Donor-ligand-substituted cyclopentadienylchromium(III) complexes: A new class of alkene polymerization catalyst. 2. Phosphinoalkyl-substituted systems

Article abstract of DOI:10.1021/om010146m

A series of phosphinoalkyl-substituted cyclopentadienylchromium complexes, e.g., (η¹:η⁵-R₂ PC₂H₄C₅H₄)CrCl₂, have been synthesized. The complexation of the P atom to the chromium has been confirmed by crystal structure determinations. Activated by methylalumoxane (MAO), these compounds catalyze the oligomerization and polymerization of ethylene. The catalytic activity and the degree of oligomerization are controlled by the steric properties of the substituents on the donor atom: the smaller the substituent, the greater the activity and the lower the molecular weight of the oligomer. Density functional calculations indicate that propagation and termination through β-hydrogen transfer are competitive for small substituents and that the latter process, which involves spin inversion, becomes selectively disfavored with increasing size of the substituents. For large substituents β-hydrogen elimination to the chromium atom is found to be the preferred route for termination, although this reaction is less facile than insertion.

Full text of DOI:10.1021/om010146m

2234
Organometallics 2001, 20, 2234-2245
Don or -Liga n d -Su bstitu ted
Cyclop en ta d ien ylch r om iu m (III) Com p lexes: A New Cla ss
of Alk en e P olym er iza tion Ca ta lyst. 2.
P h osp h in oa lk yl-Su bstitu ted System s
Arno Do¨hring, Vidar R. J ensen,* Peter W. J olly,* Walter Thiel, and
J an C. Weber1
Max-Planck-Institut fu¨r Kohlenforschung, Kaiser-Wilhelm-Platz 1,
D-45470 Mu¨lheim an der Ruhr, Germany
Received February 22, 2001
A series of phosphinoalkyl-substituted cyclopentadienylchromium complexes, e.g., (η1:η5-
R2PC2H4C5H4)CrCl2, have been synthesized. The complexation of the P atom to the chromium
has been confirmed by crystal structure determinations. Activated by methylalumoxane
(MAO), these compounds catalyze the oligomerization and polymerization of ethylene. The
catalytic activity and the degree of oligomerization are controlled by the steric properties of
the substituents on the donor atom: the smaller the substituent, the greater the activity
and the lower the molecular weight of the oligomer. Density functional calculations indicate
that propagation and termination through â-hydrogen transfer are competitive for small
substituents and that the latter process, which involves spin inversion, becomes selectively
disfavored with increasing size of the substituents. For large substituents â-hydrogen
elimination to the chromium atom is found to be the preferred route for termination, although
this reaction is less facile than insertion.
In tr od u ction
(THF)3Cl3, and their accessibility depends on the ease
of preparation of the cyclopentadienyl derivative.
Recently we reported that highly active, homogeneous
catalysts for the polymerization of ethylene under mild
conditions can be generated by activating amino-
substituted cyclopentadienyl chromium(III) complexes,
e.g., (η1:η5-R2NC2H4C5Me4)CrCl2, with methylalumox-
ane.2,3 We have now extended these investigations to
the related phosphinoalkyl-substituted analogue and
have observed a remarkable dependence of the product
composition of the reaction with ethylene upon the steric
properties of the substituent (R) on the P atom. A
preliminary account of this work has been published.4,5
P r ep a r a tion of th e P h osp h in oa lk yl-Su bstitu ted
Cyclop en ta d ien yl Der iva tives. The synthetic routes
available have been reviewed.6 Most easily prepared are
the R2PC2H4C5H4Li (1a -1l) and R2PC2H4IndenylLi
(2a -2c) species which may be formed in good yield by
reacting the appropriate lithium phosphide with spiro-
[2.4]hepta-4,6-diene8 or spiro[cyclopropane-1,1′-indene]9
(eqs 1 and 2).
Resu lts a n d Discu ssion
Although η1:η5-phosphinoalkyl-substituted cyclopen-
tadienyl derivatives have been prepared for many of the
transition metals,6 e.g., Mn, Ru, and Rh, examples
involving chromium were not known prior to our
investigations.7 These compounds can be prepared by
reacting the alkali metal salt of the ligand with Cr-
(1) Part of the Ph.D. Thesis submitted to Ruhr-Universita¨t Bochum
in 1999.
(2) Do¨hring, A.; Go¨hre, J .; J olly, P. W.; Kryger, B.; Rust, J .;
Verhovnik, G. P. J . Organometallics 2000, 19, 388.
(3) J ensen, V. R.; Angermund, K.; J olly, P. W.; Børve, K. J .
Organometallics 2000, 19, 403.
The related 3-phosphinopropyl-substituted deriva-
tives (3, 4) may be prepared by reacting R2PC3H6Cl with
(4) Do¨hring, A.; J ensen, V. R.; J olly, P. W.; Thiel, W.; Weber, J . C.
In Organometallic Catalysts and Olefin Polymerization; Blom, R.,
Follestad, A., Rytter, E., Tilset, M., Ystens, M., Eds.; Springer-Verlag,
2001; p 127.
(5) Do¨hring, A.; J ensen, V. R.; J olly, P. W.; Thiel, W.; Weber, J . C.
Macromol. Symp., in press.
(7) J olly, P. W.; J onas, K.; Verhovnik, G. P. J .; Do¨hring, A.; Go¨hre,
J .; Weber, J . C. (Studiengesellschaft Kohle m.b.H.) WO-A 98/04570,
1998 [Chem. Abstr. 1998, 128, 167817v].
(8) Wilcox, C. F.; Craig, R. R. J . Am. Chem. Soc. 1961, 83, 3866.
(9) Kauffmann, T.; Berghus, K.; Rensing, A.; Ennen, J . Chem. Ber.
1985, 118, 3737.
(6) Butenscho¨n, H. Chem. Rev. 2000, 100, 1527.
10.1021/om010146m CCC: $20.00 © 2001 American Chemical Society
Publication on Web 05/01/2001

Cyclopentadienylchromium(III) Complexes
Organometallics, Vol. 20, No. 11, 2001 2235
Ta ble 1. P h osp h in oa lk yl-Su bstitu ted Cyclop en ta d ien ylch r om iu m Dich lor id e Com p ou n d s
anal.: found (calcd)
compound
yield (%)
C
H
Cl
Cr
P
(Me2PC2H4C5H4)CrCl2 (7a )
(Et2PC2H4C5H4)CrCl2 (7b)
(Pr2PC2H4C5H4)CrCl2 (7c)
13
40
84
59
64
22
68
39
85
quant
84
13
quant
17
61
81
23
31
39.3 (39.2)
43.6 (43.4)
46.9 (47.0)
46.8 (47.0)
50.2 (50.0)
49.9 (50.0)
52.7 (52.6)
54.6 (54.8)
55.2 (55.4)
57.2 (57.0)
63.4 (63.4)
58.7 (58.9)
64.7 (64.8)
64.4 (64.5)
50.7 (50.9)
55.7 (55.6)
59.9 (59.8)
56.2 (56.3)
58.1 (58.0)
60.3 (60.5)
61.1 (61.3)
5.0 (5.1)
6.1 (6.0)
6.7 (6.7)
6.6 (6.7)
7.2 (7.3)
7.3 (7.3)
8.1 (7.7)
8.3 (8.2)
7.3 (7.3)
4.5 (4.5)
5.4 (5.3)
5.0 (5.2)
4.4 (4.4)
5.1 (5.1)
5.6 (5.1)
6.9 (6.9)
7.1 (7.0)
7.7 (7.6)
5.0 (4.9)
7.1 (7.2)
6.1 (6.0)
25.5 (25.7)
23.3 (23.3)
21.3 (21.3)
21.2 (21.3)
19.7 (19.7)
19.6 (19.7)
17.4 (18.3)
17.1 (17.0)
17.1 (17.2)
17.9 (17.7)
14.4 (14.4)
16.5 (16.6)
14.2 (14.2)
12.7 (12.7)
20.2 (20.0)
17.2 (17.3)
15.3 (15.3)
16.7 (16.6)
17.1 (17.1)
15.0 (14.9)
15.0 (15.1)
18.7 (18.8)
17.2 (17.1)
15.8 (15.7)
15.4 (15.7)
14.5 (14.4)
14.6 (14.4)
12.9 (13.4)
12.6 (12.5)
12.7 (12.6)
12.7 (13.0)
10.5 (10.6)
11.9 (12.1)
10.3 (10.4)
9.2 (9.3)
14.5 (14.7)
12.8 (12.7)
11.2 (11.3)
12.1 (12.2)
12.4 (12.6)
10.8 (10.9)
10.8 (11.1)
11.2 (11.2)
10.1 (10.2)
9.3 (9.3)
9.2 (9.3)
8.5 (8.6)
8.5 (8.6)
- (8.0)
7.4 (7.4)
7.7 (7.5)
7.6 (7.7)
6.2 (6.3)
7.1 (7.2)
6.2 (6.2)
5.6 (5.6)
8.8 (8.7)
7.5 (7.6)
6.6 (6.7)
7.4 (7.3)
7.3 (7.5)
6.7 (6.5)
6.4 (6.6)
(iPr2PC2H4C5H4)CrCl2 (7d )
(iBu2PC2H4C5H4)CrCl2 (7e)
(tBu2PC2H4C5H4)CrCl2 (7f)
(Neopentyl2PC2H4C5H4)CrCl2 (7g)
(Hexyl2PC2H4C5H4)CrCl2 (7h )
(Cy2PC2H4C5H4)CrCl2 (7i)
(Ph2PC2H4C5H4)CrCl2 (7j)
(Ph2PC2H4C5H4)CrCl2‚Tol (7j′)
(o-Tolyl2PC2H4C5H4)CrCl2 (7k )
(1-Naphthyl2PC2H4C5H4)CrCl2 (7l)
(1-Naphthyl2PC2H4C5H4)CrCl2‚Me2CO(7l′)
(Et2PC2H4Indenyl)CrCl2 (8a )
(iBu2PC2H4Indenyl)CrCl2 (8b)
(Cy2PC2H4Indenyl)CrCl2 (8c)
(Cy2PC3H6C5H4)CrCl2 (9a )
(Ph2PC3H6C5H4)CrCl2 (9b)
(Cy2PC3H6Indenyl)CrCl2 (10)
(Ph2PC3H6C5Me4)CrCl2 (11)
73
9
27
Sch em e 1. P r ep a r a tion of th e Or ga n och r om iu m
Com p ou n d s
NaCp/BuLi10 or IndenylLi (eqs 3 and 4).
The lithium salt of 3-tetramethylcyclopentadienyl-
propyl-1-diphenylphosphine (5) was prepared in a mul-
tistep published procedure starting from tetramethyl-
cyclopent-2-enone (eq 5).11
P r ep a r a tion a n d Str u ctu r e of th e Or ga n och r o-
m iu m Com p ou n d s. The phosphinoalkyl-substituted
cyclopentadienylchromium dichloride compounds, 7-11,
were prepared by reacting the appropriate lithium salt
with Cr(THF)3Cl3 in THF (examples are shown in
Scheme 1). The compounds are thermally stable at room
temperature, and the monosubstituted derivatives (7
and 9) can even be handled briefly in the air. The
indenyl derivatives 8 and 10 are dark green, whereas
the monosubstituted cyclopentadienyl species and the
tetramethyl-substituted compound 11 are dark blue.
The analytical data for the isolated compounds are listed
in Table 1.
In addition, Cy2AsC2H4C5H4Li (6) has been prepared
by reacting the lithium arsenide with spiro[2.4]hepta-
4,6-diene (eq 6).12
(10) Kettenbach, R. T.; Bonrath, W.; Butenscho¨n, H. Chem. Ber.
For mechanistic purposes, we have also prepared a
number of chromium-alkyl derivatives (12-18) by re-
acting the dichloride species with a Grignard reagent
or MeLi (Scheme 1), and the analytical data for these
1993, 126, 1657.
(11) Bensley, D. M.; Mintz, E. A.; Sussangkarn, S. J . J . Org. Chem.
1988, 53, 4417.
(12) Kauffmann, T.; Berghus, K.; Ennen, J . Chem. Ber. 1985, 118,
3724.

2236 Organometallics, Vol. 20, No. 11, 2001
Do¨hring et al.
Ta ble 2. P h osp h in oa lk yl-Su bstitu ted Cyclop en ta d ien ylch r om iu m Alk yl Com p ou n d s
anal.: found (calcd)
compound
yield (%)
C
H
Cr
P
(Cy2PC2H4C5H4)Cr(Et)Br (12)a
(Cy2PC2H4Indenyl)Cr(Me)Cl (13)b
(Et2PC2H4C5H4)CrMe2 (14)
(Cy2PC2H4C5H4)CrMe2 (15a )
(Cy2PC2H4C5H4)CrtBu2 (15b)
(Ph2PC2H4C5H4)CrPr2 (16a )
(Ph2PC2H4C5H4)CrtBu2 (16b)
(Ph2PC2H4C5H4)CrCy2 (16c)
(Cy2PC3H6C5H4)CrMe2 (17)
(Ph2PC3H6C5Me4)CrMe2 (18)
24
17
22
49
13
59
22
26
45
2
56.2 (56.0)
65.2 (65.2)
59.4 (59.3)
67.8 (67.9)
71.0 (71.2)
71.9 (72.3)
73.1 (73.1)
75.2 (75.1)
68.4 (68.5)
72.9 (72.7)
8.0 (7.8)
7.9 (8.0)
9.3 (9.2)
9.6 (9.8)
10.6 (10.6)
7.9 (7.7)
8.1 (8.2)
8.1 (8.1)
10.0 (9.9)
8.2 (8.0)
11.6 (11.5)
11.9 (11.8)
19.6 (19.8)
14.2 (14.0)
11.5 (11.4)
12.5 (12.5)
11.7 (11.7)
10.4 (10.5)
13.5 (13.5)
11.4 (11.1)
6.9 (6.9)
6.9 (7.0)
11.7 (11.8)
8.4 (8.3)
7.0 (6.8)
7.6 (7.5)
7.3 (7.0)
6.4 (6.3)
8.0 (8.0)
7.4 (7.2)
a
Br analysis: 17.7 (17.7). bCl analysis: 8.1 (8.0).
Ta ble 3. Selected Str u ctu r a l Da ta for P h osp h in oa lk yl- a n d Ar sin oa lk yl-Su bstitu ted
Cyclop en ta d ien ylch r om iu m Com p ou n d sa
7i
7j′
9a
11b
15a
19
Interatomic Distances (Å, esd)
Cr-D1
Cr-P1
Cr-Cl1
Cr-Cl2
P-C1
1.886
1.887
1.890
1.888
1.926
1.885
2.459(1)
2.276(1)
2.279(1)
1.850(3)
1.845(2)
1.844(2)
1.531(4)
1.501(4)
2.447(1)
2.273(1)
2.291(1)
1.821(3)
1.813(3)
1.826(3)
1.536(5)
1.505(5)
2.460(1)
2.294(1)
2.284(1)
1.834(4)
1.847(4)
1.855(4)
1.515(6)
1.512(7)
1.506(7)
2.472(1)
2.284(1)
2.284(1)
1.837(3)
1.818(1)
1.822(3)
1.520(5)
1.513(5)
1.512(5)
2.450(1)
2.058(5)d
2.083(4)d
1.845(3)
1.841(3)
1.841(3)
1.531(5)
1.518(5)
2.537(1)c
2.277(1)
2.282(1)
1.968(3)c
1.971(3)c
1.966(3)c
1.537(5)
1.512(5)
P-C(R)e
P-C′(R)e
C1-C2
C2-C3
C3-C4
Bond Angles (deg)
98.8(1)
Cl1-Cr-Cl2
P1-Cr-Cl1
P1-Cr-Cl2
P1-Cr-D1
95.9(1)
98.3(1)
102.2(1)
109.8
104.3(1)
105.5(1)
106.7(1)
105.4(1)
98.7(1)
94.4(1)
99.1(1)
110.1
100.7(1)
104.3(1)
107.7(1)
104.3(1)
97.7(1)
94.1(1)
94.0(1)
119.6
108.0(1)
105.8(1)
104.1(2)
102.3(1)
90.4(2)d
100.1(1)d
102.9(1)d
110.2
103.6(1)
105.0(2)
105.0(1)
105.0(1)
96.9(1)
94.6(1)
95.5(1)
117.5
108.2(1)
105.7(2)
105.8(2)
107.4(2)
99.9(1)c
97.2(1)c
109.6c
C1-P1-Cr
102.7(1)c
104.7(1)c
106.3(1)c
104.4(1)c
C1-P-C(R)e
C1-P-C′(R)e
C(R)-P-C′(R)e
See Figures 1 and 2 for the numbering of the atoms. D1 denotes the center of the Cp ring. bData for one of the two independent
a
molecules. As atom. dCr-CH3. P-bonded C atom of the substituent R.
c
e
are listed in Table 2. In contrast to the dichloride
compounds, the dialkyl species are readily oxidized and
are thermally less stable. All attempts to convert these
species into ionic compounds of potential mechanistic
relevance by reacting, for example, (Cy2PC2H4Indenyl)-
Cr(Me)Cl (13) with NaBPh4 or (Cy2PC2H4C5H4)CrMe2
(15a ) with B(C6F5)3 were unfortunately unsuccessful.
For comparison purposes, one dialkylarsino-substi-
tuted cyclopentadienyl derivative was prepared (19, eq
7), and this was converted into the corresponding
dimethyl derivative (20) by reaction with MeMgCl.
unpaired electrons has been confirmed using a super-
conducting quantum interference device (SQUID) for 7i
and 15a ), structural information is based upon crystal
structure investigations of selected compounds. The
molecular structures of 7i, 7j′, 9a , 11, and 15a are
shown in Figures 1 and 2 along with that of (Cy2-
AsC2H4C5H4)CrCl2 (19), and selected bond lengths and
bond angles are listed in Table 3.
The crystal structures confirm that in all cases the
donor atom is bonded to the chromium atom (Cr-P
2.45-2.47 Å). A comparison of the data for 7i and 7j′
indicates that an increase in the steric requirements
of the substituent (R) on the phosphorus atom is
accompanied by a lengthening of the P-Cr bond
(2.447(1) Å 7j′; 2.459(1) Å, 7i), while the (R)C-P-C(R)
angle increases (104.3(1)°, 7j′; 105.4(1)°, 7i). The com-
pounds 7i and 9a differ only in the length of the “spacer”
between ring and donor atom, and the less strained
arrangement in 9a results in an increase in the (R)C-
P-C′(R) angle (107.4(2)°, 9a ; 105.4(1)°, 7i) and is
accompanied by an increase in the Cl1-Cr-Cl2 angle
(98.8(1)°, 9a ; 95.9(1)°, 7i). These changes, however, have
no effect upon the Cr-P bond length (2.46 Å, 7i/9a ).
In contrast to the aminoalkyl-substituted cyclopen-
tadienyl analogue,2 the infrared spectra of the phos-
phinoalkyl-substituted species provide no readily inter-
pretable information on the bonding situation at the
donor atom, and since these Cr(III) compounds are
paramagnetic (the high-spin configuration with three
The exchange of the Cl atoms in 7i by Me groups in
15a leads to a small decrease in the Cr-P bond length
(2.450(1) Å, 15a ; 2.459(1) Å, 7i) and in a significant
increase in the separation (Cr-D) from the cyclopen-

Cyclopentadienylchromium(III) Complexes
Organometallics, Vol. 20, No. 11, 2001 2237
F igu r e 1. Molecular structures of (a) (Cy2PC2H4C5H4)CrCl2 (7i), (b) (Ph2PC2H4C5H4)CrCl2.Toluene (7j′), (c) (Cy2PC2H4C5H4)-
CrMe2 (15a ), and (d) (Cy2AsC2H4C5H4)CrCl2 (19).
tadienyl ring (1.926 Å, 15a ; 1.886 Å, 7i) as a result of
the increase in the electron density at the metal atom.
Although the Cr-Me bonds in 15a are significantly
shorter than the Cr-Cl bonds in 7i (2.058(5)/2.083(4)
Å, 15a ; 2.276(1)/2.279(1) Å, 7i), the difference in the
electrostatic properties of the two substituents shows
itself in the difference between the Cl-Cr-Cl angle
(95.9(1)°) and the Me-Cr-Me angle (90.4(1)°).
The increase in the Cr-donor atom bond length upon
exchanging the P-donor atom for an As-donor atom
(2.459(1) Å, 7i; 2.537(1) Å, 19) is the result of the
difference in the atomic radii (1.33 Å, As; 1.23 Å, P).
Ca ta lytic Oligom er iza tion a n d P olym er iza tion
of Eth ylen e. The organochromium compounds de-
scribed in the preceding section were prepared in order
to compare their catalytic behavior, in the presence of
methylalumoxane (MAO), toward ethylene with that of
the amino-substituted cyclopentadienyl chromium com-
plexes described earlier.2 The latter invariably convert
ethylene into linear polyethylene having a molecular
weight of 1-3 million with an activity that can be
influenced by introducing substituents into the ring.
ium catalysts of the general formula (R2PC2H4C5H4)-
CrCl2 since these species are relatively easy to prepare
and variation of the substituent R is unproblematic. To
facilitate comparison, the catalyses were carried out
under standard conditions in toluene at room temper-
ature and at a constant pressure of 2 bar. Near
isothermal conditions (∆T ) 3-4 °C) were obtained by
adjusting the concentration of the catalyst. The reaction
was terminated after 4 min by simultaneously stopping
the flow of ethylene into the reactor and injecting
propanol to destroy the catalyst. These conditions are
by no means optimal and considerably higher activities
can be obtained by increasing the MAO concentration,
by raising the temperature, and by changing the solvent.
These effects as well as those of introducing substituents
into the cyclopentadienyl ring will be discussed in a
subsequent publication.
The product of the oligomerization was analyzed as
three fractions: lower oligomers, nondistillable higher
oligomers soluble in toluene, and solid polyethylene. The
composition of the lower oligomer mixture has been
determined by gas chromatography. An investigation of
the composition of the soluble, higher oligomer fraction
is in progress and will be reported separately: initial
We confine our attention here to the behavior of the
monosubstituted phosphinoalkylcyclopentadienylchrom-

2238 Organometallics, Vol. 20, No. 11, 2001
Do¨hring et al.
mainly steric in origin is apparent from a comparison
with the cone angle (θ) of the related triorganophosphine
(PR3) compounds as defined by Tolman13 (Table 4), and
this is underlined by the results for the phenyl- and
o-tolyl-substituted derivatives.
An effect as dramatic as that described here has not
been reported previously for a chromium catalyst.
However, it should be mentioned that the polymeriza-
tion of ethylene using MAO-activated diimine complexes
of nickel14 and pyridinediimine complexes of iron and
cobalt15-18 having aryl substituents, e.g., 21 and 22, can
be tailored to give long-chain oligomers by decreasing
the size of the ortho-substituents on the aryl groups.
In addition, it has been reported that the degree of
oligomerization of ethylene catalyzed by (η3-C3H5)Ni(PR3)-
X-Et3Al2Cl3 is controlled by the nature of the tertiary
phosphine bonded to the nickel atom: the main product
with PMe3 is the dimer, while in the presence of PtBu2-
iPr higher oligomers are formed.19 Finally, it has
recently been shown that the classical SHOP ethylene
oligomerization catalyst (23)20 can be transformed into
a polymerization catalyst (24) by introducing a salicyl-
aldimine ligand having bulky groups in the ortho-
position of the ligand.21
F igu r e 2. Molecular structures of (a) (Cy2PC3H6C5H4)-
CrCl2 (9a ) and (b) (Ph2PC3H6C5Me4)CrCl2 (11).
Ta ble 4. (R2P C2H4C5H4)Cr Cl2-MAO-Ca ta lyzed
Oligom er iza tion a n d P olym er iza tion of Eth ylen ea
θ(PR3)d
R
product composition (%)b
activityc (deg)
Me
Et
C4 (83.6), C6 (13.0), C6+(3.5)
4620
4480
118
132
Of particular technical interest in our case is presum-
ably the formation of a 1-butene/1-hexene mixture when
R is methyl, of the mixture of long-chain oligomers when
R is phenyl or isobutyl, and of polyethylene when R is
cyclohexyl: the dimer/trimer mixture could be copoly-
merized directly with ethylene to low-density polyeth-
ylene, while the waxlike higher olefin mixture could
form the basis of a chromium-catalyzed alternative to
the SHOP process.
C4 (21.2), C6 (26.3), C8-C14 (47.7),
C
14+ (5.0)
iBu
C4 (10.6), C6 (12.5), C8-C14 (43.3),
4230
143
C
14+ (33.6)
iPr
Cy
tBu
Ph
C6-C10 (3.1), PE (96.9, Mw 6.3 × 104)
C6-C10 (3.1), PE (96.9, Mw 1.8 × 105)
C4-C8 (15.6), PE (84.4, Mw 1.3 × 105)
C6-C10 (10.3), C12-C14 (8.6), C14+
(76.7), PE (2.1)
3590
1450
590
160
170
182
145
5140
o-Tolyl C6-C10 (4.5), PE (95.5)
2330
194
a
Standard condition: solvent, toluene; P(C2H4) ) 2 bar; Cr:
MAO ) 1:100; t ) 4 min; T ) 21 °C, ∆T ) 4 °C. bC4, 1-butene; C6,
(13) Tolman, C. A. Chem. Rev. 1977, 77, 313.
(14) Killian, C. M.; J ohnson, L. K.; Brookhart, M. Organometallics
1997, 16, 2005.
c
1-hexene etc.; reproducibility ( 2%. kg product/mol Cr‚h. dTolman
cone angle.
(15) Bennett, A. M. A. Chemtech 1999, 29, 24.
(16) Britovsek, G. J . P.; Bruce, M.; Gibson, V. C.; Kimberley, B. S.;
Maddox, P. J .; Mastroianni, S.; McTavish, S. J .; Redshaw, C.; Solan,
G. A.; Stro¨mberg, S.; White, A. J . P.; Williams, D. J . J . Am. Chem.
Soc. 1999, 121, 8728.
(17) Small, B. L.; Brookhart, M. J . Am. Chem. Soc. 1998, 120, 7143.
(18) Britovsek, G. J . P.; Mastroianni, S.; Solan, G. A.; Baugh, S. P.
D.; Redshaw, C.; Gibson, V. C.; White, A. J . P.; Williams, D. J .;
Elsegood, M. R. J . Chem.-Eur. J . 2000, 6, 2221.
(19) Bogdanovic´, B. Adv. Organomet. Chem. 1979, 17, 105.
(20) Vogt, D. Appl. Homogen. Catal. Organomet. Cpds. 1996, 1, 245.
(21) Younkin, T. R.; Connor, E. F.; Henderson, J . I.; Friedrich, S.
K.; Grubbs, R. H.; Bansleben, D. A. Science 2000, 287, 460.
NMR investigations indicate that it consists exclusively
of terminal olefins. The results are summarized in Table
4.
As can be seen from Table 4, both the catalytic activity
and the degree of oligomerization are dependent upon
the size of the substituents on the P atom: the larger
the substituent, the lower the activity and the higher
the degree of oligomerization. That these effects are

Cyclopentadienylchromium(III) Complexes
Organometallics, Vol. 20, No. 11, 2001 2239
Ta ble 5. Ca lcu la ted En th a lp ies a n d F r ee En er gies (k ca l/m ol) for th e Sp ecies Sh ow n in F igu r e 3, Rela tive
to Eth ylen e + [(R2DC2H4C5H4)Cr P r ]+, (Iâ(4A))a
D ) P
D ) N
R ) Me
R ) tBu
R ) Me
species
∆H298
∆G298
∆H298
∆G298
∆H298
∆G298
Iγ(4A) + ethyleneb
Iâ(4A) + ethyleneb
IR(4A) + ethyleneb
[IRfIV]q(4A)c
7.4
0.0
8.5
8.4
-2.5
4.0
-3.7
1.4
8.9
8.5
31
7.5
0.0
7.2
13.0
8.7
16.5
11.1
16.8
9.1
8.8
0.0
6.4
9.3
4.0
8.4
0.0
5.7
0.0
0.0
17.8
15.5
21.6
26.5
34.6
11.2
10.9
25
IV(4A)
0.1
4.8
10.3
13.7
10.4
17.1
24.2
28.0
[IVfVIγ]q(4A)
8.9
IVâ(2A)
11.4
19.2
10.1
10.6
29
[IVâfVâ]q(2A)
[IâfII]q(4A) + ethylene
II(4A) + ethylene
[IIfIII]q(4A) + ethylened
III(4A) + ethylene + propene
8.1
28
21.5
10.1
31
32.8
9.6
26
20.1
33.8
30.8
18.7
a
From single-point total energies at optimized geometries, with zero-point energies and temperature corrections; see Computational
Details. bInterconversion between different agostic conformers of I is facile (∆Gq < 11 kcal/mol for R ) Me). Ethylene coordination to
c
298
â- or γ-agostic complexes is less favorable. A very shallow minimum assignable to a charge-induced dipole metal-ethylene complex is
located prior to [IRfIV]q(4A). The thermochemical data for this complex have been omitted since they are not important for the discussion.
d
Entropic barrier estimated by stepwise geometry optimization and vibrational analysis; see Computational Details.
That the high activity of many of the catalysts and
the product distribution are a consequence of the
attachment of the donor ligand to the cyclopentadienyl
ring is emphasized by the results with a CpCr(PMe3)-
Cl2-MAO catalyst: under the same standard conditions
used for the (Me2PC2H4C5H4)CrCl2-MAO catalyst, an
activity of only 120 kg product/mol Cr‚h is observed, and
moreover the product is polyethylene.22 Low activity has
also been reported for the (C5Me5)Cr(PMe3)Me2-MAO
system, and in this case it has been suggested that the
termination step involves chain transfer from chromium
to aluminum.23,24
Mech a n istic Con sid er a tion s. The remarkable de-
pendence of the product composition in the Cr-catalyzed
reactions presented above upon the size of the substit-
uents on the P-donor atom prompted us to investigate
theoretically the mechanism of the reaction in the hope
of obtaining insight into the origin of this effect.
In recent years, density functional theory (DFT) has
become the method of choice for the computational
investigation of the mechanisms of transition metal
catalyzed olefin polymerization reactions (see for ex-
ample refs 3, 25-27). In the present investigation we
have selected a gradient-corrected functional (BPW91)
in combination with DZP basis sets for geometry
optimization and TZD2P basis sets for single-point
energy evaluations; see Computational Details.
by reacting the chromium dichloride compound with
methylalumoxane (MAO) and related to the [Cp(donor)-
CrR]+ species discussed previously3 and to the metal-
locenealkyl cations identified as the active species in the
case of the group 4 metallocene-based catalysts.28
The starting point for our calculations is the cation
[(R2DC2H4C5H4)CrPr]+ (D ) N or P) formed by the
insertion of a single ethylene molecule into the initial
Cr-Me bond. The preferred routes for the propagation
and termination reactions with ethylene obtained from
the calculations are shown in Figure 3, while the
associated relative energies of the intermediates and
transition states are listed in Table 5.
In Table 5, a minimum is labeled with a Roman
numeral (I-VI), and in the case of an agostic Cr-H-C
structure, this is followed by a Greek letter identifying
the carbon atom involved. Transition states are identi-
fied by a bracket enclosing the product and the reactant
separated by an arrow and followed by the suffix ‡ and
4
2
the molecular term (high-spin, A, or low-spin, A).
The numerical results shown in Table 5 can be
rationalized by taking into account the electronic struc-
ture of the metal atom. The Cr atom in I has 15 valence
electrons (the agostic H atom is regarded as a dative
ligand), and in the high-spin (4A) configuration with
three unpaired electrons all nine metal valence orbitals
are either singly or doubly occupied. This electronic
saturation can be expected to give the system an
inherent stability analogous to that observed for an 18-
electron species.3 The high-spin species Iâ(4A) has the
lowest calculated free energy in the catalytic cycle and
is the resting state for the system. Conversion of I to
the high-spin metal-alkene species IV(4A) proceeds
with cleavage of an agostic Cr-H bond in a facile,
practically thermoneutral process. The subsequent propa-
gation step also proceeds on the high-spin surface; the
transition state (TS), [IVfVIγ]q(4A), has a significantly
lower energy than the analogous low-spin (2A) species.
In contrast, no TS for termination through â-hydrogen
transfer (BHT) could be located on the high-spin surface
starting from IV, and since coordination of the migrat-
Two catalyst systems derived from 7a (R ) Me) or 7f
t
(R ) Bu), which span the product distribution from
predominantly short oligomers to long-chain polyethyl-
ene, were selected for the computational investigations,
and the results have been compared to those obtained
with (Me2NC2H4C5H4)CrCl2, which has already been
shown to generate polyethylene.2 Although the active
species for these systems has not been isolated, we
assume that it is an alkylchromium cation generated
(22) Do¨hring, A.; J olly, P. W. Unpublished results.
(23) Thomas, B. J .; Noh, S. K.; Schulte, G. K.; Sendlinger, S. C.;
Theopold, K. H. J . Am. Chem. Soc. 1991, 113, 893.
(24) Rogers, J . S.; Bazan, G. C. Chem. Commun. 2000, 1209.
(25) Margl, P.; Deng, L. Q.; Ziegler, T. Organometallics 1999, 18,
5701.
(26) Musaev, D. G.; Morokuma, K. Top. Catal. 1999, 7, 107.
(27) Lohrenz, J . C. W.; Bu¨hl, M.; Weber, M.; Thiel, W. J . Organomet.
Chem. 1999, 529, 11.
(28) J ordan, R. F.; Dasher, W. E.; Echols, S. F. J . Am. Chem. Soc.
1986, 108, 1718.

2240 Organometallics, Vol. 20, No. 11, 2001
Do¨hring et al.
F igu r e 3. Preferred routes for the propagation and termination reactions of [(R2PC2H4C5H4)Cr-C3H6R′]+ with ethylene
from DFT calculations using R′ ) H. Iγ(4A) and VIγ(4A) differ by inversion at the metal center: a further insertion step
completes the propagation cycle. Spin inversion in Vâ(2A) to form V(4A) followed by elimination of the olefinic chain
completes the BHT-termination sequence.
ing H atom in the electronically saturated high-spin
state is energetically unfavorable, we suggest that
termination through BHT proceeds with spin-pairing to
generate a low-lying, empty d-orbital at the metal,
which is then available for hydrogen transfer, i.e., the
17-electron complex IVâ(2A) reacts further to give the
BHT product Vâ(2A). Alternatively, this empty d-orbital
can be generated by decoordination of the donor atom,
D. Cr-P bond dissociation in IV(4A) of 7a by a ∼180°
rotation around the Cp-C bond of the ethano-bridge
produces a 15-electron high-spin complex with a pro-
nounced Cr-H â-agostic interaction that is presumably
a starting point for â-hydrogen transfer to the ethylene.
However, the free energy of this metal(alkene) species
is 19.4 kcal/mol higher than that of IV(4A), which
indicates that complexes with a noncoordinated donor
do not take part in the BHT termination reaction.
The neutral catalyst precursors are found to have
three unpaired electrons (vide supra), in accord with the
observation that organometallic complexes of chromium-
(III) are usually 15-electron systems with a spin quartet
ground state,29 although in some cases it has been
possible to stabilize a 17-electron configuration.30,31 Our
calculations indicate that the high-spin state is pre-
ferred also for the active catalyst cation, Iâ(4A). For the
catalyst derived from 7a , the adiabatic 2Ar4A transition
energy in the resting state is more than 10 kcal/mol
higher than the free energy of insertion.32 This suggests
that the termination step in the catalytic cycle of 7a does
not involve an excitation of the resting state, Iâ(4A),
prior to coordination of the olefin but rather a double
spin-inversion on the reaction coordinate between re-
actants and products: one after ethylene coordination
and before â-hydrogen transfer, IV(4A)/IVâ(2A), and a
second immediately after â-hydrogen transfer, Vâ(2A)/
(29) Cacelli, I.; Keogh, D. W.; Poli, R.; Rizzo, A. J . Phys. Chem. A
1997, 101, 9801.
(30) Shen, J . K.; Freeman, J . W.; Hallinan, N. C.; Rheingold, A. L.;
Arif, A. M.; Ernst, R. D.; Basolo, F. Organometallics 1992, 11, 3215.
(31) Betz, P.; Do¨hring, A.; Emrich, R.; Goddard, R.; J olly, P. W.;
Kru¨ger, C.; Roma˜o, C. C.; Scho¨nfelder, K. U.; Tsay, Y. H. Polyhedron
1993, 12, 2651.
(32) The solution for Iâ(2A) is spin-contaminated ( S2 ) 1.75). Using
the correction scheme described in the Computational Details section,
∆H298 and ∆G298 were calculated to be 26.7 and 27.2 kcal/mol,
respectively.

Cyclopentadienylchromium(III) Complexes
Organometallics, Vol. 20, No. 11, 2001 2241
F igu r e 4. DFT-optimized transition states (TS) for (a) ethylene insertion, [IVfVIγ]q(4A) and (b) â-hydrogen transfer
t
(BHT) to ethylene, [IVâfVâ]q(2A) for the catalysts derived from 7a (R ) Me) and 7f (R ) Bu). The H and C atoms
involved in the four- and six-membered metallacycles are shown in red, Cr in dark blue, and P in orange.
V(4A). Spin inversion will of course only occur efficiently
if the two spin states have similar energies, which is
indeed seen to be the case in 7a for IV(4A) and IVâ(2A)
(cf. Table 5). Further work is in progress to identify the
minimum energy crossing points as well as to assess
their probability of undergoing spin-inversion. It has
already been suggested that the principle of two-state
reactivity discussed here could well be a “key feature
in organometallic chemistry”.33
BHT step although still significantly higher than that
of chain propagation.
As can be seen from Table 5, the activation free
energy (∆Gq298) of insertion, [IVfVIγ]q(4A), and termi-
nation through BHT, [IVâfVâ]q(2A), are calculated to
be almost identical ((1 kcal/mol) for the phosphino-
substituted system with R ) Me, whereas in the case
of R ) tBu insertion is favored over termination by more
than 10 kcal/mol for BHT and about 4 kcal/mol for BHE.
In other words, the rates of insertion and termination
are predicted to be of the same order for the catalyst
derived from 7a (R ) Me), and as a consequence the
reaction will be terminated after a few insertion steps
and the product will be predominantly short-chain
olefins. In contrast, in the case of the catalyst derived
An alternative termination process involving complete
transfer of the â-hydrogen atom to the metal (â-
hydrogen elimination, BHE, see Figure 3) to give a
Cr(olefin)H species has been considered but can be
neglected as a route to formation of the oligomers
obtained with small substituents, R. The rate-determin-
ing step in the BHE process is the subsequent elimina-
tion of the olefin, [IIfIII]q(4A), which is associated with
an entropic barrier. In the case of 7a even the separated
elimination products (hydride + olefin) have a higher
free energy than the transition states for ethylene
insertion or BHT. The entropic barrier to elimination
t
from 7f (R ) Bu) the rate of insertion will be several
orders of magnitude larger than the rate of termination
and multiple insertion can be expected before termina-
tion occurs and the product will be polymeric. Distinct
differences in barrier heights (∼9-11 kcal/mol) in favor
of insertion compared to BHT and BHE termination are
also seen for the dimethylamino-substituted system,
which has already been shown to produce mainly
polyethylene.2
t
of the olefin product (propene) in the Bu-substituted
system (7f) on the other hand is lower than that of the
Figure 4 shows a pictorial representation of the
transition states for ethylene insertion (Figure 4a) and
(33) Schro¨der, D.; Shaik, S.; Schwarz, H. Acc. Chem. Res. 2000, 33,
139.

2242 Organometallics, Vol. 20, No. 11, 2001
Do¨hring et al.
tion of elemental analyses and spectroscopic methods. The
chromium complexes are paramagnetic, and the structural
characterization is based largely on crystal structural analyses
of selected compounds.
chain termination through BHT (Figure 4b) for the
catalysts derived from 7a and 7f. As can be seen, the
six-membered metallacycle involved in the termination
sequence occupies more space than the four-membered
metallacycle formed during chain propagation. Both
metallacycles adopt a position more or less perpendicu-
lar to a plane described by the center of the Cp ring
and the Cr and P atoms, and whereas a P-bonded
methyl group has only a small steric influence, the
introduction of a tert-butyl group results in the effective
blocking of the axial positions above and below this
plane by methyl groups. The resulting destabilization
of the transition states is particularly marked in the
case of the six-membered metallacycle, and as a result
chain termination through BHT is suppressed.
A similar strategy has been discussed for the catalysts
derived from the (bisimine)Ni(II) compounds (21) de-
veloped by Brookhart et al.34,35 In our case, the distorted
tetrahedral configuration around the P atom will ensure
that the P-R bonds are directed out of the equatorial
Cp-Cr-P, plane causing the substituents to block the
axial positions and forcing the two olefin moieties closer
together to give a more compact TS.
The R2PC2H4C5H4Li (1)10 and R2PC2H4IndenylLi (2)37 de-
rivatives have been prepared by reacting the appropriate
lithium phosphide with either spiro[2.4]hepta-4,6-diene8 or
spiro[cyclopropane-1,1′-indene].9 R2PC3H6C5H4Li (3)10 and Cy2-
PC3H6IndenylLi (4) were prepared by reacting R2PC3H6Cl with
either NaCp/BuLi or IndenylLi, Ph2PC3H6C5Me4Li (5)11 by
reacting LiPPh2 with TosOC3H6C5Me4H, and Cy2AsC2H4C5H4-
Li (6) by reacting LiAsCy2 with spiro[2.4]hepta-4,6-diene in a
manner similar to that described earlier.12 The preparation
of representative examples that have not previously been
adequately described are reported below.
Me2P C2H4C5H5 (1a ). LiPMe2 was prepared by reacting
PhPMe2 (4.00 g, 29 mmol) with Li-sand (0.66 g, 94.25 mmol)
in THF (60 mL). The resulting brown solution was cooled to 0
°C and stirred for 12 h. The reaction mixture was filtered
t
through glass wool (to remove the unreacted lithium) and -
BuCl (1.59 g, 17.4 mmol) added to the red-brown solution to
destroy the PhLi generated. The reaction mixture was then
added to spiro[2.4]hepta-4,6-diene (1.60 g, 17.4 mmol) in THF
(50 mL) and refluxed for 2 h. The reaction mixture was
evaporated to dryness in an oil-pump vacuum, and the orange
residue washed several times with pentane. The product was
suspended in pentane (50 mL) and hydrolyzed with water (50
mL). The organic phase was washed (3 × 50 mL) and dried
with sodium sulfate, and the product isolated by distillation
(21-25 °C, 0.02 mbar) and shown by NMR to consist of a
mixture of two isomers. Yield: 1.47 g (33%). IR (KBr): ν 2953,
2922, 2893, 1430, 937, 897, 707. MS (EI): m/e 154 (M+), 139,
126, 111. 1H NMR (CDCl3): δ 6.46-6.39/6.26-6.23/6.18-6.17/
6.04-6.01 (:CH), 2.93/2.88 (CH), 2.50/1.60 (C2H4), 1.02 (Me).
13C NMR (CDCl3): δ 135.22/133.14/131.38/127.08/126.45 (C5H5),
43.32/41.37 (C5H5), 32.09/31.22/26.93/26.12 (C2H4), 13.88 (Me).
31P NMR (CDCl3): δ -50.11.
Et2P C2H4C5H4Li (1b). LiPEt2 (1.32 g, 13.75 mmol), pre-
pared by treating Et2PH with BuLi in pentane, was dissolved
in THF (50 mL) and treated with spiro[2.4]hepta-4,6-diene
(1.27 g, 13.75 mmol) and refluxed for 1 h. The resulting yellow-
green solution was evaporated to dryness and the residue
washed with pentane to give the compound as a colorless
powder having 74% (NMR) purity. Yield: 2.36 g (91%). MS
(EI, -10 °C): m/e 182 (M+ + H/-Li), 167, 154, 139, 125. 1H
NMR (THF-d8): δ 5.54 (C5H4), 2.59/1.60 (C2H4), 1.36/1.06 (Et).
13C NMR (THF-d8): δ 31.19/27.03 (C2H4), 19.42/9.91 (Et). 31P
NMR (THF-d8): δ -23.87.
Cy2P C2H4C5H4Li (1c) was prepared similarly. Yield: 91%.
IR (KBr): ν 2923, 2850, 1446. MS (EI): m/e 290 (M+ + H/-
Li), 208, 126. 1H NMR (THF-d8): δ 5.6 (C5H4), 2.65 (C2H4),
1.9-1.6/1.5-1.1 (Cy/C2H4). 13C NMR (THF-d8): δ 120.87/
102.80/102.49 (C5H4), 34.14/31.38/30.09/29.44/29.07/28.24/
27.44/25.76 (Cy/C2H4). 31P NMR (THF-d8): δ -7.99.
1-Cy2P C2H4In d en e (2c). Spiro[cyclopropane-1,1′-indene]
(3.55 g, 25 mmol) was added at room temperature to LiPCy2
(5.10 g, 25 mmol) in THF (100 mL) and refluxed for 1 h. The
reaction mixture was evaporated to dryness under oil-pump
vacuum and the resulting red oil treated with pentane (100
mL) and hydrolyzed with water (200 mL). The organic phase
was washed (3 × 50 mL), dried with sodium sulfate, and
distilled to give the compound in 85% (NMR) purity as an oil
(bp 192 °C, 0.02 mbar). Yield: 2.21 g (26%). IR (KBr): ν 2923,
2849, 1446, 769, 718. MS (EI, 75 °C): m/e 340 (M+), 258, 176.
1H NMR (CDCl3): δ 7.38/7.28/7.22/7.13/6.18 (indene), 3.26
(indenylH), 2.67-2.55/1.90-1.45/1.30-1.05 (Cy/C2H4). 13C NMR
(CDCl3): δ 145.32/145.07/144.39 (indene), 127.20/125.77/124.30/
123.51/118.61 (indene), 36.6/32.4/29.57/28.27/26.57/26.45/26.25/
25.69/18.88 (Cy/C2H4). 31P NMR (CDCl3): δ -1.81.
The N atom is smaller than the P atom, and hence
the Cr-D and D-R distances will be shorter for the
amino-substituted systems than for the phosphino-
substituted systems, while the associated Tolman cone
angle13 will be more acute in the former case. As a
result, the BHT transition state will be more compact
for the Me2N-substituted species than for the Me2P-
substituted species, the barrier to BHT will be much
higher than for insertion, and as a result multiple
insertion with polymer formation occurs.2 Conversely,
increasing the size of the donor atom by replacing
phosphorus by arsenic would be expected to lead to an
increase in oligomer formation, and this is indeed
observed for the system (Cy2AsC2H4C5H4)CrCl2-MAO.1
The results presented above indicate that both the
observed and calculated trends in catalytic activity have
a steric origin: bulky substituents destabilize the
structures IV-VI (and hence the TS of insertion) to a
greater extent than the monomer-free resting state
Iâ(4A), and hence the activity is expected to decrease
upon increasing the size of the substituents on the P
atom. Interestingly, this is in contrast to the trend
reported for the N-aryl-substituted (bisimine)Ni cata-
lysts, for which the metal-alkene complex is suggested
to constitute the resting state.14,34-36 The negative effect
of steric crowding upon the activity is also consistent
with the observation that the P-containing catalysts are
apparently more active than the related N-containing
systems: the calculated barrier to propagation for 7a
(∆Gq
) 16.5 kcal/mol) is found to be slightly lower
298
than that for the dimethylamino species (∆Gq298 ) 17.1
kcal/mol).
Exp er im en ta l Section
All experiments and manipulations were carried out under
argon. The compounds have been characterized by a combina-
(34) J ohnson, L. K.; Killian, C. M.; Brookhart, M. J . Am. Chem. Soc.
1995, 117, 6414.
(35) Deng, L. Q.; Woo, T. K.; Cavallo, L.; Margl, P. M.; Ziegler, T. J .
Am. Chem. Soc. 1997, 119, 6177.
(36) Froese, R. D. J .; Musaev, D. G.; Morokuma, K. J . Am. Chem.
Soc. 1998, 120, 1581.
(37) Kataoka, Y.; Saito, Y.; Shibahara, A.; Tani, K. Chem. Lett. 1997,
621.

Cyclopentadienylchromium(III) Complexes
Organometallics, Vol. 20, No. 11, 2001 2243
Cy2P C3H6C5H4Li (3a ). 3-Chlor-1-(dicyclohexylphosphano)-
propane (11.6 g, 42.3 mmol) and NaCp (14.9 g, 126.9 mmol,
75% pure) were dissolved in THF (200 mL) and heated under
reflux for 14 h. The reaction mixture was evaporated to
dryness under oil-pump vacuum and the residue suspended
in diethyl ether (200 mL) and hydrolyzed with water. The
organic phase was washed with water (3 × 200 mL), dried with
sodium sulfate, and evaporated to dryness. The residue was
taken up in pentane (100 mL) and treated with excess BuLi
(42.3 mmol from a 1.653 M solution in hexane) at 0 °C. The
compound was deposited as a white precipitate, which was
isolated and washed with a little pentane. Yield: 6.72 g having
85% (NMR) purity (51%). IR (KBr): ν 2923, 2850, 1447, 754.
(η1:η5-tBu 2P C2H4C5H4)Cr Cl2 (7f): blue needles; IR (KBr)
ν 3000, 2986, 2961, 2868, 1473, 1371, 1361, 1174, 1022, 823;
MS (EI, 155 °C) m/e 359 (M+ - H), 324, 267.
(η1:η5-Neop en tyl2P C2H4C5H4)Cr Cl2 (7g): blue powder; IR
(KBr) ν 3094, 2947, 2904, 2864, 1475, 1387, 1234,1031, 818;
MS (EI, 145 °C) m/e 387 (M+).
(η1:η5-Hexyl2P C2H4C5H4)Cr Cl2 (7h ): dark blue; IR (KBr)
ν 3067, 2955, 2858, 1451, 811; MS (EI, 125 °C) m/e 415 (M+).
(η1:η5-Cy2P C2H4C5H4)Cr Cl2 (7i): IR (KBr) ν 2927, 2856,
1444, 811; MS (EI) m/e 411 (M+ - H), 376, 339; magn. suscept.
(SQUID) µ eff/µB 3.5 B. Crystal structure determination: see
Figure 1 and Table 3.
(η1:η5-P h 2P C2H4C5H4)Cr Cl2‚tolu en e (7j′): IR (KBr) ν
1433, 1384, 828, 738, 693; MS (EI, 100 °C) m/e 399 (M+ - C7H8/
H), 364, 327. Crystal structure determination: see Figure 1
and Table 3.
1
MS (EI, 210 °C): m/e 310 (M+), 303, 227, 204, 130. H NMR
(THF-d8): δ 5.57-5.53(C5H4), 2.56 (CH2), 1.9-1.1 (Cy/CH2).
13C NMR (THF-d8): δ 119.40/102.33/1.1.61 (C5H4), 34.04/32.86/
32.24/30.82/29.46/27.80/27.68/26.99/22.0 (C3H6/Cy). 31P NMR
(THF-d8): δ -4.63.
The toluene molecule is eliminated when the compound is
heated under high vacuum to 100 °C for 6 h to give (η1:η5-
P h 2P C2H4C5H4)Cr Cl2 (7j).
1-Cy2P C3H6In d en e (4). A solution of indenyl-Li (6 g, 49.2
mmol) in THF (200 mL) was added at 0 °C to 3-chloropropyl-
dicyclohexylphosphane (4.50 g, 16.4 mmol) dissolved in THF
(50 mL). The reaction mixture was then hydrolyzed with water
(300 mL), and the organic phase was separated and washed
with water (3 × 50 mL) and dried over sodium sulfate. The
excess indene was distilled off under oil-pump vacuum. The
brown residue was dissolved in pentane (100 mL) and treated
with BuLi (16.4 mmol in hexane). A red oil was formed, which
was isolated by decantation. Yield: 0.56 g (10%). 1H NMR
(CDCl3): δ 7.5-7.16.2 (indene), 3.2, 2.6, 2.0-1.0 (C2H4/Cy).
13C NMR (CDCl3): δ 145.11/144.10/143.85 (indene), 127.51/
125.69/124.11/123.33/118.65 (indene), 37.36 (indene), 33.06/
(η1:η5-o-Tolyl2P C2H4C5H4)Cr Cl2 (7k ): IR (KBr) ν 1476,
1449, 1436, 1412, 827, 754; MS (EI, 205 °C) m/e 427 (M+
H), 392, 355.
-
(η1: η5-1-Na p h th yl2P C2H4C5H4)Cr Cl2‚Me2CO (7l′). In
contrast to the other examples, this compound was extracted
with acetone. IR (KBr): ν 1716, 1636, 1506, 1413, 1359, 1220,
797, 773. MS (EI, 195 °C): m/e 499 (M+ - H), 464, 428.
Thermolysis at 180 °C under high vacuum for 72 h leads to
the formation of the solvent-free compound (η1:η5-1-Na p h -
th yl2P C2H4C5H4)Cr Cl2 (7l): IR (KBr) ν 3110, 1506, 1414,
1359, 1213, 1091, 843, 827, 800, 773; MS (EI) m/e 499 (M+
H), 464, 428.
-
30.99/29.13/28.75/27.15/26.99/26.94/21.10/20.78 (C2H4/Cy). 31
P
(η1:η5-Et2P C2H4In d en yl)Cr Cl2 (8a ) was prepared by add-
ing 1-indenylC2H4PEt2Li (27 mL of a 0.112 mmol/mL solution
in THF, 3.02 mmol) to a solution of Cr(THF)3Cl3 (1.25 g, 3.32
mmol) in THF (50 mL) at -78 °C. The resulting green reaction
mixture was allowed to warm to room temperature over 16 h
and then evaporated to dryness to give a green oil, which was
extracted with toluene/CH2Cl2. The extract was filtered and
evaporated to give the compound as a green solid. Yield: 0.65
g (61%). Anal.: see Table 1. IR (KBr): ν 3065, 2964, 2935,
1609, 1526, 1455, 1412, 1031, 751. MS: dec.
NMR (CDCl3): δ -4.37.
Cy2AsC2H4C5H4Li (6). A solution of spiro[2.4]hepta-4,6-
diene (6.12 g, 66.5 mmol) and LiAsCy2 (13.57 g, 66.5 mmol),
prepared by reacting Cy2AsCl with LiAlH4 in diethyl ether,
was refluxed in THF (250 mL) for 5 h. The resulting brown
suspension was evaporated to dryness in an oil-pump vacuum
and the residue washed with pentane to give the compound
as a white powder. Yield: 16.61 g (73%). Anal. Calcd for C19H30
-
AsLi: C, 67.1; H, 8,9; As, 22.0; Li, 2.0. Found: C, 66.9; H, 8.8;
As, 22.2; Li, 2.1. IR (KBr): ν 2962, 2921, 2849, 1446. MS (EI,
The following compounds were prepared similarly to that
described above by reacting Cr(THF)3Cl3 with the Li-salt of
the appropriate 1-indenyl derivative in THF and extracted
with toluene.
(η1:η5-iBu 2P C2H4In d en yl)Cr Cl2 (8b): green. IR (KBr) ν
2957, 2869, 1464, 1402, 1366, 1070, 806, 752; MS (EI; 145 °C)
409 (M+).
(η1:η5-Cy2P C2H4In d en yl)Cr Cl2 (8c): green needles; IR
(KBr) ν 3080, 2926, 2850, 1446, 754, 742; MS (EI, 185 °C) m/e
461 (M+ - H), 425, 389.
1
50 °C): m/e 334 (M+ + H/-Li), 252, 169. H NMR (THF-d8):
δ 5.42 (C5H4), 2.58-2.52 (C2H4), 1.63-1.48/1.25-1.15 (Cy). 13
C
NMR (THF-d8): δ 124.87/105.56/105.42 (C5H4), 37.56/35.40/
34.30/32.93/31.85/30.71 (Cy).
(η1: η5-Et2P C2H4C5H4)Cr Cl2 (7b) was prepared by adding
a solution of C5H4C2H4PEt2Li (2.35 g, 12.5 mmol) in THF (40
mL) at -78 °C to a solution of Cr(THF)3Cl3 (4.68 g, 12.5 mmol)
in THF (50 mL). The resulting blue solution was allowed to
reach room temperature overnight and then evaporated to
dryness. The residue was washed with pentane and extracted
with boiling toluene. Cooling the extract gave the compound
as blue needles. Yield: 1.54 g (40%). Anal.: see Table 1. IR
(KBr): ν 3076, 2883, 1382, 1048, 810, 765. MS (EI, 135 °C):
m/e 303 (M+ - H), 268, 231, 203.
(η1:η5-Cy2P C3H6C5H4)Cr Cl2 (9a ) was prepared as a dark
blue solid by adding a solution of LiCy2PC3H6C5H4 (6.67 g, 22
mmol) in THF (50 mL) to Cr(THF)3Cl3 (8.24 g, 22 mmol)
dissolved in THF (50 mL) at room temperature. The reaction
mixture was evaporated to dryness and the residue washed
with pentane and extracted with toluene. The compound was
precipitated at -30 °C by adding pentane to the extract.
Yield: 2.87 g. (31%). Anal.: see Table 1. IR (KBr): ν 2928,
The following compounds were prepared similarly to that
described above by reacting Cr(THF)3Cl3 with the appropriate
Li-salt, C5H4C2H4PR2Li, in THF. The elemental analyses are
listed in Table 1.
(η1:η5-Me2P C2H4C5H4)Cr Cl2 (7a ): blue needles; IR (KBr)
ν 3082, 1479, 1417, 962, 914, 818; MS (EI, 140 °C) m/e 275
(M+ - H), 260, 240, 203, 178.
2852, 1445, 847, 814, 785. MS (EI, 175 °C): m/e 425 (M+
-
H), 390, 353. Crystal structure determination: see Figure 2
and Table 3.
(η1:η5-P h 2P C3H6C5H4)Cr Cl2 (9b) was prepared similarly
as blue needles. Anal.: see Table 1. IR (KBr): ν 2918, 2849,
(η1:η5-P r 2P C2H4C5H4)Cr Cl2 (7c): blue; IR (KBr) ν 2959,
2931, 1453, 1080, 815; MS (EI, 120 °C) m/e 331 (M+), 209.
(η1:η5-iP r 2P C2H4C5H4)Cr Cl2 (7d ): blue needles; IR (KBr)
ν 2977, 2946, 2917, 2871, 1454, 1382, 1365, 1248, 1035, 819;
MS (EI, 125 °C) m/e 331 (M+ - H), 296, 259, 217.
(η1:η5-iBu 2P C2H4C5H4)Cr Cl2 (7e): blue IR (KBr) ν 3077,
2927, 1405, 1383, 1258, 1162, 1066, 829; MS (EI, 105 °C) m/e
359 (M+), 237.
1481, 1435, 1404, 741, 698. MS (EI, 170 °C): m/e 413 (M+
H), 378, 342.
-
(η1:η5-Cy2P C3H6In d en yl)Cr Cl2 (10) was prepared by add-
ing 1-indenylC3H6PCy2Li (1.6 mmol) in THF (30 mL) to a
solution of Cr(THF)3Cl3 (0.82 g, 2.2 mmol) in THF (50 mL) at
room temperature. The dark green reaction mixture was
evaporated to dryness and the residue washed with pentane

2244 Organometallics, Vol. 20, No. 11, 2001
Do¨hring et al.
(3 × 30 mL) and then extracted with toluene. The compound
was precipitated as green needles by adding pentane. Yield:
0.11 g (9%). Anal.: see Table 1. IR (KBr): ν 2924, 2849, 1448,
812, 805, 758. MS (EI, 160 °C): m/e 475 (M+ - H), 440, 403.
(η1:η5-P h 2P C2H4C5H4)Cr tBu 2 (16b): green, decomposes at
room temperature; IR (KBr) ν 2937, 2852, 2824, 1482, 1367,
1351, 1184, 1098, 1027, 795, 736, 691; MS (EI, 80 °C) dec.
(η1:η5-P h 2P C2H4C5H4)Cr Cy2 (16c): green, decomposes at
room temperature; IR (KBr) ν 2901, 2825, 2769, 1481, 1433,
795, 750, 693; MS (EI, 100 °C) dec.
(η1:η5-Cy2P C3H6C5H4)Cr Me2 (17) was prepared as blue-
violet needles by adding 2 equiv of MeMgCl (2.73 M solution
in THF) to a solution of (Cy2PC3H6C5H4)CrCl2 (9a ) (0.29 g, 0.7
mmol) in THF (20 mL) at room temperature. The reaction
mixture was evaporated to dryness and the compound ex-
tracted with pentane and precipitated by cooling to -30 °C.
Yield: 0.11 g (45%). Anal.: see Table 2. IR (KBr): ν 2921, 2853,
2779, 1442, 792, 781. MS (EI, 120 °C): m/e 385 (M+), 370, 352,
270.
(η1:η5-P h 2P C3H6C5Me4)Cr Me2 (18) was prepared by react-
ing the compound described above (0.94 g, 2 mmol) with MeLi
(4.2 mmol of a 1.6 M solution in THF) at -70 °C. The reaction
mixture was warmed to room temperature and at -30 °C
changed color from blue to violet. The mixture was evaporated
to dryness and the residue extracted with pentane. Cooling
the pentane solution to -30 °C gave the compound as small
black needles. Yield: 0.02 g (2%). Anal: see Table 2. IR
(KBr): ν 2901, 2853, 1481, 1378, 739, 694. MS (EI, 110 °C):
m/e 429 (M+), 414, 398.
(η1:η5-Cy2AsC2H4C5H4)Cr Cl2 (19) was prepared by adding
LiC5H4C2H4AsCy2 (6.61 g, 48.8 mmol) dissolved in THF (200
mL) to a solution of Cr(THF)3Cl3 (18.28 g, 48.8 mmol) in THF
(200 mL) at room temperature. The resulting dark blue
solution was evaporated to dryness under high vacuum and
the residue extracted with toluene. The compound was recrys-
tallized from boiling toluene as blue platelets. Yield: 15.9 g
(72%). Anal. Calcd for C19H30AsCl2Cr: C, 50.0; H, 6.6; As, 16.4;
Cl, 15.5; Cr, 11.4. Found: C, 50.1; H, 6.6; As, 16.4; Cl, 15.5;
Cr, 11.5. IR (KBr): ν 3090, 2926, 2854, 1443, 813. MS (EI,
145 °C): m/e 455 (M+ - H), 420, 372, 337. Crystal structure
determination: see Figure 1 and Table 3.
(η1:η5-Cy2AsC2H4C5H4)Cr Me2 (20) was prepared as small
green-black needles by reacting 19 (2.59 g, 5.7 mmol) in THF
(40 mL) with 2 equiv of MeMgCl (2.73 M solution in THF) at
-30 °C. The resulting green solution was allowed to warm to
room temperature and evaporated to dryness under high
vacuum. The compound was obtained by cooling a pentane
extract of the residue to -30 °C. Yield: 0.92 g (39%). Anal.
Calcd for C21H36AsCr: C, 60.7; H, 8.7; As, 18.0; Cr, 12.5.
Found: C, 60.6; H, 8.7; As, 18.1; Cr, 12.6. IR (KBr): ν 2923,
2885, 2780, 1446, 1339, 1264, 1179, 994, 785. MS (EI, 100
°C): m/e 415 (M+), 400, 382.
Ca ta lytic Rea ction s. The oligomerization reactions were
carried out in a thermostated glass autoclave (Bu¨chi, BEP
280), and the procedure was similar to that described earlier.2
The reaction was terminated by simultaneously closing the
ethylene valve and injecting propanol (5 mL) into the reactor.
Cr ysta l Str u ctu r e Deter m in a tion s. The crystal structure
analyses of compounds 7i, 7j′, 15a , 19, 9a , and 11 were carried
out using a CAD-4 single-crystal diffractometer (Enraf-Non-
ius). Crystallographic data and details of the refinement are
listed in Table 6. Final coordinates and equivalent isotropic
thermal parameters are included in the Supporting Informa-
tion.
(η1:η5-P h 2P C3H6C5Me4)Cr Cl2 (11). A solution of LiPh2-
PC3H6C5Me4 (prepared from Ph2PC3H6C5Me4H (23.25 g, 66.8
mmol) and tBuLi (66.8 mmol) in THF/hexane at 0 °C) was
added to Cr(THF)3Cl3 (21.81 g, 66.8 mmol) in THF (100 mL)
at room temperature. The green reaction mixture was evapo-
rated to dryness under oil-pump vacuum and the residue
dissolved in toluene. The toluene solution was filtered through
Celite (to remove a green impurity) and the resulting blue
solution evaporated to dryness. The residue was washed with
pentane and recrystallized from boiling toluene. Yield: 8.5 g
(27%). Anal.: see Table 1. IR (KBr): ν 2954, 2919, 2866, 1484,
1435, 1378, 1096, 741, 695, 518. MS (EI, 140 °C): m/e 469 (M+
- H), 434, 398. Crystal structure determination: see Figure
2 and Table 3.
(η1:η5-Cy2P C2H4C5H4)Cr (Et)Br (12) was prepared by re-
acting a solution of (Cy2PC2H4C5H4)CrCl2 (7i) (0.82 g, 2 mmol)
in THF (20 mL) with 2 equiv of EtMgBr (1.46 M solution in
diethyl ether) at -78 °C. The reaction mixture was allowed to
reach room temperature overnight and evaporated to dryness.
The residue was washed with pentane and extracted with
toluene. Filtration and cooling the extract to -78 °C gave the
compound as a brown powder. Yield: 0.22 g (24%). Anal.: see
Table 2. IR (KBr): ν 2925, 2851, 1442, 804. MS (EI, 120 °C):
m/e 422 (M+ + H/-Et), 341, 257, 177.
(η1:η5-Cy2P C2H4In d en yl)Cr (Me)Cl (13) was prepared as
a violet powder by adding 2 equiv of MeMgCl (2.73 M in THF)
to (Cy2PC2H4Indenyl)CrCl2 (8c) (0.26 g, 0.6 mmol) in THF (10
mL) at -78 °C. The resulting violet solution was warmed to
room temperature and evaporated to dryness, and the residue
was washed with pentane and taken up in toluene. This
procedure was repeated twice to remove traces of unreacted
MeMgCl and the compound precipitated by adding pentane
to a toluene solution. Yield: 0.06 g (17%). Anal.: see Table 2.
IR (KBr): ν 2924, 2849, 1446, 747. MS (EI, 185 °C): m/e 441
(M+), 426.
(η1:η5-Et2P C2H4C5H4)Cr Me2 (14) was prepared by adding
a solution of MeMgCl (10 equiv of a 2.73 M solution in THF)
to (Et2PC2H4C5H4)CrCl2 (7b) (0.59 g, 1.9 mmol) in THF (20
mL) at -30 °C. Warming the reaction mixture to room
temperature was accompanied by a color change from blue, to
violet, to blue-green. The reaction mixture was evaporated to
dryness and the residue extracted with pentane. This proce-
dure was repeated several times until the extract was homo-
geneous. The compound was isolated as blue-violet needles by
cooling the final pentane extract to -80 °C. Yield: 0.11 g (22%).
Anal.: see Table 2. IR (KBr): ν 2935, 2780, 1456, 1418, 1379,
1029, 804. MS (EI, 75 °C): m/e 264 (M+ + H), 263, 248, 233,
219, 205, 191.
The following compounds were prepared similarly to that
described above by reacting the appropriate (R2PC2H4C5H4)-
CrCl2 compound with a Grignard reagent or MeLi (15a ) in
THF/diethyl ether. The analytical data are listed in Table 2.
In addition, (η1:η5-Cy2P C2H4C5H4)Cr P r 2 was isolated as a
green solid at -30 °C (yield: 48.3%) but proved too unstable
to analyze.
(η1:η5-Cy2P C2H4C5H4)Cr Me2 (15a ): green-black needles;
IR (KBr) ν 2924,2852, 2780, 1448, 784; MS (EI, 95 °C) m/e
371 (M+), 356, 338, 256, 177; magn. suscept. (SQUID) µexp/µB
3.5 B. Crystal structure determination: see Figure 1 and Table
3.
Com p u ta tion a l Deta ils. The study used gradient-cor-
rected density functional theory (DFT) with the gradient
corrections included self-consistently during both geometry
optimization and energy evaluation. We have employed the
local exchange-correlation potential developed by Vosko et
al.38 augmented with Becke’s39 nonlocal exchange corrections
and Perdew and Wang’s40 nonlocal correlation corrections. The
(η1:η5-Cy2P C2H4C5H4)Cr tBu 2 (15b): dark green needles;
IR (KBr) ν 2924, 2850, 2795, 2735, 1449, 1411, 1368, 1349,
793; MS (EI, 100 °C) m/e 455 (M+), 398, 341, 338, 258.
(η1:η5-P h 2P C2H4C5H4)Cr P r 2 (16a ): dark green, decom-
poses at room temperature; IR (KBr) ν 2940, 2854, 1435, 794,
740, 694; MS (EI, 95 °C) m/e 415 (M+), 372, 329.
(38) Vosko, S. H.; Wilk, L.; Nusair, M. Can. J . Phys. 1980, 58, 1200.
(39) Becke, A. D. Phys. Rev. A 1988, 38, 3098.
(40) Perdew, J . P.; Wang, Y. Phys. Rev. B 1992, 45, 13244.

Cyclopentadienylchromium(III) Complexes
Organometallics, Vol. 20, No. 11, 2001 2245
Ta ble 6. Cr ysta llogr a p h ic Da ta
7i
7j′
15a
19
9a
11
formula
mol wt
C
19H30Cl2CrP
C26H26Cl2CrP
492.34
C21H36CrP
371.47
C19H30Cl2CrAs
456.25
C20H32Cl2CrP
426.33
C24H28Cl2CrP
470.33
412.30
cryst size, mm
0.11 × 0.53 × 0.60 0.14 × 0.32 × 0.63 0.11 × 0.18 × 0.35 0.07 × 0.19 × 0.34 0.46 × 0.32 × 0.18 1.16 × 0.60 × 0.77
V (Å3)
2013.0(7)
1.360
20
1195.8(3)
1.367
20
2074.0(4)
1.190
20
2010.0(3)
1.508
20
2073.7(5)
1.366
20
9251.6(13)
1.351
20
Fcalcd (g/cm3)
Tmeas (°C)
λ(Mo KR) (Å)
Z
0.71069
4
0.71069
2
0.71069
4
0.71069
4
0.71069
4
0.71069
16
µabs (mm-1
)
0.911
4591
3626
0.780
4854
3209
375
0.628
4211
2649
2.466
7635
6358
0.887
3627
2228
0.802
9379
5206
no. rflns msd
no. rflns obsd
no. variables
space group
(No.)
328
208
328
217
505
P21/n (14)
P1 (2)
P21/n (14)
P21/n (14)
P21/n (14)
Pbca (61)
a (Å)
b (Å)
c (Å)
8.396(2)
20.064(3)
12.398(3)
90
105.44(2)
90
0.0434
0.1197
0.556
9.2684(10)
9.7942(11)
14.477(3)
98.722(11)
96.066(11)
110.833(8)
0.0361
8.5482(9)
19.671(3)
12.7262(11)
90
104.263(8)
90
0.0466
0.1277
0.457
8.4350(10)
20.1530(10)
12.3500(3)
90
106.780(10)
90
0.0624
0.1681
1.869
13.693(2)
7.5311(9)
20.151(3)
90
93.662(12)
90
0.0464
0.1249
0.775
16.6206(11)
29.5156(15)
18.859(2)
90
90
90
0.0469
0.1155
0.377
R (deg)
â (deg)
γ (deg)
R
Rw
0.1054
0.319
rsd electron
density (e Å-3
)
resulting BPW91 functional was used in the spin-unrestricted
formulation implemented in the Gaussian 98 set of programs,41
and stability tests of the resulting solutions were performed.
Extensive studies42,43 show that the BPW91 functional is
capable of providing accurate energy profiles for the monomer
insertion step during metal-catalyzed olefin polymerization.
During the geometry optimizations, a contracted [10s,8p,-
3d] basis was applied for Cr.42 P, N, C, and H were described
by standard Dunning-Hay44 valence double-ú basis sets, with
a scale factor of 1.2 (1.15) applied for the inner (outer)
exponents of H (exception: tBu-methyl groups represented by
STO-3G sets45). Polarization functions were added to C atoms
(Rd ) 0.75) being part of the ethylene or the polymer chain as
well as to P and N (Rd ) 0.60 and 0.80, respectively). The
Gaussian 9841 defaults were applied for integration grid and
convergence criteria. Each stationary point was characterized
through analytical calculation of the second derivative matrix.
Zero-point and thermal corrections to the energies were
computed from the harmonic frequencies using standard
procedures. The barrier to elimination of the olefinic chain
from the chromium hydride, II(4A), was found to be entropic
in nature, and estimates thereof were obtained by stepwise
geometry optimization and vibrational analysis with con-
strained Cr-C(propene) distances to locate the maximum on
the free energy curve of propene decoordination.
All energies reported in the current work are based on
single-point energy calculations using basis sets that were
improved compared to those of the geometry optimizations:
C and H atoms forming part of the ethylene or the polymer
chain were described by augmented Dunning triple-ú sets
denoted TZD2P43 to account for known basis set sensitivities,43
the tBu-methyl groups were represented by the standard
double-ú basis,44 and polarization functions were included for
the C atoms of the Cp rings (Rd ) 0.75). The unrestricted
solutions for the quartet 15-electron or doublet 17-electron Cr
compounds (agostic H atoms counted as dative ligands) display
negligible spin-contamination. In contrast, the solution for a
15-electron doublet (Iâ(2A)) was significantly contaminated
( Sˆ2 ) 1.75), and therefore the energy was corrected according
to a scheme taking into account the contribution from the S+1
state.46
Ack n ow led gm en t. We thank Borealis Polymers Oy
(Dr. O. Andell) for financial support and the Gesellschaft
fu¨r wissenschaftliche Datenverarbeitung in Go¨ttingen
and the Max-Planck-Institute for Biological Cybernetics
in Tu¨bingen for computer facilities.
(41) Frisch, M. J .; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J . R.; Zakrzewski, V. G.; Montgomery, J . A.,
J r.; Stratmann, R. E.; Burant, J . C.; Dapprich, S.; Millam, J . M.;
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of data collection parameters, final atomic positional and
thermal parameters, and interatomic distances and angles as
well as ORTEP diagrams. This material is available free of
charge via the Internet at http://pubs.acs.org.
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