Mono- and bi-dentate Group 6-coordinated and titanium-containing isocyanide ligands prepared from benzoxazole

Article abstract of DOI:10.1039/b200859a

Reaction of lithiated benzoxazole with Group 6 carbonyl complexes and subsequently with Cp₂TiCl₂ affords bimetallic systems in which the titanium is O-bonded and the Group 6 metal isocyanide-coordinated. Depending on starting materia

Full text of DOI:10.1039/b200859a

View Article Online / Journal Homepage / Table of Contents for this issue
Mono- and bi-dentate Group 6-coordinated and titanium-
containing isocyanide ligands prepared from benzoxazole†
Jin An, Lizette van Niekerk, Catharine Esterhuysen and Helgard G. Raubenheimer*
Department of Chemistry, University of Stellenbosch, Private Bag X1, 7602 Matieland,
South Africa. E-mail: hgr@sun.ac.za
Received 23rd January 2002, Accepted 6th March 2002
First published as an Advance Article on the web 1st May 2002
Reaction of lithiated benzoxazole with Group 6 carbonyl complexes and subsequently with Cp2TiCl2 affords
bimetallic systems in which the titanium is O-bonded and the Group 6 metal isocyanide-coordinated. Depending
on starting material and reaction conditions the cyclopentadienyl titanium complex may act as either a mono- or
bi-dentate ligand. Crystal and molecular structures of [(CO)5Cr{CN(C6H4-o)O}Ti(Cl)Cp2] (1) and [(CO)4Cr-
{CN(C6H4-o)O}2TiCp2] (2), are reported. The heterometallacyclic ring in 2 contains 12 atoms.
titanium-containing isocyanide ligands coordinated to Group 6
carbonyl complexes.
Introduction
Anionic Fischer-type carbene ligands, prepared by the standard
addition of organolithium compounds to metal carbonyls, act
as monodentate ligands towards transition metals like titanium
and zirconium.1 We were recently able to show that such
compounds, with certain heteroatom-containing organo-
groups, also coordinate in a bidentate fashion.2 In a preliminary
attempt to utilise an anionic carbene complex, [(CO) Cr᎐
Results and discussion
Synthesis
Deprotonation of benzoxazole with butyllithium at Ϫ78 ЊC,
substitutive addition to Cr(CO)5(THF) at 0 ЊC, and transmetal-
lation with Cp2TiCl2 afforded the bimetallic compounds 1 and
2 (Scheme 2). The yield of the disubstituted carbonyl (and thus
᎐
5
C(O)C᎐NC H O-o]Ϫ, as a bidentate ligand towards Cp TiCl ,
᎐
6
4
2
2
Cr(CO)6 was treated with lithiated benzoxazole and the product
mixture reacted with titanocene dichloride. The penta- and
tetra-carbonyl chromium isocyanide complexes 1 and 2 (vide
infra) formed in low yields, indicating that the tautomeric
equilibrium in Scheme 13 cannot be reversed to afford nucleo-
Scheme 1
philic CO attack. Di- and even tri-dentate isocyanide con-
taining ligands have been prepared and studied in the groups
of Angelici,4 Hahn5 and others.6 Chelate formation is only
possible if twelve or larger membered rings are formed. Usually,
complex formation involves the substitution of labile ligands
such as of COD (COD = cyclooctadiene), NOR (NOR =
norbornadiene) or η6-C7H8 respectively, in [Rh(COD)Cl]2,4
[M(CO) (NOR)] (M᎐Cr, Mo),5 [M(CO) (η6-C H )] (M = Cr,
᎐
4
3
7
8
Mo, W)5 or by occupying the free coordination position after
reaction of [M(CO)5I][Et4N] (M = Cr, W) and Agϩ ions.4 All
ligands are similar in that they consist of isocyanide units
connected by nonmetallic atoms or groups, thus forming
nonmetallic di- and tri-dentate isocyanide ligands. The chem-
istry of multidentate isocyanide ligands has attracted special
attention, due to their potential use in nuclear medicine for the
complexation of 99mTc.7
We describe here labile ligand substitution in M(CO)5(THF)
and M(CO)4(NOR) (M = Cr, Mo or W) with lithiated benz-
oxazole in isocyanide isomeric form and subsequent
O-coordination of Cp2TiCl2 to furnish mono- and bi-dentate
Scheme 2
disubstituted metallocene derivative as the only product) was
increased from 30 to 49% by replacing Cr(CO)5(THF) with
Cr(CO)4(NOR). Molybdenum (3 and 4) and tungsten (5 and 6)
analogues were prepared similarly. We have previously also
observed disubstitution despite the presence of only one labile
ligand in Group 6 metal complexes, with ligands containing
exocyclic S- and endocyclic N- and S-donor atoms.8
† Electronic supplementary information (ESI) available: rotatable 3-D
molecular structure and packing diagrams for 1 and 2 in CHIME
format. See http://www.rsc.org/suppdata/dt/b2/b200859a/
It is significant that the lithiated oxazole prefers C-isocyanide
coordination to M(CO)5 (M = Cr, Mo, W) whereas CN–C6H4–
2386
J. Chem. Soc., Dalton Trans., 2002, 2386–2389
This journal is © The Royal Society of Chemistry 2002
DOI: 10.1039/b200859a

View Article Online
OH-o readily and quantitatively converts into the amino-
carbene complexes [(CO)5MCNHC6H4O-o].9 The oxophilic
titanium complex, however, would drive the equilibrium
completely away from a carbene form towards the isocyanide
containing isomer. The ring-opened isomers in Scheme 1 have
not previously been successfully trapped by O-coordination
11
to metal compounds. Both Me3SnCl10 and ZnCl2 afford
C-coordinated azolyls. Even addition of only Cp2TiCl2 has not
yet provided an exception since, in our efforts, no single
products could be separated (probably due to isocyanide
coordination).
Spectroscopic characterisation of complexes 1 to 6
The infrared spectra (CH2Cl2 solutions) of the two classes of
compounds were normal in the ν(CO) region (see Experimental
section). The CN frequencies of the monodentate isocyanide
complexes 1, 3 and 5 appear as one peak between 2142 and
2145 cmϪ1 for the pentacarbonyl complexes and increase from
chromium to tungsten. The corresponding vibrations in the
tetracarbonyls are more constant at 2146–2150 cmϪ1 and at
2110 cmϪ1.
Molecular ions for all the new compounds were observed in
the 70 eV mass spectra. This was followed by consecutive loss
of carbonyl ligands as indicated in the Experimental section.
The NMR resonances are in general normal and the
chemical shifts for carbonyl ligands agree with previous studies.
It is significant that the doublet of doublets for H6 (Scheme 2)
appearing at ca. δ 7.0 for compounds 1, 3 and 5 is shifted
significantly upfield — anisotropic effects of the Cp-rings — in
the disubstituted carbonyl complexes 2 (δ 6.37) and 4 (δ 6.39)
but less so in complex 6 (δ 6.80) that contains the large W
central atom.
Fig. 2 Molecular structure of complex 2 showing the numbering
scheme; for clarity one disordered Cp ring has been omitted.
Displacement ellipsoids are plotted at the 50% probability level.
Table 1 Selected bond lengths (Å) and angles (Њ) for complexes 1 and 2
1
2
Ti–O(5)
Ti–O(6)
Ti–Cl(1)
Cr–C(5)
Cr–C(6)
1.9015(15)
1.8883(17)
1.9046(14)
2.3766(7)
1.981(2)
1.993(3)
1.995(3)
Cl–Ti–O(6)
O(5)–Ti–O(6)
C(5)–Cr–C(6)
95.71(5)
95.33(7)
86.90(9)
86.76(10)
complexes 1 and 2. C–Cr–C angles vary between 86.8(1) and
92.7(1)Њ for complex 1, while for complex 2 they vary between
86.5(1) and 93.3(1)Њ, with a chelate “bite angle” of 86.90(9)Њ.
The bond angles around the Ti are also very similar for com-
plexes 1 and 2, with Cl–Ti–O(6) (1) and O(5)–Ti–O(6) (2) angles
of 95.71(5) and 95.33(7)Њ respectively (see Table 1). The Cp
rings are similarly oriented at angles of 23.71(10) and 28.42Њ
with respect to the O(6)–Ti–Cl plane in complex 1 and 26.6(7)
and 26.7(2)Њ with respect to the O(5)–Ti–O(6) plane in complex
2. This is a common characteristic: a search of the Cambridge
Structural Database12 shows that in 95% of comparable com-
plexes (2389 structures containing any atom coordinated to two
η5-Cp rings and any two other atoms were found), the Cp rings
are orientated at angles of between 16 and 37Њ. However, the
orientation of the TiCp2 moiety as a whole is the most affected
by the addition of the second isocyanide donor group in com-
plex 2, as the severe twisting of the TiCp2 unit toward the ligand
plane observed in complex 1 is reduced in complex 2. In add-
ition, the Ti lies significantly above the isocyanide ligand plane
(1.067(2) Å) in complex 1, whereas it only elevates 0.073(1) Å
above the best plane through the bidentate ligand (maximum
deviation of 0.200(2) Å for C(5) in complex 2). The opposite is
observed for Cr, where in complex 1 it lies only 0.088(2) Å above
the ligand plane, while in complex 2 the distance is 0.419(2) Å.
The packing in complex 1 is directed by weak C–H ؒ ؒ ؒ O13
interactions between carbonyl oxygens and Cp or phenyl
hydrogens (H atoms are placed in calculated positions, so
H-bonds are given in terms of C ؒ ؒ ؒ O and C ؒ ؒ ؒ Cl distances
— C(21) ؒ ؒ ؒ O(3) = 3.362(3) Å, C(21)–H(21) ؒ ؒ ؒ O(3) = 159.5Њ;
C(19) ؒ ؒ ؒ O(5) = 3.463(4) Å, C(19)–H(19) ؒ ؒ ؒ O(5) = 153.5Њ)
and C–H ؒ ؒ ؒ Cl interactions (C(17) ؒ ؒ ؒ Cl = 3.585(3) Å,
C(17)–H(17) ؒ ؒ ؒ Cl = 143.1Њ), resulting in an interlinking
network of molecules with the TiCp2 moieties directed towards
each other in layers. These H-bonding distances compare well
with literature values, with separations up to 3.59 Å ascribed
to C–H ؒ ؒ ؒ O bonding14 and distances up to 3.74 Å to
C–H ؒ ؒ ؒ Cl bonding.15 Similar weak C–H ؒ ؒ ؒ O interactions
Crystal and molecular structures of 1 and 2
The molecular structures of complexes 1 (Fig. 1) and 2 (Fig. 2)
Fig. 1 Molecular structure of complex 1 showing the numbering
scheme. Displacement ellipsoids are plotted at the 50% probability
level.
confirm that complex 1 contains only one isocyanide group
linking the Cr and Ti moieties, whereas there are two such
groups in complex 2 (the second group replacing a Cl ligand
in complex 1), resulting in the formation of a 12-membered
chelate ring. In both instances the ligands are planar (maximum
deviations from planarity: in complex 1: 0.037(2) Å for C(9); in
complex 2: 0.130(1) Å for C(5) and 0.104(2) Å for C(6) in the
respective isocyanide groups). In complex 2 the two isocyanide
ligands are nearly co-planar, with the angle between the two
planes being 5.61(9)Њ.
Surprisingly the formation of the chelate ring has no signifi-
cant effect on the bond lengths and angles involving Ti and Cr.
All Ti–O, Ti–C and Cr–C bond lengths are comparable for
J. Chem. Soc., Dalton Trans., 2002, 2386–2389
2387

View Article Online
are also observed in complex 2 between carbonyl oxygens and
phenyl hydrogens (C(15) ؒ ؒ ؒ O(3) = 3.417(3) Å, C(15)–
H(15) ؒ ؒ ؒ O(3) = 138.3Њ; C(24) ؒ ؒ ؒ O(4) = 3.449(3) Å, C(24)–
H(24) ؒ ؒ ؒ O(4) = 138.9Њ). There is also a relatively short
C–H ؒ ؒ ؒ O distance on one of the disordered Cp ligands
(C(32A) ؒ ؒ ؒ O(2) = 3.26(2) Å, C(32A)–H(32A) ؒ ؒ ؒ O(2) =
146.0Њ), although the accuracy of this value could be suspect.
The orange fraction containing complex 2 was collected, and
dried. Red prismatic crystals were obtained by layering a
solution of CH2Cl2 with hexane and cooling to Ϫ20 ЊC (0.17 g,
30%). mp 229–231 ЊC (Found: C, 57.9; H, 3.2; N, 4.9%.
C28H18CrN2O6Ti requires C, 58.2; H, 3.1; N, 4.8%); νmax/cmϪ1
(CH2Cl2) 2150m, 2110m (CN); 2010m, 1924s br (CO);
δH (CDCl3) 7.31–7.21 (4H, m, H3, H5), 6.78 (2H, td, H4), 6.46
(10H, s, 2Cp), 6.37 (2H, dd, H6); δC (CDCl3) 222.5 (trans CO),
219.2 (cis CO), 176.0 (CN), 165.3, 130.5, 128.0, 119.2,
119.1 (aromatic carbons), 117.7 (2Cp); m/z 578 (Mϩ, 8), 494
(M Ϫ 3CO, 2), 466 (M Ϫ 4CO, 28).
Experimental
General procedures
Repeating the above procedure with Cr(CO)4(NOR) instead
of (CO)5Cr(THF) afforded only complex 2 in 49% yield.
All reactions and manipulations were carried out under a dry
argon atmosphere using standard Schlenk and vacuum-line
techniques. All solvents were dried and purified by conventional
methods and were freshly distilled under argon shortly before
use. Other reagents were used without further purification.
Elemental analyses (C, H, N) were done on a Carlo Erba 1106
instrument. Melting points were measured in sealed capillaries
with a Büchi 535 melting point apparatus and are uncorrected
and NMR spectra on a Varian VXR 300 spectrometer (1H, 300
MHz; 13C, 75.48 MHz) at 25 ЊC. Chemical shifts are reported in
[(CO)5Mo{CN(C6H4-o)O}Ti(Cl)Cp2] (3) and [(CO)4Mo-
{CN(C6H4-o)O}2TiCp2] (4). Complexes 3 and 4 can be
synthesised using a similar method to the one above, with
Mo(CO)6 replacing Cr(CO)6.
Red crystals of complex 3 were obtained (0.067 g, 12%). mp
168–170 ЊC (Found: C, 46.6; H, 2.5; N, 2.3%. C22H14-
ClMoNO6Ti requires C, 46.6; H, 2.5; N, 2.5%); νmax/cmϪ1
(CH2Cl2) 2143m (CN); 2063m, 2009sh, 1953s br (CO);
δH (CD2Cl2) 7.30–7.20 (2H, m, H3, H5), 7.00 (1H, dd, H6), 6.80
(1H, td, H4), 6.41 (10H, s, 2Cp); δC (CD2Cl2) 208.0 (trans CO),
206.9 (cis CO), 166.9, 131.7, 128.2, 120.7, 120.2 (aromatic
carbons), 119.6 (2Cp); m/z 567 (Mϩ, 0.2), 538 (M Ϫ CO, 4), 511
(M Ϫ 2CO, 3), 455 (M Ϫ 4CO, 3), 427 (M Ϫ 5CO, 24).
Yellow crystals of complex 4 were obtained (0.13 g, 21%). mp
182 ЊC (dec.) (Found: C, 54.3; H, 2.9; N, 4.3%. C28H18MoN2-
O6Ti requires C, 54.0; H, 2.9; N, 4.5%); νmax/cmϪ1 (CH2Cl2)
2146m, 2110m (CN); 2014m, 1935s br (CO); δH (CDCl3) 7.25–
7.18 (4H, m, H3, H5), 6.72 (2H, td, H4), 6.40 (10H, s, 2Cp), 6.30
(2H, dd, H6); δC (CD2Cl2) 211.4 (trans CO), 206.9 (cis CO),
164.5, 130.3, 127.7, 118.7, 118.6 (aromatic carbons), 117.4
(2Cp); m/z 622 (Mϩ, 12), 537 (M Ϫ 3CO, 22), 510 (M Ϫ 4CO,
10).
1
ppm relative to the H and 13C in the deuterated solvents. The
IR spectra were recorded on a Perkin-Elmer 1600 Series FT-IR
spectrometer. Mass spectra (EI, 70 eV) were obtained using a
Finnigan Mat 8200 instrument. Only characteristic fragments
containing the isotopes of the highest abundance are listed.
Relative intensities, in %, are given in parentheses.
Materials
Benzoxazole, [Cr(CO)6], [Mo(CO)6], [W(CO)6], silica gel 60 and
n-butyllithium (Merck) were used without further purification.
M(CO)5(THF) (M = Cr, Mo, W), bicyclo[2,2,1]heptadiene
(tetracarbonyl)chromium and bicyclo[2,2,1]heptadiene (tetra-
carbonyl)molybdenum were prepared according to literature
methods.16 Tetrahydrofuran and diethyl ether were distilled
under N2 from sodium diphenylketyl, pentane and hexane from
sodium wire and CH2Cl2 from CaH2.
Replacing (CO)5Mo(THF) by Mo(CO)4(NOR) yielded only
complex 4.
[(CO)5W{CN(C6H4-o)O}Ti(Cl)Cp2] (5) and [(CO)4W{CN-
(C6H4-o)O}2TiCp2] (6). Using a similar method to that for
preparing complexes 1 and 2, complexes 5 and 6 were
synthesized from W(CO)6 instead of the Cr(CO)6.
Synthesis of compounds
[(CO)5Cr{CN(C6H4-o)O}Ti(Cl)Cp2] (1) and [(CO)4Cr-
{CN(C6H4-o)O}2TiCp2] (2). Benzoxazole (0.60 g, 5 mmol) was
dissolved in THF (50 ml) and cooled to Ϫ78 ЊC. Standardised
n-butyllithium in hexane (3.3 ml, 1.6 M, 5.3 mmol) was slowly
added. The yellow solution was stirred at Ϫ78 ЊC for 30 min,
then slowly warmed to 0 ЊC. After stirring for an additional
15 min, the solution was added slowly to a solution of
Cr(CO)5(THF), prepared from [Cr(CO)6] (3 mmol, 0.66 g) in
THF (100 ml) under UV light for 3 hours. The mixture changed
colour to a deep red–brown. The mixture was stirred overnight
between 0 and 10 ЊC, to yield a red–brown solution. It was
slowly added to a solution of Cp2TiCl2 (0.75 g, 3.0 mmol) in
THF (50 ml) at Ϫ78 ЊC. The mixture was allowed to warm to
room temperature overnight, during which time the colour
changed from red–brown to deep red–brown. Solvent was
removed under vacuum. The residue was purified by column
chromatography (SiO2) at Ϫ15 ЊC and eluted with CH2Cl2–
pentane (1 : 1). The red fraction containing complex 1 was
collected and dried. Red–orange crystals were obtained by
layering a solution of CH2Cl2 with pentane and cooling to Ϫ20
ЊC (0.053 g, 10%). mp 154–156 ЊC (Found: C, 50.7; H, 2.5; N,
Red crystals of complex 5 were obtained (0.19 g, 29%). mp
158–160 ЊC (Found: C, 40.4; H, 2.2; N, 2.3%. C22H14ClWNO6Ti
requires C, 40.3; H, 2.2; N, 2.1%); νmax/cmϪ1 (CH2Cl2) 2145m
(CN); 2060m, 1998sh, 1947s br (CO); δH (CD2Cl2) 7.30–7.22
(2H, m, H3, H5), 7.01 (1H, dd, H6), 6.80 (1H, td, H4), 6.41 (10H,
s, 2Cp); δC (CD2Cl2) 196.3 (trans CO), 194.4 (cis CO), 178.0
(CN), 165.7, 130.5, 126.9, 119.3, 118.9 (aromatic carbons),
118.2 (2Cp); m/z 655 (Mϩ, 8), 627 (M Ϫ CO, 35), 599
(M Ϫ 2CO, 2), 571 (M Ϫ 3CO, 28), 543 (M Ϫ 4CO, 23), 515
(M Ϫ 5CO, 100).
Yellow crystals of complex 6 were obtained (0.062 g, 8.7%).
mp 174–176 ЊC (Found: C, 47.6; H, 2.4; N, 3.9%. C28H18WN2-
O6Ti requires C, 47.4; H, 2.6; N, 3.9%); νmax/cmϪ1 (CH2Cl2)
2146m, 2110w (CN); 2014m, 1930s br (CO); δH (CD2Cl2) 7.29
(2H, dd, H3), 7.19 (2H, td, H5), 6.80 (2H, dd, H6), 6.78 (2H, td,
H4), 6.36 (10H, s, 2Cp); δC (CD2Cl2) 196.5 (trans CO), 194.5 (cis
CO), 165.9, 130.8, 127.4, 120.3, 119.2 (aromatic carbons), 117.6
(2Cp); m/z 710 (Mϩ, 6), 625 (M Ϫ 3CO, 8), 599 (M Ϫ 4CO, 20).
X-Ray structure determination of complexes 1 and 2
2.4%. C22H14ClCrNO6Ti requires C, 50.5; H, 2.7; N, 2.7%); νmax
/
cmϪ1 (CH2Cl2) 2142m (CN); 2056m, 1996sh, 1951s br (CO); δH
(CD2Cl2) 7.31–7.28 (2H, m, H3, H5), 7.05 (1H, dd, H6), 6.83
(1H, td, H4), 6.44 (10H, s, 2Cp); δC (CD2Cl2) 217.3 (trans CO),
215.4 (cis CO), 178.0 (CN), 165.5, 130.4, 127.2, 119.7,
119.3 (aromatic carbons), 118.5 (2Cp); m/z 523 (M+, 68), 495
(M Ϫ CO, 45), 439 (M Ϫ 3CO, 14), 411 (M Ϫ 4CO, 18), 383
(M Ϫ 5CO, 100).
Complex 1. Recrystallisation from CH2Cl2–pentane (1 : 1)
at Ϫ20 ЊC gave crystals suitable for X-ray structure analysis.
Diffraction data for an red–orange crystal of complex 1 were
collected at 173(2) K on a Nonius Kappa CCD diffractometer
with graphite monochromated Mo-Kα radiation (λ
=
0.71073 Å) using ꢀ and ω scans to fill the Ewald sphere (Nonius
COLLECT).17
2388
J. Chem. Soc., Dalton Trans., 2002, 2386–2389

View Article Online
Table 2 Crystal data and structure refinement for complexes 1 and 2
1
2
Empirical formula
Formula weight
T /K
Crystal system
Space group
a/Å
C22H14ClCrNO6Ti
523.69
173(2)
Monoclinic
C2/c
25.700(1)
C28H18CrN2O6Ti
578.34
298(2)
Monoclinic
P21/c
11.9512(1)
b/Å
c/Å
10.426(1)
16.804(2)
14.8432(2)
15.7525(2)
β/Њ
99.044(2)
4446.6(7)
111.644(1)
2597.2(9)
V/Å3
Z
8
4
Calculated density/Mg mϪ3
1.565
1.006
1.479
0.771
µ/mmϪ1
F (000)
2112
0.35 × 0.25 × 0.15
10123
1176
0.28 × 0.25 × 0.23
17312
Crystal size/mm
Reflections collected
Unique reflections
Refinement method
Data/restraints/parameters
R (I > 2σ(I ))
R (all data)
WRЈ (I > 2σ(I ))
WRЈ (all data)
4163 [Rint = 0.023]
5900 [Rint = 0.025]
Full-matrix least-squares on F 2
Full-matrix least-squares on F 2
4163/0/289
0.035
0.048
0.094
0.102
5900/10/389
0.038
0.056
0.095
0.104
Details of the data collection and structural refinement are
summarised in Table 2. Data reduction was performed using
DENZO.18 The positions of the Ti and Cr atoms were identified
from a Patterson synthesis, while the rest of the atomic
positions were found from difference Fourier maps. All non-
hydrogen atoms were refined anisotropically by full-matrix
least-squares methods. All calculations were performed using
SHELX-9719 within the WINGX package.20 Figures were
generated using Ortep3 for Windows;21 displacement ellipsoids
are at the 50% probability level. Selected bond lengths and
angles are given in Table 1.
References
1 J. Barluenga and F. J. Fañanás, Tetrahedron, 2000, 56, 4597.
2 J. An, L. Van Niekerk, C. Esterhuysen and H. G. Raubenheimer,
unpublished work.
3 P. Jutzi and U. Gilge, J. Organomet. Chem., 1983, 246, 159; R. R.
Fraser, T. S. Mansour and S. Savard, Can. J. Chem., 1985, 63, 3505;
C. Hilf, F. Bosold, K. Harms, M. Marsch and G. Boche, Chem. Ber.,
1997, 130, 1213.
4 D. T. Plummer, B. A. Karcher, R. A. Jacobson and R. J. Angelici,
J. Organomet. Chem., 1984, 260, 347 and references therein.
5 F. E. Hahn, M. Tamm, L. Imhof and T. Lügger, J. Organomet.
Chem., 1996, 526, 149 and references therein.
6 K. R. Mann, R. A. Bell and H. B. Gray, Inorg. Chem., 1979, 18,
2671.
7 S. Jurisson, D. Berning, W. Jia and D. Ma, Chem. Rev., 1993, 93,
1137.
Complex 2. Diffraction data for a red crystal of complex 2
were collected as for complex 1. Details of the data collection
and structural refinement are summarised in Table 2. Data
reduction was performed using DENZO.18 The positions of the
Ti and Cr atoms were identified from a Patterson synthesis.
After identifying the remainder of the structure from difference
Fourier maps the presence of further peaks of electron density
indicated that one of the Cp rings was disordered. The bond
lengths in the disordered Cp ring were restrained to be identical
and the sum of the site occupancies was constrained to 1. All
non-hydrogen atoms were refined anisotropically by full-matrix
least-squares methods. All calculations were performed using
SHELX-9719 within the WINGX package.20 Figures were
generated using Ortep3 for Windows.21 Selected bond distances
and angles are given in Table 1.
8 H. G. Raubenheimer, E. K. Marais, S. Cronje, C. Esterhuysen and
G. J. Kruger, J. Chem. Soc., Dalton Trans., 2000, 3016.
9 F. E. Hahn, M. Tamm and T. Lügger, Angew. Chem., Int. Ed. Engl.,
1994, 33, 1356.
10 P. Jutzi and U. Gilge, J. Organomet. Chem., 1983, 246, 159;
A. Dondoni, G. Fantin, M. Fogagnolo, A. Medici and P. Pedrini,
Synthese, 1987, 8, 693.
11 B. A. Anderson and N. K. Harn, Synthese, 1996, 5, 583.
12 F. H. Allen and O. Kennard, Chem. Des. Autom. News, 1993, 8, 1;
F. H. Allen and O. Kennard, Chem. Des. Autom. News, 1993, 8, 31.
13 G. A. Jeffrey, in An introduction to hydrogen bonding, Oxford
University Press, New York, 1997.
14 T. Steiner, Chem. Commun., 1997, 727.
15 D. Braga, S. M. Draper, E. Champeil and F. Grepioni, J. Organomet.
Chem., 1999, 573, 73.
CCDC reference numbers 178238 and 178239.
See http://www.rsc.org/suppdata/dt/b2/b200859a/ for crystal-
lographic data in CIF or other electronic format.
16 R. B. King, in Organometallic Syntheses, Transition Metal
Compounds, Academic Press, New York, 1965, vol. 1, p. 122;
J. A. Costamagna and J. Granifo, Inorg. Synth., 1985, 23, 1.
17 COLLECT, Data Collection Software, Nonius BV, Delft, The
Netherlands, 1998.
18 Z. Otwinowski and W. Minor, Methods Enzymol., 1997, 276, 307.
19 G. M. Sheldrick, SHELX-97, Program for Crystal Structure
Analysis, University of Göttingen, Germany, 1997.
20 L. J. Farrugia, J. Appl. Crystallogr., 1999, 32, 837.
21 L. J. Farrugia, J. Appl. Crystallogr., 1997, 30, 565.
Acknowledgements
We thank the National Research Foundation and the Claude
Harris Leon Foundation and Stellenbosch University in South
Africa for supporting for this work.
J. Chem. Soc., Dalton Trans., 2002, 2386–2389
2389