Angewandte Chemie International Edition
10.1002/anie.201809833
COMMUNICATION
deduced to be similarly kinetically accessible for both possible
pathways.
Figure 2: DFT (B3PW91) computed enthalpy reaction profile at room temperature for the direct hydrogenation vs the 1-hexene insertion of the
dicalcium n-hexyl-hydride complex C (6).
monometallic species.[28,29] Although largely a consequence of
The hydrogenation transition states are particularly notable and
display features which discriminate them from a classical -bond
metathesis. Examination of the relevant molecular orbitals and
the NBO analysis of the hydrogenation of the n-hexyl-hydride
species C (6) is clearly indicative of a heterolytic cleavage of the
the highly polarized nature of the Ca-C bonding, more generally
these observations underscore the view that group
organometallic reactivity is not simply ‘lanthanide mimetic’, but
displays features that are unique to each of the available
elements. We are continuing to examine these possibilities.
2
H
2
molecule. The HOMO-2 (Figure S22) involves the filled sp3
orbital of the n-hexyl chain, the H σ* and a 3d orbital of both Ca
2
Acknowledgements
centers. The involvement of 3d orbitals on Ca has recently been
invoked as a potentially significant factor in the structural and
reaction chemistry of organocalcium species.[26,27] This analysis
indicates, therefore, that the hydrogen atom interacting with the
n-hexyl unit is better viewed as a proton, whereas the hydrogen
atom interacting with the two Ca centers is much more hydridic in
nature. This interpretation is further corroborated by the
corresponding NBO analysis in which a strong second order
We thank the EPSRC (UK) for the support of a DTP studentship
(ASSW).
Conflict of interest
The authors declare no conflict of interest.
Keywords: calcium • hydrogenation • catalysis • main group
chemistry • density functional theory
3
interaction is observed between the filled -methylene sp orbital
2
of the n-hexyl chain and the σ* orbital of the H molecule,
[
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This electron density is then redistributed via by a less strong
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atoms. The highly polarized nature of this process is underscored
by the NPA charge analysis, which indicates a charge of 1.0 on
the -methylene carbon of the n-hexyl chain, charges of +1.50
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H
2
hydrogen atoms. An effectively identical
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[
[
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