Alfred Brandl

Reaktionen an komplexgebundenen liganden: XVIII. Ligandeneigenschaften und reaktivität von distickstoff, diimin, hydrazin und ammoniak inpentacarbonylchrom(0)-komplexen

Abstract Synthesis, properties and reactions of [(OC)5Cr]2N2H2, [(OC)5Cr]2N2H4, (OC)5CrN2H4 and (OC)5CrNH3 and attempts to prepare [(OC)5Cr]2N2 and (OC)5CrN2 are reported. The hydrasine and a with (OC)5CrTHF yields [(OC)5Cr]2N2H4, whereas the reaction with organic carbonyl compounds leads to hydrazone or azine complexes. IR, 1H NMR and UV spectra of the complexes are reported and discussed. The IR spectra (KBr) point to a C2h-symmetry of N2H4 in [(OC)5Cr]2N2H4 and a cis-diimine structure of N2H2 in [(OC)5Cr]2N2H2. In solution [(OC)5Cr]2-N2H2 possibly exists as a mixture of cistrans isomers.

Reaktionen an komplexgebundenen liganden : XIV. Basenkatalysierter H—D-austausch und disproportionierung von komplexgebundenem diimin in μ-N2H2[Cr(CO)52; modellreaktionen der enzymatischen N2-fixierung

Abstract Complexed diimine in μ-N2H2[Cr(CO)5]2 undergoes a rapid H — D-exchange with deuterium ions, which is inhibited completely by acids; the rate of the H — D exchange is significantly larger for the diimine complex that for the corresponding hydrazine and ammonia complexes, which is explained by the acidic properties of the diimine protons. In the presence of catalytic amounts of strong base N2H2[Cr(CO)5]2 disproportionates fast and irreversibly to N2[Cr(CO)5]2 and N2H4[Cr(CO)5]2; a mechanism is proposed for this reaction. The reactions of the complexed diimine are compared to those of the free diimine; their significance with respect to intermediated steps of the enzymatic N2 fixation is discussed.

Reaktionen Komplexgebundener liganden : XV. Diimin-, hydrazin- und ammoniak-complexes des molybdäns; Synthese und eigenschaften von μ-H2H2[Mo(CO)5]2, μ-N2H4[Mo(CO)5]2, [μ-(N2H4)2{Mo(CO)4}2], Mo(CO)5H2H4 und Mo(CO)5NH3

Abstract Synthesis and properties of N2H2, H2h4 and NH3 complexes of molybdenum are described. N2H4 and NH3 react in solution with Mo(CO)6 under normal conditions yielding Mo(CO)5H2H4 and Mo(CO)5NH3 respectively. The oxidation of Mo(CO)5H2H4 with H2/Cu2+ yields μ-N2H2[Mo(CO)5]2; this complex contains the N2H2 ligand as diimine, HN=NH, which is presumed to be the first stage of reduction of the N2 molecule in N2 fixation. μ-N2H4[Mo(CO)5]2 is obtained by low temperature synthesis from Mo(CO)5THF and N2H4; decomposition of this complex leads to the bis-μ-hydrazine complex [N2H4]2[Mo(CO)4]2- μ-N2H2[Mo(CO)5]2 can be converted to μ-N2H4[Mo(CO)5]2, which is another proof for the (1) oxidation state of nitrogen in the N2H2 complex. A comparison of the analogous Cr, Mo and W complexes shows that the molybdenum compounds exhibit the highest reactivity and lowest stability.

Wolfram-Carbonylkomplexe mit Stickstoff-Wasserstoff-Liganden [1] / Tungsten Carbonyl Complexes with Nitrogen Hydride Ligands [1]

Abstract Synthesis, properties and reactions of [(OC)5W]2N2H2, [(OC)5W]2N2H4, (OC)5WN2H4, (OC)5WNH3, [(OC)4PØ3W]2N2H4, [(OC)4PØ3WN2H4], [(OC)5W-N2H2-W(CO)4PØ3], [(OC)5W-N2H2-W(CO)4P(CH3)3] and [(OC)5WNHCH3NHC6H5] are reported. The hydrazine complexes are synthesized by ligand exchange from the corresponding tetra-hydrofuran complexes. Oxidation by various oxidizing agents yields the diazene complexes, in most cases very low yields. Substitution of CO by phosphanes leads to reduced stability of the compounds. All complexes undergo base catalysed H-D exchange yielding the corresponding ND derivatives; the diazene complexes show a much faster exchange than the corresponding hydrazine and ammonia complexes, which is explained by the higher acidity of the N2H2 protons. The diazene complexes disproportionate under base catalysis to hydrazine and dinitrogen compounds, the latter of which loose the N2 ligand immediately. The diazene ligand of [(OC)5W]2N2H2 cannot be alkylated by reactions with (CH3)2SO4, LiCH3 or CH2N2; instead, LiCH3 as well as CH2N2 cause disproportionation to N2H4 and N2 complexes. UV irradiation of [(OC)5W]2N2H2 in THF leads to substitution of CO by THF. The THF complexes can be converted to the phosphane substituted diazene complexes. The IR, UV-VIS and 1H NMR spectra of the (OC)5W complexes are nearly identical to those of the analogous Cr and Mo compounds. The unsymmetrical phosphane diazene complexes, however, show a quartet of the N2H2 protons in the 1H NMR spectra with coupling constants of 25-26 Hz for the protons on the NN double bond. This value points to a trans configuration of the diazene ligand and its complexes respectively.