Synthesis, characterization, and structure of novel borane- and borate-containing ruthenocenes

Article abstract of DOI:10.1021/om9608521

The addition of (p-bromo- or (p-iodophenyl)lithium to 6,6-dimethylfulvene results in the formation of the anionic cyclopentadienyl (Cp) ligands LiCpC(CH₃)₂C₆H₄Br (1) and LiCpC-(CH₃)₂C₆H₄I (2), respectively. Reaction of 4 equiv of ligand 1 or 2 with 1 equiv [Cp*RuCl]₄ 0 yields ruthenocenes Cp*RuCpC(CH₃)₂C₆H₄Br (3) and Cp*RuCpC(CH₃)₂C₆H₄I (4) in high yield. Cp*RuCpC(CH₃)₂C₆H₄Br undergoes bromo-lithium exchange with BuLi, and the resulting lithiate can be trapped with Ph₂BOMe to give the neutral boron-containing ruthenocene Cp*RuCpC(CH₃)₂C₆H₄BPh ₂Py (5) or with BPh₃ to give the anionic borate-containing ruthenocene Cp*RuCpC(CH₃)₂C₆H₄BPh ₃Li, which can be isolated either base-free (6), as a diethyl etherate (6a), or as a tetrahydrofuranate (6b). All new compounds have been characterized in solution by NMR spectroscopy. An X-ray structure analysis of 3 indicates that the neutral ruthenocene adopts a slightly bent, eclipsed structure with the phenyl group directed away from the metal center. An X-ray structure analysis of 6b indicates that the anionic ruthenocene adopts a slightly bent, partially staggered conformation with the borate directed away from the metal center. The staggered conformation appears to be due to the intermolecular interactions within the crystal packing and not intramolecular interactions between sterically-demanding Cp ligands.

Full text of DOI:10.1021/om9608521

1628
Organometallics 1997, 16, 1628-1634
Syn th esis, Ch a r a cter iza tion , a n d Str u ctu r e of Novel
Bor a n e- a n d Bor a te-Con ta in in g Ru th en ocen es
H. J errold Miller, Brent S. Strickler, Khalil A. Abboud, J ames M. Boncella,* and
David E. Richardson*
Department of Chemistry, University of Florida, Gainesville, Florida 32611-7200
Received October 7, 1996X
The addition of (p-bromo- or (p-iodophenyl)lithium to 6,6-dimethylfulvene results in the
formation of the anionic cyclopentadienyl (Cp) ligands LiCpC(CH3)2C6H4Br (1) and LiCpC-
(CH3)2C6H4I (2), respectively. Reaction of 4 equiv of ligand 1 or 2 with 1 equiv [Cp*RuCl]4
yields ruthenocenes Cp*RuCpC(CH3)2C6H4Br (3) and Cp*RuCpC(CH3)2C6H4I (4) in high yield.
Cp*RuCpC(CH3)2C6H4Br undergoes bromo-lithium exchange with BuLi, and the resulting
lithiate can be trapped with Ph2BOMe to give the neutral boron-containing ruthenocene
Cp*RuCpC(CH3)2C6H4BPh2Py (5) or with BPh3 to give the anionic borate-containing
ruthenocene Cp*RuCpC(CH3)2C6H4BPh3Li, which can be isolated either base-free (6), as a
diethyl etherate (6a ), or as a tetrahydrofuranate (6b). All new compounds have been
characterized in solution by NMR spectroscopy. An X-ray structure analysis of 3 indicates
that the neutral ruthenocene adopts a slightly bent, eclipsed structure with the phenyl group
directed away from the metal center. An X-ray structure analysis of 6b indicates that the
anionic ruthenocene adopts a slightly bent, partially staggered conformation with the borate
directed away from the metal center. The staggered conformation appears to be due to the
intermolecular interactions within the crystal packing and not intramolecular interactions
between sterically-demanding Cp ligands.
In tr od u ction
as well as highly active group 4 polymerization cata-
lysts.4 Recently, Marks and co-workers7 developed an
even bulkier anion, tetrakis(p-(trimethylsilyl)tetrafluo-
rophenyl)borate, for use in these systems.
The development of weakly-coordinating anions (WCA)
has been of increasing interest in recent years because
of their usefulness in a wide variety of chemical ap-
plications. The diversity of WCA spans the classical
Several examples of borates bound to metal complexes
through both σ and π interactions have been reported.8,9
Bochmann and co-workers10 reported the syntheses of
novel anionic and zwitterionic group 4 metallocene
complexes by employing the (cyclopentadienyl)tris(per-
fluorophenyl)borate ligand. These complexes exhibit
moderate activity toward olefin polymerization, al-
though the metal center must still be activated by
addition of a cocatalyst (i.e., AlMe3). Under some
conditions, the ligand systems displayed loss of borane
and decomposition, which may be due to an associated/
dissociated boron equilibrium process.11 Other ex-
amples of cyclopentadienyl (Cp) ligands containing
anions ClO4-, SO3CF3-, BF4-, PF6-, and SbF6 to the
-
even more weakly coordinating anions BPh4-, CB11H12
,
-
C60-, and methylalumoxane (MAO).1 Tetraarylborates
have been extensively used in electrolytes,2 as phase-
transfer catalysts,3 and as WCA for group 4 polymeri-
zation catalysts,4 Rh(I) hydride hydrogenation cata-
lysts,5 and thousands of other transition metal
complexes.1 Fluorinated tetraphenylborates are among
the most weakly-coordinating anions known, and tet-
rakis[3,5-bis(trifluoromethyl)phenyl]borate3 (TFPB) and
tetrakis(perfluorophenyl)borate4d have been used as
counterions for late transition-metal catalyst systems6
(6) (a) J ohnson, L. K.; Killian, C. M.; Brookhart, M. J . Am. Chem.
Soc. 1995, 117, 6414-6415. (b) Wilke, G. Angew. Chem., Int. Ed. Engl.
1988, 27, 185-206. (c) Schmidt, G. F.; Brookhart, M. J . Am. Chem.
Soc. 1985, 107, 1443-1444. (d) Brookhart, M.; Volpe, A. F.; Lincoln,
D. M.; Horvath, I. T.; Millar, J . M. J . Am. Chem. Soc. 1990, 112, 5634-
5636.
X Abstract published in Advance ACS Abstracts, March 1, 1997.
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H. Bull. Chem. Soc. J pn. 1984, 57, 2600-2604.
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14, 3135-3137.
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ganomet. Chem. 1991, 32, 325-387. (f) Gillis, D. J .; Tudoret, M.-J .;
Baird, M. C. J . Am. Chem. Soc. 1993, 115, 2543-2545. (g) Pellechia,
C.; Pappalardo, D.; Oliva, L.; Zambelli, A. J . Am. Chem. Soc. 1995,
117, 6593-6594. (h) Deck, P. A.; Marks, T. J . J . Am. Chem. Soc. 1995,
117, 6128-6129. (i) Yang, X.; Stern, C. L.; Marks, T. J . J . Am. Chem.
Soc. 1991, 113, 3623-3625. (j) Yang, X.; Stern, C. L.; Marks, T. J . J .
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Int. Ed. Engl. 1994, 33 (14), 1480-1482. (b) Ruwwe, J .; Erker, G.;
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Hlatky, G. G.; Turner, H. W.; Eckman, R. R. J . Am. Chem. Soc. 1989,
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8, 2659-2664.
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Chem. Commun. 1995, 2081-2082.
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S0276-7333(96)00852-7 CCC: $14.00 © 1997 American Chemical Society

Borane- and Borate-Containing Ruthenocenes
Organometallics, Vol. 16, No. 8, 1997 1629
distillation from Na. NMR solvents were purchased from
Cambridge Isotopes and were dried over 4-Å molecular sieves
and not further purified. Pyridine was distilled prior to use.
tethered boranes have been synthesized by hydro-
boration12 and other methods,13 but to our knowl-
edge, no Cp ligands with tethered borates have been
reported.
17
[Cp*RuCl]4 and Ph2BOMe18 were prepared according to
literature methods. p-Diiodobenzene, p-dibromobenzene, 6,6-
dimethylfulvene, and BuLi (2.5 M in hexanes) were purchased
from Aldrich and used as received.
1H and 13C NMR spectra were obtained by using either a
Varian VXR-300, Gemini-300, or GE QE-300. Mass spectra
were obtained with a Finnigan MAT MAT95Q liquid secondary
ion mass spectrometer (LSI MS, Cs+); the selected (m + 1)/z
values given refer to the isotopes 1H, 12C, 79Br, 127I, 11B, and
101Ru. Elemental analyses were obtained by the Microana-
lytical Department at the University of Florida.
P r oced u r es. LiCp C(CH3)2P h Br (1). To a solution of
p-dibromobenzene (3.00 g, 12.7 mmol) in 150 mL of Et2O at
-78 °C was added BuLi (5.10 mL, 12.7 mmol). The mixture
was allowed to warm to room temperature over 30 min. To
this solution was added 6,6-dimethylfulvene (1.54 g, 14.5
mmol) via syringe, and a white solid precipitated immediately.
The mixture was stirred for 2 h at 25 °C and then filtered.
The white solid was washed with 3 × 20 mL pentane and then
dried in vacuo yielding 3.20 g (92.3% yield) of 1 as a white
solid. NMR in C6D6/THF-d8: δ(1H) ) 1.67 (s, 6H), 5.73 (t, 2H),
5.85 (t, 2H), 7.20 (s, 4H).
LiCp C(CH3)2P h I (2). To a solution of p-diiodobenzene
(3.01 g, 9.10 mmol) in 150 mL of Et2O at -78 °C was added
BuLi (3.64 mL, 9.10 mmol). The mixture was allowed to warm
to room temperature over 30 min. To this solution was added
6,6-dimethylfulvene (1.10 g, 9.13 mmol) via syringe, and a
white solid precipitated immediately. The mixture was stirred
for 2 h at 25 °C and then filtered. The white solid was washed
with 3 × 20 mL pentane and then dried in vacuo yielding 2.62
g (91.2% yield) of 2 as a white solid. NMR in C6D6/THF-d8:
δ(1H) ) 1.67 (s, 6H), 5.63 (t, 2H), 5.72 (t, 2H), 7.10 (s, 2H),
7.40 (d, 2H).
Cp *Ru Cp C(CH3)2P h Br (3). To a mixture of [Cp*RuCl]4
(0.51 g, 0.47 mmol) and 1 (0.50 g, 1.85 mmol) was added 15
mL of THF, and the reddish solution was refluxed for 10 h.
The THF was then pumped away, and 5 g of basic alumina
was added. The mixture was extracted twice with 20 mL of
hot hexanes, and the slightly yellow solution was evaporated
to yield 3 (0.79 g, 85% yield) as an off-white solid. Needlelike,
X-ray-quality crystals were obtained by cooling a concentrated
solution of 3 in hot hexanes. Anal. Calcd for C24H29BrRu: C,
57.81; H, 5.86. Found: C, 57.66; H, 5.98. LSI MS [(m+1)/z]:
Calcd, 498; found, 498. NMR in C6D6: δ(1H) ) 1.41 (s, 6H),
1.88 (s, 15H), 4.00 (t, 2H), 4.11 (t, 2H), 7.02 (d, 2H), 7.24 (d,
2H).
Cp *Ru Cp C(CH3)2P h I (4). To a mixture of [Cp*RuCl]4
(0.66 g, 2.44 mmol) and 2 (0.77 g, 2.44 mmol) was added 15
mL of THF, and the reddish solution was refluxed for 10 h.
The THF was then pumped away, and 5 g of basic alumina
added. The mixture was dissolved in 20 mL of hot hexanes
and filtered, and the solid was washed again with 20 mL of
hot hexanes. The slightly yellow solution was evaporated to
yield 4 (1.02 g, 77% yield) as an off-white solid. Recrystalli-
zation from hexanes yielded yellow needlelike crystals. Anal.
Calcd for C24H29IRu: C, 52.81; H, 5.36. Found: C, 53.89; H,
5.61. LSI MS [(m+1)/z]: Calcd, 546. Found 546. NMR in
C6D6: δ(1H) ) 1.41 (s, 6H), 1.88 (s, 15H), 4.00 (t, 2H), 4.11 (t,
2H), 6.89 (d, 2H), 7.43 (d, 2H).
Tetraphenylborates have also been used as ligands
through η6-coordination of a phenyl group to a multitude
of metal centers,1 including various group 4 metal
complexes.14 These group 4 zwitterionic complexes are
active polymerization catalysts; however, the dissocia-
tion of the borate ligand to form an ion pair precedes
the coordination of olefin. Given the instability of the
known σ-bound borates and the impermanent nature
of the π-bound borates, we have prepared borate-
containing cyclopentadienyl (Cp) ligands in which the
boron is not bound directly to the Cp ring. For initial
applications of the new tethered-borate ligands, we have
chosen to synthesize ruthenocene derivatives.
During the past several years, a number of new
cyclopentadienyl ligands have been synthesized and
characterized with the (pentamethylcyclopentadienyl)-
ruthenium(II) (Cp*Ru) moiety as a template.15 The
benefits of using the Cp*Ru moiety are many. It allows
for the simple high-yield synthesis of stable ruthenocenes
from the readily accessible [Cp*RuCl]4 tetramer. Since
the Cp*Ru moiety is held constant, the electronic and
steric properties of the new ligand can be compared with
other ligands. The oxidation properties of many ru-
thenocenes have been studied, and the nature of the
counterion plays an important role in the oxidation
process. For example, TFPB, when used2 as an elec-
trolyte in the electrochemical oxidation studies of osmo-
cene and ruthenocene, leads to a quasi-reversible single-
electron ruthenium(II/III) electrochemical couple. (In
common solvent/electrolyte systems, osmocene16 exhibits
an irreversible one-electron oxidation, and ruthenocene16
exhibits an irreversible two-electron oxidation.) There-
fore, we sought to produce ruthenocenes containing
tethered borates and investigate the effect of the borate-
containing ligand on the oxidation chemistry of the
resultant ruthenocenes.
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All manipulations were per-
formed under Ar by using standard Schlenk techniques or
under N2 in a Vacuum Atmospheres glovebox. Glassware was
oven dried prior to use. Solvents were distilled prior to use
and stored over 4-Å molecular sieves in sealed bulbs under
Ar. Diethyl ether and tetrahydrofuran were dried by distil-
lation from Na/benzophenone ketyl. Pentane was dried by
(12) Erker, G.; Aul, R. Chem. Ber. 1991, 124, 1301-1310.
(13) (a) Spence, R. E. v. H.; Piers, W. E. Organometallics 1995, 14,
4617-4624. (b) Herberich, G. E.; Fischer, A. Organometallics 1996,
15, 58-67. (c) Larkin, S. A.; Golden, J . T.; Shapiro, P. J .; Yap, G. P.
A.; Foo, D. M. J .; Rheingold, A. L. Organometallics 1996, 15, 2393-
2398.
(14) (a) Horton, A. D.; Frijns, J . H. G. Angew. Chem., Int. Ed. Engl.
1991, 30 (9), 1152-1154. (b) Pellechia, C.; Immirzi, A.; Grassi, A.;
Zambelli, A. Organometallics 1993, 12, 4473-4478. (c) Bochmann, M.;
Karger, G.; J aggar, A. J . J . Chem. Soc., Chem. Commun. 1990, 1038-
1039.
Cp *Ru Cp C(CH3)2P h BP h 2P y (5). To a solution of 3 (0.16
g, 0.59 mmol) in 20 mL of Et2O at -78 °C was added BuLi
(0.13 mL, 0.59 mmol), and the solution was warmed to room
temperature over 30 min. To this solution was added Ph2-
BOMe (0.064 mL, 0.59 mmol) via syringe. The solution stirred
for 7 h by which time white solid had precipitated. The solvent
(15) (a) Burk, M. J .; Arduengo, A. J .; Calabrese, J . C.; Harlow, R.
L. J . Am. Chem. Soc. 1989, 111, 8938-8940. (b) Winter, C.; Han, Y.-
H.; Heeg, M. J . Organometallics 1992, 11, 3169-3171. (c) Albers, M.
O.; Liles, D. C.; Robinson, D. J .; Shaver, A.; Singleton, E.; Wiege, M.
B.; Boeyens, J . C. A.; Levendis, D. C. Organometallics 1986, 5, 2321-
2327. (d) Gassman, P. G.; Winter, C. H. J . Am. Chem. Soc. 1988, 110,
6130-6135. (e) Ryan, M. F.; Siedle, A. R.; Burk, M. J .; Richardson, D.
E. Organometallics 1992, 11, 4231-4237.
(17) Fagan, P. J .; Ward, M. D.; Calabrese, J . C. J . Am. Chem. Soc.
1989, 111, 1698-1719.
(18) J acob, P. J . Organomet. Chem. 1978, 156, 101-110.
(16) Gubin, S. P.; Smirnova, S. A.; Denisovich, L. I.; Lubovich, A.
A. J . Organomet. Chem. 1971, 30, 243-255.

1630 Organometallics, Vol. 16, No. 8, 1997
Miller et al.
Ta ble 1. Cr ysta l Da ta a n d Str u ctu r e Refin em en t
for 3
Ta ble 2. Cr ysta l Da ta a n d Str u ctu r e Refin em en t
for 6b
empirical formula
fw
C24H29BrRu
498.45
empirical formula
fw
C58H76BLiO4Ru
956.01
temp
173(2) K
temp
173(2) K
wavelength
cryst system
space group
unit cell dimens
0.710 73 Å
monoclinic
P21/c
wavelength
cryst system
space group
unit cell dimens
0.71073 Å
orthorhombic
Pbcn
a ) 10.3587(1) Å, R ) 90°
b ) 24.9529(2) Å, â ) 99.030(1)°
c ) 8.3765(1) Å, γ ) 90°
2138.34(4) Å3, 4
1.548 Mg/m3
a ) 40.9162(6) Å, R ) 90°
b ) 14.4443(3) Å, â ) 90°
c ) 17.6316(3) Å, γ ) 90°
10420.4(3) Å3, 8
1.219 Mg/m3
V, Z
D(calcd)
abs coeff
V, Z
D(calcd)
abs coeff
2.607 mm-1
0.345 mm-1
F(000)
1008
F(000)
4064
cryst size
θ for data collcn
limiting indices
0.22 × 0.28 × 0.34 mm
cryst size
θ range for data collcn
limiting indices
0.32 × 0.25 × 0.18 mm
1.63 to 27.50°
1.50-25.00°
-14 e h e 14, -33 e k e 16,
-11 e l e 7
11 687
4875 [R(int) ) 0.0326]
integration, SHELXTL
0.6002 and 0.4621
full-matrix least-squares on F2
4836/0/236
-53 e h e 50, -16 e k e 18,
-22 e l e 24
53 780
9167 [R(int) ) 0.0490]
integration, SHELXTL
0.949 and 0.748
full-matrix least-squares on F2
9069/202/735
no. of reflns collected
no. of indepdt reflcns
abs corr
max and min transm
refinement method
data/restraints/params
goodness-of-fit on F2
final R indices [I > 2σ(I)]
R indices (all data)
extinction coeff
no. of reflns collected
no. of indepdt reflns
abs corr
max and min transm
refinement method
data/restraints/params
foodness-of-fit on F2
final R indices [I > 2σ(I)]
R indices (all data)
extinction coeff
1.175
1.135
R1 ) 0.0326, wR2 ) 0.0750
R1 ) 0.0378, wR2 ) 0.0816
0.00062(14)
R1 ) 0.0450, wR2 ) 0.0989
R1 ) 0.0663, wR2 ) 0.1180
0.000 00(4)
largest diff peak and hole
0.530 and -0.550 e‚Å-3
largest diff peak and hole
0.488 and -0.747 e‚Å-3
was removed in vacuo, and the solid was extracted twice with
10 mL of hot hexanes. The solution was concentrated to 5 mL,
and then pyridine (0.05 mL) was added via syringe. The solid
that formed was filtered out and washed with 5 mL of hexanes
and then dried in vacuo yielding 5 (0.15 g, 71% yield) as a
white solid. Recrystallization from THF/hexanes yielded
crystals suitable for X-ray diffraction studies. NMR in C6D6:
δ(1H) ) 1.65 (s, 6H), 1.90 (s, 15H), 4.02 (t, 2H), 4.30 (t, 2H),
6.10 (br t, 2H), 6.54 (br t, 1H), 7.16-7.52 (mult, 14H), 8.24 (br
d, 2H).
to yield R1 and ωR2 of 0.0326 and 0.075, respectively.
Refinement was done using F2.
X-r a y Str u ctu r a l An a lysis of 6b. Data were collected at
173 K on a Siemens SMART PLATFORM equipped with a
CCD area detector and a graphite monochromator utilizing
Mo KR radiation (λ ) 0.710 73 Å). Cell parameters were
refined using up to 8192 reflections. A hemisphere of data
(1381 frames) was collected using the ω-scan method (0.3°
frame width). The first 50 frames were remeasured at the
end of data collection to monitor instrument and crystal
stability (maximum correction on I was <1%). ψ scan absorp-
tion corrections were applied based on the entire data set.
The structure was solved by direct methods in SHELXTL519
and refined using full-matrix least squares. The non-H atoms
were treated anisotropically, whereas the hydrogen atoms were
calculated in ideal positions and were riding on their respective
carbon atoms. The four THF ligands around the Li atom are
disordered over eight psoitions with site occupation factors of
one set being 0.51(3), 0.56(1), 0.70(2), and 0.52(1) with the
other four parts having occupation factors of the complement
to 1.0. The oxygen atoms of each THF molecule were not
disordered. A total of 735 parameters were refined in the final
cycle of refinement using 7092 reflections with I > 2σ(I) to
yield R1 and ωR2 of 0.045 and 0.0989, respectively. Refine-
ment was done using F2.
Cp *Ru Cp C(CH3)2P h BP h 3Li(Et2O)1/2 (6a ). To a solution
of 3 (0.50 g, 1.0 mmol) in 20 mL of Et2O at -78 °C was added
BuLi (0.40 mL, 1.0 mmol), and the solution was warmed to
room temperature over 30 min. To this solution was added
BPh3 (0.24 g, 1.0 mmol). A white solid precipitated im-
mediately, and the mixture was stirred for an additional 1 h.
The solid was filtered out, washed twice with 5 mL of hexanes,
and then dried in vacuo yielding 6a (0.47 g, 70% yield) as a
white solid. Recrystallization from cold THF/hexanes yielded
crystals suitable for X-ray diffraction studies. LSI MS (for
anion) (m/ z): Calcd, 661; found, 661. NMR in C6D6: δ(1H) )
1.10 (t, 3H), 1.66 (s, 6H), 1.93 (s, 15H), 3.25 (q, 2H), 4.01 (t,
2H), 4.33 (t, 2H), 7.08 (t, 3H), 7.10 (t, 8H), 7.76 (m, 2H), 7.86
(m, 6H).
X-r a y Str u ctu r a l An a lysis of 3. Data were collected at 173
K on a Siemens SMART PLATFORM equipped with A CCD
area detector and a graphite monochromator utilizing Mo KR
radiation (λ ) 0.710 73 Å). Cell parameters were refined using
up to 8192 reflections. A hemisphere of data (1381 frames)
was collected using the ω-scan method (0.3° frame width). The
first 50 frames were remeasured at the end of data collection
to monitor instrument and crystal stability (maximum cor-
rection on I was <1%). ψ scan absorption corrections were
applied based on the entire data set.
The structure was solved by direct methods in SHELXTL519
and refined using full-matrix least squares. The non-H atoms
were treated anisotropically, whereas the hydrogen atoms were
calculated in ideal positions and were riding on their respective
carbon atoms. A total of 236 parameters were refined in the
final cycle of refinement using 4472 reflections with I > 2σ(I)
Resu lts a n d Discu ssion
Syn th eses. The use of 6,6-dimethylfulvene to pre-
pare anionic Cp ligands has been previously demon-
strated in preparing both nonbridged20 and bridged21
metallocenes. The usefulness of this precursor arises
from the exclusive addition of a nucleophile at the
exocyclic carbon,20d leading to anionic Cp salts that are
unable to undergo Diels-Alder dimerizations.
(20) (a) Yanlong, Q.; Guisheng, L.; Weichum, C.; Bihua, L.; Xianglin,
J . Transition Met. Chem. 1990, 15, 478-482. (b) LeComte C.; Dusau-
soy, Y.; Protas, J .; Tiroflet, J .; Dormond, A. J . Organomet. Chem. 1974,
73, 67-76. (c) Little, W. F.; Koestler, R. C. J . Org. Chem. 1961, 26,
3245-3247. (d) Little, W. F.; Koestler, R. C. J . Org. Chem. 1961, 26,
3247-3250.
(19) Sheldrick, G. M. SHELXTL5; Nicolet XRD Corp.: Madison, WI,
1995.
(21) Gutmann, S.; Burger, P.; Hund, H.-U.; Hofmann, J .; Brintz-
inger, H.-H. J . Organomet. Chem. 1989, 369, 343-357.

Borane- and Borate-Containing Ruthenocenes
Organometallics, Vol. 16, No. 8, 1997 1631
Precipitation of the lithium salt allows for the con-
venient and simple isolation of the product by filtration
from a relatively nonpolar solvent (diethyl ether).
Para-substituted dihalobenzenes undergo monolithia-
tion reactions via the halo-lithium exchange22 process
leading to a nucleophilic carbanion. Thus, using both
dibromo- and diiodobenzene with 6,6-dimethylfulvene
as synthons, we have developed a new class of deriva-
tizable Cp ligands.
The addition of 1 equiv of BuLi to a solution of
p-dibromobenzene in diethyl ether leads to the forma-
tion of (p-bromophenyl)lithium. The slow addition of 1
equiv of 6,6-dimethylfulvene to this solution quickly
forms the desired lithium salt LiCpC(CH3)2PhBr (1),
which precipitates as a white solid (eq 1). Similarly,
LiCpC(CH3)2PhI (2) is prepared in the same way by
using p-diiodobenzene.
ecules present in the crystal contributed substantial
disorder, and an anisotropically refined structure could
not be obtained. Similarly, the presence of solvent made
it difficult to obtain a precise chemical analysis. How-
ever the NMR data, preliminary structure, and elemen-
tal analysis clearly indicate the formation of the desired
neutral complex.
The addition of BuLi to 3 in Et2O, followed by the
addition of triphenylboron, leads to the formation of the
borate-ruthenocene 6a as a lithium-etherate salt (eq 4).
If a mixture of 1 equiv of [Cp*RuCl]4 and 4 equiv of 1
in THF is refluxed for 10 h, the Cp*RuCpC(CH3)2PhBr
product (3) is isolated in good yield after standard
workup17 (eq 2). Similarly, the iodo-ruthenocene (4) is
prepared by using [Cp*RuCl]4 and 2. Both ruthenocenes
are easily crystallized, and X-ray-quality crystals are
obtained by cooling a hot hexanes solution of the
appropriate ruthenocene. These ruthenocenes are air-
stable and can be manipulated without any pre-
cautions.
Boron-containing derivitives have been synthesized
from the bromo-ruthenocene precursor 3. The addition
of BuLi to a solution of 3 in Et2O forms the phenyl-
lithiate, which can be trapped by the addition of
Ph2BOMe (eq 3). Addition of pyridine leads to the Et2O-
insoluble pyridine adduct (5), which can be recrystal-
lized from THF/hexanes. Unfortunately, solvent mol-
When the reaction is run in THF at -78 °C, the borate
product remains soluble and the solvent must be
removed in vacuo. The product (6b) is isolated as a
Li(THF)4 salt. The base-free salt (6) is prepared by
stripping the diethyl ether from 6a by suspending the
solid in benzene or toluene and then removing the
solvent under vacuum (eq 4).
The reaction of the lithiated ruthenocene with the
perfluorinated triphenylborane, B(C6F5)3, was also at-
tempted, and the anticipated product was observed by
1H NMR spectroscopy. However, attempts to isolate the
product proved difficult due to the similar solubilities
of the ruthenocene-borate and undesirable side prod-
ucts.
(22) (a) Gilman, H.; Longhorn, K. L.; Moore, G. J . J . Am. Chem.
Soc. 1940, 62, 2327. (b) Gilman, H.; Gorsich, R. D. J . Am. Chem. Soc.
1955, 77, 3919. (c) Gilman, H.; Gorsich, R. D. J . Am. Chem. Soc. 1956,
78, 2217. (d) Gilman, H.; Gorsich, R. D. J . Am. Chem. Soc. 1957, 79,
2625.
NMR Stu d ies. In 1, the Cp protons are observed at
5.73 and 5.85 ppm. The signals are tight triplets similar
to that observed20a for most monosubstituted Cp ligands.

1632 Organometallics, Vol. 16, No. 8, 1997
Miller et al.
The two phenyl resonances, which typically are two
doublets, overlap in one broadened singlet. The overlap
in the chemical shifts is a result23 of similar effects on
both the ortho- and meta-positions by the Br substitu-
1
ent. The H NMR spectrum of 2 is similar to 1, except
that the phenyl region is cleanly split as two doublets,
with the resonance for the proton ortho to the iodide
further downfield.
The 1H NMR spectra of the three neutral ru-
thenocenes, 3-5, can be compared to examine the effects
of the substitution on the molecular and electronic
structure of the metal complexes. The spectra of
compounds 3 and 4 show that altering the halogen on
the phenyl group affects the electronics of the ring but
has little or no effect on the ruthenocene moiety of the
complex. As in the NMR spectra of the free ligands 1
and 2, the iodo substituent has a much greater effect
on the ortho and meta resonances (7.42 and 6.90 ppm,
respectively) versus the bromo substituent (7.23 and
7.02 ppm). However, all other chemical shifts of the
protons within the three molecules are identical. This
similarity indicates that the sp3 carbon bridging the Cp
and the phenyl group prevents significant intraligand
electronic effects at the metal by the substituted phenyl
group.
F igu r e 1. Thermal ellipsoid plot of 3.
1
The H NMR spectrum of 5 is comparable to that of
the bromo- and iodo-ruthenocenes but with a few
minor differences. The chemical shift of the Cp* protons
is at 1.88 ppm, which is identical to the two other
neutral ruthenocenes. However, the chemical shift of
the terminal methyl protons of the bridging carbon is
at 1.65 ppm, which is shifted downfield 0.23 ppm from
the halo-ruthenocenes. Likewise, there is a small
difference in the Cp protons which are at 4.02 and 4.41
ppm, as compared to 3.99 and 4.11 ppm for the halo-
ruthenocenes. The aromatic region clearly indicates the
presence of a coordinated pyridine ligand with broad-
ened triplets at 6.09 ppm (meta) and 6.55 ppm (para)
and a broadened doublet at 8.23 ppm (ortho). The
phenyl region displays unresovable overlapping signals.
The 1H NMR spectrum of 6 displays a unique splitting
pattern for the protons ortho to the borate. These
signals come downfield of the normal aromatic region
(7.44 and 7.58 ppm), and the splitting patterns are
complex. The signal observed for the protons ortho to
the boron has a characteristic symmetrical seven-line
pattern similar to other p-substituted phenylborates
observed in our laboratory. The signal for protons H13
is also highly complex and symmetrical. The Cp reso-
nances are at 3.89 and 4.17 ppm and are more broadly
split than in the neutral ruthenocenes, possibly due to
the orientation of the counterion. The Cp* resonances
and terminal methyl resonances are at 1.83 and 1.49
ppm, respectively, which are similar to those of the
equivalent protons in the neutral ruthenocenes.
F igu r e 2. Thermal ellipsoid plot of 6b.
F igu r e 3. End-on view of 3, showing the eclipsed Cp rings
and the molecular mirror plane.
ures 1 and 3) and a molecular mirror plane that passes
through the plane of the phenyl ring and bisects each
of the two Cp rings. The Cp rings are slightly tilted
from parallel by 5.4°, and the centroid-Ru-centroid
angle is 176.1°. This diversion from the typical planar-
ity occurs due to the interaction of the two methyl
groups of C12 and C13 with the Cp* methyl group of
C1′ (Figure 1). Another effect of this interaction is that
C11 is raised 0.22 Å above the plane of the Cp ring, with
the phenyl ring almost perpindicular (83.7°) to the plane
of the Cp ring. The Ru-Cp* centroid distance is 1.806
Å, which is comparable to the Ru-Cp* centroid distance
of 1.803 Å in pentaiodopentamethylruthenocene16b and
1.800 Å in decamethylruthenocene.16c The Ru-
CpC(CH3)2PhBr centroid distance is 1.826 Å.
The 1H NMR spectrum of the diethyl etherate 7 is
slightly different from the nonsolvated salt 6 only in that
all corresponding resonances are shifted downfield,
although by varying amounts.
X-r a y Str u ctu r a l An a lyses. Single crystals of 3
were grown by cooling a hot, concentrated solution of 3
in hexanes. The structure has eclipsed Cp rings (Fig-
The crystal structure of 6b was also solved after single
crystals were grown by the slow diffusion of pentane
into a concentrated THF solution of 6a . The crystal
structure of 6b is similar to that of 3, with one major
exception being that the Cp rings are not eclipsed. In
6b, the rings are twisted by 17.5° from the eclipsed
(23) Silverstein, R. M.; Bassler, G. C.; Morrill, T. C. Spectrometric
Identification of Organic Compounds, 5th ed.; J ohn Wiley & Sons: New
York, 1991.

Borane- and Borate-Containing Ruthenocenes
Organometallics, Vol. 16, No. 8, 1997 1633
slightly staggered conformation. Other examples of
noneclipsed ruthenocenes16a,b,24 have been observed,
although the staggered conformation is rare.16c,d,25 Only
in cases where the Cp rings are extremely bulky, as in
octaphenylruthenocene24b and pentaiodopentamethyl-
ruthenocene,16b or when the ring rotation is locked by
another covalently bound metal24a are the rings stag-
gered. Decamethylruthenocene16c and decachloro-
ruthenocene25c both maintain an eclipsed structure, and
the C-Cl bonds of decachlororuthenocene are length-
ened and bent out of the plane of the Cp ring rather
than staggering the conformation. Therefore, the half-
staggered conformation of 6b is somewhat unique and
appears to be the first display of a staggered rutheno-
cene due to intermolecular packing conditions.
F igu r e 4. End-on view of 6b, showing the slightly stag-
gered Cp rings. The phenyl rings of the BPh3 moiety have
been omitted for clarity.
Oxid a tion Rea ction s w ith 6. The oxidation chem-
istry of many ruthenocenes has been examined,16c,d,26
and a method to chemically oxidize Cp2RuII to [Cp2RuIII +
]
has not yet been found. When Cp2RuII is allowed to
react with halogens,26a the Cp2RuII complex is oxidized
to the ruthenium(IV) halide cation. Attempts to stabi-
lize [Cp2RuIII]+ by altering the oxidants, oxidant ratios,
solvents, and reaction conditions have not been suc-
cessful.26 However, when the steric environment around
the metal center is increased by substituting Cp* for
Cp, the decamethylruthenocenium(III) ion has been
Ta ble 3. Selected Bon d Len gth s a n d An gles for
Cp *Ru Cp C(CH3)2C6H4Br (3)
Bond Distances (Å)
Ru-C1
2.199(3)
2.178(3)
2.171(3)
2.173(3)
2.182(3)
1.806(3)
1.499(4)
1.543(4)
Ru-C6
2.213(3)
2.189(3)
2.178(3)
2.185(3)
2.198(3)
1.826(3)
1.513(4)
Ru-C2
Ru-C7
Ru-C3
Ru-C8
Ru-C9
Ru-C10
Ru-Cp′(cent)
C6-C11
Ru-C4
Ru-C5
Ru-Cp*(cent)
avg Cx-Cx′
C11-C14
-
synthesized as a PF6 salt.27 We have examined the
ability of the tethered borate to stabilize the ruthe-
nium(III) oxidation product and found that the borate
does not stabilize the ruthenium(III) complex. Follow-
ing the standard procedure26a for oxidation of ru-
thenocene with iodine, oxidation reactions of 6a with
iodine apparently leads to a ruthenium(IV) complex that
has not been fully characterized.
Bond Angles (deg)
Cent-Ru-Cent
C6-C11-C13
ring tilt
176.1(2)
110.2(2)
5.4(3)
C6-C11-C14
109.3(2)
110.3(3)
2.0(3)
C6-C11-C12
C1-cent-cent-C6
Ta ble 4. Selected Bon d Len gth s a n d An gles for
Cp *Ru Cp C(CH3)2C6H4BP h 3Li(THF )4 (6)
The addition of 3 equiv of I2 to a solution of 6a in
carbon tetrachloride (CCl4) leads immediately to the
formation of a red precipitate which can be filtered out
and washed with CCl4. The product is diamagnetic, and
Bond Distances (Å)
Ru-C1
2.164(3)
2.159(3)
2.189(3)
2.197(3)
2.195(3)
1.809(3)
1.508(5)
1.539(4)
1.645(4)
1.654(4)
Ru-C6
2.185(3)
2.182(3)
2.186(3)
2.201(3)
2.220(3)
1.830(3)
1.525(4)
1.641(5)
1.648(5)
Ru-C2
Ru-C7
Ru-C3
Ru-C8
Ru-C9
Ru-C4
1
the H NMR spectrum in CD3CN suggests the presence
Ru-C5
Ru-C10
Ru-Cp′(cent)
C10-C13
B-C32
of a ruthenium(IV) species. The two Cp resonances are
shifted downfield and are more separated than in the
original ruthenocene(II) complex. However, the aro-
matic region is obscure and does not integrate to the
correct number of protons if simple oxidation of the
metal occurred. Further studies on the oxidation of 6
are being performed to determine the nature of the
observed chemistry.
Ru-Cp*(cent)
avg Cx-Cx′
C13-C14
B-C20
B-C26
B-C17
Bond Angles (deg)
Cent-Ru-Cent
C10-C13-C14
ring tilt
C17-B-C26
C17-B-C20
175.7(2)
109.0 (2)
6.4 (3)
104.5 (2)
112.5 (2)
C10-C13-C11
C10-C13-C12
C1-cent-cent-C6
C17-B-C32
110.1(3)
109.6 (3)
17.5 (3)
110.6 (2)
Con clu sion s. p-Dihalobenzenes with 6,6-dimethyl-
fulvene provide a useful starting point for the synthesis
of derivitized Cp ligands, including borane- and borate-
position (Figures 2 and 4), which is approximately
halfway between the eclipsed and staggered conforma-
tions. This staggering is apparently due to the packing
of the molecules in the crystal because the bond lengths
and angles of the ligands in the structures of both 3 and
6 are very similar (Tables 3 and 4). The two Cp rings
are tilted from parallel by 6.4°, and the centroid-Ru-
centroid angle is 175.7°. The Ru-Cp* centroid distance
is 1.809 Å, and the Ru-CpC(CH3)2PhBPh3 centroid
distance is 1.830 Å.
Examination of the crystal packing (not shown) of
both structures reveals similar interactions between the
C3′ and C4′ methyl groups of the Cp* and the p-
substituted phenyl ring of an adjacent ruthenocene
complex. In 6b, the Cp* ring has to rotate by 17.5° in
order to accommodate such interactions, leading to the
(24) For examples of noneclipsed ruthenocenes see: (a) Rheingold,
A. L.; Mueller-Westerhoff, U. T.; Swiegers, G. F.; Haas, T. J . Organo-
metallics 1992, 11, 3411-3417. (b) Hoobler, R. J .; Adams, J . V.; Hutton,
M. A.; Francisco, T. W.; Haggerty, B. S.; Rheingold, A. L.; Castellani,
M. P. J . Organomet. Chem. 1991, 412, 157-167.
(25) For examples of eclipsed ruthenocenes see: (a) Abel, E. W.;
Long, N. J .; Orrell, K. G.; Osborne, A. G.; Sik, V. J . Organomet. Chem.
1991, 403, 195-208. (b) Bruce, M. I.; Wallis, R. C.; Williams, M. L.;
Skelton, B. W.; White A. H. J . Chem. Soc., Dalton Trans. 1983, 2183-
2189. (c) Brown, G. M.; Hedberg, F. L.; Rosenberg, H. J . Chem. Soc.,
Chem. Commun. 1972, 5-6. (d) Trotter, J . Acta Crystallogr. 1963, 16,
571-572. (e) Blake, A. J .; Gould, R. O.; Osborne, A. G. J . Organomet.
Chem. 1986, 308, 297-302. (f) Hughes, R. P.; Zheng, X.; Ostrander,
R. L.; Rheingold, A. L. Organometallics 1994, 13, 1567-1568.
(26) (a) Sohn, Y. S.; Schlueter, A. W.; Hendrickson, D. N.; Gray, H.
B. Inorg. Chem. 1974, 13(2), 301-304. (b) Denisovich, L. I.; Zakurin,
N. V.; Bezrukova, A. A.; Gubin, S. P. J . Organomet. Chem. 1974, 81,
207-216.
(27) (a) Koelle, U.; Salzer, A. J . Organomet. Chem. 1983, 243, C27-
C30. (b) Ko¨lle, U.; Grub, J . J . Organomet. Chem. 1985, 289, 133-139.

1634 Organometallics, Vol. 16, No. 8, 1997
Miller et al.
containing ligands. The substitution of the halogen is
possible in the ruthenocene systems studied, and the
synthesis of a novel borate-containing ruthenocene has
been accomplished. This ruthenocene exhibits similar
oxidation chemistry to other ruthenocenes, and the
presence of the ligated borate does not stabilize the
ruthenocenium(III) complex. Further studies on the
oxidation of the borate complex are in progress. Group
4 metal complexes containing the halogenated ligand
have been synthesized, and the borate-substitution
reactions are being examined.28
Ack n ow led gm en t. K.A.A. wishes to acknowledge
the National Science Foundation and the University of
Florida for funding of the purchase of the X-ray equip-
ment. This work was partially supported by a grant
from the National Science Foundation to D.E.R. (CHE
9311614).
Su p p or tin g In for m a tion Ava ila ble: Tables of X-ray
parameters, positional and thermal parameters, bond dis-
1
tances and angles, and H and 13C NMR data and numbering
scheme for NMR assignments (23 pages). Ordering informa-
tion is given on any current masthead page.
(28) Miller, H. J .; Boncella, J . M.; Richardson, D. E. Work in
progress.
OM9608521