Post-assembly functionalization of organoplatinum(II) metallacycles via copper-free click chemistry.

We describe the use of a strain-promoted copper-free click reaction in the post-self-assembly functionalization of organoplatinum(II) metallacycles. The coordination-driven self-assembly of a 120° cyclooctyne-tethered dipyridyl donor with 60° and 120° di-Pt(II) acceptors forms molecular rhomboids and hexagons bearing cyclooctynes. These species undergo post-self-assembly [3+2] Huisgen cycloaddition with a variety of azides to give functionalized ensembles under mild conditions.

Design, synthesis, and characterizations of a series of Pt(4) macrocycles and fluorescent sensing of Fe3+/Cu2+/Ni2+ through metal coordination.

A Pt(II)(2) organometallic "clip" (1a) containing ethynyl functionality is synthesized. Multinuclear NMR and electrospray ionization mass spectrometry characterized this "clip", and the molecular structure was determined in an X-ray single-crystal diffraction study. A series of discrete molecular rectangles (2a-d) have been synthesized from this "clip" in combination with dipyridyl-based linear linkers (L(1-4)) by a metal-ligand coordination driven self-assembly approach [where L(1) = 4,4'-bipyridine, L(2) = trans-1,2-bis(4-pyridyl)ethylene, L(3) = N-(4-pyridyl)isonicotinamide, and L(4) = N,N'-bis(4-pyridylidene)ethylenediamine]. Rectangle 2d was designed using the imine-based ligand L(4) to make it a system composed of a fluorophore-receptor-fluorophore combination. The imine N(4) pocket is the receptor site, while the anthracene-based "clip" is the fluorophore. Complex 2d is fluorescent in nature and showed fluorescence quenching in solution upon the binding of hard transition metal ions (Fe(3+), Cu(2+), Ni(2+), and Mn(2+)) into the N(4) pocket. The nonresponsive nature of the fluorescence intensity upon the addition of soft metal ions (Zn(2+) and Cd(2+)) having d(10) configuration makes it a suitable sensor for transition metal ions. The fluorescence intensity of the Ni(2+) bound complex was regained when the metal was removed by a stronger chelating 2,2'-dipyridyl ligand.

Self-assembly of a Pd6-molecular double-square and a Cu3-trigonalbipyramidal cage via a new tripodal flexible ligand.

A new tripodal flexible ligand (L) containing pyrazolyl functionality has been prepared and successfully used to obtain a pd(6) (1) molecular double-square and a cu(3) trigonalbipyramidal cage (2), where complex 1 represents the first example of a double-square obtained using a flexible tripodal ligand.

Cu(II)-azide polymers of Cu3 and Cu6 building units: synthesis, structures, and magnetic exchange mechanism.

Two new neutral copper-azido polymers [Cu(3)(N(3))(6)(tmen)(2)](n) (1) and [Cu(6)(N(3))(12)(deen)(2)](n) (2) [tmen = N,N,N',N'-tetramethylethylenediamine and deen = N,N'-diethylethylenediamine] have been synthesized by using lower molar equivalents of the chelating diamine ligands with Cu(NO(3))(2).3H(2)O and an excess of NaN(3). The single crystal X-ray structure shows that in the basic unit of the 1D complex 1, the three Cu(II) ions are linked by double end-on azido bridges with Cu-N(EO)-Cu angles on both sides of the magnetic exchange critical angle of 108 degrees. Complex 2 is a 3D framework of a basic Cu(6) cluster. Cryomagnetic susceptibility measurements over a wide range of temperature exhibit dominant ferromagnetic behavior in both the complexes. Density functional theory calculations (B3LYP functional) have been performed on the trinuclear unit to provide a qualitative theoretical interpretation of the overall ferromagnetic behavior shown by the complex 1.

Catalytic properties of cobalt(III)-oxo cubanes in the TBHP oxidation of benzylic alcohols.

Two series of oxo-bridged Co(III) complexes of the type Co(4)O(4)(O(2)CC(6)H(4)-X)(4)(py)(4) (1) and Co(4)O(4)(O(2)CC(6)H(4)-X)(4)(4-Mepy)(4) (2), where X = H (a), Me (b), MeO (c), Cl (d), NO(2) (e), have been synthesized and characterized in detail. The molecular structures of the complexes consist of a cubelike Co(4)(mu(3)-O)(4) core having Co and O atoms at alternate vertices with carboxylato ligands bridging the Co(3+) ions along four face diagonals of the approximate cube. Nitrogen atoms from pyridyl ligands complete the distorted-octahedral coordination around each Co(III). These neutral Co(III) complexes undergo a nearly reversible one-electron oxidation involving the redox couple [Co(4)(III)(mu(3)-O)(4)](4+) <--> [Co(3)(III)Co(IV)(mu(3)-O)(4)](5+) at potentials (approximately 0.7-1.0 V) that linearly depend on the electronic influence of X. The cobalt(III) clusters of types 1 and 2 have been found to effectively promote the TBHP oxidation of benzylic alcohols under homogeneous conditions to produce the corresponding carbonyl compounds.

Use of 2-pyrimidineamidoxime to generate polynuclear homo-/heterometallic assemblies: synthesis, crystal structures and magnetic study with theoretical investigations on the exchange mechanism.

Three new transition metal complexes using 2-pyrimidineamidoxime (pmadH(2)) as multidentate chelating and/or bridging ligand have been synthesized and characterized. The ligand pmadH(2) has two potential bridging functional groups [µ-O and µ-(N-O)] and consequently shows several coordination modes. While a polymeric 1D Cu(II) complex [Cu(pmadH(2))(2)(NO(3))](NO(3)) (1) was obtained upon treatment of Cu(NO(3))(2)·3H(2)O with pmadH(2) at room temperature in the absence of base, a high temperature reaction in the presence of base yielded a tetranuclear Cu(II)-complex [Cu(4)(pmad)(2)(pmadH)(2)(NO(3))](NO(3))(H(2)O) (2). One of the Cu(II) centers is in a square pyramidal environment while the other three are in a square planar geometry. Reaction of the same ligand with an equimolar mixture of both Cu(NO(3))(2)·3H(2)O and NiCl(2)·6H(2)O yielded a tetranuclear heterometallic Cu(II)(2)Ni(II)(2) complex [Cu(2)Ni(2)(pmad)(2)(pmadH)(2)Cl(2)]·H(2)O (3) containing both square planar (Ni(II)) and square pyramidal (Cu(II)) metal centers. Complexes 1-3 represent the first examples of polynuclear metal complexes of 2-pyrimidineamidoxime. The analysis of variable temperature magnetic susceptibility data of 2 reveals that both ferromagnetic and antiferromagnetic interactions exist in this complex (J(1) = +10.7 cm(-1) and J(2) = -2.7 cm(-1) with g = 2.1) leading to a resultant ferromagnetic behavior. Complex 3 shows expected antiferromagnetic interaction between two Cu(II) centers through -N-O- bridging pathway with J(1) = -3.4 cm(-1) and g = 2.08. DFT calculations have been used to corroborate the magnetic results.

Synthesis and characterisation of heterometallic molecular triangles using ambidentate linker: self-selection of a single linkage isomer.

The coordination driven self-assembly of discrete molecular triangles from a non-symmetric ambidentate linker 5-pyrimidinecarboxylate (5-pmc) and Pd(II)/Pt(II) based 90 degrees acceptors is presented. Despite the possibility of formation of a mixture of isomeric macrocycles (linkage isomers) due to different connectivity of the ambidentate linker, formation of a single and symmetrical linkage isomer in both the cases is an interesting observation. Moreover, the reported macrocycles represent the first example of discrete metallamacrocycles of bridging 5-pmc. While solution composition in both the cases was characterised by multinuclear NMR study and electrospray ionization mass spectrometry (ESI-MS), the identity of the assemblies in the solid state was established by X-ray single crystals structure analysis. Variable temperature NMR study clearly ruled out the formation of any other macrocycles by [4 + 4] or [2 + 2] self-assembly of the reacting components.

Coordination driven self-assembly of four new molecular boats using a flexible imidazole-containing donor linker.

Using a metal-ligand coordination bonding approach, the self-assembly of four new metallamacrocycles from Pd(ii)-based 90 degrees acceptors and a diimidazole donor ligand 1,3-bis(imidazole-1-ylmethyl)-2,4,6-trimethylbenzene (L) has been achieved. The assemblies are characterized fully by NMR and electrospray ionization-mass spectroscopic (ESI-MS) analysis and in two cases the X-ray single-crystal structure analysis established the gross structures. The selective formation of a diimidazole-based linker (L) containing macrocycle [(en)Pd(micro-L)2Pd(en)]4+ from a 1 : 1 : 1 mixture of cis-Pd(en)(NO3)2, and 1,2-bis(4-pyridyl)ethane is also established. Measuring the binding constants established the stronger Pd- binding force compared to traditional Pd-N(pyridyl linker) interaction, which reveals the possibility of using imidazole donor ligands as potential linkers or even better ligands compared to the widely used pyridyl donor ligands in the construction of metal-based large supramolecular assemblies.

Dual role of azide in the formation of a 3D coordination polymer containing bridging 5-pyrimidinecarboxylate.

A new 3D framework [Mn4(5-pmc)4(1,1-N3)4]n () composed of a rare MnII4 square as the repeating secondary building unit, representing the first coordination polymer of 5-pyrimidinecarboxylate (5-pmc) has been successfully synthesized and characterized by X-ray single crystal structure analysis.

Synthesis, structure, spectral and electrochemical properties, and catalytic use of cobalt(III)-oxo cubane clusters.

Olive-green cobalt(III) complexes having the general formula Co4O4(O2CMe)4L4 (1) where L = py (1a), 4-Mepy (1b), 4-Etpy (1c), and 4-CNpy (1d) have been prepared by the H2O2 oxidation of a mixture of Co2+, MeCO2-, and pyridine or 4-substituted pyridines in a 1:2:1 molar ratio in methanol. Spectroscopic and X-ray crystallographic studies show that these complexes contain a tetrameric cubane-like core [Co4(mu3-O)4]4+ where the four cobalt atoms form an approximate tetrahedron with edge lengths of approximately 2.75 A. Each cobalt in the crystallographically determined structure of Co4(mu3-O)4(mu-O2CMe)4L4 in 1a.NaClO4.3.5H2O and 1b.3H2O is hexacoordinate. Infrared spectra of the complexes show characteristic bands near 700, 635, and 580 cm-1 due to the central cubane-like core. 1H NMR spectra of the complexes show that the dissolved species are essentially diamagnetic and also that the complexes maintain their integrity in solution. UV-vis spectra of the green solutions have been interpreted in terms of ligand-field and charge-transfer bands. The electrochemical behavior of the complexes studied by cyclic and differential pulse voltammetric techniques indicates that the [(CoIII)4(mu3-O)4]4+ core present in the complexes undergoes a reversible one-electron oxidation to the [(CoIII)3CoIV(mu3-O)4]5+ core with an E1/2 value below 1 V. This suggests that these complexes of cobalt may be suitable as catalysts for the oxidation of organic compounds. Preliminary investigations indicate that 1a has a role to play in the cobalt-catalyzed aerobic oxidation of neat ethylbenzene and p-xylene.