Phosphorescent Cyclometalated Palladium(II) and Platinum(II) Complexes Derived from Diaminocarbene Precursors.

Metal-mediated self-assembly of isocyanides and methyl 4-aminopyrimidine-5-carboxylate leads to luminescent PdII and PtII complexes featuring C,N-cyclometalated acyclic diaminocarbene (ADC) ligands. The solid-state luminescent properties of these diaminocarbene derivatives are attributed to their triplet-state metal/metal-to-ligand charge-transfer (3MMLCT) nature, which is driven by attractive intermolecular M···M interactions further reinforced by the intramolecular π-π interactions even in the structure of the Pd compound, which is the first Pd-ADC phosphor reported.

Mutual Placement of Isocyanide and Phosphine Ligands in Platinum(II) Complexes [PtHal2L1L2] (Hal = Cl, Br, I; L1,L2 = CNCy, PPh3) Leads to Highly-Efficient Photocatalysts for Hydrosilylation of Alkynes.

A series of platinum complexes featuring phosphine and isocyanide ligands [PtX2(PPh3)(CNCy)] (X = Cl, Br, and I) as well as their parent phosphine [PtX2(PPh3)2] and isocyanide [PtX2(CNCy)2] analogues have been prepared and evaluated as catalysts for the photocatalytic hydrosilylation of alkynes. Under violet light irradiation (λmax = 400 nm), phosphine-isocyanides complexes [PtX2(PPh3)(CNCy)] gave high yields of silylated products (product yield up to 99%, TONs up to 1.98 × 103). The blue light irradiation (λmax = 450 nm) was more suitable for the parent phosphine complexes [PtX2(PPh3)2], which showed comparable efficiency (product yield up to 99%, TON up to 1.98 × 103), while isocyanide complexes [PtX2(CNCy)2] were not active.

Experimental and computational tuning of metalla-N-heterocyclic carbenes at palladium(II) and platinum(II) centers.

Palladium(II) and platinum(II) complexes featuring metalla-N-heterocyclic carbenes (7-12) were synthesised via metal-mediated coupling between equimolar cis-[MCl2(CNR)2] (R = 2,6-Me2C6H3 (Xyl), 2,4,6-Me3C6H3 (Mes)) and 2-aminopyridine or 2-aminopyrazine. Thiocyanate complexes 13-18 with two thiocyanate ligands were obtained through the ligand exchange in the parent compounds 7-12 with NH4CNS in acetone/CH2Cl2. Complexes 7-18 were isolated and characterised by HRESI+-MS, IR, 1H and 13C{1H} NMR spectroscopy and single-crystal X-ray diffraction (in the case of 11, 16, and 18). The UV-vis properties of 7-18 and the electrochemical properties of 7-12 were also evaluated. To study the electronic structure and bonding nature in the new compounds, the quantum theory of atoms in molecules (QTAIM) and Mayer bond order analysis together with the extended transition state with the natural orbitals for chemical valence (ETS-NOCV) method, were used. X-ray diffraction studies and theoretical considerations indicate that the thiocyanate derivatives 16 and 18 form supramolecular dimers by two symmetrical pairs M1⋯C5 and S1⋯C2 with short intermolecular contacts between an electron-rich MII-center and thiocyanate ligand on the one side and the electron-poor π-system of an azaheterocyclic ring on the other side. Representative carbenes 8, 11 and 12 were evaluated as photocatalysts for the hydrosilylation of diphenylacetylene with triethylsilane giving 1,2-(diphenylvinyl)triethylsilane in 98% yield under visible light irradiation (blue light, 445 nm).

High-Yielding Flow Synthesis of a Macrocyclic Molecular Hinge.

Many molecular machines are built from modular components with well-defined motile capabilities, such as axles and wheels. Hinges are particularly useful, as they provide the minimum flexibility needed for a simple and pronounced conformational change. Compounds with multiple stable conformers are common, but molecular hinges almost exclusively operate via dihedral rotations rather than truly hinge-like clamping mechanisms. An ideal molecular hinge would better reproduce the behavior of hinged devices, such as gates and tweezers, while remaining soluble, scalable, and synthetically versatile. Herein, we describe two isomeric macrocycles with clamp-like open and closed geometries, which crystallize as separate polymorphs but interconvert freely in solution. An unusual one-pot addition cyclization reaction was used to produce the macrocycles on a multigram scale from inexpensive reagents, without supramolecular templating or high-dilution conditions. Using mechanistic information from NMR kinetic studies and at-line mass spectrometry, we developed a semicontinuous flow synthesis with maximum conversions of 85-93% and over 80% selectivity for a single isomer. The macrocycles feature voids that are sterically protected from guests, including reactive species such as fluoride ions, and could therefore serve as chemically inert hinges for adaptive supramolecular receptors and flexible porous materials.

Phosphorescent Iridium(III) Complexes with Acyclic Diaminocarbene Ligands as Chemosensors for Mercury.

A new application for bis(cyclometalated) iridium(III) species containing ancillary acyclic diaminocarbene ligands, viz. for sensing of mercury(II) ions, is disclosed. A family of bis(cyclometalated) iridium(III) species supported by both parent isocyanide and acyclic diaminocarbene ligands was prepared, and their electrochemical and photophysical properties were evaluated, revealing efficient blue-green phosphorescence in solution with quantum yields of up to 55%. We uncovered that the photophysical properties of these complexes are dramatically altered by the presence of metal ions and that the complex [Ir(ppy)2(CN){C(NH2)(NHC6H4-4-X)}] with an ADC ligand reacts selectively with Hg2+ ions, enabling its use for sensing of mercury(II) ions in solution. The limit of detection was as low as 2.63 × 10-7 M, and additional mechanistic studies indicated the formation of an unusual dinuclear iridium(III) cyclometalated intermediate, bridged by a mercury dicyano fragment as a driving force of mercury sensing.

Controlling Gas Selectivity in Molecular Porous Liquids by Tuning the Cage Window Size.

Control of pore window size is the standard approach for tuning gas selectivity in porous solids. Here, we present the first example where this is translated into a molecular porous liquid formed from organic cage molecules. Reduction of the cage window size by chemical synthesis switches the selectivity from Xe-selective to CH4 -selective, which is understood using 129 Xe, 1 H, and pulsed-field gradient NMR spectroscopy.

Cleavage of acyclic diaminocarbene ligands at an iridium(iii) center. Recognition of a new reactivity mode for carbene ligands.

Reaction of [Ir(µ-Cl)(ppy)2]2 (1) with 4 equivs of CNC6H4X (X = F 2a, Cl 2b, Br 2c, I 2d) in the presence of 2 equivs of AgOTf in dichloromethane at 20-25 °C furnished the bisisocyanide complexes [Ir(ppy)2(CNC6H4X)2](OTf) ([3a-d](OTf); 72-87%). Reaction of [3a-d](OTf) with an excess of gaseous ammonia at room temperature gave the bisdiaminocarbene species [Ir(ppy)2{C(NH2)NHC6H4X}2](OTf) [5a-d](OTf) (73-83%); the two-step addition proceeds through an intermediate formation of appropriate monocarbene complexes [4a-d](OTf). Further reaction of [5a-d](OTf) with an excess of gaseous ammonia at 50 °C led to the cleavage of one diaminocarbene ligand to the cyanide ligand in [Ir(ppy)2(CN){C(NH2)NHC6H4X}] (6a-d) and this transformation is accompanied with the elimination of a substituted aniline. Treatment of [5a-d](OTf) with N(CH2CH2OH)3 at 50 °C resulted in the cleavage of the diaminocarbene ligand to the isocyanide and uncomplexed NH3; isocyanide remains bound to the iridium(iii) center in [Ir(ppy)2{C(NH2)NHC6H4X}(CNC6H4X)](OTf) (4a-d). All isolated compounds were characterized by elemental analyses (C, H, N), molar conductivity measurements, TG/DTA, HRESI+/--MS, FTIR, 1D (1H, 13C{1H}, 19F{1H}) and 2D (1H,1H-COSY, 1H,13C-HMQC/1H,13C-HSQC, 1H,13C-HMBC) NMR, and also by X-ray diffraction (for the bisisocyanide 3, the diaminocarbene/isocyanide 4, the bisdiaminocarbene 5, and the diaminocarbene/cyanide 6 type complexes).

Visible light accelerated hydrosilylation of alkynes using platinum-[acyclic diaminocarbene] photocatalysts.

Platinum-[diaminocarbene] complexes work as transition-metal photocatalysts for the hydrosilylation of alkynes. A catalytic system operates under visible light irradiation (blue LED) enabling the conversion of a range of terminal and internal alkynes to respective vinyl silanes in excellent yields.

Dramatically Enhanced Solubility of Halide-Containing Organometallic Species in Diiodomethane: The Role of Solvent⋠⋠⋠Complex Halogen Bonding.

In the current study, we evaluated the solubility of a number of organometallic species and showed that it is noticeably improved in diiodomethane when compared to other haloalkane solvents. The better solvation properties of CH2 I2 were associated with the substantially better σ-hole-donating ability of this solvent, which results in the formation of uniquely strong solvent-(metal complex) halogen bonding. The strength of the halogen bonding is attenuated by the introduction of additional halogen atoms in the organometallic species owing to the competitive formation of more favourable intermolecular complex-complex halogen bonding. The exceptional solvation properties of diiodomethane and its inertness towards organometallic species make this solvent a good candidate for NMR studies, in particular, for the acquisition of spectra of insensitive spins.

Chemistry of the 8-Nitroguanine DNA Lesion: Reactivity, Labelling and Repair.

The 8-nitroguanine lesion in DNA is increasingly associated with inflammation-related carcinogenesis, whereas the same modification on guanosine 3',5'-cyclic monophosphate generates a second messenger in NO-mediated signal transduction. Very little is known about the chemistry of 8-nitroguanine nucleotides, despite the fact that their biological effects are closely linked to their chemical properties. To this end, a selection of chemical reactions have been performed on 8-nitroguanine nucleosides and oligodeoxynucleotides. Reactions with alkylating reagents reveal how the 8-nitro substituent affects the reactivity of the purine ring, by significantly decreasing the reactivity of the N2 position, whilst the relative reactivity at N1 appears to be enhanced. Interestingly, the displacement of the nitro group with thiols results in an efficient and specific method of labelling this lesion and is demonstrated in oligodeoxynucleotides. Additionally, the repair of this lesion is also shown to be a chemically feasible reaction through a reductive denitration with a hydride source.

Platinum Complexes with Chelating Acyclic Aminocarbene Ligands Work as Catalysts for Hydrosilylation of Alkynes.

This work describes the preparation of a series of platinum-aminocarbene complexes [PtCl{C(N=C a (C6R2R3R4R5CON b ))=N(H)R1}(CNR1)] a-b (8-19, 65-75% isolated yield) via the reaction of cis-[PtCl2(CNR1)2] (R1 = Cy 1, t-Bu 2, Xyl 3, 2-Cl-6-MeC6H3 4) with 3-iminoisoindolin-1-ones HN=C a (C6R2R3R4R5CON b H) (R2-R5 = H 5; R3 = Me, R2, R4, R5 = H 6; R3, R4 = Cl, R2, R5 = H 7). New complexes 17-19 were characterized by elemental analyses (C, H, N), ESI+-MS, Fourier transform infrared spectroscopy (FT-IR), one-dimensional (1H, 13C{1H}), and two-dimensional (1H,1H correlation spectroscopy (COSY), 1H,13C heteronuclear multiple quantum correlation (HMQC)/1H,13C heteronuclear single quantum coherence (HSQC), 1H,13C heteronuclear multiple bond correlation (HMBC)) NMR spectroscopy, and authenticity of known species 8-16 was confirmed by FT-IR and 1H and 13C{1H} NMR. Complexes 8-19 were assessed as catalysts for hydrosilylation of terminal alkynes with hydrosilanes to give vinyl silanes, and complex [PtCl{C(N=C a (C6H3(5-Me)CON b ))=N(H)(2-Cl-6-MeC6H3)}{CN(2-Cl-6-MeC6H3)}] a-b (18) showed the highest catalytic activity. The catalytic system proposed operates at 80-100 °C for 4-6 h in toluene and with catalyst loading of 0.1 mol %, enabling the reaction of a number of terminal alkynes (PhC≡CH, t-BuC≡CH, and 4-(t-Bu)C6H4C≡CH) with hydrosilanes (Et3SiH, Pr3SiH, i-Pr3SiH, and PhMe2SiH). Target vinyl silanes were prepared in 48-95% yields (as a mixture of α/ß isomers) and with maximum turnover number of 8.4 × 103. Hydrosilylation of internal alkynes (PhC≡CPh, Me(CH2)2C≡C(CH2)2Me, and PhC≡CMe) with hydrosilanes (Et3SiH, PhMe2SiH) led to the corresponding trisubstituted silylated alkenes in 86-94% yields. Initial observations on the mechanism of the catalytic action of platinum-ADC catalysts 8-19 suggested a molecular catalytic cycle.

Substrate-Selective C-H Functionalization for the Preparation of Organosulfur Compounds from Crude Oil-Derived Components.

The direct utilization of a natural feedstock in organic synthesis is an utmost challenge because the selective production of one product from a mixture of starting materials requires unprecedented substrate selectivity. In the present study, a simple and convenient procedure is evaluated for the substrate-selective alkenylation of a single component in a mixture of organosulfur compounds. Pd-catalyzed alkenylation of two-, three-, four-, and five-component mixtures of crude oil-derived sulfur species led to the exclusive C-H functionalization of only one compound. The observed remarkable substrate selectivity opens new opportunities for sustainable organic synthesis.

Single-Molecule Conductance of Viologen-Cucurbit[8]uril Host-Guest Complexes.

The local molecular environment is a critical factor which should be taken into account when measuring single-molecule electrical properties in condensed media or in the design of future molecular electronic or single molecule sensing devices. Supramolecular interactions can be used to control the local environment in molecular assemblies and have been used to create microenvironments, for instance, for chemical reactions. Here, we use supramolecular interactions to create microenvironments which influence the electrical conductance of single molecule wires. Cucurbit[8]uril (CB[8]) with a large hydrophobic cavity was used to host the viologen (bipyridinium) molecular wires forming a 1:1 supramolecular complex. Significant increases in the viologen wire single molecule conductances are observed when it is threaded into CB[8] due to large changes of the molecular microenvironment. The results were interpreted within the framework of a Marcus-type model for electron transfer as arising from a reduction in outer-sphere reorganization energy when the viologen is confined within the hydrophobic CB[8] cavity.

A novel samarium(ii) complex bearing a dianionic bis(phenolate) cyclam ligand: synthesis, structure and electron-transfer reactions.

The reaction of the hexadentate dianionic 1,4,8,11-tetraazacyclotetradecane-based bis(phenolate) ligand, (tBu2ArO)2Me2-cyclam(2-), with [SmI2(thf )2] in thf resulted in the formation of the divalent samarium complex [Sm(κ(6)-{(tBu2ArO)2Me2-cyclam})] (1). X-ray diffraction studies revealed that after recrystallization from n-hexane/thf complex 1 has a monomeric structure and does not contain thf molecules coordinated to the Sm(II) center. However, UV-vis and (1)H NMR spectroscopy of 1 evidenced the formation of thf-solvated complexes in neat thf. Reductive studies show that complex 1 can act as a single electrontransfer reagent and form well-defined Sm(III) species. The reaction of 1 with several substrates, namely, TlBPh4, pyridine N-oxide, OPPh3, SPPh3 and bipyridines, are reported. Spectroscopy studies, including NMR, and single crystal X-ray diffraction data are in agreement with the formation of cationic Sm(III) species, monochalcogenide bridged Sm(III) complexes and Sm(III) complexes with bipyridine radical ligand, respectively.

Metal-mediated coupling of amino acid esters with isocyanides leading to new chiral acyclic aminocarbene complexes.

Metal-mediated coupling between equimolar amounts of cis-[PdCl2(CNR1)2] (1­5) and the amino acid esters L-HTyrOMe (7) or L-HProOtBu (8) proceeds at 40 °C in chloroform over ca. 6 h. The subsequent workup affords the complexes cis-[PdCl2(CNR1){C(TyrOMe)vNHR1}] (R1 = Xyl 9, 2-Cl-6-Me-C6H3 10) or cis-[PdCl2(CNR1){C(ProOtBu)vNHR1}] (R1 = Xyl 11, 2-Cl-6-Me-C6H3 12, Cy 13, tBu 14, 2-naphthyl 15) in good to excellent isolated yields (75­94%). The corresponding reaction between trans-[PdI2(CNR1)2] (6) and 8 brings about the formation of trans-[PdI2(CNCy){C(ProOtBu)vNHCy}] (16, 76% isolated yield). The reaction of 6 with 7 proceeds non-selectively giving a broad mixture of products. Complexes 9­16 were characterized by elemental analyses (C, H, N), ESI+/−-MS, IR, 1D (1H, 13C{H}) and 2D (1H,1H-COSY, 1H,13C-HMQC/1H,13C-HSQC, 1H,13C-HMBC) NMR spectroscopic techniques, and by single-crystal X-ray diffraction (for 9, 11­13, and 16).

NiII, CuII and ZnII complexes with a sterically hindered scorpionate ligand (TpmsPh) and catalytic application in the diasteroselective nitroaldol (Henry) reaction.

The Ni(II) and Zn(II) complexes [MCl(Tpms(Ph))] (Tpms(Ph) = SO3C(pz(Ph))3, pz = pyrazolyl; M = Ni 2 or Zn 3) and the Cu(II) complex [CuCl(Tpms(Ph))(H2O)] (4) have been prepared by treatment of the lithium salt of the sterically demanding and coordination flexible tris(3-phenyl-1-pyrazolyl)methanesulfonate (Tpms(Ph))(-) (1) with the respective metal chlorides. The (Tpms(Ph))(-) ligand shows the N3 or N2O coordination modes in 2 and 3 or in 4, respectively. Upon reaction of 2 and 3 with Ag(CF3SO3) in acetonitrile the complexes [M(Tpms(Ph))(MeCN)](CF3SO3) (M = Ni 5 or Zn 6, respectively) were formed. The compounds were obtained in good yields and characterized by analytic and spectral (IR, (1)H and (13)C{(1)H} NMR, ESI-MS) data, density functional theory (DFT) methods and {for 4 and [(n)Bu4N](Tpms(Ph)) (7), the latter obtained upon Li(+) replacement by [(n)Bu4N](+) in Li(Tpms(Ph))} by single crystal X-ray diffraction analysis. The Zn(II) and Cu(II) complexes (3 and 4, respectively) act as efficient catalyst precursors for the diastereoselective nitroaldol reaction of benzaldehydes and nitroethane to the corresponding ß-nitroalkanols (up to 99% yield, at room temperature) with diastereoselectivity towards the formation of the anti isomer, whereas the Ni(II) complex 2 only shows a modest catalytic activity.

Metal-mediated coupling of a coordinated isocyanide and indazoles.

A reaction between equimolar amounts of cis-[PdCl2(CNCy)2] (1) and indazole (HInd, 2) or 5-methylindazole (HInd(Me), 3) proceeded in refluxing CHCl3 for ca. 6 h affording the aminocarbene species cis-[PdCl2{C(Ind)=N(H)Cy}(CNCy)] (4) or cis-[PdCl2{C(Ind(Me))=N(H)Cy}(CNCy)] (5) in good (72-83%) isolated yields. Complexes 4 and 5 were characterized by elemental analyses (C, H, N), HR ESI(+)-MS, IR, and 1D ((1)H, (13)C{(1)H}) and 2D ((1)H,(1)H-COSY, (1)H,(13)C-HMQC/(1)H,(13)C-HSQC, (1)H,(13)C-HMBC) NMR spectroscopies, and complex 4 as well by X-ray diffraction. The observed coupling represents the first example of metal-mediated integration between any isocyanide and any aromatic heterocyclic system having an HN center.

Ortho-hydroxyphenylhydrazo-ß-diketones: tautomery, coordination ability, and catalytic activity of their copper(II) complexes toward oxidation of cyclohexane and benzylic alcohols.

New hydrazone o-HO-phenylhydrazo-ß-diketones (OHADB), R(1)NHN═CR(2)R(3) [R(1) = HO-2-C(6)H(4), R(2) = R(3) = COMe (H(2)L(1), 1), R(2)R(3) = COCH(2)C(Me)(2)CH(2)CO (H(2)L(2), 2), R(2) = COMe, R(3) = COOEt (H(2)L(4), 4); R(1) = HO-2-O(2)N-4-C(6)H(3), R(2)R(3) = COCH(2)C(Me)(2)CH(2)CO (H(2)L(3), 3), R(2) = COMe, R(3) = COOEt (H(2)L(5), 5), R(2)R(3) = COMe (H(2)L(6), 6A)], and their Cu(II) complexes [Cu(2)(CH(3)OH)(2)(µ-L(1))(2)] 7, [Cu(2)(H(2)O)(2)(µ-L(2))(2)] 8, [Cu(H(2)O)(L(3))] 9, [Cu(2)(µ-L(4))(2)](n) 10, [Cu(H(2)O)(L(5))] 11, [Cu(2)(H(2)O)(2)(µ-L(6))(2)] 12A and [Cu(H(2)O)(2)(L(6))] 12B were synthesized and fully characterized, namely, by X-ray analysis (4, 5, 7-12B). Reaction of 6A, Cu(NO(3))(2) and ethylenediamine (en) leads, via Schiff-base condensation, to [Cu{H(2)NCH(2)CH(2)N═C(Me)C(COMe)═NNC(6)H(3)-2-O-4-NO(2)}] (13), and reactions of 12A and 12B with en give the Schiff-base polymer [Cu{H(2)NCH(2)CH(2)N═C(Me)C(COMe)═NNC(6)H(3)-2-O-4-NO(2)}](n) 14. The dependence of the OHADB tautomeric equilibria on temperature, electronic properties of functional groups, and solvent polarity was studied. The OHADB from unsymmetrical ß-diketones exist in solution as a mixture of enol-azo and hydrazo tautomeric forms, while in the solid state all the free and coordinated OHADB crystallize in the hydrazo form. The relative stabilities of various tautomers were studied by density functional theory (DFT). 7-14 show catalytic activities for peroxidative oxidation (in MeCN/H(2)O) of cyclohexane to cyclohexanol and cyclohexanone, for selective aerobic oxidation of benzyl alcohols to benzaldehydes in aq. solution, mediated by TEMPO radical, under mild conditions and for the MW-assisted solvent-free synthesis of ketones from secondary alcohols with tert-butylhydroperoxide as oxidant.

Push-pull nitrile ligands exhibit specific hydration patterns.

The reaction between K[PtCl(3)(Me(2)SO)] or prepared in this work cis- and trans-[PtCl(2)(NCNR(2))(Me(2)SO)] (R(2) = Me(2), 1; C(4)H(8)O, 2; C(5)H(10) 3) with an excess of NCNR(2) in water gives the cationic bischelate [Pt{κ(2)-N,N'''-NH=C(NMe(2))OC(NMe(2))=NH}(2)](2+) (4(2+)) and the monochelates [PtCl{κ(2)-N,O-NH=C(NR(2))NC(NR(2))=O}(Me(2)SO)] (R(2) = C(4)H(8)O, 5; C(5)H(10), 6). Complex 4(2+) was released from the reaction mixture as 4·[PtCl(3)(Me(2)SO)](2)·(H(2)O)(2) or it was precipitated as 4·[A](2) (A = pic, 4·[pic](2); PF(6), 4·[PF(6)](2); BPh(4), 4·[BPh(4)](2)·(NH(2)CONMe(2))) by addition of picric acid, NaPF(6), or NaBPh(4), respectively, to the filtrate obtained after separation of 4·[PtCl(3)(Me(2)SO)](2)·(H(2)O)(2). In 2, the dialkylcyanamide ligand undergoes bond cleavage giving the known trans-[PtCl(2){N(H)C(4)H(8)O}(Me(2)SO)] (trans-7). All complexes were characterized by elemental analyses (C, H, N), high resolution ESI-MS, IR, (1)H and (13)C{(1)H} NMR spectroscopic techniques, including 2D NMR correlation experiments ((1)H,(1)H-COSY, (1)H,(13)C-HMQC/(1)H,(13)C HSQC, (1)H,(13)C-HMBC, and (1)H,(1)H-NOESY). The structures of cis-1, cis-3, 4·[PtCl(3)(Me(2)SO)](2)·(H(2)O)(2), 4·[BPh(4)](2)·(NH(2)CONMe(2)) and 5 were determined by a single-crystal X-ray diffraction.