The reaction of 1,3,5-trimethyl-1,3,5-triazacyclohexane (TMTAC) with [La{Al(CH(3))(4)}(3)] resulted in C-H activation, leading to the formation of [(TMTAC)La{Al(CH(3))(4)}{(mu(3)-CH(2))[Al(CH(3))(2)(mu(2)-CH(3))](2)}] (1) containing a bis(aluminate) dianion and subsequent extrusion of methane. A similar reaction with [Y{Al(CH(3))(4)}(3)] led to the formation of CH(4), [TMTAC{Al(CH(3))(3)}(2)] (2) and {[(TMTAC)Y][Y(2)(mu(2)-CH(3))][{(mu(6)-C)[Al(mu(2)-CH(3))(2)(CH(3))](3)}{(mu(3)-CH(2))(mu(2)-CH(3))Al(CH(3))(2)}(2)] (3), containing a six-coordinate carbide ion and two [CH(2)Al(CH(3))(3)](2)(-) anions. Compound 3 is a product of multiple C-H activation.
View Article and Find Full Text PDFA new procedure for the generation of cationic methyl complexes of rare-earth metals has been developed for yttrium and praseodymium as two examples from the rare-earth series. The reactions of the rare-earth-metal tetramethylaluminates [Ln(AlMe(4))(3)] of yttrium and praseodymium with three differently sized crown ethers in thf, namely [12]crown-4, [15]crown-5 and [18]crown-6, respectively, led to the compounds [YMe([12]crown-4)(2)](2+)[AlMe(4)](-)(2) (1), [PrMe([12]crown-4)(2)](2+)[AlMe(4)](-)(2) (2), [YMe([15]crown-5)(thf)(2)](2+)[AlMe(4)](-)(2) (3), [Pr([15]crown-5)(2)](3+)[AlMe(4)](-)(3) (4), [YMe([18]crown-6)(thf)](2+)[AlMe(4)](-)(2) (5) and [PrMe([18]crown-6)(thf)(2)](2+) [AlMe(4)](-)(2) (6). With the exception of 4, all compounds contain molecular di-cations with a Ln-CH(3) unit bonded to one (3, 4, 6) or two (1, 2) crown-ether molecules.
View Article and Find Full Text PDFNovel procedures have been developed to condense benzaldehyde effectively with beta-amino acid amides to cyclic benzyl aminals. Double carbamate protection of the heterocycle resulted in fully protected chiral beta-alanine derivatives. These serve as universal precursors for the asymmetric synthesis of functionalised beta(2)-amino acids containing acid-labile protected side chains.
View Article and Find Full Text PDFPhytochemical investigation of the stem bark of Beilschmiedia zenkeri led to the isolation of four new methoxylated flavonoid derivatives, (2S,4R)-5,6,7-trimethoxyflavan-4-ol (1), (2S,4R)-4,5,6,7-tetramethoxyflavan (2), beilschmieflavonoid A (3), and beilschmieflavonoid B (4), together with seven known compounds. The structures of 1-4 were established by spectroscopic methods, and their relative configurations confirmed by X-ray crystallographic and CD analysis. The isolated compounds were evaluated in vitro for their antibacterial activity against three strains of bacteria, Pseudomonas agarici, Bacillus subtilis, and Streptococcus minor, and for their antiplasmodial activity against Plasmodium falciparum, chloroquine-resistant strain W2.
View Article and Find Full Text PDFReactions of the lithiated carbanion [(RLi)(2).(RH)] (R = MeN[CH(2)N(Me)](2)CH, 2,4,6-trimethyl-2,4,6-triazacyclohex-1-yl) with dialkylaluminium and -gallium chlorides lead to the corresponding dialkylaluminium and -gallium compounds (RAlMe(2))(2), (RAlEt(2))(2) and (RGaEt(2))(2). They were characterised by elemental analyses, NMR spectroscopy ((1)H, (13)C, (27)Al) and crystal structure determinations.
View Article and Find Full Text PDFThe reaction of the donor-functionalised N,N-bis(2-{pyrid-2-yl}ethyl)hydroxylamine and [LnCp3] (Cp=cyclopentadiene) resulted in the formation of bis(cyclopentadienyl) hydroxylaminato rare-earth metal complexes of the general constitution [Ln(C5H5)2{ON(C2H4-o-Py)2}] (Py=pyridyl) with Ln=Lu (1), Y (2), Ho (3), Sm (4), Nd (5), Pr (6), La (7). These compounds were characterised by elemental analysis, mass spectrometry, NMR spectroscopy (for compounds 1, 2, 4 and 7) and single-crystal X-ray diffraction experiments. The complexes exhibit three different aggregation modes and binding motifs in the solid state.
View Article and Find Full Text PDFtert-Butyllithium deprotonates bis(3-methyl-1,3-diazacyclohex-1-yl)methane and its five-ring analogue regioselectively at both endocyclic NCH2N units; a deprotonation intermediate has been isolated and structurally characterised.
View Article and Find Full Text PDFThe salt (eta(5)-pentamethylcyclopentadienyl)silicon(II) tetrakis(pentafluorophenyl)borate (5) reacts at -78 degrees C with lithium bis(trimethylsilyl)amide in dimethoxyethane (DME) as solvent to give quantitatively the compound [bis(trimethylsilyl)amino][pentamethylcyclopentadienyl]silicon(II) 6A in the form of a colorless viscous oil. The reaction performed at -40 degrees C leads to the silicon(IV) compound 7, the formal oxidative addition product of 6A with DME. Cycloaddition is observed in the reaction of 6A with 2,3-dimethylbutadiene to give the silicon(IV) compound 8.
View Article and Find Full Text PDFHydroxylamine units, bonded via their oxygen atom to a cyclo-pentadienyldimethylsilyl group are transformed into siloxy ligands and hydrazide units by the reaction with tetrakis(dimethylamido)-titanium and -zirconium by the same reaction principle but resulting in different aggregates of the products.
View Article and Find Full Text PDFA series of pi-conjugated systems with two and three 1,3-diethyl-1,3,2-benzodiazaborolyl end-groups was synthesised in 58-91% yields using established 1,3,2-diazaborole methodologies. The bis(diazaborolyl) compounds contain thiophene -2,5-C4H2S- (2a), dithiophene -5,5'-(2,2'-C4H2S)2- (2b), phenylene -1,4-C6H4- (2c), biphenylene -4,4'-(1,1'-(C6H4)2)- (2d) and dioctylfluorene -2,7-(9,9-(C8H7)2C11H6)- (2e) bridges. The three-way linkers in the tris(diazaborolyl) assemblies contain a central phenylene unit -1,3,5-C6H3- linked to the borolyl end groups via thiophene -2,5-C4H2S- (3a), directly bonded (3b) or via phenylene -1,4-C6H4- (3c) units.
View Article and Find Full Text PDFThree endiandric acid derivatives, beilschmiedic acids A, B and C were isolated from the stem bark of Beilschmiedia anacardioides together with the known beta-sitosterol. Their structures were established by means of modern spectroscopic techniques. The relative configuration of compound 1 was determined by single crystal X-ray analysis.
View Article and Find Full Text PDFNew 2-arylalkynyl benzo-1,3,2-diazaboroles, 2-(4'-XC(6)H(4)C[triple bond, length as m-dash]C)-1,3-Et(2)-1,3,2-N(2)BC(6)H(4) (X =Me ; MeO ; MeS ; Me(2)N ), were prepared from B-bromodiazaborole, 2-Br-1,3-Et(2)-1,3,2-N(2)BC(6)H(4), with the appropriate lithiated arylacetylene, ArC[triple bond, length as m-dash]CLi. Molecular structures of , and were determined by X-ray diffraction studies. UV-vis and luminescence spectroscopic studies on these diazaboroles reveal intense blue/violet fluorescence with very large quantum yields of 0.
View Article and Find Full Text PDFAngew Chem Int Ed Engl
April 2009
Si takes a rest: A bulky sigma-bound terphenyl substituent and a pi-bound Cp* ligand enable the isolation and full characterization of the first aryl-substituted, monomeric silicon(II) compound 1, which can be regarded as the "resting state" of a true silylene containing a sigma-bound Cp* group. The conformation of the aryl group prevents aryl-Si pi back-bonding.
View Article and Find Full Text PDFCubic aggregation: The racemic C(3)-symmetrical tribenzotriquinacene 1 was synthesized and found to crystallize in cubic aggregates consisting of eight homochiral molecules. The major driving force for this unique supramolecular aggregation may be attributed to the 24 equivalent sub-van der Waals interactions between the bromine atoms located at the convex surface of the triquinacene cores, rather than to polar interactions between the nitrobenzene units within and between the nanocubes.
View Article and Find Full Text PDFN,N-Dimethylaminopropylsilane H(3)Si(CH(2))(3)NMe(2) was synthesised by the reaction of (MeO)(3)Si(CH(2))(3)NMe(2) with lithium aluminium hydride. Its solid-state structure was determined by X-ray diffraction, which revealed a five-membered ring with an SiN distance of 2.712(2) A.
View Article and Find Full Text PDFVarious tribenzotriquinacenes (TBTQs), most of which incorporate six functional groups at the periphery of their C3v-symmetrical, rigid and convex-concave molecular framework, have been studied with respect to their ability to form supramolecular complexes with the C60 and C70 fullerenes, either in the solid state or in solution. The hexabromo derivative Br6-TBTQ was cocrystallized with C60 as [Br6-TBTQ
[reaction: see text] Two short synthetic approaches toward cryptophycin unit A comprise a catalytic asymmetric dihydroxylation as the sole source of chirality, while all further stereogenic centers are introduced under substrate control. The key step of the first route is a vinylogous Mukaiyama aldol addition, which introduces the alpha,beta-unsaturated ester moiety with defined configuration at the delta-carbon atom. Likewise, allylation with allyltributylstannane diastereoselectively gives the homoallylic alcohol that can be converted by a metathesis reaction to a unit A precursor.
View Article and Find Full Text PDFThe chloro and azido complexes trans-[PdCl(4-C5NF4)(PiPr3)2] (3) and trans-[Pd(N3)(4-C5NF4)(PiPr3)2] (4) can be prepared by reaction of [PdF(4-C5NF4)(PiPr3)2] (2) with Et3SiCl or MeSiN3, respectively. In contrast, reactions of 2 with Ph3SiH or Me2FSiSiFMe2 give the products of reductive elimination 2,3,5,6-tetrafluoropyridine (5) or 4-(fluorodimethylsilyl)tetrafluoropyridine (6) as well as [Pd(PiPr3)2] (1). In a catalytic experiment, pentafluoropyridine can be converted with Ph3SiH into 5 in 62% yield, when 10% of 2 is employed as catalyst.
View Article and Find Full Text PDFThe pentamethylcyclopentadienylsilicon(II) cation, Me5C5Si+, opens up access to novel silicocene derivatives; the penta-iso-propylcyclopentadienylsilicon(II) cation, iPr5C5Si+, is obtained by reaction of the mixed silicocene (iPr5C5)(Me5C5)Si with H(OEt2)2+ Al[OC(CF3)3]4-.
View Article and Find Full Text PDFReaction of 2-bromo-1,3-diethyl-1,3,2-benzodiazaborole (1) with equimolar amounts of thienyl lithium or 2,2-dithienyl lithium led to the generation of benzodiazaboroles 2 and 3 which are functionalized at the boron atom by a 2-thienyl or a 5-(2,2-dithienyl) unit. Similarly 2-bromo-1,3-diethyl-1,3,2-naphthodiazaborole (4) and thienyl lithium or 2,2-dithienyl lithium afforded the naphthoborolyl-substituted thiophene 5 or dithiophene 6. Treatment of 2,5-bis(dibromoboryl)-thiophene 7 with 2 eq.
View Article and Find Full Text PDFThe trinuclear ferrocenophane [{Fe(eta(5)-C(5)H(4))(3)}(2)Ga(2)] (3) featuring two sp(2)-hybridized gallium atoms in bridging positions between three ferrocene-1,1'-diyl units represents a novel type of ferrocene derivative. Compound 3 is obtained by thermal treatment of 1,1'-bis(dimethylgallyl)ferrocene (1) in nondonor solvents or in diethyl ether as solvent and subsequent thermal decomplexation. The [1.
View Article and Find Full Text PDFReaction of 1,4-bis(dibromoboryl)benzene (1a) with 2 equiv. of the diazabutadiene tBuN=CH-CH=NtBu and subsequent reduction of the obtained bis(1,3,2-diazaborolium)salt 2a with sodium amalgam afforded the 1,4-bis(1,3,2-diazaborolyl)benzene 3a. Similarly, 1,3-bis(dibromoboryl)benzene (1b), 1,3,5-tris(dibromoboryl)benzene (1c) and 4,4'-bis(dibromoboryl)biphenyl (1d) were converted into compounds 3b, 3c and 3d which contain two or three diazaborolyl substituents at the arene core.
View Article and Find Full Text PDFReactions of hexanuclear carbonyl clusters of rhodium Rh(6)(CO)(16) and ruthenium Ru(6)(eta(6)-C)(micro(2)-CO)(CO)(16) with GaCp*(Cp*= C(5)Me(5)) in the mild conditions result in substitution of CO ligands and formation of the Rh(6)(CO)(12)(micro(3)-GaCp*)(4) and the Ru(6)(eta(6)-C)(micro(2)-CO)(CO)(13)(micro(3)-GaCp*)(2)(micro(2)-GaCp*) cluster derivatives.
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