New bulky bis(amino)cyclodiphosph(III)azanes and their titanium(IV) complexes: Synthesis, structures and ethene polymerization studies

Article abstract of DOI:10.1002/ejic.200300487

Bis(amino)cyclodiphosph(III) azanes cis-[(RNH)(PN-tBu)]₂, R = 2,6-iPr₂C₆H₃ (2), 2-tBuC₆H ₄ (3), 2-CF₃C₆H₄ (4), 2,5-tBu ₂C₆H₃ (5), Ph₂CH (6), 2,4-Me ₂C₆H₃ (7), 2,6-Et₂C ₆H₃ (8), have been synthesized in the presence of Et ₃N by a nucleophilic substitution reaction of cis-(ClPN-tBu) ₂ (1) with the corresponding bulky aryl and alkylamines. The bis(amino)-cyclodiphosph(III)azanes 2-8 adopt the thermodynamically stable cis-configuration - a prerequisite for efficient metal complex formation. Deprotonation of bis(amino)cyclodiphosph(III)azanes with nBuLi slowly afforded the corresponding salts, cis-[(2,4-Me₂C₆H ₃N)(PN-tBu)]₂Li₂(THF)₂. The crystal structure of cis-[(2,4-Me₂C₆H₃N)(PN-tBu)] ₂Li₂(THF)₂ (9) consists of a heterocube of two lithium atoms, two nitrogen atoms and a cyclodiphosph(III)azane ring. Transmetallation of Li compounds by TiCl₄ was unselective and led to a complex mixture of products. The direct reaction of cis-bis (amino)cyclodiphosph(III)azanes with Ti(NMe₂)₄ is the most efficient method to prepare the corresponding titanium(IV) bis-amido complexes cis-[(RN)(PNtBu)]₂Ti(NMe₂)₂ (11a, 12a, 14a, 15a). In the solid state, cis-[(PhN)(PN-tBu)]₂Ti(NMe ₂)₂ (11a) adopts a highly distorted trigonal-bipyramidal configuration at the metal center. These bis-amido titanium(IV) complexes have been subsequently transformed into the dichlorides cis-[(RN)(PN-tBu)] ₂TiCl₂ (12-15) with Me₃SiCl. After MAO activation the complexes possess moderate catalytic activity in ethene polymerization and produce linear polyethylene with molar masses of up to 2.6 × 10⁶ g/mol and with narrow polydispersities. The catalytic activity and polymer properties depend strongly on the bulkiness of the ligand substituents; cis-[(2,6-iPr₂C₆H₃N)(PN-tBu)] ₂TiCl₂ (14) gave the highest activity (231 kg PE/mol _cat × bar × h). ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004).

Full text of DOI:10.1002/ejic.200300487

FULL PAPER
New Bulky Bis(amino)cyclodiphosph(III)azanes and Their Titanium(IV
Complexes: Synthesis, Structures and Ethene Polymerization Studies
)
Kirill V. Axenov,[a] Vasily V. Kotov,[b] Martti Klinga,[a] Markku Leskelä,[a] and Timo Repo*[a]
Keywords: Phosphazenes / Titanium / Homogeneous catalysis / Polymerization
Bis(amino)cyclodiphosph(III)azanes
cis-[(RNH)(PN-tBu)]2,
method to prepare the corresponding titanium(IV) bis-amido
complexes cis-[(RN)(PNtBu)]2Ti(NMe2)2 (11a, 12a, 14a, 15a).
In the solid state, cis-[(PhN)(PN-tBu)]2Ti(NMe2)2 (11a) adopts
a highly distorted trigonal-bipyramidal configuration at the
metal center. These bis-amido titanium(IV) complexes have
been subsequently transformed into the dichlorides cis-
[(RN)(PN-tBu)]2TiCl2 (12−15) with Me3SiCl. After MAO ac-
R = 2,6-iPr2C6H3 (2), 2-tBuC6H4 (3), 2-CF3C6H4 (4), 2,5-
tBu2C6H3 (5), Ph2CH (6), 2,4-Me2C6H3 (7), 2,6-Et2C6H3 (8),
have been synthesized in the presence of Et3N by a nucleo-
philic substitution reaction of cis-(ClPN-tBu)2 (1) with the
corresponding bulky aryl and alkylamines. The bis(amino)-
cyclodiphosph(III)azanes 2−8 adopt the thermodynamically
stable cis-configuration − a prerequisite for efficient metal tivation the complexes possess moderate catalytic activity in
complex formation. Deprotonation of bis(amino)cyclodi- ethene polymerization and produce linear polyethylene with
phosph(III)azanes with nBuLi slowly afforded the correspond- molar masses of up to 2.6 × 106 g/mol and with narrow poly-
ing salts, cis-[(2,4-Me2C6H3N)(PN-tBu)]2Li2(THF)2. The crys-
tal structure of cis-[(2,4-Me2C6H3N)(PN-tBu)]2Li2(THF)2 (9)
consists of a heterocube of two lithium atoms, two nitrogen
atoms and a cyclodiphosph(III)azane ring. Transmetallation of
Li compounds by TiCl4 was unselective and led to a complex
mixture of products. The direct reaction of cis-bis(amino)cy-
dispersities. The catalytic activity and polymer properties de-
pend strongly on the bulkiness of the ligand substituents; cis-
[(2,6-iPr2C6H3N)(PN-tBu)]2TiCl2 (14) gave the highest activ-
ity (231 kg PE/molcat × bar × h).
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
clodiphosph(III)azanes with Ti(NMe2)4 is the most efficient Germany, 2004)
Introduction
having novel polymerization properties,[5] as well as on
The highly efficient homogeneous α-olefin polymeri-
zation catalysts based on methylalumoxane (MAO) acti-
vated Group 4 metallocene dichlorides have stimulated in-
tensive polymerization catalysis research over the past three
decades.[1] The major focus has been on the preparation of
various ansa-metallocenes, especially ones intended for the
stereoselective polymerization of propene.[2] Numerous
studies have also been made on late transition metal com-
plexes,[3] constrained geometry catalysts[4] and complexes of
Group 4 metals with non-cyclopentadienyl ligands. The
substantial progress on non-metallocene polymerization ca-
talysis has been achieved by both the ‘‘right’’ choice of a
transition metal and the rational design of the ligand sys-
tems. Recent highly successful catalysts have been based on
titanium and zirconium phenoxyimino-type complexes
highly efficient C1-symmetric Group 4 pyridyl-amine cata-
lysts aimed for isospecific propene polymerization.[6]
Ligands containing heteroatoms (e.g. phosphorus, nitro-
gen) are candidates for catalyst components because they
bind strongly to the early transition metals and their mode
of coordination as well as ligand hapticity can be varied.[7a]
This allows the electronic character, geometric properties
and steric protection of the catalytic center to be modi-
fied.[7] Bis(amido) complexes of titanium() have attracted
considerable attention because of their high activity in eth-
ene polymerization after activation with MAO.[7,8] Thus, we
found bis-amino type cis-2,4-bis(amino)cyclodiphosph()-
azanes of the general formula cis-[(RNH)(PN-tBu)]2 to be
interesting ligand precursors for olefin polymerization
catalysts. The coordination chemistry of simple
cis-2,4-bis(amino)cyclodiphosph()azanes, namely cis-
[(tBuNH)(PN-tBu)]2 and cis-[(PhNH)(PN-tBu)]2 (structure
A), has been described in the synthesis of both main group
compounds[9] and titanium(), zirconium() and haf-
nium() complexes (structure B).[10,11,12] Their polymeriz-
ation properties have not, to our knowledge, been pub-
lished.
[a]
Department of Chemistry, Laboratory of Inorganic Chemistry,
P. O. Box 55, 00014 University of Helsinki, Finland
Fax: (internat.) ϩ 358-9-19150198
E-mail: Timo.Repo@helsinki.fi
[b]
Organisch-Chemisches Institut, Westfälische Wilhelms-
Universität Münster,
Corrensstrasse 40, 48149 Münster, Germany
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
Eur. J. Inorg. Chem. 2004, 695Ϫ706
DOI: 10.1002/ejic.200300487
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K. V. Axenov, V. V. Kotov, M. Klinga, M. Leskelä, T. Repo
FULL PAPER
excess of Et3N (4 equiv.), after refluxing for four days, gave,
finally, the desired disubstituted compound cis-[(2,6-
iPr2C6H3NH)(PN-tBu)]2 (2) in good yield. Further experi-
ments with different ratios of reactants and reaction times
showed the limitations of this reaction; the selectivity de-
pends strongly on the ratio of arylamine to Et3N, and on
the refluxing time (Scheme 1). This optimized synthetic
procedure was then applied to give various bis(amino)cyclo-
diphosph()azanes (3؊8 in Scheme 2).
The relatively straightforward synthesis of various cis-
2,4-bis(amino)cyclodiphosph()azanes make them attrac-
tive candidates to study the ligand’s influence on the poly-
merization properties. In the present work, a synthetic ap-
proach to new cis-2,4-bis(amino)cyclodiphosph()azane li-
gands, cis-[(RNH)(PN-tBu)]2 (2؊8), bearing bulky amino
substituents and their titanium() complexes has been de-
veloped and ethene polymerization studies carried out.
Results and Discussion
Ligand Synthesis
Scheme 1
Phosphazanes, both cyclic and acyclic,[13] are stable PϪN
compounds that are easily synthesized. Cyclodiphosph()-
azanes (containing a P2N2 moiety) were first reported by
Michaelis and Schroeter in 1894[14] but were fully charac-
terized only in the 1970s.[15,16] They have attracted most at-
tention as precursors for hybrid (organic-inorganic) PϪN
polymeric materials,[16c] and as ligand precursors for the
synthesis of main group element compounds[9] and some,
still rare, early transition metal complexes.[10,11,12] They
preparation, in good yield, is commonly based on the reac-
tion of cis-(ClPN-tBu)2 (1) with either lithium amide or an
excess of a free amine.[9] We investigated both of these
methods to access the new, bulky bis(amino)cyclodi-
phosph()azanes.
However, some modifications of these general procedures
became necessary as, for instance, 2,4-dimethylphenyllith-
iumamide in THF reacted with 1 nonselectively, and ac-
cording to 31P NMR data the cyclodiphosph()azane P2N2
ring was destroyed. Direct aminolysis of the PϪCl bond
with free amines was then explored but, even under severe
conditions, direct substitution was negligible. For example,
1 and 2,6-diisopropylphenylamine, failed to react under
various conditions, even after refluxing in THF for one
week; 31P NMR data revealed only the starting compound
1 and the free amine. Apparently, the nucleophilic substi-
Scheme 2
Et3N acts as more than a simple Brönsted base that scav-
enges the generated HCl Ϫ at least four equivalents of it
are required to obtain good yields. Some of the Et3N can
assist the nucleophilic substitution by coordination and po-
larization of the PϪCl bonds of (ClPN-tBu)2 (1), while the
rest acts as a traditional Brönsted base.
Structure of the Bis(amino)cyclodiphosph(III)azanes
The obtained bis(amino)cyclodiphosph()azanes are col-
tution did not take place because of the steric demand of orless, air-sensitive oils or solids that are very soluble even
the amine. in aliphatic hydrocarbon solvents. Despite the long re-
Another synthetic possibility is the application of Et3N fluxing times, the reactions proceed selectively and, accord-
as a base in the reaction of 1 with bulky arylamines.[9] Thus, ing to 31P NMR, yield only one product from each reaction.
the reaction of 1 with 2,6-diisopropylphenylamine and an Bis(amino)cyclodiphosph()azanes can exist as cis and
696
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Bulky Bis(amino)cyclodiphosph(III)azanes
FULL PAPER
trans isomers; the differences in chemical shifts in the 31P
NMR spectra indicate which is present.[17] According to
NMR spectroscopic data, the synthesized bis(amino)cyclo-
diphosph()azanes (2؊8) adopt the synthetically more de-
sirable, and thermodynamically more stable, cis-confor-
mation (Exp. Sect.).
The single-crystal X-ray measurements of 3؊5 also sup-
port the exclusive presence of the cis-isomer. The solid-state
structures (Figures 1Ϫ3) and selected structural parameters
(Table 1) are presented here. The solid-state structures re-
veal that the P2N2 cyclodiphosph()azane rings are bent
from the mean plane. Such disturbance of the P2N2 rings
accords with the results of earlier molecular orbital calcu-
lations for cis-cyclodiphosph()azanes with small amino
substituents,[18] and may be caused by repulsive lone
pairϪbond pair electronic interactions.[9] Despite the steri-
cally bulky aryl or alkyl substituents on these bis(amino)cy-
clodiphosph()azanes the basic structural features (bond
lengths and angles) of the ligand backbone are rather simi-
lar to ones reported earlier (Table 1).
Figure 1. ORTEP diagram of cis-[(2-tBuC6H4NH)(PN-tBu)]2 (3)
The solid-state structure of cis-[(2-tBuC6H4NH)(PN-
tBu)]2 (3) (Figure 1), which has only monosubstituted ani-
line groups, resembles that established for cis-[(PhNH)(PN-
tBu)]2.[9,12] In both structures, the tert-butyl groups on the
PϪN ring are bent towards the P2N2 mean plane [for 3:
C(1)ϪP2N2 plane 161.05(3)° and C(5)ϪP2N2 plane
170.94(3)°] and the orientation of the anilines gives an over-
all C2v symmetry. The slight asymmetry of the P2N2 ring in
3 is reflected by the PϪN endocyclic bond lengths, which
˚
vary from 1.707(3) to 1.728(3) A.
The structural features of cis-[(2-CF3C6H4NH)(PN-
tBu)]2 (4) resemble those of 3 (Figure 2). The electron-with-
Figure 2. ORTEP diagram of cis-[(2-CF3C6H4NH)(PN-tBu)]2 (4)
Table 1. Selected structural parameters for ligands 3؊5
[20]
[9]
3
4
5
cis-[(tBuNH)(tBuNP)]2
cis-[(PhNH)(tBuNP)]2
˚
Distances, A
P1ϪN3
P1ϪN4
P2ϪN3
P2ϪN4
P1ϪP2
P2ϪN2
N3ϪC1
N4ϪC5
N1ϪC9
1.728(3)
1.707(3)
1.726(3)
1.715(3)
2.5910(13)
1.680(3)
1.485(5)
1.474(4)
1.403(4)
1.7063(15)
1.7256(17)
1.7072(16)
1.7184(16)
2.5937(7)
1.7064(15)
1.472(3)
1.705(3)
1.734(3)
1.716(3)
1.724(3)
2.5997(1)
1.695(2)
1.473(4)
1.485(4)
1.411(4)
1.721(2)
1.730(2)
1.730(2)
1.721(2)
2.600(2)
1.664(2)
1.485(3)
1.485(3)
1.470(3)
1.726(2)
2.583(1)
1.689(2)
1.481(3)
1.400(3)
Angles, deg
N3ϪP1ϪN4
P1ϪN3ϪP2
P1ϪN4ϪP2
C1ϪN3ϪP1
C5ϪN4ϪP1
N2ϪP2ϪN4
N2ϪP2ϪN3
C9ϪN1ϪP1
C23ϪN2ϪP2
C22ϪN2ϪP2
80.56(14)
97.20(15)
98.43(15)
125.5(2)
81.08(8)
98.90(9)
97.72(8)
130.96(13)
124.79(13)
101.80(8)
105.20(8)
127.01(16)
80.67(13)
98.92(14)
97.50(14)
129.8(2)
80.88(1)
97.83(1)
97.83(1)
124.8(2)
125.1(2)
104.69(1)
105.03(1)
130.2(2)
128.5(2)
124.9(2)
105.01(18)
101.15(16)
128.1(3)
101.60(13)
106.21(13)
125.8(2)
127.3(2)
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FULL PAPER
drawing CF3 substituents on the aniline groups have a sig- rounded by the aniline groups of the ligand and two coordi-
nificant influence only on the P(2)ϪN(2) and P(1)ϪN(1) nated THF molecules. The exocyclic PϪN bonds are
˚
bond lengths, while the puckering of the P2N2 ring is fairly shorter than the endocyclic ones [1.674(3) vs. 1.768(3) A].
similar to that for 3. Owing to the second tert-butyl group The bond lengths between Li and the exocyclic nitrogen
˚
˚
on the aniline moiety cis-[(2,5-di-tBuC6H3NH)(PN-tBu)]2 atoms are almost equal [from 2.071(6)A to 2.095(6)A] and
(5) (Figure 3) has lost its superfacial C2v symmetry. The similar to those in related lithium amides [LiϪN in
[22]
˚
bond lengths and angles in the P2N2 ring are nevertheless {Li[N(SiMe3)2]OEt2}2 are 2.06(1) A].
Thus, the solid-
similar to those of 3.
state structure of compound 9 has similar features to those
described for cis-[(tBuN)(PN-tBu)]2Li2(THF)2,[21] but in 9
the lithium atom and endocyclic nitrogen atoms are further
˚
apart [2.133(6) A] and can be considered typical for bonds
between a coordinated lithium cation and a donor nitro-
gen atom.
Figure 3. ORTEP diagram of cis-[(2,5-tBu2C6H3NH)(PN-tBu)]2 (5)
Synthesis of Titanium(IV) Complexes
Of the various literature methods for the preparation of
early transition metal complexes the general route is the
transmetallation reaction between transition metal halides
and alkali or alkaline earth metal salts of the ligand.[19] Ap-
plying a procedure described earlier,[20] the desired dilithium
salts of cis-[(2,6-di-iPrC6H3NH)(PN-tBu)]2 (2) (see sup-
porting information) and cis-[(2,4-di-MeC6H3NH)(PN-
tBu)]2 (7) were prepared in THF (Scheme 3). According to
Figure 4. ORTEP diagram of cis-[(2,4-Me2C6H3N)(PN-tBu)]2Li2-
(THF)2 (9); one solvent molecule is omitted for clarity
1
the H and 13C NMR spectra, the lithium salts contains
two coordinated THF molecules. The phosphorus signal at
163.01 ppm in the 31P NMR spectrum confirms the forma-
tion of the lithium salt cis-[(2,4-di-MeC6H3N)(PN-tBu)]2-
Li2(THF)2 (9).[21]
Table 2. Selected structural parameters for compound 9
˚
Distances, A
P1ϪN1
1.768(3)
1.752(3)
1.674(3)
2.635(2)
1.492(4)
2.071(6)
N2ϪLi1
N2ϪLi1a
Li1ϪLi1a
Li1ϪO1
N2ϪC5
2.133(6)
2.095(6)
2.612(1)
1.911(6)
1.408(4)
P1ϪN1a[a]
P1ϪN2
P1ϪP1a
N1ϪC1
N1ϪLi1
Angles, deg
N1ϪP1ϪN1a
P1ϪN1ϪP1a
N2ϪP1ϪN1
N2ϪP1ϪN1a
Li1ϪN1ϪP1
Li1ϪN1ϪP1a
Li1ϪN2ϪLi1a
Li1ϪN2ϪP1
83.06(1)
96.92(1)
98.83(1)
98.29(1)
91.76(2)
91.55(2)
76.30(2)
92.31(2)
N2ϪLi1ϪN2a
N1ϪLi1ϪN2
Li1ϪN1ϪC1
C1ϪN1ϪP1
N1ϪLi1ϪO1
O1ϪLi1ϪN2
C5ϪN2ϪLi1
C5ϪN2ϪLi1a
99.70(2)
76.90(2)
123.80(2)
122.10(2)
123.60(3)
121.80(3)
127.10(2)
136.0(3)
[a]
Label ‘‘a’’ means a symmetry equivalent atom at Ϫx, y, Ϫz ϩ
Scheme 3
1/2.
Recrystallization of the dilithium salt 9 from THF/hex-
To synthesize titanium() dichloride complexes from the
ane solution provided crystals suitable for X-ray study (Fig- cis-2,4-bis(amino)cyclodiphosph()azanes the above-de-
ure 4). Selected bond lengths and angles are collected in scribed lithium salts were treated with TiCl4. Surprisingly,
Table 2. The P2N2 ring is almost planar, which is also re- the transmetallation reaction failed and led to a complex
lated to the symmetry of the molecule and to the equal mixture of unidentified products. Only one complex,
bond lengths in the ring. The P2N2 ring, exocyclic N, and [(tBuN)2(PN-tBu)2]TiCl2 (10), previously synthesized by
both Li atoms form an inorganic heterocube that is sur- Stahl et al.[23] was obtained. This might be due either to the
698
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Bulky Bis(amino)cyclodiphosph(III)azanes
FULL PAPER
Scheme 4
steric demand of the obtained lithium {see the solid-state
structure of [(2,4-di-MeC6H3N)(tBuNP)]2Li2(THF)2 (9)}
salts, which slow down the reaction, or to titanium tetra-
chloride, a strong Lewis acid, which may attack the PϪN
bond of the P2N2 cycle or the phosphorus lone pair more
readily than a NϪLi or NϪMg bond.
An alternative approach, the direct metallation of the li-
gand precursors through amine elimination,[24] turned out
to be efficient. The reaction of the less Lewis-acidic
Ti(NMe2)4 with [(RNH)(tBuNP)]2 (2, 5, 6, 8) occurred
selectively, according to 1H and 31P NMR data, and
the bis-amido complexes [(RNH)(tBuNP)]2Ti(NMe2)2
(11aϪ15a) were formed (Scheme 4). Such bis-amido com-
plexes are usually oils, and are highly soluble in aliphatic
solvents, making their separation and purification difficult.
1
Therefore, they were characterized on the basis of H, 13C
Figure 5. ORTEP diagram of cis-[(PhN)(PN-tBu)]2Ti(NMe2)2 (11a)
Table 3. Selected structural parameters for compound 11a
and 31P NMR spectroscopic data (see Supporting Infor-
mation). Their 1H NMR spectra revealed the C2ν symmetry
expected for such titanium() complexes and indicate the
equivalence of all alkyl and aromatic substituents. Only the
ligand precursor 4, with electron-withdrawing CF3 substitu-
ents, behaved differently, and complex formation under
similar reaction conditions was incomplete.
With cis-[(PhN)2(PN-tBu)2]Ti(NMe2)2 (11a), crystals
suitable for X-ray analysis were obtained from a saturated
hexane solution at Ϫ20 °C. The ORTEP diagram of 11a
(Figure 5) and selected bond lengths and angles (Table 3)
˚
Distances, A
TiϪN3
TiϪN1
TiϪN2
TiϪN5
TiϪN6
P1ϪN1
2.325(4)
2.020 (3)
2.011(3)
1.907(4)
1.884(4)
1.708(4)
P1ϪN3
P2ϪN3
P1ϪN4
P2ϪN4
P1ϪP2
1.791(4)
1.770(4)
1.731(4)
1.728(4)
2.653(2)
are given here. In the solid state, four metalϪamide bonds Angles, deg
and an additional donor bond from one of the cyclo-
N5ϪTiϪN6
98.66(2)
111.80(1)
101.26(2)
121.14(2)
98.67(2)
N5ϪTiϪN3
N6ϪTiϪN3
N1ϪP1ϪP2
N3ϪP1ϪN4
P1ϪN3ϪP2
P1ϪN4ϪP2
159.82(2)
101.39(2)
101.73(1)
81.38(2)
96.32(2)
100.15(2)
phosph()azane ring nitrogen atoms define a highly dis-
N1ϪTiϪN2
torted trigonal-bipyramidal coordination at the central ti-
N1ϪTiϪN5
tanium atom, reducing the symmetry of this molecule from
N1ϪTiϪN6
C2 to Cs in the solid state. In general, the coordination N5ϪTiϪN2
sphere of 11a resembles previously described structures for
N6ϪTiϪN2
118.99(2)
Ti, Zr and Hf complexes based on the cis-[(tBuNH)(PN-
tBu)]2 ligand.[10,11,12] The cyclophosph()azane ring is al-
most planar and the phenyl rings are almost perpendicular
to the P2N2 plane and, hence, leave the metal center rela- indicated by the elongated bond length [2.325 (4) A], which
tively open to nucleophilic attack.
The additional nitrogen is rather weakly coordinated, as
˚
˚
is significantly longer than the 2.267 (2) A in the related
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K. V. Axenov, V. V. Kotov, M. Klinga, M. Leskelä, T. Repo
FULL PAPER
compound [(tBuN)2(PN-tBu)2]TiCl2).[11] This may be due
to NMe2 substituents donating additional electron density
from the sp2-hybridized amido nitrogen atoms to the metal
center, thereby decreasing the Lewis acidity of the titanium.
Four amido nitrogen atoms are in a pseudo-tetrahedral en-
vironment around the metal center [N(1)ϪTiϪN(2) and
N(5)ϪTiϪN(6) are 111.80 (1)° and 98.66 (2)° respectively]
and the amido NϪTi bond lengths vary from 1.884 (4) to
Ethene Polymerization
In addition to the preparative chemistry described above
the ligand’s influence on the titanium() complexes in eth-
ene polymerization was also investigated. After methylalu-
moxane (MAO) activation all dichloro titanium() com-
plexes [(RN)2(PN-tBu)2]TiCl2 (12؊15), regardless of poly-
merization temperature, produced high molar mass linear
polyethylene. The polymerization results and the properties
of the obtained polymers are summarized in Table 4.
Catalyst 10/MAO bearing tert-butyl groups showed a re-
markably high initial catalytic activity that severely declined
after a few minutes (Figure 6, curve a). The polyethene pro-
duced had a high molar mass and a bimodal molar mass
distribution, indicating at least two different active centers
(run 1 in Table 4; Mw1 ϭ 1 927 000 g/mol, Mw2 ϭ 42 000 g/
mol, for GPC curve see supporting information). After acti-
vation with MAO, complexes 12 with diphenylmethylamino
substituents gave lower initial activities than 10/MAO, but
the steady state consumption of ethene was higher (run 2
in Table 4, curve b in Figure 6). Catalyst precursors 13 and
15 are slowly activated by MAO (Figure 6, curves c and e,
respectively) but the high steady state of 15/MAO is note-
worthy. The polymers obtained with 12/MAO and 13/MAO
exhibit a low molar mass shoulder in the GPC curve, which
also explains the relatively large polydispersity (PD) values.
15/MAO produces ultrahigh molar mass polyethene (Mw ϭ
2.56 ϫ 106 g/mol, Mw/Mn ϭ 2.8).
˚
2.020 (3) A (Table 3).
Dichlorotitanium() complexes are preferred as catalyst
precursors in olefin polymerization due to their higher
activity than the corresponding bis(amido) derivatives.[1a]
The standard transformation of early transition metal bis-
(amido) complexes into their dichloride derivatives involves
the reaction with an excess of Me3SiCl.[25] Thus, we treated
[(RN)2(PN-tBu)2]Ti(NMe2)2 (11a, 12a, 14a, 15a) with an
excess of Me3SiCl (Scheme 4). The one-pot synthesis of
[(RN)2(PN-tBu)2]TiCl2 complexes is also possible, starting
from
a
ligand precursor, tetrakis(dimethylamido)-
titanium() and Me3SiCl (see Exp. Sect., 13).
Evaporation of all solvents, followed by extraction with
a mixture of CH2Cl2/hexane, gave the dichloro titanium()
complexes [(RN)2(PN-tBu)2]TiCl2 (12؊15) in good yield.
All 1H NMR spectra display a clear singlet at δ ϭ
1.0Ϫ1.4 ppm for the imido tBu groups, peaks at δ ϭ 1.0-
4.0 ppm for the alkyl substituents, and signals at δ ϭ
7.0Ϫ7.8 ppm for the aromatic protons (see supporting in-
formation). Phosphorus signals in the 31P NMR spectra ap-
pear in the same region as the peaks of the corresponding
Complex 14/MAO displayed a combination of high in-
ligand. This indicates the covalent character of the itial activity and slow decline in productivity (Figure 6, d).
TiϪamido bond, whereas in the lithium salts the LiϪN After one hour of polymerization with the catalysts under
bonds are strongly polarized.
similar conditions, the highest polymerization activity was
With cis-[(PhN)2(PN-tBu)2]Ti(NMe2)2 (11a), amine elim- recorded for 14/MAO (121 kg of PE/(molcat ϫ bar ϫ h)
ination by Me3SiCl was unselective and led to the destruc- (run 5 in Table 4). The polymer also exhibited a high molar
tion of the parent bis-amido complex. This can be taken as mass (2.6 ϫ 106 g/mol) and a narrow PD (2.17). In a further
a limitation of the synthetic route, since, without sufficient study, we examined the influence of catalyst concentration
steric hindrance from the ligand side, breakage of the TiϪN and polymerization temperature. Lower amounts of catalyst
phosphazane amido bond may occur instead of breakage resulted in higher activities with no significant change in
of the TiϪN dimethylamido bond. Apparently, the phenyl the molar mass of the polymers. For example, when the
group alone is not bulky enough to sufficiently protect the amount of catalyst 14/MAO was halved (from 20 µmol to
bonding between the metal center and ligand moiety and 10 µmol) and then to 5 µmol, the polymerization activity
may be a reason for the lack of selectivity.
increased from 121 to 143 and 231 kg of PE/(molcat ϫ bar
Table 4. Data for ethylene polymerization
Entry no.[a] Catalyst Concentration Reaction temp. Time (min) Yield (g) Activity[b] Mw (g/mol) Mw/Mn
Tm (°C)
(µmol)
(°C)
1
2
3
4
5
6
7
8
9
10
10
12
13
14
14
14
14
15
15
15
20
20
10
10
20
10
5
10
10
20
50
50
50
50
50
70
50
50
70
50
30
20
60
60
60
60
30
30
60
60
4.22
2.1
3.33
5.45
9.23
6.24
2.2
2.1
1.74
4.38
111
79
87.6
143.4
121
164.2
231.6
110.5
45.8
818 000
1 897 000
1 479 000
2 465 000
2 558 000
1 369 000
2 375 000
2 008 000
2 564 000
2 268 000
14.17
4.70
5.18
4.17
2.17
2.19
4.32
2.73
2.84
3.70
135.3
139.0
139.0
140.7
140.3
137.7
141.7
139.7
140.7
141.0
57.9
[a]
[b]
MAO (Al/M ϭ 1000), toluene (200 mL), ethylene (3.8 bar). kg PE/(molcat ϫ bar ϫ h).
700
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Eur. J. Inorg. Chem. 2004, 695Ϫ706

Bulky Bis(amino)cyclodiphosph(III)azanes
FULL PAPER
to the amido nitrogen (13؊15) have two roles: they protect
the catalytic active center from side reactions and they pre-
vent the phosphorus atoms of the ligand from destructive
coordination to MAO.
Conclusion
New bis(amino)cyclodiphosph()azanes cis-[(RNH)-
(PN-tBu)]2 2؊8 [R ϭ 2,6-iPr2C6H3 (2), 2-tBuC6H4 (3), 2-
CF3C6H4 (4), 2,5-tBu2C6H3 (5), Ph2CH (6), 2,4-Me2C6H3
(7), 2,6-Et2C6H3 (8)] bearing bulky substituents have been
synthesized. According to NMR spectroscopic data and
single-crystal X-ray analysis, all compounds adopt the
thermodynamically more stable cis-configuration. Bis-
(amino)cyclodiphosph()azanes can be deprotonated with
nBuLi, but an extended reaction time is required for com-
plete formation of the lithium salts. The straightforward
method of TiCl4 transmetallation of these Li salts pro-
ceeded unselectively and gave a complex mixture of prod-
ucts. Direct reaction of [(RNH)(tBuNP)]2 (2, 5, 6, 8) with
the less Lewis acidic Ti(NMe2)4 and application of the
amine elimination approach led to the desired bis(amido)-
cyclodiphosph()azane titanium() dichloro complexes
[(RN)(tBuNP)]2TiCl2 (12؊15) in high yield. According to
the 31P NMR spectra, the titanium()-amido bonds in
these complexes have covalent character.
MAO activated titanium()dichloride complexes
[(RN)(tBuNP)]2TiCl2 (12؊15) display moderate ethene
polymerization activity. The polymerization behavior de-
pends on the bulkiness of the ligand substituents. Large
alkyl and aryl groups both protect the catalytically-active
site from side reactions and prevent the phosphorus atoms
of the ligand from destructive MAO coordination. Complex
[(tBuN)(tBuNP)]2TiCl2 (10), bearing tBu groups, exhibits
an initially high polymerization activity, but ethene con-
sumption falls off sharply after just a few minutes.
[(RN)(tBuNP)]2TiCl2 12؊15 produce very high molar mass
polyethylene with a relatively narrow molar mass distri-
bution. The bulky aromatic groups in 12؊15 protect the
metal center, which is seen in the slow decline of the cata-
lytic activity during prolonged polymerization. The series
of catalysts described here offers an efficient route toward
very high or even ultrahigh molar mass linear polyethene.
The focus of our future research is to introduce other early
transition metals into the coordination chemistry of bis-
(amino)cyclodiphosph()azanes so as to enhance their
catalytic performance.
Figure 6. Ethylene consumption curves from polymerization
experiments with (a) [(tBuN)(tBuNP)]2TiCl2 (10), (b)
[(Ph2CHN)(tBuNP)]2TiCl2 (12), (c) [(2,6-Et2PhN)(tBuNP)]2TiCl2
(13), (d) [(2,6-iPr2PhN)(tBuNP)]2TiCl2 (14), and (e) [(2,5-
tBu2PhN)(tBuNP)]2TiCl2 (15) as catalyst precursors
ϫ h) (runs 5, 4 and 7, respectively, in Table 4). This indi-
cates that mass transfer effects play an important role. On
increasing the temperature from 50 to 70 °C (runs 5 and 6),
the molar mass of the polymers clearly decreases, from 2.5
to 1.4 ϫ 106 g/mol, while the PD is the same. This reveals
that catalyst 14/MAO is stable at higher temperatures.
From the results above, it appears that the catalytic
performance of the bis(amido)cyclodiphosph()azane ti-
tanium()dichlorides depends strongly on the ligand
substituents. Activation with MAO was faster for the
amido complexes [(tBuN)(tBuNP)]2TiCl2 (10) and
[(Ph2CHN)(tBuNP)]2TiCl2 (12) than for the complexes
13؊15 with aniline substituents. Moreover, the rate of de-
cline of the polymerization and the steady state values de-
pend on the catalyst precursors used. This indicates that the
steric bulkiness of the ligand substituents can influence a
sensitive equilibrium between active and dormant metal
centers. The bulkiest aniline complex, 15/MAO, exhibited
the highest steady state activities followed by cis-[(2,6-
iPr2C6H3N)2(PN-tBu)2]TiCl2
(14)
and
cis-[(2,6-
Et2C6H3N)2(PN-tBu)2]TiCl2 (13), i.e. in the order of steric
bulkiness.
The
polymerization
behavior
of
10/MAO
([(tBuN)(tBuNP)]2TiCl2) is unique due to the bimodal mo-
lar mass distribution of the polymer. The relatively small
tert-butyl groups not only leave the titanium center open
for activation and polymerization but, at the same time, the
catalyst is susceptible to side reactions. Coordination of the
Lewis acidic cocatalyst (MAO) to the lone-pair electrons of
phosphorus atoms can initiate destruction of the ligand,[11]
which could explain the presence of different active centers
and could also be one reason for the fast catalyst deacti-
Experimental Section
General Remarks: All manipulations were performed under an ar-
gon atmosphere using standard Schlenk techniques. The hydro-
carbon and ethereal solvents were boiled under reflux over sodium
and benzophenone, distilled, and stored under an inert atmosphere
with pieces of sodium. Dichloromethane was boiled under reflux
with CaH2 powder and distilled before use. Mass spectra were
vation. Therefore, bulky aromatic groups attached directly measured on a JEOL SX102 spectrometer and the 1H and 13C
Eur. J. Inorg. Chem. 2004, 695Ϫ706
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K. V. Axenov, V. V. Kotov, M. Klinga, M. Leskelä, T. Repo
FULL PAPER
NMR spectra were recorded on a Varian Gemini 200 MHz spec-
fluoromethylaniline (2.4 mL, 3.05 g, 18.9 mmol) and separation of
the obtained crude product were carried out as above. The resulting
white solid was dissolved in pentane (20 mL). This solution was
1
trometer. The H and 13C NMR spectra are referenced relative to
CHCl3 (δ ϭ 7.24 and 77.0 ppm, respectively) or C6D5H (δ ϭ 7.15
and 128.0 ppm, respectively). 31P NMR spectra were collected with then concentrated to 8 mL and kept at Ϫ20 °C to yield colorless
a Bruker AMX 400 spectrometer, with phosphorus signals refer-
crystals of product (4.20 g; 85 %). Crystals suitable for X-ray crys-
enced to an external 85 % H3PO4 solution. Elemental analyses were tallographic analysis were obtained in this manner. C22H28F2N4P2
performed Analytische Laboratorien Prof. Dr. H. Malissa and G.
Reuter GmbH, Lindlar, Germany. High-temperature gel per-
meation chromatography of polyethylene samples (GPC) was per-
formed in 1,2,4-trichlorobenzene at 145 °C by using a Waters
HPLC 150 C.
(524.4): calcd. C 50.39, H 5.38, N 10.68, P 11.81; found C 49.46,
H 5.91, N 10.89, P 11.88. 1H NMR (200 MHz, CDCl3, 29 °C):
δH ϭ 1.29 (s, 18 H, tBu), 5.49 (br.s, 2 H, NH), 6.90 (t, 2 H, ArH,
J ϭ 7.7 Hz), 7.38 (t, 2 H, ArH, J ϭ 8.0 Hz), 7.48 (dd, 2 H, ArH,
1J ϭ 7.7, 2J ϭ 1.4 Hz), 7.66 (d, 2 H, ArH, J ϭ 7.7 Hz) ppm.
13C{1H} NMR (50.3 MHz, CDCl3, 29 °C): δC ϭ 30.9 (t, CH3C,
tert-Butylamine and phosphorus trichloride were purchased from
Merck and purified by distillation under argon (tBuNH2 over so-
dium hydroxide). Arylamines and diphenylmethylamine were ob-
tained from Aldrich and distilled in vacuo over sodium hydroxide
before use. Chlorotrimethylsilane was purchased from Fluka
and used as received. Ti(NMe2)4 was purchased from Aldrich and
used as solution in toluene. Methylalumoxane (MAO, 30 wt.%
solution in toluene) was received from Borealis Polymers Oy.
J
P,C ϭ 6.5 Hz), 51.6 (t, CH3C, JP,C ϭ 12.5 Hz), 116.4 (CCF3, JC,F ϭ
29.0 Hz), 116.9 (Ar), 117.4 (Ar), 119.2 (Ar), 126.6 (q, Ar, JC,F
ϭ
5.0 Hz), 132.71 (Ar), 124.5 (q, CF3, JC,F ϭ 272.0 Hz) ppm. 31P{1H}
NMR (162 MHz, CDCl3, 21 °C): δP ϭ 107.8 (s) ppm. MS(EI):
m/z (%) ϭ 524 (37) [Mϩ], 364 (94), 203(10), 161(32).
cis-[(2,5-tBu2C6H3NH)(PN-tBu)]2 (5): 2,5-Di-tert-butylaniline
(3.88 g, 18.9 mmol), cis-(ClPN-tBu)2 (1) (2.60 g, 9.5 mmol) and
Et3N (5.3 mL, 3.83 g, 37.8 mmol) were mixed in THF (80 mL) and
then boiled under reflux for four days. After filtration, all volatile
compounds were removed under vacuum. The resulting white solid
was dissolved in CH2Cl2 (15 mL) and hexane (30 mL) was added.
The resulting solution was then kept at 0 °C overnight. The suspen-
sion that formed was filtered off and all volatile components were
removed from the filtrate. The white solid product was then recrys-
tallized from CH2Cl2/hexane solution at Ϫ20 °C (colorless crystals;
3.94 g; 68 %). Crystals suitable for the X-ray analysis were obtained
in this manner. C36H62N4P2 (612.9): calcd. C 70.55, H 10.20, N
cis-[Cl(tBuNP)]2
[(C6H5NH)(tBuNP)]2
(1),[16]
cis-[(tBuNH)(tBuNP)]2,[21]
cis-
[12]
[21]
and cis-[(tBuN)2(tBuNP)2]Li2(THF)2
were prepared according to modified literature procedures.
cis-[(2,6-iPr2C6H3NH)(PN-tBu)]2 (2): 2,6-Diisopropylaniline (5.5
mL, 5.15 g, 29 mmol) and Et3N (8.1 mL, 5.87 g, 58 mmol) were
added to a stirred solution of cis-(ClPN-tBu)2 (1) (4 g, 14.5 mmol)
in THF (100 mL) and the reaction mixture was boiled under reflux
for four days. After filtration, all volatile compounds were removed
under vacuum and pentane (20 mL) was added to the residue. The
mixture was then kept in a freezer (Ϫ20 °C) overnight. After ad-
ditional filtration and removal of pentane the required product was
obtained as a colorless oil (6.42 g, 80 %). C32H54N4P2 (556.8):
calcd. C 69.03, H 9.78, N 10.06; found C 69.65, H 9.88, N 9.31.
1H NMR (200 MHz, [D6]benzene, 29 °C): δH ϭ 1.17 (s, 18 H, tBu),
1.27 (d, 24 H, CH3, iPr), 2.90 (m, 4 H, CH, iPr), 4.63 (s, 2 H,
NH), 7.05Ϫ7.18 (m, 6 H, ArH) ppm. 13C{1H} NMR (50.3 MHz,
[D6]benzene, 29 °C): δC ϭ 24.2 (CH3, iPr), 29.2 (m, CH, iPr), 31.4
(t, CH3C), 51.7 (t, CH3C), 118.8 (Ar), 124.0 (Ar), 136.3 (Ar), 141.0
1
9.14, P 10.11; found C 70.39, H 10.34, N 8.96, P 10.30. H NMR
(200 MHz, CDCl3, 29 °C): δH ϭ 1.33 (s, 18 H, tBu), 1.30 (s, 18 H,
tBuAr), 1.48 (s, 18 H, tBuAr), 5.30 (br.d, 2 H, NH, J ϭ 7.0 Hz),
6.80 (dd, 2 H, ArH, 1J ϭ 8.4, 2J ϭ 2.2 Hz), 7.20 (d, 2 H, ArH, J ϭ
8.4 Hz), 7.80 (dd, 2 H, ArH, J ϭ 5.5, J ϭ 2.0 Hz) ppm. 13C{1H}
NMR (50.3 MHz, CDCl3, 29 °C): δC ϭ 30.7 (CH3CAr), 31.2 (t,
CH3C, JP,C ϭ 6.8 Hz), 31.3 (CH3CAr), 33.8 (CH3CAr), 34.3
(CH3CAr), 51.4 (t, CH3C, JP,C ϭ 13.5 Hz), 113.4 (Ar), 114.1 (Ar),
116.0 (Ar), 126.2 (Ar), 130.8 (Ar), 141.7 (d, Ar, J ϭ 9.9 Hz) ppm.
31P{1H} NMR (162 MHz, CDCl3, 21 °C): δP ϭ 98.1 (s) ppm.
MS(EI): m/z (%) ϭ 612 (18) [Mϩ], 408 (96), 204(10), 57 (38).
1
2
(d, Ar) ppm. 31P{1H} NMR (162 MHz, [D6]benzene, 21 °C): δP
ϭ
114.8 (s) ppm. MS(EI): m/z (%) ϭ 556 (48) [Mϩ], 380 (84), 204
(35), 176 (76), 57 (87).
cis-[(Ph2CHNH)(PN-tBu)]2 (6): The reaction of diphenylmethyl-
amine (2.5 mL, 2.67 g, 18.9 mmol), cis-(ClPN-tBu)2 (1) (2.0 g,
7.3 mmol) and Et3N (4.1 mL, 2.94 g, 29.1 mmol) and the separ-
ation of the crude product were carried out as for 5. The resulting
white solid was then dissolved in CH2Cl2 (20 mL), and hexane (20
mL) was added to give a solution that was kept at 0 °C overnight.
The precipitate that formed was filtered off and solvents from the
filtrate were removed. The white solid product was then recrys-
tallized from CH2Cl2/hexane solution as colorless crystals (3.94 g;
72 %). C34H42N4P2 (568.7): calcd. C 71.81, H 7.44, N 9.85; found
C 71.64, H 7.34, N 9.77. 1H NMR (200 MHz, CDCl3, 29 °C): δH ϭ
0.97 (s, 18 H, tBu), 3.44 (dd, 2 H, Ph2CH), 5.60 (dd, 2 H, NH),
7.18 (m, 20 H, ArH) ppm. 13C{1H} NMR (50.3 MHz, CDCl3, 29
°C): δC ϭ 30.5 (t, CH3C), 51.6 (t, CH3C), 59.7 (Ph2CH), 126.8
(Ar), 127.3 (Ar), 128.3 (Ar), 145.5 (d) ppm. 31P{1H} NMR
(162 MHz, CDCl3, 21 °C): δP ϭ 100.0 (br. s) ppm. MS(EI): m/z
(%) ϭ 568 (72) [Mϩ], 403 (48), 386 (95), 204(20), 183(99), 167 (98),
77 (47), 57 (32).
cis-[(2-tBuC6H4NH)(PN-tBu)]2 (3): Reaction of cis-(ClPN-tBu)2 (1)
(0.65 g, 2.4 mmol), Et3N (1.4 mL, 1.93 g, 9.6 mmol) and 2-tert-bu-
tylaniline (0.75 mL, 0.71 g, 4.7 mmol) and separation of the re-
sulting crude product were carried out as for 2. The obtained white
solid was dissolved in pentane (10 mL) and the solution was con-
centrated to 3 mL and kept at Ϫ20 °C until colorless crystals ap-
peared (0.90 g, 76 %). Crystals suitable for X-ray crystallography
were obtained in this manner. C28H46N4P2 (500.6): calcd. C 67.17,
H 9.26, N 11.19, P 12.37; found C 66.99, H 9.33, N 11.06, P 12.47.
1H NMR (200 MHz, CDCl3, 29 °C): δH ϭ 1.29 (s, 18 H, tBu), 1.50
1
(s, 18 H, tBuAr), 5.34 (br.s, 2 H, NH), 6.80 (td, 2 H, ArH, J ϭ
2
1
2
7.8, J ϭ 1.5 Hz), 7.12 (t, 2 H, ArH, J ϭ 7.8, J ϭ 1.5 Hz), 7.30
(dd, 2 H, ArH, 1J ϭ 8.0, 2J ϭ 1.5 Hz), 7.71 (d, 2 H, ArH, J ϭ
8.0 Hz) ppm. 13C{1H} NMR (50.3 MHz, CDCl3, 29 °C): δC ϭ 31.1
(t, CH3C, JP,C ϭ 6.7 Hz), 30.6 (CH3CAr), 34.2 (CH3CAr), 51.5 (t,
CH3C, JP,C ϭ 13.7 Hz), 115.9 (Ar), 116.5 (Ar), 119.3 (Ar), 126.7
(Ar), 133.6 (Ar), 141.8 (d, Ar, J ϭ 11.0 Hz) ppm. 31P{1H} NMR
(162 MHz, CDCl3, 21 °C): δP ϭ 97.8 (s) ppm. MS(EI): m/z (%) ϭ
500 (58) [Mϩ], 364 (94), 203 (10), 162(32), 57 (99).
cis-[(2,4-Me2C6H3NH)(PN-tBu)]2 (7): Reaction of cis-(ClPN-tBu)2
(1) (5.15 g, 18.7 mmol), (11 mL, 7.58 g, 75 mmol) and 2,4-dimeth-
cis-[(2-CF3C6H4NH)(PN-tBu)]2 (4): Reaction of cis-(ClPN-tBu)2 ylaniline (4.6 mL, 4.54 g, 37.4 mmol) and separation of the crude
(1) (2.6 g, 9.5 mmol), Et3N (5.3 mL, 3.80 g, 37.8 mmol) and 2-tri- product were carried out as described for compound 2. The crude
702
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Eur. J. Inorg. Chem. 2004, 695Ϫ706

Bulky Bis(amino)cyclodiphosph(III)azanes
FULL PAPER
product was then dissolved in pentane (20 mL) to give a solution
that was kept in a freezer (Ϫ20 °C) overnight. After filtration and
removal of solvent a colorless oil was obtained (7.46 g, 90 %) and
9.9 Hz, C, tBu, P2N2 cycle), 60.2 (d, JP,C ϭ 19.2 Hz, C, tBu) ppm.
31P{1H} NMR (162 MHz, CDCl3, 21 °C): δP ϭ 117.4 (s) ppm. The
complex was prepared earlier by a different procedure and the data
given here are in good agreement with those reported.[21] MS(EI):
m/z (%) ϭ 465 (80) [Mϩ], 429 (40) [Mϩ Ϫ Cl], 352 (98, ligand).
1
used without further purification. H NMR (200 MHz, CDCl3, 29
°C): δH ϭ 1.32 (s, 18 H, tBu), 2.15 (s, 6 H, CH3Ar), 2.27 (s, 6 H,
CH3Ar), 4.91 (br.d, 2 H, NH, J ϭ 5.5 Hz), 6.96 (d, 4 H, ArH),
7.50 (d, 2 H, ArH) ppm. 13C{1H} NMR (50.3 MHz, CDCl3, 29
[(PhN)(tBuNP)]2Ti(NMe2)2 (11a): A solution of Ti(NMe2)4 (1.3 g,
5.8 mmol) in toluene (10 mL) was added dropwise to a stirred solu-
tion of cis-[(PhNH)(tBuNP)]2 (2.15 g, 5.5 mmol) in toluene (30
mL). The reaction mixture was then boiled under reflux overnight.
All volatile components were removed in vacuo. The resultant
redϪbrown residue was extracted with several portions of hexane.
The extracts were then filtered, concentrated to 10 mL, and cooled
to Ϫ20 °C to yield the product (1.34 g; 46.4 %) as a red-brown,
crystalline solid. Crystals suitable for X-ray analysis were obtained
by crystallization from hexane at Ϫ20 °C. C24H40N6P2Ti (522.5):
calcd. C 55.18, H 7.72, N 16.09; found C 55.53, H 8.00, N 15.53.
1H NMR (200 MHz, CDCl3, 29 °C): δH ϭ 1.50 (s, 18 H, tBu), 3.43
(s, 12 H, NMe2), 7.03 (t, J ϭ 7.33 Hz, 2 H, p-H-Ph) 7.20Ϫ7.50 (m,
Ph) ppm. 13C{1H} NMR (50.3 MHz, CDCl3, 29 °C): δC ϭ 29.3 (t,
JP,C ϭ 7.2 Hz, CH3, tBu), 44.0 (NMe2), 53.1 (t, JP,C ϭ 11.1 Hz, C,
tBu), 117.7 (d, Ar), 119.5 (Ar), 128.6 (Ar), 151.0 (d, Ar) ppm.
31P{1H} NMR (162 MHz, CDCl3, 21 °C): δP ϭ 142.2 (s) ppm.
MS(EI): m/z (%) ϭ 522 (50) [Mϩ], 478 (64, Mϩ Ϫ NMe2), 434 (70,
Mϩ Ϫ 2NMe2), 388 (90, ligand).
°C): δC ϭ 17.8 (CH3Ar), 20.5 (CH3Ar), 31.0 (t, CH3C, JP,C
ϭ
6.5 Hz), 51.7 (t, CH3C, JP,C ϭ 13.7 Hz), 115.0 (Ar), 117.7 (Ar),
125.0 (Ar), 127.0 (Ar), 131.2 (Ar), 139.0 (d, Ar) ppm. 31P{1H}
NMR (162 MHz, CDCl3, 21 °C): δP ϭ 99.0 (s) ppm.
cis-[(2,6-Et2C6H3NH)(PN-tBu)]2 (8): This was prepared in the same
manner as 7, starting from cis-(ClPN-tBu)2 (1) (2.6 g, 9.5 mmol),
Et3N (5.3 mL, 3.83 g, 37.8 mmol), and 2,6-diethylaniline (3.1 mL,
2.82 g, 18.9 mmol). A colorless oil (4.47 g; 94 %) was obtained and
1
used without further purification. H NMR (200 MHz, CDCl3, 29
°C): δH ϭ 1.38 (s, 18 H, tBu), 1.50 (t, 12 H, CH3, Et), 3.13 (q, J ϭ
7.7 Hz, 8 H, CH2, Et), 4.86 (s, 2 H, NH), 6.80Ϫ7.50 (m, 6 H, ArH)
ppm. 13C{1H} NMR (50.3 MHz, CDCl3, 29 °C): δC ϭ 15.3 (CH3,
Et), 26.7 (CH2, Et), 31.8 (t, CH3C, JP,C ϭ 6.5 Hz), 52.1 (t, CH3C,
JP,C ϭ 13.4 Hz), 123.2 (Ar), 130.0 (Ar), 136.1 (Ar), 141.2 (d, Ar)
ppm. 31P{1H} NMR (162 MHz, CDCl3, 21 °C): δP ϭ 114.2 (s)
ppm. MS (EI): m/z (%) ϭ 500 (64) [Mϩ], 352 (83), 204 (20),
177(99), 57 (99).
[(2,4-Di-MeC6H3N)(tBuNP)]2Li2(THF)2 (9): A solution of nBuLi
in hexane (23 mL, 1.6 , 35.5 mmol) was added dropwise to a
stirred solution of 7 (7.46 g, 16.8 mmol) in THF (60 mL) at Ϫ30
°C. The reaction mixture was then stirred 20 min at Ϫ20 °C, al-
lowed to warm to room temperature, and boiled under reflux for
5 h. The resulting yellow solution was then concentrated to 15 mL
and pentane (40 mL) was added. This suspension was then stored
overnight at Ϫ20 °C to give a white-yellow precipitate that was
then separated and washed with several portions of pentane at Ϫ20
°C. The mother liquid was then concentrated to 8 mL and pentane
(20 mL) was added. After two days at Ϫ20 °C a second lot of the
white-yellow product was obtained (8.5 g in total; 84 %). Crystals
suitable for X-ray analysis were obtained by crystallization from a
THF/hexane mixture at Ϫ20 °C. 1H NMR (200 MHz, [D6]benzene,
29 °C): δH ϭ 1.16 (m, 8 H, THF), 1.54 (s, 18 H, tBu), 2.41 (d, 12
H, CH3, Ar), 3.28 (m, 8 H, THF), 7.20 (m, 4 H, ArH), 7.80 (d,
J ϭ 7.9 Hz, 2 H, ArH) ppm. 13C{1H} NMR (50.3 MHz, [D6]ben-
zene, 29 °C): δC ϭ 20.5 (CH3, Ar), 23.1 (CH3, Ar), 25.3 (THF),
30.7 (t, CH3C, JP,C ϭ 7.60 Hz), 53.3 (t, CH3C, JP,C ϭ 16.0 Hz),
68.3 (THF), 116.72 (Ar), 118.5 (Ar), 124.3 (Ar), 127.2 (Ar), 133.8
(Ar), 142.1 (d, Ar) ppm. 31P{1H} NMR (162 MHz, [D6]benzene,
21 °C): δP ϭ 163.01 (s) ppm.
[(Ph2CHN)(tBuNP)]2TiCl2 (12): cis-[(Ph2CHNH)(tBuNP)]2 (6)
(2.23 g, 3.93 mmol) was dissolved in toluene and added via a syr-
inge to a solution of Ti(NMe2)4 (0.87 g, 3.9 mmol) at 0 °C. The
resultant mixture was boiled under reflux for 22 h to give the bis-
dimethylamido titanium() complex [(Ph2CHN)(tBuNP)]2-
Ti(NMe2)2 (12a), which was analyzed by 1H, 13C and 31P NMR.
1H NMR (200 MHz, [D6]benzene, 29 °C): δH ϭ 1.22 (s, 18 H, tBu),
1.82Ϫ2.40 (12 H, NMe2), 3.54 (dd, 2 H, J ϭ 14.0 Hz, CH, Ph2CH),
7.11 (m, 16 H, o- and m-Ph), 7.25 (d, J ϭ 7.1 Hz, 4 H, p-H-Ph)
ppm. 13C{1H} NMR (50.3 MHz, [D6]benzene, 29 °C): δC ϭ 30.9
(t, JP,C ϭ 7.2 Hz, CH3C), 43.0 (NMe2) 52.0 (t, JP,C ϭ 15.0 Hz,
CH3C), 59.3 (d, J ϭ 13.0 Hz, Ph2CH), 126.8 (Ar), 127.7 (Ar), 128.6
(Ar), 146.1 (d, Ar) ppm. 31P{1H} NMR (162 MHz, CDCl3, 21 °C):
δP ϭ 103.8 (s) ppm.
Subsequently, to form the dichloride, an excess of Me3SiCl (5.2
mL, 4.48 g, 41.2 mmol) was added and the reaction mixture was
stirred overnight at room temperature. The solvent was then re-
moved and the product purified similarly to 10, washed with pen-
tane and dried in vacuo. The product was isolated as a brown pow-
der (2.13 g, 72 %). C34H40Cl2N4P2Ti·C5H12 (757.6): calcd. C 61.83,
H 6.92, N 7.40; found C 62.47, H 6.60, N 8.04. 1H NMR
(200 MHz, [D6]benzene, 29 °C): δH ϭ 1.20 (s, 18 H, tBu), 3.50 (dd,
2 H, J ϭ 14.1 Hz, CH, Ph2CH), 7.00 (t, J ϭ 7.3 Hz, 8 H, o-H-Ph),
7.10 (t, J ϭ 7.4 Hz, 8 H, m-H-Ph), 7.27 (d, J ϭ 7.7 Hz, 4 H, p-H-
[(tBuN)(tBuNP)]2TiCl2 (10): TiCl4 (1.3 g, 0.75 mL, 6.84 mmol) was
added dropwise to a solution of cis-[(tBuN)(tBuNP)]2Li2(THF)2
(3.45 g, 6.84 mmol) in toluene at 0 °C. The reaction mixture was
then stirred at 0 °C for 20 min and boiled under reflux overnight.
The resulting brown suspension was filtered off and toluene was
removed in vacuo. The obtained brown solid residue was then dis-
solved in CH2Cl2 (30 mL), and hexane was added until precipi-
tation commenced. The solution then was cooled to Ϫ20 °C and
left overnight. The resulting suspension was filtered through Celite
and the solvents were removed. After a second recrystallization, an
Ph) ppm 13C{1H} NMR (50.3 MHz, [D6]benzene, 29 °C): δC
ϭ
30.8 (t, JP,C ϭ 7.0 Hz, CH3, tBu), 52.0 (t, JP,C ϭ 14.3 Hz, C, tBu),
59.0 (Ph2CH), 109.0 (Ar), 126.8 (Ar), 128.6 (Ar), 146.1 (Ar) ppm
31P{1H} NMR (162 MHz, CDCl3, 21 °C): δP ϭ 100.0 (s) ppm. MS
(EI): m/z (%) ϭ 684 (10) [Mϩ], 649 (15) [Mϩ Ϫ Cl], 568 (95, ligand).
[(2,6-Et2C6H3N)(tBuNP)]2TiCl2 (13): cis-[(2,6-Et2C6H3NH)(t-
BuNP)]2 (8) (1.79 g, 3.58 mmol) in toluene and a toluene solution
of Ti(NMe2)4 (0.8 g, 3.57 mmol) were treated as described above.
To this solution Me3SiCl (4.8 mL, 4.15 g, 38.2 mmol) was added
orange-brown
powder
(1.61 g;
50.6 %)
was
isolated.
C16H36Cl2N4P2Ti (465.2): calcd. C 41.31, H 7.80; found C 41.58,
H 8.01. 1H NMR (200 MHz, [D6]benzene, 29 °C): δH ϭ 1.23 (s, and the reaction mixture was stirred overnight at room tempera-
18 H, tBu, P2N2 cycle), 1.66 (s, 18 H, tBu) ppm. 13C{1H} NMR
(50.3 MHz, [D6]benzene, 29 °C): δC ϭ 28.3 (t, JP,C ϭ 7.25 Hz, CH3,
ture. The solvent was removed then under vacuum to give a red-
brown residue that was extracted first with hexane (30 mL) and
tBu, P2N2 cycle), 33.7 (d, JP,C ϭ 12.2 Hz, CH3, tBu), 54.6 (t, JP,C ϭ then twice with a mixture of hexane (20 mL) and CH2Cl2 (7 mL).
Eur. J. Inorg. Chem. 2004, 695Ϫ706
www.eurjic.org  2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 703

K. V. Axenov, V. V. Kotov, M. Klinga, M. Leskelä, T. Repo
FULL PAPER
After filtration and evaporation of solvent, the product was dried
mixture of hexane (30 mL) and CH2Cl2 (10 mL). After removal of
in vacuo to give a red-brown oil (1.9 g, 86.4 %). C28H44Cl2N4P2Ti the solvent, the product was washed with several portions (each 10
(617.4): calcd. C 54.47, H 7.18, N 9.07; found C 54.08, H 7.41, N
mL) of cold pentane and dried. A redϪbrown powder (2.40 g,
9.51. 1H NMR (200 MHz, [D6]benzene, 29 °C): δH ϭ 1.41 (s, 18 73.8%) was isolated. C36H60Cl2N4P2Ti (729.7): calcd. C 59.26, H
1
H, tBu), 1.45 (t, 12 H, CH3, Et), 3.16 (q, J ϭ 7.3 Hz, 8 H, CH2,
8.29, N 7.68; found C 58.94, H 8.41, N 7.86. H NMR (200 MHz,
Et), 7.10Ϫ7.40 (6 H, HϪAr) ppm. 13C{1H} NMR (50.3 MHz, [D6]benzene, 29 °C): δH ϭ 1.39 (s, 36 H, tBuAr), 1.52 (s, 18 H,
1
2
[D6]benzene, 29 °C): δC ϭ 14.9 (CH3, Et), 26.3 (d, J ϭ 9.9 Hz, tBu), 6.93 (dd, J ϭ 6.2, J ϭ 2.1 Hz, 2 H2 Hz, 4-HϪAr), 7.32 (2
CH2, Et), 31.2 (t, JP,C ϭ 6.5 Hz, CH3, tBu), 51.5 (t, JP,C ϭ 14.5 Hz,
H, 3-HϪAr), 8.17 (dd, 1J ϭ 3.1, 2J ϭ 2.1 Hz, 2 H, 2-HϪAr) ppm.
C, tBu), 123.3 (Ar), 127.1 (Ar), 135.7 (Ar), 138.1 (t, J ϭ 1.9 Hz, 13C{1H} NMR (50.3 MHz, [D6]benzene, 29 °C): δC ϭ 31.0 (CH3,
Ar) ppm. 31P{1H} NMR (162 MHz, CDCl3, 21 °C): δP ϭ 114.6 (s)
5-tBuAr), 31.4 (t, JP,C ϭ 6.0 Hz, CH3, tBu), 31.5 (CH3, 2-tBuAr),
ppm. MS(EI): m/z (%) ϭ 617 (55) [Mϩ], 583 (8) [Mϩ Ϫ Cl], 500 33.1 (C, 5-tBuAr), 34.5 (C, 2-tBuAr), 51.7 (t, JP,C ϭ 13.7 Hz, C,
(76, ligand).
tBu), 113.8 (Ar), 114.5 (Ar), 117.1 (Ar), 131.1 (Ar), 137.8 (Ar),
150.0 (Ar) ppm. 31P{1H} NMR (162 MHz, CDCl3, 21 °C): δP
99.72 (s) ppm. MS (EI): m/z (%) ϭ 728 (20) [Mϩ], 693 (10) [Mϩ
Cl], 612 (40, ligand).
ϭ
[(2,6-iPr2C6H3N)(tBuNP)]2TiCl2 (14): A toluene solution of cis-
[(2,6-iPr2C6H3NH)(tBuNP)]2 (2) (3.65 g, 6.56 mmol) and
Ti(NMe2)4 (1.47 g, 6.55 mmol) were treated as described above.
The titanium() bis-amido complex, generated in situ, [(2,6-
iPr2C6H3N)(tBuNP)]2Ti(NMe2)2 (14a) was then characterized by
Ϫ
Polymerization Experiments: A 1-L glass autoclave (manufacturer
Büchi) was charged with toluene (200 mL) and cocatalyst (MAO)
(Al/Ti ratio was 1000), thermostatted (50 or 70 °C), saturated with
ethene (3.8 bar), and the desired amount of complex solution was
then added. The monomer pressure (Ϯ50 mbar) and temperature
(Ϯ0.5 °C) were kept constant during each polymerization run.
Monomer consumption, polymerization temperature and pressure
were controlled by real-time monitoring. The polymerizations were
quenched with 10 % HCl solution in methanol, and the polymer
precipitated quantitatively by pouring the solution into methanol
(400 mL) acidified with aqueous hydrochloric acid. The samples
were washed several times with methanol and water, and dried at
60 °C.
1H, 13C, and 31P NMR. H NMR (200 MHz, [D6]benzene, 29 °C):
1
δH ϭ 1.32 (s, 18 H, tBu), 1.39 (d, 24 H, CH3, iPr), 3.00Ϫ3.23 (12
H, NMe2), 3.91 (m, 4 H, CH, iPr), 6.90Ϫ7.30 (6 H, H-Ar) ppm
13C{1H} NMR (50.3 MHz, [D6]benzene, 29 °C): δC ϭ 24.2 (CH3,
iPr), 31.4 (t, JP,C ϭ 6.5 Hz, CH3, tBu), 33.6 (d, J ϭ 1 Hz, CH, iPr),
45.7 (NMe2), 51.6 (t, JP,C ϭ 14.7 Hz, C, tBu), 123.0 (Ar), 123.9
(Ar), 136.3 (t, J ϭ 1.9 Hz, Ar), 140.9 (Ar) ppm. 31P{1H} NMR
(162 MHz, CDCl3, 21 °C): δP ϭ 115.6 (s) ppm.
To obtain the dichloride complex, Me3SiCl (9 mL, 7.47 g,
69 mmol) was added to the red-brown solution of [(2,6-
iPr2C6H3N)(tBuNP)]2Ti(NMe2)2 (14a) via syringe, and the reaction
mixture was stirred overnight at room temperature. The so-ob-
tained product was then purified similarly to 13 to afford a red-
brown oil that was treated with Et2O to give a red-brown solid after
drying in vacuo (3.60 g, 81 %). C32H52Cl2N4P2Ti (673.5): calcd. C
57.07, H 7.78, N 8.32; found C 56.83, H 7.98, N 8.44. 1H NMR
(200 MHz, [D6]benzene, 29 °C): δH ϭ 1.32 (s, 18 H, tBu), 1.39 (d,
24 H, CH3, iPr), 3.88 (m, 4 H, CH, iPr), 7.10Ϫ7.60 (6 H, HϪAr)
ppm. 13C{1H} NMR (50.3 MHz, [D6]benzene, 29 °C): δC ϭ 24.2
(CH3, iPr), 31.4 (t, JP,C ϭ 6.7 Hz, CH3, tBu), 32.1 (d, J ϭ 1 Hz,
CH, iPr), 51.3 (t, JP,C ϭ 14.5 Hz, C, tBu), 122.5 (Ar), 124.0 (Ar),
130.7 (Ar), 140.9 (Ar) ppm. 31P{1H} NMR (162 MHz, CDCl3, 21
°C): δP ϭ 115.6 (s) ppm. MS (EI): m/z (%) ϭ 672 (10) [Mϩ], 639
(8) [Mϩ Ϫ Cl], 556 (90, ligand).
X-ray Crystallographic Study: Crystal data of compounds 3Ϫ5 were
collected with an EnrafϪNonius CAD-4 single-crystal dif-
fractometer at 193(2) K using Cu-Kα radiation (graphite mono-
˚
chromator), 1.54179 A (scan-type omega/2-theta). Intensities were
corrected for Lorentz and polarization effects with XCAD4.[26,27]
The crystal data of compound 9 were collected with a Rigaku
AFC-7S single-crystal diffractometer at 193(2) K using Mo-Kα
˚
radiation (graphite monochromator), 0.71073 A (omega/2-theta
scans). Intensities were corrected for Lorentz and polarization ef-
fects with TEXSAN.[28] A psi-scan absorption correction was made
for each compound.[29]
The crystal data of compound 11a were collected with a Nonius
KappaCCD area-detector diffractometer at 173(2) K using Mo-Kα
[(2,5-tBu2C6H3N)(tBuNP)]2TiCl2 (15): A toluene solution of cis-
[(2,5-tBu2C6H3NH)(tBuNP)]2 (5) (2.73 g, 4.46 mmol) and
Ti(NMe2)4 (1.0 g, 4.46 mmol) was treated in the same way as 13.
The resultant titanium() bis-amido complex, generated in situ,
[(2,5-tBu2C6H3N)(tBuNP)]2Ti(NMe2)2 (15a) was characterized by
˚
radiation (graphite monochromator), 0.71073 A. Data reduction:
COLLECT;[30] absorption correction: SADABS.[31]
Solution and refinement: SHELX-97,[32,33] direct methods. All non-
hydrogen atoms were refined anisotropically. Hydrogen atoms were
refined on calculated positions. The displacement factors of the H-
atoms were 1.2ϫ (1.5ϫ) that of the host atom. Data relating to the
structure determinations are collected in Table 5. CCDC-213508
to -213512 (for compounds 3Ϫ5, 9, 11a) contain the supplementary
crystallographic data for this paper. These data can be obtained
free of charge at www.ccdc.cam.ac.uk/conts/retrieving.html [or
from the Cambridge Crystallographic Data Centre, 12 Union
Road, Cambridge CB2 1EZ, UK; Fax: (internat.) ϩ44-1223/336-
033; E-mail: deposit@ccdc.cam.ac.uk].
1H, 13C, and 31P NMR. H NMR (200 MHz, [D6]benzene, 29 °C):
1
δH ϭ 1.44 (s, 36 H, tBuAr), 1.57 (s, 18 H, tBu), 3.19 (12 H, NMe2),
6.98 (dd, J1 ϭ 6.2, J2 ϭ 2.1 Hz, 2 H, 4-HϪPh), 7.36 (2 H, 3-
HϪPh), 8.23 (dd, J1 ϭ 3.1, J2 ϭ 2.1 Hz, 2 H, 2-HϪPh) ppm.
13C{1H} NMR (50.3 MHz, [D6]benzene, 29 °C): δC ϭ 31.0 (CH3,
5-tBuAr), 31.3 (t, JP,C ϭ 6.5 Hz, CH3, tBu), 31.5 (CH3, 2-tBuAr),
33.1 (C, 5-tBuAr), 34.0 (C, 2-tBuAr), 45.2 (NMe2), 51.7 (t, JP,C
ϭ
13.7 Hz, C, tBu), 113.8 (Ar), 114.5 (Ar), 117.1 (Ar), 131.2 (Ar),
141.9 (Ar), 150.0 (t, J ϭ 1.2 Hz, Ar) ppm. 31P{1H} NMR
(162 MHz, CDCl3, 21 °C): δP ϭ 98.86 (s) ppm.
To obtain the dichloride complex, Me3SiCl (5.9 mL, 5.09 g,
46.8 mmol) was added to the red-brown solution of [(2,5-
tBu2C6H3N)(tBuNP)]2Ti(NMe2)2 (15a) and the reaction mixture
stirred overnight at room temperature. All volatiles were then re-
moved in vacuo and the residue was extracted three times with a
Acknowledgments
Financial support for this research by CIMO, University of
Helsinki and the Academy of Finland is gratefully acknowledged.
704
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2004, 695Ϫ706

Bulky Bis(amino)cyclodiphosph(III)azanes
FULL PAPER
Table 5. Crystallographic data for compounds 3؊5, 9, 11a
Compound
3
4
5
9
11a
Formula
Fw
C28H46N4P2
500.63
P21/n
10.130(1)
18.899(1)
15.907(1)
90
98.19(1)
90
3014.3(4)
1.103
C22H28F6N4P2
524.42
P1
C36H62N4P2
612.84
P212121
9.885(1)
18.136(1)
21.012(1)
90
90
90
3766.9(5)
1.081
4
C36H60Li2N4O3P2
672.70
C2/c
14.761(5)
15.070(3)
17.815(3)
90
98.94(2)
90
3914.8(17)
1.141
4
1.48
0.71073
193(2)
0.0835
0.2345
C24H40N6P2Ti
522.46
P21/c
11.903(1)
22.667(2)
11.699(1)
90
115.808(1)
90
2841.6(4)
1.221
¯
Space group
˚
a, A
9.251(1)
11.010(1)
13.790(1)
81.44(1)
82.66(1)
69.440(10)
1296.1(2)
1.344
˚
b, A
˚
c, A
α, deg
β, deg
γ, deg
3
˚
V, A
dcalcd., g cmϪ3
Z
4
2
4
µ, cmϪ1
14.60
20.73
1.54179
193(2)
0.0486
0.1417
12.45
0.436
˚
λ, A
1.54179
193(2)
0.0675
0.1911
1.54179
193(2)
0.0433
0.1158
0.71073
173(2)
0.0613
0.1434
T, K
R[a]
[b]
Rw
[a]
[b]
2
2 2
2 2
R ϭ ΣFo Ϫ Fc/ΣFo for observed reflections [I Ͼ 2σ(I)]. Rw ϭ {Σ[w(Fo Ϫ Fc ) ]/Σ[w(Fo ) ]}1/2 for all data.
[1]
[2]
[1a] C. Janiak, Metallocenes (Eds.: A. Togni, R. L. Haltermann)
G. Talarico, J. C. Stevens, Book of abstracts, EUPOC 2003,
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mond, C. Goh, K. A. Hall, A. M. LaPointe, M. Leclerc, C.
Lund, V. Murphy, J. A. W. Shoemaker, U. Tracht, H. Turner,
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1996, vol. 1 and 2.
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[2a] H. G. Alt, A. Köppl, Chem. Rev. 2000, 100, 1205. [2b] H. H.
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[7b]
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V. C.
Gibson, K. Spitzmesser, Chem. Rev. 2003, 103, 283.
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[2c]
[8] [8a]
Engl. 1995, 34, 1143.
L. Resconi, L. Cavallo, A. Fait, F.
J. D. Scollard, D. H. McConville, J. Am. Chem. Soc. 1996,
[2d]
[8b]
Piemontesi, Chem. Rev. 2000, 100, 1253.
G. W. Coates,
118, 10008.
J. D. Scollard, D. H. McConville, N. C. Payne,
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[3]
[3a] G. J. P. Britovsek, V. C. Gibson, B. S. Kimberley, P. J. Mad-
[8d] S.-J. Kim, I. N. Jung, B. R. Yoo, S. H. Kim, J. Ko, D. Byun,
[8e]
dox, S. J. McTavish, G. A. Solan, A. J. P. White, D. J. Williams,
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