The three ancillary amidomoieties in the cationic complex [(Et2N)3U][BPh4] are highly reactive nd are easily replaced when the complex s treated with primary amines. The reaction of [(Et2N)3U][BPh4] with excess BuNH2 allows the formation of the cationic complex [(tBuNH2)3(tBu- H)3U][BPh4]. X-ray diffraction studies on the complex indicate that three mido and three amine ligands are arranged around the cationic metal enter in a slightly distorted octahedral er geometry. The cationic complex eacts with primary alkynes in the presence f external primary amines to rimarily afford the unexpected cis dimmer nd, in some cases, the hydroamination products are obtained concomitantly. The formation of the cis dimer is he result of an envelope isomerization hrough a metal ± cyclopropyl cationic omplex. In the reaction of the bulkier lkyne tBuC_CH with the cationic uranium omplex in the presence of various primary amines, the cis dimer, one rimer, and one tetramer are obtained egioselectively, as confirmed by deuterium abeling experiments. The trimer nd the tetramer correspond to consecutive nsertions of an alkyne molecule nto the vinylic CH bond trans to the bulky tert-butyl group. The reaction of (TMS)CCH with the uranium catalyst in the presence of EtNH2 followed a ifferent course and produced the gem dimer along with the hydroamination mine as the major product. However, when other bulkier amines were used (iPrNH2 or tBuNH2) both hydroamination isomeric imines Z and E were btained. During the catalytic reaction, the E (kinetic) isomer is transformed nto the most stable Z (thermodynamic)isomer. The unique reactivity of the lkyne (TMS)C_CH with the secondarya mine Et2NH is remarkable because it fforded the trans dimer and the corresponding hydroamination enamine. The atter probably results from the insertion of the alkyne into a secondary metal ±amide bond, followed by protonolysis.

The cationic complex [(Et2N)3U][BPh4] reacts with a mixture of terminal alkynes inducing the synthesis of the cross dimerization products. For equimolar amounts of aliphatic alkynes (iPrC /CH, tBuC/CH) the head-to-tail geminal dimer of iPrC /CH and the geminal cross dimer resulting from the insertion of iPrC /CH into the U/C/CR(R/ iPr, tBu) moiety are obtained. When a mixture of PhC /CH is reacted with either iPrC /CH or tBuC /CH, different products are obtained depending on the molar ratio of the alkynes. The dimerization of iPrC /CH with an excess of PhC /CH produces the geminal head-to-tail cross dimer issued from the insertion of the aliphatic alkyne into the U/C/CPh moiety, and the geminal dimer of PhC /CH. Inverting the molar ratio of the alkynes and using the deuterium labeled aliphatic alkyne iPrC/CD,the deuterated geminal head-to-tail cross dimer is obtained preferentially with small amounts of the deuterated head-to-tail dimer of iPrC/CD. The mixture of tBuC/CH and PhC /CH is converted into the geminal head-to-tail cross dimer in good yield if the former alkyne is in large excess. The addition of external EtNH2 in the cross dimerization of iPrC /CH with PhC /CH induces a different chemoselectivity producing mainly the cis-dimer of PhC/CH. The use of a bulky amine, tBuNH2, with tBuC /CH causes the decomposition of the catalytic complex, forming the salt [tBuNH3][BPh4]/tBuNH2

The catalytic effect obtained by opening the coordination sphere of the organoactinide complex is presented. Replacing the pentamethylcyclopentadienyl ligand in Cp*ThCl (Cp*5C Me) by the bridge ligation [Me SiCp99]22 2[Li]1 (Cp05C Me) affords the 22552254 synthesis of ansa-Me SiCp99ThCl, which reacts with two equiv of BuLi affording the corresponding dibutyl complex ansa-222Me SiCp99Th0Bu. This latter complex was found to be an active catalyst for the dimerization of terminal alkynes, and in the222hydrosilylation of terminal alkynes with PhSiH. In both processes a large chemoselectivity and regioselectivity are achieved due to the3hindered equatorial plane, attributed to the disposition of the methyl groups in the bridge ligation, forcing the incoming substrates to react with a specific regiochemistry.

The cationic actinide complex [(Et2N)3U][BPh4] is an active catalytic precursor for the selective dimerization of terminalalkynes. The regioselectivity is mainly towards the geminal dimer but for bulky alkyne substituents, the unexpected cis-dimer isalso obtained. Mechanistic studies show that the first step in the catalytic cycle is the formation of the acetylide complex[(Et2N)2UC CR][BPh4] with the concomitant reversible elimination of Et2NH, followed by the formation of the alkyne p-complex[(Et2N)2UC CR(RC CH)][BPh4]. This latter complex (R tBu) has been characterized spectroscopically. The kinetic rate law is first order in organoactinide and exhibits a two domain behavior as a function of alkyne concentration. At low alkyne concentrations, the reaction follows an inverse order whereas at high alkyne concentrations, a zero order is observed. The turnover-limiting step is the C C bond insertion of the terminal alkyne into the actinide acetylide bond to give the corresponding alkenyl complex with DH? 15.6(3) kcal mol 1 and DS? 11.4(6) eu. The following step, protonolysis of the uranium carbon bond of the alkenyl intermediate by the terminal alkyne, is much faster but can be retarded by using CH3C CD, allowing the formation of trimers. The unexpected cis-isomer is presumably obtained by the isomerization of the trans-alkenyl intermediate via an envelope mechanism. A plausible mechanistic scenario is proposed for the oligomerization of terminal alkynes. The cationic complex [(Et2N)3U][BPh4] has been found to be also an efficient catalyst for the hydrosilylation of terminal alkynes. The chemoselectivity and regiospecificity of the reaction depend strongly on the nature of the alkyne, the solvent and the reaction temperature. The hydrosilylation reaction of the terminal alkynes with PhSiH3 at room temperature produced a myriad of products among which the cis- and trans-vinylsilanes, the alkene and the silylalkyne are the major components. At higher temperatures, besides the products obtained at room temperature, the double hydrosilylated alkene, in which the two silicon moieties are connected at the same carbon atom, is obtained. The catalytic hydrosilylation of (TMS)C CH and PhSiH3 with [(Et2N)3U][BPh4] was found to proceed only at higher temperatures. Mechanistically, the key intermediate seems to be the uranium–hydride complex [(Et2N)2U H][BPh4], as evidenced by the lack of the dehydrogenative coupling of silanes. A plausible mechanistic scenario is proposed for the hydrosilylation of terminal alkynes taking into account the formation of all products. ? 2000 Elsevier Science S.A. All rights reserved.

通过反-1-（4-甲基苯基）-2-（4-吡啶基）乙烯（E-MEP）在稀盐酸中的光二聚反应得到了接近定量的标题化合物（DMDPC）。用元素分析，IR，Uv，。H NMR和MS表征了其结构，并用x射线衍射法测定TDMDPC晶体结构．DMDPC~单斜晶系，空间群为P21/c，晶胞参数n。1.1376（6），6：1.7379（8），c=1.1590（5）nm，p=106.16（4）。z=4。由于四元环同侧苯环和吡啶环的相互排斥作用，DMDPc采取蝶式构象。研究发现，DMDPC在短波紫外光照射下易发生开环反应；同时还发现，E-MEP与其顺式异构体（z-MEP）间的反-顺异构化平衡位置受照射光波长控制。