Methyl-substituted zirconocene-bis(trimethylsilyl)acetylene complexes (C5H5-nMen)2Zr(η 2-Me3SiC≡CSiMe3) (n = 2-5)

Article abstract of DOI:10.1021/om960184j

The (C₅H_5-nMe_n)₂Zr[η ²-C₂(SiMe₃)₂] (n = 2-5; 1,3-dimethyl, 1,2,3-trimethyl) (2C-F) complexes were prepared by the reduction of corresponding zirconocene dichlorides wi

Full text of DOI:10.1021/om960184j

3752
Organometallics 1996, 15, 3752-3759
Meth yl-Su bstitu ted
Zir con ocen e-Bis(tr im eth ylsilyl)a cetylen e Com p lexes
(C5H5-n Men )2Zr (η2-Me3SiCtCSiMe3) (n ) 2-5)
J o¨rg Hiller,† Ulf Thewalt,† Miroslav Pola´sˇek,‡ Lidmila Petrusova´,‡
Vojtech Varga,‡ Petr Sedmera,§ and Karel Mach*,‡
Sektion fu¨r Ro¨ntgen- und Elektronenbeugung, Universita¨t Ulm, 89069 Ulm, Germany,
J . Heyrovsky´ Institute of Physical Chemistry, Academy of Sciences of the Czech Republic,
Dolejsˇkova 3, 182 23 Prague 8, The Czech Republic, and Institute of Microbiology,
Academy of Sciences of the Czech Republic, Prague 4, The Czech Republic
Received March 11, 1996X
The (C5H5-nMen)2Zr[η2-C2(SiMe3)2] (n ) 2-5; 1,3-dimethyl, 1,2,3-trimethyl) (2C-F )
complexes were prepared by the reduction of corresponding zirconocene dichlorides with
magnesium in THF in the presence of bis(trimethylsilyl)acetylene (BTMSA). All of them
are stable in the absence of THF. Crystal structures of (C5HMe4)2Zr[η2-C2(SiMe3)2] (2E)
and (C5Me5)2Zr[η2-C2(SiMe3)2] (2F ) and of the analogous titanium complexes are isomorphous.
The red shift of the ν(CtC) vibration and the downfield shift of 13C δ(CtC) indicate that
BTMSA in 2C-F is more strongly coordinated than in analogous titanocene complexes. The
nonisolated complex (C5H4Me)2Zr[η2-C2(SiMe3)2](THF) (2B‚THF) rearranges after the loss
of THF to give the dimer [(η5-C5H4Me)(η1-C(SiMe3)dCH(SiMe3)Zr(µ-η1:η5-C5H3Me)]2 (3B).
In tr od u ction
) Ph.4d The existence of the (C5H5)2Ti(MeCtCMe)
complex4b was not later confirmed.4h Recently, a com-
plete series of the (C5H5-nMen)2Ti[η2-C2(SiMe3)2] (n )
0-5) complexes has been obtained.4i The four-electron
coordination bond in these complexes was inferred from
large shifts of the ν(CtC) vibration (∆ν ) 400-500 cm-1
and a low-field shift of δC(CtC) into the region 196-
245 ppm.4e,j The complexes of the type (C5H5)2Ti-
(R1CtCR2)(L), for instance, L ) CO, R1 ) R2 ) Ph,5a,b
R1 ) R2 ) C6F5,5b and L ) PMe3, R1 ) R2 ) H,5c R1 )
H, R2 ) Ph,5d and R1 ) R2 ) Ph,5e bind, as judged from
ν(CtC), weakly the internal acetylenes (1785-1740
cm-1) and strongly HCtCH (1618 cm-1) and PhCtCPh
(1590 cm-1). All the complexes except those containing
bis(trimethylsilyl)acetylene (BTMSA) react with excess
acetylenes to give titanacyclopentadiene derivatives.4a,b,e,j
The BTMSA in (C5H5)2Ti[η2-C2(SiMe3)2] is easily re-
placed by other acetylenes4c,j,6a,b or by 1,4-disubstituted
1,3-butadiynes.7a-d It is also liberated upon interaction
with alcohols and carbonyl compounds.4e The reluc-
tance of BTMSA to participate in insertion reactions,
particularly with itself,8 makes BTMSA the ligand of
choice for studies of the reactivity of titanocene species.
The thermolysis of the (C5H5-nMen)2Ti[η2-C2(SiMe3)2] (n
) 0-5) complexes thus afforded in addition to the
products of titanocene rearrangements only BTMSA (for
n ) 0-4) or bis(trimethylsilyl)ethylenes (for n ) 5).4i
Highly reactive early transition metal metallocenes,
rapidly rearranging with the formation of additional Ti-
H, C-C or Ti-C bonds,1 can be stabilized by the
coordination of carbon monoxide,2 phosphanes,3 and
acetylenes4 and/or by a combination of acetylenes with
one of the former ligands.5 The titanocene-acetylene
complexes (C5H5)2Ti(R1CtCR2) have been reported for
R1 ) R2 ) Ph,4a Me,4b and SiMe3,4c R1 ) SiMe3, R2 )
Ph,4d R2 ) Bu, nBu, and nPr4e, and the permethylti-
t
tanocene complexes (C5Me5)2Ti(R1CtCR2) for R1 ) R2
) alkyl or Ph,4f R1 ) R2 ) SiMe3,4g and R1 ) SiMe3, R2
* To whom correspondence should be addressed.
† Universita¨t Ulm.
‡ J . Heyrovsky´ Institute.
§ Institute of Microbiology.
X Abstract published in Advance ACS Abstracts, J uly 15, 1996.
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S0276-7333(96)00184-7 CCC: $12.00 © 1996 American Chemical Society

Zirconocene-Bis(trimethylsilyl)acetylene Complexes
Organometallics, Vol. 15, No. 17, 1996 3753
ligands. Well-defined complexes of the type (C5H5)2Zr-
(acetylene)(PMe3) were obtained for the cyclic acetylenes
benzyne and cyclohexyne,9a-c as well as for linear
acetylenes R1CtCR2 with R1 ) H, R2 ) nBu9d and with
R1 ) R2 ) Ph.9e-h These complexes were generally
synthesized from (C5H5)2ZrClH according to eq 19a-d or
(3)
(1)
from (C5H5)2Zr(PMe3)29e or (C5H5)2Zr(η2-olefin)(PMe3)9f,g
complexes by adding the acetylene. Addition of acety-
lenes in excess to these complexes9a or to the dicarbonyl
derivative is formed.10d The tert-butyl(trimethylsilyl)-
acetylene complex (C5H5)2Zr(Me3CCtCSiMe3)(THF) was
prepared according to eq 2 and exerted the same
reactivity toward the above reagents as 2A‚THF.10e The
BTMSA ligand is readily replaced by 1,4-dialkyl-1,3-
butadiynes, and these are cleaved to give binuclear
zirconocene(III) acetylides.7c,10f The THF ligand in 2A‚
THF can be replaced by pyridine (py) to give the more
stable (C5H5)2Zr(Me3SiCtCSiMe3)(py) complex,10g and
this, at variance with 2A‚THF, reacts with 1,4-di-tert-
butyl-1,3-butadiyne yielding five- or seven-membered
zirconacyclic cumulene complexes.10h Only the reaction
with ketimines resulted in the elimination of BTMSA.10i
9h
(C5H5)2Zr(CO)2 generally affords zirconacyclopenta-
diene complexes. Interestingly, such a zirconacyclopen-
tadiene complex obtained from phenyl(trimethylsilyl)-
acetylene dissociates in the presence of PMe3 to give
(C5H5)2Zr(PhCtCSiMe3)(PMe3) and free acetylene.9i
Recently, a complex stabilized by THF, namely (C5H5)2-
Zr(Me3SiCtCSiMe3)(THF) (2A‚THF), has been obtained
by the reduction of zirconocene dichloride by magnesium
in the presence of BTMSA in THF (eq 2).10a This
The coordination of an electron-donating ligand which
is essential for the thermal stability of all the above
zirconocene acetylene complexes can, in principle, be
substituted by the electron-donation effect of methyl
substituents at the cyclopentadienyl ligands.11 Such an
effect has been clearly demonstrated in the series of
methylated titanocene monohalides (C5H5-nMen)2TiX (n
) 0, 1, 3-5; X ) Cl, Br, I) by the increasing reluctance
to dimerize or to coordinate THF when the number of
Me substituents (n) grows from 3 to 5.12 A note on the
preparation of the thermally stable (C5Me5)2Zr[η2-C2-
Ph2] complex13 and a recent report on the preparation
of rac-[1,2-ethylene-1,1′-bis(η5-tetrahydroindenyl)][η2-
bis(trimethylsilyl)acetylene]zirconium,14 the first struc-
(2)
complex easily loses THF, e.g. under reduced pressure
at room temperature and the complex (C5H5)2Zr(Me3-
SiCtCSiMe3) undergoes a dimerization induced by a
hydrogen transfer from the Cp ring to the BTMSA
ligand (eq 3).
In contrast to (C5H5)2Ti(Me3SiCtCSiMe3), complex
2A‚THF reacts with CO2, water, and acetone without
elimination of BTMSA.10b,c The zirconadihydrofurans
resulting from the reaction with acetone10c react further
with acetylenedicarboxylates with elimination of ac-
etone and BTMSA whereas a new zirconadihydrofuran
(10) (a) Rosenthal, U.; Ohff, A.; Michalik, M.; Go¨rls, H.; Burlakov,
V. V.; Shur, V. B. Angew. Chem., Int. Ed. Engl. 1993, 32, 1193-1195.
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Shur, V. B. Organometallics 1993, 12, 5016-5019. (c) Rosenthal, U.;
Ohff, A.; Baumann, W.; Tillack, A.; Go¨rls, H.; Burlakov, V. V.; Shur,
V. B. J . Organomet. Chem. 1994, 484, 203-207. (d) Rosenthal, U.; Ohff,
A.; Baumann, W.; Kempe, R.; Tillack, A.; Burlakov, V. V. Angew.
Chem., Int. Ed. Engl. 1994, 33, 1850-1852. (e) Lefeber, C.; Ohff, A.;
Tillack, A.; Baumann, W.; Kempe, R.; Burlakov, V. V.; Rosenthal, U.
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Baumann, W.; Kempe, R.; Tillack, A.; Burlakov, V. V. Organometallics
1994, 13, 2903-2906. (g) Rosenthal, U.; Ohff, A.; Baumann, W.; Tillack,
A.; Go¨rls, H.; Burlakov, V. V.; Shur, V. B. Z. Anorg. Allg. Chem. 1995,
621, 77-83. (h) Rosenthal, U.; Ohff, A.; Baumann, W.; Kempe, R.;
Tillack, A.; Burlakov, V. V. Angew. Chem., Int. Ed. Engl. 1994, 33,
1605-1607. (i) Lefeber, C.; Arndt, P.; Tillack, A.; Baumann, W.; Kempe,
R.; Burlakov, V. V.; Rosenthal, U. Organometallics 1995, 14, 3090-
3093.
(11) (a) Robbins, J . L.; Edelstein, N.; Spencer, B.; Smart, J . C. J .
Am. Chem. Soc. 1982, 104, 1882-1893. (b) Gassman, P. G.; Macomber,
D. W.; Hershberger, J . W. Organometallics 1983, 2, 1470-1472. (c)
Miller, E. J .; Landon, S. J .; Brill, T. B. Organometallics 1985, 4, 533-
538. (d) Mach, K.; Varga, V.; Antropiusova´, H.; Pola´cˇek, J . J . Orga-
nomet. Chem. 1987, 333, 205-215.
(12) Mach, K.; Raynor, J . B. J . Chem. Soc., Dalton Trans. 1992, 683-
688.
(13) McDade, C.; Bercaw, J . E. J . Organomet. Chem. 1985, 279,
281-315.
(8) (a) Vollhardt, K. P. C. Acc. Chem. Res. 1977, 10, 1-8. (b) Kru¨erke,
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3754 Organometallics, Vol. 15, No. 17, 1996
Hiller et al.
cooling of the solution to room temperature, 50 mL of aqueous
HCl was added. After standing overnight in air, light greenish
crystals were filtered from a green mother liquor. The crude
products were recrystallized from hot toluene to give fine
needlelike crystals. The purity of the compounds was checked
by MS analysis. IR spectra (regions 400-1600 cm-1) are listed
below.
(C5H4Me)2Zr Cl2 (1B). The yield of colorless crystals was
7.5 g (65%); mp 182 °C (lit. mp 180 °C18a). IR (KBr, cm-1):
1496 s, 1455 m, 1443 m, 1414 w, 1374 s, 1352 w, 1243 m, 1074
w, 1048 s, 1042 s, 1033 s, 936 m, 880 m, 852 s, 841 vs, 816 s,
618 m.
turally characterized complex without an additional
ligand, encouraged us to communicate results of our
investigation of the influence of methyl substituents at
the cyclopentadienyl ligands on the stability of zir-
conocene-acetylene complexes. Here we report the
synthesis of the (C5H5-nMen)2Zr[η2-C2(SiMe3)2] (n )
2-5) complexes which are stable in the absence of
electron donor ligands and the crystal structures of the
complexes for n ) 4 and 5 and of a dimeric product of
rearrangement of the labile (C5H4Me)2Zr[η2-C2(SiMe3)2]
complex.
(C5H3Me2)2Zr Cl2 (1C). The yield of colorless crystals was
4.6 g (37%); mp 173 °C. IR (KBr, cm-1): 1507 s, 1452 s, 1440
s, 1380 s, 1277 w, 1137 w, 1050 s, 1028 m, 944w, 901 m, 847
vs, 828 s, 620 m.
(C5H2Me3)2Zr Cl2 (1D). The yield of colorless crystals was
4.9 g (36%); mp 252 °C. IR (KBr, cm-1): 1489 s, 1474 m, 1448
s, 1374 s, 1302 w, 1196 m, 1028 s, 914 w, 904 w, 877 w, 834 s,
818 vs, 710 w, 616 w, 455 w.
(C5HMe4)2Zr Cl2 (1E). The yield of slightly yellow crystals
was 8.0 g (55%); mp 262 °C (lit. mp 211 °C18b). IR (KBr, cm-1):
1485 m, 1448 m, 1431 m, 1383 s, 1370 s, 1323 w, 1150 w, 1116
vw, 1024 s, 976 w, 902 m, 862 vs, 601 m.
(C5Me5)2Zr Cl2 (1F ). The yield of yellow crystals was 8.4 g
(54%); mp 311 °C. IR (KBr, cm-1): 1483 s, 1446 s, 1423 s,
1376 vs, 1163 w, 1062 w, 1021 s, 952 w, 805 w, 598 w. The
reported NMR data for 1E17a and 1F 17b agreed with our
records.
Exp er im en ta l Section
Gen er a l Da ta . All manipulations with reagents, synthe-
ses, and most of the spectroscopic measurements were carried
out under vacuum using all-sealed glass devices equipped with
breakable seals. The adjustment of single crystals into capil-
laries for X-ray analysis and the preparation of KBr pellets
for infrared measurements were performed in an atmosphere
of purified nitrogen. 1H and 13C NMR spectra were measured
on
a Varian VXR-400 spectrometer (400 and 100 MHz,
respectively) in C6D6 at 25 °C. Chemical shifts (given in the
δ scale) were referenced to the solvent signal (δH 7.15 ppm, δC
128.0 ppm). Assignment of spectra of the C5H5-nMen ligands
was carried out using a delayed COSY experiment. UV-vis
spectra were registered in the range 270-2000 nm on a Varian
Cary 17D spectrometer using all-sealed quartz cuvettes (Hell-
ma). Mass spectra were obtained on a J EOL D-100 spectrom-
eter at 70 eV (only important mass peaks and peaks of
intensity g5% are reported). Samples in capillaries were
opened and inserted into the direct inlet under argon. Infrared
spectra were measured on a UR-75 (Zeiss, J ena, Germany) or
on a Mattson Galaxy 2020 FTIR single beam spectrometer.
KBr pellets from estimated amounts of solid samples were
prepared in a glovebox (mBraun labmaster 130) under purified
nitrogen and were measured in a cuvette under a nitrogen
atmosphere. EDX measurements were carried out with a Zeiss
DSM-962 scanning electron microscope equipped with an
EDAX X-ray detector. An acceleration voltage of 25 kV was
used for the generation of cathodic radiation.
Ch em ica ls. The solvents THF, hexane, toluene, and
benzene-d6 were purified by conventional methods, dried by
refluxing over LiAlH4, and stored as solutions of dimeric
titanocene (C10H8)[(C5H5)Ti(µ-H)]2.15 Bis(trimethylsilyl)acet-
ylene (BTMSA) (Fluka) was degassed, stored as a solution of
dimeric titanocene for 4 h, and distilled into ampules. Mag-
nesium turnings (Fluka, purum for Grignard reactions) were
weighed and evacuated. Methylcyclopentadiene was obtained
by cracking of the dimer (Fluka) and was immediately used
for the preparation of the lithium salt. 1,3-Dimethylcyclopen-
tadiene,16 1,2,3-trimethylcyclopentadiene, tetramethylcyclo-
pentadiene, and pentamethylcyclopentadiene were prepared
as reported earlier.11d Zirconocene dichlorides (C5H5-nMen)2ZrCl2
(n ) 1-5) (1B-F ) were prepared by a modified general
method17a,b as follows. The lithium salts of the cyclopenta-
dienes were obtained by adding BuLi in hexane (1.6 M, 52 mL,
83 mmol; Chemetall GmbH, Frankfurt a.M., Germany) to the
cyclopentadiene (80 mmol) in 400 mL of toluene. After 1 h of
stirring at room temperature finely powdered ZrCl4 (8.4 g, 36
mmol; Merck) was added under argon and the mixture was
refluxed (from minimum 4 h for C5H4Me to 48 h for C5Me5).
Half the amount of toluene (200 mL) was distilled off, and after
P r ep a r a tion of (C5H5-n Men )2Zr [η2-C2(SiMe3)2] (n ) 2-5)
Com p lexes 2C-F . (C5H5-nMen)2ZrCl2 (1C-F ) (2 mmol) and
Mg (0.050 g, 2.1 mmol) were charged into an ampule equipped
with
a Teflon-coated magnetic stirrer. The ampule was
evacuated, and BTMSA (0.6 mL, 2.7 mmol) and THF (30 mL)
were distilled in on a vacuum line. The mixture was frozen
by liquid nitrogen, sealed off, and stirred at 60 °C until all
magnesium had disappeared. Turquoise solutions were ob-
tained from 1D-F , and a honey-yellow solution was obtained
from 1C. The solutions were evaporated in vacuo (the product
from 1C turned to turquoise), and the residues were extracted
with hexane. In order to remove all MgCl2 these solutions
were evaporated and the residues were extracted by a mini-
mum amount of hexane. Crystalline compounds 2E,F were
obtained by cooling of the concentrated solutions. Compounds
2C,D formed amorphous solids both by cooling and by slow
evaporation of hexane. They were purified by removing
mother liquors at -70 °C. All the compounds were also
prepared by the same procedure using a 5-fold molar excess
of magnesium with respect to 1C-F . The reaction time was
shortened to ca. 30 min at 60 °C.
(C5H3Me2)2Zr [η2-C2(SiMe3)2] (2C). The yield of green
amorphous solid was 0.76 g (85%). 1H NMR (C6D6): δ 0.03
(s, 18H, SiMe3), 1.73 (s, 12H), 5.79 (s, 4H, H-4, H-5), 6.09 (s,
2H, H-2). 13C NMR (C6D6): δ 2.1 (q, 6C), 15.2 (q, 4C), 111.0
(d, 4C), 112.1 (d, 2C), 125.1 (s, 2C), 258.2 (s, 2C). IR (KBr):
1566 (m), 1512 (w), 1462 (m), 1445 (m), 1375 (w), 1242 (s),
1028 (w), 835 (vs, b), 748 (m), 725 (w), 685 (m), 664 (m), 638
(m), 617 (w), 598 (w), 548 (vw), 470 (w). UV-vis (hexane,
green) (nm): 775 (w); THF, yellow (nm), strong absorption
decreasing in intensity to 570, 750 (vw). MS (direct inlet, 70
eV, 75-80 °C, m/z (%)): 446 (M+, 8), 276 (100). Anal. Calcd
for C22H36Si2Zr: C, 59.0; H, 8.1. Found: C, 59.8; H, 8.3.
(C5H2Me3)2Zr [η2-C2(SiMe3)2] (2D). The yield of green
amorphous solid was 0.88 g (92%); mp 214 °C. 1H NMR
(C6D6): δ 0.14 (s, 18H, SiMe3), 1.78 (s, 12H), 1.89 (s, 6H), 5.52
(s, 4H). 13C NMR (C6D6): δ 2.8 (q, 6C), 12.0 (q, 2C), 14.0 (q,
4C), 108.5 (d, 4C), 114.1 (s, 4C), 122.4 (s, 2C), 260.0 (s, 2C). IR
(KBr): 1535 (m), 1487 (w), 1445 (m), 1383 (m), 1242 (s), 1024
(14) Lefeber, C.; Baumann, W.; Tillack, A.; Kempe, R.; Go¨rls, H.;
Rosenthal, U. Organometallics 1996, 15, in press.
(15) Antropiusova´, H.; Dosedlova´, A.; Hanusˇ, V.; Mach, K. Transition
Met. Chem. 1981, 6, 90-93.
(16) Varga, V.; Mach, K.; Schmid, G.; Thewalt, U. J . Organomet.
Chem. 1994, 475, 127-137.
(17) (a) Courtot, P.; Pichon, R.; Salaun, J . Y.; Toupet, L. Can. J .
Chem. 1991, 69, 661-672. (b) Manriquez, J . M.; Bercaw, J . E. J . Am.
Chem. Soc. 1974, 96, 6229-6230.
(18) (a) Hey-Hawkins, E.; Lindenberg, F. Z. Naturforsch., B 1993,
48, 951-957. (b) J aniak, C.; Versteeg, U.; Lange, K. H. C.; Weimann,
R.; Hahn, E. J . Organomet. Chem. 1995, 501, 219-234.

Zirconocene-Bis(trimethylsilyl)acetylene Complexes
Ta ble 1. Cr ysta llogr a p h ic Da ta a n d Exp er im en ta l Deta ils for 2E,F a n d 3B
2E 2F
26H44Si2Zr C28H48Si2Zr
Organometallics, Vol. 15, No. 17, 1996 3755
3B
C40H64Si4Zr2
mol formula
mol wt
C
504.01
532.06
839.72
cryst syst
space group
cell consts
a, Å
monoclinic
C2/c (No. 15)
triclinic
P1h (No. 2)
triclinic
P1h (No. 2)
15.4388(9)
9.2206(5)
9.6327(5)
b, Å
c, Å
10.7291(6)
17.7724(13)
90
104.92(1)
90
2844.6(3)
4
1.177
1072
0.480
10.2874(6)
17.3717(7)
79.198(8)
75.628(5)
72.559(5)
1511.43(13)
2
1.169
568
0.455
10.2197(7)
13.5296(8)
110.853(6)
91.563(5)
117.016(5)
1079.89(11)
1
1.291
440
0.619
R, (deg)
â, (deg)
γ, (deg)
V, Å3
Z
dcalcd, g/cm-3
F(000)
µ(Mo KR), mm-1
cryst dimens, mm
0.6 × 0.5 × 0.5
0.7 × 0.5 × 0.5
0.4 × 0.3 × 0.3
3.20, 24.99
(11, -12 to +11, 0-16
4783
θ
min, θmax, deg
range of indices (hkl)
rflns collcd
3.07, 25.01
3.01, 4.99
-18 to +17, 0-12, 0-21
2661
(10, -11 to +12, 0-20
5301
indepdt rflns
2514
5301
3790
data/restraints/params
goodness-of-fit on F2
final R indices [I > 2σ(I)]
R indices (all data)
min, max resid density e Å-3
2514/0/142
1.083
R1)0.0325, wR2)0.0785
R1)0.0276, wR2)0.0761
-0.235, 0.272
5300/0/297
1.107
R1)0.0267, wR2)0.0766
R1)0.0314, wR2)0.0794
-0.294, 0.294
3790/0/222
1.025
R1)0.0320, wR2)0.0693
R1)0.0542, wR2)0.0765
-0.280, 0.326
(w), 858 (vs), 843 (vs), 781 (s), 748 (m), 683 (w), 654 (m), 617
(w), 482 (w), 459 (m) cm-1. UV-vis (hexane, green) (nm): 305
(sh), 745 (ꢀ ) 220 cm2 mmol-1). MS (direct inlet, 70 eV, 110-
an insoluble residue remained. The collected extracts were
concentrated and cooled to -18 °C. Dirty white crystals were
separated from the pale brown solution. The crystals were
recrystallized from a saturated hexane solution by slow cooling.
The yield of glittering white crystals was 0.18 g (43%).
Suitable crystals were selected for the X-ray diffraction
analysis which identified the compound to be 3B. The solu-
tions of 3B in C6D6 were turning green at room temperature.
The 1H and 13C NMR spectra of such solutions indicated the
presence of a mixture of compounds whose spectra could not
be assigned.
115 °C, m/z (%)): 474 (M+, 6), 304 (100). Anal. Calcd for C24
-
H
40Si2Zr: C, 60.5; H, 8.5. Found: C, 60.2; H, 8.6.
(C5HMe4)2Zr [η2-C2(SiMe3)2] (2E). The yield of turquoise
crystals was 0.79 g (78%); mp 223 °C. 1H NMR (C6D6): δ 0.14
(s, 18H, SiMe3), 1.53 (s, 12H), 2.00 (s, 12H), 5.29 (s, 2H). 13C
NMR (C6D6): δ 3.4 (q, 6C), 12.6 (q, 4C), 12.7 (q, 4C), 109.2 (d,
2C), 119.1 (s, 4C), 121.5 (s, 4C), 260.2 (s, 2C). IR (KBr): 1516
(s), 1439 (m), 1381 (m), 1238 (s), 1022 (w), 855 (vs), 828 (vs),
748 (s), 681 (w), 656 (m), 619 (w), 492 (w), 475 (m), 459 (m)
cm-1. UV-vis (hexane, turquoise) (nm): 338 (sh), 738 (w). MS
(direct inlet, 70 eV, 115-120 °C, m/z (%)): 502 (M+, 4), 332
(100). Anal. Calcd for C26H44Si2Zr: C, 62.0; H, 8.8. Found:
C, 61.8; H, 8.8.
X-r a y Cr ysta l Str u ctu r e An a lyses of 2E, 2F , a n d 3B.
Turquoise crystal fragments of 2E,F and a pale green (nearly
colorless) crystal fragment of 3B were mounted into Linde-
mann glass capillaries under purified nitrogen in a glovebox
(mBraun labmaster 130) and sealed by wax. The X-ray
measurements were carried out on a Philips PW 1100 four-
circle diffractometer using graphite-monochromated Mo KR
radiation (λ 0.710 69 Å) at room temperature. Crystal data
were collected with a scan ratio 2θ/ω ) 1. The structures were
solved by Patterson and Fourier methods which revealed the
locations of the non-hydrogen atoms. Their coordinates and
anisotropic thermal parameters were refined at first using the
SHELX-76 program.19 The final refinements were performed
(C5Me5)2Zr [η2-C2(SiMe3)2] (2F ). The yield of turquoise
crystals was 0.80 g (75%); mp 241 °C. 1H NMR (C6D6): δ 0.19
(s, 18H, SiMe3), 1.76 (s, 30 H). 13C NMR (C6D6): δ 4.0 (q, 6C),
11.8 (q, 10C), 118.8 (s, 10C), 260.5 (s, 2C). IR (KBr): 1516
(s), 1443 (m), 1377 (m), 1240 (s), 1024 (w), 855 (vs), 829 (s),
750 (m), 679 (w), 658 (m), 619 (w), 457 (m) cm-1
. UV-vis
(hexane, turquoise) (nm): 360 (s), 725 (w, ꢀ ) 140 cm2 mmol-1).
MS (direct inlet, 70 eV, 115-120 °C, m/z (%)): 530 (M+, 2),
360 (100). Anal. Calcd for C28H48Si2Zr: C, 63.2; H 9.1.
Found: C, 63.0; H, 9.2.
2
by full-matrix least-squares methods on all unique Fo data
using the SHELXL-93 program.20 The hydrogen atom H(2)
in 3B, which was clearly located in a difference electron density
map, was refined isotropically. All other hydrogen atom
contributions were included using a riding model with C-H
distances free to refine. The structures of 2E,F and the
structures of the corresponding Ti analoguess(C5HMe4)2Ti-
[η2-C2(SiMe3)2]4i and (C5Me5)2Ti[η2-C2(SiMe3)2]4g,6aswere found
to be isomorphous. The PC ULM package19 was used for the
further calculations. Crystal data are summarized in Table
1. The atomic coordinates and thermal parameters for 2E,F ,
and 3B are given in the Supporting Information.
The MS spectra contain additional ions m/z 170, 155, 97,
73, and 70 in mutual abundances fitting to free BTMSA. The
dissociation of 2C-F probably occurs on the surface of the
ionization chamber before the ionization. The intensities of
M+ ions are therefore only tentative.
The EDX measurements of 2C-F were carried out in order
to clearly detect contents >2% of chemical elements with an
atomic number >6. In all cases only sharp KR signals of Si
and LR of Zr were visible.
Isola tion of a Rea r r a n ged Dim er of 2B, [(µ-η5:η1-
C5H3Me)(η5-C5H4Me)(η1-C2H{SiMe3}2)Zr (IV)]2 (3B). 1B
(0.32 g, 1 mmol), Mg (0.025 g, 1.05 mmol), BTMSA (0.6 mL,
2.7 mmol), and THF (20 mL) were charged into an ampule,
and this mixture was heated under stirring to 60 °C until all
the magnesium had dissolved (ca. 20 h). The resulting yellow-
brown solution was evaporated, and the residue was extracted
by hexane to give a reddish-brown solution. The remained
gray residue was further extracted until the point when only
(19) Bru¨ggemann, R.; Debaerdemaeker, T.; Mu¨ller, B.; Schmid, G.;
Thewalt, U. ULM- Programmsystem (1. J ahrestagung der Deutschen
Gesellschaft fu¨r Kristallografie, Mainz, J une 9-12, 1992; Abstracts,
p 33). This includes the SHELX-76 Program for Crystal Structure
Determination (G. M. Sheldrick, University of Cambridge, Cambridge,
England, 1976).
(20) Sheldrick, G. M. SHELXL-93, Program for Crystal Structure
Refinement, Univ. Go¨ttingen, Germany, 1993.

3756 Organometallics, Vol. 15, No. 17, 1996
Hiller et al.
Resu lts a n d Discu ssion
The reduction of the zirconocene dichlorides (C5H5-n
-
Men)2ZrCl2 (n ) 1-5) (1B-F ) in THF by 1.05 equiv of
magnesium in the presence of excess BTMSA afforded
turquoise solutions for n ) 4 and 5, a green solution for
n ) 3, and honey-yellow solutions for n ) 1 and 2. The
workup of these solutions consisting of the evaporation
of the solvent in vacuum and extraction of the residue
by hexane afforded turquoise crystalline compounds 2F
for n ) 5 and 2E for n ) 4 and a green amorphous solid
2D for n ) 3. The honey-yellow solution obtained from
1C also afforded a green amorphous solid 2C. All these
compounds were identified to be zirconocene-BTMSA
derivatives (C5H5-nMen)2Zr[η2-C2(SiMe3)2] (n ) 2-5)
(2C-F ) on the basis of X-ray crystal structure analy-
F igu r e 1. ORTEP drawing of 2E, with ellipsoids drawn
at the 30% probability level. Atoms Si′, C(1)′, C(9)′, etc.,
are related to atoms Si, C(1), C(9), etc., by the symmetry
1
operation -x, y, /2 - z.
1
ses of 2E,F and H and 13C NMR, IR, UV-vis, and MS
spectra (see below). The compounds 2D-F dissolve in
THF to give green and turquoise solutions whereas 2C
gives a honey-yellow solution. This yellow color is
typical of the THF adducts of the zirconocene-BTMSA
complexes. The 1A/Mg/BTMSA/THF system afforded
a yellow solution from which the orange crystalline
complex (C5H5)2Zr[η2-C2(SiMe3)2](THF) (2A‚THF) has
recently been isolated and its X-ray crystal structure
has been determined.10a The system with 1B also
yielded a dark yellow solution from which an ochre
crystalline solid separated after partial evaporation of
THF at room temperature. This product was not
further investigated. Its conversion to 3B after the total
loss of THF in vacuum, analogous to the conversion of
2A‚THF into 3A (see eq 3), leaves, however, no doubt
that the ochre solid was 2B‚THF. These results imply
that at room temperature the BTMSA complexes are
generally formed according to eq 4.
F igu r e 2. ORTEP drawing of 2F , with ellipsoids drawn
at the 30% probability level.
ture is very similar to that of 3A (see eq 3). Compound
3B appeared to be unstable as its hydrocarbon solutions
slowly turned green at room temperature. This circum-
stance precluded its further characterization. Com-
pound 3A was reported to consist of two isomers in C6D6
solution and to dissociate in THF solution into 2A‚
THF.10a
Descr ip tion of th e Cr ysta l Str u ctu r es of 2E,F .
The X-ray diffraction analysis revealed that both struc-
tures and the structures of the analogous titanium
complexes (C5HMe4)2Ti[η2-C2(SiMe3)2]4i (4E) and (C5-
Me5)2Ti[η2-C2(SiMe3)2]6a (4F ), respectively, are isomor-
phous. The molecular structure of 2E (Figure 1) is
symmetrical with respect to a crystallographic 2-fold
rotation axis which passes the Zr atom and bisects the
acetylenic C-C bond. The overall appearance of the
molecular structure of 2F (Figure 2) is very similar to
that of 2E. The important molecular parameters of
2E,F are listed in Table 2. The Zr-Cac bond distance
in 2E is by 0.016 Å shorter than that in 2F whereas
the acetylenic C-C bond lengths are practically the
same. A slightly longer Zr-CCp as well as (C-C)Cp bond
lengths in 2F compared to 2E have to be accounted for
by both the electronic and steric effects of permethyl
substitution. The Zr-CE vector is perpendicular to the
ring plane in 2F , and this is suprising because the steric
hindrance between the C5Me5 ligands is clearly dem-
onstrated by bending of the most exposed methyl carbon
atoms C(111) and C(141) as much as 0.3 Å away from
the ring planes farther away from the Zr atom. As a
rule in metallocene structural chemistry,21 the M-CCp
distance in 2E is shorter for the hydrogen-bearing
(4)
The green and turquoise THF solutions of 2D,E
turned yellow when cooled to -30 and -80 °C, respec-
tively, and the initial colors were restored after warm-
ing. No color changes occurred upon cooling of hexane
and toluene solutions, and hence, the above color change
apparently indicates the coordination of THF at low
temperature. Only the THF solution of 2F did not
change color even when cooled to -196 °C.
Among the THF-containing complexes only 2C‚THF
remained stable as 2C after the loss of THF. The
workup of the THF solution of 2B‚THF initiated by
pumping off all THF in vacuum afforded a white
crystalline compound as the sole product. Its X-ray
crystal structure analysis proved that it is a rearranged
dimer of 2B, [(µ-η5:η1-C5H3Me)(η5-C5H4Me)(η1-C2H-
{SiMe3}2)ZrIV]2 (3B) (see below), whose molecular struc-
(21) Howie, R. A.; McQuillan, G. P.; Thompson, D. W.; Lock, G. A.
J . Organomet. Chem. 1986, 303, 213-220.
(22) Al-Hassan, M. I.; Al-Najjar, I. M.; Al-Oraify, I. M. Magn.
Resonance Chem. 1989, 27, 1112-1116.

Zirconocene-Bis(trimethylsilyl)acetylene Complexes
Organometallics, Vol. 15, No. 17, 1996 3757
Ta ble 2. Selected Bon d Dista n ces a n d An gles
for 2E,F a
Ta ble 4. NMR (δ, p p m ), IR (cm -1), a n d UV-Vis (λ,
n m ) Da ta for th e BTMSA Liga n d in 2C-F
2F
Cpd
1H(Me)
13C(Me)a
13C(CtC)a
ν(CtC)b
λ
2E
2C
2D
2E
2F
0.03 s
0.14 s
0.14 s
0.20 s
2.1 q
2.8 q
3.4 q
4.0 q
258.2 s
260.0 s
260.2 s
260.5 s
1566
1535
1516
1516
775
745
738
725
(a) Bond Distances (Å)
Zr-C(1)
2.202(2)
2.230(3)
2.529(3)
1.402(4)
1.316(3)
1.857(2)
1.869(4)
1.875(4)
1.870(4)
2.221(2)
2.247(3)
2.547(3)
1.411(4)
1.320(3)
1.858(2)
1.871(4)
1.879(4)
1.882(4)
2.216(2)
2.253(3)
2.553(3)
1.411(4)
Zr-CE(Cp ring)
Zr-C(Cp ring)(av)
C -C(Cp ring)(av)
C(1)-C(1′), C(1)-C(2), resp
Si-C(1)
a
Chemical shifts for noncoordinated BTMSA (C6D6, 23 °C):
13C(Me) δ 0.2 q, 13C(CtC) δ 113.8 s.22 The band of the highest
wavenumber in the relevant region.
b
1.859(2)
1.872(4)
1.874(4)
1.876(4)
Si-C(2)
Si-C(3)
mutual orientation of the cyclopentadienyl rings and the
placement of the hydrogen atoms of the C5HMe4 rings
in the hinge positions are the common features of these
Zr and Ti compounds.4i,6a
Si-C(4)
(b) Bond Angles (deg)
134.5(1)
CE-Zr-CE′
C(1)-Zr-C(1′)
Zr-C(1)-C(1′)
Si-C(1)-C(1′)
φb
139.0(1)
34.6(1)
72.5(1)
135.1(2)
41.0
34.8(1)
72.6(1)
135.4(2)
49.5
72.9(1)
135.9(2)
Sp ectr oscop ic Da ta for 2C-F . All the spectro-
scopic methods brought evidence of the strong coordina-
tion of BTMSA to the zirconocene moieties and con-
firmed that the molecular structures of all the compounds
in hydrocarbon solutions do not differ from those found
for 2E,F in the solid state. The EI-MS spectra regis-
tered the molecular ions in the range of intensities
2-8% and showed that the elimination of the BTMSA
molecule is the main fragmentation channel. The
fragmentation pattern typical of the free BTMSA mol-
ecule found in all the MS spectra, however, indicated
that a thermal dissociation occurred on walls of the
ionization chamber. The intensities of the molecular
ions are inversely proportional to the temperature of
evaporation and, hence, may reflect the degree of
thermal dissociation and not the strength of the coor-
dination bond. The sharp NMR lines and the absence
of EPR signals agree with the expected diamagnetism
of the Zr(II) compounds. 1H and 13C NMR spectra
resolved individual hydrogen and carbon atoms of the
methylated cyclopentadienyl ligands and gave informa-
tion on chemical shifts of the coordinated BTMSA
molecule. Infrared spectra represent fingerprints of the
cyclopentadienyl ligands (practically identical with the
spectra of the zirconocene dichlorides), strong absorp-
tions of the SiMe3 groups at 828-855 cm-1 and at 1240
cm-1, and a strongly lowered ν(CtC) vibration. The
data pertinent to the BTMSA ligand are collected in
Table 4.
a
One column of data is appropriate to 2E because of the
symmetry. The left column for 2F is appropriate to atoms with
lower numbers. Dihedral angle between least-squares planes of
b
the cyclopentadienyl rings.
Ta ble 3. Com p a r ison of Ma in Str u ctu r a l
P a r a m eter s of 2E,F w ith
(C5HMe4)2Ti[η2-C2(SiMe3)2] (4E) a n d
(C5Me5)2Ti[η2-C2(SiMe3)2] (4F )a
2E
4E
2F
4F
b
Zr-Cac
2.202
2.230
1.402
1.316
1.857
134.5
135.4
49.5
2.106
2.092
1.403
1.303
1.853
134.9
135.9
50.0
2.219
2.250
1.411
1.320
1.859
139.0
135.5
41.0
2.124
2.114
1.414
1.309
1.856
138.6
135.8
41.1
Zr-CEb
C-C(Cp ring)
Cac-Cac
b
Si-Cac
CE-Zr-CE
Si-C(1)-C(1′)b
φc
a
Structural data for 4E are taken from ref 4i, and those for
4F , from ref 6a. The accuracy of the diffraction measurements of
b
all compounds was very similar. Average values are taken for
2F and 4F . c Dihedral angle between least-squares planes of the
cyclopentadienyl rings.
carbon atom (Zr-C(5) 2.509(3) Å) than for those bearing
Me groups (e.g., Zr-C(7) 2.570(3) Å). This effect
together with a smaller CE-Zr-CE angle in 2E (134.5°)
compared to that in 2F (139.0°) brings about that the
angle between planes of C5 rings in 2E is by 8.5° larger
(φ ) 49.5°) than in 2F (φ ) 41.0°). As a consequence,
the metallocene skeleton in 2E offers a larger coordina-
tion space at the Zr atom in spite of the circumstance
that the average Zr-CCp distance is by 0.02 Å shorter
than in 2F . Both compounds differ from the analogous
titanium compounds 4E,F mainly in the parameters
controlled by a larger covalent radius and a lower
electronegativity of the Zr atom (1.45 Å and 1.4 against
1.32 Å and 1.5 for Ti). The comparison of most impor-
tant structural parameters of these Zr and Ti com-
pounds is carried out in Table 3. Of these, the Cac-Cac
bonds which are longer in 2E,F by ca. 0.01 Å than in
4E,F reflect a stronger coordination of BTMSA in the
former compounds, as also follows from the comparison
of spectroscopic parameters (see below). The bending
of the acetylene molecule is the same in all mentioned
compounds with the Si-C-C angle close to 135°. Apart
from the fact that Zr-C bonds are by ca. 0.1 Å longer
than the Ti-C bonds, the bent metallocene skeletons
show the same CE-M-CE angles and the same dihe-
dral angles φ between the cyclopentadienyl rings in
pairs of C5HMe4 and C5Me5 compounds. The staggered
All the NMR data show the dependence on the
number of Me groups in compounds 2C-F . The incre-
ments per one Me group, however, vary widely. The
comparison of these data with those for the analogous
Ti complexes shows that shifts of δ have the same
tendency although the absolute values as well as their
differences differ ((C5H5-nMen)2Ti[η2-C2(SiMe3)2], for n
) 2-5: 1H(Me) δ -0.23 to +0.02, s; 13C(Me) δ 1.5-4.2,
q; 13C(CtC) δ 245.5-248.5, s).4i Among the NMR data,
most relevant to the strength of the metal-to-BTMSA
coordination is the downfield shift of the acetylenic
carbon atoms, and this shows that the strength of the
coordination bond increases from 2C to 2F and that the
zirconocenes form even stronger complexes than the
titanocenes. This is independently confirmed by the
wavenumbers of the ν(CtC) vibration. This vibration
occurs in 2C-F at wavenumbers which are lower by
about 100 cm-1 with respect to the corresponding
titanocene compounds, and the overall shift from the
wavenumber of BTMSA (2107 cm-1 23 of 540-590 cm-1
is the largest so far reported. It has to be mentioned
that the chemical shifts found in 2C-F , as well as in
)

3758 Organometallics, Vol. 15, No. 17, 1996
Hiller et al.
Ta ble 5. Selected Bon d Dista n ces a n d An gles
for 3B
(a) Bond Distances (Å)
Zr-C(1)
2.256(3)
2.601(4)
2.486(5)
2.558(4)
2.481(3)
2.359(3)
2.509(4)
2.197(4)
2.359(3)
1.859(3)
1.874(4)
1.384(7)
1.413(5)
Zr-C(2)
2.557(3)
2.542(5)
2.495(5)
2.535(4)
2.529(3)
2.468(3)
2.247(5)
2.150(37)
1.324(5)
0.933(37)
1.864(5)
1.861(5)
4.075(1)
Zr-C(9)
Zr-C(10)
Zr-C(12)
Zr-C(14)
Zr-C(16)
Zr-C(17)
Zr-CE(1)
Zr-H(2)
Zr-C(11)
Zr-C(13)
Zr-C(15)
Zr-C(16′)
Zr-C(18)
Zr-CE(2)
Zr′-C(16)
Si(1)-C(1)
Si(2)-C(2)
C-C(9-13)av
C-C(14-18)av
C(1)-C(2)
C(2)-H(2)
Si(1)-C(Me)av
Si(2)-C(Me)av
Zr-Zr′
(b) Bond Angles (deg)
C(1)-Zr-C(2)
C(1)-Zr-H(2)
C(1)-Zr-CE(1)
C(1)-Zr-CE(2)
CE(1)-Zr-H(2)
CE(1)-Zr-CE(2)
Zr-C(1)-C(2)
Zr-C(2)-C(1)
Zr-C(2)-H(2)
31.1(1)
51.7(10)
102.0(1)
103.9(1)
109.7(10)
134.1(1)
87.1(2)
C(1)-Zr-C(16′)
120.1(1)
68.7(10)
102.2(1)
96.6(1)
116.2(10)
115.7(23)
132.0(3)
138.9(3)
105.2(23)
C(16′)-Zr-H(2)
C(16′)-Zr-CE(1)
C(16′)-Zr-CE(2)
CE(2)-Zr-H(2)
C(1)-C(2)-H(2)
Si(1)-C(1)-C(2)
Si(2)-C(2)-C(1)
Si(2)-C(2)-H(2)
F igu r e 3. PLUTON25 drawing of the molecular structure
of 3B. Atoms Zr′, Si(1)′, C(16)′, etc., are related to atoms
Zr, Si(1), C(16), etc., by the symmetry operation -x, -y,
-z.
61.8(2)
54.3(23)
the titanocene compounds, fall into the range of values
(190-270 ppm) which are assumed to be typical for
alkynes acting as four-electron donors in metal com-
plexes.4j,24 The donation of four π-electrons to the Zr-
(II) ion has to be, however, accompanied by an extensive
back-donation of d2 electrons into the LUMO of BTMSA.
A widely used description of the compounds as metal-
lacyclopropene derivatives accounts for their reactivity
in various coupling reactions9a and fits to some struc-
tural features like the C-C bond distance close to the
CdC bond length and the bending of the SiMe3 substit-
uents from the C-C vector (Table 2); however, the
presence of a zirconocene Zr(IV) compound is hardly
compatible with the color of the compounds. The sole
absorption band in the region 440-2000 nm occurring
close to 750 nm (Table 4) does not fit to the presence of
either a Zr(IV) or Zr(II) ion. We suggest that it arises
from a CT π* f d transition in the above mentioned
tentative model with the both d2 electrons residing in a
low-energy nonbonding orbital of the coordinated BT-
MSA. A similar absorption band was also observed in
the titanocene analogues with λmax in the range 920-
1060 nm.4i The molar extinction coefficients 100-200
cm2 mmol-1 for these bands may correspond to their
suggested nature.
of 3B is very similar to the structure of the analogous
compound 3A obtained from 2A‚THF after the loss of
THF.10a Most of the distances and angles are the same
as in 3A within the accuracy of measurement. The most
interesting feature of both these compounds is the
coordination mode of the ethenyl ligand where slight
differences between 3A and 3B are discernible. The
Zr-C(1) σ-bond is the shortest Zr-C bond in the
molecule but the Zr-C(2) distance falls into the range
of Zr-CCp π-bond lengths. The hydrogen atom H(2) at
this carbon atom is inclined toward the Zr atom to attain
the distance of 2.15 Å. In comparison with the struc-
ture of 3A the Zr-C(1) distance is by 0.01 Å longer and
the Zr-C(2) distance by 0.01 Å shorter. The Zr-H(2)-
C(2) angle is by 9.6° larger than that in 3A; however,
the Zr-H(2) distance is virtually the same. The agostic
interaction between the H(2) and Zr atoms was assumed
on the basis of this distance and NMR arguments drawn
from the behavior of the C(2)-H(2) fragment.10a
A
larger difference between the Si(2)-C(2)-C(1) (138.9-
(3)°) and the Si(1)-C(1)-C(2) (132.0(3)°) angles is also
at variance with the values of 135.3 and 133.3° found
in 3A.10a
The methyl substituents in the zirconocene moieties
are orientated as to minimize the steric strain arising
from their presence. The Zr-CE(2) distance is by 0.05
Å shorter than the Zr-CE(1) distance in spite of a
remarkable distortion of the former ring. The angle
C(15)-C(16)-C(17) at the bridging carbon atom amounts
to only 103.0(3)o whereas the most oblique angle in the
CE(1) ring is the C(10)-C(9)-C(13) angle, equal to
106.7(4)°, at the carbon atom bearing the Me group. The
bridging bond Zr′-C(16) of 2.359(3) Å length is by 0.1
Å longer than the Zr-C(1) bond but distinctly shorter
than the coordination bonds to sp2 carbon atoms of the
C5H4Me rings and to C(2) of the ethenyl group.
Descr ip t ion of t h e Cr yst a l St r u ct u r e of [(µ-η5:
η1-C5H 3Me )(η5-C5H 4Me )(η1-C2H {SiMe 3}2)Zr (IV)]2
(3B). The X-ray diffraction analysis of 3B revealed that
it is a centrosymmetric dimer bis[µ-(η5:η1-3-methylcy-
clopentadiendiyl)(η5-methylcyclopentadienyl)(η1-1,2-bis-
(trimethylsilyl)ethenyl)zirconium(IV)] linked via bridg-
ing methylcyclopentadienyl ligands. One hydrogen
atom originating from each bridging ligand is appar-
ently transferred to an η2-coordinated BTMSA to give
a η1-1,2-bis(trimethylsilyl)ethenyl ligand. The drawing
of 3B with its atom numbering scheme is shown in
Figure 3. Selected interatomic distances and valence
angles are listed in Table 5. The molecular structure
Ou tlook . The stable, well-characterized methyl-
substituted zirconocene-BTMSA complexes may be
used as starting materials for the coupling reactions
with aldehydes, ketones, olefins, nitriles and acety-
lenes.26 Compared to the zirconocene-alkyne deriva-
tives so far used the stabilization by the unpleasant and
(23) Kriegsmann, H.; Beyer, H. Z. Anorg. Allg. Chem. 1961, 311,
180-185.
(24) Templeton, J . L. Adv. Organomet. Chem. 1989, 29, 1-100.
(25) Spek, A. L. PLUTON Molecular Graphics Program, Utrecht
University, Utrecht, The Netherlands, 1995.

Zirconocene-Bis(trimethylsilyl)acetylene Complexes
Organometallics, Vol. 15, No. 17, 1996 3759
expensive PMe3 can be avoided and the regioselectivity
in the above mentioned coupling reactions can be
increased by the discrimination of the coordination
space at the zirconium center. A recent study of the
regioselectivity and diastereoselectivity of the insertion
of aldehydes into the zirconocene-alkyne complexes
afforded rather poor achievements.27 The use of the (C5-
Me5)2Zr and (C5HMe4)2Zr-BTMSA complexes gives new
prospects to this type of reactions, where the selectivity
is controlled by the size of the available coordination
space. A dramatic change in the reactivity has been
recently found in the titanocene series of the BTMSA
complexes, where (C5Me5)2Ti[η2-C2(SiMe3)2] has been
found to be a superior catalyst for the selective linear
head-to-tail dimerization of 1-alkynes whereas the (C5-
HMe4)2Ti[η2-C2(SiMe3)2] complex was practically inac-
tive.28 In addition, the kinetics of coupling reactions of
the substrates bearing a polar substituent can be
influenced by the Lewis acidity of the zirconium atom
which is controlled by the methyl substituents at the
cyclopentadienyl ligands. This has been demonstrated
by a decrease in affinity to THF of compounds 2C-F
with the increasing number of methyl substituents. The
investigation of the catalytic activity of the new zir-
conocene-BTMSA complexes and its comparison to that
of the titanium analogues will be an emphasis in our
further research work.
Ack n ow led gm en t. This work was supported by the
Grant Agency of the Academy of Sciences of the Czech
Republic (Grant No. 440403), by the Fonds der Che-
mischen Industrie, and by the Volkswagen Stiftung.
Chemetall, GmbH, Frankfurt a.M., FRG, is acknowl-
edged for a generous gift of n-butyllithium. We thank
Mrs. G. Do¨rfner for recording the EDX spectra.
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
data, atomic coordinates, isotropic and anisotropic thermal
parameters, bond distances, valence angles, least-squares
planes and atomic deviations therefrom, and important inter-
molecular contacts and figures giving views of the unit cell
for 2E,F and 3B (33 pages). Ordering information is given
on any current masthead page.
(26) Buchwald, S. L.; Watson, B. T.; Lum, R. T.; Nugent, W. A. J .
Am. Chem. Soc. 1987, 109, 7137-7141.
(27) Maier, M. E.; Oost, T. J . Organomet. Chem. 1995, 505, 95-
107.
(28) Varga, V.; Petrusova´, L.; Cˇ ejka, J .; Hanusˇ, V.; Mach, K. J .
Organomet. Chem. 1996, 509, 235-240.
OM960184J