C1-symmetric β-Diketiminatoiron(II) Complexes for Hydroamination of Primary Alkenylamines

Article abstract of DOI:10.1002/adsc.201801464

The synthesis and solid-state characterization of an array of well-defined low-coordinate C₁-symmetric β-diketiminatoiron(II) alkyl complexes B₃–B₆ featuring steric and electronic variations on one of the N-aryl substituen

Full text of DOI:10.1002/adsc.201801464

Title: <i>C₁</i>-symmetric β-Diketiminatoiron(II)
Complexes for Hydroamination of Primary Alkenylamines
Authors: Clément Lepori, Regis Guillot, and Jérôme Hannedouche
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10.1002/adsc.201801464
Advanced Synthesis & Catalysis
COMMUNICATION
DOI: 10.1002/adsc.201((will be filled in by the editorial staff))
C1-symmetric -Diketiminatoiron(II) Complexes for
Hydroamination of Primary Alkenylamines
Clément Lepori,a Régis Guillota and Jérôme Hannedouchea,b*
a
Institut de Chimie Moléculaire et des Matériaux d’Orsay, UMR 8182, Université Paris-Sud, Université Paris-Saclay,
rue du doyen Georges Poitou, Orsay, F-91405 (France). E-mail: jerome.hannedouche@u-psud.fr
CNRS, Orsay, F-91405 (France)
b
Received: ((will be filled in by the editorial staff))
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201######.((Please
delete if not appropriate))
electrophilic amine partners and/or the use of a large
an array of well-defined low-coordinate C1-symmetric excess of reducing agent are detrimental to the step
Abstract. The synthesis and solid-state characterization of
diketiminatoiron(II) alkyl complexes B3-B6 featuring
steric and electronic variations on one of the N-aryl
substituents of the diketiminate ligand scaffold are
reported. All complexes display unique catalytic abilities of
promoting the selective exo-cyclohydroamination of
unprotected 2,2-diphenylpent-4-en-1-amine (1a) under
and atom efficiency of the overall process. Therefore
there is still a need to tackle the search for efficient
earth-abundant, first-row late transition metal
catalysts for direct N-H bond addition of simple
amines on alkenes under functional group-free
manipulation and co-reagent-free conditions. In this
context, our group has reported the first examples of
iron(II)- and cobalt(II)-mediated alkene exo-
cyclohydroamination of electronically unbiased
primary amines using structurally-defined C2-
symmetric low-coordinate -diketiminatometal alkyl
complexes under mild reaction conditions (Scheme 1
a) for iron).[2c,d,3b,6] Inspired by our comprehensive
mechanistic investigations conducted recently on iron
systems[2d] and a precedent DFT study,[7] we have
synthesized and herein report well-defined C1-
symmetric -diketiminatometal alkyl complexes with
significantly improved catalytic activity and
hydroamination selectivity in the cyclization of
primary alkenylamines (Scheme 1 b)).
mild reactions conditions. The incorporation of
a
potentially coordinative ortho-methoxy substituent on one
of the N-aryl rings of the -diketiminate skeleton, in
conjunction with a more crowded 2,6-diisopropylphenyl
group on the other, affords a far more active catalyst (B3)
than our previously reported C2-symmetric -
diketiminatoiron(II)alkyl complex
B
(Ar1=Ar2=2,4,6-
(Me)3C6H2)/cyclopentylamine system. Comparative studies
let us postulate that this superior activity of B3, when
compared with B4-B6, is likely arising from steric effects
and/or the coordinating ability of the ortho-methoxy
substituent. The scope and limitations of this novel C1-
symmetric diketiminatoiron(II) alkyl complex B3 are
also presented.
Keywords: Hydroamination; Iron; Alkenes; Amines;
Catalyst Design
In the last decades, the catalytic alkene
hydroamination reaction has emerged as an appealing
methodology for the synthesis of important N-
containing building blocks from relative inexpensive
and ubiquitous amines and alkenes as starting
materials.[1] The recent interest for sustainable
catalysis has prompt the development of
hydroamination catalytic systems based on first row
late transition metal of high availability, low price
and relatively low toxicity. At present, noteworthy
advances in this nascent field have be gained by
systems derived from iron,[2] cobalt,[3] copper[4] and
zinc[5] metal thanks to classical N-H addition and
alternative formal approaches such as electrophilic
amination[2e,4b-e] or hydrogen-atom[2f-h,3a] transfer.
Although these formal approaches have significantly
broaden the reaction scope and unlocked some
unresolved issues, the requirement for sophisticated
Scheme 1. Previous work on iron-catalyzed N-H addition
on unactivated alkenes and this work.
1
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10.1002/adsc.201801464
Advanced Synthesis & Catalysis
In the course of our investigations towards the
development of efficient and selective iron-based
hydroamination catalysts, we established that the
selectivity of the cyclohydroamination reaction
catalyzed by our designed C2-symmetric -
diketiminatoiron(II)
alkyl
complex
B
(Ar1=Ar2=2,4,6-(Me)3C6H2 in Scheme 1) could be
enhanced, in favor of the hydroamination product, by
the addition of a catalytic amount of a noncyclizable
primary amine, such as cyclopentylamine to the
reaction media.[2c] As underscored by our depth
mechanistic studies, the reaction selectivity likely
results from the competition of pathways for rate-
limiting aminolysis (that affords the hydroamination
product) and -H elimination (that leads to the
formation of the oxidative amination product and the
reduced starting material).[2d] This selectivity
enhancement may originate from the participation of
the non-cyclizable amine addition in the turnover-
limiting aminolysis step.
Scheme 2. General two-step metathetic procedure of well-
defined iron(II) alkyl complexes [L2-6FeCH2SiMe3(THF)]
(B2-6
) from 1,3-diketimines ligands HL2-6. Reaction
conditions: 1. a) nBuLi (1 equiv), THF, 78 °C to 25°C, b)
FeCl2 (1 equiv), 25 °C; 2. a) LiCH2SiMe3 (1 equiv), Et2O,
25 °C, b) recrystallization hexane/THF, isolated yields for
B2 (0%), B3 (45%), B4 (52%), B5 (47%), B6 (72%).
Our initial efforts were focused on the two-step
metathesis synthesis of complex B2 stabilized by the
-diketiminate ligand L2 (Figure 1) bearing ortho-
methoxy substituents on the N-aryl rings as
potentially coordinating groups (Scheme 2). However,
despite the formation and solid-state characterization
,[8]
of the ate complex intermediate A2 all the attempts
to obtain the corresponding alkyl complex B2 were
unsuccessful.[9] Indeed, room-temperature metathesis
reaction of A2 with LiCH2SiMe3 leads to the isolation
of homoleptic complex C2 (Figure 2) as red crystals
in 35% yield (from 50% theoretical yield) after cold
recrystallization. Solid-state analysis of a single
crystal reveals a five-coordinated iron atom adopting
a distorted square pyramid geometry and in-plane
coordinated by one methoxy group of the N-aryl rings
(Figure 2).[8,10]
Figure 1. 1,3-diketimines ligands used in this study.
However, although the usage of this additive was
effective to achieve high selectivity, it was done at
the expense of the catalyst performance as a
prolonged reaction time was needed to reach full
conversion. To circumvent this drawback in catalyst
reactivity, we have explored an alternative strategy
based on the rational modification of the structure of
the ligand to preserve the high hydroamination
selectivity. Our goal was to seek for modification of
the -diketiminate structure that results in the
inhibition of the unwanted -hydride elimination. As
demonstrated by our comprehensive DFT
mechanistic investigations, the rival and facile-H
elimination pathway evolves through two-spin
crossover transitions, from both reactant and product
adopting a pseudo-tetrahedral geometry in a high
(quintet) spin state.[2d] The -H elimination requires a
pseudo quasi-planar geometry around the metal
center in the transition state. The first spin-crossover
to a lower (triplet) spin state will deliver the
mandatory empty d orbital to accept the incipient
hydride’s two electrons. A previous computational
study has revealed that the increase in steric demands
around the metal center disfavors the crucial low spin
transition state structure energetically.[7] With these
considerations in mind, we envisioned to explore the
coordinative ability of the -diketiminate ligand
aimed at enhancing steric bulk around the iron center.
Figure 2. Structure of homoleptic complex C2 and its
ORTEP diagram showing 30% probability ellipsoids.
Hydrogen atoms are omitted for clarity.
Although the synthesis of complex B2 was not
reached, the solid-state structure of C2 highlights the
ability of the ortho-methoxy substituents of the N-
aromatic groups to bind to the metal center and
potentially increase its coordination number. The
formation of C2 may arise from
a
ligand
redistribution resulting from the poor bulkiness of the
-diketiminate ligand L2. Such phenomenon has been
previously observed during the course of the
synthesis of -diketiminatometal complexes bearing
low substituted phenyl rings on the ligand nitrogen
atoms.[11] To address the ligand redistribution
reactivity observed during the complex synthesis, we
2
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10.1002/adsc.201801464
Advanced Synthesis & Catalysis
turned our attention to the preparation of iron(II)
alkyl complex B3 stabilized by a C1-symmetric -
diketiminate ligand having an ortho-methoxyphenyl
ring on one N atom and the more crowded 2,6-
diisopropylphenyl group on the other (Scheme 2).
Reaction of FeCl2 and the lithium salt of ligand HL3
(Figure 1) affords the ate complex A3 as confirmed
by X-ray diffraction analysis.[8] To our delight,
subsequent metathesis reaction of A3 with
LiCH2SiMe3 results, after cold recrystallization, in
the isolation of red crystals of B3 in 45% yield. X-ray
diffraction analysis of a single crystal of B3 shows a
It is worth noting that our previously reported
complex B (Ar1=Ar2=2,4,6-(Me3)C6H2) affords under
these conditions similar yield to B1.[2c,d] This
underlines the improvement of efficiency achieved
with C1-symmetric -diketiminatoiron(II) alkyl
complex B3 bearing one ortho-methoxyphenyl ring
over our previous C2-symmetric family of complexes.
To gain more insight upon the impact of the
electronic/steric ligand effects on the catalyst
efficiency, complexes B4 and B5 featuring para-
methoxyphenyl and phenyl groups, respectively, on
one of the -diketiminate N centers have been
synthesized (Scheme 2). Their molecular solid-state
structures and those of intermediates A4-5 were
confirmed by X-ray crystallography.[8] As revealed
from Figure 4, complexes B4 and B5 perform
similarly, but somewhat inferior as B3, whilst the
hydroamination selectivity achieved at >90 %
conversion is comparable in all three cases. At first
glance, the apparent absence of a noticeable
electronic effect of the para-methoxy substituent (B4)
upon the catalyst performance relative to B5 without a
methoxy substituent may seem counter-intuitive. A
closer look at the solid-state structure of complex B4
reveals that the para-methoxyphenyl ring is almost
perpendicularly aligned to the -diketiminatoiron
core.[8] As a consequence, there is no real prospect of
conjugative -orbital interactions between the para-
methoxyphenyl ring and the nitrogen nonbonding -
orbital. This may give rise to a rather small electronic
perturbation caused by the para-methoxy substituent
and thus rationalizing the similar catalytic behavior of
B4 and B5. A comparable catalytic efficiency was also
observed for alkyl complex B6 with a strong
four-coordinate iron atom having
a
trigonal-
pyramidal coordination geometry, similarly to our
previously reported complex B[2c] (Ar1=Ar2=2,4,6-
(Me3)C6H2 in Scheme 1) (Figure 3).[8]
electronic-withdrawing
3,5-
Figure 3. ORTEP diagram of complex B3 showing 30%
probability ellipsoids. Hydrogen atoms are omitted for
clarity.
bis(trifluoromethyl)phenyl substituent on one of its
nitrogen atoms (Figure 4). Based upon these
observations, we postulate that the superior activity
of B3, when compared with B4-6, is likely arising from
steric effects and/or the coordinating ability of the
ortho-methoxy substituent.
The catalytic efficiency of B3 was next evaluated in
the cyclization of benchmark aminoalkene 1a
(Scheme 3). As clearly shown in Figure 4, B3
performs distinctly better than C2-symmetric -
diketiminatoiron(II) alkyl complex B1 having only
2,6-diisopropyl substituents on both N-aryl groups of
the ligand as far as activity and selectivity towards
the hydroamination product (defined as (%)=[2a (%)
/ (2a (%) + 3a(%) + 4a (%)] are concerned. Indeed, a
cycloamine yield of 93% with a selectivity of 95%
can be achieved after only 250 min for B3, whereas
merely a 42% yield is reached with B1 (Figure 4).
Figure 4. Dependence of the conversion (%) over time for
the cyclization of 1a catalyzed by complexes B3-6 and B1.
Selectivity towards the hydroamination product (%)=[2a
(%) / (2a (%) + 3a(%) + 4a (%)] in parentheses at > 90%
conversion.
Scheme 3. Cyclization of benchmark aminoalkene 1a into
2a catalyzed by complexes B3-B6 and B1.
3
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10.1002/adsc.201801464
Advanced Synthesis & Catalysis
Encouraged by the better ability of B3 to selectively
promote the cyclization of benchmark substrate 1a,
the cyclohydroamination of various primary
aminoalkenes featuring different substitution patterns
on the alkyl chain and the alkene component or an
auxiliary functional group was examined. This
substrate scope study was performed as described in
Table 1. Under our optimized reaction conditions
(90 °C, toluene, 24 h), a variety of gem-disubstituted
aminoalkenes were suitably converted into the
corresponding five- and six-membered rings which
were isolated in moderate to excellent yields. In
almost all cases studied (excluded 1b and 1d), shorter
reaction times (24 h) are needed with B3 to observe a
comparable cyclization outcome than with our
and featuring the cyclization of 1-aminopentene and
1-aminohexene in 76 and 77% NMR yield
respectively.[13] This isolated example highlights the
challenge associated with the hydroamination of this
type of substrates. The presence of a para-fluoro
substituent on a phenyl group attached on the alkene
moiety as in 1f does not influence the outcome of the
cyclization affording the corresponding products with
high conversion. Surprisingly, and in contrast to
B/cyclopentylamine catalytic systems,[2c] complex B3
does not provide pyrrolidine 2b during the cyclization
of (1-allylcyclohexyl)methanamine (1b) and only the
product resulting from alkene isomerization of the
starting material was detected. To a lesser extent,
such alkene isomerization was also detected during
previously
reported
catalytic
system
the
cyclization
of
1b
promoted
by
B/cyclopentylamine,[2c] as it was observed for the
reaction of 1a.
[Ir(COD)Cl]2/HNEt3Cl catalytic system.[12] The same
event is also observed with 2,2-dimethylpent-4-en-1-
amine (1d). This alternative isomerization reactivity
has been previously noticed by others as the major
reactivity when the cyclohydroamination was not
favored.[13] As mentioned early on and in contrast to
previously reported [Ir(COD)Cl]2/HNEt3Cl[12] and
Table 1. Scope of the cyclohydroamination of primary
aminoalkenes
promoted
by
C1-symmetric
diketiminatoiron(II) complex B3.a,b)
[Rh(COD)2]BF4/Xantphos-based
ligand[13]
combination, which are part of the rare examples of
late d-block metal hydroamination catalysts
compatible with unprotected primary amines, trace of
olefin isomerization of the starting aminoalkene was
not detected during the cyclization of other substrates
promoted by -diketiminatoiron(II) complexes. In the
quest to establish the scope and limitations of our
current systems, we turned our attention to the
cyclization of another challenging class of substrates
that are primary amines tethered to 1,2-di-substituted
alkenes. Unfortunately, despite our numerous efforts,
no trace of product was detected during the course of
the reaction of 2,2-diphenylhex-4-en-1-amine (R1 =
Ph, R2 = Me, R3 = H for 1 in Table 1) promoted by
our various catalytic systems. To the best of our
knowledge, the cyclohydroamination of this class of
aminoalkenes has never been reported by a first-row
late transition metal catalyst, and rarely been
accomplished by noble metal catalytic systems
compatible with primary amines.[14,15] Our iron-based
methodology is not restricted to primary
aminoalkenes as it is also well-suited for the exo-
cyclization of primary aminoallenes. Indeed, under
the reaction conditions, the hydroamination of 6-
a) Reaction conditions: B3 (10 mol%), 24 h unless
otherwise stated. b) RMN yield determined by in situ H
NMR spectroscopy using ferrocene (0.4 equiv) as internal
standard and isolated yields in parentheses unless
otherwise stated. c) Determined by GC analysis. d) NMR
yield of isomerization of starting material.
1
While our methodology is efficient for the selective
cyclohydroamination
of
gem-disubstituted
methyl-2,2-diphenylhepta-4,5-dien-1-amine
(1h)
aminoalkenes having a less pronounced Thorpe-
Ingold effect substitution than with diphenyl such as
substrates 1c, 1f or 1g, more challenging substrates
unbiased toward cyclization by the chain substituents,
such as 5-phenylpent-4-en-1-amine are not converted
under our reaction conditions. This observation is in
keeping with other late d-block catalytic systems
compatible with primary amines such as the
[Ir(COD)Cl][12] or the Cu(OtBu)/Xantphos[4a] systems.
To our knowledge, the late-transition metal-mediated
hydroamination of this class of primary aminoalkenes
lacking geminal disubstitution on the alkyl backbone
occurs efficiently affording the corresponding
products (2h) in 80% isolated yield. This substrate
offers the advantage of featuring a C-C double bond
which is set for further potential functionalization.
In summary, we have reported the synthesis and
solid-state characterization of a variety of well-
defined
low-coordinate
C1-symmetric
diketiminatoiron(II) alkyl complexes B3-B6
featuring steric and electronic variations on one of the
N-aryl substituents of the diketiminate ligand
scaffold. All these low-coordinate complexes exhibit
is limited to
a
single report using the
abilities
of
mediating
the
selective
[Rh(COD)2]BF4/Xantphos-based ligand combination
4
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10.1002/adsc.201801464
Advanced Synthesis & Catalysis
= 0.6 mM-1.cm-1). IR (cm-1): 3009, 2961, 2865, 1500,
cyclohydroamination of 2,2-diphenylpent-4-en-1-
amine (1a) under mild reactions conditions. This
study has shown that introducing a potentially
coordinative ortho-methoxy substituent on one of the
N-aryl rings of the -diketiminate skeleton, in
1
1437, 1375, 1241, 1179, 1037, 885, 850. H NMR (250
MHz, C6D6, RT) δ 112.9 (br s, 1H, CH), 79.3 (br s, 3H,
Me), 74.7 (br s, 3H, Me), 40.4 (br s, 9H, SiMe3), 3.0 (br s,
2H, THF), 2.2 (s, 2H, THF), 1.3 (s, 2H, THF), 0.9 (s, 2H,
THF), 4.8 (br s, 3H, MeO Ar), 7.8 (s, 2H, m-H Ar),
10.2 (s, 2H, m-H Ar), 15.5 (s, 6H, CHMeMe), 67.3 (s,
1H, p-H Ar), 92.9 (br s, 6H, CHMeMe), 128.8 (br s, 2H,
o-H Ar).
conjunction
with
a
more
crowded
2,6-
diisopropylphenyl group on the other, provides a
noteworthy more active and selective iron catalyst
(B3) for the cyclization of benchmark substrate 1a.
Indeed, a hydroamination selectivity of 95% is
reached at 93% conversion of 1a after only 250 min
of reaction with this catalyst. A prolonged reaction
time (up to 48h) was previously required with our
General
procedure
for
the
catalytic
cyclohydroamination of primary alkenylamines
catalyzed by complex B3: To a screw-capped tube
equipped with a stir-bar were added the appropriate amine
(0.18 mmol), ferrocene (13.4 mg, 0.072 mmol) and
complex (0.018 mmol). The volume of the tube was
completed to 190 L by toluene-d8. The screw-capped tube
was placed in an oil bath at 90 °C for 24 h and next
formerly
reported
catalytic
system
1
B/cyclopentylamine to reach such high selectivity
under similar reaction conditions. Comparative
studies let us postulate that this superior reactivity of
B3, when compared with B4-6, may arise from the
coordinating ability and/or steric bulk of the ortho-
exposed to air. The yield was determined by H NMR
spectroscopy analysis of an aliquot of the reaction using
ferrocene as internal standard. The appropriate amine was
purified as described in the Supporting Information.
methoxy substituent. This study will provide Acknowledgements
foundations to design more efficient first-row late
Financial supports from MENSR, Univ Paris Sud and the CNRS,
transition metal catalysts for direct N-H bond
addition of unprotected primary amines on
unactivated alkenes by further rational modification
of the diketiminate ligand scaffold. Further work
to do so are ongoing.
are gratefully acknowledged
References
[1] a) L. Huang, M. Arndt, K. Gooßen, H. Heydt, L. J.
Gooßen, Chem. Rev. 2015, 115, 2596-2697; b) E.
Bernoud, C. Lepori, M. Mellah, E. Schulz, J.
Hannedouche, Catal. Sci. Technol. 2015, 5, 2017-2037;
c) C. Lepori, J. Hannedouche, Synthesis 2017, 49,
1158-1167.
Experimental Section
Synthesis of complex [L3Fe(-Cl)2Li(THF)2] (A3): n-
BuLi (1.3 mL, 3.25 mmol) was added to a stirred solution
of
2-(2,6-diisopropylphenylimino)-4-(2-methoxy
phenylimino)pentane (HL3) (1.184 g, 3.25 mmol) in THF
(10 mL) at 78 °C. The cooling was removed 30 min after
addition. The resulting light yellow solution was stirred for
2 h at room temperature and FeCl2 was added (0.412 g,
3.25 mmol). The solution was stirred overnight and the
solvent was removed until dryness. The resulting brown
solid was washed with hexane (2 x 10 mL) and extracted
with Et2O (2 x 10 ml). The brown solution was
concentrated and cooled to 20 °C to afford A3 as yellow
crystals (0.915 g, 1.43 mmol, 44%). Anal. Calcd for
C32H47Cl2FeLiN2O3: C, 59.92; H, 7.39; N, 4.58. Found: C,
59.73; H 6.15; N 4.54. Evans µeff (THF-d8, 298 K) = 5.9 µB.
UV-vis (toluene, nm): 339 (ɛ = 17 mM-1.cm-1), 427 (ɛ = 2.1
mM-1.cm-1), 474 (ɛ = 0.53 mM-1.cm-1). IR (cm-1): 3011,
2961, 2866, 1525, 1490, 1439, 1392, 1359, 1245, 1211,
1046, 743. 1H NMR (250 MHz, C6D6-50 µL THF-d8, RT) δ
19.5 (s, 1H, m-H Ar), 16.9 (s, 2H, m-H Ar), 16.0 (s, 1H, m-
H Ar), 4.4 (s, 8H, THF), 1.7 (s, 8H, THF), 0.9 (br s, 6H,
CHMeMe), 10.6 (s, 3H, MeO Ar), 20.8 (br s, 6H,
CHMeMe), 40.7 (br s, 3H, Me2CH and CH), 49,7 (s, 1H,
p-H Ar), 55,3 (s, 1H, p-H Ar), 70.1 (s, 3H, Me), 70.4 (s,
[2] For a selection of iron-catalyzed alkene hydroamidation
of tosylamines: a) K. Komeyama, T. Morimoto, K.
Takaki, Angew. Chem. Int. Ed. 2006, 45, 2938-2941; b)
J. Michaux, V. Terrasson, S. Marque, J. Wehbe, D.
Prim, J.-M. Campagne, Eur. J. Org. Chem. 2007, 2601-
2603. For iron-catalyzed alkene hydroamination of
primary amines: c) E. Bernoud, P. Oulié, R. Guillot, M.
Mellah, J. Hannedouche, Angew. Chem. Int. Ed. 2014,
53, 4930-4934; d) C. Lepori, E. Bernoud, R. Guillot, S.
Tobisch, J. Hannedouche Chem. Eur. J. doi:
10.1002/chem.201804681. For iron-promoted formal
alkene hydroamination: e) C. B. Huehls, A. Lin, J.
Yang, Org. Lett. 2014, 16, 3620-3623; f) J. Gui, C.-M.
Pan, Y. Jin, T. Qin, J. C. Lo, B. J. Lee, S. H. Spergel,
M. E. Mertzman, W. J. Pitts, T. E. La Cruz, M. A.
Schmidt, N. Darvatkar, S. Natarajan, P. S. Baran,
Science 2015, 348, 886-891; g) C. Obradors, R. M.
Martinez, R. A Shenvi. J. Am. Chem. Soc. 2016, 138,
4962-4971; h) K. Zhu, M. P. Shaver, S. P. Thomas,
Chem. Asian J. 2016, 11, 977-980; i) K. Zhu, M. P.
Shaver, S. P. Thomas, Chem. Sci. 2016, 17, 3031-3035.
7
3H, Me), 119.4 (br s, 1H, o-H Ar). Li NMR (117 MHz,
C6D6-50μL THF-d8, RT) δ 266.6 (br s).
Synthesis of complex [L3FeCH2TMS·THF] (B3):
LiCH2TMS (0.147 g, 1.56 mmol) was added as a solid to a
stirred yellow solution of A3 (1.0 g, 1.56 mmol) in Et2O (5
mL) at 25 °C. The solution turns red immediately and a
white precipitate appeared. After overnight stirring, the
solvent was removed under reduced pressure. The red
brown solid was extracted with hexane (2 x 5 mL). The red
solution was concentrated and cooled to 20 °C after THF
addition (0.1 mL) to afford B3 as red crystals (0.467 g,
0.807 mmol, 52%). Anal. Calcd for C32H50FeN2O2Si: C,
66.42; H, 8.82; N, 5.11. Found: C, 65.93; H 8.61; N 5.05.
Evans µeff (THF-d8, 298 K) = 5.6 µB. UV-vis (toluene,
nm): 291 (ɛ = 9.9 mM-1.cm-1), 333 (ɛ = 15.3 mM-1.cm-1),
377 (ɛ = 5.6 mM-1.cm-1), 440 (ɛ = 0.94 mM-1.cm-1), 496 (ɛ
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5
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10.1002/adsc.201801464
Advanced Synthesis & Catalysis
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6
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COMMUNICATION
C1-symmetric -Diketiminatoiron(II) Complexes
for Hydroamination of Primary Alkenylamines
Adv. Synth. Catal. Year, Volume, Page – Page
Clément Lepori, Régis Guillot, Jérôme
Hannedouche*
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