Oliver B. Locos

Near-infrared and mid-infrared spectroscopic study of sepiolites and palygorskites

Near-IR spectroscopy has been used to distinguish between palygorskites and sepiolites. Three near-IR spectral regions contain bands due to (a) the high frequency region between 6400 and 7400 cm−1 attributed to the first overtone of the hydroxyl stretching mode, (b) the 4800–5400 cm−1 region attributed to water combination modes and (c) the 4000–4800 cm−1 region attributed to the combination of the stretching and deformation modes of the M–MgOH units of palygorskites and sepiolites. Near-IR bands are observed in the first region and are assigned to the first overtone of the hydroxyl stretching frequency observed at 3620 and 3410 cm−1 in the mid-IR spectra. The near-IR bands observed in the second region are assigned to the combination of the water OH stretching and deformation vibrational modes. A complex set of low intensity bands are observed in the 4100–4600 cm−1 region and are attributed to the combination of the cation hydroxyl stretching, deformation and translation modes. The difference between the near-IR spectra of palygorskites and sepiolites depends on the dioctahedral nature of the palygorskites and the trioctahedral structure of the sepiolites. Changes in the near-IR spectra are therefore related to the Mg3(OH) and Mg2(OH) units in the palygorskites.

Infrared spectroscopic study of potassium and cesium acetate-intercalated kaolinites

Near-IR spectroscopy has been used to elucidate the structure of potassium and cesium acetate-intercalated kaolinites. Three near-IR spectral regions are identified: (a) the high frequency region between 6400 and 7400 cm−1 attributed to the first overtone of the hydroxyl stretching mode, (b) the 4800–5400 cm−1 region attributed to water combination modes and (c) the 4000–4800 cm−1 region attributed to the combination of the stretching and deformation modes of the AlOH units of kaolinite. The technique of near-IR spectroscopy for the study of intercalated kaolinites shows great potential for the understanding of the interactions between the surface hydroxyls of kaolinite and the inserting potassium and acetate ions. In particular, whereas the overlap of the hydroxyl stretching frequencies of water and the kaolinite overlap in the mid-IR, such overlap does not occur in the near-IR. In the first overtone region, a single sharp band is observed at 7045 cm−1 which is assigned to the combination of the hydroxyl stretching frequencies of the inner surface hydroxyls and water. Such an observation supports the concept of an interaction between the water and the inner surface hydroxyls of the intercalated kaolinite. It is suggested that the bonding of the acetate to the kaolinite hydroxyls is through the water molecule.

meso-iodo- and meso-iodovinylporphyrins via organopalladium porphyrins and the crystal structure of 5-iodo-10,20-diphenylporphyrin

The regiospecific halogen exchange reactions of various easily accessible meso-bromoporphyrins to obtain meso-iodoporphyrins, using η1-palladioporphyrins as intermediates, have been investigated. This one-pot methodology allows the isolation of meso-iodoporphyrins in excellent yields with short reaction times. Similarly meso-(2-bromoethenyl)porphyrins can be converted to their iodoethenyl analogues. These iodoporphyrins show great potential as starting materials for various palladium catalyzed reactions. The X-ray crystal structure of 5-iodo-10,20-diphenylporphyrin has been determined.

Homo‐ and Heteronuclear meso,meso‐(E)‐Ethene‐1,2‐diyl‐Linked Diporphyrins: Preparation, X‐ray Crystal Structure, Electronic Absorption and Emission Spectra and Density Functional Theory Calculations

Homo- and heteronuclear meso,meso-(E)-ethene-1,2-diyl-linked diporphyrins have been prepared by the Suzuki coupling of porphyrinylboronates and iodovinylporphyrins. Combinations comprising 5,10,15-triphenylporphyrin (TriPP) on both ends of the ethene-1,2-diyl bridge M(2)10 (M(2) =H(2)/Ni, Ni(2), Ni/Zn, H(4), H(2)Zn, Zn(2)) and 5,15-bis(3,5-di-tert-butylphenyl)porphyrinato-nickel(II) on one end and H(2), Ni, and ZnTriPP on the other (M(2)11), enable the first studies of this class of compounds possessing intrinsic polarity. The compounds were characterized by electronic absorption and steady state emission spectra, (1)H NMR spectra, and for the Ni(2) bis(TriPP) complex Ni(2)10, single crystal X-ray structure determination. The crystal structure shows ruffled distortions of the porphyrin rings, typical of Ni(II) porphyrins, and the (E)-C(2)H(2) bridge makes a dihedral angle of 50° with the mean planes of the macrocycles. The result is a stepped parallel arrangement of the porphyrin rings. The dihedral angles in the solid state reflect the interplay of steric and electronic effects of the bridge on interporphyrin communication. The emission spectra in particular, suggest energy transfer across the bridge is fast in conformations in which the bridge is nearly coplanar with the rings. Comparisons of the fluorescence behaviour of H(4)10 and H(2)Ni10 show strong quenching of the free base fluorescence when the complex is excited at the lower energy component of the Soret band, a feature associated in the literature with more planar conformations. TDDFT calculations on the gas-phase optimized geometry of Ni(2)10 reproduce the features of the experimental electronic absorption spectrum within 0.1 eV.

The Heck reaction for porphyrin functionalisation: synthesis of meso-alkenyl monoporphyrins and palladium-catalysed formation of unprecedented meso–β ethene-linked diporphyrins

Palladium-catalysed coupling of the vinyl derivatives methyl acrylate, styrene and acrylonitrile with 5-bromo-10,15,20-triphenylporphyrin (MTriPPBr; M = 2H, Ni, Zn) and 5,15-dibromo-10,20-bis(3,5-di-tert-butylphenyl)porphyrin (MDAPBr(2)) produced a series of mono- and disubstituted alkenylporphyrins, thus demonstrating the applicability of meso-haloporphyrins in Heck-type reactions. The same technique was also applied to meso-ethenylporphyrins and simple aryl halides, with mixed results. Only meso-vinyl nickel(ii) porphyrins showed any reactivity under our conditions. A mixture of 1,1- and 1,2-disubstitution across the alkene was observed for 5-vinyl-10,15,20-triphenylporphyrinatonickel(ii) (meso-vinylNiTriPP), whereas 5-vinyl-10,20-bis(3,5-di-t-butylphenyl)porphyrinatonickel(ii) (meso-vinylNiDAP) produced a mixture of meso-1,1-, meso-1,2- and, surprisingly, beta-1,2-disubstituted Heck products. Coupling meso-vinylNiDAP with MTriPPBr under similar Heck conditions led unexpectedly to transbeta-meso-NiDAP-ethene-MTriPP dyads, affording the first members of a new class of alkenyl-linked diporphyrins. A mechanism for the unusual meso to beta rearrangement is discussed. The electronic absorption spectra of the dyads have a red-shifted shoulder on the Soret (B) band, which is evidence of a moderate degree of electronic interaction between the porphyrins via the ethenyl bridge.