Half-Sandwich Manganese Complexes Bearing Cp Tethered N-Heterocyclic Carbene Ligands: Synthesis and Mechanistic Insights into the Catalytic Ketone Hydrosilylation

Article abstract of DOI:10.1021/acs.organomet.6b00785

Manganese(I) complexes [(Cp(CH₂)_nNHC^Mes)Mn(CO)₂] (2a, n = 1; 2b, n = 2) bearing Cp tethered NHC ligands have been prepared in good yield from [CpMn(CO)₃] and N-mesitylimidazole as main components, using a novel synthetic strategy based on the anchoring of an imidazolium moiety to the coordinated Cp ligand, followed by an intramolecular photochemical CO substitution for the pendent NHC moiety generated in situ upon addition of a base. The catalytic performances of 2a-b in the hydrosilylation of 2-acetonaphthone with Ph₂SiH₂ were found to be essentially indifferent to the length of the linker between the Cp and the NHC moieties, and lower than the one of the nontethered [Cp(CO)₂Mn(IMes)] (1) parent complex. Still, the presence of Cp tethered NHC ligands allowed isolation and full characterization of monocarbonyl η²-silane complexes [(Cp(CH₂)_nNHC^Mes)Mn(CO)(η²-H-SiHPh₂)] (8a, n = 1; 8b, n = 2), which are generated upon photochemical reactions of 2a-b with diphenylsilane. Both of these silane complexes are inactive for the catalytic 2-acetonaphthone hydrosilylation process but were found to form catalytically active noncarbonyl species under UV irradiation, being consistent with the Ojima mechanism for ketone hydrosilylation.

Full text of DOI:10.1021/acs.organomet.6b00785

Article
pubs.acs.org/Organometallics
Half-Sandwich Manganese Complexes Bearing Cp Tethered
N‑Heterocyclic Carbene Ligands: Synthesis and Mechanistic Insights
into the Catalytic Ketone Hydrosilylation
Dmitry A. Valyaev,*,† Duo Wei,‡ Saravanakumar Elangovan,‡ Matthieu Cavailles,† Vincent Dorcet,‡
Jean-Baptiste Sortais,*,‡ Christophe Darcel,*,‡ and Noel Lugan*,†
̈
†LCC-CNRS, Universite
‡UMR 6226 CNRS-Universite
Centre for Catalysis and Green Chemistry, Campus de Beaulieu, 263 av. du Gen
́
de Toulouse, INPT, UPS, 205 route de Narbonne, 31077 Toulouse Cedex 4, France
Rennes 1, Institut des Sciences Chimiques de Rennes, Team Organometallics: Materials and Catalysis,
eral Leclerc, 35042 Rennes Cedex, France
́
́
́
S
* Supporting Information
ABSTRACT: Manganese(I) complexes [(Cp(CH2)nNHCMes)Mn(CO)2] (2a, n =
1; 2b, n = 2) bearing Cp tethered NHC ligands have been prepared in good yield
from [CpMn(CO)3] and N-mesitylimidazole as main components, using a novel
synthetic strategy based on the anchoring of an imidazolium moiety to the
coordinated Cp ligand, followed by an intramolecular photochemical CO
substitution for the pendent NHC moiety generated in situ upon addition of a
base. The catalytic performances of 2a−b in the hydrosilylation of 2-acetonaph-
thone with Ph2SiH2 were found to be essentially indifferent to the length of the
linker between the Cp and the NHC moieties, and lower than the one of the
nontethered [Cp(CO)2Mn(IMes)] (1) parent complex. Still, the presence of Cp
tethered NHC ligands allowed isolation and full characterization of monocarbonyl η2-silane complexes [(Cp(CH2)nNHCMes)-
Mn(CO)(η2-H−SiHPh2)] (8a, n = 1; 8b, n = 2), which are generated upon photochemical reactions of 2a−b with
diphenylsilane. Both of these silane complexes are inactive for the catalytic 2-acetonaphthone hydrosilylation process but were
found to form catalytically active noncarbonyl species under UV irradiation, being consistent with the Ojima mechanism for
ketone hydrosilylation.
Chart 1. Half-Sandwich MnI NHC Complexes Used as
Precatalysts for Ketone Hydrosilylation (Mes = 2,4,6-
Trimethylphenyl)
INTRODUCTION
■
The use of organometallic complexes of earth abundant 3d
transition metals represents one of the most important aspects
of modern homogeneous catalysis. In contrast to the extensive
applications of iron-,1 cobalt-,2 and nickel-based3 catalysts, the
design of catalytic systems based on organometallic manganese
derivatives4 has attracted only recently attention, resulting in
the spectacular development of highly efficient Mn-catalyzed
C−H bond activation,5 (de)hydrogenation,6 hydrosilylation,7
borylation,8 CO2 reduction,9 and electrochemical hydrogen
production10 processes.
In a continuation of our work on the hydrosilylation of
carbonyl-containing compounds catalyzed by well-defined 3d
metal complexes,11 we have recently shown that half-sandwich
manganese complex 1 bearing a 1,3-bis(2,4,6-trimethylphenyl)-
imidazol-2-ylidene (IMes) ligand (Chart 1), easily available
from industrially produced cymantrene, [CpMn(CO)3], is an
effective precatalyst for the reduction of a variety of aldehydes
and ketones with diphenylsilane at room temperature under
UV light irradiation.7c Though the activity of this catalytic
system is inferior to the known σ-acyl,12 π-arene,13 salen,7e and
especially to the most active to date bis(imino)pyridine
manganese catalysts,7a,b it offers a good tolerance toward a
variety of sensitive functional groups (ester, nitrile, conjugated
or isolated CC bonds, alkyne, heterocycles).7c
During the past decade, it was shown that tethering N-
heterocyclic carbene (NHC) ligands with η5-cyclopentadienyl
(Cp) and related η5-indenyl (Ind) or η5-fluorenyl (Flu) ligands
is a viable strategy for increasing the stability of the
corresponding transition metal or lanthanide complexes and,
in some cases, their catalytic performance.14 Inspired by this
concept, we report herein the synthesis of manganese
complexes bearing Cp tethered NHC ligands [(Cp-
(CH2)nNHCMes)Mn(CO)2] (2a, n = 1; 2b, n = 2, Chart 1),
the comparison of their catalytic performance with regard to
Received: October 13, 2016
© XXXX American Chemical Society
A
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a
Scheme 1. Synthesis of Manganese Complexes 2a−b Bearing Cp Tethered NHC Ligands
a
Reagents and reaction conditions: (a) 1.1 equiv of n-BuLi, THF, −80 °C, 1.5 h; (b) 3 equiv of (CH2O)n, −80 °C to RT, 15 h then H2O at RT; (c)
1.2 equiv of SOCl2, 10% Py, CH2Cl2, 0 °C, 30 min; (d) 1.3 equiv of N-mesitylimidazole, 10% KI, MeCN, 90 °C, 5 days; (e) 1.2 equiv of KHMDS,
THF, RT, 10−30 min; (f) UV irradiation, toluene, 0 °C, 45−90 min; (g) 2-2.5 equiv of ethylene oxide, THF, −80 °C to RT, 15 h then H2O at RT;
(h) 1.1 equiv of MsCl, 1.5 equiv of Et3N, CH2Cl2, 0 °C, 30 min; (i) 1.3 equiv of N-mesitylimidazole, toluene, 110 °C, 20 h.
the parent IMes analogue 1, and experimental data relevant to
the mechanism of the ketone hydrosilylation process catalyzed
by half-sandwich MnI NHC complexes.
7a and 7b, respectively, adjusting a protocol we recently
described for the synthesis of [CpMn(CO)2(IMes)].21
Complexes 2a and 2b were isolated in 73% and 61% yield,
respectively, after purification by column chromatography and
crystallization (global yield of ca. 50% starting from
cymantrene) and were fully characterized by spectroscopic
methods and single-crystal X-ray diffraction analyses. Their IR
spectra in toluene solution display two characteristic intense
υCO bands (2a: 1924, 1857 cm−1; 2b: 1918, 1851 cm−1). The
alkyl spacers between Cp and NHC ligands appear as a singlet
at δ 3.47, and two multiplets at δ 2.98, and δ 1.70 ppm in the
1H NMR spectra for 2a and 2b, respectively, while the carbene
carbon atoms appear as very characteristic singlets at δ 207.7
ppm, and δ 207.0 ppm, respectively, in the 13C{1H} NMR
spectra. In passing, complexes 2a and 2b represent the first
examples of complexes exhibiting Cp tethered aryl-substituted
NHC ligands,22 2a featuring in addition the first example of a
C1 linker-based Cp tethered NHC ligand.
RESULTS AND DISCUSSION
■
Synthesis and Characterization of Piano-Stool MnI
Complexes [(Cp(CH2)nNHCMes)Mn(CO)2] (2a, n = 1; 2b, n
= 2) Featuring Cp Tethered NHC Ligands. Literature
precedents relative to the syntheses of Cp tethered NHC
complexes are all based on the preparation of substituted
cyclopentadiene derivatives bearing a pendent imidazolium
moiety, followed by complexation of the latter to a transition
metal.15,16 Here, owing to the excessive availability of
[CpMn(CO)3] precursor, we choose to first anchor the
imidazolium moiety to the Cp ligand through a variable length
link. In that prospect, selective deprotonation of the Cp ligand
in [CpMn(CO)3] was achieved using n-BuLi in THF at −80
°C (Scheme 1).17 Subsequent treatment of the organolithium
derivative [3]Li with either paraformaldehyde18 or ethylene
oxide19 afforded, after hydrolysis, complexes 4a18 and 4b in
85% and 91% yield, respectively. The latter were transformed
into the corresponding chloride 5a18 and mesylate 5b
derivatives, which were each subjected to nucleophilic
substitution with N-mesitylimidazole to provide complexes
[6a]Cl and [6b]OMs featuring a pendent mesitylimidazolium
moiety attached to the Cp ligand through −(CH2)− and
−(CH2)2− (C1 and C2 alkyl) links, respectively. Noticeably,
the chloride complex 5a was found to be much less reactive
than 5b and the addition of catalytic amounts of potassium
iodide (Finkelstein conditions) was necessary to accelerate the
process. The treatment of [6a]Cl and [6b]OMs with KHMDS
in THF at room temperature led to the formation of the
cymantrene derivatives [(Cp(CH2)nNHCMes)Mn(CO)3] (7a, n
= 1; 7b, n = 2) featuring pendent NHCs moieties. They were
fully characterized by 1H and 13C NMR spectroscopy, the latter
showing, in particular, signals at δ 218.0 and 215.7 ppm for the
carbene carbon atoms in 7a and 7b, respectively. Of note is that
complex 7b is relatively unstable, slowly decomposing at RT
even under an inert atmosphere to give among several
decomposition products N-mesitylimidazole and vinylcyman-
trene, (η5-C5H4CHCH2)Mn(CO)3.20 Finally, the formation
of the targeted [(Cp(CH2)nNHCMes)Mn(CO)2] (2a, n = 1; 2b,
n = 2) was achieved upon UV irradiation of toluene solutions of
Perspective views of complexes 2a and 2b are shown in
Figures 1 and 2, respectively.
Figure 1. A perspective view of complex 2a (30% probability
ellipsoids; only one of the two independent molecules in the unit cell
is shown).
B
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% loading, both complexes were found to be active in this
reaction under UV irradiation, albeit they exhibited a lower
efficiency than the parent IMes complex 1. The catalytic charge
was reduced to 0.5 mol %, still leading to an almost quantitative
yield of product after 24 h for complexes 1 and 2b, and 48 h for
complex 2a. Finally, using only 0.1 mol % of catalysts TON of
ca. 960, 330, and 290 were achieved for complexes 1, 2a, and
2b, respectively, after 24 h of reaction. It is noteworthy that
those TON values are significantly higher than the ones
11k
11h,22b
observed (up to 50) for related FeII and NiII
NHC
precatalysts. Though the rate of ketone hydrosilylation
catalyzed with complexes 1 and 2a−b is typically lower than
that for other manganese catalysts,7,12,13 only the most active to
date bis(imino)pyridine manganese catalysts are more efficient
than 1 in terms of TON (up to 6200).7a,b
Insights into the Mechanism of MnI NHC Catalyzed
Ketone Hydrosilylation through the Stoichiometric
Reactivity of the Complexes 2a−b with Diphenylsilane.
In order to shed light on the mechanism of the hydrosilylation
of carbonyl compounds catalyzed by MnI NHC complexes,
additional stoichiometric experiments were carried out. First of
all, it has been observed that UV irradiation of a solution of 1 in
toluene in the presence of 2 equiv of diphenylsilane leads to the
gradual consumption of the starting materialaccording to IR
spectroscopy monitoringwithout formation of any well-
defined organometallic species. To our delight, under the
same reaction conditions, the Cp tethered NHC complexes
2a−b cleanly afforded the products [(Cp(CH2)nNHCMes)Mn-
(CO)(η2-H−SiHPh2)] (8a, n = 1; 8b, n = 2) of photochemical
substitution of CO for diphenylsilane (Scheme 2), belonging to
Figure 2. A perspective view of complex 2b (30% probability
ellipsoids).
Both piano-stool MnI complexes show the usual pseudo-
octahedral geometry around the manganese atom, the
substituted η5-Cp ring being bounded in a pseudo-facial manner,
the remaining CO and NHC ligands having mutually cis
arrangements. The Mn−Ccarbene bond lengths being of 1.964(2)
and 1.963(2) Å for the two independent molecules in the unit
cell for 2a, and 1.989(2) Å for 2b, are slightly shorter than the
corresponding one in the nontethered parent IMes complex 1
(2.003(3) Å).23 In complex 2a, which exhibits the most
configurationally stable five-membered metallocycle, the NHC
ligand adopts a vertical orientation24 ({cntCp−Mn1−C3−N1} =
174.4° and −178.8° for two independent molecules in the unit
cell). In the case of complex 2b, the orientation of the NHC
moiety is slightly deviated from vertical position, {cntCp−Mn1−
C3−N1} = 162.0°, as it was found in the [(Cp-NHC)Fe-
(CO)I] parent complex previously reported by Royo et al.22e
Comparison of the Catalytic Performance of the MnI
NHC Complexes 1, 2a, and 2b in Ketone Hydrosilylation.
The activity of the MnI complexes 2a and 2b bearing Cp
tethered NHC ligands has been evaluated in the ketone
hydrosilylation with diphenylsilane under the same conditions
as the ones previously reported for complex 1,7c using 2-
acetonaphthone as a benchmark substrate (Table 1). At 1 mol
Scheme 2. Synthesis of η2-Silane Complexes 8a−b
the family of well-known half-sandwich manganese silane
complexes.25,26 Both compounds were isolated in good yields
and were fully characterized by spectroscopic methods,
supplemented for 8b by a single-crystal X-ray diffraction
analysis.
Table 1. Hydrosilylation of 2-Acetonaphthone with Ph2SiH2
a
Catalyzed by Manganese NHC Complexes 1, 2a, and 2b
The IR spectra of 8a and 8b in THF solution show a single
medium intensity υCO band at 1969 and 1961 cm−1, and a weak
broad υSiH band at 2075 and 2090 cm−1, respectively. For both
b
complex
catalyst (mol %)
time (h)
yield (%)
1
1.0
0.5
0.1
1.0
0.5
0.1
1.0
0.5
0.1
2
2
>98
98
1
complexes, the H and 13C{1H} spectra show four different
24
2
96
signals for C−H moieties of the Cp ligand and two signals for
the Cortho−Me and Cmeta−H fragments of the Mes group as a
consequence of the Mn atom being stereogenic. Silane protons
in the 1H NMR spectrum of 8a appear as singlets at δ 5.51 and
−10.48 ppm corresponding to the free and coordinated Si−H
entities, respectively. As for complex 8b, the corresponding
signals appear at 5.22 and −10.49 ppm as doublets with 2JHH of
2a
2b
56
c
24
24
2
92
33
66
98
29
24
24
1
a
4.0 Hz. The JSiH coupling constants in 8a and 8bobtained
Reaction conditions: 2-acetonaphthone (0.5−2 mmol), 1 equiv of
from the corresponding 29Si satellite signals in the 1H spectra
are of 195.0 and 198.5 Hz for the free Si−H bond, and 47.4 and
47.6 Hz for coordinated Si−H bond in 8a and 8b, respectively.
The latter values indicate that complexes 8a−b are closer from
Ph2SiH2, toluene (1−4 mL, 0.5 M substrate concentration), UV
b
irradiation (350 nm), 25 °C. NMR yield of the corresponding alcohol
(average of two runs) after basic hydrolysis (2 M NaOHaq, MeOH, 30
c
min, 25 °C). 98% yield after 48 h of reaction.
C
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silane σ-complexes with 3c−2e− Mn−Si−H bonds than from
alternating 20 min periods with and without UV irradiation
(see Figure S26). This revealed that the characteristic υCO band
of 8b at 1864 cm−1 gradually decreases during the UV
irradiation periods, along with the ketone υCO peak at 1684
cm−1 and silane υSiH band at 2142 cm−1, consistent with the
formation of the resulting silyl ether. It was also found that the
reaction proceeds sluggishly when the UV source was off, and
that the overall catalyst activity was considerably lower under
these interrupted conditions compared to continuous UV
irradiation conditions.
MnIII silylhydrides.27
A perspective view of complex 8b is given in Figure 3. The
hydrogen atoms H1 and H2 associated with the diphenylsilane
The proposed mechanism of ketone hydrosilylation catalyzed
by MnI NHC complexes is shown in Scheme 3. Clearly, the
Scheme 3. Proposed Catalytic Cycle for the Ketone
Hydrosilylation Catalyzed by MnI NHC Complexes
Figure 3. A perspective view of complex 8b (ellipsoids are show at the
30% probability level).
moieties were clearly located from a Fourier difference map.
Their coordinates were refined with fixed isotropic thermal
parameters, leading to reasonable Mn−H and Si−H bond
distances by reference to the corresponding bond distances
determined by neutron diffraction on parent complexes.25e,26
The position of H2 bridging the Si1−Mn1 vector (Mn1−H2 =
1.47(3) Å, Si1−H2 = 1.74(3) Å) speaks again for 8b being a
silane σ-complex. The Si−H bond adopts a horizontal
coordination mode, {cntCp−Mn1−Si1−H2} = 112.8°), the
hydrogen atoms H1 and H2 being relatively in a cis position
({H1−Si1−Mn1−H2} = 84.1°) (Figure 3). The pseudo-
octahedral environment around the Mn is complemented by
the Cp tethered NHC ligand and the remaining CO ligand.
The Mn−Ccarbene bond distance of 1.986(2) Å is similar to the
corresponding one in complex 2b, and the orientation of the
NHC ligand becomes even more deviated from vertical
(torsion angle {cntCp−Mn1−C3−N1} = −141.5°), probably
to accommodate a greater steric volume of the silane ligand
compared to CO.
Regarding the catalytic hydrosilylation of 2-acetonaphthone,
we have observed that both complexes 8a and 8b are totally
ineffective in the absence of UV light (0.5 M solution of 2-
acetonaphthone in toluene, 1 equiv of Ph2SiH2, 1% catalyst
loading, 25 °C) for up to 16 h of reaction, ruling out the
possibility of a direct SN2-type outer-sphere mechanism.28
Gratifyingly, the reaction rapidly started upon switching on the
UV irradiation, leading after 2 h to ca. 60% of ketone
conversion as estimated by the decrease of the υCO peak area
of the ketone substrate. This observation suggests that silane σ-
complexes 8a−b are the primary products of photochemical
transformation of dicarbonyl NHC complexes 2a−b in the
presence of silane, but the real catalytically active species are
produced more slowly upon further irradiation, this being
consistent with the observation of an induction period for the
hydrosilylation of acetophenone catalyzed by complex 1.7c
In order to get more insights into the reaction mechanism,
we have carried out IR monitoring of the 2-acetonaphthone
hydrosilylation by 8b (0.5 M solution of 2-acetonaphthone in
toluene, 1 equiv of Ph2SiH2, 5% catalyst loading, 25 °C) upon
remaining CO ligand in 8a−b has to be removed in order to
generate the active coordinatively unsaturated manganese
species. It is generally admitted that the photochemical
dissociation of the last carbonyl ligand in half-sandwich MnI
complexes is barely possible due to the very strong Mn−CO
bond energy.29 However, this process became feasible in the
case of half-sandwich MnIII complexes, as indicated by
successful high yield photochemical preparation of noncarbonyl
silylhydride complexes [Cp(PR3)2Mn(H)SiR3] from [CpMn-
(CO)(PR3)2] and the corresponding silane.30 On the basis of
this, we propose that the photochemical decarbonylation step
can indeed occur for MnIII silylhydride species such as [9a−b]
which could be reversibly produced in a small amount by
oxidative addition of Si−H bond in 8a−b.31
The coordination of the ketone substrate to the 16-electron
silylhydride intermediates [10a−b] to form [11a−b], followed
by a hydride transfer, the reductive elimination of silyl ether
from the MnIII intermediates [12a−b], and the coordination of
another silane molecule would constitute the catalytic cycle,
being in agreement with the classic Ojima mechanism (Scheme
3).32,33 The occurrence of the alternative Hofmann−Gade
mechanism,34 which is based on the formation of an 18-
electron electrophilic silylene dihydride intermediate [(Cp-
NHC)(H)2MnSiPh2] from [10] by α-hydride migration, is
D
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QTof (Waters) spectrometers. Elemental analyses were carried out at
the LCC-CNRS (Toulouse, France) using a PerkinElmer 2400 series
II analyzer.
unlikely due to the absence of the dehydrogenative silylation
byproduct 2-NaphC(OSiHPh2)CH2 characteristic for the
hydrosilylation process through this type of mechanism.
Synthesis of [(η5-C5H4CH2OH)Mn(CO)3] (4a).18 A solution of n-
BuLi (13.8 mL of 1.6 M solution in hexanes, 22.0 mmol) was added
dropwise over ca. 20 min to a solution of [CpMn(CO)3] (4.08 g, 20.0
mmol) in THF (30 mL) at −80 °C. The reaction mixture was further
stirred at −80 °C for 1.5 h. A suspension of paraformaldehyde (1.8 g,
60.0 mmol) in THF (30 mL) was added slowly to the resulting yellow-
orange suspension of complex [3]Li maintained at −80 °C, and the
reaction mixture was vigorously stirred at this temperature for 4 h,
then allowed to warm up slowly to room temperature overnight. Water
(3 mL) was added to the solution, and the volatiles were removed
under vacuum to afford an orange oil, which was purified by column
chromatography on silica (3 × 15 cm). Elution with a hexane/Et2O
10:1 mixture afforded a yellow band of starting cymantrene, followed
by an orange band of the product 4a, which was eluted with a hexane/
Et2O 1:1 mixture. The eluate was evaporated under vacuum to give 4a
(3.98 g, 85%) as an orange oil. The spectroscopic data were found in
agreement with a previous report.18 1H NMR (400.2 MHz, CDCl3, 25
°C): δ 4.83 (m, 2H, C5H4), 4.70 (m, 2H, C5H4), 4.33 (m, 2H, CH2),
1.70 (br s, 1H, OH). IR (CH2Cl2): νOH 3615 (w) cm−1, νCO 2020 (s),
1932 cm−1 (vs).
CONCLUSIONS
■
The first examples of MnI complexes 2a−b bearing Cp tethered
NHC ligands have been prepared using a novel synthetic
strategy based on the anchoring of an imidazolium moiety to
the coordinated Cp ligand, followed by an intramolecular
photochemical CO substitution for the pendent NHC moiety
generated in situ upon addition of a base prior to irradiation.
Though both tethered complexes were less active in ketone
hydrosilylation than a parent nontethered IMes analogue 1, we
succeeded in isolating the corresponding silane σ-complexes
8a−b, being the primary products of the photochemical CO
substitution for diphenylsilane in 2a−b. On the basis of
additional experimental data, we proposed the classic Ojima
mechanism to be operative in this case, the key step being the
formation of a catalytically active noncarbonyl MnIII silyl-
hydride intermediate that would form upon photochemical
dissociation of the last CO ligand. Finally, it is also noteworthy
that complex 1, easily available in one step from simple IMes
and industrially produced cymantrene, can achieve a TON up
to 960 in ketone hydrosilylation at room temperature using 1
equiv of diphenylsilane only, thus competing well with other
systems based on both noble and base metals. We are currently
working on the application of MnI NHC complexes for other
catalytic transformations, and on the development of efficient
catalytic systems for the enantioselective transformations using
MnI complexes bearing optically active NHC ligands. The
results will be reported in due course.
Synthesis of [(η5-C5H4CH2CH2OH)Mn(CO)3] (4b). To a
suspension of complex [3]Li in THF (30 mL) generated from
cymantrene (6.12 g, 30 mmol) and n-BuLi (20.6 mL, 33.0 mmol) as
described above was added a solution of ethylene oxide in THF (25
mL of 2.5−3.3 M, 62.5−82.5 mmol) slowly at −80 °C. After stirring at
−80 °C for 4 h and warming up to the room temperature overnight,
the resulting orange solution was hydrolyzed with water (3 mL) and
evaporated under vacuum to give a red oil, which was purified by
column chromatography on silica (3 × 15 cm). Elution with a hexane/
toluene 10:1 mixture afforded a yellow band of starting cymantrene,
followed by a red-orange band of the product 4b eluted with a
toluene/Et2O 20:1 mixture. The eluate was evaporated under vacuum
1
to give 4b (6.76 g, 91%) as an orange oil. H NMR (400.2 MHz,
EXPERIMENTAL SECTION
CDCl3): δ 4.72 (m, 2H, C5H4), 4.66 (m, 2H, C5H4), 3.77 (m, 2H,
CH2CH2OH), 2.50 (br t, 3JHH = 5.8 Hz, 2H, CH2CH2OH), 1.58 (br s,
1H, OH). 13C{1H} NMR (100.6 MHz, CDCl3): δ 225.2 (Mn−CO),
103.0 (C−CH2), 83.3, 82.0 (C5H4), 63.3 (CH2CH2OH), 31.5
(CH2CH2OH). IR (CH2Cl2): νOH 3615 (w) cm−1, νCO 2019 (s),
1931 cm−1 (vs).
■
All manipulations were carried out using Schlenk techniques under an
atmosphere of dry nitrogen or argon. Dry and oxygen-free organic
solvents (THF, Et2O, CH2Cl2, or toluene) were obtained using
LabSolv (Innovative Technology) or Braun MB-SPS-800 solvent
purification systems. Acetonitrile was distilled over CaH2 under an
argon atmosphere just prior to use. Solvents used for column
chromatography (hexane, toluene, or Et2O) were deoxygenated by
nitrogen bubbling during 15−20 min. Deuterated benzene and
chloroform used for the NMR experiments were deoxygenated by
three freeze−pump−thaw cycles and kept over 4 Å molecular sieves.
Technical quality cymantrene purchased as antiknocking essence
additive from TPL Region Company (Moscow, Russia) was purified
by recrystallization from hexane at −20 °C.21 All other reagent grade
chemicals purchased from commercial sources were used as received.
Photochemical procedures were performed either in a 250 mL
reactor with an immersed 150 W Hg medium pressure lamp TQ150
cooled by a quartz jacket with circulating water (synthesis of 2a−b), or
using a homemade external 10 W light source based on 395−405 nm
LEDs (synthesis of 8a−b, IR monitoring of catalytic hydrosilylation of
2-acetonaphthone with 8b), or using a Rayonet RPR 100 apparatus
(350 nm catalytic hydrosilylation experiments). A liquid nitrogen/
ethanol slush bath was used to maintain samples at the desired low
temperature. Chromatographic purifications of the compounds were
performed on silica (0.060−0.200 mm, 60 Å) and activated alumina
(neutral, 0.050−0.200 mm) obtained from Acros Organics, and
flushed with nitrogen just before use.
Synthesis of [(η5-C5H4CH2Cl)Mn(CO)3] (5a). To a solution of 4a
(1.91 g, 8.1 mmol) in CH2Cl2 (5 mL) was added SOCl2 (0.7 mL, 9.7
mmol) under stirring at 0 °C. Then, pyridine (0.07 mL, 0.81 mmol)
was added, and the reaction mixture was stirred at 0 °C until the
disappearance of the starting 4a by TLC (ca. 15−20 min). The
reaction mixture was then cooled to −80 °C and rapidly filtered
through a short column of alumina (2 × 3 cm) using CH2Cl2 as eluent.
The resulting yellow solution was evaporated under vacuum, and the
residue was extracted with hexane (3 × 10 mL). The extracts were
filtered through a short column of silica (2 × 4 cm) using hexane as
eluent, and the resulting yellow solution was evaporated under vacuum
to afford 5a (1.84 g, 90%) as yellow crystals. The spectroscopic data
were found in agreement with a previous report.18 1H NMR (400.2
MHz, CDCl3, 25 °C): δ 4.90 (m, 2H, C5H4), 4.72 (m, 2H, C5H4), 4.23
(s, 2H, CH2). IR (CH2Cl2): νCO 2025 (s), 1938 cm−1 (vs). HRMS
(EI): m/z calcd for C10H9MnO4: 191.9983 [M+ − 2CO], found:
192.0021.
Synthesis of [(η5-C5H4CH2CH2OMs)Mn(CO)3] (5b). To a
solution of 4b (7.69 g, 31.0 mmol) and Et3N (6.5 mL, 46.5 mmol)
in CH2Cl2 (50 mL) was added MsCl (2.64 mL, 34.1 mmol) dropwise
at 0 °C. After stirring the solution at this temperature for 45 min, the
reaction was quenched with water (20 mL). The yellow organic phase
was separated and washed consequently with 1 M HClaq (20 mL) and
brine (20 mL). The resulting solution was dried over MgSO4, filtered
through Celite, and evaporated under vacuum to give 5b (9.84 g, 97%)
Solution IR spectra were recorded in 0.1 mm CaF2 cells using a
PerkinElmer Frontier FT-IR spectrometer and given in cm−1 with
relative intensity in parentheses. H, 13C, and 29Si NMR spectra were
1
obtained on Bruker Avance 400 and Avance III HD 400 spectrometers
and referenced to the residual signals of deuterated solvents (1H and
13C) and Me4Si as internal standard (29Si). High-resolution mass
spectra (ESI and DCI modes) were obtained using GCT and Xevo G2
1
as a yellow powder. H NMR (400.2 MHz, CDCl3, 25 °C): δ 4.74 (t,
3
3JHH = 2.1 Hz, 2H, C5H4), 4.69 (t, JHH = 2.1 Hz, 2H, C5H4), 4.32 (t,
3JHH = 6.3 Hz, 2H, CH2CH2OMs), 3.01 (s, 3H, CH3SO2), 2.72 (t, 3JHH
E
DOI: 10.1021/acs.organomet.6b00785
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
= 6.3 Hz, 2H, CH2CH2OMs). 13C{1H} NMR (100.6 MHz, CDCl3): δ
224.8 (Mn−CO), 100.2 (C−CH2), 83.4, 82.3 (C5H4), 69.2 (CH2CH2-
OMs), 37.7 (SO2CH3), 31.5 (CH2CH2OMs). IR (CH2Cl2): νCO 2022
(s), 1934 cm−1 (vs). Anal. Found: C, 40.54; H, 3.29. Calcd for
C11H11MnO6S (M = 326.2) C, 40.50; H, 3.40.
(C−CH2), 83.7, 81.7 (C5H4), 48.2 (NCH2), 21.0 (CH3para‑Mes), 18.2
(CH3ortho‑Mes).
1
7b: H NMR (400.1 MHz, C6D6, 25 °C): δ 6.78 (s, 2H, CHMes),
6.35 (dd, JHH = 5.3 Hz, JHH = 1.5 Hz, 2H, CHIm4,5), 3.97 (t, 3JHH = 2.1
3
Hz, 2H, C5H4), 3.89 (t, JHH = 2.1 Hz, 2H, C5H4), 3.83 (t, 3JHH = 6.9
Hz, 2H, NCH2CH2), 2.38 (t, 3JHH = 6.9 Hz, 2H, NCH2CH2), 2.14 (s,
3H, CH3para‑Mes), 2.04 (s, 6H, CH3ortho‑Mes). 13C{1H} NMR (100.6
MHz, C6D6, 25 °C): δ 225.6 (Mn−CO), 215.7 (CN2), 139.0
(Cipso Mes), 137.5 (C−CH3para‑Mes), 135.3 (C−CH3ortho‑Mes), 129.2
(CHMes), 120.8, 118.6 (CHIm4,5), 103.1 (C−CH2CH2), 82.8, 82.0
(C5H4), 51.8 (NCH2CH2), 30.5 (NCH2CH2), 21.0 (CH3para‑Mes), 18.1
(CH3ortho‑Mes).
Synthesis of [(η5-C5H4CH2ImMes)Mn(CO)3]Cl ([6a]Cl). A solution
of 5a (0.75 g, 3.0 mmol), N-mesitylimidazole (0.73 g, 3.9 mmol), and
KI (50 mg, 0.3 mmol) in MeCN (12 mL) was heated at 90 °C until
1
the maximum conversion of 5a was achieved according to the H
NMR spectrum of the aliquot (ca. 4−5 days). The volatiles were
removed under vacuum, and the residue was dissolved in CH2Cl2 (10
mL). The solution was filtered through Celite, and ether (30 mL) was
added dropwise under stirring to induce the crystallization of [6a]Cl.
The supernatant was removed using a cannula tipped with a filter
paper, and the precipitate was washed with ether (20 mL) and dried
under vacuum to give [6a]Cl (1.13 g, 84%) as a white powder.
Though the product was found to be pure enough according to
elemental analysis, its 1H spectrum is broadened due to the systematic
Synthesis of [(η5-C5H4CH2NHCMes)Mn(CO)2] (2a). To a
suspension of [6a]Cl (0.76 g, 1.7 mmol) in THF (15 mL) was
slowly added a solution of KHMDS (4.1 mL of 0.5 M solution in
toluene, 2.04 mmol) under stirring at room temperature. The deep
yellow reaction mixture was sonicated for 15 min, then stirred for an
additional 15 min and evaporated under vacuum. The orange residue
of complex 7a was dissolved in toluene (50 mL), and the resulting
solution was transferred via cannula to the photochemical reactor. The
reactor was filled with toluene (ca. 200 mL), and the resulting solution
was irradiated with UV light at 0 °C under vigorous stirring. IR
monitoring showed the gradual transformation of the complex 7a (νCO
2021, 1938 cm−1) into the desired 2a (νCO 1924, 1857 cm−1), and the
irradiation was finished when the bands of the latter ceased to increase
(ca. 1.5 h). The resulting orange solution was filtered through a short
column of alumina (3 × 5 cm) using toluene as eluent and evaporated
under vacuum, and the residue was purified by column chromatog-
raphy on silica (3 × 15 cm). Elution with a toluene/hexane 1:1
mixture afforded a yellow band containing an unknown compound
discarded based on its IR spectra, followed by an orange band of
complex 2a eluted with pure toluene. The eluate was concentrated to
ca. 15 mL under vacuum and filtered through Celite, and hexane (50
mL) was added dropwise under stirring to induce the crystallization of
2a finished at −20 °C overnight. The supernatant was removed by
decantation, and the precipitate was dried under vacuum to afford 2a
(0.464 g, 73%) as a yellow powder. Single crystals suitable for X-ray
diffraction were obtained by slow diffusion of pentane into the solution
of 2a in toluene at room temperature. 1H NMR (400.1 MHz, C6D6, 25
°C): δ 6.88 (s, 2H, CHMes), 6.01 (d, 3JHH = 2.0 Hz, 1H, CHIm4,5), 5.97
1
presence of trace amounts of paramagnetic MnII impurities. H NMR
(400.2 MHz, dmso-d6, 25 °C): δ 10.05 (s, 1H, CHIm2), 8.30 (s, 1H,
CHIm4,5), 8.02 (s, 1H, CHIm4,5), 7.14 (s, 2H, CHMes), 5.56 (m, 4H,
C5H4), 5.06 (s, 2H, NCH2), 2.32 (s, 3H, CH3para‑Mes), 2.01 (s, 6H,
CH3ortho‑Mes). 13C{1H} NMR (100.6 MHz, dmso-d6, 25 °C): δ 224.0
(Mn−CO), 139.7 (C−CH3para‑Mes), 137.5 (CHIm4,5), 133.7 (C−
CH3ortho‑Mes), 130.6 (Cipso Mes), 128.9 (CHMes), 123.8 (CHIm4,5), 122.9
(CHIm2), 96.4 (C−CH2), 86.1, 83.1 (C5H4), 45.8 (NCH2), 20.3
(CH3para‑Mes), 16.9 (CH3ortho‑Mes). IR (CH2Cl2): νCO 2027 (s), 1944
cm−1 (vs). Anal. Found: C, 55.92; H, 4.40; N, 5.95. Calcd for
C21H20Cl0.9I0.1MnN2O3 (M = 448.0) C, 56.31; H, 4.50; N, 6.25.
Synthesis of [(η5-C5H4CH2CH2ImMes)Mn(CO)3]OMs ([6b]OMs).
A solution of 5b (0.98 g, 3.0 mmol) and N-mesitylimidazole (0.73 g,
3.9 mmol) in toluene (10 mL) was heated at 110 °C until the
1
maximum conversion of 5b was achieved according to the H NMR
spectrum of the aliquot (ca. 20 h). The volatiles were removed under
vacuum, and the brown residue was dissolved in CH2Cl2 (15 mL). The
solution was filtered through Celite, and ether (30 mL) was added
dropwise under stirring to induce the crystallization of [6b]OMs. The
supernatant was removed using a cannula tipped with a filter paper,
and the precipitate was washed with ether (20 mL) and dried under
1
vacuum to give [6b]OMs (1.46 g, 95%) as a light gray powder. H
3
3
(d, JHH = 2.0 Hz, 1H, CHIm4,5), 4.63 (t, JHH = 2.1 Hz, 2H, C5H4),
NMR (400.1 MHz, CDCl3, 25 °C): δ 9.93 (s, 1H, CHIm2), 7.71 (s, 1H,
3
4.15 (t, JHH = 2.1 Hz, 2H, C5H4), 3.47 (s, 2H, NCH2), 2.24 (s, 6H,
CH3ortho‑Mes), 2.07 (s, 3H, CH3para‑Mes). 13C{1H} NMR (100.6 MHz,
C6D6, 25 °C): δ 234.7 (Mn−CO), 207.7 (Mn−CN2), 138.8 (C−
CH3para‑Mes), 137.1 (Cipso Mes), 136.2 (C−CH3ortho‑Mes), 129.4 (CHMes),
122.8, 118.4 (CHIm4,5), 108.9 (C−CH2), 81.5, 80.0 (C5H4), 46.6
(NCH2), 21.2 (CH3para‑Mes), 18.4 (CH3ortho‑Mes). IR (toluene): νCO
1924 (s), 1857 cm−1 (s). Anal. Found: C, 63.98; H, 4.76; N, 7.49.
Calcd for C20H19MnN2O2 (M = 374.3): C, 64.17; H, 5.12; N, 7.48.
Synthesis of [(η5-C5H4CH2CH2NHCMes)Mn(CO)2] (2b). To a
suspension of [6b]OMs (0.72 g, 1.4 mmol) in THF (15 mL) was
slowly added a solution of KHMDS (3.4 mL of 0.5 M solution in
toluene, 1.68 mmol) under stirring at room temperature. The deep
yellow reaction mixture was sonicated for 15 min, then stirred for an
additional 15 min and evaporated under vacuum. The orange residue
of complex 7b was dissolved in toluene (50 mL), and the resulting
solution was transferred via cannula to the photochemical reactor. The
reactor was filled with toluene (ca. 200 mL), and the resulting solution
was irradiated with UV light at 0 °C under vigorous stirring. IR
monitoring showed the gradual transformation of the complex 7b (νCO
2019, 1934 cm−1) into the desired 2b (νCO 1918, 1851 cm−1), and the
irradiation was finished when the bands of the latter ceased to increase
(ca. 45 min). The resulting orange solution was filtered through a
short column of alumina (3 × 5 cm) using toluene as eluent and
evaporated under vacuum, and the residue was purified by column
chromatography on silica (3 × 15 cm). Elution with a toluene/hexane
1:1 mixture afforded consecutively yellow, orange, and yellow bands
containing unknown compounds discarded based on their IR and
NMR spectra, followed by an orange band of complex 2b eluted with a
toluene/ether 1:1 mixture. The eluate was evaporated under vacuum,
CHIm4,5), 7.14 (s, 1H, CHIm4,5), 7.00 (s, 2H, CHMes), 4.86 (m, 4H,
C5H4 + NCH2CH2), 4.65 (t, 3JHH = 2.0 Hz, 2H, C5H4), 2.96 (t, 3JHH
=
−
7.2 Hz, 2H, NCH2CH2), 2.69 (s, 3H, CH3SO3 ), 2.34 (s, 3H,
CH3para‑Mes), 2.04 (s, 6H, CH3ortho‑Mes). 13C{1H} NMR (100.6 MHz,
C6D6, 25 °C): δ 224.7 (Mn−CO), 141.3 (C−CH3para‑Mes), 139.0
(CHIm4,5), 134.2 (C−CH3ortho‑Mes), 130.8 (Cipso Mes), 129.9 (CHMes),
123.8 (CHIm2), 123.7 CHIm4,5), 99.9 (C−CH2CH2), 83.9, 82.6 (C5H4),
50.9 (NCH2CH2), 40.3 (CH3SO3−), 29.9 (NCH2CH2), 21.1
(CH3para‑Mes), 17.8 (CH3ortho‑Mes). IR (CH2Cl2): νCO 2023 (s), 1937
cm−1 (vs). HRMS (ESI): m/z calcd for C22H22MnN2O3: 417.1011
[M+], found: 417.1001.
Generation of [(η5-C5H4CH2NHCMes)Mn(CO)3] (7a) and [(η5-
C5H4CH2CH2NHCMes)Mn(CO)3] (7b) for NMR Characterization.
To a suspension of [6a]Cl (67 mg, 0.15 mmol) in THF (2 mL) was
slowly added a solution of KHMDS (0.36 mL of 0.5 M solution in
toluene, 0.18 mmol) under stirring at room temperature. The reaction
mixture was stirred for 5 min and evaporated under vacuum. The
residue was dissolved in dry C6D6 (1 mL), and the resulting yellow
solution of 7a was filtered through a plug of a glass wool in a Pasteur
pipet directly to the NMR tube. The NMR sample of 7b was obtained
in the same manner from [6b]OMs (77 mg, 0.15 mmol) and KHMDS
(0.33 mL of 0.5 M solution in toluene, 0.165 mmol).
1
7a: H NMR (400.1 MHz, C6D6, 25 °C): δ 6.78 (s, 2H, CHMes),
6.70 (s, 1H, CHIm4,5), 6.37 (s, 1H, CHIm4,5), 4.51 (s, 2H, C5H4), 4.35
(s, 2H, C5H4), 3.85 (s, 2H, NCH2), 2.14 (s, 3H, CH3para‑Mes), 2.09 (s,
6H, CH3ortho‑Mes). 13C{1H} NMR (100.6 MHz, C6D6, 25 °C): δ 225.2
(Mn−CO), 218.0 (CN2), 139.0 (Cipso Mes), 137.4 (C−CH3para‑Mes),
135.3 (C−CH3ortho‑Mes), 129.2 (CHMes), 120.9, 119.1 (CHIm4,5), 102.5
F
DOI: 10.1021/acs.organomet.6b00785
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
and the residue was crystallized from a CH2Cl2/hexane mixture at −20
°C to afford complex 2b (0.33 g, 61%) as an orange microcrystalline
powder. Single crystals suitable for X-ray diffraction were obtained by
slow diffusion of pentane into the solution of 2b in CH2Cl2 at room
3.35−3.25 (s overlapped with m, 3H, C5H4 + NCH2CH2), 2.15−2.04
(s overlapped with m, 4H, NCH2CH2 + CH3para‑Mes), 1.97 (s, 3H,
CH3ortho‑Mes), 1.79 (s, 3H, CH3ortho‑Mes), 1.51−1.40 (m, 3H, NCH2CH2
+ OCH2CH2THF), −10.49 (d with a satellite dd, 2JSiH = 47.4 Hz, 2JHH
=
1
4.0 Hz, 1H, Mn−H). 13C{1H} NMR (100.6 MHz, C6D6, 25 °C): δ
233.6 (Mn−CO), 206.1 (Mn−CN2), 148.8, 145.7, 138.3, 136.1, 134.9
(C−CH3para‑Mes, Cipso Mes, C−CH3ortho‑Mes), 137.9 (Cipso Ph), 136.3, 134.6
(CHMes), 129.9, 129.6, 127.5, 127.5, 127.2, 126.9 (CHPh), 122.3, 121.6
(CHIm4,5), 101.0 (C−CH2), 82.1, 81.6, 80.8, 79.4 (C5H4), 67.9
(OCH2CH2THF), 51.9 (NCH2CH2), 27.3 (NCH2CH2), 25.9 (OCH2-
CH2THF), 21.1 (CH3para‑Mes), 18.8, 18.1 (CH3ortho‑Mes). 29Si (1H−29Si
HMQC) NMR (79.5 MHz, C6D6, 25 °C): δ 16.8. IR (THF): νSiH
2090 (w br.), νCO 1871 cm−1 (m). Anal. Found: C, 69.86; H, 6.42; N,
4.94; Calcd for C34H37MnN2O1.5Si (8b×0.5THF, M = 580.7) C,
70.32; H, 6.42; N, 4.82.
temperature. H NMR (400.2 MHz, C6D6, 25 °C): δ 6.90 (s, 2H,
CHMes), 6.20 (d, 3JHH = 1.9 Hz, 1H, CHIm4,5), 6.10 (d, 3JHH = 1.9 Hz,
1H, CHIm4,5), 4.27 (t, 3JHH = 2.1 Hz, 2H, C5H4), 4.12 (t, 3JHH = 2.1 Hz,
2H, C5H4), 2.98 (m, 2H, NCH2CH2), 2.17 (s, 3H, CH3para‑Mes), 2.12
(s, 6H, CH3ortho‑Mes), 1.70 (m, 2H, NCH2CH2). 13C{1H} NMR (100.6
MHz, C6D6, 25 °C): δ 234.2 (Mn−CO), 207.0 (Mn−CN2), 138.7
(C−CH3para‑Mes), 138.1 (Cipso Mes), 136.4 (C−CH3ortho‑Mes), 129.6
(CHMes), 122.1, 121.3 (CHIm4,5), 102.1 (C−CH2CH2), 80.6, 78.9
(C5H4), 51.6 (NCH2CH2), 27.0 (NCH2CH2), 21.2 (CH3para‑Mes), 18.4
(CH3ortho‑Mes). IR (toluene): νCO 1918 (s), 1851 cm−1 (s). Anal.
Found: C, 64.63; H, 5.18; N, 7.06. Calcd for C21H21MnN2O2 (M =
388.4): C, 64.95; H, 5.45; N, 7.21.
General Procedure for Catalytic Hydrosilylation of 2-
Acetonaphthone with MnI NHC Complexes. A 10 mL oven-
dried Schlenk tube containing a stirring bar was charged with MnI
NHC catalyst (1/2a/2b) (1.0−0.1 mol %). After purging with argon
(argon-vacuum 3 cycles), toluene (1−4 mL, 0.5 M substrate
concentration) was added, followed by Ph2SiH2 (1 equiv) and 2-
acetonaphthone (0.5−2 mmol). The reaction mixture was irradiated
under UV (350 nm) using a Rayonet RPR 100 apparatus. At the end
of the reaction, MeOH (2 mL) and 2 M NaOH (2 mL) were added
consequently under vigorous stirring. The reaction mixture was stirred
for a further 2 h at room temperature and was extracted with diethyl
ether (3 × 10 mL). The combined organic layers were dried over
anhydrous MgSO4, filtered, and concentrated under vacuum. Product
Synthesis of [(η5-C5H4CH2NHCMes)(CO)Mn(η2-H−SiHPh2)]
(8a). A solution of complex 2a (113 mg, 0.3 mmol) and Ph2SiH2
(0.11 mL, 0.6 mmol) in toluene (15 mL) was irradiated by UV light
using a custom LED-based apparatus under vigorous stirring. IR
spectroscopy monitoring showed the gradual decrease of νCO bands of
2a (νCO 1924, 1857 cm−1) and the appearance of a νCO band of the
resulting complex 8a (νCO 1870 cm−1). After complete conversion of
the starting 2a (ca. 2 h), the solvent was evaporated under vacuum and
the residue was extracted with a Et2O/hexane 1:1 mixture (2 × 10
mL). The extracts were filtered through Celite and concentrated under
vacuum to ca. 30% of volume to induce the precipitation of 8a finished
at −20 °C overnight. The supernatant was removed, and the
precipitate was washed with pentane (2 × 3 mL) and dried under
1
yields were determined by H NMR spectroscopy.
1
vacuum to afford 8a (129 mg, 81%) as a yellow powder. H NMR
Catalytic Hydrosilylation of 2-Acetonaphthone with Silane
Complexes 8a and 8b. Silane complexes 8a (5.3 mg, 0.01 mmol) or
8b×0.5THF (5.8 mg, 0.01 mmol) were added to a solution of 2-
acetonaphthone (170 mg, 1 mmol) and Ph2SiH2 (185 μL, 1 mmol) in
toluene (2 mL), and the resulting yellow solution was stirred for 16 h
in the absence of UV irradiation. IR spectral monitoring of the ketone
band νCO at 1684 cm−1 showed no substrate conversion. The
reaction mixture was then irradiated under vigorous stirring for 2 h
with a UV LED-based apparatus, resulting in ca. 60−65% substrate
conversion estimated by the decrease of the νCO peak area calculated
using PerkinElmer Spectrum 10.4.00 software.
(400.1 MHz, C6D6, 25 °C): δ 7.85 (d, 3JHH = 7.2 Hz, 4H, Ph), 7.30−
7.18 (m, 5H, Ph), 7.15−7.10 (m overlapped with residual solvent
protons, 1H, Ph), 6.77 (s, 1H, CHMes), 6.42 (s, 1H, CHMes), 6.05 (br s,
1
1H, CHIm4,5), 6.02 (s, 1H, CHIm4,5), 5.51 (s with a satellite d, JSiH
=
195 Hz, 1H, Ph2SiH), 4.75 (s, 1H, C5H4), 4.38 (s, 1H, C5H4), 4.09 (s,
1H, C5H4), 3.64−3.53 (s overlapped with m, 3H, C5H4 + NCH2), 2.17
(s, 3H, CH3ortho‑Mes), 2.04 (s, 3H, CH3para‑Mes), 1.88 (s, 3H,
2
CH3ortho‑Mes), −10.48 (s with a satellite d, JSiH = 47.6 Hz, 1H, Mn−
H). 13C{1H} NMR (100.6 MHz, C6D6, 25 °C): δ 232.9 (Mn−CO),
206.8 (Mn−CN2), 147.4, 145.6, 138.4, 135.5, 135.0 (C−CH3para‑Mes
,
Cipso Mes, C−CH3ortho‑Mes), 136.5 (Cipso Ph), 136.3, 134.9 (CHMes), 129.5,
129.4, 127.7, 127.6, 127.5, 127.4 (CHPh), 123.3, 118.6 (CHIm4,5), 108.4
(C−CH2), 82.6, 81.9, 81.2, 80.9 (C5H4), 46.7 (NCH2), 21.1
(CH3para‑Mes), 18.7, 18.3 (CH3ortho‑Mes). 29Si (1H−29Si HMQC) NMR
(79.5 MHz, C6D6, 25 °C): δ 18.0. IR (THF): νSiH 2075 (w br.), νCO
1869 cm−1 (m). HRMS (DCI CH4): m/z calcd for C31H30MnN2OSi:
529.1508 [M+ − H], found: 529.1506.
Solution IR Monitoring of the Hydrosilylation of Aceto-
naphthone Catalyzed by Silane Complex 8b. A solution of 2-
acetonaphthone (102 mg, 0.6 mmol), Ph2SiH2 (110 μL, 0.6 mmol),
and 8b×0.5THF (17.5 mg, 0.03 mmol) in toluene (1.2 mL) was
irradiated under vigorous stirring with a UV LED-based apparatus for
20 min periods, followed by 20 min periods of simple stirring. The IR
spectra of the reaction mixture after each iteration are shown in Figure
S26. The substrate conversion was estimated by the decrease of the
ketone νCO peak area calculated using PerkinElmer Spectrum 10.4.00
software.
Details of X-ray Diffraction Experiments for Complexes 2a,
2b, and 8b. Single-crystal X-ray diffraction data collections were
carried out on a Bruker D8/APEX II/Incoatec IμS Microsource
diffractometer (graphite monochromator, Mo Kα radiation, λ =
0.71073 Å). All calculations were performed on a PC compatible
computer using the WinGX system.35 The structures were solved
using the SIR92 program,36 which revealed, in each instance, the
position of most of the non-hydrogen atoms. All the remaining non-
hydrogen atoms were located by the usual combination of full-matrix
least-squares refinement and difference electron density syntheses
using the SHELX program.37 Atomic scattering factors were taken
from the usual tabulations. Anomalous dispersion terms for Mn were
included in Fc. All non-hydrogen atoms were allowed to vibrate
anisotropically. The hydrogen atoms were generally set in idealized
positions (R3CH, C−H = 0.96 Å; R2CH2, C−H = 0.97 Å; RCH3, C−
H = 0.98 Å; C(sp2)−H = 0.93 Å; Uiso 1.2 or 1.5 times greater than the
Ueq of the carbon atom to which the hydrogen atom is attached), and
their positions were refined as “riding” atoms, expect for H1 and H2 in
the structure of 8b, whose positions were inferred from a residual
electron density map and refined with a Uiso arbitrarily set at 0.05 Å2.
Synthesis of [(η5-C5H4CH2CH2NHCMes)(CO)Mn(η2-H−SiHPh2)]
(8b). A solution of complex 2b (116 mg, 0.3 mmol) and Ph2SiH2
(0.11 mL, 0.6 mmol) in toluene (15 mL) was irradiated by UV light
using a custom LED-based apparatus under vigorous stirring. IR
spectroscopy monitoring showed the gradual decrease of νCO bands of
2b (νCO 1918, 1851 cm−1) and the appearance of a νCO band of the
resulting complex 8b (νCO 1861 cm−1). After complete conversion of
the starting 2b (ca. 4 h), the solvent was evaporated under vacuum and
the yellow residue was washed with pentane (2 × 3 mL) to remove the
excess of Ph2SiH2. The crude 8b was extracted with a THF/hexane 1:1
mixture (2 × 10 mL), and the extracts were filtered through Celite and
slowly evaporated under vacuum to induce the crystallization of the
product, which was finally washed with pentane (2 × 3 mL) and dried
under vacuum to afford 8b×0.5THF (144 mg, 83%) as a yellow
microcrystalline powder. Single crystals suitable for X-ray diffraction
experiment were obtained by slow diffusion of hexane vapors to the
1
solution of 8b in THF at room temperature. H NMR (400.1 MHz,
3
C6D6, 25 °C): δ 7.87 (d, JHH = 6.9 Hz, 2H, Ph), 7.55−7.50 (m, 2H,
Ph), 7.28−7.19 (m, 5H, Ph), 7.15−7.09 (m overlapped with residual
solvent protons, 1H, Ph), 6.74 (s, 1H, CHMes), 6.26 (s, 1H, CHIm4,5),
6.23 (s, 1H, CHMes), 6.08 (s, 1H, CHIm4,5), 5.22 (d with a satellite dd,
1JSiH = 198.5 Hz, 2JHH = 4.1 Hz; 1H, Ph2SiH), 4.46 (s, 1H, C5H4), 4.25
(s, 1H, C5H4), 3.91 (s, 1H, C5H4), 3.57 (m, 2H, OCH2CH2THF),
G
DOI: 10.1021/acs.organomet.6b00785
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
After completing the initial structure solution for complex 8b, it was
found that 12% of the total cell volume was filled with disordered
solvent molecules, which, however, could not be modeled in terms of
discrete molecules. The disordered solvent contribution was then
subtracted from the observed data using the SQUEEZE procedure.38
CCDC 1497716−1487718 contain the supplementary crystallographic
data for the three structures unveiled in this paper. These data can be
obtained free of charge from the Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
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ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.6b00785.
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NMR spectra for all compounds and IR monitoring data
for the hydrosilylation of 2-acetonaphthone catalyzed by
complex 8b (PDF)
Details of X-ray diffraction experiments for 2a−b and 8b
(CIF)
AUTHOR INFORMATION
Corresponding Authors
■
*E-mail: dmitry.valyaev@lcc-toulouse.fr (D.A.V.).
*E-mail: jean-baptiste.sortais@univ-rennes1.fr (J.-B.S.).
*E-mail: christophe.darcel@univ-rennes1.fr (C.D.).
*E-mail: noel.lugan@lcc-toulouse.fr (N.L.).
́
Brousses, R.; Cesar, V.; Sortais, J.-B.; Darcel, C.; Lugan, N.; Lavigne,
G. Adv. Synth. Catal. 2014, 356, 1093−1097. (d) Zheng, J.; Chevance,
S.; Darcel, C.; Sortais, J.-B. Chem. Commun. 2013, 49, 10010−10012.
(e) Chidara, V. K.; Du, G. Organometallics 2013, 32, 5034−5037.
(8) (a) Atack, T. C.; Cook, S. P. J. Am. Chem. Soc. 2016, 138, 6139−
6142. (b) Zhang, G.; Zeng, H.; Wu, J.; Yin, Z.; Zheng, S.; Fettinger, J.
C. Angew. Chem., Int. Ed. 2016, 55, 14369−14372.
ORCID
Noel Lugan: 0000-0002-3744-5252
̈
Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS
■
D.A.V. is grateful to the IDEX-UNITI for a starting grant. C.D.
and J.-B.S. thank the University of Rennes 1, the CNRS for
financial support.
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