Air-/Heat-Stable Crystalline Carbon-Centered Radicals Derived from an Annelated N‑Heterocyclic Carbene

Organic radicals are open-shell species and have been extensively applied to functional materials due to their unique physicochemical properties with unpaired electrons; however, most of them are highly reactive and short-lived. Herein, a series of stable radicals were readily accessed in two steps from a bis­(imino)­acenaphthene-supported N-heterocyclic carbene (IPr­(BIAN)) through enhancing the delocalization of spin density. The IPr­(BIAN)-based radicals 3a–c, obtained by reduction of the corresponding iminium salts 2a–c with KC8, have been spectroscopically and crystallographically (3a,c) characterized. DFT calculations indicate that increasing the electron-withdrawing properties of the para substituent on the carbene carbon atom results in the spin density evolving from the acenaphthene ring to the phenyl ring. The IPr­(BIAN)-based radicals 3a–c show excellent stability: they have half-lives of 1 week in well-aerated solutions and feature a high thermal decomposition temperature up to 200 °C

Synthesis and Characterization of Binuclear Half-Sandwich Iridium and Rhodium Carbene Complexes Containing 1,2-Dichalcogenolato Carborane or Carbonato Ligands

Reactions of bi-NHC ligands with the 16-electron half-sandwich Ir and Rh dichalcogenolato carborane complexes Cp*M[E2C2(B10H10)] (M = Ir, Rh; E = S, Se) or 16-electron half-sandwich Ir and Rh carbonate complexes Cp*M(μ-O)2CO (M = Ir, Rh) give corresponding 18-electron binuclear complexes of the type [{Cp*M(E2C2(B10H10))}2L] (L = 1,1′-(1,2-ethanediyl)bis(3-methylimidazolin-2-ylidene); M = Ir, E = S (4a), Se (4b); M = Rh, E = S (5a), Se (5b)) and [Cp*M(μ-O)2CO]2L (M = Ir (8), Rh (9)). Complexes 4−9 can also be obtained directly from the reactions of [Cp*MCl2]2L (M = Ir (2), Rh (3)) with Li2[E2C2(B10H10)] or Na2CO3 in high yields. The complexes were characterized by IR, NMR spectroscopy, and elemental analysis. In addition, the molecular structures of 4b, 5a, and 8 have been determined by X-ray crystallography

Postsynthetic Modification of Dicarbene-Derived Metallacycles via Photochemical [2 + 2] Cycloaddition

Molecular squares obtained from two olefin-bridged bis­(NHC) ligands, NHC–Ar–CC–Ar–NHC, and two Ag⁺ or Au⁺ ions undergo postsynthetic modifications via a UV-irradiation-initiated [2 + 2] cycloaddition reaction to yield the corresponding cyclobutane-bridged dinuclear tetrakis­(NHC) complexes. The tetrakis­(NHC) ligand can be liberated from the Ag^I complexes as the tetraimidazolium salt. For the Au^I complexes, the substituents at N3 and N3′ of the dicarbene ligands determine the outcome of the reaction in the solid state

Facile Separation of Regioisomeric Compounds by a Heteronuclear Organometallic Capsule

Owing to the often-similar physical and chemical properties of structural isomers of organic molecules, large efforts have been made to develop efficient strategies to isolate specific isomers. However, facile separation of regio­isomeric compounds remains difficult. Here we demonstrate a universal organometallic capsule in which two silver centers are rigidly separated from each other by two tetranuclear [Rh4] pyramidal frustums, which selectively encapsulate a specific isomer from mixtures. Not only is the present heterometallic capsule suitable as a host for the encapsulation of a series of aromatic compounds, but also the receptor shows widely differing specificity for the various isomers. Direct experimental evidence is provided for the selective encapsulation of a series of para (p)-disubstituted benzene derivatives, such as p-xylene, p-dichloro­benzene, p-dibromo­benzene, and p-diiodo­benzene. The size and shape matching, as well as the Ag−π interactions, are the main forces governing the extent of molecular recognition. The encapsulated guest p-xylene can be released by using the solid–liquid solvent washing strategy, and the other guest molecules are easily liberated by using light stimulus

Postsynthetic Modification of Dicarbene-Derived Metallacycles via Photochemical [2 + 2] Cycloaddition

Molecular squares obtained from two olefin-bridged bis­(NHC) ligands, NHC–Ar–CC–Ar–NHC, and two Ag⁺ or Au⁺ ions undergo postsynthetic modifications via a UV-irradiation-initiated [2 + 2] cycloaddition reaction to yield the corresponding cyclobutane-bridged dinuclear tetrakis­(NHC) complexes. The tetrakis­(NHC) ligand can be liberated from the Ag^I complexes as the tetraimidazolium salt. For the Au^I complexes, the substituents at N3 and N3′ of the dicarbene ligands determine the outcome of the reaction in the solid state

Synthesis, Characterization, and Properties of Half-Sandwich Iridium/Rhodium-Based Metallarectangles

Tetranuclear half-sandwich iridium or rhodium complexes were obtained in good yields from the reactions of the binuclear half-sandwich metal precursors [Cp*2M2(μ-CA)]­Cl2 (1a, M = Ir; 1b, M = Rh; CA = chloranilate) or [Cp*2M2(μ-DHNA)]­Cl2 (2a, M = Ir; 2b, M = Rh; H2DHNA = 6,11-dihydroxynaphthacene-5,12-dione) with diPyNI (diPyNI = N,N-bis­(4-pyridyl)-1,4,5,8-naphthalene­tetra­carboxydiimide) in the presence of AgOTf (OTf = CF3SO3) in CH3OH, respectively. The new metallarectangles have been characterized by elemental analysis, FT-IR, 1H NMR, electrospray mass spectrometry (ESI-MS), and UV/vis absorption spectroscopy. The interactions of these metallarectangles with aromatic molecules, especially pyrene, in solution have been studied by various NMR techniques (1D, DOSY, and ROESY) and UV–vis absorption. DOSY measurements suggest that the interactions between metallarectangle 4a and pyrene are outside of the cavity. The strong π···π interactions between pyrene and the naphthalene­tetra­carboxydiimide ring of metallarectangle 4a were further supported by single-crystal X-ray diffraction data; pyrene molecules are found outside the cavity of the metallarectangle

Synthesis, Characterization, and Properties of Half-Sandwich Iridium/Rhodium-Based Metallarectangles

Tetranuclear half-sandwich iridium or rhodium complexes were obtained in good yields from the reactions of the binuclear half-sandwich metal precursors [Cp*₂M₂(μ-CA)]­Cl₂ (<b>1a</b>, M = Ir; <b>1b</b>, M = Rh; CA = chloranilate) or [Cp*₂M₂(μ-DHNA)]­Cl₂ (<b>2a</b>, M = Ir; <b>2b</b>, M = Rh; H₂DHNA = 6,11-dihydroxynaphthacene-5,12-dione) with diPyNI (diPyNI = <i><i>N,N</i></i>-bis­(4-pyridyl)-1,4,5,8-naphthalene­tetra­carboxydiimide) in the presence of AgOTf (OTf = CF₃SO₃) in CH₃OH, respectively. The new metallarectangles have been characterized by elemental analysis, FT-IR, ¹H NMR, electrospray mass spectrometry (ESI-MS), and UV/vis absorption spectroscopy. The interactions of these metallarectangles with aromatic molecules, especially pyrene, in solution have been studied by various NMR techniques (1D, DOSY, and ROESY) and UV–vis absorption. DOSY measurements suggest that the interactions between metallarectangle <b>4a</b> and pyrene are outside of the cavity. The strong π···π interactions between pyrene and the naphthalene­tetra­carboxydiimide ring of metallarectangle <b>4a</b> were further supported by single-crystal X-ray diffraction data; pyrene molecules are found outside the cavity of the metallarectangle

Synthesis, Characterization, and Electrochemical Properties of Molecular Rectangles of Half-Sandwich Iridium Complexes Containing Bridging Chloranilate Ligands

Binuclear complex [Cp*2Ir2(μ-CA)Cl2] (2) (CA = chloranilate) was obtained by the reaction of [Cp*IrCl2]2 (1) with H2CA in the presence of base. Treatment of 2 with pyridine or 4-(4-bromophenyl)pyridine in the presence of AgOTf (OTf = CF3SO3) in CH3OH gave the corresponding binuclear complexes [Cp*2Ir2(μ-CA)(pyridine)2](OTf)2 (4a) and [Cp*2Ir2(μ-CA){4-(4-bromophenyl) pyridine}2](OTf)2 (4b). Reactions of 2 with bidentate ligands gave tetranuclear complexes [Cp*4Ir4(μ-CA)2(μ-L)2](OTf)4 (L = pyrazine, 5a; 4,4′-dipyridyl, 5b; 2,5-bis(4-pyridyl)-1,3,5-oxadiazole, 5c; 1,4-bis(4-pyridyl)benzene, 5d; (E)-1,2-bis(4-pyridyl)ethene, 5e). X-ray analyses of 5a, 5b, and 5e revealed that each of four Cp*Ir moieties was connected by pyridyl ligands and a bis-bidentate chloranilate (CA) ligand to construct a rectangular cavity with the dimensions 8.03 × 6.92 Å for 5a, 8.03 × 11.24 Å for 5b, and 8.01 × 13.55 Å for 5e. Toluene molecules are contained as solvent molecules in the crystals of 5a and 5b. For 5a, the toluene molecules appeared between the independent rectangles, but the toluene molecules appeared in the rectangle cavity for 5b. The electrochemical properties of 5b and 5e were investigated preliminarily, using cyclic voltammetry

Postsynthetic Modification of Dicarbene-Derived Metallacycles via Photochemical [2 + 2] Cycloaddition

Molecular squares obtained from two olefin-bridged bis­(NHC) ligands, NHC–Ar–CC–Ar–NHC, and two Ag⁺ or Au⁺ ions undergo postsynthetic modifications via a UV-irradiation-initiated [2 + 2] cycloaddition reaction to yield the corresponding cyclobutane-bridged dinuclear tetrakis­(NHC) complexes. The tetrakis­(NHC) ligand can be liberated from the Ag^I complexes as the tetraimidazolium salt. For the Au^I complexes, the substituents at N3 and N3′ of the dicarbene ligands determine the outcome of the reaction in the solid state

Postsynthetic Modification of Dicarbene-Derived Metallacycles via Photochemical [2 + 2] Cycloaddition

Molecular squares obtained from two olefin-bridged bis­(NHC) ligands, NHC–Ar–CC–Ar–NHC, and two Ag⁺ or Au⁺ ions undergo postsynthetic modifications via a UV-irradiation-initiated [2 + 2] cycloaddition reaction to yield the corresponding cyclobutane-bridged dinuclear tetrakis­(NHC) complexes. The tetrakis­(NHC) ligand can be liberated from the Ag^I complexes as the tetraimidazolium salt. For the Au^I complexes, the substituents at N3 and N3′ of the dicarbene ligands determine the outcome of the reaction in the solid state