Formation of C-C, C-N, and C-O links between isonitrile, cyclopentadienyl, and hydroxide ligands bound to molybdenum(III): Syntheses and crystal structures of μ-aminocarbyne and μ-amino-oxycarbene dimolybdenum complexes

Article abstract of DOI:10.1021/om060383v

Reaction of the bis-isonitrile complex [Mo₂Cp ₂(μ-SMe)₃(xylNC)₂](BF₄) (2b) with NaOH (suspension) under reflux in tetrahydrofuran produced, in quantitative yields, the μ-alkylidyne species [Mo₂Cp(μ-SMe) ₃{μ-(η⁵-C₅H₄)(xylN)CN(xyl)C}] (4), in which a deprotonated Cp and both isonitrile ligands of 2b are now linked by new C-C and C-N bonds. Under prolonged reflux (72 h) in tetrahydrofuran 2b with either NaOH (suspension) or (Me₄N)OH (in MeOH) in the presence of excess isonitrile RNC (R = xyl, Bu^t) was converted in high yields into the mixed (μ-alkylidyne)(μ-amino-oxycarbene) derivatives [Mo₂Cp(μ-SMe)₂{μ-(η⁵- C₅H₄)(xylN)CN(xyl)C}{μ-η¹(O), η¹(C)-OCNHR}] (R = xyl (5a1), R = Bu^t (5b2)) and [Mo₂Cp(μ-SMe)₂{μ-(η⁵C ₅H₄) (xylN)CN(xyl)C}{μ-η¹(O), η¹(C)-OCNMeR}] (R = xyl (6a)). All these products result from hydroxide-isonitrile coupling reactions. When the mixture of 2b, (Me ₄N)OH (excess), and Bu^tNC (excess) in tetrahydrofuran was heated under reflux for a short time (2 h), complex 5b1 was formed in good yields. Compounds 5b1 and 5b2 are linkage isomers, which differ only in the mode of coordination of the μ-amino-oxycarbene ligand to the Mo1-Mo2 unit; 5b1 converts into 5b2 on prolonged heating. Reaction of the secondary amino-oxycarbene derivative 5a1 with a base (NaOH) and an alkylating agent R″₄NBr (R″ = Et, Buⁿ) afforded the corresponding tertiary(amino)-oxycarbene complexes [Mo₂Cp(μ-SMe) ₂{μ-(η⁵-C₅H₄)(xylN)CN(xyl)C} {μ-η¹(O),η¹(C)-OCNxylR″}] [R″ = Et (6b), Buⁿ (6c)]. On heating a tetrahydrofuran solution of the μ-alkylidyne compound 4 with NaOH (suspension) and an excess of either xylNC or Bu^tNC, the mixed μ-alkylidyne and μ-amino-oxycarbene species 5a1 and 5b2 were obtained, demonstrating that 4 is an intermediate in the formation of 5a1 and 5b2 from 2b. Treatment of the mixed isonitrile-nitrile species [Mo₂Cp₂(μ-SMe)₃(MeCN)(xylNC)] (BF₄) (3), containing a labile MeCN group, under reflux in tetrahydrofuran with NaOH (suspension) afforded quantitatively the μ-amino-oxycarbene compound [Mo₂Cp₂(μ-SMe) ₃{μ-η¹(O),η¹(C)-OCNHxyl}] (7). All new complexes have been characterized by elemental analyses and spectroscopic methods, supplemented for 5a1, 5b1, 5b2, 6a, 6b, and 7 by X-ray diffraction studies.

Full text of DOI:10.1021/om060383v

Organometallics 2006, 25, 4009-4018
4009
Formation of C-C, C-N, and C-O Links between Isonitrile,
Cyclopentadienyl, and Hydroxide Ligands Bound to
Molybdenum(III): Syntheses and Crystal Structures of
µ-Aminocarbyne and µ-Amino-oxycarbene Dimolybdenum
Complexes
Wilfried-Solo Ojo, Eddy Paugam, 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
Kenneth W. Muir*
Chemistry Department, UniVersity of Glasgow, Glasgow G128QQ, U.K.
ReceiVed May 3, 2006
Reaction of the bis-isonitrile complex [Mo2Cp2(µ-SMe)3(xylNC)2](BF4) (2b) with NaOH (suspension)
under reflux in tetrahydrofuran produced, in quantitative yields, the µ-alkylidyne species [Mo2Cp(µ-
SMe)3{µ-(η5-C5H4)(xylN)CN(xyl)C}] (4), in which a deprotonated Cp and both isonitrile ligands of
2b are now linked by new C-C and C-N bonds. Under prolonged reflux (72 h) in tetrahydrofuran 2b
with either NaOH (suspension) or (Me4N)OH (in MeOH) in the presence of excess isonitrile RNC (R )
xyl, But) was converted in high yields into the mixed (µ-alkylidyne)(µ-amino-oxycarbene) derivatives
[Mo2Cp(µ-SMe)2{µ-(η5-C5H4)(xylN)CN(xyl)C}{µ-η1(O),η1(C)-OCNHR}] (R ) xyl (5a1), R ) But (5b2))
and [Mo2Cp(µ-SMe)2{µ-(η5C5H4) (xylN)CN(xyl)C}{µ-η1(O),η1(C)-OCNMeR}] (R ) xyl (6a)). All these
products result from hydroxide-isonitrile coupling reactions. When the mixture of 2b, (Me4N)OH (excess),
and ButNC (excess) in tetrahydrofuran was heated under reflux for a short time (2 h), complex 5b1 was
formed in good yields. Compounds 5b1 and 5b2 are linkage isomers, which differ only in the mode of
coordination of the µ-amino-oxycarbene ligand to the Mo1-Mo2 unit; 5b1 converts into 5b2 on prolonged
heating. Reaction of the secondary amino-oxycarbene derivative 5a1 with a base (NaOH) and an alkylating
agent R′′4NBr (R′′ ) Et, Bun) afforded the corresponding tertiary(amino)-oxycarbene complexes
[Mo2Cp(µ-SMe)2{µ-(η5-C5H4)(xylN)CN(xyl)C }{µ-η1(O),η1(C)-OCNxylR′′}] [R′′ ) Et (6b), Bun (6c)].
On heating a tetrahydrofuran solution of the µ-alkylidyne compound 4 with NaOH (suspension) and an
excess of either xylNC or ButNC, the mixed µ-alkylidyne and µ-amino-oxycarbene species 5a1 and 5b2
were obtained, demonstrating that 4 is an intermediate in the formation of 5a1 and 5b2 from 2b. Treatment
of the mixed isonitrile-nitrile species [Mo2Cp2(µ-SMe)3(MeCN)(xylNC)](BF4) (3), containing a labile
MeCN group, under reflux in tetrahydrofuran with NaOH (suspension) afforded quantitatively the µ-amino-
oxycarbene compound [Mo2Cp2(µ-SMe)3{µ-η1(O),η1(C)-OCNHxyl}] (7). All new complexes have been
characterized by elemental analyses and spectroscopic methods, supplemented for 5a1, 5b1, 5b2, 6a,
6b, and 7 by X-ray diffraction studies.
pounds. The insertion reaction can be initiated in various ways:
by oxidative addition of alkyl halides to [M(RNC)n] complexes,6
by addition of an excess of isocyanide to metal complexes,4b,7
or by thermolysis.8 Most coupling reactions between isocyanides
involve formation of C-C bonds,6-8 while only a few give rise
to new C-N bonds.9 It has been shown that many different
alkyl or aryl groups can migrate onto an isocyanide carbon
Introduction
The formation of new C-X bonds, where X ) C, N, O, etc.,
through the mediation of transition metals is an important route
to novel organic compounds and ligands.1,2 For example,
coupling reactions involving isocyanides have led to the
successful synthesis of a wide variety of new nitrogen-containing
organic ligands and compounds during the past decade.3,4 These
reactions can proceed either through metal-mediated reductive
coupling of the isocyanides5 or by consecutive insertion of
isocyanides into M-C bonds to give N-chelated cyclic com-
(2) For recent examples see: (a) Ruiz, J.; Mosquera, M. E. G.; Garc´ıa,
G.; Marqu´ınez, F.; Riera, V. Angew. Chem., Int. Ed. 2005, 44, 102. (b)
Pittard, K. A.; Cundari, T. R.; Gunnoe, T. B.; Day, C. S.; Petersen, J. L.
Organometallics 2005, 24, 5015. (c) Bokach, N. A.; Kukushkin, V. Y.;
Haukka, M.; Frau´sto da Silva, J. J. R.; Pombeiro, A. J. L. Inorg. Chem.
2003, 42, 3602. (d) Makarycheva-Mikhailova, A. V.; Kukushkin, V. Y.;
Nazarov, A. A.; Garnovskii, D. A.; Pombeiro, A. J. L.; Haukka, M.; Keppler,
B. K.; Galanski, M. Inorg. Chem. 2003, 42, 2805.
(3) (a) Pombeiro, A. J. L.; Guedes da Silva, M. F. C.; Michelin, R. A.
Coord. Chem. ReV. 2001, 218, 43. (b) Michelin, R. A.; Pombeiro, A. J. L.;
Guedes da Silva, M. F. C. Coord. Chem. ReV. 2001, 218, 75. (c) Tamm,
M.; Hahn, F. E. Coord. Chem. ReV. 1999, 182, 175.
* Corresponding authors. E-mail: francois.petillon@univ-brest.fr (F.Y.P);
schollha@univ-brest.fr (P.S); ken@chem.gla.ac.uk (K.W.M).
(1) For recent reviews see: (a) Negishi, E.-i.; Anastasia, L. Chem. ReV.
2003, 103, 1979. (b) Hassan, J.; Se´vignon, M.; Gozzi, C.; Schulz, E.;
Lemaire, M. Chem. ReV. 2002, 102, 1359. (c) Beletskaya, I. P.; Cheprakov,
A. V. Chem. ReV. 2000, 100, 3009. (d) Miyaura, N.; Suzuki, A. Chem.
ReV. 1995, 95, 2457.
10.1021/om060383v CCC: $33.50 © 2006 American Chemical Society
Publication on Web 06/24/2006

4010 Organometallics, Vol. 25, No. 16, 2006
Ojo et al.
atom.10 In contrast, there are only very few examples involving
a comparable migratory insertion of cyclopentadienyl, despite
its ubiquity as a ligand.11 Accordingly, we have tried to exploit
the close proximity of the two isonitrile and two cyclopenta-
dienyl groups in the readily accessible bis-isonitrile derivative
[Mo2Cp2(µ-SMe)3(RNC)2](BF4) (2) in attempts to induce cou-
pling between these ligands. We have already shown12 that 2a
(R ) But) reacts with various bases (OH-, Bu-) to give both
the dealkylated product [Mo2Cp2(µ-SMe)3(CN)(ButNC)] and the
µ-alkylidyne derivative [Mo2Cp(µ-SMe)3{µ-(η5-C5H4)(ButN)-
CN(But)C}]. In the µ-alkylidyne derivative new C-C and C-N
bonds link a deprotonated Cp and both isonitrile ligands of the
starting complex 2a. These reactions occur in both the presence
and absence of excess isonitrile, but the ratio of dealkylated to
µ-alkylidyne product strongly depends on the reaction condi-
tions, dealkylation being favored in the absence of excess
isonitrile. The unusual character of these transformations, which
are summarized in Scheme 1, has prompted us to follow up
our preliminary study12 with a wider investigation of the activity
of [Mo2Cp2(µ-SMe)3(RNC)2](BF4) (2) toward hydroxides. We
now describe the reaction with hydroxide of complex 2b, which
contains aromatic isocyanide ligands (namely, XylNC) in place
of the aliphatic isocyanides present in 2a, and of the mixed
isonitrile-nitrile compound [Mo2Cp2(µ-SMe)3(MeCN)(xylNC)]-
(BF4) (3). The reactions have been performed under thermolytic
conditions in both the presence and absence of excess isocya-
nide. The products contain novel µ-alkylidyne and µ-amino-
oxycarbene ligands. The results are used to evaluate how the
Scheme 1
Scheme 2
terminal ancillary ligands in tris(µ-thiolato)dimolybdenum
complexes [Mo2Cp2(µ-SMe)3L2](BF4) influence reactivity to-
ward bases.
Results and Discussion
Synthesis and Characterization of the Precursors 2b and
3. The dimolybdenum complexes [Mo2Cp2(µ-SMe)3(xylNC)2]-
(BF4) (2b) and [Mo2Cp2(µ-SMe)3(MeCN)(xylNC)] (BF4) (3),
suitable precursors for 4-6 and 7, respectively, were prepared
from [Mo2Cp2(µ-SMe)3(MeCN)2](BF4) (1) by a double or single
substitution process,13 using either 2 or 1 equiv of isonitrile as
reagent. The synthesis and the characterization of 2b have
already been reported,14 but those of 3 are novel. The formula-
tion of 3 (Scheme 2) was deduced from the IR and NMR data
(see Experimental Section).
(4) (a) Ruiz, J.; Garc´ıa, G.; Mosquera, M. E. G.; Perandones, B. F.;
Gonzalo, M. P.; Vivanco, M. J. Am. Chem. Soc. 2005, 127, 8584. (b) Deng,
L.; Chan, H.-S.; Xie, Z. J. Am. Chem. Soc. 2005, 127, 13774. (c) Hahn, F.
E.; Langenhahn, V.; Meier, N.; Lu¨gger, T.; Fehlhammer, W. P. Chem. Eur.
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J. A. Inorg. Chim. Acta 2002, 334, 419. (e) Becker, T. M.; Alexander, J.
J.; Krause-Bauer, J. A.; Nauss, J. L.; Wireko, F. C. Organometallics 1999,
18, 5594. (f) Tanase, T.; Ohizumi, T.; Kobayashi, K.; Yamamoto, Y.
Organometallics 1996, 15, 3404.
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Carnahan, E. M.; Protasiewicz, J. D.; Lippard, S. J. Acc. Chem. Res. 1993,
26, 90, and references therein.
(6) See for example: (a) Basset, J. M.; Green, M.; Howard, J. A. K.;
Stone, F. G. A. J. Chem. Soc., Dalton Trans. 1980, 1779. (b) Otsuka, S.;
Nakamura, A.; Yoshida, T. J. Am. Chem. Soc. 1969, 91, 7196.
(7) Recent references: (a) Ramakrishna, T. V. V.; Lushnikova, S.; Sharp,
P. R. Organometallics 2002, 21, 5685. (b) Owen, G. R.; Vilar, R.; White,
A. J. P.; Williams, D. J. Organometallics 2002, 21, 4799. (c) Stroot, J.;
Saak, W.; Haase, D.; Beckhaus, R. Z. Anorg. Allg. Chem. 2002, 628, 755.
(d) Vicente, J.; Abad, J.-A.; Martinez-Viviente, E.; Jones, P. G. Organo-
metallics 2002, 21, 4454. (e) Yamamoto, M.; Onitsuka, K.; Takahashi, S.
Organometallics 2000, 19, 4669. (f) Bashall, A.; Collier, P. E.; Gade, L.
H.; McPartlin, M.; Mountford, P.; Pugh, S. M.; Radojevic, S.; Schubart,
M.; Scowen, I. J.; Tro¨sch, D. J. M. Organometallics 2000, 19, 4784. (g)
Tomaszewski, R.; Lam, K.-C.; Rheingold, A. L.; Ernst, R. D. Organome-
tallics 1999, 18, 4174.
Reaction of 2 with Bases. We have shown previously that
2a reacts with hydroxides to afford mainly the dealkylation
product [Mo2Cp2(µ-SMe)3(ButNC)(NC)] via R-cleavage of one
isonitrile; 4′ is also formed in low yield by isonitrile coupling
[see Scheme 3 (a)].12 The stability of the Me3C+ ion favors
dealkylation in the case of 2a.15 This effect does not operate in
the case of 2b. It is, therefore, not surprising that the only
product of the reaction of 2b with NaOH under reflux in THF
is the µ-alkylidyne derivative 4. 4 is obtained in nearly
quantitative yield (84%) [Scheme 3 (b)] without the presence
of excess xylNC. When 2a reacts with OH- in the presence of
excess ButNC, the yield of the µ-alkylidyne complex 4′ improves
(e.g., from 30 to 69%, when NaOH is used as a base).12
The elemental analysis confirms the coupling of two isonitrile
units in 4, while its NMR spectra clearly indicate a structure
analogous to 4′, which has been reliably characterized.12
Particularly informative are the four resonances of relative
(8) (a) Ang, T.-G.; Wood, D.; Yap, G. P. A.; Richeson, D. S.
Organometallics 2002, 21, 1. (b) Kloppenburg, L.; Petersen, J. L. Orga-
nometallics 1997, 16, 3548.
(9) See for example: (a) Jeffery, J. C.; Green, M.; Lynam, J. M. J. Chem.
Soc., Chem. Commun. 2002, 3056. (b) Motz, P. L.; Alexander, J. J.; Ho,
D. M. Organometallics 1989, 8, 2589. (c) Bellachioma, G.; Cardaci, G.;
Zanazzi, P. Inorg. Chem. 1987, 26, 84. (d) Bocarsly, J. R.; Floriani, C.;
Chiesi-Villa, A.; Guastini, C. Organometallics 1986, 5, 2380.
(10) (a) Thorn, M. G.; Lee, J.; Fanwick, P. E.; Rothwell, I. P. J. Chem.
Soc., Dalton Trans. 2002, 3398. (b) Fandos, R.; Hernandez, C.; Otero, A.;
Rodriguez, A.; Ruiz, M. J.; Terreros, P. Eur. J. Inorg. Chem. 2003, 493.
(c) Cadierno, V.; Zablocka, M.; Donnadieu, B.; Igau, A.; Majoral, J. P.;
Skowronska, A. J. Am. Chem. Soc. 1999, 121, 11086. (d) Yamamoto, Y.;
Yamazaki, H. Inorg. Chem. 1977, 16, 3182. See also refs 6, 7a-e, and 8.
(11) (a) Alias, F. M.; Belderrain, T. R.; Paneque, M.; Poveda, M. L.;
Carmona, E.; Valerga, P. Organometallics 1998, 17, 5620. (b) Tanase, T.;
Fukushima, T.; Nomura, T.; Yamamoto, Y.; Kobayashi, K. Inorg. Chem.
1994, 33, 32.
1
intensity 1 at 6.00, 5.66, 5.29, and 5.00 ppm in the H NMR
spectrum assigned to the four hydrogen atoms of a modified
cyclopentadienyl ring, whereas a single peak of relative intensity
5, detected at 5.10 ppm, is indicative of an unmodified
(13) Barrie`re, F.; Le Mest, Y.; Pe´tillon, F. Y.; Poder-Guillou, S.;
Schollhammer P.; Talarmin, J. J. Chem. Soc., Dalton Trans. 1996, 3967.
(14) Cabon, N.; Pe´tillon, F. Y.; Orain, P.-Y.; Schollhammer, P.; Talarmin,
J.; Muir, K. W. J. Organomet. Chem. 2005, 690, 4583.
(12) Cabon, N.; Paugam, E.; Pe´tillon, F. Y.; Schollhammer, P.; Talarmin,
J.; Muir, K. W. Organometallics 2003, 22, 4178.
(15) Treichel, P. M. AdV. Organomet. Chem. 1973, 11, 21.

µ-Aminocarbyne Dimolybdenum Complexes
Organometallics, Vol. 25, No. 16, 2006 4011
Scheme 3
Scheme 4
Scheme 5
cyclopentadienyl ligand. Thus, these data are in agreement with
the coupling of one cyclopentadienyl ring via one of its carbon
atoms with an adjacent coordinated isonitrile. Moreover, a reso-
nance characteristic of the Mo-bound 13C atom of an µ-alky-
lidyne moiety appears at low field (δ 374.7), and a signal that
could be assigned to an imine-like carbon (CdN-R) is detected
at 156.5 ppm. In agreement with the presence of a CdN bond
in 4, the IR spectrum shows one absorption at 1642 cm-1
.
Reaction of 2b with Bases in the Presence of Isonitrile.
Prolonged heating (72 h) of a THF solution of complex 2b and
NaOH (suspension) in the presence of 3 equiv of RNC (R )
xyl, But) produced in high yield a µ-alkylidyne, µ-amino-
oxycarbene complex, [Mo2Cp(µ-SMe)2{µ-(η5-C5H4)(xylN)CN-
(xyl)C}(µ-OCNHR)] (5a1, R ) xyl; 5b2, R ) But), as the only
Cp′Mo2Cp species (Cp′ ) η5-C5H4R′; Cp ) η5-C5H5) detectable
and 5b2 result from attacks by hydroxide ions on different atoms
of 2b. Finally, it should be noted that under similar conditions
heating the xylNC compound 5a1 did not produce isomer 5a2.
1
in the H NMR spectrum of the crude product (Scheme 4).
All the new complexes, 5a1, 5b1, 5b2, and 6a, have been
characterized by elemental analysis and conventional spectro-
scopic measurements, and for some species by mass spectros-
copy (see the Experimental Section). As the NMR data alone
cannot discriminate with assurance between possible adducts,
X-ray analyses (see below) have established that all these
complexes are formed via similar condensation reactions,
initiated by base and excess isonitrile. The presence in all the
complexes of a µ-alkylidyne ligand, (η5-C5H4)(xylN)CN(xyl)C,
derived from the condensation of a cyclopentadienyl and two
isonitrile units, can be deduced from the NMR spectra, which
closely resemble that of 4, except that the amino-oxycarbene
X-ray analyses indicate that 5a1 and 5b2 both contain
µ-amino-oxycarbene ligands; however, these ligands are oriented
differently with respect to the Mo′-Mo units, as shown in
Scheme 4. To see if a complex 5b with a µ-amino-oxycarbene
coordinating in a mode similar to that observed in 5a1 could
be obtained, 2b was treated with Me4NOH in the presence of
excess ButNC under reflux in THF. Complex 5b1, containing
a µ-amino-oxycarbene ligand with the expected mode of
coordination, was formed in good yield after only 2 h (Scheme
5). Somewhat unexpectedly, 2b and Me4NOH in the presence
of excess xylNC under prolonged reflux (72h) in THF produced
6a, in which a tertiary(amino)-oxycarbene ligand coordinates
in the same mode as in 5b1 (Scheme 5). Contrastingly, pro-
longed heating of 5b1 in THF gave mainly 5b2, together with
some decomposition products. This shows clearly that 5b2
was formed via 5b1 and that it is unlikely that isomers 5b1
1
derivatives show only two Cp′ H NMR signals, rather than
the four observed for complex 4. This difference may be
ascribed to the orientations of the bridging SMe groups: syn in
the amino-oxycarbene products (see crystallographic section)
1
and anti in 4.12 The most distinctive features of the H NMR

4012 Organometallics, Vol. 25, No. 16, 2006
Ojo et al.
Scheme 6. Alternative Pathways for the Formation of
spectra of the µ-amino-oxycarbene complexes are the ligand
N-H resonances: these appear in the 7.36-5.65 range for 5a1
and 5b and are absent for 6a. A downfield signal (δ 7.36) is
observed for 5a1, which contains a NH-xyl unit, whereas 5b1
and 5b2, which have a NH-But group, exhibit upfield N-H
signals (δ ∼5.65). Salient characterization features of 5a1 and
Complexes 5a1 and 5b1 from 2ba
1
5b include also H-13C HMBC experiments that reveal the
expected correlations (2JC-H) of the N-H signals with both the
carbene carbon resonances and also with the signals for either
the Cipso (xyl) or CMe3 (But) carbon atoms. For the methyl-
amino-derived complex 6a the methyl resonance (δ 3.09)
correlates with both the Cipso (xyl) (δ 146.8) and carbene carbon
(δ 242.4) signals. Interestingly, these experiments also show
an apparent correlation between the signals for the Cp C-H
and carbene carbon atom in the 2D spectrum of 5b2, but not in
those of 5b1 and 5a1. This is further evidence that the mode of
coordination of the amino-oxycarbene group to the Mo′-Mo
unit in 5b2 differs from that in 5b1 and 5a1.
1
It should also be noted that a H-15N HMBC experiment
(CDCl3; RT) for 5b1 shows correlations (3JN-H) between 15N
and methyl resonances (δ 1.33); the 15N chemical shift (δ
-214.1) is observed in the range (δN -200 to -300) expected
for an amide-like compound.16 Finally, no fluxionality is
apparent in the 1H and 13C NMR spectra of complexes 5b1 and
5b2 (Experimental Section).
Syntheses of Amino-oxycarbene Compounds 5a1 and 5b
via the µ-Alkylidyne Derivative 4 and Mechanistic Consid-
erations. Independent preparations of 5a1 and 5b2 verified that
the reaction of complex 4 with NaOH and excess isonitrile RNC
also produces complexes 5a1 (R ) xyl) and 5b2 (R ) But) in
good yield.
a (a) + base; (i) + RNC, thiolate substitution; (ii) + NaOH, -
NaSMe, nucleophilic substitution; (iii) internal rearrangement (tauto-
meric hydrogen shift and nucleophilic addition); (ij) + OH- (NaOH),
nucleophilic addition; (ik) tautomeric hydrogen shift; (il) - SMe-
(NaSMe), nucleophilic substitution.
These results indicate clearly that the formation of µ-amino-
oxycarbene derivatives 5a1 and 5b by reaction of the bis-
isonitrile tris(µ-thiolato) compound 2b with bases (see previous
section) proceeds through the µ-alkylidyne derivative 4, as
shown in Scheme 6. The mechanism of formation of compound
4 has been previously discussed.12 4 can react to give either
5a1 (R ) xyl) directly or 5b2 (R ) But) via 5b1 by nucleophilic
addition of hydroxide to a Mo atom (pathway I) or to the carbon
atom of an additional coordinated isocyanide group (pathway
II) with retention of the µ-alkylidyne ligand.
Scheme 7
As no intermediate except 4 has been detected, the mechanism
of the reaction can only be a matter of speculation at present.
However, there are precedents for several steps in both possible
mechanisms depicted in Scheme 6. The first step is common to
paths I and II: it involves thiolate substitution promoted by
addition of an excess of RNC (R ) xyl, But) to 4 giving
intermediate A. It is followed in path I by nucleophilic (OH-)
substitution at a molybdenum atom with elimination of the
thiolate group as NaSMe, yielding hydroxide intermediate B.
Concerted nucleophilic addition of the coordinated hydroxide
group to the isonitrile carbon atom and a tautomeric hydrogen
shift15 finally leads to the formation of a bridging amino-
oxycarbene ligand in the two complexes 5. The available
evidence does not allow us to exclude the existence of a second
pathway to 5a1 or 5b1 via direct hydroxide addition to the
carbon atom of the coordinated isonitrile intermediate A,
affording amide transient C. As one might suspect, the amide
nitrogen in this intermediate is basic and can be protonated via
tautomeric hydrogen transfer,17 giving an amidate derivative D
that by further nucleophilic substitution yields the final product
5a1 or 5b. It is interesting to observe that 4′, which has aliphatic
(e.g., But) instead of aromatic groups (e.g., xylyl) in the
µ-alkylidyne ligand, is inert to thiolate substitution reactions;
thus, no amino-oxycarbene complex was formed when 4′ reacted
with an excess of NaOH and isonitrile. We conclude that the
presence in 4 of a µ-alkylidyne ligand with aromatic groups
(e.g., xylyl) labilizes the trans-thiolate ligand, facilitating the
transformation of 4 into 5a1 or 5b.
As suggested above, alternative attack of OH- at either MoCp
or MoCp′ would be an attractive way to account for the
formation of isomers 5b1 and 5b2. However, it is not consistent
with our observation that 5b2 is formed from 5b1. X-ray
(17) See for example: (a) Schollhammer, P.; Le He´nanf, M.; Le Roy-Le
Floch, C.; Pe´tillon, F. Y.; Talarmin, J.; Muir, K. W. J. Chem. Soc., Dalton
Trans. 2001, 1573, and references therein. (b) Treichel, P. M.; Knebel, W.
J. Inorg. Chem. 1972, 11, 1285.
(16) Berger, S.; Braun, S.; Kalinowski, H.-O. In NMR Spectroscopy
of the Non-Metallic Elements; John Wiley & Sons: Chichester, 1997;
Chapter 4.

µ-Aminocarbyne Dimolybdenum Complexes
Organometallics, Vol. 25, No. 16, 2006 4013
Scheme 8
Scheme 9
characteristics closely match those of the methyl analogue 6a.
Complexes 6b and 6c are therefore formulated as µ-alkylidyne,
µ-tertiary(amino)-oxycarbene derivatives, consistent with X-ray
analysis of single crystals of 6b (see below). The tertiary amine
nature of the amino-oxycarbene ligand in 6b and 6c is deduced
from the presence of additional 1H NMR resonances in the alkyl
region [6b: 3.70 (intensity 2) and 1.02 (intensity 3) ppm; 6c:
3.56 (intensity 2) [1.41 (intensity 2) and 0.83 (intensity 3) ppm]
1
relative to those of the mother compound 5a1. All other H
NMR resonances observed for 6b and 6c are in full agreement
with the structure proposed above, particularly the presence of
two resonances both of intensity 2 at 5.14 and 4.34 ppm (6b)
and at 5.14 and 4.32 ppm (6c), which can be assigned to the
modified cyclopentadienyl ligand, C5H4R′.
Reaction of 3 with a Base. We have shown above that
formation of an amino-oxycarbene ligand by addition of OH-
to a coordinated isonitrile is only observed when the transition
metal complex contains labile ancillary ligands. Therefore, it
could reasonably be expected that the mixed isonitrile-nitrile
compound 3, which contains a labile MeCN group, will undergo
a similar reaction. Indeed, refluxing 3 with NaOH in THF gave
high yields of the target amino-oxycarbene complex 7 (Scheme
9). 3 is derived from 2 by replacing a terminal isonitrile by
acetonitrile. This replacement changes the regiochemistry of the
reaction and precludes formation of a µ-alkylidyne unit by
coupling the isonitrile, nitrile, and cyclopentadienyl ligands.
Consistent with the structure depicted in Scheme 9 for 7, the
1H NMR spectrum displays two cyclopentadienyl resonances
at δ 5.42 and 5.15 and a singlet at δ 6.70 (intensity 1) assigned
to the N-H group. The presence of an amino-oxycarbene ligand
in 7 is supported both by the carbene 13C chemical shift (δ
240.8), similar to values (∼244 ppm) for the related complexes
5 and 6, and by an X-ray structure analysis (see next section).
It is likely that 7 is formed by processes such as those
proposed above for 5a1 and 5b1: alternative pathways involving
hydroxide attack at either Mo or the C atom of the coordinated
isonitrile, followed by an internal rearrangement, can be
envisaged.
analyses of 5b1 and 5b2 (see below) show that the isomers
differ only in the mode of coordination of the C(NHBut)-O
ligand to the Mo atoms: in 5b1 the linkage to MoCp is through
oxygen, whereas in 5b2 it is through the carbon atom. In both
isomers the C-O bond axis is nearly parallel to the Mo-Mo
axis and the dimetallacyclo-oxycarbene µ-η1(O):η1(C) coordina-
tion mode is comparable with that of the µ-η1:η1-dimetallacy-
clobutene ligand in [Mo2Cp2(µ-SMe)3(RCCH)](BF4).18 An
exchange of alkyne from one molybdenum site to the other has
been suggested to account for the fluxionality of these alkyne
derivatives.18 Here, a similar exchange process would explain
the transformation of 5b1 into 5b2 (Scheme 7). Thus, 5b1 and
5b2 are respectively the kinetic and thermodynamic products
of the reaction of 2 or 4 with an excess of base and isonitrile.
Finally, it should be noted that when an aromatic group (e.g.,
xylyl) is bound to the amine nitrogen atom, only one isomer,
5b1, could be obtained as a stable species. In contrast, two
isomers, 5b1 and 5b2, are formed when an alkyl group (e.g.,
But) is linked to the amine nitrogen atom.
Reaction of µ-Amino-oxycarbene Complexes with NaOH
and Tetraalkylammonium Bromide. Complexes 5a1 and 5b
would seem to be suitable substrates for reaction with base,
followed by an alkylating agent, to give the corresponding
tertiary(amino)-oxycarbene derivatives. Indeed, reaction of 5a1
with NaOH and tetraalkylammonium bromide, R′′4NBr (R′′ )
Et, Bun), proceeds with high selectivity, and the targeted
alkylated derivative 6b (R′′ ) Et) or 6c (R′′ ) Bun) is obtained.
However, similar reactions involving complexes 5b1 and 5b2
do not give the desired products. The presence of a But group
at the nitrogen atom probably lessens the acidic character of
the geminal hydrogen atom relative to that observed in the
related xylyl compound 5a1 and thus prevents the acid-base
reaction (Scheme 8).
Molecular Structures of 5a1, 5b1, 5b2, 6a, 6b, and 7. The
compounds 5a1, 5b1, 5b2, 6a, and 6b (Figures 1-4, Table 1)
share a common structural architecture: an Mo2(µ-SMe)2Cp
moiety is stabilized by bridging (η5-C5H4)(xylN)CN(xyl)C
alkylidyne and R′R′′NCO amino-oxycarbene ligands. The
S-methyl groups are invariably syn to the Mo2S2 plane and
enfold the R′R′′NCO ligand. However, in 6a disorder of a
methyl group suggests that the anti form may also be present
as a minor component. In 7 (Figure 5) where a xylHNCO ligand
bridges a Cp2Mo2(µ-SMe)3 unit and in 4′ where the same unit
is bridged by a (η5-C5H4)(ButN)CN(But)C alkylidyne an anti
arrangement of S-methyl groups is also found.12 In the following
discussion less weight is given to the markedly less precise
results for 5a1 and 6b (see below).
Complexes 6b and 6c have been successfully characterized
from analytical and NMR data. Their NMR spectroscopic
The η5-(C5H4)(xylN)CN(xyl)C alkylidyne ligands in
5a1-6b arise from condensation of a Cp and two xylNC lig-
ands: C49, originally the donor atom of an isonitrile, has
detached from Mo1 and is now bonded through C21 to a
(18) Schollhammer, P.; Cabon, N.; Capon, J.-F.; Pe´tillon, F. Y.; Talarmin,
J.; Muir, K. W. Organometallics 2001, 20, 1230.

4014 Organometallics, Vol. 25, No. 16, 2006
Ojo et al.
Table 1. Selected Bond Lengths (Å) and Bond and Torsion Angles (deg) for the
[Mo2Cp(µ-SMe)2{µ-(η5-C5H4)(xylN)CN(xyl)C}{µ-OCNRR′}] Complexes 5a1 (R ) H, R′ ) xyl),
5b1/b2 (R ) H, R′ ) But), 6a (R ) Me, R′ ) xyl), and 6b (R ) Et, R′ ) xyl) and for 7
(a) µ-(η5-C5H4)(xylN)CN(xyl)C Ligands
5a1
5b1
5b2
6a
6b
7
Mo1-Mo2
2.654(2)
1.99(2)
1.97(2)
1.44(2)
1.39(2)
1.46(2)
1.29(2)
1.44(2)
1.46(2)
124.3(10)
151.3(10)
115.0(11)
113.9(12)
118.9(13)
127.2(14)
115.4(13)
-176(1)
180(1)
2.649(1)
2.012(6)
1.993(6)
1.386(7)
1.386(7)
1.453(7)
1.278(7)
1.416(8)
1.473(8)
123.4(4)
153.4(5)
118.2(5)
112.3(5)
117.6(5)
130.2(6)
120.2(5)
-179.6(5)
-175.3(5)
2.654(1)
1.976(4)
2.053(4)
1.358(5)
1.400(6)
1.460(6)
1.257(5)
1.423(6)
1.509(6)
126.0(3)
151.7(3)
117.4(4)
111.0(3)
120.7(4)
128.3(5)
122.5(4)
179.5(4)
-177.6(6)
2.660(1)
2.019(5)
2.004(5)
1.370(6)
1.409(6)
1.436(6)
1.262(6)
1.427(6)
1.498(7)
125.7(3)
151.2(4)
116.5(4)
111.7(4)
119.6(4)
128.7(4)
119.8(4)
168.1(4)
-179.8(4)
2.652(1)
2.00(1)
2.00(1)
1.38(1)
1.39(1)
1.42(1)
1.27(1)
1.45(1)
1.51(1)
125.5(6)
151.3(7)
117.8(8)
111.1(8)
120.0(9)
128.9(9)
118.2(8)
-179(1)
179(1)
2.666(1)
Mo1-C39
Mo2-C39
N3-C39
N3-C49
N3-Cxyl
N4-C49
N4-Cxyl
C49-C21
Mo1-C39-N3
Mo2-C39-N3
C39-N3-C49
N3-C49-C21
N3-C49-N4
N4-C49-C21
C49-N4-C41
C39-N3-C49-N4
N3-C49-N4-C41
(b) µ-OCNRR′ Ligands
5a1
5b1
5b2
6a
6b
7
Mo1-O1
2.167(3)
2.161(3)
Mo2-O1
2.20(1)
2.14(2)
2.171(4)
2.165(6)
2.181(3)
2.168(5)
2.166(6)
2.15(1)
Mo1-C50
Mo2-C50
2.148(4)
1.287(5)
1.352(6)
1.486(6)
2.140(4)
1.294(5)
1.358(6)
1.438(6)
O1-C50
1.29(2)
1.36(2)
1.43(2)
1.304(7)
1.340(8)
1.488(7)
1.291(6)
1.363(6)
1.440(7)
1.489(7)
104.9(3)
111.8(3)
116.7(4)
131.6(4)
119.8(4)
123.4(4)
116.8(4)
2.3(3)
1.30(1)
1.38(1)
1.41(1)
1.50(1)
104.7(6)
111.9(7)
115.6(9)
132.6(7)
120.9(8)
119.7(8)
119.0(8)
1.2(7)
N5-C50
N5-C51
N5-C3
Mo-O1-C50
Mo-C50-O1
O1-C50-N5
Mo-C50-N5
C50-N5-C3
C50-N5-C51
C51-N5-C3
Mo-C50-O1-Mo
103.5(9)
102.7(3)
113.5(4)
116.7(6)
129.6(5)
102.6(2)
114.5(3)
117.0(4)
128.5(3)
102.8(3)
114.4(3)
114.2(4)
131.4(4)
113.2(10)
115.1(12)
131.7(11)
123.3(11)
132.3(5)
130.8(4)
0.7(3)
124.8(4)
5.1(3)
-1(1)
-2.5(4)
cyclopentadienyl ring, displacing a hydrogen atom, and through
N3 to the second isonitrile ligand. The resulting µ-alkylidyne
uses C39 to bridge the two molybdenum atoms but also engages
in a conventional η5-cyclopentadienyl interaction with Mo1. C39
is virtually equidistant from the metal atoms in 5a1, 5b1, 6a,
and 6b (see Table 1): the Mo-C39 bond distances [1.976(4)-
2.019(5) Å] in these four complexes lie between the value of
1.894(5) Å for the formally double bond ModC in the
vinylidene compound [Mo2Cp2(µ-SMe)3(µ-η1:η2-CdCHTol)]-
(BF4) and that of 2.068(3) Å for the single Mo-C bond in the
acetylide derivative [Mo2Cp2(µ-SMe)3(µ-η1:η2-CtC-Ph)];18
they thus indicate a symmetrical coordination of the alkylidyne
group through Mo-C bonds of order 1.5. However, the
Mo-C39 distances differ in 5b2, where the amino-oxycarbene
C50 is bonded to Mo2 rather than Mo1, by 0.077(6) Å and in
4′ by 0.111(3) Å, indicating sensitivity to the nature of the
ancillary ligands. Otherwise, as may be seen from Table 1, the
µ-alkylidyne ligands of 5a1-6b are remarkably similar. The
bonds radiating from C39, N3, C49, and N4 are nearly coplanar;
compared with the single N-Cxyl bonds the N3-C39,
N3-C49, and N4-C49 show conjugative shortening, with
N4-C49 aproaching a bond order of 2. The conjugation does
not extend to the xyl and C5H4 ring π-systems because of their
unfavorable orientation.The angles at C39 show severe devia-
tions (see Table 1) from sp2 hybridization but broadly agree
with those found in the µ-alkylidyne derivative [Mo2Cp2(µ-
Figure 1. Molecular structure of complex 5a1. Non-hydrogen
atoms are shown with 20% probability ellipsoids, and H atoms
bonded to C atoms are omitted for clarity.
Figure 2. Molecular structure of complexes 5b1 (a) and 5b2 (b).

µ-Aminocarbyne Dimolybdenum Complexes
Organometallics, Vol. 25, No. 16, 2006 4015
replaced by alkyl at N5. The Mo-O and Mo-C distances fall
in narrow ranges of 2.161(3)-2.20(1) and 2.140(4)-2.168(5)
Å, respectively. The C50-N5 and C50-O1 distances imply
some multiple character. The former are more than 0.1 Å shorter
than the N5-C3 distances in 6, a difference too great to be
explained by the difference in C hybridization, while the latter
are ca. 0.15 Å shorter than, for example, the single C-O bond
of 1.451(9) Å in [{Fe(CO)3}2{µ-S(Me)C(CF3)C(NHNHC(O)-
OMe)C (NHNHC(O)OMe)}].20 As previously noted, 5b1 and
5b2 can be regarded as novel linkage isomers: in 5b1 O1 bonds
to Mo2 (which carries the η5-C5H5 ring) and C50 to Mo1, while
in 5b2 O1 is attached to Mo1 and C50 to Mo2. It is striking
that the N5 But substituent in 5b1 and 5b2 bends away from
the adjacent Cp or Cp′ ligand, whereas the corresponding xyl
groups in 5a1, 6a, and 6b (but, surprisingly, not in 7) bend
toward the adjacent Cp′ ring. This feature appears to have a
steric origin.
Figure 3. Molecular structure of 6a. Disorder of the methyl group
attached to S2 is not shown.
The dimensions of the Mo2(µ-SMe)2Cp moieties in 5-7 agree
with results of many previous studies on related compounds.21
The single Mo-Mo bonds show remarkably little variation in
length [from 2.649(1) to 2.666(1) Å]. Finally, we note that, while
structurally characterized alkylidyne-transition metal complexes
M2(µ2-C-Csp3) (e.g., M ) W, Mo)22 are well-known, the new
µ-alkylidyne derivatives 5a1, 5b1, 5b2, 6a and 6b, and 4′,12
with a Mo2 (µ2-C-N) core, are without precedent.
Concluding Remarks
The bis-isonitrile dimolybdenum complex [Mo2Cp2(µ-SMe)3-
(xylNC)2](BF4) (2b), containing labile bridging groups, has been
shown to be an excellent starting point for the construction of
new bridging alkylidyne and amino-oxycarbene ligands. These
ligands are formed by coupling reactions of an unprecedented
nature: when base is added to the molybdenum complex in the
presence of excess isonitrile, a new alkylidyne ligand is first
formed by linking a cyclopentadienyl and two isonitrile ligands;
subsequently, a second isonitrile and hydroxide link to give an
amino-oxycarbene. When the added isonitrile is ButNC, the
kinetic adduct 5b1 transforms by heating into the thermody-
namic isomer 5b2; when the added isonitrile is xylNC, only
5a1, an analogue of 5b1, is isolated.
Figure 4. Molecular structure of complex 6b.
Addition of a base and excess isonitrile to the mixed
isonitrile-nitrile derivative [Mo2Cp2(µ-SMe)3(MeCN)(xylNC)]-
(BF4) (3), containing labile acetonitrile, leads only to the
formation of an amino-oxycarbene ligand by coupling between
additional isonitrile and hydroxide.
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
synthesis of [Mo2Cp2(µ-SMe)3 L2](BF4) [L ) MeCN (1),13 xylNC
(2b)14]. Other reagents were purchased from the usual commer-
cial suppliers and used as received. Infrared spectra were re-
corded on a Nicolet-Nexus FT IR spectrophotometer from KBr
pellets. Chemical analyses were performed by the Service de
Microanalyse ICSN-CNRS, Gif sur Yvette (France). The mass
spectra were measured with a LC-MS Thermo-Finnigan spectrom-
Figure 5. Molecular structure of 7. Selected bonds lengths (Å),
angles (deg), and torsion angles (deg): Mo1-S1 2.466(1),
Mo1-S2 2.453(1), Mo1-S3 2.443(1), Mo2-S1 2.449(1),
Mo2-S2 2.458(1), Mo2-S3 2.480(1), C50-N5-Cxyl 124.8(4),
C50-N5-H1 115(5), Cxyl-N5-H1 120(5), Cxyl-N5-C50-
Mo2 177.9(4), Cxyl-N5-C50-O1 -4.5(7). Also see Table 1.
SMe)3(µ-CCH2Prn)].19 Trends in bond angles at C39, N3, and
C49 (Table 1) reflect the constraint imposed by the attachment
of the alkylidyne to Mo1 through both C39 and the η5-C5 ring.
Complexes 5-7 also contain µ-amino-oxycarbene ligands:
in 5 and 7 they are the result of C-O and N-H bond formation
between incoming isonitrile and hydroxide ligands; in 6 H is
(20) Guennou-de Cadenet, K.; Rumin, R.; Pe´tillon, F. Y.; Yufit, D. S.;
Muir, K. W. Eur. J. Inorg. Chem. 2002, 639.
(21) Pe´tillon, F. Y.; Schollhammer, P.; Talarmin, J.; Muir, K. W. Coord.
Chem. ReV. 1998, 178-180, 203.
(22) See for example ref 19, and: Liu, A.-H.; Murray, R. C.; Dewan, J.
C.; Santarsiero, B. D.; Schrock, R. R. J. Am. Chem. Soc. 1987, 109, 4282.
(19) Cabon, N.; Schollhammer, P.; Pe´tillon, F. Y.; Talarmin, J.; Muir,
K. W. Organometallics 2002, 21, 448.

4016 Organometallics, Vol. 25, No. 16, 2006
Ojo et al.
eter at the Laboratoire de Biochimie, Faculte´ de Me´decine (Brest,
France). The NMR spectra (1H, 13C) were recorded at room
temperature in CDCl3, C6D6, or (CD3)2CO solutions with a Bruker
AMX 400 spectrometer and were referenced to SiMe4. 1H-13C and
1H-15N 2D experiments were carried out on a Bruker DRX 500
spectrometer.
Synthesis of [Mo2Cp2(µ-SMe)3(MeCN)(xylNC)](BF4) (3). A
solution of complex 1 (200 mg, 0.317 mmol) in dichloromethane
(30 mL) was stirred in the presence of 1 equiv of xylNC (41.5 mg)
for 4 h at room temperature. The color of the solution turned from
red to orange. The volume of the solution was reduced under
vacuum, and diethyl ether (50 mL) was added to precipitate a
maroon powder that was washed twice with pentane (2 × 15 mL).
After drying, compound 3 was obtained; its NMR spectra were
those expected of a pure sample (163 mg, 71% yield) and gave its
structure without ambiguity. IR (KBr, cm-1): ν(CN) 2075 (s), ν(BF)
1150-1050 (s). 1H NMR [(CD3)2CO]: δ 7.28-6.82 (m, 3H, C6H3-
(CH3)2), 5.64 (s, 5H, C5H5), 5.41 (s, 5H, C5H5), 2.45 (s, 6H, C6H3-
(CH3)2), 2.20 (s, 3H, CH3CN), 1.81 (s, 3H, SCH3), 1.80 (s, 3H,
SCH3), 1.56 (s, 3H, SCH3).
Reaction of [Mo2Cp2(µ-SMe)3(xylNC)2](BF4) (2b) with NaOH:
Synthesis of [Mo2Cp(µ-SMe)3{µ-(η5-C5H4)(xylN)CN(xyl)C}] (4).
The complex 2b (400 mg, 0.492 mmol) and a large excess of NaOH
(201 mg, 5 mmol) were heated in tetrahydrofuran (30 mL) at reflux
for 24 h. After filtration, the solvent was removed under vacuum
and one organometallic product was extracted with diethyl ether
(3 × 10 mL). Evaporation of volatiles afforded complex 4 as a red
powder, which was washed twice with pentane (2 × 15 mL) (300
mg, 84% yield). Anal. Calcd for C31H36Mo2N2S3: C, 51.4; H, 5.0;
N, 3.9. Found: C, 51.7; H, 5.0; N, 3.9. IR (KBr, cm-1): ν(CN)
1642 (m). 1H NMR [(CD3)2CO]: δ 7.17-6.96 (m, 6H, C6H3(CH3)2),
6.00 (m, 1H, C5H4), 5.66 (m, 1H, C5H4), 5.29 (m, 1H, C5H4), 5.10
(s, 5H, C5H5), 5.00 (m, 1H, C5H4), 2.29 (s, 3H, CH3(xyl)), 2.27 (s,
3H, CH3(xyl)), 2.17 (s, 6H, CH3(xyl)), 1.89 (s, 3H, SCH3), 1.82
(s, 3H, SCH3), 1.60 (s, 3H, SCH3). 13C{1H}NMR (C6D6): δ 374.7
(Mo2C), 156.5 (CdN), 147.3, 143.1, 137.2, 134.2, 128.8, 128.6,
123.4 (C6H3(CH3)2), 105.9, 103.6, 95.9 (C5H4), 92.0 (C5H5), 90.6,
84.3 (C5H4), 29.2 (SCH3), 20.3, 19.4 (C6H3(CH3)2), 8.0 (SCH3),
6.6 (SCH3).
and 5b2, in a 11:1 ratio by chromatography. When the reaction
was conducted under reflux for 72 h, compound 5b was recovered
in lower yields (71 mg, 74.5%), but isomers 5b1 and 5b2 were
then obtained in a 1:10 ratio (1H NMR analysis).
Method C. Complex 5b2 can also be synthesized in moderate
yields (48%) by refluxing a tetrahydrofuran solution of the above
mixture of 5b1 (92%) and 5b2 (8%) for 72 h (1H NMR analysis
only). However, this thermal reaction gave rise to appreciable
decomposition of 5b into an unidentified product (∼31%).
Orange crystals of 5a1, 5b1, and 5b2, suitable for X-ray analysis,
were obtained by crystallization at room temperature from a
CH2Cl2 solution layered with diethyl ether. Analytical data for 5a1
have been confirmed by electrospray mass spectroscopy. The
observed characteristic multiplets, caused by the polyisotopic nature
of Mo, N, and S, allowed an unambiguous assignment of the
detected signals: in particular, the upper parts of the spectrum of
5a1 were dominated by the molecular ion [M]+ . Full 13C NMR
assignments of compounds 5a1 and 5b were based on 1H-13C and
1H-15N HMBC experiments.
5a1. Anal. Calcd for C39H43 Mo2N3OS2: C, 56.7; H, 5.25; N,
5.0. Found: C, 55.7; H, 5.4; N, 4.5. ESI-MS (m/z): 825.6 [M]+. IR
(KBr, cm-1): ν(NH) 3412 (s), ν(CN) 1637 (s). 1H NMR (CDCl3):
δ 7.36 (s, 1H, NH), 7.17-6.72 (m, 9H, C6H3Me2), 5.22 (pt, JH-H
) 2.0 Hz, 2H, C5H4), 4.98 (s, 5H, C5H5), 4.49 (pt, JH-H ) 2.0 Hz,
2H, C5H4), 2.26, 2.21, 2.07 (s, 6H, CH3(xyl)), 1.81 (s, 6H, SCH3).
13C{1H} NMR (CDCl3): δ 369.3 (Mo2C), 248.4 (MoCO), 155.5
(CdN), 146.4, 141.8, 138.0, 135.5, 128.4, 128.3, 127.7, 127.4,
122.4, 122.2 (C6H3Me2), 98.6 (C5H4), 92.8 (Ci(C5H4)), 92.7 (C5H5),
87.4 (C5H4), 20.5, 19.1, 18.3 (CH3(xyl)), 15.3 (SCH3).
5b. Anal. Calcd for C35H43Mo2N3OS2: C, 54.05; H, 5.6; N, 5.4.
Found: C, 54.5; H, 5.3; N, 4.8. IR (KBr, cm-1), 5b1: ν(NH) 3424
1
(s), ν(CN) 1643 (m); 5b2: ν(NH) 3456 (vs), ν(CN) 1654 (s). H
NMR (CDCl3), 5b1: δ 7.11, 6.91, and 6.80 (m, 6H, C6H3Me2),
5.65 (s, br, 1H, NH), 5.45 (s, 4H, C5H4), 4.93 (s, 5H, C5H5), 2.20,
2.15 (s, 6H, C6H3Me2), 1.81 (s, 6H, SCH3), 1.33 (s, 9H, CMe3);
5b2: δ 7.11, 6.85, and 6.77 (m, 6H, C6H3Me2), 5.72 (pt, JH-H
)
2.2 Hz, C5H4), 5.65 (s, br, NH), 5.48 (pt, JH-H ) 2.2 Hz, 2H, C5H4),
4.77 (s, 5H, C5H5), 2.14 (s, 12H, C6H3Me2), 1.80 (s, 6H, SCH3),
1
1.34 (s, 9H, CMe3). H NMR (C6D6), 5b1: δ 6.97, 6.87, and 6.79
Reaction of [Mo2Cp2(µ-SMe)3(xylNC)2](BF4) (2b) with Hy-
droxide in the Presence of Excess RNC: Preparation of [Mo2Cp-
(µ-SMe)2 {µ-(η5-C5H4)(xylN)CN(xyl)C}{µ-OCNHR}] [R ) xyl
(5a1), But (5b1, 5b2)]. Method A. Complex 2b (500 mg, 0.615
mmol) was treated with an excess of NaOH (201 mg) in the
presence of 3 equiv of xylNC (242 mg) in refluxing tetrahydrofuran
(50 mL) for 72 h. Then NaOH in excess and Na(BF4) were
eliminated by filtration, and the solvent was removed under reduced
pressure. The resulting residue was washed three time with cold
diethyl ether (3 × 15 mL), affording complex 5a1 as an orange
powder (449 mg, 88% yield).
Complex 5b (5b2) was obtained by a procedure like that
described for the synthesis of 5a1, by reacting 2b (600 mg, 0.738
mmol) with an excess of NaOH (201 mg) in the presence of 3
equiv of ButNC (V ) 253 µL) in tetrahydrofuran (50 mL) and
extracting compound 5b2 from the residue with diethyl ether (3 ×
15 mL) at room temperature. Evaporation of the solvent afforded
5b2 as an orange powder (401 mg, 70% yield).
Method B. Complex 5b can also be prepared as a mixture of
two isomers, 5b1 and 5b2, by a process like that described above,
but using Me4NOH in MeOH (2.2 M) instead of NaOH.
In a typical procedure, a mixture of 2b (100 mg, 0.123 mmol)
and an excess of Me4NOH (V ) 168 µL) in the presence of 3 equiv
of ButNC (V ) 42 µL) in tetrahydrofuran (20 mL) was refluxed
for 2 h. Insoluble materials were eliminated by filtration, the solvent
was removed under pressure, and the residue was washed with cold
(-60 °C) diethyl ether (3 × 15 mL) to give orange powders of 5b
(78.5 mg, 82% yield) as a mixture of two inseparable isomers, 5b1
(m, 6H, C6H3Me2), 5.57 (pt, JH-H ) 2.2 Hz, 2H, C5H4), 5.55 (s,
1H, NH), 5.15 (pt, JH-H ) 2.2 Hz, 2H, C5H4), 5.00 (s, 5H, C5H5),
2.39, 2.20 (s, 6H, C6H3Me2), 1.98 (s, 6H, SCH3), 1.24 (s, 9H, CMe3);
5b2: δ 6.99, 6.95, and 6.84 (m, 6H, C6H3Me2), 5.50 (pt, JH-H
2.2 Hz, 2H, C5H4), 5.50 (s concealed, 1H, NH), 5.38 (pt, JH-H
)
)
2.2 Hz, 2H, C5H4), 4.82 (s, 5H, C5H5), 2.34, 2.18 (s, 6H, C6H3Me2),
1.98 (s, 6H, SCH3), 1.25 (s, 9H, CMe3). 13C{1H} NMR (CDCl3),
5b1: δ 362.7 (Mo2C), 242.9 (MoCO), 155.3 (CdN), 146.9, 142.1
(Ci (xyl)), 135.4, 128.2, 128.1, 127.8, 127.75, 127.6, 122.6
(C6H3Me2), 112.5 (Ci (C5H4)), 100.2 (C5H4), 92.5 (C5H5), 85.0
(C5H4), 53.5 (CMe3), 30.6 (CMe3), 19.2, 18.25 (CH3(xyl)), 15.3
(SCH3); 5b2: 366.4 (Mo2C), 242.7 (MoCO), 156.0 (CdN), 147.2,
142.9 (Ci (xyl)), 135.7 (C6H3Me2), 128.0-127.5 (C6H3Me2), 106.6
(Ci (C5H4)), 100.1 (C5H4), 91.6 (C5H5), 88.4 (C5H4), 53.7 (CMe3),
30.3 (CMe3), 19.0, 18.5 (CH3(xyl)), 15.4 (SCH3).
Reaction of [Mo2Cp(µ-SMe)3{µ-(η5-C5H4)(xylN)CN(xyl)C}]
(4) with Sodium Hydroxide in the Presence of RNC (R ) xyl,
But): Formation of 5a1 and 5b2. Complex 4 (100 mg, 0.138
mmol) was treated with an excess of NaOH (201 mg) in the
presence of 2 equiv of RNC [R ) xyl (32.5 mg), But (V ) 31 µL)]
in refluxing tetrahydrofuran (30 mL) for 24 h. After filtration the
solvent was removed under reduced pressure and the residue washed
three time with cold diethyl ether (3 × 15 mL), affording orange
powders of 5a1 (60.5 mg, 53% yield) or 5b2 (50 mg, 55% yield).
Reaction of 2b with Tetramethylammonium Hydroxide in
the Presence of xylNC: Preparation of [Mo2Cp(µ-SMe)2{µ-(η5-
C5H4)(xylN)CN(xyl)C}{µ-OCNMe xyl}] (6a). To a tetrahydro-
furan solution (50 mL) of [Mo2Cp2(µ-SMe)3(xylNC)2](BF4) (2b)

µ-Aminocarbyne Dimolybdenum Complexes
Organometallics, Vol. 25, No. 16, 2006 4017
Table 2. Crystallographic Data for Complexes 5a1, 5b1, 5b2, 6a, 6b, and 7
5a1
5b1
5b2
6a
C40H45Mo2 N3O1.14S2 C41H47Mo2N3OS2
842.10 853.82
6b
7
formula
Mr
C39H43Mo2N3OS2
825.76
C35H43Mo2N3OS2
777.72
C35H43Mo2N3OS2
777.72
C22H29Mo2NOS3
611.52
cryst size/mm
syst
space group
a/Å
b/Å
c/Å
0.30 × 0.23 × 0.03 0.08 × 0.06 × 0.04 0.50 × 0.40 × 0.05 0.40 × 0.10 × 0.08
0.20 × 0.20 × 0.05 0.60 × 0.20 × 0.05
monoclinic
P21/c
triclinic
P1h
orthorhombic
Pca21 (see note b)
16.2946(8)
monoclinic
P21/c
monoclinic
P21/c
monoclinic
P21/a
15.8718 (15)
14.3618 (9)
16.2998(16)
9.9768(9)
13.2860(16)
13.9137(18)
77.796(11)
86.048(9)
68.941(10)
1682.2(3)
2
8.3600 (1)
16.9560(2)
26.1569(4)
12.9957 (10)
18.5383(14)
16.2894(15)
15.6163 (3)
8.9018(2)
16.8896(4)
13.4907(6)
16.0487(7)
R/deg
â/deg
95.892(9)
94.300(1)
95.627(7)
93.291(1)
γ/deg
V/Å
3695.9(6)
4
3527.9(3)
4
3697.36(8)
4
3905.5(6)
4
2344.01(9)
4
Z
Dc/Mg m-3
T/K
1.484
1.535
1.464
1.513
1.452
1.351
170
170
300
120
170
120
µ/mm-1
range of θ/deg
0.826
0.902
0.860
0.827
0.784
1.351
3.1-20.6
9730
3.3-26.4
8920
3.3-31.2
35546
3.0-25.0
39623
3.3-20.8
19626
2.6-28.5
34466
a
Nmeasd
Nuniquea/Nparams
2545/396
0.080
5516/397
0.052
8842/397
0.048
6477/451
0.148
4068/442
0.107
5842/271
0.116
Rint
a
R1 (I > 2σ(I)], Nobs
R1 (all data)
wR2 (all data)
0.0807, 2176
0.0897
0.226
0.0482, 3592
0.0894
0.101
0.0427, 6223
0.0626
0.099
0.0469, 4520
0.0799
0.118
0.0650, 2923
0.106
0.122
0.0501, 3945
0.0879
0.135
goodness of fit on F2 1.089
0.956
0.952
1.028
1.107
1.081
∆Fmax., ∆Fmin./e Å-3 1.82, -0.91
1.21, -0.67
1.44, -0.53
0.70, -0.61
0.49, -0.40
1.39, -1.07
a Nmeasd ) total number of intensity measurements; Nunique ) number of intensity measurements after averaging according to point symmetry; Nobs
number of these with intensities I > 2σ(I). b Flack parameter ) -0.09(4).
)
(218 mg, 0.268 mmol) were added 3 equiv of Me4NOH-MeOH
(2.2 M) (V ) 383 µL) and 2 equiv of xylNC (70 mg), and the
mixture was heated under reflux for ca. 72 h. The solution was
then filtered to remove Me4N(BF4). After evaporation of the solvent
(THF), 6a was extracted from the residue with diethyl ether (3 ×
15 mL). Evaporation of volatiles afforded 6a as an analytically pure,
orange solid (146 mg, 64% yield). Orange crystals of 6a, suitable
for X-ray analysis, were obtained by crystallization at -20 °C
from a diethyl ether solution. Anal. Calcd for C40H45Mo2N3OS2:
C, 57.2; H, 5.4; N, 5.0. Found: C, 57.8; H, 5.5; N, 5.0. IR (KBr,
(s, 6H, CH3(xyl)), 2.06 (s, 6H, CH3(xyl)), 1.74 (s, 6H, SCH3), 1.02
(t, 3H, -CH2CH3).
1
6c. H NMR (CDCl3): δ 7.16-6.67 (m, 9H, C6H3), 5.14 (m,
2H, C5H4), 4.98 (s, 5H, C5H5), 4.32 (m, 2H, C5H4), 3.56 (t,
2H, -CH2-(CH2)2-CH3), 2.24 (s, 6H, CH3(xyl)), 2.20 (s, 6H,
CH3(xyl)), 2.06 (s, 6H, CH3(xyl)), 1.73 (s, 6H, SCH3), 1.41 and
1.28 (m, 2H, -CH2-(CH2)2-CH3), 0.83 (t, 3H, -(CH2)3-CH3).
Reaction of [Mo2Cp2(µ-SMe)3(MeCN)(xylNC)](BF4) (3) with
Sodium Hydroxide: Preparation of [Mo2Cp2(µ-SMe)3{µ-(η1-
(O),η1(C)-OCNHxyl}] (7). Solid NaOH in excess (201 mg, 26
equiv) was added to a tetrahydrofuran solution (30 mL) of
compound 3 (140 mg, 0.193 mmol). The mixture was heated under
reflux for 24 h, and the solution was then filtered to remove excess
NaOH. Removal of the solvent from the filtrate under vacuum
yielded a red residue, from which 7 was extracted with diethyl ether
(3 × 15 mL). Solvent was then evaporated to dryness and the
resulting residue washed with cold pentane (3 × 15 mL) to give
compound 7 (110 mg, 93% yield) as a red powder. Red crystals of
the complex, suitable for X-ray analysis, were obtained by
crystallization at -20 °C from a diethyl ether solution. Anal. Calcd
for C22H29Mo2NOS3: C, 43.2; H, 4.8; N, 2.3. Found: C, 43.1; H,
1
cm-1): ν(CN) 1639 (s). H NMR (CDCl3): δ 7.18-6.64 (m, 9H,
C6H3Me2), 5.15 (m, 2H, C5H4), 4.99 (s, 5H, C5H5), 4.36 (m, 2H,
C5H4), 3.09 (s, 3H, N-CH3), 2.20 (s, 12H, CH3(xyl)), 2.06 (s,
6H, CH3 (xyl)), 1.72 (s, 6H, SCH3). 13C{1H} NMR (CDCl3): δ
336.8 (Mo2C), 242.4 (MoCO), 155.4 (CdN), 146.8, 144.9,
142.0, 137.8, 135.6, 128.8, 128.6, 128.4, 128.3, 128.2, 127.7, 127.6,
127.5, 122.6, 114.4 (C6H3Me2), 98.3 (C5H4), 92.9 (C5H4), 92.7 (Ci
(C5H4)), 87.0 (C5H4), 30.9 (NCH3), 19.7, 18.9, 18.2 (CH3(xyl)),
15.8 (SCH3).
Reaction of [Mo2Cp(µ-SMe)2{µ-(η5-C5H4)(xylN)CN(xyl)C}-
{µ-OCNHxyl}] (5a1) with an Alkylating Reagent in the Presence
of Sodium Hydroxide: Synthesis of [Mo2Cp(µ-SMe)2{µ-(η5-
C5H4)(xylN)CN(xyl)C}{µ-OCNRxyl}] [R ) Et (6b), Bun (6c)].
To a tetrahydrofuran solution (50 mL) of 5a1 (200 mg, 0.242
mmol) were added 2 equiv of R4NBr [R ) Et (102 mg), Bun
(156 mg)] and an excess of NaOH (201 mg), and the mixture was
heated under reflux for 72 h. The solution was then filtered to
remove NaOH in excess. After evaporation of the volatiles the
product was extracted from the oily residue with diethyl ether (3
× 15 mL) at room temperature. Evaporation of the solvent afforded
6b or 6c as an orange powder (6b: 184 mg, 89% yield; 6c: 100
mg, 47% yield). Crystallization at -20 °C from a diethyl ether
solution afforded crystals of 6b suitable for X-ray analysis. Despite
several attempts no reliable analyses are available for 6c; however
the complex has been satisfactorily characterized by its NMR
spectroscopy.
1
4.8; N, 2.3. IR (KBr, cm-1): ν(NH) 3437 (m). H NMR (CDCl3):
δ 6.90 (s, 3H, C6H3Me2), 6.70 (s, 1H, NH), 5.42 (s, 5H, C5H5),
5.15 (s, 5H, C5H5), 2.06 (s, 6H, CH3(xyl)), 1.67 (s, 3H, SCH3),
1.55 (s, 3H, SCH3), 1.47 (s, 3H, SCH3). 13C{1H} NMR (CDCl3):
δ 240.8 (MoCO), 135.7 (Ci(xyl)), 134.4 (Co(xyl)), 127.9 (Cm(xyl)),
125.5 (Cp(xyl)), 92.3 (C5H5), 90.5 (C5H5), 20.7 (SCH3), 19.6
(CH3(xyl)), 9.9 (SCH3).
X-ray Structural Determinations. Measurements for com-
pounds 5a1, 5b1, 5b2, and 6b were made in Brest on a Oxford
Diffraction X-Calibur-2 CCD diffractometer equipped with a jet
cooler device. Measurements for 6a and 7 were made in Glasgow
on a Nonius Kappa CDD diffractometer. Graphite-monochromated
Mo KR radiation (λ ) 0.71073 Å) was used in all experiments.
The structures were solved and refined by standard procedures.23
H atoms were positioned using stereochemical considerations, the
orientations of methyl groups being initially obtained from differ-
ence maps; they then rode on their parent C or N atoms. In 7 the
N5-bonded H atom was freely refined. For 5a1 and 6b all crystal
specimens were of poor quality and gave only weak, low-angle
6b. Anal. Calcd for C41H47Mo2N3OS2: C, 57.6; H, 5.5; N, 4.9.
1
Found: C, 56.7; H, 5.4; N, 5.1. H NMR (CDCl3): δ 7.30-6.64
(m, 9H, C6H3Me2), 5.14 (t, 2H, C5H4), 4.99 (s, 5H, C5H5), 4.34 (t,
2H, C5H4), 3.70 (q, 2H, -CH2CH3), 2.25 (s, 6H, CH3(xyl)), 2.21

4018 Organometallics, Vol. 25, No. 16, 2006
Ojo et al.
diffraction patterns; the results of these analyses, in particular that
of 5a1, are in consequence appreciably less precise than the others.
In 6a an isolated site is attributed to the O atom [occupancy )
0.143(7)] of a water molecule and the CH3 group attached to S2 is
distributed over alternative sites, suggesting 0.82:0.18(1) syn:anti
disorder. Selected bond lengths and angles are given in Table 1
and the caption to Figure 5; pertinent crystal data, in Table 2.
Acknowledgment. We are grateful to Dr. F. Michaud for
the crystallographic measurements of 5a1, 5b1, 5b2, and 6b,
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, the EPSCR, and the
Universities of Glasgow and Brest for financial support. The
Ministe`re de l’Enseignement Supe´rieur et de la Recherche du
Gabon is acknowledged for providing studentships (W.-S.O.).
(23) Programs used: (a) Sheldrick, G. M. SHELX 97; University of
Go¨ttingen: Go¨ttingen, Germany, 1998. (b) Farrugia, L. J. WinGX-A
Windows Program for Crystal Analysis. J. Appl. Crystallogr. 1999, 32,
837. (c) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A. SIR
92-A program for crystal structure solution. J. Appl. Crystallogr. 1993,
26, 343. (d) CrysAlis CCD and RED, Version 1.171.28 cycle 4 beta; Oxford
Diffraction Ltd, 2005.
Supporting Information Available: X-ray crystallographic data
in CIF format. This material is available free of charge via the
Internet at http://pubs.acs.org.
OM060383V