Theoretical exploration of 2,2'-bipyridines as electro-active compounds in flow batteries.

Compounds from the 2,2'-bipyridine molecular family were investigated for use as redox-active materials in organic flow batteries. For 156 2,2'-bipyridine derivatives reported in the academic literature, we calculated the redox potential, the pKa for the second deprotonation reaction, and the solubility in aqueous solutions. Using experimental data on a small subset of derivatives, we were able to calibrate our calculations. We find that functionalization with electron-withdrawing groups leads to an increase of the redox potential and to an increase of the molecular acidity (as expressed in a reduction of the pKa value for the second deprotonation step). Furthermore, calculations of solubility in water indicate that some of the studied derivatives have adequate solubility for flow battery applications. Based on an analysis of the phyisco-chemical properties of the 156 studied compounds, we down-select five molecules with carbonyl- and nitro-based functional groups, whose parameters are especially promising for potential applications as negative redox-active materials in organic flow batteries.

Reversible sigma C-C bond formation between phenanthroline ligands activated by (C5Me5)2Yb.

The electronic structure and associated magnetic properties of the 1,10-phenanthroline adducts of Cp*2Yb are dramatically different from those of the 2,2'-bipyridine adducts. The monomeric phenanthroline adducts are ground state triplets that are based upon trivalent Yb(III), f(13), and (phen(•-) ) that are only weakly exchange coupled, which is in contrast to the bipyridine adducts whose ground states are multiconfigurational, open-shell singlets in which ytterbium is intermediate valent ( J. Am. Chem. Soc 2009 , 131 , 6480 ; J. Am. Chem. Soc 2010 , 132 , 17537 ). The origin of these different physical properties is traced to the number and symmetry of the LUMO and LUMO+1 of the heterocyclic diimine ligands. The bipy(•-) has only one π*1 orbital of b1 symmetry of accessible energy, but phen(•-) has two π* orbitals of b1 and a2 symmetry that are energetically accessible. The carbon pπ-orbitals have different nodal properties and coefficients and their energies, and therefore their populations change depending on the position and number of methyl substitutions on the ring. A chemical ramification of the change in electronic structure is that Cp*2Yb(phen) is a dimer when crystallized from toluene solution, but a monomer when sublimed at 180-190 °C. When 3,8-Me2phenanthroline is used, the adduct Cp*2Yb(3,8-Me2phen) exists in the solution in a dimer-monomer equilibrium in which ΔG is near zero. The adducts with 3-Me, 4-Me, 5-Me, 3,8-Me2, and 5,6-Me2-phenanthroline are isolated and characterized by solid state X-ray crystallography, magnetic susceptibility and LIII-edge XANES spectroscopy as a function of temperature and variable-temperature (1)H NMR spectroscopy.

Unusual activation of H2 by reduced cobalt complexes supported by a PNP pincer ligand.

The reactivity of cobalt complexes supported by a PNP pincer ligand towards H2 varies depending on whether the N-donor atom is protonated; the synthesis of [(HPNP)CoCl(H)2] (2), [(PNP)CoH]2 (4), and the trihydride species [(HPNP)CoH3] (7) (HPNP = HN(CH2CH2P(i)Pr2)2) are described.

(2,2'-Bipyrid-yl-κ(2) N,N')bis-(η(5)-penta-methyl-cyclo-penta-dien-yl)barium.

In the title compound, [Ba(C10H15)2(C10H8N2)], the Ba-N distances are 2.798 (3) and 2.886 (3) Å, and the Cp ring centroid distances to Ba(2+) are 2.7291 (7) and 2.7192 (9) Å. The angle between the N atoms in the bypyridine ligand and the metal ion is 56.80 (8)° and the N-C-C-N torsion angle in the bi-pyridine ligand is 1.7 (4)°. The bi-pyridine ligand is almost planar, the dihedral angle formed by the intersection of the planes defined by the pyridyl rings being 3.04 (19)°, and the angle between the plane defined by the Ba(2+) ion and the two bipyridyl N atoms and the plane defined by the 12 atoms of the bi-pyridine ligand is 10.2 (3)°. The average Ba-N and Ba-centroid distances are 0.16 and 0.14 Šlonger, respectively, than the equivalent distances in the isotypic strontium compound [Kazhdan et al. (2008 ▶). Acta Cryst. E64, m1134]. This difference is in accord with the difference between the ionic radii of 0.16 Šsuggested by Shannon [Acta Cryst. (1976 ▶), A32, 751-767].

5,6-Dimeth-yl-1,10-phenanthroline.

In the title compound, C14H12N2, the N⋯N distance is 2.719 (1) Å. The N-C-C-N torsion angle [0.9 (1)°] is close to the ideal value of 0° as expected. Bond lengths and angles are consistent with those observed for [1,10]phenanthroline and coordinated 5,6 dimeth-yl[1,10]phenanthroline. In the crystal, C-H⋯N hydrogen bonds link the mol-ecules into C(4) chains running parallel to the b axis. Weak π-π inter-actions between benzene and pyridine rings [centroid-centroid distance = 3.5337 (7) Å] and between benzene rings [centroid-centroid distances = 3.6627 (7) and 3.8391 (7)Å] also occur.

Chemistry of reduced monomeric and dimeric cobalt complexes supported by a PNP pincer ligand.

The reduction chemistry of cobalt complexes with HPNP (HPNP = HN(CH2CH2P(i)Pr2)2) as a supporting ligand is described. Reaction of [(HPNP)CoCl2] (1) with n-BuLi generated both the deprotonated Co(II) species [(PNP)CoCl] (2) along with the Co(I) complex [(HPNP)CoCl] (3). Products resulting from reduction of 2 with KC8 vary depending upon the atmosphere under which the reduction is performed. Monomeric square planar [(PNP)CoN2] (4) is obtained under dinitrogen, whereas dimeric [(PNP)Co]2 (5) is formed under argon. Over time, 5 activates a C-H bond in the PNP ligand to form the species [Co(H)(µ-PNP)(µ-(i)Pr2PCH2CH2NCHCH2P(i)Pr2)Co] (6). We also observed the oxidative addition of H-Si bond to complex 3 to form [(HPNP)CoCl(H)SiH2Ph] (7). (1)H NMR studies showed that species 7 is in equilibrium with 3 and silane in solution. Complex 3 can be oxidized with AgBPh4 to generate {(HPNP)CoCl}BPh4 (8), a square planar species with a formal electron count of 15 electrons.

Bimetallic ruthenium PNP pincer complex as a platform to model proposed intermediates in dinitrogen reduction to ammonia.

A series of ruthenium complexes was isolated and characterized in the course of reactions aimed at studying the reduction of hydrazine to ammonia in bimetallic systems. The diruthenium complex {[HPNPRu(N(2))](2)(µ-Cl)(2)}(BF(4))(2) (2) (HPNP = HN(CH(2)CH(2)P(i)Pr(2))(2)) reacted with 1 equiv of hydrazine to generate [(HPNPRu)(2)(µ(2)-H(2)NNH(2))(µ-Cl)(2)](BF(4))(2) (3) and with an excess of the reagent to form [HPNPRu(NH(3))(κ(2)-N(2)H(4))](BF(4))Cl (5). When phenylhydrazine was added to 2, the diazene species [(HPNPRu)(2)(µ(2)-HNNPh)(µ-Cl)(2)](BF(4))(2) (4) was obtained. Treatment of 2 with H(2) or CO yielded {[HPNPRu(H(2))](2)(µ-Cl)(2)}(BF(4))(2) (7) and [HPNPRuCl(CO)(2)]BF(4) (8), respectively. Abstraction of chloride using AgOSO(2)CF(3) or AgBPh(4) afforded the species [(HPNPRu)(2)(µ(2)-OSO(2)CF(3))(µ-Cl)(2)]OSO(2)CF(3) (9) and [(HPNPRu)(2)(µ-Cl)(3)]BPh(4) (10), respectively. Complex 3 reacted with HCl/H(2)O or HCl/Et(2)O to produce ammonia stoichiometrically; the complex catalytically disproportionates hydrazine to generate ammonia.

Metal complexes of Co, Ni and Cu with the pincer ligand HN(CH2CH2P(i)Pr2)2: preparation, characterization and electrochemistry.

A series of Co, Ni and Cu complexes with the ligand HN(CH(2)CH(2)P(i)Pr(2))(2) (HNP(2)) has been isolated and their electrochemical behaviour investigated by cyclic voltammetry. The nickel complexes [(HNP(2))NiOTf]OTf and [(HNP(2))NiNCCH(3)](BF(4))(2) display reversible reductions, as does the related amide derivative (NP(2))NiBr. The related copper(I) and cobalt(II) derivatives were also isolated and characterized. The addition of piperidine to [(HNP(2))NiNCCH(3)](BF(4))(2) led to the formation of the new species [(HNP(2))Ni(N(H)C(CH(3))NC(5)H(10))](BF(4))(2). The nucleophilic addition of piperidine to acetonitrile to produce HN=C(CH(3))NC(5)H(10) was found to be catalyzed by [(HNP(2))NiNCCH(3)](BF(4))(2).

(2,2-Bipyrid-yl)bis-(η-penta-methyl-cyclo-penta-dien-yl)strontium(II).

In the title compound, [Sr(C(10)H(15))(2)(C(10)H(8)N(2))], the Sr-N distances are 2.624 (3) and 2.676 (3) Å, the Sr⋯Cp ring centroid distances are 2.571 and 2.561 Šand the N-C-C-N torsion angle in the bipyridine ligand is -2.2 (4)°. Inter-estingly, the bipyridine ligand is tilted. The angle between the plane defined by the Sr atom and the two bipyridyl N atoms and the plane defined by the 12 atoms of the bipyridine ligand is 10.7 (1)°.