Incorporation of alkyne and vinylidene ligands into tetrazolate groups at a sulfur-rich dimolybdenum site using sodium azide

Article abstract of DOI:10.1016/S0020-1693(02)01556-6

Treatment of either the μ-alkyne complex [Mo₂Cp ₂(μ-SMe)₃(μ-PhCCH)](BF₄) (1) or the μ-vinylidene derivatives [Mo₂Cp₂(μ-SMe) ₃(μ-η¹:η²-(CCHR)](BF₄) (2) (R=Ph, Tol, nPr, C(CH₃)=CH₂) with NaN₃ in ethanol at room temperature readily afforded μ-tetrazolate carbene complexes [Mo₂Cp₂(μ-SMe)₃){μ-η ¹(C):η¹(N)-N₄CCR)}] (R=Ph (4a), Tol (4b), nPr (4c), C(CH₃)=CH₂ (4d)). A mechanism which accounts for the formation of 4 by intramolecular 1,3-dipolar cycloaddition of metal-coordinated azide ligands to metal-coordinated nitriles is discussed. The structure of complex 4a has been determined by single X-ray diffraction analysis.

Full text of DOI:10.1016/S0020-1693(02)01556-6

Inorganica Chimica Acta 350 (2003) 495ꢂ502
/
www.elsevier.com/locate/ica
Incorporation of alkyne and vinylidene ligands into tetrazolate
groups at a sulfur-rich dimolybdenum site using sodium azide
Philippe Schollhammer a, Nolwenn Cabon a, Anne-Ce´cile Kervella a,
Francois Y. Pe´tillon a,*, Rene´ Rumin a, Jean Talarmin a, Kenneth W. Muir b,*
¸
a UMR CNRS 6521, Chimie, Electrochimie Mole´culaires et Chimie Analytique, Faculte´ des Sciences, Universite´ de Bretagne Occidentale, BP 809,
29285 Brest Cedex, France
b Department of Chemistry, University of Glasgow, Glasgow G12 8QQ, UK
Received 22 July 2002; accepted 16 September 2002
Dedicated to Dr Pierre Braunstein in recognition of his many and outstanding contributions to organometallic chemistry.
Abstract
Treatment of either the m-alkyne complex [Mo2Cp2(m-SMe)3(m-PhCCH)](BF4) (1) or the m-vinylidene derivatives [Mo2Cp2(m-
SMe)3(m-h1:h2-(CCHR)](BF4) (2) (Rꢀ
/
Ph, Tol, nPr, C(CH3)ꢀ
/
CH2) with NaN3 in ethanol at room temperature readily afforded m-
tetrazolate carbene complexes [Mo2Cp2(m-SMe)3){m-h1(C):h1(N)-N4CCR)}] (Rꢀ
/
Ph (4a), Tol (4b), nPr (4c), C(CH3)ꢀCH2 (4d)). A
/
mechanism which accounts for the formation of 4 by intramolecular 1,3-dipolar cycloaddition of metal-coordinated azide ligands to
metal-coordinated nitriles is discussed. The structure of complex 4a has been determined by single X-ray diffraction analysis.
# 2003 Elsevier Science B.V. All rights reserved.
Keywords: Azides; m-Tetrazolate complexes; Carbenes; 1,3 Cycloaddition; Dimolybdenum complexes; Thiolate compounds
1. Introduction
arylidenemalononitriles, allylic acetates and trimethylsi-
lyl azide has just been reported [7].
Tetrazole derivatives frequently exhibit significant
biological activity and, in consequence, have found a
wide variety of applications as active heterocycles in
pharmacy, medicine and agriculture [1]. Two main types
of reaction have been used in their synthesis. One
The known metal complexes of unsubstituted and
substituted tetrazoles have been obtained by various
routes. A well known path to these derivatives lies in
complexing the metal to neutral [8] or anionic [9]
tetrazoles. However, 1,3-dipolar cycloaddition reactions
of organonitriles [5c,10] or isocyanides [5a,5b,5d,11] to
the azide ligand of a metal complex have proved even
more popular and have received considerable attention.
Tetrazolato-complexes are also conveniently obtained
by the facile attack of azide ion on coordinated nitriles
through a 1,3-dipolar cycloaddition reaction [12]. Re-
cently, a novel route to tetrazolato-complexes, involving
reactions of ruthenium cyclopropenyl compounds with
trimethylsilyl azide, has been described [13]; it proceeds
by successive formation of vinylidene and N-coordi-
involves [2ꢁ3] cycloaddition between organonitriles
/
and azides, such as the salt NaN3 or silyl, aliphatic, or
aromatic azides RN3 [2]. The other proceeds by alkyla-
tion of tetrazole anions and has the drawback that
mixtures of N(1)- and N(2)-alkylation isomers are often
obtained [3]. More recently it has been demonstrated
that the involvement of metal ions allows azides to add
to nitriles under milder conditions [4ꢂ6]. For example,
/
the regio-specific synthesis of 5-substituted 2-allyl-tetra-
zoles via palladium-catalyzed reactions of alkyl- and
nated nitrile intermediates; a [2ꢁ
/
3] cycloaddition of the
Cꢁ/N bond to another azide anion followed by metal
migration is proposed as the final step [13].
Alkynes and their thermodynamically less stable
vinylidene isomers are among the strongest p-acceptor
* Corresponding authors.
E-mail addresses: francois.petillon@univ-brest.fr (F.Y. Pe´tillon),
ken@chem.gl.ac.uk (K.W. Muir).
0020-1693/03/$ - see front matter # 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0020-1693(02)01556-6

496
P. Schollhammer et al. / Inorganica Chimica Acta 350 (2003) 495ꢂ502
/
ligands in organometallic chemistry. They are therefore
good candidates for reaction with nucleophilic azido-
species. Accordingly, we decided to treat these unsatu-
rated ligands with sodium azide, hoping both to obtain
new tetrazolato-complexes under mild conditions and to
gain further insight into the modes of coordination of
dimolybdenum complexes. Column chromatography
was carried out with silica gel purchased from SDS.
Chemical analyses were performed either by the Service
de Microanalyse I.C.S.N., Gif sur Yvette, France or by
the Oce´anographie Chimique Laboratory at the Uni-
versity of Brest. The mass spectra were measured with a
GC/MS Ribermag R10-10 spectrometer at the Labora-
toire de Biochimie, Faculte´ de Me´decine (Brest, France).
IR spectra were recorded on a Nicolet-Nexus FT IR
spectrometer from KBr pellets. The NMR spectra (1H,
13C), in CDCl3 or CD2Cl2 solutions, were recorded at
room temperature with a Bruker AC 300 or AMX3 400
tetrazoles. Since the cyclic tetrazolato(ꢃ1) anion is
/
isoelectronic with the cyclopentadienyl anion it may
reasonably be expected to display several different
bonding modes in coordination compounds. First, it
could act as an h5 p-bonding ligand; however, only two
examples of this mode of coordination have been
established, one from IR evidence [9d] and the other
by a crystallographic study [9e]. Secondly, the carbon
atom of the ring can form a s-bond to the metal when
the tetrazole ligand is the result of cycloaddition of
isocyanide to metal-coordinated azide 5a,5b,5c,12. In all
other cases, whether they involve cycloaddition of
organic nitrile to coordinated azide or of azide to
coordinated nitrile, N-coordinated tetrazolato-com-
pounds are obtained as a mixture of isomers in which
different tetrazolate ring nitrogen atoms are attached to
the metal [10,12].
spectrometer and were referenced to SiMe4. 1Hꢂ
/
1H 2D-
COSY and 1Hꢂ13C 2D-HMBC and HMQC spectra
/
were recorded on a Bruker 500 and AMX3 400 spectro-
meters.
2.2. Syntheses of [Mo2Cp2(m-SMe)3{m-h1(C):h1(N)-
(N4CCR)](Rꢀ
CH2 (4d))
/
Ph (4a), Tol (4b), nPr (4c), C(CH3)ꢀ
/
2.2.1. Method A
In a typical procedure a solution of complex 2 (200
mg, :0.31 mmol) in ethanol (20 ml) was stirred in the
presence of 2 equiv. of NaN3 (:41 mg, :0.62 mmol)
for 30 min at room temperature. The colour of the
solution readily turned from green to yellowꢂbrown.
A survey of transition metal tetrazolato-complexes
formed from cycloaddition reactions reveals that they
involve only Au(III), Pd(0), Pd(II), Pt(0), Pt(II), Co(III),
Rh(III), Ir(0) and Ru(II). To the best of our knowledge,
none of the earlier transition metals has till now been
shown to take part in such a cycloaddition reaction.
Accordingly, we chose a group 6 synthon, the sulfur-rich
dimolybdenum {Cp2Mo2(m-SMe)3} system, for the pre-
paration of new tetrazolato-compounds. We now report
on the reactions of both the m-alkyne dimolybdenum
complex [Mo2Cp2(m-SMe)3(m-PhCCH)] (BF4) (1) and of
/
/
/
/
The solvent was then removed under vacuum and the
organometallic products were extracted with hot
(80 8C) toluene (2ꢄ50 ml). After evaporation of the
/
toluene, the residue was dissolved in CH2Cl2 (5 ml) and
chromatographed on silica gel. Elution with CH2Cl2
(CH2Cl2:THF(99:1) when Rꢀ
band, which gave 3 as brown solids (17% (Rꢀ
(RꢀTol), 16% (RꢀnPr), 28% (RꢀC(CH3)ꢀ
/
Tol) afforded a greenish
Ph), 31%
CH2)).
/
the m-vinylidene species [Mo2Cp2(m-SMe)3 (m-h1:h2-Cꢀ
/
/
/
/
/
CHR)] (BF4) (2) [14] with sodium azide. We shall show
that the reaction of 1 involves the vinylidene species 2 as
intermediate and that, in consequence, the {Mo2Cp2(m-
SMe)3}ꢁ system allows an unprecedented multistep
activation in which the starting alkyne is ultimately
incorporated into a substituted tetrazole.
Further elution with CH2Cl2/ethanol (9.5:0.5) removed
a brown band. After evaporation of the volatiles, the
residues were washed with pentane (5 ml) to afford
complexes 4 as analytically pure yellowꢂ
These complexes 4 were obtained as mixtures of two
isomers (41 and 42), except for 4d (Rꢀ CH2)
/brown solids.
/
C(CH3)ꢀ
/
which was a mixture of four isomers (4d1a, 4d1b, 4d2a and
4d2b).
Compound 4a (74% yield): IR bands attributed to the
2. Experimental
tetrazolate ring at 1700ꢂ
1644m, 1480m, 1399m, 1298m, 1146m, 1069m, 1020w,
997w, 933m, 851m, 703m, 650w cmꢃ1 1H NMR
(CD2Cl2, ppm), d (4a1): 7.36 (m, JHH 8.0 Hz, 2H,
Ph), 7.19 (p-t, JHH 7.6 Hz, 1H, Ph), 6.74 (d, JHH 7.4
Hz, 1H, Ph), 6.63 (d, JHH 8.0 Hz, 1H, Ph), 5.74 (s, 5H,
Cp), 5.62 (s, 5H, Cp), 1.95 (s, 3H, SMe), 1.60 (s, 3H,
SMe), 1.27 (s, 3H, SMe); d (4a2): 7.36 (m, JHH 8.0 Hz,
2H, Ph), 7.19 (p-t, JHH 7.6 Hz, 1H, Ph), 6.67 (d, JHH
7.4 Hz, 1H, Ph), 6.61 (d, JHH 8.0 Hz, 1H, Ph), 5.77 (s,
/
400 cmꢃ1 region (KBr pellets):
2.1. Materials and methods
.
All reactions were performed under an atmosphere of
argon or dinitrogen using conventional Schlenk tech-
niques. Solvents were deoxygenated and dried by
standard methods. The starting materials [Mo2Cp2(m-
SMe)3(m-PhCCH)] (BF4) (1) and [Mo2Cp2(m-SMe)3(m-
ꢀ
/
ꢀ
/
ꢀ
/
ꢀ
/
ꢀ
/
h1:h2-Cꢀ
C(CH3)ꢀ
viously [14]. All other reagents were purchased commer-
/
CHR)] (BF4) (Rꢀ
/Ph (2a), Tol (2b), nPr (2c),
ꢀ
/
ꢀ
/
/CH2 (2d)) were prepared as described pre-
ꢀ
/
5H, Cp), 5.70 (s, 5H, Cp), 1.54 (s, 3H, SMe), 1.34 (s, 5H,
Cp), 1.30 (s, 5H, Cp). 13C{1H} NMR(CD2Cl2, ppm), d
cially. Yields of all products are relative to the starting

P. Schollhammer et al. / Inorganica Chimica Acta 350 (2003) 495ꢂ
/502
497
(4a1): 294.7 (MoC), 174.0 (CN4), 159.2 (Cipso, Ph),
127.1, 122.35, 122.15 (Ph), 100.15 (C5H5), 95.0 (C5H5),
18.5 (SCH3), 15.4 (SCH3), 13.2 (SCH3); d (4a2): 293.75
(MoC), 173.2 (CN4), 159.65 (Cipso, Ph), 127.35, 123.1,
122.3 (Ph), 100.2 (C5H5), 95.7 (C5H5), 16.2 (SCH3),
15.65 (SCH3), 14.2 (SCH3). Mass spectrum: m/z 621
(Mꢁ). Anal. Calc. for Mo2C21H24N4S3: C, 40.6; H, 3.90;
N, 9.0. Found C, 40.3; H, 3.77; N, 8.9%.
1135w, 1044m, 1017m, 931m, 861s, 723mw, 553w, 464w
cmꢃ1. 1H NMR (CDCl3, ppm), d (4d1a, 4d1b): 5.89, 5.88
(2s, 2ꢄ
CMe), 4.11 (s, 2H, CH2ꢀ
2CH2ꢀC(CH3)), 1.56, 1.54 (2s, 2ꢄ
1.17 (2s, 2ꢄ3H, 2SMe), 1.11, 1.06 (2s, 2ꢄ
2SMe);d(4d2a, 4d2b): 5.93, 5.92 (2s, 2ꢄ5H, 2Cp), 5.67
(s, 10H, 2Cp), 4.87, 4.86 (2s, 2H, 2CH2ꢀCMe), 4.16,
4.12 (2s, 2H, 2CH2ꢀCMe), 2.02, 1.99 (2s, 2ꢄ3H,
2CH2ꢀC(CH3)), 1.52, 1.50 (2s, 2ꢄ3H, 2SMe), 1.22,
1.20 (2s, 2ꢄ3H, 2SMe), 1.15, 1.13 (2s, 2ꢄ3H, 2SMe).
13C{1H} NMR (CDCl3, ppm), d(4d1a, 4d1b): 170.95 (s,
CN2), 160.25 (s,C(Me)ꢀCH2), 104.15 (s, CH2ꢀC(Me)),
/
/
5H, 2Cp), 5.59 (s, 10H, 2Cp), 4.85 (s, 2H, CH2ꢀ
CMe), 1.87, 1,86 (2s, 2ꢄ3H,
3H, 2SMe), 1.18,
3H,
/
/
/
/
/
/
/
/
/
Compound 4b (69% yield): IR bands attributed to the
400 cmꢃ1 region (KBr pellets):
/
/
tetrazolate ring at 1700ꢂ
/
/
/
1627br, 1450sh, 1392m, 1329w, 1293mw, 1260mw,
1143m, 1063m, 1043m, 997sh, 940mw, 849sh, 694w,
/
/
1
520mw, 473w cmꢃ1. H NMR (CDCl3, ppm), d (4b1):
/
/
7.14 (d, JHH
Tol), 6.66 (d, JHH
Hz, 1H, Tol), 5.74 (s, 5H, Cp), 5.63 (s, 5H, Cp), 2.36 (s,
br., 3H, CH3ꢂTol), 1.92 (s, 3H, SMe), 1.57 (s, 3H, SMe),
1.27 (s, 3H, SMe); d (4b2): 7.14 (d, JHH 9.6 Hz, 1H,
Tol), 7.11 (d, JHH 9.6 Hz, 1H, Tol), 6.55 (d, JHH 7.2
Hz, 1H, Tol), 6.50 (d, JHH 7.2 Hz, 1H, Tol), 5.76 (s,
5H, Cp), 5.70 (s, 5H, Cp), 2.36 (s, br, 3H, CH3ꢂTol),
ꢀ
/
9.0 Hz, 1H, Tol), 7.11 (d, JHH
ꢀ
/
9.0 Hz, 1H,
99.7 (s, C5H5), 94.65, 94.6 (2s, C5H5), 25.5 (s,CH2ꢀ
C(CH3)), 16.05 (s, SCH3), 14.05 (s, SCH3); d (4d2a,
4d2b): 298.45, 298.3 (2s, MoC), 170.35, 170.3 (2s, CN2),
ꢀ
/
7.1 Hz, 1H, Tol), 6.51 (d, JHH
ꢀ
/
7.1
/
160.7, 160.65 (2s,CH2ꢀ
CMe)), 100.1, 100.95 (2s, C5H5), 95.45, 95.4 (2s, C5H5),
25.35 (s, CH2ꢀC(CH3)), 16.65, 16.2 (2s, SCH3), 15.5,
/
C(Me)), 104.8, 104.75 (2s,CH2ꢀ
/
ꢀ
/
ꢀ
/
ꢀ
/
/
ꢀ
/
15.1 (2s, SCH3), 14.9, 13.9 (2s, SCH3). Anal. Calc. for
C18H24Mo2N4S3: C, 37.0; H, 4.14; N, 9.6. Found: C,
37.2; H, 4.28; N, 8.7%.
/
1.52 (s, 3H, SMe), 1.35 (s, 3H, SMe), 1.32 (s, 3H, SMe).
13C{1H} NMR(CDCl3, ppm), d (4b1): 296.1 (MoC),
173.1 (CN4), 156.0 (Cipso, Tol), 134.4, 129.4, 127.5,
122.4, 121.4 (C Tol), 99.6 (C5H5), 94.6 (C5H5), 21.2
2.2.2. Method B
To a solution of the m-alkyne complex [Mo2Cp2(m-
SMe)3(m-PhCCH)](BF4) (1) in ethanol (20 ml) was
added 2 equiv. of NaN3 (40 mg, 0.62 mmol). The
solution was stirred for 30 min at room temperature and
the subsequent procedure was similar to Method A. Two
products 3a and 4a were characterised by 1H NMR.
(CH3ꢂTol), 18.5 (SCH3), 15.2 (SCH3), 12.6 (SCH3);
/
d(4b2): 295.4 (MoC), 171.5 (CN4), 156.4 (Cipso, Tol),
134.6, 127.9, 121.6, 121.5 (C Tol), 99.9 (C5H5), 95.5
(C5H5), 21.1(CH3ꢂTol), 16.3 (SCH3), 25.8 (SCH3), 13.2
/
(SCH3). Anal. Calc. for C22H26Mo2N4S3: C, 41.7; H,
4.13; N, 8.8. Found: C, 42.1; H, 4.35; N, 8.1%.
Compound 4c (80% yield):IR bands attributed to the
Yields: 3a (Rꢀ
/
Ph), 6%; 4a (RꢀPh), 61%.
/
tetrazolate ring at 1700ꢂ
1629m, 1466mw, 1387s, 1293m, 1260m, 1149m, 1057s,
1031m, 938m, 849m, 695w, 520mw cmꢃ1 1H
NMR(CDCl3, ppm), d (4c1): 5.89 (s, 5H, Cp), 5.56 (s,
5H, Cp), 3.56 (m, 2H, ꢂCH2ꢂCH2CH3), 1.86 (s, 3H,
SMe), 1.54 (s, 3H, SMe), 1.25 (t, JHH
7.0 Hz, 2H, ꢂ
CH2ꢂCH2ꢂCH3), 1.09 (t, JHH 7.0 Hz, 3H, ꢂCH2ꢂ
CH2ꢂCH3), 1.00 (s, 3H, SMe); d (4c2): 5.93 (s, 5H,
Cp), 5.65 (s, 5H, Cp), 3.63 (m, 2H, ꢂCH2ꢂCH2ꢂCH3),
1.50 (m, 2H, ꢂCH2ꢂCH2ꢂCH3), 1.48 (s, 3H, SMe), 1.12
(t, JHH
/
400 cmꢃ1 region (KBr pellets):
2.3. X-ray structure analysis of [Mo2Cp2(m-SMe)3{m-
h1(C): h1(N)-(N4CCPh)}] (4a)
.
2.3.1. Crystal data
/
/
C21H24Mo2N4S3×
/
CH2Cl2, formula weight 705.43,
7.5964(3),
ꢀ
/
/
orthorhombic, space group P212121, aꢀ
/
3
˚
˚
/
/
ꢀ
/
/
/
bꢀ
Zꢀ
1408.
Single crystals suitable for X-ray analysis were
obtained from a CH2Cl2ꢂpentane (1:4) solution. All
crystallographic measurements were made on a Nonius
/
15.7764(8), cꢀ
/
23.1438(9) A, Vꢀ
/
2773.6(2) A ,
/
/
4, rꢀ
/
1.689 g cmꢃ3, mꢀ
/
1.341 mmꢃ1, F(0 0 0)ꢀ
/
/
/
/
/
/
/
ꢀ
/
7.2 Hz, 3H, ꢂ
/
CH2ꢂ
/
CH2ꢂ
/
CH3), 1.09 (s, 3H,
/
SMe), 1.08 (s, 3H, SMe). 13C{1H} NMR (CDCl3, ppm),
d (4c1): 307.3 (MoC), 173.3 (CN2), 98.45 (C5H5), 94.5
KappaCCD diffractometer with Mo Ka radiation, lꢀ
/
˚
0.70173 A, at 100 K. Transmission factors based on
Gaussian quadrature for the plate-shaped crystal of
(C5H5), 55.15 (ꢂ
CH3), 18.65 (SCH3), 15.5 (SCH3), 15.05 (ꢂ
CH3), 14.05 (SCH3); d (4c2): 305.7 (MoC), 172.8
(CN2), 98.75 (C5H5), 95.2 (C5H5), 55.5 (ꢂCH2ꢂCH2ꢂ
CH3), 25.8 (ꢂCH2ꢂCH2ꢂCH3), 16.4 (SCH3), 16.05
(SCH3), 14.7 (ꢂCH2ꢂCH2ꢂCH3), 14.4 (SCH3). Anal.
/
CH2ꢂ
/
CH2ꢂ
/
CH3), 26.15 (ꢂ
/
CH2ꢂ
/
CH2ꢂ
/
/
CH2ꢂ
/
CH2ꢂ
/
dimensions 0.28ꢄ
0.948ꢂ0.705. 15 218 Measurements yielded 8204 unique
intensities (Rint 0.084), comprising 95.2% of the in-
328. These were
/
0.11ꢄ
/
0.04 mm3 were in the range
/
/
/
/
/
/
/
ꢀ
/
/
/
/
dependent reflections with u(Mo Ka)0
/
Calc. for C18H26Mo2N4S3. 0.25 CH2Cl2: C, 36.1; H,
4.39; N, 9.2. Found: C, 36.0; H, 4.44; N, 8.2%.
Compound 4d (72% yield): IR bands attributed to the
used in the least-squares refinements on F2 with weights
chosen to give a goodness-of-fit near unity. Apart from
four molecules of 4a the unit cell also contains four
disordered CH2Cl2 molecules whose scattering was
accounted for non-parametrically [15]. For 8204 reflec-
tetrazolate ring at 1700ꢂ
/
400 cmꢃ1 region (KBr pellets):
1617m, 1450w, 1396m, 1344 mw, 1294m, 1258 mw,

498
P. Schollhammer et al. / Inorganica Chimica Acta 350 (2003) 495ꢂ502
/
tions, including 3043 Friedel pairs, R(F)ꢀ
/
0.074,
(2)) together with m-acetylide compounds [Mo2Cp2(m-
SMe)3(m-h1:h2-Cꢁ
CꢂR)] (3) (16ꢂ31% yields). From the
reaction mixture Na(BF4) and NaH were separated off
using toluene, in which there are insoluble, and Na(BF4)
was identified by IR spectroscopy.
ꢃ3
wR(F2)ꢀ
/
0.125, ½Dr½B
/
after adjustment of
˚
1.5 e A
/
/
/
274 parameters. The Flack parameter xꢀ0.02(6) con-
/
firms the correctness of the absolute structure [16].
The m-acetylide complexes 3 formed as by-products of
these reactions were characterised by comparing their
spectra with those of authentic samples [14]. Ready
deprotonation of 1 and 2 by azide is consistent with their
known reactions with other bases [14].
Complexes 4 are thermally stable in the solid state and
in solution and were characterised analytically and from
mass, infrared, and multinuclear (1H and 13C) NMR
spectroscopic data given in Section 2. It is immediately
3. Results and discussion
3.1. Syntheses and spectroscopic characterization of
(tetrazolato) complexes (4). Molecular structure of
[Mo2Cp2(m-SMe)3{m-h1(C): h1(N)-(N4CCPh)}] (4a)
Treatment of the m-alkyne complex [Mo2Cp2(m-
SMe)3(m-PhCCH)] (BF4) (1) with 2 equiv. of NaN3 in
ethanol at room temperature gave good yields of the
apparent from their spectra that complexes 4aꢂ
the same basic structure. As expected, the IR spectra of
4aꢂ4d are almost identical, showing characteristic bands
/4d have
tetrazolato-compound
h1(N)-(N4CCPh)}] (4a) within 30 min (Eq. (1)) together
with the m-acetylide complex [Mo2Cp2(m-SMe)3(m-
[Mo2Cp2(m-SMe)3{m-h1(C):
/
for the h5-Cp groups at approximately 1420, 1010 and
820 cmꢃ1. For compound 4a, the bands near 1590,
1110, 801 and 650 cmꢃ1 were assigned to stretching and
bending modes of the phenyl group. For each com-
pound 4 bands arising from ring breathing, ring
deformation and out-of-plane ring bending vibrations
of a typical tetrazolate group [17] appear at about 1630,
1460, 1360, 1335, 1295, 1260, 1150, 1060, 1040, 980, 930,
h1:h2-Cꢁ
/
CPh)] (3a). These complexes were extracted
with toluene from the residue left after evaporation of
the ethanolic solution and thus were easily separated
from the insoluble matter, namely NaH and Na(BF4).
4a was separated from 3a by column chromatography
and isolated as a spectroscopically and analytically pure
brownish powder in approximately 60% yield.
(1)
Under identical conditions treatment of [Mo2Cp2(m-
850, 690 and 450 cmꢃ1. Discussion of the NMR data is
deferred until the molecular structure of 4a obtained by
X-ray diffraction (Table 1) has been described.
SMe)3(m-h1:h2-Cꢀ
to the addition of four nitrogen atoms, readily affording
/
CHR)](BF4) (2) with NaN3 also led
Molecules of 4a (Fig. 1) contain a bidentate tetra-
zolate ligand: it coordinates to Mo1 through C4, which
is also attached to the carbon of the tetrazole ring, and
the brown tetrazolate complexes [Mo2Cp2(m-SMe)3{m-
h1(C):h1(N)-N4CCR)}] (4) (Rꢀ
/
Ph (4a), Tol (4b), nPr
(4c), C(CH3)ꢀ
/
CH2 (4d)) in good yields (69ꢂ80%) (Eq.
/
(2)

P. Schollhammer et al. / Inorganica Chimica Acta 350 (2003) 495ꢂ
/502
499
to Mo2 through N9. This is an unprecedented bonding
mode for the tetrazolate ligand. Known examples of
bridging tetrazolate ligands either use the nitrogen
atoms at the 1-, 2- and 3-positions to bridge and chelate
the metal atoms [8e,18] or are of the h2 type, with the
two nitrogens opposite the carbon [9d,10a] or the two
nitrogens at the 1-, 2-positions [8c] taking part in
bonding. The N4C tetrazole ring is planar to within
experimental error; Mo1, Mo2, C4 and C31 lie close to
the plane of the ring, with Mo1 showing the largest
˚
N
displacement (0.125(1) A). The ring Cꢂ
/
N and Nꢂ
/
bond lengths indicate strong p-electron delocalization.
C4 bond is regarded as carbene-like in
nature, a count of 18 electrons is reached around Mo1.
If the Mo1ꢂ
/
There is extensive electron delocalization along the
Mo1ꢂ
Mo1ꢂ
The orientation of the phenyl ring (C32ꢂ
90(1)8] and the length of the C4ꢂC31 bond (1.494(7) A)
indicate that there is no p-overlap across C4ꢂC31. The
N(9) distance (2.141(5) A) implies a bond order
/
C4ꢂ
/
C5 chain, as shown by the shortness of the
˚
/
C4 and C4ꢂ
/
C5 bonds (2.048(5) and 1.455(7) A).
/
C31ꢂC4ꢂC5ꢀ
/
/
/
Fig. 1. An ORTEP representation of the structure of [Mo2Cp2(m-
SMe)3{m-h1(C): h1(N)-(N4CCPh)}] (4a) at 20% probability showing
the atom labelling scheme.
˚
/
/
˚
Mo(2)ꢂ
/
˚
close to unity; it is similar to the value of 2.151(2) A in
the m-amido complex [Mo2Cp2(m-SMe)3(m-NH2)] [19],
coplanar (torsion angle 169.5(1)8) and the isomer
present in the solid has an anti-configuration of the
methyl groups attached to S1 and S2. The higher trans-
influence of C4 compared with N9 atom is evident from
˚
but longer than that of 2.058(5) A in [Mo2Cp2(m-
SMe)3(m-h2-Nꢀ
/
NMe)] [20] and much longer than the
˚
terminal Moꢂ
/N
distance of 1.809(3)
A
in
[Mo{N(CH2CH2S)3}(NNMe)] [21].
the lengthening of Mo1ꢂ
/
S3 relative to Mo2ꢂ
/S3.
˚
Mo distance (2.7913(6) A) also indicates a
bond of unit order as required by electron counting
The Moꢂ
/
Having considered the crystal structure of 4a, we now
turn to the spectroscopic data for all the complexes 4.
First, it is apparent that the solution structures are
consistent with that observed in the solid state for 4a.
However, it was shown by multinuclear NMR spectro-
scopy that in solution all of the complexes, except 4d,
are present in two interconvertible isomeric forms, 41
and 42, which differ only in the orientations (syn or anti)
of the bridging SMe groups. These isomers were
inseparable by conventional chromatographic techni-
ques and were obtained in variable ratio according to
the thermal treatment of the crude products: the longer
the solution was heated the lower the yield of 41. The 1H
NMR spectra of compounds 4 exhibited the sets of
resonances expected for the [Mo2Cp2(m-SMe)3] core and
for the R groups. The tetrazolato-vinylidene bridge m-
rules; it is longer than the values of 2.719(2), 2.709(1),
˚
2.613(1) and 2.564(1)
[Mo2Cp2(m-SMe)3{m-h1(O):h1(N)-OC(Me)NH}] [22],
[Mo2Cp2(m-SMe)3(m-O2CCF3)] [23], [Mo2Cp2(m-
SMe)3(m-h2-NꢀNMe)] [20] and [MoCp2(m-SMe)3(m-h1-
NꢀCHCH3)] [24]. In all of these complexes a fourth
A found, respectively, in
/
/
ligand bridges a Cp2MoI2II(m-SMe)3 unit and each Mo
atom has a distorted piano-stool coordination. In 4a the
atoms Mo1, S1, S2 and Mo2 are, in consequence, almost
Table 1
Selected bonds distances (A) and angles (8) of 4a×
˚
/CH2Cl2
Bond distances
Mo(1)ꢂ
Mo(1)ꢂ
Mo(1)ꢂ
Mo(1)ꢂ
Mo(1)ꢂ
Mo(2)ꢂ
Mo(2)ꢂ
Mo(2)ꢂ
/
C(4)
2.048(5)
2.4612(14) C(4)ꢂ
2.4841(13) C(4)ꢂ
2.4997(13) C(5)ꢂ
Mo(2)ꢂ
/
S(3)
2.4279(14)
1.455(7)
1.494(7)
1.351(7)
1.357(7)
1.330(7)
1.342(7)
1.341(6)
h1(C):h2(N)-Caꢀ
13C{1H}NMR spectra by the observation of two
resonances, at low field in the carbene (:300 ppm)
and in the vinyl-cyanide (:172 ppm) ranges, which
/
Cb(N4) was characterised in the
/S(1)
/
C(5)
C(31)
N(6)
N(9)
/S(2)
/
/S(3)
/
/
/
Mo(2)
N(9)
S(1)
2.7913(6)
C(5)ꢂ
N(6)ꢂ
/
/
/
2.141(5)
/
N(7)
N(8)
N(9)
were assigned to Ca and Cb, respectively. As expected
from their structural inequivalence, separate resonances
were observed for the two C5H5 groups.
/
2.4203(14) N(7)ꢂ
2.4593(14) N(8)ꢂ
/
/S(2)
/
Bond angles
Mo(1)ꢂC(4)ꢂ
Mo(1)ꢂC(4)ꢂ
C(31)ꢂC(4)ꢂ
C(4)ꢂC(5)ꢂN(6)
The 1H and 13C NMR spectra of 4d, [Mo2Cp2(m-
/
/
C(5)
121.3(4)
128.7(4)
110.1(4)
126.4(5)
C(4)ꢂ
N(6)ꢂ
N(8)ꢂ
/
C(5)ꢂ
C(5)ꢂ
N(9)ꢂ
/
N(9)
N(9)
C(5)
123.0(5)
110.5(5)
106.1(4)
SMe)3){m-h1(C):h1(N)-N4CCR}] where R is the vinyl
/
/C(31)
/
/
/
/
C(5)
/
/
?
?
group ꢂ
/
Ca(Me)ꢀCbH2, indicate the presence of four
/
/
/
interconverting isomers. These arise because the methyl
groups on the bridging sulfur atoms can be either syn or
E.s.d.s are given in parentheses, see Fig. 1 for atomic numbering.

500
P. Schollhammer et al. / Inorganica Chimica Acta 350 (2003) 495ꢂ502
/
anti; in each of these arrangements the methyl group
?
produced 4, we added excess (5 equiv.) Me3SiN3 to a
tetrahydrofuran solution of 2a. No reaction was ob-
served under the conditions used above for synthesising
4 by reacting 1 or 2 with NaN3. However, when the
tetrahydrofuran solution was heated (66 8C) for 12h 4a
was obtained, but not the m-acetylide complex 3a. This
observation implies that, unlike sodium azide, Me3SiN3
does not readily form the base N3ꢃ for the deprotona-
tion of 1 and 2a. Addition of an ethanolic solution of the
m-acetylide compound 3a to that of NaN3 at room
temperature gave 4a only in very low yield (9%), after
stirring the solution for 30 min. It is thought that the m-
tetrazolate complex, which was formed in this reaction,
resulted from slow protonation of 3a in ethanol, giving
the m-vinylidene compound 2a which in its turn was
transformed into 4a in the presence of NaN3. Thus,
unlike the m-alkyne 1 and m-vinylidene 2 complexes the
m-acetylide derivatives 3 did not react with sodium azide
to give N-tetrazolate species 4.
These results indicate that the reactions of 1 and 2
with NaN3 are not simple processes in that they involve
the addition of two azido anions. We also note that
treatment of 1 or 2 with 2 equiv. of NaN3 under 1 atm.
of dinitrogen did not afford 4 in higher yields than those
obtained when the reaction was carried out under argon.
Evidently dinitrogen is not a participant in these
reactions and azide is the sole source of the nitrogen
atoms present in the tetrazole ring.
Scheme 1 shows a reaction path consistent with the
above observations which are not, we concede, complete
enough yet to define all the elementary steps involved.
The initial step is the 1,2-shift of the hydrogen in the m-
alkyne 1, promoted by the presence of NaN3 in ethanol,
to give the m-vinylidene 2. This known reaction [14]
provides a common path from 1 or 2 to 4 which was
obtained in similar yields irrespective of whether 1 or 2
was the starting complex. Nucleophilic addition of azide
at Ca of the vinylidene ligand next gives the alkenyl
intermediate A. The electrophilic character of the a-
carbon atom of vinylidene ligands [25] is established, as
its susceptibility to azide attack [13,26]. Subsequent
internal rearrangement gives the m-alkyl derivative B
which then loses both N2 and alkyl hydrogen (in the
form of NaH), giving the N-coordinated cationic
intermediate C. Mononuclear complexes of ruthenium
provide a precedent for the existence of such intermedi-
ates [13]. C contains an electrophilic molybdenum atom
which can be attacked by a second azide anion to afford
D. Formation of E and then 4 involves intramolecular
?
?
attached to Ca in the N4Cꢂ
/
Cꢂ
/
Ca(Me)ꢀCbH2 ligand can
/
be either cis or trans to the carbon atom of the
tetrazolate ring. The coupling pattern for the methyl
and methylene protons of the vinyl groups of 4d was
determined from a 2D-COSY NMR experiment which
allowed assignment of the resonances at d 2.02 and 1.99
to the methyl groups of the vinyl unit of the major
isomer 4d2. The respective assignment of the three sets of
carbon peaks observed at approximately 25.3, 104.8 and
?
160.7 ppm (4d2) to the methyl group attached to Ca, to
?
?
the CbH2 methylene group and to Ca was readily
accomplished via 1Hꢂ13C 2D HMQC and HMBC
experiments. It is obvious from the 1Hꢂ13C 2D
HMQC spectra that methylene protons (d :4.8 and
/
/
/
4.1) are coupled (JCH) to carbon at approximately 104.8
ppm, whereas the methyl protons (d 2.02 and 1.99) are
correlated with the carbon atom at approximately 25.3
ppm. The correlation peak between the methylene
protons at approximately 4.8 and 4.1 ppm and the
carbon atom at approximately 160.7 ppm (2JCH
)
allowed the assignment of this resonance to the Ca?
carbon atom.
Full assignment of the proton chemical shifts ob-
served for the n-propyl (ꢂ
/
CgH2ꢂ
the H NMR spectra of 4c2 was achieved by means of
1Hꢂ1H 2D-COSY NMR experiments. These spectra
/
CbH2ꢂ
/
CaH3) group in
1
/
showed correlations between the two CH2 and the CH3
groups, which allowed the attribution of the resonances
at 1.12, 1.50 and 3.63 ppm to the protons of the CaH3,
CbH2 and CgH2 units, respectively. In other respects
1Hꢂ
/
13C HMBC 2D experiments also allowed full
assignment of resonances due to the carbons of the n-
propyl group. The correlation peaks between the methyl
protons at 1.12 ppm and both Cb(d 25.78) (2JCH) and
Cg(d 55.52) (3JCH), those between the protons of the
CH2 group at 1.50 ppm and Cg at 55.52 ppm (2JCH),
and, finally, those between the protons of the CH2 unit
at 3.63 ppm and three carbon atoms, Cb at 25.78 ppm
(2JCH), the carbene atom at 305.71 ppm (2JCH) and the
carbon atom of the tetrazole ring at 172.80 ppm (3JCH),
are in accord with a CaH3ꢂ
/
CbH2ꢂ
/
CgH2ꢂ
/
C(ꢀ
/
Mo)ꢂ/CN4
backbone.
3.2. Discussion and mechanistic considerations
We have shown that addition of NaN3 to an ethanolic
solution of either the m-alkyne complex 1 or the m-
vinylidene derivatives 2 led readily to the tetrazolato-
bridged bis(h-cyclopentadienylmolybdenum) com-
pounds 4. In both cases significant amounts of m-
acetylide derivatives 3 were obtained as minor products,
[3ꢁ
/
2] cycloaddition of the Cꢀ
/
N bond to the N-
coordinated azide followed by internal rearrangement.
The available evidence does not allow us to exclude the
existence of other pathways to 4, for example, via direct
cyclisation of coordinated nitrile intermediates with
azide anion [12a].
resulting in a reduction of the yields of 4 to 61ꢂ80%. To
/
show that 1 and 2 were deprotonated, at least partly, by
N3ꢃ to give 3, before reaction with sodium azide

P. Schollhammer et al. / Inorganica Chimica Acta 350 (2003) 495ꢂ
/502
501
Acknowledgements
We are grateful to N. Kervarec and Dr. R. Pichon for
the recording of two-dimensional NMR spectra on a
Bruker DRX 500 (500 MHz), spectrometer. We thank
the CNRS, the EPSRC, Glasgow University, and the
University of Brest for financial support.
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