Synthesis of [POCOP]-pincer iron and cobalt complexes via Csp3-H activation and catalytic application of iron hydride in hydrosilylation reactions

Article abstract of DOI:10.1039/c5ra00072f

C_sp3-H bond activation in diphosphinito pincer ligand (Ph₂PO(o-C₆H₂-(4,6-^tBu₂)))₂CH₂ (1) (POCH₂OP) was achieved by Fe(PMe₃)₄ and CoMe(PMe₃)₄ to afford complexes (POCHOP)Fe(H) (PMe₃)₂ (2) and (POCHOP)Co(PMe₃)₂ (4) under mild conditions. Hydrido iron complex 2 reacted with iodomethane via the elimination of methane to deliver complex (POCHOP)FeI(PMe₃) (3). The ligand replacement in Ni(PMe₃)₄ by 1 gave rise to nickel(0) complex (POCH₂OP)Ni(PMe₃)₂ (5) without C_sp3-H bond activation of the pincer ligand (1). It was confirmed that the hydrosilylation of aldehydes and ketones could be effectively catalyzed by hydrido iron complex 2. Complexes 2-5 were characterized by spectroscopic methods and X-ray single crystal diffraction analysis. This journal is

Full text of DOI:10.1039/c5ra00072f

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Synthesis of [POCOP]-pincer iron and cobalt
complexes via Csp3–H activation and catalytic
application of iron hydride in hydrosilylation
reactions†
Cite this: RSC Adv., 2015, 5, 15660
*
Shaofeng Huang,‡ Hua Zhao,‡ Xiaoyan Li, Lin Wang and Hongjian Sun
C
sp3–H bond activation in diphosphinito pincer ligand (Ph2PO(o-C6H2-(4,6-tBu2)))2CH2 (1) (POCH2OP) was
achieved by Fe(PMe3)4 and CoMe(PMe3)4 to afford complexes (POCHOP)Fe(H) (PMe3)2 (2) and (POCHOP)
Co(PMe3)2 (4) under mild conditions. Hydrido iron complex 2 reacted with iodomethane via the elimination
of methane to deliver complex (POCHOP)FeI(PMe3) (3). The ligand replacement in Ni(PMe3)4 by 1 gave rise
to nickel(0) complex (POCH2OP)Ni(PMe3)2 (5) without Csp3–H bond activation of the pincer ligand (1). It was
confirmed that the hydrosilylation of aldehydes and ketones could be effectively catalyzed by hydrido iron
complex 2. Complexes 2–5 were characterized by spectroscopic methods and X-ray single crystal
diffraction analysis.
Received 3rd January 2015
Accepted 23rd January 2015
DOI: 10.1039/c5ra00072f
www.rsc.org/advances
addition to carbonyl compounds. The hydrolysis of the silyl
ether gives rise to the corresponding alcohol. This process can
Introduction
be used as a convenient alternative to the reduction of unsat-
urated compounds under mild reaction condition.
Owing to high efficiency and atom economy for organic
synthesis, C–H bond activation and functionalization has
become one of the most attractive areas in organic chemistry.
Compared with Csp2–H bond activation, Csp3–H activation is
much more difficult due to the high bond energy and weakly
coordinating nature. In this eld, most of the work has focused
on precious metals, such as Pd,1 Ru,2 Rh,3 Ir4 etc. Because of the
low cost and toxicity, C–H bond functionalization by iron,5
cobalt6 and nickel7 complexes attracts more and more
researchers' attention. Pincer ligands have a double chelation
structure. This induces Csp3–H bond activation much easier via
double cyclometalation.8 Therefore, pincer complexes of tran-
sition metals can be prepared via Csp3–H bond activation.
Hydrido iron complexes as catalysts or key intermediates
play important roles in a wide variety of catalytic processes.
Nevertheless, these hydrido iron complexes are usually so
reactive that they cannot be isolated or even identied.9 To date,
few stable hydrido iron complexes have been synthesized and
employed as catalysts for a number of reactions, such as
hydrogenation,10–13 hydrosilylation,14,15 hydrogen-transfer reac-
tion,16 the oxidation of alcohols.17 The hydrosilylation reaction
of aldehydes and ketones generates silyl ethers with Si–H bond
In 2009, we reported the Csp3–H bond activation of a
[POCOP]-pincer ligand with an aliphatic backbone (Fig. 1(a)) by
low-valent iron and cobalt complexes under mild conditions.18
A
hydrido [PNCNP]-pincer iron complex was also isolated through
sp3–H bond activation of N,N0-bis(diphenylphosphino)dipyr-
C
romethane (Fig. 1(b)).19 When the diphosphine PCP ligand
(Ph2P-(C6H4))2CH2 was treated with Fe(PMe3)4, the Csp3–H
activation product [(Ph2P-(C6H4))2CH]Fe(H)(PMe3)2 was
obtained at room temperature (Fig. 1(c)).20 Recently, Wendt
reported
a series of new POCsp3OP-supported nickel(II)
complexes (Fig. 1(d)).21 On the basis of our early work, we
synthesized another (POCH2OP)-pincer ligand having a rela-
tively rigid backbone with two phenyl rings (Fig. 1(1)). An iron
hydride was obtained by oxidative addition of the Csp3–H bond
of the methylene group to the iron(0) center and its catalytic
property in hydrosilylation of aldehydes and ketones was also
explored.
School of Chemistry and Chemical Engineering, Key Laboratory of Special Functional
Aggregated Materials, Ministry of Education, Shandong University, Shanda Nanlu 27,
250199 Jinan, P. R. China. E-mail: hjsun@sdu.edu.cn; Fax: +86 531 88361350
† Electronic supplementary information (ESI) available: Characterization of all
compounds. CCDC 977103 and 980722–980724. For ESI and crystallographic
data in CIF or other electronic format see DOI: 10.1039/c5ra00072f
Fig. 1 [PCP]-pincer ligand.
‡ The rst two authors contributed to this paper equally.
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1
a dddd peak in the H NMR spectrum is registered at ꢀ15.13
ppm with the coupling constants of 2JPH of 69, 48, 38 and 14 Hz
(Fig. 2). It is not clear why this coupling is incompatible with
those of the 31P NMR. This coupling pattern is also different
from our early reports.19,20
The conguration of 2 was conrmed by X-ray structure
analysis (Fig. 3). Two six-membered metallacycles with a
considerable ring bending are formed through two phospho-
rous atoms of the PPh2 groups and a metalated Csp3 atom. The
iron atom is centered in a slightly distorted octahedral geom-
etry. H100 atom was located with the diffraction data of the
experiments. Bond angle P3–Fe1–P4 of 142.88(4)ꢁ bends
towards to the hydrido ligand due to the smaller space
requirement of the hydrido hydrogen. The Fe1–C31 distance
Results and discussion
Reaction of Fe(PMe3)4 with (POCH2OP) (1)
In most cases, Csp3–H bond activation in a pincer ligand was
realized by precious metals, such as Ru,8a Rh,8b Ir,8c,d Pd,8e etc. It
is conrmed that even PdCl2(PhCN)2 failed to realize the Csp3–H
bond activation in a similar ligand.22 Until now, there have been
only a few examples of hydrido iron complexes formed through
the activation of the Csp3–H bond of a [PCP]-pincer ligand.18–20
Mixing a diethyl ether solution of (POCH2OP) (1) with
Fe(PMe3)4 under an atmosphere of nitrogen afforded hydrido
iron complex 2 as yellow crystals in 56% yield aer stirring (eqn
(1)). Complex 2 is stable more than 48 h when exposed to the air
at room temperature.
(1)
The reaction starts with double replacement of the two tri- (2.165(3) A) is within the range of Fe–Csp3 bonds.23 Both Fe–P1
˚
˚
˚
methylphosphine ligands by two phosphorus atoms of ligand 1. distance (2.231(1) A) and Fe–P2 distance (2.269(1) A) are longer
˚
This ligand substitution shortens the distance of the iron(0) than Fe1–P3 distance (2.142(1) A) and Fe1–P2 distance (2.141(1)
˚
atom to the central Csp3–H bonds of the methylene group in 1 A), presumably due to the strong trans-inuence of the hydrido
and enables the Fe(0) center to activate the Csp3–H bond via H and C (sp3) atoms being greater than that of the phosphorus
oxidative addition by cyclometalation. Hydrido iron(II) complex
2 is formed through double chelation.
A typical n(Fe–H) stretching band at 1959 cmꢀ1 was found in
the IR spectrum of 1. In the 31P NMR spectrum of complex 2,
one doublet of doublets (two –PPh2) at 15.1 ppm and two trip-
lets (two PMe3) at 6.7 and 6.4 ppm are consistent with the
molecular structure. The resonance of the hydrido hydrogen as
Fig. 3 ORTEP plot of complex 2 at the 50% probability level (hydrogen
atoms except for Fe–H are omitted for clarity). Selected bond lengths
(A˚) and angles (deg): Fe1–P4 2.141(1), Fe1–P3 2.142(1), Fe1–C31
2.165(3), Fe1–P1 2.231(1), Fe1–P2 2.269(1), Fe1–H100 1.50(3);
Fig. 2 Characteristic resonance of the hydrido hydrogen of 2 in 1H C31–Fe1–P1 177.67(9), P2–Fe1–H100 170(1), P4–Fe1–C31 81.74(9),
NMR.
P3–Fe1–C31 81.99(9).
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atoms. This result is similar to that of our early report.19 ppm. In comparison with the related resonance at 3.88 ppm in
Complex 2 has a low-spin Fe(II) center.
the similar [PNC(H)NP]Co(PMe3)2 complex this is a signicant
downeld shi.19 The proton resonances of two types of PMe3
groups were recorded as one doublet at 0.78 and a triplet at 0.96
(2)
The reaction of 2 with iodomethane afforded an unsaturated
coordinated complex 3 as red crystals with the release of a
methane molecule (eqn (2)) in the yield of 87%.
The 1H NMR spectrum of 3 indicates that complex 3 is
paramagnetic. From the results of the magnetization
measurements for complex 3 it can be calculated that there are
two unpaired electrons in complex 3. This result is in accor-
dance with a paramagnetic iron(II) complex (d6) having a
trigonal bipyramidal conguration (see ESI†). This result was
conrmed by X-ray crystallography. Fig. 4 shows the molecular
structure of complex 3. It has a trigonal bipyramidal coordination
geometry with P1–Fe1–P2 ¼ 160.6(1)ꢁ in the axial direction. The
sum of the bond angles (C25–Fe1–I1 ¼ 143.6(2)ꢁ, C25–Fe1–P3 ¼
115.2(2)ꢁ and P3–Fe1–I1 ¼ 101.25(8)ꢁ) centered at the Fe atom
in the equatorial plane is 360.1ꢁ. This indicates that the four
atoms [Fe1C25I1P3] are almost in one plane.
Fig. 4 ORTEP plot of complex 3 at the 50% probability level (hydrogen
atoms are omitted for clarity). Selected bond lengths (A˚) and angles
(deg): Fe1–P1 2.194(2), Fe1–P2 2.239(2), Fe1–P3 2.422(3), Fe1–I1
2.699(2), C25–Fe1 2.095(8); C25–Fe1–I1 143.6(2), C25–Fe1–P3
115.2(2), P3–Fe1–I1 101.25(8), P1–Fe1–I1 91.89(8), P2–Fe1–I1 91.73(8),
C25–Fe1–P1 85.8(2), C25–Fe1–P2 80.0(2).
Reaction of CoMe(PMe3)4 with (POCH2OP) (1)
CoMe(PMe3)4 reacted with pincer ligand 1 to form the Csp3–H
bond activation product 4 with the elimination of a methane
molecule (eqn (3)).
(3)
1
ꢁ
The H NMR spectrum of complex 4 in C6D6 at 10 C indi- ppm with the coupling constants of 3.0 and 6.0 Hz respectively.
cated that the proton resonance of the CH group appear at 6.12 The 31P NMR spectrum shows a triplets for two PMe3 at ꢀ4.5
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(4)
2
ppm with the coupling constants J(PP) ¼ 78 Hz and a singlet Both the 1H and 31P NMR indicate that Csp3–H bond activation
for the two diphenylphosphanyl groups at 17.7 ppm.
did not occur. The molecular structure of complex 5 was
The molecular structure of complex 4 was determined by X- conrmed by X-ray single crystal diffraction (Fig. 6). A ten-
ray single crystal diffraction (Fig. 5). Two six-membered cobal- membered metallacycle is formed in 5 and every bond angle
tocycles with a considerable ring bending are formed through of the ring is approximately in 120ꢁ. The central nickel atom
two phosphorous atoms of the PPh2 groups and a metalated has a distorted tetrahedron coordination geometry. The bond
Csp3 atom. The central cobalt atom is situated in a disordered angles P1–Ni1–P2 (119.50(3)ꢁ), P1–Ni1–P3 (106.47(3)ꢁ), P1–Ni1–
trigonal bipyramid with C1–Co1–P4 ¼ 175.9(1)ꢁ in the axial P4 (109.63(3)ꢁ), P2–Ni1–P3 (107.91(3)ꢁ), P2–Ni1–P4 (101.93(3)ꢁ)
direction. The Co1–C1 distance (2.133(4) A) is within the range and P3–Ni1–P4 (111.39(3)ꢁ) are approximately close to 109.5ꢁ.
˚
of Co–Csp3 bonds (2.03–2.15 A).24 The structure of complex 4 is The four Ni–P bond distances are within the region of litera-
˚
comparable with that of [PNC(H)NP]Co(PMe3)2.19
ture values.15,19 The distance (3.62 A) between the Ni and the
methylene Csp3 atom indicates that there is no chemical
interaction between them. The reaction of ligand 1 with
NiMe2(PMe3)4 gave the same product with the elimination of
C2H6 (eqn (5)).
˚
Reaction of Ni(PMe3)4 or NiMe2(PMe3)4 with (POCH2OP) (1)
Mixing a THF solution of (POCH2OP) (1) with Ni(PMe3)4 affor-
ded nickel(0) complex 5 via ligand substitution (eqn (4)). Aer
all solvents were removed under vacuum, the residual powder
(5)
was extracted with pentane and diethyl ether. Complex 5 crys-
tallized from diethyl ether at 0 ꢁC in the yield of 87%. No Csp3–H
bond activation product could be observed.
Catalytic application of hydrido iron complex 2
Hydrido iron complexes bearing pincer ligands have been
utilized in hydrosilylation reactions of aldehydes and
ketones.14,15 We found that complex 2 could be used as catalyst
in the hydrosilylation of aldehydes (eqn (6)). In the presence of 1
mol% of 2 with (EtO)3SiH as the hydrogen source in THF at 65
ꢁC, aldehydes could be completely converted into the corre-
sponding silyl ether. The related alcohols were obtained by
following basic hydrolysis of the silyl ether. Nine aldehydes were
investigated (Table 1). Electron-donating group appeared to
make the hydrosilylation reactions sluggish (entry 5). On the
In the 1H NMR spectrum of complex 5, the resonance of the
two hydrogens of the methylene group was shied to 6.49 ppm
from 4.09 ppm in the free ligand 1. This downeld shi can be
explained in terms of an increased deshielding of the methy-
lene protons because the formation of a metallacycle results in
an additional ring current, which opposes the external eld.25
In the 31P NMR spectrum two types of signals with the integral
intensity of 1 : 1 demonstrate two kinds of phosphorus atoms.
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Table 1 Catalytic hydrosilylation of aldehydes with 2a
Entry
1
Substrate
Time (h)
2
Isolated yields (%)
92
2
3
4
5
6
16
26
18
16
1.5
91
87
90
81
90
Fig. 5 ORTEP plot of complex 4 at the 50% probability level (hydrogen
atoms are omitted for clarity). Selected bond lengths (A˚) and angles
(deg): Co1–P3 2.118(1), Co1–C1 2.133(4), Co1–P1 2.144(1), Co1–P4
2.213(1), Co1–P2 2.254(1); P3–Co1–C1 82.1(1), P3–Co1–P1 130.80(4),
C1–Co1–P1 81.5(1), P3–Co1–P4 94.73(5), C1–Co1–P4 175.9(1),
P1–Co1–P4 98.83(5), P3–Co1–P2 117.80(4), C1–Co1–P2 89.5(1),
P1–Co1–P2 108.08(4), P4–Co1–P2 94.24(5).
7
8
16
81
86
2.5
9
18
88
contrary, electron-withdrawing group at the para-position
turned out to accelerate the reduction (entry 6). ortho-Posi-
tioned groups hindered the process (entries 2–4).
a
Reaction conditions: RCHO (1.0 mmol), (EtO)3SiH (1.2 mmol),
complex 2 (0.010 mmol), 1.0 mL THF 65 ꢁC. Under the given
conditions, all the aldehydes were completely converted to the
corresponding silyl ethers (monitored by TLC and GC).
1 mol% 2
RCHO þ ðEtOÞ SiH
RCH OSiðOEtÞ
ƒƒƒƒƒƒƒ!
2
3
3
THF
10% NaOH
ƒƒƒƒƒƒƒ!
MeOH
RCH OH
2
(6)
Besides aldehydes, different ketones were also tested
under these catalytic hydrosilylation conditions (eqn (7)). It
was conrmed that acetophenone could be entirely converted
into the product even within 5 h with a catalyst loading of 2
mol% of complex 2 (Table 1, entry 1). In some cases,
reasonable yields could be obtained with a catalyst loading of
2 mol% (Table 2). In most cases, the ketones are less reactive
than the aldehydes. Additionally, several ketones could not
be completely converted even aer 48 h. Substitutents at the
para- or ortho-positions reduced the rate of the reaction for
both electron-withdrawing and electron-donating groups
(entries 2–4). These results are consistent with Guan's work.14
It is proposed that this catalytic system has a similar mech-
anism with those of the early reports.26
Fig. 6 ORTEP plot of complex 5 at the 50% probability level (hydrogen
atoms are omitted for clarity). Selected bond lengths (A˚) and angles
(deg): Ni1–P1 2.1572(8), Ni1–P2 2.1595(8), Ni1–P4 2.1955(8), Ni1–P3
2.1960(9); P1–Ni1–P2 119.50(3), O1–P1–Ni1 125.69(7), O2–P2–Ni1
117.24(8), C13–O1–P1 127.6(2), C21–O2–P2 129.1(2), P4–Ni1–P3
111.39(3).
2 mol% 2
RR0C ¼ O: þ ðEtOÞ SiH
RR0CHOSiðOEtÞ
ƒƒƒƒƒƒƒƒ!
3
3
THF
10% NaOH
ƒƒƒƒƒƒƒƒ!
MeOH
RR0HCOH
(7)
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Table 2 Catalytic hydrosilylation of ketones with 2a
known procedures and distilled under nitrogen before use.
Infrared spectra (4000–400 cmꢀ1), as obtained from Nujol mulls
between KBr disks, were recorded on a Bruker ALPHA FT-IR
instrument. NMR spectra were recorded using Bruker Avance
300 and 400 MHz spectrometers. GC-MS was recorded on a
TRACE-DSQ instrument, and GC was recorded on a Fuli 9790
instrument. A 2900 Series AGM Magnetometer was used to
measure the magnetic susceptibility. X-ray crystallography was
performed with a Bruker Smart 1000 diffractometer. Melting
points were measured in capillaries sealed under N2 and were
uncorrected. Elemental analyses were carried out on an Ele-
mentar Vario ELIII instrument. The compounds (Ph2PO(o-C6H2-
Conversation by Isolated yield
Entry Substrate
Time (h) GC (%)
(%)
1
5
99
92
88
2
3
4
48
71
81
43
(4,6-tBu2)))2CH2
(1),19
Fe(PMe3)4,27a
CoMe(PMe3)4,27b,c
10
48
99
57
Ni(PMe3)4,27d NiMe2(PMe3)3,27e were prepared according to
literature procedures.
Caution! (EtO)3SiH is ammable and highly toxic by inha-
lation and may cause skin irritation and blindness.
5
6
7
48
18
48
74
99
43
63
79
37
Synthesis of (POCHOP)Fe(H)(PMe3)2 (2)
(POCH2OP) (1) (0.82 g, 1.03 mmol) in 25 mL of diethyl ether was
mixed with Fe(PMe3)4 (0.42 g, 1.15 mmol) in 30 mL of diethyl
ether at 0 ꢁC. Aer 6 h at 0 ꢁC the reaction solution turned
brown yellow from tan. Aer 20 h a small amount of yellow
powder precipitated. Aer 3 days, the volatiles were removed
under reduced pressure and the residue was extracted with
pentane and diethyl ether. Compound 2 (0.56 g, 0.56 mmol) was
isolated as yellow crystals in 56% yield from diethyl ether at
0
ꢁC. Dec. >179 ꢁC. Anal. calcd for C59H80FeO2P4 (1000.96 g
8
18
48
99
49
86
39
molꢀ1): C, 70.79; H, 8.06. Found: C, 70.68; H, 8.09. IR (Nujol,
cmꢀ1): 3046 n(ArH), 1959 n(Fe–H), 1573 n(ArC]C), 938 r(PMe3).
1H NMR (C6D6, 300 K, ppm): ꢀ15.13 (dddd, JP–H ¼ 69, 48, 38 and
14 Hz, 1H, FeH), 0.62 (s, 9H, PMe3), 0.81 (d, 9H, 2J(PH) ¼ 6 Hz,
PMe3), 0.99 (s, 9H, p-(CH3)3C), 1.25 (s, 9H, p-(CH3)3C), 1.42 (s,
9H, o-(CH3)3C), 1.85 (s, 9H, o-(CH3)3C), 5.74 (s broad, 1H, CH),
7.07–7.53 (m, Ar, 18H), 8.08–8.33 (m, Ar, 6H); 31P NMR (C6D6,
9
a
Reaction conditions: RCOR0 (1.0 mmol), (EtO)3SiH (1.2 mmol),
complex 2 (0.020 mmol), 2.0 mL THF 65 ꢁC.
2
2
300 K, ppm): 15.1 (dd, J(PP) ¼ 37.5 Hz, J(PP) ¼ 12.1 Hz, 2P,
PPh2), 6.7 (t, 2J(PP) ¼ 22.0 Hz, 1P, PCH3), 6.4 (t, 2J(PP) ¼ 22.0 Hz,
1P, PCH3); 13C NMR (C6D6, 300 K, ppm): 21.5 (d, 1J(PC) ¼ 9.7 Hz,
PCH3), 24.4 (d, 1J(PC) ¼ 8.2 Hz, PCH3), 31.6 (s, p-(CH3)3C) 31.7 (s,
p-(CH3)3C), 31.8 (s, o-(CH3)3C), 32.6 (s, o-(CH3)3C), 34.1 (s, p-
(CH3)3C), 34.2 (s, p-(CH3)3C), 34.9 (s, o-(CH3)3C), 35.8 (s, o-
(CH3)3C), 118.5–152.9 (m, aromatic-C).
Conclusion
We investigated the reactions of the diphosphinito pincer
ligand (Ph2PO(o-C6H2-(4,6-tBu2)))2CH2 (1) (POCH2OP) with the
electron-rich low-valent iron, cobalt, and nickel complexes
supported by trimethylphosphine. The Csp3–H bond activation
of 1 was achieved by iron(0) complex Fe(PMe3)4 and cobalt(I)
complex CoMe(PMe3)4. The hydrido iron complex (POCHOP)
Fe(H)(PMe3)2 (2) reacted with iodomethane to give rise to an
iodo iron(II) complex. The catalytic property of the hydrido
iron(II) complex 2 was explored in hydrosilylation of aldehydes
and ketones.
Synthesis of (POCHOP)FeI(PMe3) (3)
CH3I (0.05 g, 0.35 mmol) was injected into the solution of 2 (0.30
g, 0.30 mmol) in 20 mL THF and stirred at 30 ꢁC. Aer 4 days the
yellow coloꢁr disappeared and the solution turned red. Aer 5
days at 30 C, the volatiles were removed under reduced pres-
sure and the residue was dissolved in pentane. Compound 3
(0.27 g, 0.26 mmol) was isolated as red crystals in 87% yield
from pentane at 0 ꢁC. Dec. >114 ꢁC. Anal. calcd for C56H70-
FeIO2P3 (1050.78 g molꢀ1): C, 64.01; H, 6.71. Found: C, 64.13; H,
Experimental section
General procedures and materials
Standard vacuum techniques were used in the manipulations of 6.78. IR (Nujol, cmꢀ1): 3030 n(ArH), 1584 n(C]C), 940 r(PMe3); c
volatile and air-sensitive materials. Solvents were dried by (20 C) ¼ 5.108 ꢂ 10ꢀ6 emu per g Oe.
ꢁ
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aromatic-C). The reaction of NiMe2(PMe3)3 was carried out by a
Synthesis of (POCHOP)Co(PMe3)2 (4)
procedure similar to above in 89% yield.
At ꢀ78 ꢁC, (POCH2OP) (1) (0.67 g, 0.84 mmol) in 25 mL of
diethyl ether was treated with CoMe(PMe3)4 (0.35 g, 0.92 mmol)
in 30 mL of diethyl ether at 0 ꢁC. Aer 30 h, the reaction mixture
turned dark red. Aer 3 days, the volatiles were removed under
reduced pressure and the residue was dissolved with pentane.
All manipulations were nished under 10 ꢁC. Compound 4 (0.35
g, 0.35 mmol) was isolated as red crystals in 42% yield from
pentane at 0 ꢁC. Dec. >152 ꢁC. Anal. calcd for C59H79CoO2P4
(1003.03 g molꢀ1): C, 70.65; H, 7.94. Found: C, 70.58; H, 7.99. IR
(Nujol, cmꢀ1): 3034 n(ArH), 1580 n(C]C), 942 r(PMe3). 1H NMR
General procedure for the catalytic hydrosilylation of
aldehydes
To a 25 mL Schlenk tube containing a solution of 2 (10.0 mg,
0.01 mmol) in 1 mL of THF were added an aldehyde (1.0 mmol)
and (EtO)3SiH (0.20 g, 1.2 mmol). The reaction mixture was
ꢁ
stirred at 65 C until there was no aldehyde le (monitored by
TLC and GC-MS). The reaction was then quenched by MeOH (1
mL) and a 10% aqueous solution of NaOH (5 mL) with vigorous
stirring at 50 ꢁC for about 2 days. The organic product was
extracted with Et2O, dried over anhydrous MgSO4, and
concentrated under vacuum. The alcohol product was further
puried using ash column chromatography. The 1H NMR and
13C{1H} NMR spectra of the primary alcohol products are
provided in the ESI.†
2
(C6D6, 283 K, ppm): 0.78 (d, J(PH) ¼ 3 Hz, 9H, PMe3), 0.96 (vt,
9H, 2J(PH) ¼ 6 Hz, PMe3), 1.08 (s, 9H, p-(CH3)3C), 1.35 (s, 9H, p-
(CH3)3C), 1.46 (s, 9H, o-(CH3)3C), 1.84 (s, 9H, o-(CH3)3C), 6.12 (s,
1H, CH), 6.93–8.41 (m, Ar, 18H); 31P NMR (C6D6, 283 K, ppm):
2
17.7 (bs, 2P, PPh2), ꢀ4.5 (t, J(PP) ¼ 78 Hz, 2P, PCH3).
Synthesis of (POCH2OP)Ni(PMe3)2 (5)
(POCH2OP) (1) (0.57 g, 0.72 mmol) in 25 mL of THF was mixed General procedure for the catalytic hydrosilylation of ketones
with Ni(PMe3)4 (0.27 g, 0.72 mmol) in 25 mL of THF with stirring
at room temperature for 24 h. The reaction mixture turned
orange from yellow. Aer removal of the volatiles under reduced
pressure, the residue was extracted with pentane and diethyl
Ketones were reduced following a similar procedure to the one
used for aldehydes except that 2 (20.0 mg, 0.02 mmol) in 2 mL of
THF were added. The 1H NMR and 13C {1H} NMR spectra of the
secondary alcohol products are provided in the ESI.†
ether. Compound 5 (0.63 g, 0.62 mmol) was isolated as orange
ꢁ
ꢁ
crystals in 87% yield from diethyl ether at 0 C. Dec. >121 C.
Anal. calcd for C59H80NiO2P4 (1003.82 g molꢀ1): C, 70.59; H,
X-ray crystal structure determinations
8.03. Found: C, 70.51; H, 8.11. IR (Nujol, cmꢀ1): 3025 n(ArH), The single crystals of all complexes for X-ray single crystal
1580 n(C]C), 938 r(PMe3). 1H NMR (C6D6, 300 K, ppm): 1.10 (d, diffraction were obtained from their n-pentane solutions at low
2
18H, J(PH) ¼ 3.0 Hz, PMe3), 1.28 (s, 18H, p-(CH3)3C), 1.45 (s, temperature. Diffraction data were collected on a Bruker
18H, o-(CH3)3C), 6.49 (s, 2H, CH2), 7.16–7.91 (m, Ar, 24H); 31P SMART Apex II CCD diffractometer equipped with graphite
NMR (C6D6, 300 K, ppm): 144.2 (dd, 2J(PP) ¼ 44.8 Hz, 2P, PMe3), monochromated Mo Ka radiation (l ¼ 0.71073 A). During
˚
2
ꢀ16.4 (dt, J(PP) ¼ 44.8 Hz, 2P, PPh2); 13C NMR (C6D6, 300 K, collection of the intensity data, no signicant decay was
ppm): 23.8 (m, PMe3), 31.2 (s, p-(CH3)3C), 31.6 (s, o-(CH3)3C), observed. The intensities were corrected for Lorentz polariza-
34.3 (s, p-(CH3)3C), 35.4 (s, o-(CH3)3C), 122.5–152.5 (m, tion effects and empirical absorption with the SADABS
Table 3 Crystallographic data for complexes 2, 3, 4 and 5
2
3
4
5
Empirical formula
Fw
Cryst syst
C
59H80FeO2P4
C56H70FeIO2P3
1050.78
Monoclinic
P2(1)/n
16.196(3)
12.997(3)
30.608(6)
90.00
97.19(3)
90.00
6392(2)
4
1.092
31 275
11 240
0.0939
25.000
0.0847
0.3013
C59H79CoO2P4
1003.03
Triclinic
ꢀ
P1
C59H80NiO2P4
1003.82
Triclinic
ꢀ
P1
1000.96
Monoclinic
P2(1)/n
21.067(4)
12.873(3)
22.808(5)
90.00
115.18(3)
90.00
5598.0(19)
4
Space group
˚
a, A
12.437(2)
13.462(2)
19.727(3)
94.511(3)
104.832(2)
91.585(3)
3178.7(8)
2
1.048
16 636
11 687
0.0694
14.2600(5)
14.5978(6)
15.3049(7)
96.364(3)
92.785(3)
118.212(3)
2771.5(2)
2
1.203
23 118
10 325
0.0638
˚
b, A
˚
c, A
R, deg
b, deg
g, deg
3
˚
V, A
Z
Dx, g cmꢀ3
No. of rns collected
No. of unique data
Rint
1.188
31 954
12 629
0.0793
27.560
0.0569
0.1701
qmax, deg
R1 (I > 2s(I))
wR2 (all data)
25.500
0.0535
0.1445
25.688
0.0442
0.0845
15666 | RSC Adv., 2015, 5, 15660–15667
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program.28 The structures were resolved by direct or Patterson
methods with the SHELXS-97 program and were rened on F2
with SHELXTL.25 All non-hydrogen atoms were rened aniso-
tropically. Hydrogen atoms were included in calculated posi-
tions and were rened using a riding model. A summary of
crystal data, data collection parameters, and structure rene-
ment details is given in Table 3.†
8 (a) O. R. Allen, L. D. Field, M. A. Magill, K. Q. Vuong,
M. M. Bhadbhade and S. J. Dalgarno, Organometallics,
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D. Gelman, Chem.–Eur. J., 2008, 14, 10364–10368; (d)
R. J. Burford, W. E. Piers and M. Parvez, Organometallics,
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2012, 31, 2949–2952; (e) S. Sjovall, O. F. Wendt and
C. Andersson, Dalton Trans., 2002, 1396–1400.
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Acknowledgements
We gratefully acknowledge the support by NSF China no.
21372143 and the Journal Grant for International Author of
RSC. We also thank the kind assistance from Prof. Dieter
Fenske and Dr Olaf Fuhr (Karlsruhe Nano-Micro Facility
(KNMF), KIT) for the X-ray diffraction analysis.
13 S. L. Zhou, S. Fleischer, K. Junge and M. Beller, Angew.
Chem., Int. Ed., 2011, 50, 5120–5124.
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RSC Adv., 2015, 5, 15660–15667 | 15667