Bulky PNP Ligands Blocking Metal-Ligand Cooperation Allow for Isolation of Ru(0), and Lead to Catalytically Active Ru Complexes in Acceptorless Alcohol Dehydrogenation |
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| Authors: | Shubham Deolka Robert R. Fayzullin Eugene Khaskin |
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| Affiliation: | 1. Okinawa Institute of Science and Technology Graduate University Onna-son, Kunigami-gun, Okinawa, 904-0495 Japan;2. Arbuzov Institute of Organic and Physical Chemistry, FRC Kazan Scientific Center of RAS, 8 Arbuzov Street, Kazan, 420088 Russian Federation |
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| Abstract: | We synthesized two 4Me−PNP ligands which block metal-ligand cooperation (MLC) with the Ru center and compared their Ru complex chemistry to their two traditional analogues used in acceptorless alcohol dehydrogenation catalysis. The corresponding 4Me−PNP complexes, which do not undergo dearomatization upon addition of base, allowed us to obtain rare, albeit unstable, 16 electron mono-CO Ru(0) complexes. Reactivity with CO and H2 allows for stabilization and extensive characterization of bis-CO Ru(0) 18 electron and Ru(II) cis and trans dihydride species that were also shown to be capable of C(sp2) −H activation. Reactivity and catalysis are contrasted to non-methylated Ru(II) species, showing that an MLC pathway is not necessary, with dramatic differences in outcomes during catalysis between iPr and tBu PNP complexes within each of the 4Me and non-methylated backbone PNP series being observed. Unusual intermediates are characterized in one of the new and one of the traditional complexes, and a common catalysis deactivation pathway was identified. |
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| Keywords: | dehydrogenation homogenous catalysis ligand design metal-ligand cooperation ruthenium |
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