RESUMEN
Metallacyclic complex [(Me2N)3Ta(η(2)-CH2SiMe2NSiMe3)] (3) undergoes C-H activation in its reaction with H3SiPh to afford a Ta/µ-alkylidene/hydride complex, [(Me2N)2{(Me3Si)2N}Ta(µ-H)2(µ-C-η(2)-CHSiMe2NSiMe3)Ta(NMe2)2] (4). Deuterium-labeling studies with [D3]SiPh show H-D exchange between the Ta-D-Ta unit and all methyl groups in [(Me2N)2{(Me3Si)2N}Ta(µ-D)2(µ-C-η(2)-CHSiMe2NSiMe3)Ta(NMe2)2] ([D2]-4) to give the partially deuterated complex [Dn]-4. In addition, 4 undergoes ß-H abstraction between a hydride and an NMe2 ligand and forms a new complex [(Me2N){(Me3 Si)2N}Ta(µ-H)(µ-N-η(2)-C,N-CH2NMe)(µ-C-η(2)-C,N-CHSiMe2NSiMe3)Ta(NMe2)2] (5) with a cyclometalated, η(2)-imine ligand. These results indicate that there are two simultaneous processes in [Dn]-4:1)â H-D exchange through σ-bond metathesis, and 2)â H-D elimination through ß-H abstraction (to give [Dn]-5). Both 4 and 5 have been characterized by single-crystal X-ray diffraction studies.
RESUMEN
The synthesis of a C-disaccharide that is designed as a mimetic for the repeating unit disaccharide of hyaluronic acid is described. The target compound was obtained via the SmI2-promoted coupling reaction of the sulfone, 2-acetamido-4,6-O-benzylidene-3-O-tert-butyldimethylsilyl-1,2-dideoxy-1-pyridinylsulfonyl-beta-D-glucopyranose (6), and the aldehyde, p-methoxyphenyl 2,3-di-O-benzyl-4-deoxy-4-C-formyl-6-O-p-methoxybenzyl-beta-D-glucopyranoside (14).
Asunto(s)
Disacáridos/síntesis química , Ácido Hialurónico/química , Conformación de Carbohidratos , Secuencia de Carbohidratos , Disacáridos/química , Glicosilación , Indicadores y Reactivos , Modelos Moleculares , Datos de Secuencia Molecular , Sulfonas/químicaRESUMEN
Reactions of Ta(NMe2)5 with D2SiR'Ph (R' = Me, Ph) were found to give a dideuteride eta 2-imine complex (Me2N)3Ta(mu-D)2(mu-N-eta 2-N,C-CH2NMe)Ta(NMe2)3(1-d2) through C-H activation of an amide ligand via beta-H abstraction, and the structure of 1 was confirmed by single crystal neutron and X-ray diffraction.
RESUMEN
(Me3SiCH2)3(Me3SiC≡)WâO=PMe3 (1), an adduct between (Me3SiCH2)3W≡CSiMe3 (2) and O=PMe3, reacts with O2 to give O=W(OSiMe3)(CH2SiMe3)3 (3) and CO2. Reaction of 2 with H2O yields 3 and the trimer [(µ-O)W(CH2SiMe3)2(=O)(THF)]3 (4). In the reaction of D2O with 2, 3-d(n) and methane isotopologues CH2D2, CHD3 and CD4 have been observed.
RESUMEN
The structures of two compounds which are intermediates in the synthesis of phenanthroindolizidine alkaloids have been determined. (8bS,13aS,14R,14aR)-8b,9,11,12,13,13a,14,14a-Octahydro-14-hydroxy-2,3,6,7-tetramethoxydibenzo[f,h]pyrrolo[1,2-b]isoquinolin-11-one acetone solvate, C24H27NO6.C3H6O, (II), crystallizes in a chiral space group with one solvent molecule (acetone) present in the asymmetric unit. On the other hand, (8bS,13aS,14S,14aR)-8b,9,11,12,13,13a,14,14a-octahydro-14-hydroxy-2,3,6,7-tetramethoxydibenzo[f,h]pyrrolo[1,2-b]isoquinolin-11-one, C24H27NO6, (III), crystallizes in a centrosymmetric space group with two molecules in the asymmetric unit and with no solvent present. The two molecules in the asymmetric unit of (III) are structurally the same. Compounds (II) and (III) are epimers at the C atom carrying the OH group; otherwise they are very similar in structure.
Asunto(s)
Isoquinolinas/química , Cetonas/química , Alcaloides/síntesis química , Cristalografía por Rayos X , Enlace de Hidrógeno , Indolizinas/síntesis química , Conformación Molecular , Estructura Molecular , Fenantrenos/síntesis química , Pirroles/química , EstereoisomerismoRESUMEN
Titanium and zirconium amido complexes containing a hydrotris(pyrazolyl)borate (Tp) or hydrotris(3,5-dimethylpyrazolyl)borate (Tp*) ligand TpM(NMe(2))(3) (M = Ti, 1; M = Zr, 2) and Tp*M(NMe(2))(3) (M = Ti, 3; M = Zr, 4) were prepared by the reactions of M(NMe(2))(3)Cl (M = Ti, Zr) with sodium hydridotris(pyrazol-1-yl)borate and potassium hydridotris(3,5-dimethylpyrazol-1-yl)borate, respectively. The structures of 1, 2, and 4.CH(2)Cl(2) were determined by X-ray diffraction and show octahedral coordination geometry around the metal centers. Density functional theory calculations at the B3PW91 level were performed to understand the orientations and the rotational behavior of amido ligands in these metal complexes.