Synthesis, coordination chemistry, and catalysis of the First 1,2-bis(diphenylphosphino)-l,2-diphenylhydrazine, Ph2PN(Ph)N(Ph) PPh2

Article abstract of DOI:10.1021/om900925b

The reaction of chlorodiphenylphosphine with dilithiohydrazobenzene gave l,2-bis(diphenylphosphino)-l,2-diphenylhydrazine, [PPh₂N(Ph)N(Ph) PPh₂] (1). Treatment of 1 with NiCl₂(DME), PdCl ₂(PhCN)₂, and

Full text of DOI:10.1021/om900925b

226 Organometallics 2010, 29, 226–231
DOI: 10.1021/om900925b
Synthesis, Coordination Chemistry, and Catalysis of the First 1,2-
Bis(diphenylphosphino)-1,2-diphenylhydrazine, Ph2PN(Ph)N(Ph)PPh2
†
€
Bhaskar R. Aluri, Normen Peulecke, Bernd H. Muller, Stephan Peitz, Anke Spannenberg,
Marko Hapke, and Uwe Rosenthal*
€
Leibniz-Institut fu€r Katalyse e. V. an der Universitat Rostock, Albert-Einstein-Strasse 29a,
18059 Rostock, Germany
Received October 22, 2009
The reaction of chlorodiphenylphosphine with dilithiohydrazobenzene gave 1,2-bis(diphenyl-
phosphino)-1,2-diphenylhydrazine, [PPh2N(Ph)N(Ph)PPh2] (1). Treatment of 1 with NiCl2(DME),
PdCl2(PhCN)2, and PtCl2(COD) resulted in the formation of complexes of the type cis-[MCl2-
{Ph2PN(Ph)N(Ph)PPh2}] (M = Ni (3), Pd (4), Pt (5)). The molecular structures of the starting ligand
1 and the complexes 3, 4, and 5 have been determined by X-ray diffraction. The ligand 1 and its Ni(II)
complex 3 were evaluated for their catalytic activity in the oligo-/polymerization of ethylene using
methylaluminoxane (MAO) and triethylaluminium (TEA) as cocatalyst.
Introduction
is noteworthy to mention that even though the first publication
on the synthesis of bis(phosphino)-substituted alkylhydrazines
appeared four decades ago,6 only very few reports are found in
the literature.7,8 Surprisingly, the catalytic potential of this
ligand system has not been discussed, except by Bollmann,
Wasserscheid, et al., who described the use of [PPh2N(Me)-
N(Me)PPh2] in ethylene tetramerization,9 giving 58.8% C8
(98.4% 1-C8) and 25.2% C6 (69.6% 1-C6) along with 8% of
polyethylene. In the same reaction carbon-bridged diphenyl-
phosphinoethane (dppe) furnished 39.2% C8 (96.6% 1-C8)
and 19.7% C6 (38.2% 1-C6) along with 35% of polyethylene.9
The substituents at the bridging carbon atom show a great
influence on the selectivity and productivity of the reaction.
The use of systems of the type (R1)(R2)P(R5)CHCH(R6)-
P(R3)(R4) (R5 and R6 are hydrocarbyl and substituted hydro-
carbyl and not hydrogen) yields different selectivities depend-
ing on the substituents. By varying the R5 and R6 groups up to
72.9% of 1-C8 can be obtained while reducing the amount of
polyethylene to as low as 1.7%.10 To our delight, very recently
D. F. Wass et al. reported the efficient utilization of [PR2N-
(Me)N(Me)PR2] (R = o-MeC6H4, o-OMeC6H4) ligands in
the selective trimerization of isoprene to form terpenes. No-
tably, dppe and dppm (bis(diphenylphosphino)methane) were
found to be inactive in this reaction.11
Phosphines are one of the most important classes of ligands
in chemistry in both the industrial and academic spheres.1 The
synthesis of new chelating bis(phosphines) and the develop-
ment of metal complexes based on them is an important area in
the field of transition metal catalysis.2 Alkane-diyl-bridged
bis(phosphines), e.g., dppe as a prominent representative,
found numerous catalytic applications due to the appropriate
bite angle provided by the ethane-diyl backbone, which sup-
ports the formation of stable five-membered chelate rings.3
This gave a powerful impetus to extend the scope of transition
metal catalysis by preparing novel bis-phosphino ligands with
spacing between the phosphorus(III) centers similar to that in
dppe. Katti4 and Woollins5 recently reported the dinitrogen-
bridged diphosphines R2PN(R0)N(R0)PR2 (R0 = Me, Et) and
bis(dihalophosphino)hydrazines, X2PN(R0)N(R0)PX2 (R0 =
Me, Et), which have similar chain length compared to dppe. It
† This work is dedicated to Professor Dirk Walther on the occasion of his
70th birthday.
*Corresponding author. E-mail: uwe.rosenthal@catalysis.de.
(1) (a) Applied Homogeneous Catalysis with Organometallic Com-
pounds; Cornils, B., Herrmann, W. A., Eds.; VCH: New York, 1996; Vol.
1, p 2. (b) Noyori, R. Asymmetric Catalysis In Organic Synthesis; John
Wiley & Sons, Inc.: New York, 1994. (c) Parshall, G. W; Ittel, S. D.
Homogeneous Catalysis, 2nd ed.; John Wiley & Sons, Inc.: New York,
1992; Chapter 8. (d) Kagan, H. B. Asymmetric Synthesis Using Organome-
tallic Catalysts. In Comprehensive Organometallic Chemistry; Wilkinson,
G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon Press: Oxford, 1982; Vol. 8,
Chapter 53.
In this regard, it is interesting to evaluate the influence of
other substituents attached to the N atom [PPh2N(R)N-
(R)PPh2] in ethylene oligo- and polymerization reactions.
(2) (a) Parshall, G. W.; Ittel, S. D. Homogeneous Catalysis; Wiley:
New York, 1992. (b) Pignolet, L. H., Ed. Homogeneous Catalysis with
Metal Phosphine Complexes; Plenum: New York, 1983.
(3) Tao, X.; Huang, J.; Yao, H.; Qian, Y. J. Mol. Catal A: Chem.
2002, 186, 53–56. (b) van Leeuwen, P. W. N. M.; Kamer, P. C. J.; Reek, J. N.
H.; Dierkes, P. Chem. Rev. 2000, 100, 2741–2769.
(4) Reddy, V. S.; Katti, K. V. Inorg. Chem. 1994, 33, 2695–2696. (b)
Reddy, V. S.; Katti, K. V.; Barnes, C. L. Chem. Ber. 1994, 127, 1355–1357.
(c) Reddy, V. S.; Katti, K. V.; Barnes, C. L. Inorg. Chem. 1995, 34, 5483–
5488.
(6) Spangenberg, S. F.; Sisler, H. H. Inorg. Chem. 1969, 8, 1004–1006.
(7) Havlicek, M. D.; Gilje, J. W. Inorg. Chem. 1972, 11, 1624–1628.
(8) Noth, H.; Ullmann, R. Chem. Ber. 1976, 109, 1942–1963.
(9) 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.
(10) (a) Han, T. K.; Chae, S. S.; Kang, S. O.; Wee, K. R.; Kim, S. K.
WO 2009/022770. (b) Han, T. K.; OK, M. A.; Chae, S. S.; Kang, S. O.;
Jung, J. H. WO 2008/088178.
€
(5) Slawin, A. M. Z.; Wainwright, M.; Woollins, J. D. J. Chem. Soc.,
Dalton Trans. 2002, 513–519.
(11) Bowen, L. E.; Charernsuk, M.; Hey, T. W.; McMullin, C. L.;
Orpen, A. G.; Wass, D. F. Dalton Trans. 2010, DOI: 10.1039/b913302j.
r
pubs.acs.org/Organometallics
Published on Web 11/23/2009
2009 American Chemical Society

Article
Organometallics, Vol. 29, No. 1, 2010 227
˚
Table 1. Selected Bond Lengths (A) and Angles (deg)
Also, to the best of our knowledge, ligands of the type
R2PN(R0)N(R0)PR2 (R0 = aryl) are not yet known.
In this paper we report for the first time the synthesis and
characterization of the arylhydrazine derivative, namely,
1,2-bis(diphenylphosphino)-1,2-diphenylhydrazine. The co-
ordination chemistry of this new phosphanyl hydrazine with
Ni(II), Pd(II), and Pt(II) precursors is also described through
X-ray structural analysis. The influence of this ligand and its
Ni(II) complex in the oligo- and polymerization of ethylene
was investigated.
1
3
4
5
N1-P1
N2-P2
N1-N2
Cl1-M
Cl2-M
P1-M
P2-M
1.7259(13)
1.721(2)
1.428(2)
1.7164(13)
1.7194(13)
1.429(2)
2.1916(4)
2.1838(4)
2.1265(4)
2.1115(4)
1.7180(14)
1.7155(14)
1.430(2)
2.3384(4)
2.3478(4)
2.1979(4)
2.2134(4)
1.720(2)
1.712(2)
1.431(3)
2.3431(6)
2.3525(6)
2.1926(6)
2.1995(6)
N1-N2-P2
C19-N2-P2
112.39(11) 108.54(9) 117.52(10)
130.75(12) 123.02(10) 128.19(11)
117.83(15)
127.9(2)
114.3(2)
109.69(14)
122.4(2)
116.0(2)
90.12(2)
93.57(2)
175.91(2)
90.81(2)
Results and Discussion
C19-N2-N1 116.68(15) 115.60(11) 114.27(12)
N2-N1-P1
C13-N1-P1
112.08(10) 116.36(9)
109.58(10)
132.20(12) 128.99(10) 122.53(10)
Synthesis of Bis(phosphanyl)hydrazine [PPh2N(Ph)N(Ph)-
PPh2], 1. 1,2-Bis(diphenylphosphino)-1,2-diphenylhydra-
zine (1; PNNP) was synthesized from well-known commer-
cially available hydrazobenzene. The dilithium derivative of
hydrazobenzene was prepared in situ by the reaction with 2
equiv of n-butyllithium in THF at -78 °C. Subsequently,
chlorodiphenylphosphine was treated with the in situ formed
dilithiated hydrazobenzene at 0 °C to afford the desired
PNNP ligand [eq 1] in good isolated yield. The addition of
ClPPh2 to the THF solution of the dilithiated hydrazine also
furnished 1, as seen by 31P NMR. However, this way lead to
essential quantities of byproducts.12 Also, working in low
polar solvents like diethyl ether or pentane increased the
formation of byproducts, which mainly consist of Ph2P-
PPh2 (31P{1H} NMR: -14.5 ppm). As mentioned earlier,
previous studies have described the preparation of related
methyl/ethyl derivative [PPh2N(R)N(R)PPh2] either by
treating Cl2PN(R)N(R)PCl2 with PhMgCl4,5 or by conden-
sation reaction of N,N0-dimethylhydrazine and PPh2Cl
at -196 °C.6
C13-N1-N2 115.53(13) 114.63(12) 116.01(12)
Cl2-M-Cl1
P1-M-Cl1
P1-M-Cl2
P2-M-Cl2
P2-M-Cl1
P2-M-P1
N1-P1-M
N2-P2-M
C7-P1-M
C1-P1-M
C25-P2-M
C31-P2-M
95.21(2)
88.42(2)
174.17(2)
90.14(2)
93.16(2)
92.270(15)
174.03(2)
89.91(2)
173.96(2)
86.03(2)
175.11(2)
84.505(15)
108.55(5)
107.30(5)
112.06(6)
115.51(6)
114.57(6)
108.78(6)
177.04(3)
85.41(2)
108.09(4)
109.60(4)
109.58(5)
115.13(6)
111.54(5)
116.58(5)
107.72(7)
106.78(7)
113.24(8)
115.61(8)
114.79(10)
109.34(9)
Colorless crystals of 1, suitable for X-ray crystal structure
analysis, were obtained by addition of absolute ethanol to a
saturated dichloromethane solution of 1 followed by storing
the resulting solution at þ4 °C. The ligand 1 is not prone to
alcoholysis at room temperature and found to be fairly stable
towards oxygen in the solid state. The 31P NMR chemical
shift was found to be at þ64.6 ppm and is in agreement with
the values reported for [PPh2N(Et)N(Et)PPh2] (64.2 ppm)
and [PPh2N(Me)N(Me)PPh2] (62.5 ppm).
Selected bond distances and angles are given in Table 1.
The molecular structure of the ligand is shown in Figure 1.
The P-N-N-P chain is constrained to the cis configura-
tion. The two nitrogen atoms are in a planar environment
with the angles adding to 359.8° around N1 and N2. The
P-N and N-N distances are in the usual range, comparable
to related diphenylphosphino-1,2-diarylhydrazines.12
Our attempts to prepare 1 in another way, using Et3N as
dehydrochlorinating agent, were not successful. In toluene
hydrazobenzene did not react with ClPPh2 in the presence of
Et3N. However, we obtained diphenylphosphino-1,2-diphe-
nylhydrazine (2) in DCM as well as in DMF at room
temperature in the presence of Et3N (eq 2).12 Using harsher
Figure 1. Molecular structure of Ph2PN(Ph)N(Ph)PPh2 (1).
Thermal ellipsoids are drawn at the 30% probability level.
The H atoms are omitted for clarity.
conditions, i.e., heating the DMF solution at 80 °C to
incorporate bis-substitution, led to decomposition by form-
ing unidentified products. Nevertheless, 2 can be converted
to 1 in moderate yield by lithiation using BuLi, followed by
addition of the in situ formed lithiated solution to ClPPh2
at 0 °C.
Coordination Chemistry of [PPh2N(Ph)N(Ph)PPh2]. Reac-
tion of the ligand 1 with group 10 metals, namely, NiCl2-
(DME), PdCl2(PhCN)2, and PtCl2(COD), in a 1:1 molar
ratio at room temperature in dichloromethane resulted in the
formation of mononuclear, square-planar complexes cis-
[NiCl2{Ph2PN(Ph)N(Ph)PPh2}] (3), cis -[PdCl2{Ph2PN(Ph)-
N(Ph)PPh2}] (4), and cis-[PtCl2{Ph2PN(Ph)N(Ph)PPh2}] (5)
(eq 3) in excellent yields. The 31P{1H} NMR spectra of 3, 4,
and 5 show singlets at δ 117.14, 126.07, and 96.34 ppm,
(12) Fedotova, Y. V.; Kornev, A. N.; Sushev, V. V.; Kursky, Y. A.;
Mushtina, T. G.; Makarenko, N. P.; Fukin, G. K.; Abakumov, G. A.;
Zakharov, L. N.; Rheingold, A. L. J. Organomet. Chem. 2004, 689,
3060–3074.

228 Organometallics, Vol. 29, No. 1, 2010
Aluri et al.
Figure 2. Molecular structure of [NiCl2{Ph2PN(Ph)N(Ph)-
PPh2-P,P}] (3). Thermal ellipsoids are drawn at the 30% prob-
ability level. The H atoms are omitted for clarity.
Figure 3. Molecular structure of [PdCl2{Ph2PN(Ph)N(Ph)-
PPh2-P,P}] (4). Thermal ellipsoids are drawn at the 30% prob-
ability level. The H atoms are omitted for clarity.
respectively, with J{195Pt-31P} of 3992 Hz for 5, comparable
to the values previously reported for [PtCl2{Ph2PN(Et)-
N(Et)PPh2}] (31P: 100.4 ppm, J{195Pt-31P}: 4055 Hz).5 An
upfield shift of approximately 6 and 4 ppm in the values of
31P NMR for 4 and 5 was observed compared to related
[MCl2{Ph2PN(Et)N(Et)PPh2}] (M = Pd, Pt).5
Slow diffusion of pentane into a chloroform solution
of 3, 4, and 5 led to the formation of yellow crystals of
3 and 4 as well as colorless crystals of 5, suitable for
X-ray diffraction. The crystals contain CHCl3 as lattice
solvent. Selected bond distances and angles are given in
Table 1, and a view of their molecular structure is shown
in Figures 2, 3, and 4.
Figure 4. Molecular structure of [PtCl2{Ph2PN(Ph)N(Ph)-
PPh2-P,P}] (5). Thermal ellipsoids are drawn at the 30% prob-
ability level. The H atoms are omitted for clarity.
As mentioned above, all the complexes possess square-
planar geometry around the metal center, and this is con-
sistent with the diamagnetism of the Ni complex 3. The five-
membered chelate ring (MP2N2) displays a classic open-
envelope conformation. Similar to other five-membered
PNNPM metallacycles, one of the two nitrogen atoms is
deviated from the five-membered-ring plane by 0.50, 0.51,
4 with AgBF4 (eq 4). Its 31P{1H} NMR spectrum contains a
singlet at δ 123.25 ppm.
13
˚
and 0.52 A respectively for 3, 4, and 5. In the case of
complex 5 the M-P, P-N, and M-Cl bond lengths are
similar to the values previously reported for single bonds in
the related cis-[PtCl2{o-C6H4OCH3)2PN(Me)N(Me)P(o-
C6H4OCH3)2}]. These data reveal that, in comparison to
the spectroscopic differences highlighted above, these com-
plexes of PNNP (N-aryl) structurally do not differ in any
substantial way from those of related PNNPM (N-alkyl)
metallacycles in that the metal-ligand bond lengths, bond
lengths within the five-membered ring chelates, and angles at
the metal center are comparable.
The structure of compound 6 was confirmed by X-ray
crystallography. Unfortunately, the crystals contained sol-
vent molecules, which could not be modeled. Furthermore
both anions are disordered. The molecular structure of the
cation and the crystal data are given in the Supporting
Information.
Catalytic Oligo- and Polymerization of Ethylene. Ethylene
oligomerization and polymerization are important processes
to prepare valuable products such as linear R-olefins, wax,
and polyethylene from basic feedstock (ethylene). As men-
tioned in the Introduction, [PPh2N(Me)N(Me)PPh2] was
used successfully in ethylene tetramerization by combining
The dicationic complex [Pd(NCMe)2{Ph2PN(Ph)N(Ph)-
PPh2}](BF4)2 (6) was prepared by chloride abstraction from
(13) Eberhardt, L.; Armspach, D.; Matt, D.; Oswald, B.; Toupet, L.
Org. Biomol. Chem. 2007, 5, 3340–3346.

Article
Organometallics, Vol. 29, No. 1, 2010 229
Table 2. Ethylene Oligomerization Using Ligand 1 in Combination with Cr or Ni and Complex 3 as Catalyst Precursors
product distributione,f
no.
PE (g)a
10
oligomers (g)b
8
TONc
12830
TOFd
8700
C4
8.9
(>98)
5.8
(>98)
69.6
75.9
24.5
(58)
C5
1.3
(>98)
1.2
(>98)
C6
C7
1.3
(>98)
1.9
(>98)
C8
C9
C10
C11
0.4
(>98)
0.8
(>98)
C12
2.0
(>98)
4.1
(>98)
C14
0.1
(>98)
0.6
(>98)
30.9
(99)
34.5
(99)
23.8
19.2
56.3
(67)
34.5
(99)
35.2
(99)
4.7
3.1
19.2
(70)
1.4
19.2
(>98)
14.5
(>98)
1.1
Cat1
(>98)
1.6
(>98)
Cat2
Cat3
Cat4
25
0.03
0.05
14
14
15
27730
10910
11980
18800
7400
8120
0.9
0.1
Cat5
0.60
1.5
1710
1160
a Isolated and purified polymer. b Amount of liquid oligomers dissolved in toluene. Volatile butenes are not taken into account. c TON in mol/mol.
d TOF in mol/mol h (over a period of 90 min). e Mol percentage of combined Cn products. Deviations from the Schulz-Flory distribution may be due to
loss of butene and hexene (to volatile fraction) and the solubility of C10 and C12 in the polymer. f In parentheses the percentage of terminal olefins, as
percentage of individual Cn fraction.
Figure 5. Ethylene uptake-time plots for the oligo-/polymerization of ethylene (*including saturation). Conditions: All reactions were
conducted in a 300 mL Parr reactor. Standard reaction conditions: ligand 0.1 mmol, Cr or Ni 0.05 mmol, MAO 300 equiv (Cat1-4),
toluene as solvent, total volume 100 mL, T 45 °C (for Cr) or 100 °C (for Ni), time 90 min, P 30 bar; Cat1 is Cr(acac)3; Cat2 is
CrCl3 3THF; Cat3 is the preformed complex 3; Cat4 is Ni(COD)2; Cat5 is Cr(acac)3, TEA (300 equiv).
3
it with Cr(acac)3 and MAO.9 Also, various nickel complexes
Table 3. Physical Data of PE
containing chelating ligands such as O-P, O-N, N-N, and
a
no.
MNMR
R/int (%) Me/1000Ca mp (°C) b,c d (g cm-3
)
N-P have been applied in the oligo- and polymerization of
ethylene.14 We studied the behavior of ligand 1 in ethylene
oligomerization by combining it with Cr(acac)3, CrCl3
Cat1 1400-1600 99/1
Cat2 3215-3518 98/2
16
11
126
125
0.929
0.946
3
a Determined by 1H NMR integration. b Measured by differential
3THF, and Ni(COD)2. The in situ formed complexes were
activated with MAO (in one example TEA), and catalytic
runs were performed in toluene at 45 or 100 °C for 90 min at
30 bar of ethylene pressure. In addition to this, complex
3 was also tested as catalyst precursor in this reaction.
The results of the catalytic studies are summarized in
Tables 2 and 3. The ethylene uptake and time plot is shown
in Figure 5.
scanning calorimetry. c Melting peak is given.
Cr(acac)3 the activity is decreased slightly (Cat1). In the
presence of TEA the catalytic reaction is very slow, and
only about 2 g of ethylene was consumed over a period of
90 min (Cat5). The catalyst precursor from the Ni com-
plex did not show any activity at 45 °C and requires higher
temperature, and therefore the tests were performed at
100 °C (Cat3, 4).
In the presence of chromium catalyst the formation of
polyethylene was observed predominantly, besides a small
amount of liquid oligomers (Cat1, 2, and 5). When nickel
catalysts were used, the major products are lower olefins, and
only a trace amount of polyethylene was formed (Cat3 and
4). As seen from Figure 5, the PNNP ligand forms an
As can be seen from Table 2, Cr catalysts (Cat1, 2) gave,
apart from polyethylene, a Schulz-Flory distribution of
oligomers. The major fraction belongs to C6 and C8 with a
selectivity of 99% for 1-C6 and 1-C8. Interestingly, here the
formation of even as well as odd chain length oligomers is
observed. In our previous publication, we reported a simpli-
fied mechanistic pathway for the formation of odd-num-
bered linear R-olefins (LAOs) in the presence of the Ph2PN-
active catalyst with CrCl3 3THF at 45 °C (Cat2), while with
3
(14) Sun, W. H.; Zhang, D.; Zhang, S.; Jie, S.; Hou, J. Kinet. Catal.
2006, 47 (2), 278–283.
(iPr)PPh2/CrCl3 3THF/MAO system at substoichiometric
3

230 Organometallics, Vol. 29, No. 1, 2010
Aluri et al.
Scheme 1. Possible Mechanistic Pathway for Odd-Numbered
LAOs
predominantly furnished lower olefins, especially butenes
and hexenes.
Experimental Section
General Procedures. All operations were carried out under
argon with standard Schlenk techniques, using predried re-
agents. The solvents were purified according to conventional
procedures and were freshly distilled prior to use. Chemicals
were obtained from Aldrich or Strem chemicals. The following
spectrometers were used: Mass spectra: AMD 402. NMR
spectra: Bruker AV 300 and AV 400. Chemical shifts are given
in ppm and are referenced to TMS or the residual nondeuterated
solvent as internal standard for 1H and 85% H3PO4 for 31P{1H}.
€
Melting points: sealed capillary, Buchi 535 apparatus (uncorrec-
ligand/Cr ratio.15 A similar mechanism involving mono-
nuclear Cr complex is expected in the present case. The
formation of a methyl compound (PNNP)Cr(Me)n after
the alkylation with MAO and elimination of methane to
give chromium carbene “CrdCH2” groups, followed by the
reaction of these carbene groups with the recently formed
even-numbered LAOs, leads to the formation of odd-num-
bered LAOs (Scheme 1). Another plausible explanation for
this uncommon behavior is that the active species follows a
typical insertion/β-elimination mechanism rather than a
simple metallacycle mechanism. Our attempts to synthesize
the Cr-PNNP complex, which can give us an insight into the
active species in the catalytic process, were not successful. In
the case of Ni catalysts, the main products are butenes along
with hexenes and a small amount of octenes and higher
olefins, each with several isomers (Cat3, 4). In contrast to
this, a very high selectivity toward terminal olefins is ob-
served for Cr catalysts (Cat1, 2). The cocatalyst shows an
influence not only on the activity but also on selectivity. The
use of TEA instead of MAO results in a dramatic decrease in
both activity and selectivity (Cat5). The formation of C15
and higher oligomers is not observed in all these attempts
under the above-mentioned conditions.
ted). Elemental analyses: Leco CHNS-932 elemental analyzer.
Gas chromatography: HP 6890 (Hewlett-Packard) chromato-
graph using a HP 5 column.
Ph2PN(Ph)N(Ph)PPh2 (1). Method A. A 2.5 M hexane
solution of n-BuLi (16.5 mL, 41.25 mmol) was added to a stirred
solution of 1,2-diphenylhydrazine (4.0 g, 21.71 mmol) in 40 mL
of THF at -78 °C. This reaction mixture was stirred for 3 h
while slowly warming to -40 °C. The formed greenish-yellow
solution was added slowly via cannula to a stirred solution of
ClPPh2 (8.0 mL, 43.42 mmol) cooled with an ice-bath, and
stirring was continued overnight at room temperature. THF was
removed from the reaction mixture under reduced pressure, and
the residue was washed with diethyl ether (3 ꢀ 20 mL) and n-
hexane (2 ꢀ 10 mL), followed by drying under vacuum, which
resulted in the isolation of a yellow solid. This solid was
recrystallized from a mixture of THF/hexane to give pure
product as a colorless (or very pale yellow) solid (7.5 g, 63%).
Single crystals suitable for X-ray diffraction were obtained from
a 1:1 mixture of CH2Cl2/EtOH, mp 131 °C. 1H NMR (THF-d8):
δ 6.58-6.64 (m, 2 H), 6.80-6.89 (m, 8 H), 7.07-7.31 (br m, 12
H), 7.51-7.64 (br m, 8 H). 13C{1H} NMR (THF-d8): δ 117.61 (s,
CH), 120.29 (s, CH), 127.53 (m, CH), 130.75 (m, Cq), 135.73 (dd,
J = 24.78, 2.55 Hz, Cq), 146.51 (t, J = 5.17 Hz, Cq). 31P{1H}
NMR (THF-d8): δ 64.64. HRMS (ESI): calcd for [M þ Hþ]
(C36H31N2P2), 553.1957; found, 553.19579. Anal. Calcd for
C36H30N2P2: C, 78.25; H, 5.47; N, 5.07. Found: C, 77.95; H,
5.48; N, 4.85.
Method B. Ph2PN(Ph)NHPh (2). Chlorodiphenylpho-
sphine (1.0 mL, 5.43 mmol) was added to a stirred solution of
1,2-diphenylhydrazine (500 mg, 2.71 mmol) in 10 mL of CH2Cl2.
To this reaction mixture was added dropwise Et3N (0.76 mL,
5.43 mmol, diluted in 40 mL of CH2Cl2) over a period of 4 h, and
the mixture was stirred at room temperature for a further 12 h.
CH2Cl2 was removed from the reaction mixture and the residue
extracted with diethyl ether. Removal of the diethyl ether gave a
yellow viscous oil. Crystallization from hot hexane gave 500 mg
(50%) of a pale yellow crystalline product, whose spectral data
agreed with those reported in the literature.12
The purified polyethylene obtained from the experiments
Cat1 and Cat2 were characterized by 1H NMR (C6D5Br),16
and the results are included in Table 3. The high selectivity
for linear R-olefins (>98%) is observed, and the average
molecular weights (MNMR) of the polyethylene depended on
the catalyst system used. The data in Table 3 revealed, by
changing the catalyst system from Cr(acac)3 to CrCl3
3
3THF, that the molecular weight of formed polyethylene
doubled, while the difference in the selectivity toward
R-olefins is negligible.
Conclusions
Ph2PN(Ph)N(Ph)PPh2 (1). A 2.5 M hexane solution of n-
BuLi (0.35 mL, 0.87 mmol) was added to a stirred solution of 2
(338 mg, 0.92 mmol) in 5 mL of THF at -78 °C. This reaction
mixture was stirred for 3 h, while slowly warming to -40 °C. The
formed greenish-yellow solution was added slowly via cannula
to a stirred solution of ClPPh2 (0.17 mL, 0.92 mmol) cooled in an
ice-bath, and stirring continued at room temperature overnight.
THF was removed from the reaction mixture under reduced
pressure, and the residue was washed with diethyl ether (3 ꢀ 5
mL) and hexane (2 ꢀ 5 mL), followed by drying under vacuum,
giving a yellow solid. This solid was recrystallized from a
mixture of THF/hexane to give pure product as a colorless (or
very pale yellow) solid (218 mg, 43%). Analytical data match
with those reported above in method A.
In conclusion, we have reported the synthesis and
characterization of 1,2-bis(diphenylphosphino)-1,2-diphe-
nylhydrazine (1) and its square-planar Ni(II) (3), Pd(II) (4),
and Pt(II) (5) complexes. The PNNP ligand in combina-
tion with Cr(III) or Ni(0) compounds activated by MAO
was found to form active catalysts for the oligomeriza-
tion of ethylene. Whereas chromium-based catalysts resulted
in the formation of polyethylene, the nickel catalysts
€
(15) For a detailed description of the experimental setup see: Wohl,
A.; Muller, W.; Peulecke, N.; Muller, B. H.; Peitz, S.; Heller, D.;
€
€
Rosenthal, U. J. Mol. Catal A: Chem. 2009, 297, 1–8.
[NiCl2{Ph2PN(Ph)N(Ph)PPh2-P,P}] (3). CH2Cl2 (10 mL) was
added to a mixture of solid Ph2PN(Ph)N(Ph)PPh2 (147 mg,
0.266 mmol) and [NiCl2(DME)] (58.5 mg, 0.266 mmol) at room
(16) For information about the polyethlyne NMR measurement see:
Aluri, B. R.; Kindermann, M. K.; Jones, P. G.; Heinicke, J. Chem.;
Eur. J. 2008, 14, 4328-4335, and references therein.

Article
Organometallics, Vol. 29, No. 1, 2010 231
temperature, and the mixture was stirred for 16 h. The solution
was filtered, and the volatiles were removed under reduced
pressure. The residue was washed with diethyl ether (2 ꢀ 10
mL) and pentane (2 ꢀ 10 mL) and dried under vacuum to give a
yellow solid. This solid was dissolved in CHCl3 and overlayered
with pentane to give 154 mg (85%) of colorless crystals of
desired product, mp 180 °C (dec). 1H NMR (CDCl3): δ
6.66-6.69 (m, 4 H), 6.75-6.83 (m, 6 H), 7.34 (t, J = 7.6 Hz, 8
H), 7.47 (t, J = 7.6 Hz, 4 H), 7.94 (m, 8 H). 31P{1H} NMR
(CDCl3): δ 117.14. Anal. Calcd for C36H30Cl2N2NiP2: C, 63.38;
H, 4.43; N, 4.11. Found: C, 63.30; H, 4.57; N, 4.02.
[PdCl2{Ph2PN(Ph)N(Ph)PPh2-P,P}] (4). [PdCl2(NCPh)2]
(145 mg, 0.377 mmol) was added to a solution of Ph2PN(Ph)N-
(Ph)PPh2 (208 mg, 0.377 mmol) in CH2Cl2 (10 mL) at room
temperature. The mixture was stirred for 16 h; then the volatiles
were removed under reduced pressure. The residue was dis-
solved in CHCl3 and overlayed with pentane to give 272 mg
(99%) of a pure yellow crystalline product, mp 221 °C (melted
with decomposition). 1H NMR (CDCl3): δ 6.76-6.80 (m, 4 H),
6.84-6.88 (m, 6 H), 7.31 (tm, J = 8.0 Hz, 8 H), 7.44 (tm, J = 7.2
Hz, 4 H), 7.79-7.86 (m, 8 H). 31P{1H} NMR (CDCl3): δ 126.07.
HRMS (ESI): m/z calcd for C36H30Cl2N2NaP2Pd, 753.01924
[M þ Na]þ; found, 753.01867. Anal. Calcd for C36H30Cl2N2-
P2Pd CHCl3: C, 52.33; H, 3.68; N, 3.30. Found: C, 52.23; H,
3.83; N, 3.19.
[PtCl2{Ph2PN(Ph)N(Ph)PPh2-P,P}] (5). [PtCl2(COD)] (85
mg, 0.227 mmol) was added to a solution of Ph2PN(Ph)N-
(Ph)PPh2 (125 mg, 0.227 mmol) in CH2Cl2 (4 mL) at room
temperature. The mixture was stirred for 16 h, and then the
volatiles were removed under reduced pressure to obtain a white
powder. This was washed with hexane to remove the free cyclo-
octadiene and dried under vacuum to obtain 180 mg of the title
complex (97%), mp 250 °C (dec). 1H NMR (CDCl3): δ
6.76-6.80 (m, 4 H), 6.83-6.86 (m, 6 H), 7.28-7.34 (m, 8 H),
7.42 (td, J = 7.6, 1.3 Hz, 4 H), 7.78-7.85 (m, 8 H). 31P{1H}
NMR (CDCl3): δ 96.34 (s, 1JPt-P = 3992 Hz). HRMS (ESI): m/
z calcd for C36H30Cl2N2NaP2Pt, 840.08012 [M þ Na]þ; found,
840.083. Anal. Calcd for C36H30Cl2N2P2Pt.CH2Cl2: C, 49.19;
H, 3.57; N, 3.10. Found: C, 49.59; H, 3.66; N, 2.77.
[Pd{Ph2PN(Ph)N(Ph)PPh2-P,P}(NCMe)2][BF4]2 (6). The
complex [PdCl2{Ph2PN(Ph)N(Ph)PPh2-P,P}] (105 mg, 0.144
mmol) was treated with AgBF4 (56 mg, 0.288 mmol) in a 1:1
mixture of CH2Cl2/CH3CN at ambient temperature. The reac-
tion mixture was stirred for 4 h; then the solution was filtered and
the volatiles were removed under reduced pressure to leave a
yellow crystalline mush. This was recrystallized from a saturated
solution of CH2Cl2 (105 mg, 80%). 1H NMR (CD2Cl2): δ 2.10 (s,
6 H, CH3CN), 6.81-6.84 (m, 4 H), 6.99-7.03 (m, 6 H), 7.53 (td,
J = 7.3, 3.6 Hz, 8 H), 7.66-7.77 (m, 12 H) (Note: at 2.10 ppm
integral ratio is excess). 31P{1H} NMR (CD2Cl2): δ 123.25.
Anal. Calcd for C40H36B2F8N4P2Pd: C, 52.52; H, 3.97; N, 6.13.
Found: C, 46.82; H, 3.79; N, 5.35 (no better analyses could be
obtained).
Oligo- and Polymerization of Ethylene. The autoclave was
heated at 150 °C under vacuum for 2 h and cooled either to 45 °C
(Cr catalyst) or to 100 °C (Ni Catalyst) under argon atmosphere.
A solution or suspension of ligand and the corresponding metal
precursor (according to Figure 5) were stirred together at
ambient temperature in toluene (∼90.4 mL) for 2 h. To this
was added 9.8 mL of MAO in toluene solution (10% w/w), and
the resulting solution was transferred into a preheated autoclave
(300 mL) under an argon atmosphere. Afterward, the autoclave
was pressurized with 30 bar of ethylene by opening the valve of a
2 kg aluminum cylinder. During the run, a constant ethylene
pressure of 30 bar was applied, and the temperature was
controlled through an internal cooling spiral against the
exotherm of the reaction. The weight loss of the ethylene
cylinder was recorded and the amount of ethylene consumed
was deduced from the weight loss of the ethylene cylinder after
saturation.15 After the run, the autoclave was cooled to below
10 °C. After releasing the excess ethylene from the autoclave, the
contents (polymer with solvent and oligomers) were transferred
to a flask. Then all the volatiles were flash-distilled at 3-4 mbar/
70-80 °C, treated with 1 M hydrochloric acid solution, and
submitted for GC analysis. The residual polymer was extracted
with a mixture of methanol and concentrated hydrochloric acid
(1:1) by stirring overnight at room temperature and was then
washed with methanol and dried under vacuum. The melting
points of the polymers were measured on a differential scanning
calorimeter instrument, model DSC 823e (Mettler Toledo).
X-ray Structure Analysis of 1, 3, 4, and 5. Data were collected
on a STOE IPDS II diffractometer using graphite-monochro-
mated Mo KR radiation. The structures were solved by direct
methods (SHELXS-97)17 and refined by full-matrix least-
squares techniques on F2 (SHELXL-97).17 XP (Bruker AXS)
was used for graphical representations.
Acknowledgment. We thank Prof. J. Heinicke, Prof. A.
Schulz, A. Weiss, and B. Kaleswara Rao for useful
discussions. The help of PD Dr. W. Baumann with the
€
NMR data as well as of Dr. Wolfgang Muller and Dr.
Anina Wohl (both from Linde AG, Linde Engineering
€
Division) with technical setup is gratefully acknowledged.
Supporting Information Available: X-ray details and CIF files.
This material is available free of charge via the Internet at http://
pubs.acs.org.
(17) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112–122.