Synthesis and solid-state structures of pyrazolylmethane complexes of the rare earths

Article abstract of DOI:10.1021/ic062370f

In this paper, we report the first examples of trispyrazolylmethane complexes of rare earths. Reaction of LnCl₃ with Tpm* (tris(3,5-dimethylpyrazolyl)methane) in THF or acetonitrile gives good yields of the [Ln(Tpm*)Cl₃] (Ln = Y, Ce, Nd, Sm, Gd, Yb). Tpm* adducts of the lanthanide triflates [Ln(Tpm*)(OTf)₃(THF)] (Ln = Y, Ho, Dy) may also be prepared. The X-ray crystal structures of [Y(Tpm*)Cl₃], [Sm(Tpm*)Cl₃(THF)], and [Ln(Tpm*)(OTf)₃(THF)] (Ln = Y, Ho) are reported. The halide/triflate complexes may be used to prepare the aryloxide complexes [Ln(Tpm*)(OAr^Me2)₃] (Ln = Y, Nd, Sm, Yb; At ^Me2 = C₆H₃-2,6-(CH₃)₂), which are fluxional in solution as a result of interactions between the Tpm* and the aryloxide groups. The structures of the Nd and Sm complexes have been determined. Finally, the reaction of [Nd(BH₄) ₃(THF)₃] with Tpm* in THF results in the displacement of two THF molecules to give [Nd(Tpm*)(BH₄) ₃(THF)]. Infrared spectra are consistent with tridentate borohydride coordination. The X-ray structures of these compounds indicate that the Tpm* ligand is less strongly bound than its anionic trispyrazolylborate analogues.

Full text of DOI:10.1021/ic062370f

Inorg. Chem. 2007, 46, 1856−1864
Synthesis and Solid-State Structures of Pyrazolylmethane Complexes of
the Rare Earths
Andrea Sella,*,† Sarah E. Brown,† Jonathan W. Steed,‡ and Derek A. Tocher†
Department of Chemistry, Christopher Ingold Laboratories, UniVersity College London,
20 Gordon Street, London, WC1H 0AJ United Kingdom, and Department of Chemistry,
UniVersity Science Laboratories, South Road, Durham, DH1 3LE United Kingdom
Received December 12, 2006
In this paper, we report the first examples of trispyrazolylmethane complexes of rare earths. Reaction of LnCl3 with
Tpm* (tris(3,5-dimethylpyrazolyl)methane) in THF or acetonitrile gives good yields of the [Ln(Tpm*)Cl3] (Ln Y,
Ce, Nd, Sm, Gd, Yb). Tpm* adducts of the lanthanide triflates [Ln(Tpm*)(OTf)3(THF)] (Ln Y, Ho, Dy) may also
be prepared. The X-ray crystal structures of [Y(Tpm*)Cl3], [Sm(Tpm*)Cl3(THF)], and [Ln(Tpm*)(OTf)3(THF)] (Ln
Y, Ho) are reported. The halide/triflate complexes may be used to prepare the aryloxide complexes [Ln(Tpm*)-
(OArMe2)3] (Ln Y, Nd, Sm, Yb; ArMe2
C6H3-2,6-(CH3)2), which are fluxional in solution as a result of interactions
)
)
)
)
)
between the Tpm* and the aryloxide groups. The structures of the Nd and Sm complexes have been determined.
Finally, the reaction of [Nd(BH4)3(THF)3] with Tpm* in THF results in the displacement of two THF molecules to
give [Nd(Tpm*)(BH4)3(THF)]. Infrared spectra are consistent with tridentate borohydride coordination. The X-ray
structures of these compounds indicate that the Tpm* ligand is less strongly bound than its anionic trispyrazolylborate
analogues.
Introduction
protection to the metal center. By adjusting the steric demand
of the substituents in the 3-position of the pyrazolyl groups,
it has proved possible to isolate well-behaved lanthanide
complexes which have proved remarkably robust for ligand
redistribution. Of particular interest are half-sandwich com-
plexes in which a single ancillary group controls the
coordination sphere of the metal center. A series of remark-
able divalent complexes have been reported in recent years
by Takats, most notably hydrides, several hydrocarbyls, and
related derivatives.8-10 Curiously, trivalent complexes have
proved more difficult to prepare, and we are aware of only
two examples of half-sandwich Tp/hydrocarbyl complexes.11-13
The molecular chemistry of the rare earths has seen major
advances in the past 10-15 years.1-3 The availability of ever-
bulkier ancillary ligands has made possible the stabilization
of unusual oxidation states, surprising coordination environ-
ments, and unexpected reactivity.4 Although cyclopentadi-
enyl-based (Cp) ligands have largely dominated this area, a
number of alternative approaches have been used.5,6 The
anionic trispyrazolylborate (Tp) ligands have been success-
fully used as ancillaries for the 4f block.7 By contrast, with
the effectively planar Cp ligands, the tripodal pyrazolylborate
ligands have the advantage of providing greater lateral
The neutral analogues of Tp ligands, the trispyrazolyl-
methane (Tpm), have not received the same attention as the
borates, primarily because of the absence of efficient
* To whom correspondence should be addressed. E-mail: a.sella@ucl.ac.uk.
† University College London.
‡ University Science Laboratories, Durham.
(1) Kaltsoyannis, N.; Scott, P. The f-Elements; Oxford University Press:
Oxford, U.K., 1999.
(2) Aspinall, H. C. Chemistry of the f-elements; Taylor & Francis: London,
2001.
(3) Cotton, S. Lanthanide and Actinide Chemistry; Wiley-VCH: Wein-
heim, Germany, 2006.
(8) Hasinoff, L.; Takats, J.; Zhang, X. W.; Bond, P. H.; Rogers, R. D. J.
Am. Chem. Soc. 1994, 116, 8833-8834.
(9) Ferrence, G. M.; McDonald, R.; Takats, J. Angew. Chem., Int. Ed.
1999, 38, 2233-2237.
(10) Ferrence, G. M.; Takats, J. J. Organomet. Chem. 2002, 647, 84-93.
(11) Long, D. P.; Bianconi, P. A. J. Am. Chem. Soc. 1996, 118, 12453-
12454.
(4) Evans, W. J. J. Organomet. Chem. 2002, 647, 2-11.
(5) Edelmann, F. T.; Freckmann, D. M. M.; Schumann, H. Chem. ReV.
2002, 102, 1851-1896.
(12) Takats, J. Personal communication.
(6) Schumann, H.; Meese-Marktscheffel, J. A.; Esser, L. Chem. ReV. 1995,
95, 865-986.
(13) Blackwell, J. A.; Lehr, C.; Sun, Y.; Piers, W. E.; Pearce-Batchilder,
S. D.; Zaworotko, M. J.; Young, V. G. J. Can. J. Chem. 1997, 75,
702-711.
(7) Marques, N.; Sella, A.; Takats, J. Chem. ReV. 2002, 102, 2137-2160.
1856 Inorganic Chemistry, Vol. 46, No. 5, 2007
10.1021/ic062370f CCC: $37.00
© 2007 American Chemical Society
Published on Web 01/24/2007

Pyrazolylmethane Complexes of the Rare Earths
[Y(Tpm*)Cl3], 1a. Tpm* (500 mg, 1.6 mmol) was dissolved in
MeCN (20 mL) in a Schlenk flask to produce a pale yellow solution.
This was then added gradually, with stirring, to a separate flask
containing a clear, colorless solution of YCl3 (330 mg, 1.6 mmol)
in MeCN (50 mL). A white precipitate formed immediately. Stirring
was continued for 1 h, and the solid was isolated by filtration and
dried under dynamic vacuum overnight to give [Y(Tpm*)Cl3] as a
white, sparingly soluble powder. Yield: 660 mg (52%). Anal. Calcd
for C16H22N6Cl3Y: C, 38.9; H, 4.5; N, 17.0. Found: C, 38.6; H,
4.3; N, 17.5. IR (KBr pellet, cm-1): 3129 m, 3095 w, 2924 m,
1560 s, 1458 s, 1414 s, 1379 s, 1304 s, 1261 s, 1155 w, 1109 m,
1040 s, 981 m, 905 m, 861 s, 795 m, 705, 633 w, 482 m. 1H NMR
(CD3CN, 400 MHz, 293 K): δ 7.90 (s, 1H, C-H), 6.08 (s, 3H,
Tpm 4-CH), 2.64 (s, 9H, 5-Me), 2.52 (3-Me). Large colorless
crystals suitable for X-ray diffraction were obtained by slow
diffusion of solutions of YCl3 and Tpm* in MeCN in a sealed tube.
[Ce(Tpm*)Cl3], 1b. CeCl3 (125 mg, 0.51 mmol) was stirred in
THF (80 mL) to give a beige suspension. Upon addition of Tpm*
(150 mg, 0.51 mmol), the solid dissolved to give a slightly turbid,
beige solution. After stirring for 2 h, the solution was filtered. The
volume of the filtrate was reduced to 5 mL, and hexane was added.
Upon cooling to -20 °C, an off-white, semicrystalline material
precipitated. Drying under vacuum at 50 °C yielded [Ce(Tpm*)-
Cl3]. Yield: 120 mg (34%). Anal. Calcd for C16H22N6Cl3Ce: C,
35.3; H, 4.1; N, 15.4. Found: C, 35.7; H, 4.3; N, 15.0. IR (KBr
pellet, cm-1): 3141 w, 3086 w, 2970 m, 2890 m, 1564 s 1456 s,
1415 m, 1379 m, 1306 s, 1268 s, 1037 s, 976 w, 904 m, 858 s, 823
synthetic protocols. This changed a few years ago when
Reger reported a high-yielding route for the synthesis of
several Tpm compounds, and this has led to a steady increase
in their use.14 Tpm complexes have been applied both to
transition metals and to the labile s-15-17 and p-blocks18,19
where direct comparisons with Tp chemistry have been made.
The area has recently been reviewed.20,21 While our work
was in progress, we became aware of Mountford’s synthesis
of some halides, aryloxides, and hydrocarbyl complexes of
scandium and yttrium.22 In this paper, we report the syntheses
and characterization of a number of simple derivatives of
tris(3,5-dimethylpyrazolyl)methane (Tpm*) of yttrium and
the lanthanides which complement and extend Mountford’s
work.
Experimental Section
General Procedures and Instrumentation. All reactions were
carried out under nitrogen under anhydrous conditions using
standard Schlenk and glove box techniques. Solvents were distilled
at atmospheric pressure either from alkali metal/benzophenone ketyl
(ethers and hydrocarbons) or calcium hydride (dichloromethane and
acetonitrile) or by passage over activated alumina columns23 and
stored under nitrogen in Young’s valve ampoules over sodium
mirrors (except dichloromethane and acetonitrile, which were stored
over activated molecular sieves). Lanthanide halides were prepared
from the oxide or hydrated chloride by the NH4Cl method.24
Lanthanide triflates were prepared by reaction of a slight excess of
the appropriate oxide with hot 1 M triflic acid. After filtration, the
water was removed under reduced pressure, and the salt was
dehydrated under dynamic vacuum at 150 °C.25 The (3,5-dimeth-
ylpyrazolyl)methane (Tpm*) was prepared by the method of
Reger;14 sodium-2,6-dimethylphenoxide was prepared by reaction
of 2,6-dimethylphenol with an excess of sodium hydride in THF.
1H and 13C-{1H} NMR spectra were recorded on Bruker Avance
500, VXR-400, and AMX-300 spectrometers in Wilmad NMR tubes
equipped with Young’s valves. Spectra were referenced internally
to residual protio solvent (1H) or solvent (13C) resonances and are
reported relative to tetramethylsilane. 11B spectra were referenced
externally to BF3‚Et2O. FT-IR spectra were recorded on a Nicolet
205 FT-IR spectrometer as KBr pellets. CHN elemental analyses
were carried out by Ms. Gillian Maxwell of the UCL Chemistry
Analytical Services section.
1
m, 709 sh, 702 sh, 481 w. H NMR (CD2Cl2, 400 MHz, 293 K):
δ 1.93 (s, 9H, 5-Me), 2.3 (v br s, 9H, 3-Me, fwhh ) 140 Hz), 4.21
(s, 3H, Tpm 4-CH), 6.40 (s, 1H, C-H).
[Nd(Tpm*)Cl3], 1c. NdCl3 (400 mg, 1.6 mmol) was stirred in
THF (10 mL) to give a pale-blue suspension. Upon addition of
Tpm* (480 mg, 1.6 mmol), the solid partially dissolved to give a
pale-blue suspension. After stirring for 2 h, the solution was filtered.
The volume of the filtrate was reduced to 5 mL, and hexane was
added. Upon cooling to -20 °C, a light-blue, semicrystalline
material precipitated. Decanting off the solid and drying under
reduced pressure yielded [Nd(Tpm*)Cl3(THF)], which desolvated
upon heating to give [Nd(Tpm*)Cl3]. Yield: 480 mg (54%). Anal.
Calcd for C16H22N6Cl3Nd: C, 35.0; H, 4.0; N, 15.3. Found: C,
35.3; H, 4.3; N, 14.9. IR (KBr pellet, cm-1): 3140 w, 3086 w,
2970 m, 2890 m, 1564 sh, 1558 sh, 1458 s, 1415 m, 1380 m, 1307
s, 1262 s, 1031 s, 904 m, 858 s, 823 m, 710 sh, 701 sh, 481 w. 1H
NMR (CD3CN, 400 MHz, 293 K): δ 1.94 (s, 9H, 3-Me), 2.34 (s,
1H, Tpm C-H), 3.09 (s, 9H, 5-Me), 7.36 (s, 3H, Tpm 4-CH).
[Sm(Tpm*)Cl3], 1d. The reaction was carried out as for 1c using
SmCl3 (860 mg, 3.3 mmol) in THF to afford a white powder which
desolvated under vacuum. Yield: 960 mg (52%). Anal. Calcd for
C16H22N6Cl3Sm: C, 34.6; H, 4.0; N, 15.1. Found: C, 34.4; H, 4.0;
N, 14.9. IR (KBr pellet, cm-1): 3138 w, 3084 w, 2970 m, 2890
m, 1562 sh, 1558 sh, 1460 s, 1416 m, 1380 m, 1304 s, 1262 s,
1038 s, 980 w, 906 m, 860 s, 821 m, 721 m, 708 sh, 636 m, 482
(14) Reger, D. L.; Grattan, T. C.; Brown, K. J.; Little, C. A.; Lamba, J. J.
S.; Rheingold, A. L.; Sommer, R. D. J. Organomet. Chem. 2000, 607,
120-128.
(15) Reger, D. L.; Collins, J. E.; Matthews, M. A.; Rheingold, A. L.; Liable-
Sands, L. M.; Guzei, I. A. Inorg. Chem. 1997, 36, 6266-6269.
(16) Reger, D. L.; Little, C. A.; Smith, M. D.; Rheingold, A. L.; Liable-
Sands, L. M.; Yap, G. P. A.; Guzei, I. A. Inorg. Chem. 2002, 41,
19-27.
(17) Reger, D. L.; Collins, J. E.; Flomer, W. A.; Rheingold, A. L.; Incarvito,
C.; Guzei, L. A. Polyhedron 2001, 20, 2491-2494.
(18) Reger, D. L.; Collins, J. E.; Rheingold, A. L.; Liable-Sands, L. M.;
Yap, G. P. A. Inorg. Chem. 1997, 36, 345-351.
(19) Reger, D. L.; Collins, J. E.; Layland, R.; Adams, R. D. Inorg. Chem.
1996, 35, 1372-1376.
(20) Reger, D. L. Comments Inorg. Chem. 1999, 21, 1-28.
(21) Bigmore, H. R.; Lawrence, S. C.; Mountford, P.; Tredget, C. S. Dalton
Trans. 2005, 635-651.
1
w. H NMR (CD3CN, 400 MHz, 293 K): δ 1.67 (s, 9H, 3-Me),
1.80 (m, 4H, THF), 3.62 (m, 4H, THF), 2.76 (s, 9H, 5-Me), 6.00
(s, 3H, Tpm 4-CH), 8.59 (s, 1H, Tpm C-H). Crystals of [Sm-
(Tpm*)Cl3(THF)]‚THF, 1d-a, were obtained by layering SmCl3 and
Tpm* solutions in THF in sealed glass tube.
(22) Tredget, C. S.; Lawrence, S. C.; Ward, B. D.; Howe, R. G.; Cowley,
A. R.; Mountford, P. Organometallics 2005, 24, 3136-3148.
(23) Grubbs, R. H. Organometallics 1996, 15, 1518-1520.
(24) Meyer, G. In Syntheses of Lanthanide and Actinide Compounds;
Meyer, G., Morss, L. R., Eds.; Kluwer: Dordrecht, The Netherlands,
1991.
[Gd(Tpm*)Cl3], 1e. The reaction was carried out in THF
analogous to the procedure for 1a using GdCl3 (33 mg, 0.13 mmol)
and Tpm* (38 mg, 0.13 mmol) to afford [Gd(Tpm*)Cl3(THF)] as
a white, microcrystalline powder which desolvated upon removal
of solvent under vacuum. Yield: 52 mg (74%). Anal. Calcd for
C16H2N6Cl3Gd: C, 34.2; H, 3.9; N, 15.0. Found: C, 34.7; H, 4.3;
(25) Liu, S. Y.; Maunder, G. H.; Sella, A.; Stevenson, M.; Tocher, D. A.
Inorg. Chem. 1996, 35, 76-81.
Inorganic Chemistry, Vol. 46, No. 5, 2007 1857

Sella et al.
N, 14.6. IR (KBr pellet, cm-1): 3138 w, 3098 w, 2970 m, 2919
m, 2874 m, 1564 s, 1458 s, 1415 m, 1381 m, 1305 s, 1266 s, 1108
w, 1039 s, 980 w, 906 m, 861 s, 82 m, 806 m, 794 m, 707 sh, 482
w. The compound was NMR silent.
1038 m, 979 w, 906 w, 859 m, 800 w, 759 m, 746 m, 705 s, 531.
1H NMR (CD2Cl2, 300 MHz, 293 K): δ 1.95 (s, 18H, Me-OAr),
2.06 (s, 9H, 3- or 5-Me), 2.58 (s, 9H, 3- or 5-Me), 5.94 (s, 3H,
Tpm 4-CH), 6.31 (t, J ) 7.2 Hz, 3H, OAr p-H), 6.78 (d, J ) 7.2
Hz, 6H, OAr m-H), 8.05 (s, 1H, Tpm C-H). 13C{1H} NMR (CD2-
Cl2, 75.44 MHz, 293 K): δ 11.48 (OArMe), 13.28 (3- or 5-Me),
17.59 (3- or 5-Me), 68.75 (Tpm CH), 107.94 (Tpm 4-CH), 114.54
(p-OAr), 126.60 (2-C-OAr), 127.76 (m-OAr), 140.00 (5-C Tpm*),
155.12 (3-C Tpm*), 162.89 (d, JYC ) 5.4 Hz, ipso-OAr).
[Yb(Tpm*)Cl3], 1f. The reaction was carried out in THF
analogous to the procedure describe for 1a using YbCl3 (94 mg,
3.4 mmol) and Tpm* (100 mg, 3.4 mmol) to afford Yb(Tpm*)Cl3
as a cream-colored, THF-insoluble powder. Yield: 124 mg (64%).
Anal. Calcd for C16H22N6Cl3Yb: C, 33.3; H, 3.8; N, 14.5. Found:
C, 33.6; H, 3.7; N, 14.2. IR (KBr pellet, cm-1): 3132 m, 3090 w,
2970 w, 2920 m, 1561 s, 1456 s, 1411 s, 1380 s, 1301 s, 1259 s,
1155 w, 1109 m, 1041 s, 980 m, 905 m, 859 s, 795 m, 704 m, 635
w, 483 m. Insolubility precluded the recording of 1H NMR spectra.
[Y(Tpm*)(OTf)3‚THF], 2a. Tpm* (300 mg, 1.0 mmol) in THF
was added dropwise to a slightly turbid solution of Y(OTf)3 (540
mg, 1.0 mmol) in THF. A clear, pale-yellow solution was produced,
and stirring was continued overnight. The solution was filtered,
and the volume of THF was decreased under reduced pressure until
the product began to precipitate from solution. Precipitated product
was redissolved by warming the flask. The flask was then placed
inside a dewar and placed in a freezer at -20 °C overnight for
slow cooling. [Y(Tpm*)(OTf)3(THF)] formed as clear, flat crystals.
Yield: 370 mg (41%). Anal. Calcd for C23H30N6O10S3F9Y: C, 30.5;
H, 3.3; N, 9.3. Found: C, 29.9; H, 3.2; N, 9.5. IR (KBr pellet,
cm-1): 3150 w, 2998 m, 2938 m, 1570 m, 1460 m, 1424 m, 1328
s, 1208 s br, 1018 s, 911 w, 860 m, 804 w, 707 m, 633 s, 586 w,
512 m. 1H NMR (400 MHz, CD3CN, 293 K): δ 1.84 (m, 4H, THF),
2.43 (s, 9H, 3- or 5-Me), 2.59 (s, 9H, 3- or 5-Me), 3.67 (m, 4H,
THF), 6.16 (s, 3H, Tpm 4-CH), 7.96 (s, 1H, Tpm C-H).
[Ho(Tpm*)(OTf)3(THF)], 2b. The preparation of 2b was carried
out analogous to that of 2a using Tpm* (200 mg, 0.67 mmol) and
Ho(OTf)3 (410 mg, 0.67 mmol) in THF. [Ho(Tpm*)(OTf)3(THF)]
formed as clear crystals which desolvated upon removal of solvent.
Yield: 290 mg (45%). Anal. Calcd for C23H30N6O10S3F9Ho: C,
28.2; H, 3.1; N, 8.6. Found: C, 27.6; H, 3.1; N, 8.4. IR (KBr pellet,
cm-1): 3152 w, 2994 m, 2932 m, 1570 m, 1462 m, 1422 m, 1390
w, 1337 s, 1208 s br, 1021 s, 909 w, 861 m, 802 w, 707 m, 636 s,
586 w, 512 m. The compound was NMR silent.
[Dy(Tpm*)(OTf)3.THF], 2c. The preparation of 2c was carried
out analogous to that of 2a using Tpm* (130 mg, 0.44 mmol) and
Dy(OTf)3 (270 mg, 0.44 mmol). [Dy(Tpm*)(OTf)3‚THF] was
formed as flat, colorless crystals. Yield: 180 mg (42%). Anal. Calcd
for C23H30N6O10S3F9Dy: C, 28.2; H, 3.1; N, 8.6. Found: C, 27.8;
H, 3.0; N, 8.5. IR (KBr pellet, cm-1): 3145 w, 2996 m, 2930 m,
1569 m 1465 m, 1419 m, 1391 w, 1337 s, 1206 s br, 1187 s, 1019
s, 909 w, 861 m, 802 w, 767 w, 705 m, 636 s, 586 w, 511 m. The
compound was NMR silent.
[Nd(Tpm*)(OArMe2)3], 3b. The reaction was carried out analo-
gous to the procedure for 3a using NdCl3 (250 mg, 0.100 mmol),
Tpm* (290 mg, 0.100 mmol), and HOArMe2 (360 mg, 0.300 mmol).
After filtration, a light-greenish solution resulted from which light-
blue, block-like crystals of Nd(Tpm*)(OArMe2
) were obtained
3
which desolvated upon removal of solvent. Yield: 520 mg (69%).
Anal. Calcd for C40H49N6O3Nd: C, 59.6; H, 6.1; N, 10.4. Found:
C, 59.6; H, 6.2; N, 10.3. IR (KBr pellet, cm-1): 3135 w, 3108 w,
2920 s, 2855 s, 1600 w, 1563 m, 1475 s br, 1429 s, 1380 m, 1300
s, 1275 s, 1236 m, 1159 m, 1088 w, 1033 m, 978 w, 857 m, 820
1
s, 794 m sh, 721 m, 512 s. H NMR (CD2Cl2, 400 MHz, 204 K):
δ 0.34 (br s, 18H, Me-OAr), 0.49 (s, 9H, 5-Me), 2.62 (s, 1H,
Tpm C-H), 4.65 (br s, 9H, 3-Me), 6.72 (s, 3H, Tpm 4-CH), 6.91
(br t, J ) 5.1 Hz, 3H, p-H), 8.50 (br, 6H, m-H). 13C{1H} NMR
(CD2Cl2, 100.58 MHz, 293 K): δ 8.03 (3- or 5-Me), 11.76 (3- or
5-Me), 15.55 (OArMe), 64.55 (Tpm CH), 119.27 (Tpm 4-CH),
122.05 (p-OAr), 128.17 (m-OAr), 141.38 (br, 2-OAr), 146.08
(Tpm* qt), 151.65 (Tpm* qt), 210.95 (br, ipso-OAr).
[Sm(Tpm*)(OArMe2)3], 3c. The preparation of 3c was carried
out analogous to that of 3a using SmCl3 (150 mg, 0.57 mol), Tpm*
(170 mg, 0.57 mmol), and NaOArMe2 (250 mg, 1.88 mol). The dark-
orange solution of Sm(Tpm*)(OArMe2
) in THF was filtered to
3
remove the NaCl, and the volume of THF was reduced under
vacuum. The flask was placed in a Dewar flask and put in the
freezer for crystallization. After 2 days, large pale-orange crystals
of Sm(Tpm*)(OArMe2)3 had formed. Yield: 310 g (65%). Anal.
Calcd for C40H49N6O3Sm: C, 59.0; H, 6.1; N, 10.3. Found: C,
59.5; H, 6.5; N, 10.0. IR (KBr pellet, cm-1): 3140 w, 3105 w,
2923 s, 2852 s, 1606 w, 1568 m, 1475 s br, 1423 s, 1380 m, 1309
s, 1260 s, 1159 m, 1109 w, 1036 m, 956 w, 860 m, 818 s, 796 m
sh, 707 m, 509 s. 1H NMR (CD2Cl2, 300 MHz, 293 K): δ 1.22 (s,
18H, Me-OAr), 1.62 (s, 9H, 3-Me), 2.18 (s, 9H, 5-Me), 4.91 (s,
1H, Tpm C-H), 5.23 (s, 3H, p-H), 5.80 (s, 3H, Tpm 4-CH), 6.81
(s, 6H, m-H).
[Sm(Tpm*)(OArMe3)3], 3d. The preparation of 3d was carried
out analogous to that of 3c from SmCl3 (317 mg, 1.23 mmol).
Yield: 508 mg (48%). Anal. Calcd for C43H55N6O3Sm: C, 60.4;
H, 6.5; N, 9.8. Found: C, 60.0; H, 6.8; N, 9.6. IR (KBr pellet,
cm-1): 3135 w, 3112 m, 2925 s, 2892 s, 2848 s, 1610 w, 1562 m,
1475 s br, 1428 s, 1375 m, 1340 m, 1310 s, 1258 m, 1158 s, 1112
w, 1040 m, 960 w, 860 m, 835 w, 816 s, 795 m, 705 m, 500 s. 1H
NMR (CD2Cl2, 300 MHz, 293 K): δ 1.11 (s, 18H, o-Me), 1.65 (s,
9H, 3-Me), 2.23 (s, 9H, p-CH3), 4.93 (s, 9H, 5-Me), 4.97 (s, 1H,
Tpm C-H), 5.77 (s, 3H, Tpm 4-CH), 6.78 (s, 6H, m-H). 13C{1H}
NMR (CD2Cl2, 75.44 MHz, 293 K): δ 10.18 (3-Me), 17.62 (OAr-
o-Me), 17.72 (5-Me), 20.98 (OAr-p-Me), 62.10 (Tpm CH), 106.13
(Tpm 4-CH), 122.83 (p-OAr), 125.35 (o-OAr), 128.97 (m-OAr),
137.96 (Tpm* qt), 156.23 (Tpm* qt), 161.26 (br, ipso-OAr).
[Yb(Tpm*)(OArMe2)3], 3e. The preparation of 3e was carried
out analogous to that of 3a using YbCl3 (187 mg, 0.67 mmol),
Tpm* (200 mg, 0.67 mmol), and NaOArMe2 (245 mg, 2.0 mmol).
The pale-yellow solution yielded a mass of small, shiny crystals
upon cooling to -20 °C. These desolvated upon removal of solvent
and pumping to dryness to give a cream-colored powder. Yield:
[Y(Tpm*)(OArMe2)3], 3a. A turbid, white solution of YCl3 (150
mg, 0.77 mmol) in THF was stirred in a Schlenk flask. To this
was added dropwise a pale-yellow solution of Tpm* (230 mg, 0.77
mmol) to afford a yellow solution and a white precipitate. After
stirring for 2 h, NaOArMe2 (330 mg, 2.3 mmol) in THF (10 mL)
was added dropwise to the suspension with stirring. The white solid
dissolved during the addition of the aryloxide, and upon stirring
for 2-3 h further, a white precipitate of NaCl formed. The
suspension was allowed to settle overnight, and the salt was
removed by filtration. The volume of the filtrate was reduced to
10 mL, and the solution was placed in a freezer at -25 °C. After
ca. 48 h, [Y(Tpm*)(OArMe2)3] had formed as large, colorless
crystals. Yield: 470 mg (82%). Anal. Calcd for C40H49N6O3Y: C,
64.0; H, 6.6; N, 11.2. Found: C, 63.8; H, 6.7; N, 11.0. IR (KBr
pellet, cm-1): 3137 w, 3100 w, 3008 m, 2915 s, 2849 m, 1590 s,
1566 m, 1463 s, 1427 s, 1379 m, 1306 s, 1285 s, 1241 m, 1090 m,
1858 Inorganic Chemistry, Vol. 46, No. 5, 2007

Pyrazolylmethane Complexes of the Rare Earths
Scheme 1
170 mg (30%). Anal. Calcd for C40H49N6O3Yb: C, 57.5; H, 5.9;
N, 10.1. Found: C, 57.7; H, 5.9; N, 10.1. IR (KBr pellet, cm-1):
3140 w, 3106 w, 2907 s, 2851 m, 1606 m, 1570 m, 1470 s, 1423
s, 1375 m, 1306 s, 1253 s, 1160 sh, 1035 m, 1010 m, 1007 w, 955
1
w, 855 s, 820 s, 745 m, 707 m, 508 s. H NMR (CD2Cl2, 100.58
MHz, 204 K): δ -52.1 (s, 9H, 3-Me), -32.1 (br s, 9H, Me-
OAr), -6.3 (br s, 3H, m-H), 1.5 (t, J ) 5.1 Hz, 3H, p-H), 10.4 (br
s, 3H, m-H), 22.1 (s, 9H, 5-Me), 78.9 (br s, 9H, Me-OAr), 74.1
(s, 1H, Tpm C-H).
[Nd(Tpm*)(BH4)3(THF)], 4. To a solution of Nd(BH4)3(THF)3
(400 mg, 1.0 mmol) in THF (10 mL) was added slowly a solution
of Tpm* (298 mg, 1.0 mmol) in the same solvent (10 mL). The
yellowish-green solution was allowed to stir overnight. The volume
was reduced to 10 mL under reduced pressure, at which point some
solid was beginning to precipitate. The solution was placed in a
freezer at -20 °C overnight. The supernatant was decanted off,
and the pale-blue powder dried in vacuo. Yield: 210 mg (38%).
Anal. Calcd for C20H42N6B3ONd: C, 43.0; H, 7.6; N, 15.0.
Found: C, 42.5; H, 7.3; N, 14.6. IR (KBr pellet, cm-1): 2962 m,
2895 m, 2461 s, 2452 s br, 2227 s br, 2160 (sh), 1566 m, 1457 s,
1414 m, 1371 m, 1306 m, 1262 s, 1171 s, 1096 s, 1036 m, 1007
m, 897, 860 s, 804 m, 721, 702 s, 482 w. IR (KBr pellet mull,
cm-1): 2435 (sh), 2425, 2215, 2150 (sh). 11B NMR (THF, 160.46
MHz, 293 K): δ 168.
X-ray Crystallographic Analysis. Single crystals of 1a‚
2CH3CN, 1d-a‚THF, 3b‚3THF, and 3c‚3THF were mounted on
a glass fiber, and all geometric and intensity data were taken from
this sample on a Bruker SMART APEX CCD diffractometer using
graphite-monochromated Mo KR radiation (λ ) 0.71073 Å) at 150
( 2 K. Data reduction and integration were carried out with
SAINT+26 and absorption corrections applied using the program
SADABS.27 Structures were solved by direct methods and devel-
oped using alternating cycles of least-squares refinement and
difference Fourier synthesis. All non-hydrogen atoms were refined
anisotropically. Hydrogen atoms were placed in geometrically
reasonable positions and allowed to ride on the atoms to which
they were attached. Structure solution and refinement used the
SHELXTL PLUS V6.12 program package.28
Single crystals of 2a and 2b‚2THF were mounted on a thin glass
fiber using silicon grease and were cooled on the diffractometer to
120 K using an Oxford Cryostream low-temperature attachment.
Approximate unit cell dimensions were determined by the Nonius
Collect program29 from five index frames of width 2° in φ using a
Nonius Kappa CCD diffractometer with a detector-to-crystal
distance of 30 mm. The Collect program was then used to calculate
a data collection strategy to 99.5% completeness for θ ) 27.5°
using a combination of 2° φ and ω scans of 10-120 s deg-1
exposure times (depending on crystal quality). Crystals were
indexed using the DENZO-SMN package,30 and positional data
were refined along with diffractometer constants to give the final
unit cell parameters. Integration and scaling (DENZO-SMN,
Scalepack2) resulted in unique data sets corrected for Lorentz and
polarization effects and for the effects of crystal decay and
absorption by a combination of averaging of equivalent reflections
and an overall volume and scaling correction. Structures were solved
using SHELXS-97 and developed via alternating least-squares
cycles and difference Fourier synthesis (SHELXL-97) with the aid
of the program XSeed.31 All non-hydrogen atoms were modeled
anisotropically, except one disordered THF molecule in the case
of 2b‚2THF, while hydrogen atoms were assigned an isotropic
thermal parameter 1.2 times that of the parent atom (1.5 for terminal
atoms) and allowed to ride.
The structure of 2b‚2THF proved to contain two nondisordered
THF molecules, each of 50% occupancy possibly because of partial
desolvation. The remaining THF molecules were both disordered.
The disorder was modeled successfully by adopting two sets of
positions for the backbone CH2 groups. As a result, H atoms were
not included for these fragments.
Results and Discussion
Tpm* adducts of the lanthanide halides [Ln(Tpm*)Cl3]
(Ln ) Y, 1a; Ce, 1b; Nd, 1c; Sm, 1d; Gd, 1e; Yb, 1f) may
be prepared in good yield and purity from the anhydrous
metal chloride and the ligand in polar solvents such as dry
THF or acetonitrile. Complex 1a has previously been
reported by Mountford and co-workers.22In THF, the com-
plexes differ considerably in their solubility. Complexes 1b
and 1c are moderately soluble in THF. Complexes 1d and
1e show good solubility, and the metal halide dissolves
instantly upon addition of solvent. On the other hand, with
the smaller metal ions, very sparingly soluble precipitates
of 1a and 1f are formed, which can be isolated as analytically
pure. The difference in solubility appears to be related to
their structures since only for 1a and 1f are the complexes
obtained free of solvent. For the larger lanthanides, coordina-
tion of THF occurs. The THF molecule is quite weakly
bound, as evidenced by elemental analyses which are high
in carbon and hydrogen unless the samples are heated to
about 50 °C under dynamic vacuum. The coordination of
the THF presumably sufficiently disrupts crystal packing to
make the complex soluble. On the other hand, Y and Yb
are presumably too small to accommodate the additional
ligand. The low solubility of these complexes in such polar
solvents is slightly surprising in view of the absence of
intermolecular contacts in the crystal structure (vide infra),
though the similarity of the infrared spectra suggests largely
similar solid-state structures. We note that similar insolubility
has been noted for [M(Tpm*)Cl3] (M ) Sc, Y) by Mountford
et al.22 as well as by Bercaw for the 1,4,7-triazacyclononane
(26) Area detector control and data integration and reduction software,
Bru¨ker AXS, Madison, WI, 2001.
(27) SADABS; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
(28) SHELXTL PLUS; Bruker AXS Inc.: Madison, WI, 2001.
(29) Collect; Nonius B.V.: Delft, The Netherlands, 1998.
(30) Otwinowski, Z.; Minor, W. In Methods in Enzymology; Carter, C.
W., Sweet, R. M., Eds.; Academic Press: New York, 1997; Vol. 276,
pp 307-326.
(31) Barbour, L. J. J. Supramol. Chem. 2001, 1, 189-191.
Inorganic Chemistry, Vol. 46, No. 5, 2007 1859

Sella et al.
complex [Y(OArMe2)3(THF)3] reported by Evans.39 Clark has
reported the synthesis and structures of closely related species
with the 2,6-diisopropylphenoxide,40 including the structure
of the samarium complex, [Sm(OAriPr2)3(THF)2].41
Scheme 2
1
The H NMR spectra of the diamagnetic Y complex 3a,
the mildly paramagnetic Nd complex 3b, and samarium
complexes 3c and 3d are very simple, displaying the expected
seven peaks indicative of a symmetrical and, therefore,
fluxional coordination sphere. This is in contrast to Mount-
ford’s observations for the scandium complex where the more
crowded coordination sphere around the smaller metal center
results in slow rotation around the aryloxide metal axis and
the observation of the distinct “up” and “down” methyl
environments for the aryloxides. However, in the case of
yttrium complex.32 It may, therefore, simply result from the
efficient packing of the relatively symmetrical molecules.
As with the pyrazolylborates [Ln(TpMe2)2] (Ln ) Sm, Eu,
Yb), which were also found to be very insoluble,33-36 it may
be possible to make these complexes more soluble by
introducing substituents in the 4-position of the pyrazolyl
groups.36
The corresponding triflates can be prepared analogous to
the procedure in THF, but they are rather more soluble and
are isolated as the THF adducts, [Ln(Tpm*)(OTf)3(THF)]
(Ln ) Y, 2a; Ho, 2b; Dy, 2c). All show strong bands around
1210 cm-1 in the infrared spectrum, indicative of κ1-
coordinated triflate groups.25
1
the ytterbium complex 3e, the H NMR spectrum showed
huge paramagnetic shifts (the spectrum is spread over 100
ppm), and at room temperature, only the para-hydrogen of
the aryloxide and the Tpm* peaks were visible. However,
upon cooling to 204 K, two sets of broad singlets in a 9:3
ratio rose from the baseline. Since this is a molecule with a
well-defined principal axis, it is reasonable to assume that
protons aligned with that axis will be strongly deshielded
(the central C-H of the Tpm* ligand appears at +74 ppm),
while hydrogens located 90° to that axis will undergo a strong
upfield shift (the three methyl hydrogens of the Tpm* appear
at -52 ppm).42,43 On this basis, integrating for nine protons,
we have assigned the peak at +71 ppm to the down methyl
groups of the aryloxide, and an analogous argument was used
to assign the meta-protons of these ligands. The carbon-13
spectrum of 3e was largely uninterpretable due to the
broadness of many of the peaks, the multiplicity of which
could not be assigned.
Finally, direct reaction of Tpm* with [Nd(BH4)3(THF)3]44
in THF results in the formation of Nd(Tpm*)(BH4)3(THF),
which may be isolated in the analytically pure form by
cooling of concentrated solutions in THF. The highly
moisture-sensitive solid is insoluble in hydrocarbon solvents
but dissolves easily in the more polar THF. The infrared
spectrum shows a strong terminal B-H stretching band at
2425 cm-1, along with two overlapping broad bands at 2215
and 2150 cm-1, consistent with tridentate BH4 ligands.45
Crystallographic Studies. Of the complexes described in
the paper, six were crystallized and analyzed by X-ray
diffraction. The complexes were either six or seven coordi-
nate and, in all cases, had local C3 symmetry. They will,
therefore, be discussed by coordination number rather than
in the order in which they were presented in the preceding
section.
Ln(OTf)3 + Tpm* f Ln(Tpm*)(OTf)3(THF)
These complexes are useful starting materials for simple
aryloxides. Reaction of [Ln(Tpm*)Cl3] (isolated or simply
prepared in situ) in THF with NaOArMe2 (ArMe2 ) 2,6-
dimethylphenoxide) yields the expected [Ln(Tpm*)(OArMe2)3]
(Ln ) Y, 3a; Nd, 3b; Sm, 3c; Yb, 3e) in fairly good
yield.The moderately sensitive compounds are very soluble
in THF, less so in CH2Cl2, and virtually insoluble in
hydrocarbon solvents. The compounds could be crystallized
in the analytically pure form from the reaction mixture after
filtration of salt. However, for the larger lanthanides (Nd
and Sm), recrystallization must be carried out with care since
the use of hot THF can result in the loss of the Tpm* ligand.
Thus, after two recrystallizations of 3b from hot THF, large
pale-blue, block-like crystals of the trisaryloxide [Nd-
(OArMe2)3(THF)3] were obtained. A closely related species,
reported to have the stoichiometry Nd(OArMe2)3 and not fully
characterized, has been used previously for polar monomer
polymerization by Zhang and co-workers.37,38 We presume
this complex to be structurally analogous to the yttrium
(32) Hajela, S.; Schaefer, W.; Bercaw, J. J. Organomet. Chem. 1997, 532,
45-53.
(33) Moss, M. A. J.; Kresinski, R. A.; Jones, C. J.; Evans, W. J. Polyhedron
1993, 12, 1953-1955.
(39) Evans, W. J.; Olofson, J. M.; Ziller, J. W. Inorg. Chem. 1989, 28,
4308-4309.
(40) Barnhart, D. M.; Clark, D. L.; Gordon, J. C.; Huffman, J. C.; Vincent,
R. L.; Watkin, J. G.; Zwick, B. D. Inorg. Chem. 1994, 33, 3487-
3497.
(41) Clark, D. L.; Gordon, J. C.; Watkin, J. G.; Huffman, J. C.; Zwick, B.
D. Polyhedron 1996, 15, 2279-2289.
(34) Takats, J.; Zhang, X. W.; Day, V. W.; Eberspacher, T. A. Organo-
metallics 1993, 12, 4286-4288.
(35) Maunder, G. H.; Sella, A.; Tocher, D. A. J. Chem. Soc., Chem.
Commun. 1994, 885-886.
(36) Hillier, A. C.; Zhang, X. W.; Maunder, G. H.; Liu, S. Y.; Eberspacher,
T. A.; Metz, M. V.; McDonald, R.; Domingos, Aˆ .; Marques, N.; Day,
V. W.; Sella, A.; Takats, J. Inorg. Chem. 2001, 40, 5106-5116.
(37) Zhang, L. F.; Shen, Z. Q.; Yu, C. P.; Fan, L. Polym. Int. 2004, 53,
1013-1016.
(42) Stainer, M. V. R.; Takats, J. J. Am. Chem. Soc. 1983, 105, 410-415.
(43) Stainer, M. V. R.; Takats, J. Inorg. Chem. 1982, 21, 4050-4053.
(44) Cendrowski-Guillaume, S. M.; Nierlich, M.; Lance, M.; Ephritikhine,
M. Organometallics 2000, 19, 5654-5660.
(38) Zhang, L. F.; Shen, Z. Q.; Yu, C. P.; Fan, L. J. Macromol. Sci., Chem.
2004, A41, 927-935.
(45) Marks, T. J.; Kolb, J. R. Chem. ReV. 1977, 77, 263-293.
1860 Inorganic Chemistry, Vol. 46, No. 5, 2007

Pyrazolylmethane Complexes of the Rare Earths
Table 1. Selected Average Bond Distances (Å) and Angles (°) for the Single-Crystal X-ray Diffraction Studies
complex
1a‚2CH3CN
1d-a‚THF
2a‚2THF
2b‚2THF
3b‚3THF
3c‚3THF
Ln-Nav/Å
2.459(5)
2.555(2)
2.572(5)
2.621(2)
2.486(3)
115.29(6)
70.4(2)
2.449(8)
2.243(7)
2.391(4)
114.9(3)
73.4(3)
2.461(6)
2.258(12)
2.391(6)
114.8(5)
73.1(3)
2.599(5)
2.207(5)
2.565(5)
2.180(3)
Ln-Xav/Å
Ln-Oax /Å
(X-Ln-X)av
(N-Ln-N)av
(X-Ln-Oax)av
(CTpm-Ln-X)av
100.35(5)
73.8(2)
107.3(2)
68.2(2)
107.3(2)
69.2(1)
77.3(3)
102.7(3)
77.0(3)
103.4(3)
76.9(3)
103.52(4)
117.5(2)
111.6(2)
111.8(2)
Table 2. Summary of Crystal Data and Structure Refinement for Complexes 1a‚2CH3CN, 1d-a‚THF, 2a‚2THF, 2b‚2THF, 3b‚3THF, and 3c‚3THF
1a‚2CH3CN
1d-a‚THF
2a‚2THF
2b‚2THF
3b‚3THF
3c‚3THF
formula
C20H28Cl3N8Y
575.76
C24H38Cl3N6O2Sm
699.30
C35H54F9N6O13S3Y
1122.93
C31H46F9HoN6O12S3
1126.85
C52H73N6NdO6
1022.40
C52H73N6O6Sm
1028.51
formula weight
g mol-1
a )
9.5040(6)
10.5541(16)
13.335(2)
21.004(3)
28.698(3)
19.426(2)
19.807(2)
29.2750(2)
19.6570(10)
19.8299(15)
12.5317(11)
16.2143(14)
16.3503(14)
12.4975(8)
16.2324(10)
16.3598(10)
Å
b )
Å
c )
Å
16.3094(10)
17.1537(6)
R,
90,
94.378(3),
90
90,
90,
90
2956.0(8)
90,
97.185(2),
90
90,
95.481(3),
90
60.7790(10),
77.2050(10),
82.5080(10)
2826.5(4)
60.6900(10),
77.2960(10),
82.4930(10)
2822.1(3)
â,
γ
volume
2651.1(3)
10955(2)
11359.1(10)
Å3
Z
4
4
8
8
2
2
crystal system
space group
temperature
K
monoclinic
P21/n
100(2)
orthorhombic
P212121
150(2)
monoclinic
C2/c
293(2)
monoclinic
C2/c
120(2)
triclinic
P1h
150(2) K
triclinic
P1h
150(2) K
wavelength
Å
0.71073
1.443
0.71073
1.571
0.71073
1.362
0.71073
1.318
0.71073
1.201
0.71073
1.210
Fcalcd
g cm-3
µ
2.525
2.289
1.266
1.581
0.966
1.088
mm-1
independent
reflns
no. of
6006
(Rint ) 0.1140)
298
7102
(Rint ) 0.0252)
325
12804
(Rint ) 0.0608)
605
7478
(Rint ) 0.0793)
616
12977
(Rint ) 0.0224)
587
12821
(Rint ) 0.0175)
587
parameters
R1a
wR2
0.0614
0.1442
0.0308
0.0760
0.0881
0.2502
0.0733
0.1798
0.0502
0.1447
0.0414
0.1266
b
2
2
2
a R1 ) ∑[Fo]-Fc|∑Fo|. b wR2 ) {∑[w(Fo - Fc )2]/{∑[w(Fo )2]}1/2. The values were calculated for I > 2σ(I).
Six-Coordinate Structures. Slow diffusion of layered
acetonitrile solutions of YCl3 and Tpm* yielded colorless
crystals of [Y(Tpm*)Cl3], 1a. The complex crystallized as
discrete six-coordinate molecules in the monoclinic space
group P21/n with two molecules of acetonitrile in the lattice.
The molecular structure is shown in Figure 1 and is similar
to that of the closely related trispyrazolylsilane [Y(MeSi-
(dmpz)3)Cl3] reported by Mountford22 and the corresponding
U(IV)-pyrazolylborate complex [U(TpMe2)Cl3].46 The metal
chloride distances, Y-Clav 2.555(2) Å, are similar to those
in Mountford’s pyrazolylsilane (2.568(5) Å) and are similar
to those reported for the related half-sandwich pyrazolylbo-
rate complex [(TpMe,Me)YCl2(dmpzH)] (Y-Clav 2.555(6) Å)47
and [(TpMe,Me)YCl2(phen)] (Y-Clav 2.600(2) Å).48The Y-N
distance, 2.459(2) Å, is also similar to that in the pyrazolyl-
silane.22
The isomorphous aryloxides 3b and 3c crystallized in the
space group P1h from a concentrated THF solution at -30 °C
with three molecules of THF in the lattice. The molecular
structure of the 3c is shown in Figure 2.
In all three complexes, each center is six coordinate with
C3 symmetry, and as a result, the geometry around the metal
center is best regarded as trigonal antiprismatic, with one
tighter triangle defined by the nitrogens and with a more
open one defined by the X (X ) Cl/OArMe2) groups. This is
seen clearly by comparing the (N-Ln-N) and (X-Ln-
X) angles (∼70 vs 100-108°). In comparing the chlorides
with the aryloxides, it can be seen that the Ln-N distances
are much longer in 3b and 3c (2.565(5) Å) than those in 1a
(2.459(5) Å), even when the differences in ionic radii are
taken into account (Sm 1.098 and Y 1.040),49 suggesting
that the binding of the Tpm* ligand is sensitive to changes
in steric demand of the other ligands in the metal coordina-
tion sphere. The steric demand of the aryloxide ligands is
also reflected in the angles subtended by the X ligands and
the C3 axis of the Tpm* ligand ( (CTpm-Ln-X)av). Whereas
(46) Domingos, Aˆ .; Marques, N.; Dematos, A. P. Polyhedron 1990, 9, 69-
74.
(47) Long, D. P.; Chandrasekaran, A.; Day, R. O.; Bianconi, P. A.;
Rheingold, A. L. Inorg. Chem. 2000, 39, 4476-4487.
(48) Roitershtein, D.; Domingos, A.; Pereira, L. C. J.; Ascenso, J. R.;
Marques, N. Inorg. Chem. 2003, 42, 7666-7673.
(49) Shannon, R. D. Acta Crystallogr., Sect. B 1970, 26, 1046-1048.
Inorganic Chemistry, Vol. 46, No. 5, 2007 1861

Sella et al.
Figure 1. Molecular structure of 1a; hydrogens omitted for clarity.
Figure 3. Molecular structure of 1d-a; hydrogens omitted for clarity.
number and consistent with other related alkoxides.51-53
Consistent with the bulk of the alkoxides, the angles between
the alkoxides are larger than those in the other structures
(O-Sm-O 106.15(9)-107.59(9)°). The longer Sm-N also
results in a slightly tighter bite angle for the Tpm* ligand.
The corresponding distances and angles for 3b are consistent
with the difference in the six-coordinate ionic radii of Nd
and Sm.49
The metal-nitrogen distances are similar in all three
complexes (Y-Nav 2.459(5) 1a, 2.46(2) 2b, 2.449(8) 2a),
despite the differences in coordination number. The M-N
distances for the neutral Tpm* ligand are somewhat longer
than those in complexes of the corresponding anionic TpMe2
(2.402 Å [(TpMe,Me)YCl2(dmpzH)]).47 However, in the more
sterically crowded complex isolated by Cheng and Takats,
[(TpMe,Me)Y(CH2SiMe3)2(THF)], the distances are similar
(2.429-2.491 Å).54
Seven-Coordinate Structures. When a slow diffusion
experiment between SmCl3 and Tpm* was carried out in
THF, crystals of [Sm(Tpm*)Cl3(THF)]‚THF, 1d-a were
obtained. The molecular structure is shown in Figure 3. By
contrast, with the unsolvated 1a, 1d-a is a seven-coordinate
complex in which coordination of the additional THF ligand
can presumably be accommodated by the larger coordination
sphere of Sm than that of Y.
Figure 2. Molecular structure of 3b; hydrogens omitted for clarity.
the chlorides bend back by 117.5(2)°, for the aryloxides,
mutual interactions between the groups prevent further
tightening and limit the angle to 111.7(2) Å.
Compared with six-coordinate structures containing the
isosteric but anionic TpMe2 ligands, the average M-N
distance is also considerably longer, 2.44(1) Å for [Sm-
(TpMe2)]I and 2.443(7) Å for [Sm(TpMe2)]BPh4,36 consistent
with the weaker interaction in the absence of a charge on
the ligand.
For 3b and 3c, the aryloxide ligands lie almost aligned
parallel to C3 axis of the Tpm* ligand (torsion angles are
about 14-17°). Hence, one methyl group of each aryloxide
nestles in the groove between the pyrazolyl groups. This is
consistent with the fluxional process observed in the 1H NMR
spectra of 3e, which may well involve concerted rotation of
the aryloxides and the Tpm* ligands.
The Nd-O distances (av 2.207(5) Å) are similar to
those observed by Clark and Watkin for K[Nd(OAr2,6-iPr)4]
(2.211(12) Å),50 despite the difference in coordination
Crystals of [Ln(Tpm*)(OTf)3(THF)] (Ln ) Y, 2a; Ho, 2b)
were obtained by slow diffusion of layered THF solutions
(50) Barnhart, D. M.; Clark, D. L.; Gordon, J. C.; Huffman, J. C.; Vincent,
R. L.; Watkin, J. G.; Zwick, B. D. Inorg. Chem. 1994, 33, 3487-
3497.
(51) Clark, D. L.; Grumbine, S. K.; Scott, B. L.; Watkin, J. G. Organo-
metallics 1996, 15, 949-957.
(52) Deacon, G. B.; Feng, T.; Forsyth, C. M.; Gitlits, A.; Hockless, D. C.
R.; Shen, Q.; Skelton, B. W.; White, A. H. J. Chem. Soc., Dalton
Trans. 2000, 961-966.
(53) Hillier, A. C.; Liu, S. Y.; Sella, A.; Elsegood, M. R. J. Inorg. Chem.
2000, 39, 2635-2644.
(54) Cheng, J.; McDonald, R.; Takats, J. Unpublished results.
1862 Inorganic Chemistry, Vol. 46, No. 5, 2007

Pyrazolylmethane Complexes of the Rare Earths
Figure 4. Molecular structure of 2a; hydrogens omitted for clarity.
etries have also been observed in lanthanide55,56 and uranium
pyrazolylborate complexes, [U(TpMe2)Cl3L] ( L ) THF)57
and OP(OEt)3,58 and are dictated by the tight bite angle of
the tripodal ligand.
As with the six-coordinate species, the triangles defined
by the nitrogens ( (N-Ln-N)av ∼70-73°) are much tighter
than those defined by the three X ligands ( (X-Ln-X)av
∼115°). Surprisingly, perhaps the Ln-N distances are little
changed between the six- and seven-coordinate species,
suggesting a fairly flexible coordination sphere. However,
the introduction of the THF ligand widens the angle between
the anionic groups (e.g., 1a 100.35(5)° vs 2a 114.9(3)°).
The average Sm-Cl distance, 2.621(2) Å, in 1d-a is
broadly similar to that observed in [Tp*2SmCl] 2.637(3) Å),36
[SmCl3(THF)4] (2.683(5) Å),59 and in the curious eight-
coordinate hexakis(dimethyl)cyclotriphosphazene complex
LSmCl3 (2.640(5) Å).60 The Y-O distances in 2a (2.243(7) Å)
are a little shorter than those observed in the triazacyclon-
onane derivative [Y(TCMT)(OTf)2(H2O)]OTf (2.40(1) Å)61
after correction for the difference in coordination number.
The only other yttrium triflate in the Cambridge Crystal-
lographic Database is too disordered to allow structural
comparison.62
Figure 5. The inner coordination sphere of 2a highlighting (a) the capped
trigonal antiprismatic and (b) the tricapped trigonal pyramidal geometries.
of Tpm* and Ln(OTf)3 in a long tube. Consistent with the
almost identical ionic radii of Y and Ho, the two crystals
were isomorphous. As the molecular structures are extremely
similar, the discussion will focus on 2a, the molecular
structure of which is shown in Figure 4.
Conclusions
We have shown that Tpm* binds effectively to lanthanide
centers and that a range of derivatives can be prepared. The
The coordination spheres of all of these species may be
described in two alternative ways: (a) as a trigonal antiprism
defined by the Tpm* and X (X ) Cl, OTf) groups, with the
THF lying on the C3 axis defined by the Tpm* ligand,
capping the triangular face defined by the X ligands; (b) as
a tricapped trigonal pyramid, with the three nitrogen atoms
of the Tpm* ligand defining the base and with the THF
oxygen defining the apex (see Figure 5). In the latter view,
the chlorides cap the three faces of the pyramid, making Cl-
Sm-O(1) angles of 77 ( 2° to the apical/axial oxygen. The
metal coordination sphere of 1d-a is shown in Figure 5,
which illustrates the two alternative polyhedra. Such geom-
(55) Hillier, A. C.; Sella, A.; Elsegood, M. R. J. J. Chem. Soc., Dalton
Trans. 1998, 3871-3874.
(56) Maunder, G. H.; MacDonald, R.; Sella, A.; Takats, J.; Zhang, X. W.
Manuscript in preparation.
(57) Ball, R. G.; Edelmann, F.; Matisons, J. G.; Takats, J.; Marques, N.;
Marcalo, J.; Dematos, A. P.; Bagnall, K. W. Inorg. Chim. Acta 1987,
132, 137-143.
(58) Maier, R.; Muller, J.; Kanellakopulos, B.; Apostolidis, C.; Domingos,
A.; Marques, N.; Dematos, A. P. Polyhedron 1993, 12, 2801-2808.
(59) Lin, G.-Y.; Wei, G.-C.; Jin, Z.-S.; Chen, W.-Q. Jiegou Huaxue 1992,
11, 200-203.
(60) Koo, B. H.; Byun, Y.; Hong, E.; Kim, Y.; Do, Y. Chem. Commun.
1998, 1227-1228.
(61) Amin, S.; Marks, C.; Toomey, L. M.; Churchill, M. R.; Morrow, J.
R. Inorg. Chim. Acta 1996, 246, 99-107.
(62) Aspinall, H. C.; Dwyer, J. L. M.; Greeves, N.; McIver, E. G.; Woolley,
J. C. Organometallics 1998, 17, 1884-1888.
Inorganic Chemistry, Vol. 46, No. 5, 2007 1863

Sella et al.
crystal structures suggest that the ligand binds less tightly
than in corresponding TpMe2 structures. Although the ligands
show no evidence for dissociation at room temperature, it
appears that they can be displaced from the larger lanthanides
upon reflux. On the other hand, the Tpm* ligands appear to
be significantly more robust than the Tp* system, which has
been shown previously to hydrolyze readily at lanthanide
centers,63 presumably as a result of the greater polarity of
the B-N as opposed to the C-N bond. Pyrazolylmethanes
may, therefore, be a useful addition to the class of neutral
tridentate ancillaries for the f-block, especially in the context
of electrophilic catalytic chemistry. However, their com-
plexes have also been shown to be relatively insoluble, and
it may be advantageous to use ligands, such as those with
substituents in the 4-position of the pyrazolyl ring, designed
to disrupt crystal packing in order to enhance their solubility
in nonpolar solvents.
Acknowledgment. We thank the EPSRC for a Quota
studentship to S.E.B. Dr. Philip Mountford and Prof. Josef
Takats are thanked for helpful discussions and Dr. Abil Aliev
for assistance with the NMR spectra.
Supporting Information Available: X-ray crystallographic files
in CIF format for the structure determinations of [Y(Tpm*)Cl3]
1a, [Sm(Tpm*)Cl3(THF)]‚THF 1d-a, [Y(Tpm*)(O3SCF3)3(THF)]‚
3THF 2a, [Ho(Tpm*)(O3SCF3)3(THF)]‚3THF 2b, [Y(Tpm*)(O-2,6-
C6H3Me2)3] 3a, and [Nd(Tpm*)(O-2,6-C6H3Me2)3] 3b. This material
is available free of charge via the Internet at http://pubs.acs.org.
(63) Domingos, Aˆ .; Elsegood, M. R. J.; Hillier, A. C.; Lin, G.; Liu, S. Y.;
Lopes, I.; Marques, N.; Maunder, G. H.; McDonald, R.; Sella, A.;
Steed, J. W.; Takats, J. Inorg. Chem. 2001, 40, 5106-5116.
IC062370F
1864 Inorganic Chemistry, Vol. 46, No. 5, 2007