The reaction of L'Si [L' = CH{(C=CH(2))(CMe)(2,6-iPr(2)C(6)H(3)N)(2)}] with ammonia under oxidative addition results in L'Si(H)NH(2). H(3)NBH(3) functions as a source of hydrogen for the hydrogenation of N-heterocyclic carbenes and germylenes.

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Formate dehydrogenase (FDH) enzymes are attractive catalysts for potential carbon dioxide conversion applications. The FDH from Rhodobacter capsulatus (RcFDH) binds a bis-molybdopterin-guanine-dinucleotide (bis-MGD) cofactor, facilitating reversible formate (HCOO(-)) to CO2 oxidation. We characterized the molecular structure of the active site of wildtype RcFDH and protein variants using X-ray absorption spectroscopy (XAS) at the Mo K-edge. This approach has revealed concomitant binding of a sulfido ligand (Mo=S) and a conserved cysteine residue (S(Cys386)) to Mo(VI) in the active oxidized molybdenum cofactor (Moco), retention of such a coordination motif at Mo(V) in a chemically reduced enzyme, and replacement of only the S(Cys386) ligand by an oxygen of formate upon Mo(IV) formation. The lack of a Mo=S bond in RcFDH expressed in the absence of FdsC implies specific metal sulfuration by this bis-MGD binding chaperone. This process still functioned in the Cys386Ser variant, showing no Mo-S(Cys386) ligand, but retaining a Mo=S bond. The C386S variant and the protein expressed without FdsC were inactive in formate oxidation, supporting that both Mo-ligands are essential for catalysis. Low-pH inhibition of RcFDH was attributed to protonation at the conserved His387, supported by the enhanced activity of the His387Met variant at low pH, whereas inactive cofactor species showed sulfido-to-oxo group exchange at the Mo ion. Our results support that the sulfido and S(Cys386) ligands at Mo and a hydrogen-bonded network including His387 are crucial for positioning, deprotonation, and oxidation of formate during the reaction cycle of RcFDH.

Herein we report on the reaction of stable two-coordinate silylene, L(1)Si [L(1) = CH{(C=CH(2))(CMe)(2,6-iPr(2)C(6)H(3)N)(2)}] (1) and three-coordinate silylene (Lewis base stabilized silylene), L(2)SiCl [L(2) = PhC(NtBu)(2)] (2) with aromatic compounds containing C-F and C-H bonds. The reaction of 1 and 2 with hexafluorobenzene (C(6)F(6)) affords the silicon(IV) fluorides, L(1)SiF(C(6)F(5)) (3) and L(2)SiFCl(C(6)F(5)) (4), respectively. The reaction proceeds through the unprecedented oxidative addition of one of the C-F bonds to the silicon(II) center without any additional catalyst. When 1 and 2 are treated with octafluorotoluene (C(6)F(5)CF(3)), pentafluoropyridine (C(5)F(5)N) regioselective C-F bond activation occurs leading to the formation of L(1)SiF(4-C(6)F(4)CF(3)) (5), L(1)SiF(4-C(5)F(4)N) (6), L(2)SiFCl(4-C(6)F(4)CF(3)) (7), and L(2)SiFCl(4-C(5)F(4)N) (8), respectively. More interestingly, compounds 1 and 2 react with pentafluorobenzene (C(6)F(5)H) under formation of silicon(IV) hydride L(1)SiH(C(6)F(5)) (9) by chemoselective C-H bond activation, in the latter case producing silicon(IV) fluoride L(2)SiFCl(4-C(6)F(4)H) (10) by chemo- as well as regioselective C-F bond activation. Furthermore, the reaction of 1 with 1,3,5-trifluorobenzene (1,3,5-C(6)F(3)H(3)) leads to the chemoselective formation of silicon(IV) hydride L(1)SiH(1,3,5-C(6)F(3)H(2)) (11). The formation of compounds 9 and 11 occurs via oxidative addition of the aromatic C-H bond to the silicon(II) center instead of C-F bond activation. All reported reactions proceed without any additional catalyst. Compounds 3, 4, 5, 6, 7, 8, 9, 10, and 11 were investigated by microanalysis and multinuclear NMR spectroscopy and compounds 3, 7, 8, and 9 additionally by single crystal X-ray structural analyses.

The reactions of stable beta-diketiminate germanium(II) hydride LGeH (1) [L = HC(CMeNAr)2, Ar = 2,6-iPr2C6H3] with nitrous oxide, trimethylsilyl azide, ketones, and alkynes are described. 1 reacts with nitrous oxide to yield the germanium(II) hydroxide LGeOH (2), and with trimethylsilyl azide affords in toluene at room temperature the germanium(II) azide LGeN3 (3), and also the germanium(IV) diamide L'Ge(NHSiMe3)2 (L' = CH{(CCH2)(CMe)(2,6-iPr2C6H3N)2}) (4). Ketones (PhCOCF3, 2-C4H3SCOCF3) and 1 generated the germanium(II) alkoxides (5-6) in high yield. The activated terminal alkyne (HC[triple bond]CCO2Me) and disubstituted alkyne (EtO2CC[triple bond]CCO2Et) react with 1 to form the germanium(II) substituted alkenes (vinyl germylene) (7-8). Further reaction of the methylgermanium(II) compound LGeMe (9) with trimethylsilyl diazomethane resulted in the formation of germanium(IV) amide L'Ge(Me)NHN=CHSiMe3 (10). Compounds 2-8, and 10 were characterized by microanalysis and multi-nuclear NMR spectroscopy. Furthermore compounds 3-6, and 8 are confirmed by X-ray structural analysis.

Background: Some molybdoenzymes in prokaryotes contain the bis-molybdopterin guanine dinucleotide cofactor. Results: The bis-Mo-MPT cofactor is a novel intermediate in Moco biosynthesis in E. coli. Conclusion: Bis-MGD formed by MobA is fully functional and restores the catalytic activity in apoTorA. Significance: Bis-Mo-MPT assembles spontaneously on MobA prior to forming bis-MGD.

Although the amine transaminase from Vibrio fluvialis has often been applied as a catalyst for the biocatalytic preparation of various chiral primary amines, it is not suitable for the transamination of a-hydroxy ketones and aryl-alkyl ketones bearing an alkyl substituent larger than a methyl group. We addressed this problem through a systematic mutagenesis study of active site residues to expand its substrate scope towards two bulky ketones. We identified two mutants (F85L/ V153A and Y150F/V153A) showing 30-fold increased activity in the conversion of (S)-phenylbutylamine and (R)-phenylglycinol, respectively. Notably, they facilitated asymmetric synthesis of these amines with excellent enantiomeric purities of 98 % ee.

Keywords: Vanadium / Oxo complexes / NMR spectroscopy / Hydrazones / N ligands / O ligands The dioxovanadium(V) complexes M[VO 2 (L)solv] (2, 5, 6) have been isolated along with dimeric, oxo-bridged monooxovanadium complexes with the formula [{VOL} 2 µ-O] (1, 4), and characterised by their spectral and thermogravimetric properties and reactivity patterns. H 2 L is the hydrazone H 2 {(R-sal)-iNH} [sal derives from salicylaldehyde (R = H) or p-Cl-salicylaldehyde (R = Cl)] or H 2 hap-iNH,where hap is the o-hydroxyacetophenone moiety, and iNH stands for isonicotinic acid hydrazide. In the isolated potassium (M = K) complexes 2a, 5 and 6, solv is a water molecule, [a]