Isomers 1a Research Articles

Cationic olefin Pd(II) complexes bearing α-iminoketone N,O-ligands: synthesis, intramolecular and interionic characterization and reactivity with olefins and alkynes

Complexes [Pd(η 1, η 2-5-OMe–C 8H 12)(N,O)]BF 4 (N,O=2,6-( i-Pr) 2(C 6H 3)NC(Ph)–C(Ph)O, 1; 2,6-( i-Pr) 2(C 6H 3)NC(Me)–C(Ph)O, 2; 2-benzoylpyridine, 3) were synthesized by the reactions of [Pd(η 1,η 2-5-OMe–C 8H 12)Cl] 2 with the suitable N,O-ligand. They were tested as catalysts for olefin or alkyne polymerizations. During such reactions 1– 3 quantitatively transformed into their η 1,η 2-1-OMe–C 8H 12 isomers ( 1a– 3a). The same isomerization occurred in methylene chloride, even in the absence of olefins or alkynes, with a much slower rate. All complexes were fully characterized in solution by multinuclear and multidimensional low temperature NMR spectroscopy. The solid state structures of complexes 1 and 1a were investigated by X-ray single crystal studies. 19F, 1H-HOESY NMR experiments carried out in methylene chloride-d 2 at 217 K indicated that the anion prefers to locate on the side of N,O-ligand shifted toward the O-arm in 1– 1a and 2– 2a while it approaches the N-arm in 3 and 3a compounds.

Oxidative addition of silanes R3SiH to the unsaturated cluster [Os3(μ-H){μ3-Ph2PCH2PPh(C6H4)}(CO)8]: Evidence for reversible silane formation in the dynamic behaviour of [Os3(μ-H)(SiR3)(CO)9(μ-dppm)

Oxidative addition of the silanes R(3)SiH (R(3)= Ph(3), Et(3), EtMe(2)) to the unsaturated cluster [Os(3)(micro-H)[micro(3)-Ph(2)PCH(2)PPh(C(6)H(4))](CO)(8)] leads to the saturated clusters [Os(3)(micro-H)(SiR(3))(CO)(9)(micro-dppm)](SiR(3)= SiPh(3) 1, SiEt(3) 2 and SiEtMe(2)3) and the unsaturated clusters [Os(3)(micro -H)(2)(SiR(3))[micro(3)-Ph(2)PCH(2)PPh(C(6)H(4))](CO)(7)](SiR(3)= SiPh(3) 4, SiEt(3) 5 and SiEtMe(2)6). Structures are based on spectroscopic evidence and a XRD structure of [Os(3)(micro-H)(SiPh(3))(CO)(9)(micro-dppm)] 1 in which all non-CO ligands are coordinated equatorially and the hydride and the silyl groups are mutually cis. From variable-temperature (1)H NMR spectra of the SiEt(3) compound 2, exchange of the P nuclei is clearly apparent. Simultaneous migrations of the SiEt(3) group and of the hydride from one Os-Os edge to another generate a time-averaged mirror plane in the molecule. VT (1)H NMR spectra of the somewhat less bulky compound [Os(3)(micro-H)(SiMe(2)Et)(CO)(9)(micro-dppm)] 3 have been analysed. Two isomers 3a and 3b are observed with the hydride ligand located on different Os-Os edges. Synchronous migration of the hydride and SiMe(2)Et groups is faster than the observed interconversion of isomers which occurs by hydride migration alone. The synchronous motion of H and SiR(3)only occurs when these ligands are mutually cis as in the major isomer 3a and we propose that this process requires the formation of a transient silane complex of the type [Os(3)(eta(2)-HSiR(3))(CO)(9)(micro-dppm)]. Turnstile rotation within an Os(CO)(3)(eta(2)-HSiR(3)) group leads to the observed exchange within the major isomer 3a without exchange with the minor isomer. This process is not observed for the minor isomer 3b because the hydride and the silyl group are mutually trans. Protonation to give [Os(3)(micro-H)(2)(SiR(3))(CO)(9)(micro-dppm)](+) totally suppresses the dynamic behaviour because there are no edge vacancies.

Synthesis, Structure, and DFT Calculation of (Phosphino-o-carboranyl)silyl Group 10 Metal Complexes: Formation of Stabletrans-Bis(P,Si-chelate)metal Complexes

Addition of the silane (HSiMe2)C2B10H10(PR2) (R = Me (2a), OEt (2b)) to (PPh3)2Pt(CH2CH2) (3) affords the trans-bis(chelates) Pt(CabP,Si)2 (4a,b; CabP,Si = η2-[(SiMe2)(PR2)C2B10H10-P,Si]) in high y...

Coordinatively Unsaturated Hydridoruthenium(II) Complexes of N-Heterocyclic Carbenes

The saturated imidazolin-2-ylidene compounds RNC3H4NR, with R = mesityl (SIMes), 2,6-diisopropylphenyl, were synthesized by use of diamines that were prepared by the hydrogenation of the corresponding diimines catalyzed by RuHCl(R-binap)(R,R-dach)/KOtBu in toluene. The ligands IMes (MesNC3H2NMes) and SIMes react with RuHCl(PPh3)3 to give RuH(SIMes-H)(PPh3)2 (1) and RuH(IMes-H)(PPh3)2 (2), respectively, where there is cyclometalation of a C−H bond of an ortho Ar−CH3 group. The reaction of RuHCl(PPh3)3 with ItBu (tBuNC3H2NtBu) produces ItBu·HCl and a red solution that, upon reaction with H2, produces the dihydride Ru(H)2(ItBu)(PPh3)2 as a mixture of the two isomers 3a (trans PPh3 ligands) and 3b (cis PPh3). These isomers have an agostic C−H bond from a methyl group. There is an interesting windshield wiper exchange of coordinated tert-butyl groups occurring in isomer 3a, as monitored in solution by VT NMR with a free energy of activation of 11.8 kcal/mol. The reaction of 2 with CO at 20 °C produces (OC-34)-...

Studies towards the construction of alkylidene quinolizidines: the total synthesis of homopumiliotoxin 223G

The addition of 5-methyl-2-triisopropylsilyloxyfuran (5) to N-carbobenzyloxy-2-methoxypiperidine (6a) afforded a mixture of the corresponding erythro and threo isomers 7a and 8a, respectively, in moderate to good yields (42-85%) and diastereoisomeric ratio (7a : 8a) ranging from 1.1:1 _ 6:1 depending on the solvent system and the Lewis acid employed. The threo isomer 8a was eventually converted to (+/-)-homopumiliotoxin 223G (1) which was prepared in 5 steps and 13% overall yield from 6a.

Characterization and Preliminary Use of 1‐, 2‐ and 3‐Methyl‐5‐phenyl‐7‐chloro‐1,2,3‐triazolo[4,5‐d]pyrimidine as Reaction Intermediates.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Imidazolines as Efficacious Glucose‐Dependent Stimulators of Insulin Secretion.

AbstractFor Abstract see ChemInform Abstract in Full Text.

New arene ruthenium complexes with planar chirality

1,2,4-Trimethyl-cyclohexadiene reacts with RuCl 3 · nH 2O in refluxing ethanol to afford quantitatively [RuCl 2(1,2,4-C 6H 3Me 3)] 2 ( 1), the coordination of 1,2,4-trimethylbenzene to the ruthenium atom introducing planar chirality at the η 6-arene ligand. The dinuclear complex 1 reacts with two equivalents of triphenylphosphine (PPh 3) to give quantitatively, as a racemic mixture of enantiomers, [RuCl 2(1,2,4-C 6H 3Me 3)(PPh 3)] ( 2), the structure of which has been determined by a single-crystal X-ray structure analysis of ( rac)- 2. Similarly, 1 reacts with two equivalents of the enantiopure phosphine (1 S,2 S,5 R)-(+)-neomenthyldiphenylphosphine (nmdpp) to afford in good yield [RuCl 2(1,2,4-C 6H 3Me 3)(nmdpp)] ( 3) as a mixture of diastereoisomers, from which the isomer 3a was isolated by crystallisation. A single-crystal X-ray structure analysis of 3a allowed the determination of the absolute configuration at the planar chiral η 6-arene moiety. Finally, complex 1 reacts with one equivalent of the diphosphine ligand 1,1 ′-bis(diphenylphosphino)ferrocene (dppfc) to give the heteronuclear complex [RuCl 2(1,2,4-C 6H 3Me 3) (dppfc)RuCl 2(1,2,4-C 6H 3Me 3)] ( 4). All complexes were fully characterised by elemental analysis, mass spectrometry, NMR and IR spectroscopies.

Fluorescence Property of Photochromic Diarylethenes with Indole Groups

Abstract Diarylethenes having a fluorescent indole ring as the aryl group 1a and 2a were synthesized. Upon alternate irradiation with 366 nm and visible (λ > 480 nm) light, 1a underwent reversible photocyclization reactions to produce closed-ring isomer 1b. The fluorescence intensity also reversibly changed along with the reactions. The fluorescence quantum yields of the open-ring isomers 1a and 2a were 4.6 and 6.3% respectively, while the yields of the closed-ring isomers 1b and 2b were almost zero. The fluorescence quantum yields decreased with the increase in the photocyclization quantum yields.

Monoalkylation of C60 and C70 with Zn and Active Alkyl Bromides.

We report a convenient and simple solution-phase electron-transfer reaction of C60 with zinc and α-bromoacetonitrile, α-bromo acetate esters, allyl bromide, benzyl bromide and α-bromo ketones in DMF, with which different types of monoalkylated C60 derivatives can be prepared. When this method is employed with C70, 2-carbomethoxymethyl-1,2-dihydro[70]fullerene (isomer 5a) is produced as one of the two 1,2-monoalkylated C70 isomers, together with the first 5,6-monoalkylated C70 derivative.

Characterization and preliminary use of 1-, 2- and 3-methyl-5-phenyl-7-chloro-1,2,3-triazolo[4,5-d]pyrimidine as reaction intermediates

This paper reports synthesis and characterization, by spectroscopic methods, of three new N-methyl-5-phenyl-7-chloro-1,2,3-triazolo[4,5-d]pyrimidine isomers 3a, 3b and 3c. For comparison purpose the 3-benzyl-5-phenyl-7-chloro-1,2,3-triazolo[4,5-d]pyrimidine ( 7) was also prepared. Starting from the isomer mixture 3a– c and the chloroderivative 7, by nucleophilic substitution reaction with ethyl carbazate and subsequent intramolecular cyclization, the new tricyclic derivatives 5a– c and 9 were prepared and tested towards the benzodiazepine and adenosine A 1 and A 2A receptors.

Photochromic 2-(N-acyl-N-arylaminomethylene)benzo[b]thiophene-3(2H)-ones with fluorescent labels and/or crown-ether receptors

Novel N-acylaminovinyl ketones of the benzo[b]thiophene series (AAB) capable of molecular switching of fluorescence or complexation with metal ions have been synthesized and their photochromic behavior studied using UV-Vis absorption/emission and 1 H- / 7 Li- NMR spectroscopy. Under UV irradiation the AAB compounds 2a–c containing fluorescent labels as their N-aryl substituents undergo Z/E- photo-isomerization and N→O acyl rearrangement resulting in the formation of O-acyl isomers 3a–c. The photo-switching of fluorescence has been found in the 4-fluorenonyl derivative 2a. The benzo-15-crown-5- containing AAB 2d,e are also susceptible to the same type of photo-initiated rearrangement. The corresponding O-acyl isomers 3d–e represent a group of chemosensors which readily form stable complexes with alkali- and alkali-earth- metal cations. The AAB 2d exhibits specific selectivity for Li + ion in the presence of Na + , K + and Cs + .

Structures and Thermodynamics of the Sulfuranes SF3CN and SF2(CN)2 as well as of the Persulfurane SF4(CN)2 − An ab initio MO Study by the G3(MP2) Method

AbstractAt the G3(MP2) level of theory the trans isomer 1a of the hypothetical molecule SF4(CN)2 is more stable than the cis isomer 1b by 8 kJ·mol−1. The isomerization of 1a to 1b requires an activation enthalpy of 319 kJ·mol−1 at 298 K. The decomposition of trans‐SF4(CN)2 to SF2(CN)2 and F2 is endothermic (ΔHo298 = 395 kJ·mol−1) but the elimination of FCN from trans‐SF4(CN)2 is exothermic by −7 kJ·mol−1. The elimination of (CN)2 from cis‐SF4(CN)2 is exothermic by −137 kJ·mol−1. The activation enthalpies for the latter two reactions were calculated as 251 and 311 kJ·mol−1, respectively. Thus, SF4(CN)2 should be a thermally stable compound. In the sulfuranes SF3CN and SF2(CN)2 the CN ligands prefer the equatorial positions; mutual exchange of an axial F atom by an equatorial CN group requires a reaction enthalpy of 51 kJ·mol−1 [SF3CN] or 58 kJ·mol−1 [SF2(CN)2]. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Photochromic radical compounds based on a naphthopyran system.

[reaction: see text] Naphthopyran derivatives with aminoxyl substituents (4a,b) gave the corresponding open-formed isomers (5a,b) by irradiation, which could be changed back to the starting closed-formed naphthopyrans by the treatment with SiO(2) as a catalyst. The tuning of intermolecular magnetic interactions between the isomer couples was found to be possible in these reversible systems.

Monoalkylation of C60 and C70 with Zn and active alkyl bromides.

We report a convenient and simple solution-phase electron-transfer reaction of C(60) with zinc and alpha-bromoacetonitrile, alpha-bromo acetate esters, allyl bromide, benzyl bromide and alpha-bromo ketones in DMF, with which different types of monoalkylated C(60) derivatives can be prepared. When this method is employed with C(70), 2-carbomethoxymethyl-1,2-dihydro[70]fullerene (isomer 5a) is produced as one of the two 1,2-monoalkylated C(70) isomers, together with the first 5,6-monoalkylated C(70) derivative.

Imidazolines as efficacious glucose-dependent stimulators of insulin secretion

Synthesis of a series of imidazolines with glucose dependent effects on insulin exocytosis from pancreatic β-cells is reported. Regioisomers and enantiomers were found to exhibit marked differences in exocytotic effects as well as different activities on the K ATP-channel; the ( R (+)) isomer of 2-[2-(4,5-dihydro-1 H-imidazol-2-yl)-1-thiophene-2-ylethyl]pyridine ( 4a) and the (+) isomer of 2-[2-(4,5-dihydro-1 H-imidazol-2-yl)-1-thiophene-3-ylethyl]pyridine ( 4d) were found to give a significant increase in insulin release—in contrast to findings for their enantiomers—without influence on the K ATP-channel. The (+) isomer ( 4a) showed glucose dependent insulin release from β-cells at concentrations above 2.5 mM and a marked glucose lowering effect in ob/ ob mice as well as in fed but not in fasted rats.

Photocontrol of Ca2+ complexation with an azacrown‐containing benzochromene

AbstractThe new azacrown‐containing benzochromene 1a was synthesized in order to study the effect of its reversible photochromic reaction on complex formation with Ca2+ in acetonitrile. It was found that both the initial chromene 1a and its photoinduced merocyanine isomer 2a are able to form 1:1 complexes with Ca2+, in which the metal cation coordinates to the crown ether moiety. The complexation causes strong spectroscopic shifts and leads to an increase in the dark lifetime of 2a. The equilibrium constant for the 1:1 complexation decreases upon photoinduced ring‐opening reaction (log K = 4.9 and 4.1 for 1a and 2a, respectively). Copyright © 2003 John Wiley & Sons, Ltd.

Structure analysis of some α‐(n‐methyl‐n‐formylaminomethyl)‐quinolines

AbstractThe 1H and 13C nmr spectra of the rotational isomers 3a and 3b of 6‐N‐methyl‐N‐formylaminomefhyl)‐thioquinanthrene were completely assigned with a combination of 1D and 2D nmr techniques. The key‐parts of this methodology were long‐range proton‐carbon correlations and NOE experiments with N‐methyl‐N‐formylaminomethyl substituent. The X‐ray study of 4‐methyl‐2‐N‐methyl‐N‐formylaminomethyl)quinoline 4a as well as 1H and 13C nmr spectra show that N‐methyl‐N‐formylaminomethyl substituent in 4a and 4b has a different steric arrangement than the same substituent in 3a and 3b.

Remarkable dynamical opening and closing of platinum and palladium pentaruthenium carbido carbonyl cluster complexes.

The reaction of Ru(5)(CO)(15)(mu(5)-C), 1, with Pt(PBu(t)(3))(2) at room temperature yielded the mixed-metal cluster complex PtRu(5)(CO)(15)(PBu(t)(3))(C), 2, in 52% yield. Compound 2 consists of a mixture of two interconverting isomers in solution. One isomer, 2A, can be isolated by crystallization from benzene/octane solvent. The second isomer, 2B, can be isolated by crystallization from diethyl ether. Both were characterized crystallographically. Isomer 2A consists of a square pyramidal cluster of five ruthenium atoms with a phosphine-substituted platinum atom spanning the square base. Isomer 2B consists of a square pyramidal cluster of five ruthenium atoms with a phosphine-substituted platinum atom on an edge on the square base. The two isomers interconvert rapidly on the NMR time scale at 40 degrees C, deltaG(313)++ = 11.4(8) kcal mol(-1), deltaH++ = 8.8(5) kcal mol(-1), deltaS++ = -8.4(9) cal mol(-1) K(-1). The reaction of Pd(PBu(t)(3))(2) with compound 1 yielded two new cluster complexes: PdRu(5)(CO)(15)(PBu(t)(3))(mu(6)-C), 3, in 50% yield and Pd(2)Ru(5)(CO)(15)(PBu(t)(3))(2)(mu(6)-C), 4, in 6% yield. The yield of 4 was increased to 47% when an excess of Pd(PBu(t)(3))(2) was used. In the solid state compound 3 is structurally analogous to 2A, but in solution it also exists as a mixture of interconverting isomers; deltaG(298)++ = 10.6(6) kcal mol(-1), deltaH++ = 9.7(3) kcal mol(-1), and deltaS++ = -3(1) cal mol(-1) K(-1) for 3. Compound 4 contains an octahedral cluster consisting of one palladium atom and five ruthenium atoms with an interstitial carbido ligand in the center of the octahedron, but it also has one additional Pd(PBu(t)(3)) grouping that is capping a triangular face of the ruthenium cluster. The Pd(PBu(t)(3)) groups in 4 also undergo dynamical interchange that is rapid on the NMR time scale at 25 degrees C; deltaG(298)++ = 11(1) kcal mol(-1), deltaH++ = 10.2(4) kcal mol(-1), and deltaS++ = -3(2) cal mol(-1) K(-1) for 4.

Hydrolysis of (Me3SiCH2)PhSnCl2. Isomerisation of the dimeric tetraorganodistannoxane [(Me3SiCH2)Ph(Cl)SnOSn(Cl)Ph(CH2SiMe3)

The hydrolysis of (Me3SiCH2)PhSnCl2 (1) was studied under two different reaction conditions (i) by using an excess of aqueous NaOH in toluene at reflux temperature and (ii) by using small amounts of NEt3 and water in CH2Cl2 at room temperature. For (i) the products (Me3SiCH2)Ph2SnOSnPh2(CH2SiMe3) (2) and [(Me3SiCH2Sn)12O14(OH)6](OH)2 (3) were isolated indicating that a phenyl group migration took place. For (ii) the dimeric tetraorganodistannoxane [(Me3SiCH2)Ph(Cl)SnOSn(Cl)Ph(CH2SiMe3)]2 (4) was obtained. In solution, 4 exists as an equilibrium mixture of all five possible isomers 4a–4e; in the solid state two of these isomers 4d and 4e co-crystallized in the same crystal modification. The observation of interconvertible isomers of 4 was attributed to the kinetic lability of the ladder-like Sn4O2Cl4 structural motif. Compounds 1 and 4 were investigated by X-ray crystallography.