Metalation and transmetalation studies on Ph2PN( iPr)P(Ph)N(iPr)H for selective ethene trimerization to 1-hexene

Article abstract of DOI:10.1021/om100371f

Different organometallic compounds of the new aminodiphosphinoamine ligand Ph₂PN(ⁱPr)P(Ph)N(ⁱPr)-H (1) are reported that are relevant model complexes for the selective ethene trimerization system consisting of ligand 1, Cr

Full text of DOI:10.1021/om100371f

Organometallics 2010, 29, 5263–5268 5263
DOI: 10.1021/om100371f
Metalation and Transmetalation Studies on Ph2PN(iPr)P(Ph)N(iPr)H
for Selective Ethene Trimerization to 1-Hexene^
†
Stephan Peitz, Normen Peulecke, Bhaskar R. Aluri, Bernd H. Muller,
†
†
†
€
Anke Spannenberg,† Uwe Rosenthal,*,† Mohammed H. Al-Hazmi,‡ Fuad M. Mosa,‡
§
Anina Wohl, and Wolfgang Muller*
,§
€
€
†
€
Leibniz-Institut fu€r Katalyse an der Universitat Rostock e.V., Albert-Einstein-Strasse 29 A, D-18059
Rostock, Germany, ‡Saudi Basic Industries Corporation, P.O. Box 42503, Riyadh 11551, Saudi Arabia, and
§Linde AG, Linde Engineering Division, Dr.-Carl-von-Linde-Strasse 6-14, D-82049 Pullach, Germany
Received April 29, 2010
Different organometallic compounds of the new aminodiphosphinoamine ligand Ph2PN(iPr)P(Ph)-
N(iPr)-H (1) are reported that are relevant model complexes for the selective ethene trimerization
system consisting of ligand 1, CrCl3(THF)3, and Et3Al that produces 1-hexene in more than 90% yield
and high purity. The lithiation of 1 by n-BuLi in the presence of tetramethylethylenediamine (tmeda)
yields the mononuclear compound Ph2PN(iPr)P(Ph)N(iPr)-][Li(tmeda)] (2). Without using tmeda the
dinuclearspecies[Ph2N(iPr)P(Ph)N(iPr)-Li]2 (3) was obtained. Byaddition ofaGrignardreagent tothe
ligand solution the bis(aminodiphosphinoamide)magnesium complex [Ph2PN(iPr)P(Ph)N(iPr)-]2Mg
(4) could be isolated. Reaction of Li[CpCrCl3] with 3 leads to the formation of the model compound
CpCrCl[-N(iPr)P(Ph)N(iPr)PPh2] (5), which can be alkylated with Na[Et4Al] to form the correspond-
ing ethyl compound CpCrEt[-N(iPr)P(Ph)N(iPr)PPh2] (7). In THF the formation of EtCrCl2(THF)3
(8) directly from the reaction of CrCl3[Ph2PN(iPr)P(Ph)N(iPr)-H](THF) (6) with Et3Al could be
observed. The organometallic chemistry of 1 gives hints on possible species and activation mechanisms
in the catalysis, which have to be considered for a better understanding of the catalytic system.
Introduction
recently published.4-6 Additionally, the coordination behavior
of this ligand was examined.7
In the last years industrial as well as academic research
groups increased their activities in developing and improv-
ing novel on-purpose routes to 1-hexene and 1-octene. The
main focus lies on homogeneous chromium-based catalyst
systems.1,2 An important ligand class examined is based on
mixed P and N donors.1-3
We also work in this field toward developing a new type of
P,N donor ligand. First results of the new homogeneous
chromium-based trimerization catalyst for ethene to 1-hexene,
including detailed kinetic experiments and modeling, were very
Here we describe the characteristics of this compound in
organometallic reactions in more detail. Metalation and
transmetalation model reactions that could occur under
catalytic conditions were studied to gain a better under-
standing of the behavior and reactivity of this type of
aminophosphorus ligand in the catalytic system. That is of
great importance to understand the organometallic back-
ground leading to the outstanding catalytic selectivity to
1-hexene exhibited by this new ligand class.
Depending on the desired variation of substituents, the
synthesis of the ligand type can be carried out in two different
ways (Scheme 1, a and b). Inaddition, the Ph2P N(iPr)P(Ph)Cl
fragment of synthesis b (Scheme 1) can be used to immobilize
the ligand on amino-functionalized styrene resins. Thus, ad-
vantages of homogeneous and heterogeneous catalysis can
be merged.8
^ Dedicated to Professor Dietmar Seyferth in honor of his outstanding
service as Editor-in-Chief of Organometallics. Part of the Dietmar Seyferth
Festschrift.
*To whom correspondence should be addressed. E-mail: Uwe.
rosenthal@catalysis.de; Wolfgang.mueller@linde-le.com.
(1) Dixon, J. T.; Green, M. J.; Hess, F. M.; Morgen, D. H. J. Organomet.
Chem. 2004, 689, 3641–3668.
(2) Bollmann, A.; Blann, K.; Dixon, J. T.; Hess, F. M.; Killian, E.;
Maumela, H.; McGuinness, D. S.; Morgan, D. H.; Neveling, A.; Otto,
S.; Overett, M.; Slawin, A. M. Z.; Wasserscheid, P.; Kuhlmann, S. J. Am.
Chem. Soc. 2004, 126, 14712–14713.
€
(6) (a) Wohl, A.; Muller, W.; Peitz, S.; Peulecke, N.; Aluri, B. R.;
Muller, B. H.; Heller, D.; Rosenthal, U.; Al-Hazmi, M. H.; Mosa, F. M.
€
€
Chem.-Eur. J. 2010, DOI: 10.1002/chem.201000533. (b) M€uller, W.;
€
€
€
€
(3) Wohl, A.; Muller, W.; Peulecke, N.; Muller, B. H.; Peitz, S.;
Wohl, A.; Peitz, S.; Peulecke, N.; Aluri, B. R.; M€uller, B. H.; Heller, D.;
Heller, D.; Rosenthal, U. J. Mol. Catal. A 2009, 297, 1–8.
Rosenthal, U.; Al-Hazmi, H. H.; Mosa, F. M. ChemCatChem 2010,
accepted.
€
(7) Aluri, B. R.; Peulecke, N.; Peitz, S.; Spannenberg, A.; Muller, B.
H.; Schulz, S.; Drexler, H.-J.; Heller, D.; Al-Hazmi, M. H.; Mosa, F. M.;
€
€
A. Wohl, W. Muller, Rosenthal, U. Dalton Trans. 2010, accepted.
€
€
(4) Fritz, P. M.; Bolt, H.; Wohl, A.; Muller, W.; Winkler, F.;
Wellenhofer, A.; Rosenthal, U.; Hapke, M.; Peulecke, N.; Muller,
€
€
B. H.; Al-Hazmi, M. H.; Aliyev, V. O.; Mosa, F. M. (Linde AG/SABIC),
WO 2009/006979-A2, 2009.
(5) Peitz, S.; Peulecke, N.; Aluri, B. R.; Hansen, S.; Muller, B. H.;
€
Spannenberg, A.; Rosenthal, U.; Al-Hazmi, M. H.; Mosa, F. M.; Wohl,
€
(8) Peulecke, N.; Muller, B. H.; Peitz, S.; Aluri, B. R.; Rosenthal, U.;
€
€
€
Wohl, A.; Muller, B. H.; Al-Hazmi, M. H.; Mosa, F. M. ChemCatChem
2010, DOI:10.1002/cctc.201000087.
€
A.; Muller, W. Eur. J. Inorg. Chem. 2010, 1167–1171.
r
2010 American Chemical Society
Published on Web 06/16/2010
pubs.acs.org/Organometallics

5264 Organometallics, Vol. 29, No. 21, 2010
Peitz et al.
Scheme 1. Different methods (a and b) for synthesizing
Ph2PN(iPr)P(Ph)N(iPr)H5
Figure 1. Molecular structure of [Ph2PN(iPr)P(Ph)N(iPr)-][Li-
(tmeda)] (2) with thermal ellipsoids set at 30% probability.
All hydrogen atoms have been omitted for clarity. Important
Scheme 2. Metalation of Ph2PN(iPr)P(Ph)N(iPr)H (1) with
n-BuLi to Give [Ph2PN(iPr)P(Ph)N(iPr)-][Li(tmeda)] (2)
˚
bond lengths [A] and angles [deg]: N1-P1 1.6411(13), P1-N2
1.7709(11), N2-P2 1.6850(12), N1-Li1 1.973(3), P2-Li1
2.774(3), N2-P1-N1 107.89(6), P2-N2-P1 117.77(7), P2-
Li1-N1 84.96(10).
Results and Discussion
This work in addition to a short communication5 describes
in detail metalation and transmetalation of a novel amino-
diphosphinoamine compound. The ligand is characterized
by a R2PN(R)P(R)N(R)H backbone (PNPN-H), which, in
conjunction with a chromium compound and a suitable
aluminum-alkyl activator, leads to a selective trimerization
catalyst system that produces comonomer grade 1-hexene in
more than 90% yield.4-6
An important aspect, regarding the elucidation of the cata-
lytically active site, deals with the question of what kind of
alteration the ligand undergoes in the catalytic system, where,
due to its high complexity, several organometallic reactions
could occur. It could be shown that, besides the usage of chro-
mium as metal, the PNPN structure and in particular the ter-
minal secondary amine function are crucial for C6 selectivity.
Ph2PN(iPr)P(Ph)NR2 (R = Me, Et, iPr) as a ligand without
the NH group, in combination with CrCl3(THF)3 and Et3Al,
shows nearly no catalytic activity for ethylene trimerization
(for R = Me, mainly PE production beside very low 1-hexene
production; R = Et, low 1-hexene production of about 1 kg/
Figure 2. Molecular structure of [Ph2PN(iPr)P(Ph)N(iPr)-Li]2
(3) with thermal ellipsoids set at 30% probability. All hydrogen
˚
atoms have been omitted for clarity. Important bond lengths [A]
and angles [deg]: N1-P1 1.6612(11), P1-N2 1.7783(10), N2-P2
1.6882(10), N1-Li12.049(2), P2-Li1 2.587(2), N1-Li1A 2.023(2),
Li1-Li1A 2.362(4), N2-P1-N1 110.00(5), P2-N2-P1 120.32(6),
P2-Li1-N1 88.66(8), Li1-N1-Li1A 70.92(11), N1-Li1-N1A
109.08(11).
ligand. Thus, the planar rhombic motif Li-N-Li-N is for-
med. Interestingly, in complex 3 the P2-Li1 bond length is
shortened significantly by ca. 0.2 A compared to 2, whereas
(gCr h); R = iPr, no activity at all).5
3
˚
First hints for a deprotonation of the ligand’s amine
function, which is most likely under catalytic conditions,5,6
are given by the lithiation of 1 with n-BuLi in the presence
of tetramethylethylenediamine (tmeda), giving [Ph2PN(iPr)-
P(Ph)N(iPr)-][Li(tmeda)] (2) (Scheme 2), which could be
crystallized from a mixture of diethyl ether and hexane.
The molecular structure of 2 is depicted in Figure 1. The
terminal amide function forms a covalent bond with the
metal, and P2 acts as a donor to give a chelating [PNPN]-
fragment at the lithium ion.
˚
the N1-Li1 bond is elongated by approximately 0.06 A. A
similar dinuclear Li-N-Li-N motif from amidophosphine
ligands is already known from Bauer et al., who reported
on a comparable deprotonation of aminophosphines with
n-BuLi.9 This provided a dimeric Li amidophosphine [tBuP-
(NH-tBu)N(tBu)-Li]2 that has similar Li-amide bond lengths
˚
of 1.997(4), 2.098(4), 2.096(4), and 2.012(4) A, respectively,
˚
compared to 3 (N1-Li1 2.049(2), N1-Li1A 2.023(2) A).
The distance between both Li cations is, at Li1-Li1A =
2.362(4) A, in 3 a little bit longer than in Bauer’s molecule
˚
Without using tmeda in the reaction mixture the dinuclear
species [Ph2N(iPr)P(Ph)N(iPr)-Li]2 (3) as another Li-amide
on the basis of the ligand (Figure 2) was formed.
In complex 3 again a covalent amide bond and a coordi-
native bond of the terminal phosphorus atom to the metal
center are observed. Additionally, a dinuclear motif is present
and each amide function coordinates not only to one lithium
but also to a second ion that already bears a deprotonated
˚
(Li1-Li2 = 2.296(5) A). This is most likely due to steric rea-
sons because in 3 a larger bite angle (88.66(8)ꢀ versus 78.9(2)ꢀ)
is observed for the angle donor-Li-amide caused by the
elongated ligand backbone in 3.
(9) Bauer, T.; Schulz, S.; Nieger, M.; Kessler, U. Organometallics
2003, 22, 3134–3142.

Article
Organometallics, Vol. 29, No. 21, 2010 5265
Scheme 4. Schlenk Equilibrium Including
[Ph2PN(iPr)P(Ph)N(iPr)]2Mg (4)
Scheme 5. Formation of CpCrCl[-N(iPr)P(Ph)N(iPr)PPh2] (5)5
by Transmetalation of 3 and Formation of CpCrEt[-N(iPr)-
P(Ph)N(iPr)PPh2] (7) by Subsequent Alkylation
Figure 3. Molecular structure of [Ph2PN(iPr)P(Ph)N(iPr)-]2Mg
(4) with thermal ellipsoids set at 30% probability. All hydrogen
˚
atoms have been omitted for clarity. Important bond lengths [A]
and angles [deg]: Mg1-N1 1.998(2), Mg1-N3 2.005(2), Mg1-P2
2.7470(11), Mg1-P4 2.7126(11), N1-P1 1.666(2), N2-P1
1.762(2), N2-P2 1.676(2), N3-P3 1.662(3), N4-P3 1.765(2),
N4-P4 1.675(2), N1-P1-N2 105.10(11), N3-P3-N4
106.45(11), P2-N2-P1 117.29(13), P4-N4-P3 115.42(13),
N1-Mg1-P2 79.35(7), N3-Mg1-P4 79.50(7), N1-Mg1-N3
141.17(10).
Similar to 4 a magnesium complex containing two amido-
phosphine ligands is known in the literature. Chivers et al.10
published the compound [Mg-{(NtBu)(NSiMe3)P(NHtBu)2}2],
which has a quite similar backbone compared to Bauer’s mole-
Scheme 3. Metalation of Ph2PN(iPr)P(Ph)N(iPr)-H (1) with
iBuMgCl to Give [Ph2PN(iPr)P(Ph)N(iPr)-]2Mg (4)
t
˚
cule. Chiver’s complex has a Mg-N Bu bond (2.059(2) A) that
˚
is ca. 0.06 A longer than that of 4, most likely due to steric rea-
sons. The bite angle of [Mg-{(NtBu)(NSiMe3)P(NHtBu)2}2] is,
at 72.4(1)ꢀ, smaller compared to 4 (79.35(7)ꢀ and 79.50(7)ꢀ,
respectively), which can be attributed to the elongated ligand
backbone in 4.
Reactions of the aforementioned isolated and characte-
rized main group element amides 2, 3, and 4 of the PNPN-H
ligand with CrCl3(THF)3, the preferred chromium salt in
catalysis,5,6 were not successful so far in terms of isolating
defined complexes.
Switching to magnesium organic compounds in the reac-
tion with 1, a different coordination sphere around the metal
can be achieved. By addition of the Grignard reagent iso-
butylmagnesium chloride to the ligand solution the magne-
sium complex [Ph2PN(iPr)P(Ph)N(iPr)-]2Mg (4) could be
isolated (Scheme 3). Few crystals of the compound could
be grown from Et2O (Figure 3). The molecular structure
reveals a Mg center coordinated by two deprotonated
ligands in a distorted tetrahedral conformation. 31P NMR
investigations of these crystals show two triplets. This could
be due to coupling of the phosphorus atoms via the metal,
resulting in overlapping doublets of doublets.
As can be seen in Scheme 5, if Li[CpCrCl3]11 is used instead
of CrCl3(THF)3 in the reaction with [Ph2N(iPr)P(Ph)N(iPr)-Li]2
(3), transmetalation by elimination of two equivalents
of LiCl leads to the formation of the desired model com-
pound CpCrCl[-N(iPr)P(Ph)N(iPr)PPh2] (5).5 Its molecular
structure is depicted in Figure 4 and shows that this chro-
mium complex bears a chromium-amide bond that has
almost the same length as the Li-N bond in complex 2.
On the other hand, the Cr-Pterminal bond is shortened
˚
significantly by 0.26 A compared to the Li-Pterminal bond
The most material in this metalation reaction was obtained
as a powder. Interestingly, the elemental analysis of this
powder shows no exact correlation to the structure found by
crystal structure analysis. Instead, we assume also a complex
in 2. To the best of our knowledge only two CpCr-amidopho-
sphine complexes were described before. It was stated12a and
proved by X-ray analysis12b respectively that the complexes
contain chroma-heterocycles where both N and P are at-
tached to Cr.
of the kind {[Ph2PN(iPr)P(Ph)N(iPr)-]2Mg MgCl2} being
3
present in the powder. A Schlenk equilibrium, as depicted
in Scheme 4, could be the reason for this finding. Therefore,
compound 4, as represented by the crystal structure, seems to
be one species in a multicomponent mixture. The question
arises whether the powder contains species a, b, or a mixture
of 4 and MgCl2 (Scheme 4). To date, this could not fully
be evaluated. 31P NMR investigation of the powder reveals
two different species. One set of signals belongs to compound
4. The other signals represent a different species giving an
indication for the mentioned adduct.
In comparison to the chromium complex CrCl3[Ph2PN-
(iPr)P(Ph)N(iPr)-H](THF) (6)5 (Figure 5), which bears the
original ligand, the strong amide bond in 5 does not lead to
(10) Robertson, S. D.; Chivers, T.; Konu, J. J. Organomet. Chem.
2007, 692, 4327–4336.
(11) Arndt, P.; Kurras, E.; Otto, J. Z. Chem. 1983, 443–445.
(12) (a) Lindner, E.; Heckmann, M.; Fawzi, R.; Hiller, W. Chem. Ber.
1991, 124, 2171–2179. (b) Fryzuk, M. D.; Leznoff, D. B.; Rettig, S. J.
Organometallics 1995, 14, 5193–5202.

5266 Organometallics, Vol. 29, No. 21, 2010
Peitz et al.
Figure 6. Molecular structure of 7 with thermal ellipsoids set at
30% probability. The asymmetric unit contains two molecules, only
one is depicted. All hydrogen atoms have been omitted for clarity.
Figure 4. Molecular structure of 5 with thermal ellipsoids set
at 30% probability.5 All hydrogen atoms have been omitted
for clarity. Important bond lengths [A] and angles [deg]: N1-P1
1.6671(13), P1-N2 1.7558(14), N2-P2 1.6786(14), N1-Cr1
1.9650(13), P2-Cr1 2.5081(5), N2-P1-N1 102.74(7), P2-N2-
P1 118.08(7), P2-Cr1-N1 82.68(4).
˚
Important bond lengths [A] and angles [deg]: N1-P1 1.663(2), P1-
˚
N2 1.745(2), N2-P2 1.681(2), N1-Cr1 2.002(2), P2-Cr1 2.4822(7),
C30-Cr1 2.109(2), C30-C31 1.500(4), N2-P1-N1 102.71(9),
P2-N2-P1 117.60(11), P2-Cr1-N1 81.42(6), N1-Cr1-C30
99.27(9), C30-Cr1-P2 91.20(7), C31-C30-Cr1 118.7(2).
Figure 7. Molecular structure of EtCrCl2(THF)3 (8) with ther-
mal ellipsoids set at 30% probability. All hydrogen atoms have
˚
been omitted for clarity. Important bond lengths [A] and angles
Figure 5. Molecular structure of 6 with thermal ellipsoids set at
30% probability.5 The asymmetric unit contains (besides solvent
molecules) two molecules of 6; only one molecule is depicted.
Hydrogen atoms, except H1A, have been omitted for clarity.
[deg]: Cl1-Cr1 2.3281(5), Cl2-Cr1 2.3358(5), C13-Cr1 2.065
(2), C13-C14 1.507(3), Cr1-O3 2.0563(11), Cr1-O1 2.0604(11),
Cr1-O2 2.2220(13), O3-Cr1-O1 171.97(5), O3-Cr1-O285.42
(5), O1-Cr1-O2 86.63(5), O3-Cr1-Cl1 89.93(3), O1-Cr1-
Cl1 90.87(3), O2-Cr1-Cl1 88.11(4), O3-Cr1-Cl2 89.65(3),
O1-Cr1-Cl2 89.09(3), O2-Cr1-Cl2 88.62(4), Cl1-Cr1-Cl2
176.73(2), O1-Cr1-C13 95.49(6), C14-C13-Cr1 117.13(14).
˚
Selected bond lengths [A] and angles [deg]: N1-P1 1.643(4),
N2-P2 1.694(4), N2-P1 1.717(4), Cr1-P1 2.3974(14), Cr1-P2
2.5158(14), N1-P1-N2 110.8(2), P2-N2-P1 104.9(2), P1-
Cr1-P2 66.74(4).
To prove whether alkylation of 6 gives a complex analo-
gous to 7, we reacted 6 with Et3Al in THF. Surprisingly, this
led to the formation of EtCrCl2(THF)3 (8). It is thermally
less stable compared to the corresponding phenyl PhCrCl2-
a different terminal phosphorus-chromium bond length
˚
˚
(Cr1-P2 2.5158(14) A versus Cr1-P2 2.5081(5) A in 5).
The Cp ligand is recognized as the reason for the oligomer-
ization behavior of 5 in catalytic tests. With AlEt3 mostly
1-butene (70.2 wt %) is formed, but a small amount of other
oligomers following a Schulz-Flory distribution (14.3 wt %)
and some polyethylene (15.5 wt %) were also present. Thus,
dimerization based on a chromacyclopentane could be respon-
sible for enhanced 1-butene formation, whereas the Schulz-
Flory distribution and the polymerization could be explained
by an ethene insertion/β-elimination mechanism by chain
growth that competes with the metallacyclic route.
13
14
(THF)3 and methyl MeCrCl2(THF)3 compounds. Ob-
viously, the weak ligand coordination via both phosphorus
atoms on the chromium site of 6 is not favored in the presence
of THF and AlEt3. One can discuss whether first alkylation
of chromium takes place and the ligand is then replaced by
THF molecules or the ligand is displaced in a first step by
THF and afterward the chromium is alkylated. By fast
crystallization complex 6 can be obtained from a mixture
of THF/hexane, but after some days in solution these blue
crystals decompose under formation of violet CrCl3(THF)3
and free ligand can be observed by NMR. Hence, this
reaction behavior is one reason that THF is not a suitable
solvent for the new ethene trimerization system.5
To find out if these suggestions are appropriate, 5 was
alkylated with Na[Et4Al] (Scheme 5) to form the correspond-
ing ethyl compound CpCrEt[-N(iPr)P(Ph)N(iPr)PPh2] (7).
Its molecular structure is depicted in Figure 6. The oligomer-
ization test with AlEt3 as a cocatalyst resulted in a similar
product distribution compared to the oligomerization ex-
periment with 5.
Complex 8 was described before,15 but via a different
reaction and without a molecular structure, which is shown
Compared to 5, the Cr-N bond in 7 is elongated slightly
(13) Kurras, E. Naturwissenschaften 1959, 46, 171.
(14) Kurras, E. Monatsber. Akad. Wiss. 1963, 5, 378.
(15) Nishimura, K.; Kuribayashi, H.; Yamamoto, A.; Ikeda, S.
J. Organomet. Chem. 1972, 37, 317–329.
˚
˚
by 0.04 A and the Cr-P bond is shortened by 0.02 A, whereas
the P-Cr-N angle is reduced by ca. 1.3ꢀ. Complex 7, with an
ethyl group, is stable at room temperature.

Article
Organometallics, Vol. 29, No. 21, 2010 5267
Table 1. Summary of Important Bond Lengths and Angles
(0.35 mL, 1.6 M n-BuLi in n-hexane, 0.56 mmol) was added to
the solution, whereupon the color changed immediately to
orange-yellow. The solution was stirred for an additional two
hours at room temperature. Subsequently, half the solvent was
removed by distillation. For crystallization 2 mL of n-hexane
was added and the solution was stored at -78 ꢀC. Yield: 120 mg
(45%). Molecular weight: 530.59 g/mol [C30H45LiN4P2]. Ele-
mentary analysis was impossible because of dissociation of
tmeda. Melting point: 128-129 ꢀC. 1H NMR (THF-d8): δ 7.58-
7.48 (m, 6H, aryl-H), 7.36-7.17 (m, 6H, aryl-H), 7.04-6.91
(m, 3H, aryl-H), 3.71 (m, 1H, CHCH3), 3.57 (m, 1H, CHCH3),
2.30 (s, 4H, CH2), 2.13 (br s, 12H, NCH3), 1.38 (d, J = 6.5 Hz,
3H, CHCH3), 1.24 (d, J = 6.40 Hz, 3H, CHCH3), 1.23 (d, J =
6.4 Hz, 3H, CHCH3), 1.02 (d, J = 6.5 Hz, 3H, CHCH3). 13C
NMR (THF-d8): δ 157.1, 143.4, 141.9, 134.9, 133.3, 132.4, 129.4,
128.6, 127.9, 127.1, 125.2, (18C, arom.) 58.7 (2C, CH2), 54.4,
50.6 (2C, CHCH3), 46.2 (4C, NCH3), 30.1, 25.8, 24.5, 24.2
(4C, CHCH3). 31P{H} NMR (THF-d8): δ 40.6 (br), 100.4 ppm
(d, 2JP-P = 20.5 Hz).
distance
M-N-
(A)
distance
M-Pterminal
(A)
angle
N--M-
Pterminal (deg)
˚
˚
complex
metal
2
3
4
Li
Li
Mg
1.973(3)
2.049(2)
1.998(2)
2.005(2)
1.9650(13)
2.774(3)
2.587(2)
84.96(19)
88.66(8)
79.35(7)
79.50(7)
82.68(4)
2.7470(11)
2.7126(11)
2.5081(5)
2.5158(14)
2.4822(7)
5
6
7
Cr
Cr
Cr
2.002(2)
81.42(6)
here in Figure 7. Its coordination sphere is nearly perfect
octahedral. The ethyl group is located trans to one THF
molecule. Both chlorine atoms are situated trans to each
˚
other. The chromium-carbon bond, at 2.065 A, is slightly
shorter than that in complex 7.
Preparation of [Ph2PN(iPr)P(Ph)N(iPr)-Li]2 (3). Ph2PN(iPr)P
(Ph)N(iPr)-H (1) (8.70 g, 21.35 mmol) was dissolved in 15 mL of
toluene. After cooling to -78 ꢀC n-butyllithium (12.8 mL, 2.5 M
n-BuLi in n-heptane, 32.0 mmol) was added to the solution,
causing the color to change immediately to orange-yellow. The
solution was stirred for an additional two hours at room
temperature, and a colorless solid precipitated. The precipitate
was filtered and washed three times with 5 mL of toluene.
Remaining solvent was removed under vacuum to give a color-
less powder. Crystals could be grown from the mother liquor at
room temperature. Yield: 6.73 g (76%). Molecular weight:
414.39 g/mol [C24H29LiN2P2]. Anal. Calcd: C 69.56, H 7.05, N
6.76. Found: C 69.25, H 7.06, N 6.87. Melting point: 187-
189 ꢀC. 1H NMR (THF-d8): δ 7.50-7.57 (m, 6H, aryl-H),
7.20-7.34 (m, 6H, aryl-H), 7.02 (m, 2H, arom.), 6.93 (m, 1H,
aryl-H), 3.70 (m, 1H, CHCH3), 3.58 (m, 1H, CHCH3), 1.39 (d,
J = 6.5 Hz, 3H, CHCH3), 1.25 (d, J = 6.2 Hz, 3H, CHCH3),
1.22 (d, J = 6.2 Hz, 3H, CHCH3), 1.04 (d, J = 6.5 Hz, 3H,
CHCH3). 13C NMR (THF-d8): δ 143.4, 142.0, 134.9, 133.4,
132.5, 131.5, 129.4, 128.6, 128.0, 127.9, 127.1, 125.2 (arom.),
54.6, 54.0 (CHCH3), 31.0, 26.7 (CHCH3). 31P{H} NMR (THF-d8):
δ 40.6 (br), 100.1 ppm (d, 2JP-P = 24.6 Hz).
Conclusion
We herein present different metal amide complexes of Ph2-
PN(iPr)P(Ph)N(iPr)H (1), obtained by deprotonation of the
amine function. Lithiation of compound 1 under stabiliza-
tion with tetramethylenediamine (tmeda) forms a tmeda-
lithium-amide complex. Without tmeda, a dinuclear lithium-
amide complex can be isolated. Reaction of a Grignard
reagent with 1 yields a magnesium bis-amide compound,
which represents only a minor part of the reaction mixture.
Cr-amide complexes were prepared, showing a coordination
motif that could be part of a catalytically active species in
ethene trimerization. After storing a reaction mixture of a
Cr-ligand complex and AlEt3 in THF for several days the
ligand is replaced by solvent molecules and EtCrCl2(THF)3
can be isolated. For the first time a crystal structure of this
compound is presented.
In conclusion, the compounds show how metalation and
transmetalation of the new ligand in catalysis can look alike,
which is of major interest concerning its coordination chem-
istry as well as activation processes of the precatalyst mixture
in ethene trimerization.
Preparation of [Ph2PN(iPr)P(Ph)N(iPr)-]2Mg (4). Ph2PN(iPr)
P(Ph)N(iPr)-H (1) (3.00 g, 7.34 mmol) was dissolved in 50 mL of
diethyl ether. At room temperature a solution of isobutylmag-
nesium chloride (3.7 mL, 2.0 M C4H9ClMg in diethyl ether, 7.40
mmol) was added to the solution. The solution was stirred for an
additional two hours. After cooling to -30 ꢀC a colorless pre-
cipitate of the composition Ph2PN(iPr)P(Ph)N(iPr)-MgCl was
isolated. Yield: 2.01 g (58%). Recrystallization from diethyl
ether resulted in amorphous powders with unchanged analytical
data. Few single crystals were obtained by this method, reveal-
ing the structure of [Ph2PN(iPr)P(Ph)N(iPr)-]2Mg. Yield: 0.46 g
(15%). Molecular weight: 839.20 g/mol [C48H58MgN4P4]. Anal.
Calcd: C 68.70, H 6.97, N 6.68. Found: C 68.93, H 7.07, N 6.91.
Melting point: 202 ꢀC. 1H NMR (C6D6): δ 6.83-7.66 (m, 30H,
aryl-H), 3.54-3.62 (m, 2H, CHCH3), 3.38-3.48 (m, 2H,
CHCH3), 1.51 (d, J = 6.5 Hz, 6H, CHCH3), 1.19 (d, J = 6.5 Hz,
6H, CHCH3), 1.15 (d, J = 6.5 Hz, 6H, CHCH3), 1.10 (m, 6H,
CHCH3). 13C NMR (C6D6): δ 143.4, 142.0, 134.9, 133.4, 132.5,
131.5, 129.4, 128.6, 128.0, 127.9, 127.1, 125.2 (arom.), 52.0, 51.5
(CHCH3), 29.5, 28.6, 25.9, 24.1 (CHCH3). 31P{H} NMR
(C6D6): δ 87.05 (tr, J = 10.4 Hz), 28.32 (tr, J = 10.4 Hz).
Preparation of CpCrEt[-N(iPr)P(Ph)N(iPr)PPh2] (7). CpCrCl
[-N(iPr)P(Ph)N(iPr)PPh2] (5)5 (0.030 g, 0.054 mmol) and Na
[Et4Al] (0.009 g, 0.054 mmol) were suspended in 5 mL of Et2O at
room temperature. The color changed immediately to green-
brown, and a colorless precipitate occurred. After stirring over-
night all volatiles were removed under vacuum, and the residue
was extracted with toluene. The brown solution was reduced
to 1 mL. Brown crystals suitable for X-ray analysis formed
Experimental Section
General Procedures. All operations were carried out under
argon with standard Schlenk techniques or in a glovebox. Prior
to use nonhalogenated solvents (including deuterated solvents
benzene-d6 and THF-d8) were freshly distilled from sodium
tetraethylaluminate and stored under argon. All other chemical
reagents and solvents were obtained from commercial sources
and used without further purification. The following spectro-
meters were used: Mass spectra: MAT 95-XP and Finnigan
Polaris Q. NMR spectra: Bruker AV 300, AV 400, and AMX
400. Chemical shifts (1H, 13C) are given relative to SiMe4 and are
referenced to signals of the used solvent: benzene-d6 (δH=7.16,
δC=128.0) and THF-d8 (δH=2.73, δC=25.2). Chemical shifts
for 31P are given relative to 85% H3PO4. The spectra were
assigned with the help of DEPT. Melting points: sealed capil-
€
laries, Buchi 535 apparatus. Elemental analyses: Leco CHNS-
932 elemental analyzer.
Compounds 1, 5, and 6 were prepared according to published
literature procedures.5 Oligomerization experiments were con-
ducted as published before.3,4 Analytical details of compound 8
were published before.15
Preparation of [Ph2PN(iPr)P(Ph)N(iPr)-][Li(tmeda)] (2). Ph2-
PN(iPr)P(Ph)N(iPr)-H (1) (204 mg, 0.5 mmol) and 90 μL of
tetramethylethylenediamine (tmeda, 0.6 mmol) were dissolved
in 10 mL of THF. After cooling to -40 ꢀC n-butyllithium

5268 Organometallics, Vol. 29, No. 21, 2010
Peitz et al.
within two weeks storing time at room temperature. Molecular
weight: 553.60 g/mol [C31H39CrN2P2]. Yield: 18 mg (60%).
Anal. Calcd: C 67.26, H 7.10, N 5.06. Found: C 66.49, H 7.04,
N 4.69. Melting point: 132-134 ꢀC (dec).
ques on F2 (SHELXL-97). DIAMOND was used for graphical
representations.
Acknowledgment. The authors thank Linde Engineer-
ing and SABIC for the permission to publish this work.
Furthermore, we wish to thank Linde Engineering’s
R&D Chemistry Department for their valuable contribu-
tions as well as the analytical service and the technical
staff at LIKAT.
Preparation of EtCrCl2(THF)3 (8). CrCl3[Ph2PN(iPr)P(Ph)N
(iPr)-H](THF) (6)5 (0.20 g, 0.357 mmol) was solved in 10 mL of
THF. AlEt3 (0.28 mL, 1.9 M in toluene, 0.536 mmol) was added to
the blue solution, which turned green immediately. The solution
was mixed with 10 mL of n-hexane and stored one week at -40 ꢀC.
In that time green crystals suitable for X-ray analysis formed.
Molecular weight: 368.28 g/mol [C14H29CrO3]. Yield: 21 mg (16%).
Crystallographic Details. Diffraction data were collected on a
STOE IPDS diffractometer using graphite-monochromated Mo
KR radiation. The structures were solved by direct methods
(SHELXS-97) and refined by full-matrix least-squares techni-
Supporting Information Available: Tables of crystallographic
data in cif file format, including bond lengths and angles of
compounds 2, 3, 4, 7, and 8. This material is available free of
charge via the Internet at http://pubs.acs.org.