Reactions of a cerium(III) amide with heteroallenes: Insertion, silyl-migration and de-insertion

Article abstract of DOI:10.1039/c6cc03719d

Reactions of Ce[N(SiMe₃)Ph^F]₃ (-Ph^F = pentafluorophenyl) toward small molecules of the type E₁CE₂ (E₁, E₂ = O, S, NR), including carbon disulfide, carbodiimide, carbon dioxide, isocyanate and isothiocyanate are reported, resulting in distinct products, including cerium(iii) dithiocarbamate, cerium(iii) guanidinate, isocyanates and unsymmetric carbodiimides. These reactions were rationalized as three consecutive stages of the same reaction pathway: insertion, silyl-migration and de-insertion.

Full text of DOI:10.1039/c6cc03719d

View Article Online
View Journal
ChemComm
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: H. Yin, P. Carroll
and E. J. Schelter, Chem. Commun., 2016, DOI: 10.1039/C6CC03719D.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/chemcomm

Page 1 of 4
ChemComm
View Article Online
DOI: 10.1039/C6CC03719D
ChemComm
RSCPublishing
COMMUNICATION
Reactions of A Cerium(III) Amide with Heteroallenes:
Insertion, Silyl-migration and De-insertion
Cite this: DOI: 10.1039/x0xx00000x
Haolin Yin, Patrick J. Carroll, and Eric J. Schelter*
Received 00th January 2012,
Accepted 00th January 2012
DOI: 10.1039/x0xx00000x
www.rsc.org/
Reactions of Ce[N(SiMe3)PhF]3 (-PhF = pentafluorophenyl) migration to a more electronꢀrich heteroatom, 3) deꢀinsertion
toward small molecules of the type E1=C=E2 (E1, E2 = O, S, reaction to eliminate carbodiimide (from isocyanate) or
NR), including carbon disulfide, carbodiimide, carbon isocyanate (from CO2).
dioxide, isocyanate and isothiocyanate are reported, resulting
in distinct products, including cerium(III) dithiocarbamate,
cerium(III) guanidinate, isocyanates and unsymmetric
carbodiimides. These reactions were rationalized as three
consecutive stages of the same reaction pathway: insertion,
silyl-migration and de-insertion.
Lanthanide amides are widely used as protonlysis precusors.1
They have also been shown to be effective catalysts for ringꢀ
closure hydroamination reactions through an initial protonolysis
step of Ln−N bonds with acidic substrates.2 The insertion
chemistry of small molecule substrates into Ln−N bonds was
reported3 for CS2,4 CO2,5 carbodiimide,6 isocyanate4b, 6a, 6b, 7 and
Scheme 1 Generic representation of three stages reactions
between 1 and E=C=E type of molecules (E = S, NR, O).
6c, 7b
isothiocyanate.4,
Despite the number of examples of
lanthanide amides and extensive reports of their reactivities,
neither of these insertion reactions has been demonstrated with
homoleptic lanthanide amides nor to involve any further
reactivity other than insertion.
In this work, we focused on the insertion reactions of a
homoleptic Ce(III) amide, Ce[N(SiMe3)PhF]3 (ꢀPhF = 2,3,4,5,6ꢀ
The highly reactive isocyanate and carbodiimide species are
useful organic building blocks and thus their synthesis or in situ
formation are of great importance.8 Primary methods for the
synthesis of isocyanates are through phosgenation of amines,
direct oxidation of isocyanide or Lossen rearrangement of
hydroxamic acids.8a Carbodiimides, especially unsymmetric
carbodiimides, are typically synthesized through oxidative
sulfur extrusion from thiourea or azaꢀWittig reactions by
reacting Ph3P=NR with isocyanates.8b Metalꢀbased methods for
the synthesis of these two species have also been reported: Ito
and coꢀworkers reported palladium and nickel catalysed
synthesis of carbodiimides through the reaction of aniline and
isocyanide under oxidizing conditions;9 The Hillhouse group,
demonstrated nitrene transfer from a nickel(II) imide complex
to CO and to isocyanide, forming isocyanate and carbodiimide,
respectively.10 And Sita and coꢀworkers reported a oneꢀpot
method by reacting isocyanate with in situ generated
SnII[N(SiMe3)R]2 species to access desired carbodiimide.11
pentafluorophenyl) (1) with heteroallenes, E1=C=E2 (E1, E2 =
O, S, NR), including carbon disulfide, carbodiimide, carbon
dioxide, isocyanate and isothiocyanate. We found that with
different types of heteroatom substrates, the reactions resulted
in distinct products, featuring three consecutive stages along
one reaction pathway (Scheme 1). These stages included 1)
substrate insertion into Ce−N bond, 2) trimethylsilylꢀ group
P. Roy and Diana T. Vagelos Laboratories, Department of Chemistry, University of
Pennsylvania, 231 S. 34th Street, Philadelphia, Pennsylvania 19104, USA.
Eꢀmail: schelter@sas.upenn.edu
†Electronic supplementary information (ESI) available: Full synthetic details, NMR
data. CCDC XXX–XXXX. For ESI and crystallographic data in CIF or other
electronic format see DOI: XXXXXXXX.
This journal is © The Royal Society of Chemistry 2012
Chem. Commun., 2014, 00, 1-3 | 1

ChemComm
Page 2 of 4
View Article Online
COMMUNICATION
DOI: 10.1C0h39e/mC6.CCCo0m371m9Dun.
Similar reaction of M[N(SiMe3)2]2 (M = Sn or Ge) with CO2
yielded mixture of Me3Si−N=C=O and
Me3Si−N=C=N−SiMe3 products.12
a
In previous work,13 we adapted a strategy of applying
C−F→Ln/An interactions14 instead of a more conventional
approach of sterically bulky ligands to mask an electrophilic
metal center to stabilize monomeric complexes. These facile
C−F→Ln/An interactions allowed energetically accessible
binding pockets by their displacement including coordination of
arenes13b as well as the isolation of the first κ2ꢀ18ꢀcrownꢀ6
coordinated to fꢀblock element as a kinetic product.13c In this
work, we demonstrate that the highly electrophilic –SiMe3
group in [N(SiMe3)PhF]− ligand undergoes facile intraꢀligand
migration reactivity. This is in contrast to the interꢀligand –
SiMe3 migration reactivity postulated for the formation of
uranium imides through the loss of N(SiMe3)2PhF.15 The
Fig. 1 Thermal ellipsoid plots of
probability level.
2
(a) and
3
(b) at the 30%
In contrast, the reaction of
'−diisopropylcarbodiimide (iPr−N=C=N−iPr) in toluene at
ambient temperature overnight afforded an unexpected product
{[iPr(Me3Si)N]C(NiPr)(NPhF)}3CeIII
) as yellow crystals in
81% yield after recrystallization from ꢀpentane. Xꢀray
crystallographic analysis elucidated the trisꢀguanidinate
structural motif (Fig. 1b) in . The presence of guanidinate
1
with excess
N,
N
(
3
corresponding CeIII complex, Ce[N(SiMe3)PhF]3
(1), was
n
previously reported by us13c and used in this work for the
investigation on reactivity with heteroallenes, including carbon
3
disulfide,
isothiocyanate.
carbodiimide,
carbon
dioxide,
isocyanate,
moiety was further confirmed by observation of strong C−N
stretching bands at 1496 and 1470 cmꢀ1. Notably, all three
trimethylsilyl groups have migrated from electronꢀdeficient N
atoms (PhFN) to more electronꢀrich N atoms (iPrN) in
3,
indicating the thermodynamic preference for the 1,3ꢀsilyl
migration. Such silylꢀ migration reactions upon insertion of
16
symmetric cabodiimides have been previously observed for
[N(CH2CH2NSiMe3)3]Zr(NHR)16a and group IA metallated 2ꢀ
(trimethylsilyl)aminopyridine16b, but have not been reported
with highly electrophilic fꢀblock element cations. The 1H NMR
of
3
obtained at 300 K showed multiple paramagnetic
highly unsymmetric ligand
resonances, suggesting
a
environment (Fig. S7). This result was also confirmed by the
19F NMR spectrum featuring three sets of broad orthoꢀF
resonances at −154.7, −155.0, −158.3 ppm, respectively (Fig.
S8). Heating a tolueneꢀd8 solution containing
3 resulted in peak
coalescence at 365 K (Fig. S18−19). A solution symmetry
change from C1 to C3 with increasing temperature was
indicated by the 19F NMR spectroscopy data (Fig. 2).
Scheme 2 Insertion reaction of
Ad−N=C=O and Ad−N=C=S.
Treatment of Ce[N(SiMe3)PhF]3
(1
1
with CS2, iPrN=C=NiPr, CO2,
) with excess CS2 in
toluene at ambient temperature overnight led to an orange
solution. NMR of a reaction aliquot in C6D6 showed complete
conversion into a C3 symmetric ligand environment with broad
1H and 19F resonances (Fig. S5−6). In order to facilitate
crystallization, 2 equiv of O=PPh3 were added, enabling the
isolation
S2CN(SiMe3)PhF]3(O=PPh3)2 (
spectrum of displayed four strong absorptions at 1503, 1147,
of
colorless
crystals
of
Ce[κ2ꢀ
2
) (Fig. 1a) in 79% yield. The IR
2
1071 and 987 cmꢀ1, assigned to C−N stretching, symmetric and
asymmetric stretching of C−S bonds and P=O stretching,
respectively. The C−S stretching frequencies was in good
agreement with the υ(C−S) reported for (CH3C5H4)2Ln(κ2ꢀ
S2CNPh2) at 1157 and 1048 cmꢀ1,4a confirming the
dithiocarbamate structural moiety.
Fig. 2 19F NMR of
3
in tolueneꢀd8 at 380 K and 300 K, showing
a
C3 (bottom) and C1 (top) solution symmetry respectively on
NMR timescale.
Hydrolysis of
3
with pyHCl led to the formation of
(NHiPr)2C(=NPhF), identified by NMR spectra compared with
previous reports.17 In addition, 4,4ˊ−ditertbutylbipyridine
(tBu2bipy)
adduct
of
Ce[N(SiMe3)PhF]3,
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 2012

Page 3 of 4
Journal Name
ChemComm
View Article Online
DOI: 1C0.O10M39M/CU6CNCI0C3A71T9IDON
(tBu2bipy)Ce[N(SiMe3)PhF]3
(
1-tBu2bipy),13c showed no which underlie the thermodynamic preference for the silyl
reactivity with iPr−N=C=N−iPr under the same reaction migration and deꢀinsertion steps.
condition (Fig. S9−10). This result may be attributed to the
In summary, we demonstrated three stages along the same
more electronꢀrich and coordinatively saturated Ce3+ cation in reaction pathway leading to distinct products through the
1-tBu2bipy than that in
1
.
reaction of a homoleptic CeIII amide with heteroallenes,
The deꢀinsertion reaction was exemplified through the including carbon disulfide, carbodiimide, carbon dioxide,
reaction of with excess CO2. Stirring a THF solution of isocyanate and isothiocyanate. The availability of a
1
1
under CO2 atmosphere overnight led to a colorless solution coordination site through initial displacement of C−F→CeIII
with white precipitate. Three diamagnetic resonances at −144.5, interactions allowed insertion of heteroallenes into all three
−159.6 and −164.8 ppm were observed in the 19F NMR Ce−N bonds; the electron deficient –PhF groups lead to facile
spectrum of the supernatant. Gas chromatography mass migration of electrophilic silylꢀ groups. And the oxoꢀphilic
spectrometry (GCꢀMS) analysis confirmed the organic product nature of Ce3+ cation facilitated the deꢀinsertion reaction to
as 1ꢀpentafluorophenyl isocyanate, PhF−N=C=O (
4). The yield yield organic products. We expect the above results will
of reaction was estimated to be 70% by NMR integration using facilitate the understanding of reactions between lanthanide
1ꢀfluorobenzene as an internal standard. The formation of amides and heteroallenes. Development of closed synthetic
PhF−N=C=O was rationalized as the result of deꢀinsertion cycles employing supporting ligands for cerium complexes is
reaction to eliminate isocyanate, driven by the oxoꢀphilicity of currently underway.
Ce3+ cation after initial insertion of CO2 into a Ce−N bond and
Acknowledgements
migration of the –SiMe3 group to one of the oxygen atoms
(Scheme 1). Such insertion, silyl migration and deꢀinsertion
reactions of metal silylamides with CO2 have been previously
observed for other metal cations, including UIII, TiIV, ZrIV, NiI,
RhI, ZnII, SnII and GeII cations.12, 18 For example, the reaction
of group IV amides, M[N(SiMe3)2]2 (M = Sn or Ge) with CO2
led to the formation of Me3Si−N=C=O and [M(OSiMe3)2]2
byproduct.12a The resulting [M(OSiMe3)2]2 was also shown to
readily form oxoꢀbridged clusters, Sn6(ꢁ3ꢀO)4(ꢁ3ꢀOSiMe3)4 with
concomitant loss of (Me3Si)2O upon heating.12c The
thermodynamic preference of forming metal silyloxides
through deꢀinsertion reactions was also exemplified by the
reaction between zirconium silanimine (C5H5)2Zr(η2ꢀ
SiMe2=NtBu) and CO2, leading to the formation of
[(C5H5)2Zr(cycloꢀOSiMe2NtBu)]2.19 In our case, the reaction is
expected to produce aggregates of “Ce(OSiMe3)3”. The
corresponding CeIII aggregates were not identified however,
due to their complicated oligomerization process.
We gratefully acknowledge University of Pennsylvania and the
U.S. Department of Energy, Office of Basic Energy Sciences,
Early Career Research Program (DEꢀSC0006518) for financial
support and the U.S. NSF for support of the Xꢀray
diffractometer (Grant CHEꢀ0840438).
Notes and references
1.
M. F. Lappert, A. V. Protchenko, P. P. Power and A. L. Seeber,
Metal Amide Chemistry, John Wiley & Sons, Hoboken, 2008,
pp.85.
2.
T. E. Müller, K. C. Hultzsch, M. Yus, F. Foubelo and M. Tada,
Chem. Rev., 2008, 108, 3795ꢀ3892.
3.
4.
J. Zhang and X. Zhou, Dalton Trans., 2011, 40, 9637ꢀ9648.
(a) H. Li, Y. Yao, Q. Shen and L. Weng, Organometallics, 2002,
21, 2529ꢀ2532; (b) Q. Shen and Y. Yao, J. Organomet. Chem.,
2002, 647, 180ꢀ189.
5.
6.
W. J. Evans, C. H. Fujimoto and J. W. Ziller, Organometallics,
2001, 20, 4529ꢀ4536.
We were also interested in investigating the reactions of a
cerium(III) amide with mixed heteroatom substrates, including
isocyanates and isothiocyanates. Reaction of 3 equiv 1ꢀ
(a) J. Zhang, R. Cai, L. Weng and X. Zhou, Organometallics,
2003, 22, 5385ꢀ5391; (b) J. Zhang, F. Han, Y. Han, Z. Chen and
X. Zhou, Dalton Trans., 2009, 1806ꢀ1811; (c) L. Ma, J. Zhang, R.
Cai, Z. Chen, L. Weng and X. Zhou, J. Organomet. Chem., 2005,
690, 4926ꢀ4932; (d) J. Zhang, L. Ma, Y. Han, F. H. Z. Zhang, R.
Cai, Z. Chen and X. Zhou, Dalton Trans., 2009, 3298ꢀ3305; (e) J.
Zhang, R. Cai, L. Weng and X. Zhou, J. Organomet. Chem.,
2003, 672, 94ꢀ99; (f) J. Zhang, R. Cai, L. Weng and X. Zhou,
Organometallics, 2004, 23, 3303ꢀ3308; (g) L. Zhou, Y. Yao, Y.
Zhang, M. Xue, J. Chen and Q. Shen, Eur. J. Inorg. Chem., 2004,
2167ꢀ2172; (h) C. Pi, Z. Zhang, Z. Pang, J. Zhang, J. Luo, Z.
Chen, L. Weng and X. Zhou, Organometallics, 2007, 26, 1934ꢀ
1946; (i) C. Pi, Z. Zhu, L. Weng, Z. Chen and X. Zhou, Chem.
Commun., 2007, 2190ꢀ2192; (j) J. Tu, W. Li, M. Xue, Y. Zhang
and Q. Shen, Dalton Trans., 2013, 42, 5890ꢀ5901; (k) W. Yi, S.
Huang, J. Zhang, Z. Chen and X. Zhou, Organometallics, 2013,
32, 5409ꢀ5415; (l) X. Xu, Z. Zhang, Y. Yao, Y. Zhang and Q.
Shen, Inorg. Chem., 2007, 46, 9379ꢀ9388; (m) P. Cui, Y. Chen, G.
admantyl isocyanate (Ad−N=C=O) with
1 resulted in near
quantitative formation of an organic product as suggested by
1
the sharp and diamagnetic H and 19F NMR resonances. The
identity of the product,
5, was indicated as a carbodiimide,
Ad−N=C=N−PhF, by an intense absorption band at 2156 cmꢀ1
observed in the IR spectrum. This assignment was confirmed
by highꢀresolution mass spectroscopy (HRMS) and 13C NMR
spectroscopy
characterization
after
isolation
of
Ad−N=C=N−PhF through recrystallization from hexanes in
92% yield. The formation of this product could also be
explained by the threeꢀstep reaction pathway (Scheme 1),
consistent with postulated pathways for the reactions of
isocyanate with RhI, SnII and AlIII silyl amide complexes.11, 18g,
20
Similarly, reaction of 3 equiv 1ꢀadmantylꢀisothiocyanate
(Ad−N=C=S) with
1
in toluene for 12 h led to the isolation of
in both cases
same product, in 51% yield. The formation of
5
5
is attributable to the large steric profile of admantyl groups
This journal is © The Royal Society of Chemistry 2012
Chem. Commun., 2016, 00, 1-3 | 3

ChemComm
Page 4 of 4
View Article Online
COMMUNICATION
DOI: 10.1C0h39e/mC6.CCCo0m371m9Dun.
Li and W. Xia, Angew. Chem., Int. Ed., 2008, 47, 9944ꢀ9947; (n)
J. Zhang, Y. Han, F. Han, Z. Chen, L. Weng and X. Zhou, Inorg.
Chem., 2008, 47, 5552ꢀ5554; (o) C. Wang, X. Zhang, M. Xue, Y.
Zhang and Q. Shen, Dalton Trans., 2013, 42, 7009ꢀ7018.
(a) J. Zhang, R. Cai, Z. Chen and X. Zhou, Inorg. Chem., 2006,
46, 321ꢀ327; (b) Y. Han, J. Zhang, F. Han, Z. Zhang, L. Weng
and X. Zhou, Organometallics, 2009, 28, 3916ꢀ3921.
7.
8.
9.
(a) S. Ozaki, Chem. Rev., 1972, 72, 457ꢀ496; (b) A. Williams and
I. T. Ibrahim, Chem. Rev., 1981, 81, 589ꢀ636.
(a) Y. Ito, T. Hirao and T. Saegusa, J. Org. Chem., 1975, 40,
2981ꢀ2982; (b) T. Kiyoi, N. Seko, K. Yoshino and Y. Ito, J. Org.
Chem., 1993, 58, 5118ꢀ5120.
10.
11.
D. J. Mindiola and G. L. Hillhouse, Chem. Commun., 2002, 1840ꢀ
1841.
(a) J. R. Babcock and L. R. Sita, J. Am. Chem. Soc., 1998, 120,
5585ꢀ5586; (b) J. R. Babcock, L. LiableꢀSands, A. L. Rheingold
and L. R. Sita, Organometallics, 1999, 18, 4437ꢀ4441.
(a) L. R. Sita, J. R. Babcock and R. Xi, J. Am. Chem. Soc., 1996,
118, 10912ꢀ10913; (b) C. A. Stewart, D. A. Dickie, B. Moasser
and R. A. Kemp, Polyhedron, 2012, 32, 14ꢀ23; (c) L. R. Sita, R.
Xi, G. P. A. Yap, L. M. LiableꢀSands and A. L. Rheingold, J. Am.
Chem. Soc., 1997, 119, 756ꢀ760.
12.
13.
(a) H. Yin, A. J. Lewis, U. J. Williams, P. J. Carroll and E. J.
Schelter, Chem. Sci., 2013, 4, 798ꢀ805; (b) H. Yin, A. J. Lewis, P.
Carroll and E. J. Schelter, Inorg. Chem., 2013, 52, 8234ꢀ8243; (c)
H. Yin, J. R. Robinson, P. J. Carroll, P. J. Walsh and E. J.
Schelter, Chem. Commun., 2014, 50, 3470ꢀ3472; (d) H. Yin, P. J.
Carroll and E. J. Schelter, Inorg. Chem., 2016, 55, 5684ꢀ5692.
(a) H. Plenio, Chem. Rev., 1997, 97, 3363; (b) H. Plenio,
ChemBioChem, 2004, 5, 650ꢀ655; (c) H. Yin, A. V. Zabula and E.
J. Schelter, Dalton Trans., 2016, 45, 6313ꢀ6323.
14.
15.
16.
K. C. Mullane, A. J. Lewis, H. Yin, P. J. Carroll and E. J.
Schelter, Inorg. Chem., 2014, 53, 9129ꢀ9139.
(a) A. F. Maddox, K. A. Erickson, J. M. Tanski and R. Waterman,
Chem. Commun., 2011, 47, 11769ꢀ11771; (b) M. L. Cole and P.
C. Junk, Dalton Trans., 2003, 2109ꢀ2111.
17.
18.
T.ꢀG. Ong, G. P. A. Yap and D. S. Richeson, J. Am. Chem. Soc.,
2003, 125, 8100ꢀ8101.
(a) P. L. Arnold, Z. R. Turner, A. I. Germeroth, I. J. Casely, G. S.
Nichol, R. Bellabarba and R. P. Tooze, Dalton Trans., 2013, 42,
1333ꢀ1337; (b) C. Camp, L. Chatelain, C. E. Kefalidis, J. Pecaut,
L. Maron and M. Mazzanti, Chem. Commun., 2015, 51, 15454ꢀ
15457; (c) S. Ciruelos, T. Cuenca, R. Gómez, P. GómezꢀSal, A.
Manzanero and P. Royo, Organometallics, 1996, 15, 5577ꢀ5585;
(d) L. Kloppenburg and J. L. Petersen, Organometallics, 1996, 15,
7ꢀ9; (e) B. C. Fullmer, H. Fan, M. Pink and K. G. Caulton, Inorg.
Chem., 2008, 47, 1865ꢀ1867; (f) M. T. Whited, A. J. Kosanovich
and D. E. Janzen, Organometallics, 2014, 33, 1416ꢀ1422; (g) M.
T. Whited, L. Qiu, A. J. Kosanovich and D. E. Janzen, Inorg.
Chem., 2015, 54, 3670ꢀ3679; (h) W. Sattler and G. Parkin, J. Am.
Chem. Soc., 2011, 133, 9708ꢀ9711.
19.
20.
L. J. Procopio, P. J. Carroll and D. H. Berry, Organometallics,
1993, 12, 3087ꢀ3093.
T. Sakakibara, T. Hirabayashi and Y. Ishii, J. Organomet. Chem.,
1972, 46, 231ꢀ242.
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 2012