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A new bis(imino)pyridine compound, 2,6-{(2,6-Me2-C6H3)NC(t-Bu)}2C5H3N (6), has been synthesized with t-butyl substituents on the imino carbon atoms. The stepwise synthetic method for assembly of this compound is novel. Compound 6 and its synthetic precursor, mono(imino)pyridine 3, have been characterized using single-crystal X-ray diffraction. Metalation attempts of 6 using iron(II) chloride under forcing conditions does not yield the desired iron(II) chloride complex; the use of refluxing acetic acid solvent provides a minimal amount of a paramagnetic species that has been characterized by NMR spectroscopy and magnetic susceptibility (NMR method). Computational methods have been used to evaluate the relative energies of three conformations of bis(imino)pyridine ligands with varying alkyl substitution at the imino carbon positions. The relative energies of these closed, open and open-planar conformations of 6 reveal a thermodynamic argument for the difficulty in metalation of 6, as compared to related ligands with less steric hindrance at the imino carbon atoms. [ABSTRACT FROM AUTHOR]

Two new tetraphosphine ligands, PnC-ppb222Nph2 (1,5-diphenyl- 3,7-bis ( (diphenylphosphino )alkyl)-1,5- diaza-3,7-diphosphacyclooctane; alkyl = (CH2)2, n = 2 (L2); (CH2)3, n = 3 (L3)), have been synthesized. Coordination of these ligands to cobalt affords the complexes [Co11(L2)-(CH3CN)]2+ and [Co11(L3)(CH3CN)]2+, which are reduced by KC8 to afford [Co¹(L2)(CH3CN)]+ and [Co¹(L3)-(CH3CN)]+. Protonation of the Co¹ complexes affords [HCo111(L2)(CH3CN)]2+ and [HConi(L3)(CH3CN)]2+. The cyclic voltammetry of [HCo111(L2)(CH3CN)]2+, analyzed using digital simulation, is consistent with an ErCrEr reduction mechanism involving reversible acetonitrile dissociation from [HCo11(L2)(CH3CN)]+ and resulting in formation of HCo¹(L2). Reduction of HCo111 also results in cleavage of the H--Co bond from HCo11 or HCo¹, leading to formation of the Co¹ complex [Co¹(L2)(CH3CN)]+. Under voltammetric conditions, the reduced cobalt hydride reacts with a protic solvent impurity to generate H2 in a monometallic process involving two electrons per cobalt. In contrast, under bulk electrolysis conditions, H2 formation requires only one reducing equivalent per [HCO111(L2)(CH3CN)]2+, indicating a bimetallic route wherein two cobalt hydride complexes react to form 2 equiv of [CO¹(L2)(CH3CN)]+ and 1 equiv of H2. These results indicate that both HCo11 and HCo¹ can be formed under electrocatalytic conditions and should be considered as potential catalytic intermediates. [ABSTRACT FROM AUTHOR]

The aluminium complexes {[k[sup 2]-N,O-(t-BuNCOPh)]AlMe2}[sub 2] (2), [k[sup 2]-N,O-(t-BuNCOPh)][sub 2]AlMe (3), and [k[sup 2]-N,O-(t-BuNCOPh)][sub 3]Al (4) were prepared through the protonolysis reaction between trimethylaluminium and one, two, or three equivalents, respectively, of N-tert-butylbenzamide. Complex 2 was also prepared via a salt metathesis reaction between K(t-BuNCOPh) and dimethylaluminium chloride. Complexes 2-4 were characterized using [sup 1]H and [sup 13]C NMR spectro-scopy. Single-crystal X-ray diffraction analysis of the complexes corroborated ligand :metal stoichiometries and revealed that all the amidate ligands coordinate to the aluminium ion in a k[sup 2] fashion. The Al-amidate complexes 2-4 were viable catalyst precursors for the Meerwein-Ponndorf-Verley-Oppenauer reduction-oxidation manifold, successfully inter-converting several classes of carbonyl and alcohol substrates. [ABSTRACT FROM AUTHOR]

Highlights: [•] Two ligands form bi- and tri-nuclear complexes. [•] All complexes are alkoxide bridge compounds. [•] Cu complexes with Schiff base and its reduced form have different redox potentials. [•] The hydroxyl and phenol oxygens participate as anionic oxygens in complexation. [Copyright &y& Elsevier]

The addition of acids to ferrous dinitrogen complexes [FeX(N2)(PEtNMePEt)(dmpm)]+ (X = H, CI, or Br; pEtNMepEt _ Et2PCH2N(Me)CH2PEt2; and dmpm = Me2PCH2PMe2) gives protonation at the pendent amine of the diphosphine ligand rather than at the dinitrogen ligand. This protonation increased the vN2 band of the complex by 25 cm-1 and shifted the Fe(II/I) couple by 0.33 V to a more positive potential. A similar IR shift and a slighdy smaller shift of the Fe(H/l) couple (0.23 V) was observed for the related carbonyl complex [FeH(CO)(pEtNMepEt)(dmpm)]+. [FeH(PEtNMePEt)-(dmpm)]+ was found to bind N2 about three times more strongly than NH3. Computational analysis showed that coordination of 2 to Fe(ll) centers increases the basicity of N2 (vs free N2) by 13 and 20 pK3 units for the trans halides and hydrides, respectively. Although the iron center increases the basicity of the bound N2 ligand, the coordinated N2 is not sufficiently basic to be protonated. In the case of ferrous dinitrogen complexes containing a pendent methylamine, the amine site was determined to be the most basic site by 30 pK, units compared to the N2 ligand The chemical reduction of these ferrous dinitrogen complexes was performed in an attempt to increase the basicity of the N2 ligand enough to promote proton transfer from the pendent amine to the N2 ligand. Instead of isolating a reduced Fe(0)--N2 complex, the reduction resulted in isolation and characterization of HFe(Et2PC(H)N(Me)CH2PEt2)(PEt,NMePEt), the product'of oxidative addition of the methylene C-H bond of the PEtNMePEt ligand to Fe. [ABSTRACT FROM AUTHOR]