Unravelling the Molecular Origin of the Regiospecificity in Extradiol Catechol Dioxygenases.

Many factors have been suggested to control the selectivity for extradiol or intradiol cleavage in catechol dioxygenases. The varied selectivity of model complexes and the ability to force an extradiol enzyme to do intradiol cleavage indicate that the problem may be complex. In this paper we focus on the regiospecificity of the proximal extradiol dioxygenase, homoprotocatechuate 2,3-dioxygenase (HPCD), for which considerable advances have been made in our understanding of the mechanism from an experimental and computational standpoint.

Reversible C-C bond formation between redox-active pyridine ligands in iron complexes.

This manuscript describes the formally iron(I) complexes L(Me)Fe(Py-R)(2) (L(Me) = bulky β-diketiminate; R = H, 4-tBu), in which the basal pyridine ligands preferentially accept significant unpaired spin density. Structural, spectroscopic, and computational studies on the complex with 4-tert-butylpyridine ((tBu)py) indicate that the S = 3/2 species is a resonance hybrid between descriptions as (a) high-spin iron(II) with antiferromagnetic coupling to a pyridine anion radical and (b) high-spin iron(I). When the pyridine lacks the protection of the tert-butyl group, it rapidly and reversibly undergoes radical coupling reactions that form new C-C bonds.

Achieving C-N bond cleavage in dinuclear metal cyanide complexes.

Cleavage of cyanide is more difficult to achieve compared to dinitrogen and carbon monoxide, even though these species contain triple bonds of greater strength. In this work, we have used computational methods to investigate thermodynamic and mechanistic aspects of the C-N bond cleavage process in [L(3)M-CN-M'L(3)] systems consisting of a central cyanide unit bound in an end-on fashion to two terminal metal tris-amide complexes. In these systems, [M] is a d(3) transition metal from the 3d, 4d, 5d, or 6d series and groups 4 through 7, and [L] is either [NH(2)], [NMe(2)], [N(i)PrPh], or [N(t)BuAr].

Mechanistic study of amine to imine oxidation in a dinuclear Cu(II) complex containing an octaaza dinucleating ligand.

Density functional theory (DFT) calculations have been carried out to elucidate the mechanism of self-oxidation of a Cu(II) complex octaaza dinucleating macrocyclic ligand. The reaction is bimolecular and spontaneous, in which amine groups of one macrocycle are oxidized and the Cu(II) centers of a second macrocylic complex are reduced. No additional oxidation or external base agents are required.

Dinitrogen activation by Fryzuk's [Nb(P(2)N(2))] complex and comparison with the Laplaza-Cummins [Mo{N(R)Ar}(3)] and Schrock [Mo(N(3)N)] systems.

The reaction profile of N(2) with Fryzuk's [Nb(P(2)N(2))] (P(2)N(2)=PhP(CH(2)SiMe(2)NSiMe(2)CH(2))(2)PPh) complex is explored by density functional calculations on the model [Nb(PH(3))(2)(NH(2))(2)] system. The effects of ligand constraints, coordination number, metal and ligand donor atom on the reaction energetics are examined and compared to the analogous reactions of N(2) with the three-coordinate Laplaza-Cummins [Mo{N(R)Ar}(3)] and four-coordinate Schrock [Mo(N(3)N)] (N(3)N=[(RNCH(2)CH(2))(3)N](3-)) systems. When the model system is constrained to reflect the geometry of the P(2)N(2) macrocycle, the N--N bond cleavage step, via a N(2)-bridged dimer intermediate, is calculated to be endothermic by 345 kJ mol(-1).

Oxidative dehydrogenation of an amine group of a macrocyclic ligand in the coordination sphere of a Cu(II) complex.

The spontaneous oxidation of an amine group to an imine has been observed experimentally in an octa-aza macrocyclic dinucleating ligand LH(4) coordinated to Cu(II). The reaction is bimolecular and spontaneous in which amine groups of one macrocycle are oxidised and the Cu(II) centres of a second macrocyclic complex are reduced. No additional oxidating or external base agents are required.

Optimizing small molecule activation and cleavage in three-coordinate M[N(R)Ar]3 complexes.

The sterically hindered, three-coordinate metal systems M[N(R)Ar]3 (R = tBu, iPr; Ar = 3,5-C6H3Me2) are known to bind and activate a number of fundamental diatomic molecules via a [Ar(R)N]3M-L-L-M[N(R)Ar]3 dimer intermediate. To predict which metals are most suitable for activating and cleaving small molecules such as N(2), NO, CO, and CN(-), the M-L bond energies in the L-M(NH2)3 (L = O, N, C) model complexes were calculated for a wide range of metals, oxidation states, and dn (n = 2-6) configurations. The strongest M-O, M-N, and M-C bonds occurred for the d2, d3, and d4 metals, respectively, and for these d(n) configurations, the M-C and M-O bonds were calculated to be stronger than the M-N bonds.