Large‐Ring Carbocycles

doi:10.1002/9780470872215.ch5

Name Reactions for Carbocyclic Ring Formations 2010

DOI: 10.1002/9780470872215.ch5

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Large‐Ring Carbocycles

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Synthesis and Protonation of an Encumbered Iron Tetraisocyanide Dianion

et al. 2015

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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.

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Synthesis and Protonation of an Encumbered Iron Tetraisocyanide Dianion

et al. 2015

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Dinitrogen binding, P₄-activation and aza-Büchner ring expansions mediated by an isocyano analogue of the CpCo(CO) fragment

2016

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Synthetic studies targeting an m-terphenyl isocyanide analogue of the unstable 16e(-), S = 1 complex CpCo(CO) are reported (Cp = η(5)-C5H5). The m-terphenyl isocyanide CNAr(Dipp2) (Ar(Dipp2) = 2,6-(2,6-(i-Pr)2C6H3)2C6H3) is shown to readily bind to both CpCoI2 and Cp*CoI2 fragments (Cp* = η(5)-C5Me5) and provide mono-isocyanide starting materials that are suitable for chemical reduction. Treatment of CpCoI2(CNAr(Dipp2)) with KC8 produces the bridging isocyanide dimer, [CpCo(μ-CNAr(Dipp2))]2, thereby indicating that the steric combination of Cp and CNAr(Dipp2) ligands does not allow for the production of mononuclear complexes. However, Cp*CoI2(CNAr(Dipp2)) with KC8 under an N2 atmosphere results in the formation of the complex, Cp*Co(N2)(CNAr(Dipp2)), which is a unique two-legged piano stool complex featuring a coordinated dinitrogen ligand. The N2 ligand in Cp*Co(N2)(CNAr(Dipp2)) is shown to be labile and, upon removal by application of vacuum, leads to the production of an η(4)-coordinated 1-azabenz[b]azulene complex by aza-Büchner cyclization of the CNAr(Dipp2) ligand. This cyclization reaction is rationalized via the intermediacy of the unobserved 16e(-) species [Cp*Co(CNAr(Dipp2))]. While this intramolecular aza-Büchner cyclization prevents isolation of [Cp*Co(CNAr(Dipp2))], the dinitrogen complex Cp*Co(N2)(CNAr(Dipp2)) is shown to serve as a reliable synthon for this 16e(-) species upon reaction with small molecule substrates. Both free CNAr(Dipp2) and diphenylacetylene react with Cp*Co(N2)(CNAr(Dipp2)) to form two-legged piano stool complexes. In addition, Cp*Co(N2)(CNAr(Dipp2)) reacts readily with 0.5 and 1.0 equivalents of P4 to produce poly-phosphorus products resulting from P-P single bond cleavage.

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Large‐Ring Carbocycles

Cited by 2 publications

References 380 publications

Synthesis and Protonation of an Encumbered Iron Tetraisocyanide Dianion

Synthesis and Protonation of an Encumbered Iron Tetraisocyanide Dianion

Dinitrogen binding, P₄-activation and aza-Büchner ring expansions mediated by an isocyano analogue of the CpCo(CO) fragment

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Large‐Ring Carbocycles

Cited by 2 publications

References 380 publications

Synthesis and Protonation of an Encumbered Iron Tetraisocyanide Dianion

Synthesis and Protonation of an Encumbered Iron Tetraisocyanide Dianion

Dinitrogen binding, P4-activation and aza-Büchner ring expansions mediated by an isocyano analogue of the CpCo(CO) fragment

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Dinitrogen binding, P₄-activation and aza-Büchner ring expansions mediated by an isocyano analogue of the CpCo(CO) fragment