Synthesis, structure, and ligand-based reduction reactivity of trivalent organosamarium benzene chalcogenolate complexes (C5Me 5)Sm(EPh)(THF) and [(C5Me5) 2Sm(μ-EPh)]2

Article abstract of DOI:10.1021/ic0502170

To compare the ligand-based reduction chemistry of (EPh)^- ligands in a metallocene environment to the sterically induced reduction chemistry of the (C₅Me₅)^- ligands in (C ₅Me₅)₃Sm, (C₅Me₅) ₂Sm(EPh) (E = S, Se, Te) complexes were synthesized and treated with substrates reduced by (C₅Me₅)₃Sm: cyclooctatetraene; azobenzene; phenazine. Reactions of PhEEPh with (C ₅Me₅)₂Sm(THF)₂ and (C ₅Me₅)₂Sm produced THF-solvated monometallic complexes, (C₅Me₅)₂Sm(EPh)(THF), and their unsolvated dimeric analogues, [(C₅Me₅) ₂Sm(μ-EPh)]₂, respectively. Both sets of the paramagnetic benzene chalcogenolate complexes were definitively identified by X-crystallography and form homologous series. Only the (TePh)^- complexes show reduction reactivity and only upon heating to 65°C.

Full text of DOI:10.1021/ic0502170

Inorg. Chem. 2005, 44, 4326−4332
Synthesis, Structure, and Ligand-Based Reduction Reactivity of
Trivalent Organosamarium Benzene Chalcogenolate Complexes
(C5Me5)2Sm(EPh)(THF) and [(C5Me5)2Sm( -EPh)]2
µ
William J. Evans,* Kevin A. Miller, David S. Lee, and Joseph W. Ziller
Department of Chemistry, UniVersity of California, IrVine, California 92697-2025
Received February 9, 2005
To compare the ligand-based reduction chemistry of (EPh)- ligands in a metallocene environment to the sterically
induced reduction chemistry of the (C5Me5)- ligands in (C5Me5)3Sm, (C5Me5)2Sm(EPh) (E
S, Se, Te) complexes
)
were synthesized and treated with substrates reduced by (C5Me5)3Sm: cyclooctatetraene; azobenzene; phenazine.
Reactions of PhEEPh with (C5Me5)2Sm(THF)2 and (C5Me5)2Sm produced THF-solvated monometallic complexes,
(C5Me5)2Sm(EPh)(THF), and their unsolvated dimeric analogues, [(C5Me5)2Sm(
the paramagnetic benzene chalcogenolate complexes were definitively identified by X-crystallography and form
homologous series. Only the (TePh)- complexes show reduction reactivity and only upon heating to 65
C.
µ-EPh)]2, respectively. Both sets of
°
Introduction
that it has only been observed in sterically crowded
complexes in which the metal carbon bonds are unusually
long. For that reason, this type of reductive process has been
called sterically induced reduction (SIR).17
The reactivity of the sterically crowded (C5Me5)3M
complexes has revealed that when the normally inert
(C5Me5)- ligand is placed in sufficiently congested coordina-
tion environments, it can function as a one electron reductant
according to the half-reaction shown in eq 1.1,2 This allows
trivalent complexes such as (C5Me5)3Sm to function as one-
electron reductants as shown in eqs 2-4.1-3 Although ligand-
based reductions have been reported in lanthanide chem-
istry,4-16 the (C5Me5)- reductive chemistry is different in
(C5Me5)3Ln f 1e- + 1/2(C5Me5)2 + [(C5Me5)2Ln]+ (1)
Another ligand that has been shown to do reductive
* Author to whom correspondence should be addressed. E-mail:
wevans@uci.edu. Fax: 949-824-2210.
(1) Evans, W. J.; Forrestal, K. J.; Ziller, J. W. J. Am. Chem. Soc. 1998,
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W.; Fujimoto, C. H.; Clark, R. D.; Johnston, M. A.; Ziller, J. W.
Submitted for publication.
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2117.
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1998, 37, 4162.
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4400.
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119, 11112
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J. G. J. Am. Chem. Soc. 1999, 121, 10247.
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Am. Chem. Soc. 1999, 121, 11713.
chemistry in lanthanide complexes is the (EPh)- group. In a
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2001, 123, 11933.
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G. Inorg. Chem. 2002, 41, 121.
4326 Inorganic Chemistry, Vol. 44, No. 12, 2005
10.1021/ic0502170 CCC: $30.25
© 2005 American Chemical Society
Published on Web 05/13/2005

Organosamarium Benzene Chalcogenolate Complexes
series of studies by Brennan and co-workers, the 2(EPh)-/
PhEEPh redox couple has been shown to reduce elemental
chalcogen (E ) S) as exemplified in eq 5.4-16
sublimed before use. KSPh was prepared by the addition of 1 equiv
of PhSSPh to 2 equiv of K sand. Stirring overnight yielded a white
toluene insoluble material. Complete elemental analyses were
performed by Analytische Laboratorien (Lindlar, Germany). Com-
plexometric metal analyses were carried out in house as previously
described.27
8Ln(SPh)3 + 3/4S8 THF8 Ln8S6(SPh)12(THF)8 + 6PhSSPh
(5)
(C5Me5)2Sm(SPh)(THF), 1. In a nitrogen filled glovebox,
PhSSPh (19 mg, 0.088 mmol) in 5 mL of THF was added to a
stirring solution of purple (C5Me5)2Sm(THF)2 (100 mg, 0.177
mmol) in 5 mL of THF. A clear orange solution immediately
formed. After the mixture was stirred overnight, the orange solution
was evaporated to dryness to yield 1 as an orange powder (95 mg,
90%). Crystals of 1 suitable for X-ray diffraction were grown at
-35 °C from a concentrated toluene solution. 1H NMR (500 MHz,
To determine if the ligand-based reductive chemistry
observed for (C5Me5)3Sm could be mimicked using the
Brennan reductants, (EPh)-, the synthesis of complexes such
as (C5Me5)2Sm(EPh)(THF) and [(C5Me5)2Sm(EPh)]2 was of
interest. These complexes could be more synthetically
accessible than the highly reactive (C5Me5)3Sm (which, for
example, ring opens THF1) and would provide a new option
for reductive lanthanide chemistry with triValent lanthanide
metallocene complexes. The desired series of complexes
seemed accessible on the basis of the existence of related
compounds in the literature such as (C5Me5)2Yb(SPh)(NH3),18
(C5Me5)2Yb(TePh)(NH3),19 (C5Me5)2Sm(THF)(TeC6H2Me3-
2,4,6),20 (C5Me5)2Sm(THF)(SeC6H2(CF3)3-2,4,6),21 and [(C5H4-
CMe3)2Y(µ-SePh)]2.22 Accordingly, we prepared the orga-
nosamarium complexes (C5Me5)2Sm(EPh)(THF) and [(C5-
Me5)2Sm(EPh)]2 (E ) S, Se, Te) and report here on their
synthesis, structure, and reactivity.
THF-d8): 1.19 (s, 30H, C5Me5, ∆ν1/2 ) 2 Hz), 6.86 (t, 1H, 3JHH
)
7 Hz, p-H), 5.87 (d, 2H, 3JHH ) 8 Hz, o-H), 6.59 (t, 2H, 3JHH ) 8
Hz, m-H). 13C NMR (500 MHz, THF-d8, 25 °C): δ 17.8 (C5Me5),
116.8 (C5Me5), 129.8 (o-phenyl), 128.4 (m-phenyl), 121.0 (p-
phenyl). IR: 3057 w, 2961 m, 2907 s, 2856 s, 2725 w, 1660 w,
1579 m, 1532 w, 1475 s, 1436 s, 1378 s, 1262 m, 1162 m, 1085 s,
1046 s, 1023 s, 992 s, 895 m, 822 s, 802 s, 737 s, 694 s, 568 w
cm-1. Anal. Calcd for C30H43OSSm: Sm, 25.0. Found: Sm, 24.9.
Sublimation of 1 at 155 C at 8 × 10-4 Torr afforded 4 in 8% yield
(see below).
(C5Me5)2Sm(SePh)(THF), 2. As described for 1, 2 was obtained
as an orange powder (113 mg, 98%) from PhSeSePh (27 mg, 0.088
mmol) and (C5Me5)2Sm(THF)2 (100 mg, 0.177 mmol). Crystals of
2 suitable for X-ray diffraction were grown at -35 °C from a
concentrated toluene solution. 1H NMR (500 MHz, THF-d8): 1.18
Experimental Section
The manipulations described below were performed under argon
or nitrogen with rigorous exclusion of air and water using Schlenk,
vacuum line, and glovebox techniques. Solvents were saturated with
UHP grade argon (Airgas) and dried by passage through Glass-
contour drying columns before use. NMR solvents were dried over
NaK and vacuum transferred before use. NMR spectra were
3
(s, 30H, C5Me5, ∆ν1/2 ) 2 Hz), 7.01 (t, 1H, JHH ) 8 Hz, p-H),
3
3
6.58 (d, 2H, JHH ) 8 Hz, o-H), 6.71 (t, 2H, JHH ) 7 Hz, m-H).
13C NMR (500 MHz, THF-d8): δ 17.8 (C5Me5), 116.7 (C5Me5),
133.2 (o-phenyl), 128.6 (m-phenyl), 122.4 (p-phenyl). IR: 3061
w, 2964 m, 2907 s, 2856 s, 2725 w, 1575 s, 1471 s, 1436 s, 1378
m, 1262 m, 1162 m, 1096 s, 1069 s, 1046 s, 1019 s, 818 s, 799 s,
733 s, 694 s, 633 s, 579 w, 555 w, 521 w cm-1. Anal. Calcd for
C30H43OSeSm: Sm, 23.2. Found: Sm, 23.8.
1
recorded with a Bruker DRX 400 or 500 MHz systems. The H
and 13C NMR spectra of the initially isolated powders match the
NMR spectra of the isolated crystals for 1-6. Infrared spectra were
recorded as thin films obtained from THF-d8 (1-3) or C6D6 (4-6)
on the silicon window of the probe of an ASI ReactIR 1000
instrument.23 (C5Me5)2Sm(THF)2,24 (C5Me5)2Sm,25 and [(C5Me5)2-
Sm][(µ-Ph)2BPh2]26 were prepared as previously described. PhSSPh,
PhSeSePh, and PhTeTePh were purchased from Aldrich and
(C5Me5)2Sm(TePh)(THF), 3. As described for 1, 3 was obtained
as an orange powder (62 mg, 95%) from PhTeTePh (38 mg, 0.094
mmol) and (C5Me5)2Sm(THF)2 (107 mg, 0.19 mmol). Crystals of
3 suitable for X-ray diffraction were grown at 25 °C from a
concentrated toluene solution. 1H NMR (500 MHz, THF-d8): 1.23
3
(s, 30H, C5Me5, ∆ν1/2 ) 2 Hz), 7.10 (t, 1H, JHH ) 7 Hz, p-H),
3
3
(13) Freedman, D.; Emge, T. J.; Brennan, J. G. Inorg. Chem. 2002, 41,
492.
(14) Fitzgerald, M.; Emge, T. J.; Brennan, J. G. Inorg. Chem. 2002, 41,
3528.
(15) Kornienko, A. Y.; Huebner, L.; Freedman, D.; Emge, T. J.; Brennan,
J. G. Inorg. Chem. 2003, 42, 8476.
(16) Kornienko, A. Y.; Emge, T. J.; Kumar, G. A.; Riman, R. E.; Brennan,
J. G. J. Am. Chem. Soc. 2005, 127, 3501.
(17) Evans, W. J. Coord. Chem. ReV. 2000, 206-207, 263.
(18) Zalkin, A.; Henly, T. J.; Andersen, R. A. Acta Crystallogr. 1987, C43,
233.
(19) Berg, D. J.; Andersen, R. A.; Zalkin, A. Organometallics 1988, 7,
1858.
(20) Recknagel, A.; Noltemeyer, M.; Stalke, D.; Pieper, U.; Schmidt, H.;
Edelman, F. T. J. Organomet. Chem. 1991, 411, 347.
(21) Poremba, P.; Noltemeyer, M.; Schmidt, H.; Edelman, F. T. J.
Organomet. Chem. 1995, 501, 315.
(22) Beletskaya, I. P.; Voskoboynikov, A. Z.; Shestakova, A. K.; Yanovsky,
A. I.; Fukin, G. K.; Zacharov, L. N.; Struchkov, Y. T.; Schumann, H.
J. Organomet. Chem. 1994, 468, 121.
7.01 (d, 2H, JHH ) 7 Hz, o-H), 6.69 (t, 2H, JHH ) 7 Hz, m-H).
13C NMR (500 MHz, THF-d8): δ 18.3 (C5Me5), 116.9 (C5Me5),
139.6 (o-phenyl), 128.8 (m-phenyl), 124.0 (p-phenyl). IR: 3053
w, 2957 s, 2922 s, 2856 s, 2725 w, 1942 w, 1876 w, 1799 w, 1741
w, 1660 w, 1571 m, 1471 m, 1436 s, 1378 m, 1262 s, 1096 s,
1061 s, 1015 s, 864 m, 802 s, 725 s, 687 s cm-1. Anal. Calcd for
C30H43OSmTe‚1/2THF: C, 52.38; H, 6.46; Sm, 20.49; Te, 17.39.
Found: C, 52.81; H, 6.26; Sm, 20.60; Te, 17.75.
[(C5Me5)2Sm(µ-SPh)]2, 4. In an argon-filled glovebox free of
coordinating solvents, PhSSPh (55 mg, 0.25 mmol) in toluene (2
mL) was added slowly to a stirring green solution of (C5Me5)2Sm
(211 mg, 0.50 mmol) in toluene (5 mL). The solution immediately
turned dark red. After the reaction mixture was stirred overnight,
the solvent was removed by rotary evaporation to yield 4 as a red
orange crystalline powder (258 mg, 97%). Crystals of 4 suitable
for X-ray diffraction were grown at -35 °C from a concentrated
(23) Evans, W. J.; Johnston, M. A.; Ziller, J. W. Inorg. Chem. 2000, 39,
3421.
(24) Evans, W. J.; Bloom, I.; Hunter, W. E.; Atwood, J. L. Organometallics
1985, 4, 112.
(25) Evans, W. J.; Hughes, L. A.; Hanusa, T. P. Organometallics 1986, 5,
1285.
(26) Evans, W. J.; Seibel, C. A.; Ziller, J. W. J. Am. Chem. Soc. 1998,
120, 6745.
(27) Evans. W. J.; Engerer, S. C.; Coleson, K. M. J. Am Chem. Soc. 1981,
103, 6672.
Inorganic Chemistry, Vol. 44, No. 12, 2005 4327

Evans et al.
Table 1. X-ray Data Collection Parameters for (C5Me5)2Sm(EPh)(THF) Complexes 1-3
1
2
3
empirical formula
fw
C30H43OSmS
602.05
C30H43OSmSe
648.95
C30H43OSmTe
697.59
temp (K)
cryst system
space group
a (Å)
163(2)
orthorhombic
Pbca
17.5355(6)
15.1031(5)
21.2702(7)
5633.2(3)
8
1.420
2.178
0.0400
0.0977
168(2)
orthorhombic
Pbca
17.3589(17)
15.2692(15)
21.463(2)
5689.0(10)
8
1.515
3.363
0.0369
0.1032
163(2)
orthorhombic
Pbcn
18.3046(17)
17.2195(16)
18.1750(17)
5728.7(9)
8
1.618
3.067
0.0184
0.0442
b (Å)
c (Å)
V (Å3)
Z
F
calcd (Mg/m3)
µ (mm-1
)
R1 [I > 2.0σ(I)]a
wR2 (all data)a
a Definitions: wR2 ) [Σ[w(Fo - Fc )2]/Σ[w(Fo )2] ]1/2, R1 ) Σ||Fo| - |Fc||/Σ|Fo|.
2
2
2
1
1
toluene solution. H NMR (400 MHz, C6D6): (s, C5Me5, ∆ν1/2
)
the mixture was heated at 65 °C overnight, the H and 13C NMR
spectra of the dark green mixture showed consumption of starting
materials and the formation of (C5Me5)2Sm(N2Ph2)(THF)29 and
PhTeTePh.
10 Hz). Aryl resonances could not be located. 13C NMR (500 MHz,
C6D6): δ 23.4 (C5Me5), 116.8 (C5Me5). IR: 3057 w, 2961 s, 2910
s, 2865 s, 2729 w, 1660 w, 1579 m, 1475 s, 1436 s, 1378 m, 1332
w, 1262 s, 1085 s, 1023 s, 799 s, 737 s, 694 s, 586 w cm-1. Anal.
Calcd for C52H70S2Sm2: C, 58.92; H, 6.66; S, 6.05; Sm, 28.37.
Found: C, 59.70; H, 6.62; S, 5.40; Sm, 27.60. Addition of THF to 4
afforded 1 in quantitative yield. Complex 4 can also be made from
a trivalent precursor. In an NMR tube, [(C5Me5)2Sm][(µ-Ph)2BPh2]
(11 mg, 0.015 mmol) dissolved in C6D6 was added to KSPh (3
X-ray Data Collection, Structure Solution, and Refinement
of 2. An orange crystal of approximate dimensions 0.23 × 0.24 ×
0.25 mm was mounted on a glass fiber and transferred to a Bruker
CCD platform diffractometer. The SMART30 program package was
used to determine the unit-cell parameters and for data collection
(25 s/frame scan time for a sphere of diffraction data). Details are
given in Table 1. The raw frame data were processed using SAINT31
and SADABS32 to yield the reflection data file. Subsequent
calculations were carried out using the SHELXTL33 program. The
diffraction symmetry was mmm, and the systematic absences were
consistent with the orthorhombic space group Pbca which was later
determined to be correct. The structure was solved by direct methods
and refined on F2 by full-matrix least-squares techniques. The
analytical scattering factors34 for neutral atoms were used throughout
the analysis. Hydrogen atoms were included using a riding model.
The carbon atoms of the THF ligand were disordered and included
using multiple components with partial site occupancy factors. At
convergence, wR2 ) 0.1032 and GOF ) 1.126 for 294 variables
refined against 6961 data. As a comparison for refinement on F,
R1 ) 0.0369 for those 5141 data with I > 2.0σ(I). Structural data
on 1 and 3-6 were collected similarly. Details are given in Tables
1 and 2 and in the Supporting Information.
1
mg, 0.022 mmol). H NMR spectroscopy showed complete con-
sumption of [(C5Me5)2Sm][(µ-Ph)2BPh2] with the formation of 4
in 1 h.
[(C5Me5)2Sm(µ-SePh)]2, 5. As described for 4, 5 was obtained
as an orange crystalline powder (239 mg, 98%) from PhSeSePh
(66 mg, 0.21 mmol) and (C5Me5)2Sm (178 mg, 0.42 mmol). Crystals
of 5 suitable for X-ray diffraction were grown at -35 °C from a
concentrated toluene solution. 1H NMR (500 MHz, C6D6): δ 1.33
(s, C5Me5, ∆ν1/2 ) 10 Hz). Aryl resonances could not be located
even at low temperature (200 K). 13C NMR (500 MHz, C6D6): δ
23.4 (C5Me5), 116.7 (C5Me5). IR: 3061 m, 2961 s, 2910 s, 2856 s,
1575 s, 1471 s, 1436 s, 1378 m, 1262 m, 1096 m, 1069 s, 1023 s,
802 s, 733 s, 690 s, 663 s cm-1. Anal. Calcd for C52H70Se2Sm2:
Sm, 26.1. Found: Sm, 26.2. Addition of THF to 5 afforded 2 in
quantitative yield.
[(C5Me5)2Sm(µ-TePh)]2, 6. As described for 4, 6 was obtained
as a dark orange crystalline powder (251 mg, 99%) from PhTeTePh
(83 mg, 0.20 mmol) and (C5Me5)2Sm (170 mg, 0.40 mmol). Crystals
of 6 suitable for X-ray diffraction were grown at 25 °C from a
concentrated toluene solution. 1H NMR (500 MHz, C6D6): δ 1.34
(s, C5Me5, ∆ν1/2 ) 10 Hz). Aryl resonances could not be located.
13C NMR (500 MHz,C6D6): δ 23.4 (C5Me5), 116.9 (C5Me5). IR:
3065 w, 2961 s, 2910 s, 2856 s, 2737 w, 1656 w, 1613 w, 1571 m,
1471 m, 1436 s, 1378 m, 1328 w, 1262 s, 1096 s, 1061 s, 1015 s,
802 s, 725 s, 687 s, 579 w, 552 w cm-1. Anal. Calcd for C52H70-
Te2Sm2: Sm, 24.0. Found: Sm, 24.1. Addition of THF to 6 afforded
3 in quantitative yield.
Results
Synthesis. (C5Me5)2Sm(EPh)(THF), 1-3. In analogy to
the reactions of (C5Me5)2YbLx complexes with PhEEPh (E
) S, Se, Te),18,19 2 equiv of divalent (C5Me5)2Sm(THF)2
react with 1 equiv of PhEEPh (E ) S, Se, Te) in THF to
produce orange crystalline products, 1-3, respectively, in
24
(28) Evans, W. J.; Gonzales, S. L.; Ziller, J. W. J. Am. Chem. Soc. 1994,
116, 2600.
(29) Evans, W. J.; Drumond, D. K.; Chamberlain, L. R.; Doedens, R. J.;
Bott, S. G.; Zhang, H.; Atwood, J. L. J. Am. Chem. Soc. 1988, 110,
4983.
(30) SMART Software Users Guide, version 5.1; Bruker Analytical X-ray
Systems, Inc.: Madison, WI, 1999.
(31) SAINT Software Users Guide, version 6.0; Bruker Analytical X-ray
Systems, Inc.: Madison, WI, 1999.
(32) Sheldrick, G. M. SADABS, version 2.05; Bruker Analytical X-ray
Systems, Inc.: Madison, WI, 2001.
(33) Sheldrick, G. M. SHELXTL, version 6.12; Bruker Analytical X-ray
Systems, Inc.: Madison, WI, 2001.
(34) International Tables for X-ray Crystallography; Kluwer Academic
Publishers: Dordrecht, The Netherlands, 1992; Vol. C.
1
Reaction of 6 with C12H8N2. The H NMR spectrum of 6 (13
mg, 0.011 mmol) in C6D6 (1 mL) containing phenazine (19 mg,
0.011 mmol) showed resonances only for orange 6 after 12 h. After
the mixture was heated at 65 °C overnight, the H and 13C NMR
spectra of the dark brown mixture showed consumption of starting
materials and the formation of [(C5Me5)2Sm]2[(C12H8N2)]28 and
PhTeTePh.
Reaction of 3 with PhNdNPh. The H NMR spectrum of 3
(11 mg, 0.015 mmol) in C6D6 (1 mL) containing PhNNPh (3 mg,
1
1
0.016 mmol) showed resonances only for orange 3 after 12 h. After
4328 Inorganic Chemistry, Vol. 44, No. 12, 2005

Organosamarium Benzene Chalcogenolate Complexes
Table 2. X-ray Data Collection Parameters for [(C5Me5)2Sm]2(µ-EPh)2 Complexes 4-6
4
5
6
empirical formula
fw
temp (K)
cryst system
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
C52H70S2Sm2‚2C7H8
1244.17
163(2)
triclinic
P1h
10.3682(12)
10.5399(12)
14.7518(16)
69.395(2)
76.742(2)
83.724(2)
1468.0(3)
1
C52H70Se2Sm2‚2C7H8
1337.97
163(2)
triclinic
P1h
10.3260(4)
10.6832(4)
14.8928(7)
111.0120(10)
98.1180(10)
97.3330(10)
1489.77(11)
1
C52H70Sm2Te2
1250.98
193(2)
orthorhombic
Pca21
23.132(2)
10.2800(11)
20.361(2)
90
90
90
4841.7(9)
4
1.716
Z
F
calcd (Mg/m3)
1.407
2.090
0.0238
0.0639
1.491
3.211
0.0314
0.0812
µ (mm-1
)
3.615
0.0172
0.0416
R1 [I > 2.0σ(I)]a
wR2 (all data)a
a Definitions: wR2 ) [Σ[w(Fo - Fc )2]/Σ[w(Fo )2] ]1/2, R1 ) Σ||Fo| - |Fc||/Σ|Fo|.
2
2
2
1
high yields. 1-3 were characterized by H and 13C NMR
spectroscopy, IR spectroscopy, and elemental analysis and
were completely identified by X-ray crystallography, eq 6,
respectively. The complexes exhibit broader line widths for
the (C5Me5)- resonances (∼10 Hz) compared to 1-3 (∼2
Hz). A trivalent oxidation state is again indicated by the 13
C
1
Figure 1. The complexes have similar H NMR C5Me5
Figure 2. Molecular structure of [(C5Me5)2Sm(SPh)]2, 4, with thermal
ellipsoids drawn at the 50% probability level.
Figure 1. Molecular structure of (C5Me5)2Sm(TePh)(THF), 3, with thermal
ellipsoids drawn at the 50% probability level.
NMR spectra, and the IR spectra are very similar. Addition
of THF to 4-6 generates 1-3 quantitatively. Attempts to
form 4 by desolvation of 1 under vacuum gave very low
yields.
resonances: 1.19, 1.18, and 1.23 ppm for 1-3, respectively.
The 13C NMR C5Me5 signals are consistent with Sm3+,35 and
the IR spectra are nearly superimposable.
[(C5Me5)2Sm(-EPh)]2, 4-6. Reaction of 2 equiv of
unsolvated (C5Me5)2Sm25 with 1 equiv of PhEEPh (E ) S,
Se, Te) in toluene produces dark red (E ) S, 4) and dark
orange (E ) Se, 5; E ) Te, 6) crystalline products in high
yields, eq 7, Figure 2. Like 1-3, the H NMR C5Me5
resonances for 4-6 are similar: 1.37, 1.33, and 1.34 ppm,
[(C5Me5)2SmSPh]2, 4, was also prepared via a trivalent
route using the reaction of [(C5Me5)2Sm][(µ-Ph)2BPh2] and
KSPh, prepared from K and PhSSPh, as shown in eq 8.
The loosely ligated complex, [(C5Me5)2Sm][(µ-Ph)2BPh2],
has previously been shown to be a good precursor to (C5-
Me5)2SmX products in reactions with MX salts (M ) K,
Li; X ) C5Me5,26 CH2Ph, Me, CH2SiMe3, and Ph36).
1
(35) Evans, W. J.; Ulibarri, T. J. J. Am Chem. Soc. 1987, 109, 4292.
(36) Evans, W. J.; Perotti, J. M.; Ziller, J. W. J. Am. Chem. Soc. 2005,
126, 1068.
Inorganic Chemistry, Vol. 44, No. 12, 2005 4329

Evans et al.
Table 3. Selected Bond Distances (Å) and Angles (deg) for
(C5Me5)2Sm(EPh)(THF) Complexes 1-3
1
2
3
E
S
Se
Te
Sm(1)-O(1)
Sm(1)-E(1)
Sm(1)-Cnt1
Sm(1)-Cnt2
E(1)-C(21)
2.445(3)
2.7605(12)
2.442
2.452
1.759(5)
2.443(3)
2.8837(6)
2.448
2.445
1.913(4)
2.4490(15)
3.1279(3)
2.448
2.445
2.127(2)
Cnt1-Sm(1)-E(1)
Cnt2-Sm(1)-E(1)
Cnt1-Sm(1)-Cnt2
C(21)-E(1)-Sm(1)
Cnt1-Sm(1)-O(1)
Cnt2-Sm(1)-O(1)
O(1)-Sm(1)-E(1)
99.5
114.4
133.7
120.82(17)
104.6
98.7
114.8
134.1
118.51(14)
105.7
100.0
113.1
135.2
112.49(6)
104.1
106.1
89.72(9)
105.1
89.35(8)
103.7
92.51(4)
Structure. Monometallic Solvates, 1-3. Complexes 1-3
have the familiar structure of (C5Me5)2LnXL complexes (X
) anion; L ) neutral ligand) in which the two (C5Me5)-
ring centroids and the (EPh)- and THF ligands roughly
define a distorted tetrahedron around the Sm3+ center. As
shown in Table 3, the metrical parameters associated with
the [(C5Me5)2Sm]+ fragment are normal as are the Sm-
O(THF) distances.37 As expected, the Sm-E distances
gradually increase from 1 to 3, i.e., S to Se to Te: 2.7605-
(12), 2.8837(6), and 3.1279(3) Å, respectively. In compari-
son, Shannon radii show that S2- is 0.14 Å smaller than Se2-
which is 0.23 Å smaller than Te2-.38 Compared to the Yb-
Se and Yb-Te distances in eight-coordinate (C5Me5)2Yb-
(SPh)(NH3) (2.670(3) Å),18 (C5H5)2Yb(SC6H2(CF3)3-2,4,6)-
(THF) (2.639(3) Å) and (C5Me5)2Yb(TePh)(NH3) (3.039(1)
Å),19 these distances are in the expected range considering
that the effective ionic radius of eight-coordinate Sm3+ is
0.094 Å larger than that of eight-coordinate Yb3+.38
logues 1-3, but the difference is not large. The Sm-C(C5-
Me5) distances, 2.688(3)-2.733(3)°, are in the normal range.
The arrangement of the (EPh)- ligands in the dimers is
quite symmetrical. In 4 and 5, the Sm2E2 rings are perfectly
planar and in 6 only a 0.014 2 Å deviation from planarity is
observed in the Sm2Te2 ring. The Sm-E and Sm-E′
distances are equal within 0.01 Å in each compound. Since
there are two (EPh)- ligands in the coordination sphere of
each metal in 4-6, it is more difficult to orient the (EPh)-
ligands asymmetrically to avoid the (C5Me5)- rings as in
1-3. Nevertheless, as in 1-3, the (C5Me5 ring centroid)-
Sm-donor atom angles fall into two ranges: (C(1)-C(5)
ring centroid)-Sm-E and (C(1)-C(5) ring centroid)-Sm-
E′ are 105.3-109.8°, and the corresponding angles involving
C(11)-C(15) are 112.8-116.5°. The E to E′ distances, 3.024,
3.114, and 3.449 Å for 4-6, respectively, are outside the
usual range of E-E bond lengths.9,13,39
The Sm-E-C (ipso) angles in 1-3 decrease from S to
Se to Te with values of 120.82(17), 118.51(14), and 112.49-
(6)°, respectively. Other lanthanide metallocene chalco-
genides show similar angles: (C5H5)2Yb(SC6H2(CF3)3-2,4,6)-
(THF),21 (C5Me5)2Sm(SeC6H2(CF3)3-2,4,6)(THF),20 and
(C5Me5)2Sm(TeC6H2Me3-2,4,6)(THF)20 have angles of 121.2-
(1), 126.4(1), and 123.5(3)°, respectively. Although the
oxygen donor atom of the THF is located symmetrically
between the two (C5Me5)- rings, as evidenced by similar
103.7-106.1° (C5Me5 ring centroid)-Sm-O angles, the
(EPh)- ligands are not. The (C(1)-C(5) ring centroid)-
Sm-E angles are 99.5-100.0°, whereas the (C(11)-C(15)
ring centroid)-Sm-E angles are 113.1-114.8°. This dif-
ference, which puts the E atom closer to the C(1)-C(5) ring,
apparently minimizes steric crowding between the phenyl
ring and the C(11)-C(15) ring.
Unsolvated Bimetallic Complexes, 4-6. In the absence
of a coordinating solvent, the (C5Me5)2Sm(EPh) units dimer-
ize in the solid state to achieve the common eight-coordinate
lanthanide metallocene structure. As in compounds 1-3, the
two (C5Me5)- rings and two (EPh)- ligands in 4-6 roughly
define a distorted tetrahedral arrangement around each of
the Sm3+ centers. The 128.6-132.7° (C5Me5 ring centroid)-
Sm-(C5Me5 ring centroid) angles in 4-6 are numerically
smaller than the 133.7-135.2° range in the solvated ana-
The coordination around the E donor atoms is nearly
trigonal planar with angles that sum to near 360°: 359.7,
358.5, and 357.0° for 4-6, respectively. This is similar
to the structures of [Sm(µ-SPh)(C8H8)(THF)2]2,40 [Sm(µ-
i
SePh)(C8H8)(THF)2]2,41 and {Sm[µ-S(C6H2 Pr-2,4,6)](C8H8)-
(THF)}2,40 whose analogous angles sum to 359.1, 354.0,
and 359.3°, respectively. In contrast, [(Me3CC5H4)2Ce(µ-
SCHMe2)]2 and [(C5H5)2Yb(µ-SCH2CH2Me)]2 have angles
that sum to 348 and 326.8°, respectively.42,43
The Sm-E distances increase in the order S, Se, and Te
for 4-6, 2.9341(6), 3.0478(4), and 3.2627(4) Å, respectively
(Table 4). These distances are all longer than the Sm-E
distances in 1-3 as is common for bridging versus terminal
ligation. These Sm-E distances are similar to the 2.914(8)
and 3.095(2) Å Sm-E lengths in [Sm(µ-SPh)(C8H8)(THF)2]2
and [Sm(µ-SePh)(C8H8)(THF)2]2, respectively, compounds
which also have planar Sm2E2 units.40,41
Reactivity. Complexes 1-6 were combined with three of
the substrates reduced by (C5Me5)3Sm to see if similar
(39) Ansari, M. A.; Ibers, J. A. Coord. Chem. ReV. 1990, 100, 223.
(40) Mashima, K.; Nakayama, Y.; Kanehisa, N.; Kai, Y.; Nakamura, A. J.
Chem. Soc., Chem. Commun. 1993, 1847.
(41) Mashima, K.; Nakayama, Y.; Nakamura, A.; Kanehisa, N.; Kai, Y.;
Takaya, H. J. Organomet. Chem. 1994, 473, 85.
(42) Stults, S. D.; Andersen, R. A.; Zalkin, A. Organometallics 1990, 9,
1623.
(37) Evans, W. J.; Foster, S. E. J. Organomet. Chem. 1992, 433, 79.
(38) Shannon, R. D. Acta Crystallogr. 1976, A32, 751.
(43) Wu. Z.; Ma, W.; Huang, Z.; Cai, R.; Xu, Z.; You, X.; Sun, J.
Polyhedron 1996, 15, 3427.
4330 Inorganic Chemistry, Vol. 44, No. 12, 2005

Organosamarium Benzene Chalcogenolate Complexes
previously characterized (C5Me5)2Sm(N2Ph2)(THF)29 and
Table 4. Selected Bond Distances (Å) and Angles (deg) for
[(C5Me5)2Sm2(µ-EPh)]2 Complexes 4-6
1
PhTeTePh identified by H and 13C NMR spectroscopy, eq
4
5
6
10. Reactions of 1, 2, and 4-6 under the same conditions
leave significant amounts of starting material and no evidence
of formation of PhEEPh.
E
S
Se
Te
Sm(1)-E(1)
Sm(1)-E(1)
E(1)-C(21)
Sm(1)-Cnt1
Sm(1)-Cnt2
2.9341(6)
2.9388(6)
1.765(2)
2.429
3.0478(4)
3.0558(4)
1.912(3)
2.427
3.2627(4)
3.2606(3)
2.130(3)
2.437
2.464
2.456
2.438
E(1)-Sm(1)-E(1)
Cnt1-Sm(1)-E(1)
Cnt2-Sm(1)-E(1)
Cnt1-Sm(1)-E(1)
Cnt2-Sm(1)-E(1)
Cnt1-Sm(1)-Cnt2
C(21)-E(1)-Sm(1)
Sm(1)-E(1)-Sm(1)
61.99(2)
106.7
116.4
108.5
115.5
128.6
124.82(8)
118.01(2)
62.017(11)
105.3
116.5
109.8
113.0
130.1
123.73(10)
117.983(11)
63.844(7)
112.8
106.9
106.8
113.2
132.7
118.81(8)
116.151(9)
Discussion
reduction chemistry would result. The reduction potentials
of C8H8 (-1.83 and -1.99 V vs SCE),44 azobenzene (-1.35
to -1.41 V and -1.75 to -2.03 V vs SCE),45 and phenazine
(-0.364 V vs SCE)46 provided a range of opportunities for
reduction. In contrast to (C5Me5)3Sm, eqs 2-4, no reaction
was observed between 1-6 and any of these substrates at
room temperature. Only upon heating to 65 °C was reactivity
observed and then only with the more easily reduced
azobenzene and phenazine. C8H8 did not react with 1-6 even
after heating at 65 °C overnight.
In the case of phenazine, a clean reduction was observed
only with 6 at 65 °C. Hence, reaction of 1 equiv of [(C5-
Me5)2Sm(TePh)]2 with 1 equiv of C12H8N2 in C6D6 at 65 °C
overnight produces in quantitative yield a dark brown mixture
containing only previously characterized [(C5Me5)2Sm]2-
[(C12H8N2)]28 and PhTeTePh identified by 1H and 13C NMR
spectroscopy. This transformation, eq 9, is analogous to the
(C5Me5)3Sm reaction, eq 2, above. In contrast, no reaction
between 1-5 and phenazine was observed at 65 °C.
The syntheses in eqs 6-8 provide two series of homolo-
gous samarocene benzene chalcogenolate complexes for
comparisons of structure and reactivity. The progression of
structural features moving from S to Se to Te in each case
follows the typical periodic trends of these elements.
In contrast to the highly reactive (C5Me5)3Sm, the chal-
cogenides 1-6 have limited reductive reactivity with C8H8,
azobenzene, and phenazine. Only the tellurium complexes
react and only at elevated temperature with the most easily
reduced substrates. In contrast, (C5Me5)3Sm reduces each of
the substrates at room temperature. Although these (TePh)-
complexes show some ligand-based reduction analogous to
the (C5Me5)-/(C5Me5) reactions, the level of reactivity is
much lower.
The reason that the THF solvate, 3, is the reactive species
with azobenzene and the unsolvated dimer, 6, is the reactive
species with phenazine is not clear. Since both reactions
involve 2TePh-/PhTeTePh reduction in benzene, both 3 and
6 could be expected to react with each substrate. In general,
in comparisons of the reactivity of solvated and unsolvated
samarium metallocene complexes, the unsolvated complexes
are the more reactive. This certainly applies to (C5Me5)2-
Sm(THF)2/(C5Me5)2Sm and the (C5Me5)2SmR(THF)/[(C5-
Me5)2SmR]x pairs for R ) Me,47,48 C6H5,36,49 and CH2C6H5.36,48
The observation that the (TePh)- complexes are more
reducing than the (SePh)- and (SPh)- species is consistent
with the expectation that the Sm-Te bonds are the weakest
of these three Sm-chalcogen linkages and (TePh)- is
expected to be the most reducing (EPh)- anion (cf. I- vs
Br- vs Cl-). However, as amply shown by electrochemical
studies, the (EPh)-/PhEEPh redox couple is system depend-
ent and should not be rationalized so simply. For example,
electrochemical studies of PhSSPh and PhSeSePh by Dessy
provided reduction potentials of -1.6 and -0.9 V vs Ag/
AgNO3, respectively, but the reductions were irreversible.50
Subsequent studies by Ludvik and Nygard on these com-
In the azobenzene case, again it is a tellurium complex
which gives a clean reduction, but in this case it is the THF
solvate. Reaction of 1 equiv of (C5Me5)2Sm(TePh)(THF),
3, with 1 equiv of PhNdNPh in C6D6 at 65 °C produces a
dark green mixture in quantitative yield containing only the
(47) Evans, W. J.; Chamberlain, L. R.; Ulibarri, T. A.; Ziller, J. W. J. Am.
Chem. Soc. 1998, 110, 6423.
(48) Evans, W. J.; Ulibarri, T. A.; Ziller, J. W. Organometallics 1991, 10,
134.
(49) Castillo, I.; Tilley, T. D. J. Am. Chem. Soc. 2001, 123, 10526.
(50) Dessy, R. E.; Weissman, P. M.; Pohl, R. L. J. Am. Chem. Soc. 1966,
88, 5117.
(44) de Boer, E. AdV. Organomet. Chem. 1964, 2, 115.
(45) Thomas, F. G.; Boto, K. G. The Chemistry of the Hydrazo, Azo, and
Azoxy Groups; Patai, S., Ed.; Wiley: New York, 1975; Chapter 12.
(46) Nechaeva, O. N.; Pushkareva, Z. V. Zh. Obshch. Khim. 1958, 28, 2693.
Inorganic Chemistry, Vol. 44, No. 12, 2005 4331

Evans et al.
pounds51 and PhTeTePh indicated that the sulfur compound
differed mechanistically from the Se and Te reactions and
the formation of mercury products was an issue. The first
reduction waves for PhSeSePh and PhTeTePh were observed
at -0.335 and -0.345 V vs SCE, respectively. A further
complication is that elevated temperatures are needed for 3
and 6 to react.
In any case, the low reactivity of the (EPh)- ligands in
ligand-based reduction via the 2(EPh)-/PhEEPh couple
emphasizes the special nature of the (C5Me5)3Ln complexes
in which (C5Me5)-/(C5Me5) processes are facile. Clearly
sterically induced reduction with (C5Me5)- is a more effective
method to bring reductive chemistry to redox-inactive
lanthanides in bis(pentamethylcyclopentadienyl) complexes.
Conclusion
The use of both Sm2+ and Sm3+ starting materials has
allowed for the synthesis and characterization of new trivalent
samarocene benzene chalcogenolate complexes for the
evaluation of (EPh)- ligand-based reductions. In contrast to
the sterically crowded (C5Me5)3Sm, these benzene chalco-
genolates are not reactive reductants. Only at 65 °C with
easily reduced substrates do the (TePh)- complexes provide
reductive chemistry and formation of PhTeTePh.
Acknowledgment. We thank the National Science Foun-
dation for support of this research.
Supporting Information Available: X-ray diffraction details
(CIF) and X-ray data collection, structure solution, and refinement
of compounds 1-6 (PDF). This material is available free of charge
via the Internet at http://pubs.acs.org.
(51) Ludvik, J.: Nygard, B. Electrochim. Acta 1996, 41, 1661.
IC0502170
4332 Inorganic Chemistry, Vol. 44, No. 12, 2005