Pecak, J; Fleissner, S.; Veiros, L. F.; Pittenauer, E.; Stoger, B.; Kirchner, K. J. Organometallics (2021) 40. p.278-285.

1. Synthesis and Catalytic
Reactivity* of Cobalt
Pincer Nitrosyl Hydride
Complexes
Pecak, J; Fleissner, S.; Veiros, L. F.; Pittenauer, E.;
Stoger, B.; Kirchner, K. J. Organometallics (2021)
40. p.278-285.
Vienna University of Technology
*Hydroboration of Alkenes

2. New Pincer Nitrosyl Complex
(abbreviated [Co])
Pinacolborane: mild borane useful for the
hydroboration of sensitive substrates
Pinacolborane is also less reactive
• Generally much higher yields (up
to 99%)
• Mild conditions useful for
sensitive substrates
• Cheaper first row transition metal
catalysis
Drawbacks with Previous Hydroboration Reactions
a road to a milder, greener, higher-yielding approach

3. Synthesis of Active Hydride Catalyst
BH3NH3 was found to hydrogenate pre-catalyst 1 with the highest yield (68%). This active catalyst was
prepared solely for characterization purposes – not for use in synthesis
Instead of using the active catalyst 2 in the hydroboration, pre-catalyst 1 was added directly to the reaction. The
borane would simultaneously activate the pre-catalyst and perform its intended function.
The pre-catalyst was used since it was not air sensitive and was easier to work with
for characterization purposes

4. What is a Non-Innocent Ligand?
let’s work on assigning some oxidation states
The nitrosyl ligand 4 is like a shock
absorber. If there is too much electron
density, it takes some back (towards
bent). If there is too little electron
density, it donates back electrons
(towards linear)

5. X-ray crystallography
indicates the NO is bent
with a Co-O-N angle of
166°. This means the
NO+ is somewhere
between a 0e and a 2e
donor
Electronic Structure of
Starting Complex

6. Our alkene just donated
2e to our metal. The
nitroso ligand has even
more bent character,
indicating it accepted
some of the new electron
density
The NO ligand facilitated
internal redox chemistry
Pi-Coordination
(Alkene Coordination)

7. The insertion of H into the pi-
bond leaves an empty binding
site. That’s not very
energetically favorable!
Then why is this step so
favorable?
Insertion

8. Agostic interactions involve a
3c, 2e bond between Co, H,
and B.
This step is endergonic
because of a decrease in
entropy
Agostic Interaction

9. The alkyl group acts like a
carbanion nucleophile while
the boron is the electrophile.
Boron transfers hydride in the
process to regenerate the
starting catalyst
Internal “Alkylation”

10. Questions?