Mixed Boron(III) and Phosphorous(V) Complexes of meso-Triaryl 25-Oxasmaragdyrins.

Two unprecedented mixed B(III) /P(V) complexes of meso-triaryl 25-oxasmaragdyrins were synthesized in appreciable yields under mild reaction conditions. These unusual 25-oxasmaragdyrin complexes containing one or two seven-membered heterocyclic rings comprised of five different atoms (B, C, N, O, and P) were prepared by reacting B(OH)(Ph)-smaragdyrin and B(OH)2 -smaragdyrin complexes, respectively, with POCl3 in toluene at reflux temperature. The products were characterized by HRMS and 1D- and 2D-NMR spectroscopy. X-ray crystallography of one of the mixed B(III) /P(V) smaragdyrin complexes indicated that the macrocycle is significantly distorted and contains a stable seven-membered heterocyclic ring within the macrocycle. The bands in the absorption and emission spectra were bathochromically shifted with reduced quantum yields and singlet-state lifetimes relative to the free base, meso-triaryl 25-oxasmaragdyrin. The mixed B(III) /P(V) complexes were difficult to oxidize but easier to reduce than the free base. The DFT-optimized structure of the 25-oxasmaragdyrin complex with two seven-membered heterocycles indicated that it was a bicyclic spiro compound with two half-chair-like conformers. This was in contrast to the chair-like conformation of the complex with a single seven-membered heterocyclic ring. Moreover, incorporation of a second phosphate group in the former case stabilized the bonding geometry and resulted in higher stability, which was reflected in the bathochromic shift of the absorption spectra, more-positive oxidation potential, and less-negative reduction potential.

Synthesis, structure, and spectral, electrochemical and fluoride sensing properties of meso-pyrrolyl boron dipyrromethene.

meso-Pyrrolyl boron dipyrromethene (BODIPY) was prepared under simple reaction conditions by using commercially available chemicals. Prior to this work, the BODIPY compound was prepared in multiple steps by using precursors which were not readily available. The X-ray structure of BODIPY revealed that the meso-pyrrole ring is tilted towards the BF2-dipyrrin moiety with a dihedral angle of 33.94°. The reactivity of the meso-pyrrole ring of BODIPY was tested by subjecting it to bromination and formylation reactions, which afforded (α-bromopyrrolyl) BODIPY and (α-formylpyrrolyl) BODIPY in decent yields. The (α-formylpyrrolyl) BODIPY was used to prepare the pyrrole bridged BODIPY dyad. The pyrrole bridged BODIPY dyad exhibited a 15-20 nm bathochromic shift in the absorption band and was weakly fluorescent compared to meso-pyrrolyl BODIPY. Furthermore, our studies show that the meso-pyrrolyl BODIPY can be used as a specific sensor for F(-) ions because of the presence of meso-pyrrole NH which is involved in interactions with F(-) ions. To prove that meso-pyrrole NH is involved in sensing F(-) ions, we also prepared meso-(N-methylpyrrolyl)-BODIPY and characterized it by various spectroscopic techniques and crystallography. Our studies reveal that meso-(N-methylpyrrolyl)-BODIPY does not sense F(-) ions, supporting the involvement of meso-pyrrole NH in sensing F(-) ions.

Synthesis and specific fluoride binding properties of expanded dithiacalixphyrins.

Expanded dithiacalixphyrins with the N(2)S(2) core containing two sp(3) and three sp(2) meso-carbons have been prepared by condensation of one equivalent of butene-2,3-diyl-bisthiophene-2,5-diyl-bis(p-methoxyphenylmethanol) with one equivalent of 5,5'-dialkyldipyrromethane under mild acid catalyzed conditions in decent yields. The expanded dithiacalixphyrins were characterized by HR-MS, 1D and 2D NMR techniques and the structure of one of the expanded dithiacalixphyrin macrocycles was solved by X-ray crystallography. The crystal structure analysis indicated that the macrocycle is highly distorted and attains a boat shaped structure. The expanded thiacalixphyrins showed a specific sensing ability for F(-) ions over other anions as judged from absorption, NMR and mass spectral studies.

Stable nonaromatic [20]dithiaporphyrin (2.1.1.1) macrocycles: synthesis, structure, spectral, electrochemical, and metal ion sensing studies.

Stable nonaromatic [20]dithiaporphyrin (2.1.1.1) macrocycles were synthesized in decent yields by condensing readily available butene-2,3-diyl-bisthiophene-2,5-diyl-bis(p-methoxyphenylmethanol) with different meso-aryl dipyrromethanes under mild acid-catalyzed conditions. The [20]dithiaporphyrin (2.1.1.1) macrocycles are the first members of the expanded porphyrin analogues of [18]dithiaporphyrin (1.1.1.1) and consist of two pyrroles and two thiophenes connected through five meso-carbon bridges. The [20]dithiaporphyrin macrocycles were confirmed by mass spectroscopy, 1D and 2D NMR spectroscopy, and X-ray crystallography. The X-ray structure revealed that the macrocycle is highly distorted and that the two thiophene rings are completely out-of-plane from the "mean-plane" defined by the dipyrromethene moiety and the two meso-carbons. In the absorption spectrum, the macrocycles showed one strong band at ∼420 nm and one weak band at ∼720 nm. The electrochemical studies revealed that the macrocycles are stable under redox conditions. The metal sensing studies indicated that these macrocycles have the potential to sense specific metal ions such as Hg(2+) ions. Two covalently linked dithiahomoporphyrin-fluorophore dyads were synthesized by coupling iodo-functionalized dithiahomoporphyrin with an ethynyl-functionalized fluorophore such as boron-dipyrromethene (BODIPY) and BF2-smaragdyrin under mild Pd(0) coupling conditions. The potential of these dyads as a fluorescent sensor for Hg(2+) was explored, and the studies indicated that both dyads can be used as fluorescent sensors.