Zerovalent [Pd(NHC)(Alkene)1,2] Complexes Bearing Expanded-Ring N-Heterocyclic Carbene Ligands in Transfer Hydrogenation of Alkynes

详细信息    查看全文

• 作者：Peter Hauwert ; Jay J. Dunsford ; Dorette S. Tromp ; Jan J. Weigand ; Martin Lutz ; Kingsley J. Cavell ; Cornelis J. Elsevier
• 刊名：Organometallics
• 出版年：2013
• 出版时间：January 14, 2013
• 年：2013
• 卷：32
• 期：1
• 页码：131-140
• 全文大小：494K
• 年卷期：v.32,no.1(January 14, 2013)
• ISSN：1520-6041

文摘

In search of more active catalysts for the transfer hydrogenation of alkynes, a series of [Pd(NHC)(MA)_1,2] (8鈥?b>14) and [Pd(NHC)(dvtms)] complexes (1鈥?b>7), in which the NHC ancillary ligands are expanded-ring N-heterocyclic carbenes (erNHC鈥檚), have been prepared. These very bulky, strong 蟽-donor ligands impart a highly constrained geometry on the complexes and in some cases enable the isolation of coordinatively and electronically unsaturated complexes (10 and 14). Their strong 蟽-donor character is reflected in a decrease in IR stretching frequency for the C鈺怬 bond of the maleic anhydride ligands (8鈥?b>14) in comparison to their five-membered counterparts. Significantly enhanced catalytic activity in the transfer hydrogenation of 1-phenyl-1-propyne is observed using [Pd(erNHC)(dvtms)] complexes (1鈥?b>7) as precatalysts. The catalysts show high initial selectivity toward (Z)-alkene. However, double-bond isomerization and over-reduction to the corresponding alkane occur when all the alkyne substrate is consumed; this feature reflects the very high efficiency of these catalysts in the transfer hydrogenation of alkynes as well as alkenes.