Activation of Molecular Hydrogen and Oxygen by PSiP Complexes of Cobalt

Article abstract of DOI:10.1002/ejic.201800915

The syntheses of Co^II halide complexes supported by κ³-(2-Cy₂PC₆H₄)₂SiMe (Cy-PSiP) ligation are detailed. Reduction of (Cy-PSiP)Co(PMe₃)I could be achieved under mild conditions using magnesium metal to generate the Co^I complex (Cy-PSiP)Co(PMe₃)N₂ in high yield. When this reaction was carried out under an atmosphere of CO, (Cy-PSiP)Co(CO)₂ was obtained. Unlike the facile reduction of Co^II to Co^I, attempts to access Co^III species supported by Cy-PSiP ligation proved challenging. Attempted oxidative addition reactions involving (Cy-PSiP)Co(PMe₃)N₂ were generally unsuccessful, with the sole exception of H₂, which reacted to afford the dihydride complex (Cy-PSiP)Co(PMe₃)(H)₂. The dihydride complex undergoes Co-H site exchange in solution and readily eliminates H₂. The Co^I precursor (Cy-PSiP)Co(PMe₃)N₂ is a competent precatalyst for the hydrogenation of terminal alkenes. Exposure of (Cy-PSiP)CoI to O₂ gas under anhydrous conditions led to rapid ligand oxidation at Si and P, with no evidence observed at low temperature for a Co^III superoxo or peroxo intermediate. Exclusive oxidation at Si to afford a Co^II-siloxy complex was observed upon treatment of (Cy-PSiP)CoI with one equiv. Me₃NO. While this siloxy complex did not react further with O₂, treatment with a second equiv. of Me₃NO led to subsequent oxidation involving one phosphino donor. This observation supports the notion that in the ligand oxidation reactivity observed with O₂, the O atoms incorporated at both Si and P are likely derived from the same O₂ molecule.

Full text of DOI:10.1002/ejic.201800915

A Journal of
Accepted Article
Title: Activation of Molecular Hydrogen and Oxygen by PSiP
Complexes of Cobalt
Authors: Luke J Murphy, Adam J Ruddy, Robert McDonald, Michael J.
Ferguson, and Laura Turculet
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Eur. J. Inorg. Chem. 10.1002/ejic.201800915
Link to VoR: http://dx.doi.org/10.1002/ejic.201800915

European Journal of Inorganic Chemistry
10.1002/ejic.201800915
Activation of Molecular Hydrogen and Oxygen by PSiP
Complexes of Cobalt
a
a
b
b
,a
Luke J. Murphy, Adam J. Ruddy, Robert McDonald, Michael J. Ferguson and Laura Turculet*
a
Department of Chemistry, Dalhousie University, 6274 Coburg Road, P.O. Box 15000, Halifax,
Nova Scotia, Canada, B3H 4R2
b
X-Ray Crystallography Laboratory, Department of Chemistry, University of Alberta, Edmonton,
Alberta, Canada, T6G 2G2
*
author to whom correspondence should be addressed: laura.turculet@dal.ca
https://www.dal.ca/faculty/science/chemistry/faculty-staff/our-faculty/laura-turculet.html
1
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201800915
ABSTRACT
II
3
The syntheses of Co halide complexes supported by κ -(2-Cy
2
PC
6
H
4
)
2
SiMe) (Cy-PSiP)
ligation are detailed. Reduction of (Cy-PSiP)Co(PMe
3
)I could be achieved under mild conditions
)N in high yield. When
was obtained. Unlike
the facile reduction of Co to Co , attempts to access Co species supported by Cy-PSiP ligation
proved challenging. Attempted oxidative addition reactions involving (Cy-PSiP)Co(PMe )N
were generally unsuccessful, with the sole exception of H , which reacted to afford the dihydride
I
using magnesium metal to generate the Co complex (Cy-PSiP)Co(PMe
3
2
this reaction was carried out under an atmosphere of CO, (Cy-PSiP)Co(CO)
2
II
I
III
3
2
2
complex (Cy-PSiP)Co(PMe
3
)(H)
2
. The dihydride complex undergoes Co-H site exchange in
I
solution and readily eliminates H
2
. The Co precursor (Cy-PSiP)Co(PMe
3
)N
2
is a competent
gas under
anhydrous conditions led to rapid ligand oxidation at Si and P, with no evidence observed at low
precatalyst for the hydrogenation of terminal alkenes. Exposure of (Cy-PSiP)CoI to O
2
III
II
temperature for a Co superoxo or peroxo intermediate. Exclusive oxidation at Si to afford a Co -
siloxy complex was observed upon treatment of (Cy-PSiP)CoI with one equiv Me NO. While this
siloxy complex did not react further with O , treatment with a second equiv of Me NO led to
subsequent oxidation involving one phosphino donor. This observation supports the notion that in
the ligand oxidation reactivity observed with O , the O atoms incorporated at both Si and P are
likely derived from the same O molecule.
3
2
3
2
2
2
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201800915
INTRODUCTION
The chemistry of transition metal pincer complexes has been an area of extensive
investigation over the past 20 years.[1] While bis(phosphino) PCP pincer complexes of the type
[
2]
pioneered by Shaw in the 1970s have been among the most widely studied, numerous alternative
pincer design motifs have been developed. In this regard, our group has been interested in
exploring the synthesis and reactivity of bis(phosphino)silyl (PSiP) late transition metal pincer
complexes,[3], [4] which we anticipated could be highly reactive due to the incorporation of the
strongly -donating silyl donor. Indeed, electron-rich platinum group metal complexes supported
3
by κ -(2-Cy
2
PC
6
H
4
2
) SiMe (Cy-PSiP) ligation developed in our group can facilitate a variety of
challenging bond activation processes, including C-H and N-H bond oxidative addition,[5] Si-C
bond cleavage,[6] and the reduction of carbon dioxide to methane using tertiary silanes.[7] The
incorporation of a silyl group into the pincer framework has also been shown to promote the
II
[8]
formation of novel low-coordinate complexes, such as four-coordinate Ru species.
Over recent years there has been increasing interest in replacing platinum group metals
with first-row transition metals in various reactivity applications due to their high abundance and
significantly lower cost.[9] As such, we have become increasingly interested in examining the
reactivity properties of first-row metal complexes supported by PSiP ligation. In particular,
building on our prior investigations of Cy-PSiP Rh and Ir species,[5] including aggressive bond
activation reactivity exhibited by the latter, we sought to prepare related (Cy-PSiP)Co complexes
and study their reactivity towards small molecule substrates. Herein we detail the synthesis and
II
characterization of low-coordinate (Cy-PSiP)Co halide complexes, as well as the reactivity of
I
such species under reducing conditions aimed at accessing (Cy-PSiP)Co complexes. The ability
I
of such (Cy-PSiP)Co species to undergo oxidative addition processes was evaluated, and evidence
3
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201800915
I
of H
2
activation was observed. In this regard, such Co species were found to be precatalysts for
II
alkene hydrogenation. We also describe the reactivity of (Cy-PSiP)Co species towards O
2
and
Me
3
NO, wherein we observe the formation of a siloxo fragment by formal insertion of an oxygen
atom into the Si-Co linkage. In the course of our investigation, two relevant publications pertaining
i
1
to this work appeared. Kim, Lee and co-workers reported on the conversion of [ Pr-P( -
i
[4i]
SiH)P]CoBr to ( Pr-PSiP)CoBr in the presence of base, and Nishibayashi and co-workers
2
reported on the synthesis of (Cy-PSiP)Co(PR
3
)N
2
species and their activity in catalytic N
2
reduction.[4k], [10]
RESULTS AND DISCUSSION
II
Synthesis of Co halide complexes of Cy-PSiP. We targeted the synthesis of low-
coordinate (Cy-PSiP)Co species by treatment of simple CoX
2
(X = halide) salts with the tertiary
, treatment with one
silane (Cy-PSiP)H in the presence of base (Scheme 1). In the case of CoCl
2
equiv (Cy-PSiP)H and excess triethylamine in THF solution led to intractable mixtures from which
pure material could not be isolated reliably. A minute quantity of X-ray quality crystals was
obtained from a concentrated toluene solution containing the crude product of this reaction. X-Ray
crystallographic analysis revealed the desired four-coordinate Co complex, (Cy-PSiP)CoCl (1,
Figure 1), which adopts distorted square-planar coordination geometry in the solid state with the
chloride ligand coordinated trans to the silyl group (Cl-Co-Si 152.63(2)°, P1-Co-P2 160.30(2)°).
II
Such examples of square planar Co -Cl species are relatively rare, with previously known
examples including (PNP)CoCl species with varying ligand modifications,[11] as well as a PNCNP-
supported pincer complex featuring N-diisopropylphosphino donors.[12] Comparison of the
metrical parameters for 1 and such crystallographically characterized PNP- and PNCNP-supported
4
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201800915
complexes reveals that 1 is significantly more distorted from ideal square planar geometry
previously reported Cl-Co-X angles in range of 171° – 180° for X = C or N), and features a longer
(
Co-Cl distance (2.2710(6) Å) than has previously been noted for such complexes (previously
reported Co-Cl distances in range of 1.919(2) – 2.2291(5) Å, where the shortest distance
corresponds to N-diisopropylphosphino-derived (PNCNP)CoCl complex reported by Kirchner[12]
t
N]CoCl reported by Schneider[11d]) possibly
under the same reaction
conditions was found to be a much more reliable route for the preparation of the iodide analogue
Cy-PSiP)CoI (2), which could be reproducibly isolated in >90% yield via this route. The X-ray
and longest distance corresponds to [( Bu
2
PCH
2
2 2
CH )
reflecting the strong trans influence of the silyl donor. The use of CoI
2
(
crystal structure of 2 was recently reported by Nishibayashi and co-workers,[4k] and revealed a
similar distorted square planar coordination geometry to that observed for 1, as was also observed
i
[4i]
in the case of the closely related bromide analogue ( Pr-PSiP)CoBr.
II
Scheme 1. Synthesis of (Cy-PSiP)Co -halide complexes.
1
The H NMR spectra of 1 and 2 (benzene-d
6
) revealed a number of broad resonances
3
1
29
between -35 and 15 ppm, while no P or Si NMR signals were observed, presumably due to the
proximity of these nuclei to the paramagnetic CoII center. Solution magnetic moment
measurements[13] for 2 (room temperature, benzene-d
) resulted in a μeff value of 1.86 μ , consistent
6
B
II
with an S = ½ magnetic ground state and low-spin square-planar Co . A similar electronic structure
5
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201800915
i
[4i]
t
was observed in the case of the closely related complex ( Pr-PSiP)CoBr, as well that of ( Bu-
t
t
H
),[14] and related PNP- and PNCNP-supported
POCOP)CoI ( Bu-POCOP = 1,3-( Bu
2
PO)
2
C
6
3
II
Co -halide complexes that feature similar square planar coordination geometry in the solid
state.[11],[12] Alternatively, the comparable Co halide complexes [(Ph
II
PCH
SiMe
2
2
2
2
) N]CoX (X =
Cl, Br, I) supported by PNP pincer ligation adopt tetrahedral coordination geometries and feature
3/2 magnetic ground states,[15] as does [( Bu
t
PCH
SiMe
S
=
2
2
2
2
) N]CoI, while
(tBu
N]CoCl shows spin transition behavior in solution.[11b]
[
2
PCH
Both of complexes 1 and 2 were found to coordinate PMe
the corresponding 17-electron adducts, 1-PMe and 2-PMe (Scheme 1). In the case of 1-PMe
this complex was prepared via in situ generation of 1 and subsequent treatment with PMe . A yield
of 27% was obtained for 1-PMe prepared in this manner, despite the difficulty in isolating
appreciable amounts of the precursor complex 1. The iodide analogue 2-PMe was isolated in 78%
yield by treatment of isolated 2 with PMe . As in the case of 2, no structural information could be
deduced from NMR data obtained for 1-PMe and 2-PMe due to paramagnetic shifting and
broadening of the resonances observed. The X-ray crystal structure of 1-PMe revealed that this
2
SiMe
2
)
2
3
in a facile manner to generate
3
3
3
,
3
3
3
3
3
3
3
complex adopts distorted trigonal bipyramidal geometry in the solid state, with the chloride ligand
and the silyl donor bound in the apical positions, and the phosphines occupying the equatorial
positions. This is in contrast to the structure of (Ph-PSiP)CoCl(PMe
3
)[10a] and the related
),[10b] in which the
3
bis(diphenylphosphino)silyl complex [ -C
6
H
4
(Ph
2
PCH
2
N)
2
SiMe]CoI(PMe
3
PMe
3
ligand is coordinated in the apical position trans to Si. Solution magnetic moment
and 2-PMe (room temperature, benzene-d ) resulted in μeff values of
measurements for 1-PMe
3
3
6
1
.89 and 1.65 μ
B
, respectively, consistent with an S = ½ magnetic ground state in each case. These
II
values are comparable to that of 1.8 μ
B
reported for the related five-coordinate Co complex
6
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201800915
4
i
Si) reported by Peters and co-workers,[16] which adopts a
(SiP
3
)CoCl (SiP
3
=  -(2- Pr
2
PC
6
H )
4 3
similar trigonal bipyramidal coordination geometry in the solid state.
Figure 1. Crystallographically determined structure of 1 (left) and 1-PMe (right) with thermal
3
ellipsoids shown at the 50% probability level. Hydrogen atoms have been omitted for clarity. Only
one of the two crystallographically independent molecules of 1-PMe is shown. Selected
interatomic distances (Å) and angles (°) for 1: Co-Cl 2.2710(6), Co-P1 2.2077(5), Co-P2
.2156(5), Co-Si 2.2340(6), Cl-Co-P1 98.64(2), Cl-Co-P2 99.02(2), Cl-Co-Si 152.63(2), P1-Co-
P2 160.30(2), P1-Co-Si 83.90(2), P2-Co-Si 84.441(19). Selected interatomic distances (Å) and
angles (°) for 1-PMe : Co-Cl 2.2957(7), Co-P1 2.2634(7), Co-P2 2.2906(7), Co-P3 2.2174(8), Co-
Si 2.2597(7), Cl-Co-Si 172.61(3), P1-Co-P2 132.80(3), P1-Co-P3 105.46(3), P2-Co-P3 119.61(3).
3
2
3
II
I
Reduction of (Cy-PSiP)Co to (Cy-PSiP)Co . Several attempts were made to reduce
I
complex 2 to a potential (Cy-PSiP)Co species. Reducing agents such as Na/Hg (0.5 and 1%),
sodium naphthalenide, and Mg were used with little success. In each case, 2 reacted with the
reducing agent within minutes either at room temperature or -35 °C under a N atmosphere to
2
7
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201800915
afford dark brown solutions. Despite multiple attempts to recrystallize/purify the crude products,
no pure material was successfully isolated from these attempted reduction reactions.
I
Scheme 2. Synthesis of (Cy-PSiP)Co species via Mg reduction of 2.
Figure 2. Crystallographically determined structure of 4 with thermal ellipsoids shown at the 50%
probability level. Hydrogen atoms have been omitted for clarity. Selected interatomic distances
(
Å) and angles (°): Co-P1 2.2098(5), Co-P2 2.2098(5), Co-Si 2.3051(5), Co-C1 1.760(2), Co-C2
1
1
.739(2), O1-C1 1.144(2), O2-C2 1.155(2), P1-Co-P2 124.60(2), P1-Co-C2 114.59(6), P2-Co-C2
16.87(6), Si-Co-C1 176.49(6), Si-Co-C2 84.09(7), C1-Co-C2 97.96(10).
I
We considered that PMe
3
coordination could possibly stabilize a Co species resulting from
the one electron reduction of 2. Indeed, treatment of 2-PMe with Mg powder at room temperature
3
8
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201800915
under a N
2
atmosphere led to formation of diamagnetic (Cy-PSiP)Co(PMe
3
)(N
2
) (3), which could
be isolated in >90% yield as a red solid by use of this synthetic route (Scheme 2). Complex 3 was
also independently synthesized by Nishibayashi and co-workers[4k] via treatment of 2 with PMe
3
and KC
8
under a N
2
atmosphere, though in substantially lower yield. The coordination of N to the
2
Co center in 3 was corroborated by the use of IR spectroscopy, which revealed a characteristic N
2
−
1
stretching frequency of 2065 cm . In a similar vein, treatment of 2 with CO (ca. 1 atm) and
subsequently with Mg powder at room temperature under a CO atmosphere led to formation of the
corresponding diamagnetic dicarbonyl complex, (Cy-PSiP)Co(CO) (4, Scheme 2) in high
2
yield.[17] The X-ray crystal structure of 4 (Figure 2) indicates distorted trigonal bipyramidal
geometry at Co, such that the phosphino donors and a CO ligand are coordinated in the equatorial
positions (P1-Co-P2 124.60(2)°, P1-Co-C2 114.59(6)°, and P2-Co-C2 116.87(6)°) while Si and
the second CO ligand are in the axial positions (Si-Co-C1 176.49(6)°). The presence of
inequivalent CO ligands in 4 was confirmed by use of carbon NMR spectroscopy, whereby each
1
3
1
CO group gives rise to a unique C{ H} NMR resonance at 207.3 and 220.8 ppm, respectively.
In addition, two distinct CO stretches were observed in the infrared spectrum of 4 (1960 and 1909
cm ). Related PCP, POCOP,[19] PNCNP,[12] and PNP[11a, 11b] dicarbonyl complexes of Co have
been reported. While most such complexes that have been crystallographically characterized adopt
square pyramidal coordination geometry with a CO ligand in the apical position, the solid state
−
1
[18]
structure of 4 most closely resembles that of (Ph-PCP)Co(CO)
2
(Ph-PCP = 1,3-
(Ph
2
PCH
2
)
C
2 6
H
3
),[18] which features a similar distorted trigonal pyramidal geometry with a P-Co-
P angle of 134.6(1)° (cf. 124.60(2)° for 4). The CO stretching frequencies reported for the latter
−
1
complex (1982 and 1929 cm ) are significantly higher than those noted for 4, suggesting that there
is increased back-bonding in 4 relative to (Ph-PCP)Co(CO) . By comparison, the CO stretching
2
9
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201800915
frequencies for 4 are closest in value to those reported by Kirchner[12] for (PNCNP)Co(CO)
, which
gives rise to CO stretching bands at 1963 and 1906 cm , as well as to those reported recently by
Guan[19b] for a series of (POCOP)Co(CO) species (e.g. 1966 and 1912 cm−1 for (1,3-
). Interestingly, while the related (PNP)Co(CO) (PNP
2
−
1
2
(tBu
(tBu
PO)
C
H
)Co(CO)
=
2
2
2
6
3
2
2
−
PCH
2
SiMe
2
)
2
N ) complex has been observed in solution under 1 atm of CO and features
−

significantly reduced CO stretching frequencies (1931 and 1840 cm ) relative to 4, this complex
readily dissociates CO and is in equilibrium with the isolable monocarbonyl adduct.[11b] No
evidence for facile dissociation of CO from 4 was observed.
Investigation of oxidative addition reactions at (Cy-PSiP)CoI and alkene
I
hydrogenation catalysis. Having successfully prepared isolable Co complexes supported by Cy-
PSiP ligation, we sought to investigate the ability of such complexes to undergo oxidative addition
reactions. Treatment of 3 with I
2
(1 or 10 equiv) resulted in an exothermic reaction and the
formation of a significant amount of brown precipitate. No clean Co-containing product could be
3
1
isolated from these reaction mixtures. P NMR analysis of the reaction mixtures indicated the
presence of (Cy-PSiP)H in solution (-7.8 ppm). Alternatively, the reaction of 3 with iodobenzene
1
(
1 or 10 equiv) resulted in an immediate color change of the solution from orange to deep red. H
NMR analysis of these reaction mixtures indicated the disappearance of 3 as well as the formation
1
of new unidentified, paramagnetic products. No H NMR resonances that could be attributed to
biphenyl were observed. Attempts to cleanly isolate the products of this reaction have not been
successful thus far. The reaction of 4 with either I or MeI also led to the formation of intractable
2
mixtures containing unidentified paramagnetic species.
We next turned our attention to the reaction of 3 with H . Treatment of a degassed benzene-
2
d
6
solution of 3 with H (ca. 1 atm) at room temperature resulted in a color change from orange to
2
1
0
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201800915
3
1
1
yellow-brown over the course of two minutes. Analysis of the reaction mixture by use of P{ H}
1
and H NMR spectroscopy indicated the quantitative formation of a new diamagnetic species (5,
Figure 3), which gives rise to two broad 31P{ H} NMR resonances at 91.6 and 0.1 ppm
1
corresponding to chemically equivalent Cy-PSiP phosphino groups and PMe , respectively. The
3
1H NMR spectrum of 5 features a hydride resonance at -13.51 ppm (broad t, JPH = 38 Hz) that
integrates to two hydrogen atoms (relative to the Cy-PSiP ligand backbone). The formation of
complex 5 was also observed spectroscopically when 3 was reacted with 10 equiv H
THF solution at room temperature. The dehydrogenation of H N·BH does not appear to be
catalytic, as only a small amount of dehydrogenated [BH NH product (relative to unreacted
NBH ) was present after the reaction was complete, as determined by B NMR analysis.
Complex 5 was found to be stable in solution at room temperature for multiple days when kept
under an atmosphere of H . However, exposure of 5 to vacuum resulted in significant
decomposition, which precluded the isolation of this complex. Furthermore, when a solution of 5
3
N·BH
3
in
3
3
2
]
2 n
1
1
[20]
H
3
3
2
3
1
was simply exposed to an atmosphere of N
over the course of several hours.
2
, the regeneration of 3 was observed (by P NMR)
III
To a first approximation, complex 5 may be formulated as either a classical Co dihydride
I
complex (Cy-PSiP)Co(PMe
3
)(H)
2
or a Co dihydrogen complex (Cy-PSiP)Co(PMe
3
)(H
2
) (Figure
3
). While dihydrogen complexes of first row transition metals remain rare,[21] several well-
I
[14, 22]
characterized examples of Co -dihydrogen complexes have been reported in recent years.
In
this context, Peters and co-workers[22a] have isolated closely related Co-dihydrogen complexes
I
supported by tris-(o-diisopropylphosphinophenyl)silyl ligation (SiP
adduct with H (Figure 4). While (SiP )Co(H
crystallographic characterization of this complex, H
3
) by treatment of a Co -N
2
2
3
2
) is thermally stable, allowing for X-ray
is displaced from the Co coordination sphere
2
1
1
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201800915
to re-form (SiP
3
)Co(N
2
) upon exposure to a N
2
atmosphere. Similar reactivity was subsequently
reported by Fout and co-workers,[22b] who utilized the bis(carbene) pincer ligand bis(mesityl-
benzimidazol-2-ylidene)phenyl (MesCCC) to prepare Co -dihydrogen complexes of the type
I
(MesCCC)Co(H
)(PR
) (R = Me, Ph) by treatment of the corresponding Co -N
I
adducts with H
2
3
2
2
(
Figure 4). As in the case of (SiP
3
)Co(H
2
), (MesCCC)Co(H
2
)(PR
3
) is indefinitely stable under an
. By
H
2
atmosphere, but slowly converts to (MesCCC)Co(N
2
)(PR ) upon exposure to 1 atm of N
3
2
comparison, Caulton and co-workers have reported that treatment of the three-coordinate complex
(tBu
classical dihydride complex.[23]
[
2
PCH
2
SiMe
2
)
2
N]Co with ca. 4 atm of H afforded partial conversion to the corresponding
2
Figure 3. Some possible structural formulations for the species arising from treatment of (Cy-
PSiP)CoN (PMe ) (3) with H
2
3
2
.
1
2
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201800915
I
Figure 4. Examples of previously reported five-coordinate nonclassical Co dihydrogen
complexes.
1
1
31
Figure 5. Partial (a) H and (b) H{ P} NMR spectra (hydride region) of complex 5 in toluene-d
8
1
1
31
(
300 MHz, 25 °C), as well as (c) H and (d) H{ P} NMR spectra (hydride region) of complex 5-
d in toluene-d (300 MHz, 25 °C).
8
In the absence of neutron diffraction data, two NMR techniques that have traditionally been
1
utilized for the characterization of nonclassical dihydrogen complexes are the measurement of H
relaxation rates (T1 (min)) for the hydride resonance, and the measurement of 1JHD for the partially
deuterated complex.[21a, 24] In the case of the former approach, while reduced values of T1 (min)
(
generally less than 35 ms) are typically associated with nonclassical H complexes, it has been
2
1
3
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201800915
noted that T
1
relaxation can be significantly affected by metal nuclei that have a high gyromagnetic
ratio, such as Co.[25] Thus, low T1 (min) values are not necessarily indicative of nonclassical H
2
coordination in the case of Co. By comparison, the value of JHD for a partially deuterated sample
(1
HD in the range of 15–35 Hz has been cited as typical for nonclassical H complexes) can be
J
2
more informative in such cases, and has been correlated to the H-H distance of the coordinated
H
2
.[24, 26] As such, in an effort to gain better understanding of the H
binding mode in 5, complex
2
3
was treated with HD gas to afford the partially deuterated analogue 5-d. While the resulting
1
31
H{ P} NMR spectrum of 5-d (toluene-d
8
) does reveal changes in the appearance of the hydride
resonance relative to 5, these changes are not consistent with H-D coupling (Figure 5). Rather, it
appears that two broad overlapping hydride resonances can now be found in the region of -13 to
-
14 ppm. The broad nature of the NMR resonances observed for 5-d could in principle conceal a
small H-D coupling. While such broadening may be partly attributed to the quadrupolar nature of
the Co nucleus, we also carried out variable temperature NMR experiments for both 5 and 5-d to
determine if temperature dependent coalescence phenomena are implicated. Indeed, upon heating
1
a sample of 5 in toluene-d
8
solution up to 80 °C under an H
2
atmosphere, the Co-H H NMR
resonance at -13.5 ppm sharpens considerably to reveal an apparent triplet of doublets (2JHP = 18,
2 Hz, Figure 6a) that integrates as 2 H relative to resonances assigned to the Cy-PSiP ligand; this
temperature-dependent phenomenon is reversible upon cooling the sample back to room
4
1
31
temperature. The H{ P} NMR spectrum of 5 at 80 °C reveals a singlet at -13.5 ppm, confirming
that H-H coupling is not observed at this temperature (Figure 6b). No significant changes were
observed in the 31P{ H} NMR spectrum of 5 upon heating to 80 °C (see the Supporting
1
3
1
1
Information), and the relatively broad P{ H} NMR features of 5-d at temperatures ranging from
20 to 80 °C are not appreciably different from those observed for 5. By comparison, heating a
-
1
4
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201800915
sample of 5-d in toluene-d
8
solution under an HD atmosphere did not result in comparable
1
1
31
sharpening of the H NMR resonance centered at -13.5 ppm. However, the H{ P} NMR spectrum
of 5-d at 80 °C reveals two singlet resonances at -13.3 and -13.5 ppm (Figure 7), which we propose
correspond to a mixture of the isotopomers 5 and 5-d that may form as a result of rapid H/D
scrambling. Such H/D scrambling phenomena have been previously observed in the reaction of
low valent Co species with HD or mixtures of H
2
and D
2
.[14, 22a-c, 25c]
1
1
31
Figure 6. Partial variable temperature (a) H and (b) H{ P} NMR spectra (hydride region) of
complex 5 in toluene-d (300 MHz).
8
1
5
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201800915
1
31
Figure 7. Partial H{ P} NMR spectra (hydride region) of (a) complex 5-d formed upon addition
of HD to 3 and (b) complex 5 formed upon addition of H
2
to 3 in toluene-d (300 MHz, 80 °C).
8
1
The apparent absence of observable H-D coupling in the H NMR spectrum of 5-d suggests
III
that 5 is likely better formulated as a classical Co dihydride complex. A number of structural
formulations for such a six-coordinate dihydride species are possible (Figure 3, A - D). At first
glance, the NMR spectroscopic features observed for 5 at high temperature are not fully consistent
with any of the static dihydride structures depicted in Figure 3, as structures A – D should each
give rise to distinct Co-H environments. While the Co-H ligands are chemically non-equivalent
for A, B and D, in the case of a static structure C the hydride ligands are chemically equivalent but
magnetically nonequivalent in the presence of phosphorus coupling. As a single resonance is
1
observed in the H NMR spectrum of complex 5 at ambient temperature, a rapid dynamic process
that interchanges Co-H environments can be invoked. Such site-exchange in six-coordinate metal
dihydride complexes has been studied extensively, including the possibility of dihydrogen
complexes as intermediates.[25c, 27],[28] While such a process can involve dissociation of phosphine
(
either PMe
or a ligand arm), we have not observed direct 31P NMR evidence for such an
3
intermediate in the range of -80 to 80 °C. X-Ray crystallographic data has provided examples of
3
the flexibility of  -(Cy-PSiP) coordination, with P-Co-P angles ranging from 124 - 160° (vide
3
supra), which suggests that both fac- and mer- -(Cy-PSiP) coordination are feasible and non-
1
6
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201800915
dissociative mechanisms for exchange, such as the “trigonal twist” that has been invoked in some
circumstances,[27c, 29] can be accommodated. Upon cooling a sample of 5 in toluene-d
8
solution
under an H
2
atmosphere, decoalescence is observed, such that four relatively broad, but distinct
1
resonances (ca. 2:1:1:2 ratio) are found in the hydride region of the H NMR spectrum at -80 °C
3
1
1
(
Figure 6). The P{ H} NMR spectrum of 5 at this temperature features resonances consistent
with the presence of two (Cy-PSiP)Co(PMe )(H) species in solution in a ca. 2:1 ratio, where each
3
2
of these gives rise to a single resonance corresponding to the Cy-PSiP phosphino donors (at 87.9
br d, 2JPP = 23 Hz) and 86.6 (br s) ppm, respectively). Thus it appears that two (Cy-
(
PSiP)Co(PMe
in solution at low temperature. These observations further support the argument that (Cy-
PSiP)Co(PMe )(H) exhibits complex dynamic behavior. Given the structural similarity between
and Peters’ (SiP )Co(H ), it is interesting that the latter complex coordinates H in a -fashion,
while the former appears to cleave the H-H bond. To some degree, this may reflect the increased
3
)(H)
2
species, each featuring inequivalent Co-H ligand environments, are present
3
2
5
3
2
2
donor ability of PMe
Interestingly, (MesCCC)Co(N
alkene hydrogenation, including room temperature reactivity.[22b] Mechanistic studies revealed
that the dihydrogen complex (MesCCC)Co(H
)(PPh ) is the resting state of the active catalyst,
3
in 5 relative to the diisopropyl aryl phosphino donors of the SiP
3
ligand.
2
)(PPh ) has been shown to be an effective pre-catalyst for
3
2
3
I
III
which is proposed to cycle through Co /Co intermediates. Such examples of Co-catalyzed alkene
hydrogenation catalysis involving metal-based redox processes are relatively rare.[23b, 30] In an
effort to assess the competency of 3 in alkene hydrogenation catalysis, the reduction of 1-octene
with hydrogen gas was evaluated (Table 1, entries 1 - 6). At a loading of 5 mol% 3, no appreciable
1
conversion to octane was observed (by H NMR analysis relative to an internal standard of
hexamethylbenzene) after 22 h at room temperature under 1 atm of H . Heating of the reaction
2
1
7
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201800915
Table 1. Alkene hydrogenation catalysis.
Catalyst
Loading
H
2
Pressure
Temperature
(°C)
Time
(h)
Conversion
Entry
Substrate
a
(atm)
(%)
(
mol %)
5.0
b
1
2
3
4
5
6
7
8
9
1-octene
1
1
25
60
25
25
60
60
60
60
60
60
22
22
4
22
4
4
4
4
4
<5
28
40
50
95
96
1-octeneb
5.0
5.0
5.0
5.0
2.5
2.5
5.0
2.5
1-octene
1-octene
10
10
10
10
10
10
10
10
b
1-octene
1-octene
5-hexen-2-one
5-hexen-2-one
cyclohexene
cyclohexene
c
46
73
c
21
27
1
0
5.0
4
a
1
Conversion was determined by H NMR integration relative to an internal standard (hexamethylbenzene
for reactions in benzene-d or trimethoxybenzene for reactions in toluene-d ; average of two runs).
6
8
b
c
Reaction was carried out in benzene-d . Selective conversion to 2-hexanone.
6
mixture at 60 °C for 22 h afforded only minimal (28%) conversion to octane. Increasing the H
2
pressure to 10 atm resulted in 40% conversion after 4 h at room temperature, and 50% conversion
to octane after 22 h at room temperature. By comparison, heating the reaction mixture at 60 °C for
4
h under 10 atm of H
Table 1, entry 6) afforded comparable conversion (96%) after 4 h at 60 °C under 10 atm of H
Selectivity for alkene hydrogenation over ketone hydrogenation was demonstrated using 5-hexen-
-one, which led to 73% conversion to 2-hexanone with a 5 mol% catalyst loading (Entry 8).
Lastly, under comparable reaction conditions, the hydrogenation of cyclohexene proved
2
afforded 95% conversion to octane. Reducing the loading of 3 to 2.5 mol%
(
2
.
2
challenging, affording 27% conversion to cyclohexane after 4 h at 60 °C under 10 atm of H
2
(entry
1
0). By comparison, the related complex (MesCCC)Co(N
2
)(PPh ) achieved >99% conversion of 1-
3
octene to octane after 3 h at room temperature at a catalyst loading of 2 mol% under 4 atm of H
2
,
while >99% conversion of cyclohexene to cyclohexane was achieved after 22 h at 60 °C (2 mol%
1
8
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201800915
catalyst, 4 atm of H
2
). These results indicate that while (MesCCC)Co(N
2
)(PPh
3
) is significantly
more active for alkene hydrogenation catalysis, complex 3 is nonetheless a competent precatalyst
for the hydrogenation of terminal alkenes under similar reaction conditions. As such, the (PSiP)Co
system described herein represents a relatively rare example of Co-mediated alkene hydrogenation
featuring redox-innocent ancillary ligation.
II
Reactivity of (Cy-PSiP)Co toward molecular oxygen. In an effort to further probe the
reactivity of (Cy-PSiP)Co species with small molecule substrates, we also evaluated the reaction
of 2 with O . Molecular oxygen is the most readily available and inexpensive oxidant, and has
2
been investigated widely for application in catalytic oxidation reactions.[31] Cobalt complexes have
been studied extensively in this regard.[32] The propensity of Co species to reversibly bind[33] and
activate[34]
Co species with O
Cl, I, N ; PNP = ( Bu
O
2
has also been investigated. Studies involving the reactivity of bis(phosphino) pincer
are limited to a report by Caulton[11b] involving four-coordinate (PNP)CoX (X
2
t
−
=
3
2
PCH
2
SiMe
,[35] with no discernible intermediate even at low temperature. The
at low temperature to afford a diamagnetic
) complex that decomposed upon subsequent warming to
2
)
2
N ), which underwent rapid oxidation of both phosphino
donors upon treatment with O
2
I
three-coordinate Co complex (PNP)Co reacted with O
2
species presumed to be a (PNP)Co(O
2
generate intractable mixtures.[23b]
Interestingly, it was found that bubbling of dry O through a benzene solution of 2 at room
2
temperature led to a rapid color change of the solution from red-orange to blue. A paramagnetic
blue solid (6) was isolated in high yield from this reaction mixture (Scheme 3). The
crystallographically determined solid state structure of 6 revealed the formal insertion of two
II
oxygen atoms, one into the Si-Co bond, and the other into a P-Co bond to generate a Co -siloxo
complex with coordinated phosphine, phosphine oxide and iodide ligands in a distorted tetrahedral
1
9
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201800915
geometry (Figure 8). The value of 4.16 B was measured by Evans’ method at room temperature
for the solution-phase (benzene-d
6
) magnetic moment of 6, which is in the range of magnetic
II
moments expected for high-spin Co in a tetrahedral geometry (S = 3/2).
II
Scheme 3. Reactivity of 2 toward O
2
and Me
3
NO to generate Co products resulting from both
double- (6) and single- (7) Cy-PSiP ligand oxidation.
Figure 8. Crystallographically determined structures for 6 (left) and 7 (right) with thermal
ellipsoids drawn at the 50% probability level. Solvent molecules and hydrogen atoms have been
omitted for clarity. Only one of the two crystallographically independent molecules of 7 is shown.
Selected interatomic distances (Å) and angles (°) for 6: Co-I 2.5688(3), Co-P2 2.3573(6), Co-O1
1
.9657(14), Co-O2 1.8805(13), P1-O1 1.5141(14), Si-O2 1.6018(15), I-Co-P2 116.630(17), I-Co-
2
0
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201800915
O1 116.07(4), I-Co-O2 122.80(4), P2-Co-O1 99.11(4), P2-Co-O2 99.75(5), O1-Co-O2 98.33(6),
Co-O1-P1 139.48(9), Co-O2-Si 117.36(8). Selected interatomic distances (Å) and angles (°) for 7:
Co-I 2.5675(4), Co-P1 2.3591(7), Co-P2 2.3748(7), Co-O 1.8767(16), Si-O 1.6041(17), I-Co-P1
1
08.351(19), I-Co-P2 108.389(19), I-Co-O 123.99(5), P1-Co-P2 126.07(2), P1-Co-O 96.49(5),
P2-Co-O 94.31(5), Co-O-Si 117.10(9).
i
A similar example of PSiP ligand oxidation has been reported for an ( Pr-PSiP)Ni anilido
complex.[36] In this case, reaction with aerobic CO
led to the formation of multiple Ni species,
2
II
including a dinuclear Ni -carbonato complex featuring oxidation at P and Si (Figure 9, G).
Related reactivity involving oxidation at Si exclusively has also been reported (Figure 9, H - L).
Milstein and co-workers[37] observed that exposure of a Pt -chloride precursor supported by a
bis(diisopropylphosphino)silyl ligand featuring an Si-H unit to air in benzene solution over the
II
II
course of a month afforded a Pt -metallosilanol species (Figure 9, H). This reactivity was
accelerated by addition of an Ir catalyst that had previously been shown to facilitate the hydrolytic
oxidation of organosilanes to silanols.[38] As well, Stobart and co-workers[39] have reported on the
II
related reactivity of a bis(diphenylphosphinopropyl)silyl Ru complex under aerobic conditions in
refluxing benzene, which afforded a Ru species featuring the formal insertion of two oxygen
atoms, one into the Si-Ru linkage and a second into a Si-Me linkage in the ligand backbone (Figure
9
, J). It is noteworthy that these examples all involve exposure of silyl metal complexes to air,
which also implicates water as a possible source of reactivity. In this regard, the metal catalyzed
hydrolysis and alcoholysis of hydrosilanes is well-established,[40] and examples of similar
oxidation at Si have been reported involving hydrolysis of PSiP-supported complexes in the
absence of O
2
(Figure 9, K - L). [39, 41] Lastly, an intriguing related example of oxidation at Si was
reported by Puddephatt and co-workers[42] for a Pt -dimethyl complex supported by bis(2-pyridyl)-
II
2
1
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201800915
dimethylsilane (bps). Oxidation of (bps)PtMe
2
with oxygen/MeOH occurs with cleavage of a Me-
IV
Si bond to afford a Pt -siloxy species (Figure 9, I).
Figure 9. Previously reported examples of PSiP and related NSiN ligand oxidation.
While in most cases the mechanisms for the formation of these complexes are not fully
known, in the case of the Ru example, the (biPSi)RuHL
2
(biPSi = (Ph
2
PCH
2
CH
2
CH
2
)
2
SiMe)
may
−;
precursor is coordinatively saturated, and as such, the authors suggest that reactivity with O
2
III
occur via an outer-sphere electron transfer process to generate a cationic Ru species and O
2
subsequent attack of superoxide on Si would lead to the Si-O linkages observed in the product J
(
Figure 9).[39] Interestingly, exposure of the siloxane species K to O
2
does not lead to the formation
II
of J. In the case of the Ni example G, O
2
activation involving Ni is generally not well-
established.[43] Moreover, the observation of multiple unidentified products in this reaction further
complicates the mechanistic possibilities.[36] By comparison, Puddephatt and co-workers[42]
propose that the siloxane I (Figure 9) is formed by a pathway involving initial formation of a
IV
hydroperoxo Pt cation with a methoxide anion, which reacts rapidly with a second molecule of
IV
(bps)PtMe
2
to form a cationic Pt -hydroxo complex with a methoxide anion. Nucleophilic attack
of the methoxide group at Si and methyl group transfer to Pt, followed by the displacement of the
2
2
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201800915
methoxo group from Si by the Pt-OH group affords the product I with elimination of methanol.
This reactivity thus requires both O and an alcohol.
By comparison with the aforementioned examples, the reaction of 2 with O
2
2
was conducted
under anhydrous conditions. While we cannot discount the involvement of adventitious water in
II
this transformation, coordination of O
2
by Co species to form superoxo and -peroxo complexes
is well-established,[33, 44] which could implicate such species in the formation of 6. Attempts to
observe such an intermediate by treatment of 2 with O at -78 °C in toluene solution revealed
2
1
exclusive formation of 6, as indicated by H NMR analysis of the reaction mixture in the range of
-
80 - 0 °C.
In an effort to shed further light on the transformation described above, we also pursued
the reactivity of 2 with the oxygen atom transfer agent Me NO (Scheme 3). It was found that
NO in THF solution led to the formation of a new paramagnetic
) of the isolated blue solid gave rise to
3
treatment of 2 with one equiv Me
3
1
Co species (7). The H NMR spectrum (benzene-d
6
paramagnetically shifted resonances that are distinct from those observed for 6. The
crystallographically determined solid state structure of 7 revealed the formal insertion of a single
oxygen atom into the Si-Co bond, to afford a bis(phosphino)siloxy complex featuring a distorted
tetrahedral geometry at the Co center (Scheme 3, Figure 8). The value of 4.14 B was measured
by Evans’ method at room temperature for the solution-phase (benzene-d ) magnetic moment of
6
II
7
, which is in the range of magnetic moments expected for high-spin Co in tetrahedral geometry
(
S = 3/2). Interestingly, while 7 does not appear to react further with O
2
, treatment of 7 with a
NO led to the clean formation of 6 via formal insertion of the second oxygen
NO did not result in further reaction.
is surprising and may indicate that both O atoms in 6 are
second equiv Me
3
atom into a Co-P bond. Treatment of 6 with additional Me
The lack of reactivity of 7 toward O
3
2
2
3
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201800915
provided by a single O molecule in its reaction with 2. A similar observation was made in related
2
Ru chemistry reported by Stobart (vide supra).[39]
Related reactivity of (PNP)Co and (PCP)Ni species with oxygen atom transfer agents has
been previously documented. Caulton and co-workers reported that treatment of (PNP)CoCl (PNP
(tBu
PCH
SiMe
N ) with two equiv iodosobenzene, PhI=O, resulted in the oxidation of both
−
=
2
2
2
)
2
phosphino donors to afford the [P(O)NP(O)]CoCl product previously obtained from the reaction
.[11b] The reaction of the three-coordinate Co complex (PNP)Co with one
I
of (PNP)CoCl with O
2
equiv PhI=O resulted in the formation of three cobalt iodide species: (PNP)CoI (minor),
[
P(O)NP(O)]CoI (minor), and [P(O)NP]CoI (major).[23b] All three products feature oxidation at
II
the metal to Co , and the latter two species feature either double or single insertion, respectively,
of an oxygen atom into a Co-P linkage. While the mechanism by which the major product
[P(O)NP]CoI is formed was not determined experimentally, the authors suggest a possible
pathway involving the generation of a transient (PNP)Co=O species that undergoes subsequent
nucleophilic phosphine attack at the oxo functionality. Such an intramolecular process involving
a late transition metal oxo complex has been reported by Milstein and co-workers for a
+
[45]
[
(PCN)Pt=O] species.
In contrast, the putative Rh complex (PNP)Rh=O generated by the
t
reaction of [( Bu
2
PCH
2
SiMe
2
)
2
N]Rh with either amine-N-oxides, or N O, undergoes
2
t
intramolecular C-H bond activation involving a P Bu substituent to afford a cyclometalated
hydroxy complex.[46]
In the case of (PCP)Ni, Piers and co-workers[47] have recently reported on cationic NiII
species that reacted with amine-N-oxide reagents to afford products resulting from formal oxygen
atom insertion into either one or two of the Ni-P bonds. No experimental evidence in support of a
NiIV oxo intermediate in these transformations could be obtained, and computational studies
2
4
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201800915
supported a mechanism involving coordination of amine-N-oxide to the Ni center and direct
insertion of the oxygen atom into the Ni-P linkage in an apparently concerted manner. No evidence
for C-O bond formation involving the PCP pincer ligands was reported.
In consideration of these related studies, the formation of 7 upon treatment of 2 with one
equiv Me
3
NO and its subsequent conversion to 6 may thus be postulated to occur via coordination
of Me NO to Co and direct insertion of an oxygen atom from the bound N-oxide into Co-Si and
3
Co-P linkages, respectively. Alternatively, one or both of these insertion steps may involve a
transient, unobserved Co=O/Co-O· species.[34a, 48] The formation of a strong Si-O bond is likely a
thermodynamic driving force in this process.
CONCLUSIONS
II
The syntheses of Co halide complexes supported by Cy-PSiP ligation are detailed.
Reduction of (Cy-PSiP)Co(PMe
3
)I could be achieved under mild conditions using magnesium
I
metal as the reducing agent to generate the Co dinitrogen complex (Cy-PSiP)Co(PMe
3
)N in high
2
yield. When this reaction was carried out under an atmosphere of CO, the corresponding
dicarbonyl complex (Cy-PSiP)Co(CO) was obtained. The CO stretching frequencies observed for
this complex are comparable to those reported for related (PXCXP)Co(CO) (X = O, N) species
that feature dialkyl phosphinite and aminophosphine donors. While the one electron reduction of
2
2
II
III
Co halide complexes proved facile, access to Co species supported by Cy-PSiP ligation was
significantly more challenging. This is in contrast to observations by Sun and co-workers,[10] who
III
have reported on readily isolable Co complexes supported by closely related diphenylphosphino
PSiP derivatives. Attempted oxidative addition reactions involving (Cy-PSiP)Co(PMe
3
)N were
2
generally unsuccessful, with the sole exception of H , which reacted to afford the dihydride
2
2
5
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201800915
complex (Cy-PSiP)Co(PMe
3
)(H)
2
. The dihydride complex undergoes Co-H site exchange in
solution and readily eliminates H
2
. Evidence for H/D scrambling was also observed when HD gas
II
was used in place of H
2
. Exposure of the Co complex (Cy-PSiP)CoI to O
2
gas under anhydrous
conditions led to rapid ligand oxidation at Si and P, with no evidence observed at low temperature
III
II
for a Co superoxo or peroxo intermediate. Exclusive oxidation at Si to afford a Co -siloxy
complex was observed upon treatment of (Cy-PSiP)CoI with one equiv Me NO. While this siloxy
complex did not react further with O , treatment with a second equiv of Me NO led to subsequent
oxidation involving one phosphino donor. This observation supports the notion that in the ligand
oxidation reactivity observed with O , the O atoms incorporated at both Si and P are likely derived
from the same O molecule.
3
2
3
2
2
To some extent, the difficulty encountered in our attempts to access stable (Cy-PSiP)CoIII
species mirrors observations made by Caulton and co-workers[11b, 22b] in their investigation of
(PNP)Co; this complex also proved challenging to oxidize despite the electron-rich PNP ligation.
Caulton attributed these observations to the reducing power of the PNP ligand, and the need to
balance the redox potential of cobalt versus the energy recouped in the formation of new Co-X
bonds. It seems likely that similar arguments can be made in regard to the study described herein.
EXPERIMENTAL SECTION
General. All experiments were conducted under N in a glovebox or using standard
2
Schlenk techniques. Dry, oxygen-free solvents were used throughout. Tetrahydrofuran and diethyl
ether were distilled from Na/benzophenone ketyl. Benzene, toluene, and pentane were first sparged
with nitrogen and subsequently dried by passage through a double-column (one activated alumina
column and one column packed with activated Q-5) solvent purification system. All purified
2
6
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201800915
solvents were stored over 4 Å molecular sieves. Deuterated solvents were degassed via three
freeze-pump-thaw cycles and stored over 4 Å molecular sieves. O gas (99.999%, < 3 ppm H O)
was obtained from Air Liquide Canada. Anhydrous CoI and CoCl were purchased from Strem
2
2
2
2
and used as received. The compound (2-Cy
2
PC
6
H
4
2
) SiHMe was prepared according to literature
procedure.[5a] All other reagents were purchased from commercial sources and used without further
1
13
31
29
purification. Unless otherwise stated, H, C, P, and Si characterization data were collected at
room temperature on Bruker AV-300 or Bruker AV-500 spectrometers, with chemical shifts
1
13
29
reported in parts per million downfield of SiMe
4
(for H, C, and Si), or 95% H
3
PO
4
in D
2
O (for
3
1
1
13
13
1
13
P). H and C NMR chemical shift assignments are based on data obtained from C{ H}, C-
DEPTQ, H- H COSY, H- C HSQC, and H- C HMBC NMR experiments. 29Si NMR
1
1
1
13
1
13
1
29
assignments are based on H- Si HMBC experiments. Solution magnetic moment measurements
were determined by use of the Evans method.[13] Infrared spectra were recorded at a resolution of
-
1
4
cm .
(
Cy-PSiP)CoCl (1). A solution of (Cy-PSiP)H (0.11 g, 0.19 mmol) and NEt
3
(0.019 g, 0.19
(0.025
mmol) in ca. 5 mL of THF was added via pipette to a stirring solution of anhydrous CoCl
2
g, 0.19 mmol) in ca. 5 mL of THF at room temperature. An immediate color change to dark brown
was observed and the reaction was allowed to stir for 18 h at room temperature. After 18 h the
volatile components of the reaction mixture were removed in vacuo and the reaction mixture was
extracted with ca. 5 mL of C
6
6
H . The benzene extract was then filtered through Celite and the
filtrate was dried under vacuum. A minute amount of crystalline material of 1 suitable for X-ray
1
diffraction analysis was grown from a concentrated toluene solution at room temperature. H NMR
(
300 MHz, benzene-d
6
): δ 14.15, 7.72, 5.74, 3.55, 3.10, 2.53, 2.05, 1.66, 1.28, 0.87, 0.31, -0.10, -
0
.37, -0.99, -1.73, -6.23, -7.87, -11.74, -17.19, -21.60, -34.69.
2
7
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201800915
(
Cy-PSiP)CoI (2). A solution of (Cy-PSiP)H (0.50 g, 0.85 mmol) and NEt
mmol) in ca. 5 mL of THF was added via pipette over 2 minutes to a stirring solution of anhydrous
CoI (0.26 g, 0.85 mmol) in ca. 40 mL of THF at room temperature. A color change from blue to
3
(0.86 g, 8.5
2
brown to deep red was observed over the course of the addition. The reaction mixture was then
allowed to stir for 18 h at room temperature. After 18 h, the volatile components of the reaction
mixture were removed in vacuo and the residue was extracted with ca. 10 mL of benzene. The
benzene extract was then filtered through Celite and the filtrate was dried under vacuum. The
remaining orange-red residue was washed with 2 × 2 mL of pentane to yield 2 as an orange solid
1
(
0.63 g, 95%). H NMR (300 MHz, benzene-d
6
): δ 14.52, 9.57, 7.97, 7.84, 6.41, 4.36, 3.20, 2.19,
1
3
.62 - 0.42 (overlapping peaks), -0.26, -0.77, -1.67, -3.21, -7.40, -11.61, -14.91, -24.37, -27.55, -
4.37. μeff (benzene-d ): 1.86 μ (S = ½). Anal. Calcd. for C37 Si: C, 57.29; H, 7.15.
6
B
H55ICoP
2
Found: C, 57.20; H, 6.88.
Cy-PSiP)Co(PMe
0.34 g, 3.36 mmol) in ca. 5 mL of THF was added to a solution of CoCl
ca. 15 mL of THF. The solution was allowed to stir for 2 h, over which time a color change from
light blue to dark brown was observed. After 2 hours, PMe (0.026 g, 34 μL, 0.34 mmol) was
(
3
)Cl (1-PMe
3
). A solution of (Cy-PSiP)H (0.20 g, 0.34 mmol) and NEt
3
(
2
(0.044 g, 0.34 mmol) in
3
added to the solution via syringe and the solution immediately turned deep red in color. The
reaction mixture was then allowed to stir for 18 h at room temperature. After 18 h, the volatile
components of the reaction mixture were removed in vacuo and the residue was extracted with ca.
1
0 mL of benzene and filtered through Celite. The solvent was again removed in vacuo and the
deep red residue was washed with 2 × 2 mL pentane and dried in vacuo to afford 1-PMe (0.071
g, 27%) as a red solid. Single crystals of 1-PMe suitable for X-ray diffraction analysis were grown
from a concentrated 9:1 Et O/THF solution at -35 °C. H NMR (300 MHz, benzene-d
3
3
1
2
6
): δ 8.62,
2
8
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201800915
7
.53, 5.54, 5.0 – 2.6 (broad overlapping resonances), 2.43, 2.0 – 0.2 (broad overlapping
resonances), -3.96, -5.83. μeff (benzene-d ): 1.89 μ (S = ½). Anal. Calcd. for C40 Si: C,
3.19; H, 8.48. Found: C, 62.90; H, 8.36.
Cy-PSiP)Co(PMe )I (2-PMe ). A solution of 2 (0.10 g, 0.13 mmol) in ca. 5 mL of THF
was treated with PMe (0.010 g, 13 μL, 0.13 mmol) added via syringe. An immediate color change
6
B
H
64ClCoP
3
6
(
3
3
3
to deep red was observed and the reaction mixture was allowed to stir for 1 h at room temperature.
After 1 h the volatile components of the reaction mixture were removed in vacuo and the residue
was washed with 2 × 2 mL of pentane and dried under vacuum to afford 2-PMe (0.087 g, 78%)
3
1
as a red solid. H NMR (300 MHz, benzene-d
6
): δ 32.7 (broad), 8.41, 5.96, 5.26, 2.58, 2.35, 2.2 -
(S = ½). Anal. Calcd.
-
5.0 (broad overlapping peaks), -12.53 (broad). μeff (benzene-d6): 1.65 μ
Si: C, 56.40; H, 7.57. Found: C, 56.35; H, 7.54.
Cy-PSiP)Co(PMe )(N ) (3). Method 1: Magnesium powder (0.077g, 3.2 mmol) was
added as a solid to a stirring solution of 2-PMe (0.27, 0.32 mmol) in ca. 10 mL THF at room
B
for C40
H
64ICoP
3
(
3
2
3
temperature. The mixture was left to stir for 18 h, over which time a color change from red to
brown to orange-red was observed. After 18 h the solvent was removed in vacuo and the residue
was extracted with ca. 10 mL of benzene and filtered through Celite. The filtrate was dried in
vacuo and the resulting orange material was washed with pentane (2 × 2 mL) to afford 3 (0.22 g,
9
1%) as an orange solid. Method 2: A solution of 2 (0.63 g, 0.81 mmol) in ca. 10 mL of THF was
treated with PMe (0.062 g, 83 μL, 0.81 mmol), added via syringe. An immediate color change to
3
deep red was observed and the reaction was allowed to stir for 1 h at room temperature. After 1 h,
magnesium powder (0.20 g, 8.1 mmol) was added as a solid and the reaction mixture was stirred
for 18 h, over which time a color change from deep red to brown to orange-red was observed.
After 18 h, the solvent was removed in vacuo and the residue was extracted with ca. 15 mL of
2
9
This article is protected by copyright. All rights reserved.