Substitution reactions in dinuclear molybdenum(III) thiolato-complexes induced by isocyanato ligands

Article abstract of DOI:10.1016/S0020-1693(96)05583-1

The reactions of [Cp′₂Mo₂(CO)₄(μ-SR) ₂](BF₄)₂ with azido compounds proceeds via a mechanism analogous to the Curtius rearrangement to afford isocyanate species [Cp′₂Mo₂(NCO)(CO)₃(μ-SR) ₂](BF₄) (Cp′=C₅H₅, R=Me 1, Ph 2; Cp′=C₅Me₅, R=Me 3). Thermal substitution of CH₃CN or R′NC (R′=t-Bu, xylyl, benzyl) for CO in 1-3 results in the formation of monosubstituted derivatives [Cp′₂Mo₂(NCO)(CO)₂(L)(μ-SR) ₂](BF₄) (L=CH₃CN: Cp′=C₅H₅, R=Me 4, Ph 5 ; Cp′=C₅Me₅, R=Me 6 ; L=R′NC: Cp′=C₅Me₅, R=Me, R′=t-Bu 7, xylyl 8, benzyl 9).

Full text of DOI:10.1016/S0020-1693(96)05583-1

Inorganica Chimica Acta 261 (1997) 117–120
Note
Substitution reactions in dinuclear molybdenum(III) thiolato-complexes
induced by isocyanato ligands
Philippe Schollhammer, Sylvie Poder-Guillou, Franc¸ois Y. Pe´tillon U, Jean Talarmin
URA CNRS 322, Chimie, Electrochimie Mole´culaires et Chimie Analytique, Faculte´ des Sciences, Universite´ de Bretagne Occidentale, BP 809,
29285 Brest-Ce´dex, France
Received 27 August 1996; revised 25 October 1996; accepted 12 November 1996
Abstract
The reactionsof[Cp92Mo2(CO)4(m-SR)2](BF4)2 withazido compoundsproceedsviaamechanismanalogoustotheCurtiusrearrangement
to afford isocyanate species [Cp92Mo2(NCO)(CO)3(m-SR)2](BF4) (Cp9sC5H5, RsMe 1, Ph 2; Cp9sC5Me5, RsMe 3). Thermal
substitution of CH3CN or R9NC (R9st-Bu, xylyl, benzyl) for CO in 1–3 results in the formation of monosubstituted derivatives
[Cp92Mo2(NCO)(CO)2(L)(m-SR)2](BF4) (LsCH3CN: Cp9sC5H5, RsMe 4, Ph 5 ; Cp9sC5Me5, RsMe 6 ; LsR9NC: Cp9sC5Me5,
RsMe, R9st-Bu 7, xylyl 8, benzyl 9).
Keywords: Molybdenum complexes; Thiolate complexes; Isocyanate complexes; Dinuclear complexes; Pentamethyl cyclopentadienyl complexes
1. Introduction
carbonyl group into an isocyanate ligand. Here we report the
reaction of the dicationic compound [Cp92Mo2(CO)4(m-
SR)2](BF4)2 with natrium azideNaN3, givingtheisocyanate
products [Cp92Mo2(NCO)(CO)3(m-SR)2](BF4) (Cp9s
C5H5, RsMe 1, RsPh 2; Cp9sC5Me5, RsMe 3). The
reactivity of nitrile (CH3CN) and isocyanide (t-BuNC,
xylyNC) towardstheseisocyanatecomplexeshasbeeninves-
tigated and compared to that with the dicationic tetracarbonyl
precursor [Cp92Mo2(CO)4(m-SR)2]2q. We show that the
presence in the complexes of a pseudo-halide ligand labilises
these dinuclear compounds to carbonyl substitution.
We have investigated for some years the influence of metal
centresandof thesulfur substituentsRortheCp9rings(C5H5,
C5Me5) on the electrochemical behaviour and the reactivity
of complexes possessing {Cp92M2(m-SR)n} core (ns1–3,
MsMo, W, V) [1,2]. We were particularly interested to
generate substrate-binding sites and to control their selectiv-
ity. Very recently we have reported that the substitution of
C5H5 (Cp) rings by the C5Me5 (CpU) ligands in the series
of complexes [Cp92Mo2(CO)4(m-SR)2](BF4)2 (Cp9s
C5H5, C5Me5) affects the life time of intermediates produced
in the reduction processes [2b] and lowers the reactivity of
these complexes [2]. CpU compounds show greater resis-
tance to decarbonylation than their Cp analogues, no substi-
tution of carbonyl by acetonitrile is observed when
[CpU2Mo2(CO)4(m-SR)2](BF4)2 is stirred in refluxing
MeCN [2a]. A way to activate suchinertcarbonylcomplexes
is to introduce into the metallic frameworkahalideorpseudo-
halide ligand [3]. We have tried to activate toward carbonyl
substitution the inhibited pentamethylcyclopentadienylcom-
plex [CpU2Mo2(CO)4(m-SR)2](BF4)2 by transformingone
2. Results
A red solution of [Cp92Mo2(CO)4(m-SR)2](BF4)2 in
acetonitrile reacted instantaneously with one equivalent of
NaN3 in ethanol to give a brown solution from which were
isolated the isocyanate products [Cp92Mo2(NCO)(CO)3-
(m-SR)2](BF4) (Cp9sC5H5, RsMe 1, RsPh 2;
Cp9sC5Me5, RsMe 3) 1–3 in quantitative yields(Reaction
1).
U Corresponding author.
0020-1693/97/$17.00 q 1997 Elsevier Science S.A. All rights reserved
PII S0020-1693(96)05583-1

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P. Schollhammer et al. / Inorganica Chimica Acta 261 (1997) 117–120
Complexes 4–9 have also been characterised by standard
1
spectroscopic (Table 1) and analytical techniques. H and
13C NMR spectra of 4–9 show resonances corresponding to
one R9NC ligand for one {Cp92Mo2(m-SR)2} frame, with
two inequivalent Cp9 groups and two inequivalentSRgroups.
IR spectra display the n(CN) vibration of the isocyanide
ligand as a strong band between 2100 and 2150 cmy1 13C
.
NMR patterns show resonances assigned to CH3CN and
R9NC: for acetonitrile two resonances were noted at about
140 ppm (d(CN)) and 5 ppm (d(CH3)), and for the iso-
cyanide ligand the resonances of the R9 groups (t-Bu, xylyl,
benzyl) and of the carbon of the CN group (between 160 and
190 ppm) were observed. Only two peaks were noted in the
carbonyl region, this confirms the loss of one CO in the
reaction.
These new compounds have been characterised by various
spectroscopic methods (1H and 13C NMR, IR) (Table 1)and
1
elemental analyses. H and 13C NMR spectroscopy of 1–3
3. Discussion
shows the presence of inequivalent Cp9 rings and SR groups,
respectively. The infrared spectra of these complexes display
three strong bands, between 2500 and 1900 cmy1, which are
attributed to carbonyl and isocyanate ligands. The 13C{1H}
patterns of 1–3 show three peaks between 240 and 210 ppm,
and a resonance at about 137 ppm, which are assigned to
carbonyl and NCO groups, respectively. A cis–syn form was
proposed for complexes 1–3 on the basis (i) of the geometry
The reaction of Ny3 with the dinuclear tetracarbonyl com-
plexes [Cp92Mo2(CO)4(m-SR)2]2q leads to the isocyanate
products via a mechanism analogous to the Curtiusrearrange-
ment which has been proposed by Beck and coworkers with
carbonyl monometallic compounds [LnM–CO] [5]. Some
examples of di- or polymetallic isocyanate products have
been reported. Gladfelter et al. have described the trinuclear
ruthenium complex [Ru3(NCO)(CO)4]y obtained by reac-
tion of [Ru3(CO)12] with Ny3 [6]. Other polynuclear NCO
species have been reported: they have been formed by reac-
tion of reagents such as diazoalkanes C6H10N2, (CH3)2N2,
or HNCO and azide [PPN]N3 with [Ru3(CO)12] [7],
[(C5Me5)2Mo2(CO)4] [8], [Os3(CO)10(CH3CN)2] [9]
and [Os3(CO)11(m-CH2)] [10], respectively.
Unlike in their dicationic precursor [Cp92Mo2(CO)4(m-
SR)2]2q, carbonyl substitution by unsaturated substrates
such as acetonitrile or isocyanide was easily made in NCO–
cyclopentadienyl complexes 1–2 under mild conditions
(RT). Temperature or electrochemical activation were
required to achieve a similar CO labilisation process in the
tetracarbonyl complex [Cp2Mo2(CO)4(m-SR)2]2q [1a].
With pentamethylcyclopentadienylligandswehaveobserved
an inhibition of the carbonyl substitution and only electro-
chemical activation allows us to carry out this reaction with
CH3CN or RNC [2]. The transformation of one carbonyl
ligand into an NCO group activates carbonyl substitution on
metal. The role of the isocyanate ligand can be explained by
its hemi-labile character. NCO can act as a three-electron
donor bridging [6], and then it moves to a terminal position
of the dicationic precursor [Cp92Mo2(CO)4(m-SR)2]2q
,
which is cis–syn, and (ii) of the observation that the
substitution of one CO by an acetonitrile ligand does not
alter the arrangement of the {Cp2Mo2(m-SR)2} core
[2a,4].
On warming in acetonitrile, complexes 1–3 lost carbon
monoxide and converted into compounds 4–6 which contain
an acetonitrile group (Reaction 2).
The reaction of 3 with R9NC in refluxing THF afforded
the brown solids 7–9 (Reaction 3).

P. Schollhammer et al. / Inorganica Chimica Acta 261 (1997) 117–120
119
n
n
n
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P. Schollhammer et al. / Inorganica Chimica Acta 261 (1997) 117–120
concomitantly with the coordination of a substrate (CO,
CH3CN or R9NC); this parallels the motion observed for
halide bridges in some dinuclear complexes [11].
4.4. Preparation of [CpU2Mo2(NCO)(CO)2(R9NC)-
(m-SMe)2](BF4) (R9st-Bu 7, xylyl 8, benzyl 9)
A suspension of [CpU2Mo2(NCO)(CO)3(m-SMe)2]-
(BF4) (0.65 mmol) in 30 ml of tetrahydrofuran was stirred
at 668C for 12 h in presence of 0.65 mmol of t-BuNC,
xylylNC or benzylNC. Filtration of the mixture and removal
of the solvent gave in quantitative yields the ionic brown
In conclusion, these results are an illustration of the effect
of the pseudo-halide ligand NCO on the reactivity of the
dinuclear carbonyl framework [Cp92Mo2(CO)4(m-SR)2]2q
.
The transformation of a carbonyl group into a NCO ligand
labilises the remaining carbonyl groups in this bimetallic
system.
complexes [CpU Mo2(NCO)(CO)2(R9NC)(m-SR)2](BF4)
2
7–9 which were washed with pentane (2=5 ml).
7 (brown solid), Anal. Found: C, 42.7; H, 5.4; N, 3.2.
C30H45 Mo2N2O3S2BF4 Calc.: C, 43.7; H, 5.5; N, 3.4.
9 (brown solid), Anal. Found: C, 45.8; H, 5.0; N, 3.3.
C33H43Mo2N2O3S2BF4 Calc.: C, 46.1; H, 5.0; N, 3.3.
4. Experimental
4.1. General procedures
The reactions were performed under either a nitrogen or
an argon atmosphere using standard Schlenk techniques, and
solvents were deoxygenated and dried by standard methods.
Literature methods were used for the preparation of [Cp92-
Mo2(CO)4(m-SR)2](BF4)2 (Cp9sCp [4], Cp9sCpU
[2a]).
Infrared spectra were obtained with a Perkin-Elmer 1430
spectrophotometer. NMR spectra were recorded on a Bruker
AC300 spectrophotometer. Peak positions were relative to
tetramethylsilane as an internal reference. Chemical analyses
were performed by the ‘Centre de microanalyses du CNRS,
Vernaison’.
References
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and J. Talarmin, Organometallics, 8 (1989) 140; (b) M. Gue´guen,
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4.2. Preparation of [Cp92Mo2(NCO)(CO)3(m-SR)2](BF4)
(Cp9sCp, RsMe 1, Ph 2; Cp9sCpU, RsMe 3)
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(1995) 2277; (b) F.Y. Pe´tillon, S. Poder-Guillou, P. Schollhammer
and J. Talarmin, New J. Chem., in press.
In a typical preparation, a solution of NaN3 (0.65 mmol,
in 50 ml EtOH) was added to a solution of [Cp92Mo2-
(CO)4(m-SR)2)](BF4)2 (0.65 mmol, in 20 ml CH3CN).
The mixture was stirred for a few minutes, and the solution
changed from red to brown. The solvents were removed to
drynessand theresiduewasrecrystallisedfromCH3CN–ether
(1:1) mixture. Na(BF4) precipitated and evaporation of the
filtrate afforded 1–3 in quantitative yields as a brown powder
which was washed with ether (5 ml) and pentane (5 ml).
3 (brown solid), Anal. Found: C, 39.7; H, 4.6; N, 1.9.
C26H36 Mo2NO4S2BF4 Calc.: C, 40.5; H, 4.7; N, 1.8.
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4.3. Preparation of [Cp92Mo2(NCO)(CO)2(CH3CN)-
(m-SR)2](BF4) (Cp9sCp, RsMe 4, Ph 5; Cp9sCpU,
RsMe 6)
A solution of [Cp92Mo2(NCO)(CO)3(m-SR)2](BF4)
(0.65 mmol, in 30 ml CH3CN) was stirred at 908C for 12 h,
and then the solvent was removed under vacuum. The residue
was washed with ether (5 ml) and pentane (5 ml) and was
identified by spectroscopic data as 4–6, which were obtained
in quantitative yields.
6 (brown solid), Anal. Found: C, 41.7; H, 5.0; N, 3.5.
C27H39 Mo2N2O3S2BF4 Calc.: C, 41.4; H, 5.0; N, 3.5.