Sigma-bond metathesis reactions of zirconocene alkyl cations with phenylsilane

Article abstract of DOI:10.1021/om049099z

The zirconocene methyl cations [(C₅R₅)ZrMe(ClC ₆D₅)] [B(C₆F₅)₄] (C ₅R₅ = C₅H₅ (1a), C₅H ₄Me (1b)) react with PhSiH₃ in the dark to yield [{(C ₅R₅)₂Zr(μ-H)}₂][B(C ₆F₅)₄]₂ (5a, b) and a mixture of Ph_xMe_yH_zSi products. The reaction proceeds by initial Zr-C/Si-H σ-bond metathesis via a four-center transition state in which Si is β to Zr. In the presence of light, significant amounts of [{(C₅R₅)₂Zr(μ-Cl)}₂] [B(C ₆F₅)₄]₂ (4a,b) are formed by photochemical reaction of (C₅R₅)₂ZrH ⁺ species with the chlorobenzene solvent. The azazirconacycle [rac-(EBI)Zr{η²(C,N)-CH₂CHMe(6-phenyl-2-pyridyl)}] [B(C₆F₅)₄] (2, EBI = 1,2-ethylene-bis-indenyl) does not react with PhSiH₃ at 23°C. However at 85°C, 2 deinserts propene to afford the η²-pyridyl complex [rac-(EBI)Zr{η²(C,N)-(6-phenyl-2-pyridyl)}][B(C₆F ₅)₄] (6), which is catalytically isomerized to [rac-(EBI)Zr{η²(C,N)-2-(2-pyridyl)phenyl}][B(C₆F ₅)₄] (7) by PhSiH₃. The key step in this process is Zr-G/Si-H σ-bond metathesis of 6 with PhSiH₃ via a transition state in which Si is α to Zr. The less crowded azazirconacycle [Cp₂Zr{η²(C,N)-CH₂CHMe-(6-methyl-2-pyridyl) }][B(C₆F₅)₄] (3) reacts with PhSiH₃ directly to afford [{Cp₂Zr(SiPhH₂)}₂]-[B(C ₆F₅)₄]₂ (8) via a transition state in which Si is α to Zr. Steric factors may play a role in determining the selectivity of these reactions.

Full text of DOI:10.1021/om049099z

2688
Organometallics 2005, 24, 2688-2697
Sigma-Bond Metathesis Reactions of Zirconocene Alkyl
Cations with Phenylsilane
Fan Wu and Richard F. Jordan*
Department of Chemistry, The University of Chicago, 5735 South Ellis Avenue,
Chicago, Illinois 60637
Received November 20, 2004
The zirconocene methyl cations [(C5R5)2ZrMe(ClC6D5)][B(C6F5)4] (C5R5 ) C5H5 (1a),
C5H4Me (1b)) react with PhSiH3 in the dark to yield [{(C5R5)2Zr(µ-H)}2][B(C6F5)4]2 (5a,b)
and a mixture of PhxMeyHzSi products. The reaction proceeds by initial Zr-C/Si-H σ-bond
metathesis via a four-center transition state in which Si is â to Zr. In the presence of light,
significant amounts of [{(C5R5)2Zr(µ-Cl)}2][B(C6F5)4]2 (4a,b) are formed by photochemical
reaction of (C5R5)2ZrH+ species with the chlorobenzene solvent. The azazirconacycle [rac-
(EBI)Zr{η2(C,N)-CH2CHMe(6-phenyl-2-pyridyl)}][B(C6F5)4] (2, EBI ) 1,2-ethylene-bis-inde-
nyl) does not react with PhSiH3 at 23 °C. However at 85 °C, 2 deinserts propene to afford
the η2-pyridyl complex [rac-(EBI)Zr{η2(C,N)-(6-phenyl-2-pyridyl)}][B(C6F5)4] (6), which is
catalytically isomerized to [rac-(EBI)Zr{η2(C,N)-2-(2-pyridyl)phenyl}][B(C6F5)4] (7) by PhSiH3.
The key step in this process is Zr-C/Si-H σ-bond metathesis of 6 with PhSiH3 via a transition
state in which Si is R to Zr. The less crowded azazirconacycle [Cp2Zr{η2(C,N)-CH2CHMe-
(6-methyl-2-pyridyl)}][B(C6F5)4] (3) reacts with PhSiH3 directly to afford [{Cp2Zr(SiPhH2)}2]-
[B(C6F5)4]2 (8) via a transition state in which Si is R to Zr. Steric factors may play a role in
determining the selectivity of these reactions.
Scheme 1
Introduction
The development of productive catalytic C-H ac-
tivation processes based on σ-bond metathesis reac-
tions is an attractive goal.1 Earlier we reported that
(C5R5)2ZrR′+ species catalyze the net insertion of olefins
into the ortho C-H bonds of 2-substituted pyridines in
the presence of H2 via the mechanism shown in Scheme
1.2 However, as the key metallacycle cleavage step (step
i) in Scheme 1 occurs by Zr-C bond hydrogenolysis, the
C-Zr bond of the metallacycle is converted into a C-H
bond in the disubstituted pyridine product with at-
tendant loss of functionality. Therefore, alternative
metallacycle cleavage reactions that install a functional
group in the product are desirable.
One possible alternative metallacycle cleavage reac-
tion is σ-bond metathesis with a silane, which could be
incorporated into the hypothetical catalytic cycle in
Scheme 2.
Several stoichiometric reactions of cationic (or cat-
ionic-like) group 4 metallocene alkyl or aryl species with
PhSiH3 have been reported. Tilley showed that
CpCp*HfMe(µ-Me)B(C6F5)3 (Cp ) C5H5; Cp* ) C5Me5)
undergoes σ-bond metathesis with PhSiH3 to afford
CpCp*HfH(µ-H)B(C6F5)3 and PhMe2SiH.3 Harrod re-
ported that an in-situ generated “Cp2ZrBu+” species
reacts with PhSiH3 to afford a Cp2ZrH+ species.4 Ad-
ditionally, PhSiH3 functions as a “silanolytic” chain
transfer agent in olefin polymerization reactions cata-
lyzed by {Me2Si(C5Me4)NtBu}TiMe+, titanocene, and
* To whom correspondence should be addressed. E-mail: rfjordan@
uchicago.edu.
(1) (a) Davies, J. A.; Watson, P. L.; Liebman, J. F.; Greenberg, A.
Selective Hydrocarbon Activation; VCH: New York, 1990. (b) Pittard,
K. A.; Lee, J. P.; Cundari, T. R.; Gunnoe, T. B.; Peterson, J. L.
Organometallics 2004, 23, 5514. (c) Sadow, A. D., Tilley, T. D. J. Am.
Chem. Soc. 2003, 125, 7971. (d) Sadow, A. D., Tilley, T. D. Angew.
Chem., Int. Ed. 2003, 42, 803. (e) Labinger, J. A.; Bercaw, J. E. Nature
2002, 417, 507. (f) Shilov, A. E.; Shul’pin, G. B. Chem. Rev. 1997, 97,
2879. (g) Thompson, M. E. J. Am. Chem. Soc. 1987, 109, 203. (h)
Watson, P. L. J. Am. Chem. Soc. 1983, 105, 6491.
(2) (a) Dagorne, S.; Rodewald, S.; Jordan, R. F. Organometallics
1997, 16, 5541. (b) Rodewald, S.; Jordan, R. F. J. Am. Chem. Soc. 1994,
116, 4491. (c) Guram, A. S.; Jordan, R. F.; Tayler, D. F. J. Am. Chem.
Soc. 1991, 113, 1833. (d) Guram, A. S.; Jordan, R. F. Organometallics
1991, 10, 3470. (e) Guram, A. S.; Jordan, R. F. Organometallics 1990,
9, 2190. (f) Jordan, R. F.; Guram, A. S. Organometallics 1990, 9, 2116.
(g) Jordan, R. F.; Taylor, D. F.; Baenziger, N. C. Organometallics 1990,
9, 1546. (h) Jordan, R. F.; Tayler, D. F. J. Am. Chem. Soc. 1989, 111,
778.
(3) (a) Sadow, A. D.; Tilley, T. D. Organometallics 2003, 22, 3577.
(b) Sadow, A. D.; Tilley, T. D. Organometallics 2001, 20, 4457. (c)
Sadow, A. D., Tilley, T. D. J. Am. Chem. Soc. 2003, 125, 9462. (d)
(C5R5)2ZrMe+ species also catalyze the dehydropolymerization of
PhSiH3. See Toru, I.; Tilley, T. D. Polyhedron 1994, 13, 2231.
10.1021/om049099z CCC: $30.25 © 2005 American Chemical Society
Publication on Web 04/28/2005

Reactions of Zirconocene Cations with Phenylsilane
Organometallics, Vol. 24, No. 11, 2005 2689
Scheme 2
Figure 1. Zirconocene alkyl cations studied in this work.
-
The counterion is B(C6F5)4 in all cases.
Scheme 3
lanthanocene catalysts, and (less efficiently) Cp2ZrR+
catalysts, via reaction with active LnM(polymeryl) spe-
cies to produce LnMH and polymeryl-SiPhH2.5 In all of
these reactions, Si occupies the position that is â to the
metal in the four-center σ-bond metathesis transition
state A in eq 1.6 An analogous transition state would
be required in Scheme 2.
affords SiH4 and CpCp*HfPh+, which reacts further
with PhSiH3 to generate Ph2SiH2 and CpCp*HfH+.
To probe the feasibility of exploiting “silanolytic”
Zr-C bond cleavage reactions in olefin/pyridine coupling
processes, we have studied the stoichiometric reactions
of PhSiH3 with several representative (C5R5)2ZrR′+
complexes.
Results
Synthesis of (C5R5)2ZrR′+ Species. Four (C5R5)2-
ZrR′+ species were studied in this work: the simple
methyl complexes [(C5R5)2ZrMe(ClC6D5)][B(C6F5)4] (C5R5
) Cp (1a), C5R5 ) Cp′ (1b)) and the azazirconacy-
cles [rac-(EBI)Zr{η2(C,N)-CH2CHMe(6-phenyl-2-pyri-
dyl)}][B(C6F5)4] (2, EBI ) 1,2-ethylene-bis-indenyl)
and [Cp2Zr{η2(C,N)-CH2CHMe(6-methyl-2-pyridyl)}]-
[B(C6F5)4] (3). These species are shown in Figure 1.
Complexes 1a,b were generated in C6D5Cl solution
by the reaction of the corresponding zirconocene di-
methyl complexes with [Ph3C][B(C6F5)4] as shown in eq
2 and described in detail elsewhere.8
However, the opposite selectivity (i.e., Si R to the
metal) has been observed in other cases.7 For example,
in-situ generated Cp′2ZrH+ (Cp′ ) C5H4Me) reacts with
PhSiH3 to afford the zirconocene silyl cation Cp′2Zr-
(SiH2Ph)+, which adopts an interesting dinuclear struc-
ture.4 In addition, as shown in Scheme 3, CpCp*HfH-
(µ-H)B(C6F5)3 reacts with PhSiH3 via competitive Si-H
bond activation (transition state B) and Si-Ph bond
activation (transition state C).3b Transition state B
affords H2 and CpCp*Hf(SiPhH2)+, which catalyzes
silane dehydrocoupling reactions. Transition state C
(4) (a) Dioumaev, V. K.; Harrod, J. F. Organometallics 1997, 16,
2798. (b) Dioumaev, V. K.; Harrod, J. F. Organometallics 1996, 15,
3859. (c) Dioumaev, V. K.; Harrod, J. F. Organometallics 1994, 13,
1548.
(5) (a) Makio, H.; Koo, K.; Marks, T. J. Macromolecules 2001, 34,
4676. (b) Koo, K.; Marks, T. J. J. Am. Chem. Soc. 1999, 121, 8791. (c)
Koo, K.; Marks, T. J. J. Am. Chem. Soc. 1998, 120, 4019. (d) Fu, P.;
Marks, T. J. J. Am. Chem. Soc. 1995, 117, 10747.
Complexes 2 and 3 were prepared by the reaction of
the corresponding in-situ generated (C5R5)2Zr(η2-pyrid-
2-yl)+ species with propene, as shown in Scheme 4 and
described earlier for the corresponding MeB(C6F5)3- and
(6) For other σ-bond metathesis reactions of Zr and f-element metal
alkyl complexes with silanes that proceed via four-center transition
states in which Si is â to the metal, see: (a) Voskoboynikov, A. Z.;
Parshina, I. N.; Shestakova, A. K.; Butin, K. P.; Beletskaya, I. P.;
Kuz’mina, L. G.; Howard, J. A. K. Organometallics 1997, 16, 4041. (b)
Dash, A. K.; Gourevich, I.; Wang, J. Q.; Wang, J.; Kapon, M.; Eisen,
M. S. Organometallics 2001, 20, 5084. (c) Molander, G. A.; Julis, M. J.
Am. Chem. Soc. 1995, 117, 4415. (d) Gountchev, T. I.; Tilley, T. D.
Organometallics 1999, 18, 5661. (e) Fu, P.; Brard, L.; Li, Y.; Marks, T.
J. J. Am. Chem. Soc. 1995, 117, 7157. (f) de Haan, K. H.; Wielstraand,
Y.; Eshuis, J. J. W.; Teuben, J. H. J. Organomet. Chem. 1987, 323,
181. (g) Molander, G. A.; Corrette, C. P. Tetrahedron Lett. 1998, 39,
5011.
(7) For σ-bond metathesis reactions of group 3 and lanthanide metal
alkyl complexes with silanes that proceed via four-center transition
states in which Si is R to the metal, see ref 1d and: (a) Radu, N. S.;
Tilley, T. D.; Rheingold, A. L. J. Organomet. Chem. 1996, 516, 41. (b)
de Haan, K. H.; de Boer, J. L.; Teuben, J. H. Organometallics 1986, 5,
1726.
-
BPh4 salts.2a,h
Reaction of [Cp2ZrMe(ClC6D5)][B(C6F5)4] (1a)
with PhSiH3. The reaction of 1a and 1 equiv of PhSiH3
under ambient room light in C6D5Cl for 20 min at 23
°C results in complete consumption of the two reactants
and formation of a red oil.9 The oil gradually solidifies
over the course of several days. The resulting orange
solid is insoluble in hydrocarbon and chlorinated sol-
(8) Wu, F.; Dash, A. K.; Jordan, R. F. J. Am. Chem. Soc. 2004, 126,
15360.

2690 Organometallics, Vol. 24, No. 11, 2005
Wu and Jordan
Scheme 4
2+
Figure 2. ORTEP view of the {Cp2Zr(µ-Cl)}2 dication
of 4a. Hydrogen atoms are omitted. Key bond distances (Å)
and angles (deg): Zr(1)-Cl(1) 2.569(1); Zr(1)-Cl(1A) 2.581-
(1); Zr(1)-Centroid(1) 2.174(1); Zr(1)-Centroid(2) 2.164-
(1); Cl(1A)-Zr(1)-Cl(1) 82.0(1); Zr(1)-Cl(1)-Zr(1A) 98.0(1);
Centroid(1)-Zr(1)-Centroid(2) 129.8(1).
vents, but is soluble in THF and CH3CN. The 1H NMR
spectrum of a THF-d8 solution of the solid (isolated after
6 days), prepared and maintained at -90 °C, shows that
two dinuclear dicationic complexes, [{Cp2Zr(µ-Cl)}2]-
[B(C6F5)4]2 (4a) and [{Cp2Zr(µ-H)}2][B(C6F5)4]2 (5a), are
present in a 1:3 ratio (total > 90%). These species were
identified by independent synthesis (vide infra). Ad-
ditionally, single crystals of 4a were obtained from the
solid and identified by X-ray diffraction. A mixture of
silanes is formed, including PhSiMeH2, PhSiMe2H,
PhSiMe3, Ph2SiH2, Ph2SiMeH, Ph2SiMe2, Ph3SiH,
Ph3SiMe, and Ph4Si, which were identified by GC-MS
analysis of the reaction mixture. No disilanes or higher
polysilanes were observed by GC-MS.3d
Scheme 5
In a series of similar experiments under ambient room
light, the organometallic products were analyzed at
different stages of the oil solidification process. These
analyses revealed that the ratio of 4a/5a increases with
time. For example, the oil isolated after a 20 min
reaction time comprises a 1:12 mixture of 4a and 5a.
This ratio increases with time to 1:9 (10 h), 1:5 (20 h),
and 1:4 (40 h), and finally levels off at 1:3 after 6 days,
at which point the oil is completely solidified. In
contrast, the reaction of 1a with PhSiH3 under the same
conditions, but protected from light, affords 5a in
greater than 90% yield without formation of 4a. These
observations imply that 4a is formed from 5a or the
corresponding mononuclear species Cp2ZrH+ or Cp2ZrH-
(ClC6D5)+ by a photochemical process. The overall
reaction between 1a and 1 equiv of PhSiH3 is shown in
Scheme 5.
Scheme 6
Independent Synthesis of [{Cp2Zr(µ-Cl)}2]-
[B(C6F5)4]2 (4a). Complex 4a can be generated by two
routes (eq 3). The reaction of 1a with Ph3CCl in C6D5Cl
affords orange crystalline 4a in 90% yield. Alternatively,
the reaction of 1a with Me3SiCl in C6D5Cl affords
analytically pure 4a in 80% yield.
contacts. The dinuclear dication of 4a is shown in Figure
2 and comprises two bent zirconocene units linked by
two bridging chloride ligands. The Zr(µ-Cl)2Zr core is
planar. The Zr-(µ-Cl) bonds (average 2.575(1) Å) are
elongated compared to that in Cp2ZrCl2 (2.446(3) Å), as
expected.10
Complex 4a dissolves in CD3CN to form Cp2ZrCl-
(NCCD3)n+, which undergoes partial disproportionation
to Cp2ZrCl2 and Cp2Zr(NCCD3)32+, as shown in Scheme
-
6 and observed previously for the analogous BPh4
salt.11 The 1H NMR spectrum of the CD3CN solution of
4a consists of three resonances at δ 6.52, 6.51, and 6.39,
which correspond to the Cp resonances of Cp2ZrCl2, Cp2-
The solid state structure of 4a contains {Cp2Zr-
2+
-
(µ-Cl)}2 and B(C6F5)4 ions, with no close interionic
(10) Prout, K.; Cameron, T. S.; Forder, R. A.; Critchley, S. R.;
Denton, B.; Rees, G. V. Acta Crystallogr. 1974, B30, 2290.
(11) Jordan, R. F.; Echols, S. F. Inorg. Chem. 1987, 26, 383.
(9) In this paper, the phrase ambient room light refers to standard
fluorescent room lighting.

Reactions of Zirconocene Cations with Phenylsilane
Organometallics, Vol. 24, No. 11, 2005 2691
Scheme 7
Zr(NCCD3)32+, and Cp2ZrCl(NCCD3)n+, respectively.
The equilibrium constant, Keq ) [Cp2ZrCl2][Cp2Zr-
(NCCD3)32+][Cp2ZrCl(NCCD3)n+ -2, is 2.0(1) at 23 °C in
]
CD3CN. A similar value (Keq ) 1.0(1) at 23 °C) was
-
1
observed for the BPh4 salt.11 The H NMR spectrum
2+
Figure 3. ORTEP view of the {Cp′2Zr(µ-Cl)}2 dication
of 4a in THF-d8 comprises a singlet at δ 6.87.
of 4b. Hydrogen atoms are omitted. Key bond distances
(Å) and angles (deg): Zr(1)-Cl(1) 2.577(5); Zr(1)-Cl(1A)
2.588(5); Zr(1)-Centroid(1) 2.159(5); Zr(1)-Centroid(2)
2.177(5); Cl(1A)-Zr(1)-Cl(1) 84.2(1); Zr(1)-Cl(1)-Zr(1A)
95.8(1); Centroid(1)-Zr(1)-Centroid(2) 130.0(1).
The direct analogue of 4a, [{Cp2Zr(µ-Cl)}2][BF4]2, was
generated previously by the reaction of {Cp2Zr(µ-Cl)}2
with AgBF4 and characterized by elemental analysis
and conductivity.12a The bromide complexes [{1,2-
(SiMe2)2(η5-C5H3)2Zr(µ-Br)}2][B(C6F5)4]212b and [{Cp2Hf-
3c
(µ-Br)}2][B(C6F5)4]2 were also reported.
hydride resonances shift to δ 6.20 and 5.78 respectively,
indicating that THF-d8 converts the dimeric structure
to a monomeric terminal hydride species Cp2ZrH(THF-
d8)+ (Scheme 7).15 The 1H NMR resonances of bridging
hydrides are generally upfield of terminal hydride
resonances in d0 zirconocene systems (e.g., {Cp′2ZrH-
(µ-H)}2 (δZr-H 3.75; δµ-H -2.98),13c {(tetrahydroindenyl)2-
ZrH(µ-H)}2 (δZr-H 4.59; δµ-H -1.56),13b Cp′2ZrH(THF)+
(δ 5.88),14a (C5Me5)2ZrH2 (δ 7.46),13g (C5Me5)2ZrH(OMe)
(δ 5.70)13g). THF solutions of 5a solidify within 1 h at
23 °C due to polymerization of the solvent by 5a, as
described earlier for Cp′2ZrH(THF)+.14a
Reaction of [Cp′2ZrMe(ClC6D5)][B(C6F5)4] (1b)
with PhSiH3. Complex 1b reacts with PhSiH3 under
ambient room light in a fashion similar to 1a to yield
[{Cp′2Zr(µ-Cl)}2][B(C6F5)4]2 (4b) and [{Cp′2Zr(µ-H)}2]-
[B(C6F5)4]2 (5b) in a 1:2 ratio as the major organome-
tallic products, as shown in Scheme 5. Only 5b is formed
when the reaction is conducted in the absence of light.
In addition, the same series of silane products as formed
in the reaction of 1a is produced. The identities of 4b
and 5b were confirmed by independent synthesis, and
the structure of 4b was confirmed by X-ray diffraction
(Figure 3).
Proposed Mechanism for the Reaction of 1a,b
with PhSiH3. The key observations that are relevant
to the mechanism of the reaction of 1a,b with PhSiH3
in Scheme 5 are as follows: (i) Only a trace amount of
CH4 is formed; (ii) the exclusive Zr product in the dark
reaction is Zr-hydride species 5a,b; and (iii) the Zr-Me
group of 1a,b ends up in the PhxMeyHzSi (x + y + z )
4) silane mixture. These observations are consistent
with the σ-bond metathesis process in Scheme 8, in
which Si occupies the position â to Zr in transition state
D. The initially formed (C5R5)2ZrH+ species E (which
may be solvated) is trapped as dimer 5a,b in the dark
reaction. In the presence of light, E and/or 5a,b undergo
competitive photochemical reaction with the chloroben-
zene solvent to yield 4a,b.16,17
Independent Synthesis of [{Cp2Zr(µ-H)}2]-
[B(C6F5)4]2 (5a). The reaction of 1a with 1 atm of H2
in C6D5Cl in the absence of light (23 °C, Scheme 7)
results in complete consumption of 1a within 10 min
and precipitation of 5a as a yellow solid. 5a is isolated
as an analytically pure solid in 95% yield. However, the
reaction of 1a with H2 under ambient room light affords
a 25:1 mixture of 5a and 4a.
The IR spectrum of solid 5a contains a νZr-H band at
1337 cm-1, which shifts to 1040 cm-1 in [{Cp2Zr(µ-D)}2]-
[B(C6F5)4]2 (5a-d2; prepared from 1a and D2). The νZr-H
value for 5a is within the range observed for bridging
hydrides in other d0 metallocene systems, e.g., {Cp2Zr-
(µ-H)(CH2C6H11)}2 (1380 cm-1), {Cp2ZrH(µ-H)}2 (1300
cm-1), and {(C5R5)2M(µ-H)(THF)}2 (1240-1350 cm-1
;
C5R5 ) Cp or Cp′; M ) Lu, Er, Y).13 Higher νZr-H values
were observed for the terminal hydrides Cp2ZrH(THF)+
(1450 cm-1), Cp2ZrH(PMe3)2+ (1498 cm-1), and Cp′2ZrH-
(THF)+ (1390 cm-1).14 On the basis of these results, 5a
is assigned a dimeric dicationic structure analogous to
that of 4a.
The 1H NMR spectrum of a solution of 5a in THF-d8
prepared and maintained at -90 °C displays a Cp
resonance at δ 6.75 and a hydride resonance at δ -0.53,
which is consistent with a dinuclear µ-H structure.
When the solution is warmed to 23 °C, the Cp and
(12) (a) Cuenca, T.; Royo, P. J. Organomet. Chem. 1985, 293, 61.
(b) Brandow, C. G.; Mendiratta, A.; Bercaw, J. E. Organometallics
2001, 20, 4253. For other d0 {LnM(µ-X)}22+ species see: (c) Gomez, R.;
Green, M. L. H.; Haggitt, J. L. J. Chem. Soc., Dalton Trans. 1996,
936. (d) Zhang, Y.; Reeder, E. K.; Keaton, R. J.; Sita, L. R. Organo-
metallics 2004, 23, 3512. (e) Vollmerhaus, R.; Rahim, M.; Tomaszewski,
R.; Xin, S.; Taylor, N. J.; Collins, S. Organometallics 2000, 19, 2161.
(13) (a) Gell, K. I.; Posin, B.; Schwartz, J.; Williams, G. M. J. Am.
Chem. Soc. 1982, 104, 1846. (b) Weigold, H.; Bell, A. P.; Willing, R. I.
J. Organomet. Chem. 1974, 73, C23. (c) Jones, S. B.; Peterson, J. L.
Inorg. Chem. 1981, 20, 2889. (d) Wailes, P. C.; Weigold, H. J.
Organomet. Chem. 1970, 24, 405. (e) James. B. D.; Nanda, R. K.;
Wallbridge, M. G. H. Inorg. Chem. 1967, 6, 1979. (f) Evans, W. J.;
Meadows, J. H.; Wayda, A. L.; Hunter, W. J.; Atwood, J. L. J. Am.
Chem. Soc. 1982, 104, 2008. (g) Manriquez, J. M.; MaAlister, D. R.;
Sanner, R. D.; Bercaw, J. E. J. Am. Chem. Soc. 1976, 98, 6733.
(14) (a) Guo, Z.; Bradley, P. K.; Jordan, R. F. Organometallics 1992,
11, 2690. (b) Jordan, R. F.; Bajgur, C. S.; Dasher, W. E. Organometallics
1987, 6, 1041.
-
(15) The analogous BPh4 salt is insoluble. See ref 14a.

2692 Organometallics, Vol. 24, No. 11, 2005
Wu and Jordan
Scheme 8
Scheme 10
Scheme 11
Scheme 9
PhSiH3 (20 min, in the light) contains resonances for
Cp2ZrH(THF-d8)+ (88%), Cp2ZrCl(THF-d8)+ (8%),
Cp2ZrPh(THF-d8)+ (2%),18 and several other minor
Cp2Zr species. This oil reacts with PhSiH3 to afford
Ph2SiH2, Ph3SiH, Ph4Si, and SiH4. Also, as noted above,
Tilley showed that CpCp*HfH(µ-H)B(C6F5)3 mediates
redistribution of PhSiH3 to Ph2SiH2 and SiH4.3b,19-22
Reaction of [rac-(EBI)Zr{η2(C,N)-CH2CHMe(6-
phenyl-2-pyridyl)}][B(C6F5)4] (2) and PhSiH3. Com-
plex 2 does not react with 2.5 equiv of PhSiH3 at 23 °C
in C6D5Cl. However, heating the mixture to 85 °C for
20 h results in complete consumption of 2 and consump-
tion of 1.5 equiv of PhSiH3. The major silane product is
Ph2SiH2 (0.7 equiv vs Zr), and small amounts of
Ph3SiH, Ph4Si, and SiH4 are also formed. No other
significant Si-containing products could be identified.
1H NMR analysis of the reaction mixture shows that a
C1-symmetric Zr species, [rac-(EBI)Zr{η2(C,N)-2-(2-
pyridyl)phenyl}][B(C6F5)4] (7, Scheme 11), is formed in
90% yield and that atactic oligopropene is also produced.
These observations suggest that, at 85 °C, 2 undergoes
deinsertion of propene to generate [rac-(EBI)Zr{η2(C,N)-
(6-phenyl-2-pyridyl)}][B(C6F5)4] (6),2a which in turn
reacts with PhSiH3 to yield 7, as shown in Scheme 11.
7 is an isomer of 6. The cationic zirconocene species in
the system catalyze the propene oligomerization and
silane redistribution reactions. Independent experi-
ments show that 6 reacts rapidly (<30 min) with PhSiH3
at 23 °C to afford 7 in 90% yield. Ph2SiH2 is also formed
in this reaction.
The silane products can form by two pathways. First,
σ-bond metathesis of the Zr-Me bond of 1a,b with the
Si-H bond of PhMexH3-xSi (x ) 1, 2) will produce
PhMex+1H2-xSi, as shown in Scheme 9.
The formation of diphenyl silanes, triphenyl silanes,
and Ph4Si requires redistribution of Si-Ph groups. As
suggested in Scheme 10, the key step in this process is
probably σ-bond metathesis of the Si-Ph bond of
PhSiH3 (or other Ph-Si species) and the Zr-H bond of
the initially formed (C5R5)2ZrH+ species to produce
(C5R5)2ZrPh+ and SiH4. Subsequent reaction of (C5R5)2-
ZrPh+ with PhxMeyHzSi (x + y + z ) 4) should produce
Phx+1MeyHz-1Si with regeneration of (C5R5)2ZrH+ (cf.
(C5R5)2ZrMe+ reactions in Scheme 8). Consistent with
this proposal, the 1H NMR of spectrum of a THF-d8
solution of the oil formed in the reaction of 1a with
(16) 1a,b also react photochemically with chlorobenzene to yield
4a,b (see ref 8), but much more slowly (20% conversion after 8 days)
than 4a,b are formed in the PhSiH3 reactions (20 min). The mechanism
of these photochemical reactions is unknown at present. The reaction
of 1a,b with PhSiH3 produces 1 equiv of C6D5H per (C5R5)2ZrCl+ unit
of 4a,b, which was identified by GC-MS and 1H NMR. In addition, a
trace amount of C6D5-C6D5 was detected by GC-MS. These observa-
tions suggest that homolytic cleavage of the Cl-C6D5 bonds of (C5R5)2-
ZrR(ClPh)+ species occurs.
(17) The -90 °C 1H NMR spectrum of a THF-d8 solution of the solid
isolated from the reaction of 1a with PhSiH3 after 6 days, prepared
and maintained at -90 °C, contains resonances for Cp2ZrH(THF-d8)+,
corresponding to 2% of the total Cp2Zr species present, along with
major resonances for 4a and 5a. The mononuclear hydride Cp2ZrH-
(THF-d8)+ could form by trace solvolysis of dimer 5a or by solvolysis
The 1H NMR spectrum of 7 generated by the PhSiH3
reaction in Scheme 11 is partially obscured by the
of a mixed dinuclear hydride chloride species {Cp2Zr}2(µ-H)(µ-Cl)2+
.
We conclude that, at most, only a trace quantity of this mixed species
is present in the isolated solid.
(18) Borkowsky, S. L.; Jordan, R. F.; Hinch, G. D. Organometallics
1991, 10, 1268.

Reactions of Zirconocene Cations with Phenylsilane
Organometallics, Vol. 24, No. 11, 2005 2693
Scheme 12
Figure 4. ORTEP view of the rac-(EBI)Zr{η2(C,N)-2-(2-
pyridyl)-phenyl}+ cation of 7. Hydrogen atoms are omitted.
Key bond distances (Å) and angles (deg): Zr(1)-N(1)
The NMR spectra of 7 are fully consistent with the
solid state structure. The number, intensities, and
multiplicities of the 1H NMR aromatic resonances, and
2.260(6);
Zr(1)-C(31)
2.254(6);
Zr(1)-Centroid(1)
2.177(5); Zr(1)-Centroid(2) 2.196(5); Centroid(1)-Zr(1)-
Centroid(2) 127.5(4); C(31)-Zr(1)-N(1) 76.0(4).
1
the H-1H COSY spectrum, establish that 7 contains
two inequivalent indenyl ligands, an ortho-disubstituted
phenyl ring, and an ortho-substituted pyridine ring,
which is consistent with metalation of an ortho-phenyl
position of the phenylpyridine unit. The Zr-CPh,ipso 13C
resonance appears at δ 193.3, close to that for Cp2ZrPh-
resonances of the silane products (Ph2SiH2, Ph3SiH, and
Ph4Si), from which 7 could not be isolated cleanly.
However, 7 can be prepared independently by the
reaction of 6 with H2, as shown in eq 4.
1
(THF)+ (δ 184.9).18 The ortho-pyridine H NMR reso-
nance of 7 (H21 in Figure 4) was assigned on the basis
of NOESY data and a deuterium labeling experiment
(6 + D2) and appears at δ 6.03, far upfield of the
corresponding resonance of free 2-Ph-pyridine (δ 8.59),
due to anisotropic shielding by the proximate indenyl
C6 ring. This result establishes that the pyridine is
N-coordinated to Zr. Similarly, the ortho-phenyl reso-
nance (H30 in Figure 4) is shifted upfield to δ 5.84.
Mechanism of Formation of 7. The PhSiH3-medi-
ated isomerization of 6 to 7 likely proceeds by the
mechanism in Scheme 12. Complex 6 and PhSiH3 react
via σ-bond metathesis transition state F, in which Si
occupies a position R to Zr, to yield rac-(EBI)Zr(SiPhH2)-
(2-Ph-pyridine)+. It is not known if the N-coordination
is retained in F. Subsequent remote C-H activation
yields 7 and regenerates PhSiH3. The reaction of 2 with
0.2 equiv of PhSiH3 (85 °C, 22 h) produces 7 in 90%
yield, which confirms that the conversion of 6 to 7 is
catalytic in PhSiH3. The H2-mediated isomerization of
6 to 7 proceeds by an analogous mechanism.24
The molecular structure of 7 was established by X-ray
diffraction and is shown in Figure 4. The 2-(2-pyridyl)-
phenyl ligand is bonded in the plane between the two
indenyl ligands in an η2(C,N) fashion and forms a five-
membered chelate ring. The angle between the phenyl
and the pyridine ring planes is 7.5(1)°. The rac-(EBI)Zr
framework adopts a conformation in which the indenyl
C6 rings project forward over the two “equatorial”
coordination sites.23
(19) For examples of samarium-mediated activations of Si-aryl
bonds, see: (a) Castillo, I.; Tilley, T. D. J. Am. Chem. Soc. 2001, 123,
10526. (b) Castillo, I.; Tilley, T. D. Organometallics 2000, 19, 4733. (c)
Radu, N. S.; Hollander, F. J.; Tilley, T. D.; Rheingold, A. L. J. Chem.
Soc., Chem. Comm. 1996, 2459.
(20) The presence of (C5R5)2ZrPh+, other minor (C5R5)2Zr species,
and the silane products in the (C5R5)2ZrH+ oils formed in the reactions
of 1a,b with PhSiH3 explains why these oils solidify much more slowly
than those generated by reaction of 1a,b with H2. The slower oil
solidification in the PhSiH3 reactions explains why more extensive
reaction with the chlorobenzene solvent occurs.
The remote C-H activation to form a five-membered
metallacycle in Scheme 12 is unusual for zirconocene
systems,2 but common for group 7-10 metal systems.25
For example, MeMn(CO)5 reacts with 2-phenylpyridine
to yield Mn(CO)4{η2(C,N)-2-(2-pyridyl)phenyl}.25c,26
Reaction of [Cp2Zr{η2(C,N)-CH2CHMe(6-methyl-
2-pyridyl)}][B(C6F5)4] (3) with PhSiH3. The reaction
(21) [Ph3C][B(C6F5)4] is known to mediate organosilane redistribu-
tion reactions (see refs 3d and 22). Since [Ph3C][B(C6F5)4] is used to
generate 1a,b, it is possible that trace [Ph3C][B(C6F5)4] could play a
role in the observed silane redistribution chemistry. To ensure that
no [Ph3C][B(C6F5)4] was present, Cp2ZrMe2 was reacted with 0.9 equiv
of [Ph3C][B(C6F5)4] to produce a mixture of 1a and [{Cp2ZrMe}2(µ-Me)]-
[B(C6F5)4]. This solution, free of Ph3C+, reacted with 1 equiv of PhSiH3
to form the same silane products as observed when 1a was generated
(24) It is also possible that a trace amount of H2 is formed in the
reactions of 2 and 6 with PhSiH3 and catalyzes the conversion of
6 to 7.
(25) (a) Newkome, G. R.; Puckett, W. E.; Gupta, V. K.; Kiefer, G.
E.; Chem. Rev. 1988, 86, 451. (b) Omae, I. Chem. Rev. 1979, 79, 287.
(c) Bruce, M. I.; Goodall, B. L.; Matsuda, I. Aust. J. Chem. 1975, 28,
1259.
(26) The observed isomerization of 6 to 7 in the presence of H2 (eq
4) or PhSiH3 (Schemes 11 and 12) implies that 7 is more stable than
6. Therefore, the formation of 6 in the reaction of rac-(EBI)ZrMe-
(ClC6D5)+ and 2-phenylpyridine (Scheme 4) and the general preference
for the formation of η2-pyridyl products in related C-H activations
(ref 2) must result from kinetic control.
from 1:1 mixtures of Cp2ZrMe2 and [Ph3C][B(C6F5)4]. Additionally, 19
F
NMR studies show that extensive anion degradation occurs in the
reaction of [Ph3C][B(C6F5)4] with PhSiH3. In contrast, no anion
degradation is observed in the reaction of 1a,b with PhSiH3. Therefore,
we conclude that trace [Ph3C][B(C6F5)4] is not responsible for the silane
redistribution observed in the reaction of 1a,b with PhSiH3.
(22) Corey, J. Y. J. Am. Chem. Soc. 1975, 97, 3227.
(23) (a) Jordan, R. F.; LaPointe, R. E.; Baenziger, N.; Hinch, G. D.
Organometallics 1990, 9, 1539. (b) Schafer, A. K.; Zsolnai, L.; Huttner,
G.; Brintzinger, H. H. J. Organomet. Chem. 1987, 328, 87.

2694 Organometallics, Vol. 24, No. 11, 2005
Wu and Jordan
Scheme 13
products. However, the azazirconacycle 3 reacts with
PhSiH3 with opposite selectivity by path i to afford
+
(C5R5)2ZrSiPhH2 and 2-Me-6-iPr-pyridine. A reason-
able explanation for this difference in selectivity is that
steric crowding imposed by the bulky pyridyl-alkyl unit
in 3 disfavors transition state H in this case. The more
crowded azazirconacycle species 2 does not react directly
with PhSiH3. In this case, deinsertion of propene occurs
at elevated temperature to afford 6, which is catalyti-
cally isomerized to 7 by PhSiH3. The key step in this
isomerization is Zr-C/Si-H σ-bond metathesis via path
i. Steric crowding between the 6-phenyl-2-pyridyl ligand
of 6 and the -SiPhH2 group may disfavor transition
state H in this case as well. However, further studies
will be required to fully understand the selectivity in
these reactions.
Conclusions
Scheme 14
The (C5R5)2ZrR′+ cations 1a,b, 3, and 6 react with
PhSiH3 via σ-bond metathesis. The formation of (C5R5)2-
ZrH+ and R′SiH2Ph as initial products in the reaction
of 1a,b demonstrates that σ-bond metathesis with
silanes is a potentially viable pathway for Zr-C bond
cleavage and functionalization of (C5R5)2ZrR′+ species.
However, several issues must be addressed in order to
exploit this chemistry for the functionalization of the
azazirconacycle intermediates in catalytic olefin-pyri-
dine coupling processes, including (i) tuning the (C5R5)2-
ZrR′+ and silane steric properties to favor the desired
selectivity (path ii in Scheme 14), (ii) avoiding the
photochemical reaction of (C5R5)2ZrH+ species with
chlorinated solvents, and (iii) preventing dimerization
and concomitant deactivation of the (C5R5)2ZrH+ spe-
cies.
of 3 with 2 equiv of PhSiH3 at 85 °C in C6D5Cl re-
sults in complete consumption of 3 and consumption of
1 equiv of PhSiH3. One major organometallic prod-
uct (>90% yield) is observed and was identified as
[{Cp2ZrSiPhH2}2][B(C6F5)4]2 (8) by 1H, 19F, 29Si, and
NOESY NMR data, which are in close agreement with
data for the corresponding BBun(C6F5)4-n- (n ) 0, 1, 2)
salt reported by Harrod.4b One equivalent of 2-Me-6-
iPr-pyridine is formed per Cp2Zr unit of 8.27 These
results are consistent with a σ-bond metathesis reaction
between 3 and PhSiH3 via transition state G in Scheme
13, in which Si occupies the position R to Zr. It is not
known if the N-coordination is retained in G.
Experimental Section
General Procedures. All manipulations were performed
under purified N2 or vacuum using standard Schlenk tech-
niques or in a nitrogen-filled drybox unless otherwise noted.
Nitrogen was purified by passage through columns of activated
molecular sieves and Q-5 oxygen scavenger. Benzene and
hexanes were purified by passage through columns of activated
alumina and BASF R3-11 oxygen removal catalyst. C6D5Cl and
C6H5Cl were distilled from P2O5 and stored under vacuum
prior to use. THF-d8 was purchased from Cambridge Isotopes
and dried over Na/benzophenone and stored under vacuum
prior to use. CD3CN was purchased from Cambridge Isotopes
and dried and stored over 4 Å molecular sieves under vacuum
prior to use. [Ph3C][B(C6F5)4] was obtained from Boulder
Scientific and used as received. 2-Phenylpyridine, 2-picoline,
PhSiH3, Me3SiCl, Ph3CCl, D2, and propene were purchased
from Aldrich and used as received. Hydrogen was purchased
from Airco and used as received. Cp2ZrMe2 (Cp ) C5H5),28a
Cp′2ZrMe2 (Cp′ ) C5H4Me),28b and rac-(EBI)ZrMe2 (EBI ) 1,2-
ethylene-bis-indenyl)28c were prepared by literature proce-
dures. [Cp2ZrMe(ClPh)][B(C6D5)4] (1a) and [Cp′2ZrMe(ClPh)]-
[B(C6D5)4] (1b) were generated as described elsewhere.8 Ele-
mental analyses were performed by Midwest Microlabs (In-
dianapolis, IN). GC-MS analyses were performed on a HP-
6890 instrument equipped with a HP-5973 mass selective
detector. Infrared spectra were recorded on a Nicolet NEXUS
Discussion
The primary goal of this work is to probe the feasibil-
ity of harnessing σ-bond metathesis reactions of silanes
to convert (C5R5)2Zr{η2(C,N)-CH2CHR1(6-R2-2-pyridyl)}+
azazirconacycles to (C5R5)2ZrH+ and silyl-functionalized
disubstituted pyridines, as shown in Scheme 2. As
shown in Scheme 14, Zr-R′/Si-H σ-bond metathesis
reactions can proceed by two pathways, which differ in
the position of Si in the transition state (R or â to Zr).
To achieve the desired “silanolytic” cleavage of Zr-C
bonds in the azazirconacycles, it is required that the
Zr-C/Si-H σ-bond metathesis proceed by path ii and
transition state H in Scheme 14. The cationic Zr-Me
species 1a,b do indeed react with PhSiH3 by path ii to
generate (C5R5)2ZrH+ and PhMeSiH2 as the initial
(27) Me-6-iPr-pyridine is observed in the GC-MS of the reaction
mixture. However, the 1H NMR resonances for 2-Me-6-iPr-pyridine in
the reaction mixture are shifted slightly upfield from the free substrate
positions, which is attributed to interaction of the pyridine with trace
zirconium species in the mixture. Isolated samples of 8 always contain
a trace amount of 2-Me-6-iPr-pyridine.
(28) (a) Samuel, E.; Rausch, M. D. J. Am. Chem. Soc. 1973, 95, 6263.
(b) Couturier, S.; Tainturier, G.; Gautheron, B. J. Organomet. Chem.
1980, 195, 291. (c) Diamond, G. M.; Peterson, J. L.; Jordan, R. F. J.
Am. Chem. Soc. 1996, 118, 8024.

Reactions of Zirconocene Cations with Phenylsilane
Organometallics, Vol. 24, No. 11, 2005 2695
470 FT-IR spectrometer. ESI-MS experiments were performed
with a HP Series 1100MSD instrument using direct injection
via a syringe pump (ca. 10-6 M solutions). Good agreement
between observed and calculated isotope patterns was ob-
served, and the listed m/z value corresponds to the most
intense peak in the isotope pattern.
ambient room light and vigorously agitated. A dark red
solution formed immediately, and a dark red oil separated at
the bottom of the NMR tube within 20 min. The oil solidified
to form an orange crystalline solid within 6 days at 23 °C. The
volatiles were vacuum-transferred into another NMR tube
containing Cp2Fe as an internal standard. NMR analysis
established that C6D5H (δ 7.21, s, 0.012 mmol) was the major
species present and that trace amounts of Ph2SiH2, SiH4, and
CH4 were also present. The presence of C6D5H was confirmed
by GC-MS analysis (m/z ) 83 (M+)).
C6D5Cl (0.5 mL) was added to the residue remaining after
the removal of the volatiles from the reaction tube to afford a
slurry of an orange precipitate in a dark red supernatant. The
supernatant was decanted away from the precipitate. A portion
of the supernatant (0.2 mL) was diluted with benzene (1 mL)
and analyzed by GC-MS, which established that the fol-
lowing compounds were present (m/z values of M+ ions are
given in parentheses): PhSiMeH2 (122), PhSiMe2H (136),
PhSiMe3 (150), Ph2SiH2 (184), Ph2SiMeH (198), Ph2SiMe2
(212), Ph3SiH (260), Ph3SiMe (274), Ph4Si (336), and
C6D5-C6D5 (164). No other Si-containing species were detected
by GC-MS.
The orange precipitate from above was washed with benzene
(3 × 1 mL) and dried under vacuum overnight to afford an
orange solid. The solid was dissolved in THF-d8 at -90 °C to
yield a yellow solution, which was maintained and analyzed
by 1H NMR at -90 °C. The 1H NMR spectrum contained
resonances at δ 6.98 and 6.75 in an 1:3 intensity ratio, cor-
responding to [{Cp2Zr(µ-Cl)}2][B(C6F5)4]2 (4a) and [{Cp2Zr-
(µ-H)}2][B(C6F5)4]2 (5a). In a similar experiment under identi-
cal conditions, the yields of 4a and 5a were determined to be
23% and 72%, respectively, versus starting 1a, based on
integration of the Cp resonances versus the Ph3CMe resonance.
Additionally, single crystals of 4a were selected from the
orange solid under a microscope and characterized by X-ray
diffraction.
In a series of similar experiments under ambient room light,
the organometallic products were analyzed at different stages
of the oil solidification process. These results reveal that the
ratio of 4a/5a increases with time as described in the text.
Additionally, the reaction of 1a with PhSiH3 was conducted
under similar conditions in the dark. 1H NMR analysis showed
that 5a was formed in greater than 90% yield and 4a was not
formed.
Reaction of [Cp′2ZrMe(ClC6D5)][B(C6F5)4] (1b) with
PhSiH3 in Chlorobenzene. The reaction of 1b (0.041 mmol)
with PhSiH3 (5.0 µL, 0.041 mmol) in C6D5Cl (0.5 mL) under
ambient room light was studied, and the products were
analyzed using the procedures described above for 1a. These
analyses showed that the reaction of 1b with PhSiH3 afforded
C6D5H, [{Cp′2Zr(µ-Cl)}2][B(C6F5)4]2 (4b), and [{Cp′2Zr(µ-H)}2]-
[B(C6F5)4]2 (5b) in a 2:1:2 molar ratio. The organic products,
identified by GC-MS, include PhSiMeH2, PhSiMe2H, PhSiMe3,
Ph2SiH2, Ph2SiMeH, Ph2SiMe2, Ph3SiH, Ph3SiMe, Ph4Si, and
C6D5-C6D5. Similarly, the reaction of 1b (0.060 mmol) with
PhSiH3 (7.5 µL, 0.060 mmol) in C6H5Cl (0.5 mL) was conducted
in the dark, and the products were analyzed using the
procedures described above for 1a. These analyses showed that
5b was formed in >90% yield and 4b was not formed.
[{Cp2Zr(µ-Cl)}2][B(C6F5)4]2 (4a). Method 1: A solution of
1a (0.039 mmol) in C6D5Cl (0.5 mL) was generated in a valved
NMR tube and cooled to -196 °C. Me3SiCl (0.041 mmol) was
added by vacuum transfer. The tube was warmed to 23 °C and
vigorously agitated. The tube was maintained at 23 °C
overnight, and a suspension of a dark yellow precipitate in an
orange supernatant formed. The supernatant was decanted
away from the solid. The solid was washed with benzene (3 ×
1 mL) and dried under vacuum overnight to afford 4a as a
dark yellow solid in ca. 80% yield. Method 2: A solution of 1a
(0.047 mmol) in C6D5Cl (0.5 mL) was prepared in a valved
NMR tube, and Ph3CCl (13 mg, 0.047 mmol) was added. The
NMR spectra were recorded in sealed tubes on Bruker AMX-
400 or AMX-500 spectrometers at ambient temperature unless
1
otherwise indicated. H and 13C chemical shifts are reported
versus Me4Si and were determined by reference to the residual
solvent peaks. 11B, 19F, and 29Si chemical shifts were referenced
to external neat BF3‚Et2O, neat CFCl3, and neat Me4Si,
respectively. Coupling constants are reported in Hz. Quantita-
1
tive H NMR measurements were performed using Cp2Fe as
an internal standard.
13C, 19F, and 11B NMR spectra of ionic compounds contain
B(C6F5)4- resonances at the free anion positions. 13C{1H} NMR
(C6D5Cl): δ 148.9 (dm, J ) 240, C2), 138.7 (dm, J ) 230, C4),
136.8 (dm, J ) 238, C3), 124.4 (br, C1). 19F NMR (C6D5Cl): δ
-130.2 (br s, 2F, Fo), -160.3 (t, J ) 23, 1F, Fp), -164.3 (t, J )
19, 2F, Fm). 11B NMR (C6D5Cl): δ -15.8 (br s).
NMR spectra of in-situ generated (C5R5)2ZrMe(ClC6D5)+
species 1a,b contain resonances for Ph3CMe. NMR data for
Ph3CMe: 1H NMR (C6D5Cl): δ 7.14-7.05 (m, 15H, Ph), 2.03
(s, 3H, Me). 13C{1H} NMR (C6D5Cl): δ 149.4 (ipso Ph), 129.0
(Ph), 128.1 (Ph), 126.2 (Ph), 52.8 (C), 30.6 (Me).
[rac-(EBI)Zr{η2(C,N)-CH2CHMe(6-phenyl-2-pyridyl)}]-
[B(C6F5)4] (2). This species was prepared previously as the
MeB(C6F5)3- salt.2a A flask was charged with rac-(EBI)ZrMe2
(0.380 g, 1.08 mmol) and [Ph3C][B(C6F5)4] (1.00 g, 1.08 mmol).
A solution of 2-phenylpyridine (0.160 mL, 1.09 mmol) in
C6H5Cl (20 mL) was added by cannula. The mixture was
vigorously stirred for 2 h at 23 °C. The flask was cooled to
-196 °C, and propene (10.8 mmol, 10 equiv) was added by
vacuum transfer. The flask was warmed to 23 °C and vigor-
ously stirred overnight, resulting in a dark yellow solution.
The volatiles were removed under vacuum to yield a dark
yellow oil. The oil was washed with benzene (3 × 10 mL) and
dried under vacuum overnight to afford pure 2 as a dark yellow
1
solid (0.95 g, 85%). H NMR (C6D5Cl): δ 7.70 (d, J ) 9, 1H,
indenyl C6), 7.50 (m, 2H, Ph), 6.60 (d, J ) 3, 1H, indenyl C5),
6.39 (d, J ) 9, 1H, indenyl C6), 5.74 (d, J ) 3, 1H, indenyl C5),
5.56 (br, 2H, Ph), 5.37 (d, J ) 3, 1H, indenyl C5), 3.33 (d, J )
3, 1H, indenyl C5), 3.33 (m, 1H, CH2CH2), 3.18 (m, 1H,
CH2CH2), 3.07 (m, 1H, CH2CH2), 2.91 (m, 2H, CH2CH2 and
-CH2CHMe), 1.02 (d, J ) 5, 3H, -CH2CHMe), 0.36 (dd, J )
10, 5; 1H, -CH2CHMe), -1.31 (t, J ) 10, 1H, -CH2CHMe).
The other indenyl C6, phenyl, and pyridyl resonances are
masked by the solvent resonances.
[Cp2Zr{η2(C,N)-CH2CHMe(6-methyl-2-pyridyl)}]-
-
[B(C6F5)4] (3). This species was prepared previously as BPh4
salt.2h A flask was charged with Cp2ZrMe2 (0.902 g, 3.59 mmol)
and [Ph3C][B(C6F5)4] (3.29 g, 3.57 mmol), and 2-methylpyridine
(0.750 mL, 7.60 mmol) and C6H5Cl (60 mL) were added. The
mixture was vigorously stirred for 1 h at 23 °C. The flask was
cooled to -196 °C, and propene (28.7 mmol, ca. 8 equiv) was
added by vacuum transfer. The flask was warmed to 23 °C
and vigorously stirred overnight, resulting in a dark yellow
solution. The volatiles were removed under vacuum to yield a
dark brown oil. The oil was washed with benzene (3 × 10 mL)
and dried under vacuum overnight to afford pure 3 as a dark
yellow solid (3.69 g, 95%). 1H NMR (C6D5Cl): δ 7.31 (t, J ) 8,
1H, py), 6.81 (d, J ) 8, 1H, py), 6.57 (d, J ) 8, 1H, py), 5.97 (s,
5H, Cp), 5.96 (s, 5H, Cp), 3.13 (m, 1H, -CH2CHMe), 2.46 (dd,
J ) 6, 5; 1H, -CH2CHMe), 1.10 (d, J ) 6, 3H, -CH2CHMe),
1.09 (s, 3H, py Me), 0.41 (dd, J ) 6, 5; 1H, -CH2CHMe).
Reaction of [Cp2ZrMe(ClC6D5)][B(C6F5)4] (1a) with
PhSiH3 in C6D5Cl. A solution of 1a (0.048 mmol) and
Ph3CMe (0.048 mmol) in C6D5Cl (0.5 mL) was prepared in an
NMR tube, and PhSiH3 (6.0 µL, 0.048 mmol) was added by
microsyringe. The tube was maintained at 23 °C under

2696 Organometallics, Vol. 24, No. 11, 2005
Wu and Jordan
tube was maintained at 23 °C and monitored periodically by
NMR. After 2 days, the 1H NMR resonances of 1a had
disappeared and orange crystals had formed. The crystals were
collected, washed with benzene (3 × 1 mL), and dried under
vacuum overnight to afford 4a as a dark yellow solid in ca.
90% yield. An analytically pure sample of 4a was obtained
from method 1. Anal. Calcd: C, 43.63; H, 1.08. Found: C,
43.87; H, 1.46. ESI-MS (THF-d8 solution): Major cation
observed: [{Cp2Zr(µ-Cl)}22+ - H+ - 2H] calcd m/z 506.9, found
506.8.
Generation of [rac-(EBI)Zr{η2(C,N)-(6-phenyl-2-py-
ridyl)}][B(C6F5)4] (6). This species was prepared previously
as MeB(C6F5)3 salt.2a An NMR tube was charged with rac-
-
(EBI)ZrMe2 (15.8 mg, 0.053 mmol), [Ph3C][B(C6F5)4] (42.0 mg,
0.053 mmol), and 2-phenylpyridine (7.1 µL, 0.055 mmol). C6D5-
Cl (0.5 mL) was added by vacuum transfer at -196 °C. The
tube was warmed to 23 °C and vigorously agitated, resulting
in a dark orange solution. The tube was maintained at 23 °C
for 2 h. A 1H NMR spectrum was recorded and showed that 6
1
had formed quantitatively. H NMR (C6D5Cl): δ 7.71 (d, J )
NMR Analysis of [{Cp2Zr(µ-Cl)}2][B(C6F5)4]2 (4a). 1H
NMR (THF-d8, -90 °C): δ 6.98 (s, 10H, Cp). 13C NMR (THF-
d8, -90 °C): δ 119.7 (Cp). 1H NMR (THF-d8, 23 °C): δ 6.87 (s,
10H, Cp). 13C NMR (THF-d8, 23 °C): δ 119.8 (Cp). 4a also
dissolves in acetonitrile to form a mixture of Cp2ZrCl-
9, 1H, py), 6.87 (t, J ) 8, 1H, indenyl C6), 6.74 (d, J ) 8, 1H,
indenyl C6), 6.47 (t, J ) 8, 1H, indenyl C6), 6.17 (d, J ) 8, 1H,
indenyl C6), 6.07 (d, J ) 3, 1H, indenyl C5), 5.90 (d, J ) 3, 1H,
indenyl C5), 5.01 (d, J ) 3, 1H, indenyl C5), 4.95 (d, J ) 3, 1H,
indenyl C5), 3.50-3.12 (m, 4H, CH2CH2). The other indenyl
C6, phenyl, and pyridyl signals were masked by resonances
from the solvent and Ph3CMe.
+
2+
(NCCD3)n
, Cp2ZrCl2, and Cp2Zr(NCCD3)3 .
1H NMR
(CD3CN, -40 °C): δ 6.53 (s, Cp2ZrCl2), 6.49 (s, Cp2Zr-
1
(NCCD3)32+), 6.38 (s, Cp2ZrCl(NCCD3)n+). H NMR (CD3CN):
[rac-(EBI)Zr{η2(C,N)-2-(2-pyridyl)phenyl}][B(C6F5)4] (7).
Complex 7 was generated by three methods. Method 1: A
solution of 2 (20.5 mg, 0.017 mmol) in C6D5Cl (0.5 mL) was
prepared in an NMR tube. PhSiH3 (5.4 µL, 0.043 mmol) was
added by microsyringe. The tube was vigorously agitated,
resulting in a yellow solution. The tube was maintained at 23
°C and monitored periodically by NMR. No reaction was
observed after 10 h. The tube was maintained at 85 °C for 20
h. The color of the solution changed to dark red, and 1H NMR
analysis showed that 2 was completely consumed and 7 had
formed quantitatively. Additionally, PhSiH3 (0.017 mmol), Ph2-
SiH2 (0.012 mmol), and a trace amount of SiH4 were observed
by 1H NMR analysis, and their quantities were determined
by integration versus the -CH2CH2- resonances of 7. The
volatiles were removed under vacuum. The residue was
washed with C6D6 (1 mL) and dried under vacuum to afford 7
as a red solid in 90% purity. The 1H NMR spectrum of the
C6D6 wash contained characteristic resonances for atactic
oligopropene. 1H NMR (C6D6): δ 1.65 (br, -CH), 1.35-0.81
(br, CH2 and -Me).30 GC-MS analysis of the C6D6 wash showed
that Ph3SiH and Ph4Si were present. Method 2: A solution of
6 (0.054 mmol) in C6D5Cl (0.5 mL) at 23 °C was generated in
an NMR tube as described above, and PhSiH3 (7.0 µL, 0.056
mmol) was added by microsyringe. The tube was vigorously
agitated, resulting in a red solution. The tube was maintained
at 23 °C for 30 min. 1H NMR analysis showed that 6 was
completely consumed. The volatiles were removed under
vacuum. The residue was washed with benzene (3 × 1 mL)
and dried under vacuum to afford 7 as a red solid in 90%
purity. Method 3: An NMR tube containing a solution of 6
(0.046 mmol) in C6D5Cl (0.5 mL) was immersed in liquid
nitrogen and exposed to H2 (600 Torr, ca. 0.065 mmol). The
tube was sealed, warmed to 23 °C, and vigorously agitated,
resulting in a red solution. The tube was maintained at 23 °C
δ 6.52 (s, Cp2ZrCl2), 6.51 (s, Cp2Zr(NCCD3)32+), 6.39 (s,
Cp2ZrCl(NCCD3)n+).29
[{Cp′2Zr(µ-Cl)}2][B(C6F5)4]2 (4b). This complex was gen-
erated in 85% yield from 1b (0.052 mmol) and Me3SiCl
(0.055 mmol) using method 1 described above for 4a. 1H NMR
(THF-d8, -90 °C): δ 6.89 (m, 4H, Cp′), 6.66 (m, 4H, Cp′), 2.26
(s, 6H, Cp′Me). 13C NMR (THF-d8, -90 °C): δ 128.0 (Cp′ ipso),
118.8 (Cp′), 117.4 (Cp′), 15.8 (Cp′Me). 1H NMR (THF-d8, 23
°C): δ 6.76 (m, 4H, Cp′), 6.56 (m, 4H, Cp′), 2.29 (s, 6H, Cp′Me).
13C NMR (THF-d8, 23 °C): δ 128.9 (Cp′ ipso), 119.7 (Cp′), 117.1
(Cp′), 16.1 (Cp′Me).29
[{Cp2Zr(µ-H)}2][B(C6F5)4]2 (5a). An amberized NMR tube
containing a solution of 1a (0.043 mmol) in C6D5Cl (0.5 mL)
was immersed in liquid nitrogen and exposed to H2 (600 Torr,
ca. 0.065 mmol). The tube was sealed, warmed to 23 °C, and
vigorously agitated, resulting in a suspension of a yellow solid
in an orange supernatant. The tube was maintained at 23 °C
1
in the dark. A H NMR spectrum was recorded after 10 min
and showed that 1a had reacted completely. The volatiles were
removed under vacuum. The residue was washed with benzene
(3 × 1 mL) and dried under vacuum to afford 5a as a yellow
solid in 95% yield. Anal. Calcd: C, 45.30; H, 1.23. Found: C,
45.41; H, 1.59. IR (5a, Nujol): νZr-H ) 1337 cm-1. [{Cp2Zr-
(µ-D)}2][B(C6F5)4]2 (5a-d2) was generated from 1a and D2 using
the procedure for 5a. IR (5a-d2, Nujol): νZr-D ) 1040 cm-1
.
NMR Analysis of [{Cp2Zr(µ-H)}2][B(C6F5)4]2 (5a). 1H
NMR (THF-d8, -90 °C): δ 6.75 (s, 20H, Cp), -0.53 (s, 2H, µ-H).
1
13C NMR (THF-d8, -90 °C): δ 113.1 (Cp). H NMR (THF-d8,
23 °C): δ 6.20 (s, 10H, Cp), 5.78 (s, 1H, Zr-H). 13C NMR (THF-
d8, 23 °C): δ 108.5 (Cp). The dramatic shift of the hydride
resonance between -90 and 23 °C is attributed to the for-
mation of Cp2ZrH(THF-d8)+. Complex 5a is also soluble in
CD3CN, in which the insertion product [Cp2Zr(N-CHCD3)-
(CD3CN)][B(C6F5)4] is formed.14b 1H NMR (CD3CN): δ 8.50 (br
s, 1H, N-CHCD3), 6.25 (s, 10H, Cp).
1
for 30 min. H NMR analysis showed that 6 was completely
consumed. The volatiles were removed under vacuum. The
residue was washed with benzene (3 × 1 mL) and dried under
vacuum to afford 7 as an analytically pure, red solid in 95%
yield. Anal. Calcd: C, 55.94; H, 2.05; N, 1.19. Found: C, 56.27;
H, 1.79; N, 1.38.
[{Cp′2Zr(µ-H)}2][B(C6F5)4]2 (5b). This complex was gener-
ated in 95% yield from 1b (0.049 mmol) and H2 (0.065 mmol)
using the procedure for 5a. 5b is soluble in THF due to the
1
formation of [Cp′2ZrH(THF-d8)][B(C6F5)4]. H NMR (THF-d8,
NMR Data for [rac-(EBI)Zr{η2(C,N)-2-(2-pyridyl)-
phenyl}][B(C6F5)4] (7). The numbering system for 7 is shown
-40 °C): δ 6.25 (m, 2H, Cp′), 6.20 (m, 2H, Cp′), 6.02 (m, 2H,
Cp′), 5.89 (s, 1H, terminal Zr-H), 5.63 (m, 2H, Cp′), 2.28 (s,
6H, Cp′Me). 1H NMR (THF-d8): δ 6.30-5.90 (br, 8H, Cp), 6.19
(br s, 1H, terminal Zr-H), 2.27 (s, 6H, Cp′Me). These data
1
in Figure 4. H NMR (C6D5Cl): δ 7.41 (m, 1H, H23), 7.39 (d,
J ) 8, 1H, H24), 7.32 (d, J ) 8, 1H, H27), 7.20 (d, J ) 8, 1H,
indenyl C6), 7.05 (d, J ) 8, 1H, indenyl C6), 6.99 (m, 1H, H28),
6.94 (m, 1H, indenyl C6), 6.92 (m, 1H, H29), 6.84 (t, J ) 8,
1H, indenyl C6), 6.68 (m, 1H, H22), 6.66 (d, J ) 8, 1H, indenyl
C6), 6.58 (d, J ) 3, 1H, indenyl C5), 6.38 (m, 2H, indenyl C6),
6.25 (t, J ) 8, 1H, indenyl C6), 6.23 (d, J ) 3, 1H, indenyl C5),
6.03 (d, J ) 6, 1H, H21), 5.92 (d, J ) 3, 1H, indenyl C5), 5.84
(d, J ) 8, 1H, H30), 5.77 (d, J ) 3, 1H, indenyl C5), 3.75 (m,
agree with values for the analogous BPh4 salt.14a
-
(29) The 1H and 13C NMR spectra of THF-d8 solutions of 4a,b at
-90 °C show that these species have C2v symmetry. This is consistent
with dinuclear Zr(µ-Cl)2Zr structures, as observed in the solid state,
or mononuclear (C5R5)2ZrCl(THF-d8)+ adducts that undergo rapid
intermolecular THF-d8 exchange with accompanying site epimerization
at Zr, or rapid dimer/monomer equilibria. ESI-MS results for 4a, and
the absence of line broadening of the Cp′ 1H and 13C NMR resonances
of 4b at -90 °C, suggest that these species retain their dinuclear
structures in THF-d8 solution.
(30) Stockland, R. A.; Foley, S. R.; Jordan, R. F. J. Am. Chem. Soc.
2003, 125, 796.

Reactions of Zirconocene Cations with Phenylsilane
Organometallics, Vol. 24, No. 11, 2005 2697
Table 1. Summary of X-ray Diffraction Data for 4a, 4b, and 7
[{Cp2Zr(µ-Cl)}2][B(C6F5)4]2
(4a)
[Cp′2Zr(µ-Cl)}2][B(C6F5)4]2 (4b) +
[rac-(EBI)Zr{η2-(C,N)-2-(2-pyridyl)-
phenyl}][B(C6F5)4] (7)
2 C6D5Cl
formula
fw
C
68H20B2Cl2F40Zr2
C
84H28D10B2Cl4F40Zr2
C55H24BF20NZr
1871.80
triclinic
2163.10
triclinic
1180.78
monoclinic
P21/c
cryst syst
space group
a (Å)
P1h
P1h
10.006(2)
12.497(3)
13.971(3)
64.50(1)
87.26(1)
84.66(1)
1570(1)
11.684(2)
13.503(3)
13.712(3)
85.33(1)
68.09(1)
75.77(1)
1945(1)
27.854(6)
18.962(4)
17.008(3)
b (Å)
c (Å)
R (deg)
â (deg)
91.45(3)
γ (deg)
V (Å3)
8980(3)
8
100
Z
2
100
2
100
T (K)
cryst color, habit
GOF on F2
R indices (I > 2σ(I))a
red, fragment
1.063
R1 ) 0.0378
wR2 ) 0.0943
R1 ) 0.0417
wR2 ) 0.0969
red, fragment
0.982
R1 ) 0.0579
wR2 ) 0.1507
R1 ) 0.0681
wR2 ) 0.1589
red-orange, plate
1.342
R1 ) 0.0942
wR2 ) 0.1706
R1 ) 0.1009
wR2 ) 0.1737
R indices (all data)a
a R1 ) ∑||Fo| - |Fc||/∑|Fo|; wR2 ) [∑[w(Fo - Fc )2]/∑[w(Fo2)2]]1/2, where w ) q[σ2(Fo2) + (aP)2 + bP]-1
.
2
2
1
1H, CH2CH2), 3.47 (m, 1H, CH2CH2), 3.27 (m, 2H, CH2CH2).
13C NMR (C6D5Cl): δ 193.3 (C31), 160.7 (C25), 145.5 (C21),
141.9 (C24), 139.2 (C26), 137.4 (C30), 130.9 (C29), 130.1 (ipso
indenyl), 129.4 (indenyl C6), 129.0 (indenyl C6), 128.0 (C28),
127.1 (ipso indenyl), 126.4 (ipso indenyl), 126.2 (indenyl C6),
126.1 (indenyl C6), 125.4 (indenyl C6), 125.0 (indenyl C6), 124.8
(ipso indenyl), 124.0 (C27), 123.1 (ipso indenyl), 122.3 (C22),
121.4 (ipso indenyl), 121.1 (indenyl C6), 119.8 (C23), 119.7
(indenyl C6), 116.4 (indenyl C5), 116.3 (indenyl C5), 112.6
(indenyl C5), 110.5 (indenyl C5), 28.8 (CH2CH2), 28.3 (CH2CH2).
The 1H NMR assignments were confirmed by 1H-1H COSY
and NOESY NMR. The 13C NMR assignments were estab-
-3.15 (s, 1H, µ Si-H). H NMR (C6D6): δ 7.56 (m, 2H, Ph),
7.30 (m, 1H, Ph), 7.00 (m, 2H, Ph), 5.80 (s, 1H, Si-H), 5.13 (s,
5H, Cp), 5.06 (s, 5H, Cp), -3.38 (s, 1H, µ Si-H). 29Si NMR
(C6D5Cl): δ 105. Key 1H-1H NOESY correlations δ/δ: 7.68
(Ph)/-3.15 (µ Si-H); 5.95 (Si-H)/-3.15 (µ Si-H); 5.42 (Cp)/-
3.15 (µ Si-H); 5.34 (Cp)/-3.15 (µ Si-H).
X-ray Crystallography. Crystallographic data are sum-
marized in Table 1. Full details are provided in the Supporting
Information. Data were collected on a Bruker Smart Apex
diffractometer using Mo KR radiation (0.71073 Å). Non-
hydrogen atoms were refined with anisotropic displacement
coefficients. All hydrogen atoms were included in the structure
factor calculation at idealized positions and were allowed to
ride on the neighboring atoms with relative isotropic displace-
ment coefficients. ORTEP diagrams are drawn with 50%
probability ellipsoids. Specific comments for each structure are
as follows. 4a: Single crystals of 4a were obtained from the
reaction of 1a with Ph3CCl in C6D5Cl at 23 °C. 4b: Single
crystals of 4b were obtained from the reaction of 1b with
PhSiH3 in C6D5Cl under ambient room light at 23 °C. The
asymmetric unit contains one solvent molecule (C6D5Cl). 7:
Single crystals of 7 were obtained by slow diffusion of hexanes
into a concentrated C6D5Cl solution of 7 (generated by method
3 described above) at 23 °C. The asymmetric unit contains two
independent molecules of 7, whose structures are very similar.
1
lished by H-13C HMQC NMR.
Generation of [{Cp2Zr(SiH2Ph)}2][B(C6F5)4]2 (8). A solu-
tion of 3 (23.8 mg, 0.024 mmol) in C6D5Cl (0.5 mL) was
prepared in an NMR tube, and PhSiH3 (5.6 µL, 0.045 mmol)
was added by microsyringe at 23 °C. The tube was vigorously
agitated, resulting in a yellow solution. The tube was main-
tained at 85 °C for 20 h. The color of the solution changed to
orange, and 1H NMR analysis showed that complete consump-
tion of 3 and 50% consumption of PhSiH3 had occurred, 8 had
formed in ca. 90% yield, and 1 equiv of 2-Me-6-iPr-pyridine
had formed per Cp2ZrSiH2Ph+ unit of 8.24 Less than 10% of
unidentified impurities were also present. The volatiles were
vacuum transferred into another NMR tube. 1H NMR analysis
of the volatiles showed that 2-Me-6-iPr-pyridine was present.
1H NMR (2-Me-6-iPr-pyridine, C6D5Cl): δ 7.23 (t, J ) 8, 1H,
py), 6.76 (d, J ) 8, 1H, py), 6.70 (d, J ) 8, 1H, py), 2.98 (septet,
J ) 6, 1H, CHMe2), 2.38 (s, 3H, py Me), 1.23 (d, J ) 6, 6H,
CHMe2). GC-MS analysis of the volatiles confirmed the pres-
ence of 2-Me-6-iPr-pyridine (m/z ) 135 (M+)). The residue was
washed with benzene (3 × 1 mL) and dried under vacuum to
afford 8 as a yellow solid in 80% yield. 8 was identified by
Acknowledgment. This work was supported by the
National Science Foundation (CHE-0212210). We thank
Edward J. Stoebenau, III for helpful discussions and Dr.
Ian Steele for the X-ray diffraction analyses.
Supporting Information Available: Tables of X-ray
crystallographic data, atomic coordinates, bond lengths and
bond angles, and anisotropic thermal parameters for 4a, 4b,
and 7 (PDF and CIF files). This material is available free of
charge via the Internet at http://pubs.acs.org.
1
comparison of the H, 29Si, and NOESY NMR data for 8 with
reported data for the corresponding BBun(C6F5)4-n- (n ) 0, 1,
2) salt.4 Data for [{Cp2Zr(SiH2Ph)}2][B(C6F5)4]2 (8): 1H NMR
(C6D5Cl): δ 7.68 (d, J ) 8, 2H, Ph), 7.28 (m, 1H, Ph), 6.97 (m,
2H, Ph), 5.95 (s, 1H, Si-H), 5.42 (s, 5H, Cp), 5.34 (s, 5H, Cp),
OM049099Z