New examples of half-sandwich (borylcyclopentadienyl)titanium trichloride complexes and an x-ray structural characterization of the homobimetallic complex [TiCl3{η5-C5H4}]2BPh

Article abstract of DOI:10.1021/om9600699

A new series of half-sandwich (borylcyclopentadienyl)titanium trichloride complexes have been prepared which include the boryl substituents [1,2-(C₆H₄O₂)]B-, Ph(Cl)B-, Ph₂B- and a (PhB<)-bridged bimetallic complex. No correlation was found between the ¹H and ¹³C NMR chemical shifts of the cyclopentadienyl ring in these complexes and the Lewis acidity of the attached boryl group. The crystal structure of the phenylboron-bridged bimetallic complex PhB{(η⁵-C₅H₄)TiCl₃}₂ was determined. The cyclopentadienyltitanium units of the molecule are twisted away from each other, forming an angle of 41° between the cyclopentadienyl ring planes. Each cyclopentadienyl ring is twisted out of the trigonal plane of the boron by 24°. Preliminary results concerning the Ti-alkylation of some of these complexes are described.

Full text of DOI:10.1021/om9600699

Organometallics 1996, 15, 2393-2398
2393
New Exa m p les of Ha lf-Sa n d w ich
(Bor ylcyclop en ta d ien yl)tita n iu m Tr ich lor id e Com p lexes
a n d a n X-r a y Str u ctu r a l Ch a r a cter iza tion of th e
Hom obim eta llic Com p lex [TiCl3{η5-C5H4}]2BP h
Scott A. Larkin,† J effery T. Golden,† Pamela J . Shapiro,*,† Glenn P. A. Yap,‡
David Ming J in Foo,† and Arnold L. Rheingold‡
Departments of Chemistry, University of Idaho, Moscow, Idaho 83844-2343, and
University of Delaware, Newark, Delaware 19716
Received February 1, 1996X
A new series of half-sandwich (borylcyclopentadienyl)titanium trichloride complexes have
been prepared which include the boryl substituents [1,2-(C6H4O2)]B-, Ph(Cl)B-, Ph2B- and
1
a (PhB<)-bridged bimetallic complex. No correlation was found between the H and 13C
NMR chemical shifts of the cyclopentadienyl ring in these complexes and the Lewis acidity
of the attached boryl group. The crystal structure of the phenylboron-bridged bimetallic
complex PhB{(η5-C5H4)TiCl3}2 was determined. The cyclopentadienyltitanium units of the
molecule are twisted away from each other, forming an angle of 41° between the
cyclopentadienyl ring planes. Each cyclopentadienyl ring is twisted out of the trigonal plane
of the boron by 24°. Preliminary results concerning the Ti-alkylation of some of these
complexes are described.
In tr od u ction
in which they prepared (borylcyclopentadienyl)titanium
trichloride complexes through a dehalodesilylation reac-
tion between various (borylcyclopentadienyl)trimeth-
ylsilane compounds and titanium tetrachloride (eq 1).5
Lewis-acidic main-group compounds are essential
components of a variety of transition-metal-mediated
catalytic processes. They have gained particular promi-
nence for their use as cocatalysts for Ziegler-Natta
olefin polymerization.1 Other noteworthy, Lewis-acid-
dependent processes include nickel-catalyzed olefin hy-
drocyanation,2 nickel-catalyzed olefin dimerization,3 and
olefin metathesis by classical rhenium and tungsten
catalysts.4
(1)
Impressed by the ability of the Lewis acid to activate
the transition metal in these examples, we have em-
barked on a program to incorporate group 13 moieties
directly within the ligand framework of organotransi-
tion-metal complexes in order to accomplish this activa-
tion intramolecularly. In addition, we expect to develop
new modes of cooperation between the main-group
Lewis acid and the transition metal.
In this paper we describe the preparation of a variety
of new half-sandwich (borylcyclopentadienyl)titanium
trichloride compounds which we plan to further modify
in order to study their potential for catalysis. The
synthetic approach to these complexes was based on a
method reported briefly by J utzi and Seufert in 1979,
Since then, no further chemistry involving these
titanium complexes nor any additional applications of
this approach to introducing borylcyclopentadienyl rings
onto transition metals has been described.6
Various methods for covalently attaching group 13
moieties to the ancillary ligands of group 4 transition
metals have been pursued by others.7 In some in-
stances, these have led to active, single-component olefin
polymerization catalysts. The success of these systems
lends support to our goal of attaching the Lewis acid
directly to the cyclopentadienyl ligand framework of
transition metals in order to promote intramolecular
activation of the metal. By extending the chemistry
pioneered by J utzi, we have introduced additional
examples of boryl-derivatized, half-sandwich titanium
† University of Idaho.
‡ University of Delaware.
X Abstract published in Advance ACS Abstracts, April 15, 1996.
(1) Brintzinger, H. H.; Fischer, D.; Mu¨lhaupt, R.; Rieger, B.;
Waymouth, R. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143, and
references therein.
(7) (a) Bochmann, M.; Lancaster, S. J .; Robinson, O. B. J . Chem.
Soc., Chem. Commun. 1995, 2081. (b) Temme, B.; Erker, G.; Karl, J .;
Luftmann, H.; Fro¨hlich, R.; Kotila, S. Angew. Chem., Int. Ed. Engl.
1995, 34, 1755. (c) Piers, W. E.; Spence, R. E. v. H. Organometallics
1995, 14, 4617. (d) Skrzypczak-J ankun, E.; Cheesman, B. V.; Zheng,
B.; Lemert, R. M.; Asthana, S.; Srebnik, M. J . Chem. Soc., Chem.
Commun. 1994, 127. (e) Zheng, B.; Srebnik, M. J . Organomet. Chem.
1994, 474, 49. (f) Erker, G.; Noe, R.; Wingbermu¨hle, D. Chem. Ber.
1994, 127, 805. (g) Erker, G.; Noe, R.; Wingbermu¨hle, D.; Petersen, J .
L. Angew. Chem., Int. Ed. Engl. 1993, 32, 1213. (h) Erker, G.; Albrecht,
M.; Psiorz, C. Z. Naturforsch., B 1991, 46, 1571. (i) Erker, G.; Albrecht,
M.; Werner, S.; Kru¨ger, C. Z. Naturforsch., B 1990, 45, 1205. (j) Erker,
G.; Aul, R. Chem. Ber. 1991, 124, 1301. (k) Temme, B.; Erker, G.;
Fro¨hlich, R.; Grehl, M. J . Chem. Soc., Chem. Commun. 1994, 1713. (l)
Binger, P.; Sandmeyer, F.; Kru¨ger, C.; Erker, G. Tetrahedron 1995,
15, 4277 and references therein.
(2) Tolman, C. A.; McKinney, R. J .; Seidel, W. C.; Druliner, J . D.;
Stevens, W. R. Adv. Catal. 1985, 33, 1.
(3) Parshall, G. W.; Ittel, S. D. Homogeneous Catalysis, 2nd ed.;
Wiley: New York, 1992; pp 72-73.
(4) Ivin, K. J . Olefin Metathesis; Academic Press: London, 1983.
(5) J utzi, P.; Seufert, A. J . Organomet. Chem. 1979, 169, 373.
(6) During the writing of this paper, a report appeared describing
the formation of alkali metal salts of cyclopentadienylboranes of the
type M[C5H5B(NMe2)2] (M ) Li, Na), Li[C5H5B(OCMe2)2], and M[C5H5-
BR2] (M ) Li, Na; R ) Me, Pri). These borylcyclopentadienide salts
were used to synthesize sandwich-type complexes of Fe, Co, and Ni.
Herberich, G. E.; Fischer, A. Organometallics 1996, 15, 58.
S0276-7333(96)00069-6 CCC: $12.00 © 1996 American Chemical Society

2394 Organometallics, Vol. 15, No. 9, 1996
Larkin et al.
Sch em e 1
complexes, and we report the first X-ray crystal struc-
ture of one of these complexes, that of the homonuclear,
bimetallic complex PhB{(η5-C5H4)TiCl3}2. Absolute as-
signments of the 1H and 13C NMR chemical shifts of the
cyclopentadienyl rings of these complexes were made
through a combination of variable-temperature 1H NMR
studies and 1H/13C HETCOR analyses. Although the
11B NMR chemical shifts of these (borylcyclopentadi-
enyl)titanium complexes reflect the Lewis acidity of the
boron, no correlation between the 1H and 13C NMR
chemical shifts of the cyclopentadienyl ring on the
titanium and the Lewis acidity of the attached boryl
group was found.
Resu lts a n d Discu ssion
Syn th esis of (Bor ylcyclop en ta d ien yl)tita n iu m
Tr ich lor id e Com p lexes. From the work of J utzi and
Seufert, cyclopentadienyltitanium trichloride complexes
with rings derivatized with -BCl2, -BBr2, -B(OC2H5)2,
and -B(CH3)2 groups were known.5 We have expanded
this list to include the -BPh2, -B(Cl)Ph, and -B(Cat)
(Cat ) 1,2-(C6H4O2)2-) derivatives and the PhB-bridged
bimetallic complex. While in all cases the cyclopenta-
dienyl ligands were introduced onto the titanium via a
dehalodesilylation reaction between a trimethylsilyl-
substituted ligand precursor and TiCl4, a variety of
approaches were used to introduce the boryl groups onto
the rings in the synthesis of the (borylcyclopentadienyl)-
trimethylsilane ligand precursors. These ligand precur-
sors consist of a mixture of regioisomers in which the
boryl group generally occupies vinylic positions on the
cyclopentadiene ring.8 Due to the presence of multiple
isomers, and due to the fluxionality of the isomers with
an allylic silyl group, the 1H NMR signals for the
cyclopentadienyl ring protons in the room-temperature
spectra are generally broad and weak. Since we were
primarily interested in the titanium complexes derived
from these molecules, no effort was made to establish
their isomer distribution or to further characterize their
fluxional properties.
Syn th eses of TiCl3{η5-C5H4(BP h 2)} (3) a n d TiCl3-
{η5-C5H4(BP h Cl)} (4). Whereas boron trihalides readily
replace the silyl substituents of silyl-substituted cyclo-
pentadienyl rings, the more labile stannyl substituent
is necessary when introducing boryl groups containing
non-halide substituents such as alkoxy or, in this case,
aryl
substituents.
Thus,
the
reaction
of
[C5H4(SiMe3)(SnMe3)] with Ph2BBr and PhBCl2 afforded
the corresponding ((diphenylboryl)cyclopentadienyl)-
and ((chlorophenylboryl)cyclopentadienyl)trimethylsilane
ligand precursors with the elimination of trimethyltin
halide. Efforts to purify these ligand precursors by
distillation resulted in decomposition; therefore, the
crude materials were reacted directly with TiCl4 to form
the half-sandwich complexes.
Syn th esis of [TiCl3]2{(η5-C5H4)2BP h } (6). Selective
attachment of a single (trimethylsilyl)cyclopentadiene
ring to the boron in the reaction of PhBCl2 with [C5H4-
(SiMe3)(SnMe3)] was achieved at room temperature.
More forcing conditions were required to attach a second
ring to the boron. This was accomplished by reacting
PhBCl2 with 2 equiv of [C5H4(SiMe3)(SnMe3)] in reflux-
ing toluene to form [C5H4(SiMe3)]2BPh (5) (Scheme 1).
Apart from their role in transferring the borylcyclopen-
tadienyl ligand to titanium, the trimethylsilyl substit-
uents also appeared to stabilize the cyclopentadienyl-
boranes against polymerization, since efforts to prepare
PhB(C5H5)2 by an analogous route afforded insoluble
polymer.
Our reasons for preparing additional examples of
(borylcyclopentadienyl)titanium trichloride complexes
were multifold. Foremost was our desire to have boryl
substituents with a range of Lewis acidities in order to
examine the effect of the Lewis acidity of the ring
substituent on the electronic properties and reactivity
of the titanium center. We also wanted boryl substit-
uents which were easily introduced onto the ring and
which would not interfere with further ligand substitu-
tion at the titanium center.
Syn th esis of TiCl3{η5-C5H4(BCa t)} (2). (Cat)B-
C5H4SiMe3 (1) is prepared straightforwardly by reacting
Li{C5H4(SiMe3)} directly with (Cat)BCl in the manner
described by Grundke and Paetzold for the synthesis of
B-cyclopentadienylcatecholborane.9 This ligand was
attractive to us since its synthesis involves fewer
reaction steps than the synthesis of the diethoxyboryl
ligand,8b and it is also readily purified either by distil-
lation or by recrystallization from petroleum ether. The
corresponding ((catecholboryl)cyclopentadienyl)titanium
trichloride complex is prepared in the usual manner by
reacting 1 with TiCl4.
We were able to introduce two titanium atoms onto
(C5H4SiMe3)2PhB to form the phenylborane-bridged
cyclopentadienyltitanium bimetallic complex, 6 (Scheme
1). Single crystals suitable for an X-ray structure
determination were obtained, affording the first solid-
state structure of one of these systems (vide infra).
(8) (a) J utzi, P.; Seufert, A. Angew. Chem., Int. Ed. Engl. 1976, 15,
295. (b) J utzi, P.; Seufert, A. J . Organomet. Chem. 1979, 169, 327.
(9) Grundke, H.; Paetzold, P. I. Chem. Ber. 1971, 104, 1136.

(Borylcyclopentadienyl)titanium Trichloride Complexes
Organometallics, Vol. 15, No. 9, 1996 2395
Ta ble 1. 1H,13C, a n d 11B NMR Ch em ica l Sh ifts
(p p m ) for Bor yl-Cp TiCl3
1H
13C
boryl
group
2,5-Cp
3,4-Cp
2,5-Cp
3,4-Cp
11B
Cl2B-
6.64
6.63
7.06
6.80
7.07
6.92
6.04
6.22
6.21
6.35
6.14
6.11
130
130
131
134
134
129
126
127
127
128
128
126
32a
54a
38b
41b
c
Me2B-
Ph(Cl)B-
Ph2B-
[TiCp]PhB-
(Cat)B-
12b
C6D6 solution. CDCl3 solution. c Sample was not soluble
a
b
enough to obtain a 11B NMR spectrum.
NMR Ch a r a cter iza tion of (Bor ylcyclop en ta d i-
en yl)t it a n iu m Tr ich lor id e Com p lexes. In the 1H
NMR spectra of the boryl-CpTiCl3 complexes, the sig-
nals for the 2,5- and 3,4-protons of the cyclopentadienyl
rings appear as two pseudotriplets corresponding to an
AA′BB′ system. An unequivocal assignment of these
ring protons cannot be made by a simple consideration
of electron-acceptor effects of the boron. The relative
shielding of the protons can change from one system to
another as a consequence of magnetic anisotropy effects
from the metal. Siebert and co-workers illustrated this
situation by showing that the relative order of the
chemical shifts of the 2,5- and 3,4-cyclopentadienyl ring
protons in ferrocenylborane complexes were opposite
from their ordering in cymantrenylborane complexes.10
The relative order of the 13C chemical shifts of the ring
carbons is consistent with that of the protons. Siebert
and co-workers were able to make absolute assignments
for the ring carbon and proton signals in the ferrocene
and cymantrene complexes by demonstrating a decoa-
F igu r e 1. Molecular structure of PhB{(η5-C5H4)TiCl3}2,
(6), with the atom-labeling scheme. Thermal ellipsoid plots
are given for titanium and chloride atoms at 35% prob-
ability. Carbon and boron atoms were refined isotropically.
complexes, J utzi and Seufert correctly assumed that the
resonances of the ring protons R to the boryl substituent
of the titanium complexes occurred downfield of the â
protons. The authors also claimed a dependence of the
ring proton chemical shifts on the Lewis acidity of the
boryl substituent, yet examination of their data fails to
reveal any regular pattern among the different boryl
derivatives, with the exception of the diethoxyboryl
1
derivative, for which the H NMR chemical shifts occur
upfield of the corresponding shifts in the more Lewis-
acidic dichloroboryl, dibromoboryl, and dimethylboryl
derivatives. In contrast, greater electron-withdrawing
character of the boryl substituent has a noticeable
electron deshielding effect on the 1H and 13C NMR
chemical shifts of the cyclopentadienyl rings of cyman-
trenylborane and ferrocenylborane complexes.10,12 Ap-
parently, the Lewis-acidic titanium places a greater
demand on the π-electrons of the cyclopentadienyl ring
than the boryl substituents.
Descr ip t ion of t h e Molecu la r St r u ct u r e of
[TiCl3]2{(η5-C5H4SiMe3)2BP h } (6). An ORTEP view
of the molecular structure of 6 is shown in Figure 1. A
summary of the crystal data and structure refinement
is presented in Table 2. Selected bond lengths and
angles are listed in Table 3.
There are four dimers per unit cell, each residing on
a 2-fold rotational axis passing through the central
phenylboron bridge. Thus, the cyclopentadienyltita-
nium units are pointed in opposite directions from the
trigonal plane formed by the boron and C(1), C(5), and
C(5a). The torsion angle between the planes of the
cyclopentadienyl rings is 41°. Each cyclopentadienyl
ring is twisted out of the trigonal plane of the boron by
24°, thereby reducing the amount of conjugation possible
between the π-system of the cyclopentadienyl rings and
the formally empty p orbital on the boron. It is difficult
to assess the presence of multiple bonding from the
B-C(ring) bond distance of 1.55(2) Å, which is within
the range observed for B-C single bonds in other three-
1
lescence at low temperature of the H NMR signal for
the 2,5-protons upon freezing out the rotation of an
unsymmetrically substituted boryl substituent. We
used this same method to make definitive assignments
for the ring protons R and â to the boryl substituent of
our cyclopentadienyltitanium trichloride complexes.
1
Examination of the low-temperature H NMR behavior
of complexes 3 and 6 allowed us to assign the R-protons
of the ring as the low-field triplet, which decoalesced
with cooling. The upfield triplet assigned to the â-pro-
tons exhibited only a loss of definition with cooling.
Assignment of the ring carbon signals in the 13C NMR
spectra was accomplished by using (H,C)-HETCOR
spectra. In all cases, as with the 2,5-protons, the lower
field signal corresponded to the 2,5-carbons.
1
The H, 13C, and 11B NMR chemical shifts of a series
of (borylcyclopentadienyl)titanium trichlorides, includ-
ing the dichloro- and dimethylboryl derivatives reported
by J utzi, are tabulated in Table 1. Although the 11B
NMR chemical shifts are clearly sensitive to the electron-
1
accepting ability of the boron,11 the H and 13C NMR
chemical shifts of the cyclopentadienyl ring appear to
be unaffected by the nature of the boryl substituent.
Indeed, the relative ring proton chemical shifts for the
different complexes are inconsistent with the trends
indicated by 11B NMR chemical shifts. The 13C NMR
chemical shifts of the cyclopentadienyl ring carbons
likewise do not reflect the Lewis acidity of the attached
boryl group. In their discussion of their boryl-CpTiCl3
(12) (a) Wrackmeyer, B.; Do¨rfler, U.; Heberhold, M. Z. Naturforsch.,
B 1993, 48, 121. (b) Ruf, W.; Renk, T.; Siebert, W. Z. Naturforsch., B
1976, 31, 1028.
(13) Odom, J . D. In Comprehensive Organometallic Chemistry;
Wilkinson, G., Stone, F. G.A., Abel, E. W., Eds.; Pergamon: Oxford,
U.K., 1982; Vol. 1, Chapter 5.1.
(10) Renk, T.; Ruf, W.; Siebert, W. J . Organomet. Chem. 1976, 120,
1.
(11) (a) No¨th, H.; Vahrenkamp, H. Chem. Ber. 1976, 109, 1075. (b)
No¨th, H.; Vahrenkamp, H. Chem. Ber. 1966, 99, 1049.

2396 Organometallics, Vol. 15, No. 9, 1996
Ta ble 2. Cr ysta llogr a p h ic Da ta for C16H13BCl6Ti2 (6)
Larkin et al.
(a) Crystal Parameters
formula
fw
cryst syst
space group
a, Å
C
16H13BCl6Ti2
Z
4
524.57
orthorhombic
Pbcn
15.223(3)
11.328(4)
11.997(2)
cryst dimens, mm
0.1 × 0.2 × 0.4
D(calc), g cm-3
µ(Mo KR), cm-1
temp, K
1.684
15.44
256
b, Å
c, Å
T(max)/T(min)
1.2
(b) Data Collection
diffractometer
monochromator
radiation
Siemens P4
graphite
Mo KR (λ ) 0.710 73 Å)
4.0-50.0
data collected (h,k,l)
no. of rflns collected
no. of indpt rflns
no. of indpt obsd rflns, Fo g 4σ(Fo)
-6,+13,+14
1158
830
2θ scan range, deg
702
(c) Refinementa
R(F), %
6.56
16.66
0.8
∆(F), e Å-3
No/Nv
GOF
0.771, -0.448
11.5
1.09
R(wF2), %
∆/σ (max)
a
2
Quantity minimized: R(wF2) ) ∑[w(Fo - Fc2)2]/∑[(wFo2)2]1/2; R ) ∑∆/∑(Fo), ∆ ) |(Fo - Fc)|.
Ta ble 3. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 6
P r elim in a r y In vestiga tion s in to th e Rea ctivity
of th e Ha lf-Sa n d w ich (Bor ylCyclop en ta d ien yl)-
tita n iu m Tr ich lor id e Com p lexes. Preliminary ef-
forts to alkylate the titanium centers of the (borylcy-
clopentadienyl)titanium trichloride complexes have
revealed that these systems are unstable toward a
variety of organometallic alkylating reagents, including
alkyllithium, Grignard, and alkylaluminum reagents.
The decomposition of (Cat)B-CpTiCl3 in the presence
of these reagents appears to be due to the vulnerability
of the catechol group. For instance, Me2B-CpTiCl3 was
the only species isolated (in approximately 10% yield)
from the reaction of (Cat)B-CpTiCl3 with trimethyl-
aluminum. (Cat)B-CpTiCl3 does, however, react cleanly
with dimethylzinc, which is generally a milder alkylat-
ing agent. The monoalkylation product (Cat)B-CpTiCl2-
(Me) (7) is formed exclusively, even when the reaction
is carried out in the presence of 5 equiv of dimethylzinc.
Similar reactivity with dimethylzinc has been reported
Ti-Cl(1)
Ti-Cl(2)
Ti-Cl(3)
Ti-C(5)
Ti-C(6)
Ti-C(7)
2.211(6)
2.219(3)
2.218(4)
2.355(11)
2.342(13)
2.315(11)
2.340(13)
2.321(9)
Ti-Cnt
2.000
B-C(1)
1.57(2)
1.55(2)
1.439(12)
1.42(2)
1.43(2)
1.40(2)
1.40(2)
B-C(5)
C(5)-C(6)
C(5)-C(9)
C(6)-C(7)
C(7)-C(8)
C(8)-C(9)
Ti-C(8)
Ti-C(9)
Cl(1)-Ti-Cl(2)
Cl(1)-Ti-Cl(3)
Cl(2)-Ti-Cl(3)
C(5)-B-C(5a)
C(5)-B-C(1)
104.5(2)
C(5)-Ti-C(6)
C(5)-Ti-C(9)
C(6)-Ti-C(7)
C(7)-Ti-C(8)
C(8)-Ti-C(9)
35.7(3)
35.4(5)
35.7(6)
34.9(4)
34.8(4)
101.4(2)
103.7(2)
127.0(11)
116.5(6)
coordinate boron species.13 The phenyl ring is also
twisted out of conjugation with the boron p orbital by
47°, exhibiting a B-C bond length of 1.55(7) Å. The
CpTiCl3 units are unremarkable; the Ti-Cl bond dis-
tances are normal at 2.211(6)-2.219(3) Å,14 and the Ti-
ring centroid distance of 2.000 Å is comparable to that
of other cyclopentadienyltitanium trichloride com-
plexes.15
Whereas there are numerous examples of chelated
metallocene complexes of titanium,16 there are relatively
few reported examples of cyclopentadienyltitanium
complexes in which the bridged rings span two titanium
atoms.17 As in the structure of 6 reported here, when-
ever the cyclopentadienyltitanium units are free to
rotate about the bridging group, they adopt a trans
arrangment in the solid state in order to minimize steric
interactions.
18
for the parent complex CpTiCl3 and has been con-
firmed by us.
All efforts to form the metallocene (Cat)B-Cp(C5H5)-
TiCl2 were unsuccessful. Ill-defined polymeric material,
presumably due to cleavage of the catechol group on the
boron, was obtained upon reacting 2 with LiCp, Cp2-
Mg, or C5H5SnMe3 in toluene. As expected,19 no reac-
tion was observed between 2 and C5H5SiMe3. There
was no reaction between Cp2Zn and CpTl and 2 at room
temperature; decomposition resulted when the reaction
mixtures were heated. We were, however, able to
prepare the (dimethylboryl)- and (diphenylboryl)ti-
tanocene dichloride complexes via salt-elimination reac-
tions between the corresponding half-sandwich com-
plexes {η5-(R2B)C5H4}CpTiCl2 (R ) Me, Ph), and lithium
cyclopentadienide.20 Efforts to prepare additional de-
rivatives, particularly Ti-alkyl derivatives of the boryl-
substituted half-sandwich and bent-metallocene com-
plexes, are underway.
(14) Bochmann, M. In Comprehensive Organometallic Chemistry II,
Abel, E. W., Wilkinson, G., Stone, F. G. A., Eds.; Elsevier: Oxford,
U.K., 1995; Vol. 4, Chapter 5.
(15) (a) Ganis, P.; Allegra, G. Atti Accad. Naz. Lincei, Cl. Sci. Fis.,
Mat. Nat. Rend. 1962, 33, 303. (b) Okuda, J .; Herdtweck, E. Inorg.
Chem. 1991, 30, 1516.
(16) (a) Hitchcock, S. R.; Situ, J . J .; Covel, J . A.; Olmstead, M. M.;
Nantz, M. H. Organometallics 1995, 14, 3732 and references therein.
(b) Halterman, R. L. Chem. Rev. 1992, 92, 965 and references therein.
(c) Luttikhedde, J . G.; Lein, R. P.; Na¨sman, J . H.; Ahlgre´n, M.;
Pakkanen, T. J . Organomet. Chem. 1995, 486, 193 and references
therein. (d) Chacon, S. T.; Coughlin, E. B.; Henling, L. M.; Bercaw, J .
E. J . Organomet. Chem. 1995, 171. (e) Bu¨rgi, T.; Berke, H.; Wingber-
mu¨hle, D.; Psiorz, C.; Noe, R.; Fox, T.; Knickmeier, M.; Berlekamp,
M.; Fro¨hlich, R.; Erker, G. J . Organomet. Chem. 1995, 497, 149.
(17) (a) Ciruelos, S.; Cuenca, T.; Go´mez-Sal, P., Manzanero, A.; Royo,
P. Organometallics 1995, 14, 177. (b) Cuenca, T.; Flores, J . C.; Go´mez,
R.; Go´mez-Sal, P.; Parra-Hake, M.; Royo, P. Inorg. Chem. 1993, 32,
3608. (c) Ciruelos, S.; Cuenca, T.; Flores, J . C.; Go´mez, R.; Go´mez-Sal,
P.; Royo, P. Organometallics 1993, 12, 944. (d) Alvaro, L. M.; Cuenca,
T.; Flores, J . C.; Royo, P.; Pellinghelli, M. A.; Tiripicchio, A. Organo-
metallics 1992, 11, 3301.
Su m m a r y a n d Con clu sion s
By expanding upon J utzi’s method for attaching boryl-
substituted cyclopentadienyl rings to titanium, we have
(18) ) Erskine, G. J .; Hurst, G. J . B.; Weinberg, E. L.; Hunter, B.
K.; McCowan, J . D. J . Organomet. Chem. 1984, 267, 265.
(19) (a) Winter, C. H.; Zhou, X.-X.; Dobbs, D. A.; Heeg, M. J .
Organometallics 1991, 10, 210. (b) Cardoso, A. M.; Clark, R. J . H.;
Moorhouse, S. J . Chem. Soc., Dalton Trans. 1980, 1156.
(20) Larkin, S. A. The University of Idaho, unpublished results.

(Borylcyclopentadienyl)titanium Trichloride Complexes
Organometallics, Vol. 15, No. 9, 1996 2397
reaction mixture was stirred for 12 h. Removal of the volatiles
under reduced pressure afforded a dark red tar, which yielded
2 as a brick red precipitate upon addition of 10 mL of
methylcyclohexane (yield 0.80 g, 62%). 1H NMR (C6D6): δ
6.98-7.03 (m, 2H, Cat H), 6.92 (∼t, J ≈ 2Hz, 2H, Cp H), 6.73-
6.78 (m, 2H, Cat H), 6.11 (∼t, J ≈ 2 Hz, 2H, Cp H). 13C NMR
(C6D6): δ 128.6, 125.6 (CatB(C5H4)), 123.4, 112.9 (C6H4O2B).
11B NMR (CDCl3): δ 11.5. MS (EI): m/ z 338 (M+, 24.4), 336
(M+ - 2H, 22.6), 183 ([C6H4O2]B(C5H4)+, 100), 157 (BC5H3-
TiCl+, 18.4). Anal. Calcd for C11H8BCl3O2Ti: C, 39.18; H,
2.39. Found: C, 39.53; H, 2.31.
prepared new examples of half-sandwich boryl-CpTiCl3
complexes and have prepared the first example of a
boron-bridged cyclopentadienyl-homobimetallic com-
plex, which we have crystallographically characterized.
Comparison of the cyclopentadienyl ring 1H and 13C
NMR chemical shifts of a variety of these complexes did
not reveal any correlation with the Lewis acidity of the
attached boryl group. Further experiments are neces-
sary to assess the possible influence of the boryl sub-
stituents on the electronic properties of the titanium.
We are currently examining the redox properties of
these complexes by electrochemical methods. We are
also in the process of preparing the perfluorinated
analog of our diphenylboryl derivative (i.e. (C5F6)2B-
CpTiCl3), which should exhibit the greatest influence,
if any, of the boryl substituent on the electronic proper-
ties of the titanium center. Various avenues for replac-
ing the chlorine ligands on the titanium center in these
complexes with more reactive groups such as alkyl
groups are also being explored.
TiCl3{η5-C5H4(BP h Cl)} (3). The ligand precursor, {(Me3-
Si)C5H4}B(Cl)Ph, was prepared in situ by adding dichlorophen-
ylborane (1.06 g, 6.65 mmol) dropwise to a solution of (tri-
methylsilyl)(trimethylstannyl)cyclopentadiene (2.00 g, 6.65
mmol) in 50 mL of toluene at room temperature. After 1 h,
TiCl4 (1.26 g, 6.65 mmol) was added dropwise to the reaction
mixture. After it was stirred overnight at room temperature,
the greenish yellow solution was dried under reduced pressure
to yield a green oil. Trituration of the oil with petroleum ether
caused 3 to precipitate as an olive green powder (yield 1.34 g,
65.8%). 1H NMR (CD2Cl2): δ 7.86-7.90 (m, 2H, Ph H), 7.10-
7.25 (m, 3H, Ph H), 7.06 (∼t, J ≈ 2.7 Hz, 2H, Cp H), 6.21 (∼t,
J ≈ 2.7 Hz, 2H, Cp H). 13C NMR (C6D6): δ 136.3, 133.8, 128.4
Exp er im en ta l Section
(C6H5B), 130.7, 126.6 (C5H4Ti). 11B NMR (CDCl3): δ 38. MS
+
(EI): m/ z 342 (M+, 0.8), 305 (M+ - H2Cl, 11.1), 152 (TiCl3
,
Gen er a l Con sid er a tion s. All manipulations were per-
formed using a combination of glovebox, high-vacuum, and
Schlenk techniques. All solvents were distilled under nitrogen
over sodium benzophenone ketyl (toluene, ethyl ether, THF)
or CaH2 (petroleum ether, methylene chloride). The solvents
were then stored in line-pots, from which they were either
vacuum-transferred from sodium benzophenone ketyl or can-
nulated directly. The NMR solvents benzene-d6 and CDCl3
were dried over activated 4 Å molecular sieves. Argon was
purified by passage over oxy tower BASF catalyst (Aldrich)
and 4 Å molecular sieves. NMR spectra were recorded on an
IBM NR-300 (300.13 MHz, 1H; 75.46 MHz, 13C; 75.46 and 96.27
100), 126 (44.6, PhBClH3+). Anal. Calcd for C11H9BCl4Ti: C,
38.67; H, 2.65. Found: C, 38.95; H, 2.69.
TiCl3{η5-C5H4(BP h 2)} (4). Bromodiphenylborane (2.34 g,
9.59 mmol) was added dropwise to a solution of (trimethylsi-
lyl)(trimethylstannyl)cyclopentadiene (3.00 g, 9.59 mmol) in
25 mL of petroleum ether at room temperature. The reaction
mixture was stirred overnight under a blanket of argon. The
solvent was removed from the reaction mixture under reduced
pressure, and the Me3SnBr was removed by heating the
residue to 120 °C under vacuum. The remaining crude
({SiMe3}C5H4)BPh2, an orange-red oil, was used in the next
step without further purification. 1H NMR (CDCl3): δ 7.9-
7.6 (m, Ph H), 7.6-7.4 (m, Ph H), 7.1 (br, Cp H), 6.7 (br, Cp
H). 11B NMR (CDCl3): δ 45. MS (EI): m/ z 302 (M+, 23.6),
165 (Ph2B+, 65.3), 135 (Me3SiC5H2+, 22.8), 73 (SiMe3+, 100).
The titanium complex 4 was prepared by dissolving the
crude ({SiMe3}C5H4)BPh2 in 25 mL of dichloromethane and
adding TiCl4 (2.00 g, 10.5 mmol) dropwise to the solution at
room temperature. The solution turned immediately from
bright orange to deep red and over time assumed a greenish
tinge. The reaction mixture was stirred overnight, and the
volatiles were removed under reduced pressure, leaving a
green-black, oily residue. Trituration of the residue with
petroleum ether afforded 4 as a lime green powder (yield 1.98
g, 54%). 1H NMR (C6D6): 7.62-7.67 (m, 2H, Ph H), 7.16-
7.27 (m, 3H, Ph H), 6.76 (∼t, J ≈ 2.6 Hz, 2H, Cp H), 6.36 (∼t,
J ≈ 2.6 Hz, 2H, Cp H). 13C NMR (C6D6): δ 138, 132, 128
([C6H5]2B), 128, 134 (C5H4Ti). 11B NMR (CDCl3): δ 41. MS
1
MHz, 11B) and an IBM NR-200 (200.13 MHz, H; 50.32 MHz,
13C; 64.20 MHz, 11B). All chemical shifts are reported in ppm
and referenced to solvent (13C, 1H) or B(OH)3 (11B, external
reference, δ 0 ppm). Mass spectra were obtained on a VG
7070-HS GC/MS instrument with a heated direct-insertion
probe for solid samples. Elemental analyses were determined
by Desert Analytics and the University of Idaho analytical
facilities. Bromodiphenylborane21 and (trimethylsilyl)(trim-
ethylstannyl)cyclopentadiene22 were prepared as described in
the literature.
P r oced u r es. ({SiMe3}C5H4)(C6H4O2)B (1). Toluene (100
mL) was added to a mixture of (Me3SiC5H4)Li (5.6 g, 39 mmol),
and B-chlorocatecholborane (6.0 g, 39 mmol) and the reaction
mixture was heated at reflux for 12 h. LiCl was removed by
filtration, and the filtrate was evaporated under reduced
pressure to afford a gummy, off-white residue which was
dissolved in 20 mL of petroleum ether. Cooling of this solution
to -78 °C afforded 1 as a white precipitate (yield: 4.6 g, 46%).
The product may also be isolated as a pale yellow oil which
solidifies over time by distillation from the residue under
reduced pressure (160 °C, 2 × 10-2 Torr). 1H NMR (C6D6, 297
K): δ 7.7 (br, Cp H), 7.2-7.0 (m, arene H), 6.9-6.7 (m, arene
H), 6.6 (br, Cp H), 3.3 (br, Cp H), 0.1 (s, Si(CH3)3), -0.1 (s,
Si(CH3)3). 11B NMR (CDCl3): δ 11.3. MS (EI): m/ z 256 (M+,
(EI): m/ z 382 (M+, 32.8), 346 (M+ - HCl, 26.4), 305 (M+
-
Ph, 49.3), 269 (M+ - [Ph + HCl], 13.6), 228 (C5H3BPh2+, 100),
151 (C5H3BPh+, 75.7), 126 (C5H4BTiH3+, 65.0), 100 (?, 64.3),
65 (C5H5+, 71.4). Anal. Calcd for C17H14BCl3Ti: C, 53.26; H,
3.68. Found: C, 53.05; H, 3.53.
({SiMe3}C5H4)2BP h (5). Dichlorophenylborane (1.53 g,
9.62 mmol) was added to a solution of (trimethylsilyl)(tri-
methylstannyl)cyclopentadiene (5.69 g, 19.0 mmol) in 50 mL
of toluene at room temperature. The reaction mixture was
refluxed under a blanket of argon overnight. The volatiles
were removed in vacuo, leaving 3.40 g (97.7% theoretical yield)
of crude 5 as a viscous, red-orange oil. Attempts to purify the
oil by distillation lead to apparent decomposition. 1H NMR
(CDCl3): δ 7.6 (m, Ph H), 7.4 (m, Ph H), 7.2 (m, aryl H), 7.0
(br, Cp H), 6.7 (br, Cp H), -0.1 (br, Si(CH3)3). 11B NMR
+
59.37), 240 (M+ - CH3 - H, 59.37), 149 (C5H4BSiMe3 + H,
+
22.90), 136 (C5H4SiMe3 - H, 10.66), 73 (Me3Si+, 18.43), 64
(C5H4+, 21.65). Anal. Calcd for C14H17BO2Si: C, 65.60; H,
6.68. Found: C, 65.59; H, 6.50.
[{C6H4O2}B(η5-C5H4)]TiCl3 (2). TiCl4 (0.73 g, 3.8 mmol)
was added dropwise to a solution of 1 (1.0 g, 3.8 mmol) in 40
mL of methylene chloride at room temperature, and the
(CDCl3): δ 37. MS: m/ z 362 (M+, 5.6), 225 (M+ - Me3SiC5H4,
(21) No¨th, H.; Vahrenkamp, H. J . Organomet. Chem. 1968, 11, 399.
(22) Abel, E. W.; Dunster, M. O.; Waters, A. J . Organomet. Chem.
1973, 49, 287.
+
43.2), 152 (C5H4BPh, 13.4), 135 (C5H2SiMe3+, 13.6), 84 (BSiMe3
15.6), 73 (SiMe3+, 100).
,

2398 Organometallics, Vol. 15, No. 9, 1996
Larkin et al.
[TiCl3{η5-C5H4}]2BP h (6). An excess of TiCl4 (2.8 g, 15
mmol) was vacuum-transferred to a solution of crude 5 (2.5 g,
6.8 mmol) in chloroform (50 mL) at -78 °C. When the reaction
mixture was warmed to room temperature, compound 7
deposited as yellow-green crystals which were isolated by
filtration (yield 2.2 g, 63%). 1H NMR (C6D6): δ 7.45 (t, 1H,
Ph H), 7.41 (d, 1H, Ph H), 7.31-7.16 (m, 3H, Ph H), 7.07 (t, J
≈ 2.4 Hz, 4H, Cp H), 6.14 (t, J ≈ 2.4 Hz, 4H, Cp H). 13C NMR
(CD2Cl2): δ 136.3, 132.3, 128.3 (C6H5B), 134.2, 128.8 (C5H4)2-
Ti. Anal. Calcd for C16H13BCl6Ti: C, 36.63; H, 2.50. Found:
C, 36.58; H, 2.29.
least-squares refinement of the angular settings of 24 reflec-
tions (20° e 2θ e 24°).
The systematic absences in the diffraction data are uniquely
consistent for space group Pbcn. The structure was solved
using direct methods, completed by subsequent difference
Fourier syntheses, and refined by full-matrix least-squares
procedures. A semiempirical ellipsoid absorption correction
was applied to the data set. The molecule is located on a 2-fold
axis. The titanium and chlorine atoms were refined with
anisotropic displacement coefficients. The boron and carbon
atoms were refined isotropically. The hydrogen atoms were
treated as idealized contributions.
[{C6H4O2}B-(η5-C5H4)]Ti(Me)Cl2 (7). At room tempera-
ture, 1.4 mL (3.0 mmol) of a 2.14 M solution of dimethylzinc
in toluene was added dropwise by syringe to a solution of 2
(1.0 g, 3.0 mmol) in 20 mL of toluene, and the reaction mixture
was stirred for 12 h. The solution was filtered to remove the
insolubles, and the filtrate was dried in vacuo, leaving a
gummy, tan residue. Taking the residue up in 10 mL of
petroleum ether afforded 3 as a yellowish tan precipitate (yield
0.250 g, 24.5%). 1H NMR (C6D6): δ 7.00 (m, 2H, Cat H), 6.81
(∼t, J ≈ 4 Hz, 2H, Cp H), 6.72-6.77 (m, 2H, Cat H), 5.96 (∼t,
J ≈ 4 Hz, 2H, Cp H), 1.86 (s, 3H, TiCH3). 13C NMR (C6D6): δ
123.8, 122.7 (CatB(C5H4)), 148.3, 123.4, 112.9 (C6H4O2B), 82.6
(TiCH3). 11B NMR (C6D6): δ 9. MS (EI): m/ z 316 (M+, 2.9),
300 (33.8), 184 (35.7), 134 (53.4), 69 (100). Anal. Calcd for
All software and sources of the scattering factors are
contained in the SHELXTL (5.3) program library (G. Sheldrick,
Siemens XRD, Madison, WI).
Ack n ow led gm en t. We thank Dr. Gary Knerr of the
University of Idaho for his assistance in acquiring the
(H,C)-HETCOR and 11B NMR spectra, Mr. Dan Stelck
for contributing experimental data, and Dr. Kevin Kane
for helpful editorial comments. We are grateful to the
National Science Foundation for supporting this work
(Grant No. CHE-9320407).
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal-
lographic data collection and solution and refinement details,
atomic coordinates, complete bond lengths and angles, and
anisotropic displacement coefficients (5 pages). Ordering
information is given on any current masthead page.
C
12H11BCl2O2Ti: C, 45.49; H, 3.50. Found: C, 45.71; H, 3.69.
Cr ysta l Str u ctu r e Deter m in a tion of [TiCl3{η5-C5H4}]2-
BP h (6). Yellow-green crystals of 6 formed during the
synthesis of the compound in chloroform. A suitable crystal
was selected and mounted in a thin-walled, nitrogen-flushed
glass capillary. The unit-cell parameters were obtained by the
OM9600699