Synthesis and Protonation of an Encumbered Iron Tetraisocyanide Dianion

Abstract

Reported here are synthetic studies probing highly reduced iron centers in an encumbering tetraisocyano ligand environment. Treatment of FeCl2 with sodium amalgam in the presence of 2 equiv of the m-terphenyl isocyanide CNAr(Mes2) (Ar(Mes2) = 2,6-(2,4,6-Me3C6H2)2C6H3) produces the disodium tetraisocyanoferrate Na2[Fe(CNAr(Mes2))4]. Structural characterization of Na2[Fe(CNAr(Mes2))4] revealed a tight ion pair, with the Fe center adopting a tetrahedral coordination geometry consistent with a d(10) metal center. Attempts to disrupt the cation-anion contacts in Na2[Fe(CNAr(Mes2))4] with cation-sequestration reagents lead to decomposition, except for the case of 18-crown-6, where a mononuclear complex featuring a dianionic 1-azabenz[b]azulene ligand was isolated in low yield. Formation of this 1-azabenz[b]azulene is rationalized to proceed by an aza-Büchner ring expansion of a CNAr(Mes2) ligand mediated by a coordinatively unsaturated Fe center. Disodium tetraisocyanoferrate Na2[Fe(CNAr(Mes2))4] is readily protonated by trimethylsilanol (HOSiMe3) to produce the monohydride ferrate salt, Na[HFe(CNAr(Mes2))4], the anionic portion of which serves as an isocyano analogue of the hydrido-tetracarbonyl metalate [HFe(CO)4](-). Treatment of Na[HFe(CNAr(Mes2))4] with methyl triflate (MeOTf; OTf = [O3SCF3](-)) at low temperature in the presence of dinitrogen yields the five-coordinate Fe(0) complex Fe(N2)(CNAr(Mes2))4. The formation of Fe(N2)(CNAr(Mes2))4 in this reaction is consistent with the intermediacy of the neutral tetraisocyanide Fe(CNAr(Mes2))4. The decomposition of Fe(N2)(CNAr(Mes2))4 to the dimeric complex [Fe(η(6)-(Mes)-μ(2)-C-CNAr(Mes))]2 and a seven-membered cyclic imine derived from a CNAr(Mes2) ligand is presented and provides insight into the ability of CNAr(Mes2) and related m-terphenyl isocyanides to stabilize zerovalent four-coordinate iron complexes in a strongly π-acidic ligand field.

Biosynthesis of isonitrile lipopeptides by conserved nonribosomal peptide synthetase gene clusters in Actinobacteria

“…The isonitrile functionality is known to behave as an electron-rich analog of carbon monoxide and form coordination complexes with most transition metals (32,33). Metals are required in many life processes, and pathogenic bacteria have addressed the challenge of deficiencies in essential metals or high concentrations of toxic metal cations in the host by evolving metal homeostasis mechanisms that are frequently associated with virulence (34)(35)(36)(37)(38)(39)(40)(41).…”

“…Metals are required in many life processes, and pathogenic bacteria have addressed the challenge of deficiencies in essential metals or high concentrations of toxic metal cations in the host by evolving metal homeostasis mechanisms that are frequently associated with virulence (34)(35)(36)(37)(38)(39)(40)(41). The operon of Rv0096-0101 has been known to be critical for the virulence of M. tuberculosis and essential for the survival of this pathogen in macrophages and mice (7,9,10,27,32,33). Based on the metal binding ability of isonitrile, we postulated that this conserved biosynthetic gene cluster plays a role in metal transport and homeostasis.…”

A Molybdenum(0) Isocyanide Analogue of Ru(2,2′‐Bipyridine)32+: A Strong Reductant for Photoredox Catalysis

“…In each ligand, there are torsion angles of 51.2(7) and 55.8 (7) 3 complex;t hermal ellipsoidsa re drawn at the 50 % probability level. [20] In cyclic voltammetry,t he Mo 0 center is oxidized reversibly to Mo I at apotential (E 0 )ofÀ0.40 Vvs. trans-Standing isocyanobenzene units are nearly orthogonal to each another.The methyl substituents help shield the metal center from the environment and thus presumably contribute to the overall stability of the complex.…”

Monomeric Chini‐Type Triplatinum Clusters Featuring Dianionic and Radical‐Anionic π*‐Systems

“…[14] While the oligomeric members of [Pt 3 (CO) 6 ] n 2À with n = 2-8 have all been isolated and structurally characterized, [7][8][9][10][11]15] the parent species [Pt 3 (CO) 6 ] 2À (n = 1) has eluded complete characterization. [21] Given our success in isolating isocyano analogues to classical carbonyl metalates using sterically encumbering m-terphenyl isocyanides, [22][23][24][25] we report herein the synthesis and structural characterization of K 2 [Pt 3 (m-CO) 3 (CNAr Dipp2 ) 3 ]( Ar Dipp2 = 2,6-(2,6-(i-Pr) 2 C 6 H 3 ) 2 C 6 H 3 ), as well as the open-shell monoanion K[Pt 3 (m-CO) 3 (CNAr Dipp2 ) 3 ]. [21] Given our success in isolating isocyano analogues to classical carbonyl metalates using sterically encumbering m-terphenyl isocyanides, [22][23][24][25] we report herein the synthesis and structural characterization of K 2 [Pt 3 (m-CO) 3 (CNAr Dipp2 ) 3 ]( Ar Dipp2 = 2,6-(2,6-(i-Pr) 2 C 6 H 3 ) 2 C 6 H 3 ), as well as the open-shell monoanion K[Pt 3 (m-CO) 3 (CNAr Dipp2 ) 3 ].…”