Coordination chemistry of new selective ethylene trimerisation ligand Ph2PN(iPr)P(Ph)NH(R) (R = iPr, Et) and tests in catalysis

Article abstract of DOI:10.1039/c0dt00440e

The synthesis of [Ph₂PN(ⁱPr)P(Ph)NH(R)] (R = ⁱPr, Et) (1, 2) is described and the structure of 2 has been determined by single-crystal X-ray analysis. Compound 1 readily reacts with chromium(0), nickel(0), nickel(ii), pall

Full text of DOI:10.1039/c0dt00440e

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Coordination chemistry of new selective ethylene trimerisation ligand
i
Ph2PN(iPr)P(Ph)NH(R) (R = Pr, Et) and tests in catalysis†‡
Bhaskar Reddy Aluri,a Normen Peulecke,a Stephan Peitz,a Anke Spannenberg,a Bernd H. Mu¨ller,a
Stefan Schulz,a Hans-Joachim Drexler,a Detlef Heller,a Mohammed H. Al-Hazmi,b Fuad M. Mosa,b
Anina Wo¨hl,c Wolfgang Mu¨llerc and Uwe Rosenthal*a
Received 7th May 2010, Accepted 28th May 2010
First published as an Advance Article on the web 30th July 2010
DOI: 10.1039/c0dt00440e
i
The synthesis of [Ph2PN(iPr)P(Ph)NH(R)] (R = Pr, Et) (1, 2) is described and the structure of 2 has
been determined by single-crystal X-ray analysis. Compound 1 readily reacts with chromium(0),
nickel(0), nickel(II), palladium(II), platinum(II) and iron(II) complexes to give four-membered rings
(3–10) via P,P¢ coordination. The molecular structures of [Cr(CO)4{Ph2PN(iPr)P(Ph)NH(R)-P,P¢}]
i
(R = Pr, Et) (3, 4), [Cr(CO)3(NCCH3){Ph2PN(iPr)P(Ph)NH(iPr)-P,P¢}] (5),
[Ni{Ph2PN(iPr)P(Ph)NH(iPr)-P,P¢}2] (6), cis-[MX2{Ph2PN(iPr)P(Ph)NH(iPr)-P,P¢}] (M = Ni, Pd, Pt;
X = Cl or Br) (7, 8, 9) and trans-[Fe(NCCH3)2{Ph2PN(iPr)P(Ph)NH(iPr)-P,P¢}2](BF4)2 (10) have been
determined by X-ray diffractio◦n. In the solid state, these complexes show tight phosphine bite angles in
the range 67.89(2)◦ to 74.97(4) and the central nitrogen atom adopts an almost planar (sp2) geometry.
Complexes 3, 5, 6, 7 and 10 are tested for their catalytic activity in ethylene oligomerisation.
Additionally, complex 10 is tested in hydrogenation of olefins.
proved to be highly active in ethylene trimerisation by giving high
Introduction
yield and selectivity towards 1-hexene,6a comparable to Sasol’s
Organometallic complexes containing functionalized phosphine
PNP ligand.
and aminophosphine ligands have attracted considerable interest
To further develop our understanding of this unique ligand
in recent years, due to their wide spread application potential
system (PNPNH), we herein describe the synthesis and structural
in the field of catalysis.1 In addition, some aminophosphines
i
characterization of [Ph2PN(iPr)P(Ph)NH(R)] (R = Pr, Et) (1,
and derivatives have also been investigated as anticancer drugs,2
2), and also demonstrate that chromium(0), nickel(0), nickel(II),
herbicides and antimicrobial agents, as well as neuroactive agents.3
palladium(II), platinum(II) and iron(II) chelate complexes (3–10)
Functionalized aminophosphines are proved to be versatile lig-
can be readily prepared with these ligands. The newly synthesized
ands since the functional group can be modified to tune the
chromium, nickel and iron complexes are tested in ethylene
chemical and physical properties of the final product, resulting
oligomerisation catalysis. Further, the iron complex is also tested
in significant changes in their coordination behaviour, in the
in hydrogenation of simple olefins.
structural parameters of the resulting complexes and in their
subsequent reactivity.4
We have an ongoing interest in such compounds5 and very re-
cently, we reported the synthesis of an aminophosphine ligand type
Ph2PN(R)P(Ph)NH(R) (R π H) (PNPNH)6 which is related to the
well known bis(diphenylphosphino)-amines (PNP) and possesses
an extra terminal NH function. Coordination of PNPNH to metal
centres can occur through the lone pair of electrons at one or
both of the phosphorus centres as well as by deprotonation of the
NH group to form a tridentate ligand. The PNPNH compound
Ph2PN(iPr)P(Ph)NH(iPr) 1 in conjunction with chromium is
Results and discussion
The two different methods for the synthesis of PNPNH com-
pounds were described earlier.6a Compound 1 was already known
and prepared following the reported procedure. The reaction of
Ph2PN(iPr)PPhCl7 with a 1 : 1 mixture of EtNH2 and toluene
gave compound 2. Workup of the reaction mixture, followed by
recrystallization of the resulting residue from n-hexane gave 2 in
a moderate yield (55%) as an air-stable, crystalline white solid
readily soluble in diethyl ether, toluene, and methylene chloride.
1
(Scheme 1). The 31P{ H} NMR spectra showed two broad singlets
aLeibniz-Institut fu¨r Katalyse e. V. an der Universita¨t Rostock, Albert-
Einstein-Straße 29a, 18059, Rostock, Germany. E-mail: uwe.rosenthal@
catalysis.de
at d 41.0 and 72.6 corresponding to two phosphorus nuclei with
different chemical environments.
bSaudi Basic Industries Corporation, P.O. Box 42503, Riyadh, 11551, Saudi
Arabia
cLinde AG, Linde Engineering Division, Dr -Carl-von-Linde-Straße 6-14,
82049, Pullach, Germany
† CCDC reference numbers 780221–780229. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/c0dt00440e
‡ Dedicated to Professor Sandro Gambarotta on the occasion of his 60th
birthday.
Scheme 1 Synthesis of Ph2PN(iPr)P(Ph)NH(Et) (2).
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Crystals suitable for X-ray analysis were obtained from a
saturated n-hexane solution of 2 at -40 ◦C. Crystal data and some
details of the data collection and refinement of the ligand and
prepared complexes (vide infra) are given in Table 1. The molecular
structure of compound 2 and selected bond distances and angles
are given in Fig. 1. The N1 atom is in a slightly distorted trigonal
planar environment with the angles adding up to 359.8◦ (P1–N1–
C19 116.61(11), P2–N1–C19 120.09(12), P1–N1–P2 123.09(8)◦)
and the P2 atom is in a distorted trigonal pyramidal shape with
angles ranging from 99.75(8)◦ to 107.70(8)◦, the median value
being 100.01(7). The P–N–P, N–P–N angles and P–N distances
are in the usual range and are comparable to the earlier reported
compound 1.6
The infrared spectra of 3 and 4 reveal very similar stret-
ching frequencies and are consistent with those previously
reported for cis-phosphine-substituted tetracarbonyl com-
9
plexes Cr(CO)4{NMe(PPh2)2} (~1925 cm-1) and Cr(CO)4-
10
{(Ph2PCH2PPh2} (~1927 cm-1), and are tabulated in Table 2.
A single-crystal X-ray diffraction study confirmed the spectro-
scopic assignment of 3 and 4. Single crystals were obtained from
◦
a dichloromethane–methanol solution at -40 C. The structures
and selected bond distances and angles are illustrated in Fig. 2 and
3. Both complexes 3 and 4 show distorted octahedral coordination
at chromium with a nearly planar Cr–P–N–P ring. The sum of the
angles around N1 is 359.3◦ and 359.9◦ respectively for 3 and 4,
and implies sp2 hybridisation at this nitrogen. The Cr–CO bond
lengths trans to the phosphorus atoms are slightly shorter than
those trans to other carbonyls in 3 and are consistent with the
weaker trans-influence of the Cr–P bond. The Cr–P bond lengths,
P–Cr–P and P–N–P bond angles are similar to the ones reported
for [Cr(CO)4{Ar2PN(Me)PAr2}].8
Fig. 1 Molecular structure of Ph2PN(iPr)P(Ph)NH(Et) (2). Thermal
ellipsoids are drawn at the 30% probability level. All the H atoms except
the one attached to the N2 atom are omitted for clarity. Important bond
◦
˚
lengths [A] and angles [ ]: N1–P1 1.7092(15), N2–P2 1.678(2), N1–P2
1.7155(14), P1–N1–P2 123.09(8), N2–P2–N1 107.70(8).
Fig. 2 Molecular structure of [Cr(CO)4{Ph2PN(iPr)P(Ph)NH(iPr)-P,P¢}]
(3). Thermal ellipsoids are drawn at the 30% probability level. All the H
atoms except the one attached to the N2 atom are omitted for clarity.
◦
˚
Our previous publication6a describes a very interesting coordi-
nation behaviour of ligand 1 which coordinates with chromium
and aluminium centres in either a P,P¢ or P,N chelation
mode. To gain more knowledge about the coordination chem-
istry of this ligand, the chromium tetracarbonyl complexes
[Ph2PN(iPr)P(Ph)N(R)H]Cr(CO)4 (R = iPr, Et) (3, 4) were
prepared (Scheme 2) following the method reported by Wass
et al.8 Reaction of 1 or 2 with Cr(CO)6 in toluene at reflux
temperature furnished chromium(0) carbonyl complexes 3 and
4 by CO displacement with diphosphine, in a moderate yield
Important bond lengths [A] and angles [ ]: N1–P1 1.695(2), N2–P2
1.646(2), N1–P2 1.715(2), P1–Cr1 2.3388(6), P2–Cr1 2.3602(6), Cr1–C1
1.877(2), Cr1–C2 1.852(2), Cr1–C3 1.879(2), Cr1–C4 1.856(2); P1–N1–P2
100.61(9), N2–P2–N1 112.27(10), P1–Cr1–P2 67.90(2).
11
Reaction of fac-Cr(CO)3(NCCH3)3 with an equimolar quan-
tity of 1 in acetonitrile at 60 ◦C results in the quantitative forma-
tion of [Cr(CO)3(NCCH3) {Ph2PN(iPr)P(Ph)NH(iPr)-P,P¢}] (5)
(Scheme 3). In the room temperature NMR spectra two sets of
signals are observed in a 2 : 1 ratio belonging to two isomers. The
1
31P{ H} NMR signals appeared at 99.4, 121.7 (d, J = 16.7 Hz)
2
(60% and 55%). Spectroscopic data are consistent with a (P,P¢)-k
and 107.0, 120.6 (d, J = 25.6 Hz) for major and minor isomers
respectively. The infrared spectrum shows three carbonyl stretch-
ing vibrations at 1923, 1830, 1802 cm-1 and are comparable to the
values reported for [Mo(CO)3(NCCH3){Ph2PN(iPr)P(Ph)(DMP)-
P,P¢}] (DMP = 3,5-dimethylpyrazole).12
coordination mode.
Single crystals of 5 suitable for X-ray diffraction were obtained
from a saturated solution of acetonitrile at -20 ◦C. The molecular
structure and selected bond distances and angles are illustrated
in Fig. 4. Complex 5 is a six-coordinated complex with a
P,P¢-bidentate [PNPNH] ligand with a spectating amine but
coordinated CH3CN. It is stable in pure and dry CH3CN, and
traces of moisture in solvent led to the formation of substantial
Scheme 2 Synthesis of [Cr(CO)4 {Ph2PN(iPr)P(Ph)NH(R)-P,P¢}] (R =
iPr, Et) (3, 4).
7912 | Dalton Trans., 2010, 39, 7911–7920
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Table 2 Carbonyl stretching frequencies for complexes 3 and 4
n(CO) (CH2Cl2, cm-1)
n(CO)av (CH2Cl2, cm-1)
3
4
1870, 1896, 1918, 2005
1877, 1890, 1917, 2005
1922
1922
Fig.
4
Molecular structure of [Cr(CO)3(NCCH3){Ph2PN(iPr)–
P(Ph)NH(iPr)-P,P¢}] (5). Thermal ellipsoids are drawn at the 30%
probability level. All the H atoms except the one attached to◦N1 atom
˚
are omitted for clarity. Important bond lengths [A] and angles [ ]: N2–P2
1.6973(14), N1–P1 1.6432(15), N2–P1 1.7270(13), P2–Cr1 2.3455(5),
P1–Cr1 2.3637(5), Cr1–C25 1.853(2), Cr1–C26 1.819(2), Cr1–C27
1.855(2), Cr1–N3 2.0531(15); P1–N2–P2 100.73(7), N2–P1–N1 113.13(7),
P1–Cr1–P2 68.113(15).
Fig. 3 Molecular structure of [Cr(CO)4{Ph2PN(iPr)P(Ph)NH(Et)-P,P¢}]
(4). Thermal ellipsoids are drawn at the 30% probability level. All the
H atoms except the one attached to N2 ◦atom are omitted for clarity.
˚
Important bond lengths [A] and angles [ ]: N1–P1 1.6958(13), N2–P2
1.6519(14), N1–P2 1.7131(13), P1–Cr1 2.3342(7), P2–Cr1 2.3312(6),
Cr1–C25 1.865(2), Cr1–C26 1.863 (2), Cr1–C27 1.881(2), Cr1–C24
1.854(2); P1–N1–P2 100.15(7), N2–P2–N1 112.67(7), P1–Cr1–P2 68.16(2).
Scheme 4 Synthesis of [Ni{Ph2PN(iPr)P(Ph)NH(iPr)-P,P¢}2] (6).
1
state. Apart from it, in H NMR two sets of signals in 7 : 3 ratio
(possibly two different isomers) are observed in the aliphatic
region while the aryl region is less informative. Owing to the
adjacent chiral phosphorus atom all the (eight) methyl protons
show different resonances. Among these, two methyl resonances
are strongly upfield shifted (0.03 and 0.17 ppm) indicating that
these methyl groups are shielded by the phenyl groups. The more
preferable isomeric structure is further characterized by X-ray
crystal structure analysis.
Crystals of 6 suitable for X-ray analysis were obtained from a
saturated n-hexane solution at -40 ◦C. The molecular structure
is shown in Fig. 5. The crystal structure shows one molecule of 6
and a half n-hexane molecule in the asymmetric unit. The nickel
atom adopts a distorted tetrahedral geometry. The planes defined
by P1–N1–P2–Ni1 and P3–N3–P4–Ni1 are nearly perpendicular
to each other. The angle between these two planes is 87.12(3). The
P–Ni bond distances and P–Ni–P angles are in the range reported
for the bis-chelate nickel(0) complex [Ni{Ar2PN(Me)PAr2}2].13
The reaction of 1 with group 10 metals i.e. NiCl2(DME),
PdCl2(PhCN)2 and PtBr2(COD) in a 1 : 1 molar ratio at room
temperature affords air stable, mononuclear, square planar
complexes cis-[NiCl2{Ph2PN(iPr)P(Ph)NH(iPr)-P,P¢}] (7), cis-
[PdCl2{Ph2PN(iPr)P(Ph)NH(iPr)-P,P¢}] (8), cis-[PtBr2{Ph2PN-
(iPr)P(Ph)NH(iPr)-P,P¢}] (9) (Scheme 5) in excellent yields
Scheme 3 Synthesis of [Cr(CO)3(NCCH3){Ph2PN(iPr)P(Ph)NH(iPr)-
P,P¢}] (5).
quantities of tetracarbonyl complex 3 by redistribution. This kind
of behaviour is observed earlier in molybdenum complexes.12
In the solid state chromium possesses a distorted octahedral
geometry with acetonitrile lying trans to a CO ligand and the
remaining two carbonyls located trans to phosphorus atoms. The
three Cr–CO distances are 1.853(2), 1.819(2), 1.855(2) where the
shortest distance represents the carbonyl ligand located trans to the
acetonitrile group. The P–N–P angle is the same as that observed
for the tetracarbonyl complex 3.
Further, the coordination chemistry of 1 with group 10
transition-metals (Ni, Pd and Pt) was explored. Treatment of
Ni(COD)2 with 2 equiv. of PNPNH (1) in n-hexane at ambient
temperature afforded [Ni{Ph2PN(iPr)P(Ph)NH(iPr)-P,P¢}2] (6) in
50% yield (Scheme 4).
1
As expected, in the 31P{ H} NMR spectrum two multiplets
centered at d 77.5, 98.5 are observed for this bis-chelate complex 6
due to coupling of each phosphorus with three other phosphorus
nuclei and possible rotation around the metal center in the solution
7914 | Dalton Trans., 2010, 39, 7911–7920
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and diphosphinoalkane16 complexes. Additionally, the presence
of a four-membered ring may also have some influence on the
observed high shielding. In the 1H NMR spectrum four different
methyl(iPr) resonances are observed owing to the presence of an
adjacent phosphorus chiral centre. From these methyl resonances
two are shielded and the other two are deshielded compared to the
1
free ligand chemical shifts. The sharp signals in 1H, and 31P{ H}
NMR spectra of 7 are consistent with a diamagnetic square-planar
Ni species in solution.
Single crystals of 7, 8 and 9 suitable for X-ray diffraction studies
were obtained by slow diffusion of diethyl ether into a solution
of the complexes in dichloromethane at room temperature. A
perspective view of the molecules with important bond lengths
and angles is given in Fig. 6–8.
Fig. 5 Molecular structure of [Ni{Ph2PN(iPr)P(Ph)NH(iPr)-P,P¢}2] (6).
Thermal ellipsoids are drawn at the 30% probability level. All the
H atoms except the one attached to the N2 atom are omitted for
◦
˚
clarity. Important bond lengths [A] and angles [ ]: N1–P1 1.710(2),
N2–P2 1.674(2), N1–P2 1.729(2), N3–P3 1.707(2), N4–P4 1.668(2), N3–P4
1.723(2), P1–Ni1 2.1590(8), P2–Ni1 2.1573(8), P3–Ni1 2.1603(8), P4–Ni1
2.1558(8), P1–N1–P2 99.54(11), N2–P2–N1 110.18(12), P3–N3–P4
99.49(11), N4–P4–N3 109.79(12), P1–Ni1–P2 74.93(3), P2–Ni1–P3
130.64(3), P3–Ni1–P4 74.68(3), P4–Ni1–P1 130.35(3).
Fig. 6 Molecular structure of [NiCl2{Ph2PN(iPr)P(Ph)NH(iPr)-P,P¢}]
(7). Only one of the two molecules of the asymmetric unit is shown.
Thermal ellipsoids are drawn at the 30% probability level. All the
H
atoms except the one attached to N2 atom are omitted for
◦
˚
clarity. Important bond lengths [A] and angles [ ]: N1–P1 1.687(2),
N2–P2 1.620(2), N1–P2 1.699(2), P1–Ni1 2.1108(6), P2–Ni1 2.1220(6),
Ni1–Cl1 2.2010(6), Ni1–Cl2 2.1787(6), P1–N1–P2 96.95(9), N2–P2–N1
115.07(10), P1–Ni1–P2 73.58(2), P2–N2–C16 96.95(9), Ni1–P2–N2
119.48(7), Cl1–Ni1–Cl2 96.91(3); N3–P3 1.686(2), N4–P4 1.630(2),
N3–P4 1.694(2), P3–Ni2 2.1152(6), P4–Ni2 2.1342(5), Ni2–Cl3 2.1843(6),
Ni2–Cl4 2.2058(6), P3–N3–P4 97.88(9), N4–P4–N3 114.62(9), P3–Ni2–P4
73.71(2), P4–N4–C40 124.62(14), Ni2–P4–N4 116.25(7), Cl3–Ni2–Cl4
97.52(3).
Scheme 5 Synthesis of cis-[MX2{Ph2PN(iPr)P(Ph)NH(iPr)-P,P¢}] (M =
Ni, Pd, Pt; X = Cl or Br) (7, 8, 9).
(80–89%). These complexes are insoluble in benzene and toluene,
partially soluble in THF but are readily soluble in CH2Cl2.
1
The room temperature 31P{ H} NMR spectra of 7, 8, and 9 in
CD2Cl2 display two doublets at d 41.9, 44.1 (2JPP = 180.5 Hz);
35.5, 36.7 (2JPP = 21.2 Hz); and 16.3, 17.9 (2JPP = 35.0 Hz, 1JPtP
=
3600, 3402 Hz) ppm, respectively. The large 1JPtP coupling constant
observed for 9 is in good agreement with a cis disposition of ligands
1
(i.e. phosphorus trans to chloride). The 31P{ H} NMR spectra of
the complexes shows an AB pattern and the chemical shifts are
shifted considerably upfield compared with the free ligand. This
shift indicates that the ligand is coordinated in a P,P¢-chelating
mode, forming four-membered metallacycles,14 as has been shown
by the X-ray crystal structure determination of 7, 8 and 9. It
is well known that the shielding of the coordinated ꢀꢁP–N (Dd)
depends on the electronegativity of the substituents attached to
the phosphorus centre and decreases in the order NCP–N > CCP–
N.15 Among these complexes (7–9) the central phosphorus (NCP–
N) shows the highest shielding (Dd = -24 to -50 ppm), relative
to the terminal phosphorus (Ph2P–N) (Dd = +0.7 to -25 ppm).
This shielding effect is increased in the order Ni < Pd < Pt.
Similar types of shielding effect are observed in diphosphazane4
Fig. 7 Molecular structure of [PdCl2{Ph2PN(iPr)P(Ph)NH(iPr)-P,P¢}]
(8). Thermal ellipsoids are drawn at the 30% probability level. All the
H atoms except the one attached to N1 a◦tom are omitted for clarity.
˚
Important bond lengths [A] and angles [ ]: N2–P2 1.688(2), N1–P1
1.618(2), N2–P1 1.704(2), P2–Pd1 2.2007(5), P1–Pd1 2.2237(4), Pd1–Cl2
2.3663(5), Pd1–Cl1 2.3539(6), P1–N2–P2 99.87(9), N2–P1–N1 114.40(10),
P1–Pd1–P2 71.84(2).
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signals which are centered at 91.6 and 105.4 ppm. The chemical
shifts are deferred considerably downfield compared with the free
1
ligand. In H NMR two sets of signals are observed in a 2 : 1
ratio, belonging to two different isomers of complex 10, probably
formed by rotation of the PNPNH unit around the metal centre in
solution. The major isomer is the one where two Ph2P-groups
are trans to each other and in the minor isomer they are cis
to each other. The more preferable isomeric structure is further
characterized by X-ray crystal structure analysis. Single crystals
of 10 were obtained from an acetonitrile solution overlaying
with MTBE (methyl tbutyl ether) at room temperature. The
asymmetric unit of 10 consists of two half molecules of the cation
and two BF4 anions. The molecular structure (Fig. 9) shows
distorted octahedral coordination geometry at iron(II) with nearly
planar Fe–P–N–P rings. The two molecules of acetonitrile are
trans to each other and the PNPNH ligands coordinate in P,P¢-
chelating mode. The Fe–P bond distances and P–Fe–P bond angles
are in the range of related iron(II) complexes.17
Fig. 8 Molecular structure of [PtBr2{Ph2PN(iPr)P(Ph)NH(iPr)-P,P¢}]
(9). Thermal ellipsoids are drawn at the 30% probability level. All the
H atoms except the one attached to the N2 atom are omitted for
◦
˚
clarity. Important bond lengths [A] and angles [ ]: N1–P1 1.695(3),
N2–P2 1.623(3), N1–P2 1.708(3), P1–Pt1 2.2084(8), P2–Pt1 2.2035(8),
Pt1–Br1 2.4902(4), Pt1–Br2 2.4805(4), P1–N1–P2 100.14(14), N2–P2–N1
113.87(15), P1–Pt1–P2 72.54(3).
The solid-state structure of 7 shows the presence of two
enantiomers (R and S) in the asymmetric unit along with two
molecules of dichloromethane. The two enantiomers adopt a
similar (but not identical) conformation. The geometry at the
nickel centre is distorted square planar. The main distortions are
the acute P1–Ni1–P2 (73.58(2)◦), P3–Ni2–P4 (73.71(2)◦) angles
which results from the small bite angle of the ligand. Similar to the
nickel complex, the molecules 8 and 9 (Fig. 7, 8) adopt a distorted
square planar geometry at palladium and platinum with cis-halides
and both phosphorus of the neutral ligand coordinated to the
metal. The relative configuration of the asymmetric phosphorus
atom in the depicted ligands is S. The R enantiomer is generated
by the inversion symmetry of the space group. In addition, the
asymmetric unit of 9 contains besides one complex molecule, a
half CH2Cl2 as lattice solvent. Within the ligand, the P–N bond
lengths are similar to those in the free ligand. The central nitrogen
atom N1 (and N3 for 7) adopts a planar geometry and the sum of
the angles around the nitrogen is nearly 360◦. The bite angles in 8
and 9 (71.845(3)◦ and 72.54(3)◦) are relatively smaller compared
to Ni(II) complex 7 (73.58(2)◦ and 73.71(2)◦).
Fig. 9 Molecular structure of the cation [Fe(CH3CN)2{Ph2PN(iPr)-
P(Ph)NH(iPr)-P,P¢}2]+ of 102+ (completed by using the symmetry operator
-x + 2, -y, -z + 1). Thermal ellipsoids are drawn at the 30% probability
level. All the H atoms except the ones attached to N1 and N1A, the
second half cation of the asymmetric unit and the anions are omitted
◦
˚
for clarity. Important bond lengths [A] and angles [ ]: N1–P1 1.657(3),
N2–P1 1.709(3), N2–P2 1.706(3), Fe1–P1 2.2456(10), Fe1–P2 2.2701(12),
P1–N2–P2 101.21(15), P1–Fe1–P2 71.52(4).
Finally, trans-[Fe(CH3CN)2{Ph2PN(iPr)P(Ph)NH(iPr)-P,P¢}2]-
(BF4)2 (10) was synthesized by the reaction of [Fe(H2O)6](BF4)2
with two equivalents of compound 1 in acetonitrile at room
temperature (Scheme 6).
In all the above mentioned complexes (3–10), the nitrogen atoms
were not involved in any coordination to the metal centres because
the phosphorus atoms in the aminophosphine ligand are much
stronger donor centres and thus, coordination to the metal centre
takes place preferentially at the phosphorus atoms. However, it
deserves to be noted that lithiation of compound 1, followed
by treatment with Li[CpCrCl3] gave a P,N-coordinated Cr(III)
complex.6a
Ethylene oligomerisation
As mentioned in the introduction, the PNPNH compound 1
forms a very efficient catalytic system in combination with
CrCl3(THF)3 and triethylaluminium (TEA) for selective ethylene
trimerisation, giving over 99% of 1-hexene in the fraction of
the hexenes.6a In this context, it was interesting to check the
activity of newly synthesized Cr(0) complexes in the ethylene
Scheme 6 Synthesis of trans-[Fe(CH3CN)2{Ph2PN(iPr)P(Ph)NH(iPr)-
P,P¢}2](BF4)2 (10).
Similar to bis-chelate Ni(0) complex 6, the room temperature
1
31P{ H} NMR spectra of 10 in CD3CN display two multiplet
7916 | Dalton Trans., 2010, 39, 7911–7920
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Table 3 Ethylene oligomerisation
Oligomer wt. (%) distribution
PE/g C4e
C6 (1-C6) C8 (1-C8) C10
Entry Complex C2H4 consumed/g Productivity d(g g-1 M)
Activity (g g-1 Md/h)
C12+
1
2
3
4
5
6
7
3a
3b
5
1.6
6.0
4.6
5.8
0
1.0
2.1
154
577
442
558
0
149
188
51
1.0
0.8
0.6
1.2
12
5
27.2
23.7
64 (84)
86 (98)
54.7 (91)
55.6 (92)
9 (50)
2 (75)
6 (55)
7.6 (68)
4
4
2.8
4.1
11
3
9.3
9
289
221
279
0
75
94
5b
6
7c
10
0
0
72
68
11.9 (75)
13 (54)
1.6
1.4 (36)
3.3
2
11.2
15.6
0.2 mmol complex, Al : Cr = 100, Toluene, 120 min run time, TEA as co-catalyst, 65 ◦C, 30 bar,a 180 min run time; b Activated for 30 min with UV light;
c 0.05 mmol complex used; d M = Cr/Ni/Fe; e wt% of dissolved C4 only.
oligomerisation reaction which allows us to draw a comparison
between the activities of Cr(III) and Cr(0) (Table 3). Complex 3
showed poor activity and furnished predominantly polyethene
(PE) when TEA was used as activator and scavenger for CO
(entry 1). Treatment of 3 with TEA in the presence of 10 mol%
free ligand 1 followed by UV photolysis (30 min) gave active
trimerisation catalyst (entry 2). The active species formed during
photolysis might be stabilized by coordinating with added free
ligand or TEA. This shows that photolysis of Cr(0) leads to an
active catalyst system giving higher productivities compared to the
non photolyzed reaction. About the active species of trimerisation
catalysts one can only speculate. We have presented a possible
active coordination motif before.6a Noteworthy in the case of the
Cr(I) compound [{Cr(CO)4(Ph2PN(iPr)PPh2)} {Al{OC(CF3)3}4}]
photolysis leads to catalyst degradation forming Cr(0) resulting
in lower productivities.18 The introduction of CH3CN into the
coordination sphere enhances the activity dramatically. Complex
5 treated with TEA alone (without activation by photolysis) shows
four fold activity compared to the tetracarbonyl complex 3 (entries
1 and 3). Interestingly, selectivity towards 1-hexene is prevailed
while a significant increase in the PE formation is observed
compared to CrCl3(THF)3 system.6 Contrary to this, introduction
of acetonitrile in the CrCl3(Ph2PN(Cy)PPh2) system drastically
changes the selectivity giving exclusively PE.19 Activation of
complex 5 with UV light has only a very little effect on activity and
oligomer distribution, while a two fold increase in PE formation is
observed (entries 3 and 4). The bis-chelate nickel(0) complex 6 did
not show any activity under these conditions (entry 5). Complexes
7 and 10 did not produce any PE but the activity is considerably
low (entry 6 and 7).
ence of cyclohexene and norbornadiene also gave no fruitful
results.
Conclusion
Several transition metal complexes of new aminophosphine
compounds 1 and 2 have been prepared which are relevant to
ethylene oligomerisation. From these complexes (3–10) it becomes
clear that these novel aminophosphine ligands have a pronounced
tendency to form stable four-membered chelates. The terminal
secondary amine is not involved in complexation with any of
these metals and typically acts as a spectator group. However,
the deprotonation of this terminal nitrogen occurs in the presence
of alkylating agents such as TEA to give active catalysts for
ethylene oligomerisation. While labile the acetonitrile coordinated
chromium tricarbonyl complex can be activated by using TEA
alone, the chromium tetracarbonyl complexes are activated only
by photolysis in the presence of TEA. These complexes show tight
phosphine bite angles in the range 67.90(2)◦ to 74.97(4)◦ while
the shortest belongs to tetracarbonyl chromium(0) complex 3, the
widest belongs to bis chelate nickel(0) complex 6.
Experimental section
All air and moisture sensitive compounds were handled under
an argon atmosphere using standard Schlenk techniques or in a
glove box. 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 non-deuterated
1
solvent as internal standard for H and 13C and 85% H3PO4 for
Hydrogenation
1
31P{ H}. Melting points: sealed capillary, Bu¨chi 540 apparatus
Iron(II) hydride complexes with diphosphine ligands and pendant
amine bases show a rapid intramolecular exchange between the
protonated base of a PNP-ligand and the hydride ligand. Here
the amine group works as a proton acceptor in the heterolytic
hydrogen activation.20 With this concept in mind, it is tempting
to test the iron complex 10 in hydrogenation of olefins.21 The
hydrogenation of cyclohexene and norbornadiene with 10 in
1,2-dichloroethane and THF did not show any consumption
of hydrogen, even after addition of an external base (Et3N).
Working at a high pressure of hydrogen (56 bar) in the pres-
(uncorrected). – Elemental analyses: Leco Truspec Micro analyzer.
Gas chromatography: HP 6890 (Hewlett Packard) chromatograph
using a HP 5 column. IR: Bruker Alpha-P. Compound 1,6a
Ph2PN(iPr)PPhCl7 and fac-Cr(CO)3(NCCH3)311 were synthesized
following the previously reported procedures.
Ph2PN(iPr)P(Ph)NH(Et) (2)
Ph2PN(iPr)PPhCl (2.0 g; 5.6 mmol) in 5 mL toluene was slowly
added to a 1 : 1 mixture of EtNH2 and toluene (20 mL each) at
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-20 ◦C. The resultant turbid solution was stirred for 2 h while
slowly bringing to room temperature. Volatiles were removed
under vacuum and the product was extracted with n-hexane.
Recrystallization from n-hexane at -40 ◦C furnished 1.21 g (55%)
24 h. Then the insolubles were filtered off and the filtrate was stored
at -20 ◦C to furnish 1.8 g (80%) of yellow crystals of complex 5.
◦
-1
≡
m.p. 178 C (decomposed); IR (nujol, cm ): n(C O) 1910, 1815,
-1
≡
1780; IR (CH3CN, cm ): n(C O) 1923, 1830, 1802. Major isomer:
◦
1
of colorless crystals of the desired product. mp 96 C. H NMR
(C6D6): d 0.97 (t, 3 H, CH2CH3), 1.26 (d, 6 H, CHCH3), 2.34
(m, NH), 2.88 (m, 2 H, CH2), 3.50 (m, CH), 7.02–7.68 (m, C6H5);
1H NMR (CD2Cl2): d 0.82 (d, J = 6.8 Hz, 3 H, CHCH3), 1.03 (d,
J = 6.8 Hz, 3 H, CHCH3), 1.19 (t, J = 2.1 Hz, 3 H, CH3CN), 1.25
(d, J = 6.4 Hz, 3 H, CHCH3), 1.35 (d, J = 6.4 Hz, 3 H, CHCH3),
2.58 (m, NH), 3.71 (m, CH, merged with minor isomer), 4.12
1
13C{ H} NMR (CDCl3): d 18.5 (d, J = 9.8 Hz, CH2CH3), 25.0–
1
25.4 (m, CHCH3), 40.8 (d, J = 28.2 Hz, CH2), 50.0 (dd, J = 4.5,
14.8 Hz, CH), 127.8, 128.9–128.3 (4 signals) 128.7, 130.6, 132.7,
(m, CH), 7.26–8.03 (m, C6H5 major and minor isomer); 31P{ H}
NMR (CD3CN): d 98.3 (d, J = 16.7 Hz), 119.5 (d, J = 16.7 Hz);
1
1
133.1, 139.5, 141.1, 144.2 (C6H5); 31P{ H} NMR (C6D6): d 41.0 (s,
31P{ H} NMR (CD2Cl2): d 99.4 (d, J = 16.7 Hz), 121.7 (d, J =
br), 72.6 (s, br). Anal. Calcd for C23H28N2P2: C 70.04; H 7.16; N
7.10. Found: C 69.63; H 7.06; N 6.52.
16.7 Hz). Minor isomer: 1H NMR (CD2Cl2): d 0.38 (d, J = 6.7 Hz,
3 H, CHCH3), 1.12 (d, J = 6.7 Hz, 3 H, CHCH3), 1.29 (dd, J =
1.3, 6.3 Hz, 6 H, CHCH3), 1.41 (t, J = 2.0 Hz, 3 H, CH3CN),
2.75 (m, NH), 3.51 (m, CH), 3.71 (m, CH, merged with major
[Cr(CO)4{Ph2PN(iPr)P(Ph)NH(iPr)-P,P¢}] (3)
isomer), 7.26–8.03 (m, C6H5 major and minor isomer); 31P{ H}
1
Cr(CO)6 (175 mg, 0.8 mmol) was added to a solution of
Ph2PN(iPr)P(Ph)NH(iPr) (306 mg, 0.75 mmol) in 20 mL toluene
and the resulting solution was stirred at reflux temperature for
48 h.◦Subsequently, the formed yellow solution was cooled down
to 0 C and filtered. Toluene was removed and the product was
extracted with dichloromethane. Removal of dichloromethane
NMR (CD3CN): d 104.7 (d, J = 25.6 Hz), 118.0 (d, J = 25.6 Hz);
31P{ H} NMR (CD2Cl2): d 107.0 (d, J = 25.6 Hz), 120.6 (d, J =
1
25.6 Hz). Anal. Calcd for C29H33CrN3O3P2: C 59.49; H 5.68; N
7.18. Found: C 59.73; H 5.86; N 7.01.
[Ni{Ph2PN(iPr)P(Ph)NH(iPr)-P,P¢}2] (6)
under reduced pressure gave 258 mg (60%) of the greenish yellow
◦
≡
complex. m.p. 194 C. IR (CH2Cl2): n (C O) 1870, 1896, 1918,
A flask was charged with of Ni(COD)2 (138 mg, 0.5 mmol) and
1 (408 mg, 1.0 mmol). To this n-hexane (10 mL) was added. The
slurry was stirred for 6 h at room temperature and then the formed
reddish brown solution was filtered. The volume of the filtrate was
reduced to 3 mL. Crystallization at -40 ◦◦C furnished 220 mg
2005 cm-1. 1H NMR (CDCl3): d 0.58 (d, J = 6.7 Hz, 3 H, CHCH3),
1.10 (d, J = 6.7 Hz, 3 H, CHCH3), 1.33 (d, J = 6.3 Hz, 3 H,
CHCH3), 1.39 (d, J = 6.5 Hz, 3 H, CHCH3), 2.56 (m, NH), 3.54
(m, CH), 4.03 (m, CH), 7.31–7.83 (m, C6H5); 13C { H} NMR
1
1
(CDCl3): d 24.4 (br s, CHCH3) 26.2 (d, J = 4.5 Hz, CHCH3),
26.8 (d, J = 4.5 Hz, CHCH3), 47.6 (d, J = 11.8 Hz, CH), 54.9 (t,
J = 6.4 Hz, CH), 128.3, 128.5 128.7 (mC6H5), 129.9, 130.2, 131.2
(pC6H5), 130.5, 130.7, 133.3 (oC6H5), 136.2, 138.2, 141.0 (iC6H5),
(50%) of the desired complex. m.p. 206 C. Major isomer: H
NMR (THF-d8): d 0.03 (d, J = 6.6 Hz, 3 H, CHCH3), 0.17 (d,
J = 6.6 Hz, 3 H, CHCH3), 0.46 (d, J = 6.2 Hz, 3 H, CHCH3),
0.55 (d, J = 6.6 Hz, 3 H, CHCH3), 0.86 (t, J = 6.6 Hz, 6 H,
CHCH3), 0.98 (d, J = 6.2 Hz, 3 H, CHCH3), 1.02 (d, J = 6.6 Hz,
3 H, CHCH3), 2.89 (m, 2 NH), 3.12 (m, 2 CH), 3.34 (m, CH), 3.68
222.9, 223.7, 228.5, 228.5 (CO); 31P{ H} NMR (CDCl3): d 101.97
1
(d, J = 43.0 Hz), 121.06 (d, J = 43.0 Hz). HRMS (ESI): m/z:
calcd for C28H30CrN2O4P2: 572.1081 [M]+; found: 572.1083. Anal.
Calcd for C28H30CrN2O4P2: C 58.74; H 5.28; N 4.89. Found: C
58.52; H 5.06; N 4.65.
1
(m, CH), 6.70–7.92 (m, C6H5);31P{ H} NMR (THF-d8): 76.5–78.5
(m), 97.6–99.4 (m). Anal. Calcd for C48H60N4NiP4·0.5 hexane: C
66.68; H 7.35; N 6.10. Found: C 66.87; H 6.48; N 6.53 (no better
analysis could be obtained even from the crystalline material).
[Cr(CO)4{Ph2PN(iPr)P(Ph)NH(Et)-P,P¢}] (4)
[NiCl2{Ph2PN(iPr)P(Ph)NH(iPr)-P,P¢}] (7)
The complex 4 was prepared by following the above mentioned
procedure of complex 3 using Cr(CO)6 (175 mg, 0.8 mmol) and 2
(295 mg, 0.75 mmol); isolated yield: 230 mg (55%). m.p. 182 ◦C;
[NiCl2(DME)] (135 mg, 0.613 mmol) was added to a solution of 1
(250 mg, 0.613 mmol) in THF (10 mL) at room temperature. The
mixture was stirred for 16 h, then the volatiles were removed under
reduced pressure. The residue was dissolved in CH2Cl2 and over
layered with diethyl ether to give 280 mg (85%) of pure orange
-1
1
≡
IR (CH2Cl2): n(C O) 1877, 1890, 1917, 2005 cm . H NMR
(CDCl3): d 0.81 (d, J = 6.8 Hz, 3 H, CHCH3), 1.17 (d, J =
6.8 Hz, 3 H, CHCH3), 1.43 (t, J = 7.1 Hz, CH2CH3), 2.84 (m,
NH), 3.38 (m, 1 H, CHCH3), 3.59 (m, 2 H, CH2CH3), 7.44–
◦
1
micro crystalline product. m.p. 270 C (decomposed). H NMR
(CD2Cl2): d 0.57 (d, J = 6.8 Hz, 3 H, CH3), 0.89 (d, J = 6.8 Hz, 3
H, CH3), 1.30 (d, J = 6.4 Hz, 3 H, CH3), 1.67 (d, J = 6.4 Hz, 3 H,
CH3), 2.63 (d br, J = 10.9 Hz, NH), 3.26 (m, 1 H, CH), 4.26 (m,
7.90 (m, C6H5); 13C { H} NMR (CDCl3): d 17.9 (d, J = 7.8 Hz,
1
CH2CH3), 24.0 (CHCH3), 24.2 (CHCH3), 39.6 (d, J = 5.8 Hz,
CH2), 54.7 (t, J = 6.5 Hz, CH), 128.3 128.4 128.6 (mC6H5), 130.2
(2 signals) 130.8 (pC6H5), 130.3 131.4 132.4 (oC6H5), 136.9 137.5
1
1 H, CH), 7.45–8.24 (m, 15 H, aryl); 31P { H} NMR (CD2Cl2): d
139.6 (iC6H5), 222.2 (d,d) 224.4 228.2 (m) 228.5 (m) (CO); 31P{ H}
41.9 (d, 2JP–P = 180.5 Hz), 44.1 (d, 2JP–P = 180.5 Hz). HRMS (ESI):
m/z: calcd for C24H30Cl2N2NiP2: 535.0542 and 537.051 [M - H]-;
found: 535.0547 and 537.0514. Anal. Calcd for C24H30Cl2N2NiP2:
C 53.57; H 5.62; N 5.21. Found: C 53.56; H 5.61; N 5.14.
1
NMR (CDCl3): d 101.4 (d, J = 46.0 Hz), 122.6 (d, J = 46.0 Hz).
Anal. Calcd for C27H28CrN2O4P2: C 58.07; H 5.05; N 5.02. Found:
C 58.01; H 5.07; N 4.93.
[Cr(CO)3(NCCH3){Ph2PN(iPr)P(Ph)NH(iPr)-P,P¢}] (5)
[PdCl2{Ph2PN(iPr)P(Ph)NH(iPr)-P,P¢}] (8)
A suspension of fac-Cr(CO)3(NCCH3)3 (1.0 g, 3.86 mmol) and 1
[PdCl2(NCPh)2] (470 mg, 1.23 mmol) was added to a solution of
1 (500 mg, 1.23 mmol) in CH2Cl2 (10 mL) at room temperature.
(1.6 g, 3.91 mmol) in acetonitrile (30 mL) was stirred at 60 ◦C for
7918 | Dalton Trans., 2010, 39, 7911–7920
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The mixture was stirred for 16 h, then the volatiles were removed
under reduced pressure. The residue was dissolved in CH2Cl2
and over layered with n-hexane to give 575 mg (80%) of pure
yellow micro crystalline product. m.p. 275 C (decomposed). H
NMR (CD2Cl2): d 0.61 (d, J = 6.7 Hz, 3 H, CH3), 1.03 (d, J =
6.7 Hz, 3 H, CH3), 1.26 (d, J = 6.5 Hz, 3 H, CH3), 1.50 (d, J =
6.5 Hz, 3 H, CH3), 2.81 (dd, J = 6.4, 10.5 Hz, NH), 3.45 (m, 1
H, CHCH3), 3.89 (m, 1 H, CHCH3), 7.45–8.12 (m, 15 H, aryl);
(300 mL) under an argon atmosphere. Afterwards the autoclave
was pressurized with 30 bar ethylene. 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. After the run, the autoclave was cooled to below
10 ◦C. After releasing the excess ethylene from the autoclave,
an internal standard was added (dodecahydrotriphenylene). After
quenching with 10% HCl, the organic phase was analyzed by GC,
and the while solids were filtered, washed, dried, and weighed.
◦
1
1
2
31P { H} NMR (CD2Cl2): d 35.5 (d, JP–P = 21.2 Hz), 36.7 (d,
2JP–P = 21.2 Hz). HRMS (ESI): m/z: calcd for C24H30Cl2N2P2Pd:
583.0227 and 585.02517 [M - H]-; found: 583.0234 and 585.0225.
Anal. Calcd for C24H30Cl2N2P2Pd: C 49.21; H 5.16; N 4.78; Cl
12.10. Found: C 49.16; H 5.31; N 4.88; Cl 11.73.
Hydrogenation. For a detailed description of the hydrogena-
tion equipment used see ref. 22.
X-ray structure analysis of 2–9. Data were collected on a
STOE IPDS II diffractometer using graphite-monochromated
Mo-Ka radiation. The structures were solved by direct methods
(SHELXS-97)23 and refined by full-matrix least-squares tech-
niques on F2 (SHELXL-97).23 XP (Bruker AXS) was used for
graphical representations. For complex 3 PLATON/SQUEEZE24
was used to remove disordered solvent.
[PtBr2{Ph2PN(iPr)P(Ph)NH(iPr)-P,P¢}] (9)
[PtBr2(COD)] (284 mg, 0.613 mmol) was added to a solution of
1 (250 mg, 0.613 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 dissolved in CH2Cl2 and
over layered with n-hexane to give 415 ◦mg (89%) of pure colorless
1
micro crystalline product. m.p. >285 C. H NMR (CD2Cl2): d
Acknowledgements
0.55 (d, J = 6.7 Hz, 3 H, CH3), 0.99 (d, J = 6.7 Hz, 3 H, CH3), 1.26
We thank PD Dr W. Baumann and our technical and analytical
staff for their help.
(d, J = 6.4 Hz, 3 H, CH3), 1.47 (d, J = 6.4 Hz, 3 H, CH3), 2.79 (m,
NH), 3.34 (m, 1 H, CH), 3.99 (m, 1 H, CH), 7.44–8.10 (m, 15 H,
1
aryl); 31P { H} NMR (CD2Cl2): d 16.3 (d, 2JPP = 35.0 Hz, 1JPt–P
=
3660 Hz), 17.9 (d, 2JPP = 35.0 Hz, 1JPt–P = 3402 Hz). HRMS (ESI):
m/z: calcd for C24H30Br2N2P2Pt: 760.9803 and 762.9805 [M - H]-;
found: 760.9798 and 762.981. Anal. Calcd for C24H30Br2N2P2Pt:
C 37.76; H 3.96; N 3.67. Found: C 37.49; H 4.01; N 3.38.
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¨
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◦
MTBE gave 1.5 g (65%) red-orange crystals of 10. m.p. 167 C.
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CHCH3), 1.16 (d, J = 6.2 Hz, 9 H, CHCH3), 1.22 (d, J = 6.2 Hz, 6
H, CHCH3), 1.30 (d, J = 6.5 Hz, 3 H, CHCH3), 1.33 (d, J = 6.7 Hz,
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2.88–4.11 (m, 2 NH, 4 CH, merged with minor isomer), 7.20–7.88
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J = 6.7 Hz, 3 H, CHCH3), 1.03 (t, J = 6.7 Hz, 6 H, CHCH3),
1.18 (d, J = 6.7 Hz, 3 H, CHCH3), 1.29 (d, J = 6.7 Hz, 3 H,
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3 H, CHCH3), 1.50 (d, J = 6.7 Hz, 3 H, CHCH3), 1.98 (s br, 6
H, CH3CN, merged with major isomer), 2.88–4.11 (m, 2 NH, 4
CH, merged with major isomer), 7.20–7.88 (m, 30 H, aryl, merged
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1
with major isomer); 31P { H} NMR (CD3CN): d 89.2–93.9 (m),
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