Disproportionation and reduction of hydrazine at a molybdenum-thiolate centre: Crystal structures of [MoH(SC6H2Pri3-2,4,6) 3(NH3)-(PMePh2)] and [MoH(SC6H2Pri3-2,4,6) 3(NH2NHPh)(PMePh2)]

Article abstract of DOI:10.1039/a705886a

In the presence of [MoH(SC₆H₂Prⁱ₃-2,4,6) ₃(PMePh₂)] in tetrahydrofuran (thf), anhydrous N₂H₄ disproportionates to N₂ and NH₃ or is reduced to NH₃ by Zn-HOC₆H₃Prⁱ₂-2,6 (69-81% conversion over 16 h). Reaction of [MoH(SC₆H₂Prⁱ₃-2,4,6) ₃(PMePh₂)] with anhydrous N₂H₄ in thf-MeOH at low temperature gave the complex [MoH(SC₆H₂Prⁱ₃-2,4,6) ₃(NH₃)(PMePh₂)] which was shown by a crystal-structure determination to have a trigonal girdle of thiolate ligands with essentially apical NH₃ and PMePh₂ ligands [d(Mo-N), 2.298(15); d(Mo-S) (mean), 2.339(5) A]. A similar reaction using NH₂NHPh instead of N₂H₄ gave [MoH(SC₆H₂Prⁱ₃-2,4,6) ₃(NH₂NHPh)-(PMePh₂)], which has an analogous crystal structure to [MoH(SC₆H₂Prⁱ₃-2,4,6) ₃(NH₃)(PMePh₂)] [d(Mo-N), 2.278(5); d(Mo-S) (mean), 2.332(2); d(N-N) 1.451(7) A]. Spectroscopic data for these compounds are discussed in terms of their structures. The unstable adduct [MoH(SC₆H₂Prⁱ₃-2,4,6) ₃(NH₂NMe₂)(PMePh₂)] has been characterised spectroscopically in solution.

Full text of DOI:10.1039/a705886a

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Disproportionation and reduction of hydrazine at a molybdenum–
thiolate centre: crystal structures of [MoH(SC6H2Pri3-2,4,6)3(NH3)-
(PMePh2)] and [MoH(SC6H2Pri3-2,4,6)3(NH2NHPh)(PMePh2)]
Peter B. Hitchcock,a David L. Hughes,b Michael J. Maguire,a Katayoun Marjania and
Raymond L. Richards*,b
a School of Chemistry, Physics and Environmental Sciences, University of Sussex, Brighton,
UK BN1 9RQ
b John Innes Centre, Nitrogen Fixation Laboratory, Norwich Research Park, Norwich,
UK NR4 7UH
In the presence of [MoH(SC6H2Pri3-2,4,6)3(PMePh2)] in tetrahydrofuran (thf), anhydrous N2H4 disproportionates
to N2 and NH3 or is reduced to NH3 by Zn–HOC6H3Pri2-2,6 (69–81% conversion over 16 h). Reaction of
[MoH(SC6H2Pri3-2,4,6)3(PMePh2)] with anhydrous N2H4 in thf–MeOH at low temperature gave the complex
[MoH(SC6H2Pri3-2,4,6)3(NH3)(PMePh2)] which was shown by a crystal-structure determination to have a trigonal
girdle of thiolate ligands with essentially apical NH3 and PMePh2 ligands [d(Mo᎐N), 2.298(15); d(Mo᎐S) (mean),
2.339(5) Å]. A similar reaction using NH2NHPh instead of N2H4 gave [MoH(SC6H2Pri3-2,4,6)3(NH2NHPh)-
(PMePh2)], which has an analogous crystal structure to [MoH(SC6H2Pri3-2,4,6)3(NH3)(PMePh2)] [d(Mo᎐N),
2.278(5); d(Mo᎐S) (mean), 2.332(2); d(N᎐N) 1.451(7) Å]. Spectroscopic data for these compounds are discussed
in terms of their structures. The unstable adduct [MoH(SC6H2Pri3-2,4,6)3(NH2NMe2)(PMePh2)] has been
characterised spectroscopically in solution.
The reduction of N2H4 to NH3 and its disproportionation to
Results and Discussion
Disproportionation and reduction of hydrazine
NH3 and N2 are catalysed by a limited number of metal com-
plexes, e.g. the mononuclear compound [W(C5Me5)Me3(η2-
N2H4)]1 and cluster anions such as [MoFe3S4Cl3(C6Cl4O2)-
(MeCN)]2Ϫ catalyse2 the disproportionaton and reduction of
hydrazine. The site of binding of N2H4 in the last case appears
to be the molybdenum, since PhNHNH2 has been shown to
bind at Mo in the above cluster.3 These observations have rele-
vance to the possible function of nitrogenase in that bound
The results of this study are presented in Table 1. As can be seen
from these data, when hydrazine was treated with 1 in tetra-
hydrofuran (thf) alone there was a moderate and rather slow
conversion to N2 and NH3 by disproportionation [reaction (1)].
3N2H4 → N2 ϩ 4NH3
(1)
2Ϫ
hydrazine, and derivatives of it such as N2H2, NNH2 or
In the presence of methanol as proton source but with no added
reductant, disproportionation was still the predominant
reaction, but clearly ammonia was produced by reduction
[reaction (2)] in addition to that produced by disproportion-
NNH3Ϫ, are likely intermediates in the reduction of N2,
whether at a mononuclear or a multinuclear site.4
Molybdenum–thiolate complexes have also been used to
model aspects of nitrogenase chemistry, in particular the reduc-
tion of hydrazine and also the binding of hydrogen to sulfur-
ligated metal centres. In one such demonstration of the catal-
ytic disproportionation and reduction of hydrazine, the cat-
alyst precursor is the binuclear complex [Mo2Cl4{2-SC5H3N-
(SiMe3)-3}2(µ-S2){µ-2-SC5H3NH(SiMe3)-3}] and the catalyst
itself may be binuclear also, but this has not been established.5
The binuclear complex [Mo2(η-C5H5)2(µ-Cl)(µ-SMe)3] has been
shown to catalyse the disproportionation of hydrazine and a
binuclear amido complex [Mo2(η-C5H5)2(µ-NH2)(µ-SMe)3] has
been isolated, although it is unclear whether the last complex is
an intermediate on the reaction pathway.6
The present study involves the use of the unsaturated
thiolate–hydride complex [MoH(SC6H2Pri3-2,4,6)3(PMePh2)]
1.7 This compound was prepared to examine the behaviour of
hydride ligands at a metal which also carries sulfur-donor
groups; its electronically unsaturated nature generates a variety
of reactions including S᎐C bond cleavage of thiolate ligands8
and formation of adducts such as [MoH(SC6H2Pri3-2,4,6)3-
(C5H5N)(PMePh2)].9 When 1 was treated with N2H4, the com-
plex [MoH(SC6H2Pri3-2,4,6)3(NH3)(PMePh2)] 2 was obtained
as described in detail below. This observation prompted an
investigation to see if disproportionation and reduction of
hydrazine are catalysed by 1.
N2H4 ϩ 2Hϩ ϩ 2eϪ → 2NH3
(2)
ation, especially at higher hydrazine ratios. The extent of dis-
proportionation was monitored for the methanol system by
measurement of the amount of N2 evolved in the reaction,
then the yield of NH3 produced by disproportionation was
calculated from this value assuming that reaction (1) occurs.
Ammonia produced in excess of this value was assumed to
arise from a competing reduction reaction.
In the presence of 1, with zinc as reductant and HOC6H3Pri2-
2,6 as proton source, high (69–81%) conversion of hydrazine to
ammonia occurred over a period of around 16 h in thf solution.
The highest levels of disproportionation and reduction were at
relatively low ratios of hydrazine to Mo, as has been observed
in other systems and attributed to precipitation of product or
of starting material, as their ammonium salts, at higher ratios
of hydrazine.2,10
As described below, the adducts [MoH(SC6H2Pri3-2,4,6)3-
(NH2NHPh2)(PMePh2)] 3 (from reaction of PhNHNH2) and
[MoH(SC6H2Pri3-2,4,6)3(NH3)(PMePh2)] 2 (from reaction of
NH2NH2) have been structurally characterised and the adduct
[MoH(SC6H2Pri3-2,4,6)3(NMe2NH2)(PMePh2)]
4
has been
characterised in solution. These results indicate that at least in
J. Chem. Soc., Dalton Trans., 1997, Pages 4747–4752
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Table 1 Catalytic disproportionation and reduction of hydrazine by complex 1
Moa
N2H4 :Mo
N2
NH3
NH3
Conversione (%)
b
b,c
d
1.4f
0.7
0.5
1.1:1
1.1:1
15.6:1
26.0:1
64.0:1
6.3:1
5.7:1
12.7:1
21.1:1
0.2 (0.4)
0.3 (0.4)
1.8 (5.2)
1.8 (8.7)
6.1 (21.3)
—
—
—
—
0.8 (1.5, 0.8)
1.4 (1.5, 1.1)
10.4 (20.8, 7.2)
25.3 (34.7, 7.2)
59 (85.3, 24.4)
10.2 (12.6)
8.0 (11.4)
19.7 (25.4)
29.2 (42.2)
0
0.3
3.2
18.1
25.6
10.2
8.0
19.7
29.2
55.2, 0
78.4, 12.7
34.6, 10.2
20.8, 34.8
26.5, 28.3
—, 80.9
—, 70.1
—, 77.5
—, 69.2
0.3
1.0
0.3g
0.45g
0.3g
0.3e
a Concentration of Mo, mol × 10Ϫ4; solvent thf–MeOH 3:1 unless otherwise stated; reaction time 16–18 h; all reactions repeated three times. b Yield;
maximum possible in parentheses, in equivalents relative to Mo, according to 3 N2H4 → N2 ϩ 4NH3 or N2H4 → 2NH3 as appropriate. c In bold,
yield of NH3 calculated from disproportionation, based on N2 evolved. d Yield of NH3 produced by reduction. e Conversion of N2H4 to product (by
disproportionation, by reduction). f thf Solution. g 16 Equivalents Zn and 12 equivalents of HOC6H3Pri2-2,6 (per N2H4) added, reliable N2 evolution
data could not be monitored in system used (see Experimental section).
Table 2 Selected intramolecular distances (Å) and angles (Њ) for
[MoH(SC6H2Pri3-2,4,6)3(NH3)(PMePh2)] 2, with estimated standard
deviations (e.s.d.s) in parentheses
H
R
S
R
Mo
S
S
Mo(1)᎐S(1)
Mo(1)᎐S(3)
Mo(1)᎐N(1)
S(2)᎐C(29)
Mo(2)᎐S(4)
Mo(2)᎐S(6)
Mo(2)᎐N(2)
S(5)᎐C(87)
2.331(5)
2.332(5)
2.298(15)
1.81(2)
2.343(5)
2.335(5)
2.298(14)
1.77(2)
Mo(1)᎐S(2)
Mo(1)᎐P(1)
S(1)᎐C(14)
S(3)᎐C(44)
Mo(2)᎐S(5)
Mo(2)᎐P(2)
S(4)᎐C(72)
S(6)᎐C(102)
2.354(4)
2.365(5)
1.81(2)
1.81(2)
2.358(5)
2.365(5)
1.78(2)
1.77(2)
R
N2H4
P
–NH3
R
S
NH2
NH3
H
S
R
H2N
R
H
S
Mo
S
R
Mo
P
S
S(1)᎐Mo(1)᎐S(2)
S(1)᎐Mo(1)᎐P(1)
S(2)᎐Mo(1)᎐S(3)
S(2)᎐Mo(1)᎐N(1)
S(3)᎐Mo(1)᎐N(1)
S(4)᎐Mo(2)᎐S(5)
S(4)᎐Mo(2)᎐P(2)
S(5)᎐Mo(2)᎐S(6)
S(5)᎐Mo(2)᎐N(2)
S(6)᎐Mo(2)᎐N(2)
110.0(2)
81.0(2)
117.4(2)
82.7(4)
88.6(4)
111.3(2)
81.8(2)
116.8(2)
82.6(4)
88.7(3)
S(1)᎐Mo(1)᎐S(3)
S(1)᎐Mo(1)᎐N(1)
S(2)᎐Mo(1)᎐P(1)
S(3)᎐Mo(1)᎐P(1)
P(1)᎐Mo(1)᎐N(1)
S(4)᎐Mo(2)᎐S(6)
S(4)᎐Mo(2)᎐N(2)
S(5)᎐Mo(2)᎐P(2)
S(6)᎐Mo(2)᎐P(2)
P(2)᎐Mo(2)᎐N(2)
131.7(2)
88.6(4)
119.2(2)
84.1(2)
157.8(4)
131.1(2)
89.0(4)
118.3(2)
83.4(2)
S
R
P
R
H+, 2e–
–NH3
+
NH3
H+
R
H2N
H
S
S
R
159.0(4)
Mo
S
R
P
MeOH at 0 ЊC produced a green-brown solution after 30 min.
Slow crystallisation of the reaction solution at Ϫ20 ЊC follow-
ing addition of ice-cold MeOH gave, after about 2 weeks, grass
green crystals of complex 2 which were suitable for X-ray
analysis. Complex 2 as produced above is very air- and
temperature-sensitive, but when carefully purified it is moder-
ately stable at room temperature in the absence of air. Anal-
ytical data for 2, its spectroscopic properties (see Experimental
section) and analogy with complexes such as [MoH(SC6H2Pri3-
2,4,6)3(C5H5N)(PMePh2)]9 are consistent with the formulation
Fig. 1 Scheme of catalytic reduction of hydrazine at a single molyb-
denum site
outline, the disproportionation and reduction reactions occur
via initial adduct formation at a single Mo site. The further
mechanism of the disproportionation reaction is unclear, since
although it undoubtedly occurs at molybdenum, it presumably
involves a multiple sequence of steps or polynuclear species at
some stage [see equation (1)]. The further mechanism of reduc-
tion of hydrazine might only require a single Mo site; an outline
scheme for reduction is shown in Fig. 1. This scheme is similar
to that proposed by Coucouvanis and co-workers2 for reduction
of hydrazine at the single Mo site in cluster anions such as
[MoH(SC6H2Pri3-2,4,6)3(NH3)(PMePh2)]. Thus
2 shows a
broad N᎐H stretching absorption at 3200–3400 cmϪ1 and a
weak Mo᎐H stretching absorption at 1890 cmϪ1; its proton-
coupled 31P resonance is a doublet centred at δ Ϫ86.8
[2J(PMoH) = 86.7 Hz], a pattern typical of such molybdenum
hydrides with the hydride cis to the phosphine.8,9 It shows a
broad singlet 14N NMR resonance at δ Ϫ72.1 (relative to liquid
MeNO2). The molecular structure of 2 is shown in Fig. 2 and
selected bond lengths and angles are in Table 2. The structure
shows two very similar, independent molecules, each with the
Mo on a local, pseudo-mirror plane of symmetry; the ligand
atoms S(2), N(1) and P(1) lie in this plane through Mo(1), and
S(5), N(2) and P(2) are in a similar plane through Mo(2). Each
complex has an equatorial trigonal array of thiolate ligands
with the typical ‘two-up-one-down’ arrangement found in this
class of thiolate complex,8,9 together with apical PMePh2 and
NH3 ligands. Although the hydrogen atoms could not be
located, the infrared data discussed above and each Mo᎐N
distance of 2.298(15) Å are consistent with an NH3 rather than
[MoFe3S4Cl3(C6Cl4O2)(MeCN)]2Ϫ
.
Clearly this type of activation of hydrazine has relevance to
the reduction of N2 by nitrogenase, particularly since hydrazine
can be obtained from the enzyme by quenching10 and bound
hydrazine may therefore lie on the N2 reduction path, assuming
that the process involves activation of N2 at a sulfur-ligated Mo
or other metal site. Although binding of N2 at a thiolate-ligated
molybdenum site has not yet been demonstrated, isolation of
such a compound may only be a matter of time, since a
thiolate–dinitrogen complex of the related metal rhenium,
[Re(SC6H2Pri3-2,4,6)3(N2)(PPh3)], is known.11
Preparation and structure of [MoH(SC6H2Pri3-2,4,6)3(NH3)-
(PMePh2)] 2
The reaction of complex 1 with anhydrous hydrazine in thf–
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Fig. 2 Crystal structure of one of the two very similar molecules
of [MoH(SC6H2Pri3-2,4,6)3(NH3)(PMePh2)] 2 and the core of that
molecule; in this and later figures, the orientation of the core diagram
is the same. The two S atoms subtending the largest angle at the Mo
atom are horizontal and the P and N atoms are in a plane parallel to
that of the paper
Fig. 3 Crystal structure of [MoH(SC6H2Pri3-2,4,6)3(C5H5N)(PMe-
Ph2)] and its core, taken from ref. 7
We were unable to isolate any other molybdenum complex
from these reactions, even when all manipulations were carried
out at 0 ЊC.
an NH2 or an NH group. None of the hydrogen atoms of either
NH3 ligand appears to be involved in any hydrogen bonds;
these ligands are effectively screened from intermolecular inter-
actions by the bulky thiolate ligands.
Preparation and structure of [MoH(SC6H2Pri3-2,4,6)3-
(NH2NHPh)(PMePh2)] 3
The hydride ligand could not be located but is clearly present
as noted above. In this respect the structure of 2 is in fact very
similar to the distorted trigonal pyramidal structure of
[MoH(SC6H2Pri3-2,4,6)3(C5H5N)(PMePh2)],7 which is repro-
duced in Fig. 3 for ease of reference. In this structure the hydride
ligand is considered to occupy a position roughly in the equa-
torial plane between the S(2) and S(2Ј) atoms (see Fig. 3)
since the angle subtended at Mo by these atoms is considerably
larger than the other S᎐Mo᎐S angles and is sufficiently large
to accommodate the hydride, which will also probably lie off the
trigonal plane towards the phosphorus.7,9,12 The corresponding
angles in the structure of 2 are S(1)᎐Mo᎐S(3) [131.7(2)Њ] and
S(4)᎐Mo(2)᎐S(6) [131.1(2)Њ], and we therefore suggest that the
hydrides in 2 are located on the pseudo-mirror planes and some-
where in the faces defined by P(1)S(1)S(3) and P(2)S(4)S(6). This
is the hydride position found in the low-temperature crystal
structure of the analogue [WH(SeC6H2Pri2-2,4,6)3(PMe2Ph)2].13
The Mo᎐S distances and Mo᎐S᎐C angles are in the ranges usu-
ally observed for thiolate complexes of this type.7
Compound 1 reacts with NH2NHPh in thf–MeOH at room
temperature to produce grass green crystals of [MoH(SC6H2-
Pri3-2,4,6)3(NH2NHPh)(PMePh2)] 3 which are diamagnetic
and stable at room temperature for many weeks in the absence
of air. The NH2NHPh ligand gives rise to NH stretching
absorptions at 3200–3400 cmϪ1 and NH2 bending absorptions
at 1560–1640 cmϪ1. The weak Mo᎐H absorption is at 1900 cmϪ1
and the hydride resonance is a doublet at δ 2.6 with the same
coupling as is observed in the proton-coupled 31P doublet
resonance at δ Ϫ86.5 [2J(PMoH) = 84.7 Hz].
The molecular structure of 3 is shown in Fig. 4 and selected
bond dimensions are in Table 3. As for complex 2, complex 3
has the three sulfur atoms of the thiolate ligands in the ‘two-up-
one-down’ configuration in the equatorial plane with the
NH2NHPh and PMePh2 ligands in the apical sites. The hydride
ligand was not conclusively located, but using the arguments
developed for complex 2, since the S(1)᎐Mo᎐S(2) angle (129.3Њ)
is the largest in the equatorial plane, one would expect to find
the hydride on the plane which bisects the S(1)᎐S(2) vector and
J. Chem. Soc., Dalton Trans., 1997, Pages 4747–4752
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Table 3 Selected molecular dimensions in [MoH(SC6H2Pri3-2,4,6)3-
(NH2NHPh)(PMePh2)] 3. Bond lengths in Å, angles in Њ, e.s.d.s in
parentheses
(a) About the Mo atom
Mo᎐S(1)
Mo᎐S(2)
Mo᎐S(3)
2.314(1)
2.327(2)
2.356(1)
Mo᎐P(4)
Mo᎐N(5)
2.426(2)
2.278(5)
S(1)᎐Mo᎐S(2)
S(1)᎐Mo᎐S(3)
S(2)᎐Mo᎐S(3)
S(1)᎐Mo᎐N(5)
S(3)᎐Mo᎐N(5)
129.3*
116.1(1)
114.0(1)
85.6(1)
79.6(1)
S(1)᎐Mo᎐P(4)
S(2)᎐Mo᎐P(4)
S(3)᎐Mo᎐P(4)
S(2)᎐Mo᎐N(5)
P(4)᎐Mo᎐N(5)
83.3*
80.9(1)
117.3*
96.1(1)
162.8(1)
(b) In the thiolate ligands
S(1)᎐C(11)
S(2)᎐C(21)
1.801(5)
1.805(4)
S(3)᎐C(31)
1.795(4)
114.4(2)
Mo᎐S(1)᎐C(11)
Mo᎐S(2)᎐C(21)
118.2(2)
123.6(2)
Mo᎐S(3)᎐C(31)
(c) In the phosphine ligand
P(4)᎐C(41)
P(4)᎐C(421)
1.820(5)
1.810(5)
P(4)᎐C(431)
1.839(6)
Mo᎐P(4)᎐C(41)
Mo᎐P(4)᎐C(421) 119.4(2)
Mo᎐P(4)᎐C(431) 116.8(2)
114.7(3)
C(41)᎐P(4)᎐C(421)
C(41)᎐P(4)᎐C(431)
C(421)᎐P(4)᎐C(431) 101.8(3)
101.7(3)
99.5(3)
(d) In the phenylhydrazine ligand
N(5)᎐N(6)
1.451(7)
N(6)᎐C(61)
1.425(7)
117.4(5)
Mo᎐N(5)᎐N(6)
112.8(4)
N(5)᎐N(6)᎐C(61)
* E.s.d. is less than 0.05Њ.
nevertheless this result indicates that after first binding
NH2NHPh to Mo as in 3 the N᎐N bond has been cleaved. A
similar result has been observed in more extensive work by
Coucouvanis et al.3 who demonstrated the stoichiometric and
catalytic reduction of NH2NHPh to NH3 and NH2Ph in the
presence of [MoFe3S4Cl3(NH2NHPh)]2Ϫ
.
Reaction of [MoH(SC6H2Pri3-2,4,6)3(PMePh2)] 1 with
NMe2NH2
Fig.
4
Crystal structure of [MoH(SC6H2Pri3-2,4,6)3(NH2NHPh)-
(PMePh2)] 3 and its core; two of the isopropyl groups have been omit-
Treatment of compound 1 under the same conditions as for its
reaction with NH2NHPh gave a grass green oily compound 4
which was air- and temperature-sensitive and could not be
obtained as a pure solid. In solution it showed N᎐H absorp-
ted for clarity
on the S(1)P(4)S(2) face. Thus the six-fold co-ordination might
be described as either octahedral or capped trigonal bipyrami-
dal, much distorted in either case.
tions at 3310–3240 cmϪ1 and an Mo᎐H absorption at 1900 cmϪ1
.
Its proton-coupled 31P NMR spectrum showed a doublet δ
Ϫ86.7 with a coupling constant of 85.2 Hz. Since these proper-
ties are so similar to those of 3, we formulate 4 as [MoH-
(SC6H2Pri3-2,4,6)3(NH2NMe2)(PMePh2)].
The hydrazine ligand adopts a trans conformation in the
Mo᎐N᎐N᎐C group [torsion angle 179.0(4)Њ]. The three hydro-
gen atoms on the hydrazine N atoms were all located in differ-
ence maps and refined satisfactorily. These atoms appear to be
screened from any intermolecular interactions by the large
neighbouring thiolate ligands: there are short intramolecular
N ؒ ؒ ؒ S contacts, but not in the right direction for the formation
of good hydrogen bonds. The N(5)᎐N(6) bond distance
[1.451(7) Å] is consistent with an N᎐N single bond (1.424 Å).14
The Mo᎐N(5) bond distance [2.278(5) Å] lies between the
Conclusion
We have shown that catalysis of disproportionation or reduc-
tion of anhydrous hydrazine occurs in the presence of the
electronically and co-ordinatively unsaturated complex [Mo-
H(SC6H2Pri3-2,4,6)3(PMePh2)] 1. Although precise knowl-
edge of the mechanism of these reactions requires detailed
study, isolation of the adducts [MoH(SC6H2Pri3-2,4,6)3-
(NH3)(PMePh2)] and [MoH(SC6H2Pri3-2,4,6)3(NH2NR2)-
(PMePh2)] (NR2 = NHPh or NMe2) indicates that the reduction
process is likely to occur at the single Mo centre of the starting
complex 1. This observation lends support to the suggested
mechanism of reduction of hydrazine3 at the Mo in hetero-
clusters such as [MoFe3S4Cl3(C6Cl4O2)(MeCN)]2Ϫ, and also to
the possibility of such a reduction at the sulfur-ligated Mo site
of nitrogenase.4
Mo᎐N distances in
2 [each 2.298(15) Å] and that in
[MoH(SC6H2Pri3-2,4,6)3(C5H5N)(PMePh2)] [2.244(9) Å].7 The
Mo᎐S distances and Mo᎐S᎐C angles are unexceptional.
During this work we found that if in the preparation of 3 2
equivalents of NH2NHPh were used and the reaction mixture
was layered with MeOH after 5 h, followed by standing the
solution at Ϫ20 ЊC, green crystals of complex 2 were obtained
in low yield (see Experimental section). Although we were
unable to detect NH2Ph from this reaction by GC/MS in
repeated attempts, probably because the yield was very low,
4750
J. Chem. Soc., Dalton Trans., 1997, Pages 4747–4752

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(0.26 g, 0.27 mmol) in thf–MeOH (20 cm3 of 1:1 solution).
Experimental
The resulting dark green solution was stirred at 0 ЊC for 3 h then
at 20 ЊC for 18 h. The grass green solid product was precipitated
by reduction of the volume of solution under vacuum to ≈5 cm3
followed by addition of cold MeOH (15 cm3). Crystallisation of
the product by slow diffusion of hexane into a thf solution at
Ϫ20 ЊC produced dark green single crystals which were suitable
for X-ray crystallography (0.09 g, 31%) (Found: C, 69.0; H, 8.0;
N, 2.8. C64H91MoN2PS3 requires: C, 69.2; H, 8.2; N, 2.5%). IR
(Nujol): ν(N᎐H) 3200–3400 (br), 1560–1640 (br); ν(Mo᎐H)
2,4,6-Triisopropylbenzenethiol15 and [MoH(SC6H2Pri3-2,4,6)3-
(PMePh2)]8 were prepared by published methods. Other reagent
chemicals were used as purchased from Aldrich Chemical Co.
All manipulations were carried out under a dinitrogen
atmosphere using conventional Schlenk tube and syringe or
glove-box techniques unless otherwise stated. Reaction solvents
were dried and freshly distilled under dinitrogen. The NMR
spectra were measured using a JEOL GSX270 spectrometer
and infrared spectra with a Perkin-Elmer 883 spectrometer.
Elemental analyses were carried out by Microanalytical Ser-
vices, University of Surrey, or by Butterworth Analytical
Laboratories, Ltd.
1
2
1900w cmϪ1. NMR (CD2Cl2): H δ 2.6 [d, Mo᎐H, J(HMoP)
84.7], 2.8–2.9 and 3.4–3.5 (spt, CHMe2), 1.6 [d, PCH3Ph,
2J(PH) 57.7 Hz], 7.0–7.2 (m, aromatic); 31P [proton-coupled,
relative to P(OMe)3] δ Ϫ86.5 [d, 2J(PMoH) 84.7 Hz].
Disproportionation and reduction studies
[MoH(SC6H2Pri3-2,4,6)3(NH2NMe2)(PMePh2)] 4. Reaction
of NH2NMe2 with [MoH(SC6H2Pri3-2,4,6)3(PMePh2)] under
the same conditions as used for NH2NHPh gave a very air- and
temperature-sensitive oily compound which could not be puri-
fied but whose analysis showed the presence of nitrogen in
roughly the correct value for the proposed formulation. IR
The method given is general. Full details of individual experi-
ments are given in Table 1, where all data are the average of
three separate determinations.
In experiments without Zn added, degassed anhydrous
hydrazine was added to [MoH(SC6H2Pri3-2,4,6)3(PMePh2)] in
suspension in degassed thf or thf–MeOH (3:1) in a sealed ves-
sel under a vacuum. After a suitable reaction time the vessel was
opened to the vacuum line and the evolved gas quantified with a
Töpler pump and shown to be pure N2 by mass spectrometry.
About one third of the volume of the solution was then distilled
under vacuum into 0.05  H2SO4 (15 cm3), to which was added,
under pure argon, aqueous NaOH (15 cm3, 10% w/v) and the
NH3 thus released was distilled into 0.05  H2SO4 (15 cm3). The
remaining solvent was removed in a vacuum and the resulting
brown, oily solid was treated with aqueous NaOH (15 cm3, 10%
w/v) and the NH3 released distilled into 0.05  H2SO4 (15 cm3).
The ammonium content of the H2SO4 solutions was then
determined by the indophenol test16 and the residual hydrazine
monitored by the aminobenzaldehyde test.17 Nitrogen balance
was >90% in all cases. Blank experiments with hydrazine alone
gave only very low levels of ammonia.
(Nujol): ν(N᎐H) 3240–3310 (br); ν(Mo᎐H) 1900w (br) cmϪ1
.
NMR (CD2Cl2): 31P [proton-coupled, relative to P(OMe)3]
δ Ϫ86.7 [d, 2J(PMoH) 85.2 Hz].
Crystallography
Crystal data for complex 2. C58H86MoNPS3, M = 1020.4, tri-
¯
clinic, space group P1 (no. 2), a = 12.789(3), b = 12.830(4),
c = 36.807(11) Å, α = 87.80(2), β = 81.04(2), γ = 88.17(2)Њ,
U = 5959 Å3, Z = 4, Dc = 1.14 g cmϪ3, F(000) = 2184, µ(Mo-
Kα) = 3.7 cmϪ1, T = 173 K.
A bright green crystal, size 0.2 × 0.2 × 0.1 mm, was mounted
on a glass fibre and coated with paraffin. The crystal was trans-
ferred to an Enraf-Nonius CAD4 diffractometer (with mono-
chromated Mo radiation). Accurate cell dimensions were
determined using 25 reflections with θ between 7 and 10Њ, each
reflection centred in four different orientations of the reflection
In experiments with added zinc and HOC6H3Pri2-2,6, the
protocol of Schrock et al.1 was used: [MoH(SC6H2Pri3-
2,4,6)3(PMePh2)], amalgamated zinc, HOC6H3Pri2-2,6, and thf
were added to a flask sealed under argon with a rubber septum.
After addition of the appropriate ratio of hydrazine via the
septum, the mixture was stirred for 16–18 h, then 0.05  H2SO4
(15 cm3) was injected into the flask and the mixture stirred for
20 min. The solvent was then removed in a vacuum and the
residual oily solid was treated with aqueous NaOH (15 cm3,
10% w/v) and the NH3 released distilled into 0.05  H2SO4 (15
cm3) followed by analysis as above.
plane. For the structure analysis intensities of 8166 unique
2
2
reflections, of which 5136 had F > 2σF , were measured to
θmax = 18Њ. Measurement was curtailed at this point which was
the time limit beyond which the low-temperature system could
not maintain temperature. The crystal system and space group
were determined from the intensity measurements and the
structure was solved using the heavy atom method in the
SHELXS 86 program.18 Lorentz-polarisation and empirical
absorption corrections were applied but a decay correction was
unnecessary. A check was made for any higher symmetry space
group but none was found. The structure contains two very
similar, independent molecules which have some differences
between them, notably in the orientation of the C(41), C(42)
and C(43) isopropyl group and the C(8) to C(13) phenyl group.
Thus they are not related by symmetry.
The refinement was carried out using full-matrix least-
squares methods in the MOLEN program.19 The Mo, S and P
atoms were refined anisotropically, C and N atoms isotropically.
The hydrogen atoms on the C atoms were placed in idealised
positions and their thermal parameters, Uiso, allowed to ride
with the parent atom (Uiso = 1.3 Ueq of C atoms); the hydride H
and H’s on N were not located and so were omitted. The final
refinement resulted in an R factor of 0.081 and RЈ of 0.08819 for
the 5136 ‘observed’ reflections weighted w = σFϪ2. There were
peaks to 0.8 e ÅϪ3 in the final difference map. The final drawing
was done using ORTEP.20
Preparations
[MoH(SC6H2Pri3-2,4,6)3(NH3)(PMePh2)] 2. Anhydrous
hydrazine (0.06 g, 1.9 mmol) was added via a syringe to an ice-
cold, filtered solution of freshly prepared [MoH(SC6H2Pri3-
2,4,6)3(PMePh2)] (1.16 g, 1.12 mmol ) in thf–MeOH (20 cm3 of
1:1 solution). The resulting green-brown solution was stirred
for 30 min at 0 ЊC, filtered from a small amount of yellowish
green powder, then layered with MeOH and left at Ϫ20 ЊC to
produce light green crystals which were suitable for X-ray crys-
tallographic study (0.4 g, 34%) (Found: C, 68.2; H, 8.7; N, 1.4.
C58H86MoNPS3 requires: C, 68.3; H, 8.5; N, 1.4%). IR (Nujol):
ν(N᎐H) 3200–3400 (br); ν(Mo᎐H) 1890w cmϪ1
. NMR
1
(CD2Cl2): H δ 2.6 and 3.8 (spt, CHMe2), 0.99 [d, PCH3Ph,
2J(PH) 57.7 Hz], 7.0–7.2 (m, aromatic); 31P [proton-coupled,
2
relative to P(OMe)3] δ Ϫ86.8 [d, J(PMoH) 86.7 Hz]; 14N (rel-
ative to liquid MeNO2) δ Ϫ72.1 (br s).
Crystal data for complex 3. C64H91MoN2PS3, M = 1111.5, tri-
clinic, space group P1 (no. 2), a = 13.239(2), b = 13.344(1),
c = 18.989(2) Å, α = 80.691(8), β 70.305(9), γ = 86.112(10)Њ,
U = 3116.4(6) Å3, Z = 2, Dc = 1.184 g cmϪ3, F(000) = 1188,
µ(Mo-Kα) = 3.6 cmϪ1, λ(Mo-Kα) = 0.710 69 Å.
¯
[MoH(SC6H2Pri3-2,4,6)3(NH2NHPh)(PMePh2)] 3. Phenyl-
hydrazine (0.05 g, 0.5 mmol) was added by syringe to a filtered
solution of freshly prepared [MoH(SC6H2Pri3-2,4,6)3(PMePh2)]
J. Chem. Soc., Dalton Trans., 1997, Pages 4747–4752
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Crystals were dark green, approximately cubic blocks. One,
≈0.33 × 0.33 × 0.36 mm, was mounted on a glass fibre and
after photographic examination transferred to an Enraf-Nonius
CAD4 diffractometer (with monochromated Mo radiation).
Accurate cell dimensions were determined using 25 reflections,
θ ≈10.5Њ, each reflection centred in four different orientations
of the reflection plane. Diffraction intensities were measured
by the ω–θ scan method to θmax = 22Њ.
References
1 R. R. Schrock, T. E. Glassman, M. G. Vale and M. Kol, J. Am.
Chem. Soc., 1993, 115, 725.
2 K. D. Demadis, S. M. Malinak and D. Coucouvanis, Inorg. Chem.,
1996, 35, 4038 and refs. therein.
3 D. Coucouvanis, P. E. Mosier. K. D. Demadis, S. Patton, S. M.
Malinak, C. G. Kim and M. A. Tyson, J. Am. Chem. Soc., 1993, 115,
12 193.
4 R. L. Richards, Coord. Chem. Rev., 1996, 154, 83 and refs. therein.
5 E. Block, G. Ofori-Okai, H. Kang and J. Zubieta, J. Am. Chem.
Soc., 1992, 114, 758.
6 P. Schollhammer, F. Y. Petillon, S. Poder-Guillou, J. Y. Saillard,
J. Talarmin and K. W. Muir, Chem. Commun., 1996, 2633.
7 D. L. Hughes, N. J. Lazarowych, M. J. Maguire, R. H. Morris and
R. L. Richards, J. Chem. Soc., Dalton Trans., 1995, 5.
8 T. E. Burrow, D. L. Hughes, A. J. Lough, M. J. Maguire, R. H.
Morris and R. L. Richards, J. Chem. Soc., Dalton Trans., 1995,
1315.
9 T. E. Burrow, A. Hills, D. L. Hughes, J. D. Lane, N. J. Lazarowych,
M. J. Maguire, R. H. Morris and R. L. Richards, J. Chem. Soc.,
Dalton Trans., 1991, 2519.
10 R. N. F. Thorneley, R. R. Eady and D. J. Lowe, Nature (London),
1978, 272, 557.
11 J. R. Dilworth, J. Hu, R. Thompson and D. L. Hughes, J. Chem.
Soc., Chem. Commun., 1992, 551.
12 T. E. Burrow, A. J. Lough, R. H. Morris and R. L. Richards, Can. J.
Chem., 1995, 73, 1092.
13 T. E. Burrow, A. J. Lough, R. H. Morris and R. L. Richards, Inorg.
Chim. Acta, 1997, 259, 125.
14 International Tables for X-Ray Crystallography, Kynoch Press,
Birmingham, 1974, vol. IV, pp. 99 and 149.
15 P. J. Blower, J. R. Dilworth, J. P. Hutchinson and J. A. Zubieta,
J. Chem. Soc., Dalton Trans., 1985, 1533.
16 A. L. Chaney and E. P. Marbach, Clin. Chem., 1962, 8, 130.
17 G. W. Watt and J. D. Chrisp, Anal. Chem., 1952, 24, 2006.
18 G. M. Sheldrick, Acta Crystallogr., Sect. A, 1990, 46, 467.
19 C. K. Fair, MOLEN, Structure Determination System, Enraf-
Nonius, Delft, 1990.
20 C. K. Johnson, ORTEP II, Report ORNL-5138, Oak Ridge
National Laboratory, Oak Ridge, TN, 1976.
21 G. M. Sheldrick, SHELX, Program for crystal structure determin-
ation, University of Cambridge, 1976; also SHELXN, an extended
version, 1977.
22 S. N. Anderson, R. L. Richards and D. L. Hughes, J. Chem. Soc.,
Dalton Trans., 1986, 245.
During processing, corrections were applied for Lorentz-
polarisation effects and crystal deterioration (three reflections
monitored throughout the data collection showed intensities
which fell steadily and uniformly to ≈56.6% of their starting
values). The intensities were corrected for absorption (by
semiempirical ψ-scan techniques) and to eliminate negative
net intensities (by Bayesian statistical methods). 7608 Unique
reflections, of which 5103 were ‘observed’ having I > 2σI, were
then entered into the SHELX21 program system and the struc-
ture was solved using the heavy-atom method and refined using
full-matrix least-squares methods. The hydrogen atoms on the
C atoms were placed in idealised positions and their thermal
parameters allowed to ride on those of the parent C atoms.
The hydrogen atoms on N were located in a difference map
and were refined with geometric constraints; the isotropic
thermal parameters of all the hydrogen atoms were refined
freely. The hydride ligand was not conclusively located and was
not included in the refinement process. All non-hydrogen atoms
were allowed anisotropic thermal parameters. The final refine-
ment resulted in an R factor of 0.082 and Rg of 0.06021 for all
reflections weighted w = (σF2 ϩ 0.000 38F2)Ϫ1; for the 5103
unobserved data only, R and Rg were 0.049 and 0.050 respect-
ively. There were only two significant peaks in the final differ-
ence map at ≈0.72 (close to the Mo atom) and ≈0.59 e ÅϪ3
(close to the phenyl ring).
Scattering factor curves for neutral atoms were from ref. 14.
Computer programs used in this analysis have been noted above
and in Table 4 of ref. 22 and were run on the MicroVAX 3600
instrument in the NFL.
CCDC reference number 186/777.
Acknowledgements
We thank the Ministry of Culture and Higher Education of the
Islamic Republic of Iran for a maintenance grant to K. M. and
the BBSRC for support of this work.
Received 12th August 1997; Paper 7/05886A
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J. Chem. Soc., Dalton Trans., 1997, Pages 4747–4752