Heteroleptic alkyl and amide iminoanilide alkaline earth and divalent rare earth complexes for the catalysis of hydrophosphination and (Cyclo) hydroamination reactions

Article abstract of DOI:10.1002/chem.201301464

[{N^N}M(X)(thf)_n] alkyl (X=CH(SiMe₃)₂) and amide (X=N(SiMe₃)₂) complexes of alkaline earths (M=Ca, Sr, Ba) and divalent rare earths (Yb^II and Eu^II) bearing an iminoanilide ligand ({N^N}^-) are presented. Remarkably, these complexes proved to be kinetically stable in solution. X-ray diffraction studies allowed us to establish size-structure trends. Except for one case of oxidation with [{N^N}Yb^II{N(SiMe₃)₂}(thf)], all these complexes are stable under the catalytic conditions and constitute effective precatalysts for the cyclohydroamination of terminal aminoalkenes and the intermolecular hydroamination and intermolecular hydrophosphination of activated alkenes. Metals with equal sizes across alkaline earth and rare earth families display almost identical apparent catalytic activity and selectivity. Hydrocarbyl complexes are much better catalyst precursors than their amido analogues. In the case of cyclohydroamination, the apparent activity decreases with metal size: Ca>Sr>Ba, and the kinetic rate law agrees with R _CHA=k[precatalyst]¹[aminoalkene]¹. The intermolecular hydroamination and hydrophosphination of styrene are anti-Markovnikov regiospecific. In both cases, the apparent activity increases with the ionic radius (CaHA=k[styrene]¹[amine]¹[precatalyst] ¹ and R_HP=k[styrene]¹[HPPh₂] ⁰[precatalyst]¹, respectively. Mechanisms compatible with the rate laws and kinetic isotopic effects are proposed. [{N^N}Ba{N(SiMe ₃)₂}(thf)₂] (3) and [{N^N}Ba{CH(SiMe ₃)₂}(thf)₂] (10) are the first efficient Ba-based precatalysts for intermolecular hydroamination and hydrophosphination, and display activity values that are above those reported so far. The potential of the precatalysts for C-N and C-P bond formation is detailed and a rare cyclohydroamination-intermolecular hydroamination "domino" sequence is presented. Activated alkenes: Long sought heteroleptic alkyl and amide complexes of large alkaline earths (Ca, Sr, Ba) and divalent rare earths (Yb, Eu) supported by a bulky iminoanilide ancillary ligand have been prepared (see figure). These complexes are very versatile, active, and selective in the catalysis of the cyclohydroamination of aminoalkenes, and the intermolecular hydroamination and hydrophosphination of activated alkenes. Copyright

Full text of DOI:10.1002/chem.201301464

FULL PAPER
DOI: 10.1002/chem.201301464
Heteroleptic Alkyl and Amide Iminoanilide Alkaline Earth and Divalent
Rare Earth Complexes for the Catalysis of Hydrophosphination and
(Cyclo)Hydroamination Reactions
Bo Liu,[a] Thierry Roisnel,[b] Jean-FranÅois Carpentier,*[a] and Yann Sarazin*[a]
Abstract:
(X=CH(SiMe3)2) and amide (X=N-
(SiMe3)2) complexes of alkaline earths
[{N^N}M(X)
E
families display almost identical appa-
rent catalytic activity and selectivity.
Hydrocarbyl complexes are much
better catalyst precursors than their
amido analogues. In the case of cyclo-
hydroamination, the apparent activity
decreases with metal size: Ca>Sr>Ba,
and the kinetic rate law agrees with
Ba) but the rate laws are different, and
obey RHA =k cat-
[styrene]1[amine]1[pre
lyst]1 and RHP =k[styrene]1[HPPh2]0-
[pre
catalyst]1, respectively. Mechanisms
compatible with the rate laws and ki-
netic isotopic effects are proposed.
E
G
E
ACHTUNGTRENNUNG
G
a
G
E
ACHTUNGTRENNUNG
(M=Ca, Sr, Ba) and divalent rare
earths (YbII and EuII) bearing an imi-
noanilide ligand ({N^N}ꢀ) are present-
ed. Remarkably, these complexes
proved to be kinetically stable in solu-
tion. X-ray diffraction studies allowed
us to establish size–structure trends.
Except for one case of oxidation with
ACHTUNGTRENNUNG
[{N^N}Ba{N
[{N^N}Ba{CH
the first efficient Ba-based precatalysts
for intermolecular hydroam nation and
A
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
R
CHA =k[precatalyst]1[aminoalkene]1.
The intermolecular hydroamination
and hydrophosphination of styrene are
anti-Markovnikov regiospecific. In
both cases, the apparent activity in-
creases with the ionic radius (Ca<Sr<
A
N
G
ACHTUNGTRENNUNG
hydrophosphination, and display activi-
ty values that are above those reported
so far. The potential of the precatalysts
[{N^N}YbII{N
ACHTUNGTRENNUNG(SiMe3)2}AHCTUNGTREN(NNGU thf)], all these
complexes are stable under the catalyt-
ic conditions and constitute effective
precatalysts for the cyclohydroamina-
tion of terminal aminoalkenes and the
intermolecular hydroamination and in-
termolecular hydrophosphination of ac-
tivated alkenes. Metals with equal sizes
across alkaline earth and rare earth
ꢀ
ꢀ
for C N and C P bond formation is
detailed and a rare cyclohydroamina-
tion–intermolecular
hydroamination
Keywords: alkaline earth metals ·
hydroamination reactions · hydro-
“domino” sequence is presented.
phosphination reactions
·
rare
earths · reaction mechanisms
Introduction
amines constitute valuable chemicals for a virtually bound-
less array of applications. Both can to some extent be cata-
lyzed by late transition-metal (TM) catalysts that display
characteristic robustness and functional-group tolerance, but
suffer from limited lifetime, low reaction rates, and limited
scope.[1,2] Hence, since the seminal breakthroughs,[3] left
main group, early TM, and especially rare earth (RE) com-
plexes have been at the forefront of catalyst development in
this area.[2a,b,4] This is particularly true of hydrophosphina-
tion reactions, which, owing to the soft nature of the phos-
phorus atom, are much more efficiently catalyzed by com-
plexes based on hard, highly Lewis acidic metals (Groups 3
and 4) than by soft, late TM-based catalysts.[2d,5–7]
Through a range of landmark contributions, Marks et al.
demonstrated the potential of lanthanidocene catalysts in
cyclohydrophosphination[7] and even more so hydroamina-
tion[3,8,9] reactions, and his work inspired that of many
others.[10] Prompted by these results and by the similarities
in the properties and reactivity of rare earth and alkaline
earth (Ae) metals, Hill et al. implemented complexes of the
large Ae metals (Sr, Ba but preponderantly Ca) as worthy
precatalysts for the cyclohydroamination of aminoalkenes,[11]
intermolecular alkene hydroamination,[12] and hydrophosphi-
nation[13] reactions, or a variety of other organic transforma-
Catalyzed alkene hydrofunctionalizations consisting of the
addition of H X (X=Si, P, N, B…) bonds across C=C unsa-
ꢀ
turations represent a significant challenge the communities
of organometallic and organic chemists are faced with.[1] Hy-
drophosphination (X=P) and even more so hydroamination
(X=N) reactions have been at the center of attention in
recent years, not least because the resulting phosphines and
[a] Dr. B. Liu, Prof. Dr. J.-F. Carpentier, Dr. Y. Sarazin
Organometallics: Materials and Catalysis
Institut des Sciences Chimiques de Rennes
UMR 6226 CNRS—Universitꢀ de Rennes 1
Campus de Beaulieu, 35042 Rennes Cedex (France)
Fax : (+33)223-236-939
E-mail: jean-francois.carpentier@univ-rennes1.fr
yann.sarazin@univ-rennes1.fr
[b] Dr. T. Roisnel
Centre de Diffractomꢀtrie X
Institut des Sciences Chimiques de Rennes
UMR 6226 CNRS—Universitꢀ de Rennes 1
Campus de Beaulieu, 35042 Rennes Cedex (France)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201301464.
Chem. Eur. J. 2013, 19, 13445 – 13462
ꢁ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
13445

tions.[14] These precatalysts, and amongst them most promi-
nently the versatile b-diketiminate calcium complex
oleptic complexes [{N^N}M(X)ACTHNGUTERNNUG
(thf)n] (M=Ca, Sr, Ba, YbII,
EuII) supported by an iminoanilide ancillary ligand
ꢀ
[{BDI}Ca{N
G
G
({BDI}H=H2C{C(Me)N-2,6-
({N^N}ꢀ)[25] and incorporating an amide (Xꢀ =N
G
ꢀ
(iPr)2C6H3}2),[15] generally featured excellent performance.
Several groups have since endeavored to develop original
Ca-based catalysts for the cyclohydroamination of aminoal-
kenes[16] (some of which displayed appreciable levels of
enantioselectivity)[16c,e–g] and hydrophosphination[17] of acti-
vated alkenes.[18,19] On the other hand, the use of Sr and Ba
precatalysts remained underexplored, because the synthesis
of stable heteroleptic complexes of the type [{L}AeX-
or alkyl (Xꢀ =CH
(SiMe3)2 ) reactive group, and their ability
to catalyze the hydrophosphination and (cyclo)hydroamina-
tion of alkenes. The competences of the respective families
are detailed and relevant kinetic parameters and plausible
mechanistic scenarios are presented.
Results and Discussion
ACHTUNGTRENNUNG
(solvent)n] (where Ae is Sr or Ba, {L}ꢀ is a monoanionic an-
cillary ligand and Xꢀ is a reactive group, typically an amide)
is hampered by their kinetic lability, which leads to facile
decomposition in solution through deleterious Schlenk-type
equilibria. Recently, we introduced several complete fami-
Synthesis and characterization: In a similar fashion to that
described for the previously reported [{N^N}Ae{N
ACHTUNGTERN(NUNG SiMe3)2}-
AHCTUNGTRENNUNG
divalent rare earth complexes [{N^N}REII{N
ACHTNUTRGENN(UG SiMe3)2}ACHTUNGTRENNUNG(thf)x]
lies of stable Ae heteroleptic complexes [{L}Ae
G
N
(REII =YbII, 4, x=1; EuII, 5, x=2) were obtained in good
(Ae=Mg, Ca, Sr or Ba; {L}ꢀ =b-diketiminate, iminoanilide
or aminophenolate; R=SiMe3 or SiMe2H; n=0–2), which
catalyzed both the intermolecular hydrophosphination and
hydroamination of activated alkenes.[20] Surprisingly, the cat-
alytic activity increased with the size of the metal, that is,
(Mg !) Ca<Sr<Ba; in the case of Ba, intermolecular hy-
droamination reaction followed the empirical rate law given
in Equation (1).
yields (ca. 60–70%) upon one-pot reaction of the iminoani-
line proteo-ligand {N^N}H and [REIII
2ACHTNUTRGNE(NUG thf)2] with 2 equiva-
lents of KNACHTNUTRGNE(NUG SiMe3)2 (Scheme 1).
1
1
1
ð1Þ
RHA ¼ k½alkeneꢁ ½amineꢁ ½Baꢁ
Yet, reaction rates in the cyclohydroamination of aminoal-
kenes catalyzed by the same b-diketiminate or aminopheno-
late Ae complexes decreased in the order Ca>Sr>Ba,[21] as
reported by Hill et al.[11]
The divalent rare earth metals (REII) YbII and EuII dis-
play almost identical ionic radii to Ca and Sr, respectively
(ionic radii for C.N.=6: Ca, 1.00 ꢂ; Sr, 1.18 ꢂ; YbII, 1.02 ꢂ;
EuII, 1.17 ꢂ),[22] and also feature many close properties. All
are hard, electropositive elements, forming d0 complexes
where non-directional bonding is prominently governed by
electrostatic and steric interactions. Comparative studies be-
tween the catalytic behavior of congeneric families of Ae
and REII catalysts remain scarce, but partial (EuII, 4f7) or
complete (YbII, 4f14) filling of low-lying f orbitals with their
limited radial extension and the redox-active nature of REII
elements have not been shown to systematically induce dif-
ferent reactivity between related REII and Ae com-
plexes.[17,23] An example pertaining to the present study was
disclosed in 2012 by Cui et al.,[17] with heteroleptic Ca and
YbII catalysts containing a tridentate iminoamidinate ligand:
commensurate activity but different selectivity were ob-
served in the hydrophosphination of alkynes; yet, both Ca
and YbII afforded very similar results in the hydrophosphi-
nation of dienes. Just as in Takakiꢃs hydrophosphination of
alkynes promoted by organoytterbium complexes,[24] no
change of the oxidation state of the (YbII) metal center was
detected.
Scheme 1.
The identity of 4 and 5 (isolated as dark purple and dark
red powders, respectively) was established by X-ray diffrac-
tion crystallography, and their purity was confirmed by com-
bustion analysis. The diamagnetic 4 was also characterized
by conventional NMR techniques which attested to the sta-
bility of the complex in solution (no sign of decomposition
was observed in C6D6 solutions after 3 days at room temper-
ature), but the strongly paramagnetic nature of the EuII
complex 5 precluded acquisition of informative NMR data.
Both complexes are highly air- and moisture-sensitive, and
this thwarted all attempts to obtain mass spectrometry data.
The iminoanilide Ca and YbII complexes 1 and 4 can be
seen as the direct analogues, yet with a more rigid ligand
framework, to the b-diketiminate complexes [{BDI}Ca{N-
Building on an earlier communication,[20] we now report
the synthesis and structural characterization of stable heter-
(thf)] (6) and [{BDI}YbII{N
AHCTNUGTERNN(GNU SiMe3)2}ACHUTGNTRENNGU ACHTNUGERTG(NNNU SiMe3)2}ACHTUNGTREN(NUNG thf)] (7) that
13446
www.chemeurj.org
ꢁ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2013, 19, 13445 – 13462

Alkaline Earth and Divalent Rare Earth Complexes
FULL PAPER
Table 1. Structural parameters for [{L}M(X)(solvent)x] complexes (M=Ca, Sr, Ba, YbII, EuII; Xꢀ =
have been reported elsewher-
e.[11a,15,26] Attempts to prepare
the samarium congener of com-
plexes 4 and 5 were inconclu-
sive, as the only product which
could be characterized beyond
doubt was the bis(iminoanilide)
N(SiMe3)2ꢀ, N(SiMe2H)2ꢀ, CH(SiMe3)2ꢀ) bearing nitrogen-based {L}ꢀ bidentate ligands.
ꢀ
Entry Complex
rionic
CN[b] M X N-M-N M···NCCCN Ref.
[ꢂ][a]
[ꢂ][c] [8][d]
[ꢂ][e]
1
2
3
4
5
6
7
8
9
[{NN}Ca(N(SiMe3)2)(thf)]
1
2’
3
4
5
6
7
1.00
1.18
1.35
1.02
1.17
1.00
1.02
1.18
1.35
1.00
1.18
1.35
4
4
5
4
5
4
4
4
4
4
5
5
5
5
2.29
2.46
2.62
2.34
2.48
2.31
2.34
2.45
2.59
2.31
2.47
2.61
2.71
2.84
77.4
71.3
66.0
76.6
71.0
81.1
82.1
74.1
69.7
80.9
74.7
68.8
71.3
66.3
0.81
0.68
1.14
1.12
0.97
1.22
1.61
0.72
1.88
0.82
1.31
1.45
1.09
1.18
[20]
this work
[20]
this work
this work
[15]
this work
[33]
[39]
[20]
[21]
[20]
[{NN}Sr(N(SiMe3)2)(thf)]
[{NN}Ba(N(SiMe3)2)(thf)2]
[{NN}YbII(N(SiMe3)2)(thf)]
[{NN}EuII(N(SiMe3)2)(thf)2]
[{BDI}Ca(N(SiMe3)2)(thf)]
[{BDI}YbII(N(SiMe3)2)(thf)]
[{BDI}Sr(N(SiMe3)2)(thf)]
[{BDI}Ba(N(SiMe3)2)(thf)]
[{BDI}Ca(N(SiMe2H)2)(thf)]
[{BDI}Sr(N(SiMe2H)2)(thf)2]
ACTHNUTRGNEUNG
complex [{N^N}2SmII(thf)];[27,28]
apparently, the targeted hetero-
leptic SmII complex suffered
from kinetic lability, but wheth-
11
12
13
14
er [{N^N}2SmII
ACHTUNGTRENNUNG(thf)] was the
10
main product of this reaction or 11
12
[{BDI}Ba(N(SiMe2H)2)(thf)2] 15
[{NN}Sr(CH(SiMe3)2)(thf)2]
[{NN}Ba(CH(SiMe3)2)(thf)2]
simply
a
minor by-product
13
14
9·C5H12 1.18
10 1.35
this work
this work
could not be ascertained.
The one-pot reaction of
KCHACHTUNGTRENNUNG(SiMe3)2, {N^N}H and
AeI2 in a 2:1:1 ratio afforded
the stable heteroleptic Ae-
[a] Ionic radius of the metal (M) for CN=6. [b] CN=Coordination number of the metal in the complex.
[c] Distance between metal center and alkyl/amide reactive group. [d] Bite angle formed through bidentate
chelation of the ancillary ligand. [e] Distance between metal center and mean plane defined by the Nancillary-C-
C-C-Nancillary backbone in the ancillary ligand.
alkyls
[{N^N}Ae{CH
complexes
(SiMe3)2}(thf)x]
N
ACHTUNGTRENNUNG
(Ae=Ca, x=1, 8; Sr, x=2, 9; Ba, x=2, 10) in 50–70%
yield as yellow solids (Scheme 1). Their identity was deter-
mined by NMR spectroscopy, and was corroborated by ele-
mental analysis and, for 9 and 10, by X-ray diffraction crys-
tallography. All are fully soluble and stable in aromatic sol-
1
vents, as indicated by H NMR monitoring in C6D6 solution
at 25–608C, and they can also be dissolved in aliphatic hy-
drocarbons. If a few heteroleptic Ca complexes of the type
[{L}CaRACHTUNGTRENNUNG(solvent)n] bearing a multidentate monoanionic
ligand ({L}ꢀ) and a hydrocarbyl group (Rꢀ) have already
been authenticated by X-ray diffraction methods,[29] to our
knowledge analogous heteroleptic Sr- and Ba-alkyl com-
plexes have only been generated in situ or characterized by
NMR spectroscopy.[11f,29c,30] Complexes 9 and 10 hence rep-
resent the first heteroleptic Sr- and Ba-alkyl species structur-
ally characterized. Much as found for their amido deriva-
tives 2 and 3,[20] their kinetic stability can be attributed to
the steric shielding conferred to the metal center by the
very hindered {N^N}ꢀ ancillary (see below); besides, by op-
Figure 1. X-ray structure of [{N^N}Sr{N(SiMe3)2}(thf)] (2’). Ellipsoids are
drawn at the 50% probability level. Hydrogen atoms are omitted for
ꢀ
ꢀ
clarity. Selected bond lengths (ꢂ) and angles (8): Sr1 N1 2.463(2), Sr1
ꢀ
ꢀ
ꢀ
ꢀ
O61 2.491(2), Sr1 N31 2.512(2), Sr1 N11 2.574(2), Si1 N1 1.692(2), Si2
N1 1.688(2); N1-Sr1-O61 101.09(6), N1-Sr1-N31 145.27(6), O61-Sr1-N31
106.51(6), N1-Sr1-N11 123.18(6), O61-Sr1-N11 101.63(6), N31-Sr1-N11
71.32(5), Si2-N1-Si1 126.1(1), Si2-N1-Sr1 115.18(9), Si1-N1-Sr1 118.7(1).
position to {BDI}ꢀ or bis
respectively undergo deprotonation[29c] or dearomatiza-
ACHTUNGTRNE(NUNG imino)acenapthene ligands which
tion[11f] in the presence of basic Aed+···dꢀCH
ACHTUNTRGENUNG(SiMe3)2 moiet-
ies for Ae=Sr or Ba, we found that the {N^N}ꢀ ligand
amidal (Figure 2). The YbII-heteroatom bond lengths in 4
are shorter than in 2’, as expected on account of the smaller
ionic radius of YbII (1.02 ꢂ) versus that of Sr (1.18 ꢂ).
The EuII complex 5 features the metal center in a slightly
distorted square pyramidal geometry (t=0.13),[34] with the
ꢀ
framework was chemically inert towards CH
G
three complexes 8–10.[31]
The crystal structures of several of these complexes were
determined, and relevant metric parameters are collected in
Table 1.
ꢀ
amide (N41) in apical position (Figure 3). The Eu1 N4anilidino
Unusually for the large Sr element,[32] the metal center in
bond length of 2.53 ꢂ is substantially shorter than that be-
tween the metal center and N25imino (2.66 ꢂ), an evidence
for the limited degree of delocalization of the negative
[{N^N}Sr{N
(Figure 1). The tetrahedral arrangement in 2’ is less distort-
ed than in equally 4-coordinate [{BDI}Sr{N(SiMe3)2}-
(thf)],[33] even if the related bond lengths in the two com-
ACHTUNGTRENNUNG(SiMe3)2}ACHTUNGTRENN(UGN thf)] (2’) is only 4-coordinate in 2’
T
charge in the N4-C3-C23-C24-N25 backbone. By compari-
II
ꢀ
G
son, the two Eu NATI distances are almost identical (2.54
plexes all fall within the same range.
and 2.56 ꢂ) in Roeskyꢃs aminotroponiminate ({ATI}ꢀ)
The YbII complex 4 is also 4-coordinate and rests in a dis-
[{ATI}EuII{N
G
E
II
ꢀ
torted tetrahedral geometry, approaching trigonal monopyr-
in Shenꢃs 5-coordinate [{BDI}2EuII
(thf)], where the charge is
Chem. Eur. J. 2013, 19, 13445 – 13462
ꢁ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
13447

J.-F. Carpentier, Y. Sarazin et al.
Figure 4. X-ray structure of [{BDI}YbII{N(SiMe3)2}(thf)] (7). Ellipsoids
are drawn at the 50% probability level. Hydrogen atoms are omitted for
Figure 2. X-ray structure of [{N^N}YbII{N(SiMe3)2}(thf)] (4). Ellipsoids
are drawn at the 50% probability level. Hydrogen atoms are omitted for
ꢀ
ꢀ
clarity. Selected bond lengths (ꢂ) and angles (8): Yb1 N3 2.341(3), Yb1
ꢀ
ꢀ
N2 2.363(3), Yb1 N1 2.379(3), Yb1 O61 2.424(3); N3-Yb1-N2 120.3(1),
N3-Yb1-N1 127.8(1), N2-Yb1-N1 82.1(1), N3-Yb1-O61 115.6(1), N2-Yb1-
O61 104.3(1), N1-Yb1-O61 100.5(1).
ꢀ
ꢀ
clarity. Selected bond lengths (ꢂ) and angles (8): Yb1 N1 2.339(2), Yb1
ꢀ
ꢀ
N21 2.375(2), Yb1 O11 2.395(1), Yb1 N41 2.412(2); N1-Yb1-N21
127.82(5), N1-Yb1-O11 119.16(5), N21-Yb1-O11 96.51(5), N1-Yb1-N41
111.14(5), N21-Yb1-N41 76.60(5), O11-Yb1-N41 118.97(5).
first time (Figure 4). The metal center in 7 is 4-coordinate
and much as in 4, it exists in a highly distorted, almost trigo-
nal monopyramidal, environment. Significant discrepancies
between the arrangement in the two complexes include the
distance from YbII to the N1-C2-C3-C4-N5 mean plane
(1.61 ꢂ in 7, and “only” 1.12 ꢂ in 4, see above) and a wider
N
ancillary-YbII-Nancillary bite angle for the b-diketiminate com-
plex (76.68 in 4 versus 82.18 in 7).
The 5-coordinate Sr atom in [{N^N}Sr{CHACTHUNGTRNEUNG(SiMe3)2}-
ACHNUTTGERGUN(NN thf)2]·C5H12 (9·C5H12) exits in a near-perfect square pyrami-
ꢀ
dal environment (t=0.06),[34] with the bulky CH
ACTHNUTRGEN(UNG SiMe3)2
ꢀ
group located on the apex (Figure 5). The Sr1 N31 bond
ꢀ
length (2.52 ꢂ) is noticeably shorter than the Sr1 N11 one
(2.63 ꢂ), again highlighting the limited delocalization on the
negative charge over the N11-C24-C25-C30-N31 backbone.
ꢀ
The long Sr1 C1 distance (2.71 ꢂ) in 9·C5H12 suggests that
d+
dꢀ
ꢀ
this Sr Calkyl bond is highly ionic, but it matches that
found in related organometallic Sr complexes exhibiting s-
bound alkyl groups;[36] amongst these, 9·C5H12 stands out as
being the only heteroleptic mononuclear alkyl complex of
Figure 3. X-ray structure of [{N^N}EuII{N(SiMe3)2}(thf)2] (5). Ellipsoids
are drawn at the 50% probability level. Hydrogen atoms are omitted for
clarity. Only the mains components of the disordered coordinated THF
molecules are represented. Selected bond lengths (ꢂ) and angles (8):
the type [{L}SrR
The arrangement about Ba in [{N^N}Ba{CH
(thf)2] (10) resembles that in the Sr analogue 9·C5H12
ACHTUNGTRNEUN(NG solvent)n].
AHCTUNTGREN(GNUN SiMe3)2}-
ꢀ
ꢀ
ꢀ
ꢀ
AHCTUNGTRENNUNG
Eu1 N41 2.483(8), Eu1 N4 2.529(7), Eu1 O51A 2.600(7), Eu1 N25
ꢀ
2.656(7), Eu1 O61A 2.689(7); N41-Eu1-N4 115.6(2), N41-Eu1-O51A
(Figure 6). The 5-coordinate metal center sits in a square
pyramidal geometry (t=0.06),[34] with the apical position oc-
105.4(2), N4-Eu1-O51A 136.6(2), N41-Eu1-N25 110.7(2), N4-Eu1-N25
71.0(2), O51A-Eu1-N25 81.9(2), N41-Eu1-O61A 119.3(3), N4-Eu1-O61A
96.0(2), O51A-Eu1-O61A 74.9(2), N25-Eu1-O61A 128.7(2).
ꢀ
cupied by CH
N
66.38 is narrow, and the distance from the very large Ba
atom to the mean plane delineated by N141-C142-C147-
C148-N111 is 1.18 ꢂ; both values match those found in the
fully delocalized over the NBDI-C-C-C-NBDI core, fall in the
range 2.53–2.59 ꢂ.[35]
amido derivative
3
(66.08 and 1.14 ꢂ respectively).[20]
ꢀ
The structure of the known b-diketiminate complex
Barium compounds featuring Ba C s bonds are not excep-
[{BDI}YbII{N (thf)] (7)[26] is discussed here for the
ACHTUNGTRENNUNG(SiMe3)2}ACHTUGNTRENNUGN
tional,[36,37] but to our knowledge 10 represents the first ex-
13448
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Chem. Eur. J. 2013, 19, 13445 – 13462

Alkaline Earth and Divalent Rare Earth Complexes
FULL PAPER
Pertinent structural data for the families of Ae and REII
complexes supported by the isoelectronic N,N-bidentate li-
gands {N^N}ꢀ (1–5 and 9–10) and {BDI}ꢀ (6,7, 11–15) are
displayed in Table 1. Several features emerge from the com-
parison of the structural data for 1–15. The N-M-N bite
angle depends largely on the ionic radius of the element: ir-
relevantly of the coordination number of the metal in a
given family of complexes (i.e. b-diketiminate or iminoani-
lide), the bite angle decreases with increasing metal size
(Table 1, entries 1–6 and 8–14), but remains constant for
metals of identical ionic radii (compare entries 1 and 4, 2
and 5, 6 and 7). Besides, the bite angle shows no depend-
ꢀ
ence upon the identity of the reactive group (N
(SiMe3)2 , N-
ꢀ
ꢀ
ACHTUNGERNN(UG SiMe2H)2 , or CHACHTUNGTREN(NUNG SiMe3)2 ) attached to the metal, com-
pare entries 6 and 10, 8 and 11, 9 and 12, 2 and 13, or 3 and
14. If the very large Ba atom is essentially 5-coordinate in
these complexes, coordination of 4 atoms is sufficient to
meet the stereoelectronic requirements for the smaller Ca
and YbII metals. No obvious pattern emerges in the case of
strontium, which features intermediate size between Ca and
Ba. It is unclear why the M···N-C-C-C-N distance in com-
plexes 6 (1.22 ꢂ) and 7 (1.61 ꢂ) exhibit such a difference
when all other metric parameters between the two com-
plexes remain commensurate.[40] Similar observations are
made between 1 and 4, as well as between 2 and 5, even if
the coordination differs in these last two complexes. Dis-
crepancies in the location of the metal center are observed
in related Ca, Sr, and Ba complexes (e.g., 6, 11, and 12).
The important role of d orbitals (with 4d orbitals in Sr being
energetically more accessible than 3d orbitals in Ca) in the
bonding pattern in neutral and cationic b-diketiminate com-
plexes of Ca and Sr has been highlighted,[41] and was shown
to be a decisive factor in the relative position of the metal
vis-ꢄ-vis the NBDI-C-C-C-NBDI average plane; these consider-
ations may explain the peculiar position of the Ba atom in
Hillꢃs complex 12.[39] The nature and overall steric bulk of
Figure 5. X-ray structure of [{N^N}Sr{CH(SiMe3)2}(thf)2]·C5H12 (9·C5H12).
Ellipsoids are drawn at the 50% probability level. Hydrogen atoms and
the non-interacting pentane molecule are omitted for clarity. Only the
main component of the disordered coordinated THF molecule (namely
ꢀ
O51A) is represented. Selected bond lengths (ꢂ) and angles (8): Sr1
ꢀ
ꢀ
ꢀ
N31 2.524(3), Sr1 O61 2.528(3), Sr1 O51A 2.570(3), Sr1 N11 2.627(3),
ꢀ
Sr1 C1 2.706(4); N31-Sr1-O61 133.5(1), N31-Sr1-O51A 95.6(1), O61-Sr1-
O51A 75.16(9), N31-Sr1-N11 71.3(1), O61-Sr1-N11 84.9(1), O51A-Sr1-
N11 137.1(1), N31-Sr1-C1 124.6(1), O61-Sr1-C1 100.5(1), O51A-Sr1-C1
111.7(1), N11-Sr1-C1 109.1(1).
ꢀ
ꢀ
the amido group (Xꢀ =N
ACTHNGURTEN(NUGN SiMe3)2 or NACHTNUGTRENNUNG
ꢀ
found to play no part in the pertaining Ae Namide bond
lengths even for complexes where the coordination number
of the metal varies (compare entries 6 and 10, 8 and 11, 9
ꢀ
and 12). Yet, the Ba Calkyl bond length in 10 (entry 14,
ꢀ
2.84 ꢂ) is much greater than the related Ba Namide one in 3
(entry 3, 2.62 ꢂ).
Figure 6. X-ray structure of [{N^N}Ba{CH(SiMe3)2}(thf)2] (10). Ellipsoids
are drawn at the 50% probability level. Hydrogen atoms omitted for
clarity. Only one of the two independent molecules is depicted, and only
the main component of the disordered coordinated THF molecule
Catalysis of hydroelementation reactions: The performance
of heteroleptic complexes 1–5 and 8–10 incorporating the
{N^N}ꢀ ligand as catalysts in the cyclohydroamination of
aminoalkenes, intermolecular hydroamination and hydro-
phosphination of activated alkenes were interrogated
(Figure 7). The aptitude of complexes supported by the b-di-
ketiminate ligand {BDI}ꢀ was reported elsewhere,[20,21] and
the Ca and YbII complexes 6 and 7 are therefore only in-
cluded for comparative purposes.
ꢀ
(namely O151) is shown. Selected bond lengths (ꢂ) and angles (8): Ba2
ꢀ
ꢀ
ꢀ
N141 2.652(6), Ba2 O151 2.741(5), Ba2 O161 2.782(5), Ba2 N111
ꢀ
2.815(6), Ba2 C101 2.840(7); N141-Ba2-O151 131.2(2), N141-Ba2-O161
99.8(2), O151-Ba2-O161 73.8(2), N141-Ba2-N111 66.3(2), O151-Ba2-
N111 83.4(2), O161-Ba2-N111 133.6(2), N141-Ba2-C101 118.5(2), O151-
Ba2-C101 104.0(2), O161-Ba2-C101 122.6(2), N111-Ba2-C101 101.7(2).
ample of an heteroleptic Ba-alkyl complex that has been
structurally authenticated.[38] The Ba2 C101 bond length of
Cyclohydroamination reactions: The ability of 1–10 to cata-
lyze cyclohydroamination reactions was probed by examin-
ing their performance in the cyclization of 1-amino-2,2-di-
ꢀ
2.84 ꢂ is typical of alkyl or alkyne groups s-bonded to
Ba.[36]
Chem. Eur. J. 2013, 19, 13445 – 13462
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13449

J.-F. Carpentier, Y. Sarazin et al.
10 in Table 2), and therefore Ca (and YbII) provided the
most efficient precatalysts for the cyclohydroamination of
alkenes, whereas Ba ones were the least efficient. This is in
agreement with earlier reports by several groups;[11,16b,21]
however, this trend is reversed during intermolecular reac-
tions (see below). Secondly, metals with similar ionic radii
across Ae and REII families exhibit essentially identical cat-
alytic activity (compare entries 1 and 4, 6 and 7, or 2 and 5).
No sign of oxidation of the REII-based catalysts 4 and 5 was
detected under catalytic conditions, since the color of the
solution remained the same throughout the whole duration
of the catalyzed reactions (purple for 4 and dark red for 5),
and reactions involving the diamagnetic 4 could be ade-
1
quately monitored by H NMR spectroscopy until comple-
tion. This contrasts with tidings from Roesky et al., who
found that [{ATI}YbII{N
ACHTUNGTRNENUG(SiMe3)2}ACHTUTGNREN(NUGN thf)2] was catalytically
competent (albeit generally less so than its direct Ca ana-
logue), but was very rapidly oxidized under the chosen con-
ditions;[16b] the bis(phosphinimino)methanide complex
Figure 7. (Cyclo)hydroelementation reactions catalyzed by complexes 1–
10.
[{(Me3SiNPPh2)2CH}YbIACTHUNTRGNEU(GN thf)2] also oxidized during the cy-
clohydroamination of aminoalkenes and aminoalkynes.[23b]
Hence, the {N^N}ꢀ iminoanilide appears as a valuable ancil-
lary to stabilize these reactive redox centers. Moreover, for
a given metal, the {N^N}ꢀ iminoanilide displays markedly
higher performance than the b-diketiminate scaffold, com-
pare for instance entries 1 and 6 (for Ca) or entries 4 and 7
Table 2. Representative data for the cyclohydroamination of S catalyzed
by 1–10.
for YbII. Finally, complexes incorporating the highly reactive
ꢀ
CH
G
Entry
Precatalyst
Reaction
time
[min]
Conversion
[%][b]
kapp
ꢀ
[c]
conditions[a]
[10ꢀ4 sꢀ1
]
cient than their derivatives bearing the NACTHNUGRTNEUNG(SiMe3)2 group
(as in 1-3). This has also been seen by Hill et al.,[11 g] and
1
2
1
2
A
B
4
7
90
97
120
68
can be explained in terms of relative acidity:[21,42] With a
3
4
5
6
7
8
9
10
11
3
4
5
6
7
8
9
10
10
B
A
B
A
A
A
A
A
C
60
4
7
4
4
<2
<3
20
5
96
6
pKa difference greater than 15 between N
(SiMe3)2 in favor of the latter,[43] the more basic the reac-
96
140
nd[e]
15
98[d]
27
tive Xꢀ group, the more easily the [M] X bond reacts with
the acidic aminoalkene to generate the catalytically active
29
100
98
96
97
16
nd[f]
nd[f]
22
ꢀ
species [M] N(H)CH2CMe2CH2CH=CH2 in the case of sub-
strate S upon release of HX. The NMR spectra of in situ re-
actions catalyzed by 3 and 10 confirmed this interpretation:
101
whereas the presence of free HN
tected in the reaction catalyzed by 3 (as seen with other Ae
catalysts),[11,21] quantitative release of CH
2A(SiMe3)2 was ob-
served in the case of 10. These reactivity features are epito-
mized with [{N^N}Ca{CH(SiMe3)2}(thf)] (8), for which com-
ACHTUNGTREN(NGNU SiMe3)2 could never be de-
[a] Reaction conditions A: [precat]/[S]=1:100, precat: 5.0 mmol, C6D6:
1.2 mL, 258C; Reaction conditions B: [precat]/[S]=1:50, precat:
10.0 mmol, C6D6: 0.6 mL, 608C; Reaction conditions C: [10]:[S]=1:50,
precat: 10.0 mmol, C6D6: 0.6 mL, 258C. [b] Conversion determined by
1H NMR spectroscopy. [c] Determined by 1H NMR monitoring experi-
ments. [d] Determined after quenching of the reaction and removal of
paramagnetic EuII species. [e] NMR measurements precluded by the par-
amagnetic nature of the complex. [f] Reaction too fast to allow accurate
NMR kinetic monitoring.
CTHUNGTRENNUNG
A
ACHTUNGTRENNUNG
plete conversion of 100 equivalents of S is observed within
2 min at room temperature; 8 is to date the most effective
Ae-based catalyst for the cyclohydroamination of the ami-
noalkene S (Table 2, entry 8), outperforming the ubiquitous
6,[11a] homoleptic Ae complexes such as [Ae{N
ACHTUNGTRENNUNG
methyl-4-pentene (S), a common aminoalkene for which
abundant data is available in the literature. Representative
results are given in Table 2. Ring-closure of 50–100 equiva-
lents of substrate proceeded at 25–608C according to Bald-
winꢃs guideline (5-exo-trig) in all cases, leading to the exclu-
sive formation of 2,4,4-trimethylpyrrolidine (P1).
Several trends appear upon examination of these qualita-
tive results. First, the apparent catalytic activity increases
with decreasing ionic radius (compare entries 1–3, 4–5 or 8–
ACHTNUGTNERU(NGN thf)x] (x=0 or 2) or [Ae{CHACHTNUTRGENNG(UN SiMe3)2}2ACHUTNTGRENNUNG
leptic aminophenolate-, bis(oxazoline)- or aminotroponimi-
nate-based ones.[16,21]
Kinetic monitoring was performed by 1H NMR spectro-
scopy to inform us on the behavior of these precatalysts.
Complex 5, which is paramagnetic, and complexes 8 and 9,
which are too fast for reliable measurements, were excluded
from this set of experiments. The number of coordinated
molecules of substrate could not be assessed. The fate of the
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Chem. Eur. J. 2013, 19, 13445 – 13462

Alkaline Earth and Divalent Rare Earth Complexes
FULL PAPER
1
1
ð2Þ
THF molecules during catalysis could not be established
clearly because of partial overlap of resonances in the
1H NMR spectra of in situ monitored reactions; yet, based
on comparison the downfield resonances of free and coordi-
nated THF in C6D6, it seemed that the solvent molecule(s)
were released from the metal center under catalytic condi-
tions. In all other cases, the monitoring indicated that sub-
strate consumption followed first order kinetics in substrate
concentration; no induction period was observed. The semi-
logarithmic plots of monomer conversion versus reaction
time are linear over 3 half-lives.[28] The values for the appa-
rent rate constants (kapp, with kapp =k[3]1 expressed in sꢀ1
and in which k is the reaction rate constant in Lmolꢀ1 sꢀ1,
see below) extracted from these plots (Table 2) are in the
range 0.0005–0.0020 sꢀ1 for the less effective precatalysts to
0.012–0.014 sꢀ1 for the most effective ones (1 and 4) that
could be measured. They are consistent with the relation-
RCHA ¼ k½3ꢁ ½aminoalkeneꢁ
The same rate law was also established for the Ba-alkyl
precatalyst 10.[28] Catalytic systems featuring such kinetic
rate laws are uncommon;[42,44] to our knowledge there is no
example with large Ae-based (Ca, Sr, or Ba) precatalysts.
Relevant examples include Sadowꢃs Mg complex supported
by a tris(oxazolinyl)phenylborate ligand,[19f] and Hultzschꢃs
phenoxyamine-Mg enantioselective precatalysts.[19h] Sadow
proposed a convincing mechanism compatible with this rate
law, whereby cyclization did not occur through migratory in-
ꢀ
sertion of the polarized olefin into the Mg N bond, as com-
monly proposed for zeroth order in [substrate], but rather
through a six-centered concerted transition state (TS) mech-
anism involving transfer of a proton from a coordinated sub-
strate molecule concomitant with ring-closure.[19f] It is plau-
sible that such a mechanistic scenario is also at work in the
case of 3. A significant kinetic isotope effect (kHap2p/kaDp2p
=
ships previously discussed, that is, Ca>Sr>Ba, Ca~YbII,
2.60; Figure 9) during the cyclohydroamination of S (kaHp2p
=
ꢀ
{N^N}ꢀ > {BDI}ꢀ, and CH
(SiMe3)2ꢀ @N
N
14.47
(0.36)ꢅ10ꢀ4 sꢀ1) or its ND2 deuterated analogue S-[D2]
order dependence upon substrate concentration was also
measured for the complexes [{BDI}Ae{N(SiMe2H)2}(thf)2]
(kDapp =5.56
E
2
A
ACHTUNGTRENNUNG
13–15,[21] but this contrasts with findings by others that the
rate law for cyclohydroamination reactions catalyzed by tri-
valent rare earth systems is zeroth-order in [substrate].[3,8,10l]
Other unusual behaviors have been mentioned before: Hill
has reported that reaction rates were inversely proportional
to substrate concentration in cyclohydroamination reactions
catalyzed by 6 and its magnesium equivalent,[11d,g] whereas
Hultzsch has described magnesium–phenolate precatalysts
which exhibited either zeroth or second order decay in sub-
strate concentration.[19e]
The activation energy for 3 (Ea,3 =98.2
10 (Ea,10 =29.2
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
rhenius plot of lnACHTUNRGTNEUNG(kapp) versus 1/T in the temperature range
25–608C.[28] Although performed with a limited (4) set of
Competent barium precatalysts for hydroelementation re-
actions are seldom,[20,21] hence more attention was paid to 3
and 10. The cyclohydroamination of S catalyzed by 3 at
608C was performed with [3]0 varying in a 12-fold range
(3.80–46.3 mm). The linear plot of lnACHTNUTRGNE(UGN kapp) versus ln([3]0) has
a slope of 1.05 (R2 =0.975) indicating first-order dependence
upon precatalyst concentration (Figure 8). Thus, the rate law
for the cyclohydroamination of the aminoalkenes S cata-
lyzed by 3 is given by Equation (2).
Figure 9. Kinetic isotopic measurements: Semi-logarithmic plot of sub-
&
strate consumption versus time for the cyclohydroamination of S ( ) and
^
)
S-d2
(
catalyzed in C6D6 (0.6 mL) at 608C by [{N^N}Ba{N(Si-
Me3)2}(thf)2] (3), using 10.0 mmol of 3 and [substrate]0/[3]0 =50:1.
Figure 8. Plots of ln(kapp) versus ln([3]0) (left) and kapp versus [3]0 (right) for the cyclohydroamination of S catalyzed by [{N^N}Ba{N(SiMe3)2}(thf)2] (3) at
different precatalyst concentrations (3.8, 8.7, 17.5, and 46.3 mm). Reaction conditions: 608C, C6D6: 0.6 mL.
Chem. Eur. J. 2013, 19, 13445 – 13462
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13451

J.-F. Carpentier, Y. Sarazin et al.
data points for practical reasons, the quality of the data for
3 and 10 was overall excellent (R2 >0.99). The value of Ea
found for 10 is considerably lower than that for 3, in agree-
ment with the higher catalytic efficiency detected for the
former during qualitative runs (Table 2, entries 3, 10, and
11). Eyring analysis was performed with the same data set
(Table 3). As expected for a concerted six-centered mecha-
step consisting of the insertion of the polarized alkene into
[21]
ꢀ
the Ae N bond.
Intermolecular and domino hydroamination reactions: The
unique behavior of amido Ca, Sr, and Ba precatalysts sup-
ported by b-diketiminate (such as [{BDI}Ca{N
ACHTUNGTRENNUNG
A
R
ACHTUNGTRENNUNG
13–15), aminoether-phenolate and iminoanilide (such as 1–
3) ligand scaffolds during intermolecular hydroamination of
activated alkenes (dienes, styrenics) has been reported in a
preliminary communication,[20] and shall not be discussed in
many details here. Complementary experiments have been
performed with the new alkyl heteroleptic compounds 8–10.
Precatalyst loading of 2 mol% and neat substrates were
used at 608C.
Table 3. Arrhenius and Eyring analyses in the temperature range 25–
608C for the cyclohydroamination of S catalyzed by 3 and 10 in C6D6
([3]/[S]=1:20; [10]/[S]=1:100).
¼
¼
Ea
DH
DS
[kJmolꢀ1
]
[kJmolꢀ1
]
[Jmolꢀ1 Kꢀ1
]
3
10
98.2(4.5)
29.2(2.1)
95.4(4.5)
26.7(2.1)
ꢀ13.2(13.8)
ꢀ206.0(6.6)
General lines can be drawn from the data displayed in
Table 4. In agreement with the proposed theoretical models
¼
nism, the large, negative activation entropy for 10 (DS =
ꢀ206.0
Table 4. Representative data for the hydroamination of styrene with
ACHTUNGTRENNUNG
(6.6) Jmolꢀ1 Kꢀ1) could tentatively be seen as diag-
amines catalyzed by 1–5 and 8–10.[a]
nostic of a highly ordered transition state, as often cited for
with oxophilic metals.[8,11,12] At the same time, the activation
energy and entropy for 3 are quite different from those
found for 10, while these two different precatalysts are an-
ticipated to generate the same active species. The moderate
KIE (kH /kD =2.6) observed for 3 perhaps reflects the fact
that in the case of this amido precatalyst, the overall rate-
limiting step consists in the preliminary acid-base reversible
equilibrium (involving 3 and S) rather than any subsequent
step in the actual catalytic cycle.
Based on literature precedents, and neglecting the poten-
tial role of THF, a mechanism for cyclohydroaminations cat-
alyzed by Ba precatalysts 3 and 10 compatible with the rate
law [Eq. (2)] and the determined activation parameters is
proposed in Scheme 2.[19f] This mechanism is different from
that we have recently presented for several aminophenolate
Ae precatalysts, for which no dependence in substrate con-
centration was found, as expected for a rate-determining
2
2
Entry
Precatalyst
Amine
time
[min]
Conversion
[%][b]
1
2
3
4
5
1
2
3
1
2
3
3
4
5
8
8
9
10
BnNH2
BnNH2
BnNH2
1080
1080
1080
30
30
30
120
30
30
5
30
34
71
86
65
75
95
85
0
82
28
90
85
97
pyrrolidine
pyrrolidine
pyrrolidine
pyrrolidine
pyrrolidine
pyrrolidine
pyrrolidine
pyrrolidine
pyrrolidine
pyrrolidine
6
7[c]
8
9
10
11
12
13
5
5
[a] [precatalyst]0/[styrene]0/[amine]0 =1:50:50 unless otherwise specified,
precatalyst: 10.0 mmol, 608C. [b] Conversion determined by 1H NMR
spectroscopy. [c] [3]0/[styrene]0/[amine]0 =1:500:500.
and experimental observations,[12] the reaction systematically
proceeded with strict anti-Markovnikov regioselectivity. Pre-
catalysts 1–3 promoted the hydroamination of styrene with
benzylamine
([precatalyst]0/ACTHNGURTEN[NUG styrene]0/ACHTUNGTERNN[UNG amine]0 =1:50:50)
with high efficacy (entries 1–3), but contrary to anticipations
based on DFT computations for homoleptic precatalysts for
intermolecular reactions,[12] the catalytic activity improved
regularly from Ca to Ba, that is, with increasing ionic radius.
This trend is the opposite of that reported above for cyclo-
hydroamination reactions, but it was confirmed with two
other families of ancillary ligands.[20] In the series of amido
precatalysts, the Ba complex 3 achieved near-complete con-
version over 18 h (entry 3), the Ca (1) and Sr (2) complexes
converted respectively 34% and 71% of the substrates (en-
Scheme 2. Proposed mechanism for the cyclohydroamination of 1-amino-
2,2-dimethyl-4-pentene (S) catalyzed by Ba-based precatalysts 3 and 10.
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Alkaline Earth and Divalent Rare Earth Complexes
FULL PAPER
tries 1 and 2). Faster reaction rates were achieved with pyr-
rolidine, as 50 equivalents of substrates were transformed
almost quantitatively by 3 within 30 min (entry 6); with
[styrene]0/[pyrrolidine]0/[3]0 =500:500:1, 85% of the sub-
strates was converted in 2 h, with a corresponding turnover
frequency of 212 hꢀ1 (entry 7). As found for cyclohydroami-
nation reactions, the new alkyl precatalysts 8–10 outclassed
by far their amido analogues (Table 4, entries 4, 10, and 11;
5 and 12; 6 and 13), and the activity still decreased regularly
according to Ba>Sr>Ca (compare entries 1–3, 4–6, or 10–
13). Notably, the Ba complex 10 affords the most active
(and yet fully regioselective) catalyst for intermolecular hy-
droamination of activated alkenes reported to date.[45] The
EuII complex 5 exhibited catalytic activity matching that of
its Sr analogue 2, with 82% and 75% of the substrates re-
spectively converted in 30 min for [styrene]0/[pyrrolidine]0/
[precatalyst]0 =50:50:1 (entries 5 and 9). On the other hand,
the YbII complex 4 was decomposed during intermolecular
hydroamination reactions and eventually proved inefficient.
The complex immediately oxidized in the presence of styr-
ene and pyrrolidine (as evidenced by the rapid color change
from purple to yellow concomitant with the formation of a
precipitate, and the fact that exploitable NMR data could
not be recorded), and the newly formed species (which
could not be characterized) was entirely incapable of cata-
lyzing the reaction. We double-checked that 4 was inert
toward styrene (in particular polymerization of styrene was
not seen under the chosen conditions) and pyrrolidine taken
separately, and therefore it is only the combination of the
two that leads to oxidation of 4; similar observations were
made when isoprene and/or benzylamine were employed.
Note also that 4 did not decompose in the presence of mix-
tures of phosphine and activated alkenes (vide infra), and
that 5 did not oxidize under the presence of amine and/or
styrene. The different behaviors of 4 and 5 are certainly to
be linked to the standard redox potential of their metal cen-
ters, with YbII complexes such as 4 being much more sensi-
tive to oxidation (E0 =ꢀ1.05 and ꢀ0.35 V for Yb3+/Yb2+
and Eu3+/Eu2+, respectively). It is unclear why 4 should be
sensitive toward mixtures of amines and activated alkenes,
but not toward mixtures of phosphines and activated al-
kenes, or toward aminoalkenes (see above), even if the fac-
ulty of activated alkenes to attract electrons can certainly be
evoked. We were unable to find literature precedent for
such behavior, even if Roesky et al. have recently reported
the oxidation (through disproportionation) of a bis(imidazo-
lin-2-iminato)YbII complex that led to the formation of a
crystallographically characterized bis(imidazolin-2-imina-
to)YbIII-iodide complex.[46]
alkenes with amines can be combined advantageously, was
selected to catalyze the one-pot “domino” sequence consist-
ing of the cyclohydroamination of S and subsequent hydroa-
mination of styrene with the resulting 2,4,4-trimethylpyrroli-
dine (P1) (Scheme 3). Upon simultaneous mixing of 3, S
Scheme 3. One-pot “domino” cyclohydroamination-hydroamination se-
quence.
~
Figure 10. Plot of concentrations in styrene ( ), 1-amino-2,2-dimethyl-4-
&
^
pentene (S; ), 2,4,4-trimethylpyrrolidine (P1, ) and 2-(2,4,4-trimethyl-
cyclopentyl)ethyl)benzene (P2; &) versus reaction time during the one-
pot “domino” synthesis of P2 catalyzed by [{N^N}Ba{N(SiMe3)2}(thf)2]
(3). Reaction conditions: [styrene]0/[S]0/[3]0 =50:50:1, [3]0 =0.018m, 608C,
solvent: C6D6, total volume (styrene+S+C6D6)=0.6 mL.
and styrene in C6D6 ([styrene]0/[S]0/[3]0 =50:50:1, 608C),
rapid consumption of the aminoalkene and concomitant for-
mation of P1 was monitored by 1H NMR spectroscopy
(Figure 10). The linear semi-logarithmic plot of ln([S]0/[S]t)
versus reaction time suggested partial first-order in substrate
concentration. The intermediateꢃs concentration ([P1]t) rose
to a maximum, then decayed until complete disappearance;
consumption of [P1]t and styrene occurred simultaneously
with formation of 2-(2,4,4-trimethylcyclopentyl)ethyl)ben-
zene (P2) through intermolecular hydroamination of styrene
with P1 catalyzed by 3. Again, the semi-logarithmic plots of
substrate consumption versus reaction time for P1 and styr-
ene were linear. Overall, the profile for the concentrations
in S, P1, and P2 (Figure 10) is characteristic of consecutive
elementary reactions. This method represents an efficient
tool for the synthesis of a wide range of non-symmetrical
tertiary amines starting from readily available aminoalkenes
and activated alkenes.[47]
On the whole, under reactions conditions fairly similar for
cyclohydroamination and intermolecular reactions, the
former took place much more rapidly than the latter upon
catalysis with 1–5 and 8–10. Moreover, the order of activity
switched with the nature (size) of the Ae metal between the
two catalyzed reactions. The barium precatalyst 3, for which
the catalytic activity in the cyclohydroamination of aminoal-
kenes and the intermolecular hydroamination of activated
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13453

J.-F. Carpentier, Y. Sarazin et al.
The Ae-alkyl precatalysts 8–10 were more active than their
Ae-amide congeners 1–3 (Table 5, entries 5 and 11, or also 7
and 13). Overall, these intermolecular hydrophosphination
precatalysts, and in particular the barium ones 3 and 10, are
second to none in terms of activity and regioselectivi-
ty.[2d,7,13,17]
Hydrophosphination reactions: Since hard, oxophilic nature
of Ae and REII elements offers ideal conditions for the cat-
ꢀ
alysis of C P bond formation using soft HPR2 phosphines,
ability of 1–5 and 8–10 to catalyze the hydrophosphination
of activated alkenes with secondary phosphines was interro-
gated.
The Ba precatalysts afforded the highest apparent activity
figures by some margin. The amido precatalyst 3, albeit
slightly less efficient than its alkyl analogue 10, was the
most suited to assess qualitatively the influence of substitu-
tion at the para position of the aromatic ring in the styrenic
substrates, as reactions with the latter were too fast to be
conveniently and reliably monitored (Table 5, entry 13).[48]
The electron-withdrawing inductive effect of chlorine led to
increased activity, as full conversion of p-Cl-styrene was ach-
ieved within less than 10 min (Table 5, entries 7 and 17).
With the even more electron-withdrawing CF3, high to com-
plete conversions were now achieved with 10 or 8 within 5–
10 min (Table 5, entries 14 and 16). By contrast, with elec-
tron-donating para substituents (Me, tBu, or OMe, en-
tries 18–20) lower reaction rates were measured, decreasing
with increasing electron-donating strength according to
(CF3 >Cl>)H>Me>tBu>OMe. This recalls observations
made independently by our group and that of Hill during
the intermolecular hydroamination of styrene deriva-
tives.[12b,20] These Ae-catalyzed intermolecular hydrophosphi-
nation reactions afford regiospecifically the anti-Markovni-
kov product, presumably through a rate-determining step
consisting of insertion of the highly polarized double bond
In a preliminary set of experiments, the addition of
HPCy2 or HPPh2 across the vinylic bond in styrene deriva-
tives was examined with a catalyst loading of 2.0 mol%
(Table 5). In all cases, the reactions afforded exclusively the
Table 5. Hydroamination of styrene with amines catalyzed by 1–5 and 8–
10.[a]
Entry
Precatalyst
HPR2
X
time
[min]
Conversion
[%][b]
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
1
2
3
4
1
2
3
4
5
8
8
9
10
1
1
3
3
3
HPCy2
HPCy2
HPCy2
HPCy2
HPPh2
HPPh2
HPPh2
HPPh2
HPPh2
HPPh2
HPPh2
HPPh2
HPPh2
HPPh2
HPPh2
HPPh2
HPPh2
HPPh2
HPPh2
HPPh2
H
H
H
H
H
H
H
H
H
H
H
H
1080
1080
1080
1080
15
15
15
15
15
3
15
3
3
10
10
5
<10
15
31
41
50
35
42
92
>96
45
93
20
76
55
95
92
80
80
95
79
44
27
ꢀ
into the Ba P bond as suggested by the empirically deter-
mined rate law (see below). The observed trend is compati-
ꢀ
ble with this scenario for C P bond formation since during
the rate-determining step, deleterious electron-donating sub-
stituents at the para position of the styrene derivative tend
to destabilize the developing negative charge on the benzyl-
ic (a) carbon atom, whereas electron-withdrawing para-sub-
stituents stabilize this growing negative charge and hence
afford higher reaction rates (Figure 11). Yet one should note
H
CF3
Cl
CF3
Cl
Me
tBu
OMe
3
3
30
30
[a] [precatalyst]0/[styrene]0/[phosphine]0 =1:50:50, no solvent, precatalyst:
1
10.0 mmol, 608C. [b] Conversion determined by H NMR spectroscopy.
anti-Markovnikov product. Reactions involving styrene and
HPCy2 were relatively slow, with substrate conversion in the
range 31–50% after 18 h (entries 1–4). By comparison, reac-
tion rates were much greater with the less basic HPPh2
(Table 5, entries 5–20), with full conversion of the substrate
being essentially achieved in as little as 3–15 min with the
Ba derivatives 3 and 10 (entries 7 and 13). As found for in-
termolecular hydroamination, the order of catalytic activity
decreased with the size of the metal according to Ba>Sr~
EuII >Ca~YbII. No notable difference was found between
Ae and REII metals with identical sizes (compare entries 5
and 8 as well as 6 and 9). Unlike seen for intermolecular hy-
droamination, no oxidation of the YbII precatalyst 4 was de-
tected here, either with HPCy2 (entry 4) or HPPh2 (entry 8).
Figure 11. Proposed transition state and observed reactivity trend in the
intermolecular hydrophosphination of p-substituted styrenics with HPPh2
catalyzed by 1–5 or 8–10.
that EW p-groups most likely have a detrimental effect on
the ability of the styrenic substrates to bind to the metal, so
that the results of these experiments probably describe the
global effect of several composite contributions.[48]
Kinetic measurements were conducted to gain insight in
the hydrophosphination of styrene with HPPh2 catalyzed by
13454
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Alkaline Earth and Divalent Rare Earth Complexes
FULL PAPER
1–5 or 8–10. In the presence of a high excess of styrene (as
customarily done to maintain its concentration virtually un-
changed), the plots of phosphine conversion versus reaction
time were linear in all cases, indicating absence of depend-
ence upon [HPPh2].[28,49] This was corroborated by examina-
tion of the turnover frequencies (TOF) for the hydrophos-
phination catalyzed by 1 at three different HPPh2 concentra-
tions spreading in a 4-fold range (88.3, 166.7, and 333.3 mm),
all other parameters remaining unchanged: identical TOFs
were found in all cases (24.0, 24.2, and 24.3
molproduct·molCaꢀ1 hꢀ1 respectively). The apparent rate con-
stants (k1app) were also determined for different catalyst (in
the range 1.90–58.5 mm) and styrene (between 1.34–5.25m)
concentrations. The corresponding semi-logarithmic plots of
ln(k1app) versus ln([1]0) and ln(ka1pp) versus ln([styrene]0) were
both linear with slopes of 0.95 (R2 =0.9768) and 1.08 (R2 =
0.9908),[28] indicating that the reaction kinetics followed first
order in both precatalyst and styrene concentrations (Fig-
ures 12 and 13). The empirical rate law for the hydrophos-
Figure 13. Plots of ln (kapp) versus ln([styrene]0) for the intermolecular
hydrophosphination of styrene and HPPh2 catalyzed by [{N^N}M{N(Si-
Me3)2}(thf)x] (M=Ca, x=1 1; Sr, x=2 2; Ba, x=2 3; YbII, x=1 4) at dif-
ferent styrene concentrations in the range 1.34 to 5.25m. Reaction condi-
tions: 1: 10.0 mmol, 608C, [1]0/[HPPh2]0 =1:8, C6D6+HPPh2+styrene=
0.6 mL; 2: 10 mmol; 408C, [2]0/[HPPh2]0 =1:8, C6D6+HPPh2+styrene=
0.6 mL; 3: 5.0 mmol; 408C, [3]0/[HPPh2]0 =1:32, C6D6+HPPh2+styrene=
1.2 mL; 4: 10.0 mmol, 608C, [4]0/[HPPh2]0 =1:8, C6D6+HPPh2+styrene=
0.6 mL.
Figure 12. Plots of ln (kapp) versus ln([precatalyst]0) for the intermolecular
hydrophosphination of styrene and HPPh2 catalyzed by [{N^N}M{N(Si-
Me3)2}(thf)x] (M=Ca, x=1, 1; Sr, x=2 2; Ba, x=2 3; YbII, x=1 4) at dif-
ferent precatalyst concentrations in the range 1.9 to 58.5 mm. Reaction
conditions: 1: 608C, [styrene]0 =1.34m, [styrene]0:[HPPh2]0 =10:1,
C6D6+Ph2PH+styrene=0.6 mL; 2: 408C, [styrene]0 =1.34m, [styre-
ne]0:[HPPh2]0 =10:1, C6D6+Ph2PH+styrene=0.6 mL; 3: 408C, [styr-
Figure 14. Eyring plots of ln ((kapph)/(kBT)) versus 1/T for the intermolec-
ular hydrophosphination of styrene and HPPh2 catalyzed by
[{N^N}M{N(SiMe3)2}(thf)x] (M=Ca, x=1, 1; Sr, x=2 2; Ba, x=2 3; YbII,
x=1 4) or [{N^N}Ca{CH(SiMe3)2}(thf)] (8) in the temperature range
303–343 K. Reaction conditions: 1: 10.0 mmol, [1]0/[styrene]0/[HPPh2]0 =
1:80:8, C6D6+HPPh2+styrene=0.6 mL; 2: 3.0 mmol; [2]0/[styrene]0/
[HPPh2]0 =1:270:27, C6D6+HPPh2+styrene=0.6 mL; 3: 2.3 mmol, [3]0/
ene]0 =1.34m,
1.2 mL; 4:
C6D6+Ph2PH+styrene=0.6 mL.
[styrene]0:[HPPh2]0 =10:1,
C6D6+Ph2PH+styrene=
[styrene]0:[HPPh2]0 =10:1,
608C, [styrene]0 =1.34m,
[styrene]0/[HPPh2]0 =1:700:70,
C6D6+HPPh2+styrene=1.2 mL;
4:
10.0 mmol, [4]0/[styrene]0/[HPPh2]0 =1:80:8,
C6D6+HPPh2+styrene=
0.6 mL; 8: [8]0/[styrene]0/[HPPh2]0 =1:80:8, C6D6+HPPh2+styrene=
0.6 mL.
phination of styrene with HPPh2 catalyzed by 1 can there-
fore be expressed as in Equation (3).
¼
DH were also calculated from the relevant Eyring plots
(Table 6).
0
1
1
ð3Þ
RHP ¼ k½HPPh2ꢁ ½styreneꢁ ½1ꢁ
Based on our experimental findings, the mechanism rep-
resented in Scheme 4 (which ignores the potential influence
of THF in these precatalysts as its exact role could not be
assessed, even if as before the 1H NMR spectra of in situ
monitored hydrophosphination reactions seemed to hint
that THF was released under catalytic conditions) is pro-
posed for the hydrophosphination of styrene derivatives
with secondary phosphines catalyzed by Ae and REII preca-
talysts 1–5 and 8–10. In such mechanism, two essential pa-
rameters will affect the overall kinetics: the amount of cata-
lytically active species existing in the medium, and the
Investigations performed for the Sr, Ba, and YbII precata-
lysts 2–4 provided the same outcome, and therefore the rate
law given in Equation (3) can be extended to each of
these.[50] The activation energy values, Ea =70.5(5.4) (1),
43.3(6.0) (2), 34.2(2.4), (3) and 60.7(5.4) (4) kJmolꢀ1, were
determined for 1–4 by an Arrhenius analysis performed in
the temperature range 30–708C (Figure 14). These values
were in good agreement with the qualitative trend disclosed
in Table 5, that is, Ba>Sr>Ca~Yb, established already for
¼
hydrophosphination reactions.[51] The values of DS and
Chem. Eur. J. 2013, 19, 13445 – 13462
ꢁ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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13455

J.-F. Carpentier, Y. Sarazin et al.
¼
¼
Table 6. Activation energy (Ea), enthalpy (DH ) and entropy (DS ) of
the hydrophosphination of styrene with diphenylphosphine catalyzed by
complexes 1–4 and 8.
rent activity detected for the para-substituent on the styrenic
substrate (R=Cl>H>Me>tBu>OMe), and with the strict
2,1-anti-Markovnikov regiospecifity observed in these cata-
lyzed reactions. To our knowledge, there are only two perti-
nent examples of Ae-catalyzed hydrophosphination of al-
kenes, but the mechanisms at work have not been de-
tailed.[13,17] The catalytic cycle herein suggested relates to
that of Marks et al. for the cyclohydrophosphination of
phosphinoalkenes.[7,55] We have tried but so far not been
able to isolate the putative species (Cat). Yet, Hill et al.
have isolated and characterized the related [{BDI}-
Ca(PPh2)(thf)] after equimolar reaction of 6 and HPPh2.[13]
Although kinetically unstable at elevated temperature, this
complex was able to catalyze (albeit slowly) styrene/HPPh2
hydrophosphination, and this finding combined with our
study provide strong claim for the plausibility of the pro-
posed mechanism. Moreover, like 6, the tetramethyldisila-
zide derivatives [{BDI}Ae{N(SiMe2H)2}(thf)2] 13–15 are effi-
cient hydrophosphination precatalysts, being outclassed only
by 1–3 and 8–10 and showing the same regioselectivity as
them.[20]
¼
¼
Entry
Precatalyst
Ea
DH
DS
[Jmolꢀ1 Kꢀ1
]
[kJmolꢀ1
]
[kJmolꢀ1
]
1[a]
2[b]
3[c]
4[a]
5[a]
1
2
3
4
8
70.5(5.4)
43.3(6.0)
34.2(2.4)
60.7(5.4)
55.4(2.5)
67.7(5.4)
40.6(6.0)
31.5(2.4)
58.0(5.4)
52.7(2.5)
ꢀ101.8(16.5)
ꢀ180.7(18.4)
ꢀ212.1(7.3)
ꢀ115.4(22.3)
ꢀ139.6(7.7)
[a] Precatalyst: 10.0 mmol; [precatalyst]0/[styrene]0/[HPPh2]0 =1:80:8,
C6D6 Ph2PH styrene=0.6 mL; [b] 2: 3.0 mmol; [2]0/[styrene]0/
[HPPh2]0 =1:270:27, C6D6 + Ph2PH + styrene=0.6 mL; [c] 3: 2.3 mmol;
[3]0/[Styrene]0/[HPPh2]0 =1:700:70, C6D6 + Ph2PH + styrene=1.2 mL.
+
+
The catalysis of isoprene hydrophosphination was exam-
ined next. The addition of HPPh2 was very rapid at 608C
with a catalyst loading of 2.0 mol% in neat substrates, but
was not fully regioselective (Table 7). The Sr and Ba preca-
Table 7. Isoprene/HPPh2 hydrophosphination catalyzed by 1–3 and 8–
10.[a]
Entry
Precatalyst
time
[min]
Conversion
[%][b]
Regioselectivity
Scheme 4. Proposed catalytic cycle for the hydrophosphination of styrene
derivatives with diphenylphosphine catalyzed by Ae and REII precata-
lysts (1–5 and 8–10).
1,4
3,4
1
2
3
4
5
6
1
8
2
9
3
15
15
9
9
9
94
96
97
98
99
99
26
25
40
39
74
73
74
75
60
61
26
27
nature of the rate-determining step, which on account of the
zero-dependence in [phosphine] we propose consists of in-
sertion of the polarized alkene into the metal–phosphide
bond. The higher acidity of HPPh2 (pKa (DMSO)=22.9;
pKa (THF)=21.7) compared with that of HPCy2 (pKa
(DMSO)=34.6; pKa (THF)=35.7)[52] is consistent with the
much greater reaction rates observed with the former, as the
catalytic active species (Cat) is first generated by protonoly-
10
9
[a] Reaction conditions: [precatalyst]0/[isoprene]0/[HPPh2]0 =1:75:50, no
solvent (bulk), precatalyst: 10.0 mmol, 608C. [b] Conversion determined
1
by H NMR spectroscopy.
talysts proved much more active than the Ca-based ones,
but under the chosen conditions it was not possible to dis-
criminate between Sr and Ba, as full conversion was always
achieved within 9 min for 2–3 as well as 9–10, nor between
amido and hydrocarbyl reactive groups. The regioselectivity
varied largely with the identity of the metal. Whereas the
Ca precatalysts 1 and 8 afforded preponderantly the 3,4-ad-
dition product, the Ba complexes 3 and 10 gave a 3:1 regio-
selectivity in favor of the 1,4-addition product. In the case
of the Sr precatalysts 2 and 9, the product of 1,4-addition
was very modestly favored. Such moderate levels of regiose-
lectivity contrast starkly with the entire 2,1-regiospecificity
seen for the intermolecular hydroamination of isoprene with
pyrrolidine catalyzed by 1–3;[20] yet Hill et al. reported near-
ꢀ
sis of the M X bond with the secondary phosphine. The
extent of deprotonation/reprotonation equilibria also ex-
plains the somewhat better efficiency discerned for Ae-alkyl
ꢀ
precatalysts 8–10 (X=CH(SiMe3)2 ) in comparison with the
Ae-amides 1–3 and their REII analogues 4 and 5 (X=
ꢀ
N(SiMe3)2 ): this initial acid–base equilibrium shifts very
much toward the formation of Cat with the strongly basic
ꢀ
hydrocarbyl group CH(SiMe3)2 , whereas the amount of cat-
alytically active species that exists at a given time of the cat-
alyzed reaction will be lesser for the comparatively more
ꢀ
acidic N(SiMe3)2 (pKa (HN(SiMe3)2/N(SiMe3)2ꢀ =25.8 in
DMSO).[53,54] As discussed above, the mechanism displayed
in Scheme 4 is in agreement with the overall order of appa-
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Alkaline Earth and Divalent Rare Earth Complexes
FULL PAPER
Table 8. Hydrophosphination of activated alkenes catalyzed by [{N^N}Ca{N(SiMe3)2}(thf)] (1), [{N^N}Ba{N(SiMe3)2}(thf)2] (3) and [{N^N}-
YbII{N(SiMe3)2}(thf)] (4).[a]
ACHTUNGTRENNUNG
Entry
Substrate
Time
[min]
1
3
4
conv.
[%][b]
regio.[b]
conv. [%][b]
regio.[b]
1,4
conv.
[%][b]
regio.[b]
1,4
3,4
3,4
1,4
3,4
1[c]
2
3
isoprene
myrcene
a-methylstyrene
styrene
15
15
240
15
94
96
2
26
51
–
74
49
–
99
99
90
74
83
–
26
17
–
98
97
6
28
53
–
72
47
–
4
42
–
–
>96
–
–
45
–
–
[a] Reactions conditions: [precatalyst]0/[alkene]0/[HPPh2]0 =1:50:50, precatalyst: 10.0 mmol, 608C unless otherwise specified. [b] Conversion and selectivi-
1
ty determined by H NMR spectroscopy. [c] [precatalyst]0/[isoprene]0/[HPPh2]0 =1:75:50. [d] C6D6: 0.45 mL.
identical regioselectivity to that observed with 1/8 for the
hydrophosphination of isoprene/HPPh2 catalyzed by 6.[13]
For a given metal, the product distribution was not altered
with the nature of the basic X group, consistent with no in-
volvement of this moiety in the catalytically active species
(Scheme 4).
Conclusion
The synthesis, solid-state structures, and catalytic performan-
ces of several alkyl and amide complexes of Ae and REII
metals supported by a bulky iminoanilide ligand have been
detailed. These heteroleptic complexes are fully stable in
solution, and in particular they are not prone to Schlenk-
type equilibria that often plague the coordination and reac-
tivity chemistries of these large and highly oxophilic ele-
ments. The complexes [{N^N}Ae{CH(SiMe3)2}(thf)x] consti-
tute in particular the first complete set of heteroleptic alkyl
complexes for the large alkaline earth metals Ca, Sr, and
Ba.
These complexes display high aptitude in the catalysis of
three key transformations: the cyclohydroamination of ami-
noalkenes, and the intermolecular hydroamination and hy-
drophosphination of activated alkenes (conjugated dienes,
styrene derivatives). Except in one instance where a peculiar
case of immediate oxidation of the YbII was observed upon
mixing with styrene (or isoprene) and pyrrolidine (or ben-
zylamine), the REII precatalysts did not undergo oxidation
under catalytic conditions, and essentially showed the same
ability as their direct alkaline earth cousins with almost
identical ionic radii (YbII and Ca; EuII and Sr), both in
terms of selectivity and catalytic activity. In this regard, the
iminoanilide ligand {N^N}ꢀ proved particularly efficient for
stabilizing redox active REII centers, as compared with other
ancillaries. Overall, the complexes based on Ca (and YbII),
Sr (and EuII), and Ba represent some of the most efficient
precatalysts reported to date for the considered organic
transformations. Full anti-Markovnikov regiospecificity was
observed in the case of intermolecular hydroamination and
hydrophosphination of styrene derivatives, whereas ring-clo-
sure is also strictly regioselective (5-exo-trig) during the cy-
clohydroamination of terminal aminoalkenes. The selectivity
is lesser during the hydrophosphination of dienes, and it de-
pends on the size of the metal. If the size of the metal did
The influence of the size of the metal on the regioselectiv-
ity of hydrophosphination of a variety of other activated
substrates was probed (Table 8). Under the chosen condi-
tions (2.0 mol% precatalyst loading), the YbII and Ca com-
plexes displayed poor (Table 8, entry 3, R=Me, a-methyl-
styrene) to moderate (Table 8, R=H, entry 4, styrene) activ-
ities in the hydrophosphination of styrene derivatives,
whereas even under such mild conditions the Ba-based 3 ex-
hibited high catalytic activity and complete anti-Markovni-
kov regiospecificity. Isoprene (entry 1) and myrcene
(entry 2) afforded fast reactions, with complete conversion
being observed in all cases within 15 min. The YbII (4) and
Ca (1) displayed the same selectivity, with as previously in
bulk reactions a 1:3 ratio in favor of the 3,4-addition product
in the case of isoprene, and total absence of regioselectivity
with myrcene. As found before, the Ba precatalyst 3 dis-
closed regioselectivity of its own, leading prominently to the
formation of the 1,4-addition product both for myrcene and
isoprene. Note that with all precatalysts, the non-activated
(non-conjugated) C=C moiety in myrcene was fully inert
toward hydrophosphination. In a screening experiment, 3 ef-
fectively catalyzed the hydrophosphination of diphenyle-
thyne with HPPh2 (82% conversion was observed after 4 h
at 608C, with [3]0/[diphenylethyne]0/[HPPh2]0 =1:50:50 in
0.45 mL of C6D6), leading to the formation of 1,2-diphenyle-
thene with a E/Z ratio of 65:35. Finally, attempts to carry
out hydrophosphination of 2-vinylpyridine with 1–3 were
unfruitful, and instead extremely fast and exothermic poly-
merization of the vinylic substrate was observed (formation
of a gel was observed in a few seconds) under a range of
conditions (T0 =25–608C).
Chem. Eur. J. 2013, 19, 13445 – 13462
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J.-F. Carpentier, Y. Sarazin et al.
Table 9. Overview of hydroelementation reactions catalyzed by heteroleptic iminoanilide Ae precatalysts [{N^N}AeX(thf)x] 1–3 and 8–10 (Ae=Ca, Sr,
Ba; Xꢀ =CH(SiMe3)2ꢀ, N(SiMe3)2<M->; x=1–2).
Cyclohydroamination[a]
Intermolecular hydroamination
Intermolecular hydrophosphination
ꢀ
ꢀ
ꢀ
reactive group
metal size
kinetic rate law
maximal TOF
CH(SiMe3)2ꢀ >N(SiMe3)2
CH(SiMe3)2ꢀ >N(SiMe3)2
CH(SiMe3)2ꢀ >N(SiMe3)2
Ca<Sr<Ba
Ca>Sr>Ba
Ca<Sr<Ba
k[M]1[aminoalkenes]1
k[M]1[styrene]1[amine]1
9.7 molprod molBaꢀ1 minꢀ1[c]
k[M]1[styrene]1[phosphine]0
15.8 molprod molBaꢀ1 minꢀ1[d]
50.0 molprod molCaꢀ1 minꢀ1[b]
[a] M=metal precatalyst. [b] Non-optimized, obtained with 8, Table 2, entry 8. [c] Obtained with 10, Table 4, entry 13. [d] Obtained with 10, Table 5,
entry 13.
not influence the stability of the complexes, it was found to
play a crucial role on catalytic activity. The alkyl compounds
proved better catalyst precursors than their amido ana-
logues. Following these considerations, [{N^N}Ba{N(Si-
ene, and precatalyst concentrations [Eq. (3)]. Reaction rates
for hydrophosphination varied according to CF3 >Cl>H>
Me>tBu>OMe upon introduction of substituents at the
para position of the aromatic ring of the styrene derivative.
The combination of this trend and the complete anti-Mar-
kovnikov regioselectivity of the addition is seen as being
consistent with a transition state such as that depicted in
Figure 11 and Scheme 4, with a growing negative charge on
the benzylic carbon atom that is stabilized with increasing
efficiency upon introduction of para-substituents of higher
electron-withdrawing strength; nonetheless, it is important
to take the amount of catalytically active species (generated
Me3)2}(thf)2]
(3)
and
especially
[{N^N}Ba{CH(Si-
Me3)2}(thf)2] (10) emerged as the most competent precata-
lysts for the intermolecular version of these catalyzed reac-
tions.
Mechanistic details and reactivity trends, which sometimes
appear conflicting, were revealed in the course of this study
(Table 9). During cyclohydroamination reactions, the cata-
lytic activity decreases when descending in the column of
Ae metals (Ba<Sr<Ca); this is in agreement with other re-
ports.[14,16,21] Rather unusually, the rate law that was deter-
mined indicated first order dependence upon catalyst and
susbstrate concentrations [Eq. (2)]; a different rate-law, with
zeroth order dependence upon [substrate], was for instance
presented for some aminophenolate Ca–Ba precatalysts.[21]
A mechanism is proposed for the cyclohydroamination cata-
lyzed by the iminoanilide Ae complexes, in which the transi-
tion state does not correspond to insertion of the polarized
ꢀ
by protonolysis of the M X bond with the acidic substrate)
existing at any given time into account when the apparent
reaction rates and precatalyst efficiency are compared. The
observed kinetic rate law agrees with the mechanistic sce-
nario proposed for REIII-catalyzed cyclohydrophosphination
of phosphinoalkenes,[7] involving a rate-determining step
consisting of insertion of the polarized C=C double bond in
ꢀ
the metal P(phosphide) bond.
Examination of the specificities for these catalyzed alkene
hydroelementation reactions (Table 9) highlights rich, yet di-
verse features that are not yet well understood. The conflict-
ing metal size versus catalytic activity relationships observed
for intra- and intermolecular reactions obviously spring to
mind, and so do the discrepancies observed between preca-
talysts based on the same metal but carrying different ancil-
lary ligands.[21] The input of theoretical calculations will now
be valuable to assess the finesses of Ae-catalyzed hydroele-
mentations, and we will direct our efforts in this aim. In
view of the somewhat limited number of truly efficient
(pre)catalysts for intermolecular hydrophosphination (or in
ꢀ
alkene into the metal N bond, as often observed for lantha-
nide precatalysts,[2a–b,3,8] but instead consists in a highly or-
ꢀ
dered 6-centered structure with ring-closure and N C bond
formation occurring concomitantly with the transfer of a
proton from a second coordinated molecule of substrate
(Scheme 2). This is reminiscent of Sadowꢃs recent report for
the Mg-catalyzed cyclohydroamination of aminoalkenes,[19f]
and is also very similar to the mechanism proposed in our
preliminary communication on the intermolecular hydroa-
mination of activated alkenes.[20] For this latter catalyzed re-
action, the empirically determined kinetic rate law was of
the first order in each of the three components [precatalyst,
styrene, and amine; Eq. (1)] and a very large kinetic isotope
effect (kaHp2p/kaDp2p =6.8–7.3) was measured.[20] However, in this
case the reactivity decreased systematically according to
Ba>Sr>Ca. Although it was contrary to expectations
mostly based on theoretical calculations for homoleptic Ae
precatalysts,[12] this trend was not a fortuitous isolated case,
as it was revealed for three complete families of heteroleptic
Ae complexes bearing a b-diketiminate (13–15), aminophe-
nolate or iminoanilide ligand (1–3). The investigations relat-
ed to the intermolecular hydrophosphination of styrene de-
rivatives unveiled still different insight. The same reactivity
versus metal size relationship as that disclosed for intermo-
lecular hydroamination was observed: Ba>Sr(~EuII)>Ca(~
YbII). Nonetheless, the kinetic rate law was different, with
orders of 0, 1, and 1 found respectively for phosphine, styr-
[1,2b,d,5,7]
ꢀ
fact C P bond formation)
and despite the considera-
ble synthetic challenges associated to these metals, it seems
fit to consider these new (and related)[13,17,56] alkaline earth
complexes as a most valuable addition to the arsenal of
tools available to synthetic organometallic and organic
chemists. The rare ability of these complexes to catalyze a
domino cyclohydroamination/intermolecular hydroamina-
tion sequence opens up new opportunities, and future efforts
will also be aimed at extending this sequential approach to a
variety of combinations of hydroelementation reactions.
Experimental Section
All manipulations were performed under inert atmosphere using stand-
ard Schlenk techniques or in a Jacomex glovebox (O2 <1 ppm, H2O<
13458
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ꢁ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2013, 19, 13445 – 13462

Alkaline Earth and Divalent Rare Earth Complexes
FULL PAPER
5 ppm) for catalyst loading. NMR spectra were recorded on Bruker AC-
300, AC-400 and AM-500 spectrometers. All chemicals shifts were deter-
mined using residual signals of the deuterated solvents. Assignment of
the signals was carried out using 1D (1H, 13C{1H}) and 2D (COSY,
HMBC, HMQC) NMR experiments. Elemental analyses were performed
on a Carlo Erba 1108 Elemental Analyser instrument at the London
Metropolitan University by Stephen Boyer and were the average of a
minimum of two independent measurements. CaI2, SrI2, BaI2 (anhydrous
beads, 99.995%) were purchased from Aldrich and used as received. Yt-
terbium and europium was purchased from Strem. HN(SiMe3)2 (Acros)
was dried over activated 3 ꢂ molecular sieves and distilled under reduced
pressure prior to use. [YbI2(thf)2] and [EuI2(thf)2] were synthesized ac-
cording to the literature.[57] Styrene, 4-chlorostyrene, 4-methoxystyrene,
4-methylstyrene, 4-tert-butylstyrene, 4-trifluoromethylstyrene, 2-vinylpyri-
dine, isoprene, pyrrolidine, a-methylstyrene, and myrcene were pur-
chased from Aldrich, Acros or ABCR. All were vacuum-distilled over
CaH2 and then were degassed by freeze-pump-thaw methods. Diphenyl-
phosphine and dicyclohexylphosphine were purchased from Aldrich and
used as received. THF was distilled under argon from Na/benzophenone
prior to use. Other solvents (pentane, toluene, dichloromethane, Et2O)
were collected from MBraun SPS-800 purification alumina columns. Deu-
terated solvents (Eurisotop, Saclay, France) were stored in sealed am-
poules over 3 ꢂ molecular sieves and degassed by several freeze-thaw
cycles. [{N^N}Ae{N(SiMe3)2}(thf)] (1–3), [{BDI}Ca{N(SiMe3)2}(thf)] (6),
[{BDI}YbII{N(SiMe3)2}(thf)] (7), and KCH(SiMe3)2, were synthesized ac-
cording to published procedures.[15,20,26,58]
70%) as a yellow solid. 1H NMR (C6D6, 298 K, 500.13 MHz): d=8.02 (s,
1H; CH=N), 7.31 (d, 3JHH =7.0 Hz, 2H; NC6H3), 7.27 (t, 3JHH =6.9 Hz,
3
1H; NC6H3), 7.16 (overlapping signals, 3H; NC6H3), 7.00 (d, JHH
=
3
7.7 Hz, 1H; C6H4), 6.82 (t, 3JHH =7.8 Hz, 1H; C6H4), 6.27 (d, JHH
=
8.9 Hz, 1H; C6H4), 6.24 (t, 3JHH =7.3 Hz, 1H; C6H4), 3.46 (brm, 4H;
OCH2CH2), 3.25 (m, 2H; CH(CH3)2), 3.10 (m, 2H; CH(CH3)2), 1.35 (d,
3JHH =6.8 Hz, 6H; CH(CH3)2), 1.34 (d, 3JHH =6.6 Hz, 6H; CH(CH3)2),
1.18 (d, 3JHH =6.7 Hz, 6H; CH(CH3)2), 1.13 (d, 3JHH =6.8 Hz, 6H;
CH(CH3)2), 1.10 (brm, 4H; OCH2CH2), ꢀ0.01 (s, 18H; CH(Si(CH3)3)2),
ꢀ1.84 ppm (s, 1H; CH(Si(CH3)3)2); 13C{1H} NMR (C6D6, 298 K,
125.76 MHz): d=172.3 (CH=N), 160.1 (i-N=CHC6H4), 149.6 (i-NC6H3),
146.5 (i-NC6H3), 144.3 (o-NC6H3), 141.1 (o-NC6H3), 139.3 (C6H4), 134.1
(C6H4), 127.0 (p-NC6H3), 125.6 (m-NC6H3), 125.5 (p-NC6H3), 124.8 (m-
NC6H3), 119.5 (C6H4), 117.0 (NC6H4), 112.4 (C6H4), 70.0 (OCH2CH2),
29.6 (CH(CH3)2), 29.0 (CH(CH3)2), 26.3 (CH(CH3)2), 26.1 (CH(CH3)2),
25.7 (CH(CH3)2), 25.3 (OCH2CH2), 23.5 (CH(CH3)2), 14.8
(CH(Si(CH3)3)2), 6.3 ppm (CH(Si(CH3)3)2); elemental analysis (%) calcd
for C42H66N2OSi2Ca (711.24 gmolꢀ1): C 70.93, H 9.35, N 3.94; found:
C 70.90, H 9.28, N 3.84.
[{N^N}Sr{CH(SiMe3)2}(thf)2] (9): Following a procedure similar to that
described for 8, the reaction of {N^N}H (0.63 g, 1.43 mmol) and
KCH(SiMe3)2 (0.57 g, 2.87 mmol) with SrI2 (0.50 g, 1.46 mmol) afforded 9
(0.73 g, 62%) as a yellow powder. Yellow crystals of 9·C5H12 suitable for
single-crystal X-ray crystallography were obtained overnight by storage
of a concentrated pentane solution at ꢀ308C. 1H NMR (C6D6, 298 K,
500.13 MHz): d=8.02 (s, 1H; CH=N), 7.29 (d, 3JHH =7.7 Hz, 2H;
NC6H3), 7.23 (t, 3JHH =7.2 Hz, 1H; NC6H3), 7.16 (overlapping signals,
[{N^N}Yb{N(SiMe3)2}(thf)] (4):
A
mixture of {N^N}H (0.21 g,
3
3
0.48 mmol) and KN(SiMe3)2 (0.19 g, 0.96 mmol) in THF (20 mL) was stir-
red at room temperature. After 1 h, it was added to a suspension of
[YbI2(thf)2] (0.25 g, 0.50 mmol) in THF (10 mL). The reaction mixture
was vigorously stirred for 2.5 h. The solvent was then removed in vacuo
and the residue was extracted with pentane (50 mL). Filtration followed
by evaporation of the volatile components afforded a powder which was
dried under reduce pressure to give 4 as a dark purple powder (0.29 g,
68%). Dark purple crystals of 4 suitable for single-crystal X-ray crystal-
lography were obtained overnight by storage of a concentrated pentane
solution at ꢀ308C. 1H NMR (C6D6, 298 K, 500.13 MHz): d=8.17 (s, 1H;
CH=N), 7.27 (d, 3JHH =7.0 Hz, 2H; NC6H3), 7.21 (t, 3JHH =6.9 Hz, 1HM
NC6H3), 7.16 (overlapping signals, 3H; NC6H3), 7.06 (dd, 3JHH =7.9 Hz,
4JHH =1.6 Hz, 1H; C6H4), 6.90 (td, 3JHH =7.8 Hz, 4JHH =1.7 Hz, 1H;
C6H4), 6.31 (d, 3JHH =8.8 Hz, 1H; C6H4), 6.25 (t, 3JHH =6.8 Hz, 1H;
C6H4), 3.33 (overlapping m, 4H; OCH2CH2, and 4H; CH(CH3)2), 1.36
3H; NC6H3), 7.04 (d, JHH =8.1 Hz, 1H; C6H4), 6.86 (t, JHH =8.5 Hz, 1H;
C6H4), 6.25 (overlapping m, 1H; C6H4 and 1H; C6H4), 3.43 (brm, 8H;
OCH2CH2), 3.28 (m, 2H: CH(CH3)2), 3.09 (m, 2H; CH(CH3)2), 1.31 (m,
3
12H; CH(CH3)2), 1.25 (brm, 8H; OCH2CH2), 1.20 (d, JHH =6.7 Hz, 6H;
CH(CH3)2), 1.15 (d, 3JHH =6.6 Hz, 6H; CH(CH3)2), 0.02 (s, 18H;
CH(Si(CH3)3)2), ꢀ1.84 ppm (s, 1H; CH(Si(CH3)3)2); 13C{1H} NMR (C6D6,
298 K, 125.76 MHz): d=171.1 (CH=N), 159.3 (i-N=CHC6H4), 149.7 (i-
NC6H3), 146.2 (i-NC6H3), 144.3 (o-NC6H3), 141.0 (o-NC6H3), 139.6
(C6H4), 134.0 (C6H4), 126.6 (p-NC6H3), 125.8 (m-NC6H3), 125.2 (p-
NC6H3), 124.8 (m-NC6H3), 118.9 (C6H4), 117.5 (NC6H4), 111.7 (C6H4),
68.8 (OCH2CH2), 29.5 (CH(CH3)2), 28.9 (CH(CH3)2), 26.4 (CH(CH3)2),
26.2 (CH(CH3)2), 25.9 (CH(CH3)2), 25.8 (OCH2CH2), 23.7 (CH(CH3)2),
14.7 (CH(Si(CH3)3)2), 6.4 ppm (CH(Si(CH3)3)2); elemental analysis calcd
(%) for C46H74N2O2Si2Sr (830.88 gmolꢀ1): C 66.49, H 8.98, N 3.37; found:
C 66.52, H 8.92, N 3.38.
3
3
(d, JHH =6.2 Hz, 6H; CH(CH3)2), 1.35 (d, JHH =6.2 Hz, 6H; CH(CH3)2),
1.20 (d, 3JHH =6.7 Hz, 6H; CH(CH3)2), 1.17 (d, 3JHH =6.7 Hz, 6H;
CH(CH3)2), 1.07 (brm, 4H; OCH2CH2), 0.07 ppm (s, 18H; Si(CH3)3).
13C{1H} NMR (C6D6, 298 K, 125.76 MHz): d=171.0 (CH=N), 160.1 (i-N=
CHC6H4), 149.6 (i-NC6H3), 147.8 (i-NC6H3), 144.2 (o-NC6H3), 141.4 (o-
NC6H3), 138.9 (C6H4), 133.8 (C6H4), 126.8 (p-NC6H3), 125.5 (m-NC6H3),
124.9 (p-NC6H3), 124.8 (m-NC6H3), 120.7 (C6H4), 118.4 (i-NC6H4), 112.8
(C6H4), 70.1 (OCH2CH2), 29.4 (CH(CH3)2), 29.0 (CH(CH3)2), 26.5
(CH(CH3)2), 26.3 (CH(CH3)2), 25.7 (CH(CH3)2), 25.5 (OCH2CH2), 23.9
(CH(CH3)2), 6.1 ppm (Si(CH3)3); elemental analysis calcd (%) for
C41H65N3OSi2Yb (845.18 gmolꢀ1): C 58.26, H 7.75, N 4.97; found: C 58.20,
H 7.80, N 4.85.
[{N^N}Ba{CH(SiMe3)2}(thf)2] (10): Following a procedure similar to that
described for 8, the reaction of {N^N}H (0.39 g, 0.88 mmol) and
KCH(SiMe3)2 (0.35 g, 1.77 mmol) with BaI2 (0.35 g, 0.90 mmol) afforded
10 (0.41 g, 52%) as a yellow powder. Yellow crystals of 10 suitable for
single-crystal X-ray crystallography were obtained by storage of a con-
centrated pentane solution at ꢀ308C. 1H NMR (C6D6, 298 K,
500.13 MHz): d=8.06 (s, 1H; CH=N), 7.27 (d, 3JHH =7.4 Hz, 2H;
NC6H3), 7.18 (t, 3JHH =6.6 Hz, 1H; NC6H3), 7.16 (overlapping signals,
3H; NC6H3), 7.10 (dd, 3JHH =7.9 Hz, 4JHH =1.8 Hz, 1H; C6H4), 6.91 (td,
4
3JHH =7.7 Hz, 4JHH =1.8 Hz, 1H; C6H4), 6.27 (td, 3JHH =7.3 Hz, JHH
=
1.1 Hz, 1H; C6H4), 6.19 (d, 3JHH =8.8 Hz, 1H; C6H4), 3.43 (overlapping
m, 8H; OCH2CH2 and 2H; CH(CH3)2), 3.12 (m, 2H; CH(CH3)2), 1.33
(d, 3JHH =6.7 Hz, 6H; CH(CH3)2), 1.27 (overlapping m, 8H; OCH2CH2
and 6H; CH(CH3)2), 1.21 (d, 3JHH =6.7 Hz, 6H; CH(CH3)2), 1.16 (d,
3JHH =6.3 Hz, 6H; CH(CH3)2), 0.08 (s, 18H; CH(Si(CH3)3)2), ꢀ1.78 ppm
(s, 1H; CH(Si(CH3)3)2); 13C{1H} NMR (C6D6, 298 K, 125.76 MHz): d=
169.2 (CH=N), 157.8 (i-N=CHC6H4), 149.5 (i-NC6H3), 145.9 (i-NC6H3),
144.8 (o-NC6H3), 141.0 (o-NC6H3), 139.5 (C6H4), 134.3 (C6H4), 126.3 (p-
NC6H3), 125.9 (m-NC6H3), 125.0 (p-NC6H3), 124.9 (m-NC6H3), 118.5
(C6H4), 111.5 (NC6H4), 111.4 (C6H4), 68.5 (OCH2CH2), 29.5 (CH(CH3)2),
28.8 (CH(CH3)2), 26.6 (CH(CH3)2), 26.2 (CH(CH3)2), 25.9 (CH(CH3)2),
25.7 (OCH2CH2), 23.8(CH(CH3)2), 14.7 (CH(Si(CH3)3)2), 6.3 ppm
(CH(Si(CH3)3)2); elemental analysis calcd (%) for C46H74N2O2Si2Ba
(880.55 gmolꢀ1): C 62.74, H 8.47, N 3.18; found: C 62.58, H 8.56, N 3.10.
[{N^N}Eu{N(SiMe3)2}(thf)2] (5): Following a procedure similar to that
described above for 4, the reaction of {N^N}H (0.15 g, 0.34 mmol),
KN(SiMe3)2 (0.14 g, 0.70 mmol), and [EuI2(thf)2] (0.20 g, 0.36 mmol) af-
forded 5 (0.18 g, 60%) as a dark red powder. Single crystals of 5 were
grown from a pentane solution at ꢀ308C. Elemental analysis calcd (%)
for C45H73N3O2Si2Eu (896.22 gmolꢀ1): C 60.31, H 8.21, N 4.69: found:
C 60.20, H 8.24, N 4.70.
[{N^N}Ca{CH(SiMe3)2}(thf)] (8): THF (20 mL) was added to a mixture
of {N^N}H (0.76 g, 1.73 mmol) and KCH(SiMe3)2 (0.69 g, 3.48 mmol).
The reaction mixture was stirred at room temperature for 1 h, and was
then added to a suspension of CaI2 (0.52 g, 1.77 mmol) in THF (20 mL).
After stirring at room temperature for 2.5 h, the solvent was pumped off
under vacuum and the residue was extracted with pentane (50 mL).
After filtration, the volatiles were removed in vacuo to afford 8 (0.86 g,
NMR monitoring of cyclohydroamination reactions: In a glovebox, the
catalyst was loaded into an NMR tube. The subsequent manipulations
Chem. Eur. J. 2013, 19, 13445 – 13462
ꢁ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
13459

J.-F. Carpentier, Y. Sarazin et al.
were performed using standard Schlenk techniques. The substrate and
solvent (C6D6, (0.6 or 1.2 mL as required) were then added to the NMR
tube. The tube was sealed and vigorously shaken, then inserted into the
probe of a Bruker AM 500 NMR spectrometer preheated to the required
temperature. The reaction kinetics were monitored (using the multi zgvd
command; D1=0.2 s; DS=0; NS=4 or more) over the course of 3 or
more half-lives on the basis of amine consumption, by comparing the rel-
ative intensities of resonances diagnostic of substrate and product.
1990, 1701; b) D. K. Wicht, I. V. Kourkine, B. M. Lew, J. Mulei N-
thenge, D. S. Glueck, J. Am. Chem. Soc. 1997, 119, 5039; c) D. K.
Wicht, I. V. Kourkine, I. Kovacik, D. S. Glueck, Organometallics
1999, 18, 5381; d) M. O. Shulyupin, M. A. Kazankova, I. P. Belet-
skaya, Org. Lett. 2002, 4, 761.
[6] For a case of titanium-catalyzed 1,4-hydrophosphination of 1,3-
dienes: A. Perrier, V. Comte, C. Moꢇse, P. Le Gendre, Chem. Eur. J.
2010, 16, 64.
[7] a) M. R. Douglass, T. J. Marks, J. Am. Chem. Soc. 2000, 122, 1824;
b) M. R. Douglass, C. L. Stern, T. J. Marks, J. Am. Chem. Soc. 2001,
123, 10221; c) M. R. Douglass, M. Ogasawara, S. Hong, M. V. Metz,
T. J. Marks, Organometallics 2002, 21, 283.
[8] Cyclohydroamination of aminoalkenes: a) M. R. Gagnꢀ, T. J. Marks,
J. Am. Chem. Soc. 1989, 111, 4108; b) M. R. Gagnꢀ, S. P. Nolan, T. J.
Marks, Organometallics 1990, 9, 1716; c) M. R. Gagnꢀ, T. J. Marks,
J. Am. Chem. Soc. 1992, 114, 275; d) M. A. Giardello, V. P. Conticel-
lo, L. Brard, M. R. Gagnꢀ, T. J. Marks, J. Am. Chem. Soc. 1994, 116,
10241; e) J.-S. Ryu, T. J. Marks, F. E. McDonald, Org. Lett. 2001, 3,
3091.
Typical protocol for intermolecular hydrofunctionalization reactions: In
the glovebox, the catalyst (10 mmol) was loaded into an NMR tube. The
subsequent manipulations were performed using standard Schlenk techni-
ques. Styrene (58 mL, 500 mmol) and diphenylphosphine (87 mL,
500 mmol) were added to the NMR tube using microsyringes. The NMR
tube was sealed and shaken vigorously, then put into an oil bath at 608C.
The reaction times were measured from this point. After the required
amount of time, the reaction was quenched and C6D6 was added to the
mixture at room temperature. The conversion was determined according
1
to the H NMR spectrum of the reaction mixture.
X-ray diffraction crystallography: Suitable crystals for X-ray diffraction
analysis of 2’, 4–5, 7, 9·C5H12, and 10 were obtained by recrystallization
of the purified compounds. Diffraction data were collected at 150(2) K
using a Bruker APEX CCD diffractometer with graphite-monochromat-
ed MoKa radiation (l=0.71073 ꢂ). A combination of w and F scans was
carried out to obtain at least a unique data set. The crystal structures
were solved by direct methods, remaining atoms were located from dif-
ference Fourier synthesis followed by full-matrix least-squares refinement
based on F2 (programs SIR97 and SHELXL-97).[59] Many hydrogen
atoms could be found from the Fourier difference analysis. Carbon- and
oxygen-bound hydrogen atoms were placed at calculated positions and
forced to ride on the attached atom. The hydrogen atom contributions
were calculated but not refined. All non-hydrogen atoms were refined
with anisotropic displacement parameters. The locations of the largest
signals in the final difference Fourier map calculation as well as the mag-
nitude of the residual electron densities were of no chemical significance.
Relevant collection and refinement data are summarized in the Support-
ing Information (S42).[60]
[9] Intermolecular hydroamination of alkenes: a) Y. Li, T. J. Marks, Or-
ganometallics 1996, 15, 3770; b) J.-S. Ryu, G. Y. Li, T. J. Marks, J.
Am. Chem. Soc. 2003, 125, 12584.
[10] For reviews, see references [2a], [2c] and: a) I. Aillaud, J. Collin, J.
Hannedouche, E. Schulz, Dalton Trans. 2007, 5105; b) J. Hannedou-
che, J. Collin, A. Trifonov, E. Schulz, J. Organomet. Chem. 2011,
696, 255. For key contributions, see: c) P. J. Walsh, A. M. Baranger,
R. G. Bergman, J. Am. Chem. Soc. 1992, 114, 1708; d) P. L.
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CCDC-918568 (2’), -918569 (4), -918570 (5), -918571 (7), -918572
(9)·C5H12, -918573 (10), contain the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif.
Acknowledgements
We thank the European Research Council (grant FP7-People-2010-IIF
ChemCatSusDe), the CNRS and the University of Rennes 1 for financial
support. The assistance of Stephen Boyer (London Metropolitan Univer-
sity) with elemental analyses and Dr. Vincent Dorcet (Institut des Scien-
ces Chimiques de Rennes) with the X-ray structure of complex 7 is also
gratefully acknowledged.
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Chem. Eur. J. 2013, 19, 13445 – 13462

Alkaline Earth and Divalent Rare Earth Complexes
FULL PAPER
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ꢂ
ꢀ
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ꢂ
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ꢀ
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bis(phosphinimino)methanide complex [({(Me3SiNPPh2)2CH}BaI-
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tion times (60–120 min) could not be performed with 10 in the way
it was done for 3 due to the ability of the former to promote the
Chem. Eur. J. 2013, 19, 13445 – 13462
ꢁ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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13461

J.-F. Carpentier, Y. Sarazin et al.
polymerization of styrene, even at room temperature. For the Ae-
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quantitative Hammett investigation could not be carried out owing
to experimental constraints. The observed trend CF3 >Cl>H>
Me>tBu>OMe is compatible with the proposed mechanism. Yet
caution must be paid in the global interpretation of these data as
more than one step involves styrenics in this scenario, including
binding to the metal center which should be disfavored by electron-
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phosphines with respect to amines/aminoalkenes. The protonolysis
of the Ae-amide bond in 1–3 will be shifted more towards the for-
mation of the catalytically active species with HPPh2 than with an
amine (Scheme 2 and 4), whereas the difference between the two
substrates will not be obvious with the very basic Ae-alkyl 8–10.
Consistent with this, the 1H NMR monitoring of the hydrophosphi-
nation of styrene derivatives with HPPh2 catalyzed by 3 and 10 indi-
cated quantitative release of HN(SiMe3)2 and CH2(SiMe3)2, respec-
tively.
[55] The lanthanide-catalyzed cyclohydrophosphination of phosphinoal-
kenes proceeded with the following rate-law:
RCHP =k[substra-
[49] Reaction conditions: T=608C, solvent C6D6, [precatalyst]0/[styr-
ene]0/[HPPh2]0 =1:80:8, precatalyst: 10.0 mmol, total volume C6D6 +
styrene+HPPh2 =0.6 mL.
[50] The studies could not be extended to the paramagnetic 5, nor to the
alkyl complexes 9–10 which catalyzed these reactions too rapidly for
accurate measurements.
te]0[precatalyst]1, see reference [7].
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[51] The activation energy determined for the hydrophosphination of p-
Cl-styrene catalyzed by 3, Ea =24.1(1.3) kJmolꢀ1, was smaller than
that determined for styrene under identical conditions (Ea =
34.2(2.4) kJmolꢀ1, Table 6, entry 3). Reactions with p-Me-styrene in
C6D6 were too slow to be monitored below 808C, but the following
values of kapp were determined: 1.37ꢅ10ꢀ4 (p-Me-styrene, 808C),
9.51ꢅ10ꢀ4 (styrene, 708C) and 11.27ꢅ10ꢀ4 sꢀ1 (p-Cl-styrene, 708C).
Apart from the temperature, all other parameters remained identi-
cal between the three experiments, which therefore further support-
ed the reactivity trend Cl>H>Me in para-substituted styrene deriv-
atives.
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Crystal Structures; University of Goettingen: Germany, 1997;
b) G. M. Sheldrick, SHELXL-97, Program for the Refinement of
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[60] CIF files containing complete crystallographic data for all reported
crystal structures, figures of X-ray structures of additional com-
pounds, summary of crystallographic data for complexes 2’, 4, 5, 7,
9·C5H12, and 10, detailed kinetic data for hydroelementation reac-
tions, NMR data for isolated new tertiary phosphines are contained
in the Supporting Information (32 pages).
[52] J.-N. Li, L. Liu, Y. Fu, Q.-X. Guo, Tetrahedron 2006, 62, 4453 and
references therein.
Received: April 17, 2013
Published online: August 19, 2013
13462
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Chem. Eur. J. 2013, 19, 13445 – 13462