Mono(pentamethylcyclopentadienyl)thorium chemistry: Synthesis, structural characterization, and reactivity of aryloxide and alkyl derivatives

Article abstract of DOI:10.1021/om9508694

Reaction of ThBr₄(THF)₄ with 1 equiv of Cp*MgBr(THF) (Cp* = η-C₅Me₅) produces the mono(pentamethylcyclopentadienyl) complex Cp*ThBr₃(THF)₃ (1). Treatment of 1 with 1 or 2 equiv of KOAr (Ar = 2,6-t-Bu₂C₆H₃) yields the mono and bis(aryloxide) species Cp*ThBr₂(OAr)(THF) (2) and Cp*ThBr(OAr)₂ (3), respectively. Alkylation of 2 with 2 equiv of Me₃SiCH₂MgCl leads to isolation of the bis(alkyl) complex Cp*Th(OAr)(CH₂SiMe₃)₂ (4), while 3 reacts with 1 equiv of MeMgBr to form the mono(alkyl) derivative Cp*ThMe(OAr)₂ (5). 4 reacts with dihydrogen to produce the trimeric thorium dihydride [Cp*ThH2(OAr)]3 (6), while thermolysis of 4 in the presence of triphenylphosphine oxide leads to the isolation of the metallacyclic species Cp*h(OC₆H₃-J-BuCMe₂CH ₂)(OAr)(O=PPh₃) (7). In the presence of 1 equiv of [HNMe₂Ph][B(CeF₅)₄], 4 is found to catalyze the hydrogenation of 1-hexene and also the polymerization of ethylene. Compounds 1-7 have been characterized by ¹H NMR and IR spectroscopy, by microanalysis, and, in the case of 3,4, and 7, by single-crystal X-ray diffraction studies. Cp*ThBr(OAr)₂ (3) exhibits a somewhat distorted three-legged pianostool geometry with Th-Cp*_centroid, Th-O, and Th-Br distances of 2.57(1), 2.16(1) (av), and 2.821(2) A?, respectively. Cp*Th(OAr)(CH₂SiMe₃)₂ (4) also displays a three-legged pianostool geometry with Th-C distances to the alkyl groups of 2.460(9) and 2.488(12) A?. Th-Cp*_centroid and Th-O distances are very similar to those found in 3, at 2.53(1) and 2.186(6) A?, respectively. Cp=Th(OC₆H₃-t-BuCMe₂CH ₂)(OAr)(O=PPh₃) (7) features a distorted trigonal bipyramidal geometry about the metal center, with the Cp* ligand and the oxygen atom of the cyclometalated aryloxide ligand occupying axial sites (Cp*_centroid-Th-O = 168.3(3)°). The Th-C distance to the tert-butyl methylene group is 2.521(12) A?, while Th-O distances to the aryloxide and triphenylphosphine oxide ligands are 2.199(7) (av) and 2.445(7) A?, respectively.

Full text of DOI:10.1021/om9508694

1488
Organometallics 1996, 15, 1488-1496
Mon o(p en ta m eth ylcyclop en ta d ien yl)th or iu m Ch em istr y:
Syn th esis, Str u ctu r a l Ch a r a cter iza tion , a n d Rea ctivity of
Ar yloxid e a n d Alk yl Der iva tives
Raymond J . Butcher,1a David L. Clark,*,1b Steven K. Grumbine,1c
Brian L. Scott,1c and J ohn G. Watkin*,1c
Chemical Science and Technology (CST) Division, Los Alamos National Laboratory,
Los Alamos, New Mexico 87545
Received November 6, 1995X
Reaction of ThBr4(THF)4 with 1 equiv of Cp*MgBr(THF) (Cp* ) η-C5Me5) produces the
mono(pentamethylcyclopentadienyl) complex Cp*ThBr3(THF)3 (1). Treatment of 1 with 1
or 2 equiv of KOAr (Ar ) 2,6-t-Bu2C6H3) yields the mono- and bis(aryloxide) species
Cp*ThBr2(OAr)(THF) (2) and Cp*ThBr(OAr)2 (3), respectively. Alkylation of 2 with 2 equiv
of Me3SiCH2MgCl leads to isolation of the bis(alkyl) complex Cp*Th(OAr)(CH2SiMe3)2 (4),
while 3 reacts with 1 equiv of MeMgBr to form the mono(alkyl) derivative Cp*ThMe(OAr)2
(5). 4 reacts with dihydrogen to produce the trimeric thorium dihydride [Cp*ThH2(OAr)]3
(6), while thermolysis of 4 in the presence of triphenylphosphine oxide leads to the isolation
of the metallacyclic species Cp*Th(OC6H3-t-BuCMe2CH2)(OAr)(OdPPh3) (7). In the presence
of 1 equiv of [HNMe2Ph][B(C6F5)4], 4 is found to catalyze the hydrogenation of 1-hexene and
1
also the polymerization of ethylene. Compounds 1-7 have been characterized by H NMR
and IR spectroscopy, by microanalysis, and, in the case of 3, 4, and 7, by single-crystal X-ray
diffraction studies. Cp*ThBr(OAr)2 (3) exhibits a somewhat distorted three-legged piano-
stool geometry with Th-Cp*centroid, Th-O, and Th-Br distances of 2.57(1), 2.16(1) (av), and
2.821(2) Å, respectively. Cp*Th(OAr)(CH2SiMe3)2 (4) also displays a three-legged piano-
stool geometry with Th-C distances to the alkyl groups of 2.460(9) and 2.488(12) Å. Th-
Cp*centroid and Th-O distances are very similar to those found in 3, at 2.53(1) and
2.186(6) Å, respectively. Cp*Th(OC6H3-t-BuCMe2CH2)(OAr)(OdPPh3) (7) features a distorted
trigonal bipyramidal geometry about the metal center, with the Cp* ligand and the oxygen
atom of the cyclometalated aryloxide ligand occupying axial sites (Cp*centroid-Th-O )
168.3(3)°). The Th-C distance to the tert-butyl methylene group is 2.521(12) Å, while Th-O
distances to the aryloxide and triphenylphosphine oxide ligands are 2.199(7) (av) and
2.445(7) Å, respectively.
In tr od u ction
relatively open coordination sphere of the metal center
in these systems.
The ubiquitous cyclopentadienyl and pentamethylcy-
clopentadienyl ligands have proven to be invaluable in
facilitating the development of organometallic chemistry
of the early actinide elements over the last two decades,
due to their ability to provide steric saturation of these
large metal centers.2 This field of chemistry has thus
been dominated by complexes based upon the Cp*2An
or Cp3An frameworks (Cp* ) η-C5Me5, Cp ) η-C5H5,
An ) Th, U), with reports of actinide compounds con-
taining mono(cyclopentadienyl)3 or mono(pentamethyl-
cyclopentadienyl)4 ancillary ligand sets being consider-
ably less common. However, it would appear that the
relative steric and electronic unsaturation of the mono-
(cyclopentadienyl)actinide framework would make this
class of complexes an attractive synthetic goal, with the
possibility of enhanced reactivity being provided by the
(3) See for example: (a) Cramer, R. E.; Bruck, M. A.; Gilje, J . W.
Organometallics 1988, 7, 1465. (b) Eigenbrot, C. W.; Raymond, K. N.
Inorg. Chem. 1982, 21, 2653. (c) Ernst, R. D.; Kenelly, W. J .; Day, C.
S.; Day, V. W.; Marks, T. J . J . Am. Chem. Soc. 1979, 101, 2656. (d)
Bagnall, K. W.; Benetollo, F.; Bombieri, G.; de Paoli, G. J . Chem. Soc.,
Dalton Trans. 1984, 67. (e) Bagnall, K. W.; Beheshti, A.; Heatley, F.
J . Less-Common Met. 1978, 61, 63. (f) Delavaux-Nicot, B.; Ephri-
tikhine, M. J . Organomet. Chem. 1990, 399, 77. (g) Baudry, D.; Dorion,
P.; Ephritikhine, M. J . Organomet. Chem. 1988, 356, 165. (h) Baudry,
D.; Ephritikhine, M. J . Organomet. Chem. 1988, 349, 123. (i) Dom-
ingos, A.; Marques, N.; Pires de Matos, A. Polyhedron 1990, 9, 69. (j)
Bagnall, K. W.; Edwards, J .; Tempest, A. C. J . Chem. Soc., Dalton
Trans 1978, 295. (k) Bagnall, K. W.; Beheshti, A.; Edwards, J .;
Heatley, F.; Tempest, A. C. J . Chem. Soc., Dalton Trans. 1979, 1241.
(l) Baudin, C.; Ephritikhine, M. J . Organomet. Chem. 1989, 364, C1.
(m) Edelman, M. A.; Lappert, M. F.; Atwood, J . L.; Zhang, H. Inorg.
Chim. Acta 1987, 139, 185. (n) Bombieri, G.; de Paoli, G.; Del Pra, A.;
Bagnall, K. W. Inorg. Nucl. Chem. Lett. 1978, 14, 359. (o) Cramer, R.
E.; Mori, A. L.; Maynard, R. B.; Gilje, J . W.; Tatsumi, K.; Nakamura,
A. J . Am. Chem. Soc. 1984, 106, 5920. (p) Brianese, N.; Casellato, U.;
Ossola, F.; Porchia, M.; Rossetto, G.; Zanella, P.; Graziani, R. J .
Organomet. Chem. 1989, 365, 223. (q) Rebizant, J .; Spirlet, M. R.;
Apostolidis, A.; Kanellakopulos, B. Acta Crystallogr. 1992, 48C, 452.
(4) (a) Mintz, E. A.; Moloy, K. G.; Marks, T. J . J . Am. Chem. Soc.
1982, 104, 4692. (b) Gilbert, T. M.; Ryan, R. R.; Sattelberger, A. P.
Organometallics 1989, 8, 857. (c) Bagnall, K. W.; Beheshti, A.; Heatley,
F.; Tempest, A. C. J . Less-Common Met. 1979, 64, 267. (d) Schake, A.
R.; Avens, L. R.; Burns, C. J .; Clark, D. L.; Sattelberger, A. P.; Smith,
W. H. Organometallics 1993, 12, 1497. (e) Berthet, J . C.; Le Marechal,
J . F.; Ephritikhine, M. J . Organomet. Chem. 1990, 393, C47. (f)
Cymbaluk, T. H.; Ernst, R. D.; Day, V. W. Organometallics 1983, 2,
963. (g) Ryan, R. R.; Salazar, K. V.; Sauer, N. N.; Ritchey, J . M. Inorg.
Chim. Acta 1989, 162, 221.
X Abstract published in Advance ACS Abstracts, February 1, 1996.
(1) (a) Current address: Department of Chemistry, Howard Uni-
versity, Washington, DC 20059. (b) LANL, Mail Stop G739. (c) LANL,
Mail Stop C346.
(2) (a) Marks, T. J . In Comprehensive Organometallic Chemistry;
Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon Press:
Oxford, England, 1982; Vol. 3, pp 211-223. (b) Ephritikhine, M. New
J . Chem. 1992, 16, 451. (c) Clark, D. L.; Sattelberger, A. P. In
Encyclopedia of Inorganic Chemistry; King, R. B., Ed.; Wiley: New
York, 1994; Vol. 1, pp 19-34.
0276-7333/96/2315-1488$12.00/0 © 1996 American Chemical Society

Mono(pentamethylcyclopentadienyl)thorium Chemistry
Organometallics, Vol. 15, No. 5, 1996 1489
In the case of thorium, the range of mono(penta-
methylcyclopentadienyl) complexes described in the
literature is extremely limited. Marks and co-workers
have reported the preparation of the trichloride deriva-
tive Cp*ThCl3(THF)2‚THF (eq 1) and the subsequent
somewhat less sterically hindered coordination sphere
of the mono-ring complexes would lead to enhanced
reactivity.
Resu lts a n d Discu ssion
Syn th esis a n d Rea ctivity. The reaction of anhy-
drous ThCl4 with 1 equiv of Cp*MgCl‚THF has previ-
ously been reported to produce the mono(pentamethyl-
cyclopentadienyl) species Cp*ThCl3(THF)2‚THF (eq 1).4a
A directly analogous reaction in which a THF solution
ThCl4 + Cp*MgCl‚THF f
Cp*ThCl3(THF)2‚THF + MgCl2 (1)
Cp*ThCl3(THF)2‚THF + 3LiCH2Ph f
Cp*Th(CH2Ph)3 + 3LiCl (2)
9c
of ThBr4(THF)4 is treated with 1 equiv of Cp*MgBr‚-
THF, followed by addition of dioxane to precipitate
magnesium halide, was found to lead to the formation
of the analogous tribromide complex Cp*ThBr3(THF)3
(1) in moderate yield (eq 4). 1 is soluble in THF and
reaction of this complex with 3 equiv of benzyllithium
to form the tris(benzyl) complex Cp*Th(CH2C6H5)3 (eq
2).4a More recently, Sattelberger et al. have described
the isolation of the mixed-ring complex (η-C8H8)(η-C5-
Me5)ThCl(THF)x from the reaction of (η-C8H8)ThCl2-
(THF)2 with a pentamethylcyclopentadienyl Grignard
reagent and its subsequent derivatization to produce (η-
C8H8)(η-C5Me5)Th[CH(SiMe3)2], [(η-C8H8)(η-C5Me5)ThH]x,
and (η-C8H8)(η-C5Me5)Th(µ-Cl)2Mg(CH2-t-Bu)(THF).4b
We recently reported the isolation of a mono(penta-
methylcyclopentadienyl)thorium derivative which
was prepared by utilizing an alternative synthetic
route to the more common halide metathesis methods.
Thermolysis of the thorium amido complex Th(OS-
ThBr4(THF)4 + Cp*MgBr‚THF f
Cp*ThBr3(THF)3 + MgBr2 (4)
may be recrystallized from this solvent at low temper-
ature. Crystalline samples of 1 are observed to powder
upon standing in the drybox atmosphere, presumably
due to partial loss of THF from the complex.
1 was found to react smoothly with 1 equiv of KOAr
(Ar ) 2,6-t-Bu2C6H3) to yield the mono(aryloxide) com-
plex Cp*ThBr2(OAr)(THF) (2) in 65% yield following
crystallization from toluene (eq 5). In a directly analo-
O2CF3)[N(SiMe3)2]3 with
1 equiv of pentamethyl-
cyclopentadiene was found to produce the dinuclear
triflate-bridged species Cp*[(Me3Si)2N]Th(µ2-OSO2CF3)3-
THF
Cp*ThBr3(THF)3
+ KOAr
8
Th[N(SiMe3)(SiMe2CH2)]Cp*, as indicated in eq 3.5
18 h
1
Cp*ThBr (OAr)(THF)
+ KBr (5)
2
2
THF
Cp*ThBr3(THF)3
+ 2KOAr
8
18 h
1
Cp*ThBr(OAr)2
+ 2KBr (6)
3
Ar ) 2,6-t-Bu2C6H3
gous reaction, 1 also reacts with 2 equiv of KOAr to
produce the bis(aryloxide) species Cp*ThBr(OAr)2 (3),
which may be isolated in 73% yield after crystallization
from hexane (eq 6). The colorless crystalline complexes
were characterized by NMR and IR spectroscopy and
elemental analysis.
The thorium halide derivatives 2 and 3 may be
readily alkylated with Grignard reagents in the pres-
ence of dioxane to give thorium alkyl species. Thus the
addition of 2 equiv of Me3SiCH2MgCl to a toluene
solution of Cp*ThBr2(OAr)(THF) (2), followed by addi-
tion of dioxane and crystallization from toluene, leads
In an elegant series of studies, Marks and co-workers
have shown that bis(pentamethylcyclopentadienyl) de-
rivatives of thorium possess extremely high catalytic
activity in reactions such as R-olefin polymerization and
hydrogenation and arene hydrogenation.6 By compari-
son, only limited studies have been carried out to
determine the catalytic properties of the corresponding
mono(pentamethylcyclopentadienyl) derivatives.6d,7,8 As
part of our ongoing studies of the inorganic and orga-
nometallic chemistry of the early actinide elements,9 we
were interested in further exploring the structural,
reactivity, and catalytic properties of mono(pentameth-
ylcyclopentadienyl)thorium species containing a variety
of supporting ligands and determining whether the
(9) (a) Clark, D. L.; Huffman, J . C.; Watkin, J . G. J . Chem. Soc.,
Chem. Commun. 1992, 266. (b) Clark, D. L.; Sattelberger, A. P.; Van
der Sluys, W. G.; Watkin, J . G. J . Alloys Compounds 1992, 180, 303.
(c) Clark, D. L.; Frankcom, T. M.; Miller, M. M.; Watkin, J . G. Inorg.
Chem. 1992, 31, 1628. (d) Berg, J . M.; Clark, D. L.; Huffman, J . C.;
Morris, D. E.; Sattelberger, A. P.; Streib, W. E.; Van der Sluys, W. G.;
Watkin, J . G. J . Am. Chem. Soc. 1992, 114, 10811. (e) Clark, D. L.;
Miller, M. M.; Watkin, J . G. Inorg. Chem. 1993, 32, 772. (f) Clark, D.
L.; Watkin, J . G. Inorg. Chem. 1993, 32, 1766. (g) Avens, L. R.; Bott,
S. G.; Clark, D. L.; Sattelberger, A. P.; Watkin, J . G.; Zwick, B. D.
Inorg. Chem. 1994, 33, 2248. (h) Barnhart, D. M.; Clark, D. L.; Gordon,
J . C.; Huffman, J . C.; Watkin, J . G. Inorg. Chem. 1994, 33, 3939. (i)
Barnhart, D. M.; Clark, D. L.; Grumbine, S. K.; Watkin, J . G. Inorg.
Chem. 1995, 34, 1695.
(5) Butcher, R. J .; Clark, D. L.; Grumbine, S. K.; Watkin, J . G.
Organometallics 1995, 14, 2799.
(6) See, for example: (a) J ia, L.; Yang, X.; Stern, C.; Marks, T. J .
Organometallics 1994, 13, 3755. (b) Eisen, M. S.; Marks, T. J . J . Mol.
Catal. 1994, 86, 23. (c) Yang, X.; King, W. A.; Sabat, M.; Marks, T. J .
Organometallics 1993, 12, 4254. (d) He, M. Y.; Xiong, G.; Toscano, P.
J .; Burwell, R. L., J r.; Marks, T. J . J . Am. Chem. Soc. 1985, 107, 641.
(7) Eisen, M. S.; Marks, T. J . J . Am. Chem. Soc. 1992, 114, 10358.
(8) Finch, W. C.; Gillespie, R. D.; Hedden, D.; Marks, T. J . J . Am.
Chem. Soc. 1990, 112, 6221.

1490 Organometallics, Vol. 15, No. 5, 1996
Butcher et al.
to the isolation of the bis(alkyl) complex Cp*Th(OAr)-
(CH2SiMe3)2 (4) as colorless crystals in 54% yield (eq
7).
toluene
Cp*ThBr (OAr)(THF)
+ 2Me3SiCH2MgCl dioxane, 3 h8
2
2
Cp*Th(OAr)(CH2SiMe3)2
(7)
4
7 give microanalytical data consistent with the solvent-
free formulation.
Ar ) 2,6-t-Bu2C6H3
Sp ectr oscop ic Stu d ies. Interpretation of the room-
1
temperature H NMR spectra of Cp*ThBr3(THF)3 (1),
In a similar manner, Cp*ThBr(OAr)2 (3) is found to
react smoothly with 1 equiv of MeMgBr to yield the
thorium alkyl complex Cp*ThMe(OAr)2 (5), which may
be isolated by low-temperature crystallization from
hexane solution as colorless crystals in 74% yield (eq
8).
Cp*ThBr2(OAr)(THF) (2), and Cp*ThBr(OAr)2 (3) was
straightforward. In each case the spectra revealed the
presence of Cp*, aryloxide, and/or THF ligands in the
1
expected ratio. The H NMR spectrum of the bis(alkyl)
complex Cp*Th(OAr)(CH2SiMe3)2 (4) contains reso-
nances assigned to Cp* and aryloxide ligands in a 1:1
ratio, in addition to two (trimethylsilyl)methyl groups
possessing diastereotopic methylene protons which are
observed as doublets (J HH ) 12 Hz) at -0.08 and 0.17
ppm. In the proton-coupled 13C NMR spectrum of 4,
the methylene carbon resonance appears at δ 91.23 as
a slightly broadened triplet which exhibits a coupling
constant (J CH ) 100 Hz) significantly smaller than that
expected for an sp3-hybridized carbon atom. A similarly
reduced J CH coupling constant (J CH ) 99 Hz) has been
observed previously in the bis(cyclopentadienyl)thorium
complex [Me2Si(η-C5Me4)2]Th(CH2SiMe3)2, in which R-a-
gostic interactions of the methylene groups with the
metal center were believed to be responsible for the
reduced coupling.11b Additional evidence for a possible
R-agostic interaction has also been observed in the solid-
state structure of 4 (vide infra).
toluene
Cp*ThBr(OAr)2
+ MeMgBr dioxane, 3 h8
3
Cp*MeTh(OAr)2
(8)
5
Ar ) 2,6-t-Bu2C6H3
A benzene solution of the bis(alkyl) complex Cp*Th-
(OAr)(CH2SiMe3)2 (4) is found to react with 1 atmo-
sphere of dihydrogen over a period of 18 h at room
temperature to produce a crystalline solid (6) with the
empirical formula Cp*ThH2(OAr) (eq 9). A solution
H2
Cp*Th(OAr)(CH2SiMe3)2
benzene, 18 h8
4
1H NMR spectra of Cp*ThMe(OAr)2 (5) indicate the
presence of Cp* and aryloxide ligands in a 1:2 ratio, in
addition to a distinctive resonance at δ 0.88 assigned
to the thorium-bound methyl group. Ambient-temper-
ature 1H NMR spectra of the trimeric species [Cp*ThH2-
(OAr)]3 (6) show a singlet resonance at δ 18.54 (relative
integral 2) which is indicative of thorium-bound hydride
ligands,11,12 and the appearance of this resonance
remains unchanged down to -80 °C in toluene-d8
solution. In addition to the hydride resonance in the
ambient temperature spectrum, there are three arylox-
ide tert-butyl resonances which each integrate for 18
protons and two Cp* resonances with relative integrals
of 30 and 15 protons. The aromatic portion of the
spectrum contains two triplet para-proton resonances
in a 2:1 ratio, in addition to two resonances assigned to
meta-protons in a 4:2 ratio.
1/3[Cp*ThH2(OAr)]3 + 2SiMe4 (9)
6
Ar ) 2,6-t-Bu2C6H3
molecular weight determination of the crystalline mate-
rial (isopiestic method, benzene solution) supported the
formulation of this material as a trimer (calcd for
[Cp*ThH2(OAr)]3 ) 1724, found ) 1780), which is also
consistent with the nuclearity of the closely-related
thorium dihydride species Th3(µ3-H)2(µ2-H)4(O-2,6-t-
Bu2C6H3)6 which has recently been isolated.10 6 is found
to be soluble in toluene and sparingly soluble in hexane.
Thermolysis of benzene-d6 solutions of 4 (60 °C, 12
h) resulted in the liberation of SiMe4, but no tractable
products could be isolated from the reaction mixture.
However, in the presence of 1.1 equiv of triphenylphos-
phine oxide the thermolysis of 4 (benzene-d6, 16 h, 60
°C) yielded a crystalline product which 1H NMR spec-
troscopy revealed to contain a cyclometalated aryloxide
ligand. A single-crystal X-ray diffraction study (vide
infra) confirmed the identity of this ligand redistribution
Since a limiting 1H NMR spectrum of the hydride
region of 6 could not be obtained even at -80 °C, the
arrangement of hydride ligands about the trimetallic
core cannot be determined with any certainty. How-
ever, in proposing a tentative structure for 6, we draw
precedence from the structurally characterized bis-
complex as Cp*Th(OC6H3-t-BuCMe2CH2)(OAr)(OdPPh3)
(7) (eq 10). Although freshly-prepared single crystals
of 7 are found to contain a molecule of toluene solvent
10
(aryloxide) complex Th3(µ3-H)2(µ2-H)4(O-2,6-t-Bu2C6H3)6
in which a triangular arrangement of three thorium
1
within the lattice (vide infra), H NMR data show that
(11) (a) Fendrick, C. M.; Mintz, E. A.; Schertz, L. D.; Marks, T. J .;
Day, V. W. Organometallics 1984, 3, 819. (b) Fendrick, C. M.; Schertz,
L. D.; Day, V. W.; Marks, T. J . Organometallics 1988, 7, 1828.
(12) (a) Fagan, P. J .; Manriquez, J . M.; Maatta, E. A.; Seyam, A.
M.; Marks, T. J . J . Am. Chem. Soc. 1981, 103, 6650. (b) Moloy, K. G.;
Marks, T. J . J . Am. Chem. Soc. 1984, 106, 7051. (c) Turner, H. W.;
Simpson, S. J .; Andersen, R. A. J . Am. Chem. Soc. 1979, 101, 2782.
this lattice solvent is lost quite rapidly upon exposure
to vacuum and thoroughly-dried crystalline samples of
(10) Clark, D. L.; Grumbine, S. K.; Scott, B. L.; Watkin, J . G. J .
Am. Chem. Soc. 1995, 117, 9089.

Mono(pentamethylcyclopentadienyl)thorium Chemistry
Organometallics, Vol. 15, No. 5, 1996 1491
metal centers, each bearing two terminal aryloxide
ligands, is capped by two µ3-hydride ligands. Two sides
of the trimetallic core are bridged by single µ2-hydride
ligands, while the third side is bridged by two µ2-hydride
ligands, as shown schematically in I. Other possible
F igu r e 1. ORTEP representation (40% probability el-
lipsoids) of the molecular structure of Cp*ThBr(O-2,6-t-
Bu2C6H3)2 (3) giving the atom-numbering scheme used in
the tables.
hydride configurations in 6 would have all µ2-hydride
ligands or a combination of µ2- and terminal hydrides,
since both arrangements have precedence in the litera-
ture with the structures of {[Me2Si(C5Me4)2]Th(µ2-H)2}2
and [Cp*2Th(µ2-H)H]2.11,12 The observation of two Cp*
Ta ble 1. Su m m a r y of Cr ysta llogr a p h ic Da ta
compounda
1
resonances in a 2:1 ratio in the H NMR spectrum of 6
3
4
7
is consistent with the presence of two Cp* ligands below
the plane of the three thorium metal centers and one
above (as shown schematically in II). If rotation about
the Th-O-C bonds of the aryloxide ligands was re-
stricted by the presence of the bulky Cp* moieties, then
the tert-butyl groups on the lower two aryloxides in II
would be rendered inequivalent. The upper aryloxide
resonance would be unaffected by the hindered rotation
since the aryloxide ligand lies on a mirror plane, and
thus we would expect to observe three tert-butyl reso-
nances in a 1:1:1 ratio, which is consistent with the
NMR data for 6. In the aromatic region of the spectrum,
we would expect structure II to exhibit two para-proton
resonances in a 2:1 ratio and three meta-resonances in
a 2:2:2 ratio. NMR spectra of 6 are consistent with this
expectation, given the fact that two of the meta-proton
resonances appear as an overlapping multiplet. At-
tempts to collect single-crystal X-ray data for 6 were
thwarted by extremely rapid powdering of the crystals
as soon as mother liquor was removed.
empirical formula C38H57BrO2Th C32H58OSi2Th
C63H78O3PTh
P21/c
space group
cell dimens
a, Å
b, Å
c, Å
P21/c
P21/c
18.556(4)
9.871(2)
21.104(4)
110.69(3)
3622.4
4
9.652(2)
23.314(5)
15.592(3)
92.35(3)
3505.5
4
12.802(2)
18.441(2)
23.552(4)
92.02(2)
5556.7
4
1117.1
1.335
27.54
0.710 69
-100
3.0-45.0
10 186
7267
â, deg
V, Å3
Z (molecules/cell)
fw
858
747.0
Dcalc, g cm-3
abs coeff, cm-1
λ(Mo KR)
temp, °C
2θ range, deg
measd reflns
1.573
52.5
0.710 69
-70
2.0-55.0
9005
1.415
43.43
0.710 69
-70
3.0-45.0
5006
unique intensities 8272
4535
obsd reflns
4578
3128
4730
(F > 3.0σ(F))
(F > 4.0σ(F))
(F > 4.0σ(F))
0.0521
0.0558
1.15
R(F)b
0.0644
0.0700
1.37
0.0337
0.0410
1.05
Rw(F)c
goodness-of-Fit
a
3
) Cp*ThBr(OAr)2; 4 ) Cp*Th(OAr)(CH2SiMe3)2; 7 )
b
Cp*Th(OC6H3-t-BuCMe2CH2)(OAr)(OdPPh3). R(F) ) ∑||Fo| -
1H NMR spectra of Cp*Th(OC6H3-t-BuCMe2CH2)-
(OAr)(OdPPh3) (7) may be readily explained by refer-
ence to the solid state structure (vide infra). Although
the aromatic portion of the spectrum is complicated by
overlapping resonances from the triphenylphosphine
oxide ligand, the remaining portion of the spectrum
clearly establishes the presence of a cyclometalated
aryloxide ligand, and the presence of inequivalent
substituents on the second aryloxide moiety due to
hindered rotation. Thus three tert-butyl resonances are
observed in a 1:1:1 ratio (relative integral of each
resonance is 9 protons), together with two separate
methyl group resonances and two doublet resonances
at δ 1.27 and 1.18 (J HH ) 11 Hz, relative integral 1
proton) for the diastereotopic methylene group bound
to the thorium metal center.
Fc||/∑|Fo|. c Rw(F) ) [∑w(|Fo| - Fc|)2/∑w|Fo| ]1/2
.
2
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for Cp *Th Br (O-2,6-t-Bu 2C6H3)2 (3)
Th(1)-O(1)
Th(1)-Br(1)
Th(1)-Cp*(cent)
2.18(1)
2.821(2)
2.57(1)
Th(1)-O(2)
Th(1)-C(264)
Th(1)-Cp*(av)
2.139(8)
3.19(1)
2.84(3)
Cp*(cent)-Th(1)-O(1) 151.0(3) Cp*(cent)-Th(1)-O(2) 107.6(3)
Cp*(cent)-Th(1)-Br(1) 100.7(3) O(1)-Th(1)-O(2)
96.7(4)
101.9(3)
169.8(9)
Br(1)-Th(1)-O(1)
Th(1)-O(1)-C(1)
89.3(3)
Br(1)-Th(1)-O(2)
161.6(9) Th(1)-O(2)-C(21)
Table 1, while selected bond lengths and angles are
presented in Table 2. An ORTEP drawing giving the
atom-numbering scheme used in the tables is shown in
Figure 1. The overall molecular structure of 3 consists
of a distorted three-legged piano-stool geometry about
the thorium metal center, with the Cp*centroid-Th(1)-
O(1) angle of 151.0(3)° being considerably larger than
the Cp*centroid-Th(1)-O(2) or Cp*centroid-Th(1)-Br angles,
which are close to tetrahedral values. The average
Th-C distance to the Cp* ligand of 2.84(3) Å is directly
Solid-State an d Molecu lar Str u ctu r es. Cp*Th Br -
(O-2,6-t-Bu 2C6H3)2 (3). Crystals of 3 suitable for an
X-ray diffraction study were grown by cooling a concen-
trated toluene solution to -40 °C. A summary of data
collection and crystallographic parameters is given in

1492 Organometallics, Vol. 15, No. 5, 1996
Butcher et al.
Ta ble 3. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for Cp *(O-2,6-t-Bu 2C6H3)Th (CH2SiMe3)2‚C7H8
(4)
Th(1)-C(30)
Th(1)-O(1)
Th(1)-Cp*(av)
2.460(9)
2.186(6)
2.81(1)
Th(1)-C(40)
Th(1)-Cp*(cent)
2.488(2)
2.53(1)
O(1)-Th(1)-C(30)
100.8(3) O(1)-Th(1)-C(40)
122.9(3)
Cp*(cent)-Th(1)-C(30) 105.6(5) Cp*(cent)-Th(1)-C(40) 105.3(5)
Cp*(cent)-Th(1)-O(1) 123.5(4) C(30)-Th(1)-C(40)
Th(1)-C(30)-Si(1)
Th(1)-O(1)-C(11)
91.8(4)
139.8(6)
120.0(4) Th(1)-C(40)-Si(2)
171.4(5)
comparable to the distances observed in a number of
other structurally characterized (pentamethylcyclopen-
tadienyl)thorium complexes,13 while the Th-O bond
lengths of the aryloxide ligands (2.18(1) and 2.139(8)
Å) are similar to those found in Th(O-2,6-t-Bu2C6H3)4
(2.189(6) Å),9d Th(O-2,6-Me2C6H3)4(py)2 (2.198(6) Å),9d
and Th(O-2,6-t-Bu2C6H3)2(CH2-py-6-Me)2 (2.190(9) Å).14
The Th-Br distance of 2.821(2) Å is very similar to the
distances of 2.859(3) and 2.85(2) Å found in ThBr4-
F igu r e 2. ORTEP representation (40% probability el-
lipsoids) of the molecular structure of Cp*Th(O-2,6-t-
Bu2C6H3)(CH2SiMe3)2 (4) giving the atom-numbering scheme
used in the tables.
9c
(THF)4 and â-ThBr4,15 respectively. One of the tert-
butyl methyl groups is observed to make a relatively
short nonbonding contact with the metal center
(Th(1)-C(264) ) 3.19(1) Å), presumably due to the
relative steric unsaturation of the metal center. This
Th- -Me distance may be compared with the U- -Me
distance of 3.09(2) Å found in the uranium(III) alkyl
ligand (2.81(1) Å) and the Th-O distance to the aryl-
oxide ligand (2.186(6) Å) are both directly comparable
with the values observed in 3 (vide supra). The Th-C
distances to the (trimethylsilyl)methyl ligands of 2.460-
(9) and 2.488(12) Å are slightly shorter than the average
Th-C distances of 2.55(1), 2.55(2), 2.51(2), and 2.58(1)
Å observed in the thorium alkyl complexes Th(O-2,6-t-
Bu2C6H3)2(CH2-py-6-Me)2,14 Th(CH2C6H5)4(Me2PCH2-
CH2PMe2),18 [Me2Si(Me4C5)2]Th(CH2SiMe3)2,11a and
Cp*Th(CH2C6H5)3,4a although they are comparable to
the Th-C distances found in the metallacyclic species
Cp*2Th[(CH2)2SiMe2] (2.463(13) and 2.485(14) Å).19
Th-C-Si angles within the alkyl ligands are consider-
ably larger than the tetrahedral values expected for
sp3-hybridized carbon atoms, with the Th(1)-C(30)-
Si(1) and Th(1)-C(40)-Si(2) angles having values of
120.0(4) and 139.8(6)°, respectively. Similar values for
Th-C-Si angles have previously been observed in the
16
U[CH(SiMe3)2]3 and Th- - Me distances of 3.073(10)
and 3.064(10) Å in the thorium amido complex Th-
[N(SiMe3)2]2(NMePh)2.9i In both of these cases, agostic
interactions between a methyl group and the metal
center were proposed. The large Th-O-C angles
within the aryloxide ligands (161.6(9) and 169.8(9)°) are
typical of those seen in many other f-element alkoxide
and aryloxide complexes.17
Cp *Th (O-2,6-t-Bu 2C6H3)(CH2SiMe3)2 (4). Crystals
of 4 suitable for an X-ray diffraction study were grown
by cooling a concentrated toluene solution to -40 °C. A
summary of data collection and crystallographic param-
eters is given in Table 1, while selected bond lengths
and angles are presented in Table 3. An ORTEP
drawing giving the atom-numbering scheme used in the
tables is shown in Figure 2. The four ligands bound to
the metal center in 4 define a slightly distorted three-
legged piano stool, with the Cp*centroid-Th(1)-O(1) angle
having the largest deviation from a tetrahedral value
(123.5(4)°). The average Th-C distance to the Cp*
20
complexes Cp*2Th(CH2SiMe3)2 (Th-C ) 2.51(1) and
2.46(1) Å, Th-C-Si ) 132.0(6) and 148.0(7)°, respec-
11
tively) and Me2Si(η-C5Me4)2Th(CH2SiMe3)2 (Th-C )
2.54(2) and 2.48(2) Å, Th-C-Si ) 123.7(14) and
149.5(12)°, respectively). These unusually large Th-
C-Si angles may provide additional evidence, together
with the significantly reduced J CH coupling constant
noted above, for some degree of R-agostic interaction
between the methylene groups and the metal center.
Theoretical studies21 of the large Th-CR-Câ angles in
the related bis(neopentyl) derivative Cp*2Th(CH2-t-
(13) See, for example: (a) Fagan, P. J .; Manriquez, J . M.; Vollmer,
S. H.; Day, C. S.; Day, V. W.; Marks, T. J . J . Am. Chem. Soc. 1981,
103, 2206. (b) Moloy, K. G.; Marks, T. J .; Day, V. W. J . Am. Chem.
Soc. 1983, 105, 5696. (c) Ritchey, J . M.; Zozulin, A. J .; Wrobleski, D.
A.; Ryan, R. R.; Wasserman, H. J .; Moody, D. C.; Paine, R. T. J . Am.
Chem. Soc. 1985, 107, 501. (d) Hay, P. J .; Ryan, R. R.; Salazar, K. V.;
Wrobleski, D. A.; Sattelberger, A. P. J . Am. Chem. Soc. 1986, 108, 313.
(e) Hall, S. W.; Huffman, J . C.; Miller, M. M.; Avens, L. R.; Burns, C.
J .; Arney, D. S. J .; England, A. F.; Sattelberger, A. P. Organometallics
1993, 12, 752. (f) Spirlet, M. R.; Rebizant, J .; Apostolidis, C.;
Kanellakopulos, B. Acta Crystallogr. 1992, C48, 2135. (g) Bruno, J .
W.; Smith, G. M.; Marks, T. J .; Fair, C. K.; Schultz, A. J .; Williams, J .
M. J . Am. Chem. Soc. 1986, 108, 40.
13g
Bu)2 have also concluded that R-agostic interactions
play a role in stabilizing these distortions.
Cp *Th (OC6H3-t-Bu CMe2CH2)(OAr )(OdP P h 3) (7).
Crystals of 7 suitable for an X-ray diffraction study were
grown by cooling a concentrated toluene solution to -40
°C. Data collection and crystallographic parameters are
given in Table 1, while selected bond lengths and angles
are presented in Table 4. An ORTEP drawing giving
(14) Beshouri, S. M.; Fanwick, P. E.; Rothwell, I. P.; Huffman, J . C.
Organometallics 1987, 6, 2498.
(15) Guillaumont, R. Radiochim. Acta 1983, 32, 129.
(16) Van der Sluys, W. G.; Burns, C. J .; Sattelberger, A. P.
Organometallics 1989, 8, 855.
(18) Edwards, P. G.; Andersen, R. A.; Zalkin, A. Organometallics
1984, 3, 293.
(19) Bruno, J . W.; Marks, T. J .; Day, V. W. J . Am. Chem. Soc. 1982,
104, 7357.
(20) Bruno, J . W.; Marks, T. J .; Day, V. W. J . Organomet. Chem.
1983, 250, 237.
(21) (a) Tatsumi, K.; Nakamura, A. Organometallics 1987, 6, 427.
(b) Tatsumi, K.; Nakamura, A. J . Am. Chem. Soc. 1987, 109, 3195.
(17) (a) Zozulin, A. J .; Moody, D. C.; Ryan, R. R. Inorg. Chem. 1982,
21, 3083. (b) Edwards, P. G.; Andersen, R. A.; Zalkin, A. J . Am. Chem.
Soc. 1981, 103, 7792. (c) Hitchcock, P. B.; Lappert, M. F.; Singh, A.;
Taylor, R. G.; Brown, D. J . Chem. Soc., Chem. Commun. 1983, 561.
(d) Evans, W. J .; Hanusa, T. P.; Levan, K. R. Inorg. Chim. Acta 1985,
110, 191. (e) Stecher, H. A.; Sen, A.; Rheingold, A. L. Inorg. Chem.
1988, 27, 1130.

Mono(pentamethylcyclopentadienyl)thorium Chemistry
Organometallics, Vol. 15, No. 5, 1996 1493
enylphosphine oxide ligand is 2.445(7) Å, which is
comparable to the distances of 2.376(10) (av), 2.35(2)
(av), and 2.36(1) Å found for the triphenylphosphine
oxide ligands in ThCl4(OdPPh3)3,23 Th(NO3)4(OdPPh3)2,24
and Th(NO3)2(C17H13N2O2)2(OdPPh3)2.25
Ca ta lytic Stu d ies. Marks and co-workers have
reported the extremely high catalytic activities of cat-
ionic thorium species such as [Cp*2ThMe][X] (X )
BPh4,26 B(C6F5)4,27 t-BuCH2CH[B(C6F5)2]2H6a), and the
12a
hydride complexes [Cp*2Th(µ-H)H]2 and [Me2Si(η-C5-
Me4)2Th(µ-H)2]2,11 in reactions such as ethylene poly-
merization and olefin hydrogenation. It was of interest
to compare the catalytic activities of the bis(alkyl)
complex Cp*Th(OAr)(CH2SiMe3)2 (4) and the dihydride
species [Cp*ThH2(OAr)]3 (6) with the related bis(pen-
tamethylcyclopentadienyl) complexes listed above. It
was hoped that such a comparison of catalytic activities
would provide information concerning the effects upon
reactivity of replacing one pentamethylcyclopentadienyl
ligand with an aryloxide moiety, both in terms of steric
and electronic factors.
F igu r e 3. ORTEP representation (40% probability el-
lipsoids) of the molecular structure of Cp*Th(OC6H3-t-
BuCMe2CH2)(OAr)(OdPPh3) (7) giving the atom-number-
ing scheme used in the tables.
Ta ble 4. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for
In the case of the alkyl derivative Cp*Th(OAr)(CH2-
SiMe3)2 (4), the ammonium salt [HNMe2Ph][B(C6F5)4]
was employed as a proton source to remove one alkyl
ligand and form a cationic thorium complex with the
noncoordinating tetrakis(perfluorophenyl)borate anion.
It was found that the addition of 1 equiv of 4 to a toluene
suspension of [HNMe2Ph][B(C6F5)4] resulted in the
formation of a slightly cloudy solution and the subse-
Cp *Th (OC6H3-t-Bu CMe2CH2)(OAr )(OdP P h 3) (7)
Th(1)-C(25)
Th(1)-O(2)
Th(1)-Cp*(cent)
2.521(12)
2.205(7)
2.62(1)
Th(1)-O(1)
Th(1)-O(3)
Th(1)-Cp*(av)
2.445(7)
2.192(6)
2.88(4)
Cp*(cent)-Th(1)-O(3) 168.3(3) Cp*(cent)-Th(1)-C(25) 99.2(3)
Cp*(cent)-Th(1)-O(2) 101.4(3) Cp*(cent)-Th(1)-O(1) 98.7(3)
O(3)-Th(1)-C(25)
O(3)-Th(1)-O(1)
O(2)-Th(1)-C(25)
Th(1)-C(25)-C(26)
Th(1)-O(2)-C(19)
70.6(3)
80.5(2)
O(3)-Th(1)-O(2)
O(1)-Th(1)-C(25)
86.9(3)
quent separation of an oily material.
A
1H NMR
111.6(3)
134.9(3)
166.6(4)
148.4(6)
spectrum of this material showed the presence of SiMe4,
consistent with the protonation of a ThCH2SiMe3 group,
but attempts to fully characterize the presumed ionic
species [Cp*Th(OAr)(CH2SiMe3)][B(C6F5)4] were unsuc-
cessful. Thus for the catalytic studies described in this
section, a mixture of 4 and [HNMe2Ph][B(C6F5)4] was
used in situ as the active catalyst. The addition of an
equimolar quantity of 4 to a toluene suspension of
[HNMe2Ph][B(C6F5)4] under 1 atm of ethylene led to
formation of a white precipitate of polyethylene over a
period of 130 s. GPC analysis (polystyrene standards)
indicated a moderate molecular weight polymer (Mn )
1.8 × 104, Mw ) 3.1 × 104), while the catalyst activity
was calculated to be 34 600 g h-1 atm-1 (mol catalyst)-1
(Nt ) 0.35 s-1). The catalytic activity of this system
toward ethylene polymerization is thus somewhat greater
than the cationic bis(pentamethylcyclopentadienyl) com-
104.4(3) O(1)-Th(1)-O(2)
116.8(8) Th(1)-O(1)-P(1)
162.6(6) Th(1)-O(3)-C(32)
the atom-numbering scheme used in the tables is shown
in Figure 3. 7 comprises a thorium metal center bearing
a pentamethylcyclopentadienyl ligand, a 2,6-di-tert-
butylphenoxide moiety, and a second aryloxide ligand
which has undergone a cyclometalation reaction involv-
ing one of the tert-butyl methyl groups. A triph-
enylphosphine oxide ligand completes the coordination
sphere. If the Cp* ligand in 7 is considered to occupy a
single coordination site, then the geometry about the
metal center may best be described as distorted trigonal
bipyramidal with the Cp* centroid and O(3) occupying
axial sites (Cp*centroid-Th(1)-O(3) ) 168.3(3)°). The
angles between the three ligands in the equatorial plane
sum to 350.9°, indicating near-planarity of this ligand
set. Th-C distances to the Cp* ligand and Th-O
distances to the aryloxide ligands are again comparable
to those observed in the structures of 3 and 4 (Th-Cp*
) 2.88(4) Å (av) and Th-O ) 2.199(7) Å (av)). The
Th-C distance to the cyclometalated alkyl ligand is
2.521(12) Å, which is within the range observed for other
thorium alkyl bond distances as described above. The
Th-O-C angle for the cyclometalated aryloxide ligand
(Th(1)-O(3)-C(32) ) 148.4(6)°) is, as expected, some-
what smaller than that of the monodentate aryloxide
ligand (Th(1)-O(2)-C(19) ) 162.6(6)°), due to geometric
constraints within the six-membered metallacyclic ring.
While cyclometalated aryloxide ligands have been ob-
served in a number of crystallographically characterized
transition metal complexes, especially of group 5,22
we believe 7 to be the first example of a structurally
characterized cyclometalated aryloxide ligand in f-
element chemistry. The Th-O distance to the triph-
plex [Cp*2ThMe][BPh4] (1100
g
h-1 atm-1 (mol
catalyst)-1, Nt ) 0.01 s-1),6a which contains the rela-
tively coordinating tetraphenylborate anion. However,
a more direct comparison is provided by the analogous
cationic species containing noncoordinating anions.
(22) (a) Chamberlain, L.; Keddington, J .; Rothwell, I. P.; Huffman,
J . C. Organometallics 1982, 1, 1538. (b) Baley, A.-S.; Chauvin, Y.;
Commereuc, D.; Hitchcock, P. B. New J . Chem. 1991, 15, 609. (c)
Steffey, B. D.; Chamberlain, L. R.; Chesnut, R. W.; Chebi, D. E.;
Fanwick, P. E.; Rothwell, I. P. Organometallics 1989, 8, 1419. (d)
Chesnut, R. W.; Steffey, B. D.; Rothwell, I. P.; Huffman, J . C.
Polyhedron 1988, 7, 753. (e) Rothwell, I. P. Acc. Chem. Res. 1988, 21,
153.
(23) Van den Bossche, G.; Rebizant, J .; Spirlet, M. R.; Goffart, J .
Acta Crystallogr. 1988, C44, 994.
(24) Malik, K. M. A.; J effery, J . W. Acta Crystallogr. 1973, B29, 2687.
(25) J arvinen, G. D.; Zozulin, A. J .; Larson, E. M.; Ryan, R. R. Acta
Crystallogr. 1991, C47, 262.
(26) Lin, Z.; Le Marechal, J .-F.; Sabat, M.; Marks, T. J . J . Am. Chem.
Soc. 1987, 109, 4127.
(27) Yang, X.; Stern, C. L.; Marks, T. J . Organometallics 1991, 10,
840.

1494 Organometallics, Vol. 15, No. 5, 1996
Butcher et al.
Indeed it has been reported that the complexes [Cp*2-
electrophilicity of the thorium metal center. The activ-
ity of 6 toward 1-hexene hydrogenation is found to be
somewhat greater than that of dimeric [Cp*2Th(µ-H)-
H]2, but lower than that of the “tied-back” analog [Me2-
Si(η-C5Me4)2Th(µ-H)2]2.
ThMe][B(C6F5)4] (3.6 × 106 g h-1 atm-1 (mol catalyst)-1
,
Nt ) 36 s-1 27
) and [Cp*2ThMe]{t-BuCH2CH[B(C6F5)2]2H}
(5.8 × 106 g h-1 atm-1 (mol catalyst)-1, Nt ) 58 s-1 27
)
show catalytic activity approximately 100 times greater
than 4/[HNMe2Ph][B(C6F5)4].6a
Exp er im en ta l Section
The activity of the 4/[HNMe2Ph][B(C6F5)4] system
toward the catalytic hydrogenation of 1-hexene was also
studied. The addition of 1-hexene to an equimolar
toluene solution of 4 and [HNMe2Ph][B(C6F5)4], followed
by admission of 1 atm of dihydrogen, led to the catalytic
hydrogenation of the olefin. Analysis of the volatiles
from the reaction mixture by GC-MS, and quantification
of the hexane present, allowed calculation of the turn-
over rate of 3 h-1. The activity is thus substantially
lower than that of the cationic methyl derivative [Cp*2-
ThMe][B(C6F5)4], for which a turnover rate of 16 450 h-1
has been reported.27 The dihydride species [Cp*ThH2-
(OAr)]3 (6) was also found to be a single-component
catalyst for the hydrogenation of olefins. Thus a toluene
solution of 6 was found to catalyze the hydrogenation
of 1-hexene under 1 atm of dihydrogen at a modest
Gen er a l P r oced u r es a n d Tech n iqu es. All manipula-
tions were carried out under an inert atmosphere of oxygen-
free UHP grade argon using standard Schlenk techniques or
under oxygen-free helium in a Vacuum Atmospheres glovebox.
ThBr4(THF)4 was prepared as described previously.9c MeMgBr
(3.0 M in THF) and Me3SiCH2MgCl (1.0 M in Et2O) solutions
were purchased from Aldrich and used as received. KO-2,6-
t-Bu2C6H3 was prepared from the reaction of 2,6-di-tert-
butylphenol with potassium hydride in THF. [HNMe2Ph]-
[B(C6F5)4] was obtained from Quantum Design and used as
received. Cp*MgBr was prepared from i-PrMgBr and Cp*H
using the method of Marks et al.12a Solvents were degassed
and distilled from Na or Na/benzophenone ketyl under nitro-
gen. Benzene-d6 was dried with Na/benzophenone ketyl and
then trap-to-trap distilled before use.
NMR spectra were recorded at 22 °C on a Bruker WM 300
turnover rate of 10 h-1
somewhat greater than the bis(pentamethylcyclopen-
tadienyl) analog [Cp*2Th(µ-H)H]2 (0.5 h-1 12a
but con-
.
The activity of 6 is thus
spectrometer in benzene-d6. All H NMR chemical shifts are
1
1
reported in ppm relative to the H impurity in benzene-d6 at
δ 7.15. Infrared spectra were recorded on a BioRad FTS-40
spectrophotometer as Nujol mulls between KBr salt plates.
GPC measurements were carried out by Polytech in trichlo-
robenzene solvent, using polystyrene standards. Elemental
)
siderably lower than that of the “tied-back” derivative
[Me2Si(η-C5Me4)2Th(µ-H)2]2 (610 h-1).11b
The relatively modest activity of 4/[HNMe2Ph]-
[B(C6F5)4] and 6 in catalytic reactions, in comparison
with similar bis(pentamethylcyclopentadienyl) systems,
may be rationalized by the presence of the aryloxide
ligand, which is capable of substantial π-donation to the
metal center. It has been reported previously that the
presence of alkoxide ligands in Cp*2Th(X)(Y) systems
can significantly lower the rate of alkyl ligand hydro-
genolysis by decreasing the electrophilicity of the metal
center.28 The presence of alkoxide ligands can also
result in an increase in Th-R bond disruption enthal-
analyses were performed on
a Perkin-Elmer 2400 CHN
analyzer. Elemental analysis samples were prepared and
sealed in tin capsules in the glovebox prior to combustion.
Cp *Th Br 3(THF )3 (1). THF (120 mL) was added to a flask
containing ThBr4(THF)4 (15.0 g, 17.9 mmol) and Cp*MgBr-
(THF) (5.55 g, 17.9 mmol), and the resulting solution was
stirred for 20 h at room temperature. All volatiles were
removed under vacuum, and the residue was extracted with
a 12:1 CH2Cl2/dioxane solution (130 mL) and filtered. This
solution was pumped dry, extracted with THF (3 × 100 mL),
and concentrated to 50 mL. Cooling of the solution to -40 °C
resulted in the formation of colorless crystals which were
collected by filtration. Yield: 5.3 g, 36%. 1H NMR (300 MHz,
benzene-d6): δ 4.18 (br s, 4 H, R-THF), 3.72 (br s, 8 H, R-THF),
2.42 (s, 15 H, C5Me5), 1.28 (br s, 12 H, â-THF). Anal. Calcd
for C22H39Br3O3Th: C, 32.10; H, 4.77. Found: C, 31.90; H,
4.78.
pies by 2-4 kcal mol-1 28
Thus it would appear that
.
the deleterious electronic effects of the aryloxide ligand
significantly outweigh the somewhat less sterically
hindered coordination sphere of the mono(pentameth-
ylcyclopentadienyl)thorium species.
Cp *Th Br 2(O-2,6-t-Bu 2C6H3)(THF ) (2). THF (25 mL) was
added to a flask containing Cp*ThBr3(THF)3 (4.00 g, 5.49
mmol) and KO-2,6-t-Bu2C6H3 (1.40 g, 5.74 mmol) and the
resulting mixture stirred for 18 h at room temperature,
resulting in much precipitate. All volatiles were removed
under vacuum from the mixture, and the solid was extracted
with toluene (2 × 10 mL) and filtered through Celite. Cooling
to -40 °C led to the formation of crystals which were isolated
by filtration (1.30 g). A second crop was collected upon
concentration and recooling of the mother liquor giving a total
yield of 1.84 g (65%). 1H NMR (300 MHz, benzene-d6): δ 7.19
(d, J HH ) 8 Hz, 2 H, meta OAr), 6.79 (t, J HH ) 8 Hz, 1 H,
para OAr), 3.11 (m, 4 H, R-THF), 2.33 (s, 15 H, C5Me5), 1.53
(s, 18 H, t-Bu), 1.11 (m, 4 H, â-THF). IR (cm-1): 1410 (m),
1307 (w), 1259 (w), 1223 (s), 1201 (s), 1124 (m), 1095 (w), 1039
(w), 1024 (w sh), 1013 (m), 923 (w), 868 (s), 822 (m), 796 (m),
750 (s), 723 (m), 666 (s), 596 (w), 556 (w). Anal. Calcd for
Con clu d in g Rem a r k s. We have shown that the
tribromide complex Cp*ThBr3(THF)3 (1) provides a
convenient entry into the chemistry of mono(pentam-
ethylcyclopentadienyl) derivatives of thorium. Arylox-
ide and alkyl derivatives may readily be prepared by
treatment of 1 with potassium aryloxide or alkyl Grig-
nard reagents, respectively. In the presence of the
ammonium salt [HNMe2Ph][B(C6F5)4], the bis(alkyl)
complex Cp*Th(OAr)(CH2SiMe3)2 (4) has been shown
to exhibit moderate catalytic activity in ethylene po-
lymerization and 1-hexene hydrogenation experiments.
The trimeric hydride derivative [Cp*ThH2(OAr)]3 (6) has
also been shown to be a single-component catalyst for
the hydrogenation of 1-hexene and exhibits an activity
of 10 turnovers h-1. The catalytic activity for hydroge-
nation of 4/[HNMe2Ph][B(C6F5)4] is substantially lower
than the related bis(pentamethylcyclopentadienyl) com-
plex [Cp*2ThMe][B(C6F5)4], possibly as a result of
π-donation from the aryloxide ligand reducing the
3
3
C
38H57Br2O2Th: C, 42.65; H, 5.62. Found: C, 42.31; H, 5.58.
Cp *Th Br (O-2,6-t-Bu 2C6H3)2 (3). THF (25 mL) was added
to a solid mixture of Cp*ThBr3(THF)3 (1.50 g, 2.00 mmol) and
KO-2,6-t-Bu2C6H3 (0.97 g, 4.0 mmol) and stirred at room
temperature for 18 h with much precipitate being formed. The
mixture was filtered through Celite, and all volatiles were
removed in vacuo. The resulting solid was dissolved in hexane
(10 mL) and concentrated under reduced pressure to 2 mL,
(28) Cp*2ThMe2 is found to undergo hydrogenolysis 4 × 103 times
faster than Cp*2Th(OR)(R): Lin, Z.; Marks, T. J . J . Am. Chem. Soc.
1987, 109, 7979.

Mono(pentamethylcyclopentadienyl)thorium Chemistry
Organometallics, Vol. 15, No. 5, 1996 1495
resulting in deposition of colorless crystals which were isolated
and washed with hexane (2 mL). Yield: 1.25 g (73%) with a
Solvent was removed by slow evaporation resulting in an
oil which formed crystals upon addition of toluene (0.5 mL)
and hexane (0.2 mL). The colorless needles were isolated
by decantation and washing with a small amount of cold
(-40 °C) hexane. Yield: 0.028 g (40%). 1H NMR (300 MHz,
benzene-d6): δ 7.57 (m, 6 H, OdPPh3), 7.38 (d, 3J HH ) 8 Hz, 1
H, meta OAr), 7.27 (m, 3 H, OAr), 6.98 (m, 6 H, OdPPh3), 6.87
1
trace of HO-2,6-t-Bu2C6H3 visible by H NMR. 1H NMR (300
3
MHz, benzene-d6): δ 7.19 (d, J HH ) 8 Hz, 2 H, para OAr),
3
6.79 (t, J HH ) 8 Hz, 4 H, meta OAr), 2.18 (s, 15 H, C5Me5),
1.54 (s, 36 H, t-Bu). IR (cm-1): 1583 (w), 1407 (s), 1318 (w),
1264 (m), 1218 (s), 1197 (s), 1122 (m), 1097 (m), 1020 (w), 862
(s), 819 (m), 794 (w), 750 (s), 723 (m), 657 (s), 593 (w), 549
(m), 453 (m), 417 (w). Anal. Calcd for C38H57BrO2Th: C,
53.21; H, 6.70. Found: C, 53.52; H, 6.63.
3
(m, 5 H, OdPPh3, OAr), 6.79 (t, J HH ) 8 Hz, 1 H, para OAr),
2.15 (s, 15 H, C5Me5), 1.76 (s, 3 H, ThCH2CMe2), 1.64 (s, 3 H,
ThCH2CMe2), 1.55 (s, 9 H, t-Bu), 1.44 (s, 9 H, t-Bu), 1.36 (s, 9
3
H, t-Bu), 1.27 (d, J HH ) 11 Hz, 1 H, ThCH2CMe2), 1.18 (d,
Cp *Th (O-2,6-t-Bu 2C6H3)(CH2SiMe3)2 (4). A diethyl ether
solution of Me3SiCH2MgCl (1 M, 3.1 mL, 3.1 mmol) was added
to a toluene (20 mL) solution of Cp*ThBr2(O-2,6-t-Bu2C6H3)-
(THF) (1.30 g, 1.65 mmol) and stirred for 5 min at room
temperature. Dioxane (1 mL) was then added, causing much
precipitation, and the mixture was stirred for 3 h before all
volatiles were removed under vacuum. The solid residue was
extracted with toluene (2 × 15 mL), filtered through Celite,
and then cooled to -40 °C resulting in colorless crystals.
Yield: 0.65 g (54%). 1H NMR (300 MHz, benzene-d6): δ 7.23
3J HH ) 11 Hz, 1 H, ThCH2CMe2). IR (cm-1): 1585 (w), 1407
(s), 1312 (w), 1269 (m), 1257 (m), 1239 (s), 1188 (w), 1121 (s),
1068 (s), 1026 (w), 998 (w), 871 (m sh), 863 (s), 819 (m), 795
(w), 746 (s), 723 (s), 693 (s), 656 (m), 540 (s). Anal. Calcd for
C
56H71O3PTh: C, 63.74; H, 6.78. Found: C, 63.59; H, 7.02.
Hyd r ogen a tion of 1-Hexen e by 4. Toluene (5.6 mL) was
added to a mixture of 4 (0.017 g, 0.023 mmol) and [HNMe2-
Ph][B(C6F5)4] (0.019 g, 0.023 mmol), and the resulting solution
was stirred for 3 min. Hexene (0.62 g, 7.2 mmol) was syringed
into the flask, and after 5 min a dihydrogen atmosphere was
introduced over the solution. The reaction was stirred for 3 h
and then quenched with 1-propanol. All volatiles were vacuum
transferred to a second flask and analyzed by GC-mass
3
3
(d, J HH ) 8 Hz, 2 H, meta OAr), 6.82 (t, J HH ) 8 Hz, 1 H,
para OAr), 2.00 (s, 15 H, C5Me5), 1.50 (s, 18 H, t-Bu), 0.34 (s,
3
18 H, SiMe3), 0.17 (d, J HH ) 12 Hz, 2 H, ThCH2), -0.08 (d,
3J HH ) 12 Hz, 2 H, ThCH2). IR (cm-1): 1584 (w), 1474 (m),
1409 (s), 1388 (m), 1359 (w sh), 1353 (w), 1265 (w sh), 1254
(w), 1241 (s), 1226 (s), 1197 (m), 1125 (m), 1102 (w), 1060 (w),
1021 (w), 886 (m), 867 (s), 848 (s), 822 (s), 747 (s), 730 (w),
709 (m), 675 (w), 659 (m), 551 (w), 454 (w). Anal. Calcd for
C32H58OSi2Th: C, 51.45; H, 7.83. Found: C, 50.83; H, 8.02.
spectroscopy. Hexane found: 0.20 mmol, 3 turnover h-1
.
Hyd r ogen a tion of 1-Hexen e by 6. Toluene (5.6 mL) was
added to [Cp*ThH2(OAr)]3 (6) (0.013 g, 0.0075 mmol), and a
dihydrogen atmosphere was introduced over the solution.
After 5 min of rapid stirring, hexene (0.62 g, 7.2 mmol) was
syringed into the flask and the solution was stirred for 1 h
before 1-propanol was added to quench the reaction. All
volatiles were vacuum transferred to a second flask and
analyzed by GC-mass spectroscopy. Hexane found: 0.22
Cp *Th Me(O-2,6-t-Bu 2C6H3)2 (5). In the drybox, a 3.0 M
THF solution of MeMgBr (0.44 mL, 1.4 mmol) was added to a
cold (-40 °C) mixture of Cp*ThBr(O-2,6-t-Bu2C6H3)2 (1.00 g,
1.17 mmol), hexane (20 mL), THF (15 mL), and dioxane (2 mL),
resulting in an immediate white precipitate. After the mixture
was stirred for 3 h, all volatiles were removed under vacuum,
and the solid was extracted with hexane (2 × 20 mL) and
filtered through Celite. The filtrate was concentrated to 10
mL and cooled to -40 °C resulting in the formation of colorless
crystals which were isolated by filtration. Yield: 0.68 g (74%)
mmol, 10 turnover h-1 (Th atom)-1
.
P olym er iza tion of Eth ylen e by 4. An ethylene atmo-
sphere was introduced over a toluene (40.0 mL) solution of
[HNMe2Ph][B(C6F4)4] (0.016 g, 0.020 mmol) and rapidly stirred
for 5 min. A toluene solution (0.40 mL) of 4 (0.015 g, 0.020
mmol) was syringed into the rapidly stirring ethylene solution,
and after 15 s the solution became cloudy with formation of a
precipitate. The reaction was quenched with 1 mL of methanol
after 130 s and the polymer was collected by filtration and
3
1H NMR (300 MHz, benzene-d6): δ 7.21 (t, J HH ) 8 Hz, 1 H,
para OAr), 6.78 (d, 3J HH ) 8 Hz, 2 H, meta OAr), 2.07 (s, 15 H,
C5Me5), 1.48 (s, 36 H, t-Bu), 0.88 (s, 3 H, ThMe). IR (hexane,
cm-1): 1582 (w), 1406 (m), 1300 (w br), 1262 (m), 1220 (s),
1188 (s), 1121 (m), 1101 (w), 1020 (w), 973 (w), 884 (w), 867
(s), 855 (s), 819 (s), 893 (m), 748 (s), 740 (s), 654 (s), 544 (w).
Anal. Calcd for C39H60O2Th: C, 59.07; H, 7.63. Found: C,
58.48; H, 7.61.
dried to yield 0.025 g of polyethylene (Mn ) 1.8 × 104, Mw
)
3.1 × 104).
Cr ysta llogr a p h ic Stu d ies. Cp *Th Br (O-2,6-t-Bu 2C6H3)2
(3). The clear, well-formed crystals were examined in mineral
oil under an argon stream. The chosen crystal was affixed to
the goniometer head of a CAD4 diffractometer (employing
graphite-monochromated Mo KR radiation) using Apiezon
grease and cooled to -70 °C in a cold nitrogen stream. Unit
cell parameters were determined from the least-squares
refinement of ((sin θ)/λ)2 values for 25 accurately centered
reflections with a 2θ range between 16 and 32°. Three
reflections were chosen as intensity standards and were
measured every 3600 s of X-ray exposure time.
[Cp *Th H2(O-2,6-t-Bu 2C6H3)]3 (6). A benzene solution (3
mL) of 4 (0.250 g, 0.335 mmol) contained in a Schlenk vessel
was pressurized with 1.5 atm of dihydrogen, and the resulting
solution was stirred for 18 h at room temperature. All volatiles
were removed under vacuum, and the product was crystallized
from a 1:10 toluene/hexane (1 mL) solution at -40 °C. Yield:
0.078 g (41%). 1H NMR (300 MHz, benzene-d6): δ 18.54 (s, 6
3
H, ThH), 7.36 (d, J HH ) 8 Hz, 2 H, meta OAr), 7.27 (m, 4 H,
3
3
The data were reduced using the Structure Determination
Package provided by Enraf-Nonius and corrected for absorp-
tion empirically using high-ø ψ-scans. The structure was
solved by Patterson and Fourier techniques and refined by full-
matrix least squares. After inclusion of anisotropic thermal
parameters for all non-hydrogen atoms and geometrical gen-
eration of hydrogen atoms which were constrained to “ride”
upon the appropriate carbon atoms, final refinement using
4578 unique observed [F > 3σ(F)] reflections converged at R
) 0.064 and Rw ) 0.070 {where w ) [σ2(F) + 0.0002(F)2]-1}. A
final difference Fourier contained some residual electron
density around the thorium, the largest peak being 2.63 e/Å3.
All data refinement calculations were performed using the
Siemens SHELXTL PLUS computing package.29
meta OAr), 6.89 (t, J HH ) 8 Hz, 1 H, para OAr), 6.82 (t, J HH
) 8 Hz, 2 H, para OAr), 2.32 (s, 30 H, C5Me5), 2.25 (s, 15 H,
C5Me5), 1.82 (s, 18 H, t-Bu), 1.71 (s, 18 H, t-Bu), 1.67 (s, 18 H,
t-Bu). IR (cm-1): 1583 (w), 1477 (m), 1407 (s), 1389 (m), 1359
(w sh), 1353 (w), 1322 (m br), 1265 (m), 1216 (s br), 1197 (s),
1120 (m), 1098 (w), 1021 (w), 950 (m br), 859 (s), 820 (s), 793
(w), 747 (s), 727 (w sh), 656 (s), 548 (w), 454 (w). Anal. Calcd
for C24H38OTh: C, 50.17; H, 6.67. Found: C, 52.35; H, 7.11.
Ebullioscopic molecular weight determination in benzene
solution gave M ) 1780, calculated for [Cp*ThH2(OAr)]3
1724.
)
Cp *Th (OC6H3-t-Bu CMe2CH2)(OAr )(OdP P h 3) (7). Cp*-
Th(OAr)(CH2SiMe3)2 (4) (0.050 g, 0.067 mmol) and triph-
enylphosphine oxide (0.019 g, 1.1 equiv) were dissolved in
benzene-d6 and heated to 60 °C in an oil bath. After 16 h the
(29) Siemens Analytical X-ray Instruments, Inc., 6300 Enterprise
Lane, Madison, WI 53719.
1
reaction showed two main products by H NMR spectroscopy.

1496 Organometallics, Vol. 15, No. 5, 1996
Butcher et al.
Cp *Th (O-2,6-t-Bu 2C6H3)(CH2SiMe3)2‚C7H8 (4). The clear,
well-formed crystals were examined in mineral oil under an
argon stream. The chosen platelike crystal measuring 0.25
× 0.23 × 0.13 mm was affixed to the goniometer head of a
CAD4 diffractometer (employing graphite-monochromated Mo
KR radiation) using Apiezon grease and cooled to -70 °C in a
cold nitrogen stream. Unit cell parameters were determined
from the least-squares refinement of ((sin θ)/λ)2 values for 25
accurately centered reflections with a 2θ range between 16
and 32°. Three reflections were chosen as intensity standards
and were measured every 3600 s of X-ray exposure time.
The data were reduced using the Structure Determination
Package provided by Enraf-Nonius and corrected for absorp-
tion empirically using high-ø ψ-scans. The thorium atom was
located by direct methods, and the remaining non-hydrogen
atoms were located in subsequent difference Fourier maps, the
refinement being by full-matrix least squares. After inclusion
of anisotropic thermal parameters for all non-hydrogen atoms
and geometrical generation of hydrogen atoms which were
constrained to “ride” upon the appropriate carbon atoms, final
routine in the XEMP facility of SHELXTL PC, and the
refinement was carried out using SHELXTL PLUS (VMS) due
to the large number of least-squares parameters.
The structure was solved in the space group P21/c using
direct methods and Fourier techniques and refined by full-
matrix least squares. The phenyl groups were refined as fixed
hexagons using the AFIX facility in SHELXTL PLUS. Non-
hydrogen atoms were treated anisotropically except for a
toluene molecule in the lattice. The refinement of the toluene
molecule was problematical, with large isotropic temperature
factors hampering final convergence. The large temperature
factors were taken to be an artifact of disorder, and attempts
to refine the toluene molecule anisotropically failed. In the
final refinement a damping factor was used, but two of the
toluene carbon atom temperature factors still had ∆/σ values
of approximately 0.04. Convergence was assumed since all
other parameters in the structure had reasonable ∆/σ values.
All hydrogen atoms were fixed in positions corresponding to a
C-H distance of 0.96 Å using the HFIX facility in SHELXTL
PLUS. Hydrogen atoms had their isotropic temperature
factors fixed at 0.08 Å2. The final refinement using 4730
unique observed [F > 4σ(F)] reflections converged at R ) 0.052
and Rw ) 0.056 {where w ) [σ2(F) + 0.0007(F)2]-1}.
refinement
using
3128
unique
observed
[F
>
4σ(F)] reflections converged at R ) 0.034 and Rw ) 0.041
{where w ) [σ2(F) + 0.0007(F)2]-1}. A final difference Fourier
contained some residual electron density around the thorium,
the largest peak being 1.65 e/Å3. All data refinement calcula-
tions were performed using the Siemens SHELXTL PLUS
computing package.29
Ack n ow led gm en t. This work was performed under
the auspices of the Laboratory Directed Research and
Development Program. Los Alamos National Labora-
tory is operated by the University of California for the
U.S. Department of Energy under Contract W-7405-
ENG-36.
Cp *Th (OC6H3-t-Bu CMe2CH2)(OAr )(OdP P h 3)‚C7H8 (7).
A colorless needle-shaped crystal measuring 0.17 × 0.21 × 0.42
mm was coated with mineral oil and epoxy and mounted on a
thin glass fiber under an argon stream. The crystal was then
immediately placed under a cold nitrogen stream (-100 °C)
on a Siemens P4/PC diffractometer (Mo KR, λ ) 0.710 69 Å).
The lattice parameters were optimized from a least-squares
calculation on 32 carefully centered reflections of high Bragg
angle. Three check reflections monitored every 97 reflections
showed a constant decrease in data intensity corresponding
to 15% over the course of the data collection. Lattice deter-
mination and data collection were carried out using XSCANS
Version 2.10b software. All data reduction, including Lorentz
and polarization corrections, structure solution, and graphics,
was performed using SHELXTL PC Version 3.2/360 software.29
All data were corrected for absorption using the ellipsoid
Su p p or tin g In for m a tion Ava ila ble: Tables of fractional
atomic coordinates, bond lengths and angles, isotropic and
anisotropic thermal parameters, and hydrogen atom coordi-
nates for complexes 3, 4, and 7 and a fully labeled ORTEP
plot of 7 (21 pages). This material is contained in many
libraries on microfiche, immediately follows this article in the
microfilm version of the journal, can be ordered from the ACS,
and can be downloaded from the Internet; see any current
masthead page for ordering information and Internet access
instructions.
OM9508694