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New tetrahedrane complexes from molybdenum alkynyls andCo2(CO)8
Julio Perez a,*, Lucıa Riera a, Vıctor Riera a, Santiago Garcıa-Granda b,Esther Garcıa-Rodrıguez b, David George Churchill c, Melvyn Rowen Churchill c,
Thomas S. Janik d
a Departamento de Quımica Organica e Inorganica /I.U.Q.O.E.M., 33071 Oviedo, Spainb Departamento de Quımica Fısica y Analıtica, Facultad de Quımica, Universidad de Oviedo-C.S.I.C., 33071 Oviedo, Spain
c Department of Chemistry, State University of New York, Buffalo, NY 14260-3000, USAd State University of New York College at Fredonia, Fredonia, NY, 14063, USA
Received 21 March 2002; accepted 14 May 2002
This paper is dedicated to Professor Rafael Uson, a pioneer of organometallic chemistry in Spain
Abstract
The molybdenum alkynyl complexes [Mo(C�/CPh)(h3-allyl)(CO)2(bipy)] (1) and [Mo(C�/CH)(h3-allyl)(CO)2(N�/N)] (N�/N�/
2,2?-bipyridine, 2a; 1,10-phenanthroline, 2b) react with dicobalt octacarbonyl to give the new tetrahedrane trimetallic complexes
[Co2(CO)6(m-h2:h2-M�/C�/CPh)], M�/{Mo(h3-C3H5)(CO)2(bipy)} (3) and [Co2(CO)6(m-h2:h2-M�/C�/CH)], M�/{Mo(h3-
C3H5)(CO)2(N�/N)} (N�/N�/bipy, 4a; phen, 4b), respectively. These new compounds were characterized by analytical (C, H, N),
spectroscopic (IR, 1H NMR) and crystallographic (single crystal X-ray diffraction) means.
# 2003 Elsevier Science B.V. All rights reserved.
Keywords: Tetrahedrane complexes; Molybdenum alkynyls; Crystal structures
1. Introduction
The reactions of acetylenes with [Co2(CO)8] to afford
[(m-h2:h2-R1�/C�/C�/R2)Co2(CO)6] complexes are classi-
cal processes in organometallic chemistry. In some
instances, the stability of the products allowed the
derivatization of the R substituents, and a subsequent
demetallation step afforded the new acetylenes [1]. On
the other hand, [(m-h2:h2-R1�/C�/C�/R2)Co2(CO)6] com-
plexes react with CO, olefins and acetylenes to afford
C�/C coupled products with high regioselectivity [2].
Similar [(m-h2:h2-R�/C�/C�/MLn)Co2(CO)6] compounds
can be obtained by reaction of metal alkynyl complexes
[3], LnM�/C�/C�/R, with [Co2(CO)8], although this
chemistry has been much less studied. The first com-
pounds of this kind, namely, the complexes [(m-h2:h2-
CpFe(CO)(L)�/C�/C�/R)(Co2(CO)6)] (R�/Me, Ph; L�/
CO, PMe2Ph) were reported by Yamazaki in 1972 [4],
and the structure of the derivative with R�/Ph, L�/CO
was determined by X-ray diffraction by Bruce in 1986
[5]. Riera found that complexation to the {Co2(CO)6}
unit stabilized the otherwise difficult to obtain trans
geometry of the alkynyl [Mn(C�/CPh)(CO)4(PCy3)],
which could be liberated by treatment with [I(py)2]BF4
[6].
We have recently reported the preparation of newalkynyl complexes [Mo(C�/CR)(h3-allyl)(CO)2(N�/N)]
(R�/H, Ph; N�/N�/2,2?-bipyridine, 1,10-phenanthro-
line) [7]. Their reactions with [Co2(CO)8], as well as the
crystallographical characterization of two products, are
the subject of this paper.
2. Experimental
2.1. General procedures
All manipulations were carried out under dinitrogen
using standard Schlenk techniques. Solvents were dis-* Corresponding author. Tel.: �/34-98-5102-985; fax: �/34-98-5103-
446
Inorganica Chimica Acta 347 (2003) 189�/193
www.elsevier.com/locate/ica
0020-1693/03/$ - see front matter # 2003 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 0 - 1 6 9 3 ( 0 2 ) 0 1 4 4 2 - 1
tilled from freshly wired Na (hexanes), Na/benzophe-
none (THF) and CaH2 (CH2Cl2) prior to use. CD2Cl2was degassed by three freeze-pump-thaw cycles, dried
over 4 A molecular sieves and stored in the dark in aYoung tube. Elemental analyses were obtained using a
Perkin�/Elmer 240-B microanalyzer. The IR and NMR
spectra were recorded on Perkin�/Elmer FT 1720-X and
Bruker AC-200 or AC-300 spectrometers, respectively.
[Mo(C�/CPh)(h3-allyl)(CO)2(bipy)] (1) and [Mo(C�/
CH)(h3-allyl)(CO)2(N�/N)] (N�/N�/bipy, 2a; phen, 2b)
were prepared according to literature procedures [7]. All
other chemicals were used as received from commercialsources.
2.2. X-ray crystallographic analyses for 3 and 4b
The most relevant crystal and refinement data are
collected in Table 3.
2.3. Preparation of compounds [Co2(CO)6(m-h2:h2-M�/
C�/CR)]
2.3.1. [Co2(CO)6(m-h2:h2-M�/C�/CPh)], M�/
{Mo(h3-C3H5)(CO)2(bipy)} (3)
[Co2(CO)8] (0.12 g, 0.33 mmol) was added to a
solution of [Mo(C�/CPh)(h3-allyl)(CO)2(bipy)] (1) (0.15
g, 0.33 mmol) in THF (20 ml). The solution was stirred
for 45 min and then the solvent was evaporated under
reduced pressure. The residue was extracted withCH2Cl2/hexane (1:2) and filtered through alumina
(activation grade IV). The volatiles were removed in
vacuo, and the residue was washed with hexane (3�/10
ml). Slow diffusion of hexane into a solution of 3 in
CH2Cl2 at �/20 8C produced dark red crystals. A single
crystal obtained in this way was used for the X-ray
analysis. Yield: 73% (0.17 g). Anal. Calc. for C29H18Co2-
MoN2O8: C, 47.31; H, 2.46; N, 3.80. Found: C, 47.2; H,2.5; N, 3.7%. IR (THF): 2062, 2024, 1993, 1939, 1886,
1862 (nCO). 1H NMR(CD2Cl2): 8.76, 8.13, 8.09 and 7.94
[m, 2H each, bipy], 7.39 [m, 3H, Ph], 7.23 [m, 2H, Ph],
3.11 [d (JHs,c�/6.6 Hz), 2H, Hsyn ], 3.02 [m, 1H, Hc ], 1.70
[d (JHa,c�/9.4 Hz), 2H, Hanti ].
2.3.2. [Co2(CO)6(m-h2:h2-M�/C�/CH)], M�/{Mo(h3-
C3H5)(CO)2(bipy)} (4a)
[Co2(CO)8] (0.11 g, 0.32 mmol) was added to a
solution of [Mo(C�/CH)(h3-C3H5)(CO)2(bipy)] (2a)
(0.12 g, 0.32 mmol) in THF (20 ml). The solution was
stirred for 45 min and the solvent was evaporated under
vacuum. The solid was extracted with CH2Cl2/hexane
(1:2) and filtered through alumina (activation grade IV).
Slow diffusion of hexane into a CH2Cl2 solution of 4a at
�/20 8C afforded dark red crystals, one of which wassuitable for an X-ray experiment. Yield: 61% (0.13 g).
Anal. Calc. for C23H14Co2MoN2O8: C, 41.84; H, 2.14;
N, 4.24. Found: C, 42.1; H, 2.1; N, 4.3%. IR (THF):
2063, 2024, 1992, 1940, 1886, 1865 (nCO). 1H
NMR(CD2Cl2): 8.75, 8.15, 7.99 and 7.47 [m, 2H each,
bipy], 6.52 [s, 1H, Mo�/C�/CH ], 3.05 [sbr, 2H, Hsyn ], 2.93
[m, 1H, Hc ], 1.69 [d (JHa,c�/9.1 Hz), 2H, Hanti ].
2.3.3. [Co2(CO)6(m-h2:h2-M�/C�/CH)], M�/{Mo(h3-
C3H5)(CO)2(phen)} (4b)
The procedure was similar to that described for 4a,
using [Mo(C�/CH)(h3-C3H5)(CO)2(bipy)] (2b) (0.08 g,
0.20 mmol) and [Co2(CO)8] (0.068 g, 0.20 mmol) in THF
(20 mL). The complex 4b was obtained as a dark red
microcrystalline solid. Yield: 65% (0.09 g). Anal. Calc.
for C25H14Co2MoN2O8: C, 43.89; H, 2.06; N, 4.09.Found: C, 44.1; H, 2.0; N, 4.1%. IR (THF): 2063, 2024,
1992, 1940, 1886, 1865 (nCO). 1H NMR(CD2Cl2): 9.10
[dd(JH2,3�/JH9,8�/5.1 Hz, JH2,4�/JH7,9�/1.4 Hz), 2H,
H2,9], 8.49 [dd(JH4,3�/JH7,8�/8.0 Hz), 2H, H4,7], 7.98 [s,
2H, H5,6], 7.80 [dd, 2H, H3,8], 6.54 [s, 1H, Mo�/C�/CH ],
3.15 [d (JHs,c�/5.8 Hz), 2H, Hsyn ], 2.87 [m, 1H, Hc ], 1.77
[d (JHa,c�/9.9 Hz), 2H, Hanti ].
3. Results and discussion
The complexes [Mo(C�/CPh)(h3-allyl)(CO)2(bipy)] (1)
[7] and [Mo(C�/CH)(h3-allyl)(CO)2(N�/N)] (N�/N�/
bipy, 2a; phen, 2b) [7] reacted smoothly with
[Co2(CO)8] (see Section 2) in either CH2Cl2 or tetra-
hydrofuran (THF). Hexane, usually employed as solventfor the reaction of acetylenes with [Co2(CO)8], could not
be used due to the insolubility of the molybdenum
alkynyls used as reagents. The reactions were accom-
panied by gas (CO) evolution and by a darkening in the
color of the solutions. Furthermore, the reactions could
be conveniently monitored by IR spectroscopy in the
2200�/1600 cm�1 region. The reaction products could be
purified by column chromatography followed by crys-tallization in CH2Cl2/hexane mixtures at low tempera-
ture, and were isolated in good yields (see Section 2).
Examination of the 1H NMR spectra of the isolated
products, discussed below, showed them to consist of
single compounds. The comparison between the IR
spectra of the isolated products, obtained as crystalline
solids, and those of the reaction crudes, indicated that
the isolated species were the only reaction products. Thepresence of six bands in the nCO region of their IR
spectra in THF clearly pointed to their polynuclear
nature. IR and 1H NMR spectroscopic data, C, H, N
analysis and single-crystal X-ray determinations (see
below) established a composition [(m-h2:h2-R�/C�/C�/
Mo(h3-C3H5)(CO)2(N�/N)(Co2(CO)6)](R�/Ph, N�/
N�/bipy, 3; R�/H, N�/N�/bipy, 4a; N�/N�/phen,
4b) for the new complexes, as presented in Scheme 1.The IR spectra of complexes 3 and 4a�/b present two
intense nCO absorptions at 1939 and 1862 cm�1 for 3
and at 1940 and 1865 cm�1 for 4a�/b that can be
J. Perez et al. / Inorganica Chimica Acta 347 (2003) 189�/193190
assigned to the cis -Mo(CO)2 moieties. The nCO cis -
Mo(CO)2 bands of complexes 3 and 4a�/b are little
shifted with respect to those of the mononuclear
alkynyls, indicating that the coordination to the
{Co2(CO)6} fragment of the acetylenic unit does not
alter significantly the electron density at the molybde-
num center. The additional four bands in the IR of 3
and 4a�/b correspond to the C�/O stretches of the
{Co2(CO)6} unit. The fact that only four bands for the
{Co2(CO)6} part of the IR can be seen for 3 and 4a�/b,
whereas six bands are present in the IR of typical
[(acetylene) Co2(CO)6] complexes results from band
overlap in the spectra in THF solution (even broader
spectra are obtained in CH2Cl2, whereas 3 and 4a�/b are
insoluble in hexane). The 1H NMR spectra of complexes
3 and 4a�/b show typical sets of three signals indicative
of symmetric, static h3-allyl ligands, and four-signal sets
for the N�/N chelates (see Section 2), revealing the
presence of a mirror plane in the molecules, as it
happens in the precursor alkynyls. In complexes 4a�/b
the C2-bound hydrogens, which occurred at 2.12 ppm in
the alkynyl (2a) and at 2.11 ppm in (2b, Fig. 1), appear
at 6.52 ppm in 4a and at 6.54 ppm in 4b. Similar upfield
shifts were observed in other [m-LnM�/C�/CH)-
(Co2(CO)8)] compounds [8].13C NMR, which is very informative for acetylenic
derivatives [9], could not be used for complexes 3 and
4a�/b given that their limited solubility precluded the
observation of the (inherently weak) acetylenic signals
employing adquisition times over which these com-
pounds are stable (extensive decomposition was ob-
served upon standing eight hours at room temperature
in either CDCl3 or CD2Cl2 solution). Hence, the
structures of 3 and 4b were determined by X-ray
diffraction, and the results are given in Fig. 2(a) and
Tables 1 and 3 (3) and in Fig. 2(b) and Tables 2 and 3
(4b).
The two molecules contain Co2C2 cores of approxi-
mately tetrahedral geometry, and {Mo(h3-C3H5)-
(CO)2(N�/N)} units as substituents at one of the
‘acetylenic’ carbons. In accordance with the spectro-
scopic data (see above), the molybdenum fragments
present a pseudooctahedral geometry, with the acetyle-
nic carbon and the h3-allyl group in trans positions, and
the two cis carbonyls and the two nitrogens defining an
equatorial plane. The allyl group is symmetrically
placed, with its open face pointing towards the CO’s,
as is usual in [MoX(h3-allyl)(CO)2(N�/N)] compounds
[10].As is normally encountered in the structure of
dicobalt hexacarbonyl adducts of LnM�/C�/C�/R com-
plexes,1 the main discrepancies between the structures of
3 and 4b, and those of the starting alkynyls 1 and 2b is
the lengthening of the C�/C distances from the typical
acetylenic values of 1.20(3) A for 1 and 1.166(6) A for
2b,2 to 1.320(7) A for 3 and 1.324(7) A for 4b; and the
loss of the linearity of the Mo�/C�/C�/R unit: the angle
C(ipso )�/C�/C shifts from 174(2) in 1 to 143.9(5)8 in 3,
and the Mo�/C�/C angles change from 169.6(19)8 in 1
and 177.9(4)8 in 2b to 144.6(4)8 in 3 and 141.7(4)8 in 4b.
Among the limited number of structures of [(m-LnM�/
C�/C�/R)(Co2(CO)6)] complexes crystallographically de-
termined, the only molybdenum example is, as far as we
Scheme 1.
Fig. 1. Assignation of the hydrogens in the 1H NMR spectra for the
ligand 1,10-phenanthroline.
1 Co2(CO)6 adducts of acetylenes are usually oily materials, see
Refs. [1,8b].2 These values are even slightly shorter than those found in organic
acetylenes, see Ref. [3], a fact that was interpreted as indicative of little
p-acceptor character in the alkynyl ligand of these compounds, see
Ref. [13].
J. Perez et al. / Inorganica Chimica Acta 347 (2003) 189�/193 191
Fig. 2. (a) Molecular structure and numbering scheme of 3. (b) Molecular structure and numbering scheme of 4b.
Table 1
Selected bond lengths (A) and bond angles (8) for complex 3
Bond lengths
Mo(1)�/C(1) 1.957(6) Co(1)�/C(4) 1.474(7)
Mo(1)�/C(2) 1.962(6) Co(2)�/C(4) 1.937(5)
Mo(1)�/N(1) 2.237(4) Co(1)�/Co(2) 2.4687(16)
Mo(1)�/N(2) 2.238(4) Co(1)�/C(9) 1.795(8)
Mo(1)�/C(5) 2.331(6) Co(1)�/C(10) 1.800(7)
Mo(1)�/C(6) 2.244(6) Co(1)�/C(19) 1.770(8)
Mo(1)�/C(7) 2.346(6) Co(2)�/C(8) 1.796(7)
Mo(1)�/C(3) 2.234(5) Co(2)�/C(18) 1.772(7)
C(1)�/O(1) 1.161(6) Co(2)�/C(20) 1.794(8)
C(2)�/O(2) 1.156(6) C(9)�/O(9) 1.140(7)
C(5)�/C(6) 1.399(9) C(10)�/O(10) 1.137(8)
C(6)�/C(7) 1.393(9) C(19)�/O(19) 1.137(8)
C(3)�/C(4) 1.320(7) C(8)�/O(8) 1.138(7)
C(4)�/C(41) 1.474(7) C(18)�/O(18) 1.131(7)
Co(1)�/C(3) 2.066(4) C(20)�/O(20) 1.129(8)
Co(2)�/C(3) 2.049(5)
Bond angles
C(11)�/Mo(1)�/C(2) 83.2(2) Mo(1)�/C(3)�/C(4) 144.6(4)
N(1)�/Mo(1)�/N(2) 72.34(16) Mo(1)�/C(3)�/Co(1) 134.6(2)
C(1)�/Mo(1)�/N(1) 169.53(19) Mo(1)�/C(3)�/Co(2) 137.0(3)
C(2)�/Mo(1)�/N(2) 170.50(19) Co(1)�/C(3)�/Co(2) 73.74(17)
C(1)�/Mo(1)�/C(3) 81.6(2) Co(1)�/C(4)�/Co(2) 77.2(2)
C(2)�/Mo(1)�/C(3) 86.3(2) C(3)�/C(49)�/C(41) 143.9(5)
N(1)�/Mo(1)�/C(3) 88.98(17) C(4)�/C(3)�/Co(2) 68.4(3)
N(2)�/Mo(1)�/C(3) 102.4(2) C(4)�/C(3)�/Co(1) 67.0(3)
Table 2
Selected bond lengths (A) and bond angles (8) for complex 4b
Bond lengths
Mo�/C(1) 2.355(6) C(5)�/H(5) 0.984(48)
Mo�/C(2) 2.245(5) Co(2)�/C(21) 1.801(6)
Mo�/C(3) 2.321(6) Co(2)�/C(22) 1.770(6)
Mo�/N(40) 2.257(4) Co(2)�/C(23) 1.800(6)
Mo�/N(51) 2.241(4) C(21)�/O(21) 1.136(7)
Mo�/C(11) 1.958(6) C(22)�/O(22) 1.135(8)
Mo�/C(12) 1.947(6) C(23)�/O(23) 1.132(8)
Mo�/C(4) 2.208(4) Co(3)�/C(4) 2.057(5)
C(1)�/C(2) 1.397(8) Co(3)�/C(5) 1.955(6)
C(2)�/C(3) 1.402(10) Co(3)�/C(31) 1.785(6)
C(4)�/C(5) 1.324(7) Co(3)�/C(32) 1.808(6)
C(11)�/O(11) 1.145(7) Co(3)�/C(33) 1.771(6)
C(12)�/O(12) 1.157(6) C(31)�/O(31) 1.138(7)
Co(2)�/Co(3) 2.488(2) C(32)�/O(32) 1.140(7)
Co(2)�/C(4) 2.064(4) C(33)�/O(33) 1.138(7)
Co(2)�/C(5) 1.968(5)
Bond angles
C(11)�/Mo�/C(12) 74.8(2) Mo�/C(4)�/C(5) 141.7(4)
C(11)�/Mo�/N(51) 167.0(2) Co(3)�/Co(2)�/C(4) 52.7(1)
C(12)�/Mo�/N(40) 170.2(2) Co(3)�/Co(2)�/C(5) 50.4(2)
N(40)�/Mo�/N(51) 73.2(1) C(21)�/Co(2)�/C(22) 99.1(2)
C(11)�/Mo�/C(4) 80.0(2) C(22)�/Co(2)�/C(23) 100.9(3)
C(12)�/Mo�/C(4) 86.2(2) C(31)�/Co(3)�/C(33) 97.6(3)
N(40)�/Mo�/C(4) 86.2(1) C(33)�/Co(3)�/C(32) 100.9(2)
N(51)�/Mo�/C(4) 87.1(2) C(4)�/C(5)�/H(5) 142.0(26)
J. Perez et al. / Inorganica Chimica Acta 347 (2003) 189�/193192
know, Lang’s compound [Mo2(h5-C5H5)(CO)4{m4-
h2:2:2:2-Me3SiC�/C�/C�/C�/SiMe3)Co2(CO)6}] [11], in
which one acetylenic moiety completes a tetrahedral
core with the Co2(CO)6 fragment, whereas a secondM2C2 tetrahedrane includes a Mo2Cp2(CO)4 fragment.
However, it should be noted that dicobalt hexacarbonyl
adducts of tungsten (II) alkynyls have been used in
organic synthesis [12].
The reaction of molybdenum alkynyls 1 and 2a�/b
with [Co2(CO)8] to give the 3 and 4a�/b polymetallic
compounds contrasts with the cleavage of the Mo�/
alkynyl bond that takes place when 1 reacts with othertransition-metal compounds [13].
On the other hand, the thermal stability of 3 and 4a�/b
is limited. Thus, in contrast with the metal�/metal bond
formation reported upon thermally induced decarbony-
lation by Akita and Moro-oka with iron alkynyl-
Co2(CO)6 adducts [8], heating of the THF solutions of
3 and 4a�/b led to decomposition through Mo�/C bond
scission, as evidenced by the identification of[Mo(CO)4(N�/N)] (N�/N�/bipy, phen) as the major
product in the resulting solutions by IR spectroscopy.
This ease of demetallation of the C2 unit may be useful
with regard to the application of complexes 3 and 4a�/b
in organic synthesis.
4. Supplementary material
Crystallographic data (excluding structure factors) for
the structural analysis have been deposited with the
Cambridge Crystallographic Data Centre, CCDC Nos.
181564 and 181565 for compounds 3 and 4b, respec-
tively. Copies of this information may be obtained freeof charge from The Director, CCDC, 12 Union Road,
Cambridge, CB2 1EZ, UK (fax: �/44-1223-336-033;
e-mail: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk).
Acknowledgements
We thank Ministerio de Ciencia y Tecnologıa and
Ministerio de Educacion for support of this work
(projects BQU-0220, PR-01-GE-7 and BQU-2000-
0219) and for a predoctoral fellowship (to L.R.)
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Table 3
Crystal data and refinement details for complexes 3 and 4b
3 4b
Formula C29H18Co2MoN2O8 C25H14Co2MoN2O8
fw 736.25 684.2
Crystal system monoclinic monoclinic
Space group P21/c P21/c
a (A) 12.320(2) 9.188(5)
b (A) 16.504(13) 15.890(8)
c (A) 14.255(6) 17.638(8)
a (8) 90 90
b (8) 94.58(3) 101.82(3)
g (8) 90 90
V (A3) 2889(3) 2521(2)
Z 4 8
T (K) 293(2) 297(2)
Dcalc (g cm�3) 1.693 1.803
F (000) 1464 1352
l (Mo Ka) (A) 0.71073 0.71073
Crystal size (mm) 0.11�0.18�0.21 0.18�0.20�0.22
m (mm�1) 1.615 1.828
Scan range (8) 1.435u525.97 2.55u522.5
No. of reflections
measured
5663 7098
No. of independent
reflections
2998 3306
Data/restraints/parameters 2998/0/451 3306/0/361
Goodness-of-fit on F2 1.008 1.04
R1/wR2 [I �2s (I )] 0.039/0.081 0.0295/0.0289
R1/wR2 (all data) 0.131/0.105 0.0507/0.0336
J. Perez et al. / Inorganica Chimica Acta 347 (2003) 189�/193 193
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