10.1002/chem.201801541
Chemistry - A European Journal
FULL PAPER
Humboldt foundation for a Humboldt Research Award. L. E. L. is
grateful to the Deutscher Akademischer Austauschdienst
(DAAD) for a research fellowship. The dataset underlying this
08a7-4bd5-839a-164fa5660576.
Keywords: aluminate • homogeneous catalysis • hydroboration
• lithium • metallation • structure
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Scheme 8. Reaction between 3 and pyrazine giving Al-H addition product 11.
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Conclusions
This contribution has demonstrated the synthesis, spectroscopic
and structural characterisation of a new family of donor-solvated
heteroleptic dialkyl-monoamido-monohydrido complexes. The
presence and nature of the Lewis donor imparts interesting
structural characteristics that influence the catalytic activity in
hydroboration reactions of aldehydes and ketones with
pinacolborane. Polydentate donors (PMDETA) that remain
bound to the lithium atom in solution slow down hydroboration.
On the other hand the related tridentate ligand diglyme, displays
exchange on the NMR timescale, and performs similarly to the
donor free species. We suggest this is, at least in part due to the
coordination saturation of the lithium ion. Using the Lewis donor
ligand DABCO leads to a reduction of the solvation at lithium
and leads to faster hydroboration in
a
representative
hydroboration of a ketone. In these catalytic transformations,
insertion of the polar carbonyl group into the Al-H bond is
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mooted as
a key step. Heteroleptic dialkyl-monoamido-
monohydrido complexes are also revealed to be capable of
hydroborating phenylacetylene, however this activity is
suggested to proceed via deprotonation of the substrate. The
bifunctional activity of the complexes is also demonstrated
stoichiometrically in metallation of substrates containing an
acidic hydrogen atom, and in an addition reaction with pyrazine.
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Experimental Section
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Full experimental characterisation and synthetic procedures are
described in the accompanying supporting information.
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The authors thank the EPSRC (grant award EP/N011384/1,
DTP studentship to S.A.O., and vacation bursary to N.R.J.) and
George Fraser (scholarship to S.A.O.) for their generous
sponsorship of this research. REM thanks the Alexander von
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