Cationic aryl complexes of the rare-earth metals

Article abstract of DOI:10.1021/om7007953

Neutral rare-earth metal tri(aryl) complexes [Ln(C₆H ₄-P-R)₃(THF)₂] (Ln = Lu, Sc; R = H, Me, Et), synthesized by reacting anhydrous metal trichloride with 3 equiv of the corresponding aryllithium, react with 1 or 2 equiv of [NR′₃H] [BPh₄] (R′ = Et; R′₃ = PhMe₂) to yield monocationic di(aryl) complexes [Ln(C₆H₄-P-R) ₂(THF)₄I⁺[BPh₄]^- and dicationic mono(aryl) complexes [Ln(C₆H₄-p-R)(THF) ₅]²⁺[BPh4]^-₂, respectively. Single-crystal X-ray diffraction studies of the mono- and dicationic compounds [Sc(C₆H₅)₂(THF)₄] ⁺[BPh₄]^- and [Lu(C₆H ₅)(THF)₅]²⁺[BPh₄]₂ ^- show distorted octahedral coordination geometry around the metal center in the cation. Kinetic studies for the reaction of the dicationic complex [Lu(C₆H₄-p-Me)(THF)₅]²⁺[BPh ₄]₂^- with pyridine suggest competition between C-H bond activation and insertion reactions.

Full text of DOI:10.1021/om7007953

6388
Organometallics 2007, 26, 6388-6396
Cationic Aryl Complexes of the Rare-Earth Metals
Peter M. Zeimentz and Jun Okuda*
Institute of Inorganic Chemistry, RWTH Aachen UniVersity, Landoltweg 1, D-52074 Aachen, Germany
ReceiVed August 4, 2007
Neutral rare-earth metal tri(aryl) complexes [Ln(C6H4-p-R)3(THF)2] (Ln ) Lu, Sc; R ) H, Me, Et),
synthesized by reacting anhydrous metal trichloride with 3 equiv of the corresponding aryllithium, react
with 1 or 2 equiv of [NR′3H][BPh4] (R′ ) Et; R′3 ) PhMe2) to yield monocationic di(aryl) complexes
[Ln(C6H4-p-R)2(THF)4]+[BPh4]- and dicationic mono(aryl) complexes [Ln(C6H4-p-R)(THF)5]2+[BPh4]- ,
2
respectively. Single-crystal X-ray diffraction studies of the mono- and dicationic compounds
[Sc(C6H5)2(THF)4]+[BPh4]- and [Lu(C6H5)(THF)5]2+[BPh4]- show distorted octahedral coordination
2
geometry around the metal center in the cation. Kinetic studies for the reaction of the dicationic complex
[Lu(C6H4-p-Me)(THF)5]2+[BPh4]-2 with pyridine suggest competition between C-H bond activation and
insertion reactions.
Complexes containing divalent europium and ytterbium4 or
trivalent scandium5 as the metal center were described. Neutral
phenyl complexes of the rare-earth metals without ancillary
ligands were already published 40 years ago,6 followed by THF
containing phenyl complexes,7,8 other homoleptic aryl com-
plexes,9 and mixed aryl halide compounds.10 A number of THF-
containing aryl complexes of divalent rare-earth metals are also
known.11 We report here the first examples for both mono- and
dicationic complexes of the trivalent rare-earth metals with non-
fluorinated aryl ligands.
Introduction
Recent years have seen a steady increase in interest in cationic
organometallic complexes of the rare-earth metals.1,2 This
interest has been prompted by the emergence of group 3 metal
cations as key intermediates in homogeneous R-olefin polym-
erization and other related catalytic reactions, previously
described for the group 4 metal systems.3 Significantly less is
known about cationic aryl complexes of the rare-earth metals.
A limited number of monocationic examples have been reported
so far, all of them containing a perfluorinated aryl group.
Results and Discussion
* Corresponding author. Fax: +49 241 80 92644. E-mail: jun.okuda@
ac.rwth-aachen.de.
Di(aryl) Monocations. Previously, neutral triphenyl com-
plexes of the rare-earth metals [Ln(C6H5)3(THF)n] (Ln ) Ho,
Er, Tm, Yb) were synthesized from the reaction of the metal
with diphenyl mercury or triphenyl bismuth in THF.7 In our
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10.1021/om7007953 CCC: $37.00 © 2007 American Chemical Society
Publication on Web 10/27/2007

Cationic Aryl Complexes of the Rare-Earth Metals
Organometallics, Vol. 26, No. 25, 2007 6389
Scheme 1
Figure 1. Molecular structure of the cationic part of 4a. Hydrogen
atoms are omitted for clarity. Selected bond lengths [Å] and angles
[deg]: Sc-C1 2.298(2), Sc-C7 2.259(2), Sc-O1 2.2572(16), Sc-
O2 2.2554(16), Sc-O3 2.1994(17), Sc-O4 2.1712(16); C1-Sc-
O1 169.09(7), C7-Sc-O2 171.66(7), O3-Sc-O4 169.36(6).
temperature. Figure 1 shows the molecular structure of the
cationic part of the compound displaying a slightly distorted
octahedral coordination geometry with angles of 169.09(7)°
(C1-Sc-O1), 171.66(7)° (C7-Sc-O2), and 169.36(6)° (O3-
Sc-O4) along the respective axes and the two phenyl groups
in a cis arrangement. No cation-anion interactions were
observed in the solid state.
experience, salt metathesis using aryllithium reagents proved
to be more reproducible than this transmetallation reaction. We
isolated the neutral tri(aryl) complexes of the trivalent rare-
earth elements [Ln(C6H4-p-R)3(THF)2] (Ln ) Lu, R ) H, 1a;
Me, 1b; Et, 1c; Ln ) Sc, R ) H, 2a; Me, 2b; Et, 2c) in variable
yields in a metathesis reaction of the anhydrous lutetium or
scandium trichloride with slightly more than 3 equiv of the
corresponding aryllithium, following a modification of a
procedure previously reported for the synthesis of 2a (Scheme
1).8
The Sc-C(aryl) distances of 2.259(2) and 2.298(2) Å in 4a
are in the range reported for other scandium aryl complexes
(2.214(3)-2.266(4) Å),12 but slightly longer than in the neutral
triphenyl complex [Sc(C6H5)3(THF)2] (2.240(3), 2.245(4), and
2.266(4) Å).8 This counter-intuitive finding may be due to the
increase of coordination number from five to six upon cation-
ization (overriding the expected bond shortening) and/or due
to some Sc-C bond shortening in the ground state of the neutral
triphenyl complex. The distances between scandium and the
oxygen atoms of the THF ligands range from 2.1712(16) to
2.2572(16) Å, being also comparable to those found in other
organometallic scandium complexes with THF ligands.2w,8,12a,13
Interestingly, the Sc-O separations trans to the phenyl groups
are significantly longer than those in cis positions (2.2554(16)
and 2.2572(16) versus 2.1712(16) and 2.1994(17) Å). Such a
trans influence14 could also be observed in other lanthanide
When these neutral lutetium complexes 1a-c or scandium
complexes 2a-c were treated with 1 equiv of the Brønsted acid
[NEt3H]+[BPh4]- in THF, the monocationic bis(aryl) complexes
[Ln(C6H4-p-R)2(THF)4]+[BPh4]- (Ln ) Lu, R ) H, 3a; Me,
3b; Et, 3c; Ln ) Sc, R ) H, 4a; Me, 4b; Et, 4c) were isolated
as colorless microcrystals in yields of 50-66% for lutetium and
68-82% for scandium (Scheme 1).
Single crystals of the scandium complex [Sc(C6H5)2(THF)4]+-
[BPh4]- (4a) suitable for X-ray diffraction were obtained from
a THF solution by slow evaporation of the solvent at room
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6390 Organometallics, Vol. 26, No. 25, 2007
Zeimentz and Okuda
complexes,10f,15 and in the monocationic bis(alkyl) complexes
[Y(CH2SiMe3)2(THF)4]+[El(CH2SiMe3)4]- (El ) Al,16 Ga2v).
In the hepta-coordinate monocationic dimethyl complex
[YMe2(THF)5]+[BPh4]-, the two methyl groups were found to
be trans to each other.17 For the crystallographically character-
ized monocationic dibenzyl complex containing THF ligands,
[La(CH2C6H5)2(THF)4]+[BPh4]-, a trans influence could not be
observed as this system shows more distortion from the
octahedral coordination due to polyhapto bonding of the benzyl
groups.2a The scandium center in the cation of 4a is situated
0.1890(3) and 0.2324(4) Å away from the planes defined by
the two phenyl groups. Usually the central atoms are located in
the planes defined by the phenyl groups,7b,c,f,8,12b,21 whereas some
other crystallographically characterized phenyl complexes of
the rare-earth metals show similar distances (0.1384(11) and
0.1475(15) Å for [Sc(η6-C5H5BPh)Ph2(THF)],12a 0.2293(17)
and 0.2495(17) Å for two crystallographically independent
molecules of [Li(DME)3]+[Nd(η5-C5H5)3Ph]-,18 0.3928(3) Å for
[Sm(η5-C5Me5)2Ph(THF)],19 and 0.1703(2) Å for [Yb{PhP(CH2-
SiMe2NSiMe2CH2)2PPh}Ph]20).
Scheme 2
Scheme 3
All signals of the monocationic compounds are unambigu-
ously assignable in the 1H and 13C NMR spectra with the
exception of the ipso carbon atoms of the aryl groups in the
scandium complexes, which are not observed due to quadrupolar
relaxation (I ) 7/2 for 45Sc). The cation-independent resonance
of δ ) -6.6 ppm in the 11B NMR spectrum is indicative of a
non-coordinating anion.
Aryl Dications. One of the most remarkable aspects of the
organometallic chemistry of the cationic rare-earth metal com-
plexes is the availability of dicationic mono(alkyl) complexes.1a,b,16
Analogously to the synthesis of dicationic mono(alkyl)
complexes,2a,16,17,22 the isolation of mono(aryl) dication was
successfully accomplished by the reaction of the neutral
triphenyl complex with 2 equiv of an appropriate Brønsted acid
in THF. Thus, the reaction of 2 equiv of the ammonium salt
[NEt3H]+[BPh4]- with the neutral lutetium complexes 1a-c in
THF resulted in the precipitation of the dicationic mono(aryl)
The same reaction carried out with the analogous scandium
complexes 2a-c gave only a mixture of the monocationic com-
plexes 4a-c and unreacted [NEt3H]+[BPh4]-. However, the use
of 2 equiv of the more acidic anilinium salt [NPhMe2H]+[BPh4]-
allowed for the isolation of the dicationic scandium complexes
[Sc(C6H4-p-R)(THF)5]2+[BPh4]-2 (R ) H, 6a; Me, 6b; Et, 6c)
as colorless microcrystals in yields of 36-67% (Scheme 3).
The requirement for a stronger acid to protonolyze a scandium-
aryl bond as compared to the lutetium-aryl bond can be
ascribed to the difference of the basicity between scandium and
lutetium.
complexes of the rare-earth metals [Lu(C6H4-p-R)(THF)5]2+
-
[BPh4]-2 (R ) H, 5a; Me, 5b; Et, 5c) as colorless microcrystals
in yields of 41-66% (Scheme 2).
Single crystals of [Lu(C6H5)(THF)5]2+[BPh4]- (5a) could
2
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tallics 1985, 4, 112.
(20) Fryzuk, M. D.; Jafarpour, L.; Kerton, F. M.; Love, J. B.; Patrick,
B. O.; Rettig, S. J. Organometallics 2001, 20, 1387.
(21) Lin, G.; Jin, Z.; Zhang, Y.; Chen, W. J. Organomet. Chem. 1990,
396, 307.
(22) (a) Ward, B. D.; Bellemin-Laponnaz, S.; Gade, L. H. Angew. Chem.
2005, 117, 1696; Angew. Chem., Int. Ed. 2005, 44, 1668. (b) Tredget, B.
D.; Bonnet, F.; Cowley, A. R.; Mountford, P. Chem. Commun. 2005, 3301.
(c) Elvidge, B. R.; Arndt, S.; Zeimentz, P. M.; Spaniol, T. P.; Okuda, J.
Inorg. Chem. 2005, 44, 6777. (d) Arndt, S.; Elvidge, B. R.; Zeimentz, P.
M.; Spaniol, T. P.; Okuda, J. Organometallics 2006, 25, 793.
be obtained from a supersaturated THF solution at room
temperature. As for the monocationic compound 4a, no cation-
anion interactions could be observed for 5a in the crystal; two
free THF molecules were retained in the crystal lattice. Figure
2 shows the molecular structure of the cationic part of 5a. The
coordination geometry around the metal center can be described
as a slightly distorted octahedron with angles of 176.7(3)° (C1-
Lu-O3), 175.7(3)° (O2-Lu-O5), and 176.3(2)° (O1-Lu-O4)
along the respective axes.
The Lu-C(aryl) distance of 2.303(7) Å is shorter than those
previously reported for other lutetium aryl complexes (2.32-
(3)-2.877(9) Å).10e,23 Likewise, the distances between lutetium
and the oxygen donors of the THF ligands (2.207(8)-2.320(8)
Å) are among the shortest found for organometallic lutetium
compounds with THF ligands (2.268(3)-2.455(2) Å).13m,23b,d,24
This effect arises probably from the increased positive charge
in the dication. Analogously to the monocationic scandium
complex 4a, in the crystal structure of 5a a significantly longer
Lu-O distance of 2.320(8) Å to the THF molecule coordinated
trans to the phenyl group as compared to those in cis position
(2.207(8)-2.249(6) Å) could be observed. The related
16
dicationic mono(alkyl) complexes [YMe(THF)6]2+[BPh4]-
,
2
[HoMe(THF)6]2+[BPh4]- ,17 and [La(CH2C6H4-p-Me)(THF)6]2+-
2

Cationic Aryl Complexes of the Rare-Earth Metals
Organometallics, Vol. 26, No. 25, 2007 6391
Figure 2. Molecular structure of the cationic part of 5a‚2THF.
Hydrogen atoms are omitted for clarity. Selected bond lengths
[Å] and angles [deg]: Lu-C1 2.303(7), Lu-O1 2.239(6),
Lu-O2 2.207(8), Lu-O3 2.320(8), Lu-O4 2.249(6), Lu-O5
2.237(7); C1-Lu-O3 176.7(3), O2-Lu-O5 175.7(3), O1-Lu-
O4 176.3(2).
Figure 3. Eyring plot for the reaction of 5a with pyridine-d5.
11B NMR spectra arising from the tetraphenylborate anions
could be observed. This indicates that ion separation is retained
in solution. Similar to the observations made for the monoca-
tionic complexes, all of the resonances in the 1H and 13C NMR
spectra were detected except for that corresponding to the ipso
carbon atom at the scandium center.
[BPh4]- 2a showed a higher coordination number of seven at
2
the metal center and no such trans influence. Moreover,
in the structurally similar cationic parts of [Yb(C6F5)-
(THF)5]+[Yb(C6F5)2{N(SiMe3)2}2]- and [Yb(C6F5)(THF)5]+
[BPh4]-, no such trans influence could be observed either.4 A
difference in the trans influence of phenyl and perfluorinated
phenyl ligand was also reported for the trigonal bipyramidal
coordinated germatrane compounds [(C6X5)Ge{(OCH2CH2)3N}]
(X ) H, F).25 As for the monocationic complex 4a, the metal
center in 5a is located outside of the plane defined by the phenyl
group; here, the distance is 0.6928(3) Å.
These dicationic complexes were found to be insoluble in
THF. Thus, NMR spectra were recorded in pyridine-d5, as their
reactivity toward pyridine is quite low at room temperature. For
all compounds, the same resonance of δ ) -5.8 ppm in the
Reaction with Pyridine. Many C-H bond activation pro-
cesses proceed via σ-bond metathesis using complexes of metals
with an fxd0 electron configuration.26,27 As could be shown
previously for dicationic alkyl complexes of the rare-earth
metals, they easily react with pyridine by C-H bond activation
to yield η2-(C,N)-pyridyl complexes.22c,d,28 Because of the large
number of signals in the aromatic region, the dicationic lutetium
complex 5b with the p-methyl-substituted aryl group was used
for kinetic measurements as the sharp resonance of the methyl
group could be easily observed. For the determination of the
activation parameters, four separate runs at 35, 45, 55, and
1
65 °C were performed by monitoring H NMR spectra of a
solution of 5b in pyridine-d5. The decrease of the signal intensity
attributed to the p-methyl group of the dicationic complex 5b
was found to follow pseudo-first-order kinetics, and the half-
lives at the respective temperatures were determined to be as
follows: τ1/2 (35 °C) ) 1962 min, τ1/2 (45 °C) ) 625 min, τ1/2
(55 °C) ) 243 min, and τ1/2 (65 °C) ) 93 min. The activation
parameters were calculated by means of an Eyring plot to be
∆Sq ) -70 ( 4 J K-1 mol-1 and ∆Hq ) 85 ( 5 kJ mol-1
(Figure 3).
In the 1H NMR spectrum of the reaction of 5b with pyridine-
d5, the formation of toluene deuterated in the para position (p-
CH3-C6H4-D, singlet at δ ) 2.21 ppm for p-CH3) was
observed as well as the formation of 2-p-tolyl-pyridine-d4 (two
doublets at δ ) 7.16 and 8.21 ppm with 3JHH ) 8.0 Hz). When
5b was stirred at 50 °C for 5 days in pyridine and worked up,
the examination of the volatile organic products via GC/MS
confirmed the formation of 2-p-tolyl-pyridine (Rt ) 9.54 min,
(23) (a) Cotton, S. A.; Welch, A. J.; Hursthouse, M. B.; Hart, F. A. J.
Chem. Soc., Chem. Commun. 1972, 1225. (b) Schumann, H.; Genthe, W.;
Bruncks, N.; Pickardt, J. Organometallics 1982, 1, 1194. (c) Wayda, A.
L.; Atwood, J. L.; Hunter, W. E. Organometallics 1984, 3, 939. (d) Wayda,
A. L.; Rogers, R. D. Organometallics 1985, 4, 1440. (e) Protchenko, A.
V.; Almazova, O. G.; Zakharov, L. N.; Fukin, G. K.; Struchkov, Y. T.;
Bochkarev, M. N. J. Organomet. Chem. 1997, 536-537, 457. (f) 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. (g)
Rabe, G. W.; Zhang-Presse, M.; Riederer, F. A.; Incarvito, C. D.; Golen, J.
A.; Rheingold, A. L. Acta Crystallogr. 2004, E60, m1389. (h) Evans, W.
J.; Lee, D. S.; Johnston, M. A.; Ziller, J. W. Organometallics 2005, 24,
6393.
(24) (a) Evans, W. J.; Wayda, A. L.; Hunter, W. E.; Atwood, J. L. J.
Chem. Soc., Chem. Commun. 1981, 292. (b) Schumann, H.; Genthe, W.;
Bruncks, N. Angew. Chem. 1981, 93, 126; Angew. Chem., Int. Ed. Engl.
1981, 20, 119. (c) Roitershtein, D. M.; Ellern, A. M.; Antipin, M. Y.;
Rybakova, L. F.; Struchkov, Y. T.; Petrov, E. S. MendeleeV Commun. 1992,
118. (d) Schumann, H.; Meese-Marktscheffel, J. A.; Dietrich, A.; Pickardt,
J. J. Organomet. Chem. 1992, 433, 241. (e) Schumann, H.; Keitsch, M. R.;
Winterfeld, J.; Mu¨hle, S.; Molander, G. A. J. Organomet. Chem. 1998,
559, 181. (f) Arndt, S.; Spaniol, T. P.; Okuda, J. Chem. Commun. 2002,
896. (g) Schumann, H.; Freckmann, D. M. M.; Dechert, S. Z. Anorg. Allg.
Chem. 2002, 628, 2422. (h) Arndt, S.; Spaniol, T. P.; Okuda, J. Organo-
metallics 2003, 22, 775. (i) Nishiura, M.; Hou, Z.; Wakatsuki, Y.; Yamaki,
T.; Miyamoto, T. J. Am. Chem. Soc. 2003, 125, 1184. (j) Tardif, O.;
Nishiura, M.; Hou, Z. Organometallics 2003, 22, 1171. (k) Tardif, O.;
Nishiura, M.; Hou, Z. Tetrahedron 2003, 59, 10525. (l) Cameron, T. M.;
Gordon, J. C.; Scott, B. L. Organometallics 2004, 23, 2995. (m) Rufanov,
K. A.; Freckmann, D. M. M.; Kroth, H. J.; Schutte, S.; Schumann, H. Z.
Naturforsch., B: Chem. Sci. 2005, 60, 533. (n) Schumann, H.; Freckmann,
D. M. M.; Schutte, S.; Dechert, S.; Hummert, M. Z. Anorg. Allg. Chem.
2007, 633, 888. (o) Liu, X.; Shang, X.; Tang, T.; Hu, N.; Pei, F.; Cui, D.;
Chen, X.; Jing, X. Organometallics 2007, 26, 2747. (p) Miao, W.; Li, S.;
Cui, D.; Huang, B. J. Organomet. Chem. 2007, 692, 3823. (q) Liu, B.;
Yang, Y.; Cui, D.; Tang, T.; Chen, X.; Jing, X. Dalton Trans. 2007, 4252.
(25) (a) Lukevics, E.; Ignatovich, L.; Belyakov, S. J. Organomet. Chem.
1999, 588, 222. (b) Kultyshev, R. G.; Prakash, G. K. S.; Olah, G. A.; Faller,
J. W.; Parr, J. Organometallics 2004, 23, 3184.
(26) For C-H bond activation by lanthanide complexes, see: (a) Watson,
P. G. J. Chem. Soc., Chem. Commun. 1983, 276. (b) Shilov, A. E.; Shul’pin,
G. B. Chem. ReV. 1997, 97, 2879. (c) Gossage, R. A.; van Koten, G. Top.
Organomet. Chem. 1999, 3, 9. (d) Labinger, J. A.; Bercaw, J. E. Nature
2002, 417, 507. (e) Thompson, M. E.; Baxter, S. M.; Bulls, A. R.; Burger,
B. J.; Nolan, M. C.; Santarsiero, B. D.; Schaefer, W. P.; Bercaw, J. E. J.
Am. Chem. Soc. 1987, 109, 203.
(27) For C-H bond activation by actinide complexes, see: (a) Boaretto,
R.; Roussel, P.; Kingsley, A. J.; Munslow, I. J.; Sanders, C. J.; Alcock, N.
W.; Scott, P. Chem. Commun. 1999, 1701. (b) Kiplinger, J. L.; Morris, D.
E.; Scott, B. L.; Burns, C. J. Chem. Commun. 2002, 30. (c) Pool, J. A.;
Scott, B. L.; Kiplinger, J. L. J. Am. Chem. Soc. 2005, 127, 1338. (d) Pool,
J. A.; Scott, B. L.; Kiplinger, J. L. J. Alloys Compd. 2006, 418, 178.
(28) For the formation of a neutral η2-(C,N)-pyridyl complex from the
reaction of [Lu(η5-C5Me5)(CH2SiMe3)2(THF)] with pyridine and its crystal
structure, see: Jantunen, K. C.; Scott, B. L.; Gordon, J. C.; Kiplinger, J. L.
Organometallics 2007, 26, 2777.

6392 Organometallics, Vol. 26, No. 25, 2007
Zeimentz and Okuda
Scheme 4
M+: 169.0).29 Additionally, the formation of 2,2′-bipyridyl
could be detected (Rt ) 7.76 min, M+: 156.0).30 A possible
explanation for the formation of these products is shown in
Scheme 4.
bipyridyl.32 Such reactions have been reported earlier for neutral
yttrium alkyl and hydride complexes with two benzamidinato33
or pentamethylcyclopentadienyl ligands.34 The involvement of
radicals in this reaction cannot be excluded, but seems to be
quite unlikely as the reaction of either 2- or 3-pyridyl radicals
with an excess of pyridine should lead almost exclusively to
the formation of 2,3′-bipyridyl.29e In a reaction competing with
the C-H bond activation of pyridine, the aryl group attacks a
pyridine ligand as a nucleophile, resulting upon hydride elimina-
In the first step, the THF ligands are rapidly replaced by
pyridine. When the dicationic complex 5b was dissolved in
pyridine and immediately precipitated upon addition of pentane,
only the resonances of the THF-free complex [Lu(C6H4-p-Me)-
(py)5]2+[BPh4]-2 (5b′) could be observed in the 1H NMR spectra
in pyridine-d5. The 1H NMR data for 5b′ are identical to those
arising from 5b in pyridine-d5, except for the absence of free
THF. For neutral cyclopentadienyl-containing complexes, such
a greater affinity of lanthanide centers for the nitrogen donors
of pyridine over oxygen donors of other Lewis bases has already
been noted.31 After the initial Lewis base exchange, two reaction
pathways are conceivable: the first one leading via C-H bond
activation of pyridine and loss of toluene to the formation of a
η2-(C,N)-pyridyl lutetium complex. This might react further with
a second molecule of pyridine under insertion into the Lu-C
bond, which leads after hydrolysis to the observed 2,2′-
tion (to give formally a dicationic hydride complex [LuHpy5]2+
-
[BPh4]-2) in the formation of 2-p-tolyl-pyridine. The two
transition states must be energetically different, as a product
ratio of 3:2 is observed. Such a competition between C-H bond
activation and insertion of pyridine for organometallic rare-earth
metal compounds was also found for reactions of pyridine and
neutral yttrium complexes with two benzamidinato ligands.33
In comparison with the results previously obtained for the C-H
bond activation of pyridine with the dicationic methyl complex
[LuMe(THF)6]2+[BPh4]-2 (τ1/2 (35 °C) ≈ 8 d),22d the dicationic
aryl complex 5b reacts significantly faster (τ1/2 (35 °C) ) 1962
min). This agrees well with studies of metallocene derivatives
[Sc(η5-C5Me5)2R] (R ) Me, Ph).26d,35 Despite the higher relative
bond dissociation energy of the Sc-C bond for the phenyl
complex as compared to that of the methyl complex, the aryl
compounds were found to react faster. As an explanation for
this, the initial formation of a π complex was proposed.35
(29) (a) Terent’ev, P. B.; Khmel’nitskii, R. A.; Kost, A. N. Zh. Org.
Khim. 1971, 7, 1777; J. Org. Chem. USSR 1971, 7, 1843. (b) Terashima,
M.; Seki, K.; Yoshida, C.; Ohkura, K.; Kanaoka, Y. Chem. Pharm. Bull.
1985, 33, 1009. (c) Inada, K.; Miyaura, N. Tetrahedron 2000, 56, 8661.
(d) Heller, B.; Sundermann, B.; Buschmann, H.; Drexler, H. J.; You, J.;
Holzgrabe, U.; Heller, E.; Oehme, G. J. Org. Chem. 2002, 67, 4414. (e)
Nu´n˜ez, A.; Sa´nchez, A.; Burgos, C.; Alvarez-Builla, J. Tetrahedron 2004,
60, 6217. (f) Wang, L.; Zhang, Y.; Liu, L.; Wang, Y. J. Org. Chem. 2006,
71, 1284.
(30) (a) Brown, E. V.; Ahmad, I. Phytochemistry 1972, 2, 3485. (b)
Gillard, R. D.; Hill, R. E. E. J. Chem. Soc., Dalton Trans. 1974, 1217. (c)
Keats, N. G.; Summers, L. A. J. Heterocycl. Chem. 1976, 13, 369. (d)
Hassanaly, P.; Vernin, G.; Dou, H. J. M.; Metzger, J. Bull. Soc. Chim. Fr.
1976, 461. (e) Luanratana, O.; Griffin, W. J. Phytochemistry 1982, 21, 449.
(f) Crank, G.; Gately, G. E.; Makin, M. I. H. Aust. J. Chem. 1984, 37,
2499.
Conclusion
We have shown that cationic aryl complexes of scandium
and lutetium are accessible in a manner analogous to that of
(32) From the reaction mixture of [Y(CH2SiMe3)2(THF)4]+[BPh4]- with
pyridine, a crystallographically characterized dicationic complex that
contains a bipyridyl ligand, [Y{η2-(C,N)-C5H4N}(bpy)(py)-fac-(THF)3]2+
-
[BPh4]2-, was isolated in low yield: Nakajima, Y.; Spaniol, T. P.; Okuda,
J., unpublished results.
(31) (a) Evans, W. J.; Meadows, J. H.; Hunter, W. E.; Atwood, J. L. J.
Am. Chem. Soc. 1984, 106, 1291. (b) Clark, D. L.; Gordon, J. C.; Scott, B.
L.; Watkin, J. G. Polyhedron 1999, 18, 1389. (c) Li, J. S.; Neumu¨ller, B.;
Dehnicke, K. Z. Anorg. Allg. Chem. 2002, 628, 45. (d) Giesbrecht, G. R.;
Clark, D. L.; Gordon, J. C.; Scott, B. L. Appl. Organomet. Chem. 2003,
17, 473.
(33) Duchateau, R.; van Wee, C. T.; Teuben, J. H. Organometallics 1996,
15, 2291.
(34) Deelman, B.-J.; Stevels, W. M.; Teuben, J. H.; Lakin, M. T.; Spek,
A. L. Organometallics 1994, 13, 3881.
(35) Bulls, A. R.; Bercaw, J. E.; Manriquez, J. M.; Thompson, M. E.
Polyhedron 1988, 7, 1409.

Cationic Aryl Complexes of the Rare-Earth Metals
Organometallics, Vol. 26, No. 25, 2007 6393
all volatiles were removed in vacuo and the residue was extracted
with toluene (2 × 40 mL) at 0 °C. After removal of the solvent in
vacuo, recrystallization from THF (20 mL) afforded 1b (1.14 g,
64%) as a colorless powder. 1H NMR (400.1 MHz, C6D6): δ 1.22
(br s, 8H, â-THF), 2.40 (s, 9H, CH3), 3.57 (br s, 8H, R-THF), 7.46
(d, JHH ) 7.4 Hz, 6H, LuC6H4-3), 8.17 (d, JHH ) 7.4 Hz, 6H,
LuC6H4-2). 13C{1H} NMR (100.6 MHz, C6D6): δ 21.8 (CH3), 25.4
(â-THF), 68.8 (R-THF), 128.1 (LuC6H4-4), 135.3 (LuC6H4-3), 136.6
(LuC6H4-2), 195.2 (LuC6H4-1). Anal. Calcd for C29H37LuO2
(592.58): C, 58.78; H, 6.29; Lu, 29.53. Found: C, 53.76; H, 5.65;
Lu, 29.21.
the still growing number of cationic alkyl complexes of the rare-
earth metals. Whereas the number of previous reports on
monocationic aryl complexes is very limited, the first examples
of dicationic derivatives have been synthesized and character-
ized. In the solid state, both crystallographically characterized
mono- and dications adopt a slightly distorted octahedral
coordination geometry, in which a significant trans influence
of the aryl ligands is observed. The dicationic aryl complexes
activate pyridine. In contrast to the C-H bond activation found
for related methyl dication, evidence has been found that the
C-H bond activation competes with insertion of pyridine into
the aryl complexes.
3
3
[Lu(C6H4-p-Et)3(THF)2] (1c). LuCl3 (0. 844 g, 3.00 mmol) was
suspended in THF (10 mL) and stirred at 40 °C overnight. After
addition of Et2O (10 mL) to the suspension, a solution of Li(C6H4-
p-Et) (1.03 g, 9.15 mmol) in Et2O (25 mL) was added dropwise at
0 °C. After the mixture was stirred for 2.5 h at this temperature,
all volatiles were removed in vacuo and the residue was extracted
with toluene (2 × 40 mL) at 0 °C. After removal of the solvent in
vacuo, recrystallization from THF (20 mL) afforded 1c (0.782 g,
41%) as a colorless powder. 1H NMR (400.1 MHz, C6D6): δ 1.08
Experimental Section
General Procedures. All operations were performed under an
inert atmosphere of argon using standard Schlenk-line or glove box
techniques. Diethyl ether, THF, and toluene were distilled from
sodium benzophenone ketyl. Pentane was purified by distillation
from sodium/triglyme benzophenone ketyl. Anhydrous rare-earth
metal trichlorides (Strem or Aldrich) were used as received. [Sc-
(C6H5)3(THF)2] (2a)7 and the lithium aryls36 were prepared by
literature procedures. NMR spectra were recorded on a Varian
Mercury 200 BB (1H, 200.0 MHz), Varian Unity 500 (1H, 499.6
MHz; 13C, 125.6 MHz; 11B, 160.3 MHz), or Bruker DRX 400
spectrometer (1H, 400.1 MHz; 13C, 100.6 MHz; 11B, 128.4 MHz)
3
(t, JHH ) 7.5 Hz, 9H, CH2CH3), 1.34 (br s, 8H, â-THF), 2.71
3
(quartet, JHH ) 7.5 Hz, 6H, CH2CH3), 3.54 (br s, 8H, R-THF),
3
3
7.48 (d, JHH ) 6.7 Hz, 6H, LuC6H4-3), 8.21 (d, JHH ) 6.7 Hz,
6H, LuC6H4-2). 13C{1H} NMR (100.6 MHz, C6D6): δ 16.4
(CH2CH3), 25.7 (â-THF), 29.7 (CH2CH3), 67.8 (br, R-THF), 126.6
(LuC6H4-4), 134.4 (LuC6H4-3) 140.1 (LuC6H4-2), 194.2 (LuC6H4-
1). Anal. Calcd for C32H43LuO2 (634.66): C, 60.56; H, 6.83; Lu,
27.57. Found: C, 59.91; H, 7.04; Lu, 27.46.
1
at 25 °C, unless otherwise stated. Chemical shifts for H and 13C
NMR spectra were referenced internally using the residual solvent
resonances and are reported relative to tetramethylsilane. 11B NMR
spectra were referenced externally to a 1 M solution of NaBH4 in
D2O. Elemental analyses were performed by the Microanalytical
Laboratory of the Institute of Organic Chemistry at the RWTH
Aachen University. In many cases, the results were not satisfactory
and the best values from repeated runs were given. Moreover, the
results were inconsistent from run to run and therefore irreproduc-
ible. In the context of organometallic rare-earth metal compounds,
this difficulty was also observed by other groups and may be
ascribed to the formation of inert carbides.37 Metal analysis was
performed by complexometric titration.38 The GC/MS(EI) experi-
ments were run on a Varian VF-5ms spectrometer.
[Sc(C6H4-p-Me)3(THF)2] (2b). ScCl3 (0.454 g, 3.00 mmol) was
suspended in THF (10 mL) and stirred at 40 °C overnight. After
addition of Et2O (10 mL) to the suspension, a solution of Li(C6H4-
p-Me) (0.897 g, 9.15 mmol) in Et2O (25 mL) was added dropwise
at 0 °C. After the mixture was stirred for 2.5 h at this temperature,
all volatiles were removed in vacuo and the residue was extracted
with toluene (2 × 40 mL) at 0 °C. After removal of the solvent in
vacuo, recrystallization twice from THF (70 mL each) afforded 2b
(1.10 g, 79%) as a colorless powder. 1H NMR (400.1 MHz,
C6D6): δ 1.18 (br s, 8H, â-THF), 2.38 (s, 9H, CH3), 3.64 (br s,
8H, R-THF), 7.34 (d, 3JHH ) 7.5 Hz, 6H, ScC6H4-3), 8.14 (d, 3JHH
) 7.5 Hz, 6H, ScC6H4-2). 13C{1H} NMR (100.6 MHz, C6D6): δ
21.9 (CH3), 25.3 (â-THF), 70 (br, R-THF), 127.8 (ScC6H4-4), 134.7
(ScC6H4-3), 135.3 (ScC6H4-2), resonance for ScC6H4-1 not detected.
Anal. Calcd for C29H37O2Sc (462.57): C, 75.30; H, 8.06; Sc, 9.72.
Found: C, 74.92; H, 7.62; Sc, 9.89.
[Lu(C6H5)3(THF)2] (1a). LuCl3 (0.844 g, 3.00 mmol) was
suspended in THF (10 mL) and stirred at 40 °C overnight. After
addition of Et2O (10 mL) to the suspension, a solution of Li(C6H5)
(0.769 g, 9.15 mmol) in Et2O (25 mL) was added dropwise at 0
°C. After the mixture was stirred for 2.5 h at this temperature, all
volatiles were removed in vacuo and the residue was extracted with
toluene (2 × 40 mL) at 0 °C. After removal of the solvent in vacuo,
recrystallization from THF (40 mL) afforded 1a (0.482 g, 24%) as
[Sc(C6H4-p-Et)3(THF)2] (2c). ScCl3 (0.454 g, 3.00 mmol) was
suspended in THF (10 mL) and stirred at 40 °C overnight. After
addition of Et2O (10 mL) to the suspension, a solution of Li(C6H4-
p-Et) (1.03 g, 9.15 mmol) in Et2O (25 mL) was added dropwise at
0 °C. After the mixture was stirred for 2.5 h at this temperature,
all volatiles were removed in vacuo and the residue was extracted
with toluene (2 × 40 mL) at 0 °C. After removal of the solvent in
vacuo, recrystallization twice from THF (40 mL each) afforded 2c
(0.760 g, 50%) as a colorless powder. 1H NMR (400.1 MHz,
1
a colorless powder. H NMR (400.1 MHz, C6D6): δ 1.10 (br s,
8H, â-THF), 3.54 (br s, 8H, R-THF), 7.37 (d, 3JHH ) 7.4 Hz, 6H,
3
3
LuC6H5-4), 7.59 (d, JHH ) 7.3 Hz, 6H, LuC6H5-3), 8.18 (d, JHH
) 6.0 Hz, 3H, LuC6H5-2). 13C{1H} NMR (100.6 MHz, C6D6): δ
25.3 (â-THF), 69.2 (R-THF), 126.8 (LuC6H5-4), 127.4 (LuC6H5-
3), 136.3 (LuC6H5-2), 198.7 (LuC6H5-1). Anal. Calcd for C26H31-
LuO2 (550.50): C, 56.73; H, 5.68; Lu, 31.78. Found: C, 56.75; H,
6.44; Lu, 31.56.
3
C6D6): δ 0.91 (br s, 8H, â-THF), 1.29 (t, JHH ) 7.6 Hz, 9H,
CH2CH3), 2.69 (quartet, 3JHH ) 7.6 Hz, 6H, CH2CH3), 3.68 (br s,
8H, R-THF), 7.37 (d, 3JHH ) 7.5 Hz, 6H, ScC6H4-3), 8.18 (d, 3JHH
) 7.5 Hz, 6H, ScC6H4-2). 13C{1H} NMR (100.6 MHz, C6D6): δ
16.4 (CH2CH3), 24.8 (â-THF), 29.7 (CH2CH3), 71 (br, R-THF),
126.6 (ScC6H4-4), 134.7 (ScC6H4-3), 142.0 (ScC6H4-2), signal for
ScC6H4-1 not detected. Anal. Calcd for C32H43O2Sc (504.65): C,
76.16; H, 8.59; Sc, 8.91. Found: C, 75.27; H, 8.20; Sc, 9.10.
[Lu(C6H4-p-Me)3(THF)2] (1b). LuCl3 (0.844 g, 3.00 mmol) was
suspended in THF (10 mL) and stirred at 40 °C overnight. After
addition of Et2O (10 mL) to the suspension, a solution of Li(C6H4-
p-Me) (0.897 g, 9.15 mmol) in Et2O (25 mL) was added dropwise
at 0 °C. After the mixture was stirred for 2.5 h at this temperature,
[Lu(C6H5)2(THF)4]+[BPh4]- (3a). A solution of [NEt3H]+[BPh4]-
(0.102 g, 0.242 mmol) in THF (5 mL) was added dropwise at 0 °C
to a solution of 1a (0.133 g, 0.242 mmol) in THF (10 mL) and
stirred at this temperature for 30 min. Evaporation of all volatiles
in vacuo and washing the colorless residue with pentane (3 × 10
(36) Schlosser, M.; Ladenberger, V. J. Organomet. Chem. 1967, 8, 193.
(37) (a) Mitchell, J. P.; Hajela, S.; Brookhart, S. K.; Hardcastle, K. I.;
Henling, L. M.; Bercaw, J. E. J. Am. Chem. Soc. 1996, 118, 1045. (b)
Bambirra, S.; Brandsma, M. J. R.; Brussee, E. A. C.; Meetsma, A.; Hessen,
B.; Teuben, J. H. Organometallics 2000, 19, 3197.
1
(38) Das, B.; Shome, S. C. Anal. Chim. Acta 1971, 56, 483.
mL) afforded 3a (0.119 g, 52%) as a colorless powder. H NMR

6394 Organometallics, Vol. 26, No. 25, 2007
Zeimentz and Okuda
(400.1 MHz, THF-d8): δ 1.77 (m, 16H, â-THF), 3.62 (m, 16H,
R-THF), 6.73 (m, 4H, BPh-4), 6.87 (m, 8H, BPh-3), 7.00 (m, 2H,
LuC6H5-4), 7.11 (m, 4H, LuC6H5-3), 7.28 (m, 8H, BPh-2), 7.52
(m, 4H, LuC6H5-2). 13C{1H} NMR (100.6 MHz, THF-d8): δ 26.3
(â-THF), 68.2 (R-THF), 122.0 (BPh-4), 125.8 (quartet, 3JBC ) 2.6
Hz, BPh-3), 126.8 (LuC6H5-4), 127.5 (LuC6H5-3), 137.1 (BPh-2),
dropwise at 0 °C to a solution of 2b (0.285 g, 0.616 mmol) in
THF (20 mL) and stirred at this temperature for 30 min. Evaporation
of all volatiles in vacuo and washing the colorless residue with
pentane (3 × 10 mL) afforded 4b (0.351 g, 68%) as a colorless
powder. 1H NMR (400.1 MHz, THF-d8): δ 1.77 (br s, 16H,
â-THF), 2.18 (s, 6H, CH3), 3.62 (br s, 16H, R-THF), 6.72 (t, 3JHH
) 7.2 Hz, 4H, BPh-4), 6.86 (m, 8H + 4H, BPh-3 + ScC6H4-3),
7.28 (m, 8H + 4H, BPh-2 + ScC6H4-2). 13C{1H} NMR (100.6
MHz, THF-d8): δ 21.6 (CH3), 26.3 (br, â-THF), 68.2 (br, R-THF),
1
138.5 (LuC6H5-2), 165.1 (quartet, JBC ) 49.4 Hz, BPh-1), 192.7
(LuC6H5-1). 11B{1H} NMR (128.4 MHz, THF-d8): δ -6.6. Anal.
Calcd for C52H62BLuO4 (936.84): C, 66.67; H, 6.67; Lu, 18.68.
Found: C, 62.22; H, 6.14; Lu, 18.97.
3
121.9 (BPh-4), 125.7 (quartet, JBC ) 3.2 Hz, BPh-3), 127.9
[Lu(C6H4-p-Me)2(THF)4]+[BPh4]- (3b). A solution of [NEt3H]+
[BPh4]- (0.213 g, 0.506 mmol) in THF (10 mL) was added
dropwise at 0 °C to a solution of 1b (0.300 g, 0.506 mmol) in
THF (20 mL) and stirred at this temperature for 30 min. Evaporation
of all volatiles in vacuo and washing the colorless residue with
pentane (3 × 10 mL) afforded 3b (0.311 g, 66%) as a colorless
powder. 1H NMR (400.1 MHz, THF-d8): δ 1.77 (br s, 16H,
â-THF), 2.21 (s, 6H, CH3), 3.62 (br s, 16H, R-THF), 6.72 (t, 3JHH
(ScC6H4-4), 135.7 (ScC6H4-3), 136.6 (ScC6H4-2), 137.1 (BPh-2),
1
165.1 (quartet, JBC ) 49.4 Hz, BPh-1), resonance for ScC6H4-1
not detected. 11B{1H} NMR (160.3 MHz, THF-d8): δ -6.6. Anal.
Calcd for C54H66BO4Sc (834.88): C, 77.69; H, 7.97; Sc, 5.38.
Found: C, 77.30; H, 7.78; Sc, 5.35.
[Sc(C6H4-p-Et)2(THF)4]+[BPh4]- (4c). A solution of [NEt3H]+-
[BPh4]- (0.212 g, 0.503 mmol) in THF (10 mL) was added
dropwise at 0 °C to a solution of 2c (0.254 g, 0.503 mmol) in THF
(15 mL) and stirred at this temperature for 30 min. Evaporation of
all volatiles in vacuo and washing the colorless residue with pentane
(3 × 10 mL) afforded 4c (0.356 g, 82%) as a colorless powder. 1H
3
) 7.2 Hz, 4H, BPh-4), 6.86 (t, JHH ) 7.2 Hz, 8H, BPh-3), 6.95
3
(d, JHH ) 7.5 Hz, 4H, LuC6H4-3), 7.28 (m, 8H, BPh-2), 7.43 (d,
3JHH ) 7.5 Hz, 4H, LuC6H4-2). 13C{1H} NMR (100.6 MHz, THF-
d8): δ 21.6 (CH3), 26.3 (br, â-THF), 68.2 (br, R-THF), 121.9 (BPh-
4), 125.7 (quartet, 3JBC ) 3.2 Hz, BPh-3), 128.1 (LuC6H4-4), 135.6
(LuC6H4-3), 137.1 (BPh-2), 138.6 (LuC6H4-2), 165.1 (quartet, 1JBC
) 49.4 Hz, BPh-1), 189.1 (LuC6H4-1). 11B{1H} NMR (160.3 MHz,
THF-d8): δ -6.6. Anal. Calcd for C54H66BLuO4 (964.90): C,
67.22; H, 6.89; Lu, 18.13. Found: C, 66.07; H, 6.41; Lu, 17.96.
3
NMR (499.6 MHz, THF-d8): δ 1.16 (t, JHH ) 7.5 Hz, 6H,
3
CH2CH3), 1.77 (m, 16H, â-THF), 2.50 (quartet, JHH ) 7.5 Hz,
4H, CH2CH3), 3.62 (m, 16H, R-THF), 6.72 (m, 4H, BPh-4), 6.86
(m, 8H + 4H, BPh-3 + ScC6H4-3), 7.28 (m, 8H, BPh-2), 7.32 (d,
3JHH ) 7.8 Hz, 4H, ScC6H4-2). 13C{1H} NMR (100.6 MHz, THF-
d8): δ 16.0 (CH2CH3), 26.3 (br, â-THF), 29.6 (CH2CH3), 68.2 (br,
3
[Lu(C6H4-p-Et)2(THF)4]+[BPh4]- (3c). A solution of [NEt3H]+-
[BPh4]- (0.133 g, 0.315 mmol) in THF (10 mL) was added
dropwise at 0 °C to a solution of 1c (0.200 g, 0.315 mmol) in THF
(15 mL) and stirred at this temperature for 30 min. Evaporation of
all volatiles in vacuo and washing the colorless residue with pentane
(3 × 10 mL) afforded 3c (0.156 g, 50%) as a colorless powder. 1H
R-THF), 121.9 (BPh-4), 125.7 (quartet, JBC ) 2.6 Hz, BPh-3),
126.6 (ScC6H4-4), 136.6 (ScC6H4-3), 142.2 (ScC6H4-2), 137.1 (m,
BPh-2), 165.1 (quartet, 1JBC ) 49.4 Hz, BPh-1), signal for ScC6H4-1
not detected. 11B{1H} NMR (160.3 MHz, THF-d8): δ -6.6. Anal.
Calcd for C56H70BO4Sc (862.94): C, 77.94; H, 8.18; Sc, 5.21.
Found: C, 75.25; H, 7.91; Sc, 5.12.
3
[Lu(C6H5)(THF)5]2+[BPh4]- (5a). To a mixture of 1a (0.133
NMR (499.6 MHz, THF-d8): δ 1.17 (t, JHH ) 7.5 Hz, 6H,
2
3
g, 0.242 mmol) and [NEt3H]+[BPh4]- (0.204 g, 0.483 mmol) was
added THF (20 mL) at -78 °C. After the stirred mixture was
allowed to slowly warm to room temperature overnight, the
supernatant was decanted and the colorless precipitate was washed
with THF (3 × 20 mL). All volatiles were removed under reduced
pressure to yield 5a (0.200 g, 66%) as a colorless powder. 1H NMR
(400.1 MHz, pyridine-d5): δ 1.60 (br s, 20H, â-THF), 3.64 (br s,
CH2CH3), 1.78 (m, 16H, â-THF), 2.52 (quartet, JHH ) 7.7 Hz,
4H, CH2CH3), 3.62 (m, 16H, R-THF), 6.73 (t, 3JHH ) 7.2 Hz, 4H,
3
3
BPh-4), 6.86 (t, JHH ) 7.4 Hz, 8H, BPh-3), 6.98 (d, JHH ) 7.8
Hz, 4H, LuC6H4-3), 7.28 (m, 8H, BPh-2), 7.47 (d, 3JHH ) 7.5 Hz,
4H, LuC6H4-2). 13C{1H} NMR (100.6 MHz, THF-d8): δ 16.1
(CH2CH3), 26.4 (br, â-THF), 29.7 (CH2CH3), 68.2 (br, R-THF),
3
121.9 (BPh-4), 125.8 (quartet, JBC ) 2.6 Hz, BPh-3), 126.9
20H, R-THF), 7.07 (t, 3JHH ) 7.2 Hz, 8H, BPh-4), 7.24 (t, 3JHH
7.5 Hz, 16H, BPh-3), 7.43-7.51 (m, 1H + 2H, LuC6H5-4 +
)
(LuC6H4-3), 137.1 (BPh-2), 138.7 (LuC6H4-3), 142.2 (LuC6H4-2),
165.2 (quartet, JBC ) 49.4 Hz, BPh-1), 189.6 (LuC6H4-1). 11B-
1
{1H} NMR (160.3 MHz, THF-d8): δ -6.6. Anal. Calcd for C56H70-
BLuO4 (992.95): C, 67.74; H, 7.11; Lu, 17.62. Found: C, 67.57;
H, 6.60; Lu, 17.47.
3
3
LuC6H5-3), 8.02 (m, 16H, BPh-2), 8.12 (dd, JHH ) 7.7 Hz, JHH
) 1.6 Hz, 2H, LuC6H5-2). 13C{1H} NMR (100.6 MHz, pyridine-
d5): δ 25.8 (â-THF), 67.8 (R-THF), 122.4 (BPh-4), 126.2 (q, 3JBC
) 2.6 Hz, BPh-3), 128.4 (LuC6H5-4), 135.2 (LuC6H5-3), 137.2
(BPh-2), 139.7 (LuC6H5-2), 165.0 (q, 1JBC ) 49.4 Hz, BPh-1), 192.2
(LuC6H5-1). 11B{1H} NMR (128.4 MHz, pyridine-d5): δ -5.8.
Anal. Calcd for C74H85B2LuO5 (1251.08): C, 71.04; H, 6.85; Lu,
13.99. Found: C, 67.61; H, 6.63; Lu, 14.27.
[Sc(C6H5)2(THF)4]+[BPh4]- (4a). A solution of [NEt3H]+[BPh4]-
(0.240 g, 0.568 mmol) in THF (10 mL) was added dropwise at
0 °C to a solution of 2a (0.239 g, 0.568 mmol) in THF (20 mL)
and stirred at this temperature for 30 min. Evaporation of all
volatiles in vacuo and washing the colorless residue with pentane
(3 × 10 mL) afforded 4a (0.399 g, 70%) as a colorless powder. 1H
NMR (499.6 MHz, THF-d8): δ 1.78 (m, 16H, â-THF), 3.62 (m,
[Lu(C6H4-p-Me)(THF)5]2+[BPh4]- (5b). To a mixture of 1b
2
(0.200 g, 0.363 mmol) and [NEt3H]+[BPh4]- (0.306 g, 0.723 mmol)
was added THF (20 mL) at -78 °C. After the stirred mixture was
allowed to slowly warm to room temperature overnight, the
supernatant was decanted and the colorless precipitate was washed
with THF (3 × 20 mL). All volatiles were removed under reduced
pressure to yield 5b (0.189 g, 41%) as a colorless powder. 1H NMR
(400.1 MHz, pyridine-d5): δ 1.60 (m, 20H, â-THF), 2.38 (s, 3H,
CH3), 3.64 (m, 20H, R-THF), 7.07 (m, 2H + 8H, LuC6H4-3 +
16H, R-THF), 6.73 (t, 3JHH ) 7.2 Hz, 4H, BPh-4), 6.87 (t, 3JHH
)
7.2 Hz, 8H, BPh-3), 7.01 (m, 2H + 4H, ScC6H5-4 + ScC6H5-3),
7.29 (m, 8H, BPh-2), 7.38 (m, 4H, ScC6H5-2). 13C{1H} NMR (125.6
MHz, THF-d8): δ 26.4 (br, â-THF), 68.2 (br, R-THF), 121.9 (BPh-
4), 125.7 (quartet, 3JBC ) 3.2 Hz, BPh-3), 126.3 (ScC6H5-4), 127.3
(ScC6H5-3), 136.4 (ScC6H5-2), 137.1 (BPh-2), 165.1 (quartet, 1JBC
) 49.4 Hz, BPh-1), signal for ScC6H5-1 not detected. 11B{1H} NMR
(160.3 MHz, THF-d8): δ -6.6. Anal. Calcd for C52H62BO4Sc
(806.83): C, 77.41; H, 7.75; Sc, 5.57. Found: C, 75.72; H, 7.51;
Sc, 5.59. Single crystals suitable for X-ray structure analysis were
obtained by slow evaporation of a concentrated THF solution at
room temperature.
3
3
BPh-4), 7.23 (t, JHH ) 7.4 Hz, 16H, BPh-3), 7.31 (d, JHH ) 7.5
Hz, 2H, LuC6H4-2), 8.02 (m, 16H, BPh-2). 13C{1H} NMR (100.6
MHz, pyridine-d5): δ 21.5 (CH3), 25.8 (br, â-THF), 67.8 (br,
3
R-THF), 122.4 (BPh-4), 126.2 (quartet, JBC ) 3.2 Hz, BPh-3),
129.0 (LuC6H4-4), 137.0 (LuC6H4-3), 137.1 (BPh-2), 139.9 (LuC6H4-
2), 165.0 (q, 1JBC ) 49.4 Hz, BPh-1), 188.7 (LuC6H4-1). 11B{1H}
NMR (128.4 MHz, pyridine-d5): δ -5.8. Anal. Calcd for C75H87B2-
[Sc(C6H4-p-Me)2(THF)4]+[BPh4]- (4b). A solution of [NEt3H]+-
[BPh4]- (0.260 g, 0.616 mmol) in THF (10 mL) was added

Cationic Aryl Complexes of the Rare-Earth Metals
Organometallics, Vol. 26, No. 25, 2007 6395
Table 1. Experimental Data for the Crystal Structure
Determination of the Complexes 4a and 5a‚2THF
was added THF (20 mL) at -78 °C. After the stirred mixture was
allowed to slowly warm to room temperature overnight, the
supernatant was decanted and the colorless precipitate was washed
with THF (3 × 20 mL). All volatiles were removed under reduced
pressure to yield 5c (0.228 g, 57%) as a colorless powder. 1H NMR
(400.1 MHz, pyridine-d5): δ 1.25 (t, 3JHH ) 7.7 Hz, 3H, CH2CH3),
4a
5a·2THF
empirical formula
C52H62BO4Sc
806.79
C82H101B2LuO7
1395.22
Mr
cryst size/mm
cryst syst
space group
a/Å
0.22 × 0.34 × 0.62 0.09 × 0.17 × 0.31
3
monoclinic
P21/c
orthorhombic
P212121
1.60 (m, 20H, â-THF), 2.68 (quartet, JHH ) 7.7 Hz, 2H, CH2-
CH3), 3.63 (m, 20H, R-THF), 7.07 (t, 3JHH ) 7.2 Hz, 8H, BPh-4),
10.110(2)
26.266(5)
16.681(3)
94.084(4)
4418.3(15)
4
12.3689(15)
13.8132(16)
41.361(5)
3
3
7.23 (t, JHH ) 7.3 Hz, 16H, BPh-3), 7.34 (t, JHH ) 7.3 Hz, 2H,
LuC6H4-3), 8.02 (m, 16 + 2H, BPh-2 + LuC6H4-2). 13C{1H} NMR
(100.6 MHz, pyridine-d5): δ 22.5 (CH2CH3), 25.8 (br, â-THF),
29.1 (CH2CH3), 67.8 (br, R-THF), 122.4 (BPh-4), 126.2 (quartet,
3JBC ) 3.2 Hz, BPh-3), 127.8 (LuC6H4-4), 135.2 (LuC6H4-3), 137.1
b/Å
c/Å
â/deg
V/Å3
7066.7(15)
4
Z
F
calc/g cm-1
1.213
1.311
1
(BPh-2), 139.9 (LuC6H4-2), 165.0 (quartet, JBC ) 49.4 Hz, BPh-
µ (Mo KR), mm-1
F(000)
0.211
1.452
1), 189.1 (LuC6H4-1). 11B{1H} NMR (128.4 MHz, pyridine-d5):
δ -5.8. Anal. Calcd for C76H89B2LuO5 (1279.13): C, 71.36; H,
7.01; Lu, 13.68. Found: C, 69.28; H, 7.19; Lu, 13.81.
1728
2920
T/K
110(2)
130
θ range/deg
no. of reflns collected
1.45-28.34
58 078
0.98-25.00
40 836
[Sc(C6H5)(THF)5]2+[BPh4]- (6a). To a mixture of 2a (0.200
2
no. of reflns obsd [I > 2σ(I)] 9869
no. of indep reflns (Rint 10 894 (0.0490)
no. of data/restraints/params 10 894/0/523
8186
g, 0.476 mmol) and [NPhMe2H]+[BPh4]- (0.420 g, 0.951 mmol)
was added THF (20 mL) at -78 °C. After the stirred mixture was
allowed to slowly warm to room temperature overnight, the
supernatant was decanted and the colorless precipitate was washed
with THF (3 × 20 mL). All volatiles were removed under reduced
pressure to yield 6a (0.356 g, 67%) as a colorless powder. 1H NMR
(400.1 MHz, pyridine-d5): δ 1.60 (br, 20H, â-THF), 3.63 (br, 20H,
)
12 426 (0.0917)
12 426/0/399
1.019
GOF
1.221
final R indices R1,a wR2b
(obsd data)
0.0744, 0.1793
0.0692, 0.1450
final R indices R1, wR2
(all data)
0.0827, 0.1847
0.1024, 0.1555
largest e(max), e(min)/e Å-3 0.502 and -0.896
0.892 and -1.918
3
3
R-THF), 7.06 (t, JHH ) 7.2 Hz, 8H, BPh-4), 7.22 (t, JHH ) 7.4
Hz, 16H, BPh-3), 7.31-7.38 (m, 1H + 2H, ScC6H5-4 + ScC6H5-
2
2
a R1(F) ) ∑||F0| - |Fc||/∑|F0|. b wR2(F) ) [∑w(F0 - Fc )2/
2
∑w(F0 )2]1/2
.
3
3
3), 7.49 (dd, JHH ) 8.3 Hz, JHH ) 1.3 Hz, 2H, ScC6H5-2), 8.00
(m, 16H, BPh-2). 13C{1H} NMR (100.6 MHz, pyridine-d5): δ 26.3
(â-THF), 68.3 (R-THF), 122.9 (BPh-4), 126.7 (quartet, 3JBC ) 2.6
Hz, BPh-3), 128.4 (ScC6H5-4), 135.7 (ScC6H5-3), 137.6 (BPh-2),
LuO5 (1265.10): C, 71.21; H, 6.93; Lu, 13.83. Found: C, 69.67;
H, 6.76; Lu, 13.81.
[Lu(C6H4-p-Me)(C5H5N)5]2+[BPh4]-2 (5b′). Complex 5b (0.070
g, 0.0552 mmol) was dissolved in pyridine (1.5 mL) and stirred
for 1 min. Pentane (10 mL) was added to the colorless solution to
give an oily deposit. Further washings with pentane (3 × 10 mL)
gave 54.0 mg (41.5 µmol, 75%) of 20b′ as a slightly yellow powder
after drying in vacuo. 1H NMR (400.1 MHz, pyridine-d5): δ 2.38
(s, 3H, CH3), 7.07 (m, 2H + 8H, LuC6H4-3 + BPh-4), 7.23 (t,
3JHH ) 7.4 Hz, 16H, BPh-3), 7.31 (d, 3JHH ) 7.5 Hz, 2H, LuC6H4-
2), 8.02 (m, 16H, BPh-2). 13C{1H} NMR (100.6 MHz, pyridine-
1
137.1 (ScC6H5-2), 165.4 (quartet, JBC ) 49.4 Hz, BPh-1), signal
for ScC6H5-1 not detected. 11B{1H} NMR (128.4 MHz, pyridine-
d5): δ -5.8. Anal. Calcd for C74H85B2O5Sc (1121.06): C, 79.28;
H, 7.64; Sc, 4.01. Found: C, 75.96; H, 7.27; Sc, 4.07.
[Sc(C6H4-p-Me)(THF)5]2+[BPh4]- (6b). To a mixture of 2b
2
(0.200 g, 0.423 mmol) and [NPhMe2H]+[BPh4]- (0.382 g, 0.865
mmol) was added THF (20 mL) at -78 °C. After the stirred mixture
was allowed to slowly warm to room temperature overnight, the
supernatant was decanted and the colorless precipitate was washed
with THF (3 × 20 mL). All volatiles were removed under reduced
pressure to yield 6b (0.172 g, 36%) as a colorless powder. 1H NMR
(400.1 MHz, pyridine-d5): δ 1.60 (m, 20H, â-THF), 2.28 (s, 3H,
CH3), 3.64 (m, 20H, R-THF), 7.04 (d, 3JHH ) 7.8 Hz, 2H, ScC6H4-
3
d5): δ 21.5 (CH3), 122.4 (BPh-4), 126.2 (quartet, JBC ) 3.2 Hz,
BPh-3), 129.0 (LuC6H4-4), 137.0 (LuC6H4-3), 137.1 (BPh-2), 139.9
(LuC6H4-2), 165.0 (q, 1JBC ) 49.4 Hz, BPh-1), 188.7 (LuC6H4-1).
11B{1H} NMR (128.4 MHz, pyridine-d5): δ -5.8.
Reaction of 5b with Pyridine. Complex 5b (0.0350 g, 27.7
µmol) was dissolved in pyridine (2 mL) and stirred at 50 °C for 5
days. After addition of one drop H2O, filtration on silica gel, and
washing with pyridine (10 mL), the volume of the solution was
slowly reduced by evaporation of the solvent to approximately 2
mL. The resulting yellow solution was analyzed via GC/MS(EI),
and two products could be detected: 2,2′-bipyridyl, Rt ) 7.76 min,
MS m/z (rel. int.), 156.0 (M+, 100), 129.0 (17), 127.9 (20), 77.9
(16); and 2-p-tolyl-pyridine, Rt ) 9.54 min, MS m/z (rel. int.), 169.0
(M+, 100), 154.0 (6), 83.4 (11).
3
3
3), 7.07 (t, JHH ) 7.2 Hz, 8H, BPh-4), 7.24 (t, JHH ) 7.4 Hz,
3
16H, BPh-3), 7.30 (d, JHH ) 7.8 Hz, 2H, ScC6H4-2), 8.02 (m,
16H, BPh-2). 13C{1H} NMR (100.6 MHz, pyridine-d5): δ 21.5
(CH3), 25.8 (br, â-THF), 67.8 (br, R-THF), 122.4 (BPh-4), 126.2
(quartet, 3JBC ) 3.2 Hz, BPh-3), 128.3 (ScC6H4-4), 136.8 (ScC6H4-
1
3), 137.2 (BPh-2), 138.6 (ScC6H4-2), 165.0 (quartet, JBC ) 49.4
Hz, BPh-1), resonance ScC6H4-1 not detected. 11B{1H} NMR (128.4
MHz, pyridine-d5): δ -5.8. Anal. Calcd for C75H87B2O5Sc
(1135.09): C, 79.36; H, 7.73; Sc, 3.96. Found: C, 77.33; H, 7.77;
Sc, 3.88.
Kinetic Measurements of the Reaction of 5b with Pyridine-
d5. Complex 5b (0.0250 g, 20.0 µmol) was dissolved in pyridine-
d5 (0.5 mL). In four separate experiments, the sample was heated
in the NMR spectrometer to 35, 45, 55, and 65 °C, respectively.
1H NMR spectra were recorded at regular intervals (35 °C, every
30 min for 14 h; 45 °C, every 15 min for 14.25 h; 55 °C, every 15
min for 7.5 h; 65 °C, every 15 min for 4.5 h) using short delay (d1
) 0.2 s) and acquisition (nt ) 2) times. The rate constants were
detemined by plotting ln(I0/I) against t (I ) integral of the Lu-
(C6H4-p-Me) group). The Ph-2 group of the tetraphenylborate anion
was used as an internal standard for the integration by which the
extent of the conversion of 5b was calculated.
[Sc(C6H4-p-Et)(THF)5]2+[BPh4]- (6c). To a mixture of 2c
2
(0.200 g, 0.396 mmol) and [NPhMe2H]+[BPh4]- (0.350 g, 0.793
mmol) was added THF (20 mL) at -78 °C. After the stirred mixture
was allowed to slowly warm to room temperature overnight, the
supernatant was decanted and the colorless precipitate was washed
with THF (3 × 20 mL). All volatiles were removed under reduced
pressure to yield 6c (0.304 g, 67%) as a colorless powder. 1H NMR
(400.1 MHz, pyridine-d5): δ 1.17 (t, 3JHH ) 7.5 Hz, 3H, CH2CH3),
3
1.63 (m, 20H, â-THF), 2.58 (quartet, JHH ) 7.5 Hz, 2H, CH2-
CH3), 3.63 (m, 20H, R-THF), 7.06 (m, 8H + 2H, BPh-4 + ScC6H4-
3
3
3), 7.22 (t, JHH ) 7.4 Hz, 16H, BPh-3), 7.33 (d, JHH ) 7.5 Hz,
2H, ScC6H4-2), 8.00 (m, 16H, BPh-2). 13C{1H} NMR (100.6 MHz,
pyridine-d5): δ 15.7 (CH2CH3), 25.8 (br, â-THF), 29.1 (CH2CH3),
[Lu(C6H4-p-Et)(THF)5]2+[BPh4]- (5c). To a mixture of 1c
2
(0.200 g, 0.315 mmol) and [NEt3H]+[BPh4]- (0.266 g, 0.630 mmol)

6396 Organometallics, Vol. 26, No. 25, 2007
Zeimentz and Okuda
3
67.8 (br, R-THF), 122.4 (BPh-4), 126.2 (quartet, JBC ) 3.2 Hz,
data for 4a and 5a are summarized in Table 1. Pronounced disorder
in the conformationally soft THF rings of 5a‚2THF, both in the
peripheric atoms of the metal coordinated moieties and in the
solvent THF, resulted in less well-defined electron density maxima.
To obtain a sufficiently simple model without major artifacts in
displacement parameters, most atoms were treated as isotropic in
refinement. While the disorder limits the accuracy, the results are
adequate to describe the overall geometry. An alternative, much
more complicated model with refinement of the disordered atoms
at separate split positions did not improve the model.
BPh-3), 127.1 (ScC6H4-4), 136.9 (ScC6H4-3), 137.1 (BPh-2), 144.9
1
(ScC6H4-2), 165.0 (quartet, JBC ) 49.4 Hz, BPh-1), signal for
ScC6H4-1 not detected. 11B{1H} NMR (128.4 MHz, pyridine-d5):
δ -5.8. Anal. Calcd for C76H89B2O5Sc (1149.12): C, 79.44; H,
7.81; Sc, 3.91. Found: C, 78.91; H, 7.89; Sc, 4.17.
X-ray Crystal Structure Determination. Crystallographic data
for 4a and 5a‚2THF are summarized in Table 1. X-ray diffraction
data were collected on a Bruker CCD area-detector with Mo KR
radiation (graphite monochromator, λ ) 0.71073 Å) using ω scans.
The SMART program package was used for the data collection
and unit cell determination; processing of the raw frame data was
performed using SAINT.39 The structures were solved by direct
methods using the SHELXS-97 program40 and refined against F2
using all reflections with the SHELXL-97 software.41 The hydrogen
atoms were placed in calculated positions. Relevant crystallographic
Acknowledgment. We thank the Deutsche Forschungsge-
meinschaft and the Fonds der Chemischen Industrie for financial
support, Prof. Dr. U. Englert and his group for recording the
crystallographic data and the assistance in the refinement of
the structure of 5a, and Mr. H. Kulinna for experimental support.
(39) Siemens, ASTRO, SAINT, and SADABS. Data Collection and
Processing Software for the SMART System; Siemens Analytical X-ray
Instruments Inc.: Madison, WI, 1996.
(40) Sheldrick, G. M. SHELXS-97, A program for automatic solution of
crystal structures; University of Go¨ttingen: Go¨ttingen, Germany, 1997,
Release 97-2.
(41) Sheldrick, G. M. SHELXL-97, A program for crystal structure
refinement; University of Go¨ttingen: Go¨ttingen, Germany, 1997, Release
97-2.
Supporting Information Available: CIF files giving full
crystallographic data, and ORTEP plots for 4a and 5a‚2THF and
time-conversion and Arrhenius plots for the reaction of 5b with
pyridine-d5. This material is available free of charge via the Internet
at http://pubs.acs.org.
OM7007953