Synthesis, structure, and solution properties of [(mim-TASN)FeCl2]+ and its μ-oxo derivative

A series of iron(III) complexes based on the tetradentate ligand 4-((1-methyl-1H-imidazol-2-yl)methyl)-1-thia-4,7-diazacyclononane (L) has been synthesized, and their solution properties investigated. Addition of FeCl(3) to methanol solutions of L yields [LFeCl(2)]FeCl(4) as a dark red solid. X-ray crystallographic analysis reveals a pseudo-octahedral environment around iron(III) with the three nitrogen donors of L coordinated facially. Ion exchange reactions with NaPF(6) in methanol facilitate chloride exchange resulting in a different diastereomer for the [LFeCl(2)](+) cation. X-ray analysis of [LFeCl(2)]PF(6) finds meridional coordination of the three nitrogen donors of L. Electrochemical studies of [LFeCl(2)](+) in acetonitrile display a single Fe(III)/(II) reduction potential at -280 mV versus ferrocenium/ferrocene. In methanol, a broad cathodic wave is observed because of partial exchange of one chloride for methoxide with half-potentials of -170 mV and -440 mV for [LFeCl(2)](+/0) and [LFeCl(OCH(3))](+/0), respectively. The equilibrium constants for chloride exchange are 7 × 10(-4) M(-1) for Fe(III) and 2 × 10(-8) M(-1) for Fe(II). In aqueous solutions chloride exchange yields three accessible complexes as a function of pH. Strongly acidic conditions yield the aqua complex [LFeCl(OH(2))](2+) with a measured pK(a) of 3.8 ± 0.1. Under mildly acidic conditions, the μ-OH complex [(LFeCl)(2)(OH)](3+) with a pK(a) of 6.1 ± 0.3 is obtained. The μ-oxo complex [(LFeCl)(2)(O)](2+) is favored under basic conditions. The diiron Fe(III)/Fe(III) complexes [(LFeCl)(2)(OH)](3+) and [(LFeCl)(2)(O)](2+) can be reduced by one electron to the mixed valence Fe(III)/Fe(II) derivatives at -170 mV and -390 mV, respectively. From pH dependent voltammetric studies, the pK(a) of the mixed valent μ-OH complex [(LFeCl)(2)(OH)](2+) is calculated at 10.3.

Dibenzo[b,h][1,4,7]thiadiazonines: examples of a novel ring system

Acetanilides 1a-e react with 1,1'-sulfinylbis(benzotriazole)/trimethylchlorosilane at 45-65 degrees C to form 1,2-di(benzotriazol-1-yl)-2-arylimino-1-ethanethiones 3a-e, while heating the same reagents at 110 degrees C results in dibenzo[b,h][1,4,7]thiadiazonines 5a,c,d, and 6. X-ray crystal structures are reported for three representative examples.

Tridentate Ligand Effects on Enthalpies of Protonation of (L(3))M(CO)(3) Complexes (M = W, Mo)

Titration calorimetry has been used to determine the enthalpies of protonation (DeltaH(HM)) for the reaction of (L(3))M(CO)(3) complexes, where M = W and Mo and L(3) = cyclic and noncyclic tridentate ligands of the N, S, and P donor atoms, with CF(3)SO(3)H in 1,2-dichloroethane solution at 25 degrees C to give (L(3))M(CO)(3)(H)(+)CF(3)SO(3)(-). The basicities (-DeltaH(HM)) increase with the ligand donor groups (X, Y, or Z) in the order S </= PPh << NR (R = Me, Et) for both cyclic and noncyclic ligand complexes that have the same structure of the protonated product. Although the metal basicity (-DeltaH(HM)) generally increases as the ligand donor group basicities (pK(a)'s of the conjugate acids) increase, the large difference between the pK(a) values of thioethers (-6.8) and phosphines (6.25) suggests that thioether donor groups should be much weaker donors than phosphines. The observation that thioether groups contribute nearly as much as phosphine groups to the basicity of the metal in the (L(3))M(CO)(3) complexes may be explained by suggesting that repulsion between the pi-symmetry lone electron pair on sulfur and the filled metal d orbitals increases the energies of the d orbitals thereby making the metal more basic than expected from only the sigma-donor ability of the sulfur. There is a good correlation (r = 0.973) between -DeltaH(HM) and average nu(CO) values of the eight (L(3))W(CO)(3) complexes that have the same structure of their protonated forms. A plot of the average of the three nu(CO) frequencies for the (L(3))W(CO)(3) complexes vs the average nu(CO) frequencies for the analogous Mo complexes is linear (r = 0.9996), and the slope of 1.07 indicates that the tridentate ligands have nearly the same electronic effects on both W and Mo complexes. Noncyclic ligands make the metal more basic by 1.6 +/- 0.3 kcal/mol than cyclic ligands with the same donor atoms. The tungsten complexes are 2.8 +/- 0.1 kcal/mol more basic than their molybdenum analogs. Determinations of DeltaH(HM) values for both fac- and mer-(PNP)M(CO)(3) complexes (M = W, Mo; PNP = MeN(C(2)H(4)PPh(2))(2)) allowed the calculation of enthalpies of mer-to-fac isomerization for both the tungsten (-2.0 kcal/mol) and molybdenum (-4.8 kcal/mol) complexes. These studies demonstrate that the metal, ligands, and geometry of the protonated products all substantially affect the heats of protonation (DeltaH(HM)) of (L(3))M(CO)(3) complexes.