Yttrium complexes of a phenanthrene-fused cyclopentadienyl: Synthetic, structural, and reactivity studies

Article abstract of DOI:10.1021/om7007343

The tris-alkyl complex Y(CH₂SiMe₃) ₃(THF)₂ reacts with 1,2,3-trimemyl-1H-cyclopenta[l] phenanthrene (PCp*H) to give (PCp*)Y(CH₂SiMe ₃)₂(THF) (1), characterized structurally by X-ray crystallography. VT NMR spectra of 1 reveal a dynamic equilibrium between the THF-free and mono(THF) solvate in solution. Complex 1 undergoes substitution of THF by 2,2′-bipyridine (bipy) to give (PCp*)-Y(CH ₂SiMe₃)₂(bipy) (2); the latter complex does not undergo ligand exchange in solution. Insertion reactions of 1 with CO ₂, Me₃ SiNCO, and Me₂CHN=C=NCHMe₂ afford (PCp*)Y[k^2-(O, O)-O₂C(CH₂SiMe ₃)]₂ (3), (PCp*)Y[k²-(N,O)-(Me ₃Si)NC(CH₂SiMe₃)O]₂ (4), and (PCp*)Y[k²-(N,N)-(Me₂CH)NC(CH₂SiMe ₃)N(CHMe₂)]₂ (5). Reaction of 1 with 2 equiv of Me₃SiCCH affords a terminal bis(acetylide) (PCp*)Y(CCSiMe ₃)₂(THF) (6) in solution; however, X-ray analysis of crystals obtained from a solution of 6 shows that it dimerizes to {[(PCp*)Y(CCSiMe₃)(THF)]₂(μ-CCSiMe ₃)₂} (7). A toluene solution of complex 1 and 1 equiv of [Ph₃C]⁺[B(C₆F₅)₄] ^- shows modest catalytic activity for the polymerization of ethylene at room temperature (20 kg mol^-1 h^-1bar^-1).

Full text of DOI:10.1021/om7007343

Organometallics 2008, 27, 683–690
683
Yttrium Complexes of a Phenanthrene-Fused Cyclopentadienyl:
Synthetic, Structural, and Reactivity Studies
Jianlong Sun, David J. Berg,* and Brendan Twamley†
Department of Chemistry, UniVersity of Victoria, P.O. Box 3065, Victoria,
British Columbia, Canada V8W 3V6
ReceiVed July 20, 2007
The tris-alkyl complex Y(CH2SiMe3)3(THF)2 reacts with 1,2,3-trimethyl-1H-cyclopenta[l]phenanthrene
(PCp*H) to give (PCp*)Y(CH2SiMe3)2(THF) (1), characterized structurally by X-ray crystallography.
VT NMR spectra of 1 reveal a dynamic equilibrium between the THF-free and mono(THF) solvate in
solution. Complex 1 undergoes substitution of THF by 2,2′-bipyridine (bipy) to give (PCp*)-
Y(CH2SiMe3)2(bipy) (2); the latter complex does not undergo ligand exchange in solution. Insertion
reactions of 1 with CO2, Me3SiNCO, and Me2CHNdCdNCHMe2 afford (PCp*)Y[κ2-(O,O)-
O2C(CH2SiMe3)]2 (3), (PCp*)Y[κ2-(N,O)-(Me3Si)NC(CH2SiMe3)O]2 (4), and (PCp*)Y[κ2-(N,N)-
(Me2CH)NC(CH2SiMe3)N(CHMe2)]2 (5). Reaction of 1 with 2 equiv of Me3SiCCH affords a terminal
bis(acetylide) (PCp*)Y(CCSiMe3)2(THF) (6) in solution; however, X-ray analysis of crystals obtained
from a solution of 6 shows that it dimerizes to {[(PCp*)Y(CCSiMe3)(THF)]2(µ-CCSiMe3)2} (7). A toluene
solution of complex 1 and 1 equiv of [Ph3C]+[B(C6F5)4]- shows modest catalytic activity for the
polymerization of ethylene at room temperature (20 kg mol-1 h-1bar-1).
ligands are known.4 Surprisingly, larger aromatic-fused cyclo-
pentadienyl ligands have not received very much attention in
yttrium or lanthanoid chemistry, although a few examples have
been reported for the group 4 metals.5 One criticism of this
approach might be that extensive delocalization of charge within
the extended aromatic system weakens the bonding between
the metal and the Cp unit since this bonding is primarily ionic
in nature. However, calculations on the phenanthrene-fused
(PCp) or bis(phenanthrene)-fused (sCp) anions indicate that the
reduction in charge on the five carbons of the Cp subunit caused
by fusion of two (PCp) or four (sCp) additional benzene units
Introduction
Cyclopentadienyl complexes of yttrium and the lanthanoids
have been extensively studied over the past 30 years and
constitute the best known class of ancillary ligand in the
organometallic chemistry of these elements.1 In the development
of this chemistry, pentamethylcyclopentadienyl, bis(trimethyl-
silyl)cyclopentadienyl, and other alkyl-substituted Cp ligands
have been most extensively used because their increased bulk
allows isolation of soluble, monomeric or dimeric complexes
free from extensive bridging interactions that plague Cp and
its smaller analogues.2 While this strategy has obvious merit,
excessive ancillary ligand bulk is usually detrimental to reactiv-
ity at any remaining metal–carbon bonds because the alkyl
substituents block reactant access;3 in the case of bent metal-
locenes, this is clearly because the substituents on the Cp ligands
project into the metallocene wedge. One possible solution to
this problem is to incorporate planar bulk on the Cp ligand so
that bridging interactions between adjacent metal centers are
disrupted, but access within the metallocene wedge is still
relatively unimpeded.
(4) (a) A complete list of all yttrium and lanthanoid indenyl and fluorenyl
systems is too extensive to give here; recent examples, many containing
pendant functionality, are given below: Zhou, S.; Wang, S.; Yang, G.; Li,
Q.; Zhang, L.; Yao, Z.; Zhou, Z.; Song, H. Organometallics 2007, 26, 3755.
(b) Downing, S. P.; Conde Guadaño, S.; Pugh, D.; Danopoulos, A. A.;
Bellabarba, R. M.; Hanton, M.; Smith, D.; Tooze, R. P. Organometallics
2007, 26, 3762. (c) Wang, B.; Wang, D.; Cui, D.; Gao, W.; Tang, T.; Chen,
X.; Jing, X. Organometallics 2007, 26, 3167. (d) Trifonov, A. A.; Federova,
E. A.; Borovkov, I. A.; Fukin, G. K.; Baranov, E. V.; Larionova, J.;
Druzhkov, N. O. Organometallics 2007, 26, 2488. (e) Wang, S.; Tang, X.;
Vega, A.; Saillard, J.-Y.; Zhou, S.; Yang, G.; Yao, W.; Wei, Y. Organo-
metallics 2007, 26, 1512. (f) Lewin, J. L.; Woodrum, N. L.; Cramer, C. J.
Organometallics 2006, 25, 5906. (g) Pi, C.; Zhang, Z.; Liu, R.; Weng, L.;
Chen, Z.; Zhou, X. Organometallics 2006, 25, 5165. (h) Wang, S.; Tang,
X.; Vega, A.; Saillard, J.-Y.; Sheng, E.; Yang, G.; Zhou, S.; Huang, Z.
Organometallics 2006, 25, 2399. (i) Shen, H.; Chan, H.-S.; Xie, Z.
Organometallics 2006, 25, 2617.
Indenyl and fluorenyl complexes represent the simplest
implementation of this idea, and many complexes of these
* Corresponding author. E-mail: djberg@uvic.ca.
† University Research Office, 109 Morrill Hall, University of Idaho,
Moscow ID 83844-3010.
(1) (a) Edelmann, F. T.; Lorenz, V. Coord. Chem. ReV. 2000, 209, 99.
(b) Schumann, H.; Meese-Marktscheffel, J. A.; Esser, L. Chem. ReV. 1995,
95, 865. (c) Schaverien, C. J. AdV. Organomet. Chem. 1994, 36, 283.
(2) (a) Evans, W. J.; Anwander, R.; Doedens, R. J.; Ziller, J. W. Angew.
Chem., Int. Ed. Engl. 1994, 33, 1641. (b) Arndt, S.; Okuda, J. Chem. ReV.
2002, 102, 1953. (c) van der Heijden, H.; Schaverien, C. J.; Orpen, A. G.
Organometallics 1989, 8, 255. (d) Heeres, H. J.; Meetsma, A.; Teuben,
J. H.; Rogers, R. D. Organometallics 1989, 8, 2637.
(5) (a) To the best of our knowledge, there are no structurally
characterized examples of aromatic-fused cyclopentadienyls (excluding
fullerene systems) larger than fluorenyl for yttrium or the lanthanoids;
examples from group 4 are as follows: Spaleck, W.; Kuber, F.; Winter, A.;
Rohrmann, J.; Bachmann, B.; Antberg, M.; Dolle, V.; Paulus, E. F.
Organometallics 1994, 13, 954. (b) Stehling, U.; Diebold, J.; Kirsten, R.;
Röll, W.; Brintzinger, H. H.; Jüngling, S.; Mülhaupt, R.; Langhauser, F.
Organometallics 1994, 13, 964. (c) Schneider, N.; Huttenloch, M. E.;
Stehling, U.; Kirsten, R.; Schaper, F.; Brintzinger, H. H. Organometallics
1997, 16, 3413. (d) Schneider, N.; Prosenc, M. H.; Brintzinger, H. H. J.
Organomet. Chem. 1997, 545–546, 291. (e) Schneider, N.; Schaper, F.;
Schmidt, K.; Kirsten, R.; Geyer, A.; Brintzinger, H. H. Organometallics
2000, 19, 3597.
(3) (a) The exception to this rule is the remarkable chemistry uncovered
by Evans for “sterically oversaturated” Ln(C5Me5)3 systems; see for
example: Evans, W. J.; Kozimor, S. A.; Ziller, J. W. Inorg. Chem. 2005,
44, 7960. (b) Evans, W. J.; Perotti, J. M.; Kozimor, S. A.; Champagne,
T. M.; Davis, B. L.; Nyce, G. W.; Fujimoto, C. H.; Clark, R. D.; Johnston,
M. A.; Ziller, J. W. Organometallics 2005, 24, 3916.
10.1021/om7007343 CCC: $40.75
2008 American Chemical Society
Publication on Web 01/19/2008

684 Organometallics, Vol. 27, No. 4, 2008
Sun et al.
to the indenyl or fluorenyl core, respectively, is very small.6,7
The greatest reduction in charge on the Cp occurs when the
benzene unit is fused directly to the Cp as in indenyl or fluorenyl
themselves, while more remote fusion has relatively little effect.7
Therefore, inasmuch as indenyl and fluorenyl complexes of
yttrium and the lanthanoids are stable, there is no reason a priori
to expect weak metal–ligand bonding to dominate larger systems
because the Cp is effectively isolated electronically from these
remote aromatic groups. However, it should be noted that a large
conjugated aromatic system fused to a Cp might have redox
chemistry of its own that becomes significant for metals with
multiple oxidation states.7
In this contribution we report the synthesis of yttrium
complexes containing a phenanthrene-fused Cp bearing three
methyl groups on the remaining Cp carbons (PCp*). This is a
relatively bulky ligand so it is not surprising that stable
mono(PCp*) complexes that show no tendency to redistribute
dominate this chemistry. The synthesis of a PCp* yttrium dialkyl
complex, its acid–base reaction with trimethylsilylacetylene, and
its insertion chemistry with unsaturated substrates are discussed
below.
(250 mg, 0.5 mmol), and the mixture was stirred overnight.
Removal of toluene under reduced pressure gave a yellow residue,
which was dissolved completely in hexanes and filtered through
Celite to give a clear yellow solution. Removal of hexanes afforded
259 mg of a yellow powder. Recrystallization of this yellow powder
from hexane afforded 80 mg of 1 as pale yellow prisms. Yield
(recrystallized): 20%. Mp: 110 °C (dec). 1H NMR (500 MHz,
3
4
C6D6): δ 8.47 (dd, JHH ) 8.2 Hz, JHH ) 0.8 Hz, 2H, 1-arylH),
3
4
8.25 (dd, JHH ) 8.4 Hz, JHH ) 1.0 Hz, 2H, 4-arylH), 7.34 (m,
2H, 2-arylH), 7.20 (m, 2H, 3-arylH), 2.78 (s, 6H, CpMe), 2.52 (t,
4H, R-THF CH2), 2.32 (s, 3H, CpMe), 0.60 (m, 4H, ꢀ-THF CH2),
2
0.26 (s, 18H, SiMe3), -0.60 (d, JYH) 3.2 Hz, 4H, YCH2). 13C
NMR (125.8 MHz, C6D6): δ131.73, 129.00, 128.58, 127.70, 124.72,
124.43, 123.94, 118.26, 113.70 (arylC), 70.21 24.69 (THF), 37.40
1
(d, JYC) 45 Hz, Y-CH2), 16.30 (CpMe2), 11.75 (CpMe), 4.76
(SiMe3). Anal. Calcd for C32H47OSi2Y: C 64.84, H 8.00. Found: C
64.98, H 8.07.
(PCp*)Y(CH2SiMe3)2(bipy) (2). Addition of a solution of 27
mg of 2.2′-bipyridine (0.17 mmol) in 1 mL of toluene to a solution
of 100 mg of 1 (0.169 mmol) in 5 mL of toluene resulted in a
color change to deep red. After stirring for 5 min, the solvent was
removed by vacuum to give a red solid. Repeated washing with
hexane and drying under vacuum gave a deep red powder in
1
3
Experimental Section
quantitative yield. H NMR (300 MHz, C6D6): δ 8.26 (d, JHH
)
3
4
5.2 Hz, 2H, 6-bipy), 7.94 (dd, JHH ) 7 Hz, JHH ) 2.2 Hz, 2H,
General Procedures. All reactions were carried out under a
nitrogen atmosphere, with the exclusion of water and oxygen, using
glovebox (Braun MB150-GII) or vacuum line techniques. All
compounds described below were prepared on NMR tube scale first
3
4
1-arylH), 7.73 (dd, JHH ) 7 Hz, JHH ) 2.6 Hz, 2H, 4-arylH),
7.03–6.91 (m, 4H, 2,3-arylH), 6.64 (dt, 2H, 3JHH ) 7 Hz, 4-bipy),
3
3
4
6.35 (d, 2H, JHH ) 8 Hz, 3-bipy), 6.28 (dd, JHH ) 6.6 Hz, JHH
) 2.2 Hz, 2H, 5-bipy), 2.76 (s, 6H, CpMe), 2.58 (s, 3H, CpMe),
1
(except for 3) followed by preparative scale reactions. H NMR
2
3
0.29 (s, 18H, SiMe3), -0.22 (dd, JYH ) 3.0 Hz, JHH ) 11 Hz,
2H, YCH2), -0.45 (dd, 2JYH )3.0 Hz, 3JHH ) 11 Hz, 2H, YCH2);
13C NMR (75.5 MHz, C6D6) δ151.70, 138.64, 128.40, 128.08,
126.80, 124.35, 123.92, 123.35, 122.78, 120.47, 113.30 (arylC),
32.98 (d, 1JYC ) 38.6 Hz, Y-CH2), 16.44 (CpMe2), 12.47 (CpMe),
5.27 (SiMe3). Anal. Calcd for C38H47N2Si2Y: C 67.43, H 7.01, N
4.14. Found: C 68.05, H 6.91, N 4.00. This sample did not give an
obvious melting point below 200 °C but rather darkened steadily
on heating.
data from NMR tube scale reactions and isolated solids from
preparative scale reactions matched very well for 1/2 and 4-6;
only NMR data from the preparative scale reaction is given in the
text. Tetrahydrofuran (THF) and diethyl ether were dried by
distillation from sodium benzophenone ketyl under argon im-
mediately prior to use; hexane and toluene were dried and
deoxygenated using an MBraun solvent purification system and
were stored over activated
4 Å sieves in the glovebox.
Y(CH2SiMe3)3(THF)28 and 1,2,3-trimethyl-1H-cyclopenta[l]phenan-
threne (PCp*H)9 were prepared as previously reported. The PCp*H
ligand was dried over 4 Å sieves prior to use.
(PCp*)Y(K2-(O,O)-O2CCH2SiMe3)2 (3). An evacuated Schlenk
flask was filled with CO2 gas that had been dried by passage through
a column of activated 4 Å sieves. A solution of 1 (50 mg, 0.082
mmol) in 5 mL of hexanes was injected into the flask by syringe.
A white precipitate formed immediately. The suspension was
allowed to stir overnight and the solvent was removed under reduced
pressure. In the glovebox, the precipitate was washed with hexane
and dried under reduced pressure to give 30 mg of 3 as a white
powder. Yield: 60%. Mp: 234 °C (dec). 1H NMR (C6D6, 500 MHz):
NMR spectra were recorded using a Bruker Avance-500 MHz
spectrometer: 1H (500.13 MHz) and 13C (125.8 MHz) unless
otherwise specified. All deuterated solvents were dried over
activated 4 Å molecular sieves except for d8-tetrahydrofuran (d8-
THF), which was dried by distillation from sodium benzophenone
ketyl under argon and stored over activated 4 Å molecular sieves.
The spectra were recorded using 5 mm tubes fitted with a Teflon
valve (Brunfeldt) at room temperature unless otherwise specified
and were referenced to residual solvent resonances. Melting points
were recorded using a Büchi melting point apparatus in sealed
capillary tubes and are not corrected. Elemental analyses were
performed by Canadian Microanalytical, Delta, BC; co-oxidants
(V2O5 or PbO2) were used during combustion of the metal
complexes.
3
3
δ 8.55 (d, JHH ) 8.1 Hz, 2H, 1-arylH), 8.43 (d, JHH ) 7.6 Hz,
2H, 4-arylH), 7.42 (m, 2H, 2-arylH), 7.28 (m, 2H, 3-arylH), 2.72
(s, 6H, CpMe), 2.30 (s, 3H, CpMe), 1.10 (s, 4H, CO2CH2), 0.00 (s,
18H, SiMe3). 13C NMR (125.7 MHz, C6D6): δ 185.42 (CO2),
132.57, 128.68, 128.39, 128.07, 127.05, 125.38, 124.22, 118.80,
114.46 (arylC), 29.63 (CO2CH2), 15.26 (CpMe2), 11.53 (CpMe),
-0.62 (SiMe3). Anal. Calcd for C30H39O4Si2Y: C 59.20, H 6.46.
Found: C 60.18, H, 6.29.
(PCp*)Y(CH2SiMe3)2(THF) (1). A 5 mL toluene solution of
PCp*H (129 mg, 0.5 mmol) was added to Y(CH2SiMe3)3(THF)2
(PCp*)Y[K2-(N,O)-Me3SiN(CH2SiMe3)CO]2 (4). Me3SiNCO (6
mg, 0.05 mmol) was added to 6 mg of 1 (0.01 mmol) in 1 mL of
toluene solution and allowed to stir for 5 h. Removal of solvent
under vacuum afforded an off-white powder. Repeated washing
with hexane and drying under vacuum gave a cream powder in
(6) Simple extended Hückel calculations indicate that direct fusion of
an aromatic ring to cyclopentadienide has the greatest effect on the charge
on the five-membered ring carbons, while remote fusion has substantially
less effect: Cp- (-1.0 charge on the five-membered ring carbons), indenide
(-0.84), fluorenide (-0.59), cyclopenta[l]phenanthrenide (PCp, -0.78).
(7) A more in-depth theoretical study of aromatic-fused cyclopentadi-
enyls in the gas phase and in solution supports the trend in ref 6 and clearly
shows that the position of ring fusion is also important as might be
expected. Yoshizawa, K.; Yahara, K.; Taniguchi, A.; Yamabe, T.; Kinoshita,
T.; Takeuchi, K. J. Org. Chem. 1999, 64, 2821.
1
3
quantitative yield. H NMR (C6D6, 300 MHz): δ 8.58 (d, JHH
)
8.0 Hz, 2H, 1-aryl H), 8.42 (d, 3JHH ) 8.0 Hz, 2H, 4-aryl H), 7.45
(t, 3JHH ) 7.3 Hz, 2H, 2-aryl H), 7.32 (t, 3JHH ) 7.4 Hz, 2H, 3-aryl
H), 2.79 (s, 6H, CpMe), 2.31 (s, 3H, CpMe), 1.65 (s, 4H,
CH2SiMe3), 0.06 (s, 18H, CH2SiMe3), -0.05 (s, 18H, NSiMe3).
13C NMR (75.5 MHz, C6D6): δ 188.54 (NCO), 129.68, 128.72,
128.40, 127.25, 125.18, 124.33 (arylC), 31.40 (CH2), 15.28
(8) Barker, F. K.; Lappert, M. F. J. Organomet. Chem. 1974, 76, C45.
(9) Jones, D. W. J. Chem. Soc., Perkin Trans. 1 1977, 980.

Yttrium Complexes of a Phenanthrene-Fused Cyclopentadienyl
Organometallics, Vol. 27, No. 4, 2008 685
Table 1. Summary of Crystallographic Data for 1 and 7 · toluenea
(CpMe2), 11.92 (CpMe), 1.67 (CH2SiMe3), -0.28 (NSiMe3). Anal.
Calcd for C36H57N2O2Si4Y: C 57.58, H 7.66, N 3.73. Found: C
57.21, H 7.64, N 4.15.
1
7 · toluene
formula
C32H47OSi2Y
592.79
C75H94O2Si4Y2
1317.68
(PCp*)Y[K2-(N,N)-iPrN(CH2SiMe3)CN(i-Pr)]2 (5). Diisopro-
pylcarbodiimide (60 mg, 0.5 mmol) (Me2CHNCNCHMe2) was
added to 60 mg of 1 (0.1 mmol) in 1 mL of toluene solution and
allowed to stir overnight. Removal of the toluene solvent under
vacuum, followed by repeated washing with hexane and drying in
Vacuo, afforded an off-white powder quantitatively. 1H NMR (C6D6,
300 MHz): δ 8.71 (d, 3JHH ) 8.6 Hz, 2H, 1-aryl H), 8.55 (d, 3JHH
fw (g mol-1
)
cryst size (mm)
cryst color and habit
a (Å)
b (Å)
c (Å)
0.32 × 0.28 × 0.21
pale yellow prism
11.1359(5)
12.7246(6)
12.9267(6)
0.21 × 0.13 × 0.07
colorless plate
10.5591(12)
24.499(3)
27.461(3)
90
100.724(10)
90
6979.7(13)
1.254
R (deg)
76.0030(10)
74.1890(10)
64.5570(10)
1574.97(13)
1.250
ꢀ (deg)
3
γ (deg)
) 9.3 Hz, 2H, 4-aryl H), 7.53 (t, JHH ) 7.8 Hz, 2H, 2-arylH),
V (Å3)
3
7.37 (m, JHH ) 7.6 Hz, 2H, 3-aryl H), 3.26 (m, 4H, CHMe2),
calc density (g cm-3
space group
Z
)
2.87 (s, 6H, CpMe), 2.41 (s, 3H, CpMe), 1.83 (s, 4H, CH2SiMe3),
j
P1 (No. 2)
P21/c (No. 14)
4
3
0.94 (d, 24H, JHH ) 7.6 Hz, CHMe2) 0.06 (s, 18H, SiMe3). 13C
2
NMR (75.5 MHz, C6D6): δ 177.40 (NCN), 127.06, 125.88, 124.35,
124.31 (arylC), 48.15 (CHMe2), 25.91 (CHMe2), 18.96 (CH2SiMe3),
17.22 (CpMe2), 13.20 (CpMe), 0.42 (SiMe3). Anal. Calcd for
C42H67N4Si2Y: C 65.25, H 8.74, N 7.25. Found: C 64.42, H 8.25,
N 6.51.
2θ range (deg)
F000
1.79 - 27.5
628
1.949
24 128
7233
334
1.51 – 25.25
2776
1.767
10 4015
12642
linear abs coeff (mm-1
no. of reflns measured
no. of unique reflns
)
no. of params refined
764
(PCp*)Y(CCSiMe3)2(THF)(6)and[PCp*Y(CCSiMe3)(THF)]2-
(µ2-CCSiMe3)2] (7). Trimethylsilylacetylene (20 mg, 0.2 mmol)
was added to 1 (32 mg, 0.05 mmol) in a mixture of 0.5 mL of
THF and 3 mL of toluene while stirring. The solution was allowed
to stir overnight. Removal of solvent under reduced pressure gave
30 mg of 7 (characterized by NMR only) as a pale yellow residue.
This solid was dissolved in hexanes and cooled at -40 °C to give
7 as nearly colorless plates. X-ray analysis showed that 7 is the
acetylide-bridged dimer of 6 as a monotoluene solvate. Yield: 91%.
Mp: 102 °C (dec). In solution, 7 reverts to the monomer 6 as
evidenced by the doublet due to 89Y coupling for the acetylide
R-carbon. H NMR (C6D6, 500 MHz): δ 8.78 (d, JHH ) 8.0 Hz,
2H, 1-arylH), 8.39 (d, 3JHH ) 7.8 Hz, 2H, 4-arylH), 7.50 (m, 2H,
2-arylH), 7.32 (m, 2H, 3-arylH), 3.26 (t, 4H, R-THF CH2), 2.98
(s, 6H, CpMe), 2.36 (s, 3H, CpMe), 0.60 (brs, 4H, ꢀ-THF CH2),
0.28 (s, 18H, SiMe3). 13C NMR (125.7 MHz, C6D6): δ 171.23 (d,
1JYC ) 53.6 Hz, R-YC), 132.37, 129.84, 129.47, 127.34, 126.35,
124.68, 123.85, 120.27, 117.23 (arylC), 71.95, 25.45 (THF), 16.53
(CpMe2), 13.80 (CpMe), 1.09 (SiMe3), ꢀ-carbon of the acetylide
was not observed. Anal. Calcd for 7 · toluene (matching the X-ray)
C75H94O2Si4Y2: C 68.37, H 7.20. Found: C 68.75, H 6.92.
no. of params restrained
0
15
R1b, wR2c
0.0305, 0.0750
0.0350, 0.0770
1.049
0.0425, 0.0849
0.0662, 0.0926
1.030
R1b, wR2c all data
GOF on F2
a T ) 86(2) K (1), 89(2) K (7) using Mo KR (λ ) 0.71073 Å). b R )
∑(|Fo| - |Fc|)/∑|Fo|. c Rw ) [∑w(|Fo| - |Fc|2)/∑w(|Fo|)2]1/2
.
X-ray Crystallographic Studies. Crystals of compound 1 or 7
(the latter as a monotoluene solvate) were removed from the flask
and covered with a layer of hydrocarbon oil. A suitable crystal
was selected, attached to a glass fiber, and placed in the low-
temperature nitrogen stream.10 Data for 1 and 7 were collected at
86(2) and 89(2) K, respectively, using a Bruker/Siemens SMART
APEX instrument (Mo KR radiation, λ ) 0.71073 Å) equipped
with a Cryocool NeverIce low-temperature device. Data were
measured using omega scans of 0.3° per frame for 5 s, and a full
sphere of data was collected. For 1, a total of 2450 frames were
collected with a final resolution of 0.77 Å; in the case of 7, 2400
frames with a final resolution of 0.83 Å were collected. The first
50 frames were re-collected at the end of data collection to monitor
for decay. Cell parameters were retrieved using SMART11 software
and refined using SAINTPlus12 on all observed reflections. Data
reduction and correction for Lp and decay were performed using
the SAINTPlus software. Absorption corrections were applied using
SADABS.13 Both structures were solved by direct methods and
refined by the least-squares method on F2 using the SHELXTL
program package.14 The structure of 1 was solved in the space group
1
3
Ethylene Polymerization by 1 Treated with Trityl Tetra-
kis(perfluorophenyl)borane. [Ph3C]+[B(C6F5)4]- (15 mg, 0.016
mmol) in 1 mL of toluene was added to complex 1 (10 mg, 0.016
mmol) in 3 mL of toluene solution with rapid stirring. The color
of the solution changed from pale yellow to red immediately and
then slowly faded back to pale yellow after 2 h. The solution was
exposed to vacuum for 20 s to remove the nitrogen gas from the
flask, and ethylene gas, dried over 4 Å sieves, was introduced into
the flask at 1 bar of pressure. After 30 min, the reaction mixture
changed to a bright yellow color with formation of significant
amounts of precipitate. Addition of methanol terminated the
polymerization, and the color of solution and precipitate changed
to white immediately. Removal of solvent, followed by washing
with a methanolic HCl solution afforded 170 mg of polyethylene.
The catalytic activity for polymerization of ethylene was estimated
to be ca. 20 kg mol-1 h-1 bar-1 based on the molar amount of 1
used.
In separate NMR tube experiments, the 1H and 19F NMR of the
species formed by addition of 1 equiv of [Ph3C]+[B(C6F5)4]- to 1
in d8-toluene and d5-bromobenzene were examined at the red and
yellow stages. In both solvents and at both stages, the spectra were
extremely complicated and contained a very large number of
resonances (1H), many of which were broad (1H and 19F). The 1H
NMR spectra in the two solvents also differed significantly from
one another. No assignments could be made for the species present
in either solvent.
j
P1 (# 2) and that of 7 in the space group P21/c (#14) by analysis
of systematic absences. All atoms of 1 were refined anisotropically.
In the case of 7, one SiMe3 group (C57, C58, C59) was disordered
and modeled in two positions with occupancies of 40:60%. The
disordered carbons were refined isotropically, while all other non-
hydrogen atoms were refined anisotropically. Details of the data
collection and refinement are given in Table 1. Further details are
provided in the Supporting Information.
Results and Discussion
Synthesis and Characterization. The acid–base reaction
between 1 equiv of PCp*H and Y(CH2SiMe3)3(THF)2 in
(10) Hope, H. Prog. Inorg. Chem. 1995, 41, 1.
(11) SMART: v.5.626, Bruker Molecular Analysis Research Tool: Bruker
AXS: Madison, WI, 2002.
(12) SAINTPlus: v.6.36a, Data Reduction and Correction Program;
Bruker AXS: Madison, WI, 2001.
(13) SADABS: v.2.01, An Empirical Absorption Correction Program;
Bruker AXS: Madison, WI, 2001.
(14) Sheldrick, G. M. SHEXTL: v.6.10, Structure Determination Software
Suite;Bruker AXS: Madison, WI, 2001.

686 Organometallics, Vol. 27, No. 4, 2008
Sun et al.
1
Figure 1. Variable-temperature H NMR spectra (500 MHz, d8-
toluene (T)) spectra for the upfield region of 1.
toluene at room temperature cleanly affords (PCp*)-
Y(CH2SiMe3)2(THF) (1) as pale yellow prisms in 20% yield
after recrystallization (eq 1). The low yield is mainly due to
the extremely high solubility of 1 in hexane. Attempts to
prepare a bis PCp* complex using 2 equiv of PCp*H resulted
in formation of 1 and unreacted PCp*H according to 1H NMR
spectroscopy. This fact, and the observation that 1 is stable
toward redistribution in solution over a period of weeks,
suggests that the bis PCp* complex is too crowded to form
by this route.
Figure 2. Chemical shift versus temperature plot for the THF
resonances of 1.
THF at room temperature.15 Taking this value as 100%
complex 1 and 3.57 ppm as 100% free THF, a van’t Hoff
plot for the equilibrium between 1 and 1′ shown in eq 2 can
be constructed (Figure 3) that yields ∆H° and ∆S° values of
10.5 ( 0.5 kJ mol-1 and 36 ( 5 J mol-1 K-1, respectively.
These values are somewhat smaller than those observed by
Okuda et al. for [{(C5Me4)SiMe2NtBu}Y(CH2SiMe3)-
(THF)] (∆H° ) 24 ( 3 kJ mol-1; ∆S° ) 61 ( 12 J mol-1
K-1),15b but they are consistent with THF dissociation.
In contrast to THF exchange, the process that renders the
alkyl CH2 resonances equivalent becomes slow on the NMR
time scale at ca. 200 K (Figure 1), so that inequivalent CHaHb
protons displaying geminal coupling (as well as coupling to 89Y)
are observed. The two alkyls remain equivalent to each other,
indicating that the low-temperature symmetry has been reduced
to Cs from C2V. An Eyring plot (Figure 4) using rate constants
derived from dynamic NMR simulations yields kinetic param-
eters of ∆H‡ and ∆S‡ of 43 ( 2 kJ mol-1 and 9 ( 5 J mol-1
K-1, respectively.
Two explanations for the dynamic behavior of the CH2 groups
are possible depending on whether the THF-free complex 1′
has pyramidal or trigonal-planar geometry at the yttrium center
(taking the Cp centroid to be one coordination site) in the ground
state. If the ground state is pyramidal, then only inversion at Y
would be required to make the protons of the CH2 groups
equivalent (Figure 5) assuming rapid rotation about the Y-PCp*
bond. A planar ground state seems more likely for a d0 metal
center on the basis of steric considerations; however, previous
ab initio and DFT calculations are divided on the preferred
ground state.16 Theoretical studies on Cp2ScMe favored a planar
[
]
PCp * H + Y CH SiMe3 3 THF 2 f
[
(
]
2
)
(
) ( )
PCp * Y CH SiMe3 2 THF 1 + SiMe4 (1)
(
)
2
The 1H NMR spectrum of 1 at 300 K in d8-toluene shows a
single doublet (2JYH ) 3.2 Hz) at -0.60 ppm for the alkyl CH2
resonance, consistent with average C2V symmetry (Figure 1).
The observation of high symmetry implies that rapid dissociation
and reassociation of coordinated THF and rapid rotation about
the PCp* centroid-yttrium bond is occurring at room temper-
ature. The THF R- and ꢀ-protons appear as multiplets at 2.52
and 0.60 ppm, respectively. An upfield shift for the THF protons
is expected on coordination, but the magnitude observed for 1
is probably due in part to the shielding effect of the phenanthrene
π-system of the PCp* ligand.
1
The upfield region of the variable-temperature H NMR
spectra for 1 recorded between 300 and 190 K are shown in
Figure 1. Two notable features are observed on cooling: (i)
the THF resonances shift continuously upfield with decreasing
temperature and (ii) the alkyl CH2 resonance decoalesces
from a doublet to a pair of doublets of doublets (2JHH ) 9.3
2
Hz, JYH ) 3 Hz). The upfield shift of the THF resonances
(15) The procedure used here is analogous to that in ref 15b, but unlike
that case, stopped exchange between THF and 1′ was not observed even at
low temperature, thus requiring estimation of the “100% coordinated” THF
chemical shifts in order to estimate the mole fraction of 1, 1′, and THF
present. This introduces additional uncertainty into estimation of ∆H° and
especially ∆S°, not included in the mathematical uncertainties quoted. The
ln K vs 1/T plot showed some curvature at high temperatures (above 240
K), but the linear fit at low temperatures shown in Figure 3 is quite good,
so we believe the assumptions made in estimating the “100% coordinated”
THF chemical shifts are reasonable. The chemical shift of THF could also
be influenced by differential anisotropic shielding for different rotamers in
a slow Y-PCp* condition (similar to Figure 6); however, THF exchange
must occur in order to achieve average C2V symmetry at high temperature.
The authors wish to thank one reviewer for helpful comments in interpreta-
tion of the dynamic behavior. (a) Sun, J. Ph.D. Thesis, University of Victoria,
Victoria, B. C., Canada, 2007. (b) Hultzsch, K. C.; Spaniol, T. P.; Okuda,
J. Angew. Chem., Int. Ed. Engl. 1999, 38, 227.
plotted in Figure 2 is consistent with a rapid equilibrium
between 1 and its THF-free analogue 1′ (eq 2). The R-protons
of free THF in d8-toluene appear at 3.57 ppm, so it is clear
that even at room temperature, 1 is present in significant
concentration in solution. However, the fact that no reso-
nances for free THF are observed at low temperature indicates
that the THF exchange process remains rapid even at 190
K. A very rough estimate of the thermodynamic parameters
for eq 2 can be obtained if we assume that the limiting (100%
in the form of 1) chemical shift for the R-THF protons is ca.
1.5 ppm. This value is a crude estimate based on the shifts
observed for related bis PCp complexes that do not exchange

Yttrium Complexes of a Phenanthrene-Fused Cyclopentadienyl
Organometallics, Vol. 27, No. 4, 2008 687
Figure 6. Two possible Cs symmetry rotamers for the ground state
of 1′.
Figure 3. van’t Hoff plot for the equilibrium between 1 and 1′ in
d8-toluene.
Figure 7. OTERP320 plot (40% probability ellipsoids) of 1.
similar to that observed in Cp*La[CH(SiMe3)2]2,17 cannot be
entirely ruled out in the base-free species 1′; however, the
13C-1H coupling constant for the Y-CH2 groups in 1 is 102
Hz and does not vary significantly with temperature, suggesting
that agostic interactions are unlikely to be present in solution
(or the solid state, see below). Interestingly, Casey18 reported a
very similar barrier to alkene dissociation and inversion (∆G‡
) 40 ( 1 kJ mol-1 at coalescence, T ) 201 K) in the tethered
alkene complex (C5Me5)2Y(η1:η2-CH2CH2CH(Me)CHdCH2),
lending credibility to slow inversion as the dynamic process at
play here.
If a trigonal planar ground state is assumed, then all CH2
protons remain equivalent if rapid rotation about the PCp*-
yttrium centroid occurs. However, if rotation becomes slow on
the NMR time scale, one of two Cs symmetry rotamers could
become the ground state (Figure 6). In order to explain the
observed inequivalence of protons on the same alkyl carbon
but the equivalence of the two alkyl groups, rotamer B shown
in Figure 6 must be the most stable geometry. This seems
reasonable in that it places neither alkyl group directly under
the phenanthrene or, perhaps more importantly, Cp* rings.
The solid-state structure of 1 determined by X-ray crystal-
lography is shown in Figure 7; crystallographic data are
summarized in Table 1, and selected bond distances and angles
Figure 4. Eyring plot for the Ha/Hb exchange process of 1′ in d8-
toluene.
Figure 5. H(a)-H(b) exchange by pyramidal inversion at yttrium
for 1′.
(16) (a) Kawamura-Kuribayashi, H.; Koga, N.; Morokuma, K. J. Am.
Chem. Soc. 1992, 114, 8687. (b) Ziegler, T.; Folga, E.; Berces, A. J. Am.
Chem. Soc. 1993, 115, 638. (c) Woo, T. K.; Fan, L.; Ziegler, T.
Organometallics 1994, 13, 2252. (d) Weiss, H.; Ehrig, M.; Ahlrichs, R.
J. Am. Chem. Soc. 1994, 116, 4919. (e) Yoshida, T.; Koga, N.; Morokuma,
K. Organometallics 1995, 14, 746. (f) Perrin, L.; Maron, L.; Eisenstein, O.
Faraday Discuss. 2003, 124, 25.
ground state,16a but alkyls with ꢀ-hydrogens (Et, n-Pr) favored
a pyramidal geometry to accommodate a ꢀ-CH agostic
interaction.16b,d More recent work suggests that a pyramidal
geometry is preferred in d0 MX3 systems when X is an alkyl
due to some d orbital participation in the bonding.16e An agostic
interaction between the R-CH2 protons and the yttrium center,
(17) den Haan, K. H.; de Boer, J. L.; Teuben, J. H. Organometallics
1986, 5, 1726.
(18) Casey, C. P.; Fagan, M. A.; Hallenback, S. L. Organometallics
1998, 17, 287.

688 Organometallics, Vol. 27, No. 4, 2008
Sun et al.
Table 2. Selected Bond Distances (Å) and Angles (deg) for 1a
Scheme 1
Bond Distances
Y(1)-C(1)
Y(1)-C(3)
Y(1)-C(5)
Y(1)-C(22)
Y(1)-O(1)
2.675(2)
2.679(2)
2.630(2)
2.390(2)
2.3239(12)
Y(1)-C(2)
Y(1)-C(4)
Y(1)-Cp1
Y(1)-C(26)
2.695(2)
2.631(2)
2.370
2.383(2)
Bond Angles
Cp1-Y(1)-C(26)
C(22)-Y(1)-C(26) 107.75(6)
Cp1-Y(1)-C(22)
Cp1-Y(1)-O(1)
C(22)-Y(1)-O(1)
116.0
115.1
138.6
93.30(5)
C(26)-Y(1)-O(1)
Y(1)-C(26)-Si(2)
112.10(5)
125.92(9)
Y(1)-C(22)-Si(1) 123.76(9)
a Estimated standard deviation in parentheses; Cp1 is the centroid of
C(1)-C(5).
are given in Table 2. Complex 1 adopts a pseudotetrahedral,
three-legged piano stool geometry in the solid state. From the
bond lengths within the PCp* ligand itself, it is apparent that
to a certain extent this ligand can be viewed as three isolated
6π-electron systems: C1-C5 of the Cp unit (mean C-C bond
length ) 1.425 Å) and C6-C11 and C12-C17 of the benzenoid
rings (mean C-C ) 1.398 and 1.397 Å, respectively) with
longer distances between these rings (C4-C17, 1.452(2) Å;
C5-C6, 1.452(2) Å; C11-C12, 1.473(3) Å). The Y-C
distances to the Cp ring fall into two distinct groups with the
shorter set of contacts between Y and the phenanthrene ring
fusion carbons (Y1-C4, 2.631(2) and Y1-C5, 2.630(2) Å) and
the longer set to the three carbons bearing the methyl groups
(Y1-C1, 2.675(2); Y1-C2, 2.695(2); Y1-C3, 2.679(2) Å).
While these differences are small, they are significant and the
opposite of the pattern usually observed in yttrium indenyl
systems.19 The most obvious explanation for this fact is that
the methyl groups represent more steric bulk than does the
phenanthrene ring and the yttrium moves toward the less
crowded edge of the Cp ring. Overall, the Y-Cp C and Y-O
distances in 1 are quite similar to other six-coordinate Y
complexes (Y-Cring: range 2.618–2.698 Å, median 2.627 Å;
Y-O range: 2.299–2.372 Å, median 2.338 Å).21 The Y-alkyl
C distances are among the shortest reported in six-coordinate
Y-alkyls (Y-Calkyl: range 2.388–2.524 Å median 2.450 Å).21
The closest Y--H contacts of 2.819 Å are to H22A and H22B
on C22. The long Y-H distance and the normal Y1-C22-Si1
angle (123.76(9)°) rule out the presence of an R-agostic
interaction in this complex.
was completed, so the initial chemistry was carried out using
the harder to prepare 1.
Complex 1 undergoes clean 1,2-insertion of CO2, Me3SiNCO,
i
or PrNdCdNiPr into both yttrium-alkyl bonds to form the
bis carboxylate (3), amidate (4) and amidinate (5) complexes
(Scheme 1). In each case, the most notable evidence for insertion
is the disappearance of the upfield CH2 doublet of 1 and the
appearance of a downfield singlet at 1.10 (3), 1.65 (4), or 1.83
(5) ppm. Similarly, all three complexes show a characteristic
downfield 13C resonance due to the central C of the carboxylate
(δ 185.42), amidate (δ 188.54), or amidinate (177.40) ligands.22
Cis and trans isomers are possible for the amidate complex (4),
but a single CH2 resonance is observed for all four protons of
the CH2SiMe3 groups bonded to the central carbon. This is
significant because the CH2 resonances of either the cis or trans
isomers of 4 should be inequivalent by symmetry. A dynamic
process involving a κ2 f κ1 rearrangement of the amidate ligand,
most likely via N dissociation, followed by rotation about the
Y-O and C(O)-CH2 bonds would interconvert the cis and trans
isomers and render the CH2 protons equivalent (Figure 8). The
crystals of these complexes lose solvent very rapidly, and we
have been unable to obtain X-ray structural data, so we cannot
rule out the possibility that 3-5 contain bridging ligands in a
dimeric (or higher array). However, if this is the case, the
bridged structures must also be undergoing rapid fluxional
processes to explain the simple spectra obtained.
Complex 1 undergoes an acid–base (protonolysis) reaction
with trimethylsilylacetylene to afford a bis(acetylide) complex.
In solution, this product (6) shows clear NMR evidence for
terminal acetylide ligation, as shown by the simple doublet due
to 89Y-13C coupling for the R-acetylide carbon resonance (δ
171.2, 1JYC ) 55.5 Hz). Crystallization of 6 from a mixture of
Reactivity Studies. Complex 1 reacts with 2,2′-bipyridine
(bipy) in toluene to form the four-legged piano stool complex
PCp*Y(CH2SiMe3)2(bipy) (2) as a red solid (Scheme 1). Unlike,
THF-adduct 1, 2 does not undergo ligand exchange on the NMR
time scale with free bipy in solution. Direct reaction of
Y(CH2SiMe3)3(THF)2 with PCp*H in the presence of bipy
affords 2 in excellent yield. This greater ease of access makes
2 a more desirable starting material than 1, but this fact was
realized after most of the reaction chemistry described below
(22) (a) Djordjevic, C.; Gonshor, L. G.; Schiavelli, M. D.; Angevine-
Malley, L. S. J. Less Common Met. 1983, 94, 355. (b) Power, M. B.; Bott,
S. G.; Clark, D. L.; Atwood, J. L.; Baron, A. L. Organometallics 1990, 9,
3086. (c) Bambirra, S.; Brandsma, M. J. R.; Brussee, E. A. C.; Meetsma,
A.; Hessen, B.; Teuben, J. H. Organometallics 2000, 19, 3197. (d) Zhang,
J.; Ruan, R.; Shao, Z.; Cai, R.; Weng, L.; Zhou, X. Organometallics 2002,
21, 1420. (e) Zhou, X. G.; Zhang, L. B.; Zhu, M.; Cai, R. F.; Weng, L. H.
Organometallics 2001, 20, 5700. (f) Haan, K. H.; Luinstra, A.; Meetsma,
A.; Teuben, J. H. Organometallics 1987, 6, 1509. (g) Schumann, H.; Meese-
Marktscheffel, J. A.; Dietrich, A.; Görlitz, F. H. J. Organomet. Chem. 1992,
430, 299.
(19) (a) Gavenonis, J.; Tilley, T. D. J. Organomet. Chem. 2004, 689,
870. (b) Qi, M.; Shen, Q.; Chen, X.; Weng, L.-H. Yingyong Huaxue (Chin.
J. Appl. Chem.) 2003, 20, 629. (c) Kretschmer, W. P.; Troyanov, S. I.;
Meetsma, A.; Hessen, B.; Teuben, J. H. Organometallics 1998, 17, 284.
(20) Farrugia, L. J. ORTEP3 for Windows. J. Appl. Crystallogr. 1997,
30, 565.
(23) (a) Reversible coupling: Lee, L.; Berg, D. J.; Bushnell, G. W.
Organometallics 1995, 14, 5021. (b) Heeres, H. J.; Teuben, J. H.
Organometallics 1991, 10, 1980. (c) Heeres, H. J.; Nijhoff, J.; Teueben,
J. H. Rogers, R. D. Organometallics 1993, 12, 2609. (d) Cameron, T. C.;
Gordon, J. C.; Scott, B. L. Organometallics 2004, 23, 2995. Irreversible
coupling. (e) Evans, W. J.; Keyer, R. A.; Zhang, H.; Atwood, J. L. J. Chem.
Soc., Chem. Commun. 1987, 837. (f) Evans, W. J.; Keyer, R. A.; Ziller,
J. W. Organometallics 1990, 9, 2628. (g) Evans, W. J.; Keyer, R. A.; Ziller,
J. W. Organometallics 1993, 12, 2618. (h) Forsyth, C. M.; Nolan, S. P.;
Stern, C. L. Marks, T. J.; Rheingold, A. L. Organometallics 1993, 12, 3618.
(21) (a) Evans, W. J.; Boyle, T. J.; Ziller, J. W. Organometallics 1993,
12, 3998. (b) Arndt, S.; Trifonov, A.; Spaniol, T. P.; Okuda, J.; Kitamura,
M.; Takahashi, T. J. Organomet. Chem. 2002, 647, 158. (c) Gendron,
R. A. L.; Berg, D. J.; Barclay, T. Can. J. Chem. 2002, 80, 1285. (d) Roesky,
P. W. Organometallics 2002, 21, 4756. (e) Trifonov, A.; Spaniol, T. P.;
Okuda, J. J. Chem. Soc., Dalton Trans. 2004, 2245. (f) Trifonov, A.; Spaniol,
T. P.; Okuda, J. Organometallics 2001, 20, 4869. (g) Hultzch, K. C.; Voth,
P.; Becherle, K.; Spaniol, T. P.; Okuda, J. Organometallics 2000, 19, 228.

Yttrium Complexes of a Phenanthrene-Fused Cyclopentadienyl
Organometallics, Vol. 27, No. 4, 2008 689
Table 3. Selected Bond Distances (Å) and Angles (deg) for
7 · toluenea
Bond Distances
Y(1)-C(1)
Y(1)-C(3)
Y(1)-C(17)
Y(1)-C(21)
Y(1)-C(60)
Y(2)-C(35)
Y(2)-C(37)
Y(2)-C(51)
Y(2)-C(26)
Y(2)-C(60)
2.670(3) Y(1)-C(2)
2.693(3) Y(1)-C(4)
2.657(3) Y(1)-Cp1
2.412(3) Y(1)-C(26)
2.521(3) Y(1)-O(1)
2.698(3) Y(2)-C(36)
2.672(3) Y(2)-C(38)
2.634(3) Y(2)-Cp2
2.517(3) Y(2)-C(55)
2.499(3) Y(2)-O(2)
Bond Angles
2.713(3)
2.637(3)
2.388
2.507(3)
2.361(2)
2.718(3)
2.663(3)
2.384
2.397(3)
2.380(2)
Cp1-Y(1)-C(21)
Cp1-Y(1)-C(60)
C(21)-Y(1)-C(26)
C(21)-Y(1)-O(1)
C(26)-Y(1)-O(1)
Cp2-Y(2)-C(26)
Cp2-Y(2)-C(60)
106.9
108.9
Cp1-Y(1)-C(26)
111.0
111.5
Cp1-Y(1)-O(1)
93.12(10) C(21)-Y(1)-C(60) 143.83(10)
83.78(8)
136.37(8)
108.5
C(26)-Y(1)-C(60)
C(60)-Y(1)-O(1)
Cp2-Y(2)-C(55)
Cp2-Y(2)-O(2)
78.94(10)
78.57(8)
109.2
109.4
113.8
C(26)-Y(2)-C(55) 142.03(10) C(26)-Y(2)-C(60)
79.17(10)
92.76(10)
136.06(9)
C(26)-Y(2)-O(2)
C(55)-Y(2)-O(2)
79.83(8)
80.97(9)
C(55)-Y(2)-C(60)
C(60)-Y(2)-O(2)
Y(1)-C(21)-C(22) 171.9(3)
Y(1)-C(26)-C(27) 105.8(2)
Y(1)-C(60)-C(61) 154.9(2)
Y(1)-C(26)-Y(2) 100.85(10)
Y(1)-C(60)-Y(2)
100.98(11) Y(2)-C(26)-C(27) 151.2(2)
Y(2)-C(60)-C(61) 154.9(2)
Y(2)-C(55)-C(56) 171.6(3)
a Estimated standard deviation in parentheses; Cp1 and Cp2 are the
centroids of C(1)-C(2)-C(3)-C(4)-C(17) and C(35)-C(36)-C(37)-
C(38)-C(51), respectively.
Y center, as noted by the widely divergent Y-CR-Cꢀ angles
(Y1-C26-C27, 105.8(2)° and Y2-C26-C27, 151.2(2)°, ∆ꢁ
)(largeM-CR-Cꢀ)–(smallM-CR-Cꢀ))45.4°;Y2-C60-C61,
102.2(2)° and Y1-C60-C61, 154.9(2)°, ∆ꢁ ) 52.7°). Despite
this fact, the closest Y-Cꢀ distance is just over 3 Å, and there
is no statistically significant difference between the C-C triple
bond distance for the bridging (mean C-C 1.224 Å) and
terminal acetylides (mean C-C 1.218 Å). In addition, the
asymmetry of the bridging acetylide angles is not reflected in
the corresponding Y-CR distances (Y1-C26, 2.507(3); Y2-C26,
2.517(3); Y1-C60, 2.521(3); Y2-C60, 2.499(3) Å). A survey
of all lanthanide and group 3 bridging acetylides shows that
the asymmetry in bridge angles is in the range ∆ꢁ ) 2.3–65.8°
with no clear relationship between the degree of asymmetry
and the Y-CR distances.23a,24 In fact, one structure consisting
of two independent molecules displays widely divergent ∆ꢁ
angles of 2.3° and 61.0° for the same compound.24f From this
we conclude that solid-state packing forces probably play a
major role in bridge angle asymmetry (∆ꢁ), and any π-interac-
tions between the alkynyl group and the metal are weak.
As commonly observed,24e the bridging Y-CR distances are
much longer than the terminal distances (mean Y-CR bridge,
2.511; mean Y-CR terminal, 2.405 Å). As in 1, the bonding
between Y and the PCp* ring is slipped somewhat so that Y is
Figure 8. Rapid cis-trans isomerization of 4.
Figure 9. OTERP320 plot (40% probability ellipsoids) of 7 · toluene.
Toluene of solvation omitted for clarity.
toluene and hexane afforded colorless crystals that proved to
be the acetylide -bridged dimer 7 by X-ray crystallography.
These crystals produce the characteristic signals of 6 when
redissolved in d6-benzene, indicating that 6 and 7 readily
interconvert (eq 3). Interestingly, although we have previously
observed reversible formation of a coupled butatrienediyl unit
from bridging acetylides in Y(DAC)(CCPh) (DAC ) 4,13-
diaza-18-crown-6)23a and others have reported similar results
in Cp-based systems,23b,h 7 shows no tendency to couple. The
factors that govern the coupling of acetylides to butatrienediyls
have not been established, but it is clear that no one ligand set
promotes this reaction.
(24) (a) Atwood, J. L.; Hunter, W. E.; Wayda, A. L.; Evans, W. J. Inorg.
Chem. 1981, 20, 4115. (b) Evans, W. J.; Bloom, I.; Hunter, W. E.; Atwood,
J. L. Organometallics 1983, 2, 709. (c) Boncella, J. M.; Tilley, T. D.;
Andersen, R. A. J. Chem. Soc., Chem. Commun. 1984, 710. (d) Zhang, S.;
Zhuang, X.; Zhang, J.; Chen, W.; Liu, J. J. Organomet. Chem. 1999, 584,
135. (e) Tazelaar, C. G. J.; Bambirra, S.; van Leusen, D.; Meetsma, A.;
Hessen, B.; Teuben, J. H. Organometallics 2004, 23, 936. (f) Forsyth, C. M.;
Deacon, G. B.; Field, L. D.; Jones, C.; Junk, P. C.; Kay, D. L.; Masters,
A. F.; Richards, A. F. J. Chem. Soc., Chem. Commun. 2006, 1003. (g)
Federova, E. A.; Glushkova, N. M.; Bochkarev, M. N.; Shuman, G.;
Khemling, K. Russ. Chem. Bull. 1996, 2201. (h) Shen, Q.; Zheng, D.; Lin,
L.; Lin, Y. J. Organomet. Chem. 1990, 391, 307. (i) Ren, J.; Hu, J.; Lin,
Y.; Xing, Y.; Shen, Q. Polyhedron 1996, 15, 2165. (j) Nishiura, M.; Hou,
Z.; Wakatsuki, Y.; Yamaki, T.; Miyamoto, T. J. Am. Chem. Soc. 2003,
125, 1184. (k) Duchateau, R.; van Wee, C. T.; Meetsma, A.; Teuben, J. H.
J. Am. Chem. Soc. 1993, 115, 4931.
(
)
(
)( )
2 PCp * Y CCSiMe3 2 THF 6 h
(
)
(
)
(
)
( )
PCp * Y CCSiMe THF µ - CCSiMe3 2 7 (3)
[
(
)
3
]2[
]
The crystal structure of dimer 7 is shown in Figure 9;
crystallographic data are summarized in Table 1, and selected
bond distances and angles are collected in Table 3. The acetylide
bridges in 7 are highly asymmetric, tilting strongly toward one

690 Organometallics, Vol. 27, No. 4, 2008
Sun et al.
closest to the phenanthrene ring fusion carbons and furthest from
the three PCp* carbons bearing the methyl groups. The amount
of this distortion is 0.05Å in both 1 and 7. Although 7 is formally
seven-coordinate, the Y-C distances to the PCp* ligand are
not significantly different from those in six-coordinate 1,
presumably reflecting the fact that the acetylides are small, rigid
rod-like ligands that take up less space than a typical ligand.
Reaction with Ethylene. Complex 1 does not react with
ethylene gas (5 atm) on its own; however, treatment with Ph3C+
[B(C6F5)4]- in toluene yields a species that polymerizes ethylene
at a modest rate (20 kg polyethylene mol [Y]-1 h-1 bar-1) at
room temperature. The pale yellow solution of 1 immediately
turns deep red on addition of Ph3C+ [B(C6F5)4]-, but this red
solution produces no polymer formation in the first 90 min. The
red color of the solution slowly fades to pale yellow over a
period of ca. 2 h, at which point, ethylene polymerization
initiates at the above rate. The 1H and 19F NMR spectra of the
mixtures in d8-THF or d5-bromobenzene at the red and pale
yellow stages are extremely complicated, so we cannot state
with any certainty what the active catalytic species is. It would
be logical to assume that an alkyl cation such as
[(PCp*)Y(CH2SiMe3)]+[B(C6F5)4]– forms, but this was not
established from the spectroscopy at hand.25
We have established that PCp* is a viable ligand in yttrium
chemistry and provides access to robust mono(ligand)
complexes that undergo donor substitution and insertion
chemistry without PCp* loss or ligand redistribution. At this
point, high solubility limits the yield of high-purity 1, making
more extensive investigation of its chemistry difficult. Less
soluble analogues such as 2 should make access to large
quantities more practical.
Acknowledgment. D.J.B. (Discovery Grant) gratefully
acknowledges the support of the Natural Sciences and
Engineering Research Council of Canada.
(25) (a) Related mono(ligand) lanthanide alkyl cations have been
preparedthatshowsignificantlygreaterethylenepolymerizationactivity:Bambirra,
S.; Otten, E.; van Leusen, D.; Meetsma, A.; Hessen, B. Z. Anorg. Allg.
Chem. 2006, 632, 1950. (b) Bambirra, S.; Bouwkamp, M. W.; Meetsma,
A.; Hessen, B. J. Am. Chem. Soc. 2004, 126, 9182. (c) Bambirra, S.; van
Leusen, D.; Meetsma, A.; Hessen, B.; Teuben, J. H. J. Chem. Soc., Chem.
Commun. 2003, 522. (d) Bambirra, S.; van Leusen, D.; Meetsma, A.; Hessen,
B. Z.; Teuben, J. H. J. Chem. Soc., Chem. Commun. 2001, 637. (e) Hayes,
P. G.; Piers, W. E.; McDonald, R. J. Am. Chem. Soc. 2002, 124, 2132. (f)
Arndt, S.; Spaniol, T. P.; Okuda, J. Organometallics 2003, 22, 775. (g)
Nakajima, Y.; Okuda, J. Organometallics 2007, 26, 1270, and references
therein.
Supporting Information Available: Tables of atomic coordi-
nates, bond distances, and angles, and anisotropic thermal param-
eters for 1 and 7 are available free of charge via the Internet at
http://pubs.acs.org.
OM7007343