Variable Ca-Caryl hapticity and its Consequences in Arylcalcium Dimers

Kyle G. Pearce, Chiara Dinoi, Ryan Schwamm, Laurent Maron, Mary Mahon, Michael Hill

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1 Citation (SciVal)


The dimeric β-diketiminato calcium hydride, [( DippBDI)CaH] 2 ( DippBDI = HC{(Me)CN-2,6-i-Pr 2C 6H 3} 2), reacts with ortho-, meta- or para-tolyl mercuric compounds to afford hydridoarylcalcium compounds, [( DippBDI) 2Ca 2(μ-H)(μ-o-,m-,p-tolyl)], in which dimer propagation occurs either via μ 211 or μ 216 bridging between the calcium centers. In each case, the orientation and hapticity of the aryl units is dependent upon the position of the methyl substituent. While wholly organometallic meta- and para-tolyl dimers, [( DippBDI)Ca(m-tolyl)] 2 and [( DippBDI)Ca(p-tolyl)] 2, can be prepared and are stable, the ortho-tolyl isomer is prone to isomerization to a calcium benzyl analog. Computational analysis of this latter process with density functional theory (DFT) highlights an unusual mechanism invoking the generation of an intermediate dicalcium species in which the group 2 centers are bridged by a toluene dianion formed by the formal attachment of the original hydride anion to the initially generated ortho-tolyl substituent. Use of a more sterically encumbered aryl substituent, {3,5-t-Bu 2C 6H 3}, facilitates the selective formation of [( DippBDI)Ca(μ-H)(μ-3,5-t-Bu 2C 6H 3)Ca( DippBDI)], which can be converted into the unsymmetrically-substituted σ-aryl calcium complexes, [( DippBDI)Ca(μ-Ph)(μ-3,5-t-Bu 2C 6H 3)Ca( DippBDI)] and [( DippBDI)Ca(μ-p-tolyl)(μ-3,5-t-Bu 2C 6H 3)Ca( DippBDI)] by reaction with the appropriate mercuric diaryl. Conversion of [( DippBDI)Ca(H)(Ph)Ca( DippBDI)] to afford [{{( DippBDI)Ca} 22-Cl)} 2(C 6H 5-C 6H 5)], comprising a biphenyl dianion, is also reported. Although this latter transformation is serendipitous, AIM analysis highlights that, in a related manner to the ortho-tolyl to benzyl isomerization, the requisite C–C coupling may be facilitated in an “across dimer” fashion by the experimentally-observed polyhapto engagement of the aryl substituents with each calcium.

Original languageEnglish
Article number2304765
JournalAdvanced Science
Early online date15 Sept 2023
Publication statusE-pub ahead of print - 15 Sept 2023

Bibliographical note

Funding Information:
The authors thank the Royal Commission for the Exhibition of 1851 for the provision of a Postdoctoral Fellowship (RJS) and the EPSRC (EP/R020752/1) for support of this research.


  • biaryls
  • calcium
  • density functional theory
  • main group chemistry

ASJC Scopus subject areas

  • General Engineering
  • General Physics and Astronomy
  • General Chemical Engineering
  • General Materials Science
  • Biochemistry, Genetics and Molecular Biology (miscellaneous)
  • Medicine (miscellaneous)


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