Please d oC hn eo mt Ca do mj u ms t margins
Page 4 of 4
COMMUNICATION
Journal Name
The role of the Lewis basicity was also probed by calculating
the energy profile for the hydrogenolysis of the phosphine
Conflicts of interest
DOI: 10.1039/C9CC09466K
There are no conflicts to declare.
+
complex Cp
heterolytic H
formation of detectable amounts of Cp
expected. In addition, the calculated barrier for H-H cleavage is
1.5 kcal/mol, i.e. about 4 kcal/mol higher than for the NMe
case, suggesting that no H activation would take place. This fits
with early observations by Jordan on the hydrogenolysis of
Cp ZrMe(PMe ) and Cp ZrMe(PMe , for which only -bond
metathesis of the Zr-Me group was observed .
2
ZrH(PMe
3
) . We find that, as in the NMe
3
case,
2
cleavage is considerably endergonic and
ZrH
2
2
is not to be Notes and references
1
(a) K. Gruet, E. Clot, O. Eisenstein, D. H. Lee, B. Patel, A.
Macchioni and R. H. Crabtree, New. J. Chem., 2003, 27, 80; (b)
G. J. Kubas, J. Organomet. Chem., 2014, 751, 33.
3
3
2
2
(a) D. W. Stephan and G. Erker, Angew. Chem. Int. Ed., 2015,
5
4, 6400; (b) D. W. Stephan, Acc. Chem. Res., 2015, 48, 306;
2
3
2
3 2
)
(
c) D. W. Stephan, J. Am. Chem. Soc. 2015, 137, 10018; (d) D.
1
6
W. Stephan, Science, 2016, 354, aaf7229.
The picture emerging from DFT calculations indicates that
2
splitting in this class of compounds is notably affected by the
delicate balance between steric and electronic factors, and that
it is made energetically feasible in this case only by the trapping
3
4
(a) S. Arndt, M. Rudolph and A. S. K. Hashmi, Gold Bull., 2017,
50, 267; (b) J. Campos, J. Am. Chem. Soc., 2017, 139, 2944; (c)
S. J. K. Forrest, J. Clifton, N. Fey, P. G. Pringle, H. A. Sparkes
and D. F. Wass, Angew. Chem. Int. Ed., 2015, 54, 2223.
(a) R. C. Neu, E. Otten, A. Lough and D. W. Stephan, Chem. Sci.,
H
2 2
of Cp ZrH into the trimetallic 2. To further validate this
2
011, 2, 170; (b) A. M. Chapman, M. F. Haddow and D. F.
hypothesis, we computationally explored H
2
activation by
Wass, J. Am. Chem. Soc., 2011, 133, 18463; (b) X. Xu, R.
Fröhlich, C. G. Daniliuc, G. Kehr and G. Erker, Chem. Commun.
+
Cp
2
Zr(OPh)(NMe
3
) , where the phenoxy substituent prevents
2
012, 48, 6109; (c) A. M. Chapman, M. F. Haddow and D. F.
the formation of any multinuclear species. In this case hydrogen
activation by the aryloxide compound proceeds very similar to I
Wass, Eur. J. Inorg. Chem. 2012, 2012, 1546; (c) X. Xu, G. Kehr,
C. G. Daniliuc and G. Erker, J. Am. Chem. Soc., 2013, 135, 6465;
2
with a somewhat higher H cleavage barrier (28.2 vs 24.3
(d) X. Xu, G. Kehr, C. G. Daniliuc and G. Erker, J. Am. Chem.
kcal/mol). However, the lack of trimerisation leaves the final
Soc., 2014, 136, 12431; (e) A. T. Normand, C. G. Daniliuc, B.
Wibbeling, G. Kehr, P. Le Gendre and G. Erker, J. Am. Chem.
Soc., 2015, 137, 10796; (f) O. J. Metters, S. J. K. Forrest, H. A.
Sparkes, I. Manners and D. F. Wass, J. Am. Chem. Soc., 2016,
2
product uphill and no H activation by this system should be
expected.
In summary, we have shown that zirconaziridinium ion pairs
1
38, 1994; (g) O. J. Metters, S. R. Flynn, C. K. Dowds, H. A.
2
[
Cp
2
Zr( -CH
2 2
NR ][B(C
6 5
F
)
4
] (1) react with H
2
undergoing a fast
Sparkes, I. Manners and D. F. Wass, ACS Catal., 2016, 6, 6601.
(a) H. B. Hamilton, A. M. King, H. A. Sparkes, N. E. Pidmore and
D. F. Wass, Inorg. Chem., 2019, 58, 6399; (b) X. Xu, G. Kehr, C.
G. Daniliuc and G. Erker, J. Am. Chem. Soc., 2015, 137, 4550;
(a) L. Rocchigiani, C. Zuccaccia, D. Zuccaccia and A. Macchioni,
Chem. Eur. J. 2008, 14, 6589; (b) L. Rocchigiani, G.
Bellachioma, G. Ciancaleoni, A. Macchioni, D. Zuccaccia and C.
Zuccaccia, Organometallics, 2011, 30, 100; (c) L. Rocchigiani,
G. Ciancaleoni, C. Zuccaccia and A. Macchioni, Angew. Chem.
Int. Ed., 2011, 50, 11752; (d) L. Rocchigiani, G. Ciancaleoni, C.
Zuccaccia and A. Macchioni, ChemCatChem, 2013, 5, 519.
(a) L. Rocchigiani, A. Macchioni and C. Zuccaccia,
Organometallics, 2012, 31, 4076; (b) K. Plössl, J. R. Norton, J.
G. Davidson and E. K. Barefield, Organometallics, 1992, 11,
534.
-bond metathesis of the Zr-C bond instead of the alternative
5
6
Frustrated Lewis Pairs pathway. This reaction affords
zirconocenium amino hydride complexes (I), which behave as
FLPs and promote heterolytic H
salts and the trimetallic zirconium hydride [Cp
2). The formation of 2 is fundamental in making the overall
2
splitting affording ammonium
6
Zr ][B(C
3
H
4
6 5 4 2
F ) ]
(
pathway energetically feasible, despite the fact that it could be
seen as just a side reaction.
Our results show that steric frustration is not a prerequisite
7
2 3
for heterolytic H activation by Zr-NR Lewis adducts. We
demonstrate how H-H bond activation can occur in the
continuum between pure FLP and strong Lewis interaction,
reminiscent of the case of weakly interacting main group FLPs
such as lutidine/B(C
and electronic factors notably affects the reactivity, to the point
that stronger bases such as PR are found computationally to
shut down H activation.
The involvement of d orbitals in the FLP reactivity scenario
opens up unexpected and varied mechanistic pathways that can
be potentially used as a toolbox for the design of novel systems
with improved or novel catalytic activity. The implication of
8
9
1
(a) R. F. Jordan and D. F. Taylor, J. Am. Chem. Soc., 1989, 111,
778; (b) R. Waterman, Organometallics, 2013, 32, 7249.
Z. Jian, C. G. Daniliuc, G. Kehr and G. Erker, Organometallics,
1
7
6 5 3
F ) . The delicate balance between steric
2
017, 36, 424.
3
0 Similar anionic M
3 4
H species have been reported with M= Er,
2
Lu or Y, see (a) W. J. Evans, J. H. Meadows, A. L. Wayda, W. E.
Hunter and J. L. Atwood, J. Am. Chem. Soc., 1982, 104, 2015;
(
b) W. J. Evans, J. H. Meadows and T. P. Hanusa, J. Am. Chem.
Soc., 1984, 106, 4454.
1
3 5
1 For a mixed-valence [Zr H ] neutral core see: P. J. Chirik, L.
M. Henling and J. E. Bercaw, Organometallics, 2001, 20, 534.
these concepts is currently under investigation in our 12 For a cationic [Zr H ] core structure see: A. G. Carr, D. M.
3
3
Dawson, M. Thornton-Pett and M. Bochmann,
Organometallics, 1999, 18, 2933.
laboratory.
We thank the European Research Council. MB is an ERC
Advanced Investigator Award holder (grant no. 338944-
GOCAT). LR is also thankful to University of East Anglia for
1
1
3 Aniline/anilinium exchange is fast also at low temperature
2 2
and no decoalescence is observed at -50 °C in CD Cl .
4 H. H. Brintzinger, J. Organomet. Chem., 1978, 171, 337.
support. AM thanks the University of Perugia and MIUR (AMIS, 15 T. A. Rokob, A. Bakó, A. Stirling, A. Hamza and I. Pápai, J. Am.
Chem. Soc., 2013, 1315, 4425.
“Dipartimenti di Eccellenza – 2018-2022” program). We also
1
1
6 R. F. Jordan, C. S. Bajgur, W. E. Dasher and A. L. Rheingold,
Organometallics, 1987, 6, 1041.
thank the National Crystallographic Centre at the University of
Southampton, U.K. for the measurement of the diffraction
intensities.
7 S. J. Geyer and D. W. Stephan, J. Am. Chem. Soc., 2009, 131,
3
476.
4
| J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins