Cationic zirconocene and hafnocene aryl complexes

Article abstract of DOI:10.1021/om700436z

Cationic (C₅H₄R)₂ZrAr⁺ aryl species (2a-d: R = H; Ar = o-tolyl (a), 2-Me-4-F-C₆H₃ (b), 3-F-C₆H₄ (c), Ph (d); 2e: R = Me, Ar = Ph) are generated by the reaction of a 1:1 mixture of (C₅H₄R) ₂ZrAr₂ and (C₅H₄R) ₂ZrMe₂ with 2 equiv of [CPh₃][B(C ₆F₅)₄] via methide abstraction and ligand exchange steps. Complex 2d and the Cp₂HfAr⁺ analogues (2f,g: Ar = o-tolyl (f), Ph (g)) are generated by the reaction Of Cp ₂MAr₂ with [C₆Me₆H] [B (C ₆F₅)₄]. NMR studies suggest that these metallocene aryl cations exist as (C₅H₄R) ₂M(Ar)(RCl)⁺ solvent adducts in chlorocarbon solution. NMR and DFT studies show that the (C₅H₄R)₂Zr(Ar) (RCl)⁺ species contain β-C-H-Zr agostic interactions involving an ortho-aryl hydrogen. The endo isomers, in which the β-agostic interaction occupies the central coordination site, are ca. 5 kcal/mol more stable than the exo isomers, in which the β-agostic interaction occupies a lateral site. The aryl agostic interactions are weaker for Hf than Zr, and Cp₂Hf(Ph)(C ₆D₅Cl)⁺ (2g·C₆D ₅Cl) does not contain an agostic interaction.

Full text of DOI:10.1021/om700436z

4746
Organometallics 2007, 26, 4746-4755
Cationic Zirconocene and Hafnocene Aryl Complexes
Orson L. Sydora, Stefan M. Kilyanek, and Richard F. Jordan*
Department of Chemistry, The UniVersity of Chicago, 5735 South Ellis AVenue, Chicago, Illinois 60637
ReceiVed May 3, 2007
Cationic (C5H4R)2ZrAr+ aryl species (2a-d: R ) H; Ar ) o-tolyl (a), 2-Me-4-F-C6H3 (b), 3-F-C6H4
(c), Ph (d); 2e: R ) Me, Ar ) Ph) are generated by the reaction of a 1:1 mixture of (C5H4R)2ZrAr2 and
(C5H4R)2ZrMe2 with 2 equiv of [CPh3][B(C6F5)4] via methide abstraction and ligand exchange steps.
Complex 2d and the Cp2HfAr+ analogues (2f,g: Ar ) o-tolyl (f), Ph (g)) are generated by the reaction
of Cp2MAr2 with [C6Me6H][B(C6F5)4]. NMR studies suggest that these metallocene aryl cations exist as
(C5H4R)2M(Ar)(RCl)+ solvent adducts in chlorocarbon solution. NMR and DFT studies show that the
(C5H4R)2Zr(Ar)(RCl)+ species contain â-C-H-Zr agostic interactions involving an ortho-aryl hydrogen.
The “endo” isomers, in which the â-agostic interaction occupies the central coordination site, are ca. 5
kcal/mol more stable than the “exo” isomers, in which the â-agostic interaction occupies a lateral site.
The aryl agostic interactions are weaker for Hf than Zr, and Cp2Hf(Ph)(C6D5Cl)+ (2g‚C6D5Cl) does not
contain an agostic interaction.
Chart 1
Introduction
We recently described the synthesis of d0 zirconocene aryl
cations [(C5H4R)2Zr(C6F5)][B(C6F5)4] (A; Chart 1; R ) H, Me)
by methyl abstraction from (C5H4R)2Zr(C6F5)Me using [Ph3C]-
[B(C6F5)4].1 Complexes A exist as solvent adducts and contain
dative o-CF‚‚‚Zr interactions in chlorobenzene solution. A reacts
with allyltrimethylsilane and propargyltrimethylsilane to form
d0 (C5H4R)2Zr(C6F5)(substrate)+ alkene and alkyne complexes.
These unusual species are stabilized by the combination of the
silyl substituent, which strengthens substrate coordination via
the â-Si effect, and the poor nucleophilicity of the -C6F5 group,
which inhibits insertion. We are interested in preparing d0
(C5H4R)2M(Ar)+ species with modified aryl groups in order to
find systems that form observable alkene or alkyne adducts and
undergo insertion, since such systems may be useful mechanistic
probes.
While cationic group 4 metallocene alkyl complexes have
been studied extensively, analogous aryl species are less
common.2 Hlatky et al. described the zwitterionic complex Cp*2-
Zr+(2-Et-5-BAr3-C6H3) (B; Cp* ) C5Me5; Ar ) p-Et-Ph),
which is formed by the reaction of Cp*2ZrMe2 with [HNMe2-
Ph][BPh4] to generate Cp*2ZrMe+ followed by CH activation
of the counterion.3 More recently, we reported [Cp*2Zr(η2-C,-
Cl-2-Cl-C6H4)][B(C6F5)4] (C), which is formed by CH activation
of the coordinated solvent in [Cp*2Zr(Me)(ClC6H5)][B(C6F5)4].4
Protonation of Cp2ZrPh2 with [HNMe2Ph][BPh4] in THF
produced [Cp2Zr(Ph)(THF)][BPh4] (D).5 Piers found that ab-
straction of the methylene group from the “tuck-in” complex
Cp*(η5-η1-C5Me4CH2)ZrPh by B(C6F5)3 produced the zwitterion
Cp*{η5-C5Me4CH2B(C6F5)3}ZrPh (E).6 Cp2Hf(Ar)(µ-Me)B-
(C6F5)3 (F; Ar ) Ph, o-, m-, p-tolyl) complexes were prepared
by the reaction of Cp2Hf(Ar)(Me) with B(C6F5)3.7
Here we describe two routes to group 4 (C5H4R)2MAr+ (R
) H, Me) complexes and NMR and computational studies of
â-C-H aryl agostic interactions in these species.
Results and Discussion
(C5H4R)2MAr2 Complexes. The neutral metallocene diaryl
complexes (C5H4R)2MAr2 (1a-d: M ) Zr; R ) H; Ar )
o-tolyl (a), 2-Me-4-F-C6H3 (b), 3-F-C6H4 (c), Ph (d); 1e: M )
Zr, R ) Me, Ar ) Ph; 1f,g: M ) Hf, R ) H; Ar ) o-tolyl (f),
Ph (g)) were prepared by the reaction of the corresponding
metallocene dichloride with LiAr (BrMgAr for Ar ) m-FC6H4).8
* Corresponding author. E-mail: rfjordan@uchicago.edu.
(1) (a) Stoebenau, E. J., III; Jordan, R. F. J. Am. Chem. Soc. 2004, 126,
11170. (b) Stoebenau, E. J., III; Jordan, R. F. J. Am. Chem. Soc. 2006,
128, 8638.
(2) Cationic Organozirconium and Organohafnium Compounds. Guram,
A. S.; Jordan, R. F. In ComprehensiVe Organometallic Chemistry, 2nd ed.;
1995; Vol. 4, pp 589-625.
(3) Hlatky, G. G.; Turner, H. W.; Eckman, R. R. J. Am. Chem. Soc.
1989, 111, 2728.
+
+
Reaction of (C5H4R)2ZrAr2 with HNMePh2 or CPh3
.
Attempts to synthesize (C5H4R)2ZrAr+ species by the reaction
of (C5H4R)2ZrAr2 with [HNMePh2][B(C6F5)4] or [Ph3C]-
[B(C6F5)4] were unsuccessful. The reaction of 1e with [HNMePh2]-
[B(C6F5)4] in C6D5Cl did generate the Cp′2ZrPh+ cation (Cp′
(4) Wu, F.; Dash, A. K.; Jordan, R. F. J. Am. Chem. Soc. 2004, 126,
15360.
(5) Borkowsky, S. L.; Jordan, R. F.; Hinch, G. D. Organometallics 1991,
10, 1268.
(6) Sun, Y.; Spence, R. E. v. H.; Piers, W. E.; Parvez, M. Yap, G. P. A.
J. Am. Chem. Soc. 1997, 119, 5132.
(7) (a) Sadow, A. D.; Tilley, T. D. J. Am. Chem. Soc. 2002, 124, 6814.
(b) Sadow, A. D.; Tilley, T. D. J. Am. Chem. Soc. 2003, 125, 9462.
10.1021/om700436z CCC: $37.00 © 2007 American Chemical Society
Publication on Web 08/09/2007

Cationic Zirconocene and Hafnocene Aryl Complexes
Organometallics, Vol. 26, No. 19, 2007 4747
Scheme 1a
Scheme 2a
a Anion ) B(C6F5)4
.
-
sentative cases (2a,d) were also characterized by elemental
analysis. Attempts to characterize these species by ESI-MS were
unsuccessful due to the instability of the cation under ESI
conditions. However, the reaction of 2e with MeCtCSiMe3
yields the insertion product Cp′2Zr{C(SiMe3)dC(Me)Ph}+,
which was characterized by ESI-MS and NMR.11
Compound 2e is stable in C6D5Cl solution at 22 °C for hours
in the dark, but decomposes in 12 h in the presence of light to
the dinuclear complex [{Cp′2Zr(µ-Cl)}2][B(C6F5)4]2, which
crystallizes from solution.12 A similar photochemical degradation
was observed for Cp2Zr(CH2Ph)(C6D5Cl)+ and Cp*2Zr(Me)-
(C6D5Cl)+.12 Complexes 2a-e are far less stable in CD2Cl2. In
this solvent, 2d decomposes slowly at -20 °C and rapidly at
room temperature to [{Cp2Zr(µ-Cl)}2][B(C6F5)4]2.
a Anion ) B(C6F5)4
.
-
) C5H4Me), but it was not possible to isolate this species free
of NMePh2. The reaction of 1d with [Ph3C][B(C6F5)4] in
chlorobenzene produced a mixture of Cp complexes, and Cp2-
ZrPh+ was not identified.
Synthesis of (C5H4R)2MAr+ Species Using Protonated
Arenes. A more straightforward route to base-free (C5H4R)2-
ZrAr+ cations is protonolysis of (C5H4R)2ZrAr2 complexes by
protonated arenes (Scheme 2).13 The reaction of 1d and [C6-
Me6H][B(C6F5)4] (3) in C6D5Cl produces [Cp2M(Ph)(C6D5Cl)]-
[B(C6F5)4] (2d‚C6D5Cl) cleanly. One equivalent of benzene and
hexamethylbenzene are also formed in this reaction, but these
arenes do not compete with the C6D5Cl solvent for binding to
the zirconocene cation. Similarly, the reaction of 1f,g and 3 in
C6D5Cl produces [Cp2Hf(o-tolyl)(C6D5Cl)][B(C6F5)4] (2f‚
C6D5Cl) and [Cp2Hf(Ph)(C6D5Cl)][B(C6F5)4] (2g‚C6D5Cl).
Complexes 2f,g‚C6D5Cl were characterized by NMR, but could
not be isolated in pure form. The reaction of 2f,g‚C6D5Cl with
MeCtCSiMe3 yields Cp2Hf{C(SiMe3)dC(Me)Ar}+ insertion
products, which were characterized by ESI-MS.
C6Me6-Induced Degradation of Cp2MAr+ in CD2Cl2. The
reaction of 1d with 3 proceeds quite differently in CD2Cl2 than
in C6D5Cl. In CD2Cl2 at -78 °C, this reaction results in
complete consumption of the starting materials and formation
of 0.5 equiv of the hexadienyl cation [C6Me6(CD2Cl)]+ (4), 0.5
equiv of [{Cp2ZrPh}2(µ-Cl)][B(C6F5)4] (5), 0.5 equiv of
C6Me6, and 1 equiv of benzene, as shown in Scheme 3. An
analogous reaction was observed for 1g and 3 in CD2Cl2 at
-78 °C.
Synthesis of (C5H4R)2ZrAr+ by Methide Abstraction and
Aryl Exchange. The potential utility of (C5H4R)2Zr(Ph)(Me)
as a precursor to (C5H4R)2ZrPh+ was investigated. The reaction
of Cp′2Zr(Me)Cl with 1 equiv of PhLi in Et2O produced a
mixture of Cp′2Zr(Ph)(Me) (70%), 1e (20%), and Cp′2ZrMe2,
from which Cp′2Zr(Ph)(Me) could not be isolated in pure form.
However, the appearance of Cp′2ZrMe2 and 1e in the product
mixture indicates that the phenyl group can exchange between
zirconocene centers under mild conditions. This observation
suggested that (C5H4R)2ZrAr+ species might be accessible from
a mixture of (C5H4R)2ZrAr2, (C5H4R)2ZrMe2, and [Ph3C]-
[B(C6F5)4] via the methide abstraction and ligand exchange
process in Scheme 1.9 Indeed, addition of an equimolar
chlorobenzene solution of (C5H4R)2ZrMe2 and (C5H4R)2ZrAr2
(1a-e) to a chlorobenzene solution of 2 equiv of [Ph3C]-
[B(C6F5)4] cleanly generates [(C5H4R)2Zr(Ar)(C6H5Cl)][B(C6F5)4]
(2a-e‚C6H5Cl) and Ph3CMe as shown in Scheme 1. Com-
pounds 2a-e were isolated free of C6H5Cl in good yields (34-
62%) as yellow solids by removal of the solvent under vacuum,
washing of the resulting pale orange oil with benzene, and
vacuum drying. These complexes strongly retain benzene (0.7
to 2.5 equiv) despite vacuum drying.10
Cations 2a-e were characterized by NMR spectroscopy in
CD2Cl2 and C6D5Cl solution. The 1H and 13C NMR resonances
of the benzene appear at the free benzene positions, indicating
that the benzene does not coordinate in solution. Two repre-
Compounds 4 and 5 were identified by NMR, ESI-MS (4
only), and independent synthesis. The cation of 4 was synthe-
sized as [C6Me6(CD2Cl)][Zr2Cl9] by Floriani’s method.14 Com-
pound 5 was generated by the reaction of Cp2ZrPh+ (2d) with
0.5 equiv of [NBu3CH2Ph]Cl.
As shown in Scheme 4, the reaction in Scheme 3 likely
proceeds by initial protonolysis of a M-Ph bond of 1 to yield
(8) (a) Samuel, E.; Rausch, M. D. J. Am. Chem. Soc. 1973, 95, 6263.
(b) Chen, S.; Liu, Y.; Wang, J. Sci. Sin. (Engl. Ed.) 1982, 25, 341. (c)
Erker, G.; Czisch, P.; Benn, R.; Rufinska, A.; Mynott, R. J. Organomet.
Chem. 1987, 328, 101. (d) Tainturier, G.; Fahim, M.; Trouve-Bellan, G.;
Gautheron, B. J. Organomet. Chem. 1989, 376, 321. (e) Erker, G. J.
Organomet. Chem. 1977, 134, 189. (f) Chen, S.-S. Kexue Tongbao 1980,
25, 270. (g) Chen, S.-S.; Liu, Y.-Y. Huaxue Tongbao 1978, 5, 275. (h)
Chen, S.-S.; Liu, Y.-Y.; Xuan, Z.-A.; Wang, Z.-K. Huaxue Xuebao 1980,
38, 497.
(11) (a) Eisch, J. J.; Piotrowski, A. M.; Brownstein, S. K.; Gabe, E. J.;
Lee, F. L. J. Am. Chem. Soc. 1985, 107, 7219. (b) Horton, A. D.; Orpen,
A. G. Organometallics 1991, 10, 3910.
(12) Wu, F.; Jordan, R. F. Organometallics 2005, 24, 2688.
(13) (a) Reed, C. A.; Fackler, N. L. P.; Kim, K.; Stasko, D.; Evans, D.
R.; Boyd, P. D. W.; Rickard, C. E. F. J. Am. Chem. Soc. 1999, 121, 6314.
(b) Stasko, D.; Reed, C. A. J. Am. Chem. Soc. 2002, 124, 1148. (c) Reed,
C. A.; Kim, K.; Stoyanov, E. S.; Stasko, D.; Tham, F. S.; Mueller, L. J.;
Boyd, P. D. W. J. Am. Chem. Soc. 2003, 125, 1796.
(9) A similar approach was used to synthesize cationic Al alkyl
compounds. Korolev, A. V.; Ihara, E.; Guzei, I. A.; Young, V. G., Jr.;
Jordan, R. F. J. Am. Chem. Soc. 2001, 123, 8291.
(10) (a) Attempts to use the reaction in Scheme 1 to synthesize hafnocene
aryl cations were unsuccessful. (b) Cp2Hf(Me)(Ph) can be prepared free of
exchange products but is not cleanly converted to Cp2HfPh+ by reaction
(14) Musso, F.; Solari, E.; Floriani, C.; Schenk, K. Organometallics 1997,
16, 4889.
+
with CPh3
.

4748 Organometallics, Vol. 26, No. 19, 2007
Sydora et al.
Scheme 3a
a Anion ) B(C6F5)4
.
-
Scheme 4a
Figure 1. 1H NMR spectra (C5H4Me region) of [Cp′2ZrPh]-
[B(C6F5)4] (2e). Spectrum A: in CD2Cl2 at -95 °C; spectrum B:
in C6D5Cl/CD2Cl2 at -90 °C; spectrum C: in C6D5Cl/CD2Cl2 at
-30 °C.
-
a M ) Zr, Hf; anion ) B(C6F5)4
.
Chart 2a
species Cp*2ScPh is known.16 (ii) 2e may be a contact ion pair
(H), which undergoes fast site epimerization at Zr (i.e., fast
exchange of the aryl ligand and anion between the sides of the
metallocene, likely mediated by the solvent). Coordination of
B(C6F5)4- to electrophilic Zr, Th, Sc, and Al cations is known.17
(iii) 2e may be a solvent adduct (I), which undergoes rapid site
epimerization at Zr. Several closely related d0 metal-haloarene
complexes have been structurally characterized, including Cp2-
Zr(η2-CH2Ph)(ClC6D5)+ and Cp*2Zr(Cl)(ClC6D5)+.4,17b,c,18 (iv)
2e may be a dinuclear cation with bridging aryl groups (J).
Phenyl groups are well-known bridging groups.19
a Cp′ ) C5H4Me.
2d,g‚CD2Cl2, C6Me6, and benzene. Nucleophilic attack of C6-
Me6 on the CD2Cl2 ligand of 2d,g‚CD2Cl2 yields Cp2M(Ph)Cl
and 4. Trapping of Cp2M(Ph)Cl by 2d,g‚CD2Cl2 produces 5
and 6, leaving 0.5 equiv of C6Me6 remaining. The reaction of
independently synthesized 2d with C6Me6 in CD2Cl2 produces
4 and 5. However, C6Me6 is stable in the presence of CD2Cl2
and 3 for hours at room temperature.
The reaction of a 1:1 mixture of 1d and 1e with [C6Me6H]-
[B(C6F5)4] gives only 2d and 2e. No new resonances or line-
broadening effects are observed in the NMR spectra of the
product mixture that can be ascribed to a mixed (C5H5)2Zr(µ-
2+
Ph)2Zr(C5H4Me)2 complex, which would likely form if 2d
A similar pathway was proposed for the reaction of [(F6-
acen)Zr(CH2CMe3)(NEt2Ph)][B(C6F5)4] in CD2Cl2.15 In this
system, nucleophilic attack of NEt2Ph on the CH2Cl2 ligand of
(F6-acen)Zr(CH2CMe3)(CH2Cl2)+ produced [NEt2Ph(CH2Cl)]+
and [{(F6-acen)Zr(CH2CMe3)}2(µ-Cl)]+.
and 2e contained dinuclear dications. This result implies that
2d and 2e exist as mononuclear species in halocarbon solution
and argues against J. The 19F NMR spectrum of 2e in CD2Cl2
at -89 °C contains resonances at the free anion positions, which
argues against tight ion pair structure H.
Solution Structures of (C5H4R)2MAr+ Cations. The 1H and
13C NMR spectra of Cp′2ZrPh+ (2e) in CD2Cl2 at -89 °C and
C6D5Cl at -38 °C each contain two Cp′ ring CH signals,
consistent with C2V symmetry. These data suggest four possible
structures for 2e in chlorocarbon solution (Chart 2): (i) 2e could
be a three-coordinate cation (G) with the aryl group occupying
the central coordination site in the metallocene wedge or
exchanging rapidly between the lateral sites. The isoelectronic
(16) Thompson, M. E.; Baxter, S. M.; Bulls, A. R.; Burger, B. J.; Nolan,
M. C.; Santarsiero, B. D.; Schaefer, W. P.; Bercaw, J. E. J. Am. Chem.
Soc. 1987, 109, 203.
(17) (a) Yang, X.; Stern, C. L.; Marks, T. J. Organometallics 1991, 10,
840. (b) Korolev, A. V.; Delpech, F.; Dagorne, S.; Guzei, I. A.; Jordan, R.
F. Organometallics 2001, 20, 3367. (c) Bouwkamp, M. W.; Budzelaar, P.
H. M.; Gercama, J.; Del Hierro Morales, I.; de Wolf, J.; Meetsma, A.;
Troyanov, S. I.; Teuben, J. H.; Hessen, B. J. Am. Chem. Soc. 2005, 127,
14310.
(18) Bochmann, M.; Jaggar, A. J.; Nicholls, J. C. Angew. Chem., Int.
Ed. Engl. 1990, 29, 780.
(19) (a) Koschmieder, S. U.; Wilkinson, G. Polyhedron 1991, 10, 135.
(15) Tjaden, E. B.; Swenson, D. C.; Jordan, R. F.; Petersen, J. L.
Organometallics 1995, 14, 371.

Cationic Zirconocene and Hafnocene Aryl Complexes
Organometallics, Vol. 26, No. 19, 2007 4749
Table 1. Key NMR Data for Cationic Metallocene Aryl Species
a
a
b
compound
∆δ Hortho-Ar
∆δ Cortho-Ar
J
CH,ortho (Hz)
∆JCH,ortho
Cp2Zr(o-tolyl)(CD2Cl2)+ (2a·CD2Cl2)c
Cp2Zr(o-tolyl)(C6D5Cl)+ (2a·C6D5Cl)d
Cp2Zr(2-Me-4-F-C6H3)(CD2Cl2)+ (2b‚CD2Cl2)c
Cp2Zr(3-F-C6H4)+ (2c·CD2Cl2)c,g
Cp2ZrPh(CD2Cl2)+ (2d‚CD2Cl2)c,h
Cp2ZrPh(C6D5Cl)+ (2d‚C6D5Cl)d,h
Cp′2ZrPh(CD2Cl2)+ (2e·CD2Cl2)c,h
Cp′2ZrPh(C6D5Cl)+ (2e·C6D5Cl)e,h
Cp2Hf(o-tolyl)(C6D5Cl)+ (2f·C6D5Cl)d
Cp2Hf(Ph)(C6D5Cl)+ (2g‚C6D5Cl)d,i
-1.1
-35.2
-33.7
-33.6
-24.5
-15.7
-12.9
124
125
129
141
147
148
-28
-27
-1.1
-1.06
-0.6
-0.15
-0.47
-0.40
-16
-9
-13.8f
-29.7
-2.4
148
131
155
-5f
-17
0
-1.26
-0.18
a ∆δ ) δ(agostic ortho-CH unit of Cp2MAr+) - δ(ortho-CH unit of Cp2MAr2). b ∆J ) J(agostic ortho-CH unit of Cp2MAr+) - J(ortho-CH unit of
Cp2MAr2). c CD2Cl2, -89 °C. d C6D5Cl, 23 °C. e C6D5Cl, -38 °C. f Relative to data for 1e in CD2Cl2 solution at -89 °C. g Data for the agostic CH unit
(C6-H) are listed. h Exchange-averaged values for the agostic and nonagostic ortho CH units. i Exchange-averaged values the two ortho CH units.
Chart 3
temperature, indicating that the sides of the Zr-Ph rings
exchange rapidly. This process may occur by rotation around
the Zr-Ph bond and/or by solvent-mediated site epimerization
at Zr. The NMR spectra of 2e contain one sharp ortho C-H
resonance under conditions where site epimerization is appar-
ently slow (Figure 1, spectrum B), which suggests that Zr-Ph
bond rotation is fast. DFT calculations (Vide infra) show that
2d,e contain one agostic and one nonagostic ortho-CH unit.
Therefore the data in Table 1 represent exchange-averaged
values for one agostic and one normal ortho-C-H unit.
The data in Table 1 show that an ortho-Me substituent on
the aryl ring enhances the agostic interaction of the ortho-H.
For example, the JCH value for the agostic CH unit in 2a‚CD2Cl2
is reduced by 28 Hz compared to the ortho-JCH value in 1a,
while JCH for the agostic CH unit in 2d‚CD2Cl2 is reduced by
only 18 Hz compared to the ortho-JCH value in 1d (assuming
that JCH for the nonagostic ortho-CH unit in 2d‚CD2Cl2 equals
the value for 1d).
The data in Table 1 also suggest that â-agostic interactions
are stronger in (C5H4R)2ZrAr+ species than in the corresponding
Hf species. For example, JCH for the agostic CH in 2a‚C6D5Cl
is lowered by 27 Hz (to 125 Hz) from the corresponding value
for 1a, while JCH for the agostic CH in 2f‚C6D5Cl is lowered
by only 17 Hz (to 131 Hz) from the value for 1f. Moreover,
while 2d‚C6D5Cl has one agostic CH unit, 2g‚C6D5Cl does not.
The agostic interactions in these systems are easily displaced
by ligands. For example, the reaction of 2e with THF yields
Cp′2Zr(Ph)(THF)+ (7), which has a nonagostic phenyl ligand
(∆JCH,ortho ) -2 Hz).23 The reaction of 2d with 1 equiv of
[NBu3CH2Ph]Cl yields Cp2Zr(Ph)(Cl) (8), which does not
exhibit a â-agostic interaction (∆JCH,ortho ) +4 Hz).
As noted above, the 1H NMR spectra of 2e contain two Cp′
ring CH peaks consistent with C2V symmetry in both CD2Cl2
and C6D5Cl down to -95 and -38 °C, respectively. However,
as shown in Figure 1, addition of excess C6D5Cl to a CD2Cl2
solution of 2e at -90 °C causes an increase in the number and
line widths of the Cp′ CH resonances. When the temperature is
raised to -30 °C, the signals coalesce to two peaks, which are
ca. 0.25 ppm upfield from the resonances of 2e in the absence
of C6D5Cl at -30 °C. These results suggest that in CD2Cl2, 2e
exists as a solvent adduct (2e‚CD2Cl2) that undergoes fast site
epimerization and that addition of C6D5Cl results in formation
of Cp′2Zr(Ph)(ClC6D5)+, which undergoes slow site epimeriza-
tion at low temperatures and fast site epimerization at higher
temperatures. Collectively, these results are most consistent with
a structure of type I for 2e in chlorocarbon solution. It is likely
that the other (C5H4R)2MAr+ cations also form solvent adducts
in RCl solution.
â-CH Agostic Interactions in (C5H4R)2M(Ar)+ Species.
Key NMR data for the aryl groups of 2a-g in chlorocarbon
solution are listed in Table 1. These data show that 2a-f contain
â-agostic interactions involving the aryl ortho C-H units, as
shown in Chart 3. The key features that are characteristic of
agostic interactions are high-field ortho-C-H 1H and 13C
resonances and low JCH-ortho values compared to the data for
the corresponding neutral (C5H4R)2MAr2 compounds.20-22 For
Aryl â-CH agostic interactions have been observed previously
in low-temperature X-ray crystal structures of metallocene aryl
complexes. In B and E (Chart 1), the aryl groups lie in the
plane between the Cp* ligands and exhibit distorted M-C-C
1
example, the aryl C6-H H and 13C resonances of Cp2Zr(o-
1
tolyl)(ClCD2Cl)+ (2a‚CD2Cl2) are shifted upfield by 1.1 and
35.2 ppm from the corresponding resonances of 1a, and JCH
for the ortho-CH unit of 2a‚CD2Cl2 (124 Hz) is significantly
reduced from the value for 1a (152 Hz). For 2c, the â-agostic
interaction involves H6, while H2 is nonagostic.
bond angles indicative of â-CH agostic interactions. The H
NMR resonance for the ortho-CH in B appears at high field (δ
4.6), which is indicative of an agostic interaction. The ansa-
metallocenes rac-Me2Si(C5Me4)2Zr(Ph)Cl and Me2Si(C5Me4)2-
Zr(Ph)H exhibit â-CH agostic interactions in the solid state but
not in solution.24 NMR studies of Cp2Zr(CH3)(picoline)+
revealed a high-field 1H NMR shift and a low JCH for the ortho-
CH of the coordinated picoline (compared to free picoline),
consistent with an agostic interaction.22
The 1H and 13C spectra of the phenyl derivatives 2d,e contain
only single resonances for the ortho-CH units, even at low
(20) (a) Brookhart, M.; Green, M. L. H.; Wong, L. Prog. Inorg. Chem.
1988, 36, 1. (b) Crabtree, R. H.; Hamilton, D. G. AdV. Organomet. Chem.
1988, 28, 299. (c) Cotton, F. A.; Luck, R. L. Inorg. Chem. 1989, 28, 3210.
(d) Dawoodi, Z.; Green, M. L. H.; Mtetwa, V. S. B.; Prout, K.; Schultz, A.
J.; Williams, J. M.; Koetzle, T. F. J. Chem. Soc., Dalton Trans. 1986, 1629.
(21) Jordan, R. F.; Bradley, P. K.; Baenziger, N. C.; LaPointe, R. E. J.
Am. Chem. Soc. 1990, 112, 1289.
Computational Results. Structures of Cp2M(Ar)(L)+ Spe-
cies. DFT calculations were used to probe the structures of
(23) ∆JCH,ortho ) change in JCH,ortho compared to the corresponding
(C5H4R)MAr2 compound.
(24) (a) Lee, H.; Desrosiers, P. J.; Guzei, I.; Rheingold, A. L.; Parkin,
G. J. Am. Chem. Soc. 1998, 120, 3255. (b) Lee, H.; Bridgewater, B. M.;
Parkin, G. J. Chem. Soc., Dalton Trans. 2000, 4490.
(22) Jordan, R. F.; Taylor, D. F.; Baenziger, N. C. Organometallics 1990,
9, 1546.

4750 Organometallics, Vol. 26, No. 19, 2007
Sydora et al.
Figure 2. Calculated structures of Cp2M(Ar)(L)+ species.
Cp2M(Ar)(L)+ species and the factors that influence the
â-agostic interactions in these compounds. All reasonable iso-
mers of Cp2Zr(Ph)(CH2Cl2)+ (2d‚CH2Cl2), Cp2Zr(o-tolyl)(CH2-
Cl2)+ (2a‚CH2Cl2), Cp2Zr(p-tolyl)(CH2Cl2)+ (K), Cp2Zr-
(Ph)(THF)+ (D), and Cp2Hf(Ph)(C6H5Cl)+ (2g‚C6H5Cl) were
which a γ-H-agostic interaction involving a tolyl-methyl
hydrogen occupies the central coordination site (2a‚CH2Cl2-
γ-endo). The optimized structures of THF adduct D and Hf
complex 2g‚C6H5Cl do not contain agostic interactions. Metrical
parameters for the optimized structures are listed in Table 2.25
The â-H-agostic interactions in 2a,d‚CH2Cl2 and K are
characterized by short Zr-H(6) distances (2.21-2.48 Å), long
C(6)-H(6) bond distances (1.11-1.13 Å), and small Zr-C(1)-
C(6) bond angles (85-93°). Interestingly, the Zr-H(6) distance
optimized. Figure
found.
2 shows the structures that were
For 2d‚CH2Cl2 and K, two isomers were found: an “endo”
isomer in which the â-agostic interaction occupies the central
coordination site, and an “exo” isomer in which the â-agostic
occupies a lateral site. Three isomers were found for 2a‚
CH2Cl2: the endo and exo â-agostic isomers and an isomer in
(25) DFT structures of Cp2Zr(Ph)(ClC6H5)+ and Cp2Zr(o-tolyl)(ClC6H5)+
also contain agostic interactions (see Supporting Information).

Cationic Zirconocene and Hafnocene Aryl Complexes
Organometallics, Vol. 26, No. 19, 2007 4751
Table 2. Selected Bond Distances (Å), Bond Angles (deg), and Dihedral Angles (deg) for Cp2MAr+ Species
2d‚CH2Cl2-
2d‚CH2Cl2-
2a‚CH2Cl2-
2a‚CH2Cl2-
parameter
endo
exo
endo
exo
K-endo
K-exo
D
2g‚C6H5Cl
M-H(6)
2.477
1.095
1.114
2.205
2.687
2.842
2.286
1.094
1.127
2.232
2.585
2.807
2.418
1.094
1.117
2.209
2.662
2.858
2.210
1.094
1.131
2.242
2.542
2.812
2.484
1.096
1.114
2.201
2.681
2.846
2.289
1.095
1.126
2.222
2.581
2.795
3.018
1.095
1.099
2.264
3.058
3.109
1.095
1.098
2.259
3.118
2.703
av C-Ha
C(6)-H(6)
M-C(1)
M-C(6)
M-Cl(1)
M-O
2.279
2.241
2.245
128.99
109.93
120.56
Cp(1)-Mb
2.234
2.224
131.15
93.49
122.01
118.42
2.241
2.239
131.79
87.63
121.71
71.73
2.228
2.234
131.18
91.77
121.87
119.14
2.239
2.255
130.86
85.24
121.72
78.19
2.233
2.227
130.59
93.41
122.10
117.79
2.239
2.247
131.42
87.86
121.76
72.74
2.224
2.209
131.12
113.62
120.40
97.99
Cp(2)-Mb
Cp-M-Cpc
M-C(1)-C(6)
C(1)-C(6)-H(6)
Cl(1)-M-C(1)
O-M-C(1
96.04
M-Cl(1)-C(S1)
Cl(1)-M-C(1)-C(6)
O-M-C(1)-C(6
M-C(1)-C(6)-H(6)
114.00
38.92
-1.26
-4.71
178.25
0.44
-1.42
-5.47
175.44
0.20
-13.09
-11.04
177.43
2.72
42.05
14.15
10.54
a The average of the bond lengths of all nonagostic aryl C-H bonds. b M-(Cp centroid) distance. c (Cp centroid)-M-(Cp centroid) angle.
Table 3. Difference in Energy between Structures with Exo
and Endo Agostic Interactions
shown in Table 2, the Zr-C(1) bond is 0.02-0.03 Å longer
and the Zr-Cp bonds are 0.01-0.02 Å longer in the exo isomers
than the endo isomers. Moreover, the exo isomers are destabi-
lized by close contacts (<2.6 Å) between the agostic hydrogen
H(6) and the Cp hydrogens.26
structure
Estructure - Eendo (kcal/mol)a
2d‚CH2Cl2-endo
2d‚CH2Cl2-exo
2a‚CH2Cl2-endo
2a‚CH2Cl2-exo
2a‚CH2Cl2-γ-endo
K-endo
0
5.4
0
6.1
5.8
0
The greater stability of the endo isomers compared to the
exo isomers may also be a result of the difference in donor
ability of the Zr-Ph ligand (strong σ-donor) and the agostic
C-H ligand (weak σ-donor). For group 4 metal Cp2M(η2-acyl)X
complexes, the O-inside isomers are more stable than the
O-outside isomers; that is, the complex is more stable when
the stronger donor (the acyl carbon sp2 orbital) occupies the
lateral coordination site. This trend was ascribed to lowering
of the HOMO energy due to greater overlap of the acyl carbon
sp2 orbital and the metal acceptor orbital in the O-inside isomer
than in the O-outside isomer.27 The greater stability of the endo
isomers of â-agostic Cp2M(Ar)(RCl)+ species compared to the
exo isomers is consistent with this trend.
K-exo
4.6
a Energy of the given species relative to that of the corresponding endo
â-C-H-Zr agostic species.
is ca. 0.2 Å shorter, the C(6)-H(6) distance is ca. 0.015 Å
longer, and the Zr-C(1)-C(6) angle is ca. 5.5° smaller in the
exo isomers of 2a,d‚CH2Cl2 and K compared to the endo
isomers, indicating that the agostic interaction is stronger in the
exo isomers than in the endo isomers.
In contrast to 2a,d‚CH2Cl2 and K, for the nonagostic
compounds D and 2g‚C6H5Cl, the M-H(6) distances are greater
than 3 Å, the C(6)-H(6) bonds are not significantly lengthened,
and the M-C(1)-C(6) bond angles are within 10° of the ideal
sp2 value of 120°. Additionally, while the aryl rings in 2a,d‚
CH2Cl2 lie in the plane between the two Cp ligands, which
maximizes overlap of the ortho-C-H bonding orbital and the
acceptor orbital on Zr, the phenyl rings of D and 2g‚C6H5Cl
are rotated ca. 40° out of this plane.
Relative Stability of Endo and Exo Isomers. Even though
the â-H agostic interaction is stronger in the exo isomers than
the endo isomers of 2a,d‚CH2Cl2 and K, the endo isomers are
ca. 5 kcal/mol more stable than the exo isomers, as summarized
in Table 3. One reason for this difference is that the strong
agostic interaction in the exo isomers requires that the Zr-
C(1)-C(6) angle be distorted to bring the C(6)-H(6) bond close
to the metal, which diminishes the overlap between the C(1)
and Zr bonding orbitals and weakens the Zr-C(1) bond. As
Effect of Ortho Methyl Groups on C-H Agostic Interac-
tions. As noted above, NMR data suggest that the aryl â-agostic
interactions are enhanced by ortho-methyl groups. This result
is confirmed by the calculations. As shown in Table 2, the Zr-
H(6) distance is smaller, the C(6)-H(6) bond is longer, and
the Zr-C(1)-C(6) angle is smaller in 2a‚CH2Cl2 compared to
the corresponding isomers of 2d‚CH2Cl2 and K. The structures
of K-endo and K-exo, which contain a para-methyl group, are
nearly identical to those of 2a‚CH2Cl2-endo and 2a‚CH2Cl2-
exo, which implies that the electron-donating effect of the
methyl group does not strongly influence the strength of the
â-agostic interaction. The enhanced agostic interaction in 2a‚
CH2Cl2 can be ascribed to steric crowding between the ortho
methyl group and the Cp2Zr(CH2Cl2) unit, which forces the
C(6)-H(6) bond closer to the Zr center. Similar effects were
noted in zirconocene alkenyl complexes.28
Electronic Features of â-Agostic Interactions in Cp2M-
(Ar)(RCl)+ Cations. Figure 3 shows the C(6)-H(6) bonding
orbital (HONLMO-46)29 of 2a‚CH2Cl2-endo generated by the
(26) The steric crowding in these structures was analyzed using natural
steric analysis (NSA). The NSA-determined “total steric exchange energy”
of 2d‚CH2Cl2-endo is 2.4 kcal mol-1 lower than that of 2d‚CH2Cl2-exo,
and the sum of the pairwise steric exchange energies between the C(6)-
H(6) bonding orbital and the Cp2Zr orbitals of 2d‚CH2Cl2-endo is 4 kcal
mol-1 lower than that for 2d‚CH2Cl2-exo. These estimates sugguest that
2d‚CH2Cl2-endo is less crowded than 2d‚CH2Cl2-exo. See the Supporting
Information for details. For NSA see: (a) Badenhoop, J. K.; Weinhold, F.
J. Chem. Phys. 1997, 107, 5406. (b) Badenhoop, J. K.; Weinhold, F. J.
Chem. Phys. 1997, 107, 5422. (c) Badenhoop J. K.; Weinhold, F. Int. J.
Quantum Chem. 1999, 72, 269.
(27) Tatsumi, K.; Nakamura, A.; Hofmann, P.; Stauffert, P.; Hoffmann,
R. J. Am. Chem. Soc. 1985, 107, 4440.
(28) Hyla-Kryspin, I.; Gleiter, R.; Kru¨ger, C.; Zwettler, R.; Erker, G.
Organometallics 1990, 9, 517.
(29) HONLMO refers to the highest occupied natural localized molecular
orbital. NLMOs are combinations of natural bonding orbitals (NBOs)
obtained by analysis of the possible overlap of the NBOs in a molecule.

4752 Organometallics, Vol. 26, No. 19, 2007
Sydora et al.
formation. Further studies are required to quantify possible
differences in the Lewis acidity of analogous Cp2Zr and Cp2Hf
species.
Conclusions
Cationic (C5H4R)2ZrAr+ aryl species (R ) H, Me) are
generated by the reaction of a 1:1 mixture of (C5H4R)2ZrAr2
and (C5H4R)2ZrMe2 with [CPh3][B(C6F5)4]. Alternatively, both
Zr and Hf Cp2MAr+ cations are generated by the reaction of
Cp2MAr2 with [C6Me6H][B(C6F5)4]. The metallocene aryl
cations exist as (C5H4R)2M(Ar)(RCl)+ solvent adducts in
chlorocarbon solution and generally contain â-C-H-M agostic
interactions. The “endo” isomers, in which the â-agostic
interaction occupies the central coordination site, are ca. 5 kcal/
mol more stable than the “exo” isomers, in which the â-agostic
interaction occupies a lateral site. The aryl agostic interactions
are weaker for Hf than Zr, and Cp2Hf(Ph)(C6D5Cl)+ does not
contain an agostic interaction.
Figure 3. C(6)-H(6) NLMO (HONLMO-46) of 2a‚CH2Cl2-endo
-3
plotted with an iso value of 0.015 ea0 to illustrate the 3.8%
contribution from Zr.
NBO method.30 NBO analysis shows that this NLMO has a
contribution of 3.8% from the Zr (85% of which is d character).
Similar results are observed for other Cp2M(Ar)(RCl)+ species.
The C(6)-H(6) NLMOs in the exo isomers of 2a,d‚CH2Cl2
and K contain a higher Zr contribution (ca. 5%) than in the
endo isomers (ca. 3.5%), consistent with the relative strengths
of the agostic interactions (exo > endo) implied by the
calculated structures. The Zr contribution to the C(6)-H(6)
NLMO is slightly (0.3%) higher in 2a‚CH2Cl2-endo and 2a‚
CH2Cl2-exo compared to the corresponding isomers of 2d‚
CH2Cl2 and K, consistent with enhancement of the agostic
interaction by the ortho methyl group.
Zr versus Hf. The NMR and computational results suggest
that â-CH aryl agostic interactions are stronger in Cp2Zr(Ar)-
(RCl)+ complexes than in analogous Hf species. Differences
in Zr-Ar and Hf-Ar bond strengths (Hf > Zr) may contribute
to this difference.31 The lengthening of the M-aryl bond and
distortion of the M-C(2)-C(6) bond angles that accompany
the agostic interaction are expected to be more difficult for Hf
complexes compared to analogous Zr complexes, and as a result,
agostic interactions may be less favored for Hf than Zr. In
particular, for 2g‚C6H5Cl, the energetic cost of distorting the
Hf-Ph bond may outweigh the stabilization gained by forming
an agostic bond.
Experimental Section
General Procedures. All manipulations were performed using
drybox or Schlenk techniques under an N2 atmosphere, or a high-
vacuum line, unless otherwise indicated. Nitrogen was purified by
passage through columns containing activated molecular sieves and
Q-5 oxygen scavenger. CD2Cl2 and C6D5Cl were distilled from
P4O10 and degassed prior to use. Pentane, hexane, benzene, and
toluene were purified by passage through columns of activated
alumina and BASF R3-11 oxygen scavenger. Cp2ZrPh2,8a Cp′2-
ZrPh2,8b Cp2HfPh2,8a Cp2Zr(o-tolyl)2,8c and Cp2Hf(o-tolyl)28d were
prepared by literature procedures. NMR data for these compounds
are listed below. All other chemicals were purchased from Aldrich
and used as received. Elemental analyses were performed by
Midwest Microlab (Indianapolis, IN).
NMR spectra were recorded on Bruker DMX-500 or DRX-400
spectrometers in Teflon-valved tubes at ambient probe temperature
unless otherwise indicated. 1H and 13C chemical shifts are reported
versus SiMe4 and were determined by reference to the residual
solvent signals. Coupling constants are reported in Hz. For cases
in which 13C{gated-1H} NMR spectra are reported, 13C{1H} NMR
spectra were also recorded to assist in interpretation. For cases in
which JHF values are reported, 1H{19F} NMR spectra were collected
to independently determine JHH values.
Differences in the Lewis acidity of the Zr and Hf species
may contribute to the difference in agostic interactions, but the
available data are insufficient to fully assess this issue. The
equilibrium constant for coordination of pyridine to M(CH2-
Ph)4 in eq 1 is 12.6(6) M-1 for M ) Zr and 460(30) M-1 for
M ) Hf.32 However, differences in the benzyl coordination
mode (η1 vs ηn) complicate interpretation of this difference.
The NMR spectra of ionic compounds contain resonances for
-
the free B(C6F5)4 anion. 19F NMR spectra were obtained for all
-
compounds that contain this anion. Data for B(C6F5)4
:
13C{1H}
1
1
NMR (C6D5Cl, 23 °C) δ 148.9 (d, JCF ) 242), 138.8 (d, JCF
)
245), 136.9 (d, 1JCF ) 245), 124.4 (br m); 13C{1H} NMR (C6D5Cl,
-38 °C) δ 148.9 (d, 1JCF ) 240), 138.8 (d, 1JCF ) 236), 136.9 (d,
1JCF ) 241), 124.7 (br m); 13C{1H} NMR (CD2Cl2, -89 °C) δ
1
1
1
147.1 (d, JCF ) 244), 137.4 (d, JCF ) 242), 135.5 (d, JCF
)
PhCl
243), 122.5 (br m); 19F{1H} NMR (C6D5Cl, 23 °C) δ -131.7 (br
s, 8F, o-F), -161.8 (t, J ) 21, 4F, p-F), -165.9 (br t, 8F, m-F);
19F{1H} NMR (C6D5Cl, -38 °C) δ -132.0 (br d, 8F, o-F), -161.4
(t, J ) 20, 4F, p-F), -165.4 (br t, 8F, m-F); 19F{1H} NMR
(CD2Cl2, -89 °C) δ -133.7 (s, 8F, o-F), -162.5 (t, J ) 19, 4F,
p-F), -166.5 (br t, 8F, m-F).
M(CH2Ph)4 + py y z M(CH2Ph)4(py)
(1)
In contrast, the reaction of a 1:1 mixture of Cp2Zr(Me)(C6D5-
Cl)+ and Cp2Hf(Me)(C6D5Cl)+ with <2 equiv of PMe3 shows
no preference for Cp2Hf(Me)(PMe3)+ over Cp2Zr(Me)(PMe3)+
Electrospray mass spectra (ESI-MS) were recorded on freshly
prepared samples (ca. 1 mg/mL in CH2Cl2) using an Agilent 1100
LC-MSD spectrometer incorporating a quadrupole mass filter with
an m/z range of 0-3000. A 5 µL sample was injected by flow
injection using an autosampler. Purified nitrogen was used as the
nebulizing and drying gas. Typical instrumental parameters: drying
gas temperature 350 °C, nebulizer pressure 35 psi, drying gas flow
12.0 L/min, fragmentor voltage 0 or 70 V. In all cases where
assignments are given, the observed isotope patterns closely
(30) Glendening, E. D.; Badenhoop, J. K.; Reed, A. E.; Carpenter, J. E.;
Bohmann, J. A.; Morales, C. M.; Weinhold, F. NBO 5.0; Theoretical
Chemistry Institute, University of Wisconsin: Madison, WI, 2001; http://
www.chem.wisc.edu/∼nbo5.
(31) (a) Chase, M. W., Jr.; Davies, C. A.; Dome, J. R., Jr.; Frurip, D. J.;
McDonald, R. A.; Syverud, A. N. JANAF Thermo-chemical Tables, 3rd
ed. J. Phys. Chem. Ref. Data 1985, 14, Suppl. 1. (b) Schock, L. E.; Marks,
T. J. J. Am. Chem. Soc. 1988, 110, 7701. (c) Martinho Simo˜s, J. A.;
Beauchamp, J. L. Chem. ReV. 1990, 90, 629.
(32) Felten, J. J.; Anderson, W. P. J. Organomet. Chem. 1972, 36, 87.

Cationic Zirconocene and Hafnocene Aryl Complexes
Organometallics, Vol. 26, No. 19, 2007 4753
matched calculated isotope patterns. The listed m/z value corre-
sponds to the most intense peak in the isotope pattern.
Cp′ Me). 13C{gated-1H} (CD2Cl2, -89 °C): δ 183.9 (s, ipso-Ph),
135.6 (d, J ) 153, o-Ph), 125.6 (d, J ) 157, m-Ph), 124.5 (d, J )
160, p-Ph), 123.4 (s, Cp′ ipso), 113.5 (d, J ) 170, Cp′ CH), 110.2
(d, J ) 172, Cp′ CH), 14.7 (q, J ) 128, Cp′ Me).
Complexes 2a-g were shielded from light when handled in
solution, and CD2Cl2 solutions of 2a-e were freshly made and kept
at temperatures below -60 °C.
1
Cp2Hf(o-tolyl)2 (1f). H NMR (C6D5Cl, 23 °C): δ 7.16 (br s,
Cp2Zr(o-tolyl)2 (1a). 1H NMR (CD2Cl2): δ 7.15 (d, J ) 7, 2H,
H3 or H6), 7.05 (d, J ) 7, 2H, H3 or H6), 6.96 (m, 4H, H4 and
2H, H3 or H6), 7.12 (br d, J ) 7.0, 2H, H3 or H6), 7.08 (t, J )
7.3, 2H, H4 or H5), 7.02 (t, J ) 7.5, 2H, H4 or H5), 5.85 (br s,
10H, Cp), 2.19 (br s, 6H, Me). 13C{1H} NMR (C6D5Cl, 23 °C): δ
190.9 (C1), 146.5 (C2), 133.0 (C6; JCH ) 148 Hz from 13C{gated-
1H} spectrum at 90 °C), 130.5 (C3), 127.8 (C4), 125.6 (C5), 111.0
(Cp), 26.5 (Me). All of the 13C signals are broad due to restricted
rotation of the o-tolyl groups.
Cp2HfPh2 (1g). 1H NMR (C6D5Cl, 23 °C): δ 7.35 (d, J ) 7.2,
4H, o-Ph), 7.23 (t, J ) 7.4, 4H, m-Ph), 7.06 (t, J ) 7.3, 2H, p-Ph),
5.89 (s, 10H, Cp). 13C{gated-1H} NMR (C6D5Cl, 23 °C): δ 191.9
(s, ipso-Ph), 137.6 (d, J ) 155, o-Ph), 127.2 (d, J ) 161, m-Ph),
125.3 (d, J ) 163, p-Ph), 111.9 (d, J ) 177, Cp).
1
H5), 6.12 (s, 10H, Cp), 2.35 (s, 6H, Me). H NMR (C6D5Cl) key
data: δ 7.2 (m, H3 and H6, 2H), 6.82 (s, 10H, Cp). 13C{gated-1H}
NMR (CD2Cl2, -89 °C): δ 182.1 (s, C1), 145.9 (s, C2), 129.0 (d,
J ) 152, C6), 128.4 (d, J ) 154), 124.7 (d, J ) 159), 122.3 (d, J
) 160), 110.3 (d, J ) 174, Cp), 25.4 (q, J ) 125, Me). 13C{gated-
1H} NMR (C6D5Cl) key data: δ 129.6 (d, J ) 152, C6), 111.8
(d, J ) 173, Cp).
Cp2Zr(2-Me-4-F-C6H3)2 (1b). A flask was charged with 2-bromo-
5-fluorotoluene (1.05 g, 5.53 mmol), and a sidearm addition tube
containing Cp2ZrCl2 (0.812 g, 2.78 mmol) was attached. Diethyl
ether (20 mL) was added, the solution was stirred at 23 °C, and
nBuLi (2.1 mL, 2.68 M in hexane, 5.63 mmol) was added dropwise.
After 30 min, the Cp2ZrCl2 was added slowly to the pale yellow
solution and the mixture was stirred for 1.5 h. The solvent was
removed under vacuum, yielding a yellow-white solid. This material
was taken up in toluene (ca. 10 mL) and filtered to give a yellow
filtrate. The filtrate was concentrated under vacuum until the
saturation point was reached. Hexane was layered onto the solution,
precipitating a white microcrystalline solid. A second recrystalli-
zation using the same procedure yielded analytically pure product
(0.18 g, 15%). 1H NMR (CD2Cl2, 23 °C): δ 7.02 (dd, 3JHH ) 8.2,
[Cp2Zr(o-tolyl)][B(C6F5)4] (2a). A chlorobenzene solution
(3 mL) of Cp2Zr(o-tolyl)2 (100 mg, 0.248 mmol) and Cp2ZrMe2
(62.3 mg, 0.248 mmol) was added dropwise to a chlorobenzene
solution (5 mL) of [Ph3C][B(C6F5)4] (457 mg, 0.495 mmol) in the
dark. The mixture was stirred for 30 min at 23 °C. The volatiles
were removed under vacuum, and the resulting orange oil was
washed with benzene (3 × 5 mL) to remove triphenylethane. The
orange oil was dried under vacuum, yielding [Cp2Zr(o-tolyl)]-
[B(C6F5)4]‚(C6H6)1.5 as an orange solid (0.28 g, 53%). The benzene
content was determined by NMR. 1H NMR (CD2Cl2, -89 °C): δ
7.35 (t, J ) 7.5, 1H, aryl), 7.19 (m, 2H, aryl), 6.27 (s, 10H, Cp),
3
4
1
4JHF ) 7.2, 2H, H6), 6.78 (dd, JHF ) 11.5, JHH ) 2.3, 2H, H3),
6.02 (d, J ) 7.3, 1H, H6), 2.32 (s, 3H, Me). H NMR (C6D5Cl)
3
3
4
6.67 (ddd, JHF ) 9.2, JHH ) 8.2, JHH ) 2.5, 2H, H5), 6.14 (s,
key data: δ 5.9 (d, J ) 7, 1H, H6), 5.74 (s, 10H, Cp). 13C{gated-
1H} NMR (CD2Cl2, -89 °C): δ 192.3 (s, C1), 145.2 (s, C2), 130.6
(d, J ) 159), 128.9 (d, J ) 159), 126.6 (poorly resolved d, C5),
112.6 (d, J ) 177, Cp), 93.8 (dd, J ) 124, 9, C6), 22.8 (qd, J )
125, 4, Me). 13C{gated-1H} NMR (C6D5Cl) key data: δ 113.5 (d,
J ) 76, Cp), 95.9 (dd, J ) 125, 10; C6). A sample of 2a for
elemental analysis was further dried under vacuum for 3 days,
yielding material containing 0.7 equiv of C6H6 as determined by
NMR. Anal. Calcd for C41H17BF20Zr‚(C6H6)0.7: C, 51.79; H, 2.03.
Found: C, 51.82; H, 2.31.
10H, Cp), 2.30 (s, 6H, Me). 13C{1H} NMR (CD2Cl2, 23 °C): δ
1
175.8 (s, C1), 162.3 (d, JCF ) 243, C4), 148.4 (br s, C2), 131.3
(br s, C6), 116.1 (d, 2JCF ) 16, C3 or C5), 111.7 (br s, Cp), 109.8
(d, JCF ) 18, C5 or C3), 26.1 (s, Me). 19F{1H} NMR (CD2Cl2,
2
23 °C): δ -119.2 (s). Anal. Calcd for C24H22F2Zr: C, 65.56; H,
5.04. Found: C, 65.29; H, 5.04.
Cp2Zr(3-F-C6H4)2 (1c). A flask was charged with a THF
solution of 3-fluorophenylmagnesium bromide (15.0 mL, 7.50
mmol). The solvent was removed under vacuum to afford a colorless
oil, and Cp2ZrCl2 (1.05 g, 3.59 mmol) was added. Diethyl ether
(20 mL) was added by vacuum transfer, and the mixture was stirred
for 2 h at room temperature, producing a suspension of a white
precipitate in a pale yellow supernatant. The volatiles were removed
under vacuum, and the white solid was triturated with hexane (ca.
15 mL). The solid was taken up in toluene and filtered, and the
filtrate was concentrated under vacuum. The concentrated solution
was layered with hexane at -35 °C, yielding 1c as a white,
[Cp2Zr(2-Me-4-F-C6H3)][B(C6F5)4] (2b). This compound was
prepared from Cp2Zr(2-Me-4-F-C6H3)2 (150 mg, 0.341 mmol), Cp2-
ZrMe2 (85.8 mg, 0.341 mmol), and [Ph3C][B(C6F5)4] (629 mg,
0.682 mmol) using the procedure for 2a. The orange oil was dried
under vacuum, yielding [Cp2Zr(2-Me-4-F-C6H3)][B(C6F5)4]‚(C6H6)1.8
1
as an orange solid (0.54 g, 34%). H NMR (CD2Cl2, -89 °C): δ
6.97 (m, 2H, H3 and H4), 6.31 (s, 10H, Cp), 5.96 (dd, 3JHH ) 7.8,
4JHF ) 4.0, 1H, H6), 2.32 (s, 3H, Me). 13C{gated-1H} NMR (CD2-
1
1
microcrystalline solid (0.35 g, 24%). H NMR (CD2Cl2): δ 7.12
Cl2, -89 °C): δ 186.3 (s, C1), 162.5 (d, JCF ) 247, C4), 147.8
3
4
(td, JHH ) 8, JHF ) 6, 2H, H5), 6.96 (m, 4H, H2 and H6), 6.71
(t, 3JHF ) 9, 3JHH ) 8, 2H, H4), 6.22 (s, 10H, Cp). 13C{gated-1H}
(CD2Cl2, -89 °C): δ 184.8 (s, C1), 160.8 (1JCF ) 249, C3), 130.2
(d, 3JCF ) 6, C2), 118.1 (dd, 1JCH ) 156, 2JCF ) 20, C3), 113.0 (d,
1JCH ) 176, Cp), 112.1 (dd, 1JCH ) 162, 2JCF ) 21, C5), 97.7 (dd,
3
1
1JCH ) 129, JCF ) 10, C6), 23.0 (q, JCH ) 127, Me). 19F{1H}
1
4
1
3
(dd, JCH ) 157, JCF ) 3, C6), 127.1 (dd, JCH ) 161, JCF ) 5,
C5), 121.8 (dd, 1JCH ) 159, 2JCF ) 15, C2), 112.3 (d, 1JCH ) 174,
(CD2Cl2, -89 °C): δ -114.6 (s).
[Cp2Zr(3-F-C6H4)][B(C6F5)4] (2c). This compound was prepared
from Cp2Zr(2-F-C6H4)2 (0.100 g, 0.243 mmol), Cp2ZrMe2 (0.061
g, 0.243 mmol), and [Ph3C][B(C6F5)4] (0.448 g, 0.486 mmol) using
the procedure for 2a. The orange oil was dried under vacuum,
yielding [Cp2Zr(3-F-C6H4][B(C6F5)4]‚(C6H6)1.5 as an orange solid
(0.24 g, 43%). 1H NMR (CD2Cl2, -89 °C): δ 7.40 (td, 3JHH ) 8,
Cp), 111.3 (dd, JCH ) 165, JCF ) 21, C4). The 1H and 13C
assignments were confirmed by HMQC. 19F{1H} (CD2Cl2,
-89 °C): δ -116.3 (s).
1
2
1
Cp2ZrPh2 (1d). H NMR (CD2Cl2, -89 °C): δ 7.20 (d, J )
6.6, 4H, o-Ph), 7.05 (t, J ) 7.2, 4H, m-Ph), 6.96 (t, J ) 6.2, 2H,
1
3
3
p-Ph), 6.17 (s, 10H, Cp). H NMR (C6D5Cl): δ 7.30 (d, J ) 7.2,
4JHF ) 5, 1H, H5), 7.19 (d, JHF ) 7, 1H, H2), 6.93 (td, JHH
)
4H, o-Ph), 7.17 (t, J ) 7.3, 4H, m-Ph), 7.07 (t, J ) 6.6, 2H, p-Ph),
5.91 (s, 10H, Cp). 13C{gated-1H} (CD2Cl2, -89 °C): δ 182.2 (ipso-
Ph), 135.5 (d, J ) 156, o-Ph), 125.8 (d, J ) 160, m-Ph), 124.6 (d,
J ) 159, p-Ph), 111.9 (d, J ) 174, Cp). 13C{1H} (C6D5Cl): δ 183.1
(ipso-Ph), 135.8 (o-Ph), 126.8 (m-Ph), 125.5 (p-Ph), 112.2 (Cp).
3JHF ) 8, 4JHH ) 2, 1H, H4), 6.42 (s, 10H, Cp), 6.37 (d, 3JHH ) 8,
1H, H6). 13C{gated-1H} (CD2Cl2, -89 °C): δ 193.4 (s, C1), 162.4
1
1
3
(d, JCF ) 256, C3), 130.3 (dd, JCH ) 164, JCF ) 6, C5), 120.2
(dd, 1JCH ) 163, 2JCF ) 18, C2), 115.6 (dd, 1JCH ) 165, 2JCF ) 23,
C4), 114.4 (d, 1JCH ) 176, Cp), 105.7 (d, 1JCH ) 141, C6). 19F{1H}
(CD2Cl2, -89 °C): δ -112.0 (s).
1
Cp′2ZrPh2 (1e). H NMR (CD2Cl2, -89 °C): δ 7.27 (d, J )
6.7, 4H, o-Ph), 7.10 (t, J ) 7.2, 4H, m-Ph), 7.02 (t, J ) 7.1, 2H,
p-Ph), 6.15 (m, 4H, Cp′ CH), 5.91 (m, 4H, Cp′ CH), 1.69 (s, 6H,
[Cp2ZrPh][B(C6F5)4] (2d). This compound was prepared from
Cp2ZrPh2 (74.9 mg, 0.199 mmol), Cp2ZrMe2 (50.1 mg, 0.199

4754 Organometallics, Vol. 26, No. 19, 2007
Sydora et al.
mmol), and [Ph3C][B(C6F5)4] (367 mg, 0.398 mmol) using the
procedure for 2a. The pale orange oil was dried under vacuum,
yielding [Cp2ZrPh][B(C6F5)4]‚(C6H6)2.3 as a pale yellow solid (0.289
g, 62%). 1H NMR (CD2Cl2, -89 °C): δ 7.39 (t, J ) 7.5, 2H, m-Ph),
7.24 (t, J ) 7.3, 1H, p-Ph), 7.05 (d, J ) 7.5, 2H, o-Ph), 6.36 (s,
10H, Cp). 13C{gated-1H} (CD2Cl2, -89 °C): δ 193.0 (s, ipso-Ph),
129.2 (d, J ) 161, m-Ph), 128.4 (d, J ) 162, p-Ph), 119.8 (d, J )
147, o-Ph), 113.7 (d, J ) 177, Cp). A sample of the product for
elemental analysis was further dried under vacuum for 3 days,
yielding material containing 1.3 equiv of C6H6 as determined by
NMR. Anal. Calcd for C40H15BF20Zr‚(C6H6)1.3: C, 53.30; H, 2.14.
Found: C, 53.24; H, 2.27.
dried under vacuum. Hexamethylbenzene (40.1 mg, 0.247 mmol)
was added to the vial, and the solids were dissolved in toluene
(3 mL). Triflic acid (5 drops, ca. 0.5 mmol) was added, producing
a yellow oil. Hexane (5 mL) was added, and a yellow solid rapidly
precipitated. The solid was recrystallized two times by layering
hexane onto toluene solutions to produce spectroscopically pure
1
product (0.15 g, 66%). H NMR (CD2Cl2, -89 °C): δ 3.96 (br s,
1H), 2.69 (s, 3H), 2.54 (s, 6H), 2.22 (s, 6H), 1.52 (d, J ) 7.8, 3H).
13C{1H} NMR (CD2Cl2, -89 °C): δ 192.8, 190.8, 139.1, 57.1,
24.3 (2C), 21.0, 15.4. ESI-MS (C6D5Cl) [C6Me6H]+: calcd m/z
163.2, found 163.1.
Generation of [Cp2Hf(o-tolyl)(ClC6D5)][B(C6F5)4] (2f‚C6D5Cl).
An NMR tube was charged with Cp2Hf(o-tolyl)2 (35.1 mg, 0.0712
mmol) and [C6Me6H][B(C6F5)4] (60.0 mg, 0.0712 mmol), and C6D5-
Cl was added by vacuum transfer at -196 °C. The tube was warmed
to 23 °C and vigorously agitated, resulting in a pale yellow solution.
NMR analysis after 15 min at 23 °C showed that clean formation
of 2f‚C6D5Cl, 1 equiv of toluene, and 1 equiv of C6Me6 had
occurred. Data for 2f‚C6D5Cl: 1H NMR (C6D5Cl, 23 °C): δ 7.19
(t, J ) 7.2, 1H, H4 or H5), 7.09 (d, J ) 7.4, 1H, H3), 7.03 (t, J )
7.4, 1H, H4 or H5), 5.88 (d, J ) 7.3, 1H, H6), 5.71 (s, 10H, Cp),
1.97 (s, 3H, Me). 13C{gated-1H} NMR (C6D5Cl, 23 °C): δ 198.3
(s, C1), 147.2 (s, C2), 132.4 (d, J ) 159, C4), 129.2 (d, J ) 155,
C3), 126.3 (d, J ) 161, C5), 112.9 (d, J ) 177, Cp), 103.3 (dd, J
) 131, 9, C6), 23.6 (qd, J ) 126, 4, Me).
Generation of [Cp2Zr(Ph)(ClC6D5)][B(C6F5)4] (2d‚C6D5Cl).
An NMR tube was charged with Cp2ZrPh2 (15.0 mg, 0.0399 mmol)
and [C6Me6H][B(C6F5)4] (33.6 mg, 0.0399 mmol), and C6D5Cl (0.6
mL) was added by vacuum transfer at -196 °C. The tube was
warmed to 23 °C with vigorous agitation, resulting in an orange
solution. NMR analysis after 15 min at 23 °C showed that clean
formation of 2d‚C6D5Cl, 1 equiv benzene, and 1 equiv of C6Me6
had occurred. 1H NMR (C6D5Cl, 23 °C): δ 7.2 (t, J ) 8, 2H, m-Ph),
7.11 (t, J ) 7.2, 1H, p-Ph), 6.83 (d, J ) 7.2, 2H, o-Ph), 5.80 (s, 10
H, Cp). 13C{gated-1H} NMR (C6D5Cl, 23 °C): δ 193.1 (s, ipso-
Ph), 122.9 (d, J ) 148, o-Ph), 114.8 (d, J ) 177, Cp); the m-Ph
and p-Ph resonances are obscured by the solvent peaks.
[Cp′2ZrPh][B(C6F5)4] (2e). This compound was prepared from
Cp′2ZrPh2 (0.151 g, 0.374 mmol), Cp′2ZrMe2 (0.104 g, 0.372
mmol), and [Ph3C][B(C6F5)4] (0.685 g, 0.743 mmol) using the
procedure for 2a. The orange oil was dried under vacuum, yielding
[Cp′2ZrPh][B(C6F5)4]‚(C6H6)2.0 as an orange solid (0.31 g, 36%).
1H NMR (CD2Cl2, -89 °C): δ 7.45 (t, J ) 7.5, 2H, m-Ph), 7.26
(t, J ) 7.5, 1H, p-Ph), 6.87 (d, J ) 7.3, 2H, o-Ph), 6.18 (m, 4H,
Cp′ CH), 6.03 (m, 4H, Cp′ CH), 1.53 (s, 6H, Me). 1H NMR (C6D5-
Cl, -38 °C): δ 7.24 (t, J ) 7.5, 2H, m-Ph), 7.13 (t, J ) 7.5, 1H,
p-Ph), 6.68 (d, J ) 7.1, 2H, o-Ph), 5.67 (m, 4H, Cp′ CH), 5.49 (m,
4H, Cp′ CH), 1.25 (s, 6H, Me). 13C{gated-1H} NMR (C6D5Cl,
-38 °C): δ 194.9 (s, ipso-Ph), 130.3 (t, 2JCH ) 5, Cp′ ipso), 129.6
(coupling obscured by solvent peak, m-Ph), 128.5 (coupling
obscured by solvent peak, p-Ph), 121.8 (d, J ) 148, o-Ph), 116.6
(d, J ) 177, Cp′ CH), 111.3 (d, J ) 177, Cp′ CH), 14.1 (q, J )
129, Me). The 13C NMR assignments of 2e were confirmed by a
1H-13C HMQC spectrum.
Generation of [Cp′2Zr{C(SiMe3)dC(Me)Ph}][B(C6F5)4]. An
NMR tube was charged with 2e (12.0 mg, 0.0105 mmol), and C6D5-
Cl (0.6 mL) was added by vacuum transfer at -196 °C. The tube
was warmed to 23 °C and shaken vigorously, giving a yellow
solution. The tube was cooled to -196 °C, and MeCtCSiMe3
(0.0714 mmol) was added by vacuum transfer. The tube was
warmed to -36 °C, giving a pale orange solution. The tube was
transferred to a precooled NMR probe (-38 °C), and NMR spectra
showed that the insertion reaction was complete. 1H NMR (C6D5-
Cl, -38 °C): δ 7.08 (t, J ) 7.3, 1H, aryl), 7.05 (d, J ) 6.5, 2H,
aryl), 6.96 (t, J ) 7.3, 2H, aryl), 5.86 (m, 2H, Cp′ CH), 5.57 (m,
2H, Cp′ CH), 5.31 (m, 2H, Cp′ CH), 5.27 (m, 2H, Cp′ CH), 1.85
(s, 3H dCMe), 1.83 (s, 6H, Cp′ Me), -0.08 (s, 9H, dCSiMe3).
13C{1H} NMR (C6D5Cl, -35 °C): δ 214.0, 149.1, 146.4, 137.0,
131.8, 131.7, 117.6 (Cp′), 116.9 (Cp′), 115.9 (Cp′), 115.3 (Cp′),
112.7, 26.0 (dCMe), 15.1 (Cp′Me), 1.3 (dCSiMe3). ESI-MS (C6D5-
Cl) [Cp′2Zr(C(SiMe3)dCMePh]+: calcd m/z 437.1, found 437.0.
Generation of [Cp2Hf{C(SiMe3)dC(Me)(o-tolyl)}][B(C6F5)4].
A solution of 2f‚C6D5Cl in C6D5Cl was generated in an NMR tube
as described above and cooled to -196 °C, and MeCtCSiMe3
(2 equiv) was added by vacuum transfer. The tube was warmed to
23 °C for 15 min, giving an orange solution. NMR and ESI-MS
1
analysis confirmed that insertion was complete. H NMR (C6D5-
Cl, 23 °C): δ 7.43 (dd, J ) 6.1, 1.4, 1H, aryl), 7.22 (d, J ) 7.6,
1H, aryl), 6.37 (t, J ) 6.7, 1H, aryl), 6.08 (br m, 1H, aryl), 5.70
(br s, 10H, Cp), 2.08 (s, 3H, o-Me), 1.79 (s, 3H, dCMe), -0.01
(s, 9H, dCSiMe3). 13C{1H} NMR (C6D5Cl, 23 °C): δ 216.5
(HfCd), 149.1, 147.9, 142.9, 140.2, 132.9, 130.8, 114.9 (Cp), 101.5
(dCMeAr), 26.1 (o-Me), 20.2 (dCMe), 1.4 (dCSiMe3). ESI-MS
(C6D5Cl) [Cp2Hf(C(SiMe3)dC(Me)(o-tolyl]+: calcd m/z 513.2,
found 513.0.
Generation of [Cp2Hf(Ph)(ClC6D5)][B(C6F5)4] (2g‚C6D5Cl).
An NMR tube was charged with Cp2HfPh2 (20.0 mg, 0.0432 mmol)
and [C6Me6H][B(C6F5)4] (36.4 mg, 0.0432 mmol), and C6D5Cl was
added by vacuum transfer at -196 °C. The tube was warmed to
23 °C with vigorous agitation, resulting in a pale yellow solution.
NMR analysis after 15 min at 23 °C showed clean formation of
1
2g‚C6D5Cl, 1 equiv benzene, and 1 equiv of C6Me6. H NMR
(C6D5Cl, 23 °C): δ 7.31 (t, J ) 7.5, 2H, m-Ph), 7.17 (m, 3H, o-,
p-Ph), 5.90 (s, 10H, Cp). 13C{1H} NMR (C6D5Cl, 23 °C): δ 192.8
(s, ipso-Ph), 135.2 (d, J ) 155, o-Ph), 129.1 (coupling obscured
by solvent peak, p-Ph), 128.6 (d, J ) 162, m-Ph), 115.4 (d, J )
177, Cp).
Generation of [Cp2Hf{C(SiMe3)dC(Me)Ph}][B(C6F5)4]. A
solution of 2g‚C6D5Cl in C6D5Cl was generated in an NMR tube
as described above and cooled to -196 °C, and MeCtCSiMe3
(30 µmol) was added by vacuum transfer. The tube was warmed
to 23 °C and agitated, giving a yellow solution. The solvent was
removed under vacuum. The solid was dried under vacuum for 30
min, and fresh C6D5Cl (0.6 mL) was added by vacuum transfer.
NMR and ESI-MS analysis confirmed that insertion was complete.
1H NMR (C6D5Cl, 23 °C): δ 7.28 (d, J ) 6.5, 2H, o-Ph), 7.15 (t,
partially obscured by solvent, p-Ph), 6.97 (t, J ) 7.4, partially
obscured by solvent, m-Ph), 5.74 (s, 10H, Cp), 1.89 (s, 3H, Me),
-0.03 (s, 9H, SiMe3). 13C{1H} NMR (C6D5Cl, 23 °C): δ 216.3
(Hf-C), 152.7 (Ph), 150.5 (Ph), 138.0 (Ph), 131.9 (Ph), 115.3 (Cp),
113.7 (dCMePh), 25.8 (Me), 1.4 (SiMe3). ESI-MS (C6D5Cl) [Cp2-
Hf(C(SiMe3)dC(Me)(Ph)]+: calcd m/z 499.1, found 499.0.
[C6Me6H][B(C6F5)4] (3). This compound was prepared using
the method developed by Reed for [H(mesitylene)][B(C6F5)4] and
[H(tetramethylbenzene)][B(C6F5)4].13 A glass vial was silylated by
treatment with a solution containing Me3SiCl and CH2Cl2 (1:3
volume ratio) for 5 min followed by an acetone rinse and oven
drying for 12 h. The vial was charged with [Ph3C][B(C6F5)4] (0.242
g, 0.262 mmol) and triethylsilane (3 mL). The mixture was stirred
overnight, and the volatiles were removed under vacuum. The
resulting white solid was washed with hexane (2 × 5 mL) and

Cationic Zirconocene and Hafnocene Aryl Complexes
Organometallics, Vol. 26, No. 19, 2007 4755
[C6Me6(CD2Cl)][Zr2Cl9] (4). The nondeuterated analogue of 4,
[C6Me6(CH2Cl)][Zr2Cl9], was previously characterized by X-ray and
elemental analysis.14 An NMR tube was charged with C6Me6 (11.6
mg, 0.0715 mmol) and ZrCl4 (33.3 mg, 0.143 mmol), and CD2Cl2
(0.9 mL) was added by vacuum transfer at -78 °C. The tube was
warmed to 40 °C for 3 h, giving a suspension of a white solid in
(5.3 mg, 17 µmol), and CD2Cl2 was added by vacuum transfer at
-78 °C. The tube was vigorously agitated at 23 °C until all of the
solids dissolved to give a colorless solution. H NMR (CD2Cl2,
-89 °C): δ 7.14 (d, J ) 7.1, 2H, o-Ph), 7.02 (t, J ) 7.3, 2H,
m-Ph), 6.94 (t, J ) 7.2, 1H, p-Ph), 6.29 (s, 10H, Cp). 13C{gated-
1H} (CD2Cl2, -89 °C): δ 182.3 (s, ipso-Ph), 136.5 (d, J ) 157,
o-Ph), 126.4 (d, J ) 158, m-Ph), 124.2 (p-Ph), 113.5 (d, J ) 175,
Cp).
1
1
a yellow supernatant. H NMR (CD2Cl2): δ 2.91 (s, 3H), 2.69 (s,
6H), 2.41 (s, 6H), 1.55 (s, 3H). 13C{1H} NMR (CD2Cl2): δ 194.6,
194.5, 142.3, 61.5, 46.7 (1-2-3-2-1 pentet, JCD ) 27 Hz), 26.2, 24.1,
22.3, 16.7. ESI-MS (C6D5Cl) [C6Me6(CD2Cl)]+: calcd m/z 213.1,
found 213.0.
Computational Methods. Structures were optimized using the
Gaussian 03 software package using density functional theory
(DFT).33 The geometry optimizations were performed using the
BP8634 density functional. All main group atoms were modeled
using the 6-31G* basis set.35 Zirconium was modeled using the
LANL2DZ basis set including an effective core potential.36 Hafnium
was modeled using the SDD basis set with a small effective core
potential replacing 60 core electrons. Calculations of reference
compounds established that this methodology correctly predicts the
structures of chlorocarbon complexes and the presence of agostic
interactions (see Supporting Information). Energies are reported
without zero-point corrections. Figures of optimized geometries
were drawn using the MOLEKEL software package.37
Generation of [{Cp2ZrPh}2(µ-Cl)][B(C6F5)4] (5). An NMR
tube was charged with [Cp2ZrPh][B(C6F5)4]‚(C6H6)2.6 (28.2 mg, 23.9
µmol) and [NBu3CH2Ph]Cl (3.7 mg, 12 µmol), and CD2Cl2 was
added by vacuum transfer at -78 °C. The tube was vigorously
agitated at 23 °C until the solids dissolved to give a colorless
1
solution. H NMR (CD2Cl2, -89 °C): δ 7.16 (d, J ) 6.6, 4H,
o-Ph), 7.07 (m, 6H, m- and p-Ph), 6.30 (s, 20H, Cp). 13C{1H} (CD2-
Cl2, -89 °C): δ 185.2 (ipso-Ph), 132.3 (o-Ph), 127.3 (p-Ph), 126.8
(m-Ph), 115.0 (Cp).
Generation of [{Cp2HfPh}2(µ-Cl)][B(C6F5)4] (6). An NMR
tube was charged with Cp2HfPh2 (3.3 mg, 0.0071 mmol) and [C6-
Me6H][B(C6F5)4] (6.5 mg, 0.0077 mmol), and CD2Cl2 (0.6 mL)
was added by vacuum transfer at -196 °C. The tube was warmed
to -78 °C and agitated to give a pale yellow solution. NMR analysis
after 30 min at -78 °C showed clean formation of 6, 1 equiv of
benzene, 0.5 equiv of 4, and 0.5 equiv of C6Me6. Data for 6: 1H
NMR (CD2Cl2, -80 °C): δ 7.31 (d, J ) 8.1, 4H, o-Ph), 7.19 (t, J
) 7.5, 4H, m-Ph), 7.10 (t, J ) 7.4, 2H, p-Ph), 6.26 (s, 20H, Cp).
13C{1H} NMR (CD2Cl2, -80 °C): δ 188.6 (ipso-Ph), 136.7 (o-
Ph), 127.1 (m-Ph), 114.5 (Cp). The p-Ph resonance is obscured by
the benzene peak.
Generation of [Cp′2Zr(Ph)(THF)][B(C6F5)4] (7). A solution
of 2f‚C6D5Cl in C6D5Cl was generated in an NMR tube and cooled
to -196 °C, and THF (4 equiv) was added by vacuum transfer.
The tube was warmed to 23 °C, giving a pale yellow solution. The
volatiles were removed under vacuum. The pale yellow solid was
washed with hexane (1 mL) and benzene (2 × 1 mL), triturated
with CD2Cl2 (0.2 mL), and dissolved in CD2Cl2 (0.6 mL), and NMR
spectra were recorded. 1H NMR (CD2Cl2, -89 °C): δ 7.23 (t, J )
7, 2H, m-Ph), 7.13 (t, J ) 7, 1H, p-Ph), 7.09 (d, J ) 7, 2H, o-Ph),
6.44 (br s, 2H, Cp′ CH), 6.27 (br s, 2H, Cp′ CH), 6.23 (br s, 2H,
Cp′ CH), 6.01 (br s, 2H, Cp′ CH), 4.04 (m, 4H, THF), 2.08 (m,
4H, THF), 1.83 (s, 6H, Cp′ Me). 13C{gated-1H} NMR (CD2Cl2,
-89 °C): δ 186.5 (s, ipso-Ph), 131.5 (d, J ) 151, o-Ph), 129.6 (s,
Cp′ ipso), 127.6 (d, J ) 160, m-Ph), 126.9 (d, J ) 161, p-Ph),
117.8 (d, J ) 174, Cp′ CH), 113.7 (d, J ) 176, Cp′ CH), 113.6 (d,
J ) 176, Cp′ CH), 112.3 (d, J ) 173, Cp′ CH), 79.3 (t, J ) 155,
THF), 25.4 (t, J ) 135, THF), 14.7 (q, J) 129, Cp′ Me).
Cp2Zr(Ph)Cl (8). An NMR tube was charged with [Cp2ZrPh]-
[B(C6F5)4]‚(C6H6)2.6 (2d, 20 mg, 17 µmol) and [NBu3CH2Ph]Cl
Acknowledgment. This work was supported by the National
Science Foundation (CHE-0516950). We acknowledge the
Burroughs Welcome Fund Interfaces Cross-Disciplinary Train-
ing Program at the University of Chicago for partial support of
the computer cluster. We thank Jeffery R. Hammond for helpful
discussions.
Supporting Information Available: Details concerning the
choice and validation of the computational methods and additional
computational results (pdf). This material is available free of charge
via the Internet at http://pubs.acs.org.
OM700436Z
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