Ditelluroether complexes of Group 6 metal carbonyls: Synthesis, spectroscopic studies and a comparison with dithio- And diseleno-ether analogues

Article abstract of DOI:10.1016/S0022-328X(99)00005-4

The syntheses of [M(CO)₄(L-L)] (M = Cr, Mo or W, L-L = MeTe(CH₂)₃TeMe, PhTe(CH₂)₃TePh or o-C₆H₄(TeMe)₂) are described along with some dithioether (L-L-MeS(CH₂)₂SMe, MeS(CH₂)₃SMe) and diselenoether (L-L = MeSe(CH₂)₂SeMe, MeSe(CH₂)₃SeMe or o-C₆H₄(SeMe)₂) analogues. The complexes have been characterised by IR, ¹H-, ¹³C{¹H}-, ⁷⁷Se{¹H}-, ¹²⁵Te{¹H}- and ⁹⁵Mo-NMR spectroscopy, FAB mass spectrometry and analysis. The structure of [Cr(CO)₄{MeSe(CH₂)₂SeMe}] is reported. Comparison of the spectroscopic data reveals that ditelluroethers are significantly better σ-donors towards low valent metal centres than their lighter analogues.

Full text of DOI:10.1016/S0022-328X(99)00005-4

Journal of Organometallic Chemistry 579 (1999) 235–242
Ditelluroether complexes of Group 6 metal carbonyls: synthesis,
spectroscopic studies and a comparison with dithio- and diseleno-ether
analogues
Andrew J. Barton, William Levason *, Gillian Reid
Department of Chemistry, Uni6ersity of Southampton, Southampton SO17 1BJ, UK
Received 9 November 1998
Abstract
The syntheses of [M(CO)4(LꢀL)] (M=Cr, Mo or W, LꢀL=MeTe(CH2)3TeMe, PhTe(CH2)3TePh or o-C6H4(TeMe)2) are
described along with some dithioether (LꢀLꢀMeS(CH2)2SMe, MeS(CH2)3SMe) and diselenoether (LꢀL=MeSe(CH2)2SeMe,
MeSe(CH2)3SeMe or o-C6H4(SeMe)2) analogues. The complexes have been characterised by IR, 1H-, 13C{1H}-, 77Se{1H}-,
125Te{1H}- and 95Mo-NMR spectroscopy, FAB mass spectrometry and analysis. The structure of [Cr(CO)4{MeSe(CH2)2SeMe}]
is reported. Comparison of the spectroscopic data reveals that ditelluroethers are significantly better s-donors towards low valent
metal centres than their lighter analogues. © 1999 Elsevier Science S.A. All rights reserved.
Keywords: Chromium; Molybdenum; Tungsten; Ditelluroether; Dithioether; Diselenoether
luroether). The corresponding dithioether and disele-
noether complexes have received considerable attention
1. Introduction
[8–17]. We have prepared a range of known and new
Substituted Group 6 carbonyls have been studied in
complexes for comparison purposes since we required
great detail with a wide variety of ligand types [1], and
vibrational data recorded under the same conditions for
are thus very suitable systems in which to explore the
all the complexes, and literature multinuclear NMR
properties of new ligands. Ditelluroether ligands have
data are very limited.
been available for about 10 years [2] and their com-
plexes with Group 8–11 metals in positive oxidation
states have been examined in some detail [3–6]. In
2. Results
contrast, their chemistry with low valent metal and
organometallic species remains largely unexplored. We
have undertaken the synthesis and study of complexes
of various metal carbonyls with these ligands in parallel
with studies of thio- or seleno- analogues, to place the
trends within Group 16 in context. Complexes with
manganese and rhenium carbonyl halides have been
described [7], and we report here complexes of type
[M(CO)4(LꢀL)] (M=Cr, Mo or W; LꢀL=ditel-
2.1. Ditelluroether complexes
The syntheses of the complexes of the three ditel-
luroethers (MeTe(CH2)3TeMe, PhTe(CH2)3TePh, o-
C6H4(TeMe)2) and
diselenoether analogues (Table 1) were straightforward,
utilising reaction of the ligand with [Cr(CO)4(nbd)]
(nbd=norbornadiene (bicyclo-[2,2,1]-hepta-2,5-diene)),
[Mo(CO)4(nbd)] or [W(CO)4{Me2N(CH2)3NMe2}] in
toluene, followed by recrystallisation from CHCl3 and
a
range of dithioether and
* Corresponding author. Fax: +44-1703-593-781.
E-mail address: wxl@soton.ac.uk (W. Levason)
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00005-4

236
A.J. Barton et al. / Journal of Organometallic Chemistry 579 (1999) 235–242
Table 1
IR spectroscopic data
For
a
[M(CO)4(ditelluroether)] complex two
stereoisomers (invertomers) are expected (meso and DL,
Scheme 1), which interconvert by pyramidal inversion
at tellurium. When inversion is slow on the NMR
timescale, the two invertomers are readily distinguished
in the 1H-NMR spectra. Previous studies [18] have
established that for dithioether and diselenoether com-
plexes, the energy barriers to inversion are dependent
on several factors, viz.: the donor Se\S; the ligand
backbone ꢀ(CH2)2ꢀ\ꢀ(CH2)3ꢀ\o-C6H4; and the
metal W\Cr\Mo. The only quantitative data on
ditelluroethers is from [PtMe3I(ditelluroether)] com-
plexes [6], which revealed that inversion was a higher
energy process in these complexes than in the disele-
noether analogues. It is clear from Table 2 that the
present complexes conform to the expected patterns.
Thus, all the ditelluroether complexes show resonances
Complex
w(CO) cm−1a
[Cr(CO)4{MeTe(CH2)3TeMe}]
[Mo(CO)4{MeTe(CH2)3TeMe}]
[W(CO)4{MeTe(CH2)3TeMe}]
[Cr(CO)4{PhTe(CH2)3TePh}]
2000(m), 1887(s,br), 1858(s)
2015(m), 1908(s,br), 1862(s)
2010(m), 1894(s,br), 1859(s)
2003(m), 1903(sh), 1891(s,br),
1870(s)
2018(m), 1907(s,br), 1875(s)
2013(m), 1895(s,br), 1869(s)
2005(m), 1902(s,br), 1873(s)
2020(m), 1920(sh), 1911(s),
1880(s)
2015(m), 1900(s,br), 1875(s)
2016(s), 1898(s,br), 1860(s)
2024(s), 1910(s,br), 1863(s)
2019(m), 1897(s,br), 1859(s)
2028(m), 1917(s,br), 1870(s)
2015(s), 1900(s), 1890(sh), 1854(s)
2023(s), 1910(s,br), 1895(sh),
1856(s)
[Mo(CO)4{PhTe(CH2)3TePh}]
[W(CO)4{PhTe(CH2)3TePh}]
[Cr(CO)4{o-C6H4(TeMe)2}]
[Mo(CO)4{o-C6H4(TeMe)2}]
[W(CO)4{o-C6H4(TeMe)2}]
[Cr(CO)4{MeS(CH2)2SMe}]
[Mo(CO)4{MeSCH2)2SMe}]
[W(CO)4{MeS(CH2)2SMe}]
[Mo(CO)4{o-C6H4(SMe)2}]
[Cr(CO)4{MeS(CH2)3SMe}]
[Mo(CO)4{MeS(CH2)3SMe}]
1
for both invertomers in the H-NMR spectra at 300 K
(at 300 MHz) consistent with relatively high inversion
barriers.
[W(CO)4{MeS(CH2)3SMe}]
2018(m), 1897(s), 1890(sh),
1852(s)
The observed 13C{1H}-NMR spectra (Table 2) also
depend upon whether the complex is undergoing fast
inversion or not, this time on the energy of the 13C-
NMR scale. If fast inversion is occuring then only two
l(CO) resonances are expected due to the CO groups
mutually trans and those transLꢀL. However, if inver-
sion is slow, five l(CO) resonances are expected by
symmetry, two due to CO transLꢀL in the meso and DL
invertomers, respectively, one due to the mutually trans
CO in the DL form, and two due to the COtransCO in the
meso form, which are distinguished by being syn or anti
to the R-groups on the ligands. In practice (Table 2),
whilst five resonances are seen in some cases, e.g.
[Cr(CO)4{MeSe(CH2)2SeMe}]
[Mo(CO)4{MeSe(CH2)2SeMe}]
[W(CO)4{MeSe(CH2)2SeMe}]
[Cr(CO)4{MeSe(CH2)3SeMe}]
[Mo(CO)4{MeSe(CH2)3SeMe}]
2011(s), 1900(sh), 1889(s), 1860(s)
2021(m), 1909(s,br), 1862(s)
2016(m), 1895(s,br), 1858(s)
2009(m), 1894(s,br), 1852(s)
2020(m), 1908(s), 1895(sh),
1855(s)
2015(m), 1896(s), 1885(sh),
1850(s)
2015(s),1902(s,br), 1866(s)
2025(m),1914(s,br), 1870(m)
2019(m), 1901(s,br), 1866(s)
[W(CO)4{MeSe(CH2)3SeMe}]
[Cr(CO)4{o-C6H4(SeMe)2}]
[Mo(CO)4{o-C6H4(SeMe)2}]
[W(CO)4{o-C6H4(SeMe)2}]
a In CH2Cl2 solution, m, medium; s, strong; br, broad.
pentane. The complexes are air-stable in the solid state
and reasonably so in solution when pure. They were
insoluble in hydrocarbons, but very soluble in chloro-
carbon solvents. The formulation of the new complexes
as cis-tetracarbonyls [M(CO)4(LꢀL)] follows from the
analyses, the FAB mass spectra, and their IR spectra
(Table 1). The FAB mass spectra (Section 4) show for
each complex a parent ion and often fragments corre-
sponding to sequential carbonyl loss. The IR spectra in
CH2Cl2 solution in most cases show only three w(CO)
bands. Theory for a trans isomer predicts one IR active
mode (Eu) and for a cis, four stretches (2A1+B1+B2).
The observation of only three bands in the majority of
cases is due to the failure to resolve the A1 and B1
modes at ca. 1900 cm−1. A similar effect has been
noted in some dithioether complexes [15].
[Cr(CO)4{MeTe(CH2)3TeMe}],
in
others,
e.g.
[Cr(CO)4{o-C6H4(TeMe)2}], only four are seen, which
is due to accidental coincidence of the l(CO) transLꢀL
in the two invertomers.
The 125Te{1H}-NMR data on the complexes are
given in Table 3. In all cases, coordination to the
M(CO)4 fragment produces characteristic frequency
shifts, the magnitude of the coordination shifts (D)
reflecting the chelate ring size present, those in 5-mem-
bered rings being markedly greater than those in 6-
membered ones [2]. For a particular ligand, the largest
high-frequency shift is observed in the chromium com-
plex, a smaller shift occurs for the molybdenum ana-
logue, and the smallest for the tungsten. In the cases of
[W(CO)4{RTe(CH2)3TeR}] (R=Me or Ph), the l(Te)
resonance is to low frequency of that of the free ligand.
The relative population of meso and DL invertomers
also varies with the metal and ligand combination. For
o-C6H4(TeMe)2 complexes of Cr or Mo in CH2Cl2
solution, the two invertomers have similar abundances,
but the for the tungsten complex the meso:DL ratio is
ca. 10:7. In the complexes of MeTe(CH2)3TeMe, the
Scheme 1. Meso and DL invertomers of [M(CO)4(ditelluroether)].

A.J. Barton et al. / Journal of Organometallic Chemistry 579 (1999) 235–242
237
Table 2
1H- and 13C{1H}-NMR data
Complex
l(1H)a
l(13C{1H})b
[Cr(CO)4{MeTe(CH2)3TeMe}]
1.70(m)(CH2) 2.12, 2.18(Me),
2.68(m)(CH2Te)
228.1, 227.9, 224.0, 223.2, 221.5(CO), 25.8, 25.6(CH2), 6.3, 5.9(CH2Te),
−10.5, −12.5(Me)
[Mo(CO)4{MeTe(CH2)3TeMe}] 1.93(m)(CH2), 2.16, 2.21(Me),
2.68(m)(CH2Te)
215.7, 211.5, 211.0, 209.3(CO), 27.2(CH2), 7.6, 6.5(CH2Te), −10.4, −
11.4(Me)
[W(CO)4{MeTe(CH2)3TeMe}]
[Cr(CO)4{PhTe(CH2)3TePh}]
[Mo(CO)4{PhTe(CH2)3TePh}]
[W(CO)4{PhTe(CH2)3TePh}]
[Cr(CO)4{o-C6H4(TeMe)2}]
[Mo(CO)4{o-C6H4(TeMe)2}]
[W(CO)4{o-C6H4(TeMe)2}]
1.90(m)(CH2), 2.23, 2.28(Me),
2.73(m)(CH2Te)
206.2(170), 204.8(−), 203.9(−), 201.9(120)(CO)c, 28.1, 27.8(CH2), 8.7,
7.6(CH2Te), −8.0, −9.5(Me)
1.71(m)(CH2), 2.83(m),
3.0(m)(CH2Te), 7.3–7.8(m)(Ph)
1.9(m)(CH2), 2.85(m),
2.95(m)(CH2Te), 7.3–7.8(m)(Ph)
1.9(m)(CH2), 2.9(m), 3.1(m)
(CH2Te), 7.4–7.8(m)(Ph)
2.31, 2.41(Me), 7.4(m),
7.8(m)(C6H4)
2.33, 2.42(Me), 7.4(m),
8.0(m)(C6H4)
2.43, 2.53(Me), 7.4(m),
8.0(m)(C6H4)
227.7, 227.3, 224.4, 222.0, 220.5(CO), 137–129 (Ph), 27.0, 26.3(CH2),
11.8, 11.6(CH2Te)
215.6, 211.2, 210.8, 208.6(CO), 137–130 (Ph), 28.0, 27.4(CH2), 13.3,
12.8(sh), (CH2Te)
205.5(–), 205.3(160), 205.0(–), 203.5(125), 203.4(–), 137–129(Ph), 28.9,
27.9(CH2), 13.9, 13.5(CH2Te)
230.7, 221.6, 220.9, 220.5(CO) 139–126(C6H4), −4.0, −4.6(Me)
218.3, 208.8, 208.6, 208.4(CO), 139–123 (C6H4), −3.5, −3.8(Me)
208.7(–), 208.6(–), 201.6(–), 201.1(–), 200.5(–)(CO), 139–123(C6H4),
−1.5, −1.7(Me)
[Cr(CO)4{MeS(CH2)2SMe}]
[Mo(CO)4{MeS(CH2)2SMe}]
[W(CO)4{MeS(CH2)2SMe}]
[Mo(CO)4{o-C6H4(SMe)2}]
[Cr(CO)4{MeS(CH2)3SMe}]
2.35(Me), 2.65(CH2)
2.44(Me), 2.74(CH2)
2.62(Me), 2.78(CH2)
2.83(Me), 7.4(m), 7.8(m)(C6H4)
2.14(m)(CH2), 2.41(Me),
2.78(m)(CH2S)
227.1, 216.3(CO), 35.4(CH2), 24.6(Me)
217.5, 206.5(CO), 35.2(CH2), 25.3(Me)
207.9(164), 201.4(135)(CO), 36.5(CH2), 26.8(Me)
217.6, 205.8 (CO), 138–130(C6H4), 32.6(Me)
225.8, 217.0 (CO), 38.6(CH2S), 25.5(Me), 24.5(CH2)
[Mo(CO)4{MeS(CH2)3SMe}]
[W(CO)4{MeS(CH2)3SMe}]
[Cr(CO)4{MeSe(CH2)2SeMe}]
2.20(m)(CH2), 2.49(Me),
2.88(m)(CH2S)
2.32(m)(CH2), 2.67(Me),
3.02(m)(CH2S)
217.0, 207.1(CO), 39.7(CH2S), 26.5(Me), 25.0(CH2)
207.6(156), 202.7(126) (CO), 39.9(CH2S), 28.0(Me), 24.9(CH2)
2.14, 2.23(Me), 3.1, 3.3(CH2)
229.0, 219.2, 217.8, 216.7(CO), 28.5, 28.0(CH2), 14.5, 13.5(Me)
217.9, 207.9, 207.4, 207.0(CO), 31.1, 26.9(CH2), 14.9(sh), 14.2(Me)
208.3(sh), 208.2(156), 203.2(–), 202.1(–), 200.8(–)(CO), 29.4, 28.0(CH2),
16.8, 15.6(Me)
[Mo(CO)4{MeSe(CH2)2SeMe}] 2.2(v,br,Me), 3.0(v,br,CH2)
[W(CO)4{MeSe(CH2)2SeMe}]
2.37, 2.55(Me), 3.3, 3.35(CH2)
[Cr(CO)4{o-C6H4(SeMe)2}]
[Mo(CO)4{o-C6H4(SeMe)2}]
[W(CO)4{o-C6H4(SeMe)2}]
2.60(br,Me), 7.4(m), 7.8(m)(C6H4) 227.8, 211.6(CO), 134–126 (C6H4), 20.1(Me)
2.66(Me), 7.4(m), 7.9(m)(C6H4)
2.43, 2.53(Me), 7.4(m),
7.9(m)(C6H4)
218.0, 206.7(CO), 135–130(C6H4), 22.9(Me)
208.4(165), ꢀ201(v,br)(–), 135–130(C6H4), 24.8(Me)
[Cr(CO)4{MeSe(CH2)3SeMe}]
2.18(CH2), 2.30(Me),
2.8(br,CH2Se)
227.0, 219.0(CO), 29.1(CH2Se), 25.5(CH2), 14.3(Me)
216.8, 208.3(CO), 30.5(CH2Se), 26.3(CH2), 15.5(Me)
ꢀ206(v,br), ꢀ203(v,br)(CO), 30.0(CH2Se), 26.0(CH2), 16.4(Me)
[Mo(CO)4{MeSe(CH2)3SeMe}] 2.25(CH2), 2.37(Me),
2.8(br,CH2Se)
[W(CO)4{MeSe(CH2)3SeMe}]
2.39(br,CH2), 2.53(Me),
3.0(br,CH2Se)
a In CDCl3 all resonances are singlets unless otherwise indicated.
b In CH2Cl2–10% CDCl3 containing Cr(acac)3.
c Values in parentheses are 1J(183Wꢀ13C)/Hz, (–) indicates couplings unclear or satellites not observed.
invertomers are of approximately equal abundance for
all three metals, but in complexes of PhTe(CH2)3TePh,
the DL invertomer predominates (\70%), possibly
indicating destabilising interactions between the Ph
groups and the axial carbonyl group in the meso form.
temperatures, consistent with previous detailed studies
[14,16]. The behaviour of the diselenoether complexes is
more complicated. Thus, the NMR spectra of
[M(CO)4(MeSeCH2CH2SeMe)] (M=Cr or W) at 300
K show sharp resonances attributable to the meso and
DL forms, whereas [M(CO)4{MeSe(CH2)3SeMe}] (M=
Cr or Mo) and [Mo(CO)4{o-C4H4(SeMe)2}] exhibit
much simpler ‘averaged’ spectra due to rapid inversion.
The other four complexes (Table 2) show broadened
resonances typical of systems near to coalescence. These
results conform with the expected trends in inversion
barriers [18] outlined above. 77Se-NMR data for the
diselenoethers are given in Table 3.
2.2. Diselenoether and dithioether complexes
A range of selenium and sulfur ligand analogues
(Tables 1 and 2) were examined for comparison pur-
1
poses as explained above. The H- and 13C{1H}-NMR
data show that all the dithioether complexes are invert-
ing rapidly on the appropriate timescales at ambient

238
A.J. Barton et al. / Journal of Organometallic Chemistry 579 (1999) 235–242
Table 3
77Se{1H}-, 125Te{1H}- and 95Mo-NMR data
Complex
l(77Se{1H} or 125Te{1H})a
Db
152
61
−10
83
l(95Mo)c
[Cr(CO)4{MeTe(CH2)3TeMe}]
[Mo(CO)4{MeTe(CH2)3TeMe}]
[W(CO)4{MeTe(CH2)3TeMe}]
[Cr(CO)4{PhTe(CH2)3TePh}]
[Mo(CO)4{PhTe(CH2)3TePh}]
[W(CO)4{PhTe(CH2)3TePh}]
[Cr(CO)4{o-C6H4(TeMe)2}]
[Mo(CO)4{o-C6H4(TeMe)2}]
[W(CO)4{o-C6H4(TeMe)2}]
[Cr(CO)4{MeSe(CH2)2SeMe}]
[Mo(CO)4{MeSe(CH2)2SeMe}]
[W(CO)4{MeSe(CH2)2SeMe}]
[Cr(CO)4{o-C6H4(SeMe)2}]
[Mo(CO)4{o-C6H4(SeMe)2}]
[W(CO)4{o-C6H4(SeMe)2}]
[Cr(CO)4{MeSe(CH2)3SeMe}]
[Mo(CO)4{MeSe(CH2)3SeMe}]
[W(CO)4{MeSe(CH2)3SeMe}]
[Mo(CO)4{MeS(CH2)2SMe}]
[Mo(CO)4{o-C6H4(SMe)2}]
[Mo(CO)4{MeS(CH2)3SMe}]
259, 253
169.5, 162
94, 93
550, 548
477, 476
396, 390
864, 856
725, 723.5
664, 657
289, 236
213, 206
183, 179
387, 384
331
–
−1597(200), −1621(200)
–
–
−1580(sh), −1594(300)
–
–
−1667(140)
–
–
−1432(160)
–
–
−1437(200)
–
–
−1340(200)
–
−1372(85)
−1375(260)
−1294(50)
10
−73
488
382
289
141.5
88.5
60
183.5
129
103
24
306, 303
98
64
−10
−43
–
37, 24d
–
–
–
–
–
a In CH2Cl2–10%CDCl3 relative to neat external Me2Se or Me2Te.
b lcomplex−lfree ligand
c Relative to external aqueous Na2MoO4 (W1/2 in parentheses Hz).
d No resonance observed at 300 K, presumably due to inversion broadening, data reported obtained at 230 K.
.
2.3. 95Mo-NMR
age excitation energy—essentially the weighted mean
ligand field splitting) and with a reduced d-electron
delocalisation. The shielding of the Mo nuclei with
donor, Te\Se\S, could thus be due to increasing
ligand field splitting as Group 16 is descended, and/or
better delocalisation (p-acceptance) in the same order.
Theoretical studies by Schumann and Hoffmann [19]
concluded that p effects were negligible in Group 16
donor ligands, and thus, the trends in the molybdenum
NMR data are most likely due to increased s-donation
in the order S“Se“Te.
The [Mo(CO)4{MeTe(CH2)3TeMe}] complex exhibits
two 95Mo resonances consistent with the presence of
both
invertomers,
whilst
for
[Mo(CO)4{PhTe(CH2)3TePh}] there is a high frequency
shoulder on the major 95Mo resonance. However, the
95Mo-NMR spectra of the other seven complexes
(Table 3), each contain only a single resonance. The
l(Mo) shifts sequentially to high frequency with donor
TeBSeBS and with chelate ring size 5B6. For seven
of the complexes, the 95Mo-NMR spectra do not distin-
guish the invertomers, indicating either that inversion is
fast on the molybdenum NMR time scale or that the
individual resonances are not resolved in the line width.
Since the lines are relatively sharp (5300 Hz), the
former seems much more likely. This behaviour is in
marked contrast to [Mn(CO)3X(ditelluroether)],
[PtX2(ditelluroether)] or [PtMe3X(ditelluroether)] (X=
halide), where the 55Mn- or 195Pt-NMR spectra show
well-separated resonances for the individual inver-
tomers [3,6,7]. On cooling the samples, the lines
broaden rapidly, possibly due to the 95Mo quadrupole
(95Mo, I=5/2) and low-temperature spectra were not
obtained, an effect previously observed for dithioether
complexes [14]. The interpretation of metal nuclei
NMR chemical shifts is usually based upon the Ramsey
equation, specifically upon the paramagnetic term |p.
Deshielding results from small values of DE (the aver-
2.4. Structure of [Cr(CO)4{MeSe(CH2)2SeMe}]
The important bond lengths and angles are shown in
Table 4 and the molecule in Fig. 1. The structure
reveals the expected cis disubstituted distorted octahe-
dron about Cr, with SeꢀCrꢀSe 86.59(5)°, the CꢀCrꢀSe
angles slightly greater than 90° and the CꢀCrꢀC less
than 90°. The ligand adopts the DL conformation with
˚
CrꢀSe 2.517(1), 2.520(2) A, and CrꢀCcisSe 1.891(8),
˚
1.892(7) and CrꢀCtransSe 1.832(7), 1.8314(8)A. The struc-
tural data may be compared with those in
[Cr(CO)4(DL-EtS(CH2)2SEt)] where CrꢀS=2.418(1),
˚
CrꢀCcisS=1.887(3), and CrꢀCtransS=1.831(3)A [10].
The differences in the Cr-chalcogen bond length reflects
the larger size of Se, and the CrꢀC distances are not
significantly different. Unfortunately, we have been un-
able to grow good quality crystals of a chromium
telluroether to complete the comparisons.

A.J. Barton et al. / Journal of Organometallic Chemistry 579 (1999) 235–242
239
Table 4
However, due to the complications related to the pyra-
midal inversion processes, line-broadening in some
cases or low abundance of one invertomer in others,
these data are incomplete and less useful. Consideration
of the data in Tables 1–3 shows that the parameters of
interest are also sensitive to the metal centre present,
the chelate ring size and the ligand substituents. Hence,
we restrict discussion initially to the complexes
[M(CO)4{MeE(CH2)3EMe}] and [M(CO)4{o-C6H4-
(EMe)2}] (E=S, Se or Te) for each metal in turn.
Consideration of w(CO) shows that for a given M, the
frequencies (especially that of the A1 mode of the CO’s
trans LꢀL) fall with donor from S to Se and then there
is a rather greater fall to Te. On the conventional
MꢀCO bonding model, this reflects greater electron
density on the metal centre resulting in greater p-back-
bonding to the CO’s and hence a weaking of the CꢀO
bond. The most obvious way of increasing the metal
electron density is increased s-donation from the
Group 16 donors. As Group 16 is descended, the
electronegativity of the donor atoms fall, and providing
the match in orbital overlap and energy remains good,
increasing s-donation would be expected. In metals in
positive oxidation states, especially as the formal charge
rises, the contraction of the metal d-orbitals has been
suggested to lead to mismatch in orbital size and energy
at tellurium, but in the expanded d-orbitals of zero-va-
lent metals as in the present case this is unlikely to be a
problem.
Selected bond lengths and angles for [Cr(CO)4(MeSeCH2CH2SeMe)]
˚
Bond lengths (A)
Se(1)ꢀCr(1)
Se(1)ꢀC(6)
Se(2)ꢀC(7)
Cr(1)ꢀC(1)
Cr(1)ꢀC(3)
O(1)ꢀC(1)
O(3)ꢀC(3)
C(6)ꢀC(7)
2.517(1) Se(1)ꢀC(5)
1.956(7) Se(2)ꢀCr(1)
1.955(7) Se(2)ꢀC(8)
1.891(8) Cr(1)ꢀC(2)
1.832(7) Cr(1)ꢀC(4)
1.149(8) O(2)ꢀC(2)
1.159(8) O(4)ꢀC(4)
1.515(10)
1.946(7)
2.520(2)
1.948(7)
1.892(7)
1.834(8)
1.154(8)
1.172(8)
Bond angles (°)
Cr(1)ꢀSe(1)ꢀC(5)
C(5)ꢀSe(1)ꢀC(6)
Cr(1)ꢀSe(2)ꢀC(8)
Se(1)ꢀCr(1)ꢀSe(2)
Se(1)ꢀCr(1)ꢀC(2)
Se(1)ꢀCr(1)ꢀC(4)
Se(2)ꢀCr(1)ꢀC(2)
Se(2)ꢀCr(1)ꢀC(4)
C(1)ꢀCr(1)ꢀC(3)
C(2)ꢀCr(1)ꢀC(3)
C(3)ꢀCr(1)ꢀC(4)
107.2(2)
Cr(1)ꢀSe(1)ꢀC(6) 102.5(2)
Cr(1)ꢀSe(2)ꢀC(7) 103.5(2)
97.1(3)
108.4(2)
86.59(5)
91.3(2)
178.9(2)
92.3(2)
92.4(2)
88.5(3)
87.6(3)
87.9(3)
C(7)ꢀSe(2)ꢀC(8)
Se(1)ꢀCr(1)ꢀC(1)
Se(1)ꢀCr(1)ꢀC(3)
Se(2)ꢀCr(1)ꢀC(1)
97.0(3)
90.2(2)
93.2(2)
91.6(2)
Se(2)ꢀCr(1)ꢀC(3) 179.7(2)
C(1)ꢀCr(1)ꢀC(2)
C(1)ꢀCr(1)ꢀC(4)
C(2)ꢀCr(1)ꢀC(4)
175.9(3)
89.6(3)
88.9(3)
3. Comparisons of Group 16 ligand properties.
The characterisation of ditelluroether complexes with
the Group 6 carbonyls is of interest in its own right, but
it also offers an opportunity to compare ligand proper-
ties of dithioethers, diselenoethers and ditelluroethers.
For this purpose we used the w(CO) stretching vibra-
tions and the relative magnitude of the 77Se- and 125Te-
NMR shifts. In principle, the l(CO) shifts in the
13C{1H}-NMR spectra and for the tungsten complexes
Turning to the 77Se and 125Te chemical shifts (Table
3), as stated above (Section 2.2) the shifts are very
sensitive to the ring size and the metal present. How-
ever, if we compare the data on complexes of the same
metal with isostructural ligands, we see similar trends,
with larger coordination shifts in the tellurium spectra
as usually observed [2]. In many organoselenium and
organotellurium systems the relative magnitude of the
heteroatom chemical shifts (l(Te)/l(Se)) are ca. 1.8
[2,20], and this ratio is also found in several series of
seleno- and telluroether complexes with platinum metal
halides [3]. However, in the present carbonyl systems
for a fixed metal and ligand type the ratios are signifi-
cantly greater [o-C6H4(EMe)2, M=Cr 2.25, M=Mo
2.2, M=W 2.2; MeE(CH2)3EMe, M=Cr 2.6, M=Mo
2.6, M=W 3.01], which indicates that the tellurium
centre is deshielded to an unexpected degree and is
consistent with greater Te“M s-donation. The 95Mo-
NMR data discussed in Section 2.3 also support the
conclusion that the telluroethers are the best s-donors
in the series of ligands. The spectroscopic data clearly
1
the J(13Cꢀ183W) coupling constants on the COtransLꢀL
resonances, should also provide useful information.
1 The 77Se{1H}-NMR spectrum of [W(CO)4{MeSe(CH2)3SeMe}]
was not observed at room temperature, and the data obtained at 230
K was used (see Table 3). Since 77Se-NMR shifts often vary with
temperature the comparison is subject to larger errors than in the
other cases, but nonetheless exhibits the expected trend.
Fig. 1. Structure of [Cr(CO)4{MeSe(CH2)2SeMe}] with atom number-
ing scheme. Ellipsoids are drawn at the 40% probability level.

240
A.J. Barton et al. / Journal of Organometallic Chemistry 579 (1999) 235–242
support the proposal of Schumann and Hoffmann [19]
that telluroethers are the best donors among group 16
ligands towards low valent metal centres.
4.3. [Cr(CO)4{PhTe(CH2)3TePh}]
Yield 73% (Found: C, 36.5; H, 2.7. C19H16CrO4Te2
requires C, 37.1; H, 2.6%). FAB-MS M+ 616, 560.
16
Calc. for C19H CrO1430Te2; (P+) 620, (P−2CO)+ 564.
52
4. Experimental
4.4. [Cr(CO)4{MeS(CH2)2SMe}]
All preparations were performed under a dinitrogen
atmosphere using standard Schlenk techniques. The
complexes are air-stable as solids. The M(CO)6 were
obtained from Aldrich and converted into
[Cr(CO)4(nbd)], [Mo(CO)4(nbd)] and [W(CO)4{Me2N-
(CH2)3NMe2}] by minor modifications of literature
routes [21,22]. The tellurium ligands were made as
described [23].
Yield 57% (Found: C, 33.7; H, 3.5. C8H10CrO4S2
requires C, 33.6; H, 3.5%). FAB-MS M+ 286, 258, 230,
10
258, (P−2CO)+ 230, (P−3CO)+ 202.
202. Calc. for C8H CrO342S2; (P)+ 286, (P−CO)+
52
4.5. [Cr(CO)4{MeS(CH2)3SMe}]
Yield 56% (Found: C, 35.4; H, 3.9. C9H12CrO4S2
requires C, 36.0; H, 4.0%). FAB-MS M+ 300, 272, 244,
12
IR spectra were run in 1 mm solution cells fitted with
NaCl optics on a Perkin Elmer 1600 FTIR spectrome-
ter. Mass spectra (FAB) on a VG analytical 70-250-SE
216. Calc. for C9H CrO342S2; (P)+ 300, (P−CO)+
52
272, (P−2CO)+ 272, (P−3CO)+ 244, (P−4CO)+
1
instrument using 3-NOBA as matrix. H NMR spectra
216.
were obtained from CDCl3 solutions on a Bruker
AM300 operating at 300 MHz and referenced to TMS.
13C{1H}-, 77Se{1H}-, 125Te{1H}- and 95Mo-NMR
4.6. [Cr(CO)4{MeSe(CH2)2SeMe}]
spectra were obtained on
a Bruker AM360 at
Yield 50% (Found: C, 25.2; H, 2.7. C8H10CrO4Se2
90.5, 68.68, 113.6 and 23.4 MHz, respectively, and
referenced respectively to TMS, neat external Me2Se,
requires C, 25.3; H, 2.6%). FAB-MS M+ 382, 354, 326.
10
Calc. for C8H CrO840Se2; (P)+ 380, (P−CO)+ 352,
52
neat external Me2Te, and aqueous [MoO4]2−
.
(P−3CO)+ 324.
Samples were contained in 10 mm OD tubes contain-
ing CH2Cl2–10% CDCl3 solutions, and for 13C{1H}
studies, Cr(acac)3 and a pulse delay of 2 s were used
to overcome the slow relaxation of the carbonyl
groups.
4.7. [Cr(CO)4{MeSe(CH2)3SeMe}]
Yield 69% (Found: C, 27.2; H, 2.7. C9H12CrO4Se2
requires C, 27.4; H, 3.1%). FAB-MS M+ 396, 368, 340,
12
The complexes were prepared by the same general
methods, examples of which are described.
312. Calc. for C9H CrO840Se2; (P)+ 396, (P−CO)+
52
368, (P−2CO)+ 340, (P−4CO)+ 312.
4.1. [Cr(CO)4{MeTe(CH2)3TeMe}]
4.8. [Cr(CO)4{o-C6H4(SeMe)2}]
[Cr(CO)4(nbd)] (0.12g, 0.47 mmol) was dissolved in
degassed toluene (15 cm3) and the ligand (0.15 g, 0.47
mmol) added via a syringe. The reaction mixture was
stirred at 50°C overnight and then the toluene removed
in vacuo. The residue was dissolved in CHCl3 (5 cm3),
filtered and cold n-pentane added to yield a bright
yellow powder. This was filtered off, washed with n-
pentane and vacuum dried. Yield 0.15 g 67%. (Found:
C, 21.7; H, 2.2. C9H12CrO4Te2 requires C, 21.9; H,
2.4%). FAB-MS M+ 492, 464, 436, 408, 380. Calc. for
Yield 72% (Found: C, 33.4; H, 2.5. C12H10CrO4Se2
requires C, 33.7; H, 2.3%). FAB-MS M+ 430, 402, 374,
10
402, (P−2CO)+ 374, (P−4CO)+ 346.
346. Calc. for C12H CrO840Se2 (P)+ 430, (P−CO)+
52
4.9. [Mo(CO)4{MeTe(CH2)3TeMe}]
[Mo(CO)4(nbd)] (0.12g, 0.4 mmol) was dissolved in
degassed toluene (15 cm3) and the ligand (0.13g, 0.4
mmol) added via a syringe. The reaction mixture was
stirred at room temperature overnight and then the
toluene removed in vacuo. The residue was dissolved in
CHCl3 (5 cm3), filtered and cold n-pentane added to
yield a pale yellow powder. This was filtered off,
washed with n-pentane and vacuum dried. Yield 0.15g,
69%. (Found: C, 20.4; H, 2.3. C9H12MoO4Te2 requires
C, 20.2; H, 2.3%). FAB-MS M+ 536, 508. Calc. for
C9H CrO1480Te2; (P)+ 496, (P−CO)+ 468, (P−
52
12
2CO)+ 440, (P−3CO)+ 412, (P−4CO)+ 384.
4.2. [Cr(CO)4{o-C6H4(TeMe)2}]
Yield 52% (Found: C, 27.8; H, 2.0. C12H10CrO4Te2
requires C, 27.4; H, 1.9%). FAB-MS M+ 526, 440.
10
Calc. for C12H CrO1430Te2; (P)+ 530, (P−3CO)+ 446.
C9H MoO1430Te2; (P)+ 542, (P−CO)+ 514.
52
98
12

A.J. Barton et al. / Journal of Organometallic Chemistry 579 (1999) 235–242
241
4.10. [Mo(CO)4{o-C6H4(TeMe)2}]
yield a pale yellow powder. This was filtered off,
washed with n-pentane and vacuum dried. Yield 0.09 g
53%. (Found: C, 17.5; H, 1.9. C9H12O4Te2W requires
C, 17.3; H, 1.9%). FAB-MS M+ 623. Calc. for
C9H12O4130Te1284W; (P)+ 628.
Yield 60% (Found: C, 25.5; H, 1.8. C12H10MoO4Te2
requires C, 25.3; H, 1.8%).
4.11. [Mo(CO)4{PhTe(CH2)3TePh}]
4.19. [W(CO)4{o-C6H4(TeMe)2}]
Yield 74% (Found: C, 34.5; H, 2.4. C19H16MoO4Te2
requires C, 34.6; H, 2.4%). FAB-MS M+ 660, 632, 604.
16
(P−2CO)+ 610.
Yield 71% (Found: C, 22.0; H, 1.7. C12H10O4Te2W
requires C, 21.9; H, 1.5%). FAB-MS M+ 657. Calc. for
C12H10O4130Te1284W; (P)+ 662.
Calc. for C19H MoO1430Te2; (P)+ 666, (P−CO)+ 638,
98
4.12. [Mo(CO)4{MeS(CH2)2SMe}]
4.20. [W(CO)4{PhTe(CH2)3TePh}]
Yield 63% (Found: C, 29.2; H, 3.1. C8H10MoO4S2
requires C, 29.1; H, 3.0%). FAB-MS M+ 332, 304, 276.
10
(P−2CO)+ 276.
Yield 63% (Found: C, 29.7; H, 2.1. C19H16O4Te2W
requires C, 30.5; H, 2.1%). FAB-MS M+ 747. Calc. for
C19H16O4130Te1284W; (P)+ 752.
Calc. for C8H MoO4S2; (P)+ 332, (P−CO)+ 304,
98
4.21. [W(CO)4{MeS(CH2)2SMe}]
4.13. [Mo(CO)4{MeS(CH2)3SMe}]
Yield 73% (Found: C, 22.8; H, 2.4. C8H10O4S2W
requires C, 23.0; H, 2.4%). FAB-MS M+ 418, 390.
Calc. for C8H10O342S2184W; (P)+ 418, (P−2CO)+ 390.
Yield 63% (Found: C, 31.2; H, 3.5. C9H12MoO4S2
requires C, 31.4; H, 3.5%). FAB-MS M+ 346, 318.
12
Calc. for C9H MoO4S2; (P)+ 346, (P−CO)+ 318.
98
4.22. [WCO)4{MeS(CH2)3SMe}]
4.14. [Mo(CO)4{o-C6H4(SMe)2}] · 1/2CH2Cl2
Yield 70% (Found: C, 24.6; H, 2.7. C9H12O4S2W
requires C, 25.0; H, 2.7%). FAB-MS M+ 432, 404.
Calc. for C9H12O4S1284W; (P)+ 432, (P−2CO)+ 404.
Yield
63%
(Found:
C,
35.6;
H,
2.6.
C10.5H11ClMoO4S2 requires C, 35.6; H, 2.6%).
4.15. [Mo(CO)4{MeSe(CH2)2SeMe}]
4.23. [W(CO)4{MeSe(CH2)2SeMe}]
Yield 61% (Found: C, 22.8; H, 2.5. C8H10MoO4Se2
requires C, 22.7; H, 2.4%). FAB-MS M+ 424, 398, 370.
10
(P−2CO)+ 372.
Yield 60% (Found: C, 18.9; H, 2.1. C8H10O4Se2W
requires C, 18.8; H, 2.1%).
Calc. for C8H MoO840Se2; (P)+ 428, (P−CO)+ 400,
98
4.24. [W(CO)4{MeSe(CH2)3SeMe}]
4.16. [Mo(CO)4{MeSe(CH2)3SeMe}]
Yield 75% (Found: C, 20.6; H, 2.4. C9H12O4Se2W
requires C, 20.5; H, 2.3%). FAB-MS M+ 526, 498.
Calc. for C9H12O840Se2184W; (P)+ 528, (P−CO)+ 500.
Yield 73% (Found: C, 24.8; H, 2.4. C9H12MoO4Se2
requires C, 24.7; H, 2.7%). FAB-MS M+ 440, 410.
12
Calc. for C9H MoO840Se2; (P)+ 442, (P−CO)+ 414.
4.25. [W(CO)4{o-C6H4(SeMe)2}]
98
4.17. [Mo(CO)4{o-C6H4(SeMe)2}]
Yield 68% (Found: C, 25.6; H, 2.0. C12H10O4Se2W
requires C, 25.7; H, 1.8%). FAB-MS M+ 560, 532, 504.
Calc. for C12H10O840Se2184W; (P)+ 562, (P−CO)+ 534,
(P−2CO)+ 506.
Yield 73% (Found: C, 29.7; H, 2.1. C12H10MoO4Se2
requires C, 30.5; H, 2.1%).
4.18. [W(CO)4{MeTe(CH2)3TeMe}]
4.26. Crystal structure of
[Cr(CO)4(MeSeCH2CH2SeMe)]
[W(CO)4(Me2N(CH2)3NMe2)] (0.12g, 0.28 mmol) was
dissolved in degassed toluene (15 cm3) and the ligand
(0.09 g, 0.28 mmol) added via a syringe. The reaction
mixture was stirred at 70°C overnight and then the
toluene removed in vacuo. The residue was dissolved in
CHCl3 (5 cm3), filtered and cold n-pentane added to
Details of the crystallographic data collection and
refinement parameters are given in Table 5. The crystals
were grown by vapour diffusion of n-pentane into a
solution of the complex in chloroform. Data collection
used
a Rigaku AFC7S four-circle diffractometer

242
A.J. Barton et al. / Journal of Organometallic Chemistry 579 (1999) 235–242
Table 5
Acknowledgements
Data collection parameters for [Cr(CO)4(MeSeCH2CH2SeMe)]
The authors thank EPSRC for support.
Formula
C8H10CrO4Se2
380.08
P1
Formula weight
Space group
˚
a (A)
8.069(5)
11.314(8)
7.909(4)
91.41(6)
115.74(4)
69.43(5)
601.8(8)
2
2.097
69.89
1.000/0.507
2125
1698
References
˚
b (A)
˚
c (A)
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h (°)
i (°)
k (°)
3
˚
V (A )
Z
Dcalc (g cm−3
)
v(Mo–Ka) (cm−1
)
C-scans (max./min. transmission factors)
Unique observed reflections
Observed reflections with [Io=2|(Io)]
No. of parameters
136
0.038
0.037
Ra
Rw
b
a R=ꢀ (ꢁFoꢁi−ꢁFcꢁi)/ꢀ ꢁFoꢁi.
b Rw=ꢂ[ꢀ wi(ꢁFoꢁi−ꢁFcꢁi)2/ꢀ wiꢁFoꢁi ].
2
[8] (a) R. Donaldson, G. Hunter, R.C. Massey, J. Chem. Soc. Dalton
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1769.
equipped with an Oxford Systems open-flow cryostat
operating at 150 K and using graphite-monochromated
Mo–Ka X-radiation (u=0.71073 A). No significant
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(1984) 1.
˚
crystal decay or movement was observed. The structure
was solved by direct methods [24] and developed by
iterative cycles of full-matrix least-squares refinement
and difference Fourier syntheses [25]. All non-H atoms
were refined anisotropically while H-atoms were placed
˚
in fixed, calculated positions with d(CꢀH)=0.96 A.
The weighting scheme w−1=|2(F) gave satisfactory
agreement analyses. Selected bond lengths and angles
are given in Table 4.
[19] H. Schumann, A.A. Arif, A.L Rheingold, C. Janiak, R. Hoff-
mann, N. Kuhn, Inorg. Chem. 30 (1991) 1618.
5. Supplementary material
[20] N.P. Luthra, J.D. Odom, in: S. Patai, Z. Rappoport (eds.), The
Chemistry of Organic Selenium and Tellurium Compounds,
Wiley, New York, 1986, Chapter 6.
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[22] G.R. Dobson, G.C. Faber, Inorg. Chim. Acta. 4 (1987) 87.
[23] (a) E.G. Hope, T. Kemmitt, W. Levason, Organometallics 7
(1988) 78. (b) T. Kemmitt, W. Levason, Organometallics 8 (1989)
1303.
[24] G.M. Sheldrick, SHELXS86, Program for crystal structure solu-
tion, Acta Crystallogr. Sect. A 46 (1990) 467.
[25] TeXsan: Crystal Structure Analysis Package, Molecular Structure
Corporation, Texas, 1995.
Crystallographic data for H-atom coordinates, an-
isotropic thermal parameters and full listings of bond
lengths and angles for the structure have been deposited
with the Cambridge Crystallographic Data Centre.
Copies of this information may be obtained free of
charge from The Director, CCDC, 12 Union Road,
Cambridge, CB2 1EZ, UK (fax: +44-1223-336-033;
e-mail:
deposit@ccdc.ac.uk
or
www:
http://
www.ccdc.cam.ac.uk).
.