Variation of the copper-catalyzed Huisgen 1,3dipolar cycloaddition inVolVing a one-pot two-step transformation of trimethylsilyl-protected alkyne reactants was used to prepare multidentate N-heterocyclic chelators containing 1,2,3triazole rings in high yields. This includes the first reported examples of 1,1′-disubstituted 4,4′-bis(triazole) bidentate chelators deriVed from click preparations.The N-heterocyclic chelators 2,2′-bipyridine (bpy) and 2,2′: 6′,2′′-terpyridine (tpy) have been widely studied, due to their predictable coordination environments and the interesting optoelectronic properties that can result from ligand-metal interactions. Such qualities can be exploited for supramolecular assembly, molecular electronics, and catalysis applications, 1 each often requiring the peripheral incorporation of synthetic handles for physical property manipulation or incorporation into functional systems. Because functionalization of polypyridine-based chelators can be synthetically demanding, 2 it remains important to seek new approaches in the preparation of analogous multidentate chelating motifs that also possess well-defined coordination properties and can be prepared and modified with high efficiency.

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A combination of metal-catalyzed cross-coupling and metal-templated cycloaddition reactions have been utilized to establish multiporphyrin compounds 5-(5'-[15',15' '-bis(10' ',20' '-di[4-(3-methoxy-3-methylbutoxy)phenyl]porphinato)zinc(II)]ethyne)-6-[(5' "-10' ",20' "-di[4-(3-methoxy-3-methylbutoxy)phenyl]porphinato)zinc(II)]indane (1) and 5,6-bis(5'-15',15' '-bis[(10',20'-di[4-(3-methoxy-3-methylbutoxy)phenyl]porphinato)zinc(II)]ethyne)indane (2). Compounds 1 and 2 feature a covalently bridged cofacial bis(porphinato)metal core; ethyne bridging moieties conjugate directly one and two respective peripheral (porphinato)zinc(II) substituents to the macrocyclic framework of their corresponding face-to-face porphyrin units. Optical spectroscopy and electrochemical studies demonstrate substantive electronic interactions between the porphyrin subunits of these compounds. Notably, structural and (1)H NMR analyses verify that 1 and 2 possess open conformations necessary for binding small molecules within their respective cofacial (porphinato)metal cores.

Syntheses, structural studies, electrochemistry, and spectroscopy of a number of [5,10,15,20-tetrakis-(heptafluoropropyl)porphinato]iron derivatives are presented. The X-ray crystal structure of 5,10,15,20-tetrakis-(heptafluoropropyl)porphinato]iron(II)‚(pyridine) 2 exhibits a substantial S 4 distortion of the porphyrin macrocycle, with the meso-carbon atoms displaced more than 0.6 Å above and below the porphyrin mean plane defined by the four central nitrogen atoms; the most notable aspect of this ferrous porphyrin structure is the fact that it exhibits metrical features commonly manifested in crystallographically characterized ferric porphyrin complexes. X-ray data are as follows: P2 1 /n with a ) 12.772(1) Å, b ) 18.895(2) Å, c ) 19.756(2) Å, β ) 99.960(6)°, V ) 4695.7(8) Å 3 , Z ) 4, and d calc ) 1.689 g/cm 3 . 19 F NMR spectroscopy confirms the sensitivity of the 19 F nucleus as a probe of macrocycle aromaticity and electronic structure, while 1 H NMR spectroscopic studies show large isotropic shifts for the β-protons of the (porphinato)iron(III) chloride derivative (δ ) 101.5 and 86.4 ppm). Electrochemical data obtained from cyclic voltammetric and spectroelectrochemical experiments reveal that the E 1/2 value for the Fe II/III redox couple for 5,10,15,20-tetrakis(heptafluoropropyl)porphinato]-iron‚(pyridine) 2 is shifted by 550 mV relative to that observed for the corresponding (porphinato)iron(III) chloride complex. The cathodic electrochemistry of [5,10,15,20-tetrakis(heptafuoropropyl)porphinato]iron‚ (pyridine) 2 is also unusual in that the first one-electron reduction of this complex produces a largely macrocyclelocalized radical anion. EPR spectroscopic data shows that 5,10,15,20-tetrakis(heptafluoropropyl)porphinato]iron(III)‚(pyridine) 2 manifests a pure axial spectrum (∆/λ ) -26.4; Σg 2 ) 12.53) congruent with a (d xz ,d yz ) 4 (d xy ) 1 electronic ground state. The extraordinary structural, potentiometric, and spectroscopic properties of these (porphinato)iron species arise from substantially reduced metal-centered electron density effected by the macrocycle's non-π-conjugating, σ-electron-withdrawing meso-perfluoroalkyl substituents.

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The synthesis, electrochemistry, and optical spectroscopy of an extensive series of cofacial bis[(porphinato)zinc(II)] compounds are reported. These species were synthesized using sequential palladium-catalyzed cross-coupling and cobalt-mediated [2+2+2] cycloaddition reactions. This modular methodology enables facile control of the nature of macrocycle-to-macrocycle connectivity and allows unprecedented modulation of the redox properties of face-to-face porphyrin species. We report the synthesis of 5,6-bis[(5',5''-10',20'-bis[4-(3-methoxy-3-methylbutoxy)phenyl]porphinato)zinc(II)]indane (1), 5,6-bis[(2'-5',10',15',20'-tetraphenylporphinato)zinc(II)]indane (2), 5-([2'-5',10',15',20'-tetraphenylporphinato]zinc(II))-6-[(5"-10'',20''-bis[4-(3-methoxy-3-methylbutoxy)phenyl]porphinato)zinc(II)]indane (3), 5-([2'-5',10',15',20'-tetrakis(trifluoromethyl)porphinato]zinc(II))-6-[(5' '-10' ',20' '-bis[4-(3-methoxy-3-methylbutoxy)phenyl]porphinato)zinc(II)]indane (4), 5-(2'-5',10',15',20'-[tetrakis(trifluoromethyl)porphinato]zinc(II))-6-[(2''-5'',10'',15'',20''-tetraphenylporphinato)zinc(II)]indane (5), 5,6-bis([2'-5',15'-diphenyl-10',20'-(trifluoromethyl)porphinato]zinc(II))indane (6), and 5,6-bis([2'-5',10',15',20'-tetrakis(trifluoromethyl)porphinato]zinc(II))indane (7); 4-7 define the first examples of cofacial bis[(porphinato)metal] compounds in which sigma-electron-withdrawing perfluoroalkyl groups serve as macrocycle substituents, while 2, 6, and 7 constitute the first such structures that possess a beta-to-beta linkage topology. Cyclic voltammetric studies show that the electrochemically determined HOMO and LUMO energy levels of these cofacial bis(porphinato) complexes can be lowered by 780 and 945 mV, respectively, relative to the archetypal members of this class of compounds; importantly, these orbital energy levels can be modulated over well-defined increments throughout these wide potentiometric domains. Analyses of these cofacial bis[(porphinato)metal] potentiometric data, in terms of the absolute and relative frontier orbital energies of their constituent [porphinato]zinc(II) building blocks, as well as the nature of macrocycle-to-macrocycle connectivity, provide predictive electronic structural models that rationalize the redox behavior of these species.