铑催化烯烃氢甲酰化反应的密度泛函研究

在B3LYP／6-31G(d,P)(Rh和P采用LANL2DZ Polar)水平下,研究了有机膦羰基铑催化乙烯的氢甲酰化反应机理,优化了反应中间体、过渡态和产物的结构．结果表明,乙烯的氢甲酰化反应有两条主要的反应路径,经历了乙烯络合、乙烯插入、膦加成、羰基插入、H2的氧化加成和丙醛还原消除及催化剂的再生等过程．乙烯插入、羰基插入、H2的氧化加成和丙醛还原消除过程中三元环的形成是协同进行的．反应以顺式活性催化剂为起始物,H2的氧化加成是反应速度控制步骤,丙酰基的消除反应是不可逆的．理论结果与实验一致．     

Molecular mechanics‐based measures of steric effects: Customized code to compute Ligand repulsive energies

Ligand repulsive energies, E_R, have been demonstrated to provide reliable steric parameters for ligands in organometallic systems. To date, ligand repulsive energies have been computed manually using commercially available molecular mechanics code. We report a customized code, ERCODE, that calculates ligand repulsive energies. Some reported E_R values differ from those in the literature due to a modified conformational search strategy presented. Updated ligand repulsive energies for 100 phosphines, 12 phosphites, 26 amines, and 54 alcohols, ethers, and sulfides are presented. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 239–246, 2000     

Effect of ligand volume correction on PMF scoring

Recently, a knowledge‐based scoring function has been introduced that estimates the protein‐binding affinity based on the 3D structure of a protein–ligand complex (J Med Chem 1999, 42, 791). A ligand volume correction factor has been proposed and applied to filter out intraligand interactions in this simplified potential approach. Here we evaluate the effect of the ligand volume correction on the predictive power of the PMF scoring function. It is found that the effect of the ligand volume correction is significant on the derived potentials and large on the overall score. However, the effect of the ligand correction on the predictive power of the scoring function appears to be smaller. For a test set containing serine proteases the predictive power of the PMF scoring function does not change with the introduction of the volume correction. For a test set of metalloprotease complexes, the predictive power of the PMF scoring function improves only slightly when the volume correction is applied. For five test sets comprising a total of 225 diverse protein ligand complexes taken from the Brookhaven Protein Data Bank it is found, however, that the introduction of the ligand volume correction consistently improves the correlation between the PMF scores and the measured binding affinities. The effect of the correction factor on docking/scoring experiments is also analyzed using a test set of 61 biphenyl inhibitor‐stromelysin complexes. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 418–425, 2001     

气相法二氧化硅负载胺-钯配合物的制备及对Heck反应催化性能的研究

以气相法二氧化硅为载体,链状胺和环胺为功能化试剂,制得一系列二氧化硅-胺基复合载体,通过配位反应得到二氧化硅负载胺-钯（Ⅱ）配合物,进一步还原得到二氧化硅负载胺-钯（0）配合物．采用IR、XRD、XPS、ICP技术对配合物进行表征,并研究了配合物的制备、反应条件以及配体差异对其催化碘苯与丙烯酸的Heck反应的性能．结果表明,该类催化剂在较低的温度下（70～90℃）即可较好地催化该反应,生成反式产物;还原后催化剂具有更好的催化活性和良好的重复使用性能;具有链状胺基配体的催化剂随着N原子数目的增加,催化活性呈上升趋势,而具有环状胺基配体的催化剂活性明显低于前者．     

Organometallische Alkoxo–Indium‐Käfigverbindungen

Compounds with Organometallic Alkoxo–Indium Cages The reaction of InMe₃ with PhCH₂OH (molar ratio 1 : 2) at 20 °C in toluene gives the tetranuclear complex [In{(PhCH₂O)₂InMe₂}₃] ( 2 ) in good yield. A further reaction under reflux conditions was not observed. However, at 160 °C in PhCH₂OH a reaction could be realized, which forms an O‐centred corner‐cutted rhombic dodecahedron, [(MeIn)₅(OCH₂Ph)₈(O)] ( 3 ), under evolution of methane. This In–O skeleton can be degraded with elemental cesium to a hexa‐ and heteronuclear complex [Cs{Cs(THF)}{[MeIn(OCH₂Ph)₂]₄O}] ( 4 ). 2 – 4 were characterized by IR, RE, NMR and MS techniques as well as by X‐ray analyses. According to them 2 can be described as In³⁺ ion, coordinated by three metalate units [Me₂In(OCH₂Ph)₂]^–. 3 loses one MeIn fragment during the transfer of two electrons. Two Cs⁺ ions complete the new rhombic dodecahedron, at which different coordination spheres were observed. One Cs⁺ ion possesses additional contacts to a THF ligand and four π‐electron systems from four phenyl rings, while the THF ligand is missing in the environment of the second alkali cation.     

Structural Requirements of 1-(2-Pyridinyl)-5-pyrazolones for Disproportionation of Boronic Acids

We observed an unusual formation of four-coordinate boron(III) complexes from the reaction of 1-(2-pyridinyl)-5-pyrazolone derivatives with arylboronic acids in the basic media. The exact mechanism is not clear; however, the use of unprotected boronic acid and the presence of a bidentate ligand appeared to be the key structural requirements for the transformation. The results suggest that base-promoted disproportionation of arylboronic acid with the assistance of the [N,O]-bidentate ligation of 1-(2-pyridinyl)-5-pyrazolone should take place and facilitate the formation of pyrazole diarylborinate. Experiments to obtain a deeper understanding of its mechanism are currently underway.     

Synthesis and Characterization of Metal Complexes of two Novel Pyridine‐Derived Macrocyclic Ligands Bearing o‐ and p‐Nitrobenzyl Pendant Groups

The pendant‐armed ligands L¹ and L² were synthesized by N‐alkylation of the two secondary aminic groups of the oxaazamacrocyclic precursor L with o‐nitrobenzylbromide (L¹) or p‐nitrobenzylbromide (L²). Metal complexes of L¹ and L² have been synthesized and characterized by microanalysis, MS‐FAB, conductivity measurements, IR, UV‐Vis, ¹H and ¹³C NMR spectroscopy and magnetic studies. Crystal structures of ligands L¹ and L², as well as complexes [CdL¹(NO₃)₂]·2CH₃CN and [Ag₂Br(L²)₂](ClO₄)·2CH₃CN have been determined by single crystal X‐ray crystallography.     

Multiple-site ligand binding to flexible macromolecules: Separation of global and local conformational change and an iterative mobile clustering approach

This article concerns the calculation of equilibria of ligand binding to multiple sites in macromolecules in the presence of conformational flexibility and conformation-dependent interaction among the sites. A formulation of this problem is presented in which global conformational changes are distinguished from conformational changes that are confined to “locally flexible regions.” The formalism is quite general in that ligands of different types, multivalent binding sites, tautomeric binding sites, and sites that bind more than one type of ligand can be accommodated. Strictly speaking, the separation of the conformational problem into global and local parts does not impose any loss of generality, although in practice it is necessary to restrict the number of global and local conformers. Because of the combinatorics of binding and conformational states, the computational complexity of a problem having only local conformational flexibility grows exponentially with the number of sites and the number of locally flexible regions. An iterative mobile clustering method for cutting off this exponential growth and obtaining approximate solutions with low computational cost is presented and tested. In this method, a binding site is selected, and a “cluster” of strongly interacting sites is set up around it; within the cluster, the binding and conformational states are fully enumerated, whereas the influences of sites outside the cluster on the sites inside are treated by a mean field approximation. The procedure then moves to the next site around which another (possibly overlapping) cluster is formed and the calculation is repeated. The procedure iterates through the list of sites in this way, using the results of previous iterations for the mean-field terms of current iterations until a convergence criterion is met. The method is tested on a large set of randomly generated problems of varying size, whose geometries are chosen to have protein-like statistical properties. It is found that the method is accurate and rapid with the computational cost scaling linearly to quadratically with the number of sites, except for a minority of cases in which large clusters occur by chance. The new method is more accurate than a Monte Carlo method, and may be faster or slower depending on the clustering criteria and details of the macromolecule. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 1091–1111, 1999     

Statistical analysis of computational docking of large compound data bases to distinct protein binding sites

The results of 16 docking simulations with rigid receptor sites and flexible ligands (∼60,000 compounds in each case) are statistically analyzed and compared. Different combinations of binding sites, scoring functions, and compound collections are used in these calculations. The docking scores are not randomly distributed over the scoring range; they follow Gaussian distributions (regardless of the binding sites), scoring functions, or screened compounds. If the docking sites are small, the Gaussian distributions are positively skewed. Peaks of the Gaussian distributions are populated with compounds having similar scores but different sizes and binding modes. These findings have implications for compound selection via computational docking. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 1634–1643, 1999