A New Class of Constrained-Geometry Metallocenes: Synthesis and Crystal Structure of a Carboranyl-Thiol-Appended Half-Sandwich Titanocene and Its Conversion to Halotitanocene

Article abstract of DOI:10.1021/om0340802

The preparation and conversion of a cyclo-pentadiene ligand was discussed. The high electron withdrawing ability of the carboranyl thiol moiety was introduced onto a Cp ligand for the synthesis process. The sulfur atom was shown to influence the binding capability of the ligands, more than the phosphorous and nitrogen atoms. The results show that the incorporation of the thiol unit in ansa ligand helps in enhancing the reactivity of the metallocene towards Ziegler-Natta catalysis.

Full text of DOI:10.1021/om0340802

Organometallics 2003, 22, 4839-4841
4839
A New Cla ss of Con str a in ed -Geom etr y Meta llocen es:
Syn th esis a n d Cr ysta l Str u ctu r e of a
Ca r bor a n yl-Th iol-Ap p en d ed Ha lf-Sa n d w ich Tita n ocen e
a n d Its Con ver sion to Ha lotita n ocen e
J ianhui Wang,†,‡ Chong Zheng,† J ohn A. Maguire,‡ and Narayan S. Hosmane*,†
Department of Chemistry and Biochemistry, Northern Illinois University,
DeKalb, Illinois 60115-2862, and Department of Chemistry, Southern Methodist University,
Dallas, Texas 75275-0314
Received August 1, 2003
Summary: A novel carboranyl-thiol-appended cyclo-
pentadiene ligand, 1-SH-2-[HCpCH(Ph)]-closo-1,2-
C2B10H10 (2), was prepared and then reacted with
Ti(NMe2)4 to form the corresponding titanium complex
[1-(σ-S)-2-(η5-C5H4CH(Ph))-1,2-C2B10H10)]Ti(NMe2)2 (3),
which undergoes exclusively a monohalogenation reac-
tion on the metal center, in the presence of Me3SiCl or
Me3NHCl, leading to the formation of [1-(σ-S)-2-(η5-
C5H4CH(Ph))-1,2-C2B10H10)]TiCl(NMe2) (4) in 71% yield.
moiety or combinations thereof.2a,5-7 Many of these
changes have resulted in effective catalytic systems.5-7
One particularly interesting modification was found in
{CpC(dCH2)OZr(NEt2)2}2, which exhibited no specific
steric constraints but which, on activation with MAO,
generated an active Ziegler-Natta catalyst.8 Recently,
there have been reports of group 4 constrained-geometry
complexes in which phenol has been used both as the
linking group and for the η1-bonding site.9 Since these
complexes have been shown to be the bases of highly
efficient catalytic systems, a further investigation of the
early-transition-metal, constrained-geometry complexes
having group 16 base sites seemed warranted. In this
study we have sought to take advantage of the high
electron-withdrawing ability of the carboranyl-thiol
moiety by introducing it onto a Cp ligand. Here we
report the synthesis of the novel ansa ligand 1-SH-2-
[HCpCH(Ph)]-closo-1,2-C2B10H10 and its metalation prod-
uct [1-(σ-S)-2-(η5-C5H4CH(Ph))-1,2-C2B10H10)]Ti(NMe2)2,
in which the appended carboranyl-thiol unit acts as
both the linking and η1-bonding group.
Metallocenes of constrained geometries, in which an
early transition metal is simultaneously bonded to a
cyclopentadienide ligand (Cp) and to an η1-bonding
pendant group of Cp, have been shown to be effective
catalysts, or cocatalysts, for olefin polymerizations.1,2
Some of the earliest, and most successful, constrained-
geometry catalyst precursors were those based on the
ansa-monocyclopentadienide-amido ligand, [C5R4-
SiMe2R′N]2- (CpA), in which an amido nitrogen is the
η1-bonding site and is linked to the Cp by a dimethylsilyl
group.3 Early-transition-metal complexes of CpA have
been the basis of both single-site and binuclear catalytic
systems.2,4 Because of these early successes, modifica-
tions of the ansa ligands have been the subject of
intensive research. Such modifications have involved
changes to the Cp, the linking group, and the η1-bonding
The reaction of 6-phenylfulvene with the dilithium
salt of 1-SH-closo-1,2-C2B10H11 (1) in a molar ratio of
1:1 in THF, followed by hydrolysis, gave the carbora-
nyl-thiol-appended cyclopentadiene ligand 1-SH-2-
[HCpCH(Ph)]-closo-1,2-C2B10H10 (2) in 85% yield (see
* To whom correspondence should be addressed. E-mail:
nhosmane@niu.edu.
(5) (a) Kunz, K.; Erker, G.; Do¨ring, S.; Bredeau, S.; Kehr, G.;
Fro¨hlich, R. Organometallics 2002, 21, 1031-1041. (b) Kunz, K.; Erker,
G.; Do¨ring, S.; Fro¨hlich, R.; Kehr, G. J . Am. Chem. Soc. 2001, 123,
6181-6182. (c) Wang, H.; Wang, Y.; Li, H.-W.; Xie, Z. Organometallics
2001, 20, 5110-5118.
† Northern Illinois University.
‡ Southern Methodist University.
(1) Stevens, J . C.; Timmers, F. J .; Wilson, D. R.; Schmidt, G. F.;
Nickias, P. N.; Rosen, R. K.; Knight, G. W.; Lai, S. Eur. Patent Appl.
Ep 416 815-A2, 1991 (Dow Chemical Co.).
(6) (a) Altenhoff, G.; Bredeau, S.; Erker, G.; Kehr, G.; Kataeva, O.;
Fro¨hlich, R. Organometallics 2002, 21, 4084-4089. (b) Trouve´, G.;
Laske, D. A.; Meetsma, A.; Teuben, J . H. J . Organomet. Chem. 1996,
511, 255-262. (c) Van der Zeijden, A. A. H.; Matteis, C. Organo-
metallics 1997, 16, 2651-2658. (d) Christoffers, J .; Bergman, R. G.
Angew. Chem., Int. Ed. Engl. 1995, 34, 2266-2267. (e) Huan, Q.;
Qian, Y.; Li, G.; Tang, Y. Transition Met. Chem. 1990, 15, 483.
(7) (a) Kaminsky, W.; Arndt, M. Adv. Polym. Sci. 1997, 127, 144-
187. (b) Bochmann, M. J . Chem. Soc., Dalton Trans. 1996, 255-270.
(c) Brintzinger, H.-H.; Fischer, D.; Mulhaupt, R.; Rieger, B.; Waymouth,
R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143-1170, (d) Marks,
T. J . Acc. Chem. Res. 1992, 25, 57-65. (e) J ordan, R. F. Adv.
Organomet. Chem. 1991, 32, 325-387.
(8) Kunz, K.; Erker, G.; Kehr, G.; Fro¨hlich, R.; J acobsen, H.; Berke,
H.; Blacque, O. J . Am. Chem. Soc. 2002, 124, 3316-3326.
(9) (a) Chen, Y.-X.; Fu, P.-F.; Stern, C. L.; Marks, T. J . Organo-
metallics 1997, 16, 5958-5963. (b) Wang, J .; Mu, Y.; Pu, W.; Zhang,
Y.; Yang, G.; Liu, J . Chem. Res. Chin. Univ. 2001, 17, 115-116. (c)
Pu, W.; Wang, J .; Ye, L.; Mu, Y.; Yang, G.; Fan, Y. Acta Crystallogr.
1999, C55, 728-729.
(2) (a) Mcknight, A. L.; Waymouth, R. M. Chem. Rev. 1998, 98,
2587-2598. (b) J utzi, P.; Siemeling, U. J . Organomet. Chem. 1995,
500, 175. (c) Okuda, J . Comments Inorg. Chem. 1994, 16, 185-205.
(3) (a) Klosin, J .; Kruper, W. J ., J r.; Nickias, P. W.; Roof, G. R.; De
Waele, P.; Abbound, K. A. Organometallics 2001, 20, 2663-2665. (b)
Amor, F.; Okuda, J . J . Organomet. Chem. 1996, 520, 245-248. (c)
Okuda, J .; Schattenmann, F. J .; Wocadlo, S.; Massa, W. Organo-
metallics 1995, 14, 789-795. (d) J utzi, P.; Kleimeier, J . J . Organo-
met. Chem. 1995, 486, 287. (e) Flores, J .; Chien, J . C. W.; Rausch, M.
D. Organometallics 1994, 13, 4140. (f) Herrmann, W. A.; Morawietz,
M. J . A. J . Organomet. Chem. 1994, 482, 169. (g) Hughes, A. K.;
Meetsma, A.; Teuben, J . H. Organometallics 1993, 12, 1936. (h) Piers,
W. E.; Shapiro, P. J .; Bunel, E. E.; Bercaw, J . E. Synlett 1990, 2, 74.
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10.1021/om0340802 CCC: $25.00 © 2003 American Chemical Society
Publication on Web 10/18/2003

4840 Organometallics, Vol. 22, No. 24, 2003
Communications
Sch em e 1
Sch em e 2
Scheme 1).10 It is important that care be taken to
completely remove the original THF solvent before the
reaction mixture is hydrolyzed.10 Otherwise, a polymeric
material will result. It should also be noted that, while
the purified ligand precursor 2 is a yellow solid, the
impure product is a dark green residue. However, the
spectroscopic and analytical data are all consistent with
the formulation of 2, given in Scheme 1. The constrained-
geometry titanium complex [1-(σ-S)-2-(η5-C5H4CH(Ph))-
1,2-C2B10H10)]Ti(NMe2)2 (3) could be obtained in 83%
yield from the reaction of 2 with Ti(NMe2)4 in toluene
via an amine elimination reaction (see Scheme 2).11
While the reactivity of 3 toward excess Me3SiCl results
in the formation of [1-(σ-S)-2-(η5-C5H4CH(Ph))-1,2-
C2B10H10)]TiCl(NMe2) (4) in 71% yield,12 with 2 equiv
of Me3NHCl the yield of 4 is only 41% (see Scheme 3).13
In neither case was there evidence for the dichlorination
of the titanium.
Several other η1 group 16 atom appended with
η5-Cp complexed organometallic species have been
synthesized and their structures determined. The (sp2-
C1)-bridged Cp/oxido-titanium complex {Cp-C(dCH2)-
8
O-Zr(NEt2)2}2 was found to be a dimer, as were
[η5:σ-C5H4Si(Me)2-O-TiCl2]214 and {[η5:σ-C5H4(CH2)2O]-
TiCl2}2.6b However, the dimers have quite different
structures, in that each oxygen of the latter species
formed a bridge between two titanium atoms, while the
first two compounds are not constrained within the
single unit; instead, the oxygens were bonded to one
neighboring titanium in the dimeric structure. On the
other hand, [η5:σ-C5H4(CH2)3O]TiCl2 was found to be
monomeric.6b Since analysis and NMR data could not
rule out the possibility that 3 could exist as a dimer,
the unambiguous structure of compound 3 was deter-
mined by X-ray diffraction studies.15 The ORTEP draw-
(10) Syn th esis of 2. A 1.00 g (5.68 mmol) sample of closo-1-SH-
1,2-C2B10H11 (1) in 40 mL of dry THF was charged into a 100 mL
Schlenk flask. To this flask was added 4.55 mL of nBuLi (11.40 mmol,
2.5 M in hexanes) dropwise with stirring at -78 °C. The reaction
mixture was warmed to room temperature and stirred for 12 h, during
which time a white precipitate formed. The mixture was then cooled
to -78 °C again, and a 10 mL THF solution of 6-phenylfulvene (0.88
g, 5.68 mmol) was added dropwise over a 10 min interval. The resulting
reaction mixture was then warmed to room temperature and stirred
overnight, during which time the suspension mixture became a clear
orange solution. The solvents from the reaction mixture were removed
in vacuo, and the remaining solid was dried in vacuo for 5 h to remove
any remaining THF. The solid was then redissolved in 100 mL of water,
and to this solution was added 10 mL of concentrated HCl was added
up to pH 1. The solution was extracted by 100 mL of CH2Cl2, and the
organic layer was separated and dried over anhydrous MgSO4. After
complete removal of the solvent, a dark green solid was obtained. The
solid was further purified by column chromatography using CH2Cl2
as the mobile phase to give a yellow solid, identified as 1-thiol-2-
[cyclopentadienylmethyl(phenyl)]-1,2-dicarba-closo-dodecaborane(12)
(2; 1-SH-2-[HCpCH(Ph)]-closo-1,2-C2B10H10), in 85% yield (1.60 g,
4.83 mmol). Anal. Calcd (found) for C14B10H22S (2): C, 50.88 (50.70);
H, 6.71 (6.72). NMR data for compound 2: 1H NMR (CDCl3, external
Me4Si) δ 2.93-3.34 (2H, m, CH2 in C5H5), 3.78 (1H, s, SH), 5.05 (1H,
s, br, Ph(CH)), 6.40-6.62 (4H, m, CdCH in C5H5), 6.94-7.52 (5H, m,
C6H5); 13C NMR (CDCl3, external Me4Si) δ 40.7, 42.1 (CH2 in C5H5),
51.7, 52.5 (Ph(CH)), 85.3 (PhCCcage), 86.3 (CcageSH), 83.52 (Ph-Ccage),
127.8-134.8 (CdCH in C5H5), 129.7-146.3 (C6H5); 11B NMR (CDCl3,
relative to external BF3‚OEt2) δ -2.06, -4.54, -7.01, -10.03, -11.29
(d (br, overlapping), BH’s, 1J (11B-1H) unresolved). IR (cm-1, KBr
cell): 3134 (br, s), 3052 (s, m), 3021 (s, m), 2960 (s, s), 2919 (s, s), 2863
(s, m), 2847 (s, s), 2582 (br, s), 1618 (s, w), 1398 (s, s), 1255 (s, s), 1117
(s, s), 1071 (s, s), 1024 (s, w), 794 (s, w), 702 (s, s).
(11) Syn th esis of 3. To a toluene (30 mL) solution of 2 (0.37 g, 1.12
mmol) was added a toluene (10 mL) solution of Ti(NMe2)4 (0.25 g, 1.12
mmol) at -78 °C. The resulting mixture was slowly warmed to room
temperature and stirred for 24 h at this temperature until it turned
to a red solution. After removal of small amounts of solid by filtration,
the solvent from the clear filtrate was removed in vacuo, to collect a
dark red residue. This residue was further purified repeatedly by
washing with hexanes to give the corresponding titanium complex
[1-(σ-S)-2-(η5-C5H4CH(Ph))-1,2-C2B10H10)]Ti(NMe2)2 (3) in 83% yield
(0.43 g, 0.93 mmol). Anal. Calcd (found) for C18H32B10N2STi (3): C,
46.54 (46.70); H, 6.94 (6.72). NMR data for compound 3: 1H NMR
(C6D6, external Me4Si) δ 2.87, 3.29 (12H, s, N(CH3)2), 5.34 (1H, s,
PhCH), 5.71 (2H, m, C5H4), 6.22 (2H, m, C5H4), 7.14-7.43 (5H, m,
C6H5); 13C NMR (C6D6, external Me4Si) δ 48.7, 49.7 (N(CH3)2), 54.7
(PhCH), 81.3 (Ph-Ccage), 83.1 (CcageSH), 109.5, 113.7, 114.9, 116.2
(C5H4), 127.5-139.8 (C6H5); 11B NMR (C6D6, relative to external BF3‚
OEt2) δ -4.86 (d, BH, 1J (11B-1H) ) 129 Hz), -6.19 (d, 1J (11B-1H) )
133 Hz), 11.6 (d, 1J (11B-1H) ) 117 Hz). IR (cm-1, KBr cell, in C6D6):
3401 (s, w), 2958 (s, s), 2920 (s, s), 2845 (s, m), 2566 (vs, br), 1635 (m,
s), 1465 (s, s), 1399 (s, s), 1380 (s, s), 1260 (s, s), 1097 (s, s), 1020 (s, s),
801 (vs, s), 705 (m, s).
(12) Syn th esis of 4 by r ea ction w ith Me3SiCl. To a toluene (30
mL) solution of 3 (0.30 g, 0.65 mmol) was added 0.85 mL (6.5 mmol)
Me3SiCl at -78 °C. The resulting solution was warmed to room
temperature slowly and stirred overnight at this temperature to give
a red solution. The solvents along with excess Me3SiCl were pumped
off, leaving a red solid, which was washed with n-hexane. Then the
solid was recrystallized from toluene to give 4 as red microcrystals in
71% yield (0.21 g, 0.46 mmol). Anal. Calcd (found) for C16H26B10ClNSTi
(4): C, 42.15 (42.40); H, 5.75 (5.72). NMR data for compound 4: 1H
NMR (C6D6, external Me4Si) δ 3.20 (6H, s, N(CH3)2), 5.04 (1H, s,
PhCH), 5.16, 5.54, 6.02, 6.41 (1H, s, C5H4), 7.12-7.27 (5H, m, C6H5);
13C NMR (C6D6, external Me4Si) δ 51.5, 54.7 (PhCH), 78.6 (PhCH-
C
cage), 83.9 (Ccage-SH), 115.1, 118.0, 118.1, 119.7 (C5H4), 125.4-138.6
(C6H5); 11B NMR (C6D6, relative to external BF3‚OEt2) δ -4.54, -10.21.
IR (cm-1, KBr cell, in C6D6): 2958 (s, s), 2920 (s, s), 2611 (m, s), 2588
(m, s), 2571 (m, s), 2555 (m, s), 1400 (s, s), 1262 (s, s), 1099 (vs, br),
1019 (s, s), 798 (vs, s), 730 (m, s), 705 (m, s).
(13) Syn th esis of 4 by r ea ction w ith Me3NHCl. To a toluene (30
mL) solution of 3 (0.30 g, 0.65 mmol) was added a dry powder of Me3-
NHCl (0.62 g, 1.30 mmol) incrementally at -78 °C. The resulting
solution was stirred at 0 °C over a period of several hours and then
slowly warmed to room temperature and stirred further overnight at
this temperature to give a red solution. The solvents from the reaction
mixture were pumped off, leaving a red solid, which was washed with
n-hexane. The solid was then recrystallized from a toluene and hexane
mixture to give red microcrystals, identified as 4, in 41% yield.
(14) Ciruelos, S.; Cuenca, T.; Go´mez-Sal, P.; Manzanero, A.; Royo,
P. Organometallics 1995, 14, 177-185.
(15) X-ray data for 3 (C18H32B10N2STi; fw, 464.52; P1h). Data were
collected at 173 (2) K on a Bruker SMART CCD PLATFORM diffrac-
tometer with a ) 10.446(2) Å, b ) 11.849(2) Å, c ) 12.280 (2) Å, R )
114.864(3)°, â ) 111.230(3)°, γ ) 91.970(4)°, V ) 1253.8 (4) Å3, Z ) 2,
and Dcalcd ) 1.230 g cm-3. Of the 6261 reflections collected (2θ ) 3.88-
50°), 4232 reflections were respectively considered as observed (I >
2σ(I)) and were corrected for Lorentz, polarization, and absorption
effects (Sheldrick, G, M, SADABS, Program for Empirical Absorption
Correction of Area Detector Data; University of Go¨ttingen, Go¨ttingen,
Germany, 1996). The structure was solved by direct methods and
refined by full-matrix least-squares techniques using SHELXTL
(Sheldrick, G. M. SHELXTL, Version 5.1; Bruker Analytical X-ray
Systems, Madison, WI, 1997). All non-H atoms were refined anisotro-
pically. The final refinements converged at R1 ) 0.0618, wR2 ) 0.1305,
and GOF ) 1.378.

Communications
Organometallics, Vol. 22, No. 24, 2003 4841
Sch em e 3
ing of 3, given in Figure 1, shows the compound to be a
monomeric complex in which the Cp group, S, and the
two NMe2 groups surround the Ti in a nearly tetrahe-
dral fashion; the Cp(centroid)-Ti-S angle is 113.4(1)°,
and the N2-Ti-N1 angle is 107.27(13)°. The Cp(cen-
troid)-Ti distance of 2.054 Å found in 3 is essentially
the same as the value of 2.00(1) Å reported for [C5H4-
PhCH(PhO)]TiCl29c but is considerably shorter than the
analogous distances found in (Me4CpPhO)Ti(CH2Ph)2
(2.36(1) Å)9a and Me2Si(Me4C5)(tBuN)TiCl2 (2.36(1) Å),1
indicating a tighter binding of the metal to the ligand
in 3. Consequently, the Cp(centroid)-Ti-S angle of
113.4(1)° is larger than the Cp-Ti-O angles found in
[C5H4PhCH(PhO)]TiCl2 (110.7°)9c and (Me4CpPhO)Ti-
(CH2Ph)2 (107.7°)9a as well as the Cp-Ti-N angles in
Me2Si(Me4C5)(tBuN)TiCl2 (107.6°).1 These structural
parameters exemplify the influence of a carboranyl-
thiol group on the metal binding to a Cp ligand.
The isolated good yields for 3 indicate that the
methods outlined in Schemes 1 and 2 should prove
to be efficient synthetic routes for a number of early-
transition-metal constrained-geometry organometallics.
Since the sulfur atom is known to influence the binding
capability of the ligands more so than the nitrogen and
phosphorus atoms, the incorporation of a thiol unit in
the ansa ligand could help in enhancing the reactivity
of the metallocene toward Ziegler-Natta type catalysis.
Such studies are the subject of our continuing investiga-
tions.
Ack n ow led gm en t. This work was supported by
grants from the National Science Foundation (Grant No.
CHE-0241319), the donors of the Petroleum Research
Fund, administered by the American Chemical Society,
The Robert A. Welch Foundation (Grant No. N-1322 to
J .A.M.), and Northern Illinois University through a
Presidential Research Professorship. The Forschungs-
preis der Alexander von Humboldt-Stiftung (to N.S.H.)
is also hereby gratefully acknowledged.
F igu r e 1. Perspective view of 3 with thermal ellipsoids
drawn at the 50% probability level. Pertinent distances (Å)
and angles (deg): Cp(centroid)-Ti, 2.054; Ti-S, 2.404(1);
Ti-N(1,2), 1.908(3), 1.896(3); C(0)-C(1), 1.562(4); C(1)-
C(2), 1.685(4); C(2)-S, 1.784(3); Cp(centroid)-Ti-S, 113.4(1);
C(2)-S-Ti, 111.3(1); N(1)-Ti-N(2), 107.3(1), C(11)-C(0)-
C(1), 118.6(3); C(11)-C(0)-C(21), 109.5(3); C(0)-C(1)-
C(2), 115.5(3). See Table S-3 in the Supporting Information
for a detailed list of bond lengths and angles.
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal-
lographic data for 3, including fractional coordinates, bond
lengths and angles, anisotropic displacement parameters, and
hydrogen atom coordinates; these data are also available as
CIF files. This material is available free of charge via the
Internet at http://pubs.acs.org.
OM0340802