A Pentacoordinate Mn(II) Precatalyst That Exhibits Notable Aldehyde and Ketone Hydrosilylation Turnover Frequencies

Article abstract of DOI:10.1021/acs.inorgchem.5b01825

Heating (THF)₂MnCl₂ in the presence of the pyridine-substituted bis(imino)pyridine ligand, ^PyEtPDI, allowed preparation of the respective dihalide complex, (^PyEtPDI)MnCl₂. Reduction of this precursor using excess Na/Hg resulted in deprotonation of the chelate methyl groups to yield the bis(enamide)tris(pyridine)-supported product, (κ⁵-N,N,N,N,N-^PyEtPDEA)Mn. This complex was characterized by single-crystal X-ray diffraction and found to possess an intermediate-spin (S = 3/2) Mn(II) center by the Evans method and electron paramagnetic resonance spectroscopy. Furthermore, (κ⁵-N,N,N,N,N-^PyEtPDEA)Mn was determined to be an effective precatalyst for the hydrosilylation of aldehydes and ketones, exhibiting turnover frequencies of up to 2475 min^-1 when employed under solvent-free conditions. This optimization allowed for isolation of the respective alcohols and, in two cases, the partially reacted silyl ethers, PhSiH(OR)₂ [R = Cy and CH(Me)(ⁿBu)]. The aldehyde hydrosilylation activity observed for (κ⁵-N,N,N,N,N-^PyEtPDEA)Mn renders it one of the most efficient first-row transition metal catalysts for this transformation reported to date.

Full text of DOI:10.1021/acs.inorgchem.5b01825

Article
pubs.acs.org/IC
A Pentacoordinate Mn(II) Precatalyst That Exhibits Notable Aldehyde
and Ketone Hydrosilylation Turnover Frequencies
Chandrani Ghosh, Tufan K. Mukhopadhyay, Marco Flores, Thomas L. Groy, and Ryan J. Trovitch*
School of Molecular Sciences, Arizona State University, Tempe, Arizona 85287, United States
S
* Supporting Information
ABSTRACT: Heating (THF)2MnCl2 in the presence of the
pyridine-substituted bis(imino)pyridine ligand, PyEtPDI, allowed
preparation of the respective dihalide complex, (PyEtPDI)-
MnCl2. Reduction of this precursor using excess Na/Hg
resulted in deprotonation of the chelate methyl groups to yield
the bis(enamide)tris(pyridine)-supported product, (κ5-
N,N,N,N,N-PyEtPDEA)Mn. This complex was characterized by
single-crystal X-ray diffraction and found to possess an
intermediate-spin (S = 3/2) Mn(II) center by the Evans
method and electron paramagnetic resonance spectroscopy.
Furthermore, (κ5-N,N,N,N,N-PyEtPDEA)Mn was determined to
be an effective precatalyst for the hydrosilylation of aldehydes
and ketones, exhibiting turnover frequencies of up to 2475 min−1 when employed under solvent-free conditions. This
optimization allowed for isolation of the respective alcohols and, in two cases, the partially reacted silyl ethers, PhSiH(OR)2 [R =
Cy and CH(Me)(nBu)]. The aldehyde hydrosilylation activity observed for (κ5-N,N,N,N,N-PyEtPDEA)Mn renders it one of the
most efficient first-row transition metal catalysts for this transformation reported to date.
hydrosilylation of ketones16 with turnover frequencies
INTRODUCTION
■
(TOFs) of up to 4 and 27 min−1, respectively. A few years
Over the past decade, the cost and toxicity of homogeneous
later, (η5-C10H9)MnI(CO)3 was reported to mediate the
precious metal catalysts have intensified the search for green
hydrosilylation of ketones when Ph2SiH2 was used as a
alternatives that mediate organic transformations with com-
reductant.17 This effort was extended to the utilization of
petitive lifetimes, activities, and selectivities.1 The development
of late first-row transition metal catalysts has remained a
naphthalene-supported [(η6-C10H8)MnI(CO)3][BF4], which
exhibited improved ketone reduction TOFs of up to 1.7
specific area of interest because Fe, Co, and Ni are earth-
min−1.18 The Mn0 (CO)10-catalyzed reduction of N-acetylpi-
abundant2 and significantly less expensive than their precious
2
peridine to N-ethylpiperidine19 and hydrosilylation of carbox-
metal counterparts.3 For example, while Pt catalysts are
ylic acids into disilylacetals20 have also been reported; however,
typically used to prepare silicone coatings and elastomers via
olefin hydrosilylation,4 recent progress has been made in the
modest TOFs were observed for both reactions. While
(3,5-tBu2-salen)MnVN has been found to catalyze 4-nitro-
development of efficient first-row metal surrogates for this
benzaldehyde hydrosilylation with a TOF of 196 min−1 at 80
reaction.5 The formation of Si−O bonds by way of carbonyl
°C, attempts to hydrosilylate benzaldehyde at ambient
hydrosilylation is considered a complementary technology for
which several efficient Fe,6 Co,7 Ni,8 Cu,9 and Zn10 catalysts
temperature using this complex (1 mol %) required 22 h for
complete conversion.21 Recently, CpMnI(CO)2(MesNHC) has
have been reported. Moreover, the hydrosilylation of ketones
been found to mediate the hydrosilylation of aldehydes and
using chiral Fe catalysts has recently emerged as an efficient
synthetic route to chiral alcohols.11
ketones with modest TOFs upon being exposed to 350 nm
light.22
For all the attention granted to the development of late first-
row metal hydrosilylation catalysts, Mn-based catalysts for this
In 2014, we reported that the phosphine-substituted
transformation have remained largely overlooked.12 In 1983, it
bis(imino)pyridine (or pyridine diimine, PDI) Mn complex,
Ph PPrPDI)Mn (Figure 1, A), exhibits ketone hydrosilylation
2
was reported that (CO)5MnISiPh3 catalyzes 1-pentene hydro-
(
TOFs of up to 1280 min−1 (76800 h−1) in the absence of
solvent.23 This catalyst yields either tertiary or quaternary
silanes, depending on the reaction conditions, and also
mediates the dihydrosilylation of esters to form a mixture of
silylation upon irradiation or heating to 180 °C.13 Similarly,
Mn0 (CO)10 was found to mediate the hydrosilylation of 1-
2
hexene with tertiary silanes under mild conditions (40 °C).14
Outside of these reports, Mn hydrosilylation catalysts have
been used for the reduction of carbonyl-containing substrates.
Cutler and co-workers demonstrated that (Ph3P)(CO)4MnIC-
(O)CH3 catalyzes the dihydrosilylation of esters15 and
Received: August 10, 2015
Published: October 19, 2015
© 2015 American Chemical Society
10398
DOI: 10.1021/acs.inorgchem.5b01825
Inorg. Chem. 2015, 54, 10398−10406

Inorganic Chemistry
Article
cm−1) with no observable d−d transitions. These observations
5
are consistent with a high-spin Mn(II) center (SMn = /2), as
previously reported for related (PDI)MnCl2 complexes.23,26
To confirm that the PDI chelate of 1 adopts κ3 coordination,
the solid state structure of this complex was determined by
single-crystal X-ray diffraction (Figure 2). The metrical
Figure 1. Previously described Mn hydrosilylation catalyst, (Ph PPrPDI)
Mn (A), and the elusive pyridine-substituted variant that inspired this
study (B).
2
silyl ethers.12,23 Although the Mn center of A is formally
zerovalent, the electronic structure of this complex is consistent
with a Mn(II) center supported by a chelate dianion (PDI2−).12
While the mechanism by which A performs hydrosilylation
remains under investigation, chelate redox noninnocence is
suspected to play a role because of reports that have linked
ligand redox activity with late first-row transition metal
catalysis.24 With this in mind, the high degree of modularity
that can be achieved for donor-substituted imine substituents
inspired our search for second-generation (PDI)Mn hydro-
silylation catalysts that exhibit improved catalytic properties. In
this work, we detail our efforts to prepare pyridine-substituted
precatalyst B (Figure 1). This complex has remained elusive;
however, deprotonation of this reduction intermediate has
afforded a highly active Mn(II) hydrosilylation precatalyst, (κ5-
N,N,N,N,N-PyEtPDEA)Mn. Herein, we report the substrate
scope and functional group tolerance of this catalyst and
compare its activity to those of leading first-row metal
hydrosilylation catalysts.
Figure 2. Solid state structure of 1 shown with 30% probability
ellipsoids. Labeled atoms ending with A have been generated by
symmetry. Hydrogen atoms and cocrystallized dichloromethane
molecules have been omitted for the sake of clarity. For complete
atom labeling and metrical parameters, see Figure S1 and Table S2 of
the Supporting Information.
RESULTS AND DISCUSSION
■
Synthesis and Characterization. Anticipating that the
weakly coordinated pyridine arms of B would dissociate to
allow for substrate coordination throughout the course of
hydrosilylation, we commenced with the stoichiometric
addition of PyEtPDI25 to (THF)2MnCl2. When the mixture
was heated to 95 °C for 3 days in toluene, partial conversion to
a light orange product was observed. Optimization upon
addition of excess PyEtPDI (1.9 equiv; see Experimental
Procedures) and heating the reaction mixture to 125 °C
allowed for the isolation of (PyEtPDI)MnCl2 (1, eq 1) in 93%
Table 1. Notable Bond Lengths (angstroms) and Angles
(degrees) Determined for 1 and 2
1
2
Mn(1)−N(1)
Mn(1)−N(2)
Mn(1)−N(3)
Mn(1)−Cl(1)
N(1)−C(2)
C(1)−C(2)
C(2)−C(3)
2.264(4)
2.224(6)
−
2.3740(15)
1.291(7)
1.505(7)
1.505(7)
2.1123(18)
2.158(3)
2.2178(17)
−
1.369(3)
1.363(3)
1.491(3)
N(1)−Mn(1)−N(1A)
N(1)−Mn(1)−Cl(1)
N(1)−Mn(1)−N(3)
N(2)−Mn(1)−Cl(1)
N(2)−Mn(1)−N(3)
Cl(1)−Mn(1)−Cl(1A)
N(3)−Mn(1)−N(3A)
142.3(2)
102.16(12)
−
148.67(10)
−
86.38(7)
126.97(4)
−
−
126.59(5)
−
106.81(9)
106.06(8)
−
parameters in Table 1 indicate that 1 possesses distorted
trigonal bipyramidal geometry with an N(1)−Mn(1)−N(1A)
angle of 142.3(2)°. Although the Mn−Nimine distance of
2.264(4) Å determined for this complex is shorter than the
yield. Analysis of this complex by 1H nuclear magnetic
resonance (NMR) spectroscopy revealed broad resonances at
62.76, 13.51, and −31.63 ppm, and the ambient-temperature
magnetic susceptibility of 1 was found to be 6.3 μB (Guoy
balance). UV−visible spectra of 1 feature charge transfer bands
at 306 nm (ε = 3844 M−1 cm−1) and 318 nm (ε = 2601 M−1
same distances reported for (iPr ArPDI)MnCl2 [2.333(5) and
2
2.318(5) Å]26 and (Ph PPrPDI)MnCl2 [2.300(2) and 2.338(2)
2
Å],23 the Mn(1)−N(1) and Mn(1)−Cl(1) contacts observed
for 1 are indicative of high-spin Mn. The N(1)−C(2) and
10399
DOI: 10.1021/acs.inorgchem.5b01825
Inorg. Chem. 2015, 54, 10398−10406

Inorganic Chemistry
Article
C(2)−C(3) distances of 1.291(7) and 1.505(7) Å, respectively,
are consistent with minimal backbonding and an unreduced
PDI chelate.27
Having isolated and characterized 1, we explored its
conversion to a suitable hydrosilylation catalyst precursor.
Adding an excess of Na/Hg to 1 in the presence of a catalytic
quantity of 1,3,5,7-cyclooctatetraene (COT, used to accelerate
reduction23) afforded a greenish-brown THF solution after 12
h at ambient temperature. Following workup, the resulting
product was identified as (κ5-N,N,N,N,N-PyEtPDEA)Mn (2, eq
2), which features a doubly deprotonated bis(enamide)tris-
Figure 3. Solid state structure of 2 shown with 30% probability
ellipsoids. Labeled atoms ending with A have been generated by
symmetry. Hydrogen atoms and a cocrystallized toluene molecule have
been omitted for the sake of clarity. For complete atom labeling and
metrical parameters, see Figure S2 and Table S3 of the Supporting
Information.
(pyridine) chelate. Analysis of this complex by 1H NMR
spectroscopy revealed paramagnetically broadened resonances
over a 100 ppm range. The ambient-temperature magnetic
susceptibility of 2 was found to be 3.8 μB (Evans method), and
UV−visible spectra of this complex were found to feature d−d
transitions at 512 nm (ε = 524 M−1 cm−1) and 624 nm (ε =
504 M−1 cm−1), suggesting that 2 possesses an intermediate-
spin Mn(II) center. To further investigate the electronic
structure, the X-band (9.40 GHz) electron paramagnetic
resonance (EPR) spectrum of 2 was recorded in toluene
glass at 106 K. The spectrum showed multiline signals typical of
Mn(II) around 330 mT (geff = 2.0) and 150 mT (geff = 4.3) (see
suitable reductant in A-mediated (Figure 1) hydrosilylation
reactions,23 equimolar quantities of PhSiH3 and aldehyde were
added to benzene-d6 solutions containing 1.0 mol % 2 at 25 °C
(Table 2). Regardless of the aldehyde chosen, complete
1
carbonyl reduction (>99% as judged by H NMR spectrosco-
py) to generate a mixture of silyl ethers was observed after 1 h
(TOF = 1.7 min−1, determined at full conversion). The
hydrosilylation of benzaldehyde was found to result in an
approximate 13:1 ratio of PhSi(OCH2(Ph))3 to PhSiH-
(OCH2(Ph))2 (entry 1). A significant amount of unreacted
PhSiH3 was also identified by 1H NMR spectroscopy following
catalysis (Figure S8), and both observations indicate that in situ-
generated PhSiH2(OCH2(Ph)) is more reactive toward 2-
mediated carbonyl reduction than PhSiH3. Repeating this
reaction in the presence of 0.33 equiv PhSiH3 resulted in
PhSi(OCH2(Ph))3 formation (>99% conversion in 1 h, 88%
yield as determined by 1H NMR integration against an internal
anisole standard). An analogous ratio of quaternary to tertiary
silane products was observed for a range of substituted
benzaldehydes (entries 2−5), suggesting that peripheral
electron-donating and -withdrawing groups do not interfere
with selectivity or conversion. The alkene functionality of
substrates such as trans-cinnamaldehyde (entry 6) and 3-
cyclohexene-1-carboxaldehyde (entry 8) remained unsaturated
following hydrosilylation, demonstrating that 2 chemoselec-
tively reduces aldehydes over alkenes. Moreover, attempts to
hydrosilylate 1-hexene and cyclooctene using 2 were
unsuccessful. It should be noted that a higher proportion of
tertiary silane was generated during the hydrosilylation of the
aliphatic substrates, 3-cyclohexene-1-carboxaldehyde (entry 8)
and cyclohexanecarboxaldehyde (entry 9).
5
Figure S3, which features a broad S = /2 impurity). These
spectral features are consistent with an intermediate-spin 55Mn
3
5
center (S = /2; I = /2) and correspond to resonances within
3
both Kramer’s doublets of a /2 spin system with large and
rhombic zero-field splitting (i.e., D ≫ gβeB0/h, and E/D =
0.333) (see Experimental Procedures).28
To verify chelate deprotonation, the solid state structure of 2
was determined via single-crystal X-ray diffraction (Figure 3).
As observed for 1, the structure of 2 contains a C2 symmetry
axis along the Mn(1)−N(2) bond and the geometry about Mn
is best described as distorted trigonal bipyramidal. Metrical
parameters for this complex are listed in Table 1. Notably, the
Mn(1)−N(1) and Mn(1)−N(2) distances found for 2 are
shorter than the same distances determined for 1, consistent
with PDEA2− coordination and the contrasting spin states of
these complexes. More importantly, complex 2 possesses a
C(1)−C(2) distance of 1.363(3) Å, which is consistent with
double bond formation and methyl group deprotonation. The
N(1)−C(2) contact of 1.369(3) Å indicates that the imine has
been converted to a N−C single bond and that the chelate is
dianionic.
Having determined that 2 is active for aldehyde hydro-
silylation, we investigated the ability of this precatalyst to
hydrosilylate ketones to permit comparison with catalyst A.23
Employing the same reaction conditions used to generate Table
2, eight different ketones were transformed to their respective
silyl ethers after 1 h at ambient temperature (Table 3). The
Hydrosilylation Catalysis. Although the chemical struc-
ture of 2 was not targeted because of its apparent lack of chelate
redox noninnocence, we decided to screen its activity as a
carbonyl hydrosilylation precatalyst. Because PhSiH3 was a
10400
DOI: 10.1021/acs.inorgchem.5b01825
Inorg. Chem. 2015, 54, 10398−10406

Inorganic Chemistry
Article
Table 2. Hydrosilylation of Aldehydes Using 2 as a
Precatalyst
Table 3. Hydrosilylation of Ketones Using 2 as a Precatalyst
a
Product ratios and percent conversion determined by 1H NMR
spectroscopy (Figures S20−S27 of the Supporting Information).
attempted. Only 2% conversion was achieved after 1 h, and
allowing the reaction mixture to stand for 5 days resulted in
67% conversion (Figure S28), slightly lower than the
conversion reported using A (80%).23
a
Product ratios and percent conversion determined by 1H NMR
spectroscopy (Figures S8−S19 of the Supporting Information).
b
1
To investigate the synthetic utility of 2, efforts were made to
reduce the catalyst loading and eliminate solvent use (Table 4).
The hydrosilylation of 2-hexanone using PhSiH3 and 0.02 mol
% 2 in the absence of solvent was exothermic, and complete
Overall silyl ether yield of 96% determined by H NMR integration
c
vs anisole internal standard. Overall silyl ether yield of 91%
determined by H NMR integration vs anisole internal standard.
1
1
hydrosilylation of acetophenone using 1.0 mol % 2 resulted in
the formation of PhSiH(OCH(Me)(Ph))2 and PhSi(OCH-
(Me)(Ph))3 in an approximate 3:1 ratio (entry 1). The
electron-donating functionalities of p-acetanisole (entry 3) and
p-dimethylaminoacetophenone (entry 4) appear to promote
formation of the tertiary silane product. The complete
hydrosilylation of p-fluoroacetophenone (entry 2) and p-
dimethylaminoacetophenone (entry 4) within 1 h using 2 is
notable because catalyst A required 4 and 6 h to transform
these substrates, respectively.23 When the hydrosilylation of
aliphatic ketones was conducted using 2 (entries 6−8), tertiary
silanes were identified as the primary reaction product;
however, small quantities of monosilylated product were also
observed.29 In addition to the ketones in Table 3, the
hydrosilylation of 2′,4′,6′-trimethylacetophenone using 2 was
substrate consumption was observed after 5 min by H NMR
spectroscopy (entry 1; TOF = 990 min−1; TON = 4950).
Treatment of the resulting silyl ethers with 10% aqueous
NaOH followed by extraction with Et2O and silica gel filtration
allowed for the isolation of 2-hexanol in 72% yield. The
analogous hydrosilylation and workup starting from cyclo-
hexanone resulted in a 99% isolated yield of cyclohexanol
(entry 2). The tertiary silyl ether products, PhSiH(OCH(Me)-
(nBu))2 and PhSiH(OCy)2,23 have alternatively been isolated
from these transformations in 63 and 55% yields, respectively.
Considering that aldehydes are easier to hydrosilylate than
ketones,25 the optimized conditions were extended to the 2-
mediated hydrosilylation of aldehydes (entries 3 and 4).
Complete reduction of benzaldehyde and p-fluorobenzaldehyde
was observed after only 2 min, equating to an aldehyde
10401
DOI: 10.1021/acs.inorgchem.5b01825
Inorg. Chem. 2015, 54, 10398−10406

Inorganic Chemistry
Article
Table 4. Alcohol Preparation via Carbonyl Hydrosilylation Using 0.02 mol % 2
a
b
For spectral data of isolated silyl ether and alcohol products, see the Supporting Information. Time of hydrosilylation reaction prior to catalyst
c
quench. Isolated yields based on substrate added. All hydrosilylation reactions had reached >99% conversion as judged by 1H NMR spectroscopy.
d
TOF values are based on substrate conversion.
hydrosilylation TOF of 2475 min−1 (TON = 4950). To
determine the maximal TON for 2-catalyzed benzaldehyde
hydrosilylation, entry 3 was repeated and 5000 equiv each of
benzaldehyde and PhSiH3 were added every 10 min for 1 h
complete transformation of this substrate to the corresponding
silyl ether products was observed within 5 min at 25 °C.
Attempts to achieve this reaction using Mn0 powder were
unsuccessful (entry 2), further indicating that heterogeneous
species are unlikely to be responsible for catalysis. The Mn-
containing precursors (THF)2MnCl2 and 1 were also found to
be inactive under these conditions (entries 3 and 4). To
investigate the possibility that 2 is acting as a radical initiator,
2,2′-azobis(2-methylpropionitrile) (AIBN) was screened as a
precatalyst. No conversion was noted after 5 min at ambient
temperature, and heating the reactants to 90 °C failed to result
in cyclohexanone hydrosilylation after 7 min (entries 5 and 6).
These observations imply that hydrosilylation does not proceed
through a radical chain mechanism but, rather, at the Mn
center.
1
(five additions, 30000 total equiv of substrate). Analysis by H
NMR spectroscopy revealed 47% conversion (Figure S45),
equating to a TON of 14170. Notably, the ambient-temper-
ature TOFs observed using 2 are roughly twice those reported
for A-mediated ketone hydrosilylation (1240−1280 min−1)23
and 2 orders of magnitude greater than the TOFs reported for
(Ph3P)(CO)4MnC(O)CH3 (27 min−1).16
Finally, a series of control experiments were conducted to
confirm hydrosilylation catalysis is mediated by 2 or a
homogeneous derivative (Table 5). To assay catalyst
homogeneity, the neat hydrosilylation of cyclohexanone using
PhSiH3 and 0.1 mol % 2 was conducted in the presence of
50000 equiv of Hg0. As anticipated for a homogeneous catalyst,
Role of the Chelate. Although PDI methyl group
deprotonation has been observed following addition of
30
alkyllithium to (iPr ArPDI)MnCl2, its occurrence during the
2
reduction of 1 was surprising because the naphthalene-
Table 5. Cyclohexanone Hydrosilylation Control
Experiments in the Absence of Solvent
31
promoted Na reduction of (iPr ArPDI)MnCl2 and COT-
2
23
promoted Na/Hg reduction of (Ph PPrPDI)MnCl2 do not
2
result in chelate modification. Because of the weak π-acidity of
pyridine relative to the phosphine donors of Ph PPrPDI, this is
2
believed to be a function of chelate covalency. As 1 is reduced
by two electrons, coordination of the donor arms of PyEtPDI is
thought to result in increased electron density at the metal and
ultimately multielectron reduction of the chelate, as observed
for A.12,23 Whereas synergistic phosphine ligands stabilize the
chemical and electronic structures of A, the pyridine donors of
PyEtPDI force electron density onto the noninnocent PDI core
upon coordination, leading to its deprotonation.
a
entry
catalyst
time (min) temp (°C) conversion (%)
1
2
3
4
5
6
2 + 50000 Hg0
Mn0
5
5
5
5
5
7
25
25
25
25
25
90
>99
0
(THF)2MnCl2
0
1
0
AIBN
AIBN
0
0
While chelate modification may not appear to be overly
a
significant, the deprotonation of PyEtPDI disrupts its π-system
1
Determined by H NMR spectroscopy.
10402
DOI: 10.1021/acs.inorgchem.5b01825
Inorg. Chem. 2015, 54, 10398−10406

Inorganic Chemistry
Article
Table 6. Carbonyl Hydrosilylation Activities Reported for Leading First-Row Metal Catalysts
a
entry
metal
catalyst
silane
substrate
temp (°C)
TOF (min−1
)
ref
b
c
1
2
Sc
(κ4-N3O)Sc(O2CCH2SiMe2Ph)·(BC6F5)3
Et3SiH
(EtO)3SiH
−
Ph2SiH2
PhSiH3
PhSiH3
Ph2SiH2
PhSiH3
PhSiH3
carbon dioxide
methyl benzoate
−
p-anisaldehyde
benzaldehyde
acetophenone
propanal
65
25
−
70
25
25
25
25
25
0.2
33
d
Ti
(Cp)2TiCl2 + 2nBuLi
0.7
34
3
V
−
−
0.1
−
35
4
Cr
Mn
Fe
Co
Ni
Cu
Zn
(η6-C6H6)2Cr
5
2
2475
393
this work
6b
e
6
(κ2-PN)Fe(N(SiMe3)2)
f
7
(DPB)Co(N2)
49.5
38.4
7f
8
(Cp*-NHCMe)Ni(OtBu)
CuF2 + (S)-Xyl-P-Phos
p-CF3-benzaldehyde
p-NO2-acetophenone
acetaldehyde
8c, 36
9k
g
9
660
h
10
(κ3-Tptm)ZnH
PhSiH3
25
20
10m
a
b
c
d
Least-substituted example. N3O = analido(bipyridyl)carboxylate. TOF based on Si−H bond utilization. TOF based on ester dihydrosilylation,
e
f
g
assuming a reaction time of 0.5 h. PN = N-phosphinoamidinate. DPB = bis(o-diisopropylphosphinophenyl)phenylborane. Calculated relative to
ligand, not Cu loading. Tptm = tris(2-pyridylthio)methyl.
h
such that the PyEtPDEA LUMO’s are rendered inaccessible. The
relative redox innocence of this chelate can be considered a
disadvantage in preparing first-row metal complexes for
reductive catalysis; traditional first-row metal complexes tend
to engage in radical chemistry rather than two-electron
organometallic reaction pathways.24 Nonetheless, this study
confirms that the application of a redox noninnocent
supporting ligand is not a prerequisite for the development of
highly active Mn hydrosilylation catalysts. In considering 2-
mediated hydrosilylation, it is believed that Si−H oxidative
addition to yield a Mn(IV) intermediate is unlikely to occur.32
While the mechanism of this transformation remains under
investigation, we believe that Mn−Namide hydrosilylation to
yield an active Mn−H intermediate is the most likely reaction
pathway. It has previously been proposed that in situ reduction
of (3,5-tBu2-salen)MnN gives rise to a low-valent complex that
is active for hydrosilylation.21 Furthermore, the most active Fe-
based hydrosilylation precatalysts reported to date contain
readily removable amido ligands.6b,d
Comparison to Leading First-Transition Series Hydro-
silylation Catalysts. To further contextualize the activity of 2,
a comparison to prominent first-row metal catalysts is
warranted (Table 6). Relative to the late metals, early transition
metal catalysts have been sparingly used for carbonyl
hydrosilylation. Of the examples reported, the most effective
Sc,33 Ti,34 and Cr35 catalysts exhibit maximal TOFs of <1
min−1 (entries 1, 2, and 4). Late first-row metal catalysts for this
transformation have been more extensively investigated. A
recent report by Sydora, Turculet, and Stradiotto described an
N-phosphinoamidinate Fe complex (entry 6) that mediates
acetophenone hydrosilylation with TOFs of up to 393 min−1
(23600 h−1).6b While the most efficient Co, Ni, and Zn
catalysts for this transformation (entries 7, 8, and 10,
respectively) operate with maximal TOFs lower than those
determined for 2, comparison to leading Cu catalysts is more
difficult. The reaction in entry 9 proceeds with TOFs of up to
660 min−1; however, this is calculated relative to ligand instead
of Cu because the authors sought to minimize the most
expensive reagent, (S)-Xyl-P-Phos.9k Using a similar method-
ology, Lipshutz and co-workers reported an asymmetric
acetophenone hydrosilylation TOF of 77 min−1 at −50 °C,9n
suggesting greater TOFs might have been achieved at or near
ambient temperature. A number of well-defined Cu−H
hydrosilylation catalysts have since been described; however,
they have mostly been used for low-temperature asymmetric
ketone hydrosilylation and have not been evaluated for their
maximal TOF.9
CONCLUSION
■
The synthesis and characterization of a highly active Mn(II)
catalyst for the hydrosilylation of aldehydes and ketones have
been described. Even though PDI deprotonation resulted in a
redox innocent bis(enamido)tris(pyridine)-supporting chelate,
carbonyl hydrosilylation TOFs of up to 2475 min−1 and TONs
of up to 14170 were achieved using 2 under mild conditions.
This catalyst has also been found to tolerate a range of
functional groups and chemoselectively reduce aldehydes over
alkenes. Our results indicate that Mn complexes featuring redox
innocent supporting ligands have been greatly underutilized in
hydrosilylation catalysis and that their full utility in bond-
forming organic transformations has yet to be realized.
EXPERIMENTAL PROCEDURES
■
General Considerations. All reactions were performed inside an
MBraun glovebox under an atmosphere of purified nitrogen. Toluene,
tetrahydrofuran, pentane, and diethyl ether were purchased from
Sigma-Aldrich, purified using a Pure Process Technology solvent
system, and stored in the glovebox over activated 4 Å molecular sieves
and sodium before use. Benzene-d6 and chloroform-d were purchased
from Cambridge Isotope Laboratories and dried over 4 Å molecular
sieves. 1,3,5,7-Cyclooctatetraene was purchased from Strem, while
Mn0 powder and Hg0 were used as received from Sigma-Aldrich. 2,6-
Diacetylpyridine, 2-(2-aminoethyl)pyridine, acetophenone, p-methox-
yacetophenone, p-dimethylaminoacetophenone, p-chlorobenzalde-
hyde, 3-cyclohexene-1-carbaldehyde, and trans-cinnamaldehyde were
obtained from TCI America. Cyclohexanone, 2-hexanone, 2,4-
dimethyl-3-pentanone, cyclohexanecarboxaldehyde, p-tolualdehyde,
furfural, benzaldehyde, and p-anisaldehyde were purchased from
Sigma-Aldrich. p-Fluoroacetophenone and phenylsilane were obtained
from Oakwood. Celite, sodium hydroxide, anhydrous sodium sulfate,
(THF)2MnCl2, and p-fluorobenzaldehyde were purchased from Acros.
Ketones, aldehydes, and phenylsilane were scrupulously dried over 4 Å
molecular sieves, and solid substrates were recrystallized from ether
before use. Cyclohexanone, 2-hexanone, p-fluorobenzaldehyde, and
furfural were distilled prior to use. PyEtPDI was synthesized according
to a literature procedure.25
Solution 1H NMR spectra were recorded at room temperature on a
Varian 400-MR (400 MHz) NMR spectrometer. All 1H NMR and 13
C
NMR chemical shifts are reported in parts per million relative to
Si(CH3)4 using 1H (residual) and 13C chemical shifts of the solvent as
secondary standards. Elemental analyses were performed at Robertson
Microlit Laboratories Inc. (Ledgewood, NJ). Solid state magnetic
susceptibilities were determined at 23 °C using a Johnson Matthey
magnetic susceptibility balance calibrated with HgCo(SCN)4 and
10403
DOI: 10.1021/acs.inorgchem.5b01825
Inorg. Chem. 2015, 54, 10398−10406

Inorganic Chemistry
Article
K3Fe(CN)6. Solution state magnetic susceptibility was determined via
the Evans method on the Varian 400 MHz NMR spectrometer. UV−
visible spectra were recorded on an Agilent model 8453 spectropho-
tometer.
14.08%. Found: C, 55.27%; H, 4.90%; N, 13.79%. Magnetic
susceptibility (Guoy balance, 23 °C): μeff = 6.3 μB. 1H NMR
spectroscopy (benzene-d6, 23 °C): δ 62.76 (peak width at half-height
of 9830 Hz), 13.51 (2020 Hz), −31.63 (3000 Hz). UV−vis (from five
independent concentrations in CHCl3): λmax = 306 (ε = 3844 M−1
cm−1), 318 nm (ε = 2601 M−1 cm−1).
X-ray Crystallography. Single crystals suitable for X-ray
diffraction were coated with polyisobutylene oil in the glovebox and
transferred to a glass fiber with Apiezon N grease, which was then
mounted on the goniometer head of a Bruker APEX diffractometer
equipped with Mo Kα radiation. A hemisphere routine was used for
data collection and determination of the lattice constants. The space
group was identified, and the data were processed using the Bruker
SAINT+ program and corrected for absorption using SADABS. The
structures were determined using direct methods (SHELXS)
completed by subsequent Fourier synthesis and refined by full-matrix,
least-squares procedures on [F2]. Crystallographic parameters for 1
and 2 are provided in Table S1.
Electron Paramagnetic Resonance Spectroscopy. Instrumen-
tation. Studies were performed at the EPR Facility of Arizona State
University. Continuous wave EPR spectra were recorded at 106 K
using a Bruker ELEXSYS E580 continuous wave X-band spectrometer
(Bruker, Rheinstetten, Germany) equipped with a liquid nitrogen
temperature control system (ER 4131VT). The magnetic field
modulation frequency was 100 kHz with a field modulation of 1
mT from peak to peak. The microwave power was 1 mW, the
microwave frequency 9.40 GHz, and the sweep time 168 s.
Spin Hamiltonian. The EPR spectrum of 2 was interpreted using a
spin Hamiltonian, H, containing the electron Zeeman interaction with
the applied magnetic field B0, the zero-field interaction, and the
hyperfine coupling (hfc) term:37
Preparation of (PyEtPDEA)Mn (2). In the glovebox, a 20 mL
scintillation vial was charged with 8.12 g (40.62 mmol) of Hg0 in
approximately 6 mL of dry THF. To this was added 0.047 g (2.030
mmol) of freshly cut Na0, and the resulting amalgam was stirred for 25
min. After this, 0.017 g (0.162 mmol) of 1,3,5,7-cyclooctatetraene was
added and the mixture stirred for 5 min while it turned yellow in color.
Then a 10 mL THF slurry of 1 (0.202 g, 0.406 mmol) was added. An
instant color change to a greenish-brown solution was observed. The
reaction mixture was stirred at ambient temperature for 12 h, after
which time it was filtered through Celite under vacuum and the THF
was evacuated. The resulting residue was washed with pentane (2 × 5
mL) and dried. The residue was dissolved in toluene (∼15 mL) and
filtered through a Celite column. This was repeated once again, and
the filtrate was dried under vacuum to afford 2 (0.084 g, 49% yield).
Single crystals suitable for X-ray diffraction were grown from a
concentrated toluene solution layered with diethyl ether (1:1). Anal.
Calcd for C23H23N5Mn·C7H8: C, 69.76%; H, 6.05%; N, 13.56%.
Found: C, 68.39%; H, 5.78%; N, 13.10%. Complex 2 quickly
decomposes in the presence of air or water. Magnetic susceptibility
(Evans method, 23 °C): μeff = 3.8 μB. 1H NMR spectroscopy
(benzene-d6, 23 °C): δ 52.85 (7320 Hz), 33.10 (31850 Hz), −8.08
(16000 Hz, shoulder), −48.20 (3600 Hz). UV−vis (from five
independent concentrations in toluene): λmax = 348 (ε = 5066 M−1
cm−1), 428 (ε = 2528 M−1 cm−1), 512 (ε = 524 M−1 cm−1), 624 nm (ε
= 504 M−1 cm−1).
H = βS·g·B0 + hS·D·S + hS·A·I
e
where S is the electron spin operator, I is the nuclear spin operator of
55Mn, D and A are the zero-field interaction and hfc tensors,
respectively, both in frequency units, g is the electronic g tensor, βe is
the electron magneton, and h is Planck’s constant. The so-called zero-
field interaction occurs in the absence of an applied magnetic field
because of electron−electron repulsion. For d5 systems [e.g., Fe(III)
and Mn(II)], the zero-field interaction partially breaks the degeneracy
of the Kramer’s doublets causing the energy of these levels to shift by
General Procedure for the Hydrosilylation of Aldehydes. In
the glovebox, a benzene-d6 solution containing approximately 0.56
mmol of PhSiH3 and 0.56 mmol of aldehyde was added to a vial
containing approximately 0.0056 mmol of 2 at ambient temperature.
Upon turning brown in color following catalyst dissolution, the
resulting solution was transferred to a J. Young tube. The progress of
the reaction was monitored by 1H NMR spectroscopy at ambient
temperature.
General Procedure for the Hydrosilylation of Ketones. In the
glovebox, a benzene-d6 solution containing approximately 0.66 mmol
of PhSiH3 and 0.66 mmol of ketone was added to a vial containing
approximately 0.0066 mmol of 2 at ambient temperature. Upon
turning brown in color following catalyst dissolution, the resulting
solution was transferred to a J. Young tube. The progress of the
reaction was monitored by 1H NMR spectroscopy at ambient
temperature. For acetophenone and substituted acetophenone
substrates, enantiomeric products were observed.
2
the term DmS , where D is the axial zero-field splitting (ZFS)
parameter and mS is the magnetic quantum number corresponding to
the d5 system. Additional shifting of the energy of the Kramer’s
doublet is induced by the rhombic zero-field splitting term, which is
characterized by the parameter E. The electron Zeeman interaction
contributes to the Hamiltonian when an external magnetic field is
applied. This interaction is anisotropic and depends on the relative
orientation between the magnetic field and the molecular axes of the
Mn(II) ion. The Zeeman interaction breaks the remaining degeneracy
of the Kramer’s doublets causing an additional shift given by the term
gβeB0mS/h in the energy of these levels, where g is the g value. A
further energetic consideration is the contribution of the hfc
interaction, which represents the interaction between the magnetic
moment of the unpaired electron system and the magnetic moment of
the 55Mn nucleus. The hyperfine interaction is described to first order
by the expression AmSmI, where A is the hfc interaction along an
arbitrary magnetic field direction and mI is the magnetic quantum
number of the nucleus.
ASSOCIATED CONTENT
■
S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.5b01825.
Detailed hydrosilylation procedures and EPR and NMR
spectroscopic data (PDF)
Crystallographic information for 1 (CCDC 1403511)
Preparation of (PyEtPDI)MnCl2 (1). A 100 mL thick-walled glass
bomb was charged with 0.275 g (1.018 mmol) of (THF)2MnCl2,
0.728 g (1.962 mmol) of PyEtPDI, and approximately 20 mL of toluene
under an inert atmosphere. The bomb was then sealed under N2, taken
out of the glovebox, and heated to 125 °C in an oil bath for 48 h while
its contents were being stirred. Upon cooling, the reaction vessel was
brought back into the glovebox; the resulting light orange suspension
was vacuum filtered, and the insoluble solid was washed with toluene
(4 × 5 mL) and diethyl ether (3 × 5 mL) to remove the excess ligand.
The remaining solid material was dried under vacuum to afford 0.473 g
of 1 (93% yield) as a light orange solid. Single crystals suitable for X-
ray diffraction were obtained following recrystallization from dichloro-
methane. Anal. Calcd for C23H25N5Cl2Mn: C, 55.55%; H, 5.07%; N,
and 2 (CCDC 1403512) (CIF)
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: ryan.trovitch@asu.edu. Phone: (480) 727-8930.
Notes
The authors declare no competing financial interest.
10404
DOI: 10.1021/acs.inorgchem.5b01825
Inorg. Chem. 2015, 54, 10398−10406

Inorganic Chemistry
Article
Zhang, X.-C.; Sui, Y.-Z.; Wu, F.-F.; Xie, L.-J.; Chan, A. S. C.; Wu, J.
Chem. - Eur. J. 2011, 17, 14234−14240. (d) Zhang, X.-C.; Wu, F.-F.;
Li, S.; Zhou, J.-N.; Wu, J.; Li, N.; Fang, W.; Lam, K. H.; Chan, A. S. C.
ACKNOWLEDGMENTS
■
Acknowledgment is made to the Donors of the American
Chemical Society Petroleum Research Fund for support of this
research. We also thank Piper S. Boyll for screening 2 for olefin
hydrosilylation activity.
Adv. Synth. Catal. 2011, 353, 1457−1462. (e) Díez-Gonzal
́
ez, S.;
Escudero-Adan, E.; Benet-Buchholz, J.; Stevens, E. D.; Slawin, A. M.
́
Z.; Nolan, S. P. Dalton Trans. 2010, 39, 7595−7606. (f) Fujihara, T.;
Semba, K.; Terao, J.; Tsuji, Y. Angew. Chem., Int. Ed. 2010, 49, 1472−
1476. (g) Mostefaï, N.; Sirol, S.; Courmarcel, J.; Riant, O. Synthesis
REFERENCES
■
́
2007, 2007, 1265−1271. (h) Díez-Gonzalez, S.; Scott, N. M.; Nolan,
(1) (a) Junge, K.; Schroder, K.; Beller, M. Chem. Commun. 2011, 47,
̈
S. P. Organometallics 2006, 25, 2355−2358. (i) Lipshutz, B. H.; Lower,
A.; Kucejko, R. J.; Noson, K. Org. Lett. 2006, 8, 2969−2972. (j) Díez-
4849−4859. (b) Le Bailly, B. A. F.; Thomas, S. P. RSC Adv. 2011, 1,
1435. (c) Bullock, R. M. Catalysis without Precious Metals; Wiley-VCH:
́
Gonzalez, S.; Kaur, H.; Zinn, F. K.; Stevens, E. D.; Nolan, S. P. J. Org.
́
Weinheim, Germany, 2010. (d) Gosmini, C.; Begouin, J.-M.;
Moncomble, A. Chem. Commun. 2008, 3221−3233. (e) Gaillard, S.;
Renaud, J.-L. ChemSusChem 2008, 1, 505−509.
(2) Haynes, W. M. CRC Handbook of Chemistry and Physics: A Ready-
reference Book of Chemical and Physical Data, 94th ed.; Taylor &
Francis: Boca Raton, FL, 2013−2014.
(3) (a) Enthaler, S.; Junge, K.; Beller, M. Angew. Chem., Int. Ed. 2008,
47, 3317−3321. (b) Plietker, B. Iron Catalysis in Organic Chemistry;
Wiley-VCH: Weinheim, Germany, 2008.
Chem. 2005, 70, 4784−4796. (k) Wu, J.; Ji, J.-X.; Chan, A. S. C. Proc.
Natl. Acad. Sci. U. S. A. 2005, 102, 3570−3575. (l) Lee, D.; Yun, J.
Tetrahedron Lett. 2004, 45, 5415−5417. (m) Kaur, H.; Zinn, F. K.;
Stevens, E. D.; Nolan, S. P. Organometallics 2004, 23, 1157−1160.
(n) Lipshutz, B. H.; Noson, K.; Chrisman, W.; Lower, A. J. Am. Chem.
Soc. 2003, 125, 8779−8789. (o) Lipshutz, B. H.; Noson, K.; Chrisman,
W. J. Am. Chem. Soc. 2001, 123, 12917−12918. (p) Sirol, S.;
Courmarcel, J.; Mostefai, N.; Riant, O. Org. Lett. 2001, 3, 4111−4113.
(q) Brunner, H.; Miehling, W. J. Organomet. Chem. 1984, 275, C17−
C21.
(4) (a) Hitchcock, P. B.; Lappert, M. F.; Warhurst, N. J. W. Angew.
Chem., Int. Ed. Engl. 1991, 30, 438−440. (b) Speier, J. L.; Webster, J.
A.; Barnes, G. H. J. Am. Chem. Soc. 1957, 79, 974−979.
(10) For leading Zn examples, see: (a) Rit, A.; Zanardi, A.; Spaniol,
T. P.; Maron, L.; Okuda, J. Angew. Chem., Int. Ed. 2014, 53, 13273−
13277. (b) Lummis, P. A.; Momemi, M. R.; Lui, M. W.; McDonald, R.;
Ferguson, M. J.; Miskolzie, M.; Brown, A.; Rivard, E. Angew. Chem., Int.
Ed. 2014, 53, 9347−9351. (c) Łowicki, D.; Bezłada, A.; Mlynarski, J.
Adv. Synth. Catal. 2014, 356, 591−595. (d) Boone, C.; Korobkov, I.;
Nikonov, G. I. ACS Catal. 2013, 3, 2336−2340. (e) Pang, S.; Peng, J.;
Li, J.; Bai, Y.; Xiao, W.; Lai, G. Chirality 2013, 25, 275−280.
(5) (a) Srinivas, V.; Nakajima, Y.; Ando, W.; Sato, K.; Shimada, S.
Catal. Sci. Technol. 2015, 5, 2081−2084. (b) Peng, D.; Zhang, Y.; Du,
X.; Zhang, L.; Leng, X.; Walter, M. D.; Huang, Z. J. Am. Chem. Soc.
2013, 135, 19154−19166. (c) Tondreau, A. M.; Atienza, C. C. H.;
Darmon, J. M.; Milsmann, C.; Hoyt, H. M.; Weller, K. J.; Nye, S. A.;
Lewis, K. M.; Boyer, J.; Delis, J. G. P.; Lobkovsky, E.; Chirik, P. J.
Organometallics 2012, 31, 4886−4893. (d) Hojilla Atienza, C. C.;
Tondreau, A. M.; Weller, K. J.; Lewis, K. M.; Cruse, R. W.; Nye, S. A.;
Boyer, J. L.; Delis, J. G. P.; Chirik, P. J. ACS Catal. 2012, 2, 2169−
2172. (e) Tondreau, A. M.; Atienza, C. C. H.; Weller, K. J.; Nye, S. A.;
Lewis, K. M.; Delis, J. G. P.; Chirik, P. J. Science 2012, 335, 567−570.
(f) Troegel, D.; Stohrer, J. Coord. Chem. Rev. 2011, 255, 1440−1459.
(6) For leading Fe examples, see: (a) Blom, B.; Enthaler, S.; Inoue,
S.; Irran, E.; Driess, M. J. Am. Chem. Soc. 2013, 135, 6703−6713.
(b) Ruddy, A. J.; Kelly, C. M.; Crawford, S. M.; Wheaton, C. A.;
Sydora, O. L.; Small, B. L.; Stradiotto, M.; Turculet, L. Organometallics
2013, 32, 5581−5588. (c) Bhattacharya, P.; Krause, J. A.; Guan, H.
Organometallics 2011, 30, 4720−4729. (d) Yang, J.; Tilley, T. D.
Angew. Chem., Int. Ed. 2010, 49, 10186−10188. (e) Kandepi, V. V. K.
M.; Cardoso, J. M. S.; Peris, E.; Royo, B. Organometallics 2010, 29,
2777−2782. (f) Tondreau, A. M.; Darmon, J. M.; Wile, B. M.; Floyd,
S. K.; Lobkovsky, E.; Chirik, P. J. Organometallics 2009, 28, 3928−
3940. (g) Tondreau, A. M.; Lobkovsky, E.; Chirik, P. J. Org. Lett. 2008,
10, 2789−2792.
(f) Enthaler, S.; Schroder, K.; Inoue, S.; Eckhardt, B.; Junge, K.; Beller,
̈
M.; Drieβ, M. Eur. J. Org. Chem. 2010, 2010, 4893−4901. (g) Gajewy,
J.; Kwit, M.; Gawron
(h) Ger
́
ski, J. Adv. Synth. Catal. 2009, 351, 1055−1063.
́
ard, S.; Pressel, Y.; Riant, O. Tetrahedron: Asymmetry 2005, 16,
1889−1891. (i) Bette, V.; Mortreux, A.; Savoia, D.; Carpentier, J.-F.
Adv. Synth. Catal. 2005, 347, 289−302. (j) Bette, V.; Mortreux, A.;
Savoia, D.; Carpentier, J.-F. Tetrahedron 2004, 60, 2837−2842.
(k) Mastranzo, V. M.; Quintero, L.; Anaya de Parrodi, C. A.;
Juaristi, E.; Walsh, P. J. Tetrahedron 2004, 60, 1781−1789. (l) Mimoun,
H. J. Org. Chem. 1999, 64, 2582−2589. (m) Sattler, W.; Ruccolo, S.;
Rostami Chaijan, M.; Nasr Allah, T.; Parkin, G. Organometallics 2015,
34, 4717.
(11) For leading examples, see: (a) Bleith, T.; Wadepohl, H.; Gade,
L. H. J. Am. Chem. Soc. 2015, 137, 2456−2459. (b) Darwish, M.; Wills,
M. Catal. Sci. Technol. 2012, 2, 243−255. (c) Inagaki, T.; Ito, A.; Ito, J.;
Nishiyama, H. Angew. Chem., Int. Ed. 2010, 49, 9384−9387.
(d) Inagaki, T.; Phong, L. T.; Furuta, A.; Ito, J.; Nishiyama, H.
Chem. - Eur. J. 2010, 16, 3090−3096. (e) Morris, R. H. Chem. Soc. Rev.
2009, 38, 2282−2291. (f) Langlotz, B. K.; Wadepohl, H.; Gade, L. H.
Angew. Chem., Int. Ed. 2008, 47, 4670−4674. (g) Shaikh, N. S.;
Enthaler, S.; Junge, K.; Beller, M. Angew. Chem., Int. Ed. 2008, 47,
2497−2501. (h) Nishiyama, H.; Furuta, A. Chem. Commun. 2007,
760−762.
(7) For leading Co examples, see: (a) Zhou, H.; Sun, H.; Zhang, S.;
Li, X. Organometallics 2015, 34, 1479−1486. (b) Niu, Q.; Sun, H.; Li,
X.; Klein, H.-F.; Florke, U. Organometallics 2013, 32, 5235−5238.
̈
(c) Sauer, D. C.; Wadepohl, H.; Gade, L. H. Inorg. Chem. 2012, 51,
12948−12958. (d) Yu, F.; Zhang, X.-C.; Wu, F.-F.; Zhou, J.-N.; Fang,
W.; Wu, J.; Chan, A. S. C. Org. Biomol. Chem. 2011, 9, 5652.
(e) Brunner, H.; Amberger, K. J. Organomet. Chem. 1991, 417, C63−
C65. (f) Nesbit, M. A.; Suess, D. L. M.; Peters, J. C. Organometallics
2015, 34, 4741.
(12) (a) Valyaev, D. A.; Lavigne, G.; Lugan, N. Coord. Chem. Rev.
2015. (b) Trovitch, R. J. Synlett 2014, 25, 1638−1642.
(13) Pratt, S. L.; Faltynek, R. A. J. Organomet. Chem. 1983, 258, C5−
C8.
(8) For leading Ni examples, see: (a) Porter, T. M.; Hall, G. B.; Groy,
T. L.; Trovitch, R. J. Dalton Trans. 2013, 42, 14689−14692.
(b) Bheeter, L. P.; Henrion, M.; Brelot, L.; Darcel, C.; Chetcuti, M.
J.; Sortais, J.-B.; Ritleng, V. Adv. Synth. Catal. 2012, 354, 2619−2624.
(c) Postigo, L.; Royo, B. Adv. Synth. Catal. 2012, 354, 2613−2618.
(d) Tran, B. L.; Pink, M.; Mindiola, D. J. Organometallics 2009, 28,
2234−2243. (e) Chakraborty, S.; Krause, J. A.; Guan, H. Organo-
metallics 2009, 28, 582−586 and references cited therein. (f) MacMil-
lan, S. N.; Hill Harman, W.; Peters, J. C. Chem. Sci. 2014, 5, 590−597.
(g) Steiman, T. J.; Uyeda, C. J. Am. Chem. Soc. 2015, 137, 6104−6110.
(9) For leading Cu examples, see: (a) Roy, S. R.; Sau, S. C.; Mandal,
S. K. J. Org. Chem. 2014, 79, 9150−9160. (b) Albright, A.; Gawley, R.
E. J. Am. Chem. Soc. 2011, 133, 19680−19683. (c) Yu, F.; Zhou, J.-N.;
(14) Hilal, H. S.; Abu-Eid, M.; Al-Subu, M.; Khalaf, S. J. Mol. Catal.
1987, 39, 1−11.
(15) Mao, Z.; Gregg, B. T.; Cutler, A. R. J. Am. Chem. Soc. 1995, 117,
10139−10140.
(16) DiBiase Cavanaugh, M.; Gregg, B. T.; Cutler, A. R.
Organometallics 1996, 15, 2764−2769.
(17) Son, S. U.; Paik, S.-J.; Lee, I. S.; Lee, Y.-A.; Chung, Y. K.; Seok,
W. K.; Lee, H. N. Organometallics 1999, 18, 4114−4118.
(18) Son, S. U.; Paik, S.-J.; Chung, Y. K. J. Mol. Catal. A: Chem. 2000,
151, 87−90.
(19) Igarashi, M.; Fuchikami, T. Tetrahedron Lett. 2001, 42, 1945−
1947.
10405
DOI: 10.1021/acs.inorgchem.5b01825
Inorg. Chem. 2015, 54, 10398−10406

Inorganic Chemistry
Article
(20) Zheng, J.; Chevance, S.; Darcel, C.; Sortais, J.-B. Chem. Commun.
2013, 49, 10010−10012.
(21) Chidara, V. K.; Du, G. Organometallics 2013, 32, 5034−5037.
́
(22) Zheng, J.; Elangovan, S.; Valyaev, D. A.; Brousses, R.; Cesar, V.;
Sortais, J.-B.; Darcel, C.; Lugan, N.; Lavigne, G. Adv. Synth. Catal.
2014, 356, 1093−1097.
(23) Mukhopadhyay, T. K.; Flores, M.; Groy, T. L.; Trovitch, R. J. J.
Am. Chem. Soc. 2014, 136, 882−885.
(24) (a) Luca, O. R.; Crabtree, R. H. Chem. Soc. Rev. 2013, 42, 1440.
(b) Lyaskovskyy, V.; de Bruin, B. ACS Catal. 2012, 2, 270−279.
(c) Chirik, P. J.; Wieghardt, K. Science 2010, 327, 794−795.
(d) Bouwkamp, M. W.; Bowman, A. C.; Lobkovsky, E.; Chirik, P. J.
J. Am. Chem. Soc. 2006, 128, 13340−13341.
(25) Pal, R.; Groy, T. L.; Bowman, A. C.; Trovitch, R. J. Inorg. Chem.
2014, 53, 9357−9365.
(26) Reardon, D.; Aharonian, G.; Gambarotta, S.; Yap, G. P. A.
Organometallics 2002, 21, 786−788.
(27) Knijnenburg, Q.; Gambarotta, S.; Budzelaar, P. H. M. Dalton
Trans. 2006, 5442−5448.
(28) Palmer, G. In Physical Methods in Bioinorganic Chemistry.
Spectroscopy and Magnetism; Que, L. J., Ed.; University Science Books:
Sausalito, CA, 2000; pp 145−153.
(29) In the case of diisoproyl ketone, the formation of 30%
PhSiH2(OCH(iPr)2) is likely due to steric hindrance.
(30) Sugiyama, H.; Aharonian, G.; Gambarotta, S.; Yap, G. P. A.;
Budzelaar, P. H. M. J. Am. Chem. Soc. 2002, 124, 12268−12274.
(31) Russell, S. K.; Bowman, A. C.; Lobkovsky, E.; Wieghardt, K.;
Chirik, P. J. Eur. J. Inorg. Chem. 2012, 2012, 535−545.
(32) Commonly invoked Ojima and modified Ojima hydrosilylation
pathways rely on Si−H oxidative addition. For more information, see:
Ojima, I.; Kogure, T.; Kumagai, M.; Horiuchi, S.; Sato, T. J. Organomet.
Chem. 1976, 122, 83−97.
(33) LeBlanc, F. A.; Piers, W.; Parvez, M. Angew. Chem., Int. Ed.
2014, 53, 789−792.
(34) Berk, S. C.; Kreutzer, K. A.; Buchwald, S. L. J. Am. Chem. Soc.
1991, 113, 5093−5095.
(35) Le Bideau, F.; Henique, J.; Samuel, E.; Elschenbroich, C. Chem.
Commun. 1999, 1397−1398.
(36) In a prior assessment of Ni-mediated carbonyl hydrosilylation,
catalysts in refs 8e (ref 23) and 8b (ref 12b) were cited as the most
active for this transformation. However, TOFs of up to 2304 h−1 have
been reported in ref 8c.
(37) Weil, J. A.; Bolton, J. R. Electron paramagnetic resonance:
Elementary theory and practical applications; Wiley: Hoboken, NJ, 2007.
10406
DOI: 10.1021/acs.inorgchem.5b01825
Inorg. Chem. 2015, 54, 10398−10406