Photoinduced generation of catalytic complexes from substituted-titanocene-bis(trimethylsilyl)ethyne complexes: Contribution to the mechanism of the catalytic head-to-tail dimerization of terminal alkynes

Article abstract of DOI:10.1021/om9905714

A number of substituted-titanocene-alkynyl-alkenyl complexes, [(η⁵-C₅Me₄R¹) ₂Ti(η¹-C≡ CR²)(η¹-(E)-CH=CHR²)] (R¹ = H, Me Ph, Bz; R² = CMe₃, SiMe₃, ferrocenyl; A type complexes), were obtained by reacting the corresponding bis(trimethylsilyl)ethyne complexes [(η⁵-C₅Me₄R¹) ₂Ti(η²-Me₃SiC≡CSiMe₃)] with 1-alkynes R²C≡CH in the dark at 60°C. The complexes undergo a coupling of the carbyl ligands upon exposure to sunlight to give titanocene complexes with 1,4-disubstituted but-1-en-3-ynes, [(η⁵-C₅Me₄R¹) ₂Ti(3,4-η-R²C≡ CCH=CHR²)] (B type complexes). In contrast to A type complexes that do not react further with an excess of tert-butylethyne and (trimethylsilyl)ethyne in the dark, B type complexes induce rapid dimerization of these terminal alkynes to 2,4-disubstituted but-1-en-3-ynes (head-to-tail dimers). This implies that the known dimerization of 1-alkynes in the presence of [(η⁵-C₅Me₄R¹) ₂Ti(η²-Me₃SiC≡CSiMe₃)] (R¹ = H, Me) performed in diffuse daylight is initiated by the B type complexes originating from photoinduced conversion of the initially formed A type products. Titanocene complexes with 2,4-disubstituted but-1-en-3-ynes, [(η⁵-C₅Me₄R¹) ₂Ti(3,4-η-R²C≡CC(R²)=CH₂)] (R¹ = H, Me, Ph; R² = SiMe₃), were also prepared and their participation in the catalytic cycle was demonstrated.

Full text of DOI:10.1021/om9905714

Organometallics 1999, 18, 4869-4880
4869
P h otoin d u ced Gen er a tion of Ca ta lytic Com p lexes fr om
Su bstitu ted -Tita n ocen e-Bis(tr im eth ylsilyl)eth yn e
Com p lexes: Con tr ibu tion to th e Mech a n ism of th e
Ca ta lytic Hea d -to-Ta il Dim er iza tion of Ter m in a l Alk yn es
Petr Sˇteˇpnicˇka, Ro´bert Gyepes, and Ivana C´ısarˇova´
Department of Inorganic Chemistry, Charles University, Hlavova 2030,
128 40 Prague 2, Czech Republic
Michal Hora´cˇek, J irˇ´ı Kubisˇta, and Karel Mach*
J . Heyrovsky´ Institute of Physical Chemistry, Academy of Sciences of the Czech Republic,
Dolejsˇkova 3, 182 23 Prague 8, Czech Republic
Received J uly 13, 1999
A number of substituted-titanocene-alkynyl-alkenyl complexes, [(η5-C5Me4R1)2Ti(η1-Ct
CR2)(η1-(E)-CHdCHR2)] (R1 ) H, Me, Ph, Bz; R2 ) CMe3, SiMe3, ferrocenyl; A type
complexes), were obtained by reacting the corresponding bis(trimethylsilyl)ethyne complexes
[(η5-C5Me4R1)2Ti(η2-Me3SiCtCSiMe3)] with 1-alkynes R2CtCH in the dark at 60 °C. The
complexes undergo a coupling of the carbyl ligands upon exposure to sunlight to give
titanocene complexes with 1,4-disubstituted but-1-en-3-ynes, [(η5-C5Me4R1)2Ti(3,4-η-R2Ct
CCHdCHR2)] (B type complexes). In contrast to A type complexes that do not react further
with an excess of tert-butylethyne and (trimethylsilyl)ethyne in the dark, B type complexes
induce rapid dimerization of these terminal alkynes to 2,4-disubstituted but-1-en-3-ynes
(head-to-tail dimers). This implies that the known dimerization of 1-alkynes in the presence
of [(η5-C5Me4R1)2Ti(η2-Me3SiCtCSiMe3)] (R1 ) H, Me) performed in diffuse daylight is
initiated by the B type complexes originating from photoinduced conversion of the initially
formed A type products. Titanocene complexes with 2,4-disubstituted but-1-en-3-ynes, [(η5-
C5Me4R1)2Ti(3,4-η-R2CtCC(R2)dCH2)] (R1 ) H, Me, Ph; R2 ) SiMe3), were also prepared
and their participation in the catalytic cycle was demonstrated.
In tr od u ction
catalysts, decamethyltitanocene-derived systems pro-
duce HTT dimers with an astonishing selectivity.1a The
turnover numbers (TN) (0.5-1.2) × 103 and a selectivity
to HTT dimers of around 99% were achieved for (tri-
methylsilyl)ethyne (TMSE), propyne, 1-butyne, 1-pen-
tyne, 1-hexyne, and cyclohexylethyne using either the
[(η5-C5Me5)2TiCl2]/i-PrMgCl/ether (ether ) Et2O, THF)
systems5 or the [(η5-C5Me5)2Ti(η2-Me3SiCtCSiMe3)]
complex6 as the catalyst precursor. Although tert-
butylethyne (TBUE) was found to be unreactive toward
all the above catalysts,1a,5,6 it is dimerized to its HTT
dimer by the [(η5-C5Me4H)2TiCl2]/i-PrMgCl/THF cata-
lytic system or the [(η5-C5Me4H)2Ti(µ-H)2Mg(µ-Cl)]2
complex, the TN value (∼8.8 × 103) appearing to have
been limited by trace amounts of tert-butyl alcohol in
Linear dimerizations of terminal acetylenes are cata-
lyzed by various organometallic complexes of early,1
first-row,2 and late3 transition metals as well as by
complexes of rare-earth metals, lanthanides, and ac-
tinides,4 affording 2,4-disubstituted but-1-en-3-ynes
(head-to-tail or HTT dimers), 1,4-disubstituted but-1-
en-3-ynes (head-to-head or HTH dimers), and 1,4-
disubstituted buta-1,2,3-trienes. Among the numerous
* To whom correspondence should be addressed. E-mail: mach@
jh-inst.cas.cz.
(1) (a) Ti: Akita, H.; Yasuda, H.; Nakamura, A. Bull. Chem. Soc.
J pn. 1984, 57, 480. (b) Zr: Horton, A. D. J . Chem. Soc., Chem.
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1997, 16, 4508.
(2) (a) Cr: Hagihara, N.; Tamura, M.; Yamazaki, H.; Fujiwara, M.
Bull. Chem. Soc. J pn. 1961, 34, 892. (b) Cu: Akhtar, M.; Richards, T.
A.; Weedon, B. C. L. J . Chem. Soc. 1959, 933. (c) Cu: Balciogˇlu, N.;
Uraz, I.; Bozkurt, C.; Sevin, F. Polyhedron 1997, 16, 327.
(3) (a) Ru: Wakatsuki, Y.; Yamazaki, H.; Kumegawa, N.; Satoh, T.;
Satoh, J . Y. J . Am. Chem. Soc. 1991, 113, 9604. (b) Ru: Yo, C. S.; Liu,
N. Organometallics 1996, 15, 3968. (c) Ru: Slugovc, C.; Mereiter, K.;
Zobetz, E.; Schmid, R.; Kirchner, K. Organometallics 1996, 15, 5275.
(d) Rh: Scha¨fer, M.; Mahr, N.; Wolf, J .; Werner, H. Angew. Chem.,
Int. Ed. Engl. 1993, 32, 1315. (e) Rh: Kovalev, I. P.; Yevdakov, K. V.;
Strelenko, Yu. A.; Vinogradov, M. G.; Nikishin, G. I. J . Organomet.
Chem. 1990, 386, 139. (f) Pd: Trost, B. M.; Sorum, M. T.; Chan, C.;
Harms, A. E.; Ru¨hter, G. J . Am. Chem. Soc. 1997, 119, 698. (g) Os:
Barbaro, P.; Bianchini, C.; Peruzzini, M.; Polo, A.; Zanobini, F.;
Frediani, P. Inorg. Chim. Acta 1994, 220, 5. (h) Ir: J un, C.-H.; Lu, Z.;
Crabtree, R. H. Tetrahedron Lett. 1992, 47, 7119.
(4) (a) Sc: Thompson, M. E.; Baxter, S. M.; Bulls, A. R.; Burger, B.
J .; Nolan, M. C.; Santarsiero, B. D.; Schaefer, W. P.; Bercaw, J . E. J .
Am. Chem. Soc. 1987, 109, 203. (b) Y: den Haan, K. H.; Wielstra, Y.;
Teuben, J . H. Organometallics 1987, 6, 2053. (c) Y: Schaverien, C. J .
Organometallics 1994, 13, 69. (d) Ce: Heeres, H. J .; Nijhoff, J .; Teuben,
J . H.; Rogers, R. D. Organometallics 1993, 12, 2609. (e) Th, U: Hasket,
A.; Wang, J . Q.; Straub, T.; Neyroud, T. G.; Eisen, M. S. J . Am. Chem.
Soc. 1999, 121, 3025. (f) Th, U: Straub, T.; Haskel, A.; Eisen, M. S. J .
Am. Chem. Soc. 1995, 117, 6364. (g) U: Wang, J . Q.; Dash, A. K.;
Berthet, J . C.; Ephritikhine, M.; Eisen, M. S. Organometallics 1999,
18, 2407.
(5) Varga, V., Petrusova´, L.; Cˇ ejka, J .; Mach, K. J . Organomet.
Chem. 1997, 532, 251.
(6) Varga, V., Petrusova´, L.; Cˇ ejka, J .; Hanusˇ, V.; Mach, K. J .
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10.1021/om9905714 CCC: $18.00 © 1999 American Chemical Society
Publication on Web 10/16/1999

4870 Organometallics, Vol. 18, No. 23, 1999
Sˇ teˇpnicˇka et al.
Sch em e 1. Syn th esis of th e A a n d B Typ e
TBUE, which deactivates the catalyst.7 Investigations
of the above titanocene dichloride-Grignard reagent
catalytic systems showed that the catalytic species
arises from a titanocene diacetylide tweezer complex
that contains Mg2+ cation embedded between the twee-
zer acetylide arms. The true catalytic species is to be
either a monomeric titanocene acetylide8 or a titanocene
Ti(II) complex generated from the latter compound by
an as yet unknown redox reaction.5 The latter possibility
is supported by the fact that all nonpolar 1-alkynes
tested (except TBUE) are dimerized to their HTT dimers
by [(η5-C5Me5)2Ti(η2-Me3SiCtCSiMe3)] with similar ac-
tivities and selectivities. The catalytic cycle of the HTT
dimer formation was proposed; however, no products
resulting from the reaction of [(η5-C5Me5)2Ti(η2-Me3-
SiCtCSiMe3)] with 1-alkynes were isolated and identi-
fied.6 This was mainly due to a slow conversion of this
complex to the catalytically active species, whose con-
centration remained very low during the alkyne dimer-
ization. The validity of the catalytic cycle has recently
been brought in doubt by an observation that [(η5-C5-
Me5)2Ti(η2-Me3SiCtCSiMe3)] reacts with terminal
alkynes to afford the decamethyltitanocene (η1-(E)-
alkenyl)(η1-alkynyl) complexes, which cannot obviously
be the precursors of the HTT dimers.9
Com p lexes
Here we report the formation of [(η5-C5Me4R1)2Ti(η1-
CtCR2){η1-(E)-CHdCHR2}] complexes from [(η5-C5-
Me4R1)2Ti(η2-BTMSE)] (R1 ) H, Me, Ph, Bz (benzyl);
BTMSE ) bis(trimethylsilyl)ethyne) and alkynes R2Ct
CH (R2 ) t-Bu, SiMe3, Fc (ferrocenyl)), as well as their
photoinduced transformation to [(η5-C5Me4R1)2Ti{η2-(E)-
R2CtCCHdCHR2}] complexes, containing a η2-coordi-
nated triple bond. Some titanocene complexes with the
η2-coordinated HTT dimer (TMSE)2, [(η5-C5Me4R1)2Ti-
{3,4-η-Me3SiCtCC(SiMe3)dCH2}] (R1 ) H, Me, Ph),
which have to be involved in the dimerization reaction,
were also prepared, and their reactivity toward selected
terminal alkynes has been examined in order to throw
more light on the catalytic cycle.
formed with no admixture of head-to-tail dimers from
either of the alkynes. Compounds A are orange-yellow
oils or waxy solids, except for A1, which was obtained
in a crystalline form from a concentrated hexane solu-
tion, and the red ferrocene derivative A6, which crystal-
lized from its concentrated toluene solution. The struc-
1
tures of A type complexes have been determined by H
1
and 13C NMR spectroscopy. The H NMR spectra are
suggestive of a trans configuration at the η1-coordinated
carbon-carbon double bond in all cases, as judged from
3J HH values. The 13C NMR spectra (Table 1) are in full
accordance with the proposed structures as well but
provide much clearer information about the coordination
of the hydrocarbyl ligands.10 The low-field signals
observed at δC 145-180 and 115-125 belong to the CR
and Câ carbon atoms of the σ-bonded triple bond,
whereas those at δC 190-225 and 130-145 are due to
the σ-bonded double bond (CR and Câ, respectively).
Cr ysta l Str u ctu r e of A1. In the solid state, complex
A1 exhibits a combined statistical and rotational dis-
order even at low temperature that lowers the precision
of the structure determination (see Experimental Sec-
tion). Hence, geometrical parameters describing the
disordered hydrocarbyl ligands will not be discussed
here in detail. Nevertheless, the chemical picture is
unambiguous (Figure 1, Table 2) and verifies the
structure assigned on the basis of spectral data. The
molecular geometry of A1 corresponds favorably to that
of [(η5-C5Me5)2Ti(η-CtCPh){η1-(E)-CHdCHPh}].9 The
titanocene cyclopentadienyls are eclipsed with the
C(Me)-CH edges at the hinge position, thus reflecting
mimicked crystallographic C2/σ symmetry.
Resu lts a n d Discu ssion
The substituted-titanocene-η2-bis(trimethylsilyl)-
ethyne (BTMSE) complexes [(η5-C5Me4R1)2Ti(η2-Me3-
SiCtCSiMe3)] (R1 ) H (1), Me (2), Ph (3), Bz (4)) react
with terminal alkynes such as tert-butylethyne (TBUE),
(trimethylsilyl)ethyne (TMSE), or ferrocenylethyne (FCE)
in a uniform way to yield exclusively (η1-(E)-alkenyl)-
(η1-alkynyl)titanocenes A1-A6 (Scheme 1). The reaction
is slow, even at a 20-fold excess of the alkyne, and
requires at least several hours to reach completion at
60 °C, as evidenced by following the conversion of the
BTMSE complexes through decay of their absorption
band at 920 nm.6 When the reaction is carried out under
strict exclusion of light, complexes of the A type are
(7) Hora´cˇek, M.; C´ısarˇova´, I.; Karban, J .; Petrusova´, L.; Mach, K.
J . Organomet. Chem. 1999, 577, 103.
(8) (a) The stable, paramagnetic titanocene acetylide [(η5-C5Me5)2-
Ti(η1-CtCMe)] was characterized: Luinstra, G. A.; ten Cate, L. C.;
Heeres, H. J .; Pattiasina, J . W.; Meetsma, A.; Teuben, J . H. Organo-
metallics 1991, 10, 3227. (b) An in situ generation of the cationic Ti-
(IV) titanocene monoacetylide [(η5-C5H5)2Ti(η1-CtCMe)] was also
reported: Ahlers, R.; Erker, G.; Fro¨hlich, R. J . Organomet. Chem. 1998,
571, 83.
(10) (a) Cohen, S. A.; Bercaw, J . E. Organometallics 1985, 4, 1006.
(b) Burlakov, V. V.; Polyakov, A. V.; Yanovski, A. I.; Struchkov, Yu.
T.; Shur, V. B.; Vol’pin, M. E.; Rosenthal, U.; Go¨rls, H. J . Organomet.
Chem. 1994, 476, 197. (c) Burlakov, V. V.; Rosenthal, U.; Beckhaus,
R.; Polyakov, A. V.; Struchkov, Yu. T.; Oehme, G.; Shur, V. B.; Vol’pin,
M. E. Organomet. Chem. USSR 1990, 3, 237. (d) Beckhaus, R.; Sang,
J .; Oster, J .; Wagner, T. J . Organomet. Chem. 1994, 484, 179.
(9) Beckhaus, R.; Wagner, W.; Burlakov, V.; Baumann, W.; Peulecke,
N.; Spannenberg, A.; Kempe, R.; Rosenthal, U. Z. Anorg. Allg. Chem.
1998, 624, 129.

Head-to-Tail Dimerization of Terminal Alkynes
Ta ble 1. Selected 13C NMR Da ta (δC/p p m )a for A, B, a n d D Typ e Com p lexes
[(η5-C5R1Me4)2Ti(η1-CtCR2){η1-(E)-CHdCHR2}]
Organometallics, Vol. 18, No. 23, 1999 4871
compd
R1
R2
Ti-CtC
Ti-CtC
Ti-CHdCH
Ti-CHdCH
A1
A2
A3
A4
A5
A6
C5HMe4
C5Me5
C5PhMe4
C5BzMe4
C5HMe4
C5HMe4
t-Bu
t-Bu
t-Bu
t-Bu
SiMe3
Fc
126.3
124.2
121.8
124.6
118.1
115.7
147.4
149.4
151.9
150.1
181.1
160.3
143.8
142.5
144.2
143.1
137.3
128.6
190.8
193.2
193.9
193.5
227.6
200.8
[(η5-C5R1Me4)2Ti{η2-(E)-R2CtCCHdCHR2}]
compd
R1
R2
R2-CtC
R2-CtC
CHdCHR2
CHdCHR2
B1
B2
B3
B4
B5
B6
C5HMe4
C5Me5
C5PhMe4
C5BzMe4
C5HMe4
C5HMe4
t-Bu
t-Bu
t-Bu
t-Bu
SiMe3
Fc
199.4
203.9
205.4
204.7
222.5
204.3
218.0
218.6
220.5
219.6
231.5
210.0
144.2
144.0
142.8
144.7
142.5
129.4
122.5
123.1
123.9
123.2
132.1
126.4
[(η5-C5R1Me4)2Ti{η2-(E)-R2CtCC(R2)dCH2}]
compd
R1
R2
R2-CtC
R2-CtC
-C(R2)d
dCH2
D1
D2
D3
C5HMe4
C5Me5
C5PhMe4
SiMe3
SiMe3
SiMe3
208.7
205.9
209.1
216.1
219.4
221.2
150.3
149.3
150.0
130.7
133.3
132.7
a
In C6D6 at 298 K.
titanium atom is pseudotetrahedrally coordinated,
though, with angles markedly deviated from the value
of the regular tetrahedron; C(1)-Ti-C(3) is more acute
(92.1(3)°) because of unlike steric requirements of the
cyclopentadienyl and both hydrocarbyl ligands. The Ti-
Cd and Ti-Ct bond lengths of 2.127(7) and 2.102(7)
Å, respectively, compare well with those observed for
other titanium(IV) organometallics: [(η5-C5Me5)2Ti(η1-
CtCPh)(η1-CHdCHPh)], 2.124(4) and 2.099(5) Å;9 [(η5-
C5Me5)2Ti(η1-CHdCH2)(η1-CtCPh)], 2.14 and 2.10 Å (in
the same order);11 [(η5-C5Me5)2TiF(η1-CHdCH2)], 2.098-
(6) Å (Ti-Cd);10d [(η5-C5H5)2Ti(η1-C(Ph)dCMe2)Br0.5
-
F igu r e 1. Molecular structure of A1 with thermal el-
lipsoids drawn at the 30% probability level. For clarity, only
one of the disordered hydrocarbyl ligands is shown and all
methyl hydrogen atoms are omitted. Selected bond dis-
tances (Å) and angles (deg): Ti(1)-C(100) ) 2.08(2),
C(100)-C(200) ) 1.26(2), C(200)-C(300) ) 1.45(2), C(300)-
C(320) ) 1.46(2), C(300)-C(330) ) 1.51(2), C(300)-C(310)
) 1.52(2), Ti(1)-C(102) ) 2.17(2), C(102)-C(202) ) 1.27-
(2), C(202)-C(302) ) 1.50(2), C(302)-C(312) ) 1.51(2),
C(302)-C(322) ) 1.56(2), C(302)-C(332) ) 1.46(2); C(100)-
Ti(1)-C(102) ) 91.3(3), Ti(1)-C(100)-C(200) ) 173(1),
C(100)-C(200)-C(300) ) 171(2), Ti(1)-C(102)-C(202) )
129.3(8), C(102)-C(202)-C(302) ) 138(1)°.
Cl0.5], 2.234(4) Å (Ti-Cd);13 [{η5-C5(SiMe3)H4}2Ti(η1-Ct
C-CtFc)2], 2.090(7) and 2.099(7) Å (Ti-Ct);14 [(η5-
C5Me5)2Ti(OH)(η1-CtPh)], 2.117(2) Å (Ti-Ct).15 The
fact that both Ti-C bond lengths are similar indicates
that the η1 ligands are simply σ-bonded with no signifi-
cant π-bond contribution to the Ti-C bond such as Ti-
CdC T Ti.C.C and Ti-CtC T TidCdC.
The η1-(E)-2-(ferrocenyl)ethenyl moiety possesses an
arrangement typical for trans-disubstituted ethenes; the
C(1)-C(2) bond length 1.312(9) Å is identical with the
mean double-bond length observed in “organic” (E)-CCd
CC fragments (1.31(1) Å; average value of 19 entries).16
The Ti-C(1)-C(2) and C(1)-C(2)-C(11) angles are
more opened due to different sizes of the substituents
at the double bond, but no significant torsion occurs, as
implied by the torsion angle Ti-C(1)-C(2)-C(11) of
-170.7(5)°. Similarly, there is no deformation within the
Cr ysta l Str u ctu r e of A6. The molecule of A6 (Figure
2) consists of three metallocene units, whose bond
lengths and angles are unexceptional (Table 2). Ti-
tanocene cyclopentadienyls adopt a conformation half-
way between staggered and eclipsed, bearing the non-
methylated cyclopentadienyl carbons inclined toward
each other to reduce the steric strain of the methyl
groups on the rings. Cyclopentadienyls of both ferroce-
nyl groups are almost perfectly eclipsed, with dihedral
angles of the least-squares cyclopentadienyl planes of
1.5 and 2.6° for the ethynyl- and ethenyl-substituted
ferrocenyl group, respectively. The ferrocenyl groups are
mutualy rotated at the dihedral angle subtended by the
substituted cyclopentadienyls of 45.1°.
(11) The structure determination is of low precision because of the
presence of disordered η5-C5Me5 ligands. Distances were retrieved from
the Cambridge Crystallographic Data Centre12 (CODEN: ZUXHEF).
For the original reference see ref 23.
(12) Allen, F. H.; Kennard, O. Chem. Design Automation News 1993,
8, 1, 31.
(13) Cardin, C. J .; Cardin, D. J .; Morton-Blake, D. A.; Parge, H. E.;
Roy, A. J . Chem. Soc., Dalton Trans. 1987, 1641.
(14) Hayashi, Y.; Osawa, M.; Kobayashi, K.; Wakatsuki, Y. J . Chem.
Soc., Chem. Commun. 1996, 1617.
(15) Polse, J . L.; Andersen, R. A.; Bergman, R. G. J . Am. Chem. Soc.
1995, 117, 5393.
Undoubtedly, the most meaningful feature in the
structure of A6 is the geometry of ligation (Table 3). The
(16) Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; Orpen,
A. G.; Taylor, R. J . Chem. Soc., Perkin Trans. 2 1987, S1.

4872 Organometallics, Vol. 18, No. 23, 1999
Sˇ teˇpnicˇka et al.
Ta ble 2. Selected Geom etr ic P a r a m eter s of th e Meta llocen e Un its in A1, A6, B1, a n d D2 (in Å a n d d eg)a
A6
A1
(C5H5)Fe
alkenic
(C5H5)Fe
alkynic
B1
D2
(C5Me5)2Ti
compd
(Me4HC5)2Ti
(Me4HC5)2Ti
3.887
2.096, 2.099
2.357(6)-2.450(7)
1.40(1)
(C5Me4H)2Ti
CE-CE
3.897
3.301
3.290
3.917
3.982
M-CE
2.082b
1.648, 1.653
av 2.04(2)
1.40(2)
1.649, 1.643
av 2.03(1)
1.40(2)
2.109, 2.107
2.347(6)-2.491(5)
1.402(8)
1.504(6)
44.9
2.111, 2.136
2.412(2)-2.478(3)
1.407(8)
M-C(Cp)
2.348(2)-2.438(2)
1.410(5)
1.498(4)
47.8
av C-C(Cp)
av C(Cp)-C(Me)
(Cp,Cp)
1.51(1)
48.3
1.500(5)
1.5
2.6
40.2
CE-M-CE
av C-C-C(Cp)
138.9
108.0(5)
135.9
108(1)
177.8
108(1)
177.9
108(2)
136.6
108(1)
139.3
108.0(3)
a
b
CE denotes the centroid of a cyclopentadienyl ring. The M-CE distances are identical due to crystallographic symmetry.
F igu r e 2. Molecular structure of A6 (30% probability
level, PLATON plot). Only alkenic hydrogen atoms are
shown. For clarity, only pivot and adjacent carbon atoms
of ferrocene rings are labeled and the numbering of the
lower titanocene C5HMe4 ligand is analogous to that of the
upper one.
F igu r e 3. Molecular structure of B1 (30% probability
level, PLATON plot). All hydrogen atoms except those
within the alkenyl moiety are omitted.
absorption band, observed in complexes 1-4 at 920
nm,17a is shifted for B type complexes to 720 nm, most
likely as the consequence of conjugation of the multiple
carbon-carbon bonds. The photolyses were repeated on
a larger scale, and the products were isolated. Except
for blue crystalline B1, whose crystal structure has been
determined, other complexes could be isolated only in
the form of dark blue-green (purple for B6) oils or waxy
solids.
Ta ble 3. Selected Bon d Len gth s (Å) a n d Bon d
An gles a n d Dih ed r a l An gles (d eg) for A6a ,b
Ti-C(1)
C(1)-C(2)
C(2)-C(11)
2.127(7)
1.312(9)
1.445(9)
Ti-C(3)
C(3)-C(4)
C(4)-C(31)
2.102(7)
1.174(8)
1.445(9)
C(1)-Ti-C(3)
Ti-C(1)-C(2)
C(1)-C(2)-C(11)
92.1(3)
135.5(6)
131.1(8)
Ti-C(3)-C(4)
C(3)-C(4)-C(31)
172.3(6)
174.2(8)
Cr ysta l Str u ctu r e of B1. The coordination geometry
of B1 (Figure 3, Table 4) resembles closely that of other
titanacyclopropene-like titanocene-η2-alkyne complexes.
The most characteristic features are lengthening of the
triple bond (1.304(6) Å) close to the value in cyclopro-
penes (1.29(2) Å, mean of 10 entries;16 cf. the C-C bond
lengths of 1.303 Å in both 117a and [(η5-C5Me4H)2Ti(η2-
FcCtCSiMe3)]17c) and bending of the originally linear
arrangement at the triple bond. Both Ti-C bond lengths
are similar, thus pointing to a rather symmetric bonding
of the alkyne to the titanocene framework with negli-
gible torsion at the coordinated triple bond, as follows
from the C(11)-C(1)-C(2)-C(3) torsion angle of -6(1)°.
Similarly, the double bond exhibits no torsional distor-
tion, adopting a typical trans double-bond geometry
(1.314(7) Å vs mean value 1.31(1) Å for 19 (E)-CCHd
CHC moieties).16 The titanocene cyclopentadienyls are
about halfway between staggered and eclipsed, with the
nonmethylated carbon atoms mutually rotated simi-
larly, as observed for the aforementioned [(η5-C5Me4H)2-
Ti(η2-FcCtCSiMe3)] complex.17c The dihedral angle
Ti-C(1)-C(2)-C(11)
-170.7(6)
(TiC2,Cp1)
(TiC2,Cp3)
24.6(3)
18.5(4)
(TiC2,Cp2)
(TiC2,Cp4)
23.8(4)
50.9(3)
a
b
Cf. Table 2. Planes are defined as follows: TiC2, Ti, C(3), and
C(4); Cp1, C(151)-C(155); Cp2, C(161)-C(165); Cp3, C(11)-C(15);
Cp4, C(31)-C(35).
η1-bonded alkynyl ligand, as may be demonstrated by
the bond lengths and angles within the Ti-C(3)-C(4)-
C(31) fragment.
On exposure to direct sunlight, samples A1-A6 (as
C6D6 solutions in NMR tubes) change from orange-
yellow to dark green or dark blue. Following the
transformation by NMR indicated that the compounds
were quantitatively converted into sole products (Scheme
1), all of them displaying similar features in their NMR
spectra (Table 1). Large downfield shifts of the triple-
bond carbon atoms into the region δC 190-250 are
typical for triple-bonded carbons η2-coordinated to a
titanocene moiety.10b,c,17 Furthermore, the presence of
an uncoordinated (E)-CHdCH moiety was confirmed by
(17) (a) Varga, V.; Mach, K.; Pola´sˇek, M.; Sedmera, P.; Hiller, J .;
Thewalt, U.; Troyanov, S. I. J . Organomet. Chem. 1996, 506, 241. (b)
Rosenthal, U.; Go¨rls, H.; Burlakov, V. V.; Shur, V. B.; Vol’pin, M. E.
J . Organomet. Chem. 1992, 426, C53. (c) Sˇteˇpnicˇka, P.; Gyepes, R.;
C´ısarˇova´, I.; Varga, V.; Pola´sˇek, M.; Hora´cˇek, M.; Mach, K. Organo-
metallics 1999, 18, 627.
3
the δC, δH and J HH values, indicating that the photo-
induced reductive coupling of the hydrocarbyl ligands
proceeds with no isomerization at the double bond. In
UV-near-IR spectra, the long-wavelength electronic

Head-to-Tail Dimerization of Terminal Alkynes
Organometallics, Vol. 18, No. 23, 1999 4873
Ta ble 4. Selected Bon d Len gth s (Å) a n d Bon d
An gles a n d Dih ed r a l An gles (d eg) for B1a ,b
Sch em e 2. Syn th esis of th e D Typ e Com p lexes
Ti-C(1)
2.068(5)
2.084(4)
1.304(6)
1.458(6)
1.314(7)
1.516(6)
1.526(6)
C(3)-C(4)
1.529(7)
1.538(7)
1.516(6)
1.525(6)
1.518(6)
1.523(6)
Ti-C(2)
C(3)-C(6)
C(1)-C(2)
C(1)-C(11)
C(11)-C(12)
C(2)-C(3)
C(3)-C(5)
C(12)-C(13)
C(13)-C(14)
C(13)-C(15)
C(13)-C(16)
C(1)-Ti-C(2)
Ti-C(1)-C(11)
Ti-C(2)-C(3)
36.6(2) C(4)-C(3)-C(5)
150.6(4) C(4)-C(3)-C(6)
151.4(3) C(5)-C(3)-C(6)
108.6(4)
107.5(4)
108.7(5)
C(2)-C(1)-C(11)
C(1)-C(2)-C(3)
C(1)-C(11)-C(12)
137.0(5) C(12)-C(13)-C(14) 108.1(4)
136.6(4) C(12)-C(13)-C(15) 112.6(4)
125.4(5) C(12)-C(13)-C(16) 109.0(4)
C(11)-C(12)-C(13) 129.3(5) C(14)-C(13)-C(15) 109.9(4)
Ta ble 5. Selected Bon d Len gth s (Å) a n d Bon d
An gles a n d Dih ed r a l An gles (d eg) for D2a ,b
C(2)-C(3)-C(4)
C(2)-C(3)-C(5)
C(2)-C(3)-C(6)
108.9(4) C(14)-C(13)-C(16) 107.4(4)
111.3(4) C(15)-C(13)-C(16) 109.6(4)
111.6(4)
Ti-C(1)
2.163(2)
2.102(2)
1.300(3)
1.467(3)
1.317(4)
1.855(2)
1.873(3)
Si(1)-C(6)
Si(1)-C(7)
C(3)-Si(2)
Si(2)-C(8)
Si(2)-C(9)
Si(2)-C(10)
1.885(3)
1.870(3)
1.887(2)
1.849(3)
1.858(4)
1.864(3)
Ti-C(2)
C(11)-C(1)-C(2)-C(3)
C(1)-C(11)-C(12)-C(13)
-6(1)
-176.0(5)
C(1)-C(2)
C(2)-C(3)
C(3)-C(4)
C(1)-Si(1)
Si(1)-C(5)
(TiC2,Cp1)
24.6(4)
(TiC2,Cp2)
21.0(4)
a
b
Cf. Table 2. Planes are defined as follows: TiC2: Ti, C(1) and
C(2); Cp1: C(20)-C(24); Cp2: C(30)-C(34).
C(2)-Ti-C(1)
35.44(8)
C(1)-Si(1)-C(7)
C(5)-Si(1)-C(6)
C(5)-Si(1)-C(7)
C(6)-Si(1)-C(7)
C(3)-Si(2)-C(8)
C(3)-Si(2)-C(9)
C(3)-Si(2)-C(10)
C(8)-Si(2)-C(9)
C(8)-Si(2)-C(10)
C(9)-Si(2)-C(10)
111.0(1)
105.4(2)
105.4(2)
107.3(2)
111.0(1)
107.8(1)
110.3(2)
112.5(2)
107.4(2)
107.8(2)
Ti-C(1)-Si(1)
Ti-C(2)-C(3)
141.6(1)
140.2(2)
148.6(2)
145.0(2)
119.0(2)
123.0(2)
118.0(2)
114.7(2)
112.6(1)
subtended by the least-squares planes of the cyclopen-
tadienyl rings (44.9°) in B1 is about the average of those
in 1 (50.0°) and 2 (41.1°),18 apparently because only one
of the CH groups on the η5-C5Me4H ligands is placed at
the hinge position. The CH group of the other η5-C5-
Me4H ligand is directed toward the t-Bu group of the
cordinated alkyne (see Figure 3). In the structure of 1,
two bulky SiMe3 groups at the coordinated triple bond
constrain both CH groups to reside at the hinge position.
A significantly shorter C(2)-C(3) distance in B1 (1.516-
(6) Å) compared to the tC-Si distance in 1 (1.853(3)
Å;17a cf. the C(1)-Si(1) distance 1.855(2) Å in D2 below
or 1.859(3) Å (average) in 210b) boosts steric demands
of the coordinated alkyne and, hence, results in an
opening of the titanocene framework and also increases
strain of the substituents on its cyclopentadienyls.
As the B type complexes cannot obviously participate
in the catalytic cycle yielding HTT dimers, we set out
to prove the stability of the titanocene-HTT dimer
complexes which have to occur as intermediates in the
catalytic cycle. The reduction of the appropriate ti-
tanocene dichlorides by magnesium in THF in the
presence of Me3SiCtCC(SiMe3)dCH2 afforded com-
pounds D1-D3 in nearly quantitative yields (Scheme
2). Their NMR spectra indicated η2 coordination of the
triple bond with the double bond kept intact (Table 1).
The fact that the compounds display an absorption band
at 925 nm, i.e., in the same region as the titanocene-
BTMSE complexes 1-4, may indicate that the conjuga-
tion of unsaturated bonds in HTT dimer is interrupted.
Cr ysta l Str u ctu r e of D2. The parameters of the
molecular structure of D2 determined by single-crystal
X-ray diffraction (Tables 2 and 5) confirmed that the
HTT dimer is bonded to the titanocene framework as a
simple η2-alkyne (Figure 4). The C-C bond length of
the coordinated alkyne corresponds nicely to the values
reported for [(η5-C5Me5)2Ti(η2-R1CtCR2)] complexes (R1/
R2: (SiMe3)2, 1.309(4) Å; Ph/SiMe3, 1.308(3)Å;9b Fc/Ph,
1.312(5) Å17c) and the (η5-C5Me4H)2Ti complexes B1 and
Si(1)-C(1)-C(2)
C(1)-C(2)-C(3)
C(2)-C(3)-C(4)
C(2)-C(3)-Si(2)
C(4)-C(3)-Si(2)
C(1)-Si(1)-C(5)
C(1)-Si(1)-C(6)
Si(1)-C(1)-C(2)-C(3)
C(1)-C(2)-C(3)-Si(2)
C(1)-C(2)-C(3)-C(4)
-1.2(6)
-8.8(4)
173.8(3)
(TiC2,Cp1)
19.7(2)
(TiC2,Cp2)
20.6(2)
a
b
Cf. Table 2. Planes are defined as follows: TiC2, Ti, C(1) and
C(2); Cp1, C(11)-C(15); Cp2, C(21)-C(25).
F igu r e 4. Molecular structure of D2 (30% probability
level, PLATON plot). Hydrogen atoms, except those of the
terminal methylene group, are omitted for clarity.
1 mentioned above. The dihedral angle of the cyclopen-
tadienyl planes in D2 (40.2°) is similar to that of [(η5-
C5Me5)2Ti(η2-PhCtCSiMe3)] (40.6°), and very slightly
lower than that in 2 (41.1°).9b The arrangement of the
SiC(dC)CtCSi moiety deviates only marginally from
an overall planarity, as indicated by torsion angles. The
CdCH2 moiety is directed out of the titanocene frame-
work, and bond lengths and angles within it appear
conventional when compared to the values for “organic”
C2CdCH2 units (CdC ) 1.32(1) Å, arithmetic mean of
77 entries).16 In keeping with the interruption of
(18) Varga, V.; Hiller, J .; Gyepes, R.; Pola´sˇek, M.; Sedmera, P.;
Thewalt, U.; Mach, K. J . Organomet. Chem. 1997, 538, 63.

4874 Organometallics, Vol. 18, No. 23, 1999
Sˇ teˇpnicˇka et al.
Sch em e 3. Ch em istr y Un d er lyin g th e HTT Dim er iza tion of Ter m in a l Alk yn es Ca ta lyzed by
Tita n ocen e-BTMSE Com p lexes (Cp ′′ ) η5-C5Me4H, η5-C5Me5)
conjugation deduced from UV-near-IR spectra, the
C(2)-C(3) distance (1.467(3) Å) is slightly longer than
the mean CdC-CtC bond length observed in nonco-
ordinated enynes (1.43(1) Å; 11 entries).16
and 2 react in the dark with an excess of terminal
alkynes to give A type complexes (Scheme 3, left),
whereas upon exposure to sunlight, the complexes 1 and
2 induce a rapid HTT dimerization of TBUE and TMSE,
respectively. Although the experiments with these
highly air- and moisture-sensitive materials performed
in all-sealed optical cells did not enable us to follow the
kinetics of the dimerization rigorously under constant
concentration of the alkynes, it is obvious that reaction
rates as high as 5 × 102 turnovers h-1 were achieved,
much higher than dimerization rates observed for 2 in
diffuse daylight.6 The assumption that this photoin-
duced catalysis is closely connected with the photoin-
duced reductive coupling of the carbyl ligands in A type
complexes, affording complexes with HTH dimers η2-
coordinated through their triple bond (type B), was
proved by the observation that complexes B1 and B2
effectively dimerize TBUE and TMSE, respectively, in
the dark.
Different results were obtained using the HTT dimer
(TBUE)2 as the alkyne, since a similar reduction of a
t-BuCCtC(t-Bu)dCH2/[(η5-C5Me5)2TiCl2] mixture af-
forded a purple solution which contained the paramag-
netic complex [(η1:η5-C5Me4CH2)(η5-C5Me5)Ti],19 instead
of the desired compound [(η5-C5Me5)2Ti{η2-t-BuCCtC(t-
Bu)dCH2}]. This may well reflect the fact that deca-
methyltitanocene-based catalysts do not dimerize TBUE
as the only terminal alkyne. Under similar conditions,
the less sterically crowded20 complex [(η5-C5Me4H)2Ti-
{η2-(t-Bu)CCtC(t-Bu)dCH2}] was formed according to
NMR spectra; however, it was accompanied by another
product whose nature remains yet unclear.
Rea ctivity of Com p lexes 1 a n d 2, a n d Com -
p ou n d s of th e A, B, a n d D Typ es Der ived Th er eof,
tow a r d TBUE a n d TMSE. It has been shown previ-
ously that (η5-C5Me5)2Ti-based complexes catalyze the
HTT dimerization of all nonpolar 1-alkynes except
TBUE,1a,5,6 whereas (η5-C5Me4H)2Ti-derived complexes
accomplish this catalysis for TBUE only.7 The present
results demonstrate in addition that both complexes 1
Furthermore, titanocene complexes with the HTT
dimer (TMSE)2 were prepared (type D), and its deca-
methyltitanocene representative D2 showed a high
catalytic activity toward the HTT dimerization of TMSE
in the dark. The high reactivity of D2 was also demon-
strated by its facile conversion into A2 by addition of
TBUE (note that TBUE does not dimerize on (η5-C5-
Me5)2Ti catalysts). On the other hand, the reluctance
of the HTT dimer (TBUE)2 to form a D type complex
with decamethyltitanocene accounts very likely for the
inactivity of decamethyltitanocene complexes in the
HTT dimerization of TBUE. Complexes B1 and D2 also
(19) (a) Fischer, J . M.; Piers, W. E.; Young, V. G., J r. Organometallics
1996, 15, 2410. (b) Bercaw, J . E.; Brintzinger, H. H. J . Am. Chem.
Soc. 1971, 93, 2048. (c) Bercaw, J . E. J . Am. Chem. Soc. 1974, 96, 5087.
(d) Luinstra, G. A.; Teuben, J . H. J . Am. Chem. Soc. 1992, 114, 3361.
(20) Dihedral angles between the least-squares planes of the cyclo-
pentadienyl rings in the [(η5-C5Me4H)2TiLn] complexes (Ln ) Cl, Cl2,
and BTMSA) are ca. 9° larger than those in their [(η5-C5Me5)2TiLn]
analogues.18

Head-to-Tail Dimerization of Terminal Alkynes
Organometallics, Vol. 18, No. 23, 1999 4875
underwent a smooth ligand exchange with BTMSE to
give 1 and 2, respectively, and noncoordinated (TMSE)2.
to rearrange into the complexes with coupled carbyl
ligands. Taking into account that the substituent in the
alkenic part of the C type complexes is separated from
the titanocene framework by only a C1 spacer whereas
A type complexes possess a C2 spacer that reduces the
steric strain, the different reactivities are in full ac-
cordance with the general observation that bulky sub-
stituents facilitate reductive elimination. The unfavor-
able reductive coupling A f B becomes possible on
irradiation, since photoexcitation lowers electron density
at the titanium atom through its transfer into diffuse
orbitals with higher principal quantum number or
ligand-based orbitals (MLCT) and, in this way, enhances
susceptibility of the titanocene complex to undergo
reductive elimination.25 Similar reductive couplings of
vinyl groups to 1,3-butadiene22 and two alkynyl groups
to butadiynes are known for permethyltitanocene and
permethylzirconocene complexes.26
A facile exchange of the coordinated alkyne dimers
for BTMSE in both B and D type complexes may
represent one of the deactivation pathways,27 which
converts ultimately in the absence of light all titanium
complexes into the A type complexes. However, in light,
the catalytic cycle is easily resumed via triggering by a
B type complex. Although the leaving BTMSE or HTH
dimer may play some role in the control of the reaction
pathway, it can hardly account for the high selectivity
of the HTT dimer formation. The photoinitiated mech-
anism should produce at least one molecule of HTH
dimer per one molecule of the BTMSE complex and
another molecule for each photoreinitiation step. With
total turnover numbers of about 1 × 103,6,7 the presence
of less than 1% of HTH in HTT dimers falls below the
precision of GC-MS and NMR analysis.
Im p lica tion s for th e Ca ta lysis of Dim er iza tion
a n d Rela ted Rea ction s. Regarding the above results,
the catalytic cycle suggested previously6 is essentially
valid; however, it requires initiation by light. The A type
complexes formed in the dark by a formal displacement
of the coordinated BTMSE with two molecules of a
terminal alkyne have to be first photoconverted to B
type complexes (Scheme 3, left) which then trigger the
catalytic cycle (Scheme 3, right). Complexes B undergo
easily a displacement of the η2-coordinated HTH dimer
with terminal alkynes, thus affording the plausible
intermediates [(Cp′′)2Ti(η2-RCtCH)] and [(Cp′′)2Ti(H)-
(η1-CtCR)] (Cp′′ ) η5-C5Me4H, η5-C5Me5) (steps S1 and
S2). The involvement of titanocene-acetylide-hydride
in the mechanism is corroborated by the reaction of 2
with MeOH, yielding the hydride [(η5-C5Me5)2Ti(H)-
(OMe)], though it did not exert any reaction with
1-hexyne,9 very likely due to the formation of a strong
Ti-O bond. Although the following step, i.e., regiose-
lective insertion of the second molecule of 1-alkyne into
the Ti-H bond (step S3, tail-on insertion) providing C
type complexes, lacks direct experimental evidence, it
leads, after reductive coupling of the carbyl ligands (step
S4), to the characterized but rather reactive D type
complexes. Then, the cycle is reinitiated by an exchange
of the coordinated HTT dimer for the terminal alkyne
(step S1)sbut started anew, it proceeds with no par-
ticipation of A and B type complexes (Scheme 3, right).
A conversion of the titanocene-acetylide-hydride
intermediate into the titanocene-vinylidene species
proposed by Beckhaus et al.9 can be inserted in the
reaction mechanism as an alternative to step S2, since
such rearrangements are well-documented for late-
transition-metal21 and even decamethyltitanocene com-
plexes.22 It has been shown that the vinylidene complex
[(η5-C5Me5)2TidCdCH2] reacts with 1-alkynes to afford
η1-vinyl η1-alkynyl compounds.23 Nonetheless, the vi-
nylidene intermediate cannot furnish C type complexes,
which are the apparent precursors of the D type
compounds. The D type complexes undoubtedly belong
in the catalytic cycle, since they efficiently initiate the
HTT dimerization in the dark.
Although the reactions connected to the photoassisted
catalytic HTT dimerization of terminal alkynes seem
to be reliably clarified, we anticipate that our present
knowledge does not allow us to prove unequivocally the
role of the plausible C type intermediates. Further
studies on the stability of the C type complexes and the
rate of their conversion into the corresponding D type
complexes as well as the stability of D type complexes
with (TBUE)2 are in progress.
Exp er im en ta l Section
The formation of the A type complexes proceeds
analogously, differing only in an opposite insertion
(head-on) of the 1-alkyne into the Ti-H bond. The origin
of such a reaction dichotomy remains unknown.24 In a
comparison of the reactivity of A and C type complexes,
the former are less reactive, requiring a photoexcitation
Gen er a l Con sid er a tion s. All manipulations with titanium
complexes and the dimerization experiments were carried out
on a high-vacuum-argon line operated by means of non-
greased glass-to-metal sealed valves (Hoke) in all-sealed glass
devices equipped with breakable seals, sealed quartz cuvettes,
and ESR sample tubes. Glass-to-glass sealed NMR sample
tubes were filled with C6D6 solutions using evacuated all-glass
devices and were sealed off by flame. The adjustment of single
crystals into Lindemann glass capillaries for X-ray analyses
and the preparations of KBr pellets for IR measurements were
made in a glovebox under purified nitrogen (mBraun, O2 and
(21) Bruce, M. I. Chem. Rev. 1991, 91, 197.
(22) Beckhaus, R. In Metallocenes; Togni, A., Halterman, R. L., Eds.;
Wiley-VCH: Weinheim, Germany, 1998; Vol. 1, Chapter 4.4, pp 175-
210.
(23) Beckhaus, R.; Sang, J .; Wagner, T.; Ganter, B. Organometallics
1996, 15, 1176.
(24) Similarly to other hydrometalations with neutral hydrides, the
insertion step is a cis addition (at least step S3) but, surprisingly, it
lacks the regioselectivity encountered in other hydrometalations; the
following references may serve as leading examples. (a) Addition of
[(η5-C5H5)Zr(H)Cl] and other transition-metal-H bonds: Labinger, J .
A. In Comprehensive Organic Synthesis; Trost, B. M., Ed.; Pergamon
Press: Oxford, U.K., 1991; Vol. 8, pp 667-702. (b) R2AlH: Eisch, J . J .
In Comprehensive Organic Synthesis; Trost, B. M., Ed.; Pergamon
Press: Oxford, U.K., 1991; Vol. 8, pp 733-753. (c) [RuH(Cl)(CO)-
(PPh3)2]: Hill, A. F. In Comprehensive Organometallic Chemistry II;
Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon Press:
Oxford, U.K., 1995; Vol. 7, pp 399-406.
(25) See, for instance: (a) Collman, J . P.; Hegedus, L. S. Principles
and Applications of Organotransition Metal Chemistry; University
Science Books: Mill Valley, CA, 1980; pp 232-251. (b) Crabtree, R.
H. The Organometallic Chemistry of the Transition Metals, 2nd ed.;
Wiley: New York, 1994; pp 151-158.
(26) Pellny, P.-M.; Kirchbauer, F. G.; Burlakov, V. V.; Baumann,
W.; Spannenberg, A.; Rosenthal, U. J . Am. Chem. Soc. 1999, 121, 8313.
(27) One of the reviewers suggested that the deactivation may
proceed as a side reaction of the alkynyl-hydrido intermediate with
the alkyne: [(η5-C5Me5)2Ti(H)(CtCR)] + RCtCH f [(η5-C5Me5)2Ti-
(η1-CtCR)2] + H2.26

4876 Organometallics, Vol. 18, No. 23, 1999
Sˇ teˇpnicˇka et al.
H2O concentrations lower than 2.0 ppm). 1H (399.95 MHz) and
13C (100.58 MHz) NMR spectra were measured on a Varian
UNITY Inova 400 spectrometer in C6D6 solutions at 298(1) K.
Chemical shifts (δ/ppm) are referenced to the solvent signal
(δH 7.15, δC 128.0). 29Si (79.46 MHz) NMR spectra were
recorded by the standard DEPT technique; 29Si chemical shifts
are given relative to external tetramethylsilane (δSi 0) and
assigned by comparison with δSi values of related compounds.28
Mass spectra were measured on a VG 7070E spectrometer at
75 eV using a direct inlet probe (samples in sealed capillaries
were opened and inserted into the probe under argon). UV-
near-IR spectra were measured in the range of 270-2000 nm
on a Varian Cary 17D spectrometer using all-sealed quartz
cuvettes (Hellma). Infrared spectra in KBr pellets or as hexane
solutions were obtained on a Specord IR-75 (Carl Zeiss, J ena,
Germany) spectrometer. GC analyses were performed on a
CHROM 5 gas chromatograph (Laboratory Instruments, Pra-
gue, Czech Republic) equipped with 10% SE-30 on a Chroma-
ton N-AW-DMCS column. GC-MS analyses were carried out
on a Hewlett-Packard gas chromatograph (5890 series II;
capillary column SPB-1 (Supelco)) interfaced to a mass spec-
trometric detector (5791 A). Melting points were determined
for samples in N2-filled sealed capillaries on a Kofler apparatus
and are uncorrected.
(s), 1503 (m), 1436 (m,b), 1371 (m), 1245 (vs), 1239 (vs), 1071
(m), 847 (vs,b), 827 (sh), 755 (vs), 698 (vs), 653 (m), 444 (m).
UV-near-IR (hexane, nm): 915.
[(η5-C5Me4Bz)2Ti(η2-BTMSE)] (4). 1H NMR (C6D6): δ 0.03
(s, 9 H, SiMe3), 1.61, 1.76 (2 × s, 6 H, C5Me4Bz); 3.69 (s, 2 H,
PhCH2), 7.11-7.53 (m, 5 H, Ph). 13C{1H} NMR (C6D6): δ 4.5
(SiMe3), 12.4, 13.1 (C5Me4Bz); 34.2 (PhCH2), 121.8, 122.9 (C5-
Me4Bz, CMe); 126.1 (Ph, Cipso), 126.2 (Ph, CHp), 128.6, 128.9
(Ph, CHo,m); 142.2 (C5Me4Bz, CCH2), 249.1 (η2-CtC). EI MS
(direct inlet, 120 °C): M•+ not observed; the ion of titanocene
[(C5Me4Bz)2Ti]•+ (m/z 470) during the course of measurement
is replaced by the signal of the allyl diene compound [(C5Me4-
Bz)2Ti - 2H]+ (m/z 468); ions due to BTMSE (m/z 155, 97, 73)
and bis(trimethylsilylethene) (m/z 157) are also observed,
varying in intensity. IR (KBr, cm-1): 1595. UV-near-IR
(hexane, nm): 920.
R ea ct ion of t h e Com p lexes [(η5-C5Me4R )2Ti(η2-BT-
MSE)] (R ) H, Me, P h , Bz) w ith TBUE, TMSE, a n d F CE.
Only a representative synthesis of A1 is given in detail, since
the other experiments with TBUE and TMSE were performed
similarly. The procedures differ only in the reaction time
necessary to convert all of the BTMSE complex.
[(η5-C5Me4H )2Ti{η1-(E)-CH dCH CMe3}(η1-CtCCMe3)]
(A1). Purified TBUE (1.0 mL, 8 mmol) was condensed on a
vacuum line into the solution of 1 (0.46 g, 1.0 mmol) in hexane
(20 mL). The resulting yellow solution was heated in the dark
to 60 °C in a sealed ampule equipped with an all-sealed quartz
cell (d ) 1.0 mm), while conversion was monitored by following
the intensity decrease of the absorption bands at 920 and 1530
nm, which are due to complex 1 and TBUE (2 × ν(tCH)),
respectively. The absorption band of the starting titanocene
complex disappeared after about 6 h at 60 °C in the dark, and
approximately 2 mmol of TBUE was consumed within this
period. No further consumption of TBUE was observed there-
after. All volatiles were distilled under vacuum into a trap
cooled by liquid nitrogen overnight, and the remaining yellow
solid was dissolved in a minimum amount of hexane (2 mL).
After it was cooled overnight to -18 °C, this solution afforded
large yellow crystals. The mother liquor was separated, and
the crystallization was repeated. Despite the fact that the
conversion was apparently quantitative, the yield of yellow
crystals of A1 was only 0.34 g (75%) due to their high solubility
in hexane. In all the experiments, the volatiles were controlled
for the presence of the liberated BTMSE and the content of
HTT dimer. The molar ratio HTT dimer/BTMSE varied from
0.2 to 2.0 when the reaction was carried out in the dark. Data
Hexane, toluene, and tetrahydrofuran (THF) were dried by
refluxing over LiAlH4 under an argon atmosphere, degassed,
and stored as solutions of green dimeric titanocene [(µ-η5:η5-
C
10H8){(η5-C5H5)Ti(µ-H)}2]29 on a vacuum line. Likewise, C6D6
was degassed and stored as a solution of green dimeric
titanocene on a vacuum line. tert-Butylethyne (TBUE) and
(trimethylsilyl)ethyne (TMSE) (Aldrich) were degassed and
distilled onto dimeric titanocene under vacuum. After the
solutions had turned green-brown (ca. 3 h), the alkynes were
distilled under vacuum into storage vessels. Similarly, TBUE
was further treated with solid [{(η5-C5Me5)2Ti(µ-H)2}2Mg]
complex30 to remove traces of tert-butyl alcohol. Ferrocenyl-
ethyne31 was carefully degassed under vacuum and dissolved
in toluene. The complexes [(η5-C5Me4R)2TiCl2] (R ) H, Me,32
Ph,33 Bz34) were prepared by the literature procedures.
All [(η5-C5Me4R)2Ti(η2-BTMSE)] complexes were prepared
by the reduction of the corresponding titanocene dichlorides
[(η2-C5Me4R)2TiCl2] in THF using an excess of Mg and
BTMSE.10b,c,17a The compounds [(η5-C5Me4R)2Ti(η2-BTMSE)],
where R ) H (1) and Me (2), were identical with those
previously described.17a
1
[(η5-C5Me4P h )2Ti(η2-BTMSE)] (3). Mp: 157 °C. H NMR
1
(C6D6): δ -0.06 (s, 9 H, Me3Si), 1.83, 1.98 (2 × s, 6 H, C5Me4-
Ph), 6.25-6.32 (apparent bd, 2 H, Ph), 6.91-7.40 (m, 3 H, Ph).
13C{1H} NMR (C6D6): δ 3.8 (Me3Si), 13.4, 14.7 (2 × C5Me4Ph),
123.1, 125.2 (C5Me4Ph, CMe), 126.0, 129.2 (Ph, CH), 126.6,
137.8 (Ph, Cipso Ph, and C5Me4Ph, CPh), 251.0 (η2-CtC). One
of the CH(Ph) signals is overlapped by the solvent resonance.
29Si NMR (C6D6): δ -15.8 (Me3Si). EI MS (direct inlet, 120
°C): M•+ not observed; ions due to BTMSE (m/z 155, 97, 73,
70, 45) and titanocene (m/z 442 [(C5Me4Ph)2Ti]•+ and m/z 221
[(C5Me4Ph)2Ti]2+) indicate that the complex dissociates on
heating in the probe or during electron impact. IR (KBr, cm-1):
3043 (m,b), 2948 (s,b), 2889 (s,b), 2850 (sh), 1597 (s), 1557
for A1 are as follows. H NMR (C6D6): δ 1.09, 1.24 (2 × s, 9
H, Me3C); 1.60, 1.77, 1.96, 2.22 (4 × s, 6 H, C5Me4H); 4.74 (s,
3
2 H, C5Me4H), 4.90 (d, 1 H, J HH ) 17.0 Hz, TiCHdCH), 5.19
3
(d, 1 H, J HH ) 17.0 Hz, TiCHdCH). 13C{1H} NMR (C6D6): δ
13.2, 14.1 (2 C), 15.0 (C5Me4H), 28.1 (Me3C), 30.4, 31.8 (Me3C),
35.3 (Me3C), 108.8 (C5Me4H, CH), 119.8, 120.1 (C5Me4H, CMe),
122.7 (TiCtC), 126.3, 126.8 (C5Me4H, CMe), 143.8 (TiCHd
CH), 147.4 (TiCtC), 190.8 (TiCHdCH). EI-MS (direct inlet,
70 eV, 90 °C): m/z (relative abundance) 454 (M•+; 1), 372 ([M
- TBUE]+; 14), 292 (10), 291 (26), 290 ([M - 2 TBUE]+; 100),
289 (25), 288 (17), 168 (7), 167 (12), 166 (9), 164 (15), 149 (9),
121 (8), 107 (10), 105 (8), 91 (10), 77 (7), 57 (7), 41 (15). IR
(KBr, cm-1): 2940 (vs), 2900 (vs,b), 2847 (vs), 2076 (s), 1500
(m), 1477 (s), 1466 (s), 1451 (vs), 1433 (s), 1377 (s), 1365 (s),
1356 (s), 1245 (vs), 1200 (s), 1148 (m), 1113 (m), 1032 (sh),
1022 (s), 1002 (s), 980 (m), 894 (m), 832 (vs), 821 (vs), 797 (m),
731 (s), 697 (m), 606 (m), 506 (m), 468 (s), 458 (vs), 420 (m).
UV-near-IR (hexane, nm): 410 > 465 (sh). Anal. Calcd for
(28) δSi: BTMSE -19.2, [(η5-MenC5H5-n)2Ti(η2-BTMSE)]; -15.7 for
n ) 5, -17.2 for n ) 4 under the same conditions.
(29) Antropiusova´, H.; Dosedlova´, A.; Hanusˇ, V.; Mach, K. Transition
Met. Chem. 1981, 6, 90.
(30) Troyanov, S. I.; Varga, V.; Mach, K. J . Chem. Soc., Chem.
Commun. 1993, 1174.
(31) (a) Rosenblum, M.; Brawn, N.; Papenmeier, J .; Applebaum, M.
J . Organomet. Chem. 1966, 6, 173. (b) Rosenblum, M.; Brawn, N. M.;
Ciappenelli, D.; Tancrede, J . J . Organomet. Chem. 1970, 24, 469.
(32) Mach, K.; Antropiusova´, H.; Varga, V.; Pola´cˇek, J . J . Organomet.
Chem. 1987, 333, 205.
(33) Hora´cˇek, M.; Pola´cˇek, M.; Kupfer, V.; Thewalt, U.; Mach, K.
Collect. Czech. Chem. Commun. 1999, 64, 61.
C
30H46Ti: C, 79.27; H, 10.20. Found: C, 79.30; H, 10.22.
[(η5-C5Me5)2Ti{η1-(E)-CHdCHCMe3}(η1-CtCCMe3)] (A2).
As indicated by the decay of the absorption band of 2 at 916
nm, the reaction was completed after 10 h at 60 °C. Ap-
proximately 2 mmol of TBUE was consumed, and no further
consumption was observed after that time. Volatiles were
evaporated under vacuum, leaving a yellow residue, which was
(34) Langmaier, J .; Samec, Z.; Varga, V.; Hora´cˇek, M.; Mach, K. J .
Organomet. Chem. 1999, 579, 348.

Head-to-Tail Dimerization of Terminal Alkynes
Organometallics, Vol. 18, No. 23, 1999 4877
dissolved in the minimum amount of hexane and cooled to give
A2 as an yellow waxy solid, yield 0.42 g (87%). Volatiles
contained HTT dimer and BTMSE in the molar ratio ca. 2:1.
1H NMR (C6D6): δ 1.11, 1.28 (2 × s, 9 H, Me3C), 1.82 (s, 30 H,
C5Me5), 4.77 (d, 1 H, 3J HH ) 16.6 Hz, TiCHdCH), 5.03 (d, 1 H,
3J HH ) 16.6 Hz, TiCHdCH). 13C{1H} NMR (C6D6): δ 12.9
(C5Me5), 28.2 (Me3C), 30.4, 31.9 (Me3C), 35.4 (Me3C), 121.1 (C5-
Me5), 124.2 (TiCtC), 142.5 (TiCHdCH), 149.4 (TiCtC), 193.2
(TiCHdCH). UV-near-IR (hexane, nm): 405 (sh) > 480 (sh).
[(η5-C5Me4P h )2Ti{η1-(E)-CH dCH CMe3}(η1-CtCCMe3)]
(A3). The absorption band of 3 at 915 nm disappeared after 4
h at 60 °C. The consumption of TBUE was approximately 2
equiv. A3 was formed as an orange waxy solid, yield 0.61 g
TiCHdCH). 13C{1H} NMR (C6D6): δ 13.1, 14.0, 14.1, 14.9
(C5Me4H), 65.7, 67.7 (C5H4Fe, CH), ca. 67.7 (C5H4Fe, Cipso
;
overlapped by CH of C5H4Fe), 68.8 (C5H4Fe, CH), 69.1, 69.9
(C5H5Fe, CH), 71.7 (C5H4Fe, CH), 90.7 (C5H4Fe, Cipso), 109.1
(C5Me4H, CH), 120.4, 120.4, 127.0, 127.2 (C5Me4H, CMe), 115.7
(TiCtC), 128.6 (TiCHdCH), 160.3 (TiCtC), 200.8 (TiCHdCH).
IR (KBr): 2893 (m), 2053 (m), 1434 (m), 1365 (m), 1221 (m),
1104 (m), 1032 (sh), 1018 (s), 997 (s), 984 (m), 915 (s), 851 (m),
835 (m), 810 (vs), 800 (sh), 652 (m), 631 (m), 580 (m), 531 (m),
483 (vs). UV-near-IR (hexane, nm): 450. Anal. Calcd for
C
42H46Fe2Ti: C, 71.01; H, 6.53. Found: C, 70.96; H, 6.52.
P h otoa ssisted Syn th esis of B Typ e Com p lexes. NMR
sample tubes (5 mm diameter) containing solutions of com-
pounds A1-A6 in C6D6 were exposed to sunlight for various
periods (from a few hours to several days), whereupon the
yellow color of compounds A1-A5 disappeared and the solu-
tions turned blue or green. The progress in conversion of the
A type compounds into the titanocene complexes of head-to-
1
(ca. 100%). H NMR (C6D6): δ 1.10, 1.30 (2 × s, 9 H, Me3C),
3
1.70, 1.91, 2.00, 2.03 (4 × s, 6 H, C5Me4Ph), 5.17 (d, 1 H, J HH
3
) 16.2 Hz, TiCHdCH), 5.25 (d, 1 H, J HH ) 16.2 Hz, TiCHd
CH), 6.98-7.17 (m, 10 H, Ph). 13C{1H} NMR (C6D6): δ 13.3,
14.5 (C5Me4Ph), 28.3 (Me3C), 30.3, 31.7 (Me3C), 35.6 (Me3C),
121.8 (TiCtC), 124.3, 125.1 (C5Me4Ph5, CMe), 125.7 (C5Me4-
Ph, CPh or Ph, Cipso), 126.2, 130.4 (C5Me4Ph, CH of Ph); 136.1
(C5Me4Ph, CPh or Ph, Cipso), 144.2 (TiCHdCH), 151.9 (TiCt
C), 193.9 (TiCHdCH). One of the CH(Ph) signals is overlapped
by the solvent multiplet. UV-near-IR (hexane, nm): 400 (sh)
> 470 (sh).
1
head dimers was followed by H and 13C NMR spectra, which
showed that the conversion proceeds very cleanly, affording
quantitatively one product. However, the reaction seems to
be autocatalytic, since the reaction times varied widely. This
discouraged us from studying the optimum wavelength region
and quantum yields of the photolysis. In the absence of light,
the samples of A type complexes are stable for at least 1 year
at room temperature. For preparative purposes compounds
A1-A6 were obtained from 1 mmol quantities of 1-4 as given
above and exposed to sunlight in the form of hexane solutions.
The photolysis was continued until the solutions reached the
color obtained in NMR tubes. The workup consisted of evapo-
ration of all volatiles and attempted crystallization from
concentrated hexane solution. Unfortunately, a crystalline
product was obtained for B1 only; the other complexes formed
noncrystallizing oils or waxy solids.
[(η5-C5Me4Bz)2Ti{η1-(E)-CH dCH CMe3}(η1-CtCCMe3)
(A4). The absorption band of 4 at 920 nm disppeared after 7
h at 60 °C, and the consumption of TBUE ceased at the same
time. A4 formed as a noncrystallizing dark yellow waxy
1
product, yield 0.64 g (ca. 100%). H NMR (C6D6): δ 1.12, 1.29
(2 × s, 9 H, Me3C), 1.78, 1.80, 1.86, 1.90 (4 × s, 6 H, C5Me4-
Bz), 3.87 (s, 4 H, PhCH2), 4.85 (d, 1 H, 3J HH ) 16.5 Hz, TiCHd
3
CH), 5.11 (d, 1 H, J HH ) 16.5 Hz, TiCHdCH), 7.03-7.23 (m,
10 H, Ph). 13C{1H} NMR (C6D6): δ 12.6, 12.6, 13.5, 13.5 (C5Me4-
Bz), 28.3 (Me3C), 30.4, 31.8 (Me3C), 34.6 (PhCH2), 35.5 (Me3C),
120.8, 121.2, 121.9, 122.3 (C5Me4Bz, CMe), 124.6 (TiCtC),
125.3 (Ph, Cipso), 126.0, 128.5, 128.7 (Ph, CH), 142.0 (C5Me4-
Bz, CCH2), 143.1 (TiCHdCH), 150.1 (TiCtC), 193.5 (TiCHd
CH). UV-near-IR (hexane, nm): 390 (sh) > 480 (sh).
[(η5-C5Me4H)2Ti{η2-(E)-Me3CCtC(CHdCHCMe3)}] (B1).
According to NMR measurements the conversion was practi-
cally quantitative; however, the yield of blue crystals of pure
B1 was only 80 mg (18% related to 1) due to the high solubility
of the complex in hexane. Mp: 96 °C. 1H NMR (C6D6): δ 0.94,
1.03 (2 × s, 9 H, Me3C), 1.36, 1.79, 1.97, 2.08 (4 × s, 6 H,
[(η5-C5Me4H )2Ti{η1-(E)-CH dCH SiMe3}(η1-CtCSiMe3)]
(A5). TMSE (1.1 mL, 8.0 mmol) was added to a solution of 1
(0.46 g, 1.0 mmol) in hexane (20 mL), and the solution was
heated to 60 °C. After 4 h the absorption band of 1 at 920 nm
disappeared and the absorption band of TMSE at 1540 nm
indicated the consumption of ca. 2 mmol of TMSE. A5 was
formed as an orange-yellow waxy solid, yield 0.45 g (93%). 1H
NMR (C6D6): δ 0.12, 0.19 (2 × s, 9 H, Me3Si), 1.56, 1.72, 1.90,
2.20 (4 × s, 6 H, C5Me4H), 4.71 (s, 2 H, C5Me4H), 5.73 (d, 1 H,
3
C5Me4H), 4.15 (d, 1 H, J HH ) 15.4 Hz, CHdCHCMe3), 5.85
(s, 2 H, C5Me4H), 6.17 (d, 1 H, 3J HH ) 15.4 Hz, CHdCHCMe3).
13C{1H} NMR (C6D6): δ 12.8, 13.0, 13.6, 14.3 (C5Me4H), 29.7,
32.6 (Me3C), 33.1, 42.1 (Me3C), 112.0 (C5Me4H, CH), 119.8 (C5-
Me4H, CMe), 122.5 (CHdCHCMe3), 122.6, 123.4, 124.9 (C5-
Me4H, CMe), 144.2 (CHdCHCMe3), 199.4 (Me3CCtC), 218.0
(Me3CCtC). EI-MS (direct inlet, 70 eV, 90 °C): m/z (relative
abundance) 454 (M•+; 5), 292 (10), 291 (27), 290 (100), 289 (22),
288 (16), 167 (9), 166 (7), 164 (12), 57 (6). IR (hexane, cm-1):
1640. UV-near-IR (hexane, nm): 315 > 390 (sh) > 550 ≈ 725.
Anal. Calcd for C30H46Ti: C, 79.27; H, 10.20. Found: C, 79.31;
H, 10.23.
3
3J HH ) 20.5 Hz, TiCHdCH), 6.22 (d, 1 H, J HH ) 20.5 Hz,
TiCHdCH). 13C{1H} NMR (C6D6): δ -0.4, 0.7 (Me3Si), 13.2,
14.1, 14.2, 15.0 (C5Me4H), 109.2 (C5Me4H, CH), 118.1 (TiCt
C), 120.6, 120.7, 126.5, 127.2 (C5Me4H, CMe), 137.3 (TiCHd
CH), 181.1 (TiCtC), 227.6 (TiCHdCH). UV-near-IR (hexane,
nm): 405 (sh) > 475(sh).
[(η5-C5Me5)2Ti{η2-(E)-Me3CCtCCHdCHCMe3}] (B2): blue
1
[(η5-(C5Me4H)2Ti{η1-(E)-CHdCHF c}(η1-CtCF c)] (A6). A
hexane solution (20 mL) of 1 (0.5 mmol in 3.5 mL) and a
toluene solution of FcCtCH (0.25 g in 6 mL of toluene) were
mixed in an ampule equipped with a quartz cell (d ) 0.2 cm)
and kept in the dark. After 2 days at room temperature, the
absorption band at 920 nm of the BTMSE complex disap-
peared. Addition of 10 mL of hexane resulted in precipitation
of a red voluminous precipitate. The yellow mother liquor was
separated and the precipitate washed twice with hexane and
dried under vacuum. The solid was dissolved in toluene and
crystallized by slow evaporation of the solvent to give dark
red crystals of A6 in rich aggregates; yield 0.30 g (83%). The
mother liquor contained BTMSE and a trace of HTT dimer
(FCE)2. Mp: 85 °C. 1H NMR (C6D6): δ 1.61, 1.73, 2.04, 2.31 (4
× s, 6 H, C5Me4H), 3.99, 4.34 (2 × apparent t, 2 H, AA′BB′ of
C5H4Fe), 4.00, 4.24 (2 × apparent t, 2 H, AA′BB′ of C5H4Fe),
4.19, 4.25 (2 × s, 5 H, C5H5Fe), 4.81 (s, 2 H, C5Me4H), 5.72 (d,
waxy solid, yield 0.41 g (85% related to 2). H NMR (C6D6): δ
0.97, 1.12 (2 × s, 9 H, Me3C), 1.85 (s, 30 H, C5Me5), 4.16 (d, 1
3
3
H, J HH ) 15.3 Hz, CHdCHCMe3), 6.24 (d, 1 H, J HH ) 15.4
Hz, CHdCHCMe3). 13C{1H} NMR (C6D6): δ 12.9 (C5Me5), 29.8
(Me3C), 33.1 (Me3C), 33.3 (Me3C), 42.5 (Me3C), 121.7 (C5Me5),
123.1 (CHdCHCMe3), 144.0 (CHdCHCMe3), 203.9 (Me3CCt
C), 218.6 (Me3CCtC). IR (hexane, cm-1): 1627. UV-near-IR
(hexane, nm): 540 ≈ 730.
[(η5-C5Me4P h )2Ti{η2-(E)-Me3CCtC(CHdCHCMe3)}] (B3):
turquoise waxy solid, yield 0.49 g (81% related to 3). 1H NMR
(C6D6): δ 0.95, 0.97 (2 × s, 9 H, Me3C), 1.90, 1.95, 1.97, 2.19
3
(4 × s, 6 H, C5Me4Ph), 4.58 (d, 1 H, J HH ) 15.5 Hz, CHd
CHCMe3), 6.09 (d, 1 H, 3J HH ) 15.5 Hz, CHdCHCMe3), 6.57-
6.65 (br d, 4 H, Ph), 6.94-7.13 (m, 6 H, Ph). 13C{1H} NMR
(C6D6): δ 13.0, 13.8, 14.1, 14.9 (C5Me4Ph), 29.8, 32.9 (Me3C),
33.2, 43.1 (Me3C), 122.7, 123.9 (C5Me4Ph, CMe), 123.9 (CHd
CHCMe3), 124.0, 125.0 (C5Me4Ph, CMe), 125.3 (C5Me4Ph, CPh
or Ph, Cipso), 126.0, 129.5 (C5Me4Ph, CH of Ph), 137.7 (C5Me4-
3
3J HH ) 17.2 Hz, 1H, TiCHdCH), 6.06 (d, J HH ) 17.2 Hz, 1H,

4878 Organometallics, Vol. 18, No. 23, 1999
Sˇ teˇpnicˇka et al.
Ph, CPh or Ph, Cipso), 142.8 (CHdCHCMe3), 205.4 (Me3CCt
C), 220.5 (Me3CCtC); one CH(Ph) signal is overlapped by the
solvent multiplet. IR (hexane, cm-1): 1630. UV-near-IR
(hexane, nm): 650.
cm-1): 1670 (s), 1646 (m), 1245 (vs), 1180 (m), 1020 (m), 947
(s), 915 (m), 840 (vs,b), 746 (s). UV-near-IR (hexane, nm): 500
(sh) ≈ 910.
[(η5-C5Me5)2Ti{3,4-η-Me3SiCtCC(SiMe3)dCH2}] (D2): yel-
low-brown crystals, yield 0.68 g (76%). 1H NMR (C6D6): δ 0.02,
0.18 (2 × s, 9 H, Me3Si), 1.76 (s, 30 H, C5Me5), 2.88, 5.12 (2 ×
[{η5-C5Me4Bz)2Ti{η2-(E)-Me3CCtCCHdCHCMe3}] (B4):
dark green oil, 0.52 g (82% related to 4). 1H NMR (C6D6): δ
0.97, 1.14 (2 × s, 9 H, Me3C), 1.79, 1.82, 1.84, 1.94 (4 × s, 6 H,
C5Me4Bz), 3.77, 3.85 (2 × d, 2 H, 2J HH ) 16.3 Hz, AB of PhCH2),
4.26 (d, 1 H, 3J HH ) 15.3 Hz, CHdCHCMe3), 6.26 (d, 1 H, 3J HH
) 15.3 Hz, CHdCHCMe3), 6.98-7.32 (m, 10 H, Ph). 13C{1H}
NMR (C6D6): δ 12.7, 12.8, 13.1, 13.5 (C5Me4Bz), 29.8 (Me3C),
33.3 (Me3C), 33.5 (Me3C), 33.9 (PhCH2), 42.84 (Me3C), 121.8,
122.0, 122.6, 123.0 (C5Me4Bz, CMe), 123.2 (CHdCHCMe3),
125.1 (Ph, Cipso), 126.0, 128.4, 128.7 (Ph, CH), 142.30 (C5Me4-
Bz, CCH2), 144.7 (CHdCHCMe3), 204.7 (Me3CCtC), 219.6
(Me3CCtC). IR (hexane, cm-1): 1635. UV-near-IR (hexane,
nm): 580 (sh) < 680.
2
d, 1 H, J HH ) 4.6 Hz, AB of dCH2). 13C{1H} NMR (C6D6): δ
0.2, 5.5 (2 × Me3Si), 12.9 (C5Me5), 122.2 (C5Me5), 133.3 (dCH2),
149.3 (dC(SiMe3)-), 205.9 (Me3SiCtC), 219.4 (Me3SiCtC).
29Si DEPT (C6D6): -20.5 (s, CtCSiMe3), -4.1 (s, CdCSiMe3).
MS (direct inlet, 70 eV, 140-150 °C): m/z (relative abundance)
M•+ not observed; 337 (7), 320 (9), 319 (26), 318 ([M -
(TMSA)2]+; 89), 317 (33), 316 (23), 315 (9), 314 (7), 313 (7),
301 (6), 299 (6), 197 (8), 196 (33), 183 (8), 182 (19), 181 (88),
180 (6), 179 (6), 178 (10), 177 (7), 176 (5), 157 (9), 156 (19),
155 (91), 119 (9), 108 (27), 97 (10), 83 (9), 74 (8), 73 (100), 70
(11), 45 (17). IR (KBr, cm-1): 2950 (s,b), 2887 (s,b), 2848 (m),
1658 (s), 1630 (m), 1430 (s,b), 1374 (s), 1240 (vs), 1019 (m),
935 (s), 920 (m), 833 (vs,b), 747 (s), 700 m), 671 (m), 643 (m),
440 (m). UV-near-IR (hexane, nm): 400(sh) . 510 (sh) ≈ 925.
Anal. Calcd for C30H50Si2Ti: C, 70.00; H, 9.79. Found: C, 70.03;
H, 9.80.
[(η5-C5Me4H)2Ti{η2-(E)-Me3SiCtCCHdCHSiMe3} (B5):
yellow-green oil, yield 0.39 g (80% related to 1). 1H NMR
(C6D6): δ 0.04, 0.07 (2 × s, 9 H, Me3Si), 1.34, 1.40, 2.12, 2.16
3
(4 × s, 6 H, C5Me4H), 4.59 (d, 1 H, J HH ) 18.3 Hz, CHd
3
CHSiMe3), 4.89 (s, 2 H, C5Me4H), 6.53 (d, 1 H, J HH ) 18.3
Hz, CHdCHSiMe3). 13C{1H} NMR (C6D6): δ -1.1, 3.1 (2 × s,
9 H, Me3Si), 13.4, 13.5, 13.6, 13.7 (C5Me4H), 112.4 (C5Me4H,
CH), 120.0, 120.4, 125.1, 126.5 (C5Me4H, CMe), 132.1 (CHd
CHSiMe3), 142.5 (CHdCHSiMe3), 222.5 (Me3SiCtC), 231.5
(Me3SiCtC). IR (hexane, cm-1): 1645. UV-near-IR (hexane,
nm): 540 (sh) > 700 (b).
[(η5-C5Me4P h )2Ti{3,4-η-Me3SiCtCC(SiMe3)dCH2}] (D3):
1
dark yellow crystalline material, yield 0.47 g (74%). H NMR
(C6D6): δ 0.04, 0.18 (2 × s, 9 H, Me3Si), 1.79, 1.88, 2.11, 2.17
2
(4 × s, 6 H, C5Me4Ph), 3.62, 5.22 (2 × d, 1 H, J HH ) 4.4 Hz,
dCH2), 6.27 (br d, 4 H, J ) 7.1 Hz, Ph), 6.89-7.02 (m, 6 H,
Ph). 13C NMR (C6D6): δ 0.42, 5.13 (Me3Si), 13.9, 14.3, 14.3,
14.6 (C5Me4Ph), 122.1, 123.2 (C5Me4Ph, CMe), 125.9 (Ph, CH),
126.6, 127.2 (C5Me4Ph, CMe), 127.7, 128.9 (Ph, CH), 132.7 (d
CH2), 137.3 (C5Me4Ph, CPh or Ph, Cipso), 150.0 (CdCH2), 209.1
(η2-Me3SiCtC), 221.2 (η2-Me3SiCtC). One of the Ph, Cipso and
C5Me4Ph, CPh signals was not found due to its overlap with
the solvent resonance. MS (direct inlet, 70 eV, 145-155 °C):
m/z (relative abundance) M•+ not observed; 444 (14), 443 (40),
442 ([(C5Me4Ph)2Ti]+; 100), 441 (34), 440 (19), 439 (6), 242 (5),
241 (5), 240 (5), 221 (5), 196 (10), 181 (16), 165 (5), 155 (14),
73 (27). IR (KBr): 1635-1655 cm-1. UV-near-IR (hexane,
nm): 910.
[(η5-C5Me4H)2Ti(η2-(E)-F cCtCCHdCHF c)] (B6): red oil
adhering on glass walls, yield ca. 0.4 g (56%). 1H NMR (C6D6):
δ 1.42, 1.51, 2.12, 2.23 (4 × s, 6 H, C5Me4H), 3.71, 3.99 (2 ×
apparent t, 2 H, AA′BB′ of C5H4Fe), 4.09, 4.37 (2 × apparent
t, 2 H, AA′BB′ of C5H4Fe), 4.14, 4.24 (2 × s, 5 H, C5H5Fe),
3
5.04 (s, 2 H, C5Me4H), 5.39 (d, J HH ) 15.4 Hz, 1 H, CHd
CHFc), 7.13 (d, 3J HH ) 15.4 Hz, 1 H, CHdCHFc). 13C{1H} NMR
(C6D6): δ 13.4, 13.5, 13.6, 13.7 (C5Me4H), 66.7, 67.2, 68.5, 69.0
(C5H4Fe, CH), 69.3, 69.4 (C5H5Fe), 85.9, 89.2 (C5H4Fe, Cipso),
112.3 (C5Me4H, CH), 120.1, 120.3, 126.3, 126.7 (C5Me4H, CMe),
126.4 (CHdCHFc), 129.4 (CHdCHFc), 204.4 (FcCtC), 209.97
(FcCtC). IR (hexane, cm-1): 1620, 1640. UV-near-IR (hexane,
nm): 440 . 650 (b).
Analogous reduction of [(η5-C5Me5)2TiCl2] in the presence
of Me3CCtCC(CMe3)dCH2 gave after the usual workup a
purple paramagnetic solution which contained the “tucked in”
compound [(η1:η5-C5Me4CH2)(η5-C5Me5)Ti] according to MS and
EPR spectra.19 Under the same conditions, [(η5-C5Me4H)2TiCl2]
afforded a complicated mixture in which the [(η5-C5Me4H)2Ti-
{η2-Me3CCtCC(CMe3)dCH2}] complex was detected by NMR
spectroscopy.
Rea ctivity Exp er im en ts. Rea ction betw een 1 a n d
TBUE Assisted by Su n ligh t. A hexane solution of 1 (90 mg,
0.2 mmol in 4.9 mL) and TBUE (2.6 mL, 21.2 mmol) were
mixed in an ampule equipped with a pair of 1.0 and 0.1 cm
quartz cells. After 4.5 h in the dark, the concentration of the
BTMSE complex decreased to 90% of the initial value while
the concetration of TBUE remained virtually unchanged
within the precision of the measurement. However, after 2 h
in sunlight the concentration of the BTMSE complex decreased
to 62% of its initial value and TBUE was consumed completely.
When more TBUE (1.5 mL, 12 mmol) was added, this was
consumed after another 2 h of exposure to sunlight and the
amount of the BTMSE complex decreased to ca. 20% of the
original amount. This corresponds to a turnover number (TN)
of 210 molecules of TBUE per molecule of 1.
Syn th esis of Tita n ocen e Com p lexes w ith η2-Coor d i-
n a ted HTT Dim er s. Titanocene dichlorides [(η5-C5Me4R)2-
TiCl2] (R ) H, Me, Ph; 1.0 mmol) were reduced by a 10-50-
fold molar excess of magnesium metal in THF (20 mL) in the
presence of Me3SiCtCC(SiMe3)dCH2 (0.7 mL, 5.0 mmol) at
60 °C. With commercial magnesium turnings (Aldrich for
Grignard reagents), induction periods did not exceed 2 h, but
with magnesium recovered from previous reductions under
vacuum conditions, the reduction began immediately and was
completed within 30 min. The resulting solution was separated
from excess magnesium and evaporated under vacuum over-
night. The residue was extracted by hexane to give brown-
yellow solutions from which the D type complexes were
crystallized.
[(η5-C5Me4H)2Ti{3,4-η-Me3SiCtCC(SiMe3)dCH2}] (D1):
yellow-brown crystalline material, yield 0.32 g (66%). 1H NMR
(C6D6): δ -0.10, 0.15 (2 × s, 9 H, Me3Si), 1.03, 1.88, 1.90, 1.93
(4 × s, 6 H, C5Me4H), 3.13, 5.04 (2 × d, 1 H, 2J HH ) 4.5 Hz, AB
of dCH2), 5.83 (s, 2 H, C5Me4H). 13C{1H} NMR (C6D6): δ -0.4,
3.8 (2 × Me3Si), 12.4, 12.7, 14.4, 14.5 (C5Me4H), 112.7 (C5Me4H,
CH), 121.0, 123.8, 124.5, 125.4 (C5Me4H, CMe), 130.7 (dCH2),
150.3 (dC(SiMe3)-), 208.7 (Me3SiCtC), 216.1 (Me3SiCtC).
29Si DEPT (C6D6): -21.2 (s, CtCSiMe3), -4.3 (s, CdCSiMe3).
MS (direct inlet, 70 eV, 130-140 °C): m/z(relative abundance)
486 (M•+; 0.1), 327 (5), 325 (13), 309 (6), 292 (5), 291 (13), 290
([M - (TMSA)2]+; 46), 289 (25), 288 (15), 287 (11), 286 (6), 285
(7), 204 (6), 203 (5), 197 (7), 196 ([(TMSA)2]+; 31)), 183 (7),
182 (15), 181 (72), 168 (6), 167 (9), 166 (8), 165 (6), 164 (8),
163 (6), 157 (7), 156 (15), 155 (82), 108 (26), 105 (8), 97 (9), 83
(9), 74 (8), 73 (100), 70 (10), 45 (17), 43 (11). IR (hexane,
Rea ction betw een 2 a n d TMSE Assisted by Su n ligh t.
A hexane solution of 2 (98 mg, 2 mmol in 2.0 mL) and TMSE
(3.0 mL, 21.2 mmol) were mixed in an ampule equipped with
a pair of 1.0 and 0.1 cm quartz cells. After 2 h in the dark the
concentration of 2 decreased to 91% and a corresponding
decrease of the TMSE concentration ranged the precision of
the measurement. Upon exposure to direct sunlight for 2 h,
however, the concentration of 2 and TMSE decreased to 50%
and to about 2% of their initial values, respectively. This

Head-to-Tail Dimerization of Terminal Alkynes
Organometallics, Vol. 18, No. 23, 1999 4879
Ta ble 6. Cr ysta llogr a p h ic Da ta , Da ta Collection a n d Str u ctu r e Refin em en t for A1, A6, B1, a n d D2
A1
C30H46Ti
A6
B1
D2a
formula
Mr
C42H46Fe2Ti
710.39
C30H46Ti
454.57
C30H50Si2Ti
514.78
454.57
cryst syst
space group
monoclinic
C2/c
monoclinic
P21/n
monoclinic
P21/n
orthorhombic
P212121
T (K)
100(1)
294(1)
294(1)
294(1)
a (Å); R (deg)
14.383(3); 90
11.172(2); 113.46(1)
18.575(3); 90
2738.0(9); 4
30-32
15.868(3); 90
10.553(2); 102.03(1)
20.881(3); 90
3419.9(9); 4
26-28
17.533(2); 90
9.5876(9); 115.747(8)
18.183(1); 90
2753.0(3); 4
26-28
10.036(2); 90
16.101(3); 90
19.030(3); 90
3075(1); 4
26-28
b (Å); â (deg)
c (Å); γ (deg)
V (Å3); Z
2θ range for cell param determn (deg)
Dc (g mL-1
)
1.10
1.38
1.10
1.11
cryst size (mm3)
cryst descripn
µ(Mo KR) (mm-1
F(000)
0.30 × 0.30 × 0.40
yellow bar
0.326
0.25 × 0.32 × 0.39
orange-red fragment
1.09
0.20 × 0.35 × 0.35
0.46 × 0.68 × 0.79
red-brown prism
0.372
blue bar
)
0.325
992
992
1488
1120
2θ range (deg); hkl
4.8-51.9; +h,+k,(l
2.9-49.9; (h,+k,+l
2.7-44.0; +h,+k,(l
3.3-49.9; (h,(k,(l
vari in stdsb
9.8
5.8
2.1
2.4
no. of diffractions collected; R(σ)c
no. of unique diffractions
no. of diffractions obsd; Fo g 4σ(Fo)
2795; 1.91
2693
2341
0.0948; 3.6836
254
5.25; 4.22
12.8; 12.0
0.899
6190; 11.0
6009
3360
0.0682; 4.7108
466
15.1; 5.73
16.4; 13.8
1.04
3491; 13.2
3369
1819
0.0517; 0.0423
311
15.8; 4.94
12.1; 9.80
1.00
4732; 2.23
4391
3973
0.0567; 0.2158
304
3.98; 3.05
8.42; 8.04
1.08
d
weighting scheme: w1; w2
no. of params
R
R
all(F); Robsd(F) (%)c
w,all(F2); Rw,obsd(F2) (%)c
c
GOFall
∆F (e Å-3
)
0.80; -0.31
0.49, -0.33
0.21; -0.24
0.18; -0.41
Flack’s absolute structure parameter x ) 0.00(2). Three standard diffractions were monitored every 1 h in all cases. c R(σ) ) ∑σ(Fo2)/
a
b
∑Fo2, R(F) ) ∑||Fo| - |Fc||/∑|Fo|, Rw(F2) ) [∑(w(Fo2-Fc2)2)/(∑w(Fo2)2)]1/2, GOF ) [∑(w(Fo2-Fc2)2)/(Ndiffrs-Nparams)]1/2
.
Weighting scheme:
d
w ) [σ2(Fo2) + (w1P)2 + w2P]-1, where P ) 1/3[max(Fo2) + 2Fc2].
corresponds to the conversion of 210 molecules of TMSE per
molecule of the converted BTMSE complex. Another 3.0 mL
of TMSE was added, and the mixture was exposed to full
sunlight for another 1 h. As a result, the amount of 2 decreased
to 25% of the original value and all TMSE dimerized. In all,
0.15 mmol of 2 converted a total of 42.4 mmol of TMSE, which
gives a TN value of 283.
Con ver sion of D2 in to A2 a n d B2. Complex D2 obtained
as described above (ca. 1.0 mmol) in hexane (10 mL) was mixed
with TBUE (1.0 mL, 8.1 mmol) in the dark at room temper-
ature. The absorption band of D2 at 925 nm decayed within
30 min, while the yellow color of the solution did not change.
The usual workup gave a yellow crystalline solid whose NMR
spectra were identical with those of A2. The volatiles evapo-
rated under vacuum showed the ratio of HTT dimers (TBU)2/
(TMSE)2 ca. 2:1. After exposure of A2 in C6D6 to sunlight it
rapidly turned into B2, as shown by NMR and UV-near-IR
spectra.
Rea ction of D2 w ith TMSE. A solution of D2 in hexane
(0.1 mmol in 2 mL) in an ampule equipped with a quartz cell
(0.1 cm) was mixed with 2.5 mL of TMSE (17.7 mmol) in
diffuse daylight. Within 10 min after mixing, the absorption
bands of D2 (925 nm) and of TMSE (1640 nm) were not
observable. Then another portion of TMSE (2.0 mL, 14.2 mmol)
was added; this was consumed within 10 min. The volatiles
were removed, and GC-MS analysis revealed in addition to
hexane only the HTT dimer (TMSE)2 (TN ) 319).
Rea ction of B1 w ith TBUE. A solution of B1 from an
NMR tube (ca. 0.2 mmol of B1) was evaporated, the residue
was redissolved in hexane (4.0 mL), and the hexane solution
was mixed with TBUE (2.0 mL, 16.2 mmol) in the dark at room
temperature. Immediately after addition the blue solution
turned brown-yellow and the UV-near-IR spectrum did not
show absorption bands at wavelengths longer than 550 nm.
All TBUE was consumed within 3 h in the dark (TN ) 81).
Rea ction of B2 w ith TMSE. A solution of B2 from an
NMR tube (ca. 0.4 mmol of B2) was evaporated, the residue
was dissolved in hexane (6.0 mL), and the solution was treated
with TMSE (3 mL, 24.0 mmol) in the dark. Immediately after
addition, the green solution of B4 turned orange and TMSE
was slowly consumed (to 87% of its initial content during 3.5
h in the dark). After exposure to sunlight for 20 min, all the
remaining TMSE was converted to its HTT dimer (TN ) 60)
and the color of the reaction mixture changed from orange to
yellow.
Rea ction of B1 w ith BTMSE. Crystalline B1 (0.050 g,
0.11 mmol) was dissolved in hexane (4.0 mL), and BTMSE (0.1
mL, 0.45 mmol) was added. The electronic absorption spectrum
of B1 was replaced by the spectrum of 1, dominated by the
absorption band at 920 nm after standing overnight.
Rea ction of D2 w ith BTMSE. Crystalline D2 (0.20 g, 0.39
mmol) was dissolved in hexane (5.0 mL), and BTMSE (0.1 mL,
0.45 mmol) was added. After 1 h at room temperature the
concentration of D2 decreased by less than 10%, as indicated
by a decrease in intensity of the shoulder at 500 nm. After
the temperature was raised to 60 °C for 1 h, the above-
mentioned shoulder disappeared completely and the solution
turned yellow. The GC-MS analysis of volatiles revealed a
molar ratio of the HTT dimer (TMSE)2 and BTMSE of 6.5/1.
A yellow crystalline residue was identified by an IR spectrum
in KBr pellet to be pure complex 2.
Str u ctu r e Deter m in a tion . Gen er a l Com m en ts. Crystals
suitable for X-ray analyses were grown by slow cooling or slow
evaporation from hexane (A1, B1, D2) or toluene (A6) solutions
in evacuated ampules. The selected crystals were inserted into
Lindemann glass capillaries and sealed by wax under nitrogen
in a glovebox. Diffraction intensities were measured on a
CAD4-MACHIII four-circle diffractometer with Mo KR radia-
tion (λ ) 0.710 69 Å) and θ-2θ scan mode. An Oxford
Cryostream low-temperature device was used for the case of
complex D2. The cell parameters were determined by least
squares from 25 automatically centered diffractions selected
within 2θ ranges given in Table 6. No absorption correction
was applied. The structures have been solved by direct
methods (SIR9235) and refined by full-matrix least squares on
weighted F2 (SHELXL9736). Some relevant crystallographic
(35) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G.; Giaco-
vazzo, C.; Guagliardi, A.; Polidori, G. J . Appl. Crystallogr. 1994, 27,
435.
(36) Sheldrick, G. M. SHELXL97: Program for Crystal Structure
Refinement from Diffraction Data; University of Go¨ttingen: Go¨ttingen,
Germany, 1997.

4880 Organometallics, Vol. 18, No. 23, 1999
Sˇ teˇpnicˇka et al.
data are given in Table 6. Structural data for all compounds
were deposited at the Cambridge Crystallographic Data Centre
and are also available as Supporting Information. Thermal
ellipsoid plots were drawn by the PLATON9237 program.
Cr ysta l Str u ctu r e of A1. The refinement in the noncen-
trosymmetric space group Cc proved unstable due to high
correlations of the parameters since the Ti-CtC and Ti-CHd
CH moieties that only violate the virtual 2-fold symmetry of
the molecule are randomly distributed throughout the lattice.
Hence, the calculation was carried out in the related cen-
trosymmetric space group C2/c, where the alkynyl and alkenyl
moieties were refined each with equal probability over the two
positions related by the crystallographic 2-fold symmetry axis
(-x, y, /2 - z) (Ti is located in a special position (0, y, /4) with
y ) 0.21905(4)). Furthermore, the methyls of both tert-butyl
groups exhibit an extensive rotational disorder along the
pivotal C-C(t-Bu) bonds, resulting in an almost toroidal
electron density distribution. Two sets of methyl groups were
refined for both tert-butyl substituents as ideal tetrahedra
(CCH3) with C-C-H angles of 109.5°, C-H bond lengths of
0.96 Å and Uiso(H) ) 1.2[Ueq(C)]. All other hydrogen atoms
were identified from difference electron density maps and
freely isotropically refined. It is worth noting that a similar
statistical disorder of hydrocarbyl ligands has been reported
for [(η5-C5Me5)2Ti(η1-CtCPh)(η1-CHdCHPh)].9
of 109.5° and C-H bond lengths of 0.96 Å) and in this
arrangement isotropically refined by being allowed to rotate
freely around the pivotal C-C bond to fit the electron density
maxima.
Cr ysta l Str u ctu r e of B1. For compoud B1, an empirical
correction for exctinction was applied during the structure
refinement as implemented in SHELX97; i.e., the calculated
structure factors Fc were multiplied by k[1 + 0.001xFc2λ3(sin
2θ)-1 -1/4, where k is the overall scaling factor, λ the wave-
]
length, and θ the diffraction angle. The refined x value was
0.0015(4). Hydrogen atoms of the double bond and those of
cyclopentadienyl CH groups were identified on the difference
electron density maps and isotropically refined. Methyl groups
on the titanocene cyclopentadienyls as well as those of tert-
butyl groups were treated in the same manner as for A6.
Cr ysta l Str u ctu r e of D2. The methyl hydrogens in SiMe3
groups and on cyclopentadienyl ligands were treated like those
in A6 but with Uiso(H) ) 1.2[Ueq(C)]; the dCH2 hydrogens were
identified on an electron density map and isotropically refined.
1
1
Ack n ow led gm en t. This research was supported by
the Grant Agency of the Czech Republic (Grant No. 203/
99/0846) and by the Volkswagen Stiftung. The Grant
Agency of the Czech Republic sponsored access to the
Cambridge Structure Database (Grant No. 203/99/0067).
Cr ysta l Str u ctu r e of A6. The two double-bond hydrogen
atoms were found on the difference electron density map and
isotropically refined. Other hydrogen atoms were handled as
follows: ferrocene hydrogens were fixed so that the C-H bond
of 0.93 Å bisects the outer C-C-C angle of the aromatic ring
and their Uiso values were freely refined. All methyl hydrogens
were attributed ideal tetrahedral geometry (C-C-H angles
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal-
lographic data, atomic coordinates, thermal parameters, and
interatomic and interplanar distances and angles and packing
diagrams for A1, A6, B1, and D2. This material is available
free of charge via the Internet at http://pubs.acs.org.
(37) Spek, A. L. Acta Crystallogr. 1990, A46, C34.
OM9905714