Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 136, Issue 18, Pages 6672-6683Publisher
AMER CHEMICAL SOC
DOI: 10.1021/ja501572g
Keywords
-
Categories
Funding
- NSF through the CCI Center for Enabling New Technologies through Catalysis (CENTC) Phase II Renewal [CHE-1205189]
- Division Of Chemistry
- Direct For Mathematical & Physical Scien [1205189] Funding Source: National Science Foundation
Ask authors/readers for more resources
New carbazolide-based iridium pincer complexes ((PNP)-P-carb)Ir(C2H4), 3a, and ((PNP)-P-carb)Ir(H)(2), 3b, have been prepared and characterized. The dihydride, 3b, reacts with ethylene to yield the cis-dihydride ethylene complex cis-((PNP)-P-carb)Ir(C2H4)(H)(2). Under ethylene this complex reacts slowly at 70 degrees C to yield ethane and the ethylene complex, 3a. Kinetic analysis establishes that the reaction rate is dependent on ethylene concentration and labeling studies show reversible migratory insertion to form an ethyl hydride complex prior to formation of 3a. Exposure of cis-((PNP)-P-carb)Ir(C2H4)(H)(2) to hydrogen results in very rapid formation of ethane and dihydride, 3b. DFT analysis suggests that ethane elimination from the ethyl hydride complex is assisted by ethylene through formation of ((PNP)-P-carb)Ir(H)(Et)(C2H4) and by H-2 through formation of ((PNP)-P-carb)Ir(H)(Et)(H-2). Elimination of ethane from Ir(III) complex ((PNP)-P-carb)Ir(H)(Et)(H-2) is calculated to proceed through an Ir(V) complex ((PNP)-P-carb)Ir(H)(3)(Et) which reductively eliminates ethane with a very low barrier to return to the Ir(III) dihydride, 3b. Under catalytic hydrogenation conditions (C2H4/H-2), cis-((PNP)-P-carb)Ir(C2H4)(H)(2) is the catalyst resting state, and the catalysis proceeds via an Ir(III)/Ir(V)/Ir(III) cycle. This is in sharp contrast to isoelectronic (PCP)Ir systems in which hydrogenation proceeds through an Ir(III)/Ir(I)/Ir(III) cycle. The basis for this remarkable difference is discussed.
Authors
I am an author on this paper
Click your name to claim this paper and add it to your profile.
Reviews
Recommended
No Data Available