Two new bimetallic complexes, [Cp*Yb-2](2)(mu-1,3-(2,2'-bipyridyl)-5-(BU)-B-t-C6H3) (1) and [Cp*Yb-2](2)(mu-1,4-(2,2'-bipyridyl)-C6H4) (2), and their corresponding two-electron oxidation products [1](2+) and [2](2+) have been synthesized with the aim of determining the impact of the bridging ligand geometry on the electronic and magnetic properties of these materials. Electrochemistry, optical spectroscopy, and bulk susceptibility measurements all support a ground-state electronic configuration of the type [(f)(13)-(pi(a)*)(1)-(pi(b)*)(1)-(f)(13)]. Density functional theory calculations on the uncomplexed bridging ligands as doubly reduced species also indicate that the diradical electronic configuration is the lowest lying for both meta- and para-bis(bipyridyl) systems. The electrochemical and optical spectroscopic data indicate that the electronic coupling between the metal centers mediated by the diradical bridges is weak, as evidenced by the small separation of the metal-based redox couples and the similarity of the f-f transitions of the associated dicationic complexes ([1](2+) and [2](2+)) relative to those of the monometallic [CP*Yb-2(bpy)](+) analogue. The magnetic susceptibility data show no evidence for exchange coupling between the paramagnetic metal centers in the neutral complexes, but do indicate weak exchange coupling between Yb-III and ligand radical spins on each of the effectively independent halves of the bimetallic complexes. These findings are in contrast to those reported recently for Co-III/II dioxolene bimetallic complexes bridged by these same bis(bipyridyl) ligands. The difference is attributed in part to the dominant singlet diradical character of the bridging ligands in the ytterbocene complexes. These experimental and theoretical results are consistent with expectations for organic diradical spin orientations for meta versus para substituents across a phenylene linker, but this effect does not induce significant longer-range superexchange or electronic interactions between the metal centers in these systems.

A systematic study of the novel charge-transfer [(f)14-(pi)0-(f)14 --> (f)13-(pi)2-(f)13] electronic state found in 2:1 metal-to-ligand adducts of the type [(Cp)2Yb](BL)[Yb(Cp)2] [BL = tetra(2-pyridyl)pyrazine (tppz) (1), 6',6' '-bis(2-pyridyl)-2,2':4',4'':2'',2'''-quaterpyridine (qtp) (2), 1,4-di(terpyridyl)-benzene (dtb) (3), Cp = (C5Me5)] has been conducted with the aim of determining the effects of increased Yb-Yb separation on the magnetic and electronic properties of these materials. The neutral [(f)13-(pi)2-(f)13], cationic [(f)13-(pi)1-(f)13] and dicationic [(f)13-(pi)0-(f)13] states of these complexes were studied by cyclic voltammetry, UV-vis-NIR electronic absorption spectroscopy, NMR, X-ray crystallography, and magnetic susceptibility measurements. The spectroscopic and magnetic data for the neutral bimetallic complexes is consistent with an [(f)13(pi)2(f)13] ground-state electronic configuration in which each ytterbocene fragment donates one electron to give a singlet dianionic bridging ligand with two paramagnetic Yb(III) centers. The voltammetric data demonstrate that the electronic interaction in the neutral molecular wires 1-3, as manifested in the separation between successive metal reduction waves, is large compared to analogous transition metal systems. Electronic spectra for the neutral and monocationic bimetallic species are dominated by pi-pi and pi-pi transitions, masking the f-f bands that are expected to best reflect the electronic metal-metal interactions. However, these metal-localized transitions are observed when the electrons are removed from the bridging ligand via chemical oxidation to yield the dicationic species, and they suggest very little electronic interaction between metal centers in the absence of pi electrons on the bridging ligands. Analysis of the magnetic data reveals that the qtp complex displays antiferromagnetic coupling of the type Yb(alpha)(alphabeta)Yb(beta) at approximately 13 K.

[reaction: see text] Under the appropriate conditions, the combination of two tritopic pyridyl ligands with three metal-containing molecular "clips" spontaneously generates supramolecular coordination cages with trigonal prismatic frameworks.

The electron-transfer capacity of molecular rectangle ions [Pt(II)(4)(PEt(3))(8)(mu-anth(2-))(2)(mu-L)(2)](4+) with anth = anthracene-1,8-diyl and L = 4,4'-bipyridine (bp) or 1,2-bis(4-pyridyl)ethene (bpe) was investigated in acetonitrile and dichloromethane using cyclic voltammetry, EPR, and UV-vis-near-IR spectroelectrochemistry. The compounds can be reversibly reduced, first in a two-electron process and then via two closely separated one-electron steps. Oxidation was also possible at rather low potentials in a reversible two-electron step, followed by an electrochemically irreversible process. The spectroscopic results indicate reduction at the neutral acceptor ligands L and oxidation at the formally dianionic anthracene "clips". In contrast, the prototypical molecular square ([Pt(triphos)(mu-bp)](4))(8+) undergoes only irreversible reduction.

Coordination-driven self-assembly reactions have been used in the preparation of a variety of discrete supramolecular species, some of which have shown promise as synthetic receptors. Many highly ordered coordination polymers and porous networks have been prepared in a similar fashion. While a few of these solids are capable of the uptake of small organic molecules in the resultant molecular channels, the formation of truly porous structures has frequently been thwarted by lattice interpenetration. A strategy for the formation of porous solids that may circumvent this problem is based on the covalent construction of nanoscale macrocycles which, when eclipsed in the solid state, may lead to porous, tubular assemblies. We have incorporated these concepts toward the realization of a bidirectionally porous solid. The metal-directed, self-assembly of a conjugated, macrocyclic ligand provides a discrete, supramolecular entity in solution and the solid state. X-ray crystallographic analysis establishes that this assembly packs such that bidirectional channels are realized, and the incorporation of only ClCH2CH2Cl into the crystal lattice demonstrates that these channels are potentially suitable for the selective uptake of small organic guests.

A family of nanoscale-sized supramolecular cage compounds with a trigonal prismatic framework was prepared by means of spontaneous self-assembly from the combination of a predesigned molecular "clip" with tritopic pyridyl subunits. As confirmed by x-ray crystallography, the smallest structure of the reported series is approximately 1 x 2 nm and possesses a nitrate anion incarcerated inside its molecular cavity. The largest structure has dimensions of approximately 1 x 4 nm.

The synthesis and X-ray crystal structures of two novel cationic metal complexes bearing ligands capable of multiple hydrogen-bonding interactions (isonicotinamide) are reported. cis-(Et3P)(2)Pt(NC5H4CONH2)(2)(NO3)(2) (2) crystallizes as its monohydrate via the amide functionality, resulting in infinite, parallel zigzag chains. (C5Me5)Rh(NC5H4CONH2)(3)(OTf)(2) (3), along with one molecule of acetone, crystallizes via the amide functionality, resulting in infinite, doubly stranded, interwoven chains. The preparation and X-ray crystal structure of cis-(Et3P)(2)Pt(NO3)(2) (1) is also reported.

Interaction of a predesigned molecular "clip" (4) with rigid dipyridyl bridging ligands, in acetone/water mixtures, leads to the formation of molecular rectangles (5-8) in 92-97% isolated yields via spontaneous self-assembly. Characterization was accomplished with multinuclear NMR and UV-vis spectroscopy, FAB mass spectrometry, and X-ray crystallography. The length of these metallamacrocycles ranges from 2 to 3 nm. Postmodification via non-nucleophilic counterion exchange results in enhanced structural integrity for the assemblies.

The combination of linear dipyridyl ligands with a new type of modular building unit, based upon a 1,8-platinum-functionalized anthracene, leads to the self-organization of rectangular frameworks. X-ray crystallography confirms the cyclic structure of the supramolecular cationic complexes. Spectral assignments were provided by 2D NOESY (1)H NMR experiments.

The high-yield preparation, by double oxidative addition, of nine novel platinum and palladium bis(trans-M(PR3)(2)X)aryl (M = Pt or Pd; R = PPh3 or PEt3; X = Br or I; aryl = 1,4-benzene, 4,4'-biphenyl, 4,4''-ter-p-phenyl, 4,4'-tolane, or 4,4'-benzophenone) complexes from the reaction of Pt(PPh3)4, Pt(PEt3)(4), or Pd(PPh3)(4) with the respective dihalo aromatic in toluene is described. These complexes were fully characterized by elemental analysis, mass spectrometry, and NMR (H-1, C-13{H-1} and P-31{H-1}) and vibrational (IR or Raman) spectroscopies. The single-crystal molecular structure of 4,4'-bis(trans -Pt(PEt3)(2)I)biphenyl (2a) was determined by X-ray crystallography. The key structural feature of this complex is the dihedral angle of 18.9 degrees between the two planes defined by the phenyl groups of the biphenyl linkage. The nature of the palladium-carbon bond is investigated by C-13{H-1) NMR spectroscopy; Taft's sigma(R) parameter is found to correlate in a linear fashion with [delta(C-ipso) - delta(C-0)] for these palladium complexes. These data indicate the C-13 chemical shift of C-ipso is linearly related to the amount of pi-electron density of the carbon bound to the palladium center. The potential utility of these bimetallic platinum and palladium complexes as subunits in the generation of organometallic macrocycles is described.

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Six nanoscale molecular squares are reported. They are prepared in essentially quantitative yields via spontaneous self-assembly of preprogrammed 90 degrees angular units with diverse bimetallic linear linkers. Characterization was accomplished with multinuclear NMR and, in two cases, via ESI-FTICR mass spectral data. The size of these novel metallomacrocycles range from 3.6 nm (diagonal) and 2.6 nm (side) for the smallest to 4.7 nm (diagonal) and 3.4 nm (side) for the largest as estimated by extensible systematic force field calculations. The molecular squares incorporating alkynyl units as corners are able to complex four Ag+ ions via the pi-tweezer effect.

The supramolecular synthesis and chemistry of organic macrocycles has been the focus of considerable study for over thirty years. In contrast, the chemistry of analogous inorganic and organometallic macrocycles is in it infancy; little is know about the stability, spectroscopic and physical properties, and chemistry of these species. We will report on the design of several unique supramolecular macrocycles and the characterization of these species by a range of spectroscopic techniques, including electrospray-ionization Fourier transform ion cyclotron resonance spectrometry. Preliminary data concerning the host-guest chemistry of these macrocycles will also be presented.

Stable, crystalline cyanoiodolane 3 has been prepared in two steps by sequential reactions of 1-hydroxy-3, 3-bis(trifluoromethyl)-1,3-dihydro-1 lambda(3),2-benzoiodoxole 1 with trimethylsilyltriflate and then with cyanotrimethysilane; X-ray structure analysis reveals a distorted T-shaped structure for iodine with an endocyclic I-O bond distance of 2.117 Angstrom, which is significantly shorter than usual in C-substituted benzoiodoxole derivatives.

Organosulfonyloxy derivatives of 1,2-benziodoxol-3(1H)-one (3a-c) and 3,3-bis(trifluoromethyl)-3(1H)-1,2-benziodoxole (5a-c) can be prepared in high yield by the reaction of 1-hydroxybenziodoxoles 1 or 4 and the corresponding sulfonic acids or Me(3)SiOTf in the form of stable, but moderately hygroscopic, microcrystalline solids. Reaction of the triflate derivatives 3a and 5a with alkynyltrimethylsilanes affords either alkynyliodonium triflates 6, or (E)-beta-(trifluoromethanesulfonyloxy)alkenyliodonium triflates 7, while the same reaction in the presence of pyridine selectively gives the respective 1-alkynylbenziodoxoles 8 and 9 in 82-90% yield.

Iodosylperfluoroalkanes (CnF2n + 1IO, n = 2,3,4,6) were prepared in high yield by mild hydrolysis of [bis(trifluoroacetoxy)iodo] perfluoroalkanes with sodium bicarbonate and ice. Reaction of iodosylperfluoroalkanes with 1,4-bis (trimethylsilyl) benzene in the presence of trimethylsilyltriflate gave the corresponding perfluoroalkyl(aryl) iodonium triflates in 70–83% yield.

1-[Hydroxy(sulfonyloxy)iodo]-1H,1H-perfluoroalkanes 3 [R(f)CH(2)I(OH)OSO(2)R; R = CH(3), CF(3), p-CH(3)C(6)H(4), R(f) = CF(3), C(2)F(5)] can be prepared in two steps from the appropriate iodofluoroalkanes by oxidation with peroxytrifluoroacetic acid and subsequent reaction with TsOH, MsOH, or Me(3)SiOTf. The tosylate derivative 3a reacts with silyl enol ethers under mild conditions to give the respective alpha-(tosyloxy) ketones. A similar reaction of cyclohexene furnishes cis-1,2-bis(tosyloxy)cyclohexane as the major product. Triflates 3c,f react with (trimethylsilyl)arenes under mild conditions to afford the respective (fluoroalkyl) (aryl)iodonium triflates 7, while the analogous reaction with alkynyltrimethylsilanes leads to novel (fluoroalkyl)(alkynyl)iodonium salts 8.

Azidoiodinanes 2 and 4a,b can be prepared from the appropriate benziodoxoles 1 and 3a,b and trimethylsilyl azide in the form of stable, crystalline compounds. A single-crystal X-ray analysis for azide 4b revealed the expected hypervalent iodine distorted T-shaped geometry with the N1-I-O bond angle of 169.5 (2) degrees. The lengths of the bonds to the iodine atom, I-N (2.18 Angstrom), I-O (2.13 Angstrom), and I-C (2.11 Angstrom), are within the range of typical single covalent bonds in organic derivatives of polyvalent iodine, while the previously reported benziodoxoles generally have an elongated I-O bond. The geometry of the I-(III)NNN fragment in 4b is similar to the literature electron diffraction data on monomeric iodine azide, IN3, in gas phase. Azidobenziodoxoles 2,4 are potentially useful reagents for direct azidation of organic substrates, such as dimethylanilines, alkanes, and alkenes. Reaction of 2 with dimethylanilines proceeds under mild conditions to afford the respective N-azidomethyl-N-methylanilines in excellent yield. Alkanes, cycloalkanes, and adamantanes react with azidobenziodoxoles 2 or 4b in the presence of radical initiators at 80-132 degrees C with the formation of tertiary alkylazides, while reaction of norbornane lends to exo-2-azidonorbornane. Under similar conditions cyclohexene is selectively azidated at the allylic position.

1-[Hydroxy(sulfonyloxy)iodo]-2,2,2-trifluoroethanes [CF3CH2I(OH)OSO2R; R = CH3, CF3, p-CH3C6H4] can be prepared in two steps from trifluoroethyliodide by oxidation with pertrifluoroacetic acid and subsequent reaction with TsOH, MsOH, or Me3SiOTf. Reaction of the tosylate derivative 3 with silyl enol ethers affords α-tosyloxyketones, while triflate 5 smoothly reacts with trimethylsilylbenzene to give the respective trifluoroethyl(phenyl)iodonium triflate 8.