Carbon monoxide and tertiary phosphines as ligands in cyclopentadienyl derivatives of Group 4 elements in high oxidation state

Article abstract of DOI:10.1016/S0022-328X(99)00233-8

The titanocene dicarbonyl dication [TiCp₂(CO)₂][BPh₄]₂, (1) has been obtained in toluene under carbon monoxide by double protonation of TiCp₄ with [NHⁿBu₃][BPh₄] or by two-electron oxidation of TiCp₂(CO)₂ with [FeCp₂][BPh₄]. Protonation reactions on ZrCp₄ and HfCp₄ proceed with elimination of 1 mol of cyclopentadiene independently on the ammonium salt/MCp₄ molar ratio used. By this route the high electrophilic, solvent-free [ZrCp₃]⁺ cation has been isolated and characterized by IR, ¹H-NMR and elemental analysis. In the case of hafnium, the isolation has not been possible; nevertheless, in the presence of CO a rare example of a carbonyl derivative of hafnium(IV), [HfCp₃(CO)][BPh₄], has been isolated and characterized.

Full text of DOI:10.1016/S0022-328X(99)00233-8

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 593–594 (2000) 19–26
Carbon monoxide and tertiary phosphines as ligands in
cyclopentadienyl derivatives of Group 4 elements in high oxidation
state
Guido Pampaloni *, Giovanna Tripepi
Dipartimento di Chimica e Chimica Industriale, Uni6ersita` di Pisa, Via Risorgimento 35, I-56126 Pisa, Italy
Received 4 March 1999; accepted 20 April 1999
Dedicated to our ‘maestro’, Professor Fausto Calderazzo, on the occasion of his 70th birthday.
Abstract
The titanocene dicarbonyl dication [TiCp2(CO)2][BPh4]2, (1) has been obtained in toluene under carbon monoxide by double
protonation of TiCp4 with [NHnBu3][BPh4] or by two-electron oxidation of TiCp2(CO)2 with [FeCp2][BPh4]. Protonation reactions
on ZrCp4 and HfCp4 proceed with elimination of 1 mol of cyclopentadiene independently on the ammonium salt/MCp4 molar
1
ratio used. By this route the high electrophilic, solvent-free [ZrCp3]+ cation has been isolated and characterized by IR, H-NMR
and elemental analysis. In the case of hafnium, the isolation has not been possible; nevertheless, in the presence of CO a rare
example of a carbonyl derivative of hafnium(IV), [HfCp3(CO)][BPh4], has been isolated and characterized. © 2000 Elsevier Science
S.A. All rights reserved.
Keywords: Titanium; Zirconium; Hafnium; Carbonyl; Cyclopentadienyl
1. Introduction
On the other hand, electrophilic, high oxidation
state, early transition metals are capable of coordinat-
ing carbon monoxide and examples of such carbonyl
derivatives of Group 4 metals have been previously
reported [4].
In the framework of our research projects on
organometallic derivatives of early transition elements,
we recently described [5] a high yield procedure for the
preparation of MCp4, M=Ti, Zr, Hf. These species are
reactive towards proton sources so that one or two
cyclopentadienyl rings are protonated to give
MCp3(O3SCF3) or MCp2L2 (L=Cl, O3SCF3, CF3-
COO, Ph3SiO) and cyclopentadiene [5].
It is known that the highly electrophilic organyl
cations [MCp2R]+ can be obtained, inter alia, by proto-
nation of the corresponding MCp2R2 compounds with
trialkylammonium salts of weakly coordinating anions
[6]. For this reason, we decided to examine the reactiv-
ity of the tetracyclopentadienyl derivatives of Group 4
elements with [NnBu3H][BPh4] in the presence or ab-
sence of donor molecules.
Metal carbonyl chemistry is dominated by low valent
metal compounds (metals with d2–d8 electronic
configurations) in which d“p* back-bonding con-
tributes significantly to the M–CO bond. However,
metal carbonyl derivatives are known which exhibit w˜CO
values higher than that of the free CO (2143 cm−1 in
the gas phase), suggesting that those M–CO bonds are
primarily s-donor in character and that the d“p*
back-bonding is well reduced. To this regard, much
attention has been paid to late transition element spe-
cies [neutral or cationic derivatives of Pd(II), Pt(II),
Cu(I), Ag(I), Au(I) and Hg(II) have been prepared [1]].
Moreover, hexacarbonyl cations of Fe(II), Ru(II),
Os(II) and Ir(III) have been recently added [1] to the
isostructural M(I) species, M=Mn, Tc, Re, obtained
by Fischer and coworkers [2] and by Hieber and
coworkers [3] more than 30 years ago.
Dealing with carbonyl derivatives and, in particu-
lar, with the synthesis and the characterization of the
first dicationic metallocene dicarbonyl species,
* Corresponding author. Fax: +39-50-20-237.
E-mail address: pampa@dcci.unipi.it (G. Pampaloni)
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00233-8

20
G. Pampaloni, G. Tripepi / Journal of Organometallic Chemistry 593–594 (2000) 19–26
[TiCp2(CO)2][BPh4]2, this paper wishes to be a contribu-
tion [7] to a field in which Professor Fausto Calderazzo
has made many important contributions.
Carbon
monoxide
is
readily
lost
from
[TiCp2(CO)2][BPh4]2 in the presence of chloride ions:
the reactions with [PPN]Cl or [NH2Et2]2[ZrCl6] in
toluene give quantitative yields of TiCp2Cl2 and
[PPN][BPh4] or [NH2Et2][BPh4] and ZrCl4, respectively
(Eqs. (3) and (4)). Gas-volumetric controls of the reac-
tions showed the treatment of 1 with [PPN]Cl or
[NH2Et2]2[ZrCl6] in toluene at 26.8°C causes CO evolu-
tion corresponding to a CO/Ti molar ratio of 1.98 and
1.96, respectively:
2. Results and discussion
2.1. Titanium
By reaction of TiCp4 with [NnBu3H][BPh4] in toluene
under
a
CO atmosphere, the ionic species
[TiCp2(CO)2][BPh4]2+2[PPN]Cl
[TiCp2(CO)2][BPh4]2, (1), (Eq. (1)) was isolated [8].
Compound 1 has also been synthesized by oxidizing
TiCp2(CO)2 with two equivalents of [FeCp2][BPh4] in
toluene under a CO atmosphere (Eq. (2)) [9]:
“TiCp2Cl2+2[PPN][BPh4]+2CO
[TiCp2(CO)2][BPh4]2+[NH2Et2]2[ZrCl6]
“TiCp2Cl2+ZrCl4+2CO+2[NH2Et2][BPh4]
(3)
(4)
TiCp4+2[NnBu3H][BPh4]+2CO
Carbon monoxide displacement is also observed in
the reaction of 1 with NHEt2 or dmpe. In both cases,
the products consist of dicationic derivatives of ti-
tanocene (see Eq. (5)):
“[TiCp2(CO)2][BPh4]2+2CpH+2NnBu3
(1)
TiCp2(CO)2+2[FeCp2][BPh4]
“[TiCp2(CO)2][BPh4]2+2FeCp2
(2)
[TiCp2(CO)2][BPh4]2+L2“[TiCp2L2][BPh4]2+2CO
[TiCp2(CO)2][BPh4]2 is an exceedingly moisture-sensi-
tive brown solid, whose IR spectrum in the solid state
shows two strong carbonyl absorptions at 2119 and
2099 cm−1, besides the bands typical of the carbocyclic
groups (Cp− and phenyl). Compound 1 is thermally
stable and does not lose CO at room temperature (r.t.)
even under high vacuum. On the other hand, rapid
evolution of gas and sublimation of BPh3 is observed
by heating the complex in vacuo at ca. 50°C.
Instability to moisture and to basic solvents (CO is
promptly evolved on treatment of 1 with THF or
acetone) and limited solubility in hydrocarbon solvents
did not allow single crystals of 1 to be grown. Never-
(5)
L2=2NHEt2, dmpe.
[TiCp2(NHEt2)2][BPh4]2 is a brown solid, substan-
tially insoluble in all hydrocarbon solvents. Its IR
spectrum in the solid state shows the bands typical of
the carbocyclic groups (Cp− and phenyl: 3096 m, 3052
m-s, 3038 m-s, 862 m, 848 m-s, 806 s, 743 s, 710 s). A
medium intensity absorption at 3141 cm−1 has been
assigned to the N–H stretching vibration of the coordi-
nated amine; the lower wavenumber of this band with
respect to both the free or coordinated amine [15]
suggests that some H-bond interaction is involved. No-
ticeable is that, in reaction 5, NHEt2 does not react by
nucleophilic attack on the coordinated CO [16], but it
behaves as a better donor ligand with respect to CO
and displaces it from the coordination sphere of the
metal.
[TiCp2(dmpe)][BPh4]2 has been characterized by ele-
mental analysis, IR and 31P-NMR spectra. The Nujol
mull IR spectrum shows some very intense bands at 867
m, 848 m, 800 s, 748 s, 732 s, 707 vs cm−1 assigned to
the C–H bending vibrations of the aromatic rings.
[TiCp2(dmpe)][BPh4]2 is slightly soluble in toluene and
is soluble in THF, where it is stable over short periods
of time. This higher solubility with respect to
[TiCp2(CO)2][BPh4]2 and [TiCp2(NHEt2)2][BPh4]2 has to
be attributed to the presence of coordinated dmpe,
because of its increased stability in basic solvents. The
31P-NMR spectrum presents the resonance of the coor-
dinated phosphine at −9.1 ppm in toluene and at
−8.1 ppm in THF, to be compared with the peak of
free PEt3 at −18.8 ppm.
theless,
a
pseudotetrahedral structure of the
[TiCp2(CO)2]2+ cation can be proposed on the basis of
its spectral pattern in the carbonyl stretching region,
similar to that of MCp2(CO)2, M=Ti, Zr, Hf [10], and
[VCp2(CO)2]+ [11], i.e. two carbonyl stretching vibra-
tions of approximate equal intensity (A1+B1 symme-
try). The OC–M–CO angle of the [TiCp2(CO)2]2+
cation, calculated on the basis of the integrated areas of
the symmetric and asymmetric carbonyl stretching vi-
brations [12] is 86.8°, compared with 88° [13] as ob-
tained from the Nujol mull spectrum of TiCp2(CO)2
[CO=1962 and 1874 cm−1]. The decreased interligand
angle for 1 is qualitatively in agreement with the in-
creased oxidation state on going from titanium(II) to
titanium(IV).
Compound 1 is the first dicationic metallocene dicar-
bonyl derivative to be described; moreover,
[TiCp2(CO)2][BPh4]2 adds to the still restricted family of
the dicationic carbonyl compounds of recent acquisi-
tion in the literature [14].
The reactivity of the new dicarbonyl derivative 1 has
been examined.
The oxidation state IV of titanium in 1 was further
confirmed by the reaction of [TiCp2(CO)2][BPh4]2 with

G. Pampaloni, G. Tripepi / Journal of Organometallic Chemistry 593–594 (2000) 19–26
21
CoCp2 in toluene under an argon atmosphere which
gives quantitative yields of TiCp2(CO)2 and
[CoCp2][BPh4] (Eq. (6)):
the carbonylation reactions have shown that the
amount of CO absorbed corresponds to a Zr/CO molar
ratio of 1. The same product is formed when using an
[NnBu3H][BPh4]/ZrCp4 molar ratio of 2 [21]:
[TiCp2(CO)2][BPh4]2+2CoCp2
[ZrCp3][BPh4]+CO“[Cp3Zr(CO)][BPh4]
ZrCp4+[NnBu3H][BPh4]+CO
(8)
“TiCp2(CO)2+2[CoCp2][BPh4]
(6)
Noteworthy is the reaction of 1 with water. A sus-
pension of 1 in toluene promptly reacts with water to
give TiCp2(CO)2 (90%, IR analysis), biphenyl (GC-MS
analysis), suggesting that the Ti(IV)“Ti(II) reduction
is promoted by the BPh−4 anion [17]. Some benzene was
observed in solution (GC-MS analysis) probably due to
hydrolysis of the triphenylboron formed during the
reduction.
“[ZrCp3(CO)][BPh4]+CpH+NnBu3
(9)
The solid state IR spectrum of [ZrCp3(CO)][BPh4]
presents, besides the absorptions due to the aromatic
rings (3070, 3052, 841, 819, 764, 736, 707 cm−1), a
carbonyl band at 2132 cm−1 (Nujol mull) slightly
below that of the free CO (2143 cm−1 in the gas phase).
Noteworthy is the fact that the reported value of the
carbonyl stretching frequency of [ZrCp3(CO)]-
[CH3B(C6F5)3] [4j] is 2150 cm−1 (KBr), slightly above
2.2. Zirconium and hafnium
that of the free CO, 2143 cm−1
.
Whereas TiCp4 decomposes and HfCp4 does not
react in toluene or decomposes in CH2Cl2 when treated
with [NnBu3H][BPh4] (vide infra), ZrCp4 promptly and
cleanly reacts with [NnBu3H][BPh4] in CH2Cl2 to give
[ZrCp3][BPh4] (2) (Eq. (7)):
Even though dichloromethane solutions of HfCp4 do
not react with [NnBu3H][BPh4] even after prolonged
reaction times [22], in the presence of CO a fast reac-
tion
is
observed
with
precipitation
of
[HfCp3(CO)][BPh4] (Eq. (10)), the third member of the
ZrCp4+[NnBu3H][BPh4]
restricted family of d0 carbonyl species of hafnium [4d,
“[ZrCp3][BPh4]+CpH+NnBu3
(7)
4k]:
CO
HfCp4+[NnBu3H][BPh4]ꢀꢀꢀꢀꢁ[HfCp3(CO)][BPh4]
The [ZrCp3]+ cation was not previously isolated as a
pure material; nevertheless its presence in solution [as
obtained by reaction of ZrCp3Me with B(C6F5)3] has
been deduced on the basis of the reactivity of the
freshly prepared solutions with Lewis bases [4j, 18].
We have observed that when solutions of ZrCp4 in
CH2Cl2 are treated with [NnBu3H][BPh4], a yellow solid
forms which is not stable in the reaction medium [19];
in order to isolate 2 in reasonable yields, it has to be
separated quickly from the solution (see Section 3). The
lower solubility of [ZrCp3][BPh4] in CH2Cl2 with re-
spect to [ZrCp3][MeB(C6F5)3], may be the reason for
the successful isolation of 2. [ZrCp3][BPh4] is a pale-yel-
low solid extremely sensitive to moisture either in the
solid state and in solution [20]. The Nujol mull IR
spectrum shows, among the others, a weak band at
3116 cm−1 due to the C–H stretching vibration of the
Cp rings, some weak absorptions at 3094, 3077 and
3048 cm−1 attributed to the C–H stretching vibrations
of the aromatic rings and some very intense bands at
846, 810, 746, 735 and 707 cm−1 assigned to the C–H
CH Cl
2
2
+CpH+NnBu3
(10)
In the solid state IR spectrum, it presents, besides the
absorptions due to the Cp (3121 cm−1) and to the
phenyl rings (3070, 3052, 844, 799, 773, 744, 701
cm−1), a carbonyl band at 2132 cm−1. The H-NMR
1
spectrum in CD2Cl2 presents aromatic peaks at 7.6, 7.5
and 7.1 ppm assigned to the protons of the [BPh4]−
anion and a singlet at 6.3 ppm due to the Cp protons.
Also PEt3 has been used to stabilize the [MCp3]+,
M=Zr, Hf, cations. The complexes MCp4, M=Zr,
Hf, react in CH2Cl2 with [NnBu3H][BPh4] in the pres-
ence of PEt3 giving the new phosphino complexes
[MCp3(PEt3)][BPh4], M=Zr, Hf, (Eq. (11)):
PEt
3
MCp4+[NnBu3H][BPh4]ꢀꢀꢀꢀꢁ[MCp3(PEt3)][BPh4]
CH Cl
2
2
+CpH+NnBu3
(11)
M=Zr, Hf.
[ZrCp3(PEt3)][BPh4] has been synthesized also by di-
rectly treating [ZrCp3][BPh4] with an excess of PEt3 in
CH2Cl2. The compound has been characterized by ele-
mental analysis, IR and 1H and 31P-NMR spectra
[23,24]. In particular, the 31P-NMR spectrum presents
the resonance of the coordinated phosphine at 13.9
ppm, to be compared with the peak of free PEt3 at
−18.8 ppm. Under a CO atmosphere, [ZrCp3(PEt3)]-
[BPh4] does not undergo displacement of the phosphine
ligand by the CO as is observed for the bis(cyclopenta-
dienyl)diphosphine derivatives MCp2(PR3)2 [25]. The
highly electrophilic nature of zirconium in the oxidation
1
bending vibrations of the aromatic rings. The H-NMR
spectrum of 2 in CD2Cl2, registered immediately after
mixing the components, has peaks at 7.6, 7.5, 7.4, 7.1
and 6.9 ppm assigned to the protons of the [BPh4]−
anion and a singlet at 6.07 ppm due to the Cp protons.
As a confirmation of its identity, [ZrCp3][BPh4] is
quantitatively carbonylated to [Cp3Zr(CO)][BPh4] (see
Eq. (8)), which can also be obtained by direct protonol-
ysis of ZrCp4 under a CO atmosphere in CH2Cl2 or
toluene as solvent (Eq. (9)). Gas volumetric controls of

22
G. Pampaloni, G. Tripepi / Journal of Organometallic Chemistry 593–594 (2000) 19–26
state +IV can be invoked to explain its higher affi-
nity for a stronger electron-donor ligand, such as
PEt3, with respect to a better p-acceptor ligand, such as
CO.
82.6; H, 5.8; CO, 6.4. IR (Nujol and PCTFE): w˜ =3093
m, 3053 m-s, 2119 s, 2099 s, 1951 v w, 1880 v w, 1772
v w, 1591 m, 1582 m-w, 1480 m, 1430 m-s, 1376 m,
1332 m, 1263 m, 1240 m, 1185 w, 1157 w, 1108 w, 1068
w, 1031 m, 1019 m, 885 m-w, 834 s, 817 s, 773 w, 746
s, 735 s, 708 vs, 675 m, 639 w, 614 w, 604 m cm−1. The
same product is formed when using an [NnBu3H][BPh4]/
TiCp4 molar ratio of 1.
3. Experimental
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 recorded on an FT-1725X instru-
ment, on solutions or Nujol or polychlorotrifl-
uoroethylene (PCTFE) mulls prepared under rigorous
exclusion of moisture and air.
3.1.2. B. From TiCp2(CO)2 and [FeCp2][BPh4]
A suspension of [FeCp2][BPh4] (2.54 g, 5.0 mmol) in
toluene (50 ml) was saturated with CO at atmospheric
pressure, and solid TiCp2(CO)2 (0.59 g, 2.5 mmol) was
added. After 72 h stirring at r.t., a suspension of a
brown solid in an orange solution was obtained. An IR
spectrum of the solution showed no absorptions due to
TiCp2(CO)2. The suspension was filtered, and the
brown solid was washed with toluene until almost
colorless washings (5×5 ml). The solid was then dried
in vacuo at r.t. and identified as [TiCp2(CO)2][BPh4]2
(0.17 g, 78% yield). Anal. Found: C, 82.5; H, 6.0; CO,
6.3. Calc. for [TiCp2(CO)2][BPh4]2 (C60H50B2O2Ti): C,
82.6; H, 5.8; CO, 6.4. IR (Nujol and PCTFE): w˜ =3093
m, 3053 m-s, 2119 s, 2099 s, 1951 v w, 1880 v w, 1772
v w, 1591 m, 1582 m-w, 1480 m, 1430 m-s, 1376 m,
1332 m, 1263 m, 1240 m, 1185 w, 1157 w, 1108 w, 1068
w, 1031 m, 1019 m, 885 m-w, 834 s, 817 s, 773 w, 746
s, 735 s, 708 vs, 675 m, 639 w, 614 w, 604 m cm−1. The
orange solution was evaporated to dryness under re-
duced pressure at r.t., and the residue afforded FeCp2
(0.66 g, 71% yield) after sublimation (0.05 mmHg,
40°C).
1H-(200 MHz, TMS as reference) and 31P-NMR (81
MHz, H3PO4 in H2O as reference) spectra were mea-
sured on a Varian Gemini 200BB instrument.
PEt3 (Argus Chemicals) and dmpe (Aldrich) were
commercially available and were used with no further
purification. PPNCl (Strem) was commercially available
and was freed from oxygen and moisture before use by
recrystallization from H2O followed by drying in vacuo.
The following reagents were prepared according to
literature procedures: MCp4, M=Ti, Zr, Hf [5],
TiCp2(CO)2 [26], [NH2Et2]2[ZrCl6] [27], [FeCp2][BPh4]
[28], CoCp2 [29].
[NnBu3H][BPh4] was prepared from equimolar
amounts of [NnBu3H][Cl] and Na[BPh4] in H2O. The
resulting suspension was filtered and the colorless solid
was dried over P4O10 in vacuo for 24 h and then stored
in flame-sealed vials. IR (Nujol and PCTFE): w˜ =3563
s, 3506 s, 3108 m, 3050 s, 3034 s, 2962 vs, 2931 s, 2873
m, 1945 w, 1884 w, 1820 w, 1767 w, 1600 m-w, 1580 m,
1469 s, 1426 m-s, 1403 m, 1384 m-s, 1305 w, 1267 m,
1183 m, 1153 m, 1096 w, 1067 m, 1033 m, 973 w, 924
m-w, 861 w, 848 m, 797 w, 745 vs, 734 vs, 711 vs, 626
3.2. Reaction of [TiCp2(CO)2][BPh4]2 with [PPN]Cl
A suspension of [PPN]Cl (0.59 g, 1.0 mmol) in
toluene
(25
ml)
was
treated
with
solid
[TiCp2(CO)2][BPh4]2 (0.46 g, 0.5 mmol). From the ini-
tially brown suspension, a colorless solid precipitated
out and the solution turned red–orange after 15 h
stirring at r.t. The suspension was filtered, the solid was
washed with toluene (6×3 ml), dried in vacuo and
identified as [PPN][BPh4] (0.60 g, 70% yield) from its IR
spectrum. The solution was dried in vacuo at r.t. af-
fording 0.11 g (88% yield) of TiCp2Cl2, identified by IR
1
w, 615 m, 606 m-s cm−1. H-NMR (CD2Cl2, 25°C):
l=7.5 (m, 4H, ar), 7.1 (t, 8H, ar), 6.9 (t, 8H, ar), 3.8
(s, 1H, NH), 2.2 (m, 6H, CH2), 1.7 (m, 12H, CH2), 0.9
(t, 9H, CH3) ppm.
3.1. Synthesis of [TiCp2(CO)2][BPh4]2 (1)
3.1.1. A. From TiCp4 and [NnBu3H][BPh4] under a CO
atmosphere
and H-NMR spectra. A gas-volumetric control of the
1
reaction
showed
that
the
treatment
of
A suspension of [NnBu3H][BPh4] (0.35 g, 0.7 mmol)
in toluene (10 ml) was saturated with CO at atmo-
spheric pressure and TiCp4 (0.10 g, 0.32 mmol) was
then added. After 6 h stirring at r.t., a suspension of a
brown solid in an almost colorless solution was ob-
tained. The suspension was filtered and the solid was
dried in vacuo and identified as [TiCp2(CO)2][BPh4]2,
(0.22 g, 79% yield). Anal. Found: C, 82.5; H, 6.0; CO,
6.3. Calc. for [TiCp2(CO)2][BPh4]2 (C60H50B2O2Ti): C,
[TiCp2(CO)2][BPh4]2 with [PPN]Cl in toluene at 26.8°C
causes CO evolution corresponding to a CO/Ti molar
ratio of 1.98.
3.3. Reaction of [TiCp2(CO)2][BPh4]2 with
[NH2Et2]2[ZrCl6]: gas-6olumetric study
A suspension of [NH2Et2]2[ZrCl6] (0.21 g, 0.46 mmol)
in toluene (25 ml) was saturated with CO, thermostated

G. Pampaloni, G. Tripepi / Journal of Organometallic Chemistry 593–594 (2000) 19–26
23
at 20.9°C, connected to a gas-volumetric apparatus and
then contacted with solid [TiCp2(CO)2][BPh4]2 (0.41 g,
0.47 mmol) contained in a sealed glass ampoule. Evolu-
tion of CO corresponding to a CO/Ti molar ratio of
1.96 was observed. The resulting suspension was
filtered. The solvent was removed in vacuo at r.t. and
the solid washed with heptane (2×10 ml), dried in
vacuo and identified as TiCp2Cl2 (0.06 g, 51% yield) by
ml), dried in vacuo, and identified as [CoCp2][BPh4]
(0.32 g, 69% yield) from its IR spectrum.
3.7. Reaction of [TiCp2(CO)2][BPh4]2 with H2O
Degassed H2O (0.015 ml, 0.83 mmol) was added to a
suspension of [TiCp2(CO)2][BPh4]2 (0.38 g, 0.43 mmol)
in toluene (10 ml). An IR spectrum of the solution
showed the presence of TiCp2(CO)2 (90% yield calcu-
lated on the basis of the absorbance of the carbonyl
stretching vibration at 1885 cm−1; m1885=2200 M−1
cm−1). A gas-chromatographic analysis of the solution
showed the presence of C6H6 and diphenyl in solution.
1
elemental analysis (Ti, Cl), IR and H-NMR spectra.
3.4. Reaction of [TiCp2(CO)2][BPh4]2 with NHEt2:
preparation of [TiCp2(NHEt2)2][BPh4]2
To a suspension of [TiCp2(CO)2][BPh4]2 (0.43 g, 0.48
mmol) in toluene (25 ml) NHEt2 (0.3 ml, 2.9 mmol) was
added. Evolution of gas was observed. After ca. 16 h
stirring at r.t., the suspension of a red–brown solid in a
pale-orange solution was obtained. After filtration, the
solid was washed with toluene (5 ml) and dried in
vacuo, obtaining [TiCp2(NHEt2)2][BPh4]2·C7H8 as a
red–brown solid (0.32 g, 63% yield). Anal. Found: C,
83.5; H, 11.1; N, 2.5. Calc. for C73H80B2N2Ti: C, 83.1;
H, 7.6; N, 2.5. IR (Nujol and PCTFE): w˜ =3141 m
(wNH), 3096 m, 3052 m-s, 3038 m-s, 1954 v w, 1881 v w,
1816 v w, 1776 v w,1579 m-w, 1565 m-w, 1478 m-s,
1428 m-s, 1413 m, 1308 m-w, 1262 m, 1184 w, 1155 w,
1148 w, 1068 w, 1031 m, 862 m, 848 m-s, 806 s, 743 s,
3.8. Reaction of ZrCp4 with [NnBu3H][BPh4]: synthesis
of [ZrCp3][BPh4] (2)
A solution of [NnBu3H][BPh4] (1.05 g, 2.04 mmol) in
CH2Cl2 (50 ml) was treated with ZrCp4 (0.72 g, 2.05
mmol). The precipitation of a yellow solid was ob-
served after some minutes from the mixing of reagents.
After an additional 30 min stirring at r.t., the resulting
yellow suspension was filtered, the solid washed with
heptane (5 ml), dried in vacuo and identified as
[ZrCp3][BPh4] (0.63 g, 51% yield). IR (Nujol and
PCTFE): w˜ =3116 m, 3094 m, 3077 m, 3048 m, 1592
m-w, 1580 m-w, 1478 m-s, 1457 m-w, 1427 s, 1368 m-s,
1313 w, 1266 m, 1242 m, 1183 w, 1147 w, 1133 w, 1067
m, 1030 m-s, 1010 m-s, 932 w, 888 w, 846 s, 810 vs, 746
710 s, 662 m cm−1
.
3.5. Reaction of [TiCp2(CO)2][BPh4]2 with dmpe:
preparation of [TiCp2(dmpe)][BPh4]2
1
s, 735 s, 707 s, 644 m, 626 w, 606 m cm−1. H-NMR
(CD2Cl2, 25°C): l=7.6 (t, 4H, ar), 7.5 (m, 6H, ar), 7.4
(s, 6H, ar), 7.1 (t, 2H, ar), 6.9 (t, 2H, ar), 6.07 (s, 15H,
Cp) ppm.
To a suspension of [TiCp2(CO)2][BPh4]2 (0.36 g, 0.41
mmol) in toluene (10 ml), dmpe (0.07 ml, 0.42 mmol)
was added. After ca. 24 h stirring at r.t., the suspension
of a brown solid in a pale-orange solution was ob-
tained. After filtration, the solid was washed with
toluene (5 ml) and dried in vacuo, obtaining
[TiCp2(dmpe)][BPh4]2 as a brown solid (0.25 g, 63%
yield). Anal. Found: C, 80.1; H, 7.1; Ti, 4.8. Calc. for
[TiCp2(dmpe)][BPh4]2 (C64H66B2P2Ti): C, 79.5; H, 6.9;
Ti, 4.9. IR (Nujol): w˜ =3043 m, 1579 w, 1302 m, 1286
m, 1262 m, 1194 m, 1182 w, 1150 w, 1030 m, 1071 w,
1030 m, 1019 m, 939 w, 903 w, 867 m, 848 m, 800 s, 748
3.9. Reaction of MCp4, M=Zr, Hf, with
[NnBu3H][BPh4] under CO
3.9.1. A. In CH2Cl2
M=Zr: synthesis of [ZrCp3(CO)][BPh4]. A solution
of [NnBu3H][BPh4] (0.41 g, 0.8 mmol) in CH2Cl2 (25
ml) was saturated with CO at atmospheric pressure.
Then, ZrCp4 (0.28 g, 0.8 mmol) was added. The precip-
itation of a yellow solid was observed after some min-
utes from the mixing of the reagents. After an
additional 30 min stirring at r.t., the resulting yellow
suspension was filtered, the solid dried in vacuo and
identified as [ZrCp3(CO)][BPh4], (0.16 g, 31% yield). IR
(Nujol and PCTFE): w˜ =3120 m-w, 3070 m, 3052 m-s,
2132 s, 1951 w, 1884 w, 1817 w, 1592 m-w, 1581 m-w,
1479 m, 1447 m-w, 1428 s, 1370 m, 1309 w, 1266 m,
1240 m, 1184 w, 1154 w, 1127 w, 1068 w, 1023 m-s, 976
w, 841 s, 819 vs, 764 s, 736 vs, 707 vs, 675 m, 643 w,
s, 732 s, 707 vs cm−1 31P-NMR (THF): −8.1 ppm.
.
3.6. Reaction of [TiCp2(CO)2][BPh4]2 with CoCp2
A suspension of [TiCp2(CO)2][BPh4]2 (0.38 g, 0.43
mmol) in toluene (10 ml) was treated with solid CoCp2
(0.17 g, 0.90 mmol). After 1 h stirring at r.t., an IR
spectrum of the solution showed the presence of
TiCp2(CO)2 (98% yield, calculated on the basis of the
intensity of the carbonyl stretching vibration at 1885
cm−1, m1885=2200 M−1 cm−1). The suspension was
filtered and the yellow solid was washed with toluene (3
1
627 w, 605 m cm−1. H-NMR (CD2Cl2, 25°C): l=7.6
(m, 8H, ar), 7.5 (m, 8H, ar), 7.1 (t, 4H, ar), 6.4 (s, 15H,
Cp) ppm.

24
G. Pampaloni, G. Tripepi / Journal of Organometallic Chemistry 593–594 (2000) 19–26
M=Hf: synthesis of [HfCp3(CO)][BPh4]. A solution
(0.07 ml, 0.47 mmol) in CH2Cl2 (10 ml), ZrCp4 (0.17 g,
0.48 mmol) was added. After 1 h stirring at r.t., a
31P-NMR of the solution (to which some C6D6 was
added) showed a peak at 11.8 ppm. The remaining yellow
solution was evaporated to dryness under reduced pres-
sure at r.t. and heptane was added (5 ml). The suspension
was filtered and the yellow solid was dried in vacuo
affording [ZrCp3(PEt3)][BPh4] (0.30 g, 86%). Anal.
Found: C, 72.4; H, 7.4. Calc. for [ZrCp3(PEt3)][BPh4]
(C45H50BPZr): C, 74.7; H, 7.0. IR (Nujol and PCTFE):
w˜ =3112 m-w, 3051 m, 3012 m-w, 1945 w, 1878 w, 1752
w, 1580 m-w, 1561 w, 1479 m, 1456 m, 1438 s, 1426 m,
1377 m, 1307 w, 1262 m, 1183 w, 1149 w, 1134 w, 1097
w, 1068 m, 1034 m-s, 1011 m, 919 w, 848 s, 813 vs, 735
vs, 707 vs, 626 w, 608 m cm−1. 1H-NMR (CD2Cl2, 25°C):
l=7.4 (m, 8H, ar), 7.1 (t, 8H, ar), 6.9 (t, 4H, ar), 5.8
(s, 15H, Cp), 2.1 (quintet, 6H, CH2), 1.4 (d t, 9H, CH3)
ppm. 31P-NMR (CD2Cl2, 25°C): l=13.9 (s) ppm. No
displacement of the phosphine ligand was observed by
treating [ZrCp3(PEt3)][BPh4] with CO at atmospheric
pressure in toluene.
of [NnBu3H][BPh4] (0.26 g, 0.5 mmol) in CH2Cl2 (10 ml)
was saturated with CO. Then HfCp4 (0.22 g, 0.5 mmol)
was added. After 10 min stirring at r.t., the resulting
yellow suspension was filtered, the solid was washed with
heptane (3 ml), dried in vacuo and identified as
[HfCp3(CO)][BPh4] (0.14 g, 39% yield). IR (Nujol and
PCTFE): w˜ =3121 m-w, 3070 m, 3052 m-s, 2126 s, 1591
m, 1581 m-w, 1479 m, 1430 s, 1372 m, 1315 w, 1287 m,
1262 m, 1240 s, 1185 w, 1155 w, 1127 w, 1069 w, 1017
m-s, 885 m, 844 s, 799 vs, 773 s, 763 s, 744 vs, 701 vs,
1
676 m, 639 w, 626 w, 604 m cm−1. H-NMR (CD2Cl2,
25°C): l=7.6 (m, 8H, ar), 7.5 (m, 8H, ar), 7.1 (t, 4H,
ar), 6.3 (s, 15H, Cp) ppm.
3.9.2. B. In toluene
M=Zr. (i) Synthesis of [ZrCp3(CO)][BPh4]. A suspen-
sion of [NnBu3H][BPh4] (0.58 g, 1.1 mmol) in toluene (25
ml) was saturated with CO at atmospheric pressure. Then
ZrCp4 (0.40 g, 1.1 mmol) was added. After 10 h stirring
at r.t., the yellow suspension was filtered, the solid was
washed with heptane (5 ml), dried in vacuo and identified
as [ZrCp3(CO)][BPh4] (0.62 g, 89% yield). IR (Nujol and
PCTFE): w˜ =3120 m-w, 3070 m, 3052 m-s, 2132 s, 1951
w, 1884 w, 1817 w, 1592 m-w, 1581 m-w, 1479 m, 1447
m-w, 1428 s, 1370 m, 1309 w, 1266 m, 1240 m, 1184 w,
1154 w, 1127 w, 1068 w, 1023 m-s, 976 w, 841 s, 819 vs,
M=Hf. To a solution of [NnBu3H][BPh4] (0.19 g, 0.37
mmol) and PEt3 (0.05 ml, 0.34 mmol) in CH2Cl2 (10 ml),
HfCp4 (0.16 g, 0.36 mmol) was added. After 3 h stirring
at r.t., a 31P-NMR spectrum of the solution presented a
peak at −18.8 ppm (non-coordinated PEt3) and a peak
at 8.44 ppm. The remaining yellow solution was evapo-
rated to dryness under reduced pressure at r.t. and
heptane was added (2 ml). The suspension was filtered
and the yellow solid (0.30 g), dried in vacuo, was
spectroscopically identified as a mixture of HfCp4,
[NnBu3H][BPh4] and [HfCp3(PEt3)][BPh4].
764 s, 736 vs, 707 vs, 675 m, 643 w, 627 w, 605 m cm−1
.
1H-NMR (CD2Cl2, 25°C): l=7.6 (m, 8H, ar), 7.4 (t, 8H,
ar), 7.1 (t, 4H, ar), 6.4 (s, 15H, Cp) ppm. The same
product forms even if the reaction is performed with an
[NnBu3H][BPh4]/ZrCp4 molar ratio of 2.
(ii) Gas-volumetric study.
A
suspension of
[NnBu3H][BPh4] (0.25 g, 0.5 mmol) in toluene (10 ml) was
saturated with CO at atmospheric pressure, thermostated
at 20.7°C and connected to a gas-volumetric apparatus.
Then, ZrCp4 (0.16 g, 0.45 mmol), in a thin-walled glass
ampoule, was added. The reaction was over in about 2
h: 4×10−4 mol of CO were absorbed corresponding to
a CO/ZrCp4 molar ratio of 0.87.
3.11.2. B. In toluene
M=Zr. A suspension of [NnBu3H][BPh4] (0.03 g, 0.06
mmol) and PEt3 (0.01 ml, 0.07 mmol) in toluene (5 ml)
was treated with ZrCp4 (0.02 g, 0.06 mmol). After 3 h
stirring at r.t., the yellow suspension was evaporated to
dryness under reduced pressure at r.t. and the yellow
1
solid was spectroscopically (IR, H-NMR) identified as
[ZrCp3(PEt3)][BPh4].
3.10. Reaction of [ZrCp3][BPh4] with CO: synthesis of
[ZrCp3(CO)][BPh4]
3.12. Reaction of [ZrCp3][BPh4] with PEt3: synthesis of
[ZrCp3(PEt3)][BPh4]
A suspension of [ZrCp3][BPh4] (0.04 g, 0.07 mmol) in
CH2Cl2 (5 ml) was saturated with CO. After 2 h stirring
at r.t., the yellow suspension was evaporated to dryness
under reduced pressure at r.t. and the yellow solid
identified as [ZrCp3(CO)][BPh4] by IR spectroscopy.
3.12.1. A. In CH2Cl2
To a suspension of [ZrCp3][BPh4] (0.15 g, 0.25 mmol)
in CH2Cl2 (5 ml), PEt3 (0.04 ml, 0.27 mmol) was added.
After 3 h stirring at r.t., a 31P-NMR of the solution
showed absence of the free phosphine and complete
conversion of the reagents to [ZrCp3(PEt3)][BPh4].
3.11. Reaction of MCp4, M=Zr, Hf, with
[NnBu3H][BPh4] and PEt3
3.12.2. B. In toluene
3.11.1. A. In CH2Cl2
PEt3 (0.08 ml, 0.54 mmol) was added to a suspension
of [ZrCp3][BPh4] (0.35 g, 0.58 mmol) in toluene (10 ml).
After 3 h stirring at r.t., a 31P-NMR of the solution
M=Zr: synthesis of [ZrCp3(PEt3)][BPh4]. To a solu-
tion of [NnBu3H][BPh4] (0.24 g, 0.46 mmol) and PEt3

G. Pampaloni, G. Tripepi / Journal of Organometallic Chemistry 593–594 (2000) 19–26
25
[2] (a) E.O. Fischer, K. Fichtel, Chem. Ber. 94 (1961) 1200. (b) E.O.
presented a peak at −18.8 ppm due to non-coordi-
nated PEt3. The remaining yellow suspension was evap-
orated to dryness under reduced pressure at r.t. and the
8
Fischer, K. Fichtel, K. Ofele, Chem. Ber. 95 (1962) 249.
[3] (a) W. Hieber, F. Lux, C. Herget, Z. Naturforsch. 20B (1965)
1159. (b) W. Hieber, Th. Kruck, Angew. Chem. 73 (1961) 580.
(c) W. Hieber, Th. Kruck, Z. Naturforsch. 16B (1961) 709.
[4] (a) [Ti2Cp4(TCNE)(CO)2][TCNE]: B. Demerseman, M.
Pankowski, G. Bouquet, M. Bigorgne, J. Organomet. Chem. 117
(1976) C10. (b) TiCl3(CO)(PEt3): T.A. Ballintine, C.D. Schmul-
bach, J. Organomet. Chem. 164 (1979) 381. (c)
Ti(CH2Ph)4(CO)2: A. Ro¨der, K.-H. Thiele, G. Pa´lyi, L. Marko´,
J. Organomet. Chem. 199 (1980) C31. (d) MCp*2 (H)2(CO), M=
Zr, Hf: J.A. Marsella, C.J. Curtis, J.E. Bercaw, K.G. Caulton, J.
Am. Chem. Soc. 102 (1980) 7244. (e) [ZrCp2(CH{Me}{6-
ethylpyrid-2-yl})(CO)]BPh4: A.S. Guram, D.C. Swenson, R.F.
yellow solid was identified as
a
mixture of
[ZrCp3][BPh4] and [ZrCp3(PEt3)][BPh4] (1H and 31P-
NMR spectra).
4. Conclusions
This paper has shown that the tetracyclopentadienyl
derivatives of Group 4 elements are useful starting
materials for the preparation of cyclopentadienyl
cations of titanium(IV), zirconium(IV) and hafniu-
m(IV). In particular, the unsolvated species
[ZrCp3][BPh4] has been isolated from the reaction of
ZrCp4 and [NnBu3H][BPh4] in CH2Cl2. The nature of
the counterion appears to be decisive in the isolation of
Jordan, J. Am. Chem. Soc. 114 (1992) 8991. (f) [ZrCp*(p2-
2
COCH3)(CO)][CH3B(C6F5)3]: Z. Guo, D.C. Swenson, A.S.
Guram, R.F. Jordan, Organometallics 13 (1994) 766. (g)
[ZrCp2*
(p3-C H )(CO)]BPh : D.M. Antonelli, E.B. Tjaden, J.M.
3
5
4
Stryker, Organometallics 13 (1994) 763. (h) ZrCp*(p2-E2)(CO),
2
E=S, Se, Te: W.A. Howard, G. Perkin, A.L. Rheingold, Poly-
hedron 14 (1995) 25. (i) ZrCp*Se(CO): W.A. Howard, T.M.
2
Trnka, G. Perkin, Organometallics 14 (1995) 4037. (j)
[ZrCp3(CO)][CH3B(C6F5)3]: T. Brackemeyer, G. Erker, R.
Fro¨hlich, Organometallics 16 (1997) 531. (k) HfCp*{h5-
C4H4BN(CHMe2)2}(h3-C3H5)(CO): A. Pastor, A.F. Kiely, L.M.
Henling, M.W. Day, J.E. Bercaw, J. Organomet. Chem. 528
(1997) 65. (l) [TiCp2(CO)2][AlCl4]: R.T. Carlin, J. Fuller, Inorg.
Chim. Acta 255 (1997) 189.
the unsolvated species: as
a
matter of fact,
[ZrCp3][BPh4] can be isolated, whereas [ZrCp3]-
[CH3B(C6F5)3] decomposes during the isolation proce-
dure [4j].
We have demonstrated that single (M=Zr, Hf) or
double (M=Ti) protonation of the tetracyclopentadi-
enyl derivatives may occur; the size of the central atom
and the nature of the cyclopentadienyl ligand determin-
ing the nature of the product [29]. In the presence of
donor ligands, cationic adducts of formula
[MCp3(L)][BPh4] (M=Zr, L=CO, PEt3; M=Hf, L=
CO) or [TiCp2(CO)2][BPh4]2 can be prepared. The latter
can also be obtained by a two-electron oxidation of
TiCp2(CO)2 with [FeCp2][BPh4]. Noteworthy are the
titanium and the hafnium derivatives, due to the fact
that [TiCp2(CO)2][BPh4]2 represents the first example of
[5] F. Calderazzo, U. Englert, G. Pampaloni, G. Tripepi, J.
Organomet. Chem. 555 (1997) 49.
[6] (a) W. Kaminsky, M. Arndt, Adv. Polymer Sci. 127 (1997) 144.
(b) M. Bochmann, J. Chem. Soc. Dalton Trans. (1996) 255. (c)
H.H. Brintzinger, D. Fischer, R. Mu¨lhaupt, B. Rieger, R.M.
Waymouth, Angew. Chem. Int. Ed. Engl. 34 (1995) 1143. (d)
P.C. Mo¨hring, N.J. Coville, J. Organomet. Chem. 479 (1994) 1,
and references therein.
[7] Part of this work has been communicated in a preliminary form:
F. Calderazzo, G. Pampaloni, G. Tripepi, Organometallics 16
(1997) 4943.
[8] The same product is formed in low yield when using
a
[NnBu3H][BPh4]/TiCp4 molar ratio of 1.
a
metallocene dicarbonyl dication and [HfCp3-
[9] When the same reaction was conducted starting from
ZrCp2(CO)2, decomposition of the carbonyl substrate was
observed.
[10] D.J. Sikora, K.J. Moriarty, M.D. Rausch, Inorg. Synth. 24
(1986) 147.
[11] F. Calderazzo, S. Bacciarelli, Inorg. Chem. 2 (1963) 721.
[12] (a) W. Beck, A. Melnikoff, R. Stahl, Chem. Ber. 99 (1966) 3721.
(b) A.R. Manning, J. Chem. Soc. A (1967) 1984.
(CO)][BPh4] is a new member of the class of the car-
bonyl derivatives of hafnium(IV) which, at the best
of our knowledge, consists of just two members [4d,
4k].
[13] An OC–Ti–CO angle of 87.6(6)° is reported as obtained from
the X-ray crystal structure investigation on TiCp2(CO)2: J.L.
Atwood, K.E. Stone, H.G. Alt, D.C. Hrncir, M.D. Rausch, J.
Organomet. Chem. 132 (1977) 367.
Acknowledgements
The authors wish to thank the Consiglio Nazionale
delle Ricerche (C.N.R., Roma), Progetto Strategico
Metodologie Innovative for financial support and the
Scuola Normale Superiore, Pisa, for a fellowship to
G.T.
[14] (a) [Hg(CO)2]2+: M. Bodenbinder, G. Balzer-Jo¨llenbeck, H.
Willner, R.J. Batchelor, F.W.B. Einstein, C. Wang, F. Aubke,
Inorg. Chem. 35 (1996) 82. (b) [M(CO)4]2+, M=Pd, Pt: G.
Hwang, C. Wang, F. Aubke, H. Willner, M. Bodenbinder, Can.
J. Chem. 71 (1993) 1532. (c) M=Pt: G. Hwang, M. Boden-
binder, H. Willner, F. Aubke, Inorg. Chem. 32 (1993) 4667. (d)
[M(CO)6]2+, M=Fe: B. Bley, H. Willner, F. Aubke, Inorg.
Chem. 36 (1997) 158. (e) M=Ru, Os: C. Wang, B. Bley, G.
Balzer-Jo¨llenbeck, A.R. Lewis, S.C. Siu, H. Willner, F. Aubke, J.
Chem. Soc. Chem. Commun. (1995) 2071. (f) [Ir(CO6]3+: C.
Bach, H. Willner, C. Wang, S.J. Rettig, J. Trotter, F. Aubke,
Angew. Chem. Int. Ed. Engl. 35 (1996) 1974.
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G. Pampaloni, G. Tripepi / Journal of Organometallic Chemistry 593–594 (2000) 19–26
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[22] No reaction is observed in toluene: the starting materials are
recovered unchanged after 24 h of stirring at r.t.
[23] Although [HfCp3(PEt3)][BPh4] has not been isolated in a pure
state due to incomplete reaction, the solid isolated shows a
31P-NMR peak at 8.44 ppm that we assign to the resonance of
the coordinated PEt3. Although reaction (11) is incomplete for
M=Hf in CH2Cl2 and no reaction is observed in toluene (the
zirconium derivative reacts partially in this medium) the com-
pound [HfCp3(PEt3)][BPh4], identified via 31P-NMR, represents
a rare example of phosphino derivative of hafnium(IV): Ref.
[24].
[24] M.D. Fryzuk, T.S. Haddad, D.J. Berg, Coord. Chem. Rev. 99
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Chem. Ber./Recueil 130 (1997) 899.
[19] The yellow solid dissolves slowly to give
a yellow–orange
solution which does not afford 2 upon evaporation of the
solvent.
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[20] No reliable elemental analyses were obtained for this material.
[21] Zirconocene dications of formula [Zr(h5-C5H5)2L2]2+ or [Zr(h5-
C5H4–CMe2–R)2]2+, R=p-C6H4Me, PPh2 have been reported:
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.