3066 Organometallics, Vol. 16, No. 13, 1997
Spencer et al.
some free dmpe and traces of Ti(C4H6)2(dmpe). 31P{1H} NMR
(toluene-d8, 0 °C): δ 26.0 (s).
crystal movement during the collection of the third shell; full
intensity was not recovered so that data for the last part of
shell 3 (259 reflections total) were corrected by a scale factor
of 1.191 59. Standard peak search and indexing procedures
gave rough cell dimensions, and the diffraction symmetry was
confirmed by inspection of the axial photographs. Least-
squares refinement using 25 reflections yielded the cell dimen-
sions given in Table 1.
Dim eth yl(η4-tr a n s,tr a n s-1,4-d ip h en yl-1,3-bu ta d ien e)-
[1,2-bis(d im eth ylp h osp h in o)eth a n e]tita n iu m (II), 2. To a
mixture of TiMe2(dmpe)2 (0.39 g, 1.0 mmol) and 1,4-diphenyl-
1,3-butadiene (0.26 g, 1.0 mmol) at -40 °C was added diethyl
ether (30 mL). After the solution had been stirred at 0 °C for
4 h, the solution color was brown-green and a brown precipi-
tate had formed. The solvent was removed at 0 °C under
vacuum. While the temperature of the flask was kept at 0
°C, the resulting solid was washed once with pentane (50 mL)
and then was extracted with diethyl ether (50 mL). The extract
was filtered, concentrated to ca. 10 mL, and cooled to -20 °C
to afford dichroic red-green crystals. Yield: 0.10 g (40%). Anal.
Calcd: C, 66.4; H, 8.35; Ti, 11.0. Found: C, 65.1; H, 8.35; Ti,
11.3. Mp: 94 °C (dec). 31P{1H} NMR (toluene-d8, 0 °C): δ
25.5 (br s). 31P{1H} NMR (toluene-d8, -110 °C): δ 20.5 (d,
Data were collected in one quadrant of reciprocal space ((h,
-k, +l) by using the measurement parameters listed in Table
1. Systematic absences for h0l (h + l * 2n) and 0k0 (k * 2n)
were consistent only with the space group P21/n. [For 4, the
monoclinic unit cell was consistent with the space groups P1
and P1h. The average values of the normalized structure
factors suggested the choice P1h, which was confirmed by
successful refinement of the proposed model.] The measured
intensities were reduced to structure factor amplitudes and
their esd’s by correction for background, scan speed, Lorentz
and polarization effects. Crystal decay corrections were ap-
plied (see above), and absorption corrections were applied, the
maximum and minimum transmission factors being 0.970 and
0.868. [For 4, no decay correction was needed, but an
absorption correction was applied with maximum and mini-
mum transmission factors of 0.901 and 0.832.] Systematically
absent reflections were deleted, and symmetry equivalent
reflections were averaged to yield the set of unique data. Only
those data with I > 2.58σ(I) were used in the least-squares
refinement.
The structure was solved by direct methods (SHELX-86);
correct positions for all non-hydrogen atoms were deduced from
an E-map. Subsequent least-squares refinement and differ-
ence Fourier calculations revealed the positions of the hydro-
gen atoms. All remaining hydrogen atoms were included as
fixed contributors in idealized positions. [For 4, the correct
positions for the titanium and phosphorus atoms were deduced
from an E-map. Subsequent least-squares refinement and
difference Fourier calculations revealed positions for all the
remaining non-hydrogen and butadiene hydrogen atoms. The
hydrogen atoms on the phosphine ligand did not surface and
were fixed in idealized positions with C-H ) 0.96 Å.] The
quantity minimized by the least-squares program was ∑w(|Fo|
- |Fc|)2, where w ) 1.46/(σ(Fo)2 + pFo2). [For 4, w ) 1.20/(σ-
(Fo)2 + pFo2).] The analytical approximations to the scattering
factors were used, and all structure factors were corrected for
both real and imaginary components of anomalous dispersion.
In the final cycle of least-squares refinement, anisotropic
thermal coefficients were refined for the non-hydrogen atoms
and a common isotropic thermal parameter was varied for the
hydrogen atoms. No correction due to extinction was neces-
sary. [For 4, anisotropic thermal coefficients were refined for
the non-hydrogen atoms, and a common group isotropic
thermal parameter was refined for the hydrogen atoms. An
isotropic extinction parameter was also refined to a final value
of 7(2) × 10-8.] Successful convergence was indicated by the
maximum shift/error of 0.062 [0.002] for the last cycle. Final
refinement parameters are given in Table 1. The final
difference Fourier map had no significant features. A final
analysis of variance between observed and calculated structure
factors showed no systematic errors.
2
2J PP ) 36 Hz), 32.0 (d, J PP ) 36 Hz). IR (cm-1): 3060 (w),
3020 (w), 1935 (w), 1581 (s), 1490 (s), 1455 (m), 1445 (m), 1415
(m), 1375 (m), 1320 (m), 1395 (m), 1200 (s), 1175 (m), 1150
(w), 1125 (w), 1070 (w), 1020 (w), 990 (w), 945 (m), 935 (m),
930 (m), 885 (m), 825 (w), 760 (m), 745 (m), 730 (m), 700 (s),
645 (w), 520 (m), 468 (m), 428 (m).
Dim eth yl(η3,η1-tr a n s,tr a n s-octa -2,6-d ien e-1,8-d iyl)[1,2-
bis(d im eth ylp h osp h in o)eth a n e]tita n iu m (IV), 3. To a so-
lution of TiMe2(dmpe)2 (0.30 g, 0.89 mmol) in pentane (10 mL)
at -72 °C was added excess 1,3-butadiene (0.10 L, 4.6 mmol)
from a calibrated gas manifold. The flask was filled with
argon, sealed, and allowed to stand for 24 h at -20 °C. Over
this period, the solution first became green-blue and then
brown. The solvent was removed under vacuum at -72 °C to
afford an orange solid.
If the solvent is removed at -20 °C instead of at -72 °C,
some of the product (about 20% depending on the exact
conditions) is converted into the titanium(II) butadiene com-
plex TiMe2(η4-C4H6)(dmpe).
Bis(η4-bu ta d ien e)[1,2-bis(d im eth ylp h osp h in o)eth a n e]-
tita n iu m (0), 4. A solution of TiMe2(dmpe)2 (0.15 g, 0.40
mmol) in diethyl ether (30 mL) was cooled to -72 °C, and 1,3-
butadiene (ca. 0.15 L, 6.5 mmol) was condensed in. Triethyl-
aluminum (0.14 g, 1.2 mmol) was added, and then the solution
was warmed to 25 °C over 4 h; during this period, the solution
color turned green and then blue. The solvent was removed
under vacuum, and the resulting solid was extracted with
pentane (30 mL). This filtered extract was concentrated to
ca. 5 mL and cooled to -20 °C to afford crystals of the product.
Yield: 0.11 g (92%). 31P{1H} NMR (toluene-d8, 20 °C): δ 38.2
(s).
Ca ta lytic Dim er iza tion of Bu ta d ien e to 4-Vin ylcyclo-
h exen e. A solution of TiMe2(dmpe)2 (0.07 g, 0.18 mmol) in
toluene-d8 (1.0 mL) in a 5 mm o.d. NMR tube was cooled to
-78 °C, and butadiene (ca. 0.1 L, 4.5 mmol) was condensed
in. The NMR tube was flame sealed. The reaction was
monitored by 1H, 13C, and 31P NMR spectroscopy; the 13C NMR
spectra were most useful for following the catalysis. Over the
course of 24 h at 25 °C, the 13C NMR peaks due to butadiene
at δ 137.0 and 117.6 diminished and new peaks at δ 143.9,
126.8, 126.1, 112.3, 38.0, 31.5, 28.6, and 25.2 grew in. All of
these peaks are assignable to 4-vinylcyclohexene; the only
other peak detectible in the spectrum was due to dmpe.
A
similar experiment in the absence of TiMe2(dmpe)2 showed
that no detectible dimerization occurred over 24 h.
Ap p en d ix
Cr ysta llogr a p h ic Stu d ies.62 Single crystals of TiMe2(η4-
1,4-C4H4Ph2)(dmpe), 2, grown from pentane/diethyl ether, were
mounted on glass fibers with Paratone-N oil (Exxon) and
immediately cooled to -75 °C in a cold nitrogen gas stream
on the diffractometer. [Single crystals of Ti(η4-C4H6)2(dmpe),
4, grown from pentane, were treated similarly. Subsequent
comments in brackets will refer to compound 4.] The overall
diffraction pattern was weak. The nitrogen flow failed, causing
Does th e Tr igon a l-Tw ist Mech a n ism Op er a te in
Oth er Gr ou p 4 Bu ta d ien e Com p lexes? Fryzuk has
described the variable-temperature NMR spectra of
several zirconium and hafnium complexes of stoichiom-
etry MX(C4H6)[N(SiMe2CH2PR2)2], where X was either
Cl or Ph and the R groups on phosphorus were either
Me or i-Pr.28 X-ray diffraction studies showed that the
N(SiMe2CH2PR2)2 ligand occupies a meridional config-
uration in these complexes. At low temperatures, there
are two environments for the phosphorus nuclei and
(62) For details of the crystallographic procedures and programs
used, see: J ensen, J . A.; Wilson, S. R.; Girolami, G. S. J . Am. Chem.
Soc. 1988, 110, 4977-4982.
Spencer, Michael D.
