Reactive P-Block Cations Stabilized by Weakly Coordinating Anions Chem Soc Rev

Volume 45 Number 4 21 February 2016 Pages 755–1174 Chem Soc Rev Chemical Society Reviews www.rsc.org/chemsocrev Themed issue: Modern main group chemistry ISSN 0306-0012 REVIEW ARTICLE Ingo Krossing et al. Reactive p-block cations stabilized by weakly coordinating anions Chem Soc Rev View Article Online REVIEW ARTICLE View Journal | View Issue Reactive p-block cations stabilized by weakly coordinating anions Cite this: Chem. Soc. Rev., 2016, 45,789 Tobias A. Engesser, Martin R. Lichtenthaler, Mario Schleep† and Ingo Krossing* The chemistry of the p-block elements is a huge playground for fundamental and applied work. With their bonding from electron deficient to hypercoordinate and formally hypervalent, the p-block elements represent an area to find terra incognita. Often, the formation of cations that contain p-block elements as central ingredient is desired, for example to make a compound more Lewis acidic for an application or simply to prove an idea. This review has collected the reactive p-block cations (rPBC) with a comprehensive focus on those that have been published since the year 2000, but including the milestones and key citations of earlier work. We include an overview on the weakly coordinating anions (WCAs) used to stabilize the rPBC and give an overview to WCA selection, ionization strategies for rPBC-formation and finally list the rPBC ordered in their respective group from 13 to 18. However, typical, often more organic ion classes that constitute for Creative Commons Attribution-NonCommercial 3.0 Unported Licence. example ionic liquids (imidazolium, ammonium, etc.) were omitted, as were those that do not fulfill the – naturally subjective – ‘‘reactive’’-criterion of the rPBC. As a rule, we only included rPBC with crystal structure Received 28th August 2015 and only rarely refer to important cations published without crystal structure. This collection is intended for DOI: 10.1039/c5cs00672d those who are simply interested what has been done or what is possible, as well as those who seek advice on preparative issues, up to people having a certain application in mind, where the knowledge on the existence www.rsc.org/chemsocrev of a rPBC that might play a role as an intermediate or active center may be useful. This article is licensed under a Introduction Institut fu¨r Anorganische und Analytische Chemie and Freiburger Main group chemistry continues to reside at the heart of Materialforschungszentrum (FMF), Universita¨t Freiburg, Albertstr. 21, fundamental as well as applied chemistry. As such, recent years Open Access Article. Published on 27 novembro 2015. Downloaded 06/10/2021 16:38:55. 79104 Freiburg, Germany. E-mail: [email protected] † The names of the co-authors are ordered alphabetically. have seen an enormous growth of concepts that shed new light Dipl.-Chem. Tobias Engesser Martin R. Lichtenthaler (1986) obtained his intermediate diploma received his Diploma (2010) and attheTechnischeUniversita¨t PhD (2015) from the Albert- Karlsruhe (now KIT) and continued Ludwigs-Universita¨t Freiburg, his studies at the Albert-Ludwigs- Germany. As a member of the Universita¨tFreiburg,wherehealso Krossing group, he has developed wrote his diploma thesis about a novel class of highly efficient, reactive tellurium cations and main group metal-based olefin started his PhD in 2011 at the polymerization catalysts and Institute of Inorganic Chemistry discovered unprecedented cationic under the supervision of Prof. Ingo clusters of univalent indium. After Krossing. His research interests are aresearchstaywiththeNew Tobias A. Engesser reactive phosphorus cations and Martin R. Lichtenthaler Technology Office of Merck Ltd. gold(I) starting materials, both in Japan, he is likely to join the combination with weakly coordinating anions. On the basis of his University of California, Berkeley as a postdoc in 2016. His research interest for phosphorus compounds he stayed for three months in the interests are organometallic and polymer chemistry, catalysis, group of Prof. Christopher ‘‘Kit’’ Cummins at the Massachusetts Institute molecular modelling and materials science. of Technology in 2015. This journal is © The Royal Society of Chemistry 2016 Chem.Soc.Rev.,2016, 45, 789--899 | 789 View Article Online Review Article Chem Soc Rev on hitherto undiscovered, or more correctly, underdeveloped Handling of substance classes with recent reviews areas of main group chemistry. Thus, the availability of stable Some of the substance classes, which fit into this review were 1 singlet carbenes as strong donors offered tremendous new just recently and sometimes very comprehensively reviewed perspectives as did the establishment of the frustrated Lewis (cf. our contribution describing the advances in the synthesis 2 pairs (FLP) concept or the systematic investigation of (often of homopolyatomic cations of the non-metals since 200011). To 3–5 low valent) cationic mixed main group-transition metal salts. In reduce the overlap, we decided to give an overview on general 6 the framework of those approaches, next to other fundamental aspects such as WCAs in Table 1 and include a short table with 7–10 and applied questions, also the stabilization or use of reactive relevant reviews for each main group at the beginning of each p-block cations (rPBC) with weakly coordinating anions (WCAs) main group chapter and only list the compounds in these cases. was one focus that led to fascinating new rPBC. This review gives Therefore, we mainly list, but do not describe the cations of this a comprehensive overview on recent rPBC developments since category in the chapters of their corresponding element. Never- about 2000, but also cites all-time classics in the field. It also theless, the scope of this review is rather large, which in any includes the fascinating class of transition metal substituted case precludes extensive discussions and mainly serves as an rPBC for which the assignment of the positive charge to one overview on what is known. specific moiety is often not clear. Reactive p-block cations Scope of this review Many of the p-block elements have relatively high ionization The rPBC in this article need a WCA as counterion and, there- potentials and electronegativities. Thus, most of the stable examples fore, we first briefly describe typical WCAs and give some advice base on delocalization and other electronic or steric effects. In on their selection before turning to typical ionization and addition, rPBC are often very electrophilic and/or oxidizing. There- synthetic procedures for rPBC preparations. Thereafter, the fore, chemically stable and inert weakly coordinating anions (WCAs) ordering of the cation classes for the individual sections is Creative Commons Attribution-NonCommercial 3.0 Unported Licence. and solvents are needed to access their salts. These ingredients described, and finally the rPBC are grouped according to the allowed the syntheses of a large number of fundamentally main group of the relevant cationic entry. In addition, first interesting rPBC of the groups 13–18 in the condensed phase. applications emerged for rPBC salts and will be highlighted in We discuss typical synthesis routes, give a brief overview of the the respective cation sections. WCAs, and describe the rPBC ordered according to their main group as well as cation class. However, typical, often more WCA overview organic ion classes that constitute for example ionic liquids Because of their potential in fundamental and applied chem- (imidazolium, ammonium, etc.) were omitted, as were those that istry,12–15 a great variety of different WCA types are currently This article is licensed under a do not fulfill the – naturally subjective – ‘‘reactive’’-criterion of known (Fig. 2) and was frequently reviewed (Table 1). the rPBC. As a rule, we only included rPBC with crystal structure But which out of the multitude of published WCAs shown in and only rarely refer to important cations published without Fig. 2 should be used for a given problem...? Is there one best crystal structure. WCA that fulfills all needs...? Open Access Article. Published on 27 novembro 2015. Downloaded 06/10/2021 16:38:55. Dipl.-Chem. Mario Schleep is a Ingo Krossing studied chemistry in PhD student in the group of Prof. Munich (LMU) and finished his Ingo Krossing at the University of PhD thesis 1997 (with Prof. H. Freiburg, where he received his No¨th). From 1997 to 1999, he Diploma in 2012. During his worked as Feodor Lynen postdoc studies, he has undertaken a with Prof. J. Passmore at UNB, research stay dedicated to poly- Canada. In 1999, he started his metallic chromium and vanadium independent career as a Liebig- clusters in the group of Prof. Eric and DFG-Heisenberg-Fellow at McInnes at the University of the Universita¨t Karlsruhe (TH) Manchester (England) for two (mentor: Prof. H. Schno¨ckel). semesters. While dealing with 2004 he changed as assistant Mario Schleep electrolytes for lithium ion Ingo Krossing professor to the Ecole Polytechnic batteries during his thesis, his Federale de Lausanne (EPFL), current research focuses on the synthesis of reactive tin(II)cations before being appointed Chair of Inorganic Chemistry at the Albert- stabilized by weakly coordinating anions. Ludwigs-Universita¨t Freiburg in 2006. His research interests cover ionic systems from reactive cations to ionic liquids, as well as electrochemical energy storage. With an ongoing ERC Advanced Grant he develops absolute acidity and reducity scales. 790 | Chem.Soc.Rev.,2016, 45, 789--899 This journal is © The Royal

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