but the more sterically encumbered starting materials 2c and 2d
do not react with [Mo2(CO)4(η-C5H5)2] at room temperature
and require greater thermal activation ultimately yielding com-
plexes 4. The putative intermediate A or subsequent intermedi-
ates undergo facile bond cleavage as a result of the more
demanding bulk of the Me group in A. If the steric demand
of the alkyne is further increased to [{Ru(CO)2(η-C5H5)}2-
184 ЊC (Found: C, 40.5; H, 2.68. Calc. for C24H18Mo2O6Ru: C,
41.45; H, 2.61%). IR (thf): ν (CO) 2022m, 1968s, 1951m, 1908
1
(sh), 1891s and 1822m. H NMR (C6D5CD3): δ 5.01 (s, 10 H,
η-C5H5), 4.73 (s, 5 H, η-C5H5) and 2.66 (s, 3 H, CH3). 13C NMR
(C6D5CD3): δ 235.1 (s, CO), 200.1 (s, CO), 109.9 (s, Cα), 93.2 (s,
Cβ), 92.7 (s, η-C5H5), 89.3 (s, η-C5H5) and 27.1 (s, CH3). FAB
mass spectrum: m/z 696 (Mϩ, 100), 612 ([M Ϫ 3CO]ϩ, 22), 586
([M Ϫ 4CO]ϩ, 18) and 528 ([M Ϫ 6CO]ϩ, 42%).
᎐
(µ᎐C᎐C)] then even the Ru᎐C(sp) bond becomes labile and a
᎐
major fragmentation of the initially formed simple dimolybde-
num adduct occurs giving 7. The analogous iron compound
[Mo2Ru(ì-CCPh)(CO)6(ç-C5H5)3] 3b. A solution of [Mo2-
(CO)4(η-C5H5)2] (58 mg, 0.133 mmol) and [Ru(CO)2-
᎐
[{Fe(CO) (η-C Me )} (µ᎐C᎐C)] does not react with [Mo (CO) -
᎐
2
5
5
2
2
4
(η-C5H5)2]28 to form an adduct but prolonged reaction results
in carbonyl transfer to give [Mo2(CO)6(η-C5H5)2].
(C᎐CPh)(η-C H )] (43 mg, 0.133 mmol) in tetrahydrofuran (20
᎐
᎐
5
5
cm3) was stirred at reflux (18 h). The solvent was removed in
vacuo and the residue eluted through a silica column (2 × 10
cm, 100% CH2Cl2 eluent) to produce a single black band.
Recrystallisation (CH2Cl2–n-hexane) yielded black crystals of
compound 3b (60 mg, 59%), m.p. 188–190 ЊC (Found: C, 45.70;
H, 2.68. Calc. for C29H20Mo2O6Ru: C, 45.98; H, 2.66%). IR
Conclusion
The reaction of metalloalkynes with [Mo2(CO)4(η-C5H5)2] was
found to mimic the reaction of simple organic alkynes in the
main. Thus the ruthenium alkynyl adducts readily reacted to
give the dimolybdenum adducts 3 with a distorted tetrahedral
Mo2C2 core and a semibridging carbonyl group. These com-
pounds exist as rotamers in the solid state with respect to the
Ru᎐C(sp) bond. However, it is clear that if the steric require-
ments of the ‘alkyne’ are large then the simple adduct is
unstable, if formed at all, and will fragment if a suitable
pathway is available.
1
(thf): ν (CO) 2027s, 1970s, 1954s, 1905s, 1893s and 1824m. H
NMR (C6D6): δ 7.35–7.20 (m, 5 H, Ph), 5.04 (s, 10 H, η-C5H5)
and 4.70 (s, 5 H, η-C5H5). 13C NMR (CD2Cl2): δ 229.3 (s, CO),
196.4 (s, CO), 131.6–125.7 (m, Ph), 111.9 (Cα), 94.8 (Cβ), 94.2
(s, C5H5) and 91.1 (s, C5H5). FAB mass spectrum: m/z 758 (Mϩ,
20), 674 ([M Ϫ 3CO]ϩ, 17), 646 ([M Ϫ 4CO]ϩ, 10) and 588
([M Ϫ 6CO]ϩ, 22%).
The fluxional nature of this class of complex was observed by
variable-temperature solution NMR studies and rotation about
the Ru᎐C(sp) bond, suggested by the solid-state structures, was
established. The molybdenum carbonyl groups are all observed
equivalently at room temperature which is surprising given the
unsymmetrical nature of the adduct. The mechanism for the
equilibration must involve disruption of the Mo2C2 core with
rotation about an axis that passes through the midpoints of
both the C᎐C and Mo᎐Mo bonds.
[Mo2(ì-HC2Me)(CO)4(ç-C5H5)2] 4a. A solution of [Mo2-
᎐
(CO) (η-C H ) ] (51 mg, 0.12 mmol) and [Fe(CO) (C᎐CMe)-
᎐
4
5
5
2
2
(η-C5H5)] (26 mg, 0.12 mmol) in tetrahydrofuran (15 cm3) was
stirred at reflux (10 h). The solvent was removed in vacuo and
the residues eluted through a silica column (2 × 10 cm; CH2Cl2–
hexanes, 2:3) to produce two dark coloured bands. The first
band was collected and recrystallised from hexane to yield dark
red crystals of compound 4a (45 mg, 81%), the second was
collected and gave [Fe2(CO)4(η-C5H5)2] (18 mg, 85%). The
compounds exhibited spectroscopic properties identical with
those reported.34
Experimental
General conditions
[Mo2(ì-HC2Ph)(CO)4(ç-C5H5)2] 4b. A solution of [Mo2-
᎐
(CO) (η-C H ) ] (58 mg, 0.134 mmol) and [Fe(CO) (C᎐CPh)-
Oxygen- and moisture-sensitive compounds were manipulated
under an atmosphere of high-purity argon using standard
Schlenk techniques or in a dry-box (Miller Howe).
᎐
4
5
5
2
2
(η-C5H5)] (43 mg, 0.133 mmol) in tetrahydrofuran (20 cm3)
were stirred at reflux (24 h). The solvent was removed in vacuo
and the residues washed with n-hexane until the filtrates were
clear. Recrystallisation (CH2Cl2–n-hexane) gave red needles of
compound 4b (20 mg, 28%), which exhibited spectroscopic
properties identical with those reported.34
Infrared spectra were recorded using a Bio-Rad FTS 45 or 40
FTIR spectrometer, H and 13C NMR spectra using Varian
1
Gemini 200 or Bruker ARX 500 spectrometers and 31P NMR
spectra using a Bruker ARX 500 spectrometer. The 1H and 13
C
NMR spectra were referenced with respect to incompletely deu-
teriated solvent signals, 31P NMR spectra to external H3PO4 (δ
0.0) and proton decoupled. Mass spectra were obtained on a
VG AutoSpec spectrometer employing a fast atom bombard-
ment (FAB) ionisation source unless otherwise specified.
Elemental analyses were performed by Chemical and Micro
Analytical Services Pty. Ltd., Melbourne, Australia.
Tetrahydrofuran was dried over sodium metal and distilled
from potassium–benzophenone under an atmosphere of argon.
n-Hexane and toluene were dried over sodium metal and dis-
tilled from sodium–benzophenone under an atmosphere of
argon. Distilled solvents were stored over sodium or potassium
mirrors until use.
Crystallography
Unique room-temperature diffractometer data sets were meas-
ured (2θ–θ scan mode, 2θmax 50Њ; monochromatic Mo-Kα radi-
ation, λ = 0.71073 Å; T = 295 K), yielding N independent
reflections, No of these with I > 3σ(I) considered ‘observed’ and
used in the full-matrix least-squares refinement after Gaussian
absorption correction. Anisotropic thermal parameters were
refined for the non-hydrogen atoms, (x, y, z, Uiso)H being con-
strained at estimated values. Conventional residuals R, RЈ on
|F| are quoted at convergence, statistical weights being deriv-
ative of σ2(I) = σ2(Idiff) ϩ 0.0004σ4(Idiff). Neutral atom complex
scattering factors were employed. Computation used the XTAL
3.4 program system implemented by S. R. Hall.35 Pertinent
results are given in Table 3, variants being noted below.
Syntheses
[Mo2Ru(ì-CCMe)(CO)6(ç-C5H5)3] 3a. A solution of [Mo2-
Two pseudo-centrosymmetrically related molecules of com-
pound 3a comprise the asymmetric unit in the space group
Pca21. A hemisphere of data was measured in order to explore
the possibilities of refinement of alternative chiralities (inclu-
sive of ‘Flack x’) in order definitively to establish the same, and
of the symmetry being less than orthorhombic. In the event
none of these excursions yielded meaningful results, and the
data were merged (Rint = 0.060) and the structure refined to
᎐
(CO) (η-C H ) ] (82 mg, 0.191 mmol) and [Ru(C᎐CMe)-
᎐
4
5
5 2
(CO)2(η-C5H5)] (50 mg, 0.191 mmol) in tetrahydrofuran (30
cm3) was stirred at reflux (12 h). The solvent was removed in
vacuo and the residue eluted through a silica column (2 × 10
cm, 60% CH2Cl2–40% n-hexane eluent) to produce a single
black band. Recrystallisation (toluene–n-hexane, Ϫ28 ЊC)
yielded black crystals of compound 3a (74 mg, 56%), m.p. 182–
J. Chem. Soc., Dalton Trans., 1998, Pages 1575–1580
1579
Byrne, Lindsay T.
