Formation of new μ-thioalkylidene and μ-borohydride dimolybdenum complexes from the μ-alkylidyne precursor [Mo2Cp 2(μ-SMe)3(μ-CCH2Ph)]

Article abstract of DOI:10.1021/om7003496

The μ-alkylidyne complex [Mo₂Cp₂(μ-SMe) ₃(μ-CCH₂-Ph)] (1) reacts with HBF₄ in acetonitrile to give the unstable bis-nitrile species [Mo₂Cp ₂(μ-SMe)₂(μ-CCH₂P

Full text of DOI:10.1021/om7003496

Organometallics 2007, 26, 3607-3610
3607
Formation of New µ-Thioalkylidene and µ-Borohydride
Dimolybdenum Complexes from the µ-Alkylidyne Precursor
[Mo2Cp2(µ-SMe)3(µ-CCH2Ph)]
Alan Le Goff, Christine Le Roy, Franc¸ois Y. Pe´tillon, Philippe Schollhammer,* and
Jean Talarmin
UMR CNRS 6521, Chimie, Electrochimie Mole´culaires et Chimie Analytique, UFR Sciences et Techniques,
UniVersite´ de Bretagne Occidentale, CS 93837, 29238 Brest-Cedex 3, France
ReceiVed April 10, 2007
Chart 1
Summary: The µ-alkylidyne complex [Mo2Cp2(µ-SMe)3(µ-CCH2-
Ph)] (1) reacts with HBF4 in acetonitrile to giVe the unstable
bis-nitrile species [Mo2Cp2(µ-SMe)2(µ-CCH2Ph)](NCCH3)2]-
(BF4) (2). Treatment with either borohydride or chloride con-
Verts 2 into [Mo2Cp2(µ-SMe)2(µ-CCH2Ph)(µ-κ1:κ1-BH4)] (3) or
[Mo2Cp2(µ-SMe)2(µ-CCH2Ph)(µ-Cl)] (4), respectiVely. Clean eVo-
lution of 4 in non-degassed solVent affords the noVel µ-thioalkyl-
idene deriVatiVe [Mo2(O)(Cl)Cp2(µ-SMe)(µ-MeSCCH2Ph)](5).
Introduction
NaBH4 and (Et4N)Cl. The formation and the characterization
of novel µ-borohydride and µ-thioalkylidene dimolybdenum
complexes [Mo2Cp2(µ-SMe)2(µ-CCH2Ph)(µ-κ:1κ1-BH4)] (3) and
[Mo2(O)(Cl)Cp2(µ-SMe)(µ-MeSCCH2Ph)] (5) are reported.
Treatment of 1 with 1 equiv of HBF4-Et2O in acetonitrile gave
a purple solution of [Mo2Cp2(µ-SMe)2(µ-CCH2Ph)(MeCN)2]+
(2) (Scheme 1). 2 could be isolated as a purple powder after its
precipitation by the addition of diethyl ether, but fast decom-
position occurred when the solvent was removed. This prevented
any storage of 2 as a powder and any further spectroscopic char-
Dinuclear (cyclopentadienyl) organometallic molecules in-
corporating a {Mo2Cp′2} core (Cp′ ) η5-C5H5, η5-C5Me5, η5-
C5H4Me) exhibit a rich and original reactivity that continues to
be explored in view of developing new tools for molecular
activation.1 We have recently reported the synthesis and the
X-ray structure of novel tris-thiolato-bridged dimolybdenum
derivatives featuring a µ-alkylidyne group (Chart 1).2
Their structural data and their reactivity suggest that the alkyl-
idyne group weakens the bonding of the thiolate bridge in trans
position, and even in some cases it could induce the loss of this
bridging group.2c In the course of our systematic approach to the
activity of sulfur-rich dimolybdenum complexes toward hydro-
carbyl substrates we have studied the reactivity of the complex
[Mo2Cp2(µ-SMe)3(µ-CCH2Ph)] (1) toward various electrophile
and nucleophile reagents in order to compare the effect of a
µ-alkylidyne group with that of a bridging thiolate on the reac-
tivity of systems having a dimolybdenum core {Mo2Cp2(µ-
SMe)2(µ-X)} (X ) CCH2Ph or SMe). We wish to report here
some aspects of the reactivity of the µ-alkylidyne, bis-acetonitrile
species [Mo2Cp2(µ-SMe)2(µ-CCH2Ph)(MeCN)2]+ (2) toward
1
acterization of the isolated powder. The H NMR spectrum of
a sample prepared by the addition of 1 equiv of tetrafluoroboric
acid to a solution of 1 in CD3CN, at 298 K, indicated without
any ambiguity that 2 has lost a thiolate bridge and has retained
a symmetrical bimetallic core, {Mo2Cp2(µ-SMe)2(µ-CCH2Ph)}+.
Indeed, this spectrum exhibits a single resonance at 5.30 ppm
for the two cyclopendadienyl ligands (intensity 10) and one peak
at 1.82 ppm for two SMe bridges (intensity 6). Characteristic
signals of the CH2-C6H5 group are detected as a singlet at 4.52
ppm (intensity 2) and a multiplet at 7.17 ppm (intensity 5). In
addition, the release of free HSMe is detected: a quadruplet at
1.61 ppm for one proton and a doublet at 1.97 ppm for three
protons were unambiguously assigned to free HSMe.3 The forma-
tion an S-protonated intermediate could not be evidenced by
low-temperature NMR experiments. We concede that 2 could
not be fully characterized; however its spectroscopic data are
enough reliable to formulate with assurance this intermediate
as a {Mo2Cp2(µ-SMe)2(µ-CCH2Ph)}+ core stabilized by two
coordinated acetonitrile molecules. In similar reactional condi-
tions, the loss of the chloro bridge in [Mo2Cp2(µ-SMe)3(µ-Cl)]
has been reported to afford the tractable bis(acetonitrile) species
[Mo2Cp2(µ-SMe)3(MeCN)2](BF4).4 We have also previously
shown that a sulfur atom in tris-thiolato-bridged dimolybdenum-
(III) complexes could be methylated or protonated and that the
* To whom correspondence should be addressed. E-mail : schollha@
univ-brest.fr.
(1) (a) Alvarez, M. A.; Garc´ıa, M. E.; Ramos, A.; Ruiz, M. A.
Organometallics 2007, 26, 1461. (b) Amor, I.; Garc´ıa-Vivo´, D.; Garc´ıa,
M. E.; Ruiz, M. A.; Sa´ez, D.; Hamidov, H.; Jeffery, J. C. Organometallics
2007, 26, 466. (c) Alvarez, C. M.; Alvarez, M. A.; Garc´ıa, M. E.; Ramos,
A.; Ruiz, M. A.; Graiff, C.; Tiripicchio, A. Organometallics 2007, 26, 321.
(d) Newell, R.; Ohman, R.; Rakowski Dubois, M. Organometallics 2005,
24, 4406. (e) Appel, A. M.; DuBois, D. L.; Rakowski Dubois, M. J. Am.
Chem. Soc. 2005, 127, 12717. (f) Le Goff, A.; Le Roy, C.; Pe´tillon, F. Y.;
Schollhammer, P.; Talarmin, J. New J. Chem. 2007, 31, 265. (g) Ojo, W.
S.; Pe´tillon, F. Y.; Schollhammer, P.; Talarmin, J.; Muir, K. W. Organo-
metallics 2006, 22, 5503. (h) Stoffelbach, F.; Richard, P.; Poli, R.; Jenny,
T.; Savary, C. Inorg. Chim. Acta 2006, 14, 4447. (i) Demirhan, F.; Cagatay,
B.; Demir, D.; Baya, M.; Daran, J. C.; Poli, R. Eur. J. Inorg. Chem. 2006,
757. (j) Demirhan, F.; Taban, G.; Baya, M.; Dinoi, C.; Daran, J. C.; Poli,
R. J Organomet. Chem. 2006, 691, 648.
(2) (a) Cabon, N.; Schollhammer, P.; Pe´tillon, F. Y.; Talarmin, J.; Muir,
K. W. Organometallics 2002, 21, 448. (b) Cabon, N.; Paugam, E.;
Schollhammer, P.; Pe´tillon, F. Y.; Talarmin, J.; Muir, K. W. Organometallics
2003, 22, 4178. (c) Ojo, W.-S.; Paugam, E.; Schollhammer, P.; Pe´tillon, F.
Y.; Talarmin, J.; Muir, K. W. Organometallics 2006, 25, 4009.
(3) The chemical shifts were compared to those of an authentic sample
of HSMe in CD3CN.
(4) Barrie`re, F.; Le Mest, Y.; Pe´tillon, F. Y.; Poder-Guillou, S.;
Schollhammer, P.; Talarmin, J. J. Chem. Soc., Dalton Trans. 1996, 3967.
10.1021/om7003496 CCC: $37.00 © 2007 American Chemical Society
Publication on Web 06/06/2007

3608 Organometallics, Vol. 26, No. 14, 2007
Notes
Scheme 1
Figure 1. 2D 1H-1H{11B} NMR spectrum of [Mo2Cp2(µ-SMe)2-
(µ-CCH2Ph)(µ-κ1:κ1-BH4)] (3) recorded at 188 K in CD2Cl2 between
2 and -9.5 ppm
Chart 2. Possible Mechanism for the Exchange of the Two
Terminal Hydrogens Bound to the Boron Atom in 3
release of MeSMe or HSMe could arise in acetonitrile solution,
giving [Mo2Cp2(µ-SMe)4-n(MeCN)2n]n+ cations.5
A 1.5 equiv amount of sodium borohydride was added to 2 in
CH3CN at room temperature to afford in high yield (90%) the
purple borohydride compound [Mo2Cp2(µ-SMe)2(µ-CCH2Ph)-
(µ-κ:1κ1-BH4)] (3) (Scheme 1). No transfer of hydride to one
of the acetonitrile ligands was detected. 3 was identified on the
basis of its spectroscopic data and of its solid-state structure.
Spectroscopic data of the borohydride bridge are very similar
to those observed in other dimolybdenum complexes [Mo2Cp2-
(µ-SMe)3(µ-κ:1κ1-BH4)]6a and [Mo2Cp2(µ-SMe)2(µ-NCHMe)-
(µ-κ:1κ1-BH4)].6b The 11B{1H} NMR spectrum shows a single
the breaking of one B-H bond, as proposed for the compound
[ZrHCp2(κ2-H2BC5H10)] to explain the process of exchange
between terminal and bridging hydride.8 However, it should be
noted that the low activation energy (55 kJ‚mol-1) calculated
for this process would suggest another possible mechanism,
which should involve lower energy decoordination instead of
cleavage of B-H bonds, as proposed by Riera et al. in a related
bridged borohydride dimanganese complex.9 Nevertheless, such
a mechanism cannot explain why the two bridging hydrogen
atoms do not part in the observed coalescence phenomenon.
Purple crystals of 3 were obtained at room temperature from
diethyl ether solution. The X-ray analysis of 3 is of poor quality,
mainly because of unresolved twinning, but the results are
consistent with a structure based on a {Mo2Cp2(µ-SMe)2(µ-
CCH2Ph)+} core bridged through Mo-H-B bonds by a
1
broad resonance at -20.1 ppm. A H{11B} NMR spectrum,
recorded at 223 K, displays in addition to the expected
resonances for the {Mo2Cp2(µ-SMe)2(µ-CCH2Ph} core a broad,
high-field doublet at - 9.85 ppm assignable to two equivalent
Mo-H-B bridges, and two other broad signals, at -1.09 and
1.04, attributed to the terminal hydrogens bound to the boron
1
atom. A 2D H-1H {11B} correlation experiment, performed
-
distorted tetrahedral BH4 anion (Figure 2). The geometry of
at 188 K in CD2Cl2, confirms these assignments (Figure 1).
The broadening and the coalescence at 303 K of the two termi-
nal (B-H) signals when a dichloromethane-d2 solution of 3 is
warmed from 188 to 313 K suggest that the molecule is fluxional
in solution: an energy barrier of 55 ((1) kJ‚mol-1 has been
estimated.7 It is worth noting that in the same range of tem-
peratures no dynamic process was observed for the thiolate
analogue [Mo2Cp2(µ-SMe)3(µ-κ1:κ1-BH4)].6a One possible mech-
anism for the exchange of the two terminal hydrogens bound
to the boron atom in 3 is shown in Chart 2. It may proceed via
the {Mo2(µ-κ1:κ1-BH4)} group, in particular the Mo-Mo
distance [2.6238(9) Å], is comparable to those in the related
complexes [Mo2Cp2(µ-SMe)3(µ-κ1:κ1-BH4)]6a and [Mo2Cp2(µ-
SMe)2(µ-NdC(H)Me)(µ-κ1:κ1-BH4)].6b The Mo‚‚‚B distances
[2.753 and 2.740 Å] in 3 are too long for direct Mo-B
bonding.6a Other distances and angles [in particular, Mo-C3,
1.978(7), 1.993(7) Å; Mo1-C3-Mo2, 82.7(3)°] are close to
those observed in the µ-alkylidyne derivative [Mo2Cp2(µ-SMe)3-
(µ-CCH2-nPr)].2a The Cp ligands bend away from the borohy-
dride bridge, adopting a cis disposition relative to the Mo-Mo
axis with Cp-Mo-Mo angles of 167.6° (Cp ) ring centroid),
(5) (a) Schollhammer, P.; Pe´tillon, F. Y.; Talarmin, J.; Muir, K. W. Inorg
Chim. Acta 1999, 284, 107. (b) Cabon, N.; Pe´tillon, F. Y.; Schollhammer,
P.; Talarmin, J.; Muir, K. W. J. Organomet. Chem. 2006, 691, 566.
(6) (a) Schollhammer, P.; Cabon, N.; Pe´tillon, F. Y.; Talarmin, J.; Muir,
K. W. Chem. Commun. 2000, 2708. (b) Cabon, N.; Pe´tillon, F. Y.;
Schollhammer, P.; Talarmin, J.; Muir, K. W. Dalton Trans. 2004, 2708.
(7) (a) Shanan-Atidi, H.; Bar-Eli, K. H. J. Phys. Chem. 1970, 74, 961.
(b) Gutowsky, H. S.; Holm, C. H. J. Phys. Chem. 1956, 25, 1228.
-
the thiolate Me groups have an anti orientation, and the BH4
group is trans to the alkylidyne bridge.
(8) Liu, F.-C.; Liu, J.; Meyers, E. A.; Shore, S. G. Inorg. Chem. 1998,
37, 3293.
(9) Carren˜o, R.; Riera, V.; Ruiz, M. A.; Bois, C.; Jeannin, Y. Organo-
metallics 1993, 12, 1946.

Notes
Organometallics, Vol. 26, No. 14, 2007 3609
Figure 3. View of a molecule of [Mo2(O)(Cl)Cp2(µ-SMe)(µ-
MeSCCH2Ph)] (5) showing 50% probability ellipsoids. Selected
bond lenghts (Å) and angles (deg): Mo1-Mo2, 2.7680(14); Mo2-
O, 1.698(6); Mo2-S2, 2.365(3); Mo2-C3, 2.133(10); Mo1-Cl,
2.507(3); Mo1-S2, 2.372(3); Mo1-S1, 2.442(3); Mo1-C3, 2.094-
(10); C3-C4, 1.529(13); C3-S1, 1.775(10); Mo2-Mo1-Cl,
114.43(7); Mo1-Mo2-O, 107.8(2); Mo1-C3-Mo2, 81.8(4);
Mo1-C3-C4, 134.4(7); Mo2-C3-C4, 128.3(7); S1-C3-C4,
117.0(7); S1-Mo1-S2, 114.17(10); S2-Mo1-C3, 103.7(3); S2-
Mo2-C3, 102.7(3).
Figure 2. View of a molecule of [Mo2Cp2(µ-SMe)2(µ-CCH2Ph)-
(µ-κ1:κ1-BH4)] (3) showing 50% probability ellipsoids. Hydrogen
atoms are drawn as spheres of arbitrary radius. Selected bond
lenghts (Å) and angles (deg): Mo1-Mo2, 2.6238(9); Mo1-H1,
1.74(8); Mo2-H2, 1.77(8); B-H1, 1.31(8); B-H2, 1.27(9); B-H3,
1.01(9); B-H4, 1.14(8); Mo1-C3, 1.978(7); Mo2-C3, 1.993(7);
Mo1-B, 2.753(9); Mo2-B, 2.740(10); H3-B-H4, 116(6); H3-
B-H2, 108(6); H3-B-H1, 109(6); H4-B-H2, 101(6); H4-B-
H1, 109(6); H2-B-H1, 114(5); Mo1-C3-Mo2, 82.7(3), Mo1-
C3-C4, 139.4(5); Mo2-C3-C4, 137.9(5); B-H1-Mo1, 127.2;
B-H2-Mo2, 127.41
unusual,10 it is σ-bonded to Mo1 and Mo2 atoms through the
C3 atom (Mo2-C3, 2.133(10) Å; Mo1-C3, 2.094(10) Å) and
σ-bonded to Mo1 through the S1 atom (Mo1-S1, 2.442(3) Å).
The Mo-Mo bond length (2.7680(14) Å) is consistent with a
bond order of 2 required by the usual electron-counting rule,
with the presence of two bridging groups.11 The Mo-O and
Mo-Cl distances (1.698(6) and 2.507(3) Å, respectively) are
typical of terminal ModO and Mo-Cl bonds.11Several ex-
amples of dimolybdenum cyclopentadienyl complexes featuring
oxo ligands have been reported,11,12 but it is worth noting that
in the clean transformation of 4 into 5 the incoming oxygen
induces the formation of a C-S bond, giving rise to the thioal-
kylidene ligand and the opening of the chloro bridge. The forma-
tion of thioalkylidene species is generally based either on the
addition of a nucleophile to a bridging alkylidyne carbon or on
Treatment of a solution of 2 in CH2Cl2 with an excess of
Et4NCl at room temperature afforded in valuable yield (60%)
the purple, air-sensitive, chloro-bridged compound [Mo2Cp2-
(µ-SMe)2(µ-CCH2Ph)(µ-Cl)] (4) (Scheme 1). The 1H NMR
(CDCl3) spectrum of 4 is typical of a complex with a {Mo2-
Cp2(µ-SMe)2(µ-CCH2Ph)} framework. It exhibits a single reso-
nance at 5.40 ppm for the two cyclopentadienyl ligands, two
peaks, between 1.5 and 2.0 ppm, for the two SMe bridges, and
the expected set of resonances of a benzyl group, PhCH2- [4.97
(s, 2H) and 7.00-7.26 (m, 5H)]. Attempts to obtain elemental
analyses and single crystals of 4 were unsuccessful due to its
high instability. A striking feature of our work was the repro-
ducible evolution of 4 in non-degassed solvent to give cleanly
the oxo species [Mo2(O)(Cl)Cp2(µ-SMe)(µ-MeSCCH2Ph)] (5)
(Scheme 1). 5 has been characterized by NMR and IR
spectroscopy, microanalysis, and single-crystal X-ray diffraction
analysis. The 1H NMR pattern of complex 5 indicates the pres-
ence in the molecule of two cyclopentadienyl rings, two SMe,
and a CH2C6H5 group. The IR spectrum in KBr pellets shows
a band at 818 cm-1, which is characteristic of ν(MdO), and
elemental analyses are consistent with the formula C20H23ClO-
Mo2S2. These data are fully compatible with the results of a
single-crystal X-ray diffraction study of 5. The recrystallization
of 5 from diethyl ether at room temperature afforded brown
crystals. The molecule contains {CpMoCl} and {CpModO} units
bridged by a SMe group and a η1(C):η2(C,S)-thioalkylidene
ligand {MeSCCH2Ph}, which results from an intramolecular
C-S coupling between one SCH3 thiolate group and the bridg-
ing carbon atom of the alkylidyne (C3-S1, 1.775(10) Å). The
bridging coordination mode of the thioalkylidene group is not
(10) (a) Busetto, L.; Zanotti, V. J. Organomet. Chem. 2005, 690, 5430.
(b) Xiao, N.; Xu, Q.; Sun, J.; Chen, J. Dalton Trans. 2005, 3250. (c) Qiu,
Z.; Sun, J.; Chen, J. Organometallics 1998, 17, 600. (d) Bordini, S.; Busetto,
L.; Camiletti, C.; Zanotti, V.; Albano, V. G.; Monari, M.; Prestopino, F.
Organometallics 1997, 16, 1224. (e) Albano, V. G.; Bordini, S.; Busetto,
L.; Camiletti, C.; Monari, M.; Prestopino, F.; Zanotti, V. J. Chem. Soc.,
Dalton Trans. 1996, 3693. (f) Matachek, J. R.; Angelici, R. J.; Schugart,
K. A.; Haller, K. J.; Fenske, R. F. Organometallics 1984, 3, 1038.
(11) Pe´tillon, F. Y.; Schollhammer, P.; Talarmin, J.; Muir, K. W. Coord.
Chem. ReV. 1998, 178-180, 203.
(12) (a) Adatia, T.; McPartlin, M.; Mays, M. J.; Morris, M. J.; Raithby,
P. R. J. Chem. Soc., Dalton Trans. 1989, 1555. (b) Davies, J. E.; Feeder,
N.; Gray, C. A.; Mays, M. J.; Woods, A. D. J. Chem. Soc., Dalton Trans.
2000, 1695. (c) Stichbury, J. C.; Mays, M. J.; Davies, J. E.; Raithby, P. R.;
Shields, G. P.; Finch, A. G. Inorg. Chim. Acta 1997, 262, 9. (d) Stichbury,
J. C.; Mays, M. J.; Raithby, P. R.; Rennie, M.-A; Fullalove, R. J. Chem.
Soc., Chem. Commun. 1995, 1269. (e) Adams, H.;Gill, L. J.; Morris, M. J.
J. Chem. Soc., Dalton Trans. 1998, 2451. (f) Garc´ıa, G.; Garc´ıa, M. E.;
Melon, S.; Riera, V.; Ruiz, M. A.; Villafa˜ne, F. Organometallics 1997, 16,
624. (g) Saurenz, D.; Demirhan, F.; Richard, P.; Poli, R.; Sitzmann, H.
Eur. J. Inorg. Chem. 2002, 1415. (h) Gun, J.; Modestov, A.; Lev, O.;
Saurenz, D.; Vorotyntsev, M. A.; Poli, R. Eur. J. Inorg. Chem. 2003, 482.
(i) Bottomley, F.; Ferris, E. C.; White, P. S. Organometallics 1990, 9, 1166.
(j) Bottomley, F.; Boyle, P. D.; Chen, J. Organometallics 1994, 13, 370.
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Soc., Chem. Commun. 1980, 1137.

3610 Organometallics, Vol. 26, No. 14, 2007
Notes
intramolecular rearrangements of µ-alkylidyne complexes.10a
This reaction is similar to previous results that we have reported
concerning C-C and C-S couplings, induced by reaction of
electron-donating substrates such as RNC, CS2, and RCCH with
alkyne complexes [Mo2Cp2(µ-SMe)3(µ-RCCH)](BF4).13 In ad-
dition, this reaction points out the reactional versatily of such
µ-alkylidyne complexes. They react with a proton in CH2Cl2
to give cationic alkylidene compounds [Mo2Cp2(µ-SMe)3(µ-
CHCH2R)](BF4),2a but on the other hand the formation of 5 in
this work reveals the possibility of nucleophilic addition to the
bridging carbon.
The reactions of complexes [Mo2Cp2(µ-SMe)3(µ-X)] (X )
SMe, PPh2, CCH2Ph) toward sodium borohydride also demon-
strate the influence of the bridging ligands on the activity of
these dimolybdenum systems and particularly the trans-influence
of some bridges. Indeed, the complex [Mo2Cp2(µ-SMe)3(µ-κ1:
κ1-BH4)] has been isolated from the reaction of [Mo2Cp2(µ-
SMe)3(µ-Cl)] with NaBH4.6a If the thiolate bridge in trans posi-
tion to the µ-chloride is replaced by a phosphido group, the
formation of the µ-borohydride analogue is not observed and
the reaction of [Mo2Cp2(µ-SMe)2(µ-PPh2)(µ-Cl)] with NaBH4
leads to the hydride compound [Mo2Cp2(µ-SMe)2(µ-PPh2)(µ-
H)].6b This result suggests strongly that the PPh2 bridge is able
to induce the cleavage of a B-H bond in the borohydride anion.
On the other hand, the fluxional behavior of 3 reveals that the
alkylidyne bridge is able either to weaken a B-H bond but not
to break it or to labilize the Mo-H bonds. Such a labilization
is not observed if the hydrocarbyl bridge is replaced by a thiolate
group. Indeed, the complex [Mo2Cp2(µ-SMe)3(µ-κ1:κ1-BH4)]
does not present in similar conditions such a dynamic behavior.
In addition, the instability of complexes [Mo2Cp2(µ-SMe)2-
(µ-CCH2Ph)(CH3CN)2]+ and [Mo2Cp2(µ-SMe)2(µ-CCH2Ph)-
(µ-Cl)] compared to their analogues of the tris-thiolato-bridged
series suggests also a trans influence of the alkylidyne bridge.
Finally, the results reported here may suggest new strategies to
synthesize original dimolybdenum thio-alkylidene molecules.
then the solvent was removed in vacuo. 3 was extracted with diethyl
ether (3 × 20 mL). The solvent was removed in vacuo from the
pooled extracts. The residue was washed with cold pentane, and 3
was obtained as a purple powder (110 mg, 90%). Crystals of 3
were obtained at room temperature from CH2Cl2-Et2O solution.
IR (KBr, cm-1): ν(B-H) 2458 (m), 2367 (m), 2340 (m), 2060 (f),
1
1923 (f). H{11B} NMR (CDCl3, 223 K) : δ 6.92-7.29 (m, 5H,
C6H5), 5.37 (s, 10H, C5H5), 4.99 (s, 2H, CCH2Ph), 1.81 (s, 3H,
SCH3), 1.47(s, 3H, SCH3), -1.09 and 1.04 (2s, 1H + 1H, Mo2-
(µ-H)2BH2), -9.85 (d, 2H, 2JHH ) 12.5 Hz, Mo2(µ-H)2BH2). 11B-
{1H} NMR (CDCl3, 223 K): δ -20,1 (s, br, BH4). Anal. Calcd
for C20H27BMo2S2·CH2Cl2: C, 40.74; H, 4.72; B, 1.75. Found: C,
40.40; H, 4.98; B, 2.49.
Reaction of 2 with Et4NCl: Synthesis of 4. Similarly, a purple
powder of 2 was prepared from 1 (120 mg, 0.21 mmol) and was
added to a solution of Et4NCl (33 mg, 0.42 mmol) in CH2Cl2 (10
mL). This mixture was stirred for 30 min, then the solvent was
removed in vacuo. 4 was extracted with diethyl ether (4 × 15 mL).
The solvent was removed in vacuo from the pooled extracts. The
residue was washed with cold pentane, and 4 was obtained as a
purple powder (70 mg, 60%). 1H NMR (CDCl3, 298 K): δ 7.26-
7.00 (m, 5H, C6H5), 5.40 (s, 10H, C5H5), 4.97 (s, 2H, CCH2Ph),
1.79 (s, 3H, SCH3), 1.58 (s, 3H, SCH3). The high instability of 4
prevented any elemental analysis.
Evolution of 4 in Non-degassed Solvent: Synthesis of 5. A
solution of 4 (50 mg,0.09 mmol) in non-degassed diethyl ether (10
mL) was stirred overnight (15 h). The solvent was then removed,
and the residue was washed with cold pentane (2 × 10 mL). 5 was
obtained as a yellow powder (30 mg, 60%). IR (KBr, cm-1): ν-
(ModO) 818 (s). 1H NMR (CDCl3, 298 K): δ 8.00-7.50 (m, 5H,
C6H5), 5.47 (s, 5H, C5H5), 5.09 (s, 5H, C5H5), 4.60 (d, 1H, 2JHH
17 Hz, CCH2Ph), 3.76 (d, 1H, JHH ) 17 Hz, CCH2Ph), 2.41 (s,
3H, SCH3), 2.26 (s, 3H, SCH3). Anal. Calcd for C20H23ClOMo2S2:
C, 42.08; H, 4.06; Cl, 6.21. Found: C, 41.41; H, 4.08; Cl, 5.53.
)
2
Crystallographic Data. X-ray crystal data for 3: C20H27BMo2S2,
fw ) 534.23, monoclinic, space group P21/c, a ) 8.5218(7) Å, b
) 30.503(2) Å, c ) 7.8636(6) Å, â ) 94.602(7)°, V ) 2035.3(3)
Å3, T ) 170 K, Z ) 4, dcalcd ) 1.743 g/cm3; 4926 unique,
absorption-corrected intensities with θ(Mo KR) < 25.0°. R(F) )
0.0807 for 4926 reflections with I > 2σ(I) and wR(F2)(all data) )
Experimental Section
General Procedures. All reactions were routinely carried out
under a nitrogen atmosphere using standard Schlenk techniques.
Solvents were distilled immediately before use under nitrogen from
appropriate drying agents. Literature methods were used for the syn-
thesis of [Mo2Cp2(µ-SMe)3(µ-CCH2Ph)] (1).2a Other reagents were
purchased from the usual commercial suppliers and used as re-
ceived. Infrared spectra were recorded on a Nicolet-Nexus FT IR
spectrophotometer from KBr pellets. Chemical analyses were per-
formed by the Service de Microanalyse ICSN-CNRS, Gif sur
Yvette (France). The NMR spectra (1H, 11B) were recorded in
CD2Cl2, CDCl3, or CD3CN solutions with a Bruker AMX 400
spectrometer and were referenced to SiMe4 (1H) and BF3-Et2O
(11B). 2D experiments were carried out on a Bruker DRX 500
spectrometer.
Preparation of 2. To a blue solution of 1 (130 mg, 0.23 mmol)
in MeCN (20 mL) was added 32 µL (1 equiv) of H[BF4]‚Et2O.
The solution readily turned purple. After the mixture was stirred
for 15 min at ambient temperature, the volume was reduced under
vacuum and diethyl ether was added to precipitate a purple powder.
This powder was collected by filtration and immediately used.
Reaction of 2 with NaBH4: Synthesis of 3. A purple powder
of 2 was prepared from 1 (130 mg, 0.23 mmol) as described above,
and it was immediately added to a solution of NaBH4 (14 mg, 0.37
mmol) in CH3CN (10 mL). This mixture was stirred for 20 min,
0.1290 after refinement of 240 parameters. |∆F| < 1.318 e Å-3
.
X-ray crystal data for 5: C20H23ClMo2OS2, fw ) 570.83, mono-
clinic, space group C2/c, a ) 30.947(4) Å, b ) 8.3832(8) Å, c )
17.010(3) Å, â ) 112.995(15)°, V ) 4062.4(9) Å3, T ) 170 K, Z
) 8, dcalcd ) 1.867 g/cm3; 2092 unique, absorption-corrected
intensities with θ(Mo KR) < 25.0°. R(F) ) 0.0611 for 2092
reflections with I > 2σ(I) and wR(F2)(all data) ) 0.0986 after
refinement of 235 parameters. |∆F| < 0.607 e Å-3
.
Acknowledgment. We are grateful to Dr. F. Michaud for
the crystallographic measurements of 3 and 5 and to Dr. R.
Pichon and N. Kervarec for recording two-dimensional NMR
spectra on a Bruker DRX 500 (500 MHz) spectrometer. We
thank the CNRS and the University of Bretagne Occidentale
for financial support. The Ministe`re de l’Enseignement Supe´rieur
et de la Recherche is acknowledged for funding (A.L.G.).
Supporting Information Available: For 3 and 5 tables giving
details of structure determination, non-hydrogen atomic positional
parameters, all bond distances and angles, anisotropic parameters,
and hydrogen atomic coordinates. This material is available free
of charge via the Internet at http://pubs.acs.org.
(13) Schollhammer, P.; Cabon, N.; Capon, J-F.; Pe´tillon, F. Y.; Talarmin,
J.; Muir, K. W. Organometallics 2001, 20, 1230.
OM7003496