Tethered η⁵-Oxocyclohexadienyl Piano-Stool Ruthenium(II) Complexes: A New Class of Catalysts?

Abstract

The straightforward synthesis of tethered η 5 -oxocyclohexadienyl Ru(II) complexes is presented. Pioneering results in catalysis show that these original half-sandwich Ru(II) complexes allow the effective isomerization of allylic alcohols under mild conditions without further additives; η 5 -oxocyclohexadienyl ruthenium complexes may be considered as a new class of catalysts. R uthenium is one of the most intensively used metals in catalysis, 1 partly due to its lower price compared to other noble metals but also because a wide span of highly stable Rubased catalysts can be prepared. A relevant example is Shvo's catalyst I (Figure 1), 2 a cyclopentadienone-ligated diruthenium complex that efficiently promotes a number of environmentally friendly and atom-economical chemical transformations. 3 Shvo et al. proposed that I thermally dissociates into two monoruthenium active species, the 18-electron II species and the remaining elusive 16-electron III complex (Figure 1).Half-sandwich Ru(II) complexes with η 6 -arene ligands IV (Figure 2) are also efficient catalysts or catalyst precursors for a wide range of reactions, and the scope of their applications has considerably increased in the past decades. 1 Especially, their corresponding configurationally stable piano-stool tethered complexes 4 have found great interest in asymmetric catalysis. 4a,5 Within the family of six-membered rings coordinated in an η n -hapto mode to a transition metal, η 5 -oxocyclohexadienyl ligands have been relatively little studied. 6,7 To the best of our knowledge there is no example of a catalytically active halfsandwich ruthenium complex V with an η 5 -oxocyclohexadienyl as ligand (Figure 2). 6 Indeed, half-sandwich Ru-based η 5 -oxocyclohexadienyl complexes are very scarce, and their corresponding tethered complexes unknown. 8 Herein, we describe the straightforward preparation of the first tethered η 5 -oxocyclohexadienyl half-sandwich ruthenium-(II) complexes. We furthermore probed the catalytic activity of this new class of Ru(II) complexes in the redox isomerization of allylic alcohols.As shown in Scheme 1, complex 1 9 reacted quantitatively ( 31 P NMR) with 1 equiv of CsF followed by the addition of Figure 1. Shvo's catalyst I and its thermal dissociation products II and III.Figure 2. Half-sandwich-Ru(II) η 6 -arene IV and η 5 -oxocyclohexadienyl complexes V.Communication pubs.acs.org/Organometallics

An umpolung strategy to react catalytic enols with nucleophiles

“…Allylic alcohols have been proven to be a very useful class of compounds as ketone synthons during the last decades 32,33 . Our group has reported the use of allylic alcohols as enolate equivalents for the preparation of α-functionalized carbonyl compounds as single constitutional isomers [34][35][36][37][38][39][40][41] .…”

Synthetic and Mechanistic Studies on the Rhodium-Catalyzed Redox Isomerization of Cyclohexa-2,5-dienols

“…Another challenge was the difficulty in isomerizing trisubstituted double bonds. While excellent catalysts for this transformation are now accessible (mostly Ru-, Rh-, or Ir-based), the types of compounds that have been isomerized are remarkably limited. In fact, the vast majority of reported examples have been for the production of simple α and/or β-branched aldehydes and ketones with minimal to absent functionality (Scheme a). , Even in the field of natural product synthesis, the few applications of this process have mostly been on unadorned scaffolds. , Therefore, it appeared to us that the potential of this classical reaction had not yet been fully realized.…”

Design of Manganese Phenol Pi‐complexes as Shvo‐type Catalysts for Transfer Hydrogenation of Ketones

“…Arene complexes of manganese have been studied in detail and used for stoichiometric organic synthesis, but to the best of our knowledge, they have not been used previously as catalysts. Thanks to Igau et al ,. we noticed that the manganese phenol π‐complexes are isolobal to the hydroxy‐substituted cyclopentadienyl iron and ruthenium complexes (Shvo‐type catalysts), which have shown high catalytic activity in hydrogenation reactions ,.…”