Hydroalumination of Alkenes and Alkynes by Primary Aluminum Hydrides under Mild Conditions
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- 作者：James C. Fettinger ; Paul A. Gray ; Christopher E. Melton ; Philip P. Power
- 刊名：Organometallics
- 出版年：2014
- 出版时间：November 10, 2014
- 年：2014
- 卷：33
- 期：21
- 页码：6232-6240
- 全文大小：534K
- ISSN：1520-6041
文摘
The reactions of the sterically crowded primary alane (ArPri8AlH2)2 (ArPri8 = C6H-2,6(C6H2-2,4,6-Pri3)2-3,5-Pri2) with alkynes and alkenes are described. It is shown that hydroalumination of the terminal alkynes HCCSiMe3 and HCCPh readily occurs under mild conditions via the cis-addition of the Al鈥揌 moiety across the CC triple bond with no evidence of hydrogen elimination. Hydroalumination was observed also with a range of terminal olefins, but no reactivity was observed with internal alkenes or alkynes. The relatively high reactivity of (ArPri8AlH2)2 was attributed to the steric crowding of the large terphenyl substituent, which favors dissociation of the alane and increases the availability of the more reactive three-coordinate aluminum site in the monomer. In keeping with this view, studies of the reactions of the three primary alanes (ArPri8AlH2)2, (ArPri4AlH2)2 (ArPri4 = C6H3-2,6(C6H3-2,6-Pri2)2), and (ArMe6AlH2)2 (ArMe6 = C6H3-2,6(C6H2-2,4,6-Me3)2) with alkenes showed that the reaction rates are inversely proportional to the size of the terphenyl substituent, consistent with higher reactivity of the aluminum monomer. The structures of the alkenyl insertion products, ArPri8Al(CHCHPh)2 and ArPri8Al(CHCHSiMe3)2, the alkylated derivative, ArPri8Al(CH2CH2SiMe3)2, and the precursor aluminates {Li(OEt2)H3AlArPri8路Li(OEt2)2H3AlArPri8}, (LiH3AlArPri8)2, and alanes (ArPri8AlH2)2, and (ArPri4AlH2)2 were determined by X-ray crystallography.