From a Decomposition Product to an Efficient and Versatile Catalyst: The [Ru(η⁵-indenyl)(PPh₃)₂Cl] Story

Abstract

ConspectusOne of the most important challenges in catalyst design is the synthesis of stable promoters without compromising their activity. For this reason, it is important to understand the factors leading to decomposition of such catalysts, especially if side-products negatively affect the activity and selectivity of the starting complex. In this context, the understanding of termination and decomposition processes in olefin metathesis is receiving significant attention from the scientific community. For example, the decomposition of ruthenium olefin metathesis precatalysts in alcohol solutions can occur during either the catalyst synthesis or the metathesis process, and such decomposition has been found to be common for Grubbs-type precatalysts. These decomposition products are usually hydridocarbonyl complexes, which are well-known to be active in several transformations such as hydrogenation, terminal alkene isomerization, and C–H activation chemistry. The reactivity of these side products can be unwanted, and it is therefore important to understand how to avoid them and maybe also important to keep an open mind and think of ways to use these in other catalytic reactions.A showcase of these decomposition studies is reported in this Account. These reports analyze the stability of ruthenium phenylindenylidene complexes, highly active olefin metathesis precatalysts, in basic alcohol solutions. Several different decomposition processes can occur under these conditions depending on the starting complex and the alcohol used. These indenylidene-bearing metathesis complexes display a completely different behavior compared with that of other metathesis precatalysts and show an alternative competitive alcoholysis pathway, where rather than forming the expected hydrido carbonyl complexes, the indenylidene fragment is transformed into a η1-indenyl, which then rearranges to its η5-indenyl form. In particular, [RuCl(η5-(3-phenylindenylidene)(PPh3)2] has been found to be extremely active in numerous transformations (at least 20) as well as compatible with a broad range of reaction conditions, rendering it a versatile catalytic tool. It should be stated that the η5-phenyl indenyl ligand shows enhanced catalytic activity over related half-sandwich ruthenium complexes. The analogous half-sandwich (cyclopentadienyl and indenyl) ruthenium complexes show lower activity in transfer hydrogenation and allylic alcohol isomerization reactions. In addition, this catalyst allows access to new phenylindenyl ruthenium complexes, which can be achieved in a very straightforward manner and have been successfully used in catalysis. This Account provides an overview of how mechanistic insights into decomposition and stability of a well-known family of ruthenium metathesis precatalysts has resulted in a series of novel and versatile ruthenium complexes with unexpected reactivity.

Micellar promoted alkenes isomerization in water mediated by a cationic half-sandwich Ru(II) complex

“…Given the aprotic nature of the solvation sphere surrounding the catalyst (toluene, DCE, the hydrophobic part of the micelles) in the present case in-situ hydride formation seems quite unlikely. On this basis it seems reasonable to suggest that the isomerization reaction is likely to proceed via the second possible pathway with prior displacement of acetonitrile by the incoming allylbenzene substrate, as has been recently found by Nolan and coworkers for similar cyclopentadienyl Ru(II) complexes [32].…”

Indenylmetal Catalysis in Organic Synthesis

“…In 2012, the Nolan group reported that 1-phenylindenylruthenium complex 85 [63] was an exceptionally active catalyst for the transfer hydrogenation of aldehydes,k etones,a nd imines (Scheme 29). [64] Complex 85,which can be synthesized in one high yielding step from commercially available RuCl 2 -(PPh 3 ) 3 ,o utperformed CpRu(PPh 3 ) 2 Cl, (Ind)Ru(PPh 3 ) 2 Cl, and Shvosc atalyst 86 in the transfer hydrogenation of benzophenone.T his increase in activity cannot be explained by the indenyl effect alone,a s( Ind)Ru(PPh 3 ) 2 Cl actually performed worse than either CpRu(PPh 3 ) 2 Cl or 85 in the transfer hydrogenation reaction.…”

The chemistry of the carbon-transition metal double and triple bond: Annual survey covering the year 2014

“…149) for synthesis of Hagens gland lactones [493]; (8) 1-octene with an amino acid derived acrylate ester [494], and with a homoallylic alcohol derivative [495]; (9) 1-decene with a vinyl-γ-lactone derivative for preparation of disparlures [496]; (10) 1-tridecene with a homoallylic alcohol derivative for preparation of a nonadecylphenol natural product [497], and with an allyl ether connected to a bis(carbohydrate) system (also employs 1-pentadecene or an allylglycerol derivative) [498]; (11) A c c e p t e d M a n u s c r i p t 28 antimalarial premarineosins [508]; (20) benzyl 13-tetradecenoate (158) and an alkene protected polyol derivative (e.g. 157) for total synthesis of penarolide sulfate A2 [509]; (21) a 1,5-diene ester derivative and an allylic alcohol derivative [510]; (22) styrene derivatives with a vinyltetrahydropyran for preparation of rhoiptelol B [511], with allylic diol for preparation of ginger diols [512], and with an alkene-phosphine oxide (e.g.…”

“…Observation of a 5-exo pathway for gold(I) chloride versus a 6-exo pathway for gold(III) chloride was attributed to kinetic versus thermodynamic control of the process. A c c e p t e d M a n u s c r i p t 158 Carbene complexes were also generated from 1,2-shift of propargylic ester derivatives in the presence of platinum, silver, and gold complexes (see Scheme 107). Carboxylate shift-generated gold carbene complexes (e.g.…”