TY - JOUR
T1 - Diverse catalytic activity of the cationic actinide complex [(Et2N)3U][BPh4] in the dimerization and hydrosilylation of terminal alkynes. Characterization of the first f-element alkyne π-complex [(Et2N)2U(CCtBu)(η2-HCC tBu)][BPh4]
AU - Dash, Aswini K.
AU - Wang, Jia Xi
AU - Berthet, Jean Claude
AU - Ephritikhine, Michel
AU - Eisen, Moris S.
N1 - Funding Information:
This research was supported by The Israel Science Foundation, administered by The Israel Academy of Sciences and Humanities under contract 69/97-2; by the Fund for the Promotion of Research at the Technion, and by Technion V.P.R. fund Loewengart Research Fund. M.E. and M.S.E. thank the Israel Ministry of Sciences and the French Ministère de Affaires Etrangères for funding the Arc-en-Ciel/Keshet Project no. 50. A.K.D. thanks the Technion for a postdoctoral fellowship.
PY - 2000/6/5
Y1 - 2000/6/5
N2 - The cationic actinide complex [(Et2N)3U][BPh4] is an active catalytic precursor for the selective dimerization of terminal alkynes. The regioselectivity is mainly towards the geminal dimer but for bulky alkyne substituents, the unexpected cis-dimer is also obtained. Mechanistic studies show that the first step in the catalytic cycle is the formation of the acetylide complex [(Et2N)2UCCR][BPh4] with the concomitant reversible elimination of Et2NH, followed by the formation of the alkyne π-complex [(Et2N)2UCCR(RCCH)][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 CC bond insertion of the terminal alkyne into the actinide-acetylide bond to give the corresponding alkenyl complex with ΔH‡=15.6(3) kcal mol-1 and ΔS‡=-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 CH3CCD, 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)CCH 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.
AB - The cationic actinide complex [(Et2N)3U][BPh4] is an active catalytic precursor for the selective dimerization of terminal alkynes. The regioselectivity is mainly towards the geminal dimer but for bulky alkyne substituents, the unexpected cis-dimer is also obtained. Mechanistic studies show that the first step in the catalytic cycle is the formation of the acetylide complex [(Et2N)2UCCR][BPh4] with the concomitant reversible elimination of Et2NH, followed by the formation of the alkyne π-complex [(Et2N)2UCCR(RCCH)][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 CC bond insertion of the terminal alkyne into the actinide-acetylide bond to give the corresponding alkenyl complex with ΔH‡=15.6(3) kcal mol-1 and ΔS‡=-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 CH3CCD, 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)CCH 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.
KW - Alkyne complexes
KW - Catalysis
KW - Dimerization of alkynes
KW - Hydrosilylation
KW - Organoactinide
KW - π-Complexes
UR - http://www.scopus.com/inward/record.url?scp=0002410738&partnerID=8YFLogxK
U2 - 10.1016/S0022-328X(00)00207-2
DO - 10.1016/S0022-328X(00)00207-2
M3 - 文章
AN - SCOPUS:0002410738
SN - 0022-328X
VL - 604
SP - 83
EP - 98
JO - Journal of Organometallic Chemistry
JF - Journal of Organometallic Chemistry
IS - 1
ER -