Fluorenyl derivatives of early transition elements: A synthetic and structural study

Article abstract of DOI:10.1016/S0022-328X(01)01019-1

The tetracarbonyls of niobium(I) and tantalum(I), M(η⁵-9-phenylfluorenyl)(CO)₄, have been prepared from the dinuclear tetracarbonyl anions [M₂(μ-Cl)₃(CO)₈]^- and Li(9-phenylfluorenyl). A slightly distorted four-legged piano stool geometry, due to the presence of the sterically demanding phenyl substituent, has been found in the case of the niobium derivative. The crystal and molecular structures of Zr(fluorenyl)₂Me₂ and of the 9-phenyl-substituted derivative have been solved. The structure of Zr(fluorenyl)₂Me₂ is similar to that of the known dichloride, Zr(fluorenyl)₂Cl₂, where fluorenyl ligands of different hapticity are present. On the other hand, the use of the more sterically demanding phenyl-substituted fluorenyl ligand in Zr(η⁵-9-phenylfluorenyl)₂Me₂, induces the fluorenyl ligands to be symmetrically and pentahapto-coordinated to zirconium.

Full text of DOI:10.1016/S0022-328X(01)01019-1

Journal of Organometallic Chemistry 631 (2001) 110–116
www.elsevier.com/locate/jorganchem
Fluorenyl derivatives of early transition elements: a synthetic and
structural study
Fausto Calderazzo a, Fabio Marchetti b, Marta Moreno b,1, Guido Pampaloni a,*,
Francesca Tumminia a
a Dipartimento di Chimica e Chimica Industriale, Uni6ersita` di Pisa, Via Risorgimento 35, I-56126 Pisa, Italy
b Dipartimento di Ingegneria Chimica, dei Materiali e delle Materie Prime e Metallurgia, Uni6ersita` di Roma ‘La Sapienza’,
Via del Castro Laurenziano 7, I-00161 Rome, Italy
Received 4 April 2001; accepted 15 May 2001
Abstract
The tetracarbonyls of niobium(I) and tantalum(I), M(h5-9-phenylfluorenyl)(CO)4, have been prepared from the dinuclear
tetracarbonyl anions [M2(m-Cl)3(CO)8]− and Li(9-phenylfluorenyl). A slightly distorted four-legged piano stool geometry, due to
the presence of the sterically demanding phenyl substituent, has been found in the case of the niobium derivative. The crystal and
molecular structures of Zr(fluorenyl)2Me2 and of the 9-phenyl-substituted derivative have been solved. The structure of
Zr(fluorenyl)2Me2 is similar to that of the known dichloride, Zr(fluorenyl)2Cl2, where fluorenyl ligands of different hapticity are
present. On the other hand, the use of the more sterically demanding phenyl-substituted fluorenyl ligand in Zr(h5-9-phenylfluo-
renyl)2Me2, induces the fluorenyl ligands to be symmetrically and pentahapto-coordinated to zirconium. © 2001 Elsevier Science
B.V. All rights reserved.
Keywords: Zirconium; Niobium; Tantalum; Fluorenyl; Structures; Complexes
1. Introduction
diffraction [4] as containing h5- and the h3-fluorenyl
ligands. A new impetus in the field of Group 4 metal
fluorenyl derivatives came from the discovery of the
metallocene/MAO combination for the polymerization
of olefins; studies aimed at increasing the activity of the
catalytic systems allowed a number of new fluorenyl
compounds of zirconium to be prepared and struc-
turally characterized [2].
Cyclopentadienyl- and indenyl derivatives of transi-
tion d-metals have been extensively studied since the
discovery of ferrocene in 1951 [1]; on the other hand,
sandwich or half-sandwich compounds containing the
fluorenyl ligand have been elusive compounds for some
time. For example, attempts to prepare FeCp(fluorenyl)
or Fe(fluorenyl)2 failed, presumably due to the involve-
ment of the p-electrons of the central five-membered
ring with the aromaticity of the fused six-membered
rings [2]. Although some earlier reports appeared con-
cerning the use of fluorenyl derivatives of Group 4
elements as catalytic precursors for the polymerization
of olefins, the first example of a fluorenyl derivative was
Zr(fluorenyl)2Cl2 described by Samuel and Setton in
1965 [3] and characterized some years later by X-ray
In this paper we report the synthesis and the struc-
ture of the half-sandwich derivatives of niobium(I) and
tantalum(I), M(h5-9-phenylfluorenyl)(CO)4, and
a
structural study of the known [5,6] dimethyl derivatives
of zirconium(IV) containing the fluorenyl and the 9-
phenyifluorenyl ligands.
2. Results and discussion
* Corresponding author. Tel.: +39-050-91-8221219; fax: +39-
050-20-237.
2.1. Niobium and tantalum
E-mail address: pampa@dcci.unipi.it (G. Pampaloni).
1 Present Address: ISSECC CNR, Via Jacopo Nardi 39, I-50132
Florence, Italy.
By reaction of the dinuclear tetracarbonyl anions of
niobium(I) and tantalum(I), [M2(m-Cl)3(CO)8]− with
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)01019-1

F. Calderazzo et al. / Journal of Organometallic Chemistry 631 (2001) 110–116
111
Scheme 1.
Table 1
Crystallographic data and details of the structure refinement for Nb(h5-9-phenylfluorenyl)(CO)4, Zr(fluorenyl)2Me2, and Zr(h5-9-phenylfluo-
renyl)2Me2
Nb(h5-9-Ph-C13H9)(CO)4
Zr(C13H9)2Me2
Zr(h5-9-Ph-C13H9)2Me2
Empirical formula
Formula weight
Temperature (K)
Crystal system
C23H13NbO4
446.24
293(2)
Monoclinic
C2/c (no.15)
C28H24Zr
451.69
293(2)
Monoclinic
P21/c (no.14)
C40H32Zr
603.88
293(2)
Monoclinic
C2/c (no.15)
Space group
Unit cell dimensions
,
a (A)
16.190(2)
7.476(1)
31.771(3)
90.26(1)
8
1.542
3845.4(8)
0.652
13.657(3)
8.015(1)
20.248(3)
109.59(1)
4
1.437
2088.1(6)
0.538
21.035(4)
8.688(3)
17.296(4)
114.26(1)
4
1.392
2882(1)
0.409
,
b (A)
,
c (A)
i (°)
Z
zcalc (Mg m−3
)
3
,
Volume (A )
v (mm−1
)
Data/restraints/parameters
R(Fo) [I\2|(I)]
3395/0/266
0.0350
2727/0/264
0.0425
2519/0/186
0.0685
Rw(Fo) [I\2(I)]
0.0686
0.0742
0.1693
R(Fo)=ꢀ ꢁꢁFoꢁ−ꢁFcꢁꢁ/ꢀ ꢁFoꢁ; Rw(Fo2)=[ꢀ [w(F2o−F2c)2]/ꢀ [w(Fo2)2]]; w=1/[|2(F2o)+(AQ)2+BQ] where Q=[MAX(Fo2,0)+2F2c]/3.
lithium(9-phenylfluorenyl) in Et2O, the tetracarbonyl
derivatives M(h5-9-phenylfluorenyl)(CO)4 have been
obtained according to Scheme 1, a reaction sequence
successfully applied to the synthesis of cyclopentadi-
enyl-substituted tetracarbonyl derivatives of Group 5
metals [7].
fashion and to the four carbonyl groups, the coordina-
tion around niobium being square-pyramidal. The nio-
,
bium–centroid distance of 2.109 A is larger than that
observed in other tetracarbonyl cylopentadienyl deriva-
,
tives which ranges from 2.069 A in NbCp(CO)4 [10] to
The niobium and tantalum derivatives are red to
orange solids, stable in air for short periods of time,
soluble in hydrocarbons and in CH2Cl2. Although they
dissolve in THF, a colourless solid forms quickly which
Table 2
5
,
Bond distances (A) and angles (°) in Nb(h -9-phenylfluorenyl)(CO)4.
Bond distances
Nb–C(5)
Nb–C(6)
Nb–C(11)
Nb–C(12)
Nb–C(17)
Mean
2.410(4)
2.452(4)
2.446(4)
2.441(4)
2.443(4)
2.438
Nb–C(1)
Nb–C(2)
Nb–C(3)
Nb–C(4)
Mean
2.070(4)
2.077(4)
2.077(5)
2.086(4)
2.077
1
was shown to be 9-phenylfluorene by H-NMR [8]. The
well documented decomposition of transition metal
fluorenyl derivatives in the presence of THF can ex-
plain the medium-to-low yields (51 and 24% in the case
of the niobium and tantalum compounds, respectively)
[9]. Although we used Et2O as reaction medium, THF
was present in the reaction mixture due to solvation of
the cation in the starting materials Na(THF)3.35[Nb2(m-
Cl)3(CO)8] and H(THF)2[Ta2(m-Cl)3(CO)8].
a
Nb–Cp
2.109(4)
Bond angles
C(1)–Nb–C(3)
C(1)–Nb–C(2)
C(3)–Nb–C(2)
C(1)–Nb–C(4)
C(3)–Nb–C(4)
114.0(2)
75.2(2)
74.7(2)
71.7(1)
73.1(2)
C(2)–Nb–C(4)
C(1)–Nb–Cp
C(2)–Nb–Cp
C(3)–Nb–Cp
C(4)–Nb–Cp
117.8(2)
122.5(1)
120.7(2)
123.4(2)
121.6(1)
The tetracarbonyl Nb(h5-9-phenylfluorenyl)(CO)4
was studied by X-ray diffraction. Crystallographic data
are summarized in Table 1, selected bond distance and
angles are reported in Table 2, while Fig. 1 shows the
molecular structure of the compound. The niobium
centre is bonded to the fluorenyl ligand in a pentahapto
a Cp indicates the centroid of the 9-phenylfluorenyl five-membered
ring.
Estimated standard deviations in parentheses refer to the least signifi-
cant digit

112
F. Calderazzo et al. / Journal of Organometallic Chemistry 631 (2001) 110–116
Mn(h5-9-phenylfluorenyl)(CO)3 [12], which to the best
of our knowledge represents the only example known
until now of a structurally characterized metal-coordi-
nated phenylfluorenyl ligand. The Nb–CO bond angles
are between 120.3 and 122.5°, with a slightly asymmet-
ric Nb(CO)4 fragment. Such asymmetry is maintained
in solution: the infrared spectrum in heptane shows a
strong absorption at 2034s, and a very strong doublet
at 1936–1927 cm−1, the relative intensity being un-
changed after recrystallization thus excluding a mixture
of isomers. The doublet is not present in CH2Cl2. Due
to coupling with the Nb nucleus (I=9/2) [7b], no peak
due to the carbonyl fragment was found in the 13C-
NMR spectrum of Nb(h5-9-phenylfluorenyl)(CO)4; on
the other hand, a broad signal is present at 239.2 ppm
in the 13C-NMR spectrum of the corresponding tanta-
lum compound.
Fig. 1. View of the molecular structure of Nb(h5-9-phenylfluo-
renyl)(CO)4. Thermal ellipsoids are at 30% probability.
2.2. Zirconium
Table 3
,
Bond distances (A) and angles (°) in Zr(fluorenyl)2Me2.
Some bis(fluorenyl) derivatives of zirconium have
been reported in the literature [6]. The structure of
Zr(fluorenyl)2Cl2 [4], which was proposed to contain
one h5- and one h3-coordinated fluorenyl ligand,
prompted us to investigate the crystal structure of
Zr(fluorenyl)2Me2 and to compare it with the structure
of the dichloride. It was reckoned that the presence of
the two methyl groups would eliminate the proposed [4]
Cl···Cl contacts of the dichloride. The dimethyl deriva-
tive was prepared in a 60% yield by a slight modifica-
tion of the published literature (use of Et2O and toluene
instead of THF) and recrystallized from toluene–hep-
tane. Crystallographic data are summarized in Table 1,
selected bond distances and angles are reported in
Table 3. Fig. 2 shows the molecular structure of the
compound which is reminiscent of Zr(h5-fluorenyl)(h3-
fluorenyl)Cl2. The C(1)–Zr–C(2) angle [94.9(2)°] is
close to the Cl(1)–Zr–Cl(2) angle of 93.6°. The
fluorenyl ligands face the metal in a pseudo-staggered
conformation and are both warped as reversed umbrel-
las far from the metal (maximum deviation from the
Bond distances
Zr–C(1)
Zr–C(3)
Zr–C(4)
Zr–C(9)
Zr–C(10)
Zr–C(15)
Mean
2.248(5)
2.474(6)
2.566(5)
2.641(5)
2.645(5)
2.588(5)
2.583
Zr–C(2)
Zr–C(16)
Zr–C(17)
Zr–C(22)
Zr–C(23)
Zr–C(28)
Mean
2.239(5)
2.439(5)
2.589(5)
2.726(5)
2.728(5)
2.585(5)
2.613
a
Zr–Cp1
2.281(5)
Zr–Cp2
2.317(6)
Bond angles
C(1)–Zr–Cp1
C(1)–Zr–Cp2
C(1)–Zr–C(2)
106.6(2)
105.2(2)
94.9(2)
C(2)–Zr–Cp1
C(2)–Zr–Cp2
Cp1–Zr–Cp2
106.6(2)
104.6(2)
132.6(2)
a Cp indicates the centroid of the fluorenyl five-membered ring.
Estimated standard deviations in parentheses refer to the least signifi-
cant digit
5
,
2.091(4) A in Nb(h -C5H4COOCH3)(CO)4 [7b]. The
mean Nb–CO distance (2.077 A) is shorter than that
observed in analogous compounds and similar to that
observed in noncyclopentadienyl carbonyl derivatives
of niobium(I) [7a,11].
In spite of a slight distortion (the two condensed
six-membered rings are slightly bent on the opposite
side of the metal), the fluorenyl moiety is essentially
planar; on the other hand, the C(5)–C(18) vector devi-
ates by 8.4° from the five-membered ring plane. The
dihedral angle between the fluorenyl mean plane and
the plane containing the phenyl ring C(18)–C(23) is
50.3°, probably due to the repulsion between the hydro-
gens on C(7) and C(16) and those on C(19) and C(23),
respectively. The five-membered ring plane is almost
exactly perpendicular (89.2°) to the Nb–Cp vector. A
very similar coordination geometry has been found in
,
,
plane 0.19 A). Such bending does not involve the
,
five-membered ring which is planar within 0.029 A. The
five-membered rings are not exactly perpendicular to
the ZrCp vectors but they are tilted by 4.4 and 7.9°,
respectively, so that significantly different Zr–C dis-
tances are observed. As a matter of fact, the Zr–
,
C(fluorenyl-1) distances range between 2.47 and 2.64 A,
while the corresponding distances from zirconium to
the carbon atoms of the other fluorenyl ligand range
,
between 2.44 and 2.73 A: the shortest distance involves
the C(3) and C(16) atoms. Similar differences have been
considered evidence of h3-coordination of the fluorenyl
ligand [4].

F. Calderazzo et al. / Journal of Organometallic Chemistry 631 (2001) 110–116
113
In order to test whether a more sterically demanding
ligand could induce some structural changes, we studied
the crystal and molecular structure of the derivative
containing the 9-phenylfluorenyl ligand. The synthetic
pathway to Zr(h5-9-phenylfluorenyl)2Me2 was that re-
ported in the literature and the compound was isolated
in 75% yield after recrystallization from toluene–hep-
tane. Crystallographic data are summarized in Table 1,
selected bond distances and angles being reported in
Table 4. Fig. 3 shows the molecular structure of the
compound.
The zirconium atom lies in a special position on the
twofold axis parallel to b placed at 0a and (1/4)c. This
operation relates the two halves of the molecule. The
zirconium centre adopts the pseudo-tetrahedral coordi-
nation geometry generally observed in MCp2X2 com-
pounds. The 9-phenylfluorenyl ligands face the metal at
a
distance greater than that observed in
Zr(fluorenyl)2X2 (X=Cl, CH3), which is probably due
Fig. 3. View of the molecular structure of Zr(h5-9-phenylfluo-
renyl)2Me2. Thermal ellipsoids are at 30% probability.
to the presence of the sterically demanding ligands. As
observed in Nb(h5-9-phenylfluorenyl)(CO)4, the 9-
phenylfluorenyl group is substantially planar as far as
the five-membered ring is concerned, the rest of the
ligand being slightly bent far away from the metal.
,
The maximum deviation from the plane is 0.396 A at
C(3). The dihedral angle between the plane of the
phenyl substituent and that of the fluorenyl is smaller
(41.4°) than in the case of Nb(h5-9-phenylfluo-
renyl)(CO)4 (50.3°). As in Zr(fluorenyl)2Cl2, the five-
membered ring plane is almost perpendicular to the
Zr–centroid vector, the tilting angle being 2.2° with the
C(10) atom slightly closer to the metal than C(12) and
C(13). The differences in Zr–C(fluorenyl) bond lengths
are however smaller than that observed in
Zr(fluorenyl)2Me2.
Fig. 2. View of the molecular structure of Zr(fluorenyl)2Me2. Thermal
ellipsoids are at 30% probability.
The mean C–C bond distance within the five-mem-
,
bered ring is 1.434(9) A to be compared with the same
,
bond distances in the free ligand [1.462(7) A] [13].
Table 4
5
,
Bond distances (A) and angles (°) in Zr(h -9-phenylfluorenyl)2Me2
Bond distances
3. Experimental
Zr–C(1)
2.392(5)
2.299(6)
Zr–C(10)
Zr–C(11)
Zr–C(12)
Zr–C(13)
Zr–C(14)
Mean
2.532(6)
2.631(5)
2.628(6)
2.616(6)
2.605(6)
2.602
a
Zr–Cp
Unless otherwise stated, all of the operations were
carried out under an atmosphere of prepurified argon.
Solvents were dried by conventional methods prior to
use.
IR spectra were measured with the FT-1725X instru-
ment on solutions or on Nujol mulls prepared under
Bond angles
C(1)–Zr–C(1%)
C(1)–Zr–Cp
94.4(3)
102.5(2)
Cp–Zr–Cp
138.0(2)
1
rigorous exclusion of moisture and air. H- and 13C-
NMR spectra were measured with a Varian Gemini
200BB instrument.
ZrCl4 (Fluka) was treated with boiling SOCl2; the
solution was partially evaporated under reduced pres-
Symmetry transformations used to generate equivalent atoms: % −x,
y, −z+1/2.
a Cp indicates the centroid of the 9-phenylfluorenyl five-membered
ring.

114
F. Calderazzo et al. / Journal of Organometallic Chemistry 631 (2001) 110–116
3.2. Preparation of Zr( fluorenyl)2Me2
sure, and heptane was added to precipitate the product.
The suspension was filtered and the solid dried in vacuo
at ca. 200 °C. Fluorene (Fluka) was used without
further purification. 9-phenylfluorene was prepared ac-
cording to the literature [8]. Na(THF)3.35[Nb2(m-
Cl)3(CO)8] and H(THF)2[Ta2(m-Cl)3(CO)8] were ob-
tained as previously reported [7a].
A solution of fluorene (1.5 g, 9.02 mmol) in Et2O (30
ml) was treated with a 1.6 M solution of LiBu in
hexane (5.6 ml, 8.96 mmol of LiBu). The colour of the
solution turned orange. After 5 h stirring at r.t., the
orange solution was treated at r.t. with ZrCl4 (1.05 g,
4.5 mmol). The orange suspension was stirred at r.t. for
24 h, the solvent was evaporated in vacuo at r.t. and
the residue was partially dissolved in toluene (70 ml).
The suspension was cooled at ca. 0 °C and treated
dropwise with a 1.6 M solution of LiMe in Et2O (5.6
ml, 8.96 mmol of LiMe). At the end of the addition the
orange–brown suspension was stirred for 3 h at r.t.,
filtered and the filtrate was cooled at ca. 4°C. The
orange crystalline solid (0.360 g) which formed was
isolated by filtration and dried in vacuo. By cooling the
mother liquor at ca. −30 °C, an additional crop (0.936
g) of orange crystals of Zr(fluorenyl)2Me2 [5] was iso-
lated (63% total yield) and characterized by spectro-
scopic and analytical data.
3.1. Preparation of M(p5-9-phenylfluorenyl)(CO)4,
M=Nb, Ta
Only the preparation of Nb(h5-9-phenylfluo-
renyl)(CO)4 is described in detail, the tantalum com-
pound being obtained in a similar way. A solution of
fluorene (0.44 g, 1.82 mmol) in Et2O (30 ml) was
treated with a 1.6 M solution of LiBu in hexane (1.15
ml, 1.84 mmol of LiBu). The colour of the solution
turned red–orange. After 1 h stirring at room tempera-
ture (r.t.), the solution was treated at room temperature
with Na(THF)3.35[Nb2(m-Cl)3(CO)8] (0.71 g, 0.91
mmol). The red–brown suspension was stirred at r.t.
overnight, the solvent was evaporated in vacuo at room
temperature and the residue was partially dissolved in
heptane (25 ml). The suspension was stirred for 1 h and
the solid was recovered by filtration and washed with
heptane (6×2 ml). The volume of the orange solution
was reduced to ca. 20 ml and cooled at ca. −30 °C,
giving large red crystals (0.42 g, 51% yield) of Nb(h5-9-
phenylfluorenyl)(CO)4. Anal. Found: C, 61.9; H, 3.2.
Calc. for C23H13NbO4: C, 61,9; H, 2,9%. IR (Nujol):
w˜ =3053 m, 2023 s, 1923 s, 1903 s, 1658 w, 1596 w,
1262 m, 1096 m, 1074 m, 1028 m, 802 m, 744 m, 659 w,
437 m cm−1. IR (heptane): 2034 s, 1936 vs, 1927 vs
cm−1. (CH2C12): 2032 s, 1921 vs cm−1. (THF, 5 min
3.3. Preparation of Zr(p5-9-phenylfluorenyl)2Me2
A solution of 9-phenylfluorene (0.51 g, 2.09 mmol) in
Et2O (25 ml) was treated with a 1.6 M solution of LiBu
in hexane (1.3 ml, 2.1 mmol of LiBu). The colour of the
solution turned red–orange. After 1 h stirring at r.t.,
the solution was treated at r.t. with ZrCl4 (0.22 g, 0.9
mmol). The orange suspension was stirred at r.t. for 1
h, the solvent was evaporated in vacuo at r.t. and the
residue was partially dissolved in toluene (25 ml). The
suspension was cooled at ca. 0 °C and treated dropwise
with a 1.6 M solution of LiMe in Et2O (1.1 ml, 1.8
mmol of LiMe). At the end of the addition the orange
brown suspension was stirred at r.t. for 2 h, filtered and
the volume of the filtrate was reduced to ca. 5 ml.
Heptane (20 ml) was layered on the brown–orange
solution. Large orange crystals formed after 24 h which
were recovered, and briefly dried in vacuo at r.t. (0.15
g). The volume of the solution was reduced to 5 ml and
the residue was cooled at ca. −30 °C, giving another
crop (0.25 g, 75% total yield) of crystalline Zr(h5-9-
phenylfluorenyl)2Me2 [6] which was characterized by
spectroscopic and analytical data.
1
after mixing) 2030 m, 1922 vs cm−1. H-NMR (C6D6,
25°C): l=6.70–6.86 (m, 4H), 6.90–7.20 (m, 5H), 7.4–
7.7 (m, 4H) ppm. 13C-NMR (C6D6, 25°C): l=106.2,
120.1, 130.7, 134.3 (quaternary carbon atoms), 116.9,
122.3, 123.2, 124.2, 125.8, 126.2, 128.2, 129.0 (CH
carbon atoms) ppm.
Ta(h5-9-phenylfluorenyl)(CO)4. The preparation of
this compound was performed in a similar way starting
from H(THF)2[Ta2(m-Cl)3(CO)8]. Yellow orange, 24%
yield [14]. Anal. Found: C, 51.5; H, 2.3. Calc. for
C23H13O4Ta: C, 51,7; H, 2.4%. IR (Nujol): w˜ =3056 m,
2021 s, 1920 s, 1898 s, 1658 w, 1594 w, 1266 m, 1091 m,
1078 m, 1024 m, 796 m, 740 m, 651 w, 432 m cm−1. IR
(heptane): 2031 s, 1932 vs, 1923 vs cm−1. (CH2Cl2):
2028 s, 1918 vs cm−1. (THF, 5 min after mixing) 2025
3.4. Data collection and refinement of
Nb(p5-9-phenylfluorenyl)(CO)4, Zr( fluorenyl)2Me2 and
Zr(p5-9-phenylfluorenyl)2Me2
1
m, 1918 vs cm−1. H-NMR (C6D6, 25°C): l=6.68–
The X-ray diffraction measurements have been car-
ried out at 293 K by means of a Siemens P4 diffrac-
tometer equipped with graphite-monochromated
6.87 (m, 4H), 6.93–7.18 (m, SH), 7.35–7.69 (m, 4H)
ppm. 13C-NMR (C6D6, 25°C): l=106.8, 120.4, 130.6,
134.7 (quaternary carbon atoms) 117.0, 122.1, 123.5,
124.5, 125.7, 126.1, 128.5, 129.6 (CH carbon atoms),
239.2 (broad, CO) ppm.
,
Mo–Ka radiation (u=0.71073 A). The samples were
sealed in glass capillaries under argon atmosphere. The
intensity data collection was carried out with the ꢀ/2q

F. Calderazzo et al. / Journal of Organometallic Chemistry 631 (2001) 110–116
115
scan mode, collecting a redundant set of data. Three
standard reflections were measured every 97 measure-
ments to check sample decay and equipment stability.
The intensities were corrected for Lorentz and polariza-
tion effects and for absorption by means of a q-scan
method [15]. The structure solutions, obtained by
means of the automatic direct methods, and the refine-
ments, based on full-matrix least-squares on F2, were
carried out by using the SHELX97 program [16]. Data
reduction of measured intensities was performed by the
XSCANS package [17]. Some other utilities contained in
the WINGX suite [18] were also used.
tained by standard direct methods in the C2/c space
group. Hydrogen atoms were introduced in calculated
positions and allowed to ride on the connected carbon
atoms. In the final refinement cycle anisotropic thermal
parameters were used for all heavy atoms, obtaining the
reliability factors listed in Table 1.
4. Conclusions
This paper has described a synthetic pathway to
9-phenylfluorenyl derivatives of niobium and tantalum
and shown that these compounds are unstable in the
presence of Lewis base, in particular THF. As far as the
zirconium derivatives are concerned, the solution of the
3.4.1. Nb(p5-9-phenylfluorenyl)(CO)4
Red crystals suitable for the X-ray diffraction experi-
ment were obtained as reported above. A crystal of
dimensions 0.40×0.36×0.05 mm had the unit cell
parameters listed in Table 1. A set of 4422 intensity
data were collected between 2.55q525.0°. By merg-
ing the equivalent ones, a set of 3395 independent
intensities (Rint=[ꢀ ꢁF2o−Fo2(mean)ꢁ/ꢀ (Fo2)]=0.0558)
was obtained, 2554 of them satisfying the condition
I\2|(I). The structure solution was obtained in the
C2/c space group. The final refinement cycle was done
by using anisotropic thermal parameters for all heavy
atoms. The hydrogen atoms were placed in calculated
positions and allowed to ride on the connected atoms.
The resulting reliability factors are listed in Table 1.
structure
of
the
bis
fluorenyl
derivative
Zr(fluorenyl)2Me2 has shown that the coordination
mode of the fluorenyl ligand and the metric of the
molecule do not substantially differ from that of the
dichloride, Zr(fluorenyl)2Cl2. The five-membered ring
carbon atoms of the fluorenyl ligands in both these
compounds bind to the metal at uneven distances in
such a way that one fluorenyl ligand may be considered
as h3-coordinated.
In the structures examined in this paper, the fluorenyl
ligands are bent away from the metal upon coordina-
tion, the amount of bending depending on the ML
fragment. When a pseudo tetrahedral coordination is
adopted and two fluorenyls are present, they prefer to
coordinate with their major axes perpendicular to the
line bisecting the angle formed by the other ligands. In
the latter case, the plane of the phenyl ring reduces its
tilting with respect to the fluorenyl plane.
Our data indicate that the 9-substituted fluorenyl
ligand approaches closer to the metal than the unsubsti-
tuted one: the fact that the L–Zr–L angle becomes
larger [132.6(2) versus 138.0(2)° on going from
fluorenyl to the 9-substituted derivative] with similar
Zr–C distances suggests that a regular h5-coordination
of the ligand is adopted.
3.4.2. Zr( fluorenyl)2Me2
Yellow–orange crystals suitable for the X-ray dif-
fraction experiment were obtained by slow diffusion of
heptane into a diluted solution of the compound in
toluene. A crystal of dimensions 0.28×0.18×0.08 mm
showed the unit cell parameters listed in Table 1. 3660
intensity data were collected between 2.15q522.5°.
By merging the equivalent ones, a set of 2727 indepen-
dent intensities (Rint=0.0352) was obtained, 1706 of
them satisfying the condition I\2|(I). The structure
solution was obtained in the space group P21/c. The
final refinement cycle was done by using anisotropic
thermal parameters for all heavy atoms. The hydrogen
atoms were placed in calculated positions and allowed
to ride on the connected atoms. The final reliability
factors are in Table 1.
5. Supplementary material
3.4.3. Zr(p5-9-phenylfluorenyl)2Me2
Crystallographic data for the structural analyses have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC, no.159645 for Nb(h5-9-phenylflu-
orenyl)(CO)4, 159646 for Zr(fluorenyl)2Me2, 159647 for
Zr(h5-9-phenylfluorenyl)2Me2. Copies of this informa-
tion may be obtained free of charge from The Director,
CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK
(fax: +44-1223-336-033; e-mail: deposit@ccdc.cam.
ac.uk or www: http://www.ccdc.cam.ac.uk).
Yellow–orange crystals suitable for the X-ray dif-
fraction experiment were obtained by slow diffusion of
heptane into a diluted solution of the compound in
toluene. A crystal of dimensions 0.36×0.21×0.10 mm
had the cell parameters listed in Table 1. By merging
the equivalent ones among 3131 collected intensities
(3.05q525.0°), a set of 2519 independent data was
obtained (Rint=0.0510), 1837 of them satisfying the
condition I\2|(I). The structure solution was ob-

116
F. Calderazzo et al. / Journal of Organometallic Chemistry 631 (2001) 110–116
[9] All the attempts to isolate Nb(fluorenyl)(CO)4 in the solid state
Acknowledgements
failed due to its decomposition with formation of fluorene. The
presence of low concentration of the product in solution was
ascertained by IR spectroscopy.
The authors wish to thank the Ministero dell’Univer-
sita` e della Ricerca Scientifica e Tecnologica (MURST,
Roma), Programma di Ricerca Scientifica di Notevole
Interesse Nazionale, Cofinanziamento 1998–1999, for
financial support.
[10] W.A. Herrmann, W. Kaicher, H. Biersack, I. Bernal, M.
Creswick, Chem. Ber. 114 (1981) 3558.
[11] C. Felten, J. Richter, W. Priebsch, D. Rehder, Chem. Ber. 122
(1989)1617. F. Calderazzo, G.Pampaloni, L. Rocchi, J. Stra¨hle,
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Gingl, G. Pampaloni, L. Rocchi, J. Stra¨hle, Chem. Ber. 125
(1992)1005. F. Calderazzo, G. Felten, G. Pampaloni, D. Rehder,
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