Synthesis and reactivity of mono(pentamethylcyclopentadienyl) tetraphenylborate lanthanide complexes of ytterbium and samarium: Tris(ring) precursors to (C5Me5)Ln moieties

Article abstract of DOI:10.1021/om060963s

The synthesis of unsolvated (C₅Me₅)Ln(BPh ₄) complexes (Ln = Sm, Yb) has been investigated to determine if the productive chemistry of the metallocene tetraphenylborate complexes, (C ₅Me₅)₂Ln(μ-Ph)₂BPh₂, can be expanded to mono(pentamethylcyclopentadienyl) systems. Precursors (C ₅Me₅)₂Yb, 1, and (C₅Me ₅)₂Sm, 2, were both prepared by desolvation of (C ₅Me₅)₂Ln(THF)₂ under high vacuum in near quantitative yields. Compounds 1 and 2 react with [Et₃NH] [BPh₄] to form divalent (C₅Me₅)Ln(μ- η⁶:η¹Ph)₂BPh₂ (3, Yb; 4, Sm) complexes in which two of the phenyl rings of the tetraphenylborate counteranion coordinate η⁶ to the lanthanide to generate a three-ring coordination geometry involving cyclopentadienyl and arene coordination. In contrast to the expected trigonal plane defined by the three-ring centroids in 3, the structure of 4 is pyramidal with Sm 0.41 A out of the plane of the three-ring centroids. Complex 3 reacts with THF to make the polysolvated complex, [(C₅Me₅)Yb(THF) ₄][BPh₄], 5, which can also be obtained from (C ₅Me₅)₂Yb(THF)₂ and [Et ₃NH][BPh₄]. With 4, a monosolvated complex, (C ₅Me₅)Sm[(μ-η⁶:η¹-Ph) (μ-η²:η¹-Ph)BPh₂](THF), 6, can be isolated that retains rf coordination by one aryl ring and displays η² coordination with the other aryl ring. Reaction of phenazine with 3 and 4 is accompanied by ligand redistribution to form the trivalent bis(pentamethylcyclopentadienyl) products, [(C₅Me₅) ₂Ln]2-[μ-η³:η³-C₁₂H ₈N₂], (Yb, 7; Sm, 8). Reduction of azobenzene by 4 generates a mono(pentamethylcyclopentadienyl)tetraphenylborate complex, (C ₅Me₅)Sm[(μ-η⁶:η¹-Ph) BPh₃](N₂Ph₂), 9, that contains an η⁶ coordinated phenyl ring and an azobenzene radical anion.

Full text of DOI:10.1021/om060963s

1204
Organometallics 2007, 26, 1204-1211
Synthesis and Reactivity of Mono(pentamethylcyclopentadienyl)
Tetraphenylborate Lanthanide Complexes of Ytterbium and
Samarium: Tris(ring) Precursors to (C5Me5)Ln Moieties
William J. Evans,* Timothy M. Champagne, and Joseph W. Ziller
Department of Chemistry, UniVersity of California, IrVine, California 92697-2025
ReceiVed October 20, 2006
The synthesis of unsolvated (C5Me5)Ln(BPh4) complexes (Ln ) Sm, Yb) has been investigated to
determine if the productive chemistry of the metallocene tetraphenylborate complexes, (C5Me5)2Ln(µ-
Ph)2BPh2, can be expanded to mono(pentamethylcyclopentadienyl) systems. Precursors (C5Me5)2Yb, 1,
and (C5Me5)2Sm, 2, were both prepared by desolvation of (C5Me5)2Ln(THF)2 under high vacuum in near
quantitative yields. Compounds 1 and 2 react with [Et3NH][BPh4] to form divalent (C5Me5)Ln(µ-η6:η1-
Ph)2BPh2 (3, Yb; 4, Sm) complexes in which two of the phenyl rings of the tetraphenylborate counteranion
coordinate η6 to the lanthanide to generate a three-ring coordination geometry involving cyclopentadienyl
and arene coordination. In contrast to the expected trigonal plane defined by the three-ring centroids in
3, the structure of 4 is pyramidal with Sm 0.41 Å out of the plane of the three-ring centroids. Complex
3 reacts with THF to make the polysolvated complex, [(C5Me5)Yb(THF)4][BPh4], 5, which can also be
obtained from (C5Me5)2Yb(THF)2 and [Et3NH][BPh4]. With 4, a monosolvated complex, (C5Me5)Sm-
[(µ-η6:η1-Ph)(µ-η2:η1-Ph)BPh2](THF), 6, can be isolated that retains η6 coordination by one aryl ring
and displays η2 coordination with the other aryl ring. Reaction of phenazine with 3 and 4 is accompanied
by ligand redistribution to form the trivalent bis(pentamethylcyclopentadienyl) products, [(C5Me5)2Ln]2-
[µ-η3:η3-C12H8N2], (Yb, 7; Sm, 8). Reduction of azobenzene by 4 generates a mono(pentamethylcyclo-
pentadienyl)tetraphenylborate complex, (C5Me5)Sm[(µ-η6:η1-Ph)BPh3](N2Ph2), 9, that contains an η6
coordinated phenyl ring and an azobenzene radical anion.
The phenyl groups in (BPh4)1- ions can adopt η1 to η6
interactions with lanthanides. As demonstrated by Deacon et
al.,12,13 when two of the phenyl groups in the a (BPh4)1- ligand
coordinate as η6 ligands, they generate a new class of lanthanide
ansa-metallocenes, as exemplified by Ph2B(µ-η1:η6-Ph)2YbXL
where X ) N(SiMe3)2 and 3,5-di-tert-butylpyrazolyl and L )
THF.
In metallocene chemistry, the tetraphenylborate complexes,
(C5Me5)2Ln(µ-Ph)2BPh2 (Ln ) lanthanide), have provided a
convenient route to unsolvated, sterically unsaturated [(C5Me5)2-
LnR]x complexes highly reactive for C-H activation.24,25 With
the actinide analogue, (C5Me5)2U(µ-Ph)2BPh2,26 a complex that
Introduction
The tetraphenylborate anion, (BPh4)1-, has been a useful
counteranion in f element chemistry for many years. As a large
non-coordinating anion, it often balances the size of the f
element cation and provides fully characterizable crystalline
materials.1-11 However, the phenyl rings of the (BPh4)1- anion
can also interact with f elements and stabilize unsolvated cations
that would ordinarily not be isolable. In this capacity, (BPh4)1-
has been found to have a broad range of coordination modes.12-25
* Corresponding author. Tel.: (949) 824-5174. Fax: (949) 824-2210.
E-mail: wevans@uci.edu.
(1) Hazin, P. N.; Bruno, J. W.; Schulte, G. K. Organometallics 1990, 9,
416.
(2) Evans, W. J.; Ulibarri, T. A.; Chamberlain, L. R.; Ziller, J. W.;
Alvarez, D., Jr. Organometallics 1990, 9, 2124.
(3) Heeres, H. J.; Meetsma, A.; Teuben, J. H. J. Organomet. Chem. 1991,
414, 351.
(4) Evans, W. J.; Kociok-Ko¨hn, G.; Ziller, J. W. Angew. Chem., Intl.
Ed. Engl. 1992, 31, 1081.
(5) Schumann, H.; Winterfield, J.; Keitsch, M. R.; Herrmann, K.;
Demtschuk, J. Z. Anorg. Allg. Chem. 1996, 622, 1457.
(6) Zeimentz, P. M.; Arndt, S.; Elvidge, B. R.; Okuda, J. Chem. ReV.
2006, 106, 2404.
(7) Arndt, S.; Spaniol, T. P.; Okuda, J. Angew. Chem., Intl. Ed. 2003,
42, 5075.
(8) Evans, W. J.; Johnston, M. A.; Greci, M. A.; Gummersheimer, T.
S.; Ziller, J. W. Polyhedron 2003, 22, 119.
(9) Evans, W. J.; Perotti, J. W.; Brady, J. C.; Ziller, J. W. J. Am. Chem.
Soc. 2003, 125, 5204.
(10) Deacon, G. B.; Forsyth, C. M. Chem.sEur. J. 2004, 10, 1798.
(11) Yuan, F.; Shen, Q. Synth. React. Inorg. Met.-Org. Chem. 1999, 29,
23.
(14) Evans, W. J.; Seibel, C. A.; Ziller, J. W. J. Am. Chem. Soc. 1998,
120, 6745.
(15) Evans, W. J.; Johnston, M. A.; Ziller, J. W. Inorg. Chem. 2000, 39,
3421.
(16) Evans, W. J.; Kozimor, S. A.; Ziller, J. W. Chem. Commun. 2005,
37, 4681.
(17) Molander, G. A.; Rzasa, R. M. J. Org. Chem. 2000, 65, 1215.
(18) Long, D. L.; Blake, A. J.; Champness, N. R.; Wilson, C.; Schroeder,
M. J. Am. Chem. Soc. 2001, 123, 3401.
(19) Hillier, A. C.; Zhang, X. W.; Maunder, G. H.; Liu, S. Y.;
Eberspacher, T. A.; Mtez, M. V.; MacDonald, R.; Domingos, A.; Marques,
N.; Day, V. W.; Sella, A.; Takats, J. Inorg. Chem. 2001, 40, 5106.
(20) Cendrowski-Guillaume, S.; Nierlich, M.; Lance, M.; Ephritikhine,
M. Organometallics 1998, 17, 786.
(21) Schumann, H.; Winterfield, J.; Keitsch, M. R.; Herrmann, K.;
Demtschuk, J. Z. Anorg. Allg. Chem. 1996, 622, 1457.
(22) Schaverien, C. J. Organometallics 1992, 11, 3476.
(23) Evans, W. J.; Lee, D. S.; Johnston, M. A.; Ziller, J. W. Organo-
metallics 2005, 24, 6393.
(24) Evans, W. J.; Perotti, J. M.; Ziller, J. W. J. Am. Chem. Soc. 2005,
127, 1068.
(25) Evans, W. J.; Perotti, J. M.; Ziller, J. W. J. Am. Chem. Soc. 2005,
127, 3894.
(12) Deacon, G. B.; Forsyth, C. M. Chem. Commun. 2002, 21, 2252.
(13) Deacon, G. B.; Forsyth, C. M.; Junk, P. C. Eur. J. Inorg. Chem.
2005, 817.
10.1021/om060963s CCC: $37.00 © 2007 American Chemical Society
Publication on Web 01/31/2007

(C5Me5)Ln(BPh4) Complexes of Ytterbium and Samarium
Organometallics, Vol. 26, No. 5, 2007 1205
Table 1. X-ray Data Collection Parameters for
(C5Me5)Yb(µ-η6:η1-Ph)2BPh2, 3,
contains redox active trivalent uranium, unusual reactions
involving (BPh4)1- reductive chemistry,16 and the conversion
of azide to nitride27 to make polymetallic actinide complexes
of unprecedented size have been observed.
(C5Me5)Sm(µ-η6:η1-Ph)2BPh2, 4,
(C5Me5)Sm[(µ-η6:η1-Ph)(µ-η2:η1-Ph)BPh2](THF), 6, and
(C5Me5)Sm[(µ-η6:η1-Ph)BPh3](N2Ph2), 9
Mono(pentamethylcyclopentadienyl) analogs of the highly
reactive (C5Me5)2Ln(µ-Ph)2BPh2 complexes, namely, species
such as (C5Me5)Ln(BPh4), could also have an extensive
chemistry. Mono(pentamethylcyclopentadienyl) chemistry has
been much less developed than the chemistry of the bis(ring)
metallocenes,28 but recent results (e.g., with (C5Me4SiMe3)1-
complexes)29-31 show that this area has considerable potential.
The synthesis of (C5Me5)Ln(BPh4) seemed reasonable since
Deacon et al. had shown that the divalent Yb[N(SiMe3)2]2(THF)2
precursors would react cleanly with alkylammonium tetraphen-
ylborate salts to make complexes such as [(Me3Si)2N]Yb(THF)-
(BPh4),12 [(Me3Si)2N]Yb(BPh4),13 and (3,5-di-tert-butylpyrazolyl)-
Yb(THF)(BPh4).13 The high reactivity of Sm2+ makes this more
challenging,32-35 but the product would concomitantly have a
more extensive reaction chemistry. We report here the synthesis
and structure of samarium and ytterbium (C5Me5)Ln(BPh4)
complexes as well as some preliminary reactivity studies. In
addition, we report a more facile route to the unsolvated
ytterbium precursor, (C5Me5)2Yb.36,37
empirical formula
C34H35BYb•1.5C6H6
C34H35BSm•C6H6
Compound
Fw
temp (K)
cryst syst
space group
a (Å)
3
4
744.63
163(2)
monoclinic
P21/n
9.4236(11)
46.204(5)
15.8959(18)
90
91.749(2)
90
6917.9(14)
8
682.89
163(2)
monoclinic
P21/c
17.081(3)
9.9752(17)
18.816(3)
90
95.676(3)
90
3190.2(9)
4
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
vol (Å3)
Z
F
calcd (mg/m3)
1.430
2.732
0.0415
0.0841
1.422
1.867
0.0326
0.0891
µ (mm-1
)
R1a (I > 2.0σ(I))
wR2b (all data)
empirical formula
C38H43BOSm
C46H45BN2Sm•0.5C6H6
Compound
Fw
temp (K)
cryst syst
space group
a (Å)
6
9
676.88
163(2)
monoclinic
P21/c
13.4854(15)
16.1230(18)
14.6003(16)
90
101.970(2)
90
3105.4(6)
4
826.05
158(2)
Monoclinic
P21/n
10.7083(11)
12.1261(12)
29.779(3)
90
97.299(2)
90
3835.5(7)
4
Experimental Procedures
The chemistry described below was performed under argon with
rigorous exclusion of air and water using Schlenk, vacuum line,
and glovebox techniques. (C5Me5)2Sm,32 (C5Me5)2Yb(THF)2,38
AgBPh4,39 and [Et3NH][BPh4]8 were prepared as previously
reported. Phenazine (Aldrich) was sublimed before use. Azobenzene
(Aldrich) was recrystallized and degassed before use. C8H8 (Aldrich)
was distilled onto activated 4 Å molecular sieves and degassed.
Solvents were sparged with UHP argon (Airgas) and dried over
columns containing Q-5 and sieves. NMR solvents (Cambridge
Isotopes) were dried over benzophenone-ketyl, degassed, and
vacuum transferred before use. 1H and 13C NMR spectra were
recorded with Bruker 500 and 600 MHz spectrometers. Infrared
spectra were recorded as KBr pellets on a Perkin-Elmer 2000 FT-
IR or as thin films on an ASI ReactIR 1000 spectrometer.15
Elemental analyses were performed by Analytische Laboratorien
(Lindlar, Germany). Complexometric analyses were performed as
previously described.40 Details of the crystallographic studies are
given in Table 1 and in the Supporting Information.
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
vol (Å3)
Z
F
calcd (mg/m3)
1.448
1.920
0.0401
0.0841
1.431
1.568
0.0432
0.1052
µ (mm-1
)
R1c (I > 2.0σ(I))
wR2d (all data)
2
2
2
a R1 ) Σ||Fo| - |Fc||/Σ|Fo|. b wR2 ) [Σ[w(F0 - Fc )2/Σ[w(Fo )2]]1/2
.
2
2
2
c R1 ) Σ||Fo| - |Fc||/Σ|Fo|. d wR2 ) [Σ[w(F0 - Fc )2/Σ[w(Fo )2]]1/2
.
1 × 10-6 Torr (tungsten coil gauge calibration) using a Varian
VHS-4 diffusion pump. After the sample had been exposed to
vacuum for approximately 36 h and the pressure had dropped to 1
× 10-6 Torr, the solid had changed color from magenta to bright
orange. The tube was heated to 50 °C for at least 3 days or until
all the orange solid had changed to a brown solid. Note: conditions
should be avoided in which the solid sublimes. Sublimation yields
only the orange solid that has a 1H NMR spectrum identical to that
of (C5Me5)Yb(THF).41 Addition of 15 mL of toluene to the brown
solid left at the bottom of the tube followed by filtration left a red
solution. Removal of solvent left 1 as a green solid (366 mg, 96%).
1H and 13C NMR spectra were consistent with the previously
characterized unsolvated (C5Me5)2Yb.36,37
(C5Me5)2Sm, 2.32 In a similar fashion as described for 1, dark
purple (C5Me5)2Sm(THF)2 (276 mg, 0.488 mmol) was desolvated
without sublimation by heating to 45 °C for at least 3 days. Addition
of 15 mL of toluene to the green solid left at the bottom of the
tube followed by filtration left a green solution. Removal of solvent
left 2 as a green solid (193 mg, 94%). H and 13C NMR spectra
were consistent with the previously characterized unsolvated
(C5Me5)2Sm.32
(C5Me5)2Yb, 1.36,37 In a glovebox, a 20 mm × 320 mm tube
attached to a high vacuum greaseless stopcock was charged with
magenta (C5Me5)2Yb(THF)2 (505 mg, 0.860 mmol). The apparatus
was attached to a high vacuum line that can achieve pressures of
(26) Evans, W. J.; Nyce, G. W.; Forrestal, K. J.; Ziller, J. W.
Organometallics 2002, 21, 1050.
(27) Evans, W. J.; Kozimor, S. A.; Ziller, J. W. Science 2005, 309, 1835.
(28) Arndt, S.; Okuda, J. Chem. ReV. 2002, 102, 1953.
(29) Tardif, O.; Nishiura, M.; Hou, Z. Organometallics 2003, 22, 1171.
(30) Luo, Y.; Baldamus, J.; Tardif, O.; Hou, Z. Organometallics 2005,
24, 4362.
(31) Shima, T.; Hou, Z. J. Am. Chem. Soc. 2006, 128, 8124.
(32) Evans, W. J.; Hughes, L. A.; Hanusa, T. P. Organometallics 1986,
5, 1285.
(33) Evans, W. J.; Grate, J. W.; Hughes, L. A.; Zhang, H.; Atwood, J.
L. J. Am. Chem. Soc. 1985, 107, 3728.
(34) Evans, W. J. Inorg. Chim. Acta 1987, 139, 169.
(35) Evans, W. J.; Ulibarri, T. A.; Ziller, J. W. J. Am. Chem. Soc. 1988,
110, 6877.
(36) Burns, C. J.; Andersen, R. A. J. Organomet. Chem. 1987, 31, 325.
(37) Schultz, M.; Burns, C. J.; Schwartz, D. J.; Andersen, R. A.
Organometallics 2000, 19, 781.
(38) Watson, P. L. J. Chem. Soc., Chem. Commun. 1980, 14, 652.
(39) Jordan, R. F.; Echols, S. F. Inorg. Chem. 1987, 26, 383.
(40) Evans, W. J.; Engerer, S. C.; Coleson, K. M. J. Am. Chem. Soc.
1981, 103, 6672.
1
(C5Me5)Yb(µ-η6:η1-Ph)2BPh2, 3. [Et3NH][BPh4] (100 mg, 0.234
mmol) was added slowly to a stirred solution of 1 (104 mg, 0.233
mol) in 20 mL of C6H6. The reaction mixture immediately changed
(41) Tilley, T. D.; Andersen, R. A.; Spencer, B.; Ruben, H.; Zalkin, A.;
Templeton, D. H. Inorg. Chem. 1980, 19, 2999.

1206 Organometallics, Vol. 26, No. 5, 2007
EVans et al.
color from red to dark green. After 15 min, removal of a small
amount of yellow insoluble material by centrifugation and filtration
left a clear green solution. Removal of volatiles and solvent under
vacuum yielded 3 as a green solid (125 mg, 86%). Anal. Calcd for
C34H35BYb: C, 65.07; H, 5.63; B, 1.72; Yb, 27.57. Found: C,
64.94; H, 5.48; B, 1.73; Yb, 27.90. 1H NMR (C6D6, 25 °C) δ 1.67
(s, 15H, C5Me5), 7.04 (m, 12H, BPh4), 7.66 (m, 8H, BPh4). 13C
NMR δ 12.02 (C5Me5), 116.36 (C5Me5), 125.16 (C6H5), 128.11
(C6H5), 128.69 (C6H5), 134.72 (C6H5). Single crystals of 3 suitable
for X-ray diffraction were grown by slow evaporation of C6D6 at
25 °C in an NMR tube. IR (thin film) 3092s, 3073m, 3038s, 1961w,
1814w, 1575w, 1529m, 1478s, 1428w, 1393w, 1351w, 1177m,
1154w, 1034s, 849m, 776m, 749m, 710s, 676s cm-1. The 1H NMR
spectrum of the yellow insoluble material in THF-d8 was consistent
with previously characterized [Yb(THF)6][BPh4]2.8
3 from (C5Me5)2Yb and AgBPh4. AgBPh4 (51 mg, 0.120 mmol)
was added slowly to a stirred solution of 1 (53 mg, 0.120 mol) in
15 mL of C6H6. The reaction mixture slowly changed color from
red to yellow-green. After 6 h, removal of black insoluble material
by centrifugation and filtration left a clear yellow-green solution.
Removal of volatiles and solvent under vacuum yielded a tacky
yellow-green solid. The solid was washed with 3 × 10 mL of
hexane and then dried under vacuum leaving 3 as a green solid
(125 mg, 86%). 1H NMR analysis confirmed the formation of
(C5Me5)2.42
resonances were observed in the 13C NMR spectra due to the limited
solubility of 6 in benzene or toluene. 1H NMR (THF-d8, 25 °C) δ
0.58 (br s, 15H, C5Me5), 6.74 (br, 4H, p-BPh4), 6.84 (br, 8H,
m-BPh4), 7.09 (br, 8H, o-BPh4). 13C NMR δ 95.10 (s, C5Me5),
121.77 (p-BPh4), 125.32 (m-BPh4), 136.62 (o-BPh4). 164.59,
164.70, 165.38, 165.78 (ipso-BPh4). IR (KBr) 3049s, 2859s, 1580w,
1480m, 1429m, 1261w, 1152w, 1029m, 868m, 737m, 708s, 495w
cm-1
.
[(C5Me5)2Yb]2[(µ-η3:η3-C12H8N2)], 7. Phenazine (3 mg, 0.018
mmol) was added slowly to a solution of 3 (18 mg, 0.029 mol) in
2 mL of C6D6. The reaction mixture immediately changed color
from green to deep red-brown. After 30 min, the reaction mixture
was filtered leaving a deep red solution and brown insoluble
material. Anal. Calcd for C52H68N2Yb2: Yb, 32.4. Found: Yb, 31.5.
Single crystals of 7 suitable for X-ray diffraction were grown from
this solution at 25 °C (6 mg, 32%). Only broad peaks were observed
1
in the H NMR spectrum. The brown insoluble material did not
dissolve in toluene, benzene, THF, or ether. IR (KBr) 2930s, 2861s,
1595m, 1490s, 1464s, 1331s, 1283s, 849w, 717w, 477s, 466m cm-1
.
[(C5Me5)2Sm]2[(µ-η3:η3-C12H8N2)], 8. Following the procedure
stated previously, phenazine (6 mg, 0.036 mmol) was added slowly
to a solution of 4 (21 mg, 0.035 mol) in 2 mL of C6D6. The reaction
mixture immediately changed color from green to deep red, and
insoluble material formed. After 30 min, the reaction mixture was
filtered leaving a deep red solution and brown insoluble material.
Solvent was removed under vacuum leaving a dark brown solid (7
mg, 23%). The insoluble material did not dissolve in toluene,
benzene, THF, or ether. Both the unit cell of single crystals of [(C5-
Me5)2Sm]2[(µ-η3:η3-(C12H8N2)] and the 1H NMR data matched the
previously characterized complex.43
(C5Me5)Sm(µ-η6:η1-Ph)2BPh2, 4. [Et3NH][BPh4] (89 mg, 0.208
mmol) was added slowly to a stirred solution of 2 (87 mg, 0.206
mol) in 20 mL of C6H6. The reaction mixture immediately changed
color from forest green to dark blue-green. After 15 min, removal
of a small amount of purple insoluble material by centrifugation
and filtration left a dark blue-green solution. Removal of volatiles
and solvent under vacuum yielded a dark blue-green solid (99
mg, 80%). Anal. Calcd for C34H35BSm: C, 67.51; H, 5.84; B, 1.79;
Sm, 24.86. Found: C, 65.67; H, 5.82; B, 1.73; Sm, 24.50. 1H NMR
(C6D6, 25 °C) δ -2.78 (s, 15H, C5Me5). 13C NMR δ 107.20
(C5Me5). The (BPh4)- resonances could not be located in this
paramagnetic system. Single crystals of 4 suitable for X-ray
diffraction were grown by slow evaporation of C6D6 at 25 °C in
an NMR tube. IR (thin film) 3092s, 3073m, 3038s, 1961w, 1814w,
1575w, 1529m, 1478s, 1428w, 1393w, 1177m, 1100w, 1034s,
(C5Me5)Sm(C8H8). C8H8 (2.0 µL, 0.018 mmol) was added via
syringe to a stirred solution of 4 (22 mg, 0.036) in 10 mL of C6H6.
After 2 h, the reaction mixture changed color from green to orange,
and insoluble material formed. The orange mixture was filtered
leaving an orange solution and dark insoluble material. Solvent was
removed from the orange solution leaving an orange-red solid.
NMR analyses of the solid confirmed the formation of (C5Me5)-
Sm(C8H8)44 and (C5Me5)2Sm(µ-Ph)2BPh214 in a 2:1 ratio (6.5 mg,
54% yield). The insoluble material was washed with hexane and
C6H6 to leave a gray solid (4.7 mg, 52%). Anal. Calcd for C34H35-
BSm: C, 79.59; H, 5.58; Sm, 13.84. Found: C, 79.36; H, 5.40;
Sm, 13.98. 3 and C8H8 did not react.
1
849m, 776m, 749m, 710s, 676s cm-1. The H NMR spectrum of
the purple insoluble material in THF-d8 was consistent with
previously characterized [Sm(THF)7][BPh4]2.8
[(C5Me5)2Sm][BPh4] from 4 and AgBPh4. AgBPh4 (12 mg,
0.028 mmol) was added slowly to a stirred solution of 4 (16 mg,
0.026 mol) in 10 mL of toluene. The reaction mixture eventually
changed color from green to red. After 24 h, removal of insoluble
material by centrifugation and filtration left a clear red solution.
Removal of solvent under vacuum yielded a rose red solid (7.5
mg, 39%). 1H NMR analysis was consistent with previously
[(C5Me5)Yb(THF)4][BPh4], 5. Addition of 1 mL of THF to solid
3 (7 mg, 0.01 mmol) immediately formed a yellow solution. Solvent
was removed leaving 5 as a yellow tacky solid in quantitative yield.
Anal. Calcd for C50H67O4BYb: C, 65.56; H, 7.39; Yb, 18.89.
Found: C, 65.30; H, 7.21; Yb, 19.08. 1H NMR (THF-d8, 25 °C) δ
1.93 (s, 15H, C5Me5), 7.25 (d, 8H, o-BPh4), 6.85 (t, 8H, m-BPh4),
6.71 (t, 4H, p-BPh4), 3.56 (s, THF), 1.71 (s, THF). 13C NMR δ
113.36 (C5Me5), 11.39 (C5Me5), 122.00 (p-BPh4), 125.87 (m-BPh4),
137.29 (o-BPh4), 164.75, 165.14, 165.53, 165.93 (ipso-BPh4), 68.39
(THF), 26.54 (THF). Single crystals of 5 suitable for X-ray
diffraction were grown at 25 °C in an NMR tube. IR (KBr) 3056s,
3025s, 2992s, 2974s, 1942w, 1578w, 1479m, 1427m, 1188w,
characterized [(C5Me5)2Sm][BPh4] as the only soluble product.14
and AgBPh4 did not react.
3
(C5Me5)[Ph3B(µ-η1:η6-Ph)]Sm(η2-N2Ph2), 9. Azobenzene (18
mg, 0.101 mmol) was added slowly to a stirred solution of 4 (61
mg, 0.101 mmol) in 5 mL of C6H6. The green solution immediately
changed color to form a deep blue color. After 1 h, solvent was
removed under vacuum leaving 9 as a glassy dark blue solid (71
mg, 90%). Anal. Calcd for C34H35BSm: C, 70.19; H, 5.77; N, 3.56;
B, 1.37; Sm, 19.10. Found: C, 69.89; H, 6.01; N, 3.77; B, 1.27;
Sm, 19.40. 1H NMR (C6D6, 23 °C) δ 3.53 (br s, 15H, C5Me5), 4.5
(br s, 3H, N2C6H5), 5.96 (br s, 7H, B(C6H5)4), 8.19 (br s, 8H,
B(C6H5)4). No resonances were observed in the 13C NMR spectra
of this highly paramagnetic system. Single crystals of 9 suitable
for X-ray diffraction were grown by slow evaporation of C6D6 at
1039m, 870s, 737m, 706w, 535w cm-1
.
(C5Me5)Sm[(µ-η6:η1-Ph)(µ-η2:η1-Ph)BPh2](THF), 6. Addition
of THF (0.008 mL, 0.10 mmol) to solid 4 (60 mg, 0.10 mmol) in
10 mL of C6H6 immediately formed a dark green solution. After
15 min, the solvent was removed under vacuum leaving a dark
green solid (65 mg, 97%). Single crystals of 6 suitable for X-ray
diffraction were grown from a C6H6 solution of this solid at -35 °C.
Anal. Calcd for C34H35BSm: C, 67.41; H, 6.42; B, 1.60; Sm, 22.21.
1
Found: C, 67.20; H, 6.31; B, 1.69; Sm, 22.21. H NMR (C6D6,
25 °C) δ -3.37 (br s, 15H, C5Me5). Resonances attributable to THF
or BPh4 were not observed in this paramagnetic system. No
(43) Evans, W. J.; Gonzales, S. L.; Ziller, J. W. J. Am. Chem. Soc. 1994,
116, 2600.
(44) Evans, W. J.; Gonzales, S. L.; Ziller, J. W. J. Am. Chem. Soc. 1991,
113, 7423.
(42) Jutzi, P.; Kohl, F. J. Organomet. Chem. 1979, 164, 141.

(C5Me5)Ln(BPh4) Complexes of Ytterbium and Samarium
Organometallics, Vol. 26, No. 5, 2007 1207
23 °C. IR (KBr) 3059s, 3046s, 3029s, 2969m, 2920s, 1597m,
1479m, 1427w, 1152w, 737m, 708m, 690m, 612w, 538w, 466w
cm-1
.
Results
Modified Syntheses of the (C5Me5)2Ln Precursors. One
direct route to the mono(ring) (C5Me5)Ln(BPh4) targets was the
reaction of the unsolvated metallocene precursors, (C5Me5)2Ln
(Ln ) Sm, Yb), with alkylammonium tetraphenylborate salts.
This method of making divalent tetraphenylborate complexes
by selective protolytic cleavage of amide ligands had previously
been shown to be successful by Deacon et al. with Yb-
[N(SiMe3)2]2(THF)2 complexes (eq 1).12,13
Figure 1. Thermal ellipsoid plot of (C5Me5)Yb(µ-η6:η1-Ph)2BPh2,
3, with the probability ellipsoids drawn at the 50% level. Hydrogen
atoms have been excluded for clarity. (C5Me5)Sm(µ-η6:η1-Ph)2BPh2,
4, is numbered similarly.
crowded (C5Me5)3Ln complexes.45 Since the product of eq 4 is
still Yb2+, this indicates that under these conditions, 1 is not
sufficiently reactive to reduce Ag1+. The reaction may proceed
by ionic metathesis to make 3 and AgC5Me5 in which case the
latter decomposes to the observed Ag and (C5Me5)2 as described
in the literature.46 The reaction analogous to eq 4 with more
strongly reducing (C5Me5)2Sm produces the trivalent complex,
(C5Me5)2Sm(µ-Ph)2BPh2 and Ag metal.14
Before a reaction of this type was examined, more facile
routes to the unsolvated precursors were sought. (C5Me5)2Yb,
1, can be isolated in 40% yield by heating (C5Me5)2Yb(OEt2)2
in toluene at reflux under dynamic vacuum for 4 h.36,37
(C5Me5)2Sm, 2, is typically obtained in 70% yield by desolvation
of the THF solvate, (C5Me5)2Sm(THF)2, under high vacuum
followed by sublimation.32 Previously, it had been reported that
(C5Me5)2Yb(THF) could not be desolvated by the toluene reflux
method or by sublimation. We have found that with a suf-
ficiently low pressure (10-6 Torr) and the proper temperature,
desolvation of both (C5Me5)2Yb(THF)2 and (C5Me5)2Sm(THF)2
can be effected via eq 2. A key component of this procedure is
that the desolvation must be done under conditions in which
formation of sublimate is avoided. For Yb, sublimation gives
(C5Me5)2Yb(THF). However, heating at 50 °C at low pressure
for several days produces (C5Me5)2Yb in >90% yield.
Structures of 3 and 4. Both 3 and 4 readily form crystals
suitable for X-ray crystallography, and the structure of 3 is
shown in Figure 1. Complexes 3 and 4 are not isomorphous,
but they are similar in many respects. In the solid state, each
metal in 3 and 4 is ligated by one η5-(C5Me5) ring and two
η6-(C6H5) rings of the tetraphenylborate counteranion. Overall,
this gives these tris(ring) complexes a formal coordination
number of nine. Ligation by two η6-(C6H5) rings from (BPh4)1-
ligands has been observed before in the lanthanide complexes,
[(Me3Si)2N]Yb(THF)(µ-η6:η1-Ph)2BPh2,12 [(Me3Si)2N]Yb(THF)-
(µ-η6:η1-Ph)(µ-η1:η1-Ph)BPh2,12 [(Me3Si)2N]Yb(µ-η6:η1-Ph)2-
BPh2,13 and (3,5-di-tert-butylpyrazole)Yb(THF)(µ-η6:η1-Ph)2-
BPh2.13
An important difference between complexes 3 and 4 is the
relative planarity of the three coordinating ring centroids.
Trigonal planar is normally the most stable structure for ML3
complexes. In complex 3, the three-ring centroids adopt a
trigonal planar arrangement around the metal that minimizes
steric crowding. The Yb center and the three-ring centroids in
3 are coplanar to within 0.026 Å. In 4, however, the samarium
atom is 0.41 Å out of the plane of the three-ring centroids (i.e.,
the rings take on a pyramidal arrangment around Sm). The Sm-
(C5Me5 ring centroid) vector makes a 56° angle with the plane
defined by Sm and the two C6H5 ring centroids. This striking
difference in structure between 3 and 4 is shown in Figure 2.
Pyramidal structures have previously been observed for the
formally three-coordinate Ln[N(SiMe3)2]3 complexes,47,48 but
this trigonal nonplanar arrangement has been attributed to
Synthesis of (C5Me5)Yb(µ-η6:η1-Ph)2BPh2, 3, and (C5Me5)-
Sm(µ-η6:η1-Ph)2BPh2, 4. The synthesis of 3 and 4 proceeded
via eq 3 with yields over 80%.
Evidently, [Et3NH][BPh4] reacts faster with the (C5Me5)1-
rings in (C5Me5)2Ln than with the remaining (C5Me5)1- rings
in 3 and 4 or with the Sm2+ center to form Sm3+ and H2.
Surprisingly, these yields are even higher than the 26-67%
yields observed with analogous [(Me3Si)2N]2Yb(THF)2 reac-
tions.12,13
Complex 3 can also be synthesized in high yield from
(C5Me5)2Yb and AgBPh4 (eq 4). Removal of (C5Me5)1- ligands
by this method has previously been reported with sterically
(45) 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.
(46) Zybill, C.; Mu¨ller, G. Organometallics 1987, 6, 2489.
(47) Andersen, R. A.; Templeton, D. H.; Zalkin, A. Inorg. Chem. 1978,
17, 2317.

1208 Organometallics, Vol. 26, No. 5, 2007
EVans et al.
Figure 4. Thermal ellipsoid plot of (C5Me5)Sm[(µ-η6:η1-Ph)(µ-
η1:η1-Ph)BPh2](THF), 6, with the probability ellipsoids drawn at
the 50% level. Hydrogen atoms have been excluded for clarity.
Figure 2. Side-on view of (C5Me5)Yb(µ-η6:η1-Ph)2BPh2, 3, and
(C5Me5)Sm(µ-η6:η1-Ph)2BPh2, 4. Hydrogen atoms have been
excluded for clarity.
0.13 Å difference in eight coordinate radii of Yb(II) and Sm(II)
given by Shannon.50
In both 3 and 4, the Ln-(C6H5 ring centroid) distances are
about 0.2 Å longer than the Ln-(C5Me5 ring centroid) distances.
This generates average Ln-C(C6H5) distances of about 0.3 Å
longer than the Ln-C(C5Me5) distances. Although the 2.884(5)-
3.128(5) Å range of Yb-C(C6H5) distances in 3 is quite wide,
it is still within the 2.833(3)-3.297(3) Å range in [(Me3Si)2N]-
Yb(THF)(µ-η6:η1-Ph)2BPh2.12 The 2.784(11)-2.956(12) Å range
in [(Me3Si)2N]Yb(µ-η6:η1-Ph)2BPh2 and the 2.799(2)-
13
3.050(2) Å range in (3,5-di-tert-butylpyrazole)Yb(THF)(µ-η6:
η1-Ph)2BPh213 have overlaps with the range in 3, but the larger
values for 3 are reasonable considering the size of (C5Me5)1-
versus an (η2-pyrazole)1- or [N(SiMe3)2]1- ligand. Complex 4
has a narrower range of distances than those in 3, 2.996(3)-
3.191(4) Å.
It should be noted that in both 3 and 4, nine to ten of the
twelve Ln-C(C6H5) distances are within a much narrower range
than two or three other values. Hence, 3 has 3.055(5) and
3.128(5) Å distances for C(19) and C(20) that are much longer
than all the others that are below 3.02 Å. Likewise, in 4, the
distances to C(20), C(21), and C(22), namely, 3.168(4), 3.141(3),
and 3.191(4) Å, are larger than all the rest that are 3.08 Å or
less. Hence, the η6 designator does not imply completely
symmetrical bonding. A similar situation is found in [(Me3Si)2N]-
Yb(THF)(µ-η6:η1-Ph)2BPh212 and (3,5-di-tert-butylpyrazole)Yb-
(THF)(µ-η6:η1-Ph)2BPh2.13
Reactivity of 3 and 4. Solvation. The unsolvated tris(ring)
complexes 3 and 4 readily add donor solvents such as THF to
form solvated analogues. With 3, the fully solvated [(C5Me5)-
Yb(THF)4][BPh4], 5, was isolated (eq 5 and Figure 3). Complex
5 is the first example of a mono(pentamethylcyclopentadienyl)
lanthanide cation containing only THF as other ligands.
Although the overall structure of 5 could be determined by X-ray
crystallography (Figure 3), the quality of the crystals precluded
detailed discussion of metrical parameters. This could be due
to loss of the THF during the crystal mounting.
Figure 3. Thermal ellipsoid plot of [(C5Me5)Yb(THF)4][BPh4],
5, with the probability ellipsoids drawn at the 50% level. Hydrogen
atoms have been excluded for clarity.
additional bonding via agostic interations with the silyl meth-
yls.48 In 4, there is no obvious additional ligation of this type.
The divalent lanthanide metallocenes, (C5Me5)2Ln, are well-
known to have coordination geometries that do not adopt the
most sterically favored arrangement. Hence, (C5Me5)2Yb,36,37
(C5Me5)2Eu,32 and (C5Me5)2Sm32 display bent rather than linear
arrangements of rings around the metal. The amount of bending
in these compounds as well as alkaline earth analogues has been
related to metal size.49 Complexes of the smallest metals, which
have the rings closest together, have the most linear structures.
The trigonal planar versus pyramidal structures of 3 and 4 here
also follow the trend that the smallest metal gives the sterically
most favored structure, but with only two examples, there is
no gradation of bending: the Sm example is pyramidal and the
Yb analogue is not.
As expected for a (ring)M(ring’)2 system, the (ring-centroid)-
Ln-(ring centroid) angles are not all equal. The 109.5 and
103.8° (C6H5 ring centroid)-Ln-(C6H5 ring centroid) angles
for 3 and 4, respectively, are reasonable since these rings are
attached to tetrahedral boron. The 123.8-125.8° (C5Me5 ring
centroid)-Ln-(C6H5 ring centroid) angles are small as com-
pared to the (C5Me5 ring centroid)-Ln-(C5Me5 ring centroid)
angles in the precursor metallocenes, 145-146° for (C5Me5)2-
Yb, and 140.1° for (C5Me5)2Sm, but the comparison with C6H5
and C5Me5 is not direct.
The 2.38 Å Yb-(C5Me5 ring centroid) distance in 3 matches
that in (C5Me5)2Yb exactly.37 Similarly, the 2.516 Å analogue
in 4 is close to the 2.524-2.529 Å distances in (C5Me5)2Sm.32
The 0.136 Å difference in the distances in 3 and 4 matches the
(48) Brady, E. D.; Clark, D. L.; Gordon, J. C.; Hay, P. J.; Keogh, D.
W.; Poli, R.; Scott, B. L.; Watkin, J. G. Inorg. Chem. 2003, 42, 6682.
(49) Hanusa, T. P. Chem. ReV. 1993, 93, 1023.
(50) Shannon, R. D. Acta. Crystallogr., Sect. A 1976, 32, 751.

(C5Me5)Ln(BPh4) Complexes of Ytterbium and Samarium
Organometallics, Vol. 26, No. 5, 2007 1209
Table 2. Bond Distances (Å) and Angles (deg) in
(C5Me5)Yb(µ-η6:η1-Ph)2BPh2, 3,
and NMR spectra comparison with the fully characterized
material previously prepared from (C5Me5)2Sm and phenazine.43
(C5Me5)Sm(µ-η6:η1-Ph)2BPh2, 4, and
(C5Me5)Sm[(µ-η6:η1-Ph)(µ-η2:η1-Ph)BPh2](THF), 6
bond distances/angles
3
4
6
Ln(1)-Cnt(C5Me5)
2.381
2.516
2.512
Ln(1)-Cnt(C6H5)
Ln(1)-C(C5Me5) av
Ln(1)-C(C6H5) av
Ln(1)-C(11)
Ln(1)-C(12)
Ln(1)-C(13)
Ln(1)-C(14)
Ln(1)-C(15)
Ln(1)-C(16)
Ln(1)-C(17)
Ln(1)-C(18)
Ln(1)-C(19)
Ln(1)-C(20)
Ln(1)-C(21)
Ln(1)-C(22)
Ln(1)‚‚‚B(1)
2.605/2.639 2.700/2.776 2.652
2.670(4)
2.970(4)
2.926(4)
2.932(4)
2.977(4)
3.015(5)
2.973(5)
2.911(4)
2.895(4)
2.930(5)
3.055(5)
3.128(5)
3.010(5)
2.884(5)
3.712
2.789(4)
3.075(3)
3.064(3)
3.035(3)
3.020(3)
3.029(3)
3.054(3)
3.046(3)
3.080(3)
2.996(3)
3.069(4)
3.168(4)
3.191(4)
3.143(3)
3.874
2.786(5)
2.999(6)
3.007(4)
3.008(4)
3.016(5)
3.001(5)
2.980(4)
2.979(4)
3.293
2.933(4)
3.222
3.807
4.097
3.849
Ligand redistribution of this type to form metallocene moieties
is a common reaction for mono(pentamethylcyclopentadienyl)
complexes.22 The stoichiometry requires formation of cyclopen-
tadienyl-free byproducts. Such complexes are generally more chal-
lenging to characterize due to their lower solubility and crystal-
linity. To date, the byproducts of eq 7 have proven intractable.
The reduction of 1,3,5,7-C8H8 (reduction potentials of -1.83
and -1.99 V vs SCE)52 by 4 does give a mono(pentamethyl-
cyclopentadienyl) product, the known trivalent (C5Me5)Sm-
(C8H8),44 but a ligand redistribution product, (C5Me5)2Sm(µ-
Ph)2BPh2 is also formed according to eq 8. Both products have
been previously made from (C5Me5)2Sm.14,44 In this reaction,
the stoichiometric byproduct would be Ln(BPh4)3. An insoluble
byproduct is obtained that has the appropriate mass for this
composition, but it has proven to be intractable so far.
3.883
124.0
N/A
N/A
Cnt(C5Me5)-Ln(1)-Cnt(C6H5) 124.7
Cnt(C5Me5)-Ln(1)-Cnt(C6H5) 125.8
Cnt(C6H5)-Ln(1)-Cnt(C6H5)
125.0
123.8
103.8
109.5
Crystallization of 4 in the presence of excess THF did not
give material suitable for X-ray diffraction, but the mono-THF
adduct, (C5Me5)Sm[(µ-η6:η1-Ph)(µ-η1:η1-Ph)BPh2](THF), 6,
was obtained by the addition of 1 equiv of THF to 4 (eq 6 and
Figure 4).
Complex 6 contains one hexahapto phenyl ring that displays
metrical parameters similar to those in the C(11)-C(16) ring in
4. As shown in Table 2, these have Sm-C distances in the nar-
row range of 2.979(4)-3.016(5) Å and a 2.652 Å Sm-(µ-η6-
C6H5 centroid) distance smaller than those in 4. The other phenyl
ring oriented toward samarium in 6 has one short Sm-C dis-
tance, the 2.933(4) Å Sm-C(18) length. The other Sm-C dis-
tances in this ring are all over 3.229 Å. This makes the Sm-
(C6H5-centroid) distance much longer: 3.274 Å. As such, this ring
is considered to have monohapto coordination to Sm. The 124°
(C5Me5 centroid)-Sm-(η6-C6H5 centroid) angle matches the 123
and 125° analogues found in 4. The 111.4° (C5Me5-centroid)-
Sm-(η1-C6H5-centroid) angle is not in the metallocene range
consistent with the phenyl coordination through a single carbon
instead of the ring. The 2.532(3) Å Sm-O(THF) distance can
be compared with the 2.62 (1) and 2.569(3) Å analogues in
(C5Me5)2Sm(THF)2 and (C5Me5)2Sm(THF),51 respectively.
Reduction of Phenazine and C8H8 with Ligand Substitu-
tion. Complexes 3 and 4 react with phenazine (reduction poten-
tial -0.364 V vs SCE)52 to form the bis(pentamethylcyclopen-
tadienyl) products, [(C5Me5)2Ln]2[(µ-η3:η3-C12H8N2)], (Ln ) Yb,
7; Sm, 8) (eq 7). The connectivity of atoms in 7 was established
by X-ray crystallography, but the low quality of the data pre-
cluded a detailed analysis of the structure. In the samarium case,
the product of eq 7 was identified by a unit cell determination
Reduction of Azobenzene Without Ligand Substitution.
In contrast to the previous reactions that all involve ligand
redistribution, 4 reduces azobenzene (-1.35 to -1.41 V vs
SCE)53 to make a mono(pentamethylcyclopentadienyl) azoben-
zene monoanion complex, (C5Me5)(BPh4)Sm(N2Ph2), 9 (eq 9
and Figure 5). In this case, as in 6 previously, the tetraphen-
ylborate counteranion is retained in the coordination sphere of
the metal. The closest analogue of 9 in the literature is the
azobenzene radical anion complex, (C5Me5)2Sm(N2Ph2)(THF),54
10, synthesized from (C5Me5)2Sm(THF)2 and 1 equiv of
azobenzene, eq 10. Both 9 and 10 are dark blue.
(51) Evans, W. J.; Kociok-Ko¨hn, G.; Foster, S. E.; Ziller, J. W.; Doedens,
R. J. J. Organomet. Chem. 1993, 444, 61.
(52) de Boer, E. AdV. Organomet. Chem. 1964, 2, 115.

1210 Organometallics, Vol. 26, No. 5, 2007
EVans et al.
The tetraphenylborate ligand binds to Sm in 9 as it does in
6. Hence, one ring is hexahapto with a rather narrow range of
Sm-C distances, 2.888(5)-2.984(4) Å. The other ring has one
short Sm-C connection, 2.875(4) Å to C(18), and the rest of
the Sm-C distances in this phenyl ring are greater than 3.3 Å.
The (PhNNPh)1- and (BPh4)1- ligands are oriented so that the
short Sm-N(2) bond is closest to the (η6-C6H5) ring.
Discussion
Synthesis. Synthetic access to the (C5Me5)Ln(µ-η6:η1-Ph)2-
BPh2 target complexes, 3 and 4, is readily achieved by the
selective single protonation of one of the (C5Me5)1- ligands in
the (C5Me5)2Yb and (C5Me5)2Sm precursors according to eq 3.
The kinetics of the protonation of the (C5Me5)1- ligands of 3
and 4 are evidently slower than those of 1 and 2. The synthesis
of unsolvated (C5Me5)Ln(BPh4) complexes is facilitated by the
fact that both (C5Me5)2Yb(THF) and (C5Me5)2Sm(THF) can be
desolvated simply under vacuum. Since the solvated metal-
locenes are made in two steps from the metal, the synthesis of
the divalent (C5Me5)Ln(BPh4) complexes actually takes fewer
steps than the synthesis of the trivalent tetraphenylborate
metallocene cations, (C5Me5)2Ln(µ-Ph)2BPh2, complexes that
have proven to be excellent precursors for a broad range of f
element studies.14,24,25,27,45
Reactivity. Preliminary studies of the reactivity of the
(C5Me5)Ln(BPh4) complexes suggest that they will be useful
precursors for lanthanide chemistry like their trivalent analogues.
The simple solvation reactions with THF that generate com-
plexes 5 and 6 demonstrate that incoming substrates can readily
interact with the metal centers by displacing the tetraphenyl-
borate ions. The reaction of 3 with PhNdNPh to make
(C5Me5)(BPh4)Sm(N2Ph2), 9, shows that 3 and 4 can provide
access to a new types of mono(pentamethylcyclopentadienyl)
complexes. Relatively few complexes of this type are accessible
as compared to (C5Me5)2Ln systems,55-57 and their recently devel-
oping chemistry has been shown to be quite interesting.29-31,49,58,59
The reactions with phenazine and C8H8 show that some of
the divalent reactivity of 3 and 4 will involve ligand redistribu-
tion and the formation of trivalent products containing
[(C5Me5)2Ln]+ moieties. In the case of these two substrates,
there is no advantage in using 3 and 4 over 1 and 2 for formation
of the trivalent (C5Me5)2Ln products.
Figure 5. Thermal ellipsoid plot of (C5Me5)(BPh4)Sm(N2Ph2), 9,
with the probability ellipsoids drawn at the 50% level. Hydrogen
atoms have been excluded for clarity.
Table 3. Bond Distances (Å) and Angles (deg) in
(C5Me5)Sm[(µ-η6:η1-Ph)BPh3](N2Ph2), 9
bond distances/angles
11
Sm(1)-Cnt(C5Me5)
2.410
2.602
Sm(1)-Cnt(C6H5)
Ln(1)-C(C5Me5) av
Ln(1)-C(C6H5) av
Sm(1)-N(1)
2.693(5)
2.953(11)
2.530(4)
2.249(4)
2.692(5)
2.719(4)
2.699(4)
2.673(5)
2.683(5)
2.984(4)
2.983(5)
2.968(5)
2.963(5)
2.931(5)
2.888(5)
2.871(4)
2.875(4)
1.435(5)
1.452(6)
1.394(6)
126.6
Sm(1)-N(2)
Sm(1)-C(1)
Sm(1)-C(2)
Sm(1)-C(3)
Sm(1)-C(4)
Sm(1)-C(5)
Sm(1)-C(11)
Sm(1)-C(12)
Sm(1)-C(13)
Sm(1)-C(14)
Sm(1)-C(15)
Sm(1)-C(16)
Sm(1)-C(17)
Sm(1)-C(18)
N(1)-N(2)
N(1)-C(35)
N(2)-C(35)
Cnt(C5Me5)-Sm(1)-Cnt(C6H5)
Cnt(C5Me5)-Sm(1)-N(1)
Cnt(C5Me5)-Sm(1)-N(2)
Cnt(C6H5)-Sm(1)-N(1)
Cnt(C6H5)-Sm(1)-N(2)
100.6
107.2
125.7
99.8
Structure. Because of the η6 coordination mode of two of
the four phenyl rings in the (BPh4)1- anion in the (C5Me5)Ln-
(µ-η6:η1-Ph)2BPh2 complexes, the metals in 3 and 4 are
surrounded by three six-electron rings. Generally, in organo-
lanthanide chemistry, such complexes are limited to tris-
(cyclopentadienyl) complexes in which the rings are large
enough to prevent additional coordination. Hence, the simple
cyclopentadienyls, (C5H5)3Ln, oligomerize in the solid state to
In both 9 and 10, the NN distances have elongated as
compared to azobenzene, and the phenyl rings are no longer
coplanar. Detailed comparisons with 10 will not be made
because of the large error limits in that structure. The (PhNNPh)1-
ligand in 9 is asymmetrically bound. As shown in Table 3, Sm-
N(2) is 2.239(4) Å, whereas Sm-N(1) is 2.530(4) Å. This
asymmetry carries over to the N-C(Ph) distances, which are
1.394(6) Å for N(2)-C(41) and 1.452(6) Å for N(1)-C(35).
The 1.435(5) Å N-N distance in 9 is closer to the 1.45 Å N-N
single bond distance in hydrazine than to the 1.25 Å NdN
distance typical in azobenzenes. The Ph-N-N-Ph dihedral
angle is 78.4°.
(53) Thomas, F. G.; Boto, K. G. In The Chemistry of the Hydrazo, Azo,
and Azoxy Groups; Patai, S., Ed.; Wiley: New York, 1975.
(54) Evans, W. J.; Drummond, D. K.; Chamberlain, L. R.; Doedens, R.
J.; Bott, S. G.; Zhang, H.; Atwood, J. L. J. Am. Chem. Soc. 1988, 110,
4983.
(55) Evans, W. J.; Champagne, T. M.; Davis, B. L.; Allen, N. T.; Nyce,
G. W.; Johnston, M. A.; Lin, Y. -C, Khvostov, A.; Ziller, J. W. J. Coord.
Chem. 2006, 59, 1069.
(56) Schumann, H.; Meese-Marktscheffel, J. A.; Esser, L. Chem. ReV.
1995, 95, 865.
(57) Bonnet, F.; Visseaux, M.; Barbier-Baudry, D.; Hafid, A.; Vigier,
E.; Kubicki, M. M. Inorg. Chem. 2004, 43, 3682.
(58) Zhang, W.-X.; Nishiura, M.; Hou, Z. J. Am. Chem. Soc. 2005, 127,
16788.
(59) Tardif, O.; Hashizume, D.; Hou, Z. J. Am. Chem. Soc. 2004, 126,
8080.

(C5Me5)Ln(BPh4) Complexes of Ytterbium and Samarium
Organometallics, Vol. 26, No. 5, 2007 1211
form [(C5H5)3Ln]x structures with extra intermolecular ring to
metal interactions.60,61 Monometallic complexes in which the
metal is coordinated only to three six-electron rings as in 3 and
4 are found in compounds such as [C5H3(SiMe3)2]3Ln,62-64 (C5-
Me4H)3Ln,65,66 and (C5Me5)3Ln45,67 as well as mixed ligand
complexes like (C5Me5)2Sm(C5H5).68
The ring centroids in these previous examples of monome-
tallic three-ring complexes all adopt the trigonal planar arrange-
ment that is the most efficient in terms of steric packing of three
ligands. Although this expected structure is found in 3, a
pyramidal arrangement is observed in 4. Unusual structures have
previously been observed for divalent organolanthanides, but
generally, the structures are unusual for both metals. The origin
and consequences of the bent structure remain to be identified.
Conclusion
(C5Me5)Ln(µ-η6:η1-Ph)2BPh2 complexes of ytterbium and
samarium can be synthesized in good yield from (C5Me5)2Ln
precursors obtainable by vacuum desolvation of divalent (C5-
Me5)2Ln(THF)x complexes and constitute a new class of
organometallic divalent lanthanide complexes. The unsolvated
(C5Me5)Ln(µ-η6:η1-Ph)2BPh2 complexes provide new oppor-
tunities to explore sterically unsaturated pentamethylcyclopen-
tadienyl lanthanide intermediates with the added feature that a
redox active divalent metal is present. Given the extensive
chemistry of both sterically unsaturated complexes and di-
valent lanthanides, this should open many new options in the
field.
(60) Eggers, S. H.; Kopf, J.; Fischer, R. D. Organometallics 1986, 5,
383.
(61) Eggers, S. H.; Schultze, H.; Kopf, J.; Fischer, R. D. Angew. Chem.,
Intl. Ed. Engl. 1986, 25, 656-657.
(62) Stults, S. D.; Andersen, R. A.; Zalkin, A. Organometallics 1990, 9,
115.
(63) Evans, W. J.; Keyer, R. A.; Ziller, J. W. J. Organomet. Chem. 1990,
394, 87.
(64) Xie, Z.; Chui, K.; Liu, Z.; Xue, F.; Zhang, Z.; Thomas, C. W. M.;
Sun, J. J. Organomet. Chem. 1997, 549, 239.
(65) Schumann, H.; Glanz, M.; Hemling, H. J. Organomet. Chem. 1993,
445, C1.
Acknowledgment. We thank the U.S. National Science
Foundation for support.
Supporting Information Available: Synthetic, spectroscopic,
and X-ray diffraction details (PDF and CIF). This material is
available free of charge via the Internet at http://pubs.acs.org.
(66) Schumann, H.; Glanz, M.; Hemling, H.; Hahn, F. E. Z. Anorg. Allg.
Chem. 1995, 621, 341.
(67) Evans, W. J.; Davis, B. L. Chem. ReV. 2002, 102, 2119.
(68) Evans, W. J.; Ulibarri, T. A. J. Am. Chem. Soc. 1987, 109, 4292.
OM060963S