately controlled molecular weight distribution (MWD). The polymerization activity depends on the steric and electronic properties of the imino(phenolate) ligands. Kinetic studies of the most active catalyst 1 confirmed that the ROP of rac-LA and ε-CL has a first order dependence on monomer concentration. The ROP of rac-LA and ε-CL using 1-4 with BnOH gave polymers with narrow MWD and a close correlation between Mobsn and Mtheon values. Catalyst 1 was also capable of polymerizing technical-grade rac-LA and ε-CL even with large monomer-to-catalyst ratios ([M]0/[C]0) of up to 10 000 : 1 and without any additional co-initiator. The very high turnover frequencies (TOF) of 9600 h-1 (rac-LA) and 24 000 h-1 (ε-CL) prove that 1 belongs to the most active biocompatible, sustainable and nontoxic ROP catalysts under industrially relevant conditions.

5.
Dalton Trans ; 48(48): 17729-17734, 2019 Dec 28.
Artigo em Inglês | MEDLINE | ID: mdl-31754681

RESUMO

Three equivalents of LGa {L = HC[C(Me)N(2,6-i-Pr2C6H3)]2} react with AsX3 (X = Cl, Br) by insertion into two As-X bonds, followed by the elimination of LGaX2 and formation of LGaAsGa(Cl)L (1) and LGaAsGa(Br)L (2). According to single crystal X-ray analysis, 1 and 2 each exhibit one Ga-As single bond and one Ga-As double bond. The π-bonding contribution (9.71 kcal mol-11 and 9.44 kcal mol-12) was proved by variable temperature (VT) 1H NMR spectroscopy, while the electronic structure of 1' was studied by quantum chemical calculations.

6.
Dalton Trans ; 48(39): 14611-14625, 2019 Oct 07.
Artigo em Inglês | MEDLINE | ID: mdl-31475272

RESUMO

We report the synthesis of a new pincer-type triazolylidene ligand precursor H3L[Cl] with redox-active 3,5-di-tert-butylphenolate substituents on a multigram scale following a converging ten-step route. The potential of this new mesoionic carbene ligand in early transition metal chemistry is explored. This includes the synthesis of the first triazole-derived mesoionic carbene complexes of titanium, niobium and molybdenum as well as the first example of MIC imido complexes of these elements. Furthermore, the reactivity as well as the electrochemical properties of the new complexes are compared to known, comparable bis-phenolate NHC complexes.

7.
Soft Matter ; 15(36): 7117-7121, 2019 Sep 18.
Artigo em Inglês | MEDLINE | ID: mdl-31503269

RESUMO

In this contribution we describe a novel hydrogelator based on four guadiniumcarbonylpyrrole units in combination with aggregation-induced emission active aromatic thioethers which undergo self-assembly into fibrills in aqueous media as visible in AFM and TEM measurements. These fibrills are weakly luminescent and unable to induce gelation. Upon addition of malonic acid a cross-linking of the single fibres was detected leading to the formation of a highly emissive stable hydrogel. This gel responds to several external stimuli such as heat, shaking as well as pH changes.

8.
ChemistryOpen ; 8(7): 951-960, 2019 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-31338277

RESUMO

Zinc phenoxide complexes L1ZnOAr 1-4 (L1=Me2NC2H4NC(Me)CHC(Me)O) and L2ZnOAr 5-8 (L2=Me2NC3H6NC(Me)CHC(Me)O) with donor-functionalized ß-ketoiminate ligands (L1/2) and OAr substituents (Ar=Ph 1, 5; 2,6-Me2-C6H3 2, 6; 3,5-Me2-C6H3 3, 7; 4-Bu-C6H4 4, 8) with tuneable electronic and steric properties were synthesized and characterized. 1-8 adopt binuclear structures in the solid state except for 5, while they are monomeric in CDCl3 solution. 1-8 are active catalysts for the ring opening polymerization (ROP) of lactide (LA) in CH2Cl2 at ambient temperature and the catalytic activity is controlled by the electronic and steric properties of the OAr substituent, yielding polymers with high average molecular weight (M n) and moderately controlled molecular weight distribution (MWDs). 1 and 5 showed a living polymerization character and kinetic studies on the ROP of L-LA with 1 and 5 proved first order dependencies on the monomer concentration. Homonuclear decoupled 1H-NMR analyses of polylactic acid (PLA) formed with rac-LA proved isotactic enrichment of the PLA microstructure.

9.
Inorg Chem ; 58(15): 10323-10332, 2019 Aug 05.
Artigo em Inglês | MEDLINE | ID: mdl-31335127

RESUMO

A convenient synthetic route to Ga-stabilized pnictogen-centered radicals and gallapnictenes by manipulation of pnictogen-carbon bond strengths is presented. Two equivalents of LGa (L = HC[C(Me)N(Dip)]2, Dip = 2,6-i-Pr2C6H3) react with CpArAsCl2 (CpAr = C5(4-t-BuC6H4)5) with formation of the arsenic-centered radical [L(Cl)Ga]2As·1. In contrast, the analogous reaction with TerSbCl2 (Ter = 2,6-Mes2C6H3; Mes = 2,4,6-Me3C6H2) yields the gallastibene LGa═SbTer (2) containing a Ga-Sb double bond, whereas reactions of DipSbCl2 with one and two equivalents of LGa give the monoinsertion and bisinsertion products L(Cl)GaSb(ClDip) (3) and [L(Cl]Ga]2SbDip (4), respectively. 1-4 were structurally characterized by single crystal X-ray diffraction. The description of 1 as an arsenic-centered radical is consistent with results of electron paramagnetic resonance and density functional theory (DFT) studies. The π-bonding in LGa═SbTer (2) is estimated to 10.68 kcal mol-1 by variable-temperature (VT) NMR spectroscopy, and DFT studies reveal a significant π-bonding interaction between Sb and Ga.

10.
Chemistry ; 25(51): 11826-11830, 2019 Sep 12.
Artigo em Inglês | MEDLINE | ID: mdl-31152678

RESUMO

The complex class [Fe(N^N^C)(N^N^N)]+ with an Earth-abundant metal ion has been repeatedly suggested as a chromophore and potential photosensitizer on the basis of quantum chemical calculations. Synthesis and photophysical properties of the parent complex [Fe(pbpy)(tpy)]+ (Hpbpy=6-phenyl-2,2'-bipyridine and tpy=2,2':6',2''-terpyridine) of this new chromophore class are now reported. Ground-state characterization by X-ray diffraction, electrochemistry, spectroelectrochemistry, UV/Vis, and X-ray spectroscopy in combination with DFT calculations proves the high impact of the cyclometalating ligand on the electronic structure. The photophysical properties are significantly improved compared to the prototypical [Fe(tpy)2 ]2+ complex. In particular, the metal-to-ligand absorption extends into the near-IR and the 3 MLCT lifetime increases by 5.5, whereas the metal-centered excited triplet state is very short-lived.

11.
Chem Asian J ; 14(6): 814-820, 2019 Mar 15.
Artigo em Inglês | MEDLINE | ID: mdl-30478991

RESUMO

In this contribution, we present the synthesis and self-assembly of alkylated thioethers with interesting photophysical properties. To this end, the emission, absorption and excitation spectra in organic solvents and as aggregates in water were measured as well as the corresponding photoluminescence quantum yields and lifetimes. The aggregates in aqueous media were visualized and measured using transmission electron microscopy. Besides that, crystal structures of selected compounds allowed a detailed discussion of the structure-property relationship. Furthermore, the mesomorphic behavior was investigated using polarized optical microscopy (POM) as well as differential scanning calorimetry (DSC).

12.
J Am Chem Soc ; 141(3): 1337-1348, 2019 Jan 23.
Artigo em Inglês | MEDLINE | ID: mdl-30588811

RESUMO

Metal-catalyzed dimerization reactions of terminal acetylenes are well known in the literature. However, only a few examples of the dimerization of halogen-substituted acetylenes are described. The products of the latter metal-catalyzed dimerization are the branched head-to-tail enynes. The formation of the corresponding linear head-to-head enynes has not been reported yet. Herein, we demonstrate by means of quantum chemical methods and experiments that the head-to-head dimerization of chloroarylacetylenes can be achieved via mono gold catalysis. Under the optimized conditions, a clean and complete conversion of the starting materials is observed and the dimeric products are obtained up to 75% NMR yield. A mechanistic investigation of the dimerization reaction reveals that the branched head-to-tail vinyl cation is energetically more stable than the corresponding linear head-to-head cation. However, the latter can rearrange by an unusual 1,3-chlorine shift, resulting in the highly stereoselective formation of the trans product, which corresponds to the gold complex of the head-to-head E-enyne. The activation barrier for this rearrangement is extremely low (ca. 2 kcal/mol). As the mono gold-catalyzed dimerization can be conducted in a preparative scale, this simple synthesis of trans-1,2-dichloroenynes makes the gold(I)-catalyzed head-to-head dimerization of chloroarylacetylenes an attractive method en route to more complex conjugated enyne systems and their congeners.

13.
J Org Chem ; 83(23): 14568-14587, 2018 Dec 07.
Artigo em Inglês | MEDLINE | ID: mdl-30359025

RESUMO

In this account, we describe the synthesis of a series of BINOL-based bis- and trisphosphoric acids 11d/e/f, which commonly feature an unusual phosphoric acid monoester motif. This motif is generated by an acid-catalyzed 5- endo- dig cyclization of the 3-alkynyl-substituted BINOL precursors to give the corresponding Furan-annelated derivatives, followed by phosphorylation of the remaining phenolic alcohols. In the cyclization reaction, we observed an unexpected partial racemization in the bis- and tris-BINOL scaffolds, leading to mixtures of diastereomers that were separated and characterized spectroscopically and by X-ray crystal structure analyses. The cyclization and racemization processes were investigated both experimentally and by DFT-calculations, showing that although the cyclization proceeds faster, the barrier for the acid-catalyzed binaphthyl-racemization is only slightly higher.

14.
Inorg Chem ; 57(15): 9495-9503, 2018 Aug 06.
Artigo em Inglês | MEDLINE | ID: mdl-30039963

RESUMO

L1Ga {L1 = HC[C(Me)N(2,6- iPr2C6H3)]2} reversibly reacts with E2Ph4 (E = Sb, Bi) in a temperature-dependent equilibrium reaction with insertion into the E-E bond and formation of L1Ga(EPh2)2 (E = Sb 1, Bi 2). Analogous findings were observed in the reactions of L2Ga {L2 = (C6H11)2NC[N(2,6- iPr2C6H3)]2} with E2R4 (R = Ph, Et), yielding L2Ga(EPh2)2 (E = Sb 3, Bi 4) and L2Ga(EEt2)2 (E = Sb 5, Bi 6). 1-3 and 5 were isolated by fractional crystallization at low temperature, whereas 4 and 6 could not be isolated in their pure form even at low temperature. In contrast, reactions of [Cp*Al]4 (Cp* = C5Me5) with Sb2R4 (R = Ph, Et) and Bi2Et4 did not proceed with insertion into the E-E bonds but with formation of (Cp*Al)3E2 (E = Sb, 7; Bi, 8), whereas the reaction with Bi2Ph4 yielded metallic bismuth. 8 was also formed in the reaction of [Cp*Al]4 and BiEt3 at ambient temperature, whereas the analogous reaction of [Cp*Al]4 with SbEt3 did not yield 7 even under drastic reaction conditions (120 °C, 3 days). In contrast, Cp*Ga and Sb2R4 (R = Ph, Et) were found to react only at elevated temperature (120 °C) with formation of antimony metal.

15.
Dalton Trans ; 47(36): 12511-12515, 2018 Sep 18.
Artigo em Inglês | MEDLINE | ID: mdl-29786735

RESUMO

Spontaneous ion separation of the scorpionate beryllium complex, TpBeI 1 (Tp = 1-trispyrazolylborate), occurs upon treatment with THF, yielding [TpBe(thf)]I 2, which was characterized by heteronuclear NMR spectroscopy (1H, 9Be, 13C) and structurally characterized by single crystal X-ray diffraction. 2 represents a rare example of a structurally characterized monocationic beryllium complex, and to the best of our knowledge, the synthesis of 2 by a solvent-induced ion separation has previously only been observed in the reactions of beryllium dihalides with strong Lewis bases.

16.
Chemistry ; 24(36): 9157-9164, 2018 Jun 26.
Artigo em Inglês | MEDLINE | ID: mdl-29665160

RESUMO

Reactions of three equivalents of LGa {L=HC[C(Me)N(2,6-iPr2 C6 H3 )]2 } with SbX3 (X=F, Cl, Br, I) proceed with insertion into the Sb-X bond, elimination of LGaX2 , and formation of LGaSbGa(X)L (X=F 1, Cl 2, Br 3, I 4) containing a Ga=Sb double bond. In contrast, the 2:1 molar ratio reaction of LGa and SbCl3 initially gives the twofold insertion product [L(Cl)Ga]2 SbCl 7, which could not be isolated due to its strong tendency toward elimination of LGaCl2 and formation of distibene [L(Cl)GaSb]2 5 at 25 °C or cyclotristibine [L(Cl)GaSb]3 6 at 8 °C. The formation of 1-6 can be rationalized by formation of the Ga-substituted stibinidene L(X)GaSb as reaction intermediate.

17.
J Am Chem Soc ; 140(15): 5053-5056, 2018 04 18.
Artigo em Inglês | MEDLINE | ID: mdl-29537831

RESUMO

Cp*AsCl2 (Cp* = C5Me5) reacts with one equivalent of LGa (L = HC[C(Me)N(2,6- i-Pr2C6H3)]2) with formation of L(Cl)GaAs(Cl)Cp* 1, whereas the reaction with two equivalents of LGa yielded gallaarsene LGaAsCp* 2 containing a Ga═As double bond and (η1-Ga(Cp*)L(η2-GaL)(µ-As3) 3. Compounds 2 and 3 were structurally characterized by single crystal X-ray diffraction, and the π-bonding contribution in 2 was analyzed by temperature-dependent 1H NMR spectroscopy (9.65 kcal mol-1) and by quantum mechanical computation.

18.
Nat Commun ; 9(1): 87, 2018 01 08.
Artigo em Inglês | MEDLINE | ID: mdl-29311607

RESUMO

Neutral stibinyl and bismuthinyl radicals are typically short-lived, reactive species. Here we show the synthesis and solid-state structures of two stable stibinyl [L(Cl)Ga]2Sb· 1 and bismuthinyl radicals [L(I)Ga]2Bi· 4, which are stabilized by electropositive metal centers. Their description as predominantly metal-centered radicals is consistent with the results of NMR, EPR, SQUID, and DFT studies. The Lewis-acidic character of the Ga ligands allow for significant electron delocalization of the Sb- and Bi- unpaired radical onto the ligand. Single-electron reduction of [L(Cl)Ga]2Sb· gave LGaSbGa(Cl)L 5, the first compound containing a Ga=Sb double bond. The π-bonding contribution is estimated to 9.56 kcal mol-1 by NMR spectroscopy. The bonding situation and electronic structure is analyzed by quantum mechanical computations, revealing significant π backdonation from the Sb to the Ga atom. The formation of 5 illustrates the high-synthetic potential of 1 for the formation of new compounds with unusual electronic structures.

19.
Chemistry ; 24(13): 3241-3250, 2018 Mar 02.
Artigo em Inglês | MEDLINE | ID: mdl-29266416

RESUMO

Two equivalents of LGa (L=HC[C(Me)N(2,6-iPr2 C6 H3 )]2 ) reacted with PX3 (X=Cl, Br) with insertion into two P-X bonds and formation of [L(X)Ga]2 PX (X=Cl 1, Br 2), whereas the analogous reaction with AsCl3 occurred with twofold insertion and subsequent elimination of LGaCl2 and formation of the Ga-substituted diarsene [L(Cl)Ga]2 As2 (3). Analogous findings were observed in the reactions with Me2 NAsCl2 , yielding the unsymmetrically-substituted diarsene [L(Cl)Ga]As=As[Ga(NMe2 )L] (4). The reaction of As(NMe2 )3 with LGa gave [L(Me2 N)Ga]2 As2 (5) after heating at 165 °C for five days, whereas the reaction with LAl gave [L(Me2 N)Al]2 As2 (6) after heating at only 80 °C for one day. Finally, two equivalents of LGa reacted with Bi(NEt2 )3 to give [L(Et2 N)Ga]2 Bi2 (7). Complexes 1-7 were characterized by NMR spectroscopy (1 H, 13 C, 31 P), elemental analysis, and single-crystal X-ray diffraction (except for 1 and 5). The bonding situations in 4, 6, and 7 were analyzed by quantum chemical calculations.

20.
Chemistry ; 23(55): 13660-13668, 2017 Oct 04.
Artigo em Inglês | MEDLINE | ID: mdl-28661014

RESUMO

Here we report on a novel system based on aromatic thioethers with unique luminescence properties. Fifteen different compounds were investigated in detail on their luminescence properties using UV/Vis absorption and steady-state and time-resolved luminescence spectroscopy. Excited state lifetimes as well as quantum yields were determined, and the toxicity towards HeLa cells was investigated. Besides X-ray analyses also quantum chemical calculations were performed to gain deeper insights in the unique behavior of this facile system. The studied compounds reveal remarkable fluorescence emission ranging from 437 to 588 nm as well as phosphorescence (up to 5 µs).

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