Exploration of weak-field iron-nitrogen clusters: Nitrogenase-inspired synthetic inorganic chemistry

The ferrous precursor Fe[N(SiMe3)2] 2 (1) undergoes protonolysis by aryl (Ar) thiolate to yield the heteroleptic dimer Fe2(mu-SAr)2(N(SiMe3) 2)2 (2). 2 effects N-N reductive cleavage of diaryl hydrazine (Ar' = Tol, Ph) to give the ferric heterocubane cluster Fe4(mu3-NAr ')4(SAr)4 (3). A 3 Fe(III)-1 Fe(II) derivative {lcub}Fe4(mu3-NAr') 4(SAr)3[N(SiMe3)2]{rcub}- (4) can be isolated by an altered reaction stoichiometry. A range of substituted hydrazines is tested for reactivity, and the need for at least one N-H proton is demonstrated.; Clusters 3 and 4 undergo protolytic core ligand exchange with aryl amines to give mixed core heterocubane clusters. Forward and reverse rate constants for the core ligand exchange of 3 with aniline are k = 4.2 x 10-4 M-1s-1, k - = 2.3 x 10-3 M-1s -1. Tetranuclear cluster 3 undergoes an equilibrium rearrangement reaction with RNH2 (R = tBu, iPr) to 2 equivalents of the dinuclear cluster Fe2(mu-NAr ')2(SAr)2(RNH2)2 (5). The reverse reaction occurs by a concerted condensation mechanism whereby two molecules of 5 dimerize to form 3. 3 catalyzes the redox disproportionation of diaryl hydrazines into aryl amine and azoarene.; The reactivity of dinuclear three-coordinate iron cluster Fe2(mu-STriph) 2(STriph)2 (6) (Triph - 2,4,6 triphenylphenyl) with nitrogen-containing substrates gives the following results: Aniline: formation of adduct Fe2(mu-STriph)2(STriph)2 (PhNH2)2 (7); tBuNH 2: cluster fission to give monomeric Fe(STriph)2( tBuNH2)2 (8); Hydrazine: formation of octahedrally-ligated, hydrazine bridged dimer, [(N2H 4)2(STriph)2Fe]2(mu-N2H 4)2 (9); N,N' -Diphenyl hydrazine: catalytic redox disproportionation of the hydrazine; N-Methyl-N,N'-diphenylhydrazine: formation of a mixture of products which contains the ferric complex Fe(Ar-Me- o-sem)2STriph (10) (Ar-Me-o-sem = N-aryl-N'-methyl- o-diiminobenzosemiquinonate).; An improved synthesis for the terminal-amide-ligated heterocubane cluster Fe4(mu3-NtBu) 4(NtBu)Cl3 (11) is described. Fe4(mu3-NtBu) 4(NtBu)(SPh)3 (13) and [Fe4(mu3-NtBu) 4(NtBu)(SPh)3]- (14) were synthesized from 11. 13 exhibits reversible oxidation and reduction waves at -0.54 V and 1.58 V vs. SCE respectively. 14 exhibits a ground spin state of 1 based on magnetic susceptibility, and Mossbauer suggests the presence of a three-oxidation-state mixture of 1 Fe(II):2 Fe(III):1 Fe(IV) in cluster 14. t-Butyl-amide-ligated Fe4(mu 3-NtBu)4 clusters of the type Fe4(mu 3-NtBu)4(NH tBu)3X (X = [NHtBu] - for 12, X = [I]- for 15) are synthesized. 12 is prepared from FeCl3 and LiNHtBu, and 15 is prepared from 12 and I2.