Efficient syntheses of the first ruthenium alkylidene complexes bearing siloxide ligands are described. Second generation Hoveyda–Grubbs catalyst is shown to undergo efficient functionalization with a number of potassium silanolates to give disiloxy derivatives. The complexes obtained are found catalytically active in selected metathesis transformations.
Mechanistic Significance of the Si–O–Pd Bond in the Palladium-Catalyzed Cross-Coupling Reactions of Arylsilanolates
作者:Steven A. Tymonko、Russell C. Smith、Andrea Ambrosi、Michael H. Ober、Hao Wang、Scott E. Denmark
DOI:10.1021/jacs.5b02518
日期:2015.5.20
neutral 8-Si-4 intermediate; (2) with 1.0–5.0 equiv of added silanolate, activated transmetalation via an anionic 10-Si-5 intermediate; and (3) with >5.0 equiv of added silanolate, concentration-independent (saturation) activated transmetalation via an anionic 10-Si-5 intermediate. Transition states for the intramolecular transmetalation of neutral (8-Si-4) and anionic (10-Si-5) intermediates have been
通过结合反应动力学(化学计量和催化)、芳基钯(II)芳基硅烷醇化物的溶液和固态表征以及计算分析,在交叉偶联反应中含有 Si-O-Pd 键的共价加合物的中间体芳基硅烷醇盐已明确确立。已经证明了两种机制不同的途径:(1) 通过中性 8-Si-4 中间体进行金属转移,该中间体在没有游离硅烷醇化物的情况下占主导地位(即芳基钯 (II) 芳基硅烷醇化物配合物的化学计量反应),以及 (2) 通过阴离子 10-Si-5 中间体,在催化条件下(即在游离硅烷醇盐存在下)在交叉偶联中占主导地位。已分离出带有各种膦配体的芳基钯 (II) 芳基硅烷醇化物配合物,完全表征,并评估它们在热(化学计量)和阴离子(催化)条件下的动力学能力。热活化和阴离子活化速率的比较表明,但并未证明,包含 Si-O-Pd 键的中间体参与了交叉偶联过程。与 t-Bu3P 连接的配位不饱和 T 形芳基钯 (II) 芳基硅烷醇化物复合物的分离允许明确证明涉及
Reduction of Allylpalladium(II)chloride Dimer by Formation of Allyloxysilanes
作者:Scott Denmark、Russell Smith
DOI:10.1055/s-2006-951516
日期:2006.11
The reduction ofallylpalladium(II)chloride dimer (APC) to a Pd(0) species can be effected by reaction with alkali metal silanolates. The reduction is extremely rapid in the presence of chelating bisphosphine ligands and for a variety of silanolates.
烯丙基氯化钯 (II) 二聚体 (APC) 还原为 Pd(0) 物质可以通过与碱金属硅烷醇盐反应来实现。在螯合双膦配体和各种硅烷醇化物存在的情况下,还原速度非常快。
Phosphine oxides as stabilizing ligands for the palladium-catalyzed cross-coupling of potassium aryldimethylsilanolates
作者:Scott E. Denmark、Russell C. Smith、Steven A. Tymonko
DOI:10.1016/j.tet.2007.02.017
日期:2007.6
The palladium-catalyzed cross-coupling reaction of potassium (4-methoxyphenyl) dimethylsilanolate (K(+)1(-)) with aryl bromides has been demonstrated using triphenylphosphine oxide as a stabilizing ligand. Unsymmetrical biaryls can be prepared from a variety of aryl bromides in good yield with short reaction times. Qualitative kinetic studies compared effects of different phosphine oxides on the rate of cross-coupling and established the beneficial effect of these ligands in the reaction of electron-rich arylsilanolates. The improved yield and reproducibility of the cross-coupling of several bromides was demonstrated by direct comparison of reactions performed with and without triphenylphosphine oxide under non-rigorous exclusion of oxygen. (C) 2007 Elsevier Ltd. All rights reserved.
Probing the electronic demands of transmetalation in the palladium-catalyzed cross-coupling of arylsilanolates
作者:Scott E. Denmark、Russell C. Smith、Wen-Tau T. Chang
DOI:10.1016/j.tet.2011.03.066
日期:2011.6
The electronic characteristics of coupling partners in the transmetalation step for the cross-coupling reaction of arylsilanolates have been investigated. The ability to interrogate the transmetalation event by in situ preparation of the arylpalladium(II) silanolate intermediate has enabled a Hammett analysis for both the aryl electrophile and arylsilanolate to be conducted. These studies reveal that electron-donating groups on the silicon nucleophile and electron-withdrawing groups on the electrophile accelerate the transmetalation process. (C) 2011 Elsevier Ltd. All rights reserved.