Internally phosphine-stabilized zirconocene cations employing substituted ((diarylphosphino)methyl)cyclopentadienyl ligand systems

Article abstract of DOI:10.1021/om970573t

The dimethylzirconocene complex [(Cp-CMe₂-PAr₂)₂ZrMe₂], 2a (Ar = p-tolyl), was treated with 1 molar equiv of B(C₆F₅)₃ to yield the salt [(Cp-CMe₂-PAr₂)₂ZrMe₊MeB(C ₆F₅)₃^-], 3a. The X-ray crystal structure analysis of 3a shows that both -PAr₂ units are intramolecularly coordinated to zirconium in a close to C₂-symmetric arrangement with the [Zr]-CH₃ group placed in the central position in the bent metallocene σ-ligand plane. Treatment of 2a with 2 equiv of B(C₆F₅)₃ generates the highly reactive dication system [(Cp-CMe₂-PAr₂)₂Zr²⁺] (4 with two MeB(C₆F₅)₃^- anions). The highly electrophilic cation 4 abstracts chloride from, e.g., dichloromethane solvent to yield [(Cp-CMe₂-PAr₂)₂Zr-Cl⁺] (5, with MeB(C₆F₅)₃^- anion). The same cation (5′, with ClB(C₆F₅)₃^- anion) was obtained from the reaction Of[(Cp-CMe₂-PAr₂)₂ZrCl₂] (1Ia) with B(C₆F₅)₃. The C₂-symmetric, internally -PAr₂-stabilized dication adds acetonitrile or 2,6-dimethylphenyl isocyanide to give the respective C₂-symmetric donorligand adducts in which the -PAr₂ coordination to zirconium is retained. The complexes 3a (ΔG?_enant (300 K) = 14.0 ± 0.5 kcal/mol) and 5 (ΔG?_enant (360 K) = 17.5 ± 0.5 kcal/mol) show dynamic NMR spectra due to an intramolecular enantiomerization process proceeding with a rate-determining cleavage of the Zr-P linkages. Complex 5 was also characterized by an X-ray crystal structure analysis.

Full text of DOI:10.1021/om970573t

Organometallics 1997, 16, 5449-5456
5449
In ter n a lly P h osp h in e-Sta bilized Zir con ocen e Ca tion s
Em p loyin g Su bstitu ted
((Dia r ylp h osp h in o)m eth yl)cyclop en ta d ien yl Liga n d
System s
Boris E. Bosch, Gerhard Erker,* Roland Fro¨hlich, and Oliver Meyer
Organisch-Chemisches Institut der Universita¨t Mu¨nster, Corrensstrasse 40,
D-48149 Mu¨nster, Germany
Received J uly 8, 1997X
The dimethylzirconocene complex [(Cp-CMe2-PAr2)2ZrMe2], 2a (Ar ) p-tolyl), was treated
with 1 molar equiv of B(C6F5)3 to yield the salt [(Cp-CMe2-PAr2)2ZrMe+MeB(C6F5)3 ], 3a .
-
The X-ray crystal structure analysis of 3a shows that both -PAr2 units are intramolecularly
coordinated to zirconium in a close to C2-symmetric arrangement with the [Zr]-CH3 group
placed in the central position in the bent metallocene σ-ligand plane. Treatment of 2a with
2 equiv of B(C6F5)3 generates the highly reactive dication system [(Cp-CMe2-PAr2)2Zr2+
]
(4 with two MeB(C6F5)3- anions). The highly electrophilic cation 4 abstracts chloride from,
e.g., dichloromethane solvent to yield [(Cp-CMe2-PAr2)2Zr-Cl+] (5, with MeB(C6F5)3- anion).
The same cation (5′, with ClB(C6F5)3- anion) was obtained from the reaction of [(Cp-CMe2-
PAr2)2ZrCl2] (1a ) with B(C6F5)3. The C2-symmetric, internally -PAr2-stabilized dication adds
acetonitrile or 2,6-dimethylphenyl isocyanide to give the respective C2-symmetric donor-
ligand adducts in which the -PAr2 coordination to zirconium is retained. The complexes
3a (∆Gq
(300 K) ) 14.0 ( 0.5 kcal/mol) and 5 (∆Gq
(360 K) ) 17.5 ( 0.5 kcal/mol)
enant
enant
show dynamic NMR spectra due to an intramolecular enantiomerization process proceeding
with a rate-determining cleavage of the Zr-P linkages. Complex 5 was also characterized
by an X-ray crystal structure analysis.
In tr od u ction
locene cation serves as an activating organometallic
Lewis acid in these adducts that may lead to novel
stoichiometric reactions.5
Donor ligands used to stabilize the Cp2ZrR+ moiety
in these adduct systems are often nitriles or cyclic
ethers.2,3 Phosphorus-containing systems are quite rare
in this metallocene cation chemistry.6 After we had
gained some experience with internal amine stabiliza-
tion of alkylzirconocene cation-type systems, making use
of substituted ((dimethylamino)methyl)cyclopentadienyl
The chemistry of zirconocene cation systems has
become of great interest recently. The donor-ligand-free
Cp2ZrR+ species and especially the olefin complexes of
the related modified ansa-metallocene cations probably
serve as essential intermediates in homogeneous met-
allocene Ziegler catalysis.1 Also, the donor-ligand-
+
stabilized systems Cp2ZrR(L)+ or Cp2ZrR(L)2 are of
importance.2 Early examples have paved the way
toward an understanding of group 4 metallocene cation
chemistry related to homogeneous Ziegler catalysis,3
and postulated single steps of catalytic cycles could be
studied in detail using such stabilized metallocene
cations as suitable model systems.4 Also, the metal-
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X Abstract published in Advance ACS Abstracts, November 1, 1997.
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S0276-7333(97)00573-6 CCC: $14.00 © 1997 American Chemical Society

5450 Organometallics, Vol. 16, No. 25, 1997
Bosch et al.
Sch em e 1
F igu r e 1. View of the molecular geometry of 2b. Selected
bond lengths (Å) and angles (deg): Zr-C8 2.277(3), Zr-
CCp 2.544(3), C70-C1 1.524(4), C1-C2 1.542(4), C1-C3
1.521(4), C1-P4 1.904(3), P4-C50 1.840(3), P4-C60 1.844-
(3); C8-Zr-C8* 92.2(2), C2-C1-C3 109.9(3), C2-C1-P4
103.2(2), C2-C1-C70 111.2(2), C3-C1-P4 114.6(2), C3-
C1-C70 111.5(3), P4-C1-C70 106.0(2), C1-P4-C50
107.85(14), C1-P4-C60 102.38(13), C50-P4-C60 100.84-
(13).
ligand systems,7 we developed synthetic entries into
related ((diarylphosphino)methyl)cyclopentadienyl-de-
rived zirconocenes suited for conversion into the respec-
tive internally phosphine-stabilized zirconocene cation
systems.8 This has led to the development of straight-
forward synthetic routes to novel mono- and dicationic
phosphine-stabilized zirconocene systems, some of which
constitute very interesting new organometallic Lewis
acid systems.9 This synthetic development along with
a chemical and structural characterization of a variety
of key examples is described in this article.
Resu lts a n d Discu ssion
The synthesis of the [1-methyl-1-((diarylphosphino)-
ethyl)]cyclopentadienyl ligand systems used in this
study was carried out by means of the fulvene route.10
6,6-Dimethylfulvene was treated with lithiodiarylphos-
phide (Ar ) p-tolyl or phenyl), Scheme 1. The resulting
ligand system was then treated with 0.5 molar equiv of
ZrCl4 to yield the metallocene complexes 1a (Ar )
p-tolyl) and 1b (Ar ) phenyl), as was previously
described by us.8 The complexes 1a ,b were each sub-
sequently treated with 2 molar equiv of methyllithium
to furnish the dimethylzirconocene complexes 2a (Ar )
p-tolyl) and 2b (Ar ) phenyl), respectively. Out of each
series of these starting materials, one representative
example was crystallized and characterized by an X-ray
crystal structure analysis. The molecular structures of
the metallocene dichloride (1b) and dimethyl (2b)
complexes are very similar. Therefore, the structural
data of 1b are provided in the Supporting Information.
A view of the molecular geometry of 2b is given in
Figure 1. Figure 1 shows that the bonding parameters
around the pseudotetrahedrally coordinated zirconium
atom in 2b are unexceptional11 (Zr-C8 ) 2.277(3) Å,
C8-Zr-C8* ) 92.2(2)°, D1-Zr-D1* ) 132.0°, D1 and
D2 denote the centroids of the two Cp ring systems).
The conformational properties of the metallocene system
2b are noteworthy though. In the crystal, 2b is C2-
symmetric. The system shows a rotameric structure
where both -CMe2-PPh2 substituents at the Cp rings
are oriented in opposite lateral sectors at the bent
metallocene wedge. The (Cp-CMe2PPh2)2ZrMe2 com-
plex 2b, thus, exhibits a bis(lateral):anti-metallocene
(6) J ordan, R. F.; Bajgur, C. S.; Dasher, W. E.; Rheingold, A. L.
Organometallics 1987, 6, 1041. J ordan, R. F.; Bradley, P. K.; Baenziger,
N. C.; LaPointe, R. E. J . Am. Chem. Soc. 1990, 112, 1289. Razavi, A.;
Thewalt, U. J . Organomet. Chem. 1993, 445, 111. Alelyunas, Y. W.;
Guo, Z.; LaPointe, R. E.; J ordan, R. F. Organometallics 1993, 12, 544.
Guo, Z.; Swenson, D. C.; J ordan, R. F. Organometallics 1994, 13, 1424.
(7) Bertuleit, A.; Fritze, C.; Erker, G.; Fro¨hlich, R. Organometallics
1997, 16, 2891. and references cited therein. See also (reviews): J utzi,
P.; Dahlhaus, J . Phosphorus, Sulfur Silicon Relat. Elem. 1994, 87, 73.
J utzi, P.; Dahlhaus, J . Coord. Chem. Rev. 1994, 137, 179. Okuda, J .
Comm. Inorg. Chem. 1994, 16, 185. J utzi, P.; Siemeling, U. J .
Organomet. Chem. 1995, 500, 175.
(8) Bosch, B.; Erker, G.; Fro¨hlich, R. Inorg. Chim. Acta, in press.
(9) For the use of specific organometallic Lewis acids in organic
catalysis see e.g.: Erker, G.; Schamberger, J .; van der Zeijden, A. A.
H.; Dehnicke, S.; Kru¨ger, C.; Goddard, R.; Nolte, M. J . Organomet.
Chem. 1993, 459, 107 and references cited therein.
(10) Ziegler, K.; Scha¨fer, W. J ustus Liebigs Ann. Chem. 1934, 511,
101. Ziegler, K.; Gellert, H.-G.; Martin, H.; Nagel, K.; Schneider, J .
J ustus Liebigs Ann. Chem. 1954, 589, 91. Sullivan, M. F.; Little, W.
F. J . Organomet. Chem. 1967, 8, 277. Renaut, P.; Tainturier, G.;
Gautheron, B. J . Organomet. Chem. 1978, 148, 43. Brickhouse, M. D.;
Squires, R. R. J . Am. Chem. Soc. 1988, 110, 2706. Okuda, J . Chem.
Ber. 1989, 122, 1075. Squires, R. R. Acc. Chem. Res. 1992, 25, 461.
Clark, T. J .; Killian, C. M.; Luthra, S.; Nile, T. A. J . Organomet. Chem.
1993, 462, 247.
(11) Bochmann, M. Comprehensive Organometallic Chemistry; Abel,
E. W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon: New York, 1995;
Vol. 4, p 273. Ryan, E. J . Ibid. p 483. Hey-Hawkins, E. Ibid. p 501.
Gambarotta, S.; J ubb, J .; Song, J .; Richeson, D. Ibid., p. 543. Cardin,
D. J .; Lappert, M. F.; Raston, C. L. Chemistry of Organo-Zirconium
and -Hafnium Compounds; Wiley: New York, 1986.

Phosphine-Stabilized Zirconocene Cations
Organometallics, Vol. 16, No. 25, 1997 5451
conformation.12 One of the methyl groups at C1, namely
C3H3, is oriented close to the Cp-ligand plane (dihedral
angle θ C3-C1-C70-C71 ) -3.9(4)°), whereas the
phosphorus atom P4 and the remaining C2H3 group are
located out of this plane (θ P4-C1-C70-C71 121.5(3)°,
C2-C1-C70-C71 ) -127.0(3)°).
Sch em e 2
The [Cp-CMe2-P(p-tolyl)2]2Zr(CH3)2 complex 2a was
used as a starting material for generating the metal-
locene cation complexes. Complex 2a was therefore
treated with 1 molar equiv of tris(pentafluorophenyl)-
borane in toluene.13 The [(Cp-CMe2-P(p-tolyl)2)2Zr-
(CH3)+ CH3B(C6F5)3-] salt 3a was formed instanta-
neously and isolated in >90% yield. In dichloromethane-
d2, it exhibits a C2-symmetric structure in solution, as
apparent from the NMR spectra at low temperature (1H/
13C NMR (600/150 MHz at 253 K) δ 6.44, 6.40, 6.26,
5.94/111.9, 106.92, 106.79, 97.8 (Cp-); δ 1.82, 1.28/30.3,
25.5 (C(CH3)2); δ 2.37 (12H)/21.38, 21.15 (p-tolyl-CH3),
δ -0.39/17.3 (Zr-CH3)). The 1H NMR signal of the Zr-
CH3 group is split as a binominal triplet due to coupling
with the two symmetry-equivalent phosphorus nuclei
(3J PH ) 15 Hz), as is the corresponding 13C NMR
resonance (2J PC ) 10.5 Hz). The C(CH3)2 methyl-group
1H NMR resonances also show coupling to two 31P nuclei
(as part of an A3A3′XX′-type system14). The cation
complex 3a exhibits a single 31P NMR resonance as
expected, but with a very unusual chemical shift of δ
-22.0 (for comparison, the corresponding 31P NMR
resonance of the starting material 2a occurs at δ +31.2).
This enormous shifting of the 31P NMR resonance of the
system upon cation formation and establishing the
phosphine-to-metal coordination was not expected per
se. It may be explained by either a very pronounced
∆R-effect15 or by assuming that the phosphorus of the
-P(aryl)2 moiety has entered the magnetically deshield-
ing anisotropy cone of the adjacent Cp-ring system in
the unusual overall coordination geometry that has
resulted from the formation of the internally phosphine-
coordinated cationic metallocene system (further struc-
tural evidence on this point is given below).
at ∆Gq (300 K) ) 14.0 ( 0.5 kcal/mol from the temper-
1
ature-dependent dynamic H NMR spectra described
above.16 The dynamic symmetrization process requires
a “left/right-exchange” of the phosphorus ligands bonded
to zirconium in the σ-ligand plane of 3a . Due to the
specific stereoelectronic features of the bent metallocene
unit,17 this requires (reversible) rupture of both zirco-
nium-phosphorus bonds (see Scheme 2). The magni-
tude of the activation barrier is, thus, determined by a
process leading to the unsaturated intermediate 8 that
is devoid of any stabilization by coordination of electron-
donating -PAr2 ligands. Qualitatively, the activation
barrier of this dynamic automerization process of 3a ,
thus, provides a measure of the stabilization energy that
a very electrophilic “naked” [Zr]-CH3 cation gains by
(intramolecularly) coordinating two R-PAr2 donor
ligands to it. The diphenylphosphino-substituted de-
rivative 3b shows an analogous dynamic behavior.
1
From the temperature-dependent H NMR spectra, an
Complex 3a exhibits dynamic NMR spectra. Raising
the monitoring temperature of the 1H NMR experiment
(at 200 MHz) above 280 K results in a broadening of
the C5H4 resonances and the C(CH3)2 signals. Eventu-
ally, the δ 6.44/5.94 (273 K) pair of resonances reaches
coalescence (Tc ) 300 K), as does the 6.39/6.24 pair
(Tc ) 295 K) and the δ 1.82/1.31 pair of methyl signals
(Tc ) 300 K). The dynamic process that leads to a
symmetry exchange of these pairs of signals must be
described as an intramolecular enantiomerization pro-
cess of 3a . Its Gibbs activation energy was estimated
almost identical ∆Gq
obtained.
) 14.1 ( 0.5 kcal/mol was
enant
Complex 3a was characterized by an X-ray crystal
-
structure analysis. In the crystal, the CH3B(C6F5)3
anion is independent of the 3a cation. The structural
parameters of the anion are unexceptional.13 The cation
shows a pseudopenta-coordinated zirconium atom with
two substituted Cp ligands, a methyl group, and both
-P(p-tolyl)2 moieties bonded to the metal center. This
leads to a (noncrystallographic) very close to C2-sym-
metric molecular geometry of the 3a cation. The D1-
Zr-D2 angle is 137.2° (D1 and D2 denote the centroids
of the two Cp ligands). The Zr-C10 bond length is
2.350(4) Å.18 The C10H3 group is bonded to zirconium
in the front of the bent metallocene wedge in the central
position of the σ-ligand plane. The phosphorus atoms
P1 and P11 are bonded to Zr laterally adjacent to the
Zr-CH3 vector (Zr-P1 ) 2.8370(14) Å, Zr-P11 )
2.8447(14) Å, P1-Zr-C10 ) 77.55(10)°, P11-Zr-C10
) 77.31(10)°, P1-Zr-P11 ) 154.78(4)°). Both P atoms
(12) For leading references on the conformational features of group
4 bent metallocene complex chemistry, see, e.g.: Kru¨ger, C.; Nolte,
M.; Erker, G.; Thiele, S. Z. Naturforsch. 1992, 47b, 995. Erker, G.;
Temme, B. J . Am. Chem. Soc. 1992, 114, 4004. Kru¨ger, C.; Lutz, F.;
Nolte, M.; Erker, G.; Aulbach, M. J . Organomet. Chem. 1993, 452, 79.
Erker, G.; Aulbach, M.; Knickmeier, M.; Wingbermu¨hle, D.; Kru¨ger,
C.; Nolte, M.; Werner, S. J . Am. Chem. Soc. 1993, 115, 4590. Fritze,
C.; Knickmeier, M.; Erker, G.; Zaegel, F.; Gautheron, B.; Meunier, P.;
Paquette, L. A. Organometallics 1995, 14, 5446. Knickmeier, M.; Erker,
G.; Fox, T. J . Am. Chem. Soc. 1996, 118, 9623 and references cited
therein.
(13) For leading references on this method of generating group 4
bent metallocene cation complexes, see: Yang, X.; Stern, C. L.; Marks,
T. J . J . Am. Chem. Soc. 1994, 116, 10015 and references cited therein.
(14) Leoni, P.; Marchetti, F.; Paoletti, M. Organometallics 1997, 16,
2146.
(16) Gutowsky, H. S.; Holm, C. H. J . Chem. Phys. 1956, 25, 1228.
Green, M. L. H.; Wong, L.-L.; Seela, A. Organometallics 1992, 11, 2660
and references cited therein.
(15) Garrou, P. E. Inorg. Chem. 1975, 14, 1435. Garrou, P. E. Chem.
Rev. 1981, 81, 229.
(17) Brintzinger, H. H.; Bartell, L. S. J . Am. Chem. Soc. 1970, 92,
1105. Lauher, J . W.; Hoffmann, R. J . Am. Chem. Soc. 1976, 98, 1729.

5452 Organometallics, Vol. 16, No. 25, 1997
Bosch et al.
F igu r e 3. View of the molecular geometry of
5
-
(CH3B(C6F5)3 anion not depicted). Selected bond lengths
(Å) and angles (deg): Zr-Cl 2.453(2), Zr-CCp 2.499(7), Zr-
P1 2.846(2), Zr-P11 2.846(2), P1-C2 1.885(7), P11-C12
1.891(7), P1-C21 1.798(7), P11-C51 1.814(7), P1-C31
1.833(7), P11-C41 1.827(7), C2-C3 1.534(10), C12-C13
1.536(10), C2-C4 1.549(10), C12-C14 1.529(9), C2-C5
1.516(10), C12-C15 1.532(10); Cl-Zr-P1 77.83(6), Cl-Zr-
P11 78.03(6), P1-Zr-P11 155.81(6), Zr-P1-C2 88.3(2),
Zr-P11-C12 88.8(2), Zr-P1-C21 124.6(2), Zr-P11-C51
122.6(3), Zr-P1-C31 120.8(2), Zr-P11-C41 121.9(2), P1-
C2-C3 115.3(6), P11-C12-C13 113.9(5), P1-C2-C4 111.7-
(5), P11-C12-C14 112.5(5), P1-C2-C5 99.5(4), P11-
C12-C15 98.3(4).
F igu r e 2. Two projections of the molecular structure of
3a (cation only) in the crystal. Selected bond lengths (Å)
and angles (deg): Zr-C10 2.350(4), Zr-CCp 2.512(5), Zr-
P1 2.8370(14), Zr-P11 2.8447(14), P1-C2 1.894(5), P11-
C12 1.892(5), P1-C21 1.809(5), P11-C51 1.808(5), P1-
C31 1.850(5), P11-C41 1.835(5), C2-C3 1.540(7), C12-
C13 1.543(7), C2-C4 1.538(7), C12-C14 1.529(7), C2-C5
1.518(7), C12-C15 1.516(7); C10-Zr-P1 77.55(10), C10-
Zr-P11 77.31(10), P1-Zr-P11 154.78(4), Zr-P1-C2 89.0-
(2), Zr-P11-C12 89.2(2), Zr-P1-C21 125.7(2), Zr-P11-
C51 123.8(2), Zr-P1-C31 120.0(2), Zr-P11-C41 120.7(2),
P1-C2-C3 114.9(4), P11-C12-C13 113.7(3), P1-C2-C4
111.8(4), P11-C12-C14 113.5(4), P1-C2-C5 99.5(3), P11-
C12-C15 98.9(3).
(P1, P11) is similar; this leads to some lateral shielding
of the central Zr-CH3 group by the bulky substituents
at phosphorus (see Figure 2).
Next, we tried to generate the internally phosphane-
stabilized dication 4 (Ar ) p-tolyl, see Scheme 1).19 In
the first series of experiments, we treated the dimeth-
ylzirconocene complex 2a (Ar ) p-tolyl) with 2 molar
equiv of B(C6F5)3 in dichloromethane. The reaction
rapidly goes to completion when carried out at room
temperature. A single reaction product was obtained
almost quantitatively. Recrystallization from dichlo-
romethane/pentane gave single crystals suited for the
X-ray crystal structure analysis. This revealed that
instead of the expected dication complex [(Cp-CMe2-
PAr2)2Zr2+‚2 MeB(C6F5)3-] (4, see below) the [(Cp-
CMe3PAr2)2Zr-Cl+MeB(C6F5)3-] salt 5 had been formed
and isolated in excellent yield. The structure of the
chloro-containing monocation 5 (see Figure 3) is very
similar to the methyl-containing cation 3a (see above).
The overall molecular arrangement is again close to C2-
symmetric with two -P(p-tolyl)2 ligands internally
coordinating to zirconium as close to the σ-ligand plane
of the bent metallocene wedge as the rigid system
allows. The Zr-Cl vector is located in the central
position in the σ-ligand plane (Zr-Cl ) 2.453(2) Å, Zr-
P1 ) 2.846(2) Å, Zr-P11 ) 2.846(2) Å, D1-Zr-D2 )
134.9°, P1-Zr-Cl ) 77.83(6)°, P11-Zr-Cl ) 78.03(6)°,
P1-Zr-P11 ) 155.81(6)°, C2-P1-Zr ) 88.3(2)°, C12-
P11-Zr ) 88.8(2)°).
are located markedly outside the bent metallocene
σ-ligand plane (i.e., C2-symmetrically above and below,
see Figure 2). The angle between the D1-Zr-D2 and
P1-Zr-P11 planes is 80.6°. This deviation from an
electronically favored arrangement of the P1,Zr,P11 unit
in the Cp-Zr-Cp bisecting major plane of the bent
metallocene unit is enforced geometrically by the at-
tachment of the -PAr2 groups at the Cp ligands by the
CMe2 linkages (C2-P1 ) 1.894(5) Å, C12-P11 ) 1.892-
(5) Å, C5-C2-P1 ) 99.5(3)°, C2-P1-Zr ) 89.0(2)°,
C15-C12-P11 ) 98.9(3)°, C12-P11-Zr ) 89.2(2)°).
This geometric arrangement brings each phosphorus
atom rather close to one Cp edge (C5‚‚‚P1 ) 2.615 Å,
C15‚‚‚P11 ) 2.600 Å). The methyl groups at C2 (and
C12) are in a markedly different environment. The
C4H3 group points toward the front side of the bent
metallocene wedge, whereas the C3H3 substituent is
oriented toward a hind lateral sector. The relative
orientation of the aryl groups at the phosphorus atoms
Complex 5 exhibits the very characteristic NMR
spectra of the chiral C2-symmetric cation at ambient
(18) Atwood, J . L.; Barker, G. K.; Holton, J .; Hunter, W. E.; Lappert,
M. F.; Pearce, R. J . Am. Chem. Soc. 1977, 99, 6645. J effrey, J .; Lappert,
M. F.; Luong-Thi, N. T.; Webb, M.; Atwood, J . L.; Hunter, W. E. J .
Chem. Soc., Dalton Trans. 1981, 1593. Atwood, J . L.; Hunter, W. E.;
Hrncir, D. C.; Bynum, V.; Penttila, R. A. Organometallics 1983, 2, 750.
Kru¨ger, C.; Mu¨ller, G.; Erker, G.; Dorf, U.; Engel, K. Organometallics
1985, 4, 215. See also: Orpen, G. A.; Brammer, L.; Allen, F. H.;
Kennard, O.; Watson, D. G.; Taylor, R. J . Chem. Soc., Dalton Trans.
1989, S1.
(19) (a) Zirconium: J ordan, R. F.; Echols, S. F. Inorg. Chem. 1987,
26, 383. Billinger, P. N.; Claire, P. P. K.; Collins, H.; Willey, G. R. Inorg.
Chim. Acta 1988, 149, 63. Thewalt, U.; Lasser, W. J . Organomet. Chem.
1984, 276, 341. Lasser, W.; Thewalt, U. J . Organomet. Chem. 1986,
311, 69. (b) Titanium: Thewalt, U.; Klein, H.-P. J . Organomet. Chem.
1980, 194, 297. Thewalt, U.; Berhalter, K. J . Organomet. Chem. 1986,
302, 193. Honold, B.; Thewalt, U. J . Organomet. Chem. 1986, 316, 291.
Berhalter, K.; Thewalt, U. J . Organomet. Chem. 1987, 332, 123.

Phosphine-Stabilized Zirconocene Cations
Organometallics, Vol. 16, No. 25, 1997 5453
temperature (13C NMR (CD2Cl2, 150 MHz) δ 116.3,
112.8, 108.4, 100.9 (Cp), 29.8, 26.4 (C(CH3)2), 21.7, 21.4
(tolyl-CH3); 1H NMR (C6D5Br, 200 MHz, 303 K) δ 6.23,
6.22, 6.01, 5.86 (Cp), 1.49, 1.32 (C(CH3)2). The 31P NMR
resonance of 5 is at δ -33.0 ppm (in CD2Cl2).
now 20:80. Raising the temperature further then led
to an increased consumption of the dication 4 with
formation of 5. The characteristic NMR data of 4 were
obtained from a ca. 1:1 mixture of 4 and 5 at 275 K in
dichloromethane-d2 (δ 2.39, 2.29 (p-tolyl CH3); δ 1.93,
1.59 (C(CH3)2)). The 31P NMR resonance of 4 (CD2Cl2)
is at δ -48.5 ppm. Complex 4 was also obtained as an
insoluble oil by treatment of 2a with ca. 2 molar equiv
of B(C6F5)3 in toluene (see Experimental Section). Since
4 is insoluble in the aromatic hydrocarbon solvent, the
product was spectroscopically characterized using CD2-
Cl2 or C6D5Br solutions (see above).
We have characterized the dication 4 by its reaction
with external donor ligands. The resulting [(Cp-
CMe2-PAr2)2Zr-L2+‚2 CH3B(C6F5)3-] complexes are
more stable than the very electrophilic dication 4 and,
thus, are easier to handle and isolate.20
Complex 5 shows a dynamic NMR behavior at higher
temperatures similar to that previously observed for 3a .
1
The H NMR spectrum of 5 in bromobenzene-d5 shows
a broadening of the lines at temperatures above ca. 340
K (200 MHz) with subsequent coalescence of the former
δ 6.23/6.01 (Tc ) 363 K) and δ 6.22/5.86 (Tc ) 370 K)
pairs of Cp resonances as well as the former δ 1.49/1.32
1H NMR C(CH3)2 resonance pair (Tc ) 358 K). The
enantiomerization process of 5 is analogous to that
observed and described for 3 (see above and Scheme 2)
and is also likely to proceed through a nondonor-ligand-
stabilized intermediate (8), however, in the case of the
[Zr]-Cl+ complex this should be even further destabi-
lized due to the presence of the electron-withdrawing
σ-chloride ligand at zirconium instead of -CH3. Thus,
the 5 f 8 transition should have a higher activation
barrier compared to the corresponding 3 f 8 reaction,
which it has. The Gibbs activation energy of the
thermally induced intramolecular 5 h ent-5 automer-
The reaction between 3a , B(C6F5)3 (2 molar equiv),
and acetonitrile was carried out in toluene. The reac-
tion rapidly turns heterogeneous, and the reaction
product (6, see Scheme 1) separates as an oil. The
isolated (89% yield) complex [(Cp-CMe2-PAr2)2Zr-
(NtC-CH3)2+‚2 CH3B(C6F5)3-] (6) is stable in dichlo-
romethane. It shows the typical NMR spectra of a C2-
symmetric cationic species in solution (1H/13C NMR δ
6.73, 6.46, 6.38, 6.20/117.1, 108.5, 107.9, 101.2 (Cp); δ
2.43, 2.41/21.53, 21.42 (CH3 of p-tolyl), 1.78, 1.44/29.4,
ization process was derived at ∆Gq (360 K) ) 17.5 (
ent
0.5 kcal/mol from the dynamic H NMR spectra.16
1
The cation 5 was prepared independently. We have
treated the substituted zirconocene dichloride 1a (Ar )
p-tolyl) directly with 1 molar equiv of the Lewis acid
B(C6F5)3 in dichloromethane. At ambient temperature
one chloride is rapidly removed from zirconium with
formation of the [(Cp-CMe2-P(p-tolyl)2)2Zr-Cl+ClB-
(C6F5)3-] salt 5′. The ClB(C6F5)3- anion was identified
by LDI-TOF-MS (m/ z ) 547) in the negative ion mode
and by an X-ray crystal structure analysis (B-Cl2 )
1.907(8) Å; for details of this structure, see the Sup-
porting Information). The NMR spectra of the inde-
pendently prepared compound 5′ are very similar to
those of 5 (for details, see the Experimental Section).
1
26.3 (C(CH3)2)). The H NMR resonance of the coordi-
nated acetonitrile ligand appears at δ 1.32 as a triplet
due to coupling with the two adjacent symmetry-
equivalent 31P NMR nuclei (5J PH ) 3.3 Hz). The
coordinated -CtN 13C NMR resonance is at δ 141.5
ppm, and the corresponding acetonitrile methyl 13C
NMR signal is at δ 2.92. Complex 6 exhibits a 31P NMR
resonance at δ -44.7 ppm. The typical IR bands of the
coordinated acetonitrile ligand are found at 2307 (com-
bination) and 2273 cm-1 (CtN) (free acetonitrile shows
the corresponding IR bands at ν˜ ≈ 2290 and 2255
cm-1).20,21
We have also trapped the in-situ-generated metal-
locene dication 4 by addition of 2,6-dimethylphenyl
isocyanide (reaction carried out in toluene). The [(Cp-
CMe2-PAr2)2Zr(CtN-Ar′)2+‚2CH3B(C6F5)3-] salt 7 (see
Scheme 1) was isolated in ca. 80% yield. It again
exhibits the typical NMR spectra of a C2-symmetric
adduct (for details see the Experimental Section). The
ν˜ (CtN-R) IR band of 7 was monitored at ν˜ ) 2170
cm-1 (free C≡N-C6H3Me2 2122 cm-1).
It is very likely that the chloride-containing complex
[(Cp-CMe2-PAr2)2Zr-Cl+CH3B(C6F5)3-] 5 was formed
in the reaction between 2a and 2 equiv of B(C6F5)3 via
the reactive [(Cp-CMe2-PAr2)2Zr2+‚2CH3B(C6F5)3-] di-
cation intermediate 4, which is not stable under the
applied reaction conditions. It must be assumed that
the ultimately obtained reaction products originate from
4, which is converted to 5 by a subsequent chloride
abstraction reaction from the halocarbon solvent.
This was shown to be true, although the organic
stoichiometric reaction product could not be identified.
The reaction of 2a with 2 equiv of B(C6F5)3 in CD2Cl2
was carried out at variable temperatures under direct
1H and 31P NMR control. The reaction was started at
213 K, a temperature where the formation of the
monocation 3a is very rapid. After 30 min at 213 K, a
mixture containing 3a (65%), 5 (9%), and the new
complex 4 (i.e., the donor-ligand-stabilized dication,
26%) was obtained. Slowly raising the temperature
resulted in a predominant conversion of 3a to 4 (by
means of intermolecular CH3 abstraction by the B(C6F5)3
reagent) without very much subsequent chloride ab-
straction. At 228 K after a total reaction time of 60 min,
a 3a :5:4 ratio of 27:11:62 was obtained, and at 253 K
after a total reaction time of 125 min, the primary
product 3a was no longer observed, the 5:4 ratio was
Con clu sion s
This study shows that phosphine stabilization of the
very electrophilic zirconium center in the mono- and
dicationic bent metallocene complexes can become very
pronounced and dominant if the P-donor ligands become
attached to the Cp rings by suitable linkages and, thus,
can coordinate intramolecularly. In this manner, even
the very electrophilic 16-electron dication 4 has attained
a moderate stability, although it apparently is so
electrophilic that it rapidly starts to abstract chloride
(20) See, for a comparison: Brackemeyer, T.; Erker, G.; Fro¨hlich,
R. Organometallics 1997, 16, 531. Brackemeyer, T.; Erker, G.; Fro¨hlich,
R.; Prigge, J .; Peuchert, U. Chem. Ber. 1997, 130, 899.
(21) Bruce, M. R. M.; Tyler, D. R. Organometallics 1985, 4, 528.
J ordan, R. F.; Dasher, W. E.; Echols, S. F. J . Am. Chem. Soc. 1986,
108, 1718.

5454 Organometallics, Vol. 16, No. 25, 1997
Bosch et al.
C of tol), 128.9 (3J PC ) 7 Hz, m-tol), 110.3 (3J PC ) 5 Hz, C2 of
Cp), 109.6 (Cp), 37.9 (1J PC ) 21 Hz, CMe2), 32.3 (Zr-CH3), 26.4
(2J PC ) 18 Hz, C(CH3)2), 21.2 (tol-CH3). 31P NMR (benzene-
d6, 81.0 MHz): δ 31.2.
from the solvent at or above ca. -20 °C to cleanly form
the C2-symmetric chloride containing 18-electron mono-
cation 5. Similarly, there is an apparently large ther-
modynamic driving force of 4 to add neutral donor
ligands (nitrile, isonitrile) to give the respective very
stable 18-electron complexes (6,7) which have the third
donor ligand bonded at zirconium in the central position
in the σ-ligand plane. This study shows that the
selected synthetic route (1 f 2 f 3 f 4, see Scheme 1)
is suited and easy to use for generating the reactive
chiral internally donor-ligand-stabilized metallocene
dication system 4.22 Whether this rather electrophilic
dication system can be used as a catalyst or a stoichio-
metric reagent in organic transformations and whether
its inherent chirality can be utilized in such reactions
is currently being studied in our laboratory.
B is [[1-m e t h y l-1-(d ip h e n y lp h o s p h in o )e t h y l]c y c lo -
p en ta d ien yl]d im eth ylzir con iu m (2b). To a suspension of
3.11 g (4.17 mmol) of bis[[1-methyl-1-(diphenylphosphino)-
ethyl]cyclopentadienyl]dichlorozirconium (1b) in 80 mL of
pentane was added 5.0 mL of methyllithium (1.68 M in diethyl
ether, 8.4 mmol) at -78 °C. A yellow suspension was obtained
after stirring overnight. Subsequently, the solvent was evapo-
rated into a cold trap, and the residue was taken up in 150
mL of toluene and filtered through a 2 cm bed of Celite. The
toluene was evaporated, and the crude product 2b was washed
with two 20 mL portions of pentane, leaving 2.35 g (80%) of
2b as a white solid. A sample of 2b was dissolved in a 3:1
mixture of toluene and pentane. Cooling this mixture to -20
°C yielded white crystals suitable for the X-ray diffraction
analysis. Mp 178 °C. Anal. Calcd for C42H46P2Zr (704.0): C,
71.66; H, 6.59. Found: C, 70.17; H, 6.47. IR (KBr): ν˜ ) 3075,
3058, 2971, 2964, 2932, 2915, 2868, 1583 (s), 1481, 1461, 1435
(s), 1429 (s), 1412, 1377, 1358, 1223, 1091, 1068, 1051, 1039,
1025, 1000, 931, 875, 865, 854, 810 (vs), 747, 739 (s), 698 (s)
Exp er im en ta l Section
All compounds described are air and moisture sensitive.
They were prepared and handled in an argon atmosphere
using Schlenk-type glassware or in a glovebox. Solvents
(including deuterated solvents) were dried and distilled under
argon prior to use. NMR spectra were recorded on a Bruker
AC 200 P (1H, 200 MHz; 31P, 81 MHz, H3PO4 external
standard; 13C, 50.3 MHz) or a Varian Unity plus (1H, 600 MHz;
13C, 150 MHz) NMR spectrometer. IR spectroscopy: Nicolet
5 DXC FT-IR spectrometer (KBr). Elemental analyses: Foss
Heraeus CHNO-Rapid. DSC: Dupont 2910 DSC (STA instru-
ments). X-ray crystal structure analyses: Enraf-Nonius MACH
3 diffractometer (programs used, SHELX 86, SHELX 93,
DIAMOND, and SCHAKAL). The complexes 1a and 1b were
prepared as recently described by us.8 B(C6F5)3 was prepared
according to a literature procedure.23
cm-1 1H NMR (benzene-d6, 200.1 MHz): δ 7.53-7.44 (m, 8H,
.
o-Ph), 7.19-7.14 (m, 12H, p,m-Ph), 5.73 (s, 8H, C5H4), 1.39
3
(d, J PH ) 13.5 Hz, 12H, CMe2), -0.07 (s, 6H, Zr-CH3). 13C
NMR (APT, benzene-d6, 50.3 MHz): δ 136.7 (1J PC ) 23 Hz,
ipso C of Ph), 135.5 (2J PC ) 20 Hz, o-Ph), 129.0 (p-Ph), 128.2
(3J PC ) 7 Hz, m-Ph), 110.2 (3J PC ) 6 Hz, C2 of Cp), 109.6 (Cp),
37.9 (1J PC ) 21 Hz, CMe3), 32.3 (Zr-CH3), 26.3 (2J PC ) 18 Hz,
C(CH3)2); C1 of Cp not observed. 31P NMR (benzene-d6, 81.0
MHz): δ 32.5.
X-r a y Cr yst a l St r u ct u r e An a lysis of 2b . Formula
C
42H46P2Zr; M ) 703.95; 0.50 × 0.30 × 0.20 mm; a ) 31.554-
(3) Å; b ) 7.028(1) Å; c ) 16.735(2) Å, â ) 105.72(1)°, V )
3572.4(7) Å3, Fcalc ) 1.309 g cm-3, µ ) 4.26 cm-1, empirical
absorption correction via æ scan data (0.962 e C e 0.999), Z
) 4, monoclinic, space group C2/c (No. 15), λ ) 0.710 73 Å, T
) 223 K, ω scans, 3771 reflections collected ((h, -k, -l), [(sin
θ)/λ] ) 0.62 Å-1, 3636 independent and 2622 observed reflec-
tions [I g 2 σ(I)], 207 refined parameters, R1 ) 0.039, wR2 )
X-r a y Cr ysta l Str u ctu r e An a lysis of 1b. Formula C40H40
-
Cl2P2Zr; M ) 744.78; 0.20 × 0.20 × 0.10 mm; a ) 31.058(6) Å,
b ) 6.537(1) Å, c ) 18.167(4) Å, â ) 108.57(2)°, V ) 3496.2-
(12) Å3, Fcalc ) 1.415 g cm-3, µ ) 5.87 cm-1, empirical absorption
correction via æ scan data (0.925 e C e 0.998), Z ) 4,
monoclinic, space group C2/c (No. 15), λ ) 0.710 73 Å, T )
223 K, ω scans, 3660 reflections collected ((h, +k, -l), [(sin
θ)/λ] ) 0.62 Å-1, 3528 independent and 2112 observed reflec-
tions [I g 2 σ(I)], 207 refined parameters, R1 ) 0.048, wR2 )
0.083, max (min) residual electron density 0.41 (-0.32) e Å-3
hydrogens calculated and refined as riding atoms.
,
Meth ylbis{[[1-m eth yl-1-(d i-p-tolylp h osp h in o)eth yl]-η5-
cyclop en ta d ien yl]-K2-P ,P ′}zir con iu m (IV) Meth yltr is(p en -
ta flu or op h en yl)bor a te (3a ). 2a (760 mg, 1.0 mmol) and 512
mg (1.0 mmol) of B(C6F5)3 were mixed as solids and suspended
in 25 mL of toluene. The orange suspension was stirred for 1
h, and the mixture was concentrated in vacuo to 2 mL.
Pentane (20 mL) was added, and the mixture was stirred for
1 h. The pale yellow product was isolated on a Schlenk frit,
washed with two 10 mL portions of pentane, and dried in vacuo
to yield 1.15 g (91%) of the pale yellow monocation complex
3a . It was possible to grow large crystals of 3a by layering a
dichloromethane solution with an equal amount of pentane
at -20 °C. Single crystals suitable for the X-ray diffraction
analysis were obtained by slow diffusion of pentane into a
dichloromethane solution of 3a at 4 °C. Mp 160 °C (dec). Anal.
0.106, max (min) residual electron density 0.76 (-1.15) e Å-3
hydrogens calculated and refined as riding atoms.
,
Bis[[1-m eth yl-1-(d i-p-tolylp h osp h in o)eth yl]cyclop en -
ta d ien yl]d im eth ylzir con iu m (2a ). 1a (16.0 g, 20 mmol)
was suspended in 150 mL of diethyl ether, and 24 mL (40
mmol) of methyllithium (1.68 M in Et2O) was added at -78
°C. The suspension was allowed to warm to room temperature
overnight. Celite filtration and washings of the filter pad with
100 mL of diethyl ether produced a red solution. The solvent
was evaporated, the residue taken up in 60 mL of pentane,
and the product collected on a Schlenk frit, washed with two
20 mL portions of pentane, and dried in vacuo. Yield: 8.61 g,
57%. Mp 112 °C. Anal. Calcd for C46H54P2Zr (760.1): C,
72.69; H, 7.16. Found: C, 70.25; H, 7.21. IR (KBr): ν˜ 3080,
3069, 3022, 3013, 2971, 2960, 2911, 2864, 1598, 1558, 1498
(vs), 1474, 1446, 1409, 1397, 1377, 1358, 1307, 1261, 1187,
1120 (vs), 1089, 1038, 1020, 932, 874, 862, 853, 810 (br, vs),
Calcd for
C
64H54BF15P2Zr (1272.08): C, 60.43; H, 4.28.
Found: C, 59.26; H, 4.09. IR (KBr): ν˜ ) 3028, 2994, 2974,
2956, 2923, 2869, 1641 (B(C6F5)3), 1600, 1510, 1498, 1458 (br,
vs), 1265 (B(C6F5)3), 1190, 1117, 1088, 1081, 994, 975, 965, 947,
716, 710, 699, 662, 649, 623, 611 cm-1 1H NMR (benzene-d6,
.
934, 838, 822, 800, 658 cm-1 1H NMR (dichloromethane-d2,
.
200.1 MHz): δ 7.47 (m, 8H, o-tol-H), 6.99 (m, 8H, m-tol-H),
5.73 (s, 8H, C5H4), 2.08 (s, 12H, p-tol-CH3), 1.42 (d, 3J PH ) 13.6
Hz, 12H, CMe2), -0.03 (s, 6H, Zr-CH3). 13C NMR (benzene-
d6, 50.3 MHz): δ 138.8 (p-tol), 135.7 (2J PC ) 21 Hz, o-tol), 135.0
200.1 MHz, 253 K): δ 7.27 (m, 16H, p-tol-H), 6.43 (m, 4H,
C5H4), 6.27, 5.94 (each m, each 2H, C5H4), 2.36 (s, 12H, tol-
CH3), 1.81 (m, 6H, CMe2), 1.28 (m, 6H, CMe2), 0.43 (br s, 3H,
3
[B]-CH3), -0.42 (t, J PH ) 15.1 Hz, 3H, Zr-CH3). 13C NMR
(2J PC
) 7 ) 21 Hz, ipso
Hz, C1 of Cp), 133.4 (1J PC
(dichloromethane-d2, 150 MHz, 253 K): δ 148.1 (1J FC ) 228
Hz, o-C6F5), 142.05, 141.92 (each p-tol), 137.4 (1J FC ) 235 Hz,
p-C6F5), 137.1 (ipso-C of Cp), 136.3 (C6F5), 135.38 (o-tol), 134.43
(o-tol), 130.1 (m-tol), 129.9 (m-tol), 125.8 (ipso-C of tol), 121.7
(ipso-C of tol), 111.9, 106.92, 106.79, 97.8 (Cp), 34.9 (CMe2),
(22) For a structurally related neutral system, see: Christoffers, J .;
Bergman, R. G. Angew. Chem. 1995, 107, 2423; Angew. Chem., Int.
Ed. Engl. 1995, 34, 2266.
(23) Massey, A. G.; Park, A. J . J . Organomet. Chem. 1964, 2, 245.

Phosphine-Stabilized Zirconocene Cations
Organometallics, Vol. 16, No. 25, 1997 5455
X-r a y Cr ysta l Str u ctu r e An a lysis of 5. Formula C63H51
30.3, 25.5 (C(CH3)2), 21.38, 21.15 (tol-CH3) 17.3 (t, 2J PC ) 10.5
Hz, Zr-CH3), 9.8 (br, H3C[B]). 31P NMR (dichloromethane-
d2, 81.0 MHz): δ -22.0. 11B NMR (dichloromethane-d2, 64.2
MHz): δ -15.
-
BClF15P2Zr; M ) 1292.46; 0.40 × 0.30 × 0.30 mm; a ) 14.165-
(3) Å, b ) 14.950(2) Å, c ) 16.165(3) Å, R ) 113.94(2)°, â )
109.62(2)°, γ ) 95.48(2)°, V ) 2838.3(9) Å3, Fcalc ) 1.512 g cm-3
,
µ ) 3.88 cm-1, empirical absorption correction via æ scan data
(0.907 e C e 0.999), Z ) 2, triclinic, space group P1h (No. 2), λ
) 0.710 73 Å, T ) 223 K, ω/2æ scans, 10 438 reflections
collected (-h, (k, (l), [(sin θ)/λ] ) 0.59 Å-1, 9994 independent
and 6378 observed reflections [I g 2 σ(I)], 753 refined
parameters, R1 ) 0.065, wR2 ) 0.168, max (min) residual
electron density 1.13 (-0.93) e Å-3, hydrogens calculated and
refined as riding atoms.
X-r a y Cr ysta l Str u ctu r e An a lysis of 3a . Formula C64H54
-
BF15P2Zr; M ) 1272.04; 0.40 × 0.25 × 0.10 mm; a ) 14.139(2)
Å, b ) 14.976(2) Å, c ) 16.145(2) Å, R ) 113.62(1)°, â ) 109.24-
(1)°, γ ) 95.84(1)°, V ) 2847.2(7) Å3, Fcalc ) 1.484 g cm-3, µ )
3.40 cm-1, empirical absorption correction via æ scan data
(0.918 e C e 0.999), Z ) 2, triclinic, space group P1h (No. 2),
λ ) 0.710 73 Å, T ) 223 K, ω/2θ scans, 10 412 reflections
collected ((h, (k, -l), [(sin θ)/λ] ) 0.59 Å-1, 10 024 indepen-
dent and 6956 observed reflections [I g 2 σ(I)], 758 refined
parameters, R1 ) 0.063, wR2 ) 0.182, max (min) residual
electron density 0.99 (-1.25) e Å-3, hydrogens calculated and
refined as riding atoms.
Meth ylbis{[[1-m eth yl-1-(d ip h en ylp h osp h in o)eth yl]-η5-
cyclop en ta d ien yl]-K2-P ,P ′}zir con iu m (IV) Meth yltr is(p en -
ta flu or op h en yl)bor a te (3b). In a similar procedure, the
analogous cationic system with Ar ) Ph was obtained, starting
from 211 mg (0.3 mmol) of 2b and 154 mg (0.3 mmol) of
B(C6F5)3. Yield of 3b: 350 mg (95%). Large colorless crystals
were grown by diffusion of pentane into a dichloromethane
solution of 3a at -20 °C. Mp 201 °C (dec). Anal. Calcd for
Ch lor obis{[[1-m eth yl-1-(d i-p-tolylp h osp h in o)eth yl]-η5-
cyclop en ta d ien yl]-K2-P ,P ′}zir con iu m (IV) Ch lor otr is(p en -
ta flu or op h en yl)bor a te (5′). 1a (200 mg, 0.25 mmol) and 1
equiv of B(C6F5)3 (128 mg, 0.25 mmol) were mixed and then
dissolved in 20 mL of dichloromethane at room temperature.
The yellow solution was stirred for 15 min. The solvent was
then removed in vacuo and the residue was washed with two
5 mL portions of pentane and dried in vacuo to yield 290 mg
(88%) of 5′ as an off-white solid. Crystalline material was
obtained by layering a dichloromethane solution of 5′ with an
equal amount of pentane at -20 °C. Mp 99 °C (dec). IR
(KBr): ν˜ 3032, 2966, 2925, 2871, 1644, 1599, 1515, 1464 (br,
vs), 1399, 1381, 1374, 1280, 1263, 1194, 1095 (br, s), 979 (br,
C
60H46BF15P2Zr (1215.97): C, 59.27; H, 3.81. Found: C, 59.30;
H, 3.81. IR (KBr): ν˜ 3121, 3064, 2996, 2964, 2941, 2929, 2903,
s), 825, 806 (s), 772, 765, 668 cm-1
.
1H NMR (dichloromethane-
d2, 200.1 MHz): δ 7.50, 7.33, 7.14 (each m, 16H, tol-H), 6.42
(2 m), 6.26, 6.21 (each m, each 2H, C5H4), 2.41 (s, 12H, tol-
CH3), 1.75 (m, 6H, CMe2), 1.51 (m, 6H, CMe2). 13C NMR
(dichloromethane-d2, 150 MHz): δ 148.5 (1J FC ) 232 Hz,
o-C6F5), 142.77, 142.27 (each ipso-C of p-tol), (m,p-C6F5 could
not unambigously be assigned), 139.3 (br s, C1 of Cp), 136.9
(o-tol), 134.2 (o-tol), 130.6 (m-tol), 129.8 (m-tol), 126.2 (ipso-C
of tol), 122.2 (ipso-C of tol), 116.2, 112.6, 108.7, 101.1 (Cp),
2844, 1641, 1511, 1458 (br, vs), 1436, 1265, 1096 (br, vs), 995,
1
978, 965, 949, 935, 828, 802, 743, 707, 696, 659, 640 cm-1. H
NMR (dichloromethane-d2, 200.1 MHz, 243 K): δ 7.7-7.2 (m,
20H, Ph), 6.47 (m, 4H, C5H4), 6.33, 5.97 (each m, each 2H,
C5H4), 1.86 (m, 6H, CMe2), 1.29 (m, 6H, CMe2), 0.45 (br s, 3H,
3
[B]-CH3), -0.39 (t, J PH ) 15.1 Hz, 3H, Zr-CH3). 13C NMR
(dichloromethane-d2, 50.3 MHz, 238 K): δ 147.8 (1J FC ) 229
Hz, o-C6F5), 137.3 (1J FC ) 230 Hz, p-C6F5), 136.9 (ipso-C of
Cp), 136.0 (1J FC ) 250 Hz, m-C6F5), 135.3 (o-Ph), 134.5 (o-Ph),
131.13, 131.05 (p-Ph), 129.3 (m-Ph), 129.0 (m-Ph), 124.9 (ipso-C
of Ph), 111.5, 106.9 (double intensity), 97.7 (Cp), 34.8 (CMe2),
35.7 (CMe3), 29.7, 26.4 (C(CH3)2), 21.7, 21.3 (each tol-CH3). 31
P
NMR (dichloromethane-d2, 81.0 MHz): δ -33.0. 11B NMR: δ
-3. LDI-TOF (negative): m/ z ) 547 (ClB(C6F5)3-). Anal.
Calcd for C62H48BCl2F15P2Zr (1312.92): C, 56.72; H, 3.68.
Found: C, 54.29; H, 3.44.
2
30.3, 25.2 (C(CH3)2), 17.3 (t, J PC ) 10 Hz, Zr-CH3), 9.7 (br,
[B]-CH3); one ipso-C of Ph not observed. 31P NMR (dichlo-
romethane-d2, 81.0 MHz): δ -22.3.
X-r a y Cr ysta l Str u ctu r e An a lysis of 5′. Formula C62H48
-
BCl2F15P2Zr; M ) 1312.87; 0.15 × 0.10 × 0.05 mm; a ) 14.157-
(4) Å, b ) 14.964(5) Å, c ) 16.122(4) Å, R ) 114.37(2)°, â )
109.69(3)°, γ ) 95.51(2)°, V ) 2817.0(14) Å3, Fcalc ) 1.548 g
cm-3, µ ) 4.38 cm-1, empirical absorption correction via æ scan
data (0.924 e C e 0.999), Z ) 2, triclinic, space group P1h (No.
2), λ ) 0.710 73 Å, T ) 223 K, ω scans, 9230 reflections
collected ((h, +k, (l), [(sin θ)/λ] ) 0.57 Å-1, 8846 independent
and 4148 observed reflections [I g 2 σ(I)], 756 refined
parameters, R1 ) 0.057, wR2 ) 0.109, max (min) residual
electron density 1.05 (-0.48) e Å-3, hydrogens calculated and
refined as riding atoms.
Low -Tem p er a t u r e St u d y on t h e Dem et h yla t ion -
Ch lor in a tion P r ocess in Dich lor om eth a n e. 2a (15.2 mg)
and B(C6F5)3 (20.4 mg) were dissolved separately in dichlo-
romethane-d2, and the B(C6F5)3 solution was cannula-trans-
ferred to the 2a solution at -78 °C. The first NMR spectrum
was obtained at a temperature of -50 °C after keeping the
solution for 30 min at -78 °C. 31P NMR (dichloromethane-
d2, 81.0 MHz): δ -22.0 (3a ), -33 (5), -48 (4). The following
3a :5:4 ratios were observed by 31P NMR spectroscopy subse-
quently after keeping the same sample for the time indicated
at the temperatures noted: T ) 213 K (30 min), 65:9:26; 223
K (45 min), 51:9:40; 228 K (60 min), 27:11:62; 228 K (90 min),
11:15:74; 238 K (105 min), 9:18:73; 253 K (125 min), 0:20:80;
275 K (170 min) and 295 K (5 min) 0:48:52; ambient temper-
ature (225 min) and 295 K (30 min) 0:100:0.
Ch lor obis{[[1-m eth yl-1-(d i-p-tolylp h osp h in o)eth yl]-η5-
cyclop en ta d ien yl]-K2-P ,P ′}zir con iu m (IV) Meth yltr is(p en -
ta flu or op h en yl)bor a te (5). A solution of 408 mg (0.80 mmol)
of B(C6F5)3 in 20 mL of dichloromethane was added to a
solution of 304 mg (0.43 mmol) of 2a in 20 mL of dichlo-
romethane at 0 °C. A yellow solution was formed immediately.
Removal of the solvent and washing of the product with
pentane and drying in vacuo yielded 670 mg of crude 5. Mp.
222 °C (dec). By layering a dichloromethane solution of 5 with
pentane at -20 °C, big crystals covered with some oily product
could be isolated. Repetition of the crystallization process and
washing of the so-formed crystals with cold dichloromethane
yielded crystals suitable for an X-ray-diffraction analysis. IR
(KBr): ν˜ 3029, 2993, 2973, 2957, 2924, 2864, 1641, 1598, 1510,
1498, 1459 (br, vs), 1411, 1398, 1384, 1370, 1311, 1295, 1266,
1191, 1088, 1081 993, 976, 965, 947, 935, 830, 802, 766, 757,
736, 707, 659, 631, 607 cm-1 1H NMR (dichloromethane-d2,
.
200.1 MHz): δ 7.5-7.2 (m, 16H, tol-H), 6.5-6.4 (m, 8H, C5H4),
6.22 (m, 4H, C5H4), 6.12 (m, 4H, C5H4), 2.41 (s, 12H, tol-CH3),
1.75 (m, 6H, CMe2), 1.55 (m, 6H, CMe2), 0.50 (br s, 6H,
[B]-CH3). 13C NMR (dichloromethane-d2, 150 MHz): δ 148.7
(1J FC ) 221 Hz, o-C6F5), 142.88, 142.33 (each ipso-C of p-tol),
139.5 (br s, C1 of Cp), 137.9 (p-C6F5), 136.8 (1J FC ) 249 Hz,
m-C6F5), 136.89 (o-tol), 134.2 (o-tol), 130.7 (m-tol), 129.9 (m-
tol), 129.2 (br, ipso-C of H3CB(C6F5)3-), 126.3 (ipso-C of tol),
122.1 (ipso-C of tol), 116.3, 112.7, 108.3, 100.8 (Cp), 35.73
(CMe2), 29.75, 26.38 (C(CH3)2), 21.70, 21.35 (CH3) 10.6 ([B]-
CH3). 31P NMR (dichloromethane-d2, 81.0 MHz): δ -33.0.
11B NMR: δ -15. LDI-TOF MS (negative): m/ z ) 527
F or m a tion of th e Dica tion 4. Toluene (20 mL) was
vacuum-condensed from potassium/sodium alloy onto a mix-
ture of 400 mg (0.57 mmol) of 2a and 512 mg (1.00 mmol) of
B(C6F5)3 in a Schlenk tube. A red oily product formed as the
reaction mixture was warmed to room temperature. After 15
min at this temperature, the toluene was decanted inside the
(H3CB(C6F5)3-).
(1292.50): C, 58.54; H, 3.98. Found: C, 57.41; H, 3.97.
Anal.
Calcd for C63H51BClF15P2Zr

5456 Organometallics, Vol. 16, No. 25, 1997
Bosch et al.
glovebox and the remaining red oil was washed twice with 10
mL portions of pentane and then dried in vacuo yielding 850
mg (93%) of 4 as an orange solid. The product is insoluble in
toluene and slightly soluble in bromobenzene and was identi-
fied by low-temperature NMR in dichloromethane-d2 and its
dichloromethane-stable acetonitrile adduct (6), which could
also be synthesized on a preparative scale. 1H NMR of 4 (275
K, dichloromethane-d2 (spectra were recorded using a 1:1
mixture of 4 and 5)): 7.6-7.0 (m, 16H, tol-H), 6.85 (m, 4H,
C5H4), 6.49 (m, 4H, C5H4), 2.39 (s, 6H, tol-CH3), 2.29 (s, 6H,
tol-CH3), 1.93 (m, 6H, CMe2), 1.59 (m, CMe2), 0.45 ([B]-CH3).
31P NMR (dichloromethane-d2, 81.0 MHz, 275 K): δ -48.5.
31P NMR (bromobenzene-d5, 81.0 MHz): δ -48.3. Anal. Calcd
for C82H54B2F30P2Zr (1784.06); C, 55.21; H, 3.05. Found: C,
55.18; H, 3.44.
C84H57NB2F30P2Zr (1825.11): C, 55.28; H, 3.15; N, 0.77.
Found: C, 55.40; H, 3.53; N, 0.70.
((2,6-Dim eth ylp h en yl)ison itr ilo)bis{[[1-m eth yl-1-(d i-p-
t olylp h osp h in o)e t h yl]-η5-cyclop e n t a d ie n yl]-K2-P ,P ′}-
zir con iu m (IV) Bis(m eth yltr is(pen taflu or oph en yl)bor ate)
(7). Formation of the dication 4 in toluene from 234 mg (0.3
mmol) of 2a and 308 mg (0.6 mmol) of B(C6F5)3 followed by
addition of 39 mg (0.30 mmol) of (2,6-dimethylphenyl)isonitrile,
dissolved in 3 mL of toluene, resulted in the formation of
adduct 7 as a red oil. The solvent was decanted, and the
product was worked-up as described above. Yield: 470 mg
(0.24 mmol, 81%). Mp 168 °C (dec). IR (KBr): ν˜ 3123, 2964,
2927, 2871, 2170 (CtN-R), 1641, 1599, 1511 (vs), 1458 (br,
vs), 1400, 1382, 1267, 1087 (br, vs), 995, 979, 966, 952, 934,
833, 805, 660 cm-1
.
1H NMR (dichloromethane-d2, 600
P r ep a r a t ion of Acet on it r ilob is{[[1-m et h yl-1-(d i-p -
t olylp h osp h in o)e t h yl]-η5-cyclop e n t a d ie n yl]-K2-P ,P ′}-
zir con iu m (IV) Bis(m eth yltr is(pen taflu or oph en yl)bor ate)
6. (a) Homogeneously in CH2Cl2: To a solution of 152 mg (0.2
mmol) of 2a in 5 mL of dichloromethane was added a solution
of 204 mg of B(C6F5)3 (0.4 mmol) in 20 mL of dichloromethane
at -78 °C. The solution turned bright yellow within minutes.
The temperature was raised to -50 °C within 1 h. The
reaction mixture was stirred for additional 90 min at temper-
atures around -40 °C. At this temperature, 10.4 µL (0.2
mmol) of acetonitrile was added and the mixture kept over-
night at -20 °C. The solvent was removed in vacuo, yielding
350 mg of a 70:30 mixture of the acetonitrile adduct 6 and the
chlorocation 5. (b) Heterogeneously from toluene: A Schlenk
flask was charged with 234 mg (0.3 mmol) of 2a and 308 mg
(0.6 mmol) of B(C6F5)3, and then 10 mL of toluene was added
at room temperature in the glovebox. The mixture im-
mediately turned orange with the dication 4 precipitating as
a red oil. After 30 min, 16 µL (0.3 mmol) of acetonitrile was
added and the reaction mixture stirred for additional 15 min.
The toluene solvent was decanted from the oily product.
Washing with 5 mL of toluene and then 5 mL of pentane and
drying in vacuo for 24 h led to the formation of a yellow solid
product. Yield of 6: 490 mg (89%). Mp 192 °C (dec). IR
(KBr): ν˜ 3122, 2962, 2927, 2867, 2307 (ν(CtN), comb.), 2273
(ν(CtN)), 1641, 1599, 1511 (vs), 1458 (br, vs), 1400, 1382, 1267,
MHz): 7.37, 7.32, 7.07-7.03 (each m, 19H, tol-H, isonitrile-
H), 6.54, 6.46, 6.44, 6.38 (m, each 2H, each C5H4), 2.42 (s, 6H,
tol-CH3), 2.06 (s, 6H, CH3 of isonitrile), 2.02 (s, 6H, tol-CH3),
1.97 (m, 6H, CMe2), 1.42 (m, 6H, CMe2), 0.51 (br, 6H,
[B]-CH3). 13C NMR (dichloromethane-d2, 150 MHz): δ 148.6
(1J FC ) 235 Hz, o-C6F5), 144.71, 144.57 (p-tol), 137.9 (1J FC
)
242 Hz, p-C6F5), 136.7 (1J FC ) 238 Hz, m-C6F5), 136.4 (C1 of
Cp), 135.5 (C2/C6 of isonitrile), 134.45 (o-tol), 134.19 (o-tol),
133.1 (CN-Ph tentatively), 131.4 (m-tol), 130.9 (m-tol), 129.3
(m-CH of isonitrile), 123.3 (ipso-C of tol), 122.8 (C1 of isoni-
trile), 120.7 (ipso-C of tol), 117.7, 107.3, 101.6, 100.3 (Cp), 36.0
(CMe2), 28.9, 27.1 (C(CH3)2), 21.4, 21.2 (tol-CH3), 19.2 (CH3 of
isonitrile), 10.5 (br, [B]-CH3); p-CH of isonitrile not observed,
probably hidden by o-tol-CH at 134.5 ppm. GHSQC-NMR24
(dichloromethane-d2): δ 134.5/7.32 (o-tol), 134.2/7.07 (o-tol),
131.4/7.37 (m-tol), 130.9/7.03 (m-tol), 129.3/7.07 (m-CH of
isonitrile) 117.6/6.46, 107.3/6.54, 101.6/6.38, 100.3/6.44 (each
C5H4), 28.9/1.42, 27.1/1.97 (C(CH3)2), 21.4/2.42, 21.2/2.02 (tol-
CH3), 19.2/2.06 (CH3 of isonitrile), 10.5/0.51 ([B]-CH3). GH-
MBC-NMR24 (dichloromethane-d2): δ 144.71, 144.57 (p-tol)/
7.32, 7.07-7.03 (o,m-tol-H), 2.42, 2.02 (tol-CH3), 136.4 (C1 of
Cp)/6.54, 6.46, 6.44, 6.38 (C5H4), 1.97, 1.42 (C(CH3)2), 135.5
(C2/C6 of isonitrile)/7.32 (CH of isonitrile), 2.06 (CH3 of
isonitrile), 134.5, 134.2 (o-tol)/7.37, 7.32, 7.07-7.03 (o,m-tol-
H), 131.4, 130.9 (m-tol)/7.37, 7.03 (o,m-tol-H), 2.42, 2.02 (tol-
CH3), 129.3 (CH of isonitrile)/7.07 (CH of isonitrile), 2.06 (CH3
of isonitrile), 123.3 (ipso-C of tol)/7.37 (m-tol-H), 1.97, 1.42
(C(CH3)2), 122.8 (C1 of isonitrile)/7.07 (m-CH of isonitrile),
120.7 (ipso-C of tol)/7.03 (m-tol-H), 1.42 (C(CH3)2), (117.7/6.44,
6.38), (107.3/6.44, 6.38), (101.6/6.54, 6.44), (100.3/6.38) (each
C5H4/C5H4), 36.0 (CMe2)/1.97, 1.42 (C(CH3)2), 28.9 (C(CH3)2)/
1.97 (C(CH3)2), 27.08 (C(CH3)2)/1.42 (C(CH3)2), 21.4, 21.2 (tol-
CH3)/7.37, 7.07-7.03 (o,m-tol-H), 2.42, 2.02 (tol-CH3), 19.2
(CH3 of isonitrile)/2.06 (CH3 of isonitrile). 31P NMR (dichlo-
1194, 1087 (br, vs), 995, 979, 966, 952, 934, 835, 805, 660 cm-1
.
1H NMR (dichloromethane-d2, 600 MHz): 7.38 (m, 12H, o,m-
tol-H), 7.18 (m, 4H, o-tol-H), 6.73, 6.46, 6.38, 6.20 (each m,
each 2H, C5H4), 2.43, 2.41 (each s, each 6H, tol-CH3), 1.78 (m,
5
6H, CMe2), 1.44 (m, 6H, CMe2), 1.32 (t, J PH ) 3.3 Hz, 3H,
Zr-NC-CH3), 0.50 (br, [B]-CH3). 13C NMR (dichloromethane-
d2, 150 MHz): δ 148.7 (1J FC ) 240 Hz, o-C6F5), 145.1, 144.6
(each s, ipso-C of p-tol), 141.5 (s, CtN), 137.8 (1J FC ) 242 Hz,
p-C6F5), 137.8 (C1 of Cp), 136.7 (1J FC ) 245 Hz, m-C6F5), 135.5
(o-tol), 134.4 (o-tol), 131.5 (2m-tol), 122.5 (ipso-C of tol), 119.6
(ipso-C of tol), 117.1, 108.5, 107.9, 101.2 (Cp), 36.0 (CMe2), 29.4,
26.3 (C(CH3)2), 21.53, 21.42 (tol-CH3), 10.5 ([B]-CH3), 2.92 (s,
CH3CN). GHSQC-NMR24 (dichloromethane-d2): δ 135.5/7.38,
134.4/7.18, (each o-tol); 131.5/7.38 (m-tol); 117.1/6.73, 108.5/
6.46, 107.9/6.20, 101.2/6.38, (each C5H4); 29.4/1.44, 26.33/1.78
(CMe2); 21.53, 21.42/2.43, 2.41 (each tol-CH3); 10.5/0.50 ([B]-
CH3); 1.32/2.92 (CH3CN). GHMBC-NMR24 (dichlorometh-
ane-d2): δ 145.1 (p-tol)/7.38 (o,m-tol-H), 2.43, 2.41 (tol-CH3);
144.6 (p-tol)/7.18 (o-tol-H), 2.43, 2.41 (tol-CH3); 141.5 (CtN)/
1.32 (CH3CN); 137.8 (C1 of Cp)/6.44, 6.38 (C5H4), 1.78, 1.44
(CMe2); 135.5 (o-tol)/7.38 (o,m-tol-H); 134.4 (o-tol)/7.18 (o-tol-
H); 131.5 (2-m-tol)/7.38 (o,m-tol-H), 2.43, 2.41 (tol-CH3); 122.5
(ipso-C of tol)/7.38 (o,m-tol-H); 119.6 (ipso-C of tol)/7.38 (o,m-
tol-H); 117.1/6.38, 108.5/6.20, 107.9/6.46, 6.38, 101.2/6.20 (each
C5H4/C5H4); 36.0 (CMe2)/1.78, 1.44 (C(CH3)2); 29.4 (C(CH3)2)/
1.78 (C(CH3)2); 26.3 (C(CH3)2)/1.44 (C(CH3)2); 21.5, 21.4
(tol-CH3)/7.38 (o,m-tol-H), 2.43, 2.41 (tol-CH3). 31P NMR
(dichloromethane-d2, 81.0 MHz): δ -44.7. Anal. Calcd for
romethane-d2, 81.0 MHz): δ -51.7. Anal. Calcd for C91H63
-
NB2F30P2Zr (1915.24): C, 57.07; H, 3.32; N, 0.73. Found: C,
56.70; H, 3.59; N, 0.80.
Ackn owledgm en t. Financial support from the Fonds
der Chemischen Industrie, the Ministerium fu¨r Wis-
senschaft und Forschung des Landes Nordrhein-West-
falen, and the Hoechst AG is gratefully acknowledged.
Su p p or tin g In for m a tion Ava ila ble: Details about the
X-ray crystal structures; including ORTEP diagrams and
tables of crystal data and structure refinement, atomic coor-
dinates, bond lengths and angles, anisotropic displacement
parameters, and hydrogen coordinates for 1b, 2b, 3a , 5, and
5′ (52 pages). Ordering information is given on any current
masthead page.
(24) Braun, S.; Kalinowski, H.; Berger, S. In 100 and More Basic
NMR Experiments; VCH: Weinheim, 1996; and references cited
therein.
OM970573T