Activation of bis(guanidinate)lanthanide alkyl and aryl complexes on elemental sulfur: Synthesis and characterization of bis(guanidinate)lanthanide thiolates and disulfides

Article abstract of DOI:10.1021/ic100617n

The treatment of [(Me₃Si)₂NC(NCy)₂] ₂Ln(μ-Cl)₂Li(THF)₂ with 1 equiv of BnK (Bn = benzyl) in toluene affords [(Me₃Si)₂NC(NCy) ₂]₂LnBn [Ln = Er (1-

Full text of DOI:10.1021/ic100617n

Inorg. Chem. 2010, 49, 5715–5722 5715
DOI: 10.1021/ic100617n
Activation of Bis(guanidinate)lanthanide Alkyl and Aryl Complexes on Elemental
Sulfur: Synthesis and Characterization of Bis(guanidinate)lanthanide Thiolates
and Disulfides
Zhengxing Zhang,† Lixin Zhang,† Yanrong Li,† Longcheng Hong,† Zhenxia Chen,† and Xigeng Zhou*,†,‡
†Molecular Catalysis and Innovative Material Laboratory, Department of Chemistry, Fudan University,
Shanghai 200433, People’s Republic of China, and ‡State Key Laboratory of Organometallic Chemistry,
Shanghai 200032, People’s Republic of China
Received April 1, 2010
The treatment of [(Me3Si)2NC(NCy)2]2Ln(μ-Cl)2Li(THF)2 with 1 equiv of BnK (Bn = benzyl) in toluene affords [(Me3Si)2NC-
(NCy)2]2LnBn [Ln = Er (1-Er), Y (1-Y)] in good yields. Similarly, [(Me3Si)2NC(NCy)2]2LntBu [Ln = Er (2-Er), Yb (2-Yb)] are
obtained in satisfactory yields by the reaction of [(Me3Si)2NC(NCy)2]2Ln(μ-Cl)2Li(THF)2 with tBuLi in hexane. 1reacts with 1/8
equiv of S8 in toluene to form the sulfur insertion products {[(Me3Si)2NC(NCy)2]2Ln(μ-SBn)}2 [Ln = Er (3-Er), Y(3-Y)], while
the reaction of 2with elemental sulfur under the same conditions affords the oxidation products {[(Me3Si)2NC(NCy)2]2Ln}2(μ-
η2:η2-S2) [Ln = Er (4-Er), Yb (4-Yb)] regardless of the equivalency of S8 employed. Disulfide complexes 4 can also be
obtained by the reaction of 3with 1/4 equiv of S8. Furthermore, the treatment of [(Me3Si)2NC(NCy)2]2Ln(μ-Cl)2Li(THF)2 with 1
equiv of nBuLi in hexane, followed by reaction with 1/8 equiv of S8, affords the dinuclear thiolate complexes {[(Me3Si)2NC-
(NCy)2]2Ln(μ-SnBu)}2 [Ln = Y (5-Y), Er (5-Er)] in good yields. However, under the same conditions, [(Me3Si)2NC(NCy)2]2-
Yb(μ-Cl)2Li(THF)2 reacts with nBuLi and S8 to give {[(Me3Si)2NC(NCy)2]2Yb}2(μ-η2:η2-S2) (4-Yb) as the main metal-
containing product. [(Me3Si)2NC(NCy)2]2LnPh (generated in situ from [(Me3Si)2NC(NCy)2]2Ln(μ-Cl)2Li(THF)2 and PhLi)
also undergoes sulfur insertion, affording {[(Me3Si)2NC(NCy)2]2Ln(μ-SPh)}2 [Ln = Er (6-Er),Yb(6-Yb)] in good yields. All of
the complexes were characterized by spectroscopic and elemental analyses. The structures of all of these compounds, except
3-Y, are also determined by single-crystal X-ray diffraction analysis. Surprisingly, 3, 5, and 6 bear the same space group and
very similar cell parameters, despite the different thiolate ligands.
Introduction
Because stability and reactivity as well as biological and/or phy-
sical properties of molecules containing sulfur are crucial for
final application, significant effort continues to be given over to
the development of new complexes containing sulfur and
versatile strategies for their construction. Controlling the metal
coordination environment and properties through variation of
supporting ligation is a common theme in organometallic
Organometallic complexes bearing sulfur-containing ligands
have received considerable attention because of their involve-
ment in industrially relevant or enzyme-catalyzed processes.1,2
Moreover, they can also serve as intermediates in organic syn-
thesis or precursors for materials with interesting properties.3,4
*To whom correspondence should be addressed. E-mail: xgzhou@fudan.
edu.cn.
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r
2010 American Chemical Society
Published on Web 05/27/2010
pubs.acs.org/IC

5716 Inorganic Chemistry, Vol. 49, No. 12, 2010
Zhang et al.
chemistry. Considerable recent interest has focused on the
development of guanidinate anions as sterically and electro-
nically flexible ligands for the design of new organometallic
complexes.5 These compounds have been shown as excep-
tional catalysts in the transformation of organic functional-
ities and the polymerization of a variety of polar monomers
and olefins.6-8 Moreover, guanidinate complexes bear an
application potential as photoelectric materials9 and precur-
sors for ALD and MOCVD processes.10 Despite significant
recent advances in this area, the synthesis of thiolate com-
plexes containing the guanidinate coligand has no precedent.5
Furthermore, the basic chemistry of organolanthanides
containing thiolate and disulfide ligands remains relatively
little explored,11,12 in comparison to the impressive develop-
ment of their transition-metal counterparts. A major reason
may be attributed to the difficulties encountered in their
synthesis due to the intrinsic low affinity of these metals to the
soft sulfur-containing ligands. Recently, we have reported
that sulfur insertion into the Ln-C bond is a feasible route to
formation of the Ln-S bond.13 As part of a continuing effort
in our laboratory toward the development of new methods
for the synthesis of organolanthanide thiolate and disulfide
complexes, we became interested in comparing the reactivity
of complexes with alternative spectator ligand systems with
that of bis(cyclopentadienyl) and related systems and further
revealing the versatility of the sulfur insertion into Ln-C
(Ln=lanthanide metal or yttrium) bonds.
In this paper, we describe the synthesis of bis(guanidi-
nate)lanthanide(III) alkyl and aryl complexes and their reac-
tivity behavior toward elemental sulfur, which provide a
simple and efficient method for the preparation of unreported
bis(guanidinate)lanthanide thiolate and disulfide complexes
that would be difficult to prepare by classical metathetical
reactions.
Experimental Section
General Procedure. All operations involving air- and moist-
ure-sensitive compounds were carried out under an inert atmo-
sphere of purified nitrogen using standard Schlenk techniques.
Tetrahydrofuran (THF), toluene, and n-hexane were refluxed
and distilled over sodium benzophenone ketyl under nitrogen
immediately prior to use. [(Me3Si)2NC(NCy)2]2Ln(μ-Cl)2Li-
(THF)214 and BnK15 were prepared according to the literature
procedures. nBuLi, tBuLi, and PhLi were purchased from
Aldrich and used as received without further purification.
Elemental sulfur was treated under vacuum for 30 min imme-
diately prior to use. Elemental analysis for C, H, and N was
carried out on a Rapid CHN-O analyzer. IR spectra were ob-
tained on a Nicolet FT-IR 360 spectrometer with samples pre-
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1
pared as Nujol mulls. H NMR data were obtained on a Jeol
ECA-400 NMR spectrometer. The UV-visible spectra were
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Article
Inorganic Chemistry, Vol. 49, No. 12, 2010 5717
The extraction was concentrated to 3 mL, and cooling the
solution at -15 °C for several weeks yielded pink crystals of
1-Er. The crystals isolated were fast-washed with hexane and
then dried under a vacuum. Yield: 0.263 g (82%). Anal. Calcd
for C45H87N6Si4Er: C, 54.49; H, 8.84; N, 8.47. Found: C, 54.27;
H, 8.71; N, 8.63. IR (Nujol, cm-1): 2922 s, 2854 s, 1637 s, 1459 s,
1378 s, 1304 m, 1254 s, 1198 w, 1137 m, 933 s, 835 w, 723 s, 641 m.
Synthesis of [(Me3Si)2NC(NCy)2]2YBn (1-Y). Following the
procedure described above for 1-Er, the reaction of [(Me3Si)2-
NC(NCy)2]2Y(μ-Cl)2Li(THF)2 (0.605 g, 0.579 mmol) with BnK
(75.4 mg, 0.579 mmol) gave complex 1-Y as colorless crystals.
Yield: 0.386 g (73%). Anal. Calcd for C45H87N6Si4Y: C, 59.17; H,
9.60; N, 9.20. Found: C, 58.93; H, 9.51; N, 9.35. IR (Nujol, cm-1):
2925 s, 2859 s, 1631 s, 1454 s, 1377 s, 1304 m, 1251 s, 1197 w, 1134 m,
932 s, 831 w, 721 s, 640 m. 1H NMR (C6D6, 400 MHz, 25 °C): δ
7.28-7.25 (m, 2H, C6H5), 7.16-7.11 (m, 2H, C6H5), 7.07-7.00
(m, 1H, C6H5), 3.33-3.39 (m, 4H, NCH[Cy]), 2.11 (s, 2H,
CH2C6H5), 1.95-1.22 (m, 40H, CH2[Cy]), 0.30 (s, 36H, SiMe3).
Synthesis of [(Me3Si)2NC(NCy)2]2ErtBu (2-Er). To a hexane
(50 mL) solution of [(Me3Si)2NC(NCy)2]2Er(μ-Cl)2Li(THF)2
Synthesis of {[(Me3Si)2NC(NCy)2]2Er}2(μ-η2:η2-S2) 2THF
3
(4-Er 2THF). Method A. To a toluene (30 mL) solution of 2-Er
3
(0.351 g, 0.366 mmol) was added elemental sulfur S8 (23.5 mg,
0.0916 mmol) at 0 °C. After stirring for 36 h, the volatiles
were removed under a vacuum. The residue was dissolved in
10 mL of THF. Cooling the solution at -15 °C for several days
yielded yellow crystals of 4-Er 2THF. Yield: 0.305 g (83%).
3
Anal. Calcd for C84H176N12O2S2Si8Er2: C, 50.20; H, 8.83; N,
8.36. Found: C, 50.51; H, 8.98; N, 8.21. IR (Nujol, cm-1): 2904 s,
2853 s, 1635 s, 1458 s, 1377 s, 1250 m, 999 m, 935 s, 838 w, 727 s,
687 m, 641 m.
Method B. Following the procedure described above for 4-
Er 2THF (method A), the reaction of 3-Er (0.306 g, 0.149 mmol)
3
with elemental sulfur S8 (9.56 mg, 0.037 mmol), followed by crys-
tallization from THF, gave orange crystals of 4-Er 2THF. Yield:
3
0.258 g (86%).
Synthesis of {[(Me3Si)2NC(NCy)2]2Yb}2(μ-η2:η2-S2) 2THF
3
(4-Yb 2THF). Method A. Following the procedure described
above for 4-Er 2THF (method A), 2-Yb (0.468 g, 0.486 mmol)
3
3
reacted with elemental sulfur S8 (31.1 mg, 0.121 mmol) to give
orange crystals of 4-Yb 2THF. Yield: 0.402 g (82%). Anal.
Calcd for C84H176N12O2S2Si8Yb2: C, 49.91; H, 8.78; N, 8.32.
Found: C, 50.22; H, 8.95; N, 8.16. IR (Nujol, cm-1): 2905 s, 2855 s,
1637 s, 1456 s, 1377 s, 1252 m, 1132 w, 999 m, 938 s, 835 w, 722 s,
685 m, 641 m.
t
(1.704 g, 1.52 mmol) was added BuLi (0.89 mL of a 1.70 M
3
solution in pentane, 1.52 mmol) at -20 °C. The mixture was
allowed to slowly warm to room temperature and stirred for
12 h. The mixture was centrifuged, and the precipitate was fur-
ther extracted with hexane (50 mL ꢀ 2). The combined extraction
was concentrated to 10 mL. Cooling the solution at -15 °C for
several weeks yielded yellow crystals of 2-Er. Yield: 1.208 g (83%).
Anal. Calcd for C42H89N6Si4Er: C, 52.67; H, 9.37; N, 8.77. Found:
C, 52.41; H, 9.25; N, 8.89. IR (Nujol, cm-1): 2954 s, 2848 s, 1637 s,
1460 s, 1377 s, 1252 s, 1136 m, 1003 m, 943 s, 841 w, 641 m.
Synthesis of [(Me3Si)2NC(NCy)2]2YbtBu (2-Yb). Following
the procedure described above for 2-Er, the reaction of
[(Me3Si)2NC(NCy)2]2Yb(μ-Cl)2Li(THF)2 (4.455 g, 3.95 mmol)
with tBuLi (2.32 mL of a 1.70 M solution in pentane, 3.95 mmol)
in hexane gave 2-Yb as blue crystals. Yield: 3.083 g (81%). Anal.
Calcd for C42H89N6Si4Yb: C, 52.35; H, 9.31; N, 8.72. Found: C,
52.19; H, 9.16; N, 8.81. IR (Nujol, cm-1): 2950 s, 2845 s, 1637 s,
1462 s, 1377 s, 1250 s, 1136 m, 999 m, 943 s, 840 w, 641 m.
UV-vis (C6H5CH3, λmax): 386, 616 nm.
Synthesis of {[(Me3Si)2NC(NCy)2]2Er(μ-SBn)}2 (3-Er). Meth-
od A. To a toluene (30 mL) solution of 1-Er (0.401 g, 0.404 mmol)
was added elemental sulfur S8 (12.9 mg, 0.0505 mmol) at 0 °C. After
stirring for 24 h, the solution was concentrated to 3 mL and cooled
at -15 °C to afford pink crystals of 3-Er. Yield: 0.323 g (78%).
Anal. Calcd for C90H174N12S2Si8Er2: C, 52.79; H, 8.56; N, 8.21.
Found: C, 52.67; H, 8.49; N, 8.33. IR (Nujol, cm-1): 2940 s, 2848 s,
1634 s, 1455 s, 1378 s, 1252 s, 1178 w, 1132 m, 999 w, 933 s, 841 w,
727 s, 641 m.
Method B. To a toluene (30 mL) solution of [(Me3Si)2NC-
(NCy)2]2Yb(μ-Cl)2Li(THF)2 (0.675 g, 0.598 mmol) was added
LinBu (0.37 mL of a 1.60 M solution in hexane, 0.598 mmol) at
-30 °C. The solution became turbid immediately. Then, the
mixture was allowed to warm to room temperature and stirred
for 12 h. The solution changed from yellow to red slowly. Then,
to the solution was added elemental sulfur S8 (19.1 mg, 0.0748
mmol) at 0 °C, and the reaction mixture was stirred for 16 h. The
precipitate (LiCl) was removed by centrifugation, and removal
of the volatiles gave a yellow solid. It crystallized in THF to give
yellow crystals of 4-Yb 2THF. Yield: 0.429 g (71%).
3
Synthesis of {[(Me3Si)2NC(NCy)2]2Y(μ-SnBu)}2 (5-Y). To a
toluene (30 mL) solution of [(Me3Si)2NC(NCy)2]2Y(μ-Cl)2Li-
(THF)2 (0.751 g, 0.719 mmol) was added LinBu (0.45 mL of a
1.60 M solution in hexane, 0.719 mmol) at -30 °C. The mixture
was allowed to slowly warm to room temperature and stirred for
3 h. Then, to the solution was added elemental sulfur S8 (23.0
mg, 0.0899 mmol) at 0 °C, and the reaction mixture was stirred
for 16 h. The precipitate (LiCl) was removed by centrifugation,
and the solution was concentrated to ca. 10 mL and cooled at
-15 °C to afford colorless crystals of 5-Y. Yield: 0.525 g (80%).
Anal. Calcd for C84H178N12S2Si8Y2: C, 55.34; H, 9.84; N, 9.22.
Found: C, 55.26; H, 9.75; N, 9.45. IR (Nujol, cm-1): 2923 s, 2853
s, 1635 s, 1456 s, 1377 s, 1298 w, 1252 m, 1219 w, 1118 w, 1070 m,
956 s, 890 w, 840 m, 721 s, 693 m, 640 m. 1H NMR (C6D6, 400
MHz, 25 °C): δ 3.48-3.42 (m, 8H, NCH[Cy]), 2.76 (t, 4H,
SCH2), 2.05-1.38 (m, 88H, CH2[Cy and Me(CH2)2]), 1.05 (s,
6H, S(CH2)3Me), 0.39 (s, 72H, SiMe3).
Method B. To a toluene (30 mL) solution of [(Me3Si)2NC-
(NCy)2]2Er(μ-Cl)2Li(THF)2 (0.683 g, 0.608 mmol) was added
BnK (79.2 mg, 0.608 mmol) at -30 °C. The mixture was allowed
to slowly warm to room temperature and stirred for 3 h. Then, to
the solution was added elemental sulfur S8 (19.5 mg, 0.076
mmol) at 0 °C, and the reaction mixture was stirred for 16 h.
The volatiles were removed under vacuum, and the solid was
extracted with toluene (30 mL ꢀ 2). The extraction was concen-
trated to ca. 3 mL and cooled at -15 °C to afford pink crystals of
3-Er. Yield: 0.468 g (75%).
Synthesis of {[(Me3Si)2NC(NCy)2]2Er(μ-SnBu)}2 (5-Er). Fol-
lowing the procedure described above for 5-Y, the reaction of
[(Me3Si)2NC(NCy)2]2Er(μ-Cl)2Li(THF)2 (0.349 g, 0.311 mmol)
with LinBu (0.19 mL of a 1.60 M solution in hexane, 0.311
mmol) and subsequently with elemental sulfur S8 (9.95 mg,
0.0389 mmol) gave complex 5-Er as pink crystals. Yield: 0.224 g
(73%). Anal. Calcd for C84H178N12S2Si8Er2: C, 50.96; H, 9.06; N,
8.49. Found: C, 50.74; H, 8.91; N, 8.59. IR (Nujol, cm-1): 2930 s,
2858 s, 1637 s, 1455 s, 1378 s, 1301 m, 1240 s, 1173 w, 1127 m,
1070 w, 1009 s, 938 s, 835 w, 722 s, 641 m.
Synthesis of {[(Me3Si)2NC(NCy)2]2Y(μ-SBn)}2 (3-Y). Fol-
lowing the procedure described above for 3-Er (method A),
the reaction of 1-Y (0.322 g, 0.353 mmol) with elemental sulfur
S8 (11.3 mg, 0.044 mmol) gave 3-Y as colorless crystals. Yield:
0.237 g (71%). Anal. Calcd for C90H174N12S2Si8Y2: C, 57.16; H,
9.27; N, 8.89. Found: C, 56.88; H, 9.13; N, 9.02. IR (Nujol,
cm-1): 2947 s, 2845 s, 1631 s, 1458 s, 1378 s, 1249 s, 1171 w, 1130
m, 1002 w, 931 s, 840 w, 724 s, 640 m. 1H NMR (C6D6, 400 MHz,
25 °C): δ 7.35-7.30 (m, 4H, C6H5), 7.22-7.16 (m, 4H, C6H5),
7.13-7.08 (m, 2H, C6H5), 4.48 (s, 4H, SCH2), 3.42-3.37 (m, 8H,
NCH[Cy]), 2.03-1.31 (m, 80H, CH2[Cy]), 0.34 (s, 72H, SiMe3).
Synthesis of {[(Me3Si)2NC(NCy)2]2Yb(μ-SnBu)}2 (5-Yb). To
n
a toluene (15 mL) solution of BuSH (0.42 mL, 3.90 mmol) was
added LinBu (2.44 mL of a 1.60 M solution in hexane, 3.90 mmol) at
0 °C. The mixture was allowed to slowly warm to room tempera-
ture and stirred for 1 h. Then, to the solution was added a toluene
(60 mL) solution of [(Me3Si)2NC(NCy)2]2Yb(μ-Cl)2Li(THF)2

5718 Inorganic Chemistry, Vol. 49, No. 12, 2010
Zhang et al.
Scheme 1
(4.397 g, 3.90 mmol), and the reaction mixture was stirred at
80 °C for 72 h. The precipitate was removed by centrifugation.
Removal of the solvents gave a tar residue, which was dissolved
in 10 mL of hot hexane. Cooling the solution to room tempera-
ture gave a mixture containing primarily yellow crystals of the
starting material [(Me3Si)2NC(NCy)2]2Yb(μ-Cl)2Li(THF)2 and
a small amount of red crystals of 5-Yb (0.465 g, 12%). These
were separated by picking large crystals, and the pure com-
pounds were used for characterization purposes. Anal. Calcd
for C84H178N12S2Si8Yb2: C, 50.66; H, 9.01; N, 8.44. Found: C,
50.43; H, 8.93; N, 8.57. IR (Nujol, cm-1): 2918 w, 1633 m, 1603 m,
1547 m, 1469 s, 1373 s, 1306 m, 1250 s, 1219 w, 1118 w, 1070 m,
956 s, 890 w, 839 m, 767 m, 640 m.
Synthesis of {[(Me3Si)2NC(NCy)2]2Er(μ-SPh)}2 (6-Er). Fol-
lowing the procedure described above for 5-Y, the reaction of
[(Me3Si)2NC(NCy)2]2Er(μ-Cl)2Li(THF)2 (0.357 g, 0.318 mmol)
with PhLi (0.23 mL of a 1.38 M solution in butyl ether, 0.318
mmol) and subsequently with elemental sulfur S8 (10.2 mg,
0.0397 mmol) gave complex 6-Er as pink crystals. Yield: 0.283 g
(88%). Anal. Calcd for C88H170N12S2Si8Er2: C, 52.33; H, 8.48; N,
8.32. Found: C, 52.22; H, 8.35; N, 8.43. IR (Nujol, cm-1): 2930 s,
2858 s, 1634 s, 1460 s, 1378 s, 1301 m, 1250 s, 1178 w, 1132 m,
999 w, 938 s, 835 w, 722 s, 641 m.
Figure 1. ORTEP diagram of [(SiMe3)2NC(NCy)2]2LnBn [Ln = Er
(1-Er), Y (1-Y)] with the probability ellipsoids drawn at the 30% level.
˚
Hydrogen atoms are omitted for clarity. Selected bond lengths (A) and
angles (deg) for 1-Er: Er-N(1) 2.325(3), Er-N(2) 2.354(3), Er-C(1)
2.781(4), N(1)-C(1) 1.340(4), N(2)-C(1) 1.330(4), Er-C(39) 2.426(4),
Er-C(40) 2.840(5), Er-C(45) 2.975(5); N(1)-Er-N(2) 57.07(10),
N(2)-C(1)-N(1) 113.7(3), C(1)-N(1)-Er 94.9(2), C(1)-N(2)-Er
93.9(2), C(40)-C(39)-Er 90.6(3), C(39)-Er-C(40) 30.8(1). For 1-Y:
Y-N(1) 2.344(4), Y-N(2) 2.296(4), Y-C(1) 2.758(5), N(1)-C(1)
1.312(6), N(2)-C(1) 1.334(5), Y-C(39) 2.427(6), Y-C(40) 2.835(7),
Y-C(45) 2.922(7); N(1)-Y-N(2) 57.1(1), N(2)-C(1)-N(1) 113.9(5),
C(1)-N(1)-Y 93.6(3), C(1)-N(2)-Y 95.2(3), C(40)-C(39)-Y 90.9(4),
C(39)-Y-C(40) 30.2(2).
Synthesis of {[(Me3Si)2NC(NCy)2]2Yb(μ-SPh)}2 (6-Yb). Fol-
lowing the procedure describedabove for 5-Y, the treatment of
[(Me3Si)2NC(NCy)2]2Yb(μ-Cl)2Li(THF)2 (0.707 g, 0.626 mmol)
with PhLi (0.45 mL of a 1.38 M solution in butyl ether, 0.626
mmol), followed by reaction with elemental sulfur S8 (20.0 mg,
0.0783 mmol), gave complex 6-Yb as red crystals. Yield: 0.528 g
(83%). Anal. Calcd for C88H170N12S2Si8Yb2: C, 52.03; H, 8.44; N,
8.27. Found: C, 51.86; H, 8.31; N, 8.43. IR (Nujol, cm-1): 2912 s,
2854 s, 1637 s, 1458 s, 1378 s, 1253 s, 1186 w, 999 w, 938 s, 840 w,
718 s, 641 m.
in a monoclinic system and space group P21/n, while com-
plex 1-Y crystallizes in a triclinic system and space group P1.
In 1-Er, the benzyl ligand adopts an η3-coordination mode
(Figure 1),16 which is different from the observations in [HC-
(MeCNAr)2]La(η2-CH2Ph)2(THF)17a and (C5Me5)2Sm(η1-
CH2C6H5)(THF).17b The bond length of Er-C(40), 2.840(5)
X-ray Data Collection, Structure Solution, and Refinement
for 1-6. This information is available in the Supporting In-
formation.
Results and Discussion
Synthesis and Structure of Bis(guanidinate)lanthanide Ben-
zyl and tert-Butyl Complexes. The reaction of [(Me3Si)2NC-
(NCy)2]2Ln(μ-Cl)2Li(THF)2 with 1 equiv of BnK in toluene
afforded the benzyl complexes [(Me3Si)2NC(NCy)2]2LnBn
[Ln=Er (1-Er), Y (1-Y)] in good yields. Similarly, the treat-
ment of [(Me3Si)2NC(NCy)2]2Ln(μ-Cl)2Li(THF)2 with
tBuLi in hexane gave the bis(guanidinate)lanthanide t-butyl
complexes [(Me3Si)2NC(NCy)2]2LntBu [Ln=Er (2-Er), Yb
(2-Yb)] in satisfactory yields (Scheme 1).
˚
A, and the bond angle of C(40)-C(39)-Er, 90.6(3)°, suggest
a strong interaction between Er and C(40). The structural
parameters of 1-Y are very similar to those of complex 1-Er.
When the differences in metallic radii are subtracted,18 the
Ln-N and Ln-C distances of 1-Er and 1-Y are in good
agreement with each other. Complexes 2-Er and 2-Yb are
isostructural to [(Me3Si)2NC(NCy)2]2YtBu (Figure 2).19
The short distances of Er-C(42) and Yb-C(42),
Complexes 1 and 2 are air- and moisture-sensitive and are
readily soluble in THF and toluene and moderately soluble
in hexane. They are characterized by elemental analysis and
IR spectroscopy, which were in good agreement with the
proposed structure. The molecular structures of 1 and 2 were
further determined by X-ray diffraction. Both complexes 1
and 2 are mononuclear structures. Complex 1-Er crystallizes
(16) Ge, S. Z.; Meetsma, A.; Hessen, B. Organometallics 2008, 27, 5339.
(17) (a) Bambirra, S.; Perazzolo, F.; Boot, S. J.; Sciarone, T. J. J.; Meet-
sma, A.; Hessen, B. Organometallics 2008, 27, 704. (b) Evans, W. J.; Ulibarri,
T. A.; Ziller, J. W. Organometallics 1991, 10, 134.
(18) Shannon, R. D. Acta Crystallogr. 1976, A32, 751.
(19) Trifonov, A. A.; Lyubov, D. M.; Fedorova, E. A.; Fukin, G. K.;
Schumann, H.; Muhle, S.; Hummert, M.; Bochkarev, M. N. Eur. J. Inorg.
Chem. 2006, 747.

Article
Inorganic Chemistry, Vol. 49, No. 12, 2010 5719
˚
3.018(17) and 3.08(3) A, indicate an agostic interact-
ion between the lanthanide ion and one methyl of tert-
butyl.
ligands and two sulfur atoms of two bridging thiolate
anions. The bond lengths and angles within the guanidinate5a
and thiolate12 ligands are in the normal range (Table 1).
The Ln2S2 unit is planar.
Reaction of Bis(guanidinate)lanthanide Benzyl Com-
plexes with Elemental Sulfur. Bis(guanidinate)lanthanide
benzyl complexes [(Me3Si)2NC(NCy)2]2LnBn (1) reacted
with 1/8 equiv of S8 to form the dinuclear bis(guanidinate)-
lanthanide thiolate complexes {[(Me3Si)2NC(NCy)2]2Ln-
(μ-SBn)}2 [Ln=Er (3-Er), Y (3-Y)], as shown in Scheme 2.
The formation of 3 is interpreted as one sulfur atom inser-
tion into the Ln-C σ bond of 1.
In order to simplify manipulation of the sulfur insertion
process, we examined the reaction of the in situ generated
1-Er with elemental sulfur. It was found that the treat-
ment of [(Me3Si)2NC(NCy)2]2Er(μ-Cl)2Li(THF)2 and 1
equiv of BnK, followed by reaction with elemental sulfur,
could also give 3-Er without any obvious loss of yield.
Complex 3-Er was characterized by X-ray diffraction
analysis, and selected bond distances and angles are given
in Table 1. As shown in Figure 3, the X-ray structure of 3-
Er definitively proves that one sulfur atom is inserted into
an Er-C bond. 3-Er is a solvent-free dimeric structure,
with each Er atom bonded to two chelating η3-guanidinate
Reaction of Bis(guanidinate)lanthanide tert-Butyl Com-
plexes with Elemental Sulfur. To investigate the influence
of alkyl groups on the sulfur insertion, the reaction of the
corresponding bulky tert-butyl complexes 2 with elemental
sulfur was allowed to proceed under the same conditions. In
contrast to 1, the expected {[(Me3Si)2NC(NCy)2]2Ln(μ-
StBu)}2 were not isolated; instead, {[(Me3Si)2NC(NCy)2]2-
Ln}2(μ-η2:η2-S2) [Ln = Er (4-Er), Yb (4-Yb)] were obtained
in 35-41%, with the byproducts tBuStBu and tBuSStBu in a
1:4 ratio identified by gas chromatography/mass spectro-
metry (GC/MS). Employment of 2and S8 in a 4:1 ratio led to
the isolation of 4 in high yields (Scheme 3). The color change
from blue to orange within hours in the reaction of 2-Yb with
S8 indicated that sulfur insertion into the Ln-C(tBu) σ bond
was very slow probably because of the large steric hindrance
of the tBu group. Because the thiolate complex is sensitive to
S8 in solution as proven previously,13b,20 this should create an
opportunity for the competitive interaction of the resulting
thiolate intermediate with the remaining sulfur, leading to the
formation of disulfides as the main products.
0 °C, toluene
1
3-Er þ S8
4
4-Er
ð1Þ
We examine the reaction of 3-Er with elemental sulfur to
model the transformation of metal tert-butyl to metal disul-
fide via the formation of a metal thiolate intermediate. We
have found that the reaction of 3-Er with 1/4 equiv of S8 in
toluene formed 4-Er in 86% (eq 1). In contrast to the obser-
vation in the reaction of [Cp2Yb(μ-SEt)]2 with elemental
sulfur,13b wherein a ca. 4:3 mixture of [(Cp2Yb)2(μ3-S)-
(THF)]2 and [Cp2Yb(THF)]2(μ-η2:η2-S2) is obtained, no
metal sulfide was obtained in the present cases. It is clear
that replacement of cyclopentadienyl by the (Me3Si)2NC-
(NCy)2 group improves the chemoselectivity of the reaction
of lanthanide thiolates with elemental sulfur.
Complexes 4 were characterized by X-ray diffraction and
identified as dimers (Figure 4). In contrast to the observa-
tion that the interlinked bicyclic Ln2S2 fragment is generally
puckered with a significant dihedral angle between two
MS2 planes in other disulfide complexes, such as [Cp2Yb-
(THF)]2(μ-η2:η2-S2) (161.3°),13b (THF)6Yb4(μ-η2:η2-S2)4-
(μ4-S)(SC6F5)2 (average 96.2°),20a and (THF)6Yb4I2(μ-
η2:η2-S2)4(μ4-S) (average 95.2°),20b in 4-Er and 4-Yb, the
Ln2S2 unit is coplanar. In addition, for 4, all Ln-S bond
Figure 2. ORTEP diagram of [(SiMe3)2NC(NCy)2]2LntBu [Ln = Er (2-
Er), Yb (2-Yb)] with the probability ellipsoids drawn at the 30% level. Hy-
˚
drogen atoms are omitted for clarity. Selected bond lengths (A) and angles
(deg) for 2-Er: Er-N(1) 2.375(8), Er-N(2) 2.282(8), Er-C(1) 2.778(9),
N(1)-C(1) 1.326(11), N(2)-C(1) 1.328(12), Er-C(39) 2.387(12); N(1)-
Er-N(2) 56.7(3), N(2)-C(1)-N(1) 113.1(8), C(1)-N(1)-Er 92.9(6), C-
(1)-N(2)-Er 97.1(6). For 2-Yb: Yb-N(1) 2.282(5), Yb-N(2) 2.312(6),
Yb-C(1) 2.721(8), N(1)-C(1) 1.345(8), N(2)-C(1) 1.343(8), Yb-C(39)
2.509(16); N(1)-Yb-N(2) 58.4(2), N(2)-C(1)-N(1) 113.1(6), C(1)-N-
(1)-Yb 94.8(4), C(1)-N(2)-Yb 93.6(5).
Scheme 2

5720 Inorganic Chemistry, Vol. 49, No. 12, 2010
Zhang et al.
a
˚
Table 1. Bond Lengths [A] and Angles [deg] for Complexes 3, 5, and 6
bond distances/angles
3-Er
5-Y
5-Er
5-Yb
6-Er
6-Yb
Ln(1)-N(1)
Ln(1)-N(2)
Ln(1)-C(1)
Ln(1)-S(1)
Ln(2)-S(1)
S(1)-C(39)
N(1)-C(1)
N(2)-C(1)
2.388(5)
2.328(5)
2.807(6)
2.815(2)
2.832(2)
1.813(6)
1.310(7)
1.355(7)
2.356(6)
2.411(6)
2.844(6)
2.831(3)
2.804(3)
1.789(9)
1.340(8)
1.357(8)
2.350(4)
2.394(4)
2.793(5)
2.817(2)
2.801(2)
1.731(7)
1.325(7)
1.315(7)
2.309(8)
2.320(9)
2.741(11)
2.808(4)
2.784(4)
1.785(8)
1.322(10)
1.329(10)
2.372(10)
2.320(9)
2.773(13)
2.849(5)
2.798(5)
1.773(10)
1.318(14)
1.316(14)
2.320(7)
2.354(8)
2.770(11)
2.826(4)
2.804(4)
1.774(8)
1.341(13)
1.359(12)
Ln(1)-N(1)-C(1)
N(1)-C(1)-N(2)
C(1)-N(2)-Ln(1)
N(2)-Ln(1)-N(1)
Ln(1)-S(1)-Ln(2)
S(1)-Ln(2)-S(1A)
Ln(2)-S(1A)-Ln(1)
S(1A)-Ln(1)-S(1)
94.2(4)
113.6(5)
95.7(4)
56.44(16)
114.79(5)
65.43(7)
114.79(5)
64.98(7)
96.8(5)
94.8(3)
115.8(5)
93.1(3)
56.25(15
114.49(4)
65.72(6)
114.49(4)
65.29(6)
94.1(7)
93.0(8)
94.5(6)
113.1(8)
93.8(5)
56.3(2)
114.72(6)
65.63(9)
114.72(6)
64.93(9)
114.8(11)
93.4(7)
57.7(3)
115.22(6)
65.09(11)
115.22(6)
64.47(12)
115.1(11)
95.4(8)
56.5(3)
116.50(9)
64.14(15)
116.50(9)
62,86(16)
114.7(9)
92.5(6)
58.2(2)
116.68(8)
63.58(11)
116.68(8)
63.05(11)
a A: -x þ 1, -y þ 1, z.
Scheme 3
Figure 4. ORTEP diagram of {[(SiMe3)2NC(NCy)2]2Ln}2(μ-η2:η2-S2)
[Ln = Er (4-Er), Yb (4-Yb)] with the probability ellipsoids drawn at the
30% level. Hydrogen atoms are omitted for clarity. Selected bond lengths
Figure 3. ORTEP diagram of 3-Er with the probability ellipsoids drawn
at the 30% level. Hydrogen atoms are omitted for clarity.
distances are very similar, but for [Cp2Yb(THF)]2(μ-
η2:η2-S2), there are two distinctive metal-sulfur dis-
tances: one is in the normal range of an Yb3þ-S single
bond and another is between those expected for an
Yb3þ-S single bond and an Yb3þ r :S donor bond.
˚
(A) and angles (deg) for 4-Er: Er(1)-N(1) 2.303(8), Er(1)-N(2) 2.315(8),
Er(1)-C(1) 2.712(10), N(1)-C(1) 1.309(12), N(2)-C(1) 1.498(13), Er-
(1)-S(1) 2.688(5), Er(1)-S(2) 2.667(7), Er(2)-S(1) 2.692(7), Er(2)-S(2)
2.667(5), S(1)-S(2) 2.120(6); N(1)-Er(1)-N(2) 57.7(3), N(2)-C(1)-N-
(1) 115.9(8), C(1)-N(1)-Er(1) 93.2(6), C(1)-N(2)-Er(1) 92.3(5), Er-
(1)-S(1)-Er(2) 132.2(2), Er(1)-S(2)-Er(2) 134.4(2), S(1)-Er(1)-S(2)
46.6(1), S(1)-Er(2)-S(2) 46.6(1). For 4-Yb: Yb(1)-N(1) 2.306(6), Yb-
(1)-N(2) 2.299(6), Yb(1)-C(1) 2.721(8), N(1)-C(1) 1.290(10), N(2)-C-
(1) 1.320(10), Yb(1)-S(1) 2.671(3), Yb(1)-S(2) 2.652(3), Yb(2)-S(1)
2.670(3), Yb(2)-S(2) 2.645(3), S(1)-S(2) 2.114(3); N(1)-Yb(1)-N(2)
57.0(2), N(2)-C(1)-N(1) 114.7(7), C(1)-N(1)-Yb(1) 94.1(5), C(1)-N-
(2)-Yb(1) 93.6(5), Yb(1)-S(1)-Yb(2) 132.0(1), Yb(1)-S(2)-Yb(2)
134.2(1), S(1)-Yb(1)-S(2) 46.8(1), S(1)-Yb(2)-S(2) 46.9(1).
(20) (a) Melman, J. H.; Emge, T. J.; Brennan, J. G. Inorg. Chem. 2002, 41,
3528. (b) Melman, J. H.; Fitzgerald, M.; Freedman, D.; Emge, T. J.; Brennan, J. G.
J. Am. Chem. Soc. 1999, 121, 10247. (c) Freedman, D.; Emge, T. J.; Brennan,
J. G. Inorg. Chem. 1999, 38, 4400. (d) Freedman, D.; Melman, J.; Emge, T.;
Brennan, J. G. Inorg. Chem. 1998, 37, 4162. (e) Melman, J. H.; Emge, T. J.;
Brennan, J. G. Chem. Commun. 1997, 2269.

Article
Inorganic Chemistry, Vol. 49, No. 12, 2010 5721
Scheme 4
Scheme 5
The Yb-Sdistancesin4-Yb range from 2.645(3) to 2.671(3)
A, and the average value of 2.660(3) A is shorter than that in
˚
˚
2
2
˚
[Cp2Yb(THF)]2(μ-η :η -S2), average 2.725(5) A.
Reactions of Bis(guanidinate)lanthanide n-Butyl Com-
plexes with Elemental Sulfur. To extend the scope of bis-
(guanidinate)lanthanide alkyls, the reaction of the corre-
sponding n-butyl complexes (prepared in situ) with elemental
sulfur was further studied. As expected, the dinuclear thio-
latecomplexes{[(Me3Si)2NC(NCy)2]2Ln(μ-SnBu)}2 [Ln=Y
(5-Y), Er (5-Er)] were obtained in good yields when [(Me3-
Si)2NC(NCy)2]2Ln(μ-Cl)2Li(THF)2 were treated with 1
equiv of nBuLi and subsequently with 1/8 equiv of S8 under
the same conditions (Scheme 4). However, the reaction of
n
[(Me3Si)2NC(NCy)2]2Yb(μ-Cl)2Li(THF)2 with BuLi, fol-
lowed by treatment with S8 under the same conditions, gave
{[(Me3Si)2NC(NCy)2]2Yb}2(μ-η2:η2-S2) (4-Yb) as the main
metal-containing product. Presumably, the formation of 4-
Yb might result from the reduction of [(Me3Si)2NC(N-
Figure 5. ORTEP diagram of {[(SiMe3)2NC(NCy)2]2Ln(μ-SnBu)}2
[Ln = Y (5-Y), Er (5-Er), Yb (5-Yb)] with the probability ellipsoids drawn
at the 30% level. Hydrogen atoms are omitted for clarity.
n
Cy)2]2Yb(μ-Cl)2Li(THF)2 with BuLi21 and subsequent
oxidation of the insulting divalent ytterbium intermediate
with elemental sulfur.22
Moreover, only a mixture of 5-Yb and starting materials was
obtained in the reaction of [(Me3Si)2NC(NCy)2]2Yb(μ-
Cl)2Li(THF)2 and n-butyl thiolate lithium in toluene even
with prolonged heating (Scheme 5).
As shown in Figure 5, the geometry and stereochemistry
of 5are not particularly different from those observed in 3. In
particular, the bonding mode of the thiolates to metal ions is
quite similar. The bond lengths in 5 are essentially identical
with the distances in 3. The average Y-S bond length of
Given that lanthanide thiolate complexes are readily
synthesized by protolysis of organolanhanide complexes
with thiols or by the metathesis reaction of lanthanide
halides with alkali metal thiolates, the alternative routes to
{[(Me3Si)2NC(NCy)2]2Ln(μ-SnBu)}2 were tested. However,
the treatment of [(Me3Si)2NC(NCy)2]2LnN(SiMe3)2 and
[(Me3Si)2NC(NCy)2]2LnCp23 with thiols led to only the
recovery of starting materials, while the reaction of 1-Er or
2-Yb with nBuSH led to the formation of a complex mixture.
˚
2.818(3) A for 5-Y is longer than the values found in lantha-
n
13b
˚
nocene thiolates, such as [(C5H5)2Y(μ-S Bu)]2 (2.745 A)
(21) (a) Zhou, X. G.; Zhang, L. B.; Zhu, M.; Cai, R. F.; Weng, L. H.
Organometallics 2001, 20, 5700. (b) Evans, W. J.; Wayda, A. L.; Hunter, W. E.;
Atwood, J. L. J. Chem. Soc., Chem. Commun. 1981, 292.
(22) Evans, W. J.; Rabe, G. W.; Ziller, J. W.; Doedens, R. J. Inorg. Chem.
1994, 33, 2719.
t
n
and [(C5H4SiMe2 Bu)2Y(μ-S Bu)]2 (2.749 A).13a Moreover,
the Y-S-Y bond angle of 114.7(1)° in 5-Y is significantly
larger than the corresponding values observed in [(C5H4)2-
˚
Y(μ-SnBu)]2 (94.3°) and [(C5H4SiMe2 Bu)2Y(μ-SnBu)]2
t
(23) For the synthesis of [(SiMe3)2NC(NCy)2]2LnN(SiMe3)2 and
[(SiMe3)2NC(NCy)2]2LnCp, see the Supporting Information.
(95.3°), while the S-Y-S angle of 65.6(1)° is smaller than

5722 Inorganic Chemistry, Vol. 49, No. 12, 2010
Zhang et al.
Scheme 6
The bonding modes were proven by single-crystal
X-ray diffraction on complexes 6. Selected bond distances
and angles are listed in Table 1. Compounds 6-Er and 6-
Yb are isostructural (Figure 6). Complexes 6-Er and 6-Yb
have no unusual distances or angles. Surprisingly, 3, 5,
and 6 crystallize in the same space group and have very
similar cell parameters, despite the different thiolate
ligands. This phenomenon is very rare. Thus, we surmise
that the different reactivity behaviors and structural fea-
tures of these bis(guanidinate)lanthanide complexes are
largely a consequence of the less basicity and larger steric
hindrance of (Me3Si)2NC(NCy)2 compared to cyclopen-
tadienyls.
Conclusion
In summary, both sulfurinsertion into theLn-C bond and
selective oxidation of thiolate ligands of bis(guanidinate)lan-
thanide(III) complexes have been established that provide
a simple and efficient method for the preparation of unre-
ported bis(guanidinate)lanthanide thiolate and disulfide
complexes, respectively, that would be difficult to prepare
otherwise. The chemistry shown herein provides a new
opportunity to gain more insight into the reactivity of guani-
dinate lanthanide complexes and illustrates intriguing sup-
porting-ligand effects on the structure and/or properties of
lanthanide thiolate and disulfide complexes.
Figure 6. ORTEP diagram of {[(SiMe3)2NC(NCy)2]2Ln(μ-SPh)}2 [Ln=
Er (6-Er), Yb(6-Yb)] with the probability ellipsoids drawn at the 30% level.
Hydrogen atoms are omitted for clarity.
those found in the above yttrocene thiolate complexes.
These differences may be attributed to the larger steric
hindrance of the guanidinate ligand compared with C5H5
t
and C5H4SiMe2 Bu.
Reactions of Bis(guanidinate)lanthanide Phenyl Com-
plexes with Elemental Sulfur. To better understand the
influence of the alkyl ligands and to further develop the
insertion reaction, we present an extension of this reaction to
lanthanide aryl complexes. The treatment of [(Me3Si)2NC-
(NCy)2]2LnPh (generated in situ from [(Me3Si)2NC(N-
Acknowledgment. We thank the National Natural Science
Foundation of China, 973 program (2009CB825300),
NSF of Shanghai, the Research Fund for the Doctoral
Program of Higher Education of China, and Shanghai
Leading Academic Discipline Project (B108) for financial
support.
1
Cy)2]2Ln(μ-Cl)2Li(THF)2 and PhLi) with /8 equiv of S8
under the same conditions afforded the corresponding in-
sertion products {[(Me3Si)2NC(NCy)2]2Ln(μ-SPh)}2 [Ln=
Er (6-Er), Yb (6-Yb)] in good yields (Scheme 6). The forma-
tion of 6 represents the first insertion of sulfur into the
Ln-C(sp2) σ bond. This proves that organolanthanide aro-
matic thiolate complexes can also be synthesized by this
synthetic strategy.
Supporting Information Available: X-ray crystallographic
data in CIF format, experimental procedures, ORTEP diagrams
for S1-Ln and S2-Yb, and X-ray structure determination details
and crystal and data collection parameters for 1-6 and S1-2.
This material is available free of charge via the Internet at http://
pubs.acs.org.