η1-η2 rearrangement and protonation of phenyldiazo bridging ligands attached to the dimolybdenum system {Mo2Cp2(μ/-SMe)3}

Article abstract of DOI:10.1021/om971114v

Rearrangements and protonation reactions of phenyldiazo ligands bound to the bimetallic center, {Mo₂-Cp₂(μ-SMe)₃}, are reported.

Full text of DOI:10.1021/om971114v

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.
(1) (a) Hidai, M.; Mizobe, Y. Chem. Rev. 1995, 95, 5970. (b) Sutton,
D. Chem. Rev. 1993, 93, 1022.
(2) (a) Seino, H.; Ishii, Y.; Sasagawa, T.; Hidai, M. J . Am. Chem.
Soc. 1995, 117, 12181. (b) Seino, H.; Ishii, Y.; Hidai, M. Inorg. Chem.
1997, 36, 161.
(3) (a) Kuwata, S.; Mizobe, Y.; Hidai, M. Inorg. Chem. 1994, 33,
3619. (b) Coucouvanis, D. J . Bioinorg. Chem. 1996, 1, 594. (c) Pickett,
C. J . J . Bioinorg. Chem. 1996, 1, 601. (d) Gambarotta, S. J . Organomet.
Chem. 1995, 500, 117. (e) Henderson, R. A. J . Chem. Soc., Dalton
Trans. 1995, 503. (f) Sellmann, D.; Sutter, J . Acc. Chem. Res. 1997,
30, 460. (g) Schollhammer, P.; Pe´tillon, F. Y.; Poder-Guillou, S.;
Saillard; J . Y.; Talarmin, J .; Muir, K. W. Chem. Commun. 1996, 2633.
(4) King, R. B. J . Organomet. Chem. 1995, 500, 187.
(5) (a) Chi-Young Kim, G.; Batchelor, J .; Yan, X.; Einstein, F. W.
B.; Sutton, D. Inorg. Chem. 1995, 34, 6163. (b) Moller, E. R.; J orgensen,
K. A. Acta Chem. Scand. 1991, 45, 68.
(6) Yan, X.; Batchelor, J .; Einstein, F. W. B.; Sutton, D. Inorg. Chem.
1996, 35, 7818 and references cited therein.
(7) Schollhammer, P.; Pe´tillon, F. Y.; Talarmin, J .; Muir, K. W. To
be submitted for publication.
S0276-7333(97)01114-X CCC: $15.00 © 1998 American Chemical Society
Publication on Web 04/11/1998

Communications
Organometallics, Vol. 17, No. 10, 1998 1923
Sch em e 1
F igu r e 1. View of a molecule of [Cp2Mo2(η1-µ-NNPh)(µ-
SMe)3] (2) showing 50% probability ellipsoids. Hydrogen
atoms are shown as spheres of arbitrary size. Selected
distances (Å) and angles (deg): Mo(1)-N(1), 2.084(2); Mo-
(1)-S(1), 2.474(1); Mo(1)-S(2), 2.458(1); Mo(1)-S(3), 2.476-
(1); Mo(1)-Mo(2), 2.5780(3); N(1)-N(2), 1.255(3); Mo(2)-
N(1), 2.036(2); Mo(2)-S(1), 2.462(1); Mo(2)-S(2), 2.466(1);
Mo(2)-S(3), 2.483(1); N(2)-C(4), 1.440(3); Mo(2)-N(1)-
Mo(1), 77.47(7); N(2)-N(1)-Mo(2), 132.6(2); N(2)-N(1)-
Mo(1), 149.9(2); N(1)-N(2)-C(4), 116.3(2); Mo(1)-N(1)-
N(2)-C(4), -8.0(4); N(1)-N(2)-C(4)-C(5), -60.4(3).
Sch em e 2
(3) Å) is consistent with a NdN double bond. The slight
asymmetry in the Mo-N2Ph-bridge bond lengths (Mo-
(1)-N(1) ) 2.084(2) Å, Mo(2)-N(1) ) 2.036(2) Å) is most
probably attributable to the steric effect of the N-phenyl
group. These Mo-N distances are shorter than the
2.151(2) Å found in the amido complex [Mo2Cp2(µ-SMe)3-
(µ-NH2)], and the Mo(1)-N(1)-Mo(2) angle is slightly
more open (cf. 77.5(1) and 73.3(1)°), indicating some
π-acceptor character for the diazenido ligand.3g This
conclusion is also consistent with the coplanarity of N(1),
N(2), Mo(1), Mo(2), and C(4). As has been observed for
other bridging aryldiazenido ligands, the orientation of
the aromatic ring precludes conjugation between it and
the NdN π-bond.6 3 has not yet been characterized by
X-ray analysis, but preliminary results11 for its η2-
MeNdN analogue indicate a strong NdN bond of 1.200-
(5) Å and Mo-N and Mo-NMe distances (2.059(5) and
2.097(4) Å) comparable with those in 2.
by the observation of phenyl resonances in the 1H NMR
spectra and by the elemental analyses.8 For 2 a band
at 1595 cm-1 in the IR spectrum was assignable to
ν(NdN), whereas for 3 such a vibration could not be
unambiguously assigned. The coordination mode of the
diazenido bridge in 2 was determined by an X-ray
analysis (Figure 1).9 The molecular structure of 2 is
typical of a tetrabridged dinuclear complex of molyb-
denum(III): the Cp-Mo-Mo-Cp unit is nearly linear
(Cp ) C5H5 ring centroid), and a four-legged piano-stool
geometry around each Mo atom is supplemented by the
single metal-metal bond (Mo(1)-Mo(2) ) 2.5780(3) Å)
required by normal electron counting rules.10 The
phenyldiazenido ligand bridges the two molybdenum
atoms in an η1 fashion. The N(1)-N(2) distance (1.255-
Protonation of 2 and 3 led respectively to the η1-
hydrazido(2-) (or isodiazene) complex [Mo2Cp2(µ-SMe)3-
(µ-η1-NNHPh)]BF4 (4) and its η2-diazene isomer [Mo2-
Cp2(µ-SMe)3(µ-η2-NHNPh)]BF4 (5) (Scheme 2).12 Depro-
tonation of 4 and 5, easily effected with Et3N, gives the
starting complexes 2 and 3. Compounds 4 and 5 were
characterized by 1H NMR, elemental analyses, and IR.11
In the 1H NMR spectra resonances due to the NH group
were detected for 4 and 5 at 12.9 and 12.6 ppm,
respectively. The IR spectra of 4 and 5 display ν(NH)
bands at 3170 and 3220 cm-1, respectively. The struc-
ture of complex 5 has been confirmed by X-ray analysis
(Figure 2).13 There are three crystallographically in-
dependent cations (n ) 1-3) which display essentially
identical bond lengths and angles. The NdN bonds
(9) Crystallographic data for [Cp2Mo2(η1-µ-NNPh)(µ-SMe)3] (2): C19
-
H24Mo2N2S3, Mr ) 568.46, monoclinic, space group P21/c, a ) 9.1807-
(3) Å, b ) 13.9964(7) Å, c ) 16.8168(12) Å, â ) 96.859(4)°, V ) 2145.4(2)
Å3, Z ) 4, Dc ) 1.760 g cm-3, µ(Mo KR) ) 1.467 mm-1. The intensities
of 8182 reflections with θ(Mo KR) < 30.4° were corrected for minor
(2.9%) crystal decomposition and for absorption (transmission factors
0.656-0.856). Refinement of 236 parameters on F2 using all 6472
unique reflections (Rint ) 0.017; 5227 with I > 2σ(I)) gave R[I > 2σ(I)]
) 0.028 and wR2(all data) ) 0.076; |∆F| < 0.65 e Å-3
.
(10) Schollhammer, P.; Gue´nin, E.; Poder-Guillou, S.; Pe´tillon, F.
Y.; Talarmin, J .; Muir, K. W.; Baguley, P. J . Organomet. Chem. 1997,
539, 193.
(11) Schollhammer, P.; Pe´tillon, F. Y.; Talarmin, J .; Muir, K. W.;
Teat, S. J . Unpublished results.

1924 Organometallics, Vol. 17, No. 10, 1998
Communications
Sch em e 3
F igu r e 2. View of one of the [Cp2Mo2(η2-µ-NHNPh)(µ-
SMe)3] cations in 5 with 50% probability ellipsoids. Hy-
drogen atoms are shown as spheres of arbitrary size.
Selected distances (Å) and angles (deg) for the three
independent cations n ) 1-3: Mo(n1)-N(n1), 2.018(9),
2.029(9), 2.011(9); Mo(n1)-S(n3), 2.434(4), 2.439(4), 2.435-
(4); Mo(n1)-S(n1), 2.443(4), 2.446(4), 2.444(4); Mo(n1)-
S(n2), 2.456(4), 2.457(4), 2.460(3); Mo(n1)-Mo(n2), 2.650-
(2), 2.657(2), 2.644(2); Mo(n2)-N(n2), 2.137(8), 2.128(8),
2.101(9); Mo(n2)-S(n3), 2.431(4), 2.438(4), 2.434(4); Mo-
(n2)-S(n1), 2.440(4), 2.444(4), 2.445(4); Mo(n2)-S(n2),
2.476(4), 2.471(4), 2.467(4); N(n1)-N(n2), 1.324(11), 1.307-
(11), 1.309(12); N(n2)-C(n14), 1.424(10), 1.432(10), 1.438-
(11); N(n2)-N(n1)-Mo(n1), 112.2(6), 112.0(7), 113.4(7);
N(n1)-N(n2)-Mo(n2), 105.1(6), 105.9(6), 104.6(7).
indicates that the contribution of the hydrazido(2-)
resonance form of the NNHPh bridge is significant.
Complex 4 in solution at room temperature or on mild
heating gives the µ-η2-NHNPh complex 5. The inter-
1
(mean 1.313(7) Å) are slightly longer than in 2, as are
the Mo-Mo bonds (mean 2.650(4) Å). Unsurprisingly,
the Mo(n1)-N bonds (mean 2.02(1) Å) are shorter than
the Mo(n2)-N bonds (mean 2.12(1) Å).
Complex 4 exhibits dynamic behavior attributable to
rotation of the NHPh group around the NdN bond axis
with ∆Gq ) 61.3 ( 1 kJ mol-1 (Scheme 3), which
mediate 6 was observed but not isolated. Its H NMR
spectrum in CD2Cl2 showed a resonance at 12.0 ppm
for the NH group, phenyl resonances between 7.32 and
6.79 ppm, two inequivalent cyclopentadienyl groups at
6.03 and 5.85 ppm, and three peaks for the SMe bridges
at 1.71, 1.73, and 1.81 ppm. Evidently the rearrange-
ment involves inversion of one SMe group and η1 f η2
isomerization of the diazo bridge accompanied by trans-
fer of a proton across the N-N bond. Complete iden-
tification of 6 will allow us to confirm the order of these
steps.
(12) Preparation of 4 and 5: To a solution of 2 or 3 (0.2 g, 0.35 ×
10-3 mol) in THF (5 cm3) was added 1 equiv of HBF4-Et2O. The
solution turned instantly from red to orange or from green to yellow
for compound 2 or 3, respectively. Addition of pentane (10 cm3)
precipitated compound 4 or 5 as an orange or yellow air-stable solid,
respectively. 4 and 5 were washed with pentane and obtained with
ca. 90% yields (0.21 g). 4 transformed into 5 in solution at room
temperature. 4: 1H NMR (CD3CN) δ 12.9 (s, 1H, NH), 7.54 (m, 2H,
Ph), 7.45 (t, 1H, Ph), 6.97 (d, 2H, Ph), 6.01 (s, 5H, Cp), 5.64 (s, 5H,
Cp), 2.05 (s, 3H, SMe), 1.66 (s, 3H, SMe), 1.56 (s, 3H, SMe); IR (KBr,
cm-1) 3220 ν(NH), 1150-950 ν(BF). Anal. Calcd for Mo2BC19H25F4N2-
S3: C, 34.8; H, 3.8; N, 4.3. Found: C, 34.5; H, 3.9; N, 3.8. 5: 1H NMR
(CD3CN) δ 12.6 (s, 1H, NH), 7.42 (m, 2H, Ph), 7.32 (t, 1H, Ph), 6.93 (d,
2H, Ph), 6.11 (s, 5H, Cp), 5.79 (s, 5H, Cp), 1.72 (s, 3H, SMe), 1.65 (s,
3H, SMe), 1.52 (s, 3H, SMe); IR (KBr, cm-1) 3170 ν(NH), 1150-950
ν(BF). Anal. Calcd for Mo2BC19H25F4N2S3: C, 34.8; H, 3.8; N, 4.3.
Found: C, 35.2; H, 4.0; N, 4.4.
In summary, we have synthesized new µ-η1- and µ-η2-
diazenido complexes and the corresponding protonated
cations which contain µ-η1-hydrazido(2-) (isodiazene)
and µ-η2-diazene ligands. These species readily undergo
η1 f η2 isomerizations which are critical to understand-
ing the stepwise reduction of NNR ligands bound to a
thiopolymetallic system. We are now investigating how
2 and 3 are formed and the mechanism of reactions in
which their diazo ligands are reduced.
(13) Crystallographic data for {[Cp2Mo2(η2-µ-NHNPh)(µ-SMe)3]-
[BF4]}3‚2CH2Cl2‚1/2OEt2 (5): C61H84B3Cl4F12Mo6N6O1/2S9, Mr ) 2175.75,
triclinic, space group P1h, a ) 12.509(3) Å, b ) 17.052(3) Å, c ) 21.170-
(4) Å, R ) 66.67(3)°, â ) 86.02(3)°, γ ) 75.34(3)°, V ) 4009.0(14) Å3, Z
) 2, Dc ) 1.802 g cm-3, µ(Mo KR) ) 1.348 mm-1. The intensities of
15 886 reflections with θ(Mo KR) < 25.0° were corrected for absorption
(transmission factors 0.58-0.88). Refinement of 784 parameters on F2
using all 14 038 unique reflections (Rint ) 0.128; 5612 with I > 2σ(I))
gave R[I > 2σ(I)] ) 0.064 and wR2(all data) ) 0.168; |∆F| < 0.96 e
Å-3. The asymmetric unit contains three ordered dimolybdenum
Ackn owledgm en t. We thank the CNRS, the EPSRC,
Glasgow University, and the University of Brest for
financial support.
Su p p or tin g In for m a tion Ava ila ble: Tables of atomic
parameters and all bond distances and angles for 2 and 5 (14
pages). Ordering information is given on any current mast-
head page. The structures will be deposited in the Cambridge
Structural Database.
-
cations, three BF4 anions (all disordered), two CH2Cl2 solvates (one
disordered), and a diethyl ether molecule disordered over an inversion
center. Solvate and anion disorder, together with the small size of the
specimen (0.21 × 0.15 × 0.06 mm), have adversely affected the
precision of the analysis.
OM971114V