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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)].