inorganics Review CO2 Derivatives of Molecular Tin Compounds. Part 1: y Hemicarbonato and Carbonato Complexes Laurent Plasseraud Institut de Chimie Moléculaire de l’Université de Bourgogne (ICMUB), UMR-CNRS 6302, Université de Bourgogne Franche-Comté, 9 avenue A. Savary, F-21078 Dijon, France; [email protected] Paper dedicated to Professor Georg Süss-Fink on the occasion of his 70th birthday. y Received: 31 March 2020; Accepted: 24 April 2020; Published: 29 April 2020 Abstract: This review focuses on organotin compounds bearing hemicarbonate and carbonate ligands, and whose molecular structures have been previously resolved by single-crystal X-ray diffraction analysis. Most of them were isolated within the framework of studies devoted to the reactivity of tin precursors with carbon dioxide at atmospheric or elevated pressure. Alternatively, and essentially for the preparation of some carbonato derivatives, inorganic carbonate salts such as K2CO3, Cs2CO3, Na2CO3 and NaHCO3 were also used as coreagents. In terms of the number of X-ray structures, carbonate compounds are the most widely represented (to date, there are 23 depositions in the Cambridge Structural Database), while hemicarbonate derivatives are rarer; only three have so far been characterized in the solid-state, and exclusively for diorganotin complexes. For each compound, the synthesis conditions are first specified. Structural aspects involving, in particular, the modes of coordination of the hemicarbonato and carbonato moieties and the coordination geometry around tin are then described and illustrated (for most cases) by showing molecular representations. Moreover, when they were available in the original reports, some characteristic spectroscopic data are also given for comparison (in table form). Carbonato complexes are arbitrarily listed according to their decreasing number of hydrocarbon substituents linked to tin atoms, namely tri-, di-, and mono-organotins. Four additional examples, involving three CO2 derivatives of C,N-chelated stannoxanes and one of a trinuclear nickel cluster Sn-capped, are also included in the last part of the chapter. Keywords: tin complexes; carbon dioxide fixation; hypervalent compounds; X-ray crystallography 1. Introduction Over the past fifty years, the coordination of CO2 on metal centers has aroused great interest, mobilizing numerous groups around the world; even today, it continues to fascinate the community of inorganic and organometallic chemists. Pioneering works in this area are to be credited to M. E. Vol’pin et al., who highlighted in 1969 the formation of a rhodium-phosphine complex with a carbon dioxide adduct [1]. To our knowledge, the first resolution of an X-ray crystal structure showing the metal-coordination of a CO2 molecule is to be attributed to M. Aresta et al., for the characterization of a nickel complex stabilized by triscyclohexilphosphines [2]. Since then, a multitude of CO2 coordination modes has been revealed at the solid state, showing an important diversity of structures and involving most of transition metal atoms [3,4]. Knowledge in the field has regularly been reviewed and updated [5]. Nature has also been an important source of inspiration for chemists in this area. Thus, the zinc-based active site of carbonic anhydrase has been widely used as a model for the design of metal complexes in order to mimic the catalytic role of the enzyme toward carbon dioxide [6]. Inorganics 2020, 8, 31; doi:10.3390/inorganics8050031 www.mdpi.com/journal/inorganics Inorganics 2020, 8, 31 2 of 26 Inorganics 2020, 8, x FOR PEER REVIEW 2 of 26 Nowadays,Nowadays, thethe organometallic organometallic chemistry chemistry of of metal–CO metal–CO2 complexes2 complexes remains remains a topical a topical research research area whicharea which is closely is linkedclosely to linked the fields to ofthe materials fields (COof materials2-capture) (CO and2-capture) catalysis (COand2 -transformation).catalysis (CO2- Indeed,transformation). beyond the Indeed, purely beyond fundamental the purely aspect, fundamental CO2-coordination aspect, on CO a metallic2-coordination center canon bea metallic viewed ascenter a key-step can be viewed facilitating as a itskey-step activation facilitating and conversion its activation into and useful conversion chemicals. into Inuseful this chemicals. way, carbon In dioxidethis way, appears carbon todioxide be a potentialappears to renewable be a potential C1 raw renewable material, C1 rather raw material, than a waste,rather than offering a waste, new opportunitiesoffering new opportunities for chemical reactionsfor chemical [7– 9reactions]. Currently, [7–9]. a Currently, great level a of great attention level isof beingattention paid is tobeing the designpaid to of the porous design coordination of porous coordination polymers (PCPs) poly ormers metal–organic (PCPs) or metal–or frameworksganic (MOF), frameworks owing to(MOF), their absorptionowing to their properties absorption [10], butproperties also transforming [10], but COalso2 [transforming11]. Thus, the CO chemical2 [11]. utilizationThus, the ofchemical carbon dioxideutilization has of become carbon a crucialdioxide issue, has become in particular a crucial in view issue, of thein particular environmental in view challenges of the environmental that humanity haschallenges to face, that i.e., (i)humanity the depletion has to offa fossilce, i.e., carbon (i) the resources, depletion andof fossil (ii) the carbon continuous resources, increase and in(ii) CO the2 emissionscontinuous and increase its consequences in CO2 emissions on the and climate. its consequences on the climate. FromFrom aa coordination coordination chemistry chemistry point point of view,of view, the reactivitythe reactivity of main of groupmain metalgroup elements metal elements (groups 13–15)(groups with 13–15) carbon with dioxide carbon hasdioxide been, has up been, to now, up relativelyto now, relatively underreviewed underreviewed in the literature. in the literature. Within theWithin framework the framework of our previousof our previous studies studies in this in field, this field, and usingand using the supportthe support of the of the online online portal portal of theof the Cambridge Cambridge Structural Structural Database Database (WebCSD) (WebCSD) [12 [12],], we we herein herein focus focus specifically specifically on on an an inventory inventory of X-rayof X-ray crystallographic crystallographic structures structures of of tin tin compounds compounds resulting resulting from from reactivity reactivity withwith carboncarbon dioxide. ToTo the best best of of our our knowledge, knowledge, tin tin complexes complexes directly directly bearing bearing a CO a2-coordinated CO2-coordinated molecule molecule have never have neverbeen isolated been isolated in the in solid the solid state. state. However, However, CO CO2-adducts2-adducts of oftin tin complexes complexes exist exist in in the the form form ofof hemicarbonate,hemicarbonate, carbonate,carbonate, carbamate,carbamate, formate and phosphinoformate derivatives, and are generally obtainedobtained fromfrom insertion insertion reactions reactions by reactingby reacting carbon carbon dioxide dioxide (under (under atmospheric atmospheric pressure orpressure requiring or highrequiring pressure) high withpressure) precursors with precursors having Sn–X having bonds Sn–X (X = bondsO, N, H,(X P).= O, In N, some H, cases,P). In alternatively,some cases, inorganicalternatively, carbonate inorganic salts carbonate are also used salts as are reagents. also used Herein, as reagents. we will focus Herein, exclusively we will onfocus hemicarbonato exclusively andon hemicarbonato carbonato tin derivatives.and carbonato These tin two derivatives. distinctfamilies These two of compounds distinct families are successively of compounds detailed are thereafter,successively with detailed a particular thereafter, focus uponwith a the particular synthetic focus and structural upon the aspects.synthetic This and inventory structural highlights aspects. theThis hypervalence inventory highlights of tin atoms the hypervalence in hemicarbonate of tin atoms and carbonatein hemicarbonate derivatives, and carbonate which preferentially derivatives, adoptwhich penta-preferentially and hexa-coordination adopt penta- and modes, hexa-coordination with trigonal bipyramidalmodes, with and trigonal octahedral bipyramidal geometries, and respectively.octahedral geometries, An example respectively. of a heptacoordinated An example of tin a heptacoordinated atom is also described tin atom in is Section also described 3.2, which in isSection devoted 3.2, towhich carbonato is devoted tin complexes. to carbonato In tin addition, complexes. and In when addition, they wereand when available they inwere the available original 119 publications,in the original the publications, relevant spectroscopic the relevant data spectroscopic resulting from data the resulting CO2 reactivity from (inthe particular, CO2 reactivity IR, Sn(in andparticular,13C NMR IR, in119Sn solution and 13C and NMR in solid in solution state) are and also in solid specified. state) For are comparison, also specified. summary For comparison, tables of structuralsummary tables and spectroscopic of structural dataand spectroscopic are presented data at the are end presented of each at section the end (Tables of each1–10 section). The (Tables other aforementioned1–10). The other CO aforementioned2-adduct families, CO i.e.,2-adduct carbamato-, families, formato- i.e., carbamato-, and