Amido Ca and Yb(II) Complexes Coordinated by Amidine-Amidopyridinate Ligands for Catalytic Intermolecular Olefin Hydrophosphination

Article abstract of DOI:10.1021/acs.inorgchem.8b00088

A series of amido Ca and Yb(II) complexes LM[N(SiMe₃)₂](THF) (1Yb, 1-4Ca) coordinated by amidine-amidopyridinate ligands L^1-4 were synthesized via a transamination reaction between proligands L^1-4H and bisamido complexes M[N(SiMe₃)₂]₂(THF)₂ (M = Yb, Ca). The reactions of Yb[N(SiMe₃)₂]₂(THF)₂ with proligands L²H-L⁴H containing CF₃ and C₆H₄F fragments do not allow for preparing the target Yb(II) complexes, while the Ca analogues were synthesized in good yields. Complexes 1Yb and 1-4Ca were evaluated as precatalysts for hydrophosphination of styrene, p-substituted styrenes, α-Me-styrene, and 2,3-dimethylbutadiene with various primary and secondary phosphines (PhPH₂, 2,4,6-Me₃C₆H₂PH₂, 2-C₅NH₄PH₂, Ph₂PH, Cy₂PH). Complexes 1Yb, 1-4Ca performed high catalytic activities in styrene hydrophosphination with PhPH₂ and Ph₂PH and demonstrated high regioselectivity affording exclusively the anti-Markovnikov addition products. For primary PhPH₂ the reactions (1:1 molar ratio of substrates) catalyzed by 1Yb, 1Ca, and 2Ca proved to be highly chemoselective affording the secondary phosphine Ph(PhCH₂CH₂)PH; however, complexes 3Ca and 4Ca led to the formation of both secondary and tertiary phosphines in 80:20 and 86:14 ratios. Styrene hydrophosphinations with 2,4,6-Me₃C₆H₂PH₂ and 2-pyridylphosphine for all complexes 1Yb and 1-4Ca proceeded much more slowly compared to PhPH₂. Addition of 2-C₅NH₄PH₂ to styrene catalyzed by complex 1Yb turned out to be non-regioselective and led to the formation of a mixture of Markovnikov and anti-Markovnikov addition products, while all Ca complexes enabled regioselective anti-Markovnikov addition. Complexes 1Ca and 1Yb containing catalytic centers featuring similar ionic radii performed different catalytic activity: the ytterbium analogue proved to be a more active catalyst for intermolecular hydrophosphination of styrene with Cy₂PH, 2-C₅NH₄PH₂, and PhPH₂, but less active with sterically demanding 2,4,6-Me₃C₆H₂PH₂. Styrenes containing in p-position electron-donating groups (Me, tBu, OMe) performed with noticeably lower rates in the reactions with PhPH₂ compared to styrene. Complexes 1Yb, 1Ca, 2Ca, 3Ca, and 4Ca enabled addition of PhPH₂ toward the double C-C bond of α-Me-styrene, and the reaction rate for this substrate is noticeably lower; however quantitative conversions were reached in -40 h. Complexes 1Ca and 2Ca promoted 1,2-addition of PhPH₂ to 2,3-dimethyl butadiene with excellent regio- and chemoselectivity to afford linear secondary phosphines. Hydrophosphination of inert 1-nonene with Ph₂PH with 40% conversion becomes possible due to the application of complex 2Ca (40 h, 70 °C). The rate law for the hydrophosphination of styrene with Ph₂PH catalyzed by 1Ca was found to agree with the idealized equation: v = k[styrene]¹[1Ca]¹.

Full text of DOI:10.1021/acs.inorgchem.8b00088

Article
pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Amido Ca and Yb(II) Complexes Coordinated by Amidine-
Amidopyridinate Ligands for Catalytic Intermolecular Olefin
Hydrophosphination
Ivan V. Lapshin,† Olga S. Yurova,† Ivan V. Basalov,† Vasily Yu. Rad’kov,† Elvira I. Musina,‡
Anton V. Cherkasov,† Georgy K. Fukin,† Andrei A. Karasik,‡ and Alexander A. Trifonov*,†,§
†G. A. Razuvaev Institute of Organometallic Chemistry of Russian Academy of Sciences, 49 Tropinina str., 603137 Nizhny Novgorod,
GSP-445, Russia
‡A. E. Arbuzov Institute of Organic and Physical Chemistry, Kazan Scientific Center, Russian Academy of Sciences, 8 Academician
Arbuzov str., 420088 Kazan, Russia
§A. N. Nesmeyanov Institute of Organoelement Compounds of Russian Academy of Sciences, 28 Vavilova str., 119991, Moscow,
GSP-1, Russia
S
* Supporting Information
ABSTRACT: A series of amido Ca and Yb(II) complexes LM[N(SiMe3)2](THF)
(1Yb, 1−4Ca) coordinated by amidine-amidopyridinate ligands L1−4 were
synthesized via a transamination reaction between proligands L1−4H and bisamido
complexes M[N(SiMe3)2]2(THF)2 (M = Yb, Ca). The reactions of Yb[N-
(SiMe3)2]2(THF)2 with proligands L2H-L4H containing CF3 and C6H4F fragments
do not allow for preparing the target Yb(II) complexes, while the Ca analogues
were synthesized in good yields. Complexes 1Yb and 1−4Ca were evaluated as
precatalysts for hydrophosphination of styrene, p-substituted styrenes, α-Me-
styrene, and 2,3-dimethylbutadiene with various primary and secondary phosphines
(PhPH2, 2,4,6-Me3C6H2PH2, 2-C5NH4PH2, Ph2PH, Cy2PH). Complexes 1Yb, 1−4Ca performed high catalytic activities in
styrene hydrophosphination with PhPH2 and Ph2PH and demonstrated high regioselectivity affording exclusively the anti-
Markovnikov addition products. For primary PhPH2 the reactions (1:1 molar ratio of substrates) catalyzed by 1Yb, 1Ca, and 2Ca
proved to be highly chemoselective affording the secondary phosphine Ph(PhCH2CH2)PH; however, complexes 3Ca and 4Ca
led to the formation of both secondary and tertiary phosphines in 80:20 and 86:14 ratios. Styrene hydrophosphinations with
2,4,6-Me3C6H2PH2 and 2-pyridylphosphine for all complexes 1Yb and 1−4Ca proceeded much more slowly compared to
PhPH2. Addition of 2-C5NH4PH2 to styrene catalyzed by complex 1Yb turned out to be non-regioselective and led to the
formation of a mixture of Markovnikov and anti-Markovnikov addition products, while all Ca complexes enabled regioselective
anti-Markovnikov addition. Complexes 1Ca and 1Yb containing catalytic centers featuring similar ionic radii performed different
catalytic activity: the ytterbium analogue proved to be a more active catalyst for intermolecular hydrophosphination of styrene
with Cy2PH, 2-C5NH4PH2, and PhPH2, but less active with sterically demanding 2,4,6-Me3C6H2PH2. Styrenes containing in p-
position electron-donating groups (Me, tBu, OMe) performed with noticeably lower rates in the reactions with PhPH2 compared
to styrene. Complexes 1Yb, 1Ca, 2Ca, 3Ca, and 4Ca enabled addition of PhPH2 toward the double CC bond of α-Me-styrene,
and the reaction rate for this substrate is noticeably lower; however quantitative conversions were reached in ∼40 h. Complexes
1Ca and 2Ca promoted 1,2-addition of PhPH2 to 2,3-dimethyl butadiene with excellent regio- and chemoselectivity to afford
linear secondary phosphines. Hydrophosphination of inert 1-nonene with Ph2PH with 40% conversion becomes possible due to
the application of complex 2Ca (40 h, 70 °C). The rate law for the hydrophosphination of styrene with Ph2PH catalyzed by 1Ca
was found to agree with the idealized equation: v = k[styrene]1[1Ca]1.
Moreover, being a biogenic, environmentally friendly element,
calcium fits the current trend to develop new synthetic
approaches promoted by nontoxic metals and perfectly meets
all the requirements of the concept of “green” chemistry.3
However, the development of organocalcium chemistry for a
long time was constrained by limited accessibility of this
compound due to synthetic difficulties caused by enhanced
INTRODUCTION
■
Unlike transition metals catalytic properties of complexes of
main group metals have not attracted considerable attention
until very recently, and the examples of their application have
been mainly limited to Lewis-acidic catalysis.1 Calcium
combines a number of very important advantages which
makes this metal an extremely attractive candidate for
investigation of its catalytic potential. Wide abundance of this
element in the Earth’s crust (∼5 wt %)2 with nearly endless
resources and low production price ensures its availability.
Received: January 15, 2018
© XXXX American Chemical Society
A
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Scheme 1. Synthesis of Complexes 1Yb,1-4Ca
reactivity and low kinetic stability.4 The high electropositive
character and large ionic radii5 of the heavy alkaline earth
metals result in a chemistry that is mostly governed by
electrostatic and steric requirements and make it related to that
of rare earth metals. Indeed, the heavy alkaline earth and rare
earth Ln2+ (Ln = Eu, Sm, Yb) ions due to hard Lewis acidity,
oxophilicity, low polarizability4a,c,6 and close values of ionic
radii5 exhibit strong similarities in their structures and reactivity
(besides the redox reactions typical for Ln2+ complexes).
Importantly, both families of complexes feature a typical
reaction behavior, such as the ability to add to multiple C−C
bonds and facile σ-bond metathesis, which makes them
promising candidates for catalysis of hydroelementation of
unsaturated substrates.7
During the past two decades, enormous progress has been
reached in the synthesis and characterization of well-defined
calcium complexes and their application in homogeneous
catalysis.8 They have been successfully used for olefin
polymerization,9 hydroamination,10 and hydrosilylation.11 The
report of Hill and co-workers in 2007 on hydrophosphination
of unhindered activated alkenes and diphenylacetylene8c
enabled by Ca compounds gave a strong impetus to the
development of the sphere of catalytic application of alkaline
earth metals.8b,d,9c,10b,12
a one-step transamination reaction between proligands LH16
and bisamido complexes M[N(SiMe3)2]2(THF)2 (M = Yb, Ca)
(Scheme 1).
In the case of Yb, the reactions smoothly proceed at room
temperature, while for Ca high product yields can be achieved
when the reaction mixtures are heated at 50 °C for 50 h.
Complexes 1Yb and 1Ca were isolated after recrystallization
from toluene and THF/hexane solutions in high yields as black
and yellow crystals, respectively. Complex 2Ca was obtained
from toluene as orange crystals. Crystallization of complexes
3Ca and 4Ca from hexane afforded orange microcrystalline
powders. It is noteworthy that unlike L1H the reactions of
Yb[N(SiMe3)2]2(THF)2 with proligands L2H-L4H containing
CF3 and C6H4F fragments did not allow for preparing the
target Yb(II) complexes. The NMR-tube reactions monitored
1
by H NMR spectroscopy detected evolution of HN(SiMe3)2
and formation of paramagnetic Yb(III) species featuring low
solubility in C6D6 and common organic solvents. All the
attempts of isolation of tractable reaction products failed. Most
likely such a difference of reactivity of proligands L2H-L4H with
Yb[N(SiMe3)2]2(THF)2 and Ca[N(SiMe3)2]2(THF)2 is due to
the redox character of the Yb(II) center which makes possible
C−F bond activation.17
Complexes 1Yb, 2Ca, 3Ca, and 4Ca are stable both in the
solid state and in hexane or toluene solutions under conditions
excluding contact with oxygen and moisture, whereas complex
1Ca is stable in solid state in solution undergoes ligand
redistribution reaction affording in 1 week an equimolar
mixture of homoligand compounds [(L1)2Ca] and Ca[N-
(SiMe3)2]2(THF)2 which were isolated from the reaction
mixture in 31 and 33% yields, respectively. The 1H and
13C{1H} NMR spectra of all complexes display single sets of
resonances in the −20 to +70 °C temperature range, consistent
with the presence of a single C1-symmetric species in solution.
The 19F{1H} NMR spectrum of 3Ca displayed two resonances
due to CF3 and C6H4F groups, and spectrum of complexes 2Ca
and 4Ca displayed only one resonances due to the CF3 group.
In the 19F{1H} NMR spectrum of L3H (C7D8, 20 °C), the
singlet due to the F atoms of the C6H4F ring appears at −58.8
ppm, while in the spectrum of 3Ca these F atoms give rise to a
strong field shifted signal (−127.2 ppm), thus giving evidence
for Ca−F interaction. Compound 3Ca turned out to be
thermally stable in toluene solution at 70 °C: no decomposition
was observed within 5 days. No fluxional behavior was detected
by 19F{1H} NMR spectroscopy in the temperature region
−50−70 °C.
Moreover organocalcium mediated reactions present special
interest from an academic point of view since they allow deeper
insight into different ways of activation of C−C multiple bonds
in coordination spheres of transition and main group metals.13
Herein we report on the synthesis of a series of new
heteroleptic amido complexes of Ca(II) and Yb(II) supported
by multidentate amidine-amidopyridinate ligands and their
application in catalytic intermolecular hydrophosphination of
various olefins and dienes. The influence of electronic and steric
properties of both olefin and phosphine substrates will be
considered. The detailed kinetic studies of addition of Ph2PH
to styrene catalyzed by 1Ca will be described.
RESULTS AND DISCUSSION
■
As it was mentioned above due to the large ionic radii and
predominantly ionic nature of metal−ligand bonding Ca(II)
and Ln(II) complexes easily undergo ligand redistribution
reactions (Schlenk equilibrium).8a,14 Since application of bulky
and multidentate ligands can circumvent this kinetic instability
issue,15 we focused our attention on recently designed amidine-
amidopyridinate ligands.16
The heteroleptic amido complexes LM[N(SiMe3)2](THF)
(M = Yb, Ca) coordinated by polydentate nitrogen-based
donor amidine-amidopyridinate ligands L were synthesized via
The single crystals of 1Yb and 1Ca suitable for X-ray study
were obtained by slow concentration of toluene and THF/
B
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hexane solutions respectively at room temperature. The
molecular structure of complexes 1Yb and 1Ca are depicted
in Figure 1, and the crystal and structural refinement data are
and 1Ca, those involving the amidinate nitrogen N(4) are the
longest (Yb(1)−N(4) 2.499(3) Å; Ca(1)−N(4) 2.557(3) Å).
No delocalization of negative charge was detected in the
amidinate units of the ligands: the length of N(3)−C(22) bond
(1Yb:1.390(5); 1Ca:1.391(4) Å) corresponds to a single one,
while the length of the second bond N(4)−C(22) is indicative
of its double character (1Yb: 1.296(5); 1Ca: N(4)−C(6)
1.298(4) Å).
The crystals of 2Ca suitable for X-ray study were obtained by
slow concentration of the toluene solution at room temper-
ature. Complex 2Ca crystallizes as a solvate with one toluene
molecule 2Ca·C7H8. The molecular structure of complex 2Ca
is depicted in Figure 2. Complex 2Ca crystallizes in
Figure 1. Molecular structure of 1 (M = Yb (1Yb), Ca (1Ca)).
Hydrogen atoms, methylene fragments of the THF molecule, and
methyl substituents of iPr groups are omitted for clarity; thermal
ellipsoids drawn at the 30% probability level. Bond lengths (Å) and
angles (deg):1Yb: Yb(1)−N(5) 2.365(3), Yb(1)−N(2) 2.422(3),
Yb(1)−O(1) 2.436(3), Yb(1)−N(1) 2.444(3), Yb(1)−N(4)
2.499(3), N(1)−C(1) 1.415(5), N(2)−C(13) 1.331(5), N(2)−C(9)
1.375(5), N(3)−C(22) 1.390(5), N(4)−C(22) 1.296(5), N(2)−
Yb(1)−N(1) 55.3(2), N(1)−C(9)−N(2) 112.7(3), N(1)−Yb(1)−
N(4) 120.8(2), N(4)−C(22)−N(3) 122.2(3), N(5)−Yb(1)−N(4)
111.0(2); 1Ca: Ca(1)−N(5) 2.330(3), Ca(1)−O(1) 2.353(2),
Ca(1)−N(2) 2.371(3), Ca(1)−N(1) 2.394(3), Ca(1)−N(4)
2.557(3), N(1)−C(9) 1.332(4), N(2)−C(9) 1.382(4), N(2)−C(13)
1.319(4), N(3)−C(22) 1.391(4), N(4)−C(22) 1.298(4), N(2)−
Ca(1)−N(1) 56.65(9), N(1)−C(9)−N(2) 112.8(3), N(4)−C(22)−
N(3) 123.6(3), N(1)−Ca(1)−N(4) 118.8(2).
Figure 2. Molecular structure of 2Ca. Hydrogen atoms, methylene
fragments of the THF molecule and methyl substituents of iPr groups
are omitted for clarity; thermal ellipsoids drawn at the 30% probability
level. Bond lengths (Å) and angles (deg): Ca(1)−N(1) 2.415(2),
Ca(1)−N(2) 2.391(2), Ca(1)−N(4) 2.665(2), Ca(1)−N(5)
2.320(2), Ca(1)−O(1) 2.463(2), Ca(1)−O(2) 2.375(2), N(3)−
C(22) 1.374(2), N(4)−C(22) 1.284(2), N(2)−C(13) 1.323(2),
N(2)−C(9) 1.371(2), N(2)−Ca(1)−N(1) 55.98(2), N(5)−Ca(1)−
N(4) 128.59(6), N(2)−Ca(1)−N(4) 65.45(5), N(1)−Ca(1)−N(4)
116.38(5).
listed in Table S1 (Supporting Information). Complex 1Yb
crystallizes as a solvate 1Yb·1/2C7H8, while 1Ca forms a solvate
with one toluene molecule 1Ca·C7H8. According to the X-ray
data, complexes 1Yb and 1Ca have similar structures but they
are not isomorphous. They crystallize in the monoclinic crystal
system but in different space groups P21/n and P21/c. The five-
coordinate metal center in 1Yb and 1Ca adopts a distorted
square-pyramidal geometry with three of the nitrogen atoms of
the amidine-amidopyridinate ligand and one oxygen atom of
THF molecule in the base and the nitrogen atom of amido
group in the axial vertex. The X-ray diffraction studies revealed
a rather unusual geometric situation within the M-amidine-
amidopyridinate fragment: surprisingly the covalent bonds Yb−
N(1)amido (2.444(3) Å) and Ca−N(1)amido (2.394(3) Å) turned
out slightly longer than the coordination bonds Yb−
N(2)pyridinato (2.422(3) Å) and Ca−N(2)pyridinato (2.371(3) Å).
Similar bonding situation has been described previously for
aminopyridinato Ln(III) complexes.18 The M−N(5)silylamido
bond lengths in 1Yb and 1Ca (2.365(3) and 2.330(3) Å,
respectively) fall into the range of values normally measured in
five-coordinate Yb(II) and Ca complexes with terminal
N(SiMe3)2 ligands.8d,10b,19 Among the M−N bonds in 1Yb
orthorhombic crystal system in the Pna21 space group. Unlike
1Yb and 1Ca complex 2Ca contains tetradentate amidine-
amidopyridinate ligand bearing a pendant methoxy group in the
amidinate phenyl ring. The six-coordinate metal center in 2Ca
adopts a distorted octahedral geometry with three of the
nitrogen and one oxygen atoms of the amidine-amidopyridinate
ligand in the base and the nitrogen atom of amido group and
one oxygen atom of THF molecule in the axial vertex.
However, the difference of the formal coordination numbers of
the metal centers in 1Ca, 1Yb, and 2Ca does not affect the
bonding situation within the M-amidine-amidopyridinate
fragment: the covalent bond Ca−N(1)amido (2.415(2) Å) is
longer than the coordination bond distance Ca−N(2)pyridinato
(2.391(2) Å). Despite the different coordination numbers of
the metal centers the M−N(5)silylamido bond lengths in 1Yb
(2.365(3) Å), 1Ca (2.330(3) Å) and 2Ca (2.320(2) Å) have
rather similar values and fall into the region typical for five- and
six-coordinate Yb(II) and Ca(II) heteroleptic amido complex-
C
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a
Table 1. Hydrophosphination of Styrene with Phosphines Catalyzed by Complexes 1Yb, 1Ca, 2Ca, 3Ca, and 4Ca
b
c
d
no.
precatalyst [mM]
phosphine
Ph2PH
time, h
conversion
sec-P/tert-P
regioselectivity Markovnikov/anti- Markovnikov
1
1Yb
3
40
3
100
40
0/100
0/100
0/100
0/100
0/100
44/56
0/100
0/100
0/100
0/100
0/100
0/100
0/100
0/100
0/100
0/100
0/100
0/100
0/100
0/100
0/100
0/100
0/100
0/100
0/100
0/100
2
Cy2PH
3
PhPH2
100
30
95/5
4
2,4,6-Me3C6H2PH2
2,4,6-Me3C6H2PH2
2-C5NH4PH2
Ph2PH
16
70
70
3
100/0
100/0
100/0
5
43
6
100
100
25
7
1Ca
8
Cy2PH
72
3
9
PhPH2
33
99/1
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
PhPH2
10
72
72
3
100
84
97/3
2,4,6-Me3C6H2PH2
2-C5NH4PH2
Ph2PH
100/0
100/0
12
2Ca
3Ca
4Ca
100
31
Cy2PH
72
3
PhPH2
55
95/5
2,4,6-Me3C6H2PH2
2-C5NH4PH2
Ph2PH
72
72
3
93
100/0
d
47
76/24
100
30
Cy2PH
72
3
PhPH2
100
99
80/20
100/0
2,4,6-Me3C6H2PH2
2-C5NH4PH2
Ph2PH
72
72
3
d
24
100/0
100
30
Cy2PH
72
3
PhPH2
76
86/14
100/0
2,4,6-Me3C6H2PH2
2-C5NH4PH2
72
72
100
100
d
84/16
0/100
a
b
Reaction in neat substrates [phosphine]0:[styrene]0:[precat]0 = 50:50:1, [precat]0 = 87.0 mM, T [°C] = 70. Conversion of styrene, determined by
c
d
NMR spectroscopy. Chemoselectivity was determined by 31P NMR spectroscopy. Regioselectivity was determined by 1H, 31P NMR spectroscopy.
es.8d,10b,12c,19,20 The geometric parameters of the amidinate
fragment in 2Ca are similar to those in 1Ca and 1Yb. The
noticeable difference in the C(22)−N(3) and C(22)−N(4)
bond lengths (1.374(2) vs 1.284(2) Å) is indicative of the
absence of negative charge delocalization within the amidinate
fragment.21
Hydrophosphination Catalysis. Complexes 1Yb, 1Ca,
2Ca, 3Ca,and 4Ca were evaluated as precatalysts for styrene
hydrophosphination with various phosphines. The catalytic
tests were performed in the presence of 2 mol % of the catalyst
in neat substrates at 70 °C. The representative data are
collected in Table 1.
All complexes performed high catalytic activity in styrene
hydrophosphination with PhPH2 and Ph2PH: quantitative
conversions were reached in 3−10 h. The reactions were
found to be highly regioselective affording exclusively the anti-
Markovnikov addition products for both PhPH2 and Ph2PH
with no indication for the formation of other regioisomers.
Moreover, for primary PhPH2 the reactions catalyzed by 1Yb,
1Ca, and 2Ca proved to be highly chemoselective, leading to
the formation of the secondary phosphine (sec-P) in >95%
selectivity; that is, less than 5% of tertiary phosphine formed
upon double (stepwise) hydrophosphination. However, com-
plexes 3Ca and 4Ca turned out to be less chemoselective; the
formation of both secondary and tertiary phosphines was
detected in 80/20 (3Ca) and 86/14 (4Ca) ratios. The results
of styrene hydrophosphination with PhPH2 catalyzed by a
series of heteroleptic amido complexes 1Ca−4Ca unambigu-
ously imply a dramatic effect of the ancillary ligand on both
catalytic activity and selectivity of metal promoted reactions. It
is noteworthy that the transition from L4 to L3 featuring a
similar structure and steric demand but bearing in the ortho-
position of amidinate phenyl substituent a fluorine atom
capable of weak coordination to metal ions17 leads to a
noticeable increase of catalytic activity (4Ca: 3 h, 76% vs 3Ca:
3 h, 100%); however it does not affect the chemoselectivity.
Complex 1Ca which does not contain CF3 or C6H4F groups in
the ancillary ligand framework but bears sterically demanding
iPr2C6H3 substituent at the amidinate nitrogen proved to be the
least active but the most chemoselective in this series of
complexes.
Addition of more sterically demanding and more donor
primary phosphine MesPH2 to styrene proceeds much more
slowly compared to PhPH2. For the reactions catalyzed by 1−
4Ca complete conversion requires >72 h at 70 °C, while
complex 1Yb demonstrated the lowest activity: even after 70 h
the conversion did not exceed 43%. However, all precatalysts
provided excellent regio- and chemoselectivities. The nature of
phosphine was found to affect the hydrophosphination rate
dramatically. Thus, Cy2PH proved to be much less reactive than
Ph2PH in all catalytic tests. The reactions with styrene proceed
slower; the highest conversion was provided by ytterbium
compound 1Yb and reached 40% in 40 h. Ca complexes
displayed lower catalytic activity, in 72 h conversion did not
exceed 31%. Lower reactivity of Cy2PH vs Ph2PH can be
rationalized by both greater steric demand of the former
(compare the Tolman cone angles: Cy2PH, θ = 143°; Ph2PH, θ
= 128°)22 and its lower acidity (compare: Cy2PH, pKa = 34.6
(35.7); Ph2PH, pKa = 22.9 (21.7),)23 which affects phospine
deprotonation and σ-bond metathesis steps of the catalytic
D
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cycle of intermolecular olefin hydrophosphination.8d Styrene
hydrophosphination with 2-C5NH4PH2 for all complexes 1Yb
and 1−4Ca proceeds much more slowly compared to PhPH2.
Surprisingly hydrophosphination of styrene with 2-C5NH4PH2
catalyzed by complex 1Yb turned out to be non-regioselective
and led to the formation of a mixture of Markovnikov and anti-
Markovnikov addition products in a 44:56 ratio (entry 7). In
contrast all Ca complexes enable regioselective reaction
affording exclusively anti-Markovnikov addition products.
However, complexes 2Ca and 4Ca demonstrate lower
chemoselectivity, and the formation of both secondary and
tertiary phosphines was detected in 76:24 and 84:16 ratios,
respectively. It is noteworthy that complexes 1Ca and 1Yb
containing catalytic centers with very similar ionic radii
performed different catalytic activity: the ytterbium analogue
proved to be a more active catalyst for intermolecular
hydrophosphination of styrene with Cy2PH, 2-C5NH4PH2,
and PhPH2, but less active with sterically demanding MesPH2.
To elucidate the possibility of double sequential alkylation of
PhPH2 catalyzed by complexes 1Yb and 1−4Ca hydro-
phospination reactions were carried out at a molar substrates
ratio [styrene]0:[PhPH2]0 = 2:1. Complexes 1Ca and 2Ca
enable the formation of the tertiary phosphine PhP-
(CH2CH2Ph)2 in quantitative yields and excellent chemo-
selectivity (Table 2, entry 2 and 4); however 2Ca shows
donating groups (Me, tBu, OMe), a noticeable decrease of the
reaction rate was detected compared to that for unsubstituted
styrene (entry 11−25). Addition of PhPH2 to p-MeO-styrene
proceeded at the lowest rate, most likely due to blocking the
oxophilic catalytic center and competition between MeO, C
C, and phosphine for coordination site. For p-Cl-styrene no
strong deviation from the reaction rate measured for styrene
was observed (entry 6−10) with the exception of complex 1Ca
which performs noticeably higher catalytic activity in the case of
the former substrate. In the case of p-F-styrene an essential
drop of activity took place when 1Yb was used as a precatalyst
(entry 1), whereas activities of other complexes did not differ
much from those measured for styrene. Such a decrease of
activity can be rationalized either by competing coordination
between fluoride24,25 and olefinic units on catalytic center or by
C−F bond activation mediated by Yb(II) complex26 leading to
partial deactivation of the catalyst. All of the above-mentioned
complexes proved to be unable to mediate addition of PhPH2
and Ph2PH to internal double CC bonds of cyclohexene and
trans-stilbene. As it was exemplified by α-Me-styrene complexes
1Yb, 1Ca, 2Ca, 3Ca, and 4Ca enable addition of PhPH2 toward
double CC bond of 1,1-disubstituted terminal olefin. The
reaction rate for this substrate is noticeably lower; however
quantitative conversions can be reached in ∼40 h. It is
noteworthy that regio- and chemoselectivities remain excellent
for this substrate (entry 26−30). Catalytic addition of PhPH2 to
conjugated 2,3-dimethyl butadiene was tested as a prospective
synthetic approach to the formation of the phosphole ring;
however no formation of a heterocyclic product was detected.
Complexes 1−4Ca allow for the transformation of 2,3-dimethyl
butadiene into the linear phosphorus containing 1,2-addition
products in good yields and excellent regioselectivity, albeit
only 1Ca and 2Ca provide a high degree of chemoselectivity
control and afford secondary phosphines. For complexes 3Ca
and 4Ca the reactions lead to the formation of mixtures of
secondary and tertiary phosphines (entries 34 and 35).
Table 2. Double Sequential Hydrophosphination of Styrene
with PhPH2 ([PhPH2]0:[styrene]0 = 1:2) Catalyzed by
a
Complexes 1Yb, 1Ca, 2Ca, 3Ca, 4Ca
b
c
no.
precatalyst
substrates
styrene
time, h
conversion
sec-P/tert-P
1
2
3
4
5
6
1Yb
1Ca
2Ca
2Ca
3Ca
4Ca
70
70
16
48
70
70
75
100
67
50/50
0/100
67/33
0/100
50/50
52/48
PhPH2
100
75
74
Hydroelementation of inert 1-alkenes still remains a
challenging and hardly realizable transformation.7b,27 Never-
theless, complexes 3Ca and 4Ca enable addition of PhPH2 to
1-nonene and provide ∼25% conversion in 40 h at 70 °C. For
Ph2PH within the same reaction time even higher conversions
were measured and reached maximum 40% in the case of 2Ca.
Unexpectedly complex 1Yb appeared completely inert in
hydrophosphination of 1-nonene with both Ph2Ph and PhPH2.
Interestingly complexes 1Ca and 1Yb, although having
similar structures and containing catalytic centers with very
similar ionic radii, performed different catalytic activity.
Ytterbium analogue proved to be more active catalyst for
intermolecular hydrophosphination of styrene with Cy2PH, 2-
C5NH4PH2, and PhPH2. This fact is in line with the previous
observation of higher catalytic activity of (o-Me2NC6H4-
CHSiMe3)2Yb(THF)2 in styrene polymerization vs that of Ca
congener.9d A higher insertion rate was explained by the
authors as a result of a weaker Yb-ligand bond caused by
electron−electron repulsion of the completely filled f shell. At
this stage it is unclear which factors are responsible for the
different selectivity in styrene hydrophosphination with PhPH2
promoted by Yb and Ca complexes.
a
Reaction in neat substrates [PhPH2]0:[styrene]0:[precat]0
=
b
50:100:1, [precat]0 = 87.0 mM, T [°C] = 70. Conversion of styrene,
c
determined by NMR spectroscopy. Chemoselectivity was determined
by 31P NMR spectroscopy.
noticeably higher catalytic activity. Quantitative conversion was
reached in 48 h vs 70 h for 1Ca. Complexes 1Yb, 3Ca, and 4Ca
proved to be somewhat less active: in 70 h the conversion did
not exceed 75%. Surprisingly the reactions catalyzed by
complexes 1Yb, 3Ca, and 4Ca under the same reaction
conditions were nonselective and led to the formation of
mixtures of the secondary and tertiary phosphines. It is
noteworthy that heteroleptic amido complexes 1Yb, 1−4Ca
coordinated by amidine-amidopyridinate ligands provide lower
chemoselectivity compared to the related amido complexes
supported by amidinate24 and phenolate8d,25 ligands.
To assess the influence of the electronic properties of
styrenic substrate on reaction rate, a series of catalytic tests of
hydrophosphination of styrenes bearing various substituents in
the para position of the aromatic ring with PhPH2 was carried
out. The catalytic tests were performed in the presence of 2 mol
% of 1Yb, 1Ca, 2Ca, 3Ca, and 4Ca as the precatalyst. The
representative results are listed in Table 3. A number of
functional groups were found to be tolerated for the
hydrphosphination of styrene. Similar to our previous
observations8d for styrenes containing in p-position electron-
Kinetic Analysis. In order to get a deeper insight into the
mechanism of intermolecular olefin hydrophosphination
catalyzed by Ca compounds, more detailed kinetic studies
were performed for reaction of styrene with Ph2PH in the
presence of 1Ca. The reactions were carried out in C6D6, and
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a
Table 3. Olefin Hydrophosphination with PhPH2 and Ph2PH Catalyzed by Complexes 1Yb, 1-4Ca
b
c
b
c
no. precatalyst
substrates
styrene
time, h conversion selectivity
no. precatalyst
substrates
PhPH2
time, h conversion selectivity
1
1Yb
1Ca
1Ca
2Ca
3Ca
4Ca
1Yb
1Ca
2Ca
3Ca
4Ca
1Yb
1Ca
2Ca
3Ca
4Ca
1Yb
1Ca
2Ca
3Ca
4Ca
1Yb
1Ca
2Ca
3Ca
4Ca
1Yb
1Ca
2Ca
3Ca
4Ca
1Yb
1Ca
2Ca
3
3
100
33
94/6
35
36
37
3Ca
4Ca
1Yb
40
40
40
100
88
100/0
100/0
100/0
2
91/9
3
PhPH2
10
3
100
55
97/3
2,3-dimethyl-1,3-
butadiene
40
4
95/5
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
1Ca
2Ca
3Ca
4Ca
1Yb
1Ca
1Ca
2Ca
3Ca
4Ca
1Yb
1Ca
2Ca
3Ca
4Ca
1Yb
1Ca
2Ca
3Ca
4Ca
1Yb
1Ca
2Ca
3Ca
4Ca
40
40
40
40
96
72
96
40
40
40
96
40
40
40
40
40
40
40
40
40
40
40
40
40
40
100
100
90
95
0
100/0
100/0
40/60
82/18
5
3
100
76
80/20
86/14
94/6
6
3
PhPH2
7
16
3
72
8
p-F-styrene
PhPH2
82
91/9
9
3
61
92/8
nonene-1
PhPH2
12
28
3
100/0
100/0
100/0
100/0
100/0
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
3
100
67
85/15
86/14
90/10
96/4
3
3
80
23
25
0
p-Cl-styrene
PhPH2
3
86
3
71
88/12
90/10
91/9
3
79
nonene-1
Ph2PH
4
100/0
100/0
100/0
100/0
3
80
40
34
13
0
16
16
16
16
16
16
16
16
16
16
70
40
40
40
40
40
40
40
96
98/2
p-Me-styrene
PhPH2
96
90/10
68/32
83/17
84/16
100/0
91/9
100
100
88
cyclohexene
PhPH2
0
0
28
0
p-tBu-styrene
PhPH2
96
0
100
100
85
83/17
83/17
87/13
95/5
0
trans-stilbene
0
0
p-OMe-styrene
PhPH2
55
PhPH2
0
100
100
100
100
62
89/11
77/23
83/17
90/10
100/0
100/0
100/0
0
a
Reaction in neat substrates [phosphine]0:[styrene]0:[precat]0
50:50:1, [precat]0 = 87.0 mM, T [°C] = 70. Conversion of styrene,
=
b
c
determined by NMR spectroscopy. Product chemoselectivity″Anti-
Markovnikov monoaddition/double addition” determined by 31P
α-Me-styrene
82
NMR spectroscopy.
90
1
kinetic monitoring was performed by H NMR spectroscopy.
The plot of conversion of Ph2PH vs reaction time at 25 °C in
the presence of an 8-fold molar excess of styrene proved to be
linear (Figure 3), indicating a zeroth-order dependence of the
reaction rate in concentration of Ph2PH. Conversion of Ph2PH
over time was studied at two different [phosphine]/[1Ca]
ratios (see the Supporting Information, Figure S11). In both
cases, similar values of kapp were calculated (23.21 and 25.53
h−1).
A series of experiments was conducted to determine the
partial order in styrene, using a constant concentration of the
catalyst and the phosphine and varying the concentration of
styrene in the reaction mixture (0.96−1.67 mol/L). The plot of
ln(kapp) vs ln([styrene]0) gave a straight line (R2 = 0.974) with
a slope of 0.9 corresponding to the apparent kinetic order for
styrene (Figure 4; see also Figure S12).
Figure 4. Plot of lg(kapp) vs lg([styrene]0) for hydrophosphination of
styrene with Ph2PH, catalyzed by 1Ca at different styrene
concentrations (0.96; 1.28; 1.58; 1.67 mol/L). Reaction conditions:
25 °C, [1Ca]0 = 48 mM, [1Ca]0/[Ph2PH]0 = 1:77, total volume 0.6
mL.
Figure 3. Plot of Ph2PH conversion vs time for styrene hydro-
phosphination with Ph2PH, catalyzed by 1Ca. Reaction conditions: 25
°C, [1Ca]0 = 28 mM, [PPh2H]0:[styrene]0:[1Ca]0 = 26:220:1, total
volume 0.575 mL.
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In order to determine the partial order in the catalyst, the
conversion of phosphine was monitored at constant molar ratio
of substrates and at different catalyst concentrations (54.1−
161.9 mmol/L) while maintaining the total volume of reactants
and solvent constant (Figure 5).
L4H due to redox character of Yb(II) center C−F bond
activation occurs and hampers the formation of LYb[N-
(SiMe3)2](THF) complexes. The X-ray analysis revealed that
in 1Yb and 1Ca the metal centers are five-coordinate, while in
2Ca it adopts a coordination number of six because of the
additional coordination of a pendant methoxy group in the
amidinate phenyl ring.
The systematic study of styrene hydrophosphination with
PhPH2 catalyzed by a series of amido complexes 1Ca-4Ca
coordinated by amidine-amidopyridinate ligands unambigu-
ously imply a dramatic effect of the steric and electronic
properties of the ancillary ligand on both catalytic activity and
selectivity of metal promoted reactions. It is noteworthy, that
the transition from L4 to L3 featuring similar structure and
steric demand but bearing in ortho-position of amidinate
phenyl substituent a fluorine atom capable to weak
coordination to metal ions17 leads to a noticeable increase of
catalytic activity (4Ca: 3h, 76% vs 3Ca: 3h, 100%) however
does not affect chemoselectivity. Complex 1Ca which does not
contain CF3 or C6H4F groups in the ancillary ligand framework
but bears sterically demanding iPr2C6H3 substituent at the
amidinate nitrogen proved to be the least active but the most
chemoselective in this series of complexes.
Complexes 1Yb, 1−4Ca demonstrated high catalytic activity
and regioselectivity in styrene hydrophosphination with PhPH2
and Ph2PH. For primary PhPH2 the addition to styrene
catalyzed by 1Yb, 1Ca, and 2Ca is chemoselective and affords
the secondary phosphine Ph(PhCH2CH2)PH, while when 3Ca
and 4Ca were used as precatalysts mixtures of secondary and
tertiary phosphines were formed. Complexes 1Yb and 1−4Ca
enable styrene hydrophosphination with 2,4,6-Me3C6H2PH2
and 2-pyridylphosphine. Surprisingly despite the similar ionic
radii of the catalytic centers the reaction of 2-C5NH4PH2 with
styrene catalyzed by 1Yb proceeds non-regioselectively, while
all Ca complexes enable regioselective anti-Markovnikov
addition. Complexes 1Ca and 1Yb containing catalytic centers
featuring similar ionic radii performed different catalytic
activity: ytterbium analogue proved to be more active catalyst
for intermolecular hydrophosphination of styrene with Cy2PH,
2-C5NH4PH2 and PhPH2, but less active with sterically
demanding 2,4,6-Me3C6H2PH2. Complexes 1Yb and 1-4Ca
provide quantitative conversion in the addition of PhPH2
toward 1,1-disubstituted CC bond of α-Me-styrene. Ca-
catalyzed hydrophosphination of inert 1-nonene with Ph2PH
achieving 40% conversion is the most impressive result
reported in this paper.
Figure 5. Kinetic curves of accumulation of tertiary phosphine at
different concentrations of 1Ca (54.1; 80.9; 107.9; 161.9 mmol/L).
Reaction conditions: 25 °C, [styrene]0 = [Ph2PH]0 = 2.9 mol/L, total
volume 0.6 mL.
The initial reaction rates (kapp) are determined for various
initial concentrations of the catalyst below 70%. A plot of
lg(kapp) vs lg([1Ca]0) gave a straight line with a slope indicating
a first order in the precatalyst (Figure 6, see also Figure S13).
Figure 6. Plot of lg(kapp) vs lg([1Ca]0) for hydrophosphination of
styrene with Ph2PH, catalyzed by 1Ca at the different catalyst
concentrations (54.1; 80.9; 107.9; 161.9 mmol/L). Reaction
conditions: 25 °C, [styrene]0 = [Ph2PH]0 = 2.9 mol/L, [styrene]0/
[Ph2PH]0 = 1:1, total volume 0.6 mL.
Thereby the rate law for the hydrophosphination of styrene
with Ph2PH catalyzed by 1Ca agrees with the idealized
equation: v = k[styrene]1[1Ca]1 and is consistent with the
previously reported observations.7b,8d,12d,e,28
EXPERIMENTAL SECTION
■
General Considerations. All experiments were performed in
evacuated tubes or in inert atmosphere, using standard Schlenk-flask or
glovebox techniques, with rigorous exclusion of traces of moisture and
air. After being dried over KOH, THF and DME were purified by
distillation from sodium/benzophenone ketyl, hexane, and toluene by
distillation from sodium/triglyme benzophenone ketyl prior to use.
Benzene-d6, toluene-d8, and THF-d8 were dried with sodium/
benzophenone ketyl and condensed in a vacuum prior to use.
[(Me3Si)2N]2M(THF)2 (M = Yb,29 Ca,30 L1−4H16b were prepared
according to literature procedures. Diphenylphosphine, dicyclohex-
ylphosphine, and phenylphosphine were donated by Synor Ltd. and
were vacuum-distilled over CaH2 and then were degassed by freeze−
pump−thaw methods.
CONCLUSION
■
The reactions of bisamido complexes M[N(SiMe3)2]2(THF)2
(M = Yb, Ca) and amidine-aminopyridines LH was used as a
synthetic approach to the synthesis of the heteroleptic amido
complexes LM[N(SiMe3)2](THF). The reactions of Yb[N-
(SiMe3)2]2(THF)2 with proligands L2H-L4H bearing CF3 and
C6H4F groups did not result in the formation of the target
Yb(II) complexes, while in the case of Ca[N(SiMe3)2]2(THF)2
under the similar conditions afforded analogues 2−4Ca in good
yields. Taking into account the fact that in the case of L1H
which does not contain C−F bonds the transamination reaction
allows for preparing the heteroleptic amido complexes of both
Ca and Yb it is logical to assume that in the reactions of L2H-
Instruments and Measurements. NMR spectra were recorded
on a Bruker DPX 200 or Bruker Avance DRX-400 spectrometer.
Chemical shifts for 1H and 13C spectra were referenced internally
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Article
using the residual solvent resonances and are reported relative to TMS.
Lanthanide metal analysis was carried out by complexometric
titration.31 C, H, N elemental combustion analysis was performed in
the microanalytical laboratory of IOMC.
concentration of the toluene solution at room temperature resulted
in the formation of red crystals. The mother liquid was decanted, and
the crystals were washed with cold hexane and dried in a vacuum for
30 min. Complex 2Ca was isolated in 95% yield (0.299 g).1H NMR
(400 MHz, C6D6) δ = 0.09 (s, 18H, SiMe3), 1.40 (m, 4H, β-CH2
THF), 1.71 (s, 3H, CH3), 2.10 (s, 3H, CH3 toluene), 2.27 (s, 3H,
CH3), 2.38 (s, 3H, CH3), 2.59 (s, 3H, CH3), 3.38 (s, 3H, OMe), 3.56
(m, 4H, α-CH2 THF), 4.74 (d, 3JHH = 7.5 Hz, 1H m-Py), 5.58 (d, 3JHH
= 8.5 Hz, 1H m-Py), 5.75 (d, 3JHH = 8.2 Hz, 1H p-Py), 6.53 (dd, 3JHH
= 16.9, 8.4 Hz, 2H Ar), 6.61 (s, 2H Ar), 6.64 (t, 3JHH = 6.7 Hz, 2H Ar),
6.81 (d, 3JHH = 7.4 Hz, 1H Ar), 6.87 (d, 3JHH = 7.0 Hz, 1H Ar), 7.03−
6.97 (complex m, 5H Ar), 7.05 (d, 3JHH = 7.2 Hz, 2H). 13C NMR (101
MHz, C6D6) δ = 2.2 (CH3, SiMe3), 17.7 (CH3), 18.0 (CH3), 18.1
(CH3), 20.4 (CH3), 21.1 (CH3 toluene), 25.5 (β-CH2 THF), 56.8
(OMe), 67.5 (α −CH2 THF), 92.9 (m-Py), 103.0 (m-Py), 111.2 (p-
Py), 121.4, 121.5, 124.5, 125.3, 128.2, 128.6, 128.9, (C Ar), 132.2 (o-C
C6H3Me2), 133.6 (o-C C6H3Me2), 137.3 (o-C C6H3Me2), 138.2 (o-C
Py), 138.9 (o-C Py), 140.8 (o-C C6H3Me2), 149.9 (o-C, C6H4OMe),
150.5 (i-C, C6H3Me2), 150.8 (i-C, C6H3Me2), 165.1 (o-C, Py).
19F{1H} NMRδ = −58.2. IR (Nujol, KBr, ν/cm−1): 1927 (w),
1783(w), 1660 (m), 1616 (s), 1603 (s), 1587 (s), 1574 (s), 1530 (s),
1495 (s), 1460 (s), 1377 (s), 1350 (s), 1288 (s), 1250 (s),1225 (s),
1188 (s), 1148 (s), 1113 (s), 1095 (s), 1049 (s), 1030 (s), 1005 (s),
977 (s), 926 (s), 881 (s), 821 (s), 772 (s), 746 (s), 716 (s), 692 (w),
662 (w), 619 (w), 608 (w), 590 (w), 565 (w), 510(w). Elem. Anal.
Calc. for C47H62CaF3N5O2Si2 (882,27 g/mol): C 63.98; H 7.08; Ca
4.54; N 7.94. Found: C 63.88; H 7.13; Ca 4.50; N 7.99.
Synthesis of [L1YbN(SiMe3)2(THF)] (1Yb). A solution of L1H
(0.165 g, 0.317 mmol) in toluene (10 mL) was added to a solution of
Yb[N(SiMe3)2](THF)2 (0.202 g, 0.317 mmol) in toluene (10 mL) at
room temperature. The color of the reaction mixture changed
immediately from red to brownish-black. Reaction mixture was stirred
for 1 h at room temperature. The volatiles were then removed under
reduced pressure, and the solid residue was dissolved in a toluene/
hexane mixture (1:1). Slow concentration of the solution at −20 °C
resulted in the formation of 1Yb as black crystals. The mother liquid
was decanted, and the crystals were washed with cold hexane and dried
in a vacuum for 30 min. Complex 1Yb was isolated in 60% yield (0.180
g).1H NMR (400 MHz, C6D6) δ = 0.08, 0.36 (s, together 18H,
SiMe3), 1.38 (compl. m, 12H, CH3CH and 4H, β-CH2 THF), 2.10 (s,
6H, CH3), 2.14 (s, 3H, CH3 toluene), 2.55 (s, 6H, CH3), 3.44 (m, 2H,
3
CHiPr), 3.50 (m, 4H, α-CH2 THF), 4.82 (d, JHH = 7.8 Hz, 1H, m-
3
Py), 5.53 (d, JHH = 8.5 Hz,1H, m-Py), 6.66 (m, 1H, p-Py), 6.77 (d,
3
3JHH = 7.2 Hz, 1H, p-CH, NC6H3iPr2), 6.83 (d, JHH Hz, 1H, p-CH,
NC6H3Me2), 7.00−7.16 (m, 5H, toluene+7H, NC6H3Me2 and
NC6H3iPr2). 13CNMR (101 MHz, C6D6) δ= 2.3, 5.9 (SiCH3), 18.0
(CH3), 19.6 (CH3), 21.0 (CH3), 21.05 (β-CH2 THF), 25.4 (CHCH3),
28.0 (CHCH3), 67.5 (α-CH2 THF), 91.9 (m-Py), 101.8(m-Py), 124.6,
125.3, 128.9, 129.3 (C toluene), 128.0 (p-C, NC6H3iPr2), 137.5 (m-C,
C6H3Me2 and NC6H3iPr2), 139.9 (p-Py), 149.2(i-C, C6H3Me2), 151.5
(C, o-Py), 159.2 (o-C, py), 165.3 (NC). IR (Nujol, KBr, ν/cm−1):
1938 (w), 1784 (w), 1653 (w), 1614 (s), 1580 (m), 1459 (s), 1377
(s), 1285 (s), 1253 (m), 1221 (s), 1176 (s), 1159 (s), 1128 (s), 971
(m), 928 (m), 837 (m), 826 (m), 767 (s), 747 (s), 721 (s), 671 (w),
656 (w), 608 (w), 580 (w), 560 (w), 491 (w). Elem. Anal. Calc. for
C45H67N5OSi2Yb•1/2C7H8 (969.32 g/mol): C 60.04; H 7.32; N 7.22;
Yb 17.84. Found: C 60.45; H 7.40; N 7.34; Yb 17.95.
Synthesis of [L3Ca(N(SiMe3)2)(THF)] (3Ca). A solution of L3H
(0.164 g, 0.324 mmol) in toluene (10 mL) was added to a solution of
Ca(N(SiMe3)2)(THF)2 (0.164 g, 0.324 mmol) in toluene. The color
of the reaction mixture changed immediately from pale-yellow to
bright-red. Reaction mixture was stirred for 1 h at room temperature.
The solvent was then removed under reduced pressure, and residue
was dissolved in fresh toluene. Slow concentration of the toluene
solution at room temperature resulted in the formation of red powder.
The mother liquid was decanted and the powder was washed with cold
hexane and dried in a vacuum for 30 min. Complex L3Ca(N-
(SiMe3)2)(THF) was isolated in 90% yield (0.270 g, 0.275 mmol). 1H
NMR (400 MHz, C6D6) 0.09 (s, 18H, SiMe3), 1.83 (s, 3H, CH3), 2.10
(s, 9H, CH3 toluene), 2.19 (s, 3H, CH3), 2.30 (s, 3H, CH3), 2.59 (s,
Synthesis of [L1CaN(SiMe3)2(THF)] (1Ca). A solution of L1H
(0.300 g, 0.579 mmol) in toluene (10 mL) was added to a solution of
Ca[N(SiMe3)2]2(THF)2 (0.292 g, 0.579 mmol) in toluene (10 mL).
The reaction mixture was stirred for 50 h at 50 °C. The volatiles were
then removed under reduced pressure, and the solid residue was
dissolved in mixture of solvents THF/hexane (1:3). Slow concen-
tration of THF/hexane solution at room temperature resulted in the
formation of yellowish-green crystals of 1Ca. The mother liquid was
decanted and the crystals were washed with cold hexane and dried in a
vacuum for 30 min. Complex 1Ca was isolated in 83% yield (0.345 g).
1H NMR (400 MHz, C6D6) δ = 0.09, 0.28 (s,18H, SiMe3), 1.26 (d,
3JHH = 7.0 Hz, 12H, CHCH3), 1.40 (m, 4H, β-CH2 THF), 1.93 (s, 3H,
CH3), 1.99 (s, 6H, CH3), 2.14 (s, 3H, CH3 toluene), 2.29 (s, 6H,
3
3
3H, CH3), 4.83 (d, JHH = 7.5 Hz, 1H m-Py), 5.64 (d, JHH = 8.5 Hz,
3
1H m-Py), 5.75 (d, J = 8.2 Hz, 1H m-Py), 6.53 (dd, JHH = 16.9, 8.4
Hz, 2H Ar), 6.54−7.14 (complex m, 23H Ar). 13C NMR (101 MHz,
C6D6) δ = 1.1, 2.3 (CH3, SiMe3), 17.9 (CH3), 21.1 (CH3 toluene),
25.4 (β-CH2 THF), 67.7 (α-CH2 THF), 94.9 (C, p-Py), 103.6 (C, m-
Py), 114.8, 115.0, 125.1, 125.3, 128.2, 128.4, 128.8, 128.9, 137.5, 138.1,
139.0, 139.5, 140.1(C Ar), 150.7 (i-C, Py), 165.1 (o-C, Py). 19F{1H}
NMR δ = 57.8, 127.2. IR (Nujol, KBr, ν/cm−1): 1956 (w), 1786 (w),
1655 (w), 1613 (s), 1530 (m), 1460 (s), 1377 (s), 1287 (s), 1250 (m),
1221 (s), 1188 (s), 1163 (s), 1144 (s), 1095 (s), 1032 (m), 977 (m),
932 (m), 923 (m), 862 (m), 850 (m), 837 (m), 825 (m), 778 (m),
768 (s), 748 (s), 732 (s), 721 (s), 696 (m), 671 (w), 651 (w), 620
(w), 606 (w), 586 (w), 560 (w), 497 (w), 465(m). Elem. Anal. Calc.
for C56H67CaF4N5Si2 (982,41 g/mol): C 68.46; H 6.87; Ca 4.08; N
7.13;.Found: C 68.50; H 6.90; Ca 4.03; N 7.08.
3
CH3), 3.15 (sept, JHH = 6.9 Hz, 2H, CHCH3), 3.56 (m, 4H, α-CH2
3
THF), 5.56 (d, 3JHH = 7.9 Hz, 1H, m-Py), 6.38 (d, JHH = 7.6 Hz,1H,
m-Py), 6.92 (complex m, 4H, NC6H3), 7.02 (complex m, 5H, toluene
+4H, NC6H3), 7.10 (m, 2H, NC6H3). 13C NMR (101 MHz, C6D6) δ
= 2.3, (CH3, SiMe3), 17.9 (CH3), 18.0 (CH3), 19.0 (CH3), 23.1 (CH3
iPr), 23.4 (CH3 iPr), 25.8 (CH3, iPr), 25.5 (β-CH2 THF), 28.1 (CH,
iPr), 67.5 (α −CH2 THF), 99.5 (m-Py), 104.5 (m-Py), 122.9, 126.4,
127.3, 128.2, 128.4, 136.5,137.2, 137.3, 137.4, 138.8 (C, C6H3Me2 and
NC6H3iPr2), 142.4 (C, p-Py), 145.8 (i-C, C6H3Me2), 155.1 (o-C, py),
156.0 (o-C, py), 156.4 (NC). IR (Nujol, KBr, ν/cm−1): 1940 (w),
1782 (w), 1649 (w), 1614 (s), 1580 (m), 1455 (s), 1377 (s), 1282 (s),
1259 (m), 1221 (s), 1171(s), 1155 (s), 1108 (s), 971 (m), 926 (m),
837 (m), 825 (m), 767 (s), 747 (s), 721 (s), 671 (w), 653 (w), 610
(w), 580 (w), 560 (w), 490 (w). Elem. Anal. Calc. for
C45H67CaN5OSi2·C7H8 (882.43 g/mol): C 70.07; H 8.49; Ca 4.53;
N 7.93. Found: C 69.79; H 8.61; Ca 4.57; N 8.02.
Synthesis of [L4Ca(N(SiMe3)2)(THF)] (4Ca). A solution of
L4(0.115g, 0.236 mmol) in toluene (10 mL) was added to a solution
of Ca(N(SiMe3)2)(THF)2 (0.119 g, 0.236 mmol) in toluene. The
color of the reaction mixture changed immediately from pale-yellow to
bright-red. Reaction mixture was stirred for 1 h at room temperature.
The solvent was then removed under reduced pressure, and residue
was dissolved in fresh hexane. Slow concentration of the hexane
solution at room temperature resulted in the formation of red powder.
The mother liquid was decanted and the powder was washed with cold
hexane and dried in a vacuum for 30 min. Complex L4Ca(N-
(SiMe3)2)(THF) was isolated in 84% yield (0.168g, 0.198 mmol).1H
NMR (400 MHz, C6D6) 0.09 (s, 18H, SiMe3), 2.03 (m, 4H, β-CH2
THF), 1.95 (s, 3H, CH3), 2.10 (s, 3H, CH3 toluene), 2.31 (s, 6H,
Synthesis of [L2Ca(N(SiMe3)2)(THF)] (2Ca). A solution of L2H
(0.182 g, 0.360 mmol) in toluene (10 mL) was added to a solution of
Ca[N(SiMe3)2]2(THF)2 (0.185 g, 0.360 mmol) in toluene (10 mL).
The color of the reaction mixture changed immediately from pale-
yellow to bright-red. Reaction mixture was stirred for 1 h at room
temperature. The volatiles were then removed under reduced pressure,
and the solid residue was redissolved in fresh toluene. Slow
CH3), 2.40 (s, 3H, CH3), 3.82 (m, 4H, α-CH2 THF), 4.76 (d, 3JHH
7.5 Hz, 1H, m-Py), 5.50 (d, 3JHH = 8.5 Hz, 1H, m-Py), 5.69 (d, 3JHH
=
=
H
DOI: 10.1021/acs.inorgchem.8b00088
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
8.2 Hz, 1H, m-Py), 6.56−7.15 (complex m, 16H,Ar).13C NMR (101
MHz, C6D6) δ = 2.3 (CH3, SiMe3), 18.8 (CH3), 21.1 (CH3 toluene),
25.2 (β-CH2 THF), 68.2 (α-CH2 THF), 96.6 (p-Py), 103.2 (m-Py),
119.3, 120.3, 120.4, 121.0, 126.4, 128.7, 129.6, 132.0, 134.2, 137.8,
138.3, 141.1, 141.2, 146.1(CAr), 151.2 (i-C, Py), 164.75 (o-C, Py).
19F{1H} NMRδ = 56.8. IR (Nujol, KBr, ν/cm−1): 1934(w) 1788(w)
1650 (s), 1606 (s), 1591 (s), 1573 (s), 1506 (s), 1451 (s), 1377 (s),
1343 (s), 1291 (s), 1262 (s), 1232 (s), 1217 (s), 1186 (s), 1148 (s),
1120 (s), 1097 (s), 1084 (s), 1027 (s), 977 (s), 948(m), 928 (s), 910
(s), 880(m), 823(m), 788 (s), 768 (s), 760 (s), 735 (s), 719 (s), 692
(s), 669(w), 625(w), 581(w), 564(w), 532(w), 508(w). Elem. Anal.
Calc. for C46H60CaF3N5OSi2 (852.25,41 g/mol): C 64.83; H 7.10; Ca
4.70; N 8.22. Found: C 64.50; H 6.95; Ca 4.63; N 8.08.
Disproportionation Reaction of Complex 1Ca. A solution of
1Ca (0.100 g, 0.115 mmol) in 10 mL of hexane was stirred at room
temperature for 1 week. Freezing of the resulting solution to −15 °C
led to the formation of two types of crystals: [{L1}2Ca] as bright-
yellow crystals and Ca(N(SiMe3)2)(THF)2 as white crystals. The
mother liquid was decanted and the crystals were obtained by drop
crystallization from hexane at room temperature then washed with
c.uk/structures. The crystallographic data and structure refinement
details for 1Yb, 1Ca, and 2Ca are given in Table S1 (See Supporting
Information).
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.8b00088.
Representative 1H, 13C, and 19F NMR spectra of
ytterbium and calcium complexes (PDF)
Accession Codes
CCDC 1584252−1584254 contain the supplementary crystal-
lographic data for this paper. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/data_request/cif, or by email-
ing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
cold hexane (3 × 2 mL) and dried in a vacuum for 30 min. Complex
1
[{L1 Ca] was isolated in 31% yield (0.039 g, 0.036 mmol). HNMR
2
(400 MHz, C6D6) δ = 1.09 (d, 3JHH = 7.0 Hz,12H, CH3,iPr), 1.27 (d,
3JHH = 7.0 Hz,12H, CH3,iPr), 1.95(s, 6H, CH3), 2.00 (s, 12H, CH3),
AUTHOR INFORMATION
Corresponding Author
*Phone: 007 831 4623532. Fax: 007 831 4627497. E-mail:
trif@iomc.ras.ru.
■
3
2.25 (s, 12H, CH3), 3.16 (sept, JHH3 = 6.9 Hz,4H, CH,iPr), 5.07 (d,
3JHH = 7.6 Hz, 2H, m-Py), 5.61 (d, JHH = 7.9 Hz, 2H, m-Py), 6.94−
7.11 (complex m, 20H, Ar). 13CNMR (101 MHz, C6D6) δ = 13.9 (s,
CH3),17.9 (s, CH3, C6H3(CH3)), 19.6 (s, CH3), 23.2 (s,CH3, iPr),
31.6 (s, 4C, CH, iPr), 155.4; 156.0; 155.1 (s, i-C, C6H3(iPr)), 122.9,
125.3, 126.4, 127.5, 128.0, 136.0, 137.3, 138.8, 142.4, 151.6(s, Ar). IR
(Nujol, KBr, ν/cm−1): 1938 (w), 1784 (w), 1654 (w), 1614 (s), 1580
(m), 1459 (s), 1377 (s), 1285 (s), 1253 (m), 1221 (s), 1176 (s), 1159
(s), 1128 (s). Elem. Anal. Calc. for C72H87CaN8O0.5 (1112.57 g/mol):
C 77.65; H 7.82; Ca 3.60; N 10.07. Found: C 77.79; H 7.71; Ca 3.67;
N 10.02. Complex Ca(N(SiMe3)2)(THF)2 was isolated in 33% yield
ORCID
Elvira I. Musina: 0000-0003-3187-8652
Alexander A. Trifonov: 0000-0002-9072-4517
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
1
The authors thank Russian Science Foundation (Grant No. 17-
73-20262) for financial support and Synor Ltd for donation of
diphenylphosphine, dicyclohexylphosphine, and phenylphos-
phine.
(0,019g, 0,038 mmol). H NMR (400 MHz, C6D6) 0.40 (s, 36H,
SiMe3), 1.26 (m, 8H, β-CH2 THF), 3.51(m, 8H, α-CH2 THF). 13C
NMR (101 MHz, C6D6) δ = 4.1 (CH3, SiMe3), 25.8 (β-CH2 THF),
67.5 (α-CH2 THF). Elem. Anal. Calc. for C20H52CaN2O2Si4 (505.07g/
mol): C 47.56; H 10.38; Ca 7.94; N 5.55. Found: C 47.77; H 10.41;
Ca 8.00; N 5.52.
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DOI: 10.1021/acs.inorgchem.8b00088
Inorg. Chem. XXXX, XXX, XXX−XXX