Search results for "Lewis acids"

Cavitands incorporating a Lewis acid dinickel chelate function as receptors for halide anions.

2015

The halide binding properties of the cavitand [Ni2(L(Me2H4))](2+) (4) are reported. Cavitand 4 exhibits a chelating N3Ni(μ-S)2NiN3 moiety with two square-pyramidal Ni(II)N3S2 units situated in an anion binding pocket of ∼4 Å diameter formed by the organic backbone of the (L(Me2H4))(2-) macrocycle. The receptor reacts with fluoride, chloride (in MeCN/MeOH), and bromide (in MeCN) ions to afford an isostructural series of halogenido-bridged complexes [Ni2(L(Me2H4))(μ-Hal)](+) (Hal = F(-) (5), Cl(-) (6), and Br(-) (7)) featuring a N3Ni(μ-S)2(μ-Hal)NiN3 core structure. No reaction occurs with iodide or other polyatomic anions (ClO4(-), NO3(-), HCO3(-), H2PO4(-), HSO4(-), SO4(2-)). The binding ev…

Photochemical Synthesis and Reactivity of New Chloro-Bridged Complexes with Tungstenocene (η5-C5H5)(η5-C5H4PPh2)WClX (X = H, Cl) and Tetracarbonylmet…

1999

Chloro-bridged bimetallic complexes (η5-C5H5)[η5-C5H4PPh2M′(CO)4]W(μ-Cl)X [X = Cl (3), × = H (4); M′ = Cr, W] were prepared by photochemical irradiation of (η5-C5H5)[η5-C5H4PPh2M′(CO)5]WClX [X = Cl (1), × = H (2); M′ = Cr, W]. The reactivity of the chloro-bridged complexes towards Lewis bases was studied; by exposure to CO or phosphanes, a facile cleavage of the chloro bridge accompanied by regio- and stereospecific coordination at M′ occurs. The X-ray structure of complex 3 (M′ = W) is reported.

Activation of C−H Bonds in Five-Membered Heterocycles by a Half-Sandwich Yttrium Alkyl Complex

2001

Bonding Trends in Lewis Acid Adducts of S 4 N 4 – X‐ray Structure of TeCl 4 ·S 4 N 4

2006

Tetrasulfur tetranitride and tellurium tetrachloride react in dichloromethane to form a 1:1 adduct TeCl4·S4N4 (1). The crystal structure of 1 shows that TeCl4 is bonded to the S4N4 ring through a Te–N linkage. As a consequence, the transannular S···S bonds in S4N4 are broken and the molecule assumes an open, monocyclic conformation. The Te–N bond of 2.16(1) A is slightly longer than the single bond. The S–N bonds span a range of 1.55(1)–1.67(1) A. The adduct 1 was also characterized by mass spectrometry and Raman spectroscopy. The bonding and spectroscopic properties of 1 are compared by DFT calculations at the B3PW91/(RLC ECP) level of theory with those of BF3·S4N4 (2), SO3·S4N4 (3), AsF5·…

Aqueous solution chemistry of alkyltin(IV) compounds for speciation studies in biological fluids and natural waters

2012

Abstract Organotin(IV) cations behave as Lewis acids of different strength depending on the charge, according to the following acidity scale: RSn3+ > R2Sn2+ > R3Sn+. For this reason they can react with Lewis bases containing –O, –N, –S donor groups to form complex species of different stability. Complex formation of organotin(IV) moieties with a great number of inorganic and organic ligands in aqueous solution is reviewed here in the light of their environmental and biological impact. To this end, complex species formation was considered in different ionic media and at different ionic strengths, with reference to the composition of natural waters and biological fluids. In particular, the in…

Initiatoren für die polymerisation des trioxane. 20. Mitt. über polyoxymethylene1

1963

Die Polymerisation des Trioxans bei 60°C in Cyclohexan mit verschiedenen kationischen Initiatoren wurde untersucht. Die aktivsten Initiatoren sind Acetylperchlorat, Perchlorsaure, FeCl3 und SnCl4. Die Molekulargewichte der erhaltenen Polyoxymethylene sind bei den aktivsten Initiatoren am hochsten. Der Einflus der ubertragung durch Wasser und der kinetischen Kettenlange auf die Molekulargewichte wird diskutiert. Wahrend der Polymerisation kann durch den Initiator eine Spaltung bereits gebildeter Makromolekule erfolgen, welche die Molekulargewichte stark reduziert. Die Frage der Cokatalyse bei der kationischen Polymerisation des Trioxans mit Ansolvosauren wurde untersucht. Bei der Polymerisat…

Comparative G2(MP2) Molecular Orbital Study of B3H7XH3 and H3BXH3 Donor−Acceptor Complexes (X = N, P, and As)

2002

B3H7XH3 and H3BXH3 (X = N, P, and As) have been studied as donor−acceptor complex type at the G2(MP2) level of theory. Both single- and double-bridged structures of B3H7 Lewis acid are taken into account. Although the double-bridged structure is energetically favored in the isolated state, the coordination prefers the single-bridged one. The monoborane adducts adopt the staggered arrangement with C3v symmetry. The energetic analysis by natural bond orbital theory shows that the decrease of hyperconjugative contribution upon complexation in the B3H7 moiety has, as consequence, a loss of symmetry for B3H7XH3 (X= P and As) complexes. In the two series, the coordination is the result of two opp…

Cationic Cyclopentadienyl Phenylenediamido Titanium Species Generated by Reaction of TiCpR[1,2-C6H4(NCH2t-Bu)2]R (CpR = η5-C5H5, η5-C5Me5; R = CH3, C…

2006

The reaction of TiCpR[1,2-C6H4(NNp)2]R with the Lewis acid B(C6F5)3 in noncoordinating solvent affords the new zwitterionic species TiCpR[1,2-C6H4(NNp)2)][μ-RB(C6F5)3]. When the reaction is performed in dichloromethane, the [μ-RB(C6F5)3]- anion is displaced by solvent molecules, giving ionic products in which the anion is not coordinated. The cyclopentadienyl zwitterionic complexes TiCp[1,2-C6H4(NNp)2)[μ-RB(C6F5)3] decompose via ligand scrambling between boron and titanium to give the neutral titanium complex TiCp[1,2-C6H4(NNp)2](C6F5) along with the byproduct RB(C6F5)2. In contrast, the pentamethylcyclopentadienyl analogues TiCp*[1,2-C6H4(NNp)2][μ-RB(C6F5)3] evolve through C−H activation t…

Early transition metal derivatives stabilised by the phenylenediamido 1,2-C6H4(NCH2tBu)2 ligand: Synthesis, characterisation and reactivity studies: …

2009

Abstract Li 2 [1,2-C 6 H 4 (NCH 2 t Bu) 2 ] reacts with one equiv of [TiCl 4 (THF) 2 ] in refluxing toluene to give the chelate compound [Ti{1,2-C 6 H 4 (NCH 2 t Bu) 2 }Cl 2 (THF)] ( 1 ), isolated as a black product, while the reaction of the dilithio diamido salt with one equiv of [ZrCl 4 (THF) 2 ] in refluxing toluene affords the dinuclear zirconium derivative [Zr{1,2-C 6 H 4 (NCH 2 t Bu) 2 }Cl(THF)(μ-Cl)] 2 ( 2 ), obtained as an orange solid. Treatment of the dilithio diamido salt with TaCl 5 in a 2:1 molar ratio in toluene yields [Ta{1,2-C 6 H 4 (NCH 2 t Bu) 2 } 2 Cl] ( 3 ) as a red product. The reaction of 1,2-C 6 H 4 (NHCH 2 t Bu) 2 with [Zr(NMe 2 ) 4 ] in toluene at room temperature …

Synthesis of a polymer-bound galactosylamine and its application as an immobilized chiral auxiliary in stereoselective syntheses of piperidine and am…

2004

A 2,3,4-tri-O-pivaloylated beta-D-galactopyranosyl azide bearing a hydroxy-functionalized spacer unit at the C-6 position of the galactose was synthesized and immobilized on the solid phase by using a polymer-bound chlorosilane. The azide was reduced to the corresponding galactopyranosylamine, which served as a versatile chiral auxiliary in highly diastereoselective Ugi four-component condensation reactions at ambient temperature. Fluoride-induced cleavage from the polymeric support furnished N-glycosylated N-acylated alpha-amino acid amides. The reaction of the immobilized galactosylamine with aldehydes gave rise to the corresponding aldimines, which underwent a domino Mannich-Michael cond…