Interaction of Rh(I) with meso-arylsapphyrins and -rubyrins: first structural characterization of bimetallic hetero-rubyrin complex

The ligational behavior of meso-arylsapphyrins and rubyrins toward Rh(I) is investigated. Sapphyrins form monometallic complexes with coordination of one imine and amine type nitrogens of the bipyrrole unit in an η2 fashion. The Rh(I) coordination is completed by the presence of two ancillary carbon monoxide ligands. Rubyrins form both monometallic and bimetallic complexes. Two types of bimetallic complexes have been isolated. In the first type, both rhodium atoms are projected above the mean rubyrin plane, while in the second type, one rhodium atom is projected above and the other below the mean plane. Detailed 1H and 2D NMR spectral analyses along with IR and UV-visible spectra of the complexes confirm the proposed binding modes for the rhodium complexes. Furthermore, the single-crystal X-ray analysis of one of the bimetallic complexes of rubyrin shows a bowl-shaped symmetric structure where both Rh(I) atoms are projected above the mean rubyrin plane at an angle of 71.73°. The geometry around each rhodium center is approximately square planar [N1-Rh1-N2, 80.38(9)°; C15-Rh1-C16, 86.95(14)°; N1-Rh1-C15, 97.13(12)°; and N2-RH1-C16, 94.97(12)°]. The observed distance of 4.313 Å between the two rhodium centers reveals very little interaction between the two rhodium atoms. This type of metal binding is accompanied by a 180° ring flip of the heterocyclic ring connecting the two bipyrrole units. In dioxarubyrin, where one of the pyrrole rings of the bipyrrole unit is inverted, Rh(I) binds at the periphery to the pyrrole nitrogen, leaving the rubyrin cavity empty. The absence of one amino and one imino nitrogen on the dipyrromethene subunits in the sapphyrins and rubyrins described here forces Rh(I) to bind to bipyrrole nitrogens

Meso-aryl smaragdyrins: novel anion and metal receptors

An easy synthesis of core-modified meso-aryl smaragdyrins containing oxygen and sulfur in addition to pyrrole nitrogens has been achieved through an α-α coupling involving modified tripyrrane and dipyrromethane. The complexation behavior of these macrocycles toward anions (Cl-, F-, AMP-) and metal cations (Rh(I), Ni(II)) is reported. Specifically, it has been shown that the Rh(I) and Ni(II) ions bind to the smaragdyrin skeleton in its free base form. X-ray structural studies of Rh(I) complex 1 indicate an η2-type coordination involving only one imino and one amino nitrogen of the dipyrromethane unit. However, all four bipyrrole nitrogens participate in the coordination with the Ni(II) ion. Furthermore, Ni(II) coordination oxidizes the ligand, and the complex is formulated as the π-cation radical of nickel(II) smaragdyrin. The anion complexation is followed in both the solid and solution phases. Solution studies reveal that the binding constants of the ions with the protonated form of smaragdyrin vary as F- > AMP- > Cl-. The X-ray structure of the chloride anion complex reveals that the chloride ion is bound above the cavity of the smaragdyrin macrocycle through three N-HCl hydrogen bonds. Crystal data with Mo Kα (λ = 0.710 73 Å) are as follows: 1, C41H27N4O3Rh, a = 11.836(8) Å, b = 12.495(9) Å, c = 12.670(2) Å, α = 69.09(6)°, β = 78.78(6)°, γ = 77.02(5)°, V = 1692.1(17) Å3, Z = 2, triclinic, space group P-1, R1(all data) = 0.0471; 4HCl, C41H29N4O1Cl, a = 11.878(2) Å, b = 17.379(4) Å, c = 16.015(3)Å, β = 109.546(10)°, V = 3115.47(11) Å3, Z = 4, monoclinic, space group P2(1)/c, R1(all data) = 0.0850

<i>Meso</i>-mesityl dithia- and diselenarubyrins: existence of planar and inverted forms in solution

Syntheses, characterization and spectroscopic studies of meso-mesityl substituted rubyrins are reported. Specifically, it has been shown that these rubyrins behave differently from the meso-phenyl containing rubyrins in their structure. 1 H NMR studies reveal the existence of both planar and inverted isomers in solution in different ratios both in the freebase and protonated forms. </jats:p

DALTON Spectral, magnetic and electrochemical properties of metal oxa-and oxathia-porphyrins †

Metal derivatives (Cu II , Ni II ) of monooxa-, dioxa-and oxathia-tetraphenylporphyrins and their one-electron oxidised and reduced species have been studied. Electronic spectra of the monooxa and oxathia derivatives exhibit split Soret bands and a complicated pattern of Q-bands revealing their lower symmetry. The spectra of one-electron reduced species show only marginal shifts while the one-electron oxidised product of copper monooxaporphyrins show broad, red-shifted bands. Cyclic voltammetric studies indicated one-electron metalcentered reduction at fairly low potentials forming copper() and nickel() porphyrins. The ring-oxidised product exhibits weak antiferromagnetic interaction between the unpaired electrons of copper and the porphyrin ring. The ESR spectra of the copper dioxa-and oxathia-porphyrins exhibit rhombic symmetry with unusually small metal hyperfine couplings. A comparison of A Cu values and the E ₂ ₁ values for metal reduction suggests that distortion towards tetrahedral symmetry and the presence of a soft donor atom like sulfur in porphyrins are required to generate spectral and electrochemical properties like those observed for the type I copper center in proteins. Replacement of pyrrole N atoms in the porphyrin core by other heteroatoms such as S, Se, Te and O alters the core sizes and electronic structure. The crystal structure of nickel() thiaporphyrin revealed a distorted square pyramid around the metal with an axial chloride ligand, leading to five-co-ordination. 7, 11 However, relatively few reports 2 exist on the synthesis of oxaporphyrins and mixed oxathiaporphyrins in which one or more pyrrole rings have been replaced by furan rings and/or thiophene rings. To the best of our knowledge there are only two recent reports on the metal (Ni II ) binding properties of oxaporphyrins by Latos-Grazynski and co-workers 12 and Gross et al. 14 Further, our recent study 15 on free base oxa- † Non-SI units employed: G = 10 Ϫ4 T, µ B ≈ 9.27 × 10 Ϫ24 J T Ϫ1 . and oxathia-porphyrins revealed that the oxaporphyrins behave more like the parent tetraphenylporphyrin in their spectroscopic properties while their electrochemical properties resemble those of thiaporphyrins. In this paper we report the metal binding (Cu II and Ni II ) properties of monooxa-, dioxa-and oxathia-porphyrins and their one-electron reduced and oxidised species. Specifically, electronic absorption spectra have been used to study groundstate properties while the redox chemistry has been monitored by cyclic voltammetry. The changes occurring in the electron delocalisation pathway and the metal-ligand bond strength upon binding of Cu II have been studied by ESR spectroscopy. It has been shown that the first reduction is metal centered, corresponding to the formation of complexes of Cu I and Ni I , while the first oxidation of copper monoxaporphyrins is ring based with a weak antiferromagnetic coupling between the metal and the ring unpaired electrons. Results The metallation of oxaporphyrins can readily be done using literature methods. 12 The copper() and nickel() derivatives of monooxa and monothia derivatives are stable both in the solid and solution states, the dioxa derivative on a chromatographic column undergoing gradual demetallation while the oxathia derivative on standing for few hours in the solid decomposes to give the corresponding free base porphyrin. The electronic absorption spectra of various neutral, one-electron-reduced and -oxidised copper oxaporphyrins are shown in 14 The ε values are significantly reduced for the core-modified porphyrins relative to the parent [M(tpp)]. 16 The EPR spectra of the copper porphyrins described here were recorded in toluene-CH 2 Cl 2 (1 : 1) at room and liquid nitrogen temperature