Can Serendipity Still Hold Any Surprises in the Coordination Chemistry of Mixed-Donor Macrocyclic Ligands? The Case Study of Pyridine-Containing 12-Membered Macrocycles and Platinum Group Metal Ions PdII, PtII, and RhIII.

Alessandra Garau,Greta De Filippo,Alexander J Blake,M Andrea Scorciapino,Giacomo Picci,Massimiliano Arca,Claudia Caltagirone,Francesco Isaia,Francesco Demartin,M Carla Aragoni,Vito Lippolis,Anna Pintus

doi:10.3390/molecules26051286

Abstract

This study investigates the coordination chemistry of the tetradentate pyridine-containing 12-membered macrocycles L1-L3 towards Platinum Group metal ions PdII, PtII, and RhIII. The reactions between the chloride salts of these metal ions and the three ligands in MeCN/H2O or MeOH/H2O (1:1 v/v) are shown, and the isolated solid compounds are characterized, where possible, by mass spectroscopy and 1H- and 13C-NMR spectroscopic measurements. Structural characterization of the 1:1 metal-to-ligand complexes [Pd(L1)Cl]2[Pd2Cl6], [Pt(L1)Cl](BF4), [Rh(L1)Cl2](PF6), and [Rh(L3)Cl2](BF4)·MeCN shows the coordinated macrocyclic ligands adopting a folded conformation, and occupying four coordination sites of a distorted square-based pyramidal and octahedral coordination environment for the PdII/PtII, and RhIII complexes, respectively. The remaining coordination site(s) are occupied by chlorido ligands. The reaction of L3 with PtCl2 in MeCN/H2O gave by serendipity the complex [Pt(L3)(μ-1,3-MeCONH)PtCl(MeCN)](BF4)2·H2O, in which two metal centers are bridged by an amidate ligand at a Pt1-Pt2 distance of 2.5798(3) Å and feature one square-planar and one octahedral coordination environment. Density Functional Theory (DFT) calculations, which utilize the broken symmetry approach (DFT-BS), indicate a singlet d8-d8 PtII-PtII ground-state nature for this compound, rather than the alleged d9-d7 PtI-PtIII mixed-valence character reported for related dinuclear Pt-complexes.

Highlights

IntroductionMacrocyclic chemistry is a very important and active area of chemical science with implications in a wide variety of applications, such as analytical chemistry, separation science, catalysis, and medicinal chemistry [1,2,3,4,5,6], and in the development of fundamental aspects of supramolecular chemistry, such as molecular recognition, host-guest interactions, design of sensors, and smart artificial molecular devices [7,8,9,10].Novel macrocyclic chemical structures—differing in molecular shape, architecture, flexibility, arrangement of structural groups, binding sites, and reactive functions—continue to be developed, with the aim of improving performances in the chemical functions ofNovel macrocyclic chemical structures—differing in molecular shape, architecture, flexibility, arrangement of structural groups, binding sites, and reactive functions—2 coof 2n5-tinue to be developed, with the aim of improving performances in the chemical functions of interest by achieving better control over the strength, selectivity, and dynamics of the ibdbsdntiiiirnftnffaefddeetrireeirHHnenessng.ogntotwwtpbpsrsyeuerouvvobcabeceescsrertsh,tr,ssrtaitseahehtesteveseeosisb,nbfo,apagafpssavaiaibrccartevitaratciiastcsueeprputliryeaeelacrtccoytlrtoysflsnycooomtaffmrfteociccoetolaoatnotooaliirrolvicdod,nieoniairinncnnsat,a,sihtoct,aiieononconnioniscotnt,cicrnntnhehiiuenneceue,mugmtnettriihoseastt,ultobr,rstyeyobreraaoelogelff,faacammtnosfirivacaacgisic,cntacrrayanioon,ntcicidcaayny,tncigcinadlnliianocgcrdrdlelgaiyiagarginneanoaaaoninfmcrddorgsesfisuacstrtnesbooeasiwsowcrtercfasaaahtrurrthdedcibneshss-. tihnethqeuqeustefsotrfosryssytesmtesmcsacpaapbalbeloefoffofrocricnigngthtehemmeteatlacl ecnentetrertotoaaddooppttuunnuussuuaallccoooorrddiinnaattiioonn ggeeoommeettrriieess aanndd//oorrooxxiiddaattiioonnssttaatteesswwiitthhiinn ssttaabbllee ccoommpplleexxeess
This study investigates the coordination chemistry of the tetradentate pyridine-containing 12-membered macrocycles L1-L3 towards Platinum Group metal ions PdII, PtII, and RhIII
The 13C-NMR spectrum of the complex recorded in CD3CN solution at 25 ◦C shows only three peaks for the aromatic fragment of the macrocyclic ligand and three for the aliphatic chain, suggesting that the complex exists in solution in only one form having a Cs symmetry with a symmetry plane passing through the N-donor atom of the ligand

Summary

Introduction

Macrocyclic chemistry is a very important and active area of chemical science with implications in a wide variety of applications, such as analytical chemistry, separation science, catalysis, and medicinal chemistry [1,2,3,4,5,6], and in the development of fundamental aspects of supramolecular chemistry, such as molecular recognition, host-guest interactions, design of sensors, and smart artificial molecular devices [7,8,9,10].Novel macrocyclic chemical structures—differing in molecular shape, architecture, flexibility, arrangement of structural groups, binding sites, and reactive functions—continue to be developed, with the aim of improving performances in the chemical functions ofNovel macrocyclic chemical structures—differing in molecular shape, architecture, flexibility, arrangement of structural groups, binding sites, and reactive functions—2 coof 2n5-tinue to be developed, with the aim of improving performances in the chemical functions of interest by achieving better control over the strength, selectivity, and dynamics of the ibdbsdntiiiirnftnffaefddeetrireeirHHnenessng.ogntotwwtpbpsrsyeuerouvvobcabeceescsrertsh,tr,ssrtaitseahehtesteveseeosisb,nbfo,apagafpssavaiaibrccartevitaratciiastcsueeprputliryeaeelacrtccoytlrtoysflsnycooomtaffmrfteociccoetolaoatnotooaliirrolvicdod,nieoniairinncnnsat,a,sihtoct,aiieononconnioniscotnt,cicrnntnhehiiuenneceue,mugmtnettriihoseastt,ultobr,rstyeyobreraaoelogelff,faacammtnosfirivacaacgisic,cntacrrayanioon,ntcicidcaayny,tncigcinadlnliianocgcrdrdlelgaiyiagarginneanoaaaoninfmcrddorgsesfisuacstrtnesbooeasiwsowcrtercfasaaahtrurrthdedcibneshss-. tihnethqeuqeustefsotrfosryssytesmtesmcsacpaapbalbeloefoffofrocricnigngthtehemmeteatlacl ecnentetrertotoaaddooppttuunnuussuuaallccoooorrddiinnaattiioonn ggeeoommeettrriieess aanndd//oorrooxxiiddaattiioonnssttaatteesswwiitthhiinn ssttaabbllee ccoommpplleexxeess. Novel macrocyclic chemical structures—differing in molecular shape, architecture, flexibility, arrangement of structural groups, binding sites, and reactive functions—continue to be developed, with the aim of improving performances in the chemical functions of. Novel macrocyclic chemical structures—differing in molecular shape, architecture, flexibility, arrangement of structural groups, binding sites, and reactive functions—2 coof 2n5-. Tinue to be developed, with the aim of improving performances in the chemical functions of interest by achieving better control over the strength, selectivity, and dynamics of the ibdbsdntiiiirnftnffaefddeetrireeirHHnenessng.ogntotwwtpbpsrsyeuerouvvobcabeceescsrertsh,tr,ssrtaitseahehtesteveseeosisb,nbfo,apagafpssavaiaibrccartevitaratciiastcsueeprputliryeaeelacrtccoytlrtoysflsnycooomtaffmrfteociccoetolaoatnotooaliirrolvicdod,nieoniairinncnnsat,a,sihtoct,aiieononconnioniscotnt,cicrnntnhehiiuenneceue,mugmtnettriihoseastt,ultobr,rstyeyobreraaoelogelff,faacammtnosfirivacaacgisic,cntacrrayanioon,ntcicidcaayny,tncigcinadlnliianocgcrdrdlelgaiyiagarginneanoaaaoninfmcrddorgsesfisuacstrtnesbooeasiwsowcrtercfasaaahtrurrthdedcibneshss-. FFoorr tthhiiss ppuurrppoossee,, tthhee hhaarrdd-ssoofftt nnaattuurree ooff ddoonnoorr aattoommssaannddththeeirirspspaatitaial lddisipsposoistiitoino,nt,htehecacvaivtyitysizseiz, ea,nadnfdleflxeibxiilbitiylitoyf omfamcraoccryocclyicclliicgalingdasnadrseathree tmheosmt iomstpoimrtpanotrtpaanrtapmaertaemrsetthearst dthefaitndeethfienecotohredcinoaotridoinnpatrioopnperrtoipeserotfietshoesfethseyssetesmyssteinmrseilnatiroenlattioonthteosttheeresot-eerleeoc-terolencitcrorenqicurireeqmuiernetms eonf ttshoefmtheetaml ieotnals ioofnisntoefrienstte[r1e1s,t1[21]1. IInn tthhiiss ccoonntteexxtt,, wweehhaavveebbeeeenneennggaaggeeddininththeededveevleolpopmmenent tofomf mixiexdedNN/O/O//SS--ddoonnoorr mmaaccrrooccyycclleess ffeeaattuurriinngg rriiggiidd hheetteerrooccyycclliicc mmooiieettiieess,, ssuucchh aass ppyyrriiddiinnee ((ppyy)) [[1133––2211]],, aanndd 11,,1100-pphheennaanntthhrroolliinnee ((pphheenn))[2[222––3311]]asasinitnetgergarlaplaprtasrotsf tohfetmheacmroaccyrcolcicycsltircucsttururec,tuwrhe,icwh hisicchomiscpolemtepdlebteydanbyalainphaalitpichpaotirctipoonrtciaornrycianrgrydiinfgfedreifnfterdeonntodroantoomr ast.oTmhse.seThsyessteesmysstpermosvepdrotvoebde thoigbhelyhigehffliycieefnfitciaenndt asnedlescetilvecetiivoenioopnhooprheosreins isnosliodli-dp-hpahsaeseexetxrtarcatcitoionn, ,sseeleleccttiivvee ttrraannssppoorrtt,, pprreeppaarraattiioonnoof fPVPVC-Cb-absaesdedionio-sne-lseeclteivcteiveelecetlreocdtreosd, aens,daflnudorfilmuoertrimic ecthreicmcohseenmsoosresnfosor rssomfoer tsroamnseittiroannsaintidonheaanvdyhmeeatvayl imonesta. Aghlththoeusgehligthaensdes,liegsapnedcisa,lelyspLe3c,ihalalvyeLf3o,uhnadveinftoeurensdtiningateprpelsitciantgioanpspinlictahteiodnesveinlopthmeednetvoefloflpumorenscteonft fclhueomreossceennstocrhs efomrohseeanvsyorms eftoarl hioenasv[y13m–e2t1a]l, tihoneisr[c1o3o–r2d1i]n, athtieoinr cohoermdiisntarytioisnlachrgeemlyisutrnydiesvlealrogpeelyd.undeveloped

Methods

Results

Conclusion