Spacer-Directed Selective Assembly of Copper Square or Hexagon and Ring-Stacks or Coordination Nanotubes.

The use of simple self-assembly methods to direct or engineer porosity or channels of desirable functionality is a major challenge in the field of metal-organic frameworks. We herein report a series of frameworks by modifying square ring structure of [{Cu2(5-dmpy)2(L1)2(H2O)(MeOH)}2{ClO4}4]·4MeOH (1·4MeOH, 5-dmpy = 5,5'-dimethyl-2,2'-bipyridine, HL1 = 4-pyridinecarboxylic acid). Use of pyridyl carboxylates as directional spacers in bipyridyl chelated Cu(II) system led to the growth of square unit into other configurations, namely, square ring, square chain, and square tunnel. Another remarkable characteristic is that the novel use of two isomers of pyridinyl-acrylic acid directs selectively to two different extreme tubular forms-aligned stacking of discrete hexagonal rings and crack-free one-dimensional continuum polymers. This provides a unique example of two extreme forms of copper nanotubes from two isomeric spacers. All of the reactions are performed in a one-pot self-assembly process at room temperature, while the topological selectivity is exclusively determined by the skeletal characteristics of the spacers.

Transmetalation of a dodecahedral Na9 aggregate-based polymer: a facile route to water stable Cu(II) coordination networks.

A variety of network structures have been prepared by transmetalation of a polymer {Na3[Na9(Cbdcp)6(H2O)18]}n (1) (Cbdcp = N-(4-carboxybenzyl)-(3,5-dicarboxyl)pyridinium) containing dodecahedral Na9 aggregate secondary building units with Cu(II) by modulating the temperature, solvent, and pH. These complexes include a large, zwitterionic hexa-cuprometallocycle [Cu6(Cbdcp)6(H2O)18] (2) formed in H2O at room temperature, two three-dimensional polymers [Cu3(Cbdcp)2(OH)2(H2O)2]n (3) and {[Cu3(Cbdcp)2(OH)2]·2H2O}n (4) isolated from H2O and DMF/H2O at 135 °C, and a mononuclear complex [Cu(HCbdcp)2(H2O)3]·H2O (5) from H2O at 100 °C and pH = 6. All the complexes are robust and water stable. The crystal framework of macrocycle 2 is stable up to 100 °C under vacuum and selectively adsorbs CO2.

Stitching 2D polymeric layers into flexible interpenetrated metal-organic frameworks within single crystals.

A 2D coordination polymer prepared with bulky diethylformamide solvates exhibits channels which allow dipyridyl bridging ligands to diffuse into the crystal lattice. The absorbed dipyridyls thread through the pores of one layer and substitute the surface diethylformamide molecules on the neighboring layers to stitch alternate layers to form flexible interpenetrated metal-orgaic frameworks. The threading process also results in exchange of the bulky diethylformamide solvates for aqua to minimize congestion and, more strikingly, forces the slippage of two-dimensional layers, while still maintaining crystallinity.

A zwitterionic 1D/2D polymer co-crystal and its polymorphic sub-components: a highly selective sensing platform for HIV ds-DNA sequences.

Polymorphic compounds {[Cu(dcbb)2(H2O)2]·10H2O}n (2, 1D chain), [Cu(dcbb)2]n (3, 2D layer) and their co-crystal {[Cu(dcbb)2(H2O)][Cu(dcbb)2]2}n (4) have been prepared from the coordination reaction of a 2D polymer [Na(dcbb)(H2O)]n (1, H2dcbbBr = 1-(3,5-dicarboxybenzyl)-4,4'-bipyridinium bromide) with Cu(NO3)2·3H2O at different temperatures in water. Compounds 2-4 have an identical metal-to-ligand stoichiometric ratio of 1 : 2, but absolutely differ in structure. Compound 3 features a 2D layer structure with aromatic rings, positively charged pyridinium and free carboxylates on its surface, promoting electrostatic, π-stacking and/or hydrogen-bonding interactions with the carboxyfluorescein (FAM) labeled probe single-stranded DNA (probe ss-DNA, delineates as P-DNA). The resultant P-DNA@3 system facilitated fluorescence quenching of FAM via a photoinduced electron transfer process. The P-DNA@3 system functions as an efficient fluorescent sensor selective for HIV double-stranded DNA (HIV ds-DNA) due to the formation of a rigid triplex structure with the recovery of FAM fluorescence. The system reported herein also distinguishes complementary HIV ds-DNA from mismatched target DNA sequences with the detection limit of 1.42 nM.

One-step entry to olefin-tethered N,S-heterocyclic carbene complexes of ruthenium with mixed ligands.

A series of Ru(II) mixed-ligand complexes RuBr(2)(PPh(3))(2)(N-AyBzTh) (Ay = prop-2-enyl; BzTh = benzothiazol-2-ylidene) (4), RuBr(OAc)(PPh(3))(N-MeAyBzTh) (5), RuBr(OAc)(PPh(3))(N-MeBnBzTh)(2) (MeBn = 3-methylbut-2-enyl) (6) and RuCl(OAc)(PPh(3))(N-MeBnBzTh) (7) have been synthesized from Ru(OAc)(2)(PPh(3))(2) in one-pot condensation and ligand exchange reactions. X-ray single-crystal diffraction analysis revealed that they are neutral octahedral Ru(II) complexes with one or two N,S-heterocyclic carbene (NSHC) ligands and a coordinated (4, 5 and 7) or dangling (6) olefin arm. The system displays a range of self-selecting structural variations. Entry of the hybrid olefin-NSHC and halide ligands ejects either one (5, 6 and 7) phosphine ligand or keeps both phosphines (4) by replacing the acetate. It is also possible to accommodate two NSHC ligands by keeping the olefin pendant (6). Complexes 5 and 7 are isostructural with all different ligands on the coordination sphere. Complexes 4-6 are active towards transfer hydrosilylation showing good ß(Z) selectivity, with the Ru(II) bearing acetate giving higher yields.

Syntheses and structures of ruthenium(II) N,S-heterocyclic carbene diphosphine complexes and their catalytic activity towards transfer hydrogenation.

Phosphine exchange of [Ru(II) Br(MeCOO)(PPh(3))(2)(3-RBzTh)] (3-RBzTh=3-benzylbenzothiazol-2-ylidene) with a series of diphosphines (bis(diphenylphosphino)methane (dppm), 1,2-bis(diphenylphosphino)ethylene (dppv), 1,1'-bis(diphenylphosphino)ferrocene (dppf), 1,4-bis(diphenylphosphino)butane (dppb), and 1,3-(diphenylphosphino)propane (dppp)) gave mononuclear and neutral octahedral complexes [RuBr(MeCOO)(η(2)-P(2))(3-RBzTh)] (P(2)=dppm (2), dppv (3), dppf (4), dppb (5), or dppp (6)), the coordination spheres of which contained four different ligands, namely, a chelating diphosphine, carboxylate, N,S-heterocyclic carbene (NSHC), and a bromide. Two geometric isomers of 6 (6a and 6b) have been isolated. The structures of these products, which have been elucidated by single-crystal X-ray crystallography, show two structural types, I and II, depending on the relative dispositions of the ligands. Type I structures contain a carbenic carbon atom trans to the oxygen atom, whereas two phosphorus atoms are trans to bromine and oxygen atoms. The type II system comprises a carbene carbon atom trans to one of the phosphorus atoms, whereas the other phosphorus is trans to the oxygen atom, with the bromine trans to the remaining oxygen atom. Complexes 2, 3, 4, and 6a belong to type I, whereas 5 and 6b are of type II. The kinetic product 6b eventually converts into 6a upon standing. These complexes are active towards catalytic reduction of para-methyl acetophenone by 2-propanol at 82 °C under 1% catalyst load giving the corresponding alcohols. The dppm complex 2 shows the good yields (91-97%) towards selected ketones.

Ruthenium(II) N,S-heterocyclic carbene complexes and transfer hydrogenation of ketones.

A series of ruthenium(II) N,S-heterocyclic carbene (NSHC) complexes Ru(II)X(RCOO)(PPh(3))(2)(3-R'BzTh) (BzTh = benzothiazol-2-ylidene; R = Me, R'/X = Bz/Br (4), Pr(i)/I (6), Bu(i)/I (8); R = Et, R'/X = Bz/Br (5), Pr(i)/I (7), Bu(i)/I (9)) have been synthesized and characterized. Single-crystal X-ray structural analysis revealed that in each case the Ru(II) center adopts an essentially octahedral geometry, coordinated by two trans-oriented PPh(3) completed by an NSHC, chelating carboxylate and halide X (X = Br (4-5), X = I (6-9)) ligands. Although thiazol-2-ylidiene Ru(II) complexes are established and applied in metathesis, these benzothiazol-2-ylidene complexes (4-9) are the first of its kind. Their catalytic activities towards transfer hydrogenation of ketones have been examined and discussed.

Formation and crystallographic elucidation of stable [4 + 2]-coordinate nickel(II) N,S-heterocyclic carbene (NSHC) complexes.

A series of square-planar N,S-heterocyclic carbene (NSHC) complexes trans-[NiX(2)(N-RBzTh)(2)] (BzTh = benzothiazolin-2-ylidene) (R/X = Bz/Br; Me/I; Et/I; Pr(i)/I; Bu(i)/I) have been synthesized and characterized by X-ray single-crystal diffraction analysis. These are the first crystallographically established NSHC complexes of nickel in the literature. The N,S-heterocyclic carbene (NSHC) rings invariably twist away from co-planarity with the metal coordination plane such that the N-substituent moves on top and below the metal to facilitate electrostatic gamma-hydride interaction, thus giving an essentially [4 + 2] coordination at the Ni(ii) center. These compounds are active toward reductive Ullmann-type coupling reactions in Bu(4)NBr showing higher activities towards bromoanisole or bromotoluene than bromobenzene. The complex trans-[NiI(2)(N-Pr(i)BzTh)(2)] with the shortest NiH anagostic separation and a near-ideal orthogonal orientation between the carbene and metal planes gives the highest yields.