Cyclopentadienylphosphazene (CpPN) complexes of rare-earth metals: Synthesis, structural characterization, and hydroamination catalysis

Article abstract of DOI:10.1021/om200264n

Synthesis of the first series of rare-earth-metal constrained geometry complexes containing the P-(1-adamantylamino)-P-dimethyl-tetramethyl- cyclopentadienylidene-phosphorane ligand C₅Me₄PMe ₂NHAd, {Cp^#PN}H, was

Full text of DOI:10.1021/om200264n

ARTICLE
pubs.acs.org/Organometallics
Cyclopentadienylphosphazene (CpPN) Complexes of Rare-Earth
Metals: Synthesis, Structural Characterization, and
Hydroamination Catalysis
‡
‡
‡,§
‡
‡
Noa K. Hangaly, Alex R. Petrov, Konstantin A. Rufanov, Klaus Harms, Michael Elfferding, and
,‡
J €o rg Sundermeyer*
‡
Fachbereich Chemie der Philipps-Universit €a t Marburg, Hans-Meerwein-Strasse, 35032 Marburg, Germany
§
Department of Chemistry, M.V. Lomonosov State University of Moscow, 119992, Moscow, Russia
S Supporting Information
b
ABSTRACT:
Synthesis of the first series of rare-earth-metal constrained geometry complexes containing the P-(1-adamantylamino)-P-dimethyl-
#
tetramethyl-cyclopentadienylidene-phosphorane ligand C Me PMe NHAd, {Cp PN}H, was accomplished. This monoanionic
5
4
2
chelate ligand is isoelectronically related to the classical dianionic cyclopentadienyl-silylamine ligand C Me HSiMe NHtBu,
5
4
2
#
#
2 2 3 2
{
Cp SiN}H . The ligand stabilizes dialkyls [{Cp PN}M(CH SiMe ) ] (M = Sc, 1; Lu, 2; Y, 3; Sm, 4; Nd, 5; Pr, 6; Ce, 7) over the
full range of group 3 and lanthanide cation radii. Results of NMR studies of these crystalline alkyls, XRD molecular structures, and a
preliminary study revealing the high catalytic activity of complexes 3ꢀ6 in the intramolecular hydroamination/cyclization are
reported. The catalytic experiments reveal a trend in activity Lu < Y < Sm < Nd e Pr resembling the trend in rare-earth-metal radii.
Interestingly they reveal a distinctive substrate-dependent first-order kinetic profile for all metals investigated. The reaction of the
precatalyst 3 with 1.6 equiv of the standard substrate 2,2-dimethylpenten-4-ylamine leads to a fast and selective formation of
#
substrate complex [{Cp PN}Y(NHCH CMe CH CHdCH ) ] (8). Fast cyclization was observed only after addition of more
2
2
2
2 2
than 2 equiv of amine substrate. A noninsertive mechanism involving a six-membered transition state by a concerted CꢀN bond
formation and NꢀH bond cleavage at a 3:1 substrate to complex ratio is suggested on the basis of these findings.
7
’
INTRODUCTION
copolymerization catalysts. By changing the bridging atom in
+
CpSiN from Si to P , monoanionic cyclopentadienyl-phospha-
For a long time, organometallic chemistry and catalysis of rare-
1
2
zene ligands (CpPN) are generated, which are isoelectronically
related to classical dianionic CpSiN ligands. Previously, we
reported a convenient and general synthetic protocol for the
synthesis of a large variety of CpPN-type ligands with different
substitution pattern at N and P atoms and at the Cp ring, their
spectroscopic properties and molecular structures, and investiga-
tions on the tautomeric equilibria of their protonated forms.
Their use in the stabilization of highly reactive alkyls of rare-earth
and group 4 metals has been claimed, and a representative
CpPN lutetium alkyl complex has been presented. Indepen-
earth metals has largely been dominated by metallocenes. More
recently, considerable attention has been directed toward rare-
earth-metal mono-cyclopentadienyl complexes providing an elec-
tronically more unsaturated and a sterically less crowded reactive
site, thus showing unique reactivities that differ significantly from
3
those of the metallocenes. The research led, inter alia, to an
8
extensive study of a wide range of Cp substitution patterns. One
of the great achievements in half-sandwich complex design is the
constrained geometry complexes (CGCs), which contain a short
side arm bearing an additional chelating donor functionality
9
1
0
4
dently, related fluorenyl- and indenyl-phosphazene ligands
(FluPN and IndPN) and their rhodium and zirconium
at the Cp ligand. CGCs with the cyclopentadienyl-silylamido
11
12
5
(CpSiN)-type ligands, initially developed by Bercaw and
6
Okuda, became one of best developed classes of these
half-sandwich complexes. In particular, their titanium com-
plexes are highly active single-site olefin polymerization and
Received: March 25, 2011
Published: August 11, 2011
r 2011 American Chemical Society
4544
dx.doi.org/10.1021/om200264n
|Organometallics 2011, 30, 4544–4554

Organometallics
ARTICLE
#
Scheme 1. Isolobal Relationship between CpSiN- and
CpPN-Type Complex Families
Scheme 3. Synthesis of Cp PN Complexes 1ꢀ7
These complexes also exhibit a zwitterionic ligand structure like
the CpPN complexes of type III. For this reason we were
interested in investigating the catalytic performance of the
#
Cp PN complexes of type III.
Here we describe the synthesis, NMR spectroscopic studies,
and molecular structures of the first series of CpPN-type con-
strained geometry complexes with P-(1-adamantylamino)-P-
dimethyl-tetramethyl-cyclopentadienylidene-phosphorane,
Scheme 2. CGCs of Rare-Earth Metals
#
C Me dPMe NHAd ({Cp PN}H), using a representative pool
5
4
2
of rare-earth metals (Sc, Lu, Y, Sm, Nd, Pr, and Ce). In addition,
preliminary results of their application in olefin hydroamination
catalysis are presented. It was shown that these reactive organo-
lanthanide complexes efficiently mediate intramolecular hydro-
amination/cyclization reactions under mild conditions.
’
RESULTS AND DISCUSSION
complexes were presented by Bourissou and co-workers. Theo-
retical investigations of CpPN-type complexes of group 4
elements suggest them to be interesting alternatives for CpSiN-
Synthesis of Rare-Earth-Metal Dialkyl CpPN Complexes. In
our first report we applied a protocol for direct metalation of
#
{Cp PN}H with [Lu(CH SiMe ) (thf) ] that allowed us to
2
3 3
2
1
3
#
derived catalysts.
obtain the desired CpPN complex [{Cp PN}Lu(CH SiMe ) ]
2 3 2
10
CpSiN complexes of tetravalent group 4 elements are isoelec-
tronic to CpPN complexes of trivalent group 3 elements and
isolobal to trivalent lanthanide complexes (Scheme 1).
in nearly quantitative yield. However, only a few rare-earth-
21
metal tris-alkyl precursors are of sufficient thermal stability.
Therefore, we have used an alternative synthetic protocol that
comprises addition of 3 equiv of LiCH SiMe to a stirred
Having this concept in mind and considering the advantage of
rare-earth metals offering a unique and gradual variation of their
properties relating to their decreasing radii, we initiated a
research program aimed at evaluating organometallic chemistry
2
3
#
suspension of an equimolar mixture of {Cp PN}H ligand and
rare-earth-metal halide source [ScCl (thf) ] or [MCl (dme) ]
3
3
3
n
(M = Lu, Y, Sm (n = 2); M = Nd, Pr, Ce (n = 1)) in ether/hexane
or ether/toluene mixtures at 0 °C (Scheme 3). One equivalent of
the lithium alkyl is acting as a base, and the other two are acting as
nucleophiles. Applying this method and this sterically demanding
ligand, only complexes with a ligand:metal = 1:1 ratio were
isolated, whereas in other cases metallocenes with a 2:1 ratio
1
0,14
of rare-earth-metal CpPN complexes.
The simple catalytic addition of a NꢀH bond to an unsatu-
rated CꢀC bond, the hydroamination reaction, represents a
prominent, highly atom-efficient, and elegant reaction for the
synthesis of higher substituted nitrogen-containing products.
Particularly, intramolecular hydroamination/cyclizations repre-
sent an efficient route for accessing multifunctional nitrogen-
containing heterocycles for construction of a range of biologically
1
4
were obtained.
An appropriate workup (filtration, solvent removal, extraction
with hexane followed by crystallization) gave air-sensitive
15
#
active molecules and naturally occurring alkaloids. Since the
[{Cp PN}M(CH SiMe ) ], M = Sc (1), Lu (2), Y (3), Sm
2
3 2
seminal discovery of organolanthanide metallocene-catalyzed hy-
(4), Nd (5), Pr (6), and Ce (7) complexes. These rare-earth-
metal dialkyls were isolated as microcrystalline solids of analytical
purity in 50ꢀ90% yields. The complexes 1ꢀ7 show moderate
solubility in saturated hydrocarbons and are highly soluble in
etheric and aromatic solvents. Not surprisingly, the thermo-
stability of the complexes depends on the metal center ionic
radius. Colorless alkyl complexes of metals with smaller radii,
1ꢀ3 (Sc, Lu, Y), possess high thermostability. They can be
stored under inert atmosphere at ambient temperature for
months without noticeable decomposition. Fast decomposition
takes place at temperatures above 150 °C. Complexes containing
larger metal ions 4ꢀ6 (Sm, Nd, and Pr) are thermally stable at
ꢀ30 °C for months, but in solution they decompose gradually at
25 °C and completely within 6 h at 50 °C. The cerium complex
16
droamination by Marks and co-workers, rare-earth metals have
17f,18
16,17
proven to be very active for intra-
and intermolecular
hydroamination of alkenes. Catalytic activity is enhanced by both
3+
increasing the Ln radii of the precatalysts and improved coordina-
16c,17j,17k
tion sphere accessibility.
Lanthanide CpSiN constrained
geometry complexes of type I (Scheme 2) have been shown to
exhibit markedly increased activity in catalytic intramolecular hydro-
amination/cyclization processes by creating a more open coordina-
tion sphere with better access to the metal center relative to
19,15e
lanthanocenes and ansa-lanthanocenes.
Moreover, rare-earth-
metal complexes with Me Si-bridged cyclopentadienyl-imidazolin-2-
2
imine ligands (type II) studied by Tamm and co-workers showed
20
catalytic activities in the intramolecular hydroamination/cyclization.
4
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Organometallics
ARTICLE
1
Figure 1. H NMR spectrum (500.1 MHz) of samarium complex 4 in C
6
D
6
at 27 °C. Signals denoted with (*), (+), and (#) are assigned to TMS, silicon
grease, and the residual protons of C
6 6
D .
5
3+
7
shows the lowest thermal stability and decomposes readily at
complex 6 (δH 3= 13 to ꢀ7 ppm for f Sm (4), δ = 30
H
3+
1
3+
ambient temperature, which did not allow obtaining the correct
elemental analysis.
Multinuclear NMR Spectroscopy of Cp PN Complexes
to ꢀ22 ppm for f Nd (5), and 44 to ꢀ23 ppm for f Ce (7)).
In general, the relative arrangement of the signals in these spectra
is very similar, and therefore the spectrum of complex 4 is
#
22
1
ꢀ7. All complexes were characterized by multinuclear NMR
discussed as a representative example (Figure 1).
1
13
1
spectroscopy. According to the H and C{ H} NMR spectros-
copy, 1ꢀ7 were isolated without coordinated ether molecules,
which are present in the starting material. Compared with the
Generally, the resonances in the spectrum of 4 are narrow
except the two broad resonances for the diastereotopic methy-
lene protons of the Me SiCH group, which are significantly
downfield shifted to values of 10.61 and 12.53 ppm. All reso-
nances of the adamantyl protons are shifted upfield. The
diastereotopic geminal exo- and endo-δ-methylene protons of
3
2
#
10
31
1
free ligand {Cp PN}H (δ = 17.6 ppm), the P{ H} NMR
P
signals of diamagnetic 1ꢀ3 are only slightly shifted upfield and
31
1
appear in the region between δ = 9.0 and 9.6 ppm. The P{ H}
P
NMR resonances of the paramagnetic complexes 4ꢀ7 are broad,
the Ad group appear at δ = ꢀ0.29 and ꢀ0.87 ppm, respectively,
H
2
nevertheless clearly assigned as signals at δ = 25.3 (4), ꢀ3.9 (7),
as two doublets ( J = 11.6 Hz). The signal of the γ-methine
P
HH
ꢀ
59.0 (6), and ꢀ89.3 (5), respectively.
protons also appears in that region (ꢀ0.46 ppm), presumably
due to the comparable distance to the paramagnetic metal center.
The β-methylene protons of the adamantyl group situated close
to the samarium atom reveal significantly upfield shifted reso-
nances (ꢀ6.70 ppm). One set of chemically equivalent methyl
protons of the C Me moiety appears as downfield- and the other
1
H NMR spectra of the diamagnetic complexes 1ꢀ3 are very
similar, and therefore only the spectrum of representative yttrium
complex 3 is further discussed. Its H NMR spectrum at room
1
temperature is rather simple (see Supporting Information),
showing two resonances at δ = 2.03 and 2.11 ppm assigned
H
5
4
to the equivalent pairs of methyl protons of the C Me moiety, a
typical set of adamantyl signals at δH = 1.56, 1.71, and 2.00
as upfield-shifted resonances (5.06 and ꢀ4.07 ppm). Such signal
5
4
distribution was previously observed in the closely related
2
3
ppm with an integral ratio of 6:6:3, and the doublet of the Me P
homoleptic complex [Sm{C Me H} ] (0.82 and ꢀ5.70 ppm).
2
5
4
3
2
1
protons at δ = 1.16 ppm ( J = 12.5 Hz). The silylmethylene
H NMR spectra of corresponding neodymium, praseodymium,
H
HP
protons are magnetically nonequivalent and appear as two
and cerium complexes also show up- and downfield-shifted
resonances for the C Me moiety at δ = 11.44 and ꢀ13.52
2
doublets of doublets at δ = ꢀ0.70 and ꢀ0.75 ppm ( J
=
H
HH
5
4
H
2
1
24
1
1.1 Hz, J = 3.0 Hz) at +25 °C. Analogously in the H NMR
ppm for 5 (cf. [Nd{C Me H} ]: δ = 16.64 and ꢀ16.68 ppm),
HY
5
4
3
H
spectra of complex 1 and complex 2 two signals for diastereo-
topic methylene protons of CH SiMe groups at δ = ꢀ0.38,
δ = 25.94 and ꢀ30.25 ppm for 6, and δ = 11.89 and ꢀ14.77 ppm
H
H
for 7, respectively.
2
3
H
13
ꢀ
0.34 and δ = ꢀ0.95, ꢀ0.89 ppm, respectively, were observed.
To date, C NMR resonance assignment and a detailed
analysis for paramagnetic lanthanide organometallics are dis-
cussed rarely in the literature. The analysis was performed on
complexes 4 and 5. The assignment of resonances of the high-
H
The assignment of the NMR signals for the paramagnetic
complexes 4ꢀ7 requires analysis of two-dimensional NMR
spectra due to the paramagnetic shift. The signals observed in
1
13
1
the H NMR spectra recorded in C D at 25 °C are spread over a
resolution C{ H} NMR spectra was accomplished by 2D
6
6
2
3+
22
wide range up to Δppm of 139 (δ = 92 to ꢀ47 ppm) for f Pr
HMBC and HSQC experiments. Unambiguous assignment
H
4
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Organometallics
ARTICLE
of C Me methyl groups was achieved by HMBC spectroscopy
donorꢀacceptor complexes such as [{Me TACN}M(CH SiMe ) ]
5
4
3
2
3 3
(
Figure 2), resulting in the resonance at 5.06 ppm being assigned
reveal much longer average MꢀN bonds: ScꢀN 2.47 Å and
30
to β-C Me and those at ꢀ4.07 ppm to γ-C Me methyl protons.
YꢀN 2.60 Å. The relatively strong donor capacity of the
chelating phosphazene nitrogen atom, expressed by the short
MꢀN distance, corresponds with only little stabilization of the
anionic charge at nitrogen by the phosphonium center. This is
also shown by a rather long PꢀN distance of 160.0 ( 1.0 Å.
5
4
5
4
#
Molecular Structures of Cp PN Complexes. Single crystals
of 1, 3, and 4 were obtained by cooling saturated hexane
solutions to ꢀ30 °C. Their molecular structures are closely
10
related to that of the earlier reported lutetium complex 2. They
crystallize in the monoclinic space groups P2 /c (1) and P2 /n
The MꢀCpcentr and the average MꢀCH
bond lengths are
2
comparable to those reported for other complexes containing
1
1
(
3, 4) with four molecules in the unit cell (Figure 3). Selected
5 26 31
bond lengths (Å) and angles (deg) for 1ꢀ4 are presented in
η -C
Y; Sm ).
5
Me
4
and CH SiMe ligands (cf. complexes of Sc;
2 3
3
2
33
Table 1. In the case of complex 1 the CH SiMe groups are
2
3
disordered and treated with an occupancy factor of 87:13.
In the solid state 1, 3, and 4 adopt mononuclear structures, in
which metal atoms are approximately in tetrahedral coordina-
Furthermore, the CpcentrꢀMꢀN angles (97.6° for 1; 91.5° for
3; 89.4° for 4) are clearly smaller than the CpcentrꢀMꢀN angles
in closely related CpSiN alkyl complexes (M = Sc: 104.4°;
26
tion. The PꢀC bond lengths (1.753ꢀ1.774 Å) are longer than
Y: 96.4°; Sm: 94.3°).
C1
in the free ligand (1.724(2) Å), while the PꢀN bonds are
10
Catalytic Hydroamination/Cyclization Reactions. In order
to better compare the catalytic activity of complexes 2ꢀ6 with
those reported in literature, we studied the transformation of
standard ω-aminoalkene substrates 2,2-dimethyl- and 2,2-diphe-
nylpenten-4-ylamine (S1 and S2, respectively) under similar
conditions to those reported for reference compounds of CGC
of type I and II (Scheme 2). The reactions were carried out in
C D at 27 or 60 °C with ca. 5 mol % catalyst loading and were
essentially shorter (1.594ꢀ1.623 Å) than in the free amino-
10
phosphonium ylide ligand (1.659(2) Å).
The MꢀN bond distances (ScꢀN 2.185(2) Å; YꢀN 2.316(4)
Å; SmꢀN 2.366(3) Å) are short and approach the distance typically
found for amido complexes. They are only slightly longer than the
covalent MꢀN bonds in CGCs of the type [{CpSiN}M(R)(L)]
5b
25
26
(
M = Sc: 2.083 Å; Y: 2.208(6) Å; Sm: 2.343(4) Å) and
6
6
1
of homoleptic amido complexes [M{N(SiMe ) } ] (for M = Sc: av
monitored by in situ H NMR spectroscopy. The results are
3
2 3
29
27
28
2
.05 Å; Y: av 2.22 Å; Sm: av 2.28 Å). Typically, simple
summarized in Table 2.
Table 1. Selected Bond Lengths and Angles for Complexes
1
ꢀ4
1
0
1
(Sc)
2 (Lu)
3 (Y)
4 (Sm)
Bond Lengths (Å)
MꢀN
2.185(2)
2.431(2)
2.235
2.278(3)
2.316(4)
2.599(3)
2.392
2.367(3)
2.642(3)
2.450
MꢀC1
MꢀCpcentr
MꢀC12
MꢀC16
PꢀN
2.545(4)
2.285
2.243(3)
2.234(3)
1.606(2)
1.769(3)
2.360(4)
2.358(4)
1.600(3)
1.774(4)
2.416(5)
2.434(5)
1.605(4)
1.753(6)
2.472(3)
2.469(4)
1.593(3)
1.774(3)
PꢀC1
Bond Angles (deg)
C1ꢀMꢀN
68.0(1)
97.6
65.2(1)
95.8
63.3(1)
91.5
62.4(1)
89.4
CpcentrꢀMꢀN
C12ꢀMꢀN
C16ꢀMꢀN
C12ꢀMꢀC16
108.4(1)
114.6(1)
107.5(1)
109.9(2)
115.9(2)
109.9(2)
106.6(2)
118.5(1)
111.5(2)
119.9(1)
107.5(1)
113.1(1)
Figure 2. Section of the HMBC spectrum of complex 4 in C D at 27 °C.
6
6
1
13
1
The H NMR spectrum (500.1 MHz) is shown at the top and the C{ H}
NMR spectrum (125.8 MHz) is shown on the left edge in the contour plot.
#
Figure 3. ORTEP diagram of scandium (1), yttrium (3), and samarium (4) Cp PN complexes with 30% thermal ellipsoids. All hydrogen atoms have
been omitted for clarity. In structure 1, disordered Me SiCH groups with lower occupancies have also been omitted.
3
2
4
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ARTICLE
Table 2. Catalytic Intramolecular Hydroamination/Cycliza-
tion by Complexes 2 (Lu), 3 (Y), 4 (Sm), 5 (Nd), and 6 (Pr)
a
entry precatalyst (mol %) substrate T (°C) t (h) conversion (%)
1
2
3
4
5
6
7
8
2 (5.8)
2 (6.0)
3 (5.0)
3 (5.2)
3 (5.0)
4 (5.0)
5 (5.3)
6 (5.3)
S1
S1
S1
S2
S1
S1
S1
S1
27
60
27
27
60
27
27
27
15.75
14.19
4.58
0.25
1.37
0.98
0.47
36
>92
>93
>92
>92
>93
>93
>93
0.40
1
a
Conversion to pyrrolidine (yield) assigned by H NMR spectroscopy
with respect to ferrocene. Note that in entries 2ꢀ8 substrates were
quantitatively converted by the precatalyst, but under these conditions
ca. 10 mol % substrate is consumed to form the active catalyst species
(
vide infra).
Complexes 3ꢀ6 are active catalysts and show almost full
3+
conversion at 27 °C. Increasing the Ln ionic radius leads to
significant reaction rate enhancement (Figure 4, A). Complexes
of smaller ionic radii rare-earth metals 1 (Sc) and 2 (Lu) have a
low catalytic activity in hydroamination/cyclization reactions of
substrate S1 at room temperature. Complex 2 achieves a conversion
of only 36% after about 16 h, but at elevated temperature the
reaction rate dramatically increases and shows conversion of 92%
after about 14 h at 60 °C (Table 2, entries 1 and 2; Figure 4, B).
Yttrium complex 3 shows a conversion of 93% for substrate S1
after 4.6 h and an almost quantitative hydroamination after only
0
.25 h for substrate S2 (Table 2, entries 3 and 4), where the
Figure 4. (A) Conversion to pyrrolidine (yield) as a function of time
for hydroamination/cyclization of S1 using complexes of yttrium
(3, squares), samarium (4, circles), and praseodymium (6, triangles).
The plot of neodymium complex 5 is too close to the one of 6 and not
shown for clarity. (B) Conversion versus time plots for the hydroamina-
tion/cyclization of S1 at 60 °C using precatalyst 2 (triangles) and
precatalyst 3 at 27 °C (squares) and 60 °C (circles).
34
ThorpeꢀIngold effect is more pronounced. Elevated reaction
temperatures also increase the reaction rate, and complex 3
shows almost quantitative conversion after 1.4 h for S1 at 60 °C
(Table 2, entry 5; Figure 4, B). The complexes with larger metal
cations 4ꢀ6 display much higher activities. They show a near-
quantitative conversion after only 60, 28, and 24 min (Table 2,
entries 6ꢀ8; Figure 4, A), respectively, following the trend,
the lager the ionic radii, the higher the rate of conversion, as
often observed in rare-earth-metal-catalyzed hydroamination/
dramatic and constant deviation from zero-order rate law, which
is typically observed for lanthanocenes and CGCs of type I and is
commonly explained by the olefin insertion into the MꢀN bond
16c,17j,17k
cyclization reactions.
17cꢀm,19
This preliminary study reveals that CGCs of the larger rare-earth
metals (samarium, neodymium, and praseodymium) can be used as
efficient hydroamination/cyclization precatalysts. A direct compar-
ison of CpPN-type III CGCs with other CGC types is difficult due
to their different kinetic profile in olefin hydroamination. The
conversion values with the CpPN precatalysts are dependent on
substrate concentration and not independent such as with catalysts
of the CpSiN-type with zero-order kinetic profiles. Their initial
activity compares well to the activities found for CGC alkyls and
amides of type I and II (Scheme 2). Due to the first-order
kinetics, the productivity decreases significantly at higher conver-
sions; as a consequence, long reaction times are necessary for
completion of the reaction. Additional testing on nonactivated
substrates and variation of catalyst loading (<5 mol %) are required.
Mechanistic Consideration of First-Order Mechanism. The
most intriguing feature of the CpPN catalysts of type III is a
being the rate-determining step.
In contrast, all precata-
lysts 3ꢀ6 show a distinctive first-order dependence on substrate
concentration over almost the entire conversion range, more
precisely up to at least 85% conversion. A representative first-
order kinetic plot (ꢀln([S]/C ) vs t) for complex 3 is shown in
0,S
Figure 5. The other precatalysts follow the same kinetic reaction
pattern and are given in the Supporting Information. In all cases
2
the data could be convincingly fit (R > 0.998) by the least-
squares method.
19
20
The “pure” first-order kinetics over the full range of conversion
has rarely been observed in rare-earth-metal complex catalysis.
Deviations from zero-order kinetics are often observed at higher
substrate conversions (>50%) when sterically more accessible
1
7
17h,i,19
ansa-lanthanocenes and CGCꢀLn systems
were em-
ployed. This deviation has been attributed to the coordination
of the Lewis basic product, leading to competitive product
4
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Organometallics
ARTICLE
#
Scheme 4. Synthesis of Cp PN Diamidoalkene Complex 8
1
0
formation of protonated ligand (δ = 17.6 ppm) was observed
P
31
1
by P{ H} NMR spectroscopy over the full reaction time.
31
1
1
Moreover, in situ P{ H} and H NMR spectroscopic studies
indicate that complex 8 is also present during the reaction among
the other species. Furthermore, at a catalyst load of 5 mol %, we
observed that the productivity decreases significantly at high
conversions of about 90%. This might be because about 10 mol %
of the amine is consumed to form the diamido catalyst species
1
without any product formation. In situ H NMR experiments
reveal that both the substrate and the product are in rapid
equilibrium with the catalytically active species, as both substrate
and product amines resonances are paramagnetically broadened
Figure 5. Kinetic plot ꢀln([S]/C0,S) as a function of time for S1 using
precatalyst 3 in C D (27 °C). The line represents the least-squares fit to
6
6
the data points.
3+
5
3+
3
during turnover for Sm (4f ) and in particular for Nd (4f )
3+
2
inhibition. First-order kinetics have been observed by Hessen
and his group using nitrogen ligand based cationic and neutral
and Pr (4f ) catalysts. A fast substrate and product exchange on
the NMR time scale at room temperature is in accord with the
35,36
16c,17i,17m
non-metallocene rare-earth-metal complexes as precatalysts.
literature on other HA catalysts.
Interestingly, hydroamination/cyclization study of CGC of type
There are a few possible mechanistic variations discussed for
organolanthanide-mediated hydroamination/cyclization. The
common mechanism involves a rate-determining intramolecular
II also shows a significant deviation from ideal zero-order
2
0
kinetics.
17cꢀm,19
Hultzsch and co-workers reported a first-order rate depen-
insertion of the olefin into the metalꢀnitrogen bond.
An
dence on substrate concentration for biphenolate and binaphtho-
alternative mechanistic variation is a noninsertive mechanism
that involves coordination of an additional substrate molecule for
cyclization. A noninsertive mechanism was originally suggested
by Marks and co-workers to account for the observed strong
37
late rare-earth-metal amide complexes. However, a later study
clearly showed zero-order kinetics for analogous alkyl complexes.
As a consequence, the first-order dependence was related to a
hampered catalyst activation step due to the amide ligand present
primary kinetic isotope effects (KIE) in Cp Ln-catalyzed hydro-
2
3
8
16c
in the precatalyst. We can exclude this explanation in our case:
amination of aminoalkenes.
For organoactinide-catalyzed
1
According to in situ H NMR spectroscopy, the initial reaction
hydroamination Marks and co-workers again suggested that pro-
39
step is a rapid and quantitative aminolysis of both alkyl groups by the
primary amine substrates. This was shown by an immediate
tonolysis may be concurrent with cyclization. Recently, Sadow
and co-workers suggested a concerted CꢀN and CꢀH bond
formation in a magnesium-catalyzed hydroamination reaction.
They supported it with kinetic studies and isolated magnesium
amidoalkenes, which did not react without a slight excess of
formation of 2 equiv of free SiMe . In order to observe this reaction
4
in more detail, we studied the stoichiometric model reaction. The
reaction of the yttrium precatalyst 3 with only 1.6 equiv of the amine
substrate S1 leads at room temperature to a fast and selective
40
substrate. Moreover, Hill and his group suggested a mechanism
involving a concerted proton transfer step associated with rate-
determining alkene insertion in alkaline earth-metal-catalyzed
#
formation of [{Cp PN}Y(NHCH CMe CH CHdCH ) ] (8)
2
2
2
2 2
3
1
1
characterized by NMR spectroscopy. The P{ H} NMR spectrum
shows a new signal at δ = 6.7 ppm; the double bonds in the H
1
41
42
43
ω-aminoalkene hydroamination. Sadow and Scott discussed
such a mechanism for ω-aminoalkene hydroamination by zirco-
nium compounds. Furthermore, comprehensive computational
insights on the most closely related system—organolanthanide-
mediated hydroamination of conjugated ω-aminodienes and
P
NMR spectrum are represented by signals at δ = 5.10ꢀ5.19 and
H
6
.01ꢀ6.12 ppm. No cyclization at room temperature was observed;
however addition of a third equivalent of amine substrate (or any
excess > 2 equiv) to 8 leads to the formation of free pyrrolidine
product next to the active catalyst 8. No secondary amido complex
of the product or alkyl complex of an insertive pathway was
observed.
44
allenes—were provided by Tobisch, recently.
Based on the experimental kinetic observations and the
stoichiometric model reaction, we favor a noninsertive mechan-
ism for CpPN rare-earth-metal dialkyl- or diamido-mediated
hydroamination catalysis (Scheme 5). Coordination of a third
amine substrate at high amine concentration is competitive or
0
Previously, [Cp La(NHR)(NH R)] (R = CH CMe CH -
2
2
2
2
2
CHdCH ) was characterized at low temperatures (ꢀ60 °C) by
2
means of NMR spectroscopy. At ca. ꢀ20 °C cyclization occurs
0
00
00
00
0
and [Cp La(NR )(HNR )] (R = ꢀCH C(CH ) CH ꢀ
even inhibitive with respect to olefin coordination to a hard d
2
2
3 2
2
1
6c
C(CH )Hꢀ) was isolated and characterized.
metal center. In an insertive mechanism, coordination of a third
3
#
Our privileged spectator ligand system allows us to monitor
amine substrate to the catalyst [{Cp PN}M(NHR) ] B generat-
2
31
1
1
#
the catalyst conversion via P{ H} and H NMR spectroscopy.
ing [{Cp PN}M(NHR) (NH R)] C would probably suppress
2
2
3
1
1
In situ P{ H} NMR spectroscopic studies of reactions with all
five precatalysts under conditions given in Table 2 indicate that
the CpPN ligand is strongly bonded to the metal center, since no
metalꢀolefin interaction, whereas in a noninsertive mechanism,
coordination of the third amine would be required for ring-
closure. Moreover, the low activity of catalysts with smallest ionic
4
549
dx.doi.org/10.1021/om200264n |Organometallics 2011, 30, 4544–4554

Organometallics
ARTICLE
#
Scheme 5. Suggested Noninsertive Mechanism for Intramo-
as thf even for Cp PN alkyls of the larger cations is observed. The
#
lecular Hydroamination/Cyclization of ω-Aminoalkenes by
Cp PN ligand has a strong MꢀN bonding and a considerably
45
CpPN Rare-Earth-Metal Complexes
smaller Cp ꢀMꢀN angle compared to CpSiN complexes.
centr
Hydroamination/cyclization reactions on two representative ω-
penten-4-ylamines, 2,2-dimethyl- (S1) and 2,2-diphenylpenten-
4
-ylamine (S2), were investigated. The activity measured under
identical conditions increases with increasing ionic radii in the
3+
3+
3+
3+
3+
order Lu < Y < Sm < Nd e Pr . Complexes of smaller
ionic radii rare-earth metals 1 (Sc) and 2 (Lu) have a low catalytic
activity in hydroamination/cyclization reactions at room tempera-
ture. Complexes with larger ionic radii, 4ꢀ6, were found to be
catalysts of high activity. The catalytic activity increases dramatically
at higher reaction temperatures. In contrast to other literature
known CGCs we do not observe a zero-order rate dependence
on substrate concentration and characteristic deviations at higher
conversions, but we observe a distinctive substrate-dependent first-
order kinetic profile up to high conversions. Furthermore, the active
#
catalyst species [{Cp PN}Y(NHCH CMe CH CHdCH ) ] (8)
2
2
2
2 2
formed upon rapid aminolysis of yttrium precatalyst 3 with less than
2
equiv of aminoalkene S1 was characterized by NMR. No
cyclization at ambient temperature was observed for 8. However,
addition of a third equivalent of amine substrate to 8 leads to the
formation of free pyrrolidine product, while the observed concentra-
tion of the active catalyst in the reaction mixture remains constant.
Our observations of a distinctive substrate-dependent first-
order kinetic profile, the strong correlation of activity to the ionic
radii and higher coordination number associated with larger
cations, and the stoichiometric model reaction let us suggest a
concerted noninsertive mechanism with a proton transfer from a
coordinated acidic primary amine to the olefin. Three electron
pairs shifted via a six-membered transition state convert a
primary amine substrate complex to a ring-closed secondary
amine product complex. This proposal requires further support
by measuring kinetic isotope effects and by computational
studies. Furthermore, these results clearly indicate the necessity
and opportunity to tune this new class of CGCs for catalytic
hydroamination of ThorpeꢀIngold nonactivated substrates by
variation of substituents at N, P, and the Cp ring as well as by the
size of the metal cation.
radii could be explained by the fact that larger cations should be
able to bind more easily an additional primary amine, forming
species C. The latter could act as the strongest NH acid in the
system and could promote a concerted proton transfer to the
olefinic double bond via a six-membered transition state D
involving a three-electron-pair shift. The result of this transfor-
mation would be a conversion of a primary amine complex C into
a secondary amine complex E, which further dissociates into the
product and the catalytically active bis-amido species B.
The key transformation step C f E is strongly dependent on the
concentration of the substrate compared to the concentration of the
product, and it could explain the observed first-order kinetics as
supported by the model cyclization reaction with active species 8.
This proposal does not exclude that a critical dissociation step of the
secondary amine complex E with regeneration of the catalyst B
could lead to product inhibition, but it offers an alternative to the
common view that proton transfer is directed toward a carbanion
that was formed via olefin insertion into the MꢀN bond.
’
EXPERIMENTAL SECTION
’
CONCLUSIONS
General Procedures. All manipulations were performed under
purified argon or nitrogen using standard high-vacuum or Schlenk
techniques, or in a glovebox. Solvents were dried and distilled under
argon employing standard drying agents. All organic reagents were
purified by conventional methods. NMR spectra were recorded at 300 K
on a Bruker ARX200, Bruker DPX250, Bruker AMX300, Bruker
AVANCE DRX400, and Bruker DRX500. Elemental analyses were
performed at the Analytical Laboratory of the Chemistry Department/
This study reveals that monoanionic cyclopentadienylpho-
#
sphazene Cp PN is a privileged ligand to effectively stabilize
dialkyl constrained geometry complexes of small, medium, and
large rare-earth-metal ions. A straightforward one-pot syn-
5
1
thesis of complexes of the type [{η ,η -C Me PMe NAd}M-
5
4
2
(
(
CH SiMe ) ], M = Sc (1), Lu (2), Y (3), Sm (4), Nd (5), Pr
2 3 2
6), and Ce (7), was achieved without the necessity for isolation
3 3
Philipps-Universit €a t Marburg. The starting materials [MCl (thf) ]
#
of homoleptic Ln alkyls or a lithiated Cp PN ligand. For this
purpose etherates of the rare-earth-metal halides and protonated
5c
46
(
M = Sc), [MCl (dme) ] (M = Lu, Y, Sm(n = 2); Nd, Pr, Ce (n = 1)),
3
n
47
10
48
LiCH
2
SiMe
3
,
C
5
Me
4
2
PMe NHAd, and aminoalkenes were synthe-
ligand are treated with 3 equiv of LiCH SiMe ; thereby two of
2
3
sized according to the literature methods.
them act as nucleophiles and one as a base. All complexes were
thoroughly characterized by NMR spectroscopy, including the
signal assignment of the paramagnetic complexes 4ꢀ7. Further-
more, 1ꢀ4 were structurally characterized and support the
strongly chelating constrained geometry character of these
cyclopentadienyl-phosphazene ligands. Only η ,η -coordination
of the ligand was observed with small as well as with larger rare-
earth-metal cations. No coordination of additional donors such
X-ray Crystallographic Studies. Suitable crystals in all cases
were obtained by cooling a concentrated hexane solution to ꢀ30 °C.
Crystal data were collected with a Stoe-IPDSI area-detector diffracto-
meter using graphite-monochromatized Mo KR radiation (λ = 0.71073 Å)
at 150 K (3) and 193 K (1, 4). Data reduction was carried out by using
1
5
49
the IPDS software X-Area (Stoe). The data were empirically corrected
5
0
for absorption and other effects by using multiscans, except for
compound 3, where no improvement in the refinement was achieved
4
550
dx.doi.org/10.1021/om200264n |Organometallics 2011, 30, 4544–4554

Organometallics
ARTICLE
Table 3. Crystallographic Data and Structure Refinement Details for 1ꢀ4
1
0
1
2
3
4
formula
fw
C
29
H
55NPScSi
2
C
29
H
55LuNPSi
2
C
29
H
55NPSi
2
Y
29 2
C H55NPSi Sm
549.85
679.86
593.8
655.24
193(2)
yellow
temp (K)
cryst color
size (mm)
cryst syst
space group
a (Å)
193(2)
colorless
180(2)
colorless
150(2)
colorless
0.45 ꢁ 0.21 ꢁ 0.12
monoclinic
0.32 ꢁ 0.20 ꢁ 0.16
monoclinic
0.48 ꢁ 0.40 ꢁ 0.32
monoclinic
0.30 ꢁ 0.27 ꢁ 0.21
monoclinic
P2
1
/c
P2
1
/c
P2
1
/n
1
P2 /n
15.180(1)
10.344(1)
20.980(2)
90
15.284(2)
10.456(1)
21.092(2)
90
13.360(3)
17.293(3)
14.497(3)
90
13.378(1)
17.264(1)
14.520(1)
90
b (Å)
c (Å)
R (deg)
β (deg)
γ (deg)
92.52(1)
90
91.97(2)
90
91.26(2)
90
90.91(1)
90
3
V (Å )
3291.0(4)
4
3368.7(7)
4
3348.5(19)
4
3353.0(5)
4
Z
ꢀ
3
F
calcd (g cm
)
1.110
1.340
1.178
1.298
ꢀ
1
μ (mm
)
0.362
3.066
1.878
1.887
no. of rflns collected
no. of indep rflns (Rint
GOF
25 584
6113 (0.0667)
0.913
30 805
6383 (0.0549)
1.038
30 437
5486 (0.1274)
0.872
26 814
6503 (0.0522)
0.879
)
2
2
R
1
(F > 2σ(F ))
0.0462
0.1185
0.0398
0.1034
0.0500
0.1205
0.0261
0.0558
2
wR
2
(F )
through its application. The structures were solved by direct methods
Alternative Synthesis of Lutetium Complex 2. Starting from
51
52
#
(
Sir-92 and Sir-97 ) and refined by full-matrix least-squares techni-
[LuCl
0.50 mmol) in 10 mL of ether and LiCH
in 13 mL of hexane. Yield: 66% (225 mg) of a colorless solid. Anal. Calcd
for C29 55LuNPSi (679.87): C 51.23, H 8.15, N 2.06. Found: C 50.72,
H 8.17, N 2.18. Spectroscopic features are in good agreement with those
3
(dme)
2
] (232 mg, 0.50 mmol) and {Cp PN}H (165 mg,
2
53
ques against F
o
(SHELXL-97). Hydrogen atoms were included in
2
SiMe (141 mg, 1.50 mmol)
3
idealized positions and refined with isotropic displacement. The pro-
5
4
55
grams PLATON and PLUTON were used to check the results of the
H
2
5
6
X-ray analyses. Diamond was used for structure representations.
1
0
CCDC-684697 (1), -684698 (3), and -791944 (4) contain the supple-
mentary crystallographic data for this paper. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
previously reported.
Synthesis of Yttrium Complex 3. Starting from [YCl (dme) ]
3
2
#
(188 mg, 0.50 mmol) and {Cp PN}H (165 mg, 0.50 mmol) in 10 mL of
ether and LiCH SiMe (143 mg, 1.52 mmol) in 10 mL of hexane. Yield:
2
3
5
1
1
General Synthetic Protocol toward [(η ,η -C Me PMe NAd)
83% (246 mg) of a colorless solid. H NMR (300.1 MHz, C
6
D
6
):
5
4
2
2
2
M(CH SiMe ) ] (1ꢀ7). To a suspensionof [MCl (solv) ] (1.00 equiv)
δ ꢀ0.75 (dd, J = 11.1 Hz, J = 3.0 Hz, 2H, Y-HCH), ꢀ0.70 (dd,
2
3 2
3
n
HH
2
HY
#
2
and {Cp PN}H ligand (1.00 equiv) in ether was added dropwise at 0 °C
a solution of LiCH SiMe
(ca. 3.00 equiv) in hexane (for 1ꢀ3)
or toluene (for 4ꢀ7). The reaction mixture was stirred at 0 °C for another
.5 h and concentrated in vacuo to half of the original volume. Formed LiCl
J
HH HY 3
= 11.1 Hz, J = 3.0 Hz, 2H, Y-HCH), 0.38 (s, 18H, SiMe ), 1.16
2
2
3
HP 2
(d, J = 12.5 Hz, 6H, Me P), 1.56 (br s, 6H, δ-AdH), 1.71 (s, 6H, β-
AdH), 2.00 (br s, 3H, γ-AdH), 2.03 (s, 6H, β-C Me ), 2.11 (s, 6H,
5
4
1
3
5 4 6 6 3
1
0
γ-C Me ). C{ H} NMR (75.0 MHz, C D ): δ 4.7 (s, SiMe ), 11.4
(s, γ-C Me ), 13.8 (s, β-C Me ), 21.9 (d, J = 54.9 Hz, Me P), 30.2
5 4 5 4 CP 2
(s, γ-AdC), 31.4 (d, J = 41.0 Hz, Y-CH ), 36.3 (s, δ-AdC), 47.6 (d,
JCP = 8.7 Hz, β-AdC), 54.3 (d, J = 6.9 Hz, R-AdC), 84.6 (d, J
Me
) ppm. P{ H} NMR (121.5 MHz, C
55NPSi Y (593.80): C 58.66, H 9.34, N 2.36.
Found: C 59.21, H 9.71, N 2.41.
Synthesis of Samarium Complex 4. Starting from [SmCl -
1
was filtered off over Celite. The solvent was stripped off, and the residue was
extracted with hexane. Crystallization occured by storage at ꢀ30 °C. Filtration
and drying in a vacuum resulted in isolation of microcrystalline solids.
Synthesis of Scandium Complex 1. Starting from [ScCl (thf) ]
1
CY
2
3
2
1
=
=
CP
CP
2
3
116.1 Hz, R-C
14.4 Hz, γ-C
ppm. Anal. Calcd for C29
Me
), 121.9 (d, JCP = 13.4 Hz, β-C
), 123.7 (d, JCP
3
3
5
4
5
4
#
31
1
(
368 mg, 1.00 mmol) and {Cp PN}H (331 mg, 1.00 mmol) in 15 mL of
ether and LiCH SiMe (286 mg, 3.04 mmol) in 10 mL of hexane. Yield:
6 6
4% (412 mg) of a colorless solid. H NMR (400.1 MHz, C D ):
5
Me
4
6 6
D ): δ 9.0 (s)
H
2
2
3
1
7
2
2
δ ꢀ0.38 (d, J = 11.3 Hz, 2H, Sc-HCH), ꢀ0.34 (d, J = 11.3 Hz,
HH
HH
3
2
#
2H, Sc-HCH), 0.38 (s, 18H, SiMe
3
), 1.16 (d, JHP = 12.5 Hz, 6H, Me
2
P),
(dme)
2
] (437 mg, 1.00 mmol) and {Cp PN}H (332 mg, 1.00 mmol)
SiMe (282 mg, 3.00 mmol) in
1
C
.55ꢀ1.63 (m, 6H, δ-AdH), 1.82ꢀ1.83 (m, 6H, β-AdH), 2.01 (s, 6H, β-
in 15 mL of ether and LiCH
2
3
1
3
1
5
Me
4
), 2.02 (br s, 3H, γ-AdH), 2.16 (s, 6H, γ-C
5
Me
4
) ppm. C{ H}
15 mL of toluene. Yield: 67% (402 mg) of an orange solid.
4
1
NMR (62.9 MHz, C D ): δ 4.5 (s, SiMe ), 12.0 (d, J = 1.3 Hz,
H NMR (500.1 MHz, C D ): δ ꢀ6.70 (s, 6H, β-AdH), ꢀ4.07 (s,
6
6
3
CP
6
2
6
1
γ-C
5
Me
4
), 14.4 (s, β-C
5
Me
4
), 21.6 (d, JCP = 54.7 Hz, Me
2
P), 30.4 (d,
6H, γ-C
5
Me
4
), ꢀ0.87 (d, JHH = 11.6 Hz, 3H, endo-δ-AdH), ꢀ0.46
4
3
2
J
CP = 1.1 Hz, γ-AdC), 36.4 (s, δ-AdC), 36.8 (s, Sc-CH
2
), 47.2 (d, JCP
=
(s, 3H, γ-AdH), ꢀ0.29 (d, JHH = 11.6 Hz, 3H, exo-δ-AdH), 1.25 (s,
2
1
8
.6 Hz, β-AdC), 54.6 (d, J = 6.5 Hz, R-AdC), 84.8 (d, J = 114.0 Hz,
CP CP
2 3
18H, SiMe ), 3.87 (s, 6H, Me P), 5.06 (s, 6H, β-C Me ), 10.61 (br s,
3
2
5
4
13
1
R-C Me ), 122.6 (d, J = 12.8 Hz, β-C Me ), 125.7 (d, J = 14.2 Hz,
2H, Sm-HCH), 12.53 (br s, 2H, Sm-HCH) ppm. C{ H} NMR
(125.8 MHz, C ): δ 4.0 (s, SiMe ), 4.4 (s, γ-C Me ), 19.2 (s,
β-C Me ), 26.3 (d, JCP = 52.2 Hz, Me P), 26.5 (s, γ-AdC), 33.5 (s,
δ-AdC), 39.1 (s, β-AdC), 49.8 (s, R-AdC), 87.3 (d, J = 124.3 Hz,
5
4
CP
5
4
CP
31
1
γ-C
Anal. Calcd for C29
Found: 62.92, H 9.78, N 2.41.
5
Me
4
) ppm. P{ H} NMR (121.5 MHz, C
6
D
6
): δ 9.5 (s) ppm.
6
D
6
1
3
5
4
H
55NPScSi
2
(549.87): C 63.35, H 10.08, N 2.55.
5
4
2
1
CP
4
551
dx.doi.org/10.1021/om200264n |Organometallics 2011, 30, 4544–4554

Organometallics
ARTICLE
CHdCH ), 2.20
3
1
1
R-C
5
Me
4
), 98.6 (s, γ-C
5
Me
4
), 116.4 (s, β-C
5
Me
4
) ppm. P{ H}
(d, superposed with β-C
5
Me
4
, 4H, NHCH
2
CMe
2
CH
2
2
3
NMR (121.5 MHz, C D ): δ 25.3 (br s) ppm. Anal. Calcd for
(s, 6H, β-C Me ), 3.18 (d, J = 9.4 Hz, 4H, NHCH CMe CH CHd
6
6
5
4
HH
2
2
2
C
29
H
55NPSi
2
Sm (655.26): C 53.16, H 8.46, N 2.14. Found: C
CH
(m, 2H, NHCH
): δ 0.0 (s, SiMe
2
), 5.10ꢀ5.19 (m, 4H, NHCH
CMe CH CHdCH
), 11.2 (s, γ-C
P), 25.3 (s, NHCH
CHdCH ), 30.6 (s, γ-AdC), 36.6 (s, δ-AdC),
CH CHdCH
52.8 (d, JCP = 7.3 Hz, R-AdC), 45.0 (s, NHCH
60.9 (s, NHCH CMe CH CHdCH ), 86.9 (d,
R-C Me ), 115.9 (s, NHCH CMe CH CHdCH
13.5 Hz, β-C Me ), 122.7 (d, CP = 9.1 Hz, γ-C
(s, NHCH CMe CH CHdCH
): δ 6.7 (s) ppm.
2
CMe
2
CH
2
CHdCH
2
), 6.01ꢀ6.12
1
3
1
5
2.28, H 8.40, N 2.38.
2
2
2
2
). C{ H} NMR (100.6 MHz,
Me ), 13.4 (s, β-C Me ), 22.4
CMe CH CHdCH ), 25.2
Synthesis of Neodymium Complex 5. Starting from
C
6
D
6
4
5
4
5
4
#
1
[NdCl (dme)] (340 mg, 1.00 mmol) and {Cp PN}H (340 mg, 1.03 mmol)
(d, JCP = 54.2 Hz, Me
(s, NHCH CMe CH
36.7 (s, NHCH CMe
2
2
2
2
2
3
in 15 mL of ether and LiCH
toluene. Yield: 49% (315 mg) of a sky blue solid. H NMR (300.1
2
SiMe
3
(292 mg, 3.10 mmol) in 15 mL of
2
2
2
2
1
3
2
2
2
2
), 47.6 (d, JCP = 9.0 Hz, β-AdC),
CM1e CH CHdCH ),
CP = 118.7 Hz,
2
MHz, C D ): δ ꢀ21.72 (s, 6H, β-AdH), ꢀ13.52 (s, 6H, γ-C Me ),
2
2
2
2
6
6
2
5
4
ꢀ
ꢀ
5.83 (d, J = 11.9 Hz, 3H, endo-δ-AdH), ꢀ4.94 (s, 3H, γ-AdH),
2
2
2
2
J
HH
2
2
3.62 (d, JHH = 11.9 Hz, 3H, exo-δ-AdH), 2.62 (s, 18H, SiMe
3
),
5
4
2
2
2
2
), 120.3 (d, JCP
Me ), 137.6
) ppm. P{ H} NMR (161.9 MHz,
2
=
2
3
1
0.58 (d, JHP = 6.0 Hz, 6H, Me
2
P), 11.44 (s, 6H, β-C
5
Me
4
), 20.30
5
4
J
5
4
1
3
1
31
1
(
br s, 2H, Nd-HCH), 29.62 (br s, 2H, Nd-HCH) ppm. C{ H}
NMR (125.8 MHz, C Me ), ꢀ15.3 (s,
): δ ꢀ37.5 (br s, γ-C
β-C Me
), ꢀ13.4 (s, R-AdC), 19.6 (s, γ-AdC), 27.4 (s, δ-AdC), 29.3
s, β-AdC), 30.4 (s, SiMe
2
2
2
D
6
5
4
6 6
C D
6
5
4
1
(
3
), 34.7 (d, JCP = 52.7 Hz, Me
2
P), 102.8 (s,
1
’ ASSOCIATED CONTENT
Supporting Information. Detailed NMR spectroscopic
γ-C Me ), 107.1 (d, J = 124.2 Hz, R-C Me ), 146.0 (s, β-C Me )
ppm. P{ H} NMR (121.5 MHz, C
Calcd for C29 55NNdPSi (649.15): C 53.65, H 8.54, N 2.16.
Found: C 53.11, H 8.21, N 2.31.
5
4
CP
5
4
5
4
3
1
1
6
D
6
): δ ꢀ89.3 (br s) ppm. Anal.
S
b
H
2
1
13
1
data ( H, C{ H}, and 2D NMR experiments) with signal
assignment for complexes 3ꢀ6 and 8. Figures giving representa-
tive kinetic plots. This material is available free of charge via the
Internet at http://pubs.acs.org.
Synthesis of Praseodymium Complex 6. Starting from
#
[
PrCl
in 10 mL of ether and LiCH
toluene. Yield: 55% (176 mg) of a pale green solid. H NMR (300.1
MHz, C Me ),
13.14 (d, JHH = 10.2 Hz, 3H, endo-δ-AdH), ꢀ12.68 (s, 3H, γ-AdH),
3
(dme)] (169 mg, 0.50mmol) and{Cp PN}H (166 mg, 0.50 mmol)
2
3
SiMe (142 mg, 1.51 mmol) in 15 mL of
1
’
AUTHOR INFORMATION
6
D
6
): δ ꢀ46.66 (s, 6H, β-AdH), ꢀ30.25 (s, 6H, γ-C
5
4
2
ꢀ
ꢀ
Corresponding Author
Phone: +49 (0)6421 2825693. Fax: +49 (0)6421 2825711.
2
3
9.33 (d, JHH = 10.9 Hz, 3H, exo-δ-AdH), 2.96 (s, 18H, SiMe ), 13.92
*
2
(
d, J = 11.9 Hz, 6H, Me P), 25.94 (s, 6H, β-C Me ), 86.58 (br s, 2H,
HP
2
5
4
E-mail: jsu@chemie.uni-marburg.de.
31
1
Pr-HCH), 91.74 (br s, 2H, Pr-HCH) ppm. P{ H} NMR (121.5 MHz,
): δ ꢀ59.0 (br s) ppm. Anal. Calcd for C29 55NPPrSi (645.81):
C 53.93, H 8.58, N 2.17. Found: C 53.64, H 8.83, N 2.26.
C
6
D
6
H
2
’
ACKNOWLEDGMENT
Synthesis of Cerium Complex 7. Starting from [CeCl (dme)]
3
#
(168 mg, 0.50 mmol) and {Cp PN}H (166 mg, 0.50 mmol) in 10 mL of
Financial support by DFG (Priority Program Lanthanoid-
ether and LiCH
2
SiMe
3
(141 mg, 1.50 mmol) in 15 mL of toluene. Yield:
Specific Functionality SPP-1166), by Chemetall GmbH,
Frankfurt, by Deutscher Akademischer Austauschdienst (DAAD
Ostpartnerschaftsprogramm), and by Studienstiftung des
Deutschen Volkes is gratefully acknowledged. K.A.R. thanks
Prof. Em. Manfred Meisel (Institut f €u r Chemie der Humboldt-
Universit €a t zu Berlin) for his munificent support during the stay
at his research group and Dr. Brukhard Ziemer for his contribu-
tion to the X-ray analysis of 3.
1
53% (171 mg) of a yellow solid. H NMR (300.1 MHz, C D ):
6
6
δ ꢀ22.10 (s, 6H, β-AdH), ꢀ14.77 (s, 6H, γ-C Me ), ꢀ5.56 (d,
5
4
2
2
J
J
HH = 10.9 Hz, 3H, endo-δ-AdH), ꢀ5.07 (s, 3H, γ-AdH), ꢀ3.71 (d,
HH = 10.8 Hz, 3H, exo-δ-AdH), 1.69 (s, 18H, SiMe ), 8.43 (s, 6H,
3
Me P), 11.89 (s, 6H, β-C Me ), 36.86 (br s, 2H, Ce-HCH), 43.30 (br s,
2
5
1
4
3
1
2H, Ce-HCH) ppm. P{ H} NMR (121.5 MHz, C
6
D
6
): δ ꢀ3.9 (br s)
13 1
ppm. The compound was found to be too unstable to record a C{ H}
NMR spectrum and to obtain the correct values by elemental analysis.
Typical NMR-Scale Catalytic Reaction. In a N -filled glovebox,
2
a NMR tube equipped with a Teflon (Young) valve was charged with
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