1922
Organometallics 1998, 17, 1922-1924
η1-η2 Rea r r a n gem en t a n d P r oton a tion of P h en yld ia zo
Br id gin g Liga n d s Atta ch ed to th e Dim olybd en u m System
{Mo2Cp 2(µ-SMe)3}
Philippe Schollhammer, Erwann Gue´nin, Franc¸ois Y. Pe´tillon,* and
J ean Talarmin
UMR 6521, Chimie, Electrochimie Mole´culaires et Chimie Analytique, Faculte´ des Sciences,
Universite´ de Bretagne Occidentale, BP 452, 29285 Brest-Ce´dex, France
Kenneth W. Muir* and Dmitri S. Yufit
Department of Chemistry, University of Glasgow, Glasgow G12 8QQ, Great Britain
Received December 19, 1997
Summary: Rearrangements and protonation reactions of
phenyldiazo ligands bound to the bimetallic center, {Mo2-
Cp2(µ-SMe)3}, are reported.
formation of µ-η1- and µ-η2-phenyldiazenido complexes
[Mo2Cp2(µ-SMe)3(µ-η1-N2Ph)] (2) and [Mo2Cp2(µ-SMe)3(µ-
η2-N2Ph)] (3), of the µ-η1-hydrazido(2-) (or isodiazene)
compound [Mo2Cp2(µ-SMe)3(µ-η1-NNHPh)]BF4 (4), and
of the µ-η2-diazene species [Mo2Cp2(µ-SMe)3(µ-η2-NHN-
Ph)]BF4 (5). Some stereochemical aspects of these
reactions are also briefly considered.
The organometallic chemistry involved in the trans-
formation M(N2) f M(N2R) f M(N2R2) f M(N2R3),
where M is a transition-metal core and R ) H, aryl, or
alkyl, is relevant to the modeling of N2 reduction by
metalloenzymes1 and to the synthesis of nitrogen-
containing organic compounds. The generation of such
compounds, either directly from molecular nitrogen or
indirectly from diazenido (RNdN-) or hydrazido(2-)
(RN-NR2-) precursors, through C-N bond formation
is a currently developing field of organic synthesis.1a,2
In this communication we present evidence which gives
new insight into catalytic and stoichiometric processes
which involve the activation and transformation of
The thermal reaction of the complex [Mo2Cp2(µ-SMe)3-
(µ-Cl)] (1) with PhNHNH2 (2 equiv) in THF at 70 °C for
6 h afforded a red-brown solution from which the
complexes 2 and 3 were isolated in 50% and 20% yields
as red and green powders (Scheme 1).8 The reaction
conditions can be modified to favor formation of 2 (1
week, 20 °C, yield 70%) or 3 (72 h, 70 °C, yield of 2 30%,
yield of 3 40%). Thermolysis or photolysis of 2 or 3 gave
mixtures containing both isomers, showing that, what-
ever the initial mode of coordination of the phenyldiazo
bridge (η1 or η2), it can rearrange to give the alternative
isomer (Scheme 2). Compounds 2 and 3 were charac-
terized by elemental analyses and IR and 1H NMR
dinitrogenous substrates by a bimetallic center.3
A
diazenido complex is usually regarded as the first
intermediate in the reduction of the dinitrogen molecule;
its alkylation or protonation leads to hydrazido(2-) and
diazene (RNdNR) species.4 The coordination of the
diazenido ligand to a single metal atom has been
extensively studied and its various modes of bindings
singly bent, doubly bent, or side-onsare well under-
stood.1b,5 Much less is known about its behavior as a
bridging ligand in di- or polynuclear compounds.6 Ac-
cordingly, we have studied the reactions of nitrogenous
substrates with dimolybdenum systems containing a
{Mo2(µ-SMe)n} (n ) 1-3) core3g,7 and now describe the
1
spectroscopy. The H NMR (in CDCl3) spectra of 2 and
3 exhibited two inequivalent cyclopentadienyl ligand
resonances and three SMe resonances, indicating that
the complexes had a {Mo2Cp2(µ-SMe)3} core and that
the fourth bridge was not symmetric. Two isomers for
3 differing in the orientation of the S-methyl substitu-
ents relative to the Mo-Mo axis were detected in a 85:
15 ratio. The presence of the N2Ph group was supported
(8) Preparation of 2 and 3: A solution of complex 1 (0.2 g, 0.4 ×
10-3 mol) and PhNNH2 (80 µL, 0.8 × 10-3 mol) in THF (30 cm3) was
heated at 70 °C for 6 h. The solution, initially green, became brownish
red. After filtration (elimination of NH4Cl) and evaporation of the
solvent, the residue was chromatographed on a silica gel column.
Elution with CH2Cl2-THF (9:1) afforded a red band containing 2.
Complex 3 was then eluted with THF as a green band. Compounds 2
and 3 were washed with pentane and obtained as red and green air-
stable powders, respectively, with yields depending on the reaction
conditions. Compounds 2 and 3 are relatively stable in solution.
According to the described conditions the yields are 50% (0.11 g) for 2
and 20% (0.045 g) for 3. 2: 1H NMR (CDCl3) δ 7.3 (m, 2H, Ph), 7.16 (t,
1H, Ph), 6.45 (d, 2H, Ph), 5.57 (s, 5H, Cp), 4.98 (s, 5H, Cp), 1.87 (s,
3H, SMe), 1.56 (s, 3H, SMe), 1.39 (s, 3H, SMe); IR (KBr, cm-1) 1595
ν(NdN). Anal. Calcd for Mo2C19H24N2S3: C, 40.1; H, 4.2; N, 4.9. Found:
C, 40.8; H, 4.4; N, 5.4. 3: 1H NMR (CDCl3) for 3a (85%) δ 7.2 (m, 2H,
Ph), 7.03 (t, 1H, Ph), 6.61 (d, 2H, Ph), 5.89 (s, 5H, Cp), 5.44 (s, 5H,
Cp), 1.53 (s, 3H, SMe), 1.45 (s, 3H, SMe), 1.37 (s, 3H, SMe); 1H NMR
(CDCl3) for 3b (15%) δ 7.13 (m, 2H, Ph), 7.11 (m, 1H, Ph), 6.59 (m,
2H, Ph), 5.85 (s, 5H, Cp), 5.31 (s, 5H, Cp), 1.68 (s, 3H, SMe), 1.50 (s,
3H, SMe), 1.49 (s, 3H, SMe). Anal. Calcd for Mo2C19H24N2S3: C, 40.1;
H, 4.2; N, 4.9. Found: C, 41.1; H, 4.1; N, 5.1.
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(7) Schollhammer, P.; Pe´tillon, F. Y.; Talarmin, J .; Muir, K. W. To
be submitted for publication.
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