Disilver(I) macrocycles: variation of cavity size with anion binding

Incorporation of a Phosphino(pyridine) Subcomponent Enables the Formation of Cages with Homobimetallic and Heterobimetallic Vertices

Biological systems employ multimetallic assemblies to achieve a range of functions. Here we demonstrate the preparation of metal–organic cages that contain either homobimetallic or heterobimetallic vertices. These vertices are constructed using 2-formyl-6-diphenylphosphinopyridine, which forms ligands that readily bridge between a pair of metal centers, thus enforcing the formation of bimetallic coordination motifs. Two pseudo-octahedral homometallic M^I₁₂L₄ cages (M^I = Cu^I or Ag^I) were prepared, with a head-to-head configuration of their vertices confirmed by X-ray crystallography and multinuclear NMR for Ag^I. The phosphino-pyridine subcomponent also enabled the formation of a class of octanuclear Cd^II₄Cu^I₄L₄ tetrahedral cages, representing an initial example of self-assembled cages containing well-defined heterobimetallic vertices.

Selective Anion Binding Drives the Formation of AgI8L6 and AgI12L6 Six-Stranded Helicates

Here we describe the formation of an unexpected and unique family of hollow six-stranded helicates. The formation of these structures depends on the coordinative flexibility of silver and the 2-formyl-1,8-napthyridine subcomponent. Crystal structures show that these assemblies are held together by Ag4I, Ag4Br, or Ag6(SO4)2 clusters, where the templating anion plays an integral structure-defining role. Prior to the addition of the anionic template, no six-stranded helicate was observed to form, with the system instead consisting of a dynamic mixture of triple helicate and tetrahedron. Six-stranded helicate formation was highly sensitive to the structure of the ligand, with minor modifications inhibiting its formation. This work provides an unusual example of mutual stabilization between metal clusters and a self-assembled metal-organic cage. The selective preparation of this anisotropic host demonstrates new modes of guiding selective self-assembly using silver(I), whose many stable coordination geometries render design difficult.

Anion Pairs Template a Trigonal Prism with Disilver Vertices

Here we describe the formation of a trigonal prismatic cage, utilizing 2-formyl-1,8-naphthyridine subcomponents to bind pairs of silver(I) ions in close proximity. This cage is the first example of a new class of subcomponent self-assembled polyhedral structures having bimetallic vertices, as opposed to the single metal centers that typically serve as structural elements within such cages. Our new cage self-assembles around a pair of anionic templates, which are shown by crystallographic and solution-phase data to bind within the central cavity of the structure. Many different anions serve as competent templates and guests. Elongated dianions, such as the strong oxidizing agent peroxysulfate, also serve to template and bind within the cavity of the prism. The principle of using subcomponents that have more than one spatially close, but nonchelating, binding site may thus allow access to other higher-order structures with multimetallic vertices.

Photocatalytic Oxygenation of Substrates by Dioxygen with Protonated Manganese(III) Corrolazine

UV-vis spectral titrations of a manganese(III) corrolazine complex [Mn(III)(TBP8Cz)] with HOTf in benzonitrile (PhCN) indicate mono- and diprotonation of Mn(III)(TBP8Cz) to give Mn(III)(OTf)(TBP8Cz(H)) and [Mn(III)(OTf)(H2O)(TBP8Cz(H)2)][OTf] with protonation constants of 9.0 × 10(6) and 4.7 × 10(3) M(-1), respectively. The protonated sites of Mn(III)(OTf)(TBP8Cz(H)) and [Mn(III)(OTf)(H2O)(TBP8Cz(H)2)][OTf] were identified by X-ray crystal structures of the mono- and diprotonated complexes. In the presence of HOTf, the monoprotonated manganese(III) corrolazine complex [Mn(III)(OTf)(TBP8Cz(H))] acts as an efficient photocatalytic catalyst for the oxidation of hexamethylbenzene and thioanisole by O2 to the corresponding alcohol and sulfoxide with 563 and 902 TON, respectively. Femtosecond laser flash photolysis measurements of Mn(III)(OTf)(TBP8Cz(H)) and [Mn(III)(OTf)(H2O)(TBP8Cz(H)2)][OTf] in the presence of O2 revealed the formation of a tripquintet excited state, which was rapidly converted to a tripseptet excited state. The tripseptet excited state of Mn(III)(OTf)(TBP8Cz(H)) reacted with O2 with a diffusion-limited rate constant to produce the putative Mn(IV)(O2(•-))(OTf)(TBP8Cz(H)), whereas the tripseptet excited state of [Mn(III)(OTf)(H2O)(TBP8Cz(H)2)][OTf] exhibited no reactivity toward O2. In the presence of HOTf, Mn(V)(O)(TBP8Cz) can oxidize not only HMB but also mesitylene to the corresponding alcohols, accompanied by regeneration of Mn(III)(OTf)(TBP8Cz(H)). This thermal reaction was examined for a kinetic isotope effect, and essentially no KIE (1.1) was observed for the oxidation of mesitylene-d12, suggesting a proton-coupled electron transfer (PCET) mechanism is operative in this case. Thus, the monoprotonated manganese(III) corrolazine complex, Mn(III)(OTf)(TBP8Cz(H)), acts as an efficient photocatalyst for the oxidation of HMB by O2 to the alcohol.

catena-Poly[[[diaquazinc]-bis{μ-N2,N6-bis[(pyridin-3-yl)methyl]pyridine-2,6-dicarboxamide}] dinitrate]

In the title compound, {[Zn(C(19)H(17)N(5)O(2))(2)(H(2)O)(2)](NO(3))(2)}(n), the Zn(II) cation is located at an inversion centre within a slightly distorted octahedron, ligated by four N atoms from four N(2),N(6)-bis[(pyridin-3-yl)methyl]pyridine-2,6-dicarboxamide (L) ligands occupying a plane about the Zn(II) atom with the two water O atoms perpendicular to that. In the complex molecule, the bidentate bridging L ligands display helical R and S conformers, and link the Zn(II) cations into a one-dimensional centrosymmetric double-chain structure containing 32-membered rings. The nitrate anions reside in these rings and are involved in multiple N-H...O hydrogen-bond interactions. On excitation at 390 nm, the title compound displays a strong blue emission centred at 449 nm. Investigation of the thermal stability shows that the network structure is stable up to 420 K.

The first metal-organic framework containing an unprecedented in situ-generated C-substituted hexamethylenetetramine ligand

The first metal-organic framework containing an unprecedented in situ-generated C-substituted hexamethylenetetramine ligand has been successfully prepared by the reaction of silver nitrate, 4-formylbenzoic acid and hexamethylenetetramine under traditional solution conditions, which holds the unusual (3,4)-connected topological network.

Tungsten coordination chemistry of 1,4-bisdiphenylphosphinobutadiyne — Synthesis of coordination macrocycles and factors controlling diyne cycloaddition

The 1:1 reaction of [W(CO)4(2-picoline)2] (1) with Ph2PCtriple bondC-Ctriple bondCPPh2 (2) led to {[cis-W(CO)4]2(µ-Ph2PC4PPh2)2} (3), in which two bis(diphenylphosphino)butadiyne ligands bridge two tetracarbonyltungsten centres. Reaction of 1 with excess 2 led to [cis-W(CO)4(Ph2PC4PPh2-κ1-P)2] (4), in which two dangling bis-phosphines are coordinated to one metal centre, and reaction of 2 with two equivalents of 1 led to {[W(2-picoline)(CO)4]2(µ-Ph2PC4PPh2)} (5), in which one ligand bridges two tungsten centres. Combination of 4 and 5 led to the trimeric complex {[cis-W(CO)4]3(µ-Ph2PC4PPh2)3} (6), in which three tetracarbonyltungsten centres are bridged by three bisdiphenylphosphinobutadiyne ligands. The dimeric complex 3 showed no reactivity towards alkyne cycloaddition; however, the trimeric complex 6 undergoes cycloaddition at moderate temperatures to form {[W(CO)4]3[µ3-C12(Ph2P)6]} (8), which contains a cyclododecatrienetriyene ring. Comparison of structural data for the template complexes 3 and 6, as well that of previously described platinum template complexes, suggests that alkyne cycloaddition reactions are favoured by proximity of the alkynyl carbons α to phosphorus in adjacent ligands.Key words: coordination chemistry, diyne, cycloaddition, templated reaction, tungsten.

Synthesis of New Self-assembled PdII and PtII Rectangular Metallomacrocycles: A Comparative Study of their Inclusion Complexes

New palladium and platinum metallocycles have been synthesized by reacting 4,4'-bipyridinium-based ligands with PdII and PtII complexes. Strict thermodynamic self-assembly of 1 and [M(en)(NO3)2] (M=Pd, Pt) 6 a,b afforded metallocycles 7 a,b. However, the synthesis of 8 a,b and 9 a,b required a self-assembly process that used sodium p-phenylenediacetate (12) as a template. Finally, metallocycles 10 a,b were synthesized under high dilution conditions from ligand 4. The formation of inclusion complexes between metallocycles 7-10 and substrates 13 and 14 were studied by low-temperature 1H NMR, and the association constants were determined in nitromethane and water by following the characteristic charge-transfer band that these metallomacrocycles show in their UV-visible absorption spectra. A clear correlation between the affinity for a substrate and the dimensions of the metallocycle was observed. Metallocycles 8 b and 9 b exhibited the highest binding constants in water and nitromethane. This observation is in agreement with the DFT (B3LYP)-optimized geometries obtained for the different metallomacrocycles, which indicate that only macrocycles 8 and 9 possess a cavity with a width larger than 3.5 A. The insertion of hydroquinone or diol 13 into the cavity of metallocycle 11 a was confirmed by single-crystal X-ray crystallography.