Two new pentadentate {N5} donor ligands based on the N4Py (N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine) framework have been synthesized, viz. [N-(1-methyl-2-benzimidazolyl)methyl-N-(2-pyridyl)methyl-N-(bis-2-pyridyl methyl)amine] (L(1)) and [N-bis(1-methyl-2-benzimidazolyl)methyl-N-(bis-2-pyridylmethyl)amine] (L(2)), where one or two pyridyl arms of N4Py have been replaced by corresponding (N-methyl)benzimidazolyl-containing arms. The complexes [Fe(II)(CH3CN)(L)](2+) (L = L(1) (1); L(2) (2)) were synthesized, and reaction of these ferrous complexes with iodosylbenzene led to the formation of the ferryl complexes [Fe(IV)(O)(L)](2+) (L = L(1) (3); L(2) (4)), which were characterized by UV-vis spectroscopy, high resolution mass spectrometry, and Mössbauer spectroscopy. Complexes 3 and 4 are relatively stable with half-lives at room temperature of 40 h (L = L(1)) and 2.5 h (L = L(2)). The redox potentials of 1 and 2, as well as the visible spectra of 3 and 4, indicate that the ligand field weakens as ligand pyridyl substituents are progressively substituted by (N-methyl)benzimidazolyl moieties. The reactivities of 3 and 4 in hydrogen-atom transfer (HAT) and oxygen-atom transfer (OAT) reactions show that both complexes exhibit enhanced reactivities when compared to the analogous N4Py complex ([Fe(IV)(O)(N4Py)](2+)), and that the normalized HAT rates increase by approximately 1 order of magnitude for each replacement of a pyridyl moiety; i.e., [Fe(IV)(O)(L(2))](2+) exhibits the highest rates. The second-order HAT rate constants can be directly related to the substrate C-H bond dissociation energies. Computational modeling of the HAT reactions indicates that the reaction proceeds via a high spin transition state.

Reactions of Fe2(CO)6(μ-pdt) (pdt = SCH2CH2CH2S) with aminodiphosphines Ph2PN(R)PPh2 (R = allyl, (i)Pr, (i)Bu, p-tolyl, H) have been carried out under different conditions. At room temperature in MeCN with added Me3NO·2H2O, dibasal chelate complexes Fe2(CO)4{κ(2)-Ph2PN(R)PPh2}(μ-pdt) are formed, while in refluxing toluene bridge isomers Fe2(CO)4{μ-Ph2PN(R)PPh2}(μ-pdt) are the major products. Separate studies have shown that chelate complexes convert to the bridge isomers at higher temperatures. Two pairs of bridge and chelate isomers (R = allyl, (i)Pr) have been crystallographically characterised together with Fe2(CO)4{μ-Ph2PN(H)PPh2}(μ-pdt). Chelate complexes adopt the dibasal diphosphine arrangement in the solid state and exhibit very small P-Fe-P bite-angles, while the bridge complexes adopt the expected cisoid dibasal geometry. Density functional calculations have been carried out on the chelate and bridge isomers of the model compound Fe2(CO)4{Ph2PN(Me)PPh2}(μ-pdt) and reveal that the bridge isomer is thermodynamically favourable relative to the chelate isomers that are isoenergetic. The HOMO in each of the three isomers exhibits significant metal-metal bonding character, supporting a site-specific protonation of the iron-iron bond upon treatment with acid. Addition of HBF4·Et2O to the Fe2(CO)4{κ(2)-Ph2PN(allyl)PPh2}(μ-pdt) results in the clean formation of the corresponding dibasal hydride complex [Fe2(CO)4{κ(2)-Ph2PN(allyl)PPh2}(μ-H)(μ-pdt)][BF4], with spectroscopic measurements revealing the intermediate formation of a basal-apical isomer. A crystallographic study reveals that there are only very small metric changes upon protonation. In contrast, the bridge isomers react more slowly to form unstable species that cannot be isolated. Electrochemical and electrocatalysis studies have been carried out on the isomers of Fe2(CO)4{Ph2PN(allyl)PPh2}(μ-pdt). Electron accession is predicted to occur at an orbital that is anti-bonding with respect to the two metal centres based on the DFT calculations. The LUMO in the isomeric model compounds is similar in nature and is best described as an antibonding Fe-Fe interaction that contains differing amounts of aryl π* contributions from the ancillary PNP ligand. The proton reduction catalysis observed under electrochemical conditions at ca. -1.55 V is discussed as a function of the initial isomer and a mechanism that involves an initial protonation step involving the iron-iron bond. The measured CV currents were higher at this potential for the chelating complex, indicating faster turnover. Digital simulations showed that the faster rate of catalysis of the chelating complex can be traced to its greater propensity for protonation. This supports the theory that asymmetric distribution of electron density along the iron-iron bond leads to faster catalysis for models of the Fe-Fe hydrogenase active site.

Hydrogenase biomimetics with redox-active ligands: Electrocatalytic proton reduction by [Fe2(CO)4(2-diamine)(edt)] (diamine = 2,2-bipy, 1,10-phen). POLYHEDRON.

Ten bacterial isolates capable of growth on tetracyanonickelate(II) {K2[Ni(CN)4]} (TCN) as the sole nitrogen source were isolated from soil, freshwater, and sewage sludge enrichments. Seven of the 10 were identified as pseudomonads, while the remaining 3 were classified as Klebsiella species. A detailed investigation of one isolate, Pseudomonas putida BCN3, revealed a rapid growth rate on TCN (generation time, 2 h), with substrate removal and growth occurring in parallel. In addition to TCN, all isolates were able to utilize KCN, although the latter was significantly more toxic; MICs ranged from 0.2 to 0.8 mM for KCN and .50 mM for TCN. While growth occurred over a wide range of TCN concentrations (0.25 to 16 mM), degradation was most substantial under growth-limiting conditions and did not occur when ammonia was present. In addition, cells grown on TCN were found to accumulate nickel cyanide [Ni(CN)21 as a major biodegradation product. The results show that bacteria capable of growth on TCN can readily be isolated and that degradation (i) appears to parallel the capacity for growth on KCN, (ii) does not occur in the presence of ammonia, and (iii) proceeds via the formation of Ni(CN)2 as a biological metabolite.

No abstract

1969, 37 I I ; b) G. V. Ponomarev, R. P. Evstigneeva, N. A. Preobrazhenskii, J. Org. Chem. USSR 7(1971) 167. [5] Procedure (all operations carried out under argon): A mixture of 20 mL methanol (p.a.) and 0.5 mL acetic acid (p.a.) was evaporated down to 10 mL and cooled to room temperature, treated with 0.7 mL 35% formaldehyde-H,O solution and finally 147 mg (1.55 mmol) 3, and stored in the dark at room temperature. The fine crystals filtered off after 3 h were washed with methanol and dried over PaOlo at 50 "C in a vacuum. Yield 157 mg (94%) 4, colorless needles, thin-layer chromatographically and 'H-NMR spectroscopically pure (recrystallization from CHC13/CH,0H on exposure to air leads to decomposition): m.p. 234-235°C (dec.); Rr=0.53 (silica gel-TLC; CHdYbenzene I :0.5); IR (KBr): 3444.7 (N-H), 3429 (N-H), 3395 (assoc. N-H), 3368 c m -' (assoc. N-H); MS (inlet system temperature ca. 140°C); m/z=428 ( M + ; l0Oo/o); 'H-NMR (CDCII): 6 = 1.95 ( s ; 24H), 3.69 (5; SH), 6.91 ( s ; 4H). Angew. Chem. Int. Ed. Engl. 21 (1982) No. 10 1, L, = ,LloCp(CO), 3 , L m = Co(C0)2P(OCH3)3 2, L, = S1Cp 4 , L, = K i C p 5 , X = C H , L, = WCp(CO)2, M = C O 6 , X = S, L m = M O C~( C O )~, M = F e 7, X = P P h , L, = Fe(CO),, :M = C o (cob Angew. Chem. inf. Ed. Engl. 21 (1982) No. I0

The syntheses of novel dimethylbis(2-pyridyl)borate nickel(II) complexes 4 and 6 are reported. These complexes were unambiguously characterized by X-ray analysis. In dichloromethane solvent, complex 4 undergoes a unique square-planar to square-planar rotation around the nickel(II) center, for which activation parameters of ΔH⧧ = 12.2(1) kcal mol–1 and ΔS⧧ = 0.8(5) eu were measured via NMR inversion recovery experiments. Complex 4 was also observed to isomerize via a relatively slow ring flip: ΔH⧧ = 15.0(2) kcal mol–1; and ΔS⧧ = −4.2(7) eu. DFT studies support the experimentally measured rotation activation energy (cf. calculated ΔH⧧ = 11.1 kcal mol–1) as well as the presence of a high-energy triplet intermediate (ΔH = 8.8 kcal mol–1).

Phosphorus-Carbon Bond Cleavage and TetrahedraneCluster Activation in the Reaction between Bis(diphenylphosphino)maleic Anhydride (BMA) and PhCCo3(CO)9. Syntheses, Kinetic Studies, and X-ray Diffraction Structures of PhCCo3(CO)7(bma) and Co3(CO)6(M2V,V-C(Ph)C=C(PPh2)C(0)OC( 0))(M2-PPh2