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Decomposition of Ruthenium Olefin Metathesis Catalyst catalysts Review Decomposition of Ruthenium OlefinOlefin Metathesis CatalystMetathesis Catalyst Magdalena Jawiczuk 1,, Anna Anna Marczyk Marczyk 1,21,2 andand Bartosz Bartosz Trzaskowski Trzaskowski 1,* 1,* 1 1 CentreCentre of of New New Technologies, Technologies, University University of of Warsaw, Warsaw, Banacha Banacha 2c, 2c, 02-097 02-097 Warsaw, Warsaw, Poland; [email protected]@cent.uw.edu.pl (M.J.); (M.J.); [email protected] [email protected] (A.M.) (A.M.) 2 Faculty of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland 2 Faculty of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland * Correspondence: [email protected] * Correspondence: [email protected] Received: 28 28 June 2020; Accepted: 02 2 AugustAugust 2020;2020; Published:Published: 5date August 2020 Abstract: RutheniumRuthenium olefin olefin metathesis metathesis catalysts catalysts are are one one of of the most commonly used class of catalysts. There There are are multiple multiple reviews reviews on on their their us useses in in various branches of chemistry and other sciences but a detailed review of their decomposition is missing, despite a large number of recent and important advances advances in in this this field. field. In In particular, particular, in in the the last last five five years years several several new new mechanism mechanism of decomposition,of decomposition, both both olefin-driven olefin-driven as well as well as induc as induceded by external by external agents, agents, have have been been suggested suggested and usedand usedto explain to explain differences differences in the decomposition in the decomposition rates and rates the metathesis and the metathesis activities activitiesof both standard, of both N-heterocyclicstandard, N-heterocyclic carbene-based carbene-based systems and systems the recently and the developed recently developed cyclic alkyl cyclic amino alkyl carbene- amino containingcarbene-containing complexes. complexes. Here we Here present we present a revi aew review which which explores explores the thelast last 30 30years years of of the decomposition studied on ruthenium olefin olefin metathesis catalyst driven by both intrinsic features of such catalysts as well as external chemicals. Keywords: decomposition;decomposition; ruthenium; olefin olefin metathesis; catalysis 1. Introduction Introduction While the importance of ruthenium for olefin olefin me metathesis,tathesis, one of the most prominent methods to form new C–C bonds, was realized already in the 196 1960s0s [1,2], [1,2], the true dawn of the ruthenium-driven metathesis olefin olefin catalysis catalysis came came in in 1992 1992 with with the the synthesis synthesis of the of first the firstwell-defined well-defined complex complex [3]. This [3]. Thisbreakthrough breakthrough complex, complex, synthesized synthesized in the inGrubbs the Grubbs group, group, had many had manyof the ofstructural the structural features features found infound modern, in modern, highly highly efficient effi andcient specialized and specialized metathesis metathesis catalysts. catalysts. WhatWhat followed followed were werethe 1st the (GI 1st),( 2ndGI), (2ndGII ()GII and) and3rd 3rd(GIII (GIII) generation) generation catalysts catalysts [4–8] [4– 8and] and Hoveyda-Grubbs Hoveyda-Grubbs catalyst catalyst (HG (HG) )[[9]9] which which gave gave rise toto hundredshundreds of of precatalysts precatalysts with with very very distinct dist structuralinct structural features features but always but always based on based the essential, on the 16-electronessential, 16-electron skeleton with skeleton the Ru with atom the at Ru its atom core [at10 its–14 core] (Figure [10–14]1). Nowadays,(Figure 1). Nowadays, ruthenium metathesisruthenium metathesiscatalysts are catalysts used in are all used branches in all branches of chemistry, of chemistry, ranging fromranging pharmaceutical from pharmaceutical sciences sciences [15–19] [15– and 19]synthesis and synthesis of macrocyclic of macrocyclic musks [ 20musks,21] to [20,21] the petrochemical to the petrochemical industry industry [22–24]. [22–24]. N N N N N N N N PCy3 Cl Cl Cl Cl Cl Ru Ru Ru N Ru Ru Cl Cl Ph Cl Ph Cl Ph Cl Ind O PCy3 PCy3 N PCy3 GIII IndII GI GII HGII Figure 1. Common ruthenium metathesis catalysts. Soon after after the the discovery discovery of of first first ruthenium ruthenium metath metathesisesis catalysts catalysts it was it was realized realized that that they they do not do easilynot easily undergo undergo decomposition, decomposition, though though there there are are va variousrious external external agents agents that that can can degrade degrade these Catalysts 2020, 10, x; doi: FOR PEER REVIEW www.mdpi.com/journal/catalysts Catalysts 2020, 10, 887; doi:10.3390/catal10080887 www.mdpi.com/journal/catalysts Catalysts 2020, 10, 887 2 of 56 Catalysts 2020, 10, x FOR PEER REVIEW 2 of 60 catalysts asas wellwell asas several several chemical chemical groups groups that that are are not not compatible compatible with with them. them. These These studies studies were were very veryvaluable, valuable, since since by proposing by proposing the probable the probable decomposition decomposition mechanisms mechanisms they inspiredthey inspired and guided and guided other othergroups groups in the in synthesis the synthesis of new, of new, modified modified catalysts catalysts with with improved improved stabilities stabilities and and less less vulnerable vulnerable to todegradation. degradation. As As a result a result of theseof these over over 30-year 30-year long long investigations, investigations, we we have have today today vastly vastly improved improved our ourunderstanding understanding of how of structuralhow structural features features of ruthenium of ruthenium complexes complexes affect their affect stabilities their andstabilities reactivities and reactivitiesas well as what as well are theas majorwhat decompositionare the major decomp routes ofosition metathesis routes catalysts. of metathesis A good catalysts. understanding A good of understandingthe entire catalytic of the cycle entire of metathesis, catalytic cycle first of proposed metathesis, by Chauvinfirst proposed and presented by Chauvin in Figure and presented2, was also in Figurevital for 2, these was also findings vital [for25]. these findings [25]. Figure 2. SchematicSchematic representation representation of the metathesis catalytic cycle; ( a) initiation, ( b,c) propagation. The review is organizedorganized inin thethe followingfollowing manner.manner. First, we discuss the available scientificscientific literature on on the the decomposition decomposition routes routes of of ruthenium ruthenium metathesis metathesis catalysts catalysts which which are are common common for forall catalyst,all catalyst, such such as Ru as = Ru C =doubleC double bond bond and anddo not do depend not depend on the on specific the specific structural structural features features of such of catalysts,such catalysts, such as such different as diff erentauxiliary auxiliary ligands ligands These These include include the olefin-driven the olefin-driven decomposition decomposition as well as wellas decomposition as decomposition initiated initiated by various by various external external agents agents and and solvents, solvents, divided divided by by their their chemical properties. Next Next we we focus focus on on two two main main classes classes of of metathesis metathesis catalysts—phosphine-containing catalysts—phosphine-containing and and n- heterocyclicn-heterocyclic carbene carbene (NHC)-containing (NHC)-containing ones ones and and review review most most known known decomposition decomposition routes routes which are either phosphine-driven or NHC-driven. Finally we provide a summary and a future outlook for the decomposition studies of this important family ofof widelywidely usedused catalysts.catalysts. The most recentrecent reviewreview onon ruthenium ruthenium metathesis metathesis catalysts’ catalysts’ decomposition decomposition was was reported reported in 2014in 2014 by byNolan Nolan group group and and dealt dealt mostly mostly with with C–H C–H activation, activation, shortly shortly mentioning mentioning several several other other mechanisms mechanisms of ofdegradation degradation [26 ].[26]. Since Since then then a large a large number number of new of ruthenium new ruthenium metathesis metathesis catalysts catalysts has been has designed been designedand there and have there been have a plethora been ofa plethora works presenting of works newpresenting results new on their results decomposition, on their decomposition, therefore we thereforebelieve that we a believe new review that a on new this review topic ison timely this topic and is relevant. timely and relevant. 2. Non-Specific Non-Specific Decomposition Routes In this section we describe the current state of knowledgeknowledge for thethe non-specificnon-specific decompositiondecomposition routes of ruthenium metathesis catalysts. These These include all the decomposition pathways which are driven byby externalexternal agents agents and and do do not not depend depend on theon specificthe specific features features of certain of certain catalysts catalysts but are possiblebut are possiblefor all catalysts for all catalysts due to structural due to stru featuresctural andfeatures metathesis and metathesis mechanisms mechanisms shared by shared all of them.by all of them. Catalysts 2020, 10, x FOR PEER REVIEW 3 of 60 Catalysts
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