Steric stabilization of a monomeric proalumatrane: experimental and theoretical studies

Treatment of tripodal tris(3-tert-butyl-2-hydroxy-5-methylbenzyl)amine (L) with 1 equiv of trimethylaluminum in toluene gave the stable proalumatrane (AlL) (1) [wherein L = tris(3-tert-butyl-5-methyl-2-oxidobenzyl)amine] featuring a distorted trigonal monopyramidal four-coordinate aluminum geometry. An analogous reaction uses the less sterically congested isomer of L, namely, tris(5-tert-butyl-2-hydroxy-3-methylbenzyl)amine provided dimeric (AlL')2 (2) [wherein L' = tris(5-tert-butyl-3-methyl-2-oxidobenzyl)amine], which contains two bridging alumatrane moieties possessing five-coordinate TBP aluminum geometries. Reaction of AlL with water provided the adduct H2O.AlL (3), a species that is representative of a coordinatively stabilized intermediate in the hydrolysis of an aluminum alkoxide. Theoretical calculations revealed that considerable stabilization energy is obtained by the coordination of a water molecule to the tetracoordinate aluminum in AlL and that this result is consistent with the postulate that the Lewis acidity of AlL exceeds that of boron trifluoride, despite the presence of the transannular N-->Al bond in AlL.     

结构非线性分析中求解预定荷载水平的改进弧长法

本文对目前广泛应用于结构非线性分析之中的弧长法进行改进。改进后的弧长法除保持原有优点外，能够在自动跟踪结构非线性平衡路径的同时，进一步求得位于结构平衡睡径任一区段的任意预先指定的荷载水平及相应的变形。本文的方法可以推广应用于求解预先指定的应力或位移。数值算例表明了本文方法的计算精度、效率及可靠性。     

P(RNCH 2 CH 2 ) 3 N as Very Strong Non-Ionic Bases and Catalysts: Recent Advances and Applications

A rationale for the unusually strong Lewis basicity and catalytic activity of the title pro-azaphosphatranes is presented. Four stoichiometric and four catalytic uses of such pro-azaphosphatranes are described, as well as some unexpected reactions in which these bases take part. Mechanistic pathways are put forth for several of the transformations outlined.     

Steric Versus Electronic Effects in the Ligation Behavior of Trivalent Phosphorus Compounds: 59Co AND 31P NMR Spectroscopic Studies

Abstract

Using NMR techniques, the role of electronic and steric influences in phosphorus(III) ester complexes of the type CoL₆ ³⁺ and AgL_n ⁺ (where n = 1–4) are assessed.     

The first example of a monomeric alumatrane

The novel five-coordinate aluminum adduct Me(2)HN. AlL (2) [wherein L = tris(2-oxy-3,5-dimethylbenzyl)amine] containing three six-membered rings has been characterized by spectroscopic and by X-ray means. This adduct of an alumatrane is the first structurally characterized monomeric alumatrane derivative, and unlike its parent alumatrane [Al(OCH(2)CH(2))(3)N](x), 2 is monomeric in the gas, solution, and solid states. The X-ray molecular structure of 2 reveals a tricyclic cage moiety of C(3) symmetry. The aluminum geometry is a slightly distorted trigonal bipyramid in which, quite unexpectedly, the metal atom is located somewhat below the plane formed by three equatorial oxygens and its Al-N(tertiary) bond is shorter than that in Me(3)N.AlH(3).NMe(3) (Heitsch, C. W.; Nordman, C. E.; Parry, R. W. Inorg. Chem. 1963, 2, 508).     

A highly effective catalyst system for the Pd-catalyzed amination of vinyl bromides and chlorides

[reaction: see text] A highly efficient synthesis of enamines and imines by Pd-catalyzed amination of vinyl bromides or chlorides with amines is described using the Pd2(dba)3/P(i-BuNCH2CH2)3N catalyst system.     

P[N(i-Bu)CH2CH2]3N: a versatile ligand for the Pd-catalyzed amination of aryl chlorides

[reaction: see text] Palladium-catalyzed amination reactions of aryl chlorides with amines proceeded in the presence of the bicyclic triaminophosphine P[N(i-Bu)CH(2)CH(2)](3)N to afford the corresponding arylamines in good to excellent yields. Electron-poor, electron-neutral, and electron-rich aryl chlorides all participated with equal ease.     

P(RNCH(2)CH(2))(3)N: efficient 1,4-addition catalysts

The 1,4-addition of primary alcohols, higher nitroalkanes, and a Schiff's base of an alpha-amino ester to alpha,beta-unsaturated substrates produces the corresponding products in moderate to excellent yields when carried out at -63 to 70 degrees C in the presence of catalytic amounts of the nonionic strong bases P(RNCH(2)CH(2))(3)N (R = Me, i-Pr, i-Bu) in isobutyronitrile. Diastereoselectivity for the anti form of the product is high in the case of the Schiff's base in the absence of lithium ion. These catalysts are easily removed from the product by either column filtration through silica gel or via aqueous workup.