Cooperative metal-ligand reactivity and catalysis in low-spin ferrous alkoxides

Article abstract of DOI:10.1021/om501152h

This report describes examples of combined Fe- and O-centered reactivity of Fe(P₂O₂)(CO)₂ (1), where P₂O₂ is the diphosphinoglycolate (Ph₂PC₆H₄CHO)₂^2-<

Full text of DOI:10.1021/om501152h

Article
pubs.acs.org/Organometallics
Cooperative Metal−Ligand Reactivity and Catalysis in Low-Spin
Ferrous Alkoxides
Wan-Yi Chu, Xiaoyuan Zhou, and Thomas B. Rauchfuss*
School of Chemical Sciences, University of Illinois, Urbana, Illinois 61801, United States
*
S Supporting Information
ABSTRACT: This report describes examples of combined
Fe- and O-centered reactivity of Fe(P O )(CO) (1), where
2
2
2
2
2
−
P O is the diphosphinoglycolate (Ph PC H CHO) . This
2
2
2
6
4
1
8e low-spin ferrous dialkoxide undergoes substitution of CO
to give the labile monosubstituted derivatives Fe(P O )(CO)-
2
2
(
(
L) (L = PMe , pyridine, MeCN). Treatment of Fe(P O )-
3
2
2
CO) with Brønsted acids results in stepwise O-protonation,
2
affording rare examples of low-spin Fe(II) complexes
containing alcohol ligands. Substitution reactions with amides (RC(O)NH ) proceeds with binding of the carbonyl and
2
formation of an intramolecular hydrogen bond between NH and the neighboring alkoxo ligand. This two-site binding was
confirmed with crystallographic characterization of the thiourea-substituted derivative. Fe(P O )(CO) reacts with Ph SiH to
2
2
2
2
2
give the O-silylated hydrido complex, which is inactive for hydrosilylation. The monocarbonyl derivatives Fe(P O )(CO)(L) (L
2
2
=
NCMe, PMe , acetamide) are precursors to catalysts for the hydrosilylation of benzaldehyde, acetophenone, and styrene.
3
INTRODUCTION
the high basicity of alkoxo ligands and an unprecedented
activation mode of Si−H bonds by alkoxo-iron functionalities
to afford a series of new hydrido-iron complexes. We also found
that the diphosphino-dialkoxo iron species with labile ligands
■
1
Monomeric alkoxoiron(II) complexes are rare. The oxygen
centers in such complexes are expected to be highly basic owing
to electrostatic interactions between the metal and ligand,
2
(e.g., MeCN, MeC(O)NH ) are active catalysts for the
although the Fe−O bonds themselves remain strong. The
2
hydrosilylation of aldehydes, ketones, and even alkenes. The
spectroscopic features of all newly synthesized compounds are
summarized in Table 1.
enhanced basicity of the alkoxide ligand in such complexes
usually results in multinuclear complexes with bridging alkoxo
ligands. For these reasons, studies on the reactivity of ferrous
alkoxides are few.
We recently described a one-pot synthesis of an iron(II)
diphosphine-dialkoxide dicarbonyl complex Fe(P O )(CO)
2
RESULTS
■
2
2
2−
Substitution of Fe(P O )(CO) by Lewis Bases. The CO
2 2 2
(
1; P O = (Ph PC H CHO) ). This complex arises by the
2 2 2 6 4 2
ligands of 1 are labile. In CH Cl solutions, 1 exchanges with 1
2
2
coupling of 2 equiv of 2-diphenylphosphinobenzaldehyde
13
3
atm of CO over the course of several hours (see the
Supporting Information). The lability of the CO ligands was
further demonstrated by the synthesis of the acetonitrile
derivative Fe(P O )(CO)(NCMe) (2), generated by warming
(
1
PCHO) in the presence of iron(0) carbonyl reagents (eq
4
; bda = benzylideneacetone).
2
2
an acetonitrile solution of 1 for 24 h. Substitution
desymmetrizes the complex, as manifested by the appearance
of two doublets in the 31P NMR spectrum. The large value of
JP−P (289 Hz) was consistent with mutually trans phosphines.
The structure of 2 was confirmed by X-ray crystallography
(
Figure 1). The structures of 1 and 2 differ only slightly. The
MeCN ligand shows a slight contraction of the NC bond
1.135(6) Å) in comparison to that of free acetonitrile (1.157
Å). In the absence of added MeCN, CH Cl solutions of 2
(
Similar condensations had been observed using PCHO with
5
2
2
low-valent tungsten and technetium. Our iron system is
attractive because the conversion is highly efficient and the
reagents are inexpensive. As a dialkoxo iron(II) carbonyl, 1 is
unique. In the previous report, 1 was shown to form stable
decomposed at room temperature over the course of a few
hours to give 1, free MeCN, and unidentified NMR-silent
products.
adducts with a variety of Lewis acids, including BF , which bind
to the alkoxide sites. In this paper, we provide new perspectives
3
Received: November 16, 2014
on the O-centered reactivity of 1. These results demonstrate
©
XXXX American Chemical Society
A
DOI: 10.1021/om501152h
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Table 1. Spectroscopic Properties (CH Cl Solution) for
Scheme 1. Stepwise Protonation of 1
2
2
Iron Complexes Containing the P O Ligand
2
2
1
ν
δ( H) (JP−H,
CO
(cm )
‑1
31
compound
δ( P) (JP−P, Hz)
21.1
Hz)
4
Fe(P O )(CO) (1)
1965,
4.49 (OCH)
2
2
2
2
025
2003,
2052
2034,
2074
Fe[P O(OH)](CO)2
26.1 (224)
29.9
5.08, 4.63
(OCH)
2
([H1]OTf)
[
Fe[P (OH) ](CO) ]
3.95 (OCH)
2
2
2
(
OTf) ([H 1](OTf) )
2 2 2
a
Fe(P O )(CO)(MeCN)
1938
28.2, 25.5 (289)
4.67, 3.86
(OCH)
2
2
(
2)
Fe(P O )(CO)(PMe ) (3) 1918
24.4, 21.3, 19.7
4.56, 4.01
(OCH)
2
2
3
(
44.1, 44.3, 278)
confirmed coordination of PMe in the equatorial position,
Fe(P O )(CO)(py) (4)
1917
1933
1928
29.6, 25.6 (283)
32.4, 31.7 (261)
23.2, 21.1 (287)
25.6
4.83, 3.93
3
2
2
(
OCH)
whereas the diphosphine ligands remained mutually trans. The
solid-state structure of 3 showed elongated Fe(1)−P distances
and a smaller P(1)−Fe(1)−P(2) angle in comparison to that in
1, reflecting substitution of a π-acidic CO with a bulkier, more
electron donating phosphine ligand. The pyridine complex
Fe(P O )(CO)(MeC(O)
4.99, 3.78
(OCH)
2
2
NH ) (5)
2
Fe(P O )(CO)
4.64, 3.42
(OCH)
2
2
b
(
SC(NH ) ) (6)
2
2
Cy
Fe(P O )(CO) (7)
1995,
3.95 (FeH)
2
2
2
Fe(P O )(CO)(py) (4) was synthesized by dissolving 1 in
1
930
2
2
pyridine. Unlike 2, complexes 3 and 4 proved stable as CH Cl
solutions in room temperature over prolonged periods.
HFe[P O(OSiHPh )]
2004,
71.2, 52.8 (195)
5.07, 4.82
2
2
2
2
(
CO) (8)
1939
(OCH)
2
−
2.97 (76,
Reactions of Fe(P O )(CO) with Brønsted Acids.
2 2 2
4
5) (FeH)
Previous work revealed that 1 forms 1:1 and 2:1 adducts
with Lewis acids, which bond to the oxygen centers of the
alkoxide. This work explored the reactivity of 1 with Brønsted
acids, with the expectation that the alkoxides will react to form
labile neutral ligands, enabling binding of substrates to the iron
center.
HFe(P O SiEt )(CO) (9) 2000
70.2, 52.7 (197)
50.9, 74.0 (179)
4.88, 5.16
OCH)
2
2
3
2
(
−
2.92 (75,
4
6) (FeH)
HFe[PCy O(OSiHPh )]
1974
4.90, 5.06
(OCH)
2
2
(
CO) (10)
2
−
3.19 (63,
Titration of a CH Cl solution of 1 with HOTf resulted in
2
2
5
2) (FeH)
+
stepwise protonation of the alkoxo ligands to give [H1] and
H 1] . The first protonation occurs independently of the
second, suggesting very different basicities for 1 and [H1]
(Scheme 1). At ≤1 equiv of HOTf, two broad peaks were
observed in the P NMR spectrum at δ 21.1 (unreacted 1) and
δ 26.1, assigned to [H1] . Broadening of the signals results
from intermolecular transfer of protons between 1 and [H1] .
At 1 equiv of acid, the signal for [H1] sharpened into an AB
a
b
Recorded in MeCN. Recorded in THF.
2+
[
2
+
An analogous PMe complex, Fe(P O )(CO)(PMe ) (3),
was obtained in good yield by treating a THF/CH Cl solution
3
2
2
3
31
2
2
+
of 1 with excess PMe . No evidence for disubstitution was
3
observed. The 31P NMR spectrum of 3 revealed an ABX spin
system with JP−P = 44, 44, 280 Hz. X-ray crystallography of 3
+
+
Figure 1. Structure (50% probability thermal ellipsoids) of 2 (left) and 3 (right). Selected hydrogen atoms have been omitted for clarity. Selected
distances (Å) and angles (deg): 2, Fe(1)−N(1) 1.905(4), Fe(1)−P(1) 2.239(1) Fe(1)−P(2) 2.245(1), Fe(1)−O(2) 1.944(3), Fe(1)−
O(3)1.949(4), Fe(1)−C(1) 1.752(6), P(1)−Fe(1)−P(2) 168.27; 3, Fe(1)−P(1) 2.244(1), Fe(1)−P(2) 2.283(1), Fe(1)−P(3) 2.273(1), Fe(1)−
O(2) 1.973(2), Fe(1)−O(3) 1.970(2), Fe(1)−C(1) 1.737(4), P(2)−Fe(1)−P(3) 160.15(4).
B
DOI: 10.1021/om501152h
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Figure 2. Titration of 1 with HOTf monitored by 31P NMR (left) and IR spectroscopy (right).
+
F
quartet (JP−P 1= 235 Hz). Addition of HOTf to [H1] gave rise
Titration of 1 with H(OEt ) BAr gave similar results by
2 2 4
to a broad 3 P NMR signal at δ 29.9, corresponding to the
doubly protonated species [H 1] . This signal sharpened to a
singlet for ≥2 equiv of HOTf. This stepwise protonation
process was also monitored by IR spectroscopy (Figure 2).
Cations [H1] and [H 1] are rare examples of low-spin
ferrous complexes containing alcohol ligands. To confirm the
assignment, X-ray crystallographic analysis of [H 1]OTf was
carried out. The cation retains the idealized C symmetry of 1
NMR spectroscopy in terms of chemical shifts and number of
2
+
F
−
2
species (BAr 4 = B[3,5-(CF ) C H ] ). Differences in the
3 2 6 3 4
NMR spectra between protonation with HOTf and H-
OEt ) BAr are attributed to the weaker hydrogen bonding
F
(
2 2 4
+
2+
+
−
2
of H with Et O in comparison to that with OTf . Thus, faster
2
6
F
proton exchange between [H1]BAr 4 and 1 is evident. For
F
2
2
example, addition of 0.5 equiv of H(OEt ) (BAr ) to 1 gave a
2
2
4
31
2
broadened signal observed in the P NMR spectrum at the
3
1
(
Figure 3), consistent with its simple P NMR spectrum. In
+
average of the chemical shifts of [H1] and 1. Under the same
conditions but with HOTf, separate signals are observed for
+
[
H1] and 1.
Substitution of Fe(P O )(CO) by H-Bonding Ligands.
2
2
2
The 16e entity Fe(P O )(CO) should feature adjacent basic
2
2
alkoxide and Lewis acidic iron sites. Such a species is suited for
binding with ligands that could function both as Lewis bases
and H-bond donors. Indeed, under prolonged heating with
excess benzamide or acetamide, 1 converts to such a complex,
1
as evidenced by NMR spectroscopy. The H NMR spectrum of
Fe(P O )(CO)(MeC(O)NH ) (5) was characterized by a
2
2
2
strong singlet at δ 18, assigned to the NH group that is
3
1
hydrogen-bonded to the adjacent alkoxide. Curiously, the
P
NMR spectrum of 5 consists of a singlet in the presence of
excess acetamide, suggesting fast exchange between the
coordinated and free acetamide ligands. This symmetrization
is proposed to proceed via an associative mechanism (Scheme
3
1
2
). This type of symmetrization was not observed in the
P
NMR spectrum of 2 upon addition of MeCN to a CH Cl
2
2
solution. After removal of excess acetamide by multiple
recrystallizations, the 31P NMR spectrum of 5 exhibits an AB
quartet, as expected for monosubstituted compounds of 1 (see
Figure 3. Structure (50% probability thermal ellipsoids) of [H 1]-
2
(
OTf) . Selected hydrogen atoms, solvent, and anions have been
2
7
omitted for clarity. Selected distances (Å) and angles (deg): Fe(1)−
O(3) 1.993(3), Fe(1)−O(4) 1.982(2), O(3)−H(3) 0.80(4), O(4)−
H(4) 0.81(3), Fe(1)−P(1) 2.293(1), Fe(1)−P(2) 2.295(1), Fe(1)−
C(1) 1.784(4), Fe(1)−C(2) 1.783(4), P(1)−Fe(1)−P(2) 171.30(4).
the Supporting Information). Complex 5 decomposed in a
CH Cl solution in the absence of excess acetamide to give 1
2
2
and other NMR-silent species.
To obtain more stable amide adducts, thioureas were
examined. Thioureas are good hydrogen-bond donors and are
8
softer Lewis bases than ureas. Treatment of 1 with 1 equiv of
thiourea in CH Cl gave the bright green compound Fe-
comparison to the structure of 1, the Fe−O and Fe−P bonds
are elongated by 0.03 and 0.05 Å, respectively. The O−H
centers were located in the electron difference map with O−
2
2
P O )(CO)(SC(NH ) (6; ν 1928 cm− in THF solution).
1
(
2 2 2 2 CO
31
Its P NMR spectrum revealed a characteristic AB quartet
H
0.81 Å. A hydrogen-bonding interaction was also observed
(JP−P = 287 Hz) indicative of a monosubstituted derivative of 1.
avg
1
for the alcohol protons and one oxygen of each triflate anion,
A signal at δ 12.4 in the H NMR spectrum is assigned to the
with H- - -Oavg 1.71 Å.
hydrogen-bonded NH (in thiourea δ(NH) 6.58).
C
DOI: 10.1021/om501152h
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
a
Scheme 2. Mechanism Proposed for Amide Exchange in 5
a
The P O ligand is simplified for clarity.
2
2
Scheme 3. Hydrosilylation of Fe(P O )(CO) (1) and
2
2
2
Cy
2
Fe(P O )(CO) (7) with Ph SiH and Et SiH
2
2
2
2
3
Figure 4. Structure (50% probability thermal ellipsoids) of 6. Selected
hydrogen atoms have been omitted for clarity. Selected distances (Å)
and angles (deg): Fe(1)−P(1) 2.2601(7), Fe(1)−P(2) 2.2563(6),
Fe(1)−S(1) 2.3122(5), Fe(1)−O(2) 1.971(1), Fe(1)−O(3) 1.976(1),
Fe(1)−C(1) 1.736(2), S(1)−C(2) 1.719(2), O(2)−H(1)A 1.81(3),
O(2)−N(1) 2.661(2), N(1)−C(2) 1.318(3), P(1)−Fe(1)−P(2)
1
characteristic of mutually trans phosphine ligands. The H
NMR spectrum features a doublet of doublets at δ −2.97 with
J
= 44.6 and 76.4 Hz, consistent with a metal hydride
P−H
coupled to inequivalent phosphine groups. Complex 8 was
stable toward excess Ph SiH , indicating that the second alkoxo
group resisted silylation. Similarly, the Si−H bond in 8 was
2
2
168.20(3), O(2)−H(1)A−N(1) 156(3).
unreactive toward another 1 equiv of 1.
X-ray crystallographic analysis confirmed that 6 is the
Crystallographic analysis of 8 confirmed the expected endo
stereochemistry of the siloxy group, consistent with retention of
stereochemistry at carbon (and probably Fe; Figure 5). The
structure exhibited a distorted-octahedral geometry with the
trans-phosphines canted away from the cis-dicarbonyl groups
and a P−Fe−P angle of 157.68(2)°. This bending was more
prominent than that in the parent complex 1 (167.43(4)°). The
Fe(1)−C(1) distance is 1.820(2) Å, longer than the Fe-CO
bond trans to the alkoxo ligand, reflecting the stronger trans
influence of the hydride ligand in comparison to that of the
alkoxo group. Although alkoxo iron hydrides are rare, the
phenolato hydride HFe(Ph PC H O)(PMe ) and related
expected complex of thiourea (Figure 4). All four hydrogen
centers on the thiourea ligand were located in the electron
difference map, and hydrogen-bonding interaction between one
alkoxo ligand and one amino group on the thiourea ligand is
indicated. The O(2)···H(1)A distance of 1.81(3) Å and the
O(2)−H(1)A−N(1) angle of 156(3)° indicate a moderate-
9
strength H-bonding interaction.
Silane Derivatives. In view of the strength of O−H bonds,
it was reasoned that 1 would be susceptible to hydrogenation to
give the hydride complex with a pendant alcohol group: i.e., the
complex HFe[P O(OH)](CO) . Solutions of 1, however,
2
2
2
6
4
3 3
1
1
proved unreactive toward H even in the presence of a catalytic
derivatives have been characterized.
2
amount of Pd/C and acids. Similar nonreactivity was seen for
Compound 1 also reacted with Et SiH, initially affording
3
the more electron rich dicyclohexyl analogue of 1, abbreviated
HFe(P O SiEt )(CO) (9), albeit at a slower rate in
2
2
3
2
Cy
31
Fe(P O )(CO) (7), which was synthesized in a manner
comparison to the Ph SiH reaction. As seen for 8, the
P
2
2
2
2
2
10
similar to that for 1 from Cy P-2-C H CHO (Cy = C H ).
NMR spectrum of 9 showed doublets at δ 70.2 and 52.7 with a
large JP−P value of 197 Hz, indicative of mutually trans
2
6
4
6
11
Complex 1 and its substituted derivatives do react with
silanes to give hydride complexes. For example, a CH Cl2
phosphines. A doublet of doublets at δ −2.95 (J
= 74.9, 46.5
2
P−H
1
solution of 1 and Ph SiH gave the hydride HFe[P O-
Hz) in the H NMR spectrum was again consistent with a
hydrido iron(II) complex coupled to inequivalent phosphine
ligands. Upon standing in solution for several hours at room
temperature, 9 partially isomerized to a new hydrido species
(9′) of unknown structure (see the Supporting Information).
2
2
2
(
OSiHPh )](CO) (8) (Scheme 3). Spectroscopic measure-
2 2
ments are consistent with formation of a metal hydride species
with an O-silylated diphosphine. The 3 P NMR spectrum
consists of doublets at δ 71.2 and 52.8 (JP−P = 195 Hz),
1
D
DOI: 10.1021/om501152h
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
−3
k
M
vs [Ph SiH ] (Figure 6), was found to be [1.14(6)] × 10
2 2
obs
−
1
−1
s .
rate = k[Ph SiH ][1]
(2)
2
2
Mechanism of Silane Addition to 1. Prior to this report,
reactions of alkoxoiron(II) complexes with organosilanes have
not been well studied. However, hydridonickel(II) complexes
12
have been prepared by similar routes. For the formation of 8
from 1 and Ph SiH , the Lewis basic alkoxide ligand may attack
2
2
the weakly Lewis acidic silicon center, weakening the Fe−O
bond (see [H 1](OTf) ), followed by transfer of hydride to
2
2
iron. A related mechanism has been proposed for the addition
13
of silanes to (PPh ) Re(O) I. A pathway involving the
3
2
2
dissociation of CO is unlikely, since CO does not affect the rate
of hydride formation.
Hydrosilylation Studies. Neither 1 nor its silylated
derivative 8 catalyzed the hydrosilylation of benzaldehyde,
acetophenone, or styrene. We then turned to derivatives that
contained labile ligands for catalytic hydrosilylation studies.
Using 2 (1 mol %) as a catalyst, PhCHO was quantitatively
Figure 5. Structure (50% probability thermal ellipsoids) of 8. Selected
hydrogen atoms have been omitted for clarity. Selected distances (Å)
and angles (deg): Fe(1)−H(2) 1.42(2), Fe(1)−P(1) 2.1863(5),
Fe(1)−P(2) 2.2445(5), Fe(1)−O(3) 1.983(1), Fe(1)−C(1) 1.820(2),
Fe(1)−C(2) 1.745(2), Si(1)−O(4) 1.640(1), P(1)−Fe(1)−P(2)
hydrosilylated with Ph SiH and PhSiH at room temperature
157.68(2).
2
2
3
within 5 h (Table 2). No catalysis was observed using the
tertiary silanes Et SiH and PhMe SiH. Acetophenone also
3
2
underwent hydrosilylation, although more slowly than PhCHO.
Similar to the case for 2, complexes 3 (entry 4) and 4 (entry 5)
are also active catalysts. Interestingly, 2 was active as a catalyst
for the hydrosilylation of styrene, although this reaction
required more forcing conditions and lower TONs were
Complex 7 reacted with Ph SiH in a similar fashion to give
2
2
Cy
HFe[P O(OSiHPh )](CO) (10), with spectroscopic fea-
2
2
2
tures closely resembling those of 8 and 9 (Table 1).
Interestingly, complex 7 was unreactive toward Et SiH even
3
at elevated temperatures (ca. 50 °C in CH Cl ). Given that
3
achieved (entry 9). The MeC(O)NH complex 5, which was
proposed to be more labile than the MeCN derivative 2, was
twice as active for hydrosilylation of styrene.
2
2
2
Et SiH also had a lower reactivity with 1 in comparison to
Ph SiH , the nonreactivity of 7 toward Et SiH is attributed to
2
2
3
steric crowding due to the large cyclohexyl groups.
In order to clarify aspects of the hydride-forming process, the
rate of formation of 8 from 1 was monitored by H NMR
Comments on Mechanism of Catalytic Hydrosilyla-
tion. Catalytic hydrosilylation of ketones and aldehydes has
been well studied in the past decade, including several base-
metal catalysts that are active under very mild conditions and
1
spectroscopy. At 10 °C in the presence of >10 equiv of
14
Ph SiH , the conversion was first order in iron. The rate was
with low loading. Illustrative high-activity catalysts feature
2
2
−
also found to depend linearly on the concentration of silane
Figure 6). The rate was unaffected by the presence of CO (1
diiminopyridine, N(SiMe ) , iminophosphines, and N-phos-
phinoamidinate as ligands.
3
2
1
5
(
atm). These results are consistent with the rate law in eq 2. The
The mechanism of hydrosilylation using 2 is not known.
second-order rate constant (k), determined from the plot of
When the hydrosilylation of acetophenone by Ph SiH was
2
2
Figure 6. (left) Representative kinetic plot for the reaction of 1 with Ph SiH . Conditions: [1] = 0.015 M, [Ph SiH ] = 0.15 M, 10 °C in CD Cl .
2
2
2
2
2
2
1
Disappearance of the signal at 4.52 ppm was monitored by H NMR. (right) Plot of k versus the concentration of Ph SiH . Conditions: [Ph SiH ]
obs
2
2
2
2
=
0.15−0.47 M, [1] = 0.015 M, 10 °C in CD Cl .
2
2
E
DOI: 10.1021/om501152h
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
a
Table 2. Results of Hydrosilylation Catalyzed by Various Fe Complexes
b
entry
[Fe]
substrate
PhCHO
silane
time (h)
product(s)
PhCH OSiHPh , (PhCH O) SiPh (69:20)
TON
1
2
3
4
5
5
6
7
8
2
2
2
3
4
2
2
2
2
5
5
Ph SiH2
2
3
5
89
96
95
89
34
2
2
2
2
2
PhCHO
Ph SiH2
2
PhCH OSiHPh , (PhCH O) SiPh (69:27)
2 2 2 2 2
PhCHO
PhSiH3
3
PhCH OSiH Ph, (PhCH O) SiHPh (77:18)
2 2 2 2
PhCHO
Ph SiH2
2
24
24
3
PhCH OSiH Ph, (PhCH O) SiHPh (47:42)
2 2 2 2
PhCHO
Ph SiH2
2
PhCH OSiH Ph, (PhCH O) SiHPh (18:16)
2 2 2 2
PhCHO
Et SiH
3
0
0
PhCHO
PhMe SiH
3
2
PhC(O)Me
PhC(O)Me
PhCHCH
PhCHCH
Ph SiH2
2
5
PhCH(OSiHPh )Me
26
48
18
48
2
Ph SiH2
2
24
15
15
PhCH(OSiHPh )Me
2
9
Ph SiH2
2
PhCH(SiHPh )Me
2
2
2
c
10
Ph SiH2
2
PhCH(SiHPh )Me
2
a
b
Reaction conditions (unless specified otherwise): substrate (1.0 mmol), silane (1.1 mmol), [Fe] (10 μmol), CH Cl (2 mL), 25 °C. The yield was
2
2
1
c
determined by H NMR spectroscopy with an internal standard. T = 60 °C, no solvent.
monitored in situ by NMR spectroscopy, only the O-silyl
functionality is crucial in this transformation, as the strong
Si−O bond (∼108 kcal/mol) is thermodynamically favored.
The addition of silanes is proposed to proceed via alkoxide-
assisted activation of the Si−H bond. Due to the strong
coordination of the other ligands, the resulting hydrido
complexes were not catalytically active. Substituting one CO
in 1 with labile ligands gives Fe(P O )(CO)(L) (L = NCMe
3
1
hydride 8 was detected by P NMR spectroscopy in ∼50%
yield. As mentioned above, purified 8 is catalytically inactive,
reflecting the inertness of its two carbonyl ligands. The activity
of catalysts of the type Fe(P O )(CO)L correlated qualitatively
2
2
with the lability of L. This correlation suggests that an
important step in the catalytic cycle is the dissociation of L to
allow for substrate binding. In view of the rapidity of the
silylation of 1, the active catalyst is proposed to arise via the
sequence of reactions in eqs 3 and 4, consisting of formation of
an O-silylated precatalyst followed by its activation following
transfer of CO.
2
2
(2), MeC(O)NH ), which are precatalysts with good to
2
excellent activity for catalytic hydrosilylation of aldehydes,
ketones, and styrene with catalyst loadings of ≤1 mol %.
Recently, Li et al. reported hydrosilylation of benzaldehyde and
ketones using hydridoiron(II) complexes bearing labile PMe
3
19
ligands. Guan et al. also described hydridoiron(II) precata-
Fe(P O )(CO)L + H SiPh
20
2
2
2
2
lysts for hydrosilylation. In contrast to Li’s reports, the
hydrido ligand in Guan’s precatalyst is a spectator ligand. These
→
HFe[P O(OSiPh H)](CO)L
(3)
2
2
and other studies point to intermediates in the catalytic cycle
21
that could not be observed by NMR spectroscopy, which
possibly involves high-spin iron(II) complexes.
L = PMe , MeCN, MeC(O)NH
3
2
2
HFe[P O(OSiPh H)](CO)L
2 2
EXPERIMENTAL SECTION
■
→
HFe[P O(OSiPh H)](CO)
2
2
2
Materials and Methods. Unless otherwise indicated, reactions
were conducted using standard Schlenk techniques under an N or
8
(inactive)
2
2
2
+
“HFe[P O(OSiPh H)]L ”
argon atmosphere at room temperature with stirring. Fe(bda)(CO) ,
3
10 4
2
2
x
Cy
(active)
(4)
P CHO, and FeP
2
O
2
(CO)
2
were synthesized according to
literature preparations. Silanes, thiourea, acetamide, benzaldehyde,
1
Catalyst activation thus entails accumulating the CO ligands
in the thermodynamic sink 8. The remaining iron complex,
being CO-free, is possibly high spin, which would explain the
absence of detectable P NMR signals. Consistent with this
scenario, when 2 was treated with 1 equiv of Ph SiH , a
hydridoiron(II) species was observed after 10 min. This species
was characterized by an AB quartet in its P NMR spectrum
and a triplet in the high-field H NMR spectrum (see the
Supporting Information), consistent with its assignment as
styrene (Sigma-Aldrich), and PMe (Strem) were used as received. H,
3
13
31
C, and P NMR spectra were acquired on Varian UNITY INOVA
500NB and UNITY 500 NB instruments. Chemical shifts are reported
relative to the peak of residual solvent. FT-IR spectra were recorded
on a PerkinElmer 100 FT-IR spectrometer. Elemental analyses were
conducted in the School of Chemical Sciences Microanalysis
Laboratory utilizing a Model CE 440 CHN analyzer.
3
1
16
23
2
2
3
1
1
Fe(P O )(CO)(NCMe) (2). A suspension of 1 (200 mg, 0.25 mmol)
2 2
in 500 mL of acetonitrile was heated in a 80 °C oil bath for 24 h. After
the reaction mixture was cooled to room temperature, solvent was
removed under reduced pressure. The resulting brown solids were
washed with pentane (∼15 mL) to afford an analytically pure brown
powder. Yield: 145 mg (80%). Brown crystals suitable for X-ray
diffraction were obtained by slow evaporation of the CH Cl solution.
HFe[P O(OSiPh H)](CO)(NCMe).
2
2
CONCLUSIONS
■
The ferrous dialkoxodiphosphine complex 1 displays rich
reactivity involving CO substitution, reactions at the alkoxide
centers, and the cooperative behavior of these sites. This
project established ligand−substrate cooperativity.
Although 1 was anticipated to activate H , the strengths of
2
2
1
H NMR (500 MHz, CD Cl ): δ 8.01−7.13 (m, 28H, phenyl-H), 4.67
2
2
(
dd, J = 2.4, 5.5 Hz, 1H, OCH), 3.86 (d, J = 5.9 Hz, 1H, OCH), 1.01
13
1
7
(s, 3H, NCCH ). C NMR (126 MHz, CD Cl /CD CN): δ 218.7
3 2 2 3
(
1
1
CO), 157.8, 156.6, 137.7, 137.3, 136.8, 135.4, 134.5, 134.2 134.1,
2
33.9, 131.0, 130.9, 130.4, 130.2, 129.8, 129.2, 129.0, 128.7, 128.1,
the O−H and Fe−H bonds are apparently insufficient to
31
27.9, 127.4, 127.3, 126.5, 126.2, 88.54 (OCH), 87.66 (OCH).
P
1
8
overcome the H−H bond energy of 104 kcal/mol. Owing to
a much weaker Si−H bond (∼75 kcal/mol), silanes react with 1
to give hydridoiron(II) complexes. Certainly, the alkoxo
NMR (202 MHz, CD Cl ): δ 28.2, 25.5 (AB quartet, J = 289 Hz).
2
2
P−P
Anal. Calcd (found) for C H NO P Fe: C, 69.8 (69.61); H, 4.71
41
33
3 2
−1
(4.73); N, 1.99 (2.1) IR (MeCN): νCO 1938 cm .
F
DOI: 10.1021/om501152h
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Fe(P O )(CO)(PMe ) (3). A solution of 1 (200 mg, 0.25 mmol) in
resulting yellow solid was washed with pentane to give an analytically
pure product. Yield: 845 mg (90%). Yellow crystals suitable for X-ray
diffraction were obtained by vapor diffusion of pentane into a CH Cl
2
2
3
1
2
50 mL of a THF/CH Cl mixture (4/1) was added to PMe (3 mL,
2
2
3
9 mmol), and the mixture was stirred for 3 days. Evaporation of the
2
2
reaction solution yielded an orange solid. The residue was recrystal-
lized from a minimum amount of CH Cl by addition of pentane,
solution. 1H NMR (500 MHz, CD Cl ): δ 7.97−6.73 (m, 38H,
2
2
2
2
phenyl-H), 5.06 (d, JHH = 3.52 Hz, 1H, OCH), 4.81 (dd, JHH = 3.52
Hz, JPH = 7.50 Hz, 1H, OCH), 3.74 (s, 1H, SiH), −2.98 (dd, J
giving an analytically pure orange powder. Yield: 149 mg (78%). Red
=
PH
crystals suitable for X-ray diffraction were obtained by vapor diffusion
13
1
76.3, 44.7 Hz, 1H, FeH). C NMR (126 MHz, CD Cl ): δ 214.9
2 2
of pentane into a CH Cl solution. H NMR (500 MHz, CD Cl ): δ
2
2
2
2
(
1
CO), 208.8 (CO), 150.4, 147.5, 142.0, 136.9, 136.8, 136.4,
8
.40 (m, 2H, phenyl-H), 7.73 (m, 2H, phenyl-H), 7.52−6.85 (m, 26H,
35.6, 135.1, 134.8, 134.6, 134.4, 133.8, 133.5, 132.8, 132.7, 132.2,
phenyl-H), 4.54 (m, 1H, OCH), 3.99 (d, J = 5.3 Hz, 1H, OCH), 0.77
131.9, 130.9, 130.8, 130.7, 130.6, 130.5, 130.3, 130.1, 130.0, 129.7,
29.0, 128.9, 128.2, 128.1, 128.0, 128.0, 127.9, 127.8, 127.6, 125.9, 84.9
(
(
1
1
2
(
(
d, 9H, J = 8.8 Hz, PCH3). 13C NMR (126 MHz, CD Cl ): δ 215.9
2 2
1
CO), 158, 155.2, 141.8, 140.2, 137.9, 136.3, 134.5, 133.2, 132.7,
31
32.6, 129.9, 129.6, 129.1, 128.7, 128.4, 128.2, 127.5, 126.5, 126.4,
(OCH), 77.8 (OCH). P NMR (202 MHz, CD Cl ): δ 71.2 (d, JP−P =
2 2
26.1, 86.4 (OCH), 86.3 (OCH). 31P NMR (202 MHz, CD Cl ): δ
194 Hz), 52.7 (d, JP−P = 194 Hz). Anal. Calcd (found) for
C H FeO P Si·0.5CH Cl : C, 68.60 (68.58); H, 4.71 (4.69). IR
2
2
4.4, 21.3, 19.7 (ABX spin system, JP−P = 278, 44, 44 Hz). Anal. Calcd
52
42
4
2
2
2
−1
found) for C H O P Fe: C, 68.12 (68.03); H, 5.31 (5.36). IR
4
2
39
3
3
(CH Cl ): ν 2025, 1965 cm .
2 2 CO
−
1
CH Cl ): ν 1918 cm .
2
2
CO
Reaction of Et SiH with 1 To Give HFe[P O(OSiEt )](CO) (9
3 2 3 2
Fe(P O )(CO)(py) (4). A solution of 1 (140 mg, 0.18 mmol) in
2
2
and 9′). An NMR tube was charged with a solution of Fe(P O )-
2
2
pyridine (20 mL) was stirred in room temperature for 72 h to afford a
greenish brown solution. The solution was evaporated, and the
resulting solid was washed with pentane (∼15 mL) to give an
(
CO) (3 mg, 0.4 μmol) in CD Cl (0.5 mL). To the solution was
2
2
2
added Et SiH (1.2 μL, 0.8 μmol), and the reaction was monitored over
3
1
31
time by H NMR and P NMR spectroscopy. After 48 h, the ratio of
9 and the isomer 9′ is 79:21. Data for 9 are as follows. H NMR (500
MHz, CD Cl ): δ 8.01−7.88 (m, 4H, phenyl-H), 7.13−7.03 (m, 1H,
analytically pure product as a greenish brown powder. Yield: 121 mg
1
1
(
83%). H NMR (500 MHz, CD Cl ): δ 8.47 (d, J = 5.9 Hz, 1H, py-
2
2
2
2
H), 8.22 (d, J = 5.8 Hz, 1H, py-H), 8.03−7.98 (m, 2H, phenyl-H),
phenyl-H), 6.86 (dd, J = 11, 7.9 Hz, 1H, phenyl-H), 5.21 (d, J = 3.4
Hz, 1H, OCH), 4.93 (dd, J = 7.5, 3.2 Hz, 1H, OCH), 0.37 (t, J = 7.9
7
6
2
.79−7.74 (m, 2H, phenyl-H), 7.55−6.70 (m, 24H, py-H, phenyl-H),
.43−6.39 (m, 1H, py-H), 5.87−5.78 (m, 1H, py-H), 4.83 (dd, J = 5.8,
.4 Hz, 1H, OCH), 3.93 (d, J = 5.9 Hz, 1H, OCH). 31P NMR (202
Hz, 9H, CH
7.9 Hz, 3H, CH
MHz, CD Cl ): δ 72.1 (d, J
P−P
), 0.04 (dq, J = 16, 7.9 Hz, 3H, CH
), −2.88 (dd, J = 75, 46 Hz, 1H, FeH). P NMR (202
= 197 Hz), 54.6 (d, JP−P = 197 Hz).
), −0.26 (dq, J = 16,
3
2
31
MHz, CD Cl ): δ 29.6, 25.6 (AB quartet, J = 283 Hz). IR
2
2
2
P−P
−1
(
CH Cl ): ν 1917 cm .
2 2 CO
2
2
1
Fe(P O )(CO)(MeC(O)NH ) (5). A solution of 1 (70 mg, 0.1
Data for 9′ are as follows. H NMR (500 MHz, CD Cl ): 8.15−8.12
2
2
2
2
2
mmol) in CH Cl (6 mL) was treated with a solution of acetamide
2
2
(m, 4H, phenyl-H), 7.01−6.92 (m, 1H, phenyl-H), 6.58 (t, J = 8.7 Hz,
H, phenyl-H) 4.90 (d, J = 3.1 Hz, 1H, OCH), 4.87−4.82 (m, 1H,
(
3
0.36 g, 6.0 mmol) in THF (6 mL). After this solution was stirred for
6 h, solvent was removed under reduced pressure. The green residue
1
OCH), 0.73 (t, J = 7.9 Hz, 9H, CH ), 0.278−0.132 (m, 6H, CH ),
3
31
2
was mixed with toluene (5 mL) and filtered. The filtrate was
maintained at −30 °C overnight and filtered, and the filtrate was
−
4.21 (dd, J = 74, 66 Hz, 1H, FeH). P NMR (202 MHz, CD Cl ): δ
2
2
5
3.7, 53.2 (AB quartet, J = 188 Hz). IR of mixture (CH Cl ): ν
P−P 2 2 CO
diluted with pentane (∼15 mL) to precipitate the product as a green
−1
1
2000, 1939 cm .
solid. Yield: 27 mg (38%). H NMR (CD Cl ): δ 17.87 (s, 1H, NH),
2
2
Cy
Cy
2
HFe[P O(OSiHPh )](CO) (10). A solution of Fe(P O )(CO)
2
2
2
2
2
4
0
.99 (s, 1H, OCH), 3.78 (d, J = 3.9 Hz, 1H, OCH), 2.86 (s, 1H, NH),
.65 (s, 3H, CH3). 31P NMR (202 MHz, CD Cl ): δ 32.4, 31.7 (AB
(197 mg, 0.27 mmol) in THF was added to Ph SiH (55 μL, 0.27
2
2
2
2
−1
mmol). The resulting mixture was heated in a 55 °C oil bath for 1 h.
After the mixture was cooled to room temperature, solvents were
removed under reduced pressure. The resulting yellow-green solid was
washed with pentane to afford an analytically pure brown-green
quartet, JP−P = 261 Hz). IR (CH Cl ): ν = 1933 cm .
2
2
CO
Fe(P O )(CO)(SC(NH ) ) (6). A solution of 1 (61 mg, 0.08 mmol)
2
2
2 2
and thiourea (5.4 mg, 0.07 mmol) was prepared in CH Cl (3 mL).
2
2
Over the course of 20 h, the yellow solution turned green and a bright
green solid precipitated. The suspension was concentrated to 1.5 mL
and filtered to afford a fine green powder, which was washed with
CH Cl (3 × 0.5 mL) to give an analytically pure bright green powder.
1
powder. Yield: 157 mg (63%). H NMR (500 MHz, CD Cl ): δ 7.78−
2
2
6
.88 (m, 18H, phenyl-H), 5.10 (d, J = 3.6 Hz, 1H, OCH), 4.93 (s, 1H,
2
2
SiH), 4.61 (dd, J = 5.7, 3.7 Hz, 1H, OCH), 2.99−2.75 (m, 2H,
1
Yield: 53 mg (91%). H NMR (500 MHz, THF-d ): δ 12.3 (br, 1H,
8
cyclohexyl-H), 2.58−0.35 (m, 42H, cyclohexyl-H), −3.14 (dd, J = 64,
NH), 7.84 (m, 2H, phenyl-H), 7.70 (m, 2H, phenyl-H), 7.38 (m, 1H,
phenyl-H), 7.21−6.76 (m, 23H, phenyl-H), 5.49 (br, 3H, NH), 4.64
31
5
0 Hz, 1H, FeH). P NMR (202 MHz, CD Cl ): δ 74.0 (d, J
=
2
2
P−P
−
1
m, 1H, OCH), 3.42 (m, 1H OCH). 13C NMR (126 MHz, THF-d ):
179 Hz), 50.9 (d, J
P−P = 179 Hz). IR (CH
Exchange of CO on 1. A J. Young NMR tube was charged with
2
Cl
2
): νCO 1974, 1919 cm .
(
8
13
1
1
1
86.5 (SC), 157.5, 157.4, 137.8, 137.4, 135.6, 135.0, 134.7, 134.1,
30.2, 129.9, 129.8, 129.54, 128.9, 128.6, 128.5, 128.3, 127.9, 127.5,
27.4, 126.7, 126.5, 87.4 (OCH), 87.2 (OCH). The absence of the
a CH Cl solution of 1 (∼5 μM). The solution was freeze−pump−
2
2
1
3
thawed three times to remove N and then opened to CO (1 atm).
2
31
After 20 h at room temperature, the solution was analyzed. IR
FeCO signal is attributed to poor solubility. P NMR (202 MHz,
THF-d ): 23.2, 21.1 (AB quartet, J = 287). Anal. Calcd (found) for
−1
(CH Cl ): νCO 2024, 1976, 1965, 1923 cm , assigned to singly and
8
P−P
2 2
C H FeN O P S·THF: C, 65.03 (64.93); H, 5.21 (5.31), N, 3.45
doubly labeled product.
Kinetic Study. An NMR tube was charged with 1 (10 μmol),
hexamethylbenzene (internal standard), and CD Cl (0.5 mL). After
4
0
34
2
3 2
−1
(
3.67). IR (THF): ν 1928 cm .
CO
Cy
FeP O (CO) (7). A solution of Fe(bda)(CO) (472 mg, 1.65
2
2
2
3
2
2
Cy
mmol) and P CHO (998 mg, 3.30 mmol) in THF (30 mL) was
stirred in a 55 °C oil bath for 4 h. After the reaction mixture was
cooled to room temperature, solvents were removed under reduced
pressure. The resulting yellow solid was washed with pentane to afford
addition of Ph SiH , the tube was shaken vigorously, and the reaction
2
2
1
was monitored over time by H NMR spectroscopy at 10 °C.
Concentrations were determined by integration of the methine
resonances of 1 and 8.
1
an analytically pure orange powder. Yield: 782 mg (66%). H NMR
Catalytic Hydrosilylation. A vial was charged with the substrate
(
500 MHz, CD Cl ): δ 7.56 (m, 2H, phenyl-H), 7.35−7.24 (m, 4H,
2
2
(1.0 mmol), silane (1.1 mmol), and CH Cl (2 mL), followed by the
2 2
phenyl-H), 7.04 (m, 2H, phenyl-H), 3.94 (s, OCH), 2.64−0.66 (m,
4
νCO 1995, 1930 cm .
HFe[P O(OSiHPh )](CO) (8). A solution of Fe(P O )(CO) (832
4H, Cy-H). 31P NMR (202 MHz, CD Cl ): δ 25.8 (s). IR (CH Cl ):
addition of catalyst (10 μmol). The solution was stirred at room
temperature for the desired time period. Mesitylene (0.14 mmol, 20
μL) was added as the internal standard. An aliquot was taken and
2
2
2
2
−1
2
2
2
2
2
2
1
mg, 1.07 mmol) and Ph SiH (0.21 mL) in CH Cl (60 mL) was
mixed with C
spectroscopy.
6
D
6
. The yield was determined by H NMR
2
2
2
2
stirred for 8 h. Solvent was removed under reduced pressure, and the
G
DOI: 10.1021/om501152h
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(
19) Zuo, Z.; Sun, H.; Wang, L.; Li, X. Dalton Trans. 2014, 43,
ASSOCIATED CONTENT
■
1
(
3
2
1716. Zhao, H.; Sun, H.; Li, X. Organometallics 2014, 33, 3535.
20) Bhattacharya, P.; Krause, J. A.; Guan, H. Organometallics 2011,
0, 4720. Bhattacharya, P.; Krause, J. A.; Guan, H. Organometallics
014, 33, 6113.
*
S
Supporting Information
Figures, a table, and CIF files giving H NMR and 31P NMR
1
spectra for new compounds and X-ray crystallographic data for
2
, 3, [H 1](OTf) , 6 and 8. This material is available free of
(21) Wu, J. Y.; Moreau, B.; Ritter, T. J. Am. Chem. Soc. 2009, 131,
2
2
charge via the Internet at http://pubs.acs.org.
12915.
(
22) Alcock, N. W.; Richards, C. J.; Thomas, S. E. Organometallics
1991, 10, 231.
23) Fulmer, G. R.; Miller, A. J. M.; Sherden, N. H.; Gottlieb, H. E.;
AUTHOR INFORMATION
■
(
Corresponding Author
Nudelman, A.; Stoltz, B. M.; Bercaw, J. E.; Goldberg, K. I.
Organometallics 2010, 29, 2176.
*E-mail for T.B.R.: rauchfuz@illinois.edu.
Notes
The authors declare no competing financial interest.
NOTE ADDED AFTER ASAP PUBLICATION
■
This paper was published on the Web on February 6, 2015,
with an error in Scheme 3. The corrected version was reposted
on February 13, 2015.
ACKNOWLEDGMENTS
■
This research was conducted under Contract DEFG02-
90ER14146 with the U.S. Department of Energy by its
Division of Chemical Sciences, Office of Basic Energy Sciences.
We thank Dr. Hao Lei for preliminary studies on protonation
of 1 and Danielle Gray and Jeffrey Bertke for assistance with the
X-ray crystallography.
REFERENCES
1) Chambers, M. B.; Groysman, S.; Villagran
Inorg. Chem. 2013, 52, 3159. Bellow, J. A.; Martin, P. D.; Lord, R. L.;
■
(
́
, D.; Nocera, D. G.
Groysman, S. Inorg. Chem. 2013, 52, 12335.
(
(
(
2) Bryndza, H. E.; Tam, W. Chem. Rev. 1988, 88, 1163.
3) Garralda, M. A. C. R. Chim. 2005, 8, 1413.
4) Lei, H.; Royer, A. M.; Rauchfuss, T. B.; Gray, D. Organometallics
2
012, 31, 6408.
(
5) Refosco, F.; Bandoli, G.; Mazzi, U.; Tisato, F.; Dolmella, A.;
Nicolini, M. Inorg. Chem. 1990, 29, 2179. Yeh, W.-Y.; Lin, C.-S.; Peng,
S.-M.; Lee, G.-H. Organometallics 2004, 23, 917.
(
6) Nunes, G. G.; Bottini, R. C. R.; Reis, D. M.; Camargo, P. H. C.;
Evans, D. J.; Hitchcock, P. B.; Leigh, G. J.; Sa, E. L.; Soares, J. Inorg.
Chim. Acta 2004, 357, 1219.
7) Randall, S. L.; Miller, C. A.; Janik, T. S.; Churchill, M. R.;
Atwood, J. D. Organometallics 1994, 13, 141.
8) Zhang, Z.; Schreiner, P. R. Chem. Soc. Rev. 2009, 38, 1187. Russo,
U.; Graziani, R.; Calogero, S.; Casellato, U. Transition Met. Chem.
979, 4, 82. Fackler, J. P.; Moyer, T.; Costamagna, J. A.; Latorre, R.;
Granifo, J. Inorg. Chem. 1987, 26, 836.
9) Kotke, M.; Schreiner, P. R. In Hydrogen Bonding in Organic
Synthesis; Pihko, P. M., Ed.; Wiley-VCH: Weinheim, Germany, 2009; p
41.
́
(
(
1
(
1
(
10) Schenkel, L. B.; Ellman, J. A. Org. Lett. 2003, 5, 545.
(
11) Klein, H.-F.; Frey, M.; Mao, S. Z. Anorg. Allg. Chem. 2005, 631,
1
(
2
516.
12) Breitenfeld, J.; Scopelliti, R.; Hu, X. Organometallics 2012, 31,
128. Marciniec, B.; Maciejewski, H.; Gulinski, J. J. Chem. Soc., Chem.
Commun. 1995, 717. Holland, P. L.; Andersen, R. A.; Bergman, R. G.;
Huang, J.; Nolan, S. P. J. Am. Chem. Soc. 1997, 119, 12800.
(
13) Nolin, K. A.; Krumper, J. R.; Pluth, M. D.; Bergman, R. G.;
Toste, F. D. J. Am. Chem. Soc. 2007, 129, 14684.
14) Junge, K.; Schroder, K.; Beller, M. Chem. Commun. 2011, 47,
849.
15) Yang, J.; Tilley, T. D. Angew. Chem., Int. Ed. 2010, 49, 10186.
(
4
(
Tondreau, A. M.; Lobkovsky, E.; Chirik, P. J. Org. Lett. 2008, 10, 2789.
Ruddy, A. J.; Kelly, C. M.; Crawford, S. M.; Wheaton, C. A.; Sydora,
O. L.; Small, B. L.; Stradiotto, M.; Turculet, L. Organometallics 2013,
3
2, 5581. Mukhopadhyay, T. K.; Flores, M.; Groy, T. L.; Trovitch, R. J.
J. Am. Chem. Soc. 2013, 136, 882.
16) Benito-Garagorri, D.; Lagoja, I.; Veiros, L. F.; Kirchner, K. A.
Dalton Trans. 2011, 40, 4778.
(
(
17) Crabtree, R. H. New J. Chem. 2011, 35, 18.
(
18) Sanderson, R. T. Chemical Bonds and Bond Energy; Academic
Press: New York, 1976.
H
DOI: 10.1021/om501152h
Organometallics XXXX, XXX, XXX−XXX