Issue 29, 2016

Further studies of the Enhanced Structural Carborane Effect: tricarbonylruthenium and related derivatives of benzocarborane, dihydrobenzocarborane and biphenylcarborane

Abstract

Detailed comparison of the molecular structures of [1,2-μ-(C4H4)-3,3,3-(CO)3-3,1,2-closo-RuC2B9H9] (1) and [1,2-μ-(C4H6)-3,3,3-(CO)3-3,1,2-closo-RuC2B9H9] (2) reveals evidence for an Enhanced Structural Carborane Effect in 1 arising from the involvement of the cage pπ orbitals in the exopolyhedral ring to some degree. A minor co-product in the synthesis of 2 is [η-{1,2-μ-(C4H6)}-3,3-(CO)2-3,1,2-closo-RuC2B9H9] (3). Compounds 2 and 3 are readily interconverted, since heating 2 to reflux in THF or reaction with Me3NO affords 3 which readily reacts with CO to regenerate 2. The η-ene bonding in 3 is also displaced by PMe3, P(OMe)3 and t-BuNC to yield [1,2-μ-(C4H6)-3,3-(CO)2-3-PMe3-3,1,2-closo-RuC2B9H9] (4), [1,2-μ-(C4H6)-3,3-(CO)2-3-P(OMe)3-3,1,2-closo-RuC2B9H9] (5) and [1,2-μ-(C4H6)-3,3-(CO)2-3-t-BuNC-3,1,2-closo-RuC2B9H9] (6), respectively. Structural studies of 4–6, focussing on the Exopolyhedral Ligand Orientation of the {Ru(CO)2L} fragment relative to the C2B3 carborane face, are discussed in terms of the structural trans effects of PMe3, P(OMe)3 and t-BuNC relative to that of CO. An improved synthesis of [1,2-μ-(C6H4)2-1,2-closo-C2B10H10], “biphenylcarborane”, is reported following which the first transition-metal derivatives of this species, [1,2-μ-(C6H4)2-3-Cp-3,1,2-closo-CoC2B9H9] (7) and [1,2-μ-(C6H4)2-3,3,3-(CO)3-3,1,2-closo-RuC2B9H9] (8), are prepared. Comparisons of the structures of 7 and 8 with the corresponding benzocarborane derivatives [1,2-μ-(C4H4)-3-Cp-3,1,2-closo-CoC2B9H9] and 1, respectively, suggest that Clar's rule for aromaticity can be applied to polycyclic aromatic hydrocarbons fused onto carborane cages.

Graphical abstract: Further studies of the Enhanced Structural Carborane Effect: tricarbonylruthenium and related derivatives of benzocarborane, dihydrobenzocarborane and biphenylcarborane

Supplementary files

Article information

Article type
Paper
Submitted
12 may 2016
Accepted
07 iyn 2016
First published
07 iyn 2016

Dalton Trans., 2016,45, 11742-11752

Further studies of the Enhanced Structural Carborane Effect: tricarbonylruthenium and related derivatives of benzocarborane, dihydrobenzocarborane and biphenylcarborane

S. L. Powley, G. M. Rosair and A. J. Welch, Dalton Trans., 2016, 45, 11742 DOI: 10.1039/C6DT01888B

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