A “nucleophilic” iodine in a halogen-bonded iodonium complex manifests an unprecedented I+···Ag+ interaction

Abstract

•The first experimental and computational evidence of the I+···Ag+ interaction•The nucleophilic character of the I+ in the 3c–4e halogen-bonded halonium complex•The high association constant of 37,000 M−1 of the I+···Ag+ interaction in solution•The X-ray structure proof of the I+···Ag+ interaction in solution in the solid state The true nature of the electronic state of reactive species in chemical transformations and the nature of bonding in non-covalent, e.g., supramolecular, complexes have been elusive yet very topical research themes. This is due to the emerging chemical/catalytic reactions demonstrating non-conventional interactions such as closed-shell (auro- and argentophilic) and halogen or chalcogen bonding interactions. Halogen bonding (XB) has been defined to occur between electrophilic regions of halogens and nucleophilic atoms, yet, the most intriguing of them is the three-center four-electron (3c–4e) bond occurring between the two nitrogens and an iodine atom in Barluenga’s reagent [pyridine-I-pyridine]+ (a halonium ion). The now discovered I+···Ag+ interaction between a halonium ion and a Ag(I) ion adds a new aspect to halogen-bonded complexes, allowing to stabilize or activate halonium ions in an unprecedented way and possibly utilize them as new, more active, or selective reagents. When an electron is removed from a halogen atom, it forms a halenium ion X+ (X = I, Br, Cl). In halogen bonding (XB), X+ is considered as a strong XB donor, and when interacting with two XB acceptors (e.g., pyridine), it forms a halonium XB complex with a [N–I–N] three-center-four-electron bond with the two XB acceptors. An unprecedented I+···Ag+ interaction occurs between a [L1–I–L1]+ halogen-bonded complex and a [L2–Ag–L2]+ complex in which the iodonium ion acts like a nucleophile and donates electrons to the silver(I) cation. The X-ray diffraction analysis reveals a short contact [3.4608(3) Å] between the I+ and Ag+ cations, and ITC measurements give a ΔG of −6.321 kcal/mol and Ka∼37,000 M−1 for the 1:1 complex. The DFT computational study on the nature of the I+···Ag+ interaction indicates that the I+ is nucleophilic in character, manifesting an unusual and strongly attractive interaction between the I+ and Ag+ cations. When an electron is removed from a halogen atom, it forms a halenium ion X+ (X = I, Br, Cl). In halogen bonding (XB), X+ is considered as a strong XB donor, and when interacting with two XB acceptors (e.g., pyridine), it forms a halonium XB complex with a [N–I–N] three-center-four-electron bond with the two XB acceptors. An unprecedented I+···Ag+ interaction occurs between a [L1–I–L1]+ halogen-bonded complex and a [L2–Ag–L2]+ complex in which the iodonium ion acts like a nucleophile and donates electrons to the silver(I) cation. The X-ray diffraction analysis reveals a short contact [3.4608(3) Å] between the I+ and Ag+ cations, and ITC measurements give a ΔG of −6.321 kcal/mol and Ka∼37,000 M−1 for the 1:1 complex. The DFT computational study on the nature of the I+···Ag+ interaction indicates that the I+ is nucleophilic in character, manifesting an unusual and strongly attractive interaction between the I+ and Ag+ cations. Over the last 20 years, halogen bonding (XB) has matured into one of the most studied non-covalent interactions, experiencing an amazing boom since 2007.1Cavallo G. Metrangolo P. Milani R. Pilati T. Priimagi A. Resnati G. Terraneo G. The halogen bond.Chem. Rev. 2016; 116: 2478-2601Crossref PubMed Scopus (2002) Google Scholar, 2Gilday L.C. Robinson S.W. Barendt T.A. Langton M.J. Mullaney B.R. Beer P.D. Halogen bonding in supramolecular chemistry.Chem. Rev. 2015; 115: 7118-7195Crossref PubMed Scopus (808) Google Scholar, 3Kolář M.H. Hobza P. Computer modeling of halogen bonds and other σ-hole interactions.Chem. Rev. 2016; 116: 5155-5187Crossref PubMed Scopus (407) Google Scholar, 4Wang H. Wang W. Jin W.J. σ-hole bond vs π-hole bond: a comparison based on halogen bond.Chem. Rev. 2016; 116: 5072-5104Crossref PubMed Scopus (369) Google Scholar The halogen bond, which has been recently defined,5Desiraju G.R. Ho P.S. Kloo L. Legon A.C. Marquardt R. Metrangolo P. Politzer P. Resnati G. Rissanen K. Definition of the halogen bond (IUPAC recommendations 2013).Pure Appl. Chem. 2013; 85: 1711-1713Crossref Scopus (1162) Google Scholar occurs between the positive regions of the electrostatic potential surface of halogen atoms, which function as electrophilic species, and neutral or anionic Lewis bases.5Desiraju G.R. Ho P.S. Kloo L. Legon A.C. Marquardt R. Metrangolo P. Politzer P. Resnati G. Rissanen K. Definition of the halogen bond (IUPAC recommendations 2013).Pure Appl. Chem. 2013; 85: 1711-1713Crossref Scopus (1162) Google Scholar Perhaps due to the controversial nature of the halogen bonding, which among the many non-covalent interactions that are generally applied to direct the formation of supramolecular assemblies, has caused it to be somewhat ignored for a long time. This is surprising as the analogy of halogen bonding to the ubiquitous hydrogen bonding is more than evident. In spite of this, halogen bonding has been convincingly used to control the self-assembly of a diverse array of host-guest systems, with applications ranging from porous materials, liquid-crystalline, magnetic, and phosphorescent materials to ion-pair recognition, biomolecular engineering, and chemical separations.1Cavallo G. Metrangolo P. Milani R. Pilati T. Priimagi A. Resnati G. Terraneo G. The halogen bond.Chem. Rev. 2016; 116: 2478-2601Crossref PubMed Scopus (2002) Google Scholar,2Gilday L.C. Robinson S.W. Barendt T.A. Langton M.J. Mullaney B.R. Beer P.D. Halogen bonding in supramolecular chemistry.Chem. Rev. 2015; 115: 7118-7195Crossref PubMed Scopus (808) Google Scholar In contemporary crystal engineering,1Cavallo G. Metrangolo P. Milani R. Pilati T. Priimagi A. Resnati G. Terraneo G. The halogen bond.Chem. Rev. 2016; 116: 2478-2601Crossref PubMed Scopus (2002) Google Scholar, 2Gilday L.C. Robinson S.W. Barendt T.A. Langton M.J. Mullaney B.R. Beer P.D. Halogen bonding in supramolecular chemistry.Chem. Rev. 2015; 115: 7118-7195Crossref PubMed Scopus (808) Google Scholar, 3Kolář M.H. Hobza P. Computer modeling of halogen bonds and other σ-hole interactions.Chem. Rev. 2016; 116: 5155-5187Crossref PubMed Scopus (407) Google Scholar, 4Wang H. Wang W. Jin W.J. σ-hole bond vs π-hole bond: a comparison based on halogen bond.Chem. Rev. 2016; 116: 5072-5104Crossref PubMed Scopus (369) Google Scholar,6Rissanen K. Halogen bonded supramolecular complexes and networks.CrystEngComm. 2008; 10: 1107-1113Crossref Scopus (360) Google Scholar halogen bonding is thriving due to its directionality, specificity, and high strength, allowing the preparation of highly complex structures with a high degree of accuracy and precision. The modulation of polymers with halogen bond donors has led to new supramolecular and molecularly imprinted polymers, topochemical polymerization, layer-by-layer assemblies, and functional and stimuli-responsive polymeric materials.1Cavallo G. Metrangolo P. Milani R. Pilati T. Priimagi A. Resnati G. Terraneo G. The halogen bond.Chem. Rev. 2016; 116: 2478-2601Crossref PubMed Scopus (2002) Google Scholar,2Gilday L.C. Robinson S.W. Barendt T.A. Langton M.J. Mullaney B.R. Beer P.D. Halogen bonding in supramolecular chemistry.Chem. Rev. 2015; 115: 7118-7195Crossref PubMed Scopus (808) Google Scholar Surprisingly, though easily achieved with hydrogen bonding or metal coordination, hollow capsular molecular assemblies solely based on halogen bonding have only very recently been achieved.7Beyeh N.K. Pan F. Rissanen K. A halogen-bonded dimeric resorcinarene capsule.Angew. Chem. Int. Ed. Engl. 2015; 54: 7303-7307Crossref PubMed Scopus (59) Google Scholar,8Dumele O. Trapp N. Diederich F. Halogen bonding molecular capsules.Angew. Chem. Int. Ed. Engl. 2015; 54: 12339-12344Crossref PubMed Scopus (115) Google Scholar Though halogen bonding is more directional than hydrogen bonding,9Arunan E. Desiraju G.R. Klein R.A. Sadlej J. Scheiner S. Alkorta I. Clary D.C. Crabtree R.H. Dannenberg J.J. Hobza P. et al.Defining the hydrogen bond: an account (IUPAC technical report).Pure Appl. Chem. 2011; 83: 1619-1636Crossref Scopus (736) Google Scholar it is more sensitive to the environment and has thus mostly been demonstrated in the solid state.10Troff R.W. Mäkelä T. Topić F. Valkonen A. Raatikainen K. Rissanen K. Alternative motifs for halogen bonding.Eur. J. Org. Chem. 2013; 2013: 1617-1637Crossref Scopus (181) Google Scholar, 11Raatikainen K. Rissanen K. Breathing molecular crystals: halogen- and hydrogen-bonded porous molecular crystals with solvent induced adaptation of the nanosized channels.Chem. Sci. 2012; 3: 1235-1239Crossref Scopus (134) Google Scholar, 12Puttreddy R. Jurček O. Bhowmik S. Mäkelä T. Rissanen K. Very strong −N–X+⋯−O–N+ halogen bonds.Chem. Commun.(Camb). 2016; 52: 2338-2341Crossref PubMed Google Scholar, 13Raatikainen K. Rissanen K. Interaction between amines and N-haloimides: a new motif for unprecedentedly short Br⋯N and I⋯N halogen bonds.CrystEngComm. 2011; 13: 6972-6977Crossref Scopus (74) Google Scholar When the polarization of the halogen reaches the limit where the electron is completely removed from the halogen atom, it then occurs as a positively charged ion, viz., the halenium ion X+ (X = I, Br, or Cl). The halenium ions (cations) can thus be considered as extremely polarized halogen atoms and as such belong to the realm of halogen bonding as very strong XB donors. Yet, due to their reactivity, they differ remarkably from the other, classical, halogen bond donors. The first examples of trapped halenium ions are the iodonium bis(pyridine) complexes manifesting the [N–I–N]+ three-center-four-electron bond, reported in the 1960s by Hassel et al.,14Hassel O. Hope H. Sörensen N.A. Dam H. Sjöberg B. Toft J. Structure of the solid compound formed by addition of two molecules of iodine to one molecule of pyridine.Acta Chem. Scand. 1961; 15: 407-416Crossref Google Scholar Crichton et al.,15Creighton J.A. Haque I. Wood J.L. The iododipyridinium ion.Chem. Commun. (London). 1966; 1966: 229Crossref Google Scholar and Hague et al.,16Haque I. Wood J.L. The vibrational spectra and structure of the bis(pyridine)iodine(I), bis(pyridine)bromine(I), bis(γ-picoline)iodine-(I) and bis(γ-picollne)bromine(I) cations.J. Mol. Struct. 1968; 2: 217-238Crossref Scopus (37) Google Scholar and have recently been reviewed by Erdelyi.17Turunen L. Erdélyi M. Halogen bonds of halonium ions.Chem. Soc. Rev. 2020; 49: 2688-2700Crossref PubMed Google Scholar,18Hakkert S.B. Erdélyi M. Halogen bond symmetry: the N–X–N bond.J. Phys. Org. Chem. 2015; 28: 226-233Crossref Scopus (50) Google Scholar Nearly 30 years after the first reports on the iconic halonium ion complex, the bis(pyridine)iodonium(I) tetrafluoroborate, also known today as the Barluenga’s reagent, named after its best proponent in the 1990s, Jose Barluenga,19Barluenga J. Trincado M. Rubio E. González J.M. IPy2BF4-promoted intramolecular addition of masked and unmasked anilines to alkynes: direct assembly of 3-Iodoindole cores.Angew. Chem. Int. Ed. Engl. 2003; 42: 2406-2409Crossref PubMed Scopus (282) Google Scholar was found to be a mild iodination reagent and an oxidant. The Barluenga’s reagent is a relatively stable white solid and is soluble in both organic and aqueous solutions, and its applicability in organic synthesis has been widely demonstrated.20Chalker J.M. Thompson A.L. Davis B.G. Safe and scalable preparation of Barluenga’s reagent.Org. Synth. 2011; : 288-298Google Scholar Detailed studies in solution have revealed the symmetric nature of the [N–I–N]+ halogen bond.21von der Heiden D. Vanderkooy A. Erdélyi M. Halogen bonding in solution: NMR spectroscopic approaches.Coord. Chem. Rev. 2020; 407: 213147Crossref Scopus (38) Google Scholar, 22Lindblad S. Mehmeti K. Veiga A.X. Nekoueishahraki B. Gräfenstein J. Erdélyi M. Halogen bond asymmetry in solution.J. Am. Chem. Soc. 2018; 140: 13503-13513Crossref PubMed Scopus (31) Google Scholar, 23Karim A. Reitti M. Carlsson A.-C.C. Gräfenstein J. Erdélyi M. The nature of [N–Cl–N]+ and [N–F–N]+ halogen bonds in solution.Chem. Sci. 2014; 5: 3226-3233Crossref Google Scholar, 24Carlsson A.-C.C. Uhrbom M. Karim A. Brath U. Gräfenstein J. Erdélyi M. Solvent effects on halogen bond symmetry.CrystEngComm. 2013; 15: 3087-3092Crossref Scopus (49) Google Scholar, 25Carlsson A.-C.C. Gräfenstein J. Budnjo A. Laurila J.L. Bergquist J. Karim A. Kleinmaier R. Brath U. Erdélyi M. Symmetric halogen bonding is preferred in solution.J. Am. Chem. Soc. 2012; 134: 5706-5715Crossref PubMed Scopus (116) Google Scholar, 26Carlsson A.-C.C. Gräfenstein J. Laurila J.L. Bergquist J. Erdélyi M. Symmetry of [N–X–N]+ halogen bonds in solution.Chem. Commun. 2012; 48: 1458-1460Crossref PubMed Google Scholar Very recently also halonium-based dioxoiodane complexes have also been used as reagents in organic synthesis.27Muñiz K. García B. Martínez C. Piccinelli A. Dioxoiodane compounds as versatile sources for iodine(I) chemistry.Chemistry. 2017; 23: 1539-1545Crossref PubMed Scopus (24) Google Scholar The preparation of the halonium ion-based halogen-bonded complexes28Bedin M. Karim A. Reitti M. Carlsson A.-C.C. Topić F. Cetina M. Pan F. Havel V. Al-Ameri F. Sindelar V. et al.Counterion influence on the N–I–N halogen bond.Chem. Sci. 2015; 6: 3746-3756Crossref PubMed Google Scholar, 29Carlsson A.-C.C. Mehmeti K. Uhrbom M. Karim A. Bedin M. Puttreddy R. et al.Substituent effects on the [N–I–N]+ halogen bond.J. Am. Chem. Soc. 2016; 138: 9853-9863Crossref PubMed Scopus (54) Google Scholar, 30Rissanen K. Haukka M. Halonium ions as halogen bond donors in the solid state [XL2]Y complexes BT - halogen bonding II: Impact on materials chemistry and life sciences.Top Curr Chem. 2015; 359: 77-90Crossref PubMed Scopus (21) Google Scholar, 31Koskinen L. Hirva P. Kalenius E. Jääskeläinen S. Rissanen K. Haukka M. Halogen bonds with coordinative nature: halogen bonding in a S–I+–S iodonium complex.CrystEngComm. 2015; 17: 1231-1236Crossref Google Scholar commenced through the [N···Ag+···N] → [N···I+···N] cation exchange reaction, and its potential in the design and preparation of the first halonium ion mediated supramolecular capsules32Turunen L. Warzok U. Puttreddy R. Beyeh N.K. Schalley C.A. Rissanen K. N⋅⋅⋅I+⋅⋅⋅N halogen-bonded dimeric capsules from tetrakis(3-pyridyl)ethylene cavitands.Angew. Chem. Int. Ed. Engl. 2016; 55: 14033-14036Crossref PubMed Scopus (62) Google Scholar, 33Turunen L. Peuronen A. Forsblom S. Kalenius E. Lahtinen M. Rissanen K. Tetrameric and dimeric [N⋅⋅⋅I+⋅⋅⋅N] halogen-bonded supramolecular cages.Chemistry. 2017; 23: 11714-11718Crossref PubMed Scopus (32) Google Scholar, 34Turunen L. Warzok U. Schalley C.A. Rissanen K. Nano-sized I12L6 molecular capsules based on the [N⋅⋅⋅I+⋅⋅⋅N] halogen bond.Chem. 2017; 3: 861-869Abstract Full Text Full Text PDF Scopus (44) Google Scholar, 35Warzok U. Marianski M. Hoffmann W. Turunen L. Rissanen K. Pagel K. Schalley C.A. Surprising solvent-induced structural rearrangements in large [N⋯I+⋯N] halogen-bonded supramolecular capsules: an ion mobility-mass spectrometry study.Chem. Sci. 2018; 9: 8343-8351Crossref PubMed Google Scholar and a helicate36Vanderkooy A. Gupta A.K. Földes T. Lindblad S. Orthaber A. Pápai I. Erdélyi M. Halogen bonding helicates encompassing iodonium cations.Angew. Chem. Int. Ed. Engl. 2019; 58: 9012-9016Crossref PubMed Scopus (26) Google Scholar has recently been demonstrated. It should be noted that, while halonium ions usually bind two identical XB acceptor moieties to form a linear and homoleptic halonium complexes,28Bedin M. Karim A. Reitti M. Carlsson A.-C.C. Topić F. Cetina M. Pan F. Havel V. Al-Ameri F. Sindelar V. et al.Counterion influence on the N–I–N halogen bond.Chem. Sci. 2015; 6: 3746-3756Crossref PubMed Google Scholar, 29Carlsson A.-C.C. Mehmeti K. Uhrbom M. Karim A. Bedin M. Puttreddy R. et al.Substituent effects on the [N–I–N]+ halogen bond.J. Am. Chem. Soc. 2016; 138: 9853-9863Crossref PubMed Scopus (54) Google Scholar, 30Rissanen K. Haukka M. Halonium ions as halogen bond donors in the solid state [XL2]Y complexes BT - halogen bonding II: Impact on materials chemistry and life sciences.Top Curr Chem. 2015; 359: 77-90Crossref PubMed Scopus (21) Google Scholar, 31Koskinen L. Hirva P. Kalenius E. Jääskeläinen S. Rissanen K. Haukka M. Halogen bonds with coordinative nature: halogen bonding in a S–I+–S iodonium complex.CrystEngComm. 2015; 17: 1231-1236Crossref Google Scholar, 32Turunen L. Warzok U. Puttreddy R. Beyeh N.K. Schalley C.A. Rissanen K. N⋅⋅⋅I+⋅⋅⋅N halogen-bonded dimeric capsules from tetrakis(3-pyridyl)ethylene cavitands.Angew. Chem. Int. Ed. Engl. 2016; 55: 14033-14036Crossref PubMed Scopus (62) Google Scholar, 33Turunen L. Peuronen A. Forsblom S. Kalenius E. Lahtinen M. Rissanen K. Tetrameric and dimeric [N⋅⋅⋅I+⋅⋅⋅N] halogen-bonded supramolecular cages.Chemistry. 2017; 23: 11714-11718Crossref PubMed Scopus (32) Google Scholar, 34Turunen L. Warzok U. Schalley C.A. Rissanen K. Nano-sized I12L6 molecular capsules based on the [N⋅⋅⋅I+⋅⋅⋅N] halogen bond.Chem. 2017; 3: 861-869Abstract Full Text Full Text PDF Scopus (44) Google Scholar, 35Warzok U. Marianski M. Hoffmann W. Turunen L. Rissanen K. Pagel K. Schalley C.A. Surprising solvent-induced structural rearrangements in large [N⋯I+⋯N] halogen-bonded supramolecular capsules: an ion mobility-mass spectrometry study.Chem. Sci. 2018; 9: 8343-8351Crossref PubMed Google Scholar the first heteroleptic (and therefore asymmetric) halonium solid-state complexes were also recently reported by us,37Ward J.S. Fiorini G. Frontera A. Rissanen K. Asymmetric [N–I–N]+ halonium complexes.Chem. Commun. 2020; 56: 8428-8431Crossref PubMed Google Scholar further increasing the potential scope of halonium ions as supramolecular synthons. In addition to the halogen bonding, there are still a number of unconventional interactions that have not received much attention and are therefore less well understood. For example, anion-π38Frontera A. Gamez P. Mascal M. Mooibroek T.J. Reedijk J. Putting anion–π interactions Into perspective.Angew. Chem. Int. Ed. Engl. 2011; 50: 9564-9583Crossref PubMed Scopus (532) Google Scholar, 39Chifotides H.T. Dunbar K.R. Anion−π interactions in supramolecular architectures.Acc. Chem. Res. 2013; 46: 894-906Crossref PubMed Scopus (394) Google Scholar, 40Giese M. Albrecht M. Rissanen K. Anion−π interactions with fluoroarenes.Chem. Rev. 2015; 115: 8867-8895Crossref PubMed Scopus (199) Google Scholar and lone pair (lp)-π41Mooibroek T.J. Gamez P. Reedijk J. Lone pair–π interactions: a new supramolecular bond?.CrystEngComm. 2008; 10: 1501-1515Crossref Scopus (440) Google Scholar,42Ran J. Hobza P. On the nature of bonding in lone pair···π-electron complexes: CCSD(T)/complete basis set limit calculations.J. Chem. Theor. Comput. 2009; 5: 1180-1185Crossref PubMed Scopus (77) Google Scholar interactions in comparison to the more established cation–π interactions, or chalcogen, pnictogen, and tetrel bonding modes.43Bauzá A. Mooibroek T.J. Frontera A. The bright future of unconventional σ/π-hole interactions.ChemPhysChem. 2015; 16: 2496-2517Crossref PubMed Scopus (419) Google Scholar Metallophilic interactions, which account for a large portion of the interactions loosely grouped together under the general umbrella of closed-shell interactions (CSI),44Pyykkö P. Strong closed-shell interactions in inorganic chemistry.Chem. Rev. 1997; 97: 597-636Crossref PubMed Scopus (2188) Google Scholar are weak interactions between closed-shell (d10 s2) or pseudo-closed-shell (d8) metal cations. While a better understanding of the true nature of metallophilic interactions is still very much ongoing, they are at the root of some important effects, including the self-assembly of supramolecular structures,45Katz M.J. Sakai K. Leznoff D.B. The use of aurophilic and other metal–metal interactions as crystal engineering design elements to increase structural dimensionality.Chem. Soc. Rev. 2008; 37: 1884-1895Crossref PubMed Scopus (285) Google Scholar,46Deák A. Megyes T. Tárkányi G. Király P. Biczók L. Pálinkás G. Stang P.J. Synthesis and solution- and solid-state characterization of gold(I) rings with short Au….Au interactions. Spontaneous resolution of a gold(I) complex.J. Am. Chem. Soc. 2006; 128: 12668-12670Crossref PubMed Scopus (71) Google Scholar organometallic catalysis,47Weber D. Gagné M.R. Aurophilicity in gold(I) catalysis: for better or worse? BT - homogeneous gold catalysis.Top Curr Chem. 2015; 357: 167-211Crossref PubMed Scopus (27) Google Scholar,48Tkatchouk E. Mankad N.P. Benitez D. Goddard W.A. Toste F.D. Two metals are better Than one in the gold catalyzed oxidative heteroarylation of alkenes.J. Am. Chem. Soc. 2011; 133: 14293-14300Crossref PubMed Scopus (168) Google Scholar as well as luminescence and sensing applications.49Wong K.M.-C. Yam V.W.-W. Self-assembly of luminescent alkynylplatinum(II) terpyridyl complexes: modulation of photophysical properties through aggregation behavior.Acc. Chem. Res. 2011; 44: 424-434Crossref PubMed Scopus (428) Google Scholar,50Yeung M.C.-L. Yam V.W.-W. Luminescent cation sensors: from host–guest chemistry, supramolecular chemistry to reaction-based mechanisms.Chem. Soc. Rev. 2015; 44: 4192-4202Crossref PubMed Google Scholar A myriad of homo-metallophilic interactions, such as aurophilic (AuI···AuI),51Schmidbaur H. Schier A. Aurophilic interactions as a subject of current research: an up-date.Chem. Soc. Rev. 2012; 41: 370-412Crossref PubMed Google Scholar argentophilic (AgI···AgI),52Schmidbaur H. Schier A. Argentophilic interactions.Angew. Chem. Int. Ed. Engl. 2015; 54: 746-784Crossref PubMed Scopus (544) Google Scholar cupriphilic (CuII···CuII),53Hermann H.L. Boche G. Schwerdtfeger P. Metallophilic interactions in closed-shell copper(I) compounds—a theoretical study.Chem. Eur. J. 2001; 7: 5333-5342Crossref PubMed Scopus (216) Google Scholar and mercurophilic (HgII···HgII) interactions54Schmidbaur H. Schier A. Mercurophilic interactions.Organometallics. 2015; 34: 2048-2066Crossref Scopus (67) Google Scholar are richly ingrained over the many branches of science, and attract the attention of researchers to this day. Herein, we report the synthesis, solution, solid state, and computational studies of the first example of a nucleophilic halonium complex that manifests a very unusual and notably attractive interaction from the I+ cation to the Ag+ cation as a complex of complexes referred to hereafter as I∗Ag. Unlike formally similar and well-known argentophilic interactions, these halonium···Ag+ interactions have not been observed to date, with computational studies revealing that the core of this iodonium···silver(I) (I+···Ag+) interaction is unrelated from its analogous parent argentophilic (Ag+···Ag+) interaction, and is instead centered around the nucleophilic character of the I+ cation. The synthetic routes to silver(I) complexes 2, 4, and 6, and the iodonium complexes 5 and 7 are illustrated in Scheme 1. The complex [Ag(bpy)2]PF6 (2) (bpy = 2,2′-bipyridine) was obtained by following the reported procedure for the [Ag(bpy)2]ClO455Boyle P.D. Christie J. Dyer T. Godfrey S.M. Howson I.R. McArthur C. Omar B. Pritchard R.G. Williams G.R. Further structural motifs from the reactions of thioamides with diiodine and the interhalogens iodine monobromide and iodine monochloride: an FT-Raman and crystallographic study.J. Chem. Soc. Dalton Trans. 2000; 18: 3106-3112Crossref Scopus (51) Google Scholar from bpy (1) and AgPF6 (Figures S1, S9, and S10). The addition of 1-methyl-1H-1,2,3-triazole (3, mtz) and AgPF6 in a 2:1 ratio in CH2Cl2 yields the linear silver complex [Ag(mtz)2]PF6 (4) (Figures S11 and S12), which, after the addition of elemental I2, affords the corresponding linear iodonium complex [I(mtz)2]PF6 (5) (Figures S13 and S14) via the selective [N···Ag+···N] → [N···I+···N] cation exchange.28Bedin M. Karim A. Reitti M. Carlsson A.-C.C. Topić F. Cetina M. Pan F. Havel V. Al-Ameri F. Sindelar V. et al.Counterion influence on the N–I–N halogen bond.Chem. Sci. 2015; 6: 3746-3756Crossref PubMed Google Scholar, 29Carlsson A.-C.C. Mehmeti K. Uhrbom M. Karim A. Bedin M. Puttreddy R. et al.Substituent effects on the [N–I–N]+ halogen bond.J. Am. Chem. Soc. 2016; 138: 9853-9863Crossref PubMed Scopus (54) Google Scholar, 30Rissanen K. Haukka M. Halonium ions as halogen bond donors in the solid state [XL2]Y complexes BT - halogen bonding II: Impact on materials chemistry and life sciences.Top Curr Chem. 2015; 359: 77-90Crossref PubMed Scopus (21) Google Scholar, 31Koskinen L. Hirva P. Kalenius E. Jääskeläinen S. Rissanen K. Haukka M. Halogen bonds with coordinative nature: halogen bonding in a S–I+–S iodonium complex.CrystEngComm. 2015; 17: 1231-1236Crossref Google Scholar, 32Turunen L. Warzok U. Puttreddy R. Beyeh N.K. Schalley C.A. Rissanen K. N⋅⋅⋅I+⋅⋅⋅N halogen-bonded dimeric capsules from tetrakis(3-pyridyl)ethylene cavitands.Angew. Chem. Int. Ed. Engl. 2016; 55: 14033-14036Crossref PubMed Scopus (62) Google Scholar, 33Turunen L. Peuronen A. Forsblom S. Kalenius E. Lahtinen M. Rissanen K. Tetrameric and dimeric [N⋅⋅⋅I+⋅⋅⋅N] halogen-bonded supramolecular cages.Chemistry. 2017; 23: 11714-11718Crossref PubMed Scopus (32) Google Scholar, 34Turunen L. Warzok U. Schalley C.A. Rissanen K. Nano-sized I12L6 molecular capsules based on the [N⋅⋅⋅I+⋅⋅⋅N] halogen bond.Chem. 2017; 3: 861-869Abstract Full Text Full Text PDF Scopus (44) Google Scholar, 35Warzok U. Marianski M. Hoffmann W. Turunen L. Rissanen K. Pagel K. Schalley C.A. Surprising solvent-induced structural rearrangements in large [N⋯I+⋯N] halogen-bonded supramolecular capsules: an ion mobility-mass spectrometry study.Chem. Sci. 2018; 9: 8343-8351Crossref PubMed Google Scholar The [I(mtz)2]PF6∗[Ag(bpy)2]PF6 (7) complex, which exhibits the unprecedented I+···Ag+ interaction, hereafter referred to as I∗Ag, is obtained straightforwardly via the combination of complexes 2 and 5 in a 1:1 ratio in CH2Cl2, followed by slow evaporation (Route 1, Scheme 1). To illustrate the robustness of the I∗Ag interaction, 7 can also be obtained through two alternative routes. First, reacting equimolar amounts of bpy (1) and mtz (3) with AgPF6 in CH2Cl2 resulted in a 3-coordinate asymmetric heteroleptic Ag-complex37Ward J.S. Fiorini G. Frontera A. Rissanen K. Asymmetric [N–I–N]+ halonium complexes.Chem. Commun. 2020; 56: 8428-8431Crossref PubMed Google Scholar [{Ag(bpy)(mtz)}2][PF6]2 (6), which, after the addition of one equivalent of I2, yielded 7 (Route 2a, Scheme 1). Second, a simple recrystallization from CH2Cl2 of a 1:1 mixture of [Ag(bpy)2]PF6 (2) and [Ag(mtz)2]PF6 (4) led to the same heteroleptic complex 6, which upon treatment with I2 gave 7 (Route 2b, Scheme 1). All intermediate complexes 2, 4, 5, and 6 were characterized by single-crystal X-ray crystallography (Supplemental information). The 1H NMR spectra of ligand 3, silver complex 4, and iodonium complex 5 demonstrated significant complexation-induced shifts (Figure S2). The addition of AgPF6 into ligand 3 in a CD2Cl2 solution led to a noticeable downfield shift of the ligand proton signals of 3, confirming the formation of the silver complex 4. A further downfield chemical shift was noticed for the silver complex 4 after the addition of I2. The 1H-15N HMBC measurements (Figures S5–S7) of 3, 4, and 5 were also performed, in which the nitrogen nuclei showed large changes in their chemical shifts after addition to the AgPF6, and more so upon the subsequent addition of I2, which confirms the formation of the silver and iodonium complexes in solution. All three different methods for the preparation of 7, exhibiting the I∗Ag interaction, resulted in the same 1H NMR spectrum regardless of the route used (Figure 1). Moreover, the solutions of the Ag+ complex 6 prepared by routes 2a and 2b also gave the same 1H NMR spectra (Figure S3), confirming the existence of the heteroleptic complex 6 in solution. Comparison of the 1H NMR spectra of 2, 5, and 7 (Figure 1) revealed that the triazole protons of complex 7 remain unchanged when compared with the corresponding signals in complex 5. However, the protons (a, b, c, and d) of the bpy in 7 showed detectable chemical shift changes (b, c, d: shielded; a: deshielded) when compared with complex 2, attributable to the presence of the I∗Ag interaction enduring in solution. This is probably due to the fact that the I∗Ag interaction weakens the Ag-N interactions in complex 2, increasing the electron density around the nitrogen atoms, thus causing a redistribution of the π-electron density in the bipyridiyl rings. The 15N chemical shift change of −2.89 ppm; see Figures S4 and S8) between 2 and 7 from the 1H-15N NMR measurements, which is in very good agreement with the computationally predicted difference (−2.7 ppm; see Figure S28 and Section S6.5).56Hakkert S.B. Gräfenstein J. Erdelyi M. The 15N NMR chemical shift in the characterization of weak halogen bonding in solution.Faraday Discuss. 2017; 203: 333-346Crossref PubMed Google Scholar Furthermore, optical spectroscopic UV-vis and fluorescence experiments of 2, 5, and 7 were performed to further verify the presence of the I∗Ag interaction, as shown in Figure S15. The UV-vis and fluorescence studies clearly indicate that the spectra of 7 are markedly different from those of 2, 5, and the computationally generated theoretical sum of the spectra of 2 and 5 (see Section S3.4). An ITC measurement was done in DCM (see Section S4) confirming the 1:1 stoichiometry of 7 with remarkably high binding constant of 37,000 M−1 (ΔH = −5.170 kcal/mol, ΔS = 3.56 cal/mol and ΔG = −6.231 kcal/mol), which verifies the existence of the strong I∗Ag interaction in solution. The single crystals of 7 were grown from CH2Cl2, and their identity