Synthesis, characterization, and reactivity of urea derivatives coordinated to cobalt(III). Possible relevance to urease

The syntheses of a cobalt(III) complex, 2, containing N-(2-pyridylmethyl)ur ea and of six complexes, 3, containing phenyl-substituted N-2-pyridylmethyl -N'- (X)phenylureas (where X = 4-H, 4-CH3, 4-Br, 3-Cl, 4-CF3, and 4-NO2), h ave been accomplished by reaction of [(en)(2)Co(OSO2CF3)(2)](CF3SO3) with t he urea ligands in tetramethylene sulfone. The complexes have been characte rized by UV-vis, FTIR, H-1 NMR, and C-13 NMR spectra along with elemental a nalysis. Also, X-ray crystallographic analysis of 2 confirms that the urea ligand chelates as a bidentate through the pyridyl nitrogen atom and the en do deprotonated, urea nitrogen atom to form a stable five-membered ring. Cr ystals of the perchlorate salt of 2 were monoclinic, space group P2(1)/c wi th a = 9.743(1) Angstrom, b = 13.924(3) Angstrom, c = 15.006(4) Angstrom, b eta = 97.07(1)degrees, and Z = 4. Reflection data (3454) with I = 3 sigma(I ) were refined to conventional R factors of 0.037 and 0.051. In acidic solu tion (0.05-1.00 M HCl at 55 degrees C), the phenyl substituted complexes un dergo hydrolysis to form the bis(ethylenediamine)(2-picolylamine-N,N')cobal t(III) ion, 4, aniline, and CO2. The hydrolysis kinetics of the phenyl-subs tituted complexes were studied by UV-vis spectroscopy (I = 1.00 M HCl/LiCl) . At 55 degrees C the observed rare constants fit the rate law k(obsd) = kK [H+]/(1 + K[H+]). It is proposed that the protonated urea eliminates anilin e to give a coordinated isocyanate intermediate that hydrolyzes rapidly to the pyridyl methylamine complex and CO2 via the carbamate complex. Since al l of the studies of this kind to date appear to involve the NCO intermediat e, it raises the prospect that urease also functions by a similar path and that urease should be tested with NCO- as a substrate.