Electrophilic terminal phosphinidene complex-Lewis base adducts: chemistry between carbon-halide bond activation and weak Lewis base adduct formation.

Comparative studies on the reactivity of a transiently formed terminal phosphinidene complex towards various organobromide derivatives show that carbon-bromine bond insertion is preferred with benzyl bromide, whereas formal HBr-insertion resulted with 2-bromopyridine and a surprising selectivity enhancement (of the phosphinidene complex) was observed with bromobenzene; all new products were established by elemental analyses, NMR spectroscopy, mass spectrometry and single crystal X-ray diffraction studies.

Synthesis of the first 1,2,3,4-azatriphospholene complex.

Synthesis of the first 1,2,3,4-azatriphospholene complex was achieved by heating a solution of a P-phenyl-substituted 7-phosphanorbornadiene tungsten complex and triphenylphosphonio cyanomethylide, whereby CH-insertion products were formed in a competing reaction; these results also provide first evidence for the ability of electrophilic terminal phosphanediyl complexes to react at the ylide carbon atom and at the carbonitrile nitrogen atom of Wittig-ylides having a nitrile functional group; the structures of both complexes were established through X-ray single-crystal diffraction studies.

Biomimetic studies on iodothyronine deiodinase intermediates: modeling the reduction of selenenyl iodide by thiols.

Enzyme mimetic studies on the crucial intermediate (E-SeI) of the iodothyronine deiodinase cycle have been carried out by using an areneselenenyl iodide stabilized by intramolecular Se.N interactions. Treatment of this compound with aromatic thiols and thiobenzoxazole in the presence of NEt(3) affords areneselenenyl sulfides that are stable towards disproportionation reactions. The structures of three of the areneselenenyl sulfides were determined by X-ray crystallography. In one case, in the absence of NEt(3), a diselenide can be formed rather than the selenenyl sulfide. The areneselenenyl iodide also reacts with a related selenol to produce the corresponding diselenide, and this reaction is found to be much faster than that with thiols. The high reactivity of the selenenyl iodide with the selenol suggests that a reduced selenol group (R'-SeH) may react with the E-SeI intermediate to produce a diselenide (E-Se-Se-R') without any thiol cosubstrate. The intermediacy of selenenyl sulfides during the reduction of selenenyl iodide by thiols and its possible relevance to the iodothyronine deiodinase catalytic cycle is also described.

Reactions of Organoselenenyl Iodides with Thiouracil Drugs: An Enzyme Mimetic Study on the Inhibition of Iodothyronine Deiodinase.

The proposed mechanism of iodothyronine deiodinase inhibition by the thiourea-derived drugs 6-n-propylthiouracil (PTU) and 6-methylthiouracil is supported by experimental evidence. Model reactions with sterically or coordinatively stabilized organoselenyl iodides as enzyme-mimetic substrates (E-SeI; see scheme) support the proposal that PTU reacts not with the enzyme but with the enzyme-SeI intermediate containing a covalent Se-I bond, and suggest that the Se-I bond is kinetically activated by basic amino acid groups such as histidine.