New O- and N-bonded zirconocene complexes and their catalytic properties in ethylene polymerization. X-ray crystal structure of (C5H5)2Zr{2,6-OC6H 3(CH3)2}2, (C5H5)2Zr{2,4,6-OC6H 2(CH3)3}2

Article abstract of DOI:10.1016/S0022-328X(97)00775-4

A series of zirconocene complexes of formula Cp₂ZrMe_2-nL_n where Cp = C₅H^-₅, Me = methyl, L = pyrazolyl, bis(N,N′-phenylformamidinato), or substituted aryloxide and n = 1,2, were synthesized by reaction of Cp₂ZrCl₂ and Cp₂ZrMe₂ with LiL or HL, respectively. The structures of Cp₂Zr(2,6-OC₆H₃Me₂)₂, Cp₂Zr(2,4,6-OC₆H₂Me₃)₂ and Cp₂ZrMe{CH(NC₆H₅)₂} were determined by single crystal X-ray diffraction. The complexes demonstrate appreciable activity for ethylene polymerization when used as cocatalysts with methylaluminoxane and dimethylanilinium tetrafluorophenylborate.

Full text of DOI:10.1016/S0022-328X(97)00775-4

Journal of Organometallic Chemistry 555 (1998) 177–185
New O- and N-bonded zirconocene complexes and their catalytic
properties in ethylene polymerization. X-ray crystal structure of
(C5H5)2Zr{2,6-OC6H3(CH3)2}2, (C5H5)2Zr{2,4,6-OC6H2(CH3)3}2 and
(C5H5)2Zr(CH3){CH(NC6H5)2}
F. Benetollo a,*, G. Cavinato b, L. Crosara b, F. Milani c, G. Rossetto a, C. Scelza a,
P. Zanella a
a ICTIMA–MITER, CNR, Corso Stati Uniti 4, 35127, Pado6a, Italy
b Dipartimento di Chimica Inorganica Metallorganica ed Analitica, Uni6ersita` di Pado6a, Via Loredan 4, 35100, Pado6a, Italy
c Polimeri Europa, P. le Donegani 12, 44100, Ferrara, Italy
Received 2 August 1997
Abstract
A series of zirconocene complexes of formula Cp2ZrMe2−nLn where Cp=C5H5−, Me=methyl, L=pyrazolyl, bis(N,N%-
phenylformamidinato), or substituted aryloxide and n=1,2, were synthesized by reaction of Cp2ZrCl2 and Cp2ZrMe2 with LiL
or HL, respectively. The structures of Cp2Zr(2,6-OC6H3Me2)2, Cp2Zr(2,4,6-OC6H2Me3)2 and Cp2ZrMe{CH(NC6H5)2} were
determined by single crystal X-ray diffraction. The complexes demonstrate appreciable activity for ethylene polymerization when
used as cocatalysts with methylaluminoxane and dimethylanilinium tetrafluorophenylborate. © 1998 Elsevier Science S.A. All
rights reserved.
Keywords: Zirconocene compounds; Synthesis; Ethylene polimerization; Crystal structure
1. Introduction
initiates the polymerization by coordination of the
olefin double bond to zirconium, and propagates it by
insertion of the coordinated olefin into the Zr–Me
The catalytic activity of zirconocene complexes of the
type Y2ZrL2 (Y=cyclopentadienyl, indenyl, fluorenyl;
L=halide, alkyl etc.) in the polymerization of h-olefins
has been the object of both fundamental and applied
studies, especially after it was reported that the presence
of partially hydrolyzed trimethylaluminum (MAO=
methylalumoxane) has a favourable effect on the pro-
cess [1]. For the prototype catalyst Cp2ZrMe2, where
Cp=C5H5− and Me=CH3, the fundamental step of
the reaction is the interaction of Cp2ZrMe2 with MAO,
or with other acidic agents such as R3NHA or BR3
(R=tetrapentafluorophenylborate) to yield a coordina-
tively unsaturated cationic species [2–6]. The latter
bond.
The
resulting
polymeric
chain,
Zr-
(CH2CH2)nMe, eventually undergoes Zr-(polymer) scis-
sion. Thus the overall polymerization process may be
schematically represented as follows:
Cp2ZrMe2+MAO“Cp2ZrMe+ +[Me(MAO)]− (1)
Cp2ZrMe+ +olefin“Cp2Zr+ (olefin) Me
(2)
Cp2Zr+(olefin)Me+n−1 olefin“Cp2Zr(polymer)+
(3)
The activity of the catalyst, as well as several impor-
tant properties of the polymer such as molecular weight
and molecular weight distribution, are strongly depen-
dent on the electronic and steric features of the ligands
bound to the Zr center in the active cationic species.
* Corresponding author. Tel.: +39 49 8295611; fax: +39 49
8702911.
0022-328X/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved.
PII S0022-328X(97)00775-4

178
F. Benetollo et al. / Journal of Organometallic Chemistry 555 (1998) 177–185
Numerous publications and patents have focused on
the effects of the y-bonded, cyclopentadienyl, indenyl
and fluorenyl ligands, both as such and in variously
substituted (eventually bridged) forms; information on
the effects of |-bonded ligands other than CH3 or Cl
are far more limited. It was of interest, therefore, to
investigate the catalytic activity of zirconocene com-
plexes of the type Cp2ZrMe2−nLn (L=substituted ary-
loxide,
pyrazolyl,
N,N%-diphenylformamidinato;
n=1,2), which offer a variety of steric, electronic and
bonding features. Mixed ligands and amidinato Zr sys-
tems have been recently described by Green and co-
workers [7].
Fig. 1. Molecular structure and atom numbering scheme of
Cp2Zr(2,6-OC6H3Me2)2.
2. Results and discussion
previously reported [9,8] while this work was in pro-
gress. Four complexes, three of the aryloxide series and
one containing the formamidinato ligand, gave well-
formed crystals and the structures of 3, 5, 6 and 11 were
determined by X-ray crystallography and are discussed
Two series of zirconium-biscyclopentadienyl com-
plexes, of general formula Cp2ZrMeL (L=2,6-
OC6H3Me2 4, C3H3N2 8 [7,8], CH(NC6H5)2 10) and
Cp2ZrL2 (L=OC6H5 3 [7,9], 2,6-OC6H3Me2 5, 2,4,6-
t
1
OC6H2Me3 6, 4-OC6H4 Bu 7, C3H3N2 9, CH(NC6H5)2
in a following section. On the basis of the H NMR
11) were synthesized by reaction of Cp2ZrCl2 (1) and
Cp2ZrMe2 (2) with the appropriate HL ligand or its
lithium salt:
evidence, it can be concluded that in solution these
complexes retain similar structures, with the central
zirconium ion surrounded by two cyclopentadienyls
and two other ligands in a pseudotetrahedral geometry.
In all complexes the Cp and OAr ligands (Ar=phenyl
or substituted phenyl) are coordinated in their typical
p5 and p1 modes, respectively; the pyrazolyl and for-
mamidinato ligands, instead, may exist in a p2 X p1
equilibrium which accounts for the equivalence of the
corresponding protons (Scheme 1).
The mass spectra (MS), of 4 and 5 were consistent
with expectations. In 4, a weak parent peak was ob-
served at m/z 357 and an intense peak at 342
(Cp2ZrOC6H3Me2)+ resulted from the easy cleavage of
Me. Other fairly intense ions occurred at 276
(CpZrOC6H3MeCH2)+, 229 (Cp2Zr+) and 172
(CpZrO+). The MS spectrum of 5 showed a small
peaks at 463 (parent peak, M+) and 397 (M+-C5H6);
Cp2ZrMe2+nHL“Cp2ZrMe2−nLn+nCH4
Cp2ZrCl2+2LiL“Cp2ZrL2+2LiCl
(4)
(5)
All reactions were carried out using as solvents anhy-
drous toluene, benzene or diethylether. Complexes 3, 4
and 10 were prepared by route 4 at room temperature;
5, 6 and 7 were obtained by the same route in toluene
at reflux temperature; 9 and 11 were prepared by route
5. In each case yields were quantitative and the com-
plexes were easily isolated in pure form, as the by
products were either methane gas or solid LiCl, com-
pletely insoluble in the non-polar solvent medium. The
complexes were thermally stable but were sensitive to
normal atmospheric conditions, which prevented their
characterization by elemental analysis. The position
1
and intensity of the signals in the H NMR spectra,
however, provided unambiguous identification; the
spectra of compounds 3 and 8 matched closely those
Fig. 2. Molecular structure and atom numbering scheme of
Cp2Zr(2,4,6-OC6H2Me3)2 (only one of the two independent molecules
is shown).
Scheme 1. The pyrazolyl and formamidinato ligands existing in a
p2 X p1 equilibrium.

F. Benetollo et al. / Journal of Organometallic Chemistry 555 (1998) 177–185
179
for
Table 1
Table 2
˚
˚
Significant bond distances (A) and angles (°) for the 5 and 6 deriva-
Selected
bond
distances
(A)
and
angles
(°)
tives
Cp2ZrMe{CH(NC6H5)2}
Complexes
5
6
Molecule A
Molecule B
Zr–O(1)
Zr–O(2)
Zr–X(1)
Zr–X(2)
1.997(5)
1.996(5)
2.24(1)
2.23(1)
1.996(3) 1.997(4)
1.989(3) 1.997(4)
2.249(5) 2.249(8)
2.252(7) 2.246(6)
Zr(1)–N(1)
Zr(1)–N(2)
Zr(1)–C(14)
Zr(1)–X(1)
Zr(1)–X(2)
N(1)–C(1)
N(1)–C(8)
N(2)–C(1)
N(2)–C(2)
2.367(4) Zr(2)–N(1A)
2.324(4) Zr(2)–N(2A)
2.314(8) Zr(1)–C(14A)
2.238(8) Zr(2)–X(1A)
2.241(9) Zr(2)–X(2A)
1.320(8) N(1A)–C(1A)
1.400(7) N(1A)–C(8A)
1.309(6) N(2A)–C(1A)
1.418(7) N(2A)–C(2A)
2.356(4)
2.343(4)
2.341(5)
2.233(6)
2.239(9)
1.312(1)
1.411(4)
1.321(1)
1.415(5)
X(1)–Zr–X(2)
O(1)–Zr–O(2)
Zr–O(1)–C(1)
Zr–O(2)–C(9)
O(1)–Zr–O(2)–C(9)
O(2)–Zr–O(1)–C(1)
126.7(4)
98.6(2)
145.8(4)
146.2(5)
103.8(8)
112.5(9)
126.7(4) 126.6(2)
99.5(1) 98.5(1)
152.6(3) 144.7(3)
145.9(3) 146.9(3)
104.1(5) 103.2(5)
103.4(6) 102.7(6)
X(1)–Zr(1)–X(2) 129.1(3)
X(1A)–Zr(2)–X(2A) 128.8(3)
C(14A)–Zr(2)–X(1A) 99.5(3)
C(14A)–Zr(2)–X(2A) 109.9(3)
N(1A)–Zr(2)–X(1A) 98.0(2)
C(14)–Zr(1)–X(1)
C(14)–Zr(1)–X(2) 100.3(3)
N(1)–Zr(1)–X(1) 99.7(3)
98.8(4)
X=centre of the Cp rings.
N(1)–Zr(1)–X(2) 101.5(3)
N(1)–Zr(1)–C(14) 131.9(2)
N(1A)–Zr(2)–X(2A) 101.3(2)
N(1A)–Zr(2)–C(14A) 132.9(1)
additional higher intensity peaks identical to those
present in 4 probably originated from the species
Cp2ZrOC6H3Me2+.
N(1)–Zr(1)–N(2)
56.4(1)
N(1A)–Zr(2)–N(2A)
56.6(1)
N(2)–Zr(1)–X(1) 113.7(2)
N(2)–Zr(1)–X(2) 116.6(3)
N(2)–Zr(1)–C(14) 75.5(2)
N(2A)–Zr(2)–X(1A) 112.1(2)
N(2A)–Zr(2)–X(2A) 118.2(2)
N(2A)–Zr(2)–C(14A) 76.3(2)
C(1A)–N(1A)–C(8A) 120.0(4)
C(1A)–N(2A)–C(2A) 118.5(4)
N(1A)–C(1A)–N(2A) 115.6(4)
2.1. Crystal structures of the complexes
C(1)–N(1)–C(8)
C(1)–N(2)–C(2)
N(1)–C(1)–N(2)
122.3(5)
119.6(4)
114.9(5)
The molecular structure of Cp2Zr(2,6-OC6H3Me2)2
(5) is shown in Fig. 1. The ligands adopt a tetrahedral
coordination geometry around the Zr(IV) with the two
Cp ligands staggered and the two 2,6-dimethylpheno-
lates in different orientations, as shown by the different
values of the two torsion angles C(1)–O(1)–Zr–O(2)
(112.5(9)°) and C(9)–O(2)–Zr–O(1) (103.8(8)°). A
comparison with the Cp2Zr(OC6H5)2 analog [9] shows
that the presence of the two methyl groups in the
2,6-positions of the phenolate rings results in loss of the
crystallographic binary symmetry, whereas the bond
distances and angles of the Zr(IV) coordination sphere
retain comparable values. The same geometric parame-
ters were observed in a new form of the Cp2Zr(OC6H5)2
(3)1 obtained in this work as white prismatic crystals
X=centre of the Cp rings.
from the reaction mixture. This new form differs from
that previously reported [9] by having a O–Zr–O–C
torsion angle of 119.4(5)°, instead of 113(1)°.
The presence of an additional methyl group in the
Cp2Zr(2,4,6-OC6H2Me3)2 (6) complex (Fig. 2) does not
have a major effect on the overall molecular geometry,
which shows bond lengths and angles comparable to
those of the previously mentioned analogs (see Table 1)
The presence of two molecules in the asymmetric unit is
justified by the different values of the Zr–O–C angle
(152.6(3)° and 145.9(3)° in one molecule, 144.7(3),
146.9(3)° in the other) owing to the facile rotation of
the ligand about the O–C bonds. This easy conforma-
tional change also explains the existence of two distinct
crystal forms for Cp2Zr(OC6H5)2.
The molecular structure of Cp2ZrMe{CH(NC6H5)2}
(11) (Fig. 3) is characterized by the presence of two
molecular conformations in the unit cell, differing
chiefly in the mutual orientations of the phenyl rings,
which form a dihedral angle of 114° in molecule A and
of 92° in molecule B. Selected geometrical parameters
are listed in Table 2 and illustrate the other subtle
differences between the two molecules. In molecule B
the formamidinato ligand, which is coordinated to the
metal ion via the two nitrogen atoms, forms a rather
1 Crystal data −ZrC22H20O2, orthorhombic, Pbcn, a=17.761(3),
3
˚
˚
Fig. 3. Molecular structure and atom numbering scheme of
Cp2ZrMe{CH(NC6H5)2}(only one of the two independent molecules
is shown).
b=11.619(3), c=21.158(4) A; V=1908(1) A , Z=4, Dx=1.42 Mg
m−3, u=(MoKh)=0.71073 A, T=293 K, R=0.043 for 1846 ob-
˚
served reflections.

180
F. Benetollo et al. / Journal of Organometallic Chemistry 555 (1998) 177–185
Table 3
Polymerization results
Catalyst
Yielda
Mw
t (°C)
BPFb4
MAO
BPFb4
MAO
Cp2ZrCl2 (1)
50
90
1
36
11 300
58 000
68
20 000
38 500
Cp2ZrMe2 (2)
50
90
3
40
25 000
55 000
160
Cp2Zr(OAr)2 (3)
Cp2ZrMe(OAr) (4)
Cp2Zr(OAr)2 (5)
50
70
2
16
50
90
20
166 000
94 000
55
121
100
130
17 000
24 000
20 000
25000
50
70
90
32
40
52
63 000
Cp2Zr(OAr)2 (6)
Cp2Zr(OAr)2 (7)
50
70
90
46
90
70
132 000
63 000
50
70
90
2
31
Cp2ZrMe(pyr) (8)
Cp2Zr(pyr)2 (9)
Cp2Zr(dff)2 (11)
50
90
90
4
2
30 000
13 300
23
31
22 000
16 200
a Kg (PE)/10−3 mol Zr.
b [NHMe2(C6H5)][B(C6F5)4].
planar tetra-atomic ring with Zr, whereas in molecule A
significant deviations from planarity are observed. Fur-
thermore, the Me group deviates from the Zr–N–CH–
In both molecules A and B the two C–N bonds are
almost equal in length (N(1)–C(1) 1.320(8), N(2)–C(1)
1.309(6); (N(1A)–C(1A) 1.312(6), N(2A)–C(1A)
˚
˚
˚
N mean planes by 0.16(1) A in A, but only −0.02(1) A
in B. The Me–Zr is also shorter in A than in B, with
Zr–C(14) bond lengths equal to 2.314(8) and 2.341(6)
1.321(6) and their values (1.31, 1.32 A) correspond to a
bond order of 1.5 [11], suggesting extensive electron
delocalization within the tetra-atomic Zr–N–C–N ring
somewhat greater for B than for A, as in the former the
Zr–N–C–N ring is closer to planarity and two Zr–N
˚
A, respectively.
It is instructive to compare the structure of
Cp2Zr(2,6-OC6H3Me2)2, Cp2Zr(2,4,6-OC6H2Me3)2 and
Cp2ZrMe{CH(NC6H5)2} to those of other complexes of
similar type such as Cp2ZrMe2 and [Cp2ZrMe]2O [10].
In the formamidinato complex discussed here, the Zr–
˚
bond lengths (Zr(2)–N(1A) 2.356(4) A) and (Zr(2)–
˚
N(2A) 2.343(4) A) are closer to one another than those
˚
of A (Zr(1)–N(1) 2.367(4) A) and (Zr(1)–N(2) 2.324(4)
˚
A). It is worthwhile to notice that the molecular struc-
˚
Me distances (2.314(8) and 2.341(6) A) are comparable
ture of the analogous bis-cyclopentadienyl (cyclohexyl-
formamidine)-Zr-chloride derivative [12] shows similar
behaviour in the solid state including the presence of
two molecules in the asymmetric unit with differences
comparable to those of the present structures.
˚
to those of Cp2ZrMe2 (2.280(5) and 2.273(5) A) and of
˚
[Cp2ZrMe]2O (2.276(9) A)
Similarly, in the latter complexes the values of the
X(1)–Zr–X(2) angles where X indicate the centroids of
the Cp ligands, are 132.5 and 128.5° respectively; the
corresponding angles in molecule A and B of the for-
mamidinato complex have similar values 129.1(3) and
128.8(3)°.
3. Polymerization of ethylene
Also comparable are the Zr–X distances which are in
the range to 2.23 to 2.25 A in the complexes. This
values shows that the more crowed coordination sphere
of the formamidinato complex does not affect signifi-
cantly the mode of bonding of the two Cp ligands.
The polymerization of C2H4 was investigated using
compounds 1–9 and 11 as catalysts in the presence of
either MAO or [NHMe2(C6H5)][B(C6F5)4] as cocatalyst.
The results are summarized in Table 3 which also lists
for comparison the results obtained under comparable
˚

F. Benetollo et al. / Journal of Organometallic Chemistry 555 (1998) 177–185
181
Table 4
Experimental data for the crystallographic analyses
Compound
(5)
(6)
(11)
Formula
Mol wt.
ZrC26H28O2
463.7
ZrC28H32O2
491.8
ZrC24H24N2
665.4
Color
Orange
Colorless
0.32×0.44×0.48
Monoclinic
P21/a (n. 14)
15.291(3)
8.048(2)
40.990(6)
99.78(4)
4971(2)
8
Yellow
0.26×0.32×0.30
Monoclinic
Pa (n. 7)
11.721(2)
11.766(2)
15.740(3)
111.02(3)
2026.2(7)
4
Crystal size, mm
Crystal system
Space group
0.32×0.22×0.36
Orthorhombic
P212121 (n. 19)
13.636(3)
13.932(3)
11.852(2)
˚
a (A)
˚
b (A)
˚
c (A)
i (°)
V (A )
3
˚
2251.6(8)
4
1.368
960
Z
Dcalc. (g cm−3
F(000)
)
1.314
2048
1.415
888
q range (°)
3–26
Mo–Kh(0.71073)
5.06
3–26
Mo–Kh(0.71073)
4.63
3–27
Mo–Kh(0.71073)
5.52
˚
Radiation (u, A)
m (cm−1
T (K)
)
293
293
293
No. reflections collected
No. observed [I]3|(I)]
No. parameters
R=SꢀFoꢀ−ꢀFcꢀ/SꢀFoꢀ
aRw (on F2)
2249
2184
291
0.052
0.124
1.20
0.77
−0.88
8373
7915
571
0.054
0.133
1.21
0.52
−0.78
4803
4403
493
0.033
0.084
1.31
0.29
−0.91
GOF
Dzmax (e A
Dzmin (e A
−3
˚
˚
)
−3
a w=1/[|2(F2o)+(0.0397P)2+5.04P] for 5, w=1/[|2(F2o)+(0.0349P)2+10.39P] for 6, w=1/[|2(Fo2)+(0.0339P)2+1.22P] for 11; P=max(Fo2+
2F2c)/3).
conditions with the well known catalysts 1 and 2. The
polymer yields obtained with the catalysts investigated
in this work are in the range of those previously
reported for other systems of this type [3]; yields were
higher with MAO as cocatalyst than with
[NHMe2(C6H5)][B(C6F5)4]. With MAO at 90°C, the
aryloxide complexes gave polymer yields intermediate
between those of the 1 and 2, whereas 9 and 11 gave
much lower yields. With [NHMe2(C6H5)][B(C6F5)4], at
50, 70 and 90°C the same catalyst generally gave a
monotonic increase of yields; an exception was 6, which
at 70°C produced the highest yields comparable to or
even higher than those obtained with the model cata-
lysts 1 and 2. In contrast, yields obtained with
Cp2Zr(pyr)2 remained low even at high temperature.
The molecular weights of the polymers were in the
range 104–1.7x105; in general, lower molecular weights
were obtained with MAO as cocatalyst than with
[NHMe2(C6H5)][B(C6F5)4]. It should be noted that the
molecular weights obtained with 1 and 2 increased with
temperature (from 50 to 90°C), whereas the reverse
occurred with the phenoxide derivatives 5 and 6.
[NHMe2Ph][B(C6F5)4] the trend is OC6H2Me3\
OC6H3Me2\OC6H4 Bu\OC6H5. Thus, the electron
t
donating properties of the OAr ligand appear to oper-
ate in opposite direction depending on the cocatalyst.
Again when L=OAr, complexes containing substituted
phenyl groups have greater productivity than the non-
substituted analog 3, suggesting that steric affects are
negligible, at least when [NHMe2(C6H5)][B(C6F5)4] is
the cocatalyst. This relative absence of steric effects is
most likely related to the easy rotation of the phenyl
rings around the O–C bonds, as demonstrated by the
existence of different conformations of these molecules
in the solid state, which does not hamper the coordina-
tion of ethylene to the Zr atom. The Cp2ZrL2 com-
plexes of monodentate ligands were generally found to
be superior catalysts with respect to those of bidentate
ligands (L=pyrazolyl, formamidinato), in agreement
with the stronger coordination ability of bidentate lig-
ands even though p2 X p1 equilibria can not be ruled
out.
The above data indicate that different active centers
are generated from the different complexes. If this
The dependence of productivity on the type of ary-
loxide follows the trend OC6H4 Bu\OC6H3Me2\
OC6H3Me3 in presence of MAO, whereas with
occurs
by
interaction
with
MAO
and
t
[NHMe2(C6H5)][B(C6F5)4], then the following reactions
may be hypothesized:

182
F. Benetollo et al. / Journal of Organometallic Chemistry 555 (1998) 177–185
Cp2ZrL2+MAO“Cp2ZrL+ +[L(MAO)]−
Cp2ZrL2+[NHMe2(C6H5)][B(C6F5)4]
Table 6
Atomic coordinates for non-hydrogen atoms and equivalent isotropic
thermal parameters (A ×103) for Cp2ZrMe{CH(NC6H5)2}
2
˚
“Cp2ZrL+ +LH+[NMe2(C6H5)]+[B(C6F5)4]−
Atom
x
y
z
U(eq)
Here analogy with the commonly studied systems for
which the ubiquitous active cationic species is postu-
lated [Cp2ZrCH3]+ should suggest ethylene insertion
into the Zr–O and Zr–N bonds of aryloxide, for-
mamidinato and pyrazolide cations respectively, with
formation of species of the type (a)
Zr(1)
N(1)
N(2)
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
C(8)
C(9)
0.5840
0.26484(4)
0.2829(3)
0.3116(4)
0.2992(4)
0.3177(4)
0.2386(5)
0.2479(6)
0.3321(7)
0.4094(6)
0.4027(5)
0.2763(4)
0.3084(5)
0.3018(6)
0.2652(6)
0.2298(6)
0.2366(5)
0.2837(8)
0.0596(6)
0.0687(5)
0.0909(6)
0.0947(7)
0.0738(7)
0.3537(9)
0.3634(9)
0.434(1)
0.45908(2)
0.5627(3)
0.6116(3)
0.6327(3)
0.6819(3)
0.7527(3)
0.8218(4)
0.8217(4)
0.7517(5)
0.6822(4)
0.5724(3)
0.6510(4)
0.6559(5)
0.5838(5)
0.5061(5)
0.4995(4)
0.4777(5)
0.5079(6)
0.4805(7)
0.3876(6)
0.3577(6)
0.4318(7)
0.3249(7)
0.3084(5)
0.3655(8)
0.395(1)
0.4237(7)
1.12071(2)
1.0136(3)
0.9644(3)
0.9444(3)
0.8947(3)
0.8390(4)
0.7656(5)
0.7489(4)
0.8050(5)
0.8780(4)
0.9984(3)
0.9274(3)
0.9160(4)
0.9741(4)
1.0442(4)
1.0591(3)
1.1070(5)
1.1428(5)
1.2223(5)
1.2631(5)
1.2081(6)
1.1340(5)
1.1716(5)
1.1003(5)
1.1264(8)
1.2160(7)
1.2421(5)
41.0(1)
45(1)
45(1)
45(1)
45(1)
55(2)
70(2)
80(3)
79(2)
62(2)
46(2)
58(2)
68(2)
71(2)
81(3)
66(2)
79(3)
100(4)
92(3)
100(4)
91(3)
103(4)
118(4)
95(3)
126(5)
129(6)
152(9)
40.8(1)
44(1)
47(1)
42(1)
49(1)
61(2)
77(2)
77(3)
70(2)
62(2)
45(1)
53(2)
70(2)
69(2)
65(2)
53(2)
84(3)
68(2)
84(3)
95(4)
90(3)
76(3)
81(3)
82(3)
114(4)
119(4)
81(3)
0.7875(3)
0.6347(4)
0.7526(4)
0.5858(4)
0.6192(5)
0.5725(6)
0.4929(6)
0.4589(6)
0.5045(5)
0.9108(4)
1.0065(5)
1.1264(5)
1.1551(6)
1.0621(7)
0.9408(6)
0.3979(6)
0.585(1)
0.6827(8)
0.6381(9)
0.5112(8)
0.4782(8)
0.619(1)
0.4985(8)
0.479(1)
0.6759(9)
0.589(2)
0.95269(5)
0.9128(4)
0.9032(5)
0.8929(4)
0.8961(5)
0.9645(5)
0.9491(6)
0.8669(7)
0.8022(6)
0.8152(6)
0.8761(4)
0.7729(5)
0.7403(6)
0.8086(7)
0.9098(6)
0.9464(5)
0.9412(9)
1.1585(5)
1.1344(5)
1.1378(6)
1.1632(6)
1.1746(6)
0.8194(6)
0.7411(6)
0.7426(8)
0.8276(9)
0.8702(7)
C(10)
C(11)
C(12)
C(13)
C(14)
C(15)
C(16)
C(17)
C(18)
C(19)
C(20)
C(21)
C(22)
C(23)
C(24)
Zr(2)
N(1A)
N(2A)
C(1A)
C(2A)
C(3A)
C(4A)
C(5A)
C(6A)
C(7A)
C(8A)
C(9A)
C(10A)
C(11A)
C(12A)
C(13A)
C(14A)
C(15A)
C(16A)
C(17A)
C(18A)
C(19A)
C(20A)
C(21A)
C(22A)
C(23A)
C(24A)
in which internal coordination acts as a stabilizing
factor similarly to the agostic interaction [5] of the type
shown in (b). The above scheme is unprecedented and
needs more experimental support.
0.420(1)
Table 5
0.4721(7)
0.22191(3)
0.3704(3)
0.1918(3)
0.3013(4)
0.1132(4)
0.1283(5)
0.0570(6)
−0.0317(5)
−0.0509(5)
0.0220(4)
0.4851(4)
0.5179(4)
0.6319(5)
0.7137(5)
0.6816(4)
0.5686(4)
0.0237(5)
0.3144(6)
0.3294(8)
0.222(1)
Final atomic coordinates for Cp2Zr{2,6-OC6H3(CH3)2}2 and equiva-
2
lent isotropic displacement parameters (A ×103)
˚
Atom
x
y
z
U(eq)
Zr
O(1)
O(2)
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
C(8)
C(9)
C(10)
C(11)
C(12)
C(13)
C(14)
C(15)
C(16)
C(17)
C(18)
C(19)
C(20)
C(21)
C(22)
C(23)
C(24)
C(25)
C(26)
0.16261(5)
0.0418(3)
0.2562(4)
0.65998(4)
0.5789(4)
0.5652(4)
0.5660(5)
0.5964(5)
0.5863(8)
0.5436(8)
0.5119(8)
0.5195(6)
0.6398(8)
0.4788(7)
0.5034(5)
0.4105(5)
0.3491(6)
0.3750(8)
0.4646(9)
0.5311(6)
0.6256(7)
0.3773(6)
0.7352(9)
0.7241(9)
0.784(1)
0.25646(5)
0.2579(5)
0.3225(4)
0.3031(7)
0.2484(9)
0.296(1)
44.4(2)
53(2)
47(2)
50(3)
58(2)
73(4)
76(4)
64(3)
56(3)
83(4)
69(3)
44(2)
50(2)
63(3)
73(3)
74(4)
56(3)
89(4)
65(3)
85(5)
82(4)
100(6)
108(8)
105(6)
71(4)
84(5)
94(6)
93(6)
79(4)
−0.0478(6)
−0.1315(6)
−0.2239(7)
−0.2311(8)
−0.1503(8)
−0.0569(7)
−0.1216(9)
0.0301(7)
0.3299(6)
0.3088(5)
0.3879(7)
0.4816(8)
0.5004(8)
0.4269(7)
0.4477(8)
0.2068(6)
0.187(1)
0.090(1)
0.057(1)
0.136(2)
0.218(1)
0.2324(9)
0.1417(9)
0.148(1)
0.241(1)
0.2948(9)
0.401(1)
0.4558(9)
0.4089(7)
0.1296(8)
0.4694(8)
0.3022(6)
0.2622(7)
0.2417(8)
0.263(1)
0.3019(9)
0.3247(7)
0.375(1)
0.1426(8)
0.1983(7)
0.3529(6)
0.2947(8)
0.1812(9)
0.1739(8)
0.2826(7)
0.244(1)
0.4482(8)
0.4377(9)
0.354(1)
0.314(1)
0.371(1)
0.0718(7)
0.0456(7)
0.0654(8)
0.102(1)
0.8332(8)
0.802(1)
0.5975(8)
0.638(1)
0.736(1)
0.7568(9)
0.6724(9)
At present we would emphasize that all systems
present their own peculiarities and then whatever the
nature of the active species these should be related to
the respective catalyst precursor. In fact it must be
0.1062(8)

F. Benetollo et al. / Journal of Organometallic Chemistry 555 (1998) 177–185
183
Table 7
taken into account that aryloxide, amidinato and pyra-
zolide ligands are more strongly bounded to Zr than
chloride and alkyl groups and then removal of both L
ligands, especially the second one, from Zr by cocata-
lyst should result quite difficult.
Atomic coordinates and equivalent isotropic displacement parameters
2
(A ×103) for Cp2Zr{2,4,6-OC6H2(CH3)3}2
˚
Atom
x
y
z
U(eq)
Zr(1)
O(1)
O(2)
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
C(8)
C(9)
0.08679(2) 0.67893(4)
0.36937(1)
0.34578(8)
0.41373(8)
0.3245(1)
0.3332(1)
0.3112(1)
0.2805(1)
0.2726(1)
0.2940(1)
0.3664(1)
0.2563(2)
0.2846(1)
0.4455(1)
0.4531(1)
0.4856(2)
0.5107(2)
0.5029(2)
0.4708(1)
0.4275(2)
0.5462(2)
0.4629(2)
0.3923(2)
0.3581(2)
0.3486(2)
0.3764(2)
0.4027(2)
0.3712(2)
0.3650(2)
0.3343(2)
0.3210(2)
0.3440(2)
0.13532(1)
0.15598(8)
0.09004(9)
0.1766(1)
0.1654(1)
0.1879(1)
0.2200(1)
0.2300(1)
0.2088(1)
0.1298(1)
0.2442(2)
0.2204(2)
0.0581(1)
0.0340(2)
0.0010(2)
39.5(1)
46(1)
48(1)
42(1)
44(1)
52(2)
57(2)
59(2)
50(2)
56(2)
87(3)
69(2)
47(1)
59(2)
78(2)
77(2)
76(2)
61(2)
81(2)
123(4)
91(2)
90(3)
89(3)
88(3)
80(3)
83(3)
73(2)
69(2)
75(2)
89(3)
92(3)
49.5(2)
55(1)
60(1)
47(1)
49(2)
56(2)
56(2)
59(2)
54(2)
62(2)
79(2)
74(2)
64(2)
88(3)
118(4)
111(4)
96(3)
74(2)
107(3)
170(6)
147(5)
95(3)
85(3)
97(3)
111(4)
134(4)
101(3)
102(4)
87(3)
109(4)
112(4)
Therefore the formation of active species of the type
[Cp2ZrH]+ by hydrogenation of Zr–E (E=O, N)
bonds should be considered unlikely as in our experi-
ments the H2 pressure is rather low, and examples are
reported in literature in which Zr–O [13] and
−0.0378(2)
0.0731(2)
0.6524(3)
0.5932(4)
0.5739(5)
0.4196(5)
0.3420(6)
0.4111(7)
0.5630(7)
0.6459(6)
0.3416(6)
0.3203(9)
0.8130(6)
0.6334(5)
0.6978(6)
0.7428(7)
0.7236(7)
0.6519(7)
0.6047(7)
0.7132(9)
0.776(1)
0.5219(9)
0.9644(6)
0.9806(6)
0.9569(6)
0.9302(7)
0.9325(7)
0.4979(7)
0.3906(6)
0.4239(7)
0.5537(9)
0.5972(7)
−0.1015(3)
−0.1352(3)
−0.2009(3)
−0.2351(3)
−0.2019(3)
−0.1359(3)
−0.1026(3)
−0.3059(4)
−0.1031(4)
0.0668(3)
¸¹¹¹¹¹º
¸¹º
M–N–C–N (M=Y, Sc) [14] bonds are stable also
under high H2 pressure. Moreover 3-MAO and 6-MAO
systems have shown significant activity in copolymer-
ization of ethylene and propylene in H2 free atmosphere
(productivity=3, 5–6 Kg mol−3 Zr h−1) [15].
Concerning the molecular weight distribution, several
preliminary experiments of melt flow index have been
carried out. The values of melt index ratio range be-
tween 20–30, thus indicating a polydispersity (Mw/Mn)
between 2 and 3, a rather narrow molecular weight
distribution as expected for metallocene homogeneous
catalysts.
C(10)
C(11)
C(12)
C(13)
C(14)
C(15)
C(16)
C(17)
C(18)
C(19)
C(20)
C(21)
C(22)
C(23)
C(24)
C(25)
C(26)
C(27)
C(28)
Zr(2)
O(1A)
O(2A)
C(1A)
C(2A)
C(3A)
C(4A)
C(5A)
C(6A)
C(7A)
C(8A)
C(9A)
C(10A)
C(11A)
C(12A)
C(13A)
C(14A)
C(15A)
C(16A)
C(17A)
C(18A)
C(19A)
C(20A)
C(21A)
C(22A)
C(23A)
C(24A)
C(25A)
C(26A)
C(27A)
C(28A)
−0.0124(3)
−0.0151(5)
0.0569(5)
0.1319(5)
0.1391(3)
−0.0939(3)
0.0517(7)
0.2210(4)
0.0583(5)
0.0457(5)
0.1269(6)
0.1877(4)
0.1478(5)
0.2223(3)
0.1513(4)
4. Conclusion
Several new O and N-bonded zirconocene complexes
were synthesized in very high yields and excellent purity
by a convenient one-pot reaction and the structures of
four members of the series were established by X-ray
crystallography. The complexes showed catalytic activ-
ity for ethylene polymerization when combined with an
excess of MAO or a stoicheiometric quantity of
[NHMe2(C6H5)][B(C6F5]4]. Both the catalytic activity
and the molecular weight of the polymers produced
were found to depend not only on the cocatalyst and on
the temperature but also on the nature of the L,L1
ligands associated to the zirconocene moieties in the
Cp2ZrLL1 complexes. This dependence offers the op-
portunity for further control of the polymer properties.
0.1051(4)
0.1475(5)
0.2210(4)
0.18815(3) 0.68923(5)
0.0806(2)
0.1408(2)
0.0431(3)
0.0067(3)
−0.0274(3)
−0.0281(3)
0.0049(3)
0.0398(3)
0.0020(3)
−0.0625(4)
0.0750(4)
0.1076(4)
0.1605(5)
0.1264(7)
0.0435(8)
−0.0082(6)
0.0224(4)
−0.0388(5)
0.0094(9)
0.2483(5)
0.2722(6)
0.2363(4)
0.2708(6)
0.3321(5)
0.3360(5)
0.2394(7)
0.1515(6)
0.1388(5)
0.2208(7)
0.2814(5)
0.6522(4)
0.6035(4)
0.5529(5)
0.3990(6)
0.2976(6)
0.3434(6)
0.4996(6)
0.6051(6)
0.3447(6)
0.2277(8)
0.7758(7)
0.6412(6)
0.6117(9)
0.657(1)
0.727(1)
−0.0077(2)
0.0161(2)
0.0489(2)
0.0734(2)
−0.0443(2)
0.0433(3)
0.1386(2)
0.1655(2)
0.1857(2)
0.1724(3)
0.1412(3)
0.1581(2)
0.1470(2)
0.1126(2)
0.1040(2)
0.1323(3)
5. Experimental
0.7458(9)
0.7035(7)
0.722(1)
0.775(1)
0.528(1)
0.4160(9)
0.4188(8)
0.538(1)
0.6180(9)
0.550(1)
0.9686(8)
0.9892(7)
0.9725(7)
0.9468(8)
0.9460(8)
5.1. Materials and procedures
All operations were carried out in glove boxes under
a pre-purified and controlled dinitrogen atmosphere.
The hydrocarbon and ether solvents were purified by
refluxing with sodium-benzophenone. Commercially
available methyllithium (1.6 M solution in diethyl ether,
Aldrich), ZrCl4, aryloxides, pyrazole and N,N%-
diphenylformamidine were used as received. Potassium
cyclopentadiene was synthesized from cyclopentadiene
monomer (freshly distilled) and potassium hydroxide in
dimethoxyethane [16] and its concentration was deter-

184
F. Benetollo et al. / Journal of Organometallic Chemistry 555 (1998) 177–185
mined by acidimetric titration. Unless stated otherwise,
the solvent used in each synthesis was removed by
evaporation under reduced pressure and the solid
product was dried under vacuum; yields were quantita-
tive. Proton NMR spectra were recorded on a Bru¨ker
AC 200 spectrometer in anhydrous C6D6 solution with
C6D5H as internal standard; chemical shifts (as l) were
referenced to SiMe4. Mass spectra were obtained on a
VG ZAB 2F instrument operating in electron ionization
(EI) mode (70 eV, 200 mA, ion source temperature
120°C).
h. After drying, the colourless solid had 1H NMR
spectrum very similar to that published recently [8]: 5.55
(s, 10H, Cp), 0.59 (s, 3H, CH3), 6.35 (br, 1H) and 7.39
(br, 2H), both with unresolved splitting, C3H3N2.
Cp2Zr(C3H3N2)2 (9). Complex 1 (584 mg, 2 mmol)
and Li(C3H3N) (280 mg, 4 mmol) were suspended in
100 cm3 of benzene and stirred at room temperature for
1 h. The mixture was centrifuged to separate insoluble
LiCl; the supernatant solution was filtered and the solid
residue washed with two portions of benzene (10 cm3).
The solution was evaporated to give a colourless solid.
1H NMR: 5.75 (s, 10H, Cp), 6.24 (t, 2H, CHb), 7.35 (d,
4H, CHa).
5.2. Synthesis of complexes
Cp2Zr(Me)[CH(NC6H5)2] (10). Complex 2 (500 mg, 2
mmol) and (C6H5)NHCHN(C6H5) (391 mg, 2 mmol)
were dissolved in 50 cm3 of toluene and the mixture was
stirred at room temperature for 2 h. The solvent was
removed and the pale yellow solid was dried. H NMR:
5.68 (s, 10H, Cp), 0.09 (s, 3H, CH3), 7.98 (s, 1H, CH
formyl), 6.71–6.80 (m, 10H, phenyl).
Cp2ZrCl2 (1) was prepared by reaction of ZrCl4 and
CpK (1:2 molar ratio) in dimethoxyethane. The product
was purified by sublimation a 175°C (2 · 10−2 torr).
Cp2Zr(Me)2 (2) was prepared by reaction of 1 with
LiMe (1:2 molar ratio) in diethylether and purified by
sublimation at 75°C (2 · 10−2 torr).
1
Cp2Zr(OC6H5)2 (3). Complex 2 (500 mg, 2 mmol) and
C6H5OH (376 mg, 4 mmol) were dissolved in toluene
(50 cm3) and stirred for 4 h. The solvent was removed
to give pure colourless Cp2Zr(OC6H5)2 (m.p. 130°C). 1H
NMR: 5.95 (s, 10H, Cp), 6.75–7.29 (m, 10H, OC6H5).
Cp2Zr(Me)(2,6-OC6H3Me2) (4). Complex 2 (500 mg,
2 mmol) and HO-2,6-C6H3Me2 (243 mg, 1 mmol) were
stirred 2 h in toluene (50 cm3). After removal of the
solvent the pale yellow complex (m.p. 84°C) was col-
Cp2Zr[CH(NC6H5)2]2 (11). Diethylether 100 cm3,
cooled to 0°C, 2.5 ml of a 1.6 molar solution of LiCH3
(4 mmol) and N,N%-diphenylformamidine (785 mg, 4
mmol) were mixed and allowed to stand for 2 h. The
diethyl ether was removed and 100 cm3 of benzene
containing 1 (585 mg, 2 mmol) were added. After 1 h
agitation, the suspension was centrifugated. The super-
natant was filtered to give a yellow residue. H NMR
5.91 (s, 5H, Cp), 7.83 (s, 2H, CH), 6.67–7.14 (m, 10H,
phenyl).
1
1
lected. H NMR: 5.68 (s, 10H, Cp), 0.49 (s, 3H, Me),
2.07 (s, 6H, 2,6-OC6H3Me2), 6.80–7.02 (m, 3H, O-
C6H3).
Cp2Zr[2,6-OC6H3Me2]2 (5). Complex 2 (500 mg, 2
mmol), dissolved in toluene (50 cm3) was treated with
HO-2,6-C6H3Me2 (486 mg, 4 mmol). After the mixture
was refluxed for 10 h, the solvent was removed to give
a pale yellow solid (m.p. 173°C). 1H NMR: 5.89 (s,
10H, Cp), 2.23 (s, 12H, Me), 6.82–7.02 (m, 6H,
OC6H3Me2).
6. Ethene polymerization
Polymerization experiments were carried out by the
following general procedure. A 3L autoclave, electri-
cally heated and equipped with a stirring bar, was dried
under dinitrogen flux at 115°C for 2 h and cooled to
room temperature. The autoclave was charged with
purified n-hexane (2L), 50–100 mg of catalyst sus-
pended in 70 cm3 of n-hexane and 30 cm3 of toluene
containing a quantity of a 10% solution of MAO
(WITCO) calculated to give a 2500:1 MAO: catalyst
mole ratio. At this point 14.8 bar of ethylene and 0.2
bar of H2 were introduced, the system was heated to the
polymerization temperature for 1 h. The resulting mix-
ture was gravity filtered, the gummy polymer heated at
60°C for 2 h and weighed. Viscosity was determined in
1,2,4-trichlorobenzene solution, using a Schott Gerate
Mod. AS U 360 viscosimeter thermostated at 135°C.
Similar procedures were adopted when using
[NHMe2(C6H5)][B(C6F5)4] as cocatalyst. In this case
0.08 g of Al(iBu)3 were added as schavenger. Melt index
of the polymer obtained with [NHMe2(C6H5)][B(C6F5]4]
has been determined for the systems 1, 2, 4, 5 and 6
following the literature [17].
Cp2Zr[2,4,6-OC6H2Me3]2 (6). Complex 2 (500 mg, 2
mmol) was dissolved in toluene (50 cm3), HO-2,4,6-
C6H2Me3 (544 mg, 4 mmol) was added, and the solu-
tion was refluxed for 10 h. The solvent was removed
and the pale yellow solid product was washed with
1
n-hexane (10 cm3); m.p. 139°C. H NMR: 5.93 (s, 10H,
Cp), 2.24 (s, 12H, o-CH3), 2.26 (s, 6H, p-CH3), 6.92 (s,
2H, OC6H2).
Cp2Zr(OC6H4)2-4tC4H9 (7). Complex 2 (500 mg, 2
mmol) and HO-C6H6-4tC4H9 (542 mg, 4 mmol) were
refluxed for 3 h in 50 cm3 of toluene. After drying a
colourless residue was collected. 1H NMR: 6.01 (s, 10H,
t
Cp), 1.33 (s, 18H, C4H9), 6.79 and 7.32 (both doublets,
4H total, O-C6H4).
Cp2Zr(Me)(C3H3N2) (8). Complex 2 (500 mg, 2
mmol) and C3H4N2 (136 mg, 2 mmol) dissolved in 50
cm3 of toluene, were stirred at room temperature for 2

F. Benetollo et al. / Journal of Organometallic Chemistry 555 (1998) 177–185
185
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Waymouth, Angew. Chem. Int. Ed. Engl. 34 (1995) 1143.
[5] M. Bochmann, J. Chem. Soc. Dalton Trans. (1996) 255.
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Chem. Soc. 117 (1995) 12114.
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Trans. (1996) 939. (a) These compounds were described [8, 9]
when the works was in progress. P. Zanella, L. Crosara, F.
Benetollo, G. Rossetto, C. Scelza, XIX Congresso Nazionale
Ricerca e Tecnologia, Riccione, Italy, June 9–14, (1996), CI/CO-
P2.
[8] D. Rottger, G. Erker, M. Grehl, R. Fro¨lich, Organometallics 13
(1994) 3897.
[9] W.A. Howard, T.M. Trnka, G. Parkin, Inorg. Chem. 34 (1995)
5900.
[10] W.E. Hunter, D.C. Hrncir, R.V. Bynum, R.A. Penttila, J.L.
Atwood, Organometallics 2 (1983) 750.
[11] R. Duchateau, C.T. van Wee, A. Meetsma, P.T. van Duijnen,
J.H. Teuben, Organometallics 15 (1996) 2279.
[12] S. Gambarotta, S. Strologo, C. Floriani, A. Chiesi-Villa, C.
Guastini, J. Am. Chem. Soc. 107 (1985) 6278.
[13] K.I. Gell, B. Posin, J. Schwartz, G. Williams, J. Am. Chem. Soc.
104 (1982) 1846.
[14] (a) C.J. Schaverien, Organometallics 13 (1994) 69. (b) J.R.
Hagadorn, J. Arnold, Organometallics 15 (1996) 984.
[15] Our preliminary results.
[16] W.L. Jolly, Inorg. Synth, XI (1968) 113.
[17] D.W. Van Krevelen, Properties of Polymers, Elsevier, Amster-
dam, 1990, p. 675.
[18] D. Belletti, FEBO. A New Hardware and Software System for
controlling a Philips PW1100 Single Crystal Diffractometer.
Internal Report 1/93. Centro di Studio per la Strutturistica
Diffattometrica del CNR, Parma.
[19] A.C.T. North, D.C. Philips, F.S. Mathews, Acta Cryst. A24
(1968) 351.
6.1. X-ray measurements and structure determination
Crystal data, collected reflections and parameters of
the final refinement for Cp2Zr(2,6-OC6H3Me2)2 (5),
Cp2Zr(2,4,6-OC6H2Me3)2 (6), and Cp2ZrMe{CH(NC6
H5)2} (11) are reported in Table 4. Reflections were
collected using a Philips PW1100 diffractometer [18]
with graphite-monochromated Mo–Kh radiation. The
orientation matrix and cell dimensions were determined
by least squares refinement of the angular positions of
30 reflections. Two standard reflections were monitored
every 200 reflections and no significant decay was ob-
served during data collection. All intensities were cor-
rected for Lorentz polarization and absorption [19]. The
positions of the heavy atoms were obtained from Pat-
terson syntheses [20]. All non-H atoms were located in
the subsequent Fourier maps. Structures were refined
by full-matrix least squares using anisotropic tempera-
ture factors for all non-H atoms. Hydrogen atoms were
introduced at calculated positions in their described
geometries and during refinement were allowed to ride
on the attached carbon atoms with fixed isotropic
thermal parameters (1.2 U(eq) of the parent carbon
atom). For the structures 5 and 11 the Flack parameters
[21] have been refined. Calculations were performed
with the SHELX-93 program [22], using the scattering
factors inclosed therein. The program for the ORTEP
drawing was taken from ref. [23]. Final atomic coordi-
nates are given in Tables 5–7.
[20] G.M. Sheldrick, SHELXS86, Acta Cryst. A46 (1990) 467.
[21] H.D. Flack, Acta Crystallogr. A39 (1983) 876.
[22] G M. Sheldrick, SHELXL93, Programm for the Refinement of
Crystal Structures. University of Go¨ttingen, Germany.
[23] C.K. Johnson, ORTEP II report ORNL-5138, Oak Ridge National
Laboratory Tennessee, USA, 1976.
References
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.