Issue 37, 2016

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

Abstract

Synthetic studies targeting an m-terphenyl isocyanide analogue of the unstable 16e, S = 1 complex CpCo(CO) are reported (Cp = η5-C5H5). The m-terphenyl isocyanide CNArDipp2 (ArDipp2 = 2,6-(2,6-(i-Pr)2C6H3)2C6H3) is shown to readily bind to both CpCoI2 and Cp*CoI2 fragments (Cp* = η5-C5Me5) and provide mono-isocyanide starting materials that are suitable for chemical reduction. Treatment of CpCoI2(CNArDipp2) with KC8 produces the bridging isocyanide dimer, [CpCo(μ-CNArDipp2)]2, thereby indicating that the steric combination of Cp and CNArDipp2 ligands does not allow for the production of mononuclear complexes. However, Cp*CoI2(CNArDipp2) with KC8 under an N2 atmosphere results in the formation of the complex, Cp*Co(N2)(CNArDipp2), which is a unique two-legged piano stool complex featuring a coordinated dinitrogen ligand. The N2 ligand in Cp*Co(N2)(CNArDipp2) is shown to be labile and, upon removal by application of vacuum, leads to the production of an η4-coordinated 1-azabenz[b]azulene complex by aza-Büchner cyclization of the CNArDipp2 ligand. This cyclization reaction is rationalized via the intermediacy of the unobserved 16e species [Cp*Co(CNArDipp2)]. While this intramolecular aza-Büchner cyclization prevents isolation of [Cp*Co(CNArDipp2)], the dinitrogen complex Cp*Co(N2)(CNArDipp2) is shown to serve as a reliable synthon for this 16e species upon reaction with small molecule substrates. Both free CNArDipp2 and diphenylacetylene react with Cp*Co(N2)(CNArDipp2) to form two-legged piano stool complexes. In addition, Cp*Co(N2)(CNArDipp2) reacts readily with 0.5 and 1.0 equivalents of P4 to produce poly-phosphorus products resulting from P–P single bond cleavage.

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

Supplementary files

Article information

Article type
Paper
Submitted
14 ጁላይ 2016
Accepted
21 ጁላይ 2016
First published
21 ጁላይ 2016

Dalton Trans., 2016,45, 14561-14569

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

C. C. Mokhtarzadeh, A. L. Rheingold and J. S. Figueroa, Dalton Trans., 2016, 45, 14561 DOI: 10.1039/C6DT02789J

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