Mixed dinitrogen-organocyanamide complexes of molybdenum(0) and their protic conversion into hydrazide and amidoazavinylidene derivatives

Article abstract of DOI:10.1021/ic026176e

Organocyanamides, N≡CNR₂ (R = Me or Et), react with trans-[Mo(N₂)₂(dppe)₂] (1, dppe = Ph₂PCH₂CH₂PPh₂), in THF, to give the first mixed molybdenum dinitrogen-cyanamide complexes trans-[Mo(N₂)(NCNR₂)(dppe)₂] (R = Me 2a or Et 2b) which are selectively protonated at N₂ by HBF₄ to yield the hydrazide(2-) complexes trans-[Mo(NNH₂)(NCNR₂)(dppe)₂] [BF₄]₂ (R = Me, 3a, or Et, 3b). On treatment with Ag[BF₄], oxidation and metal fluorination occur, and the ligating cyanamide undergoes an unprecedented β-protonation at the unsaturated C atom to form trans-[MoF(NCHNR₂)(dppe)₂][BF₄]₂ (R = Me, 4a, or Et, 4b) compounds which present the novel amidoazavinylidene (or amidomethyleneamide) ligands. Complexes 4 are also formed from the corresponding compounds 3, with liberation of ammonia and hydrazine. The crystal structure of 2b was determined by single-crystal X-ray diffraction analysis which indicates that the N atom of the amide group has a trigonal planar geometry.

Full text of DOI:10.1021/ic026176e

Inorg. Chem. 2003, 42, 2157−2164
Mixed Dinitrogen−Organocyanamide Complexes of Molybdenum(0) and
Their Protic Conversion into Hydrazide and Amidoazavinylidene
Derivatives
So´nia M. P. R. M. Cunha, M. Fa´tima C. Guedes da Silva, and Armando J. L. Pombeiro*
Centro de Qu´ımica Estrutural, Complexo I, Instituto Superior Te´cnico, AV. RoVisco Pais,
1049-001 Lisboa, Portugal
Received November 14, 2002
Organocyanamides, NtCNR (R ) Me or Et), react with trans-[Mo(N ) (dppe)2] (1, dppe ) Ph2PCH CH PPh2),
2
2 2
2
2
in THF, to give the first mixed molybdenum dinitrogen−cyanamide complexes trans-[Mo(N )(NCNR )(dppe)2] (R)
2
2
Me 2a or Et 2b) which are selectively protonated at N by HBF to yield the hydrazide(2−) complexes trans-
2
4
[Mo(NNH )(NCNR )(dppe)2][BF ] (R ) Me, 3a, or Et, 3b). On treatment with Ag[BF ], oxidation and metal fluorination
2
2
4 2
4
occur, and the ligating cyanamide undergoes an unprecedented â-protonation at the unsaturated C atom to form
trans-[MoF(NCHNR )(dppe)2][BF ] (R ) Me, 4a, or Et, 4b) compounds which present the novel amidoazavinylidene
2
4 2
(or amidomethyleneamide) ligands. Complexes 4 are also formed from the corresponding compounds 3, with liberation
of ammonia and hydrazine. The crystal structure of 2b was determined by single-crystal X-ray diffraction analysis
which indicates that the N atom of the amide group has a trigonal planar geometry.
Introduction
with a metal-metal triple bond,14 nucleophilic addition of
an oxime15 or of an alcohol (in this case to cyanoguanidine)16
to form a five- or six-membered azametallacycle, respec-
tively, and dehydrogenation of NCNH2 followed by elec-
trophilic addition17,18 or deprotonation or deamination (of
cyanoguanidine)19 are the most significant reactions reported
so far.
In this study, we have searched for an unprecedented type
of cyanamide reactivity by ligation to an electron-rich
transition metal center, trans-{Mo(dppe)2} (dppe ) Ph2PCH2-
CH2PPh2), which is able20,21 to ligate dinitrogen and activate
Cyanamides, NtCNR2 (R ) H, alkyl or aryl), can be
regarded as amino-functionalized nitriles, but despite the well
developed coordination chemistry of organonitriles1,2 and of
the biological and synthetic interest of such species [in
particular cyanamide itself, NtCNH2, and its dimeric form,
cyanoguanidine, NCNC(NH2)2],3-8 only scarce examples of
reactions of cyanamide ligands have been reported, and the
study of their activation by coordination to a transition metal
center still remains virtually unexplored, as well as the effect
of the amino moiety on the reactivity of the cyano group.
Insertion into a metal-carbon multiple bond,9-13 metathesis
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Complexes; Kreissl, F. R., Ed.; NATO ASI Series; Kluwer Academic
Publishers: Dordrecht, The Netherlands, 1993; p 79.
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Frau´sto da Silva, J. J. R.; Pombeiro, A. J. L.; Michelin, R. A.; Belluco,
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* To whom correspondence should be addressed. E-mail:
pombeiro@ist.utl.pt.
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10.1021/ic026176e CCC: $25.00 © 2003 American Chemical Society
Published on Web 02/19/2003
Inorganic Chemistry, Vol. 42, No. 6, 2003 2157

Cunha et al.
Scheme 1. Formation of the Mixed Dinitrogen-Cyanamide Complexes and Derived Hydrazide(2-) and Amidoazavinylidene Compounds
it toward electrophilic attack. For this purpose, we have
prepared the first mixed cyanamide-dinitrogen complexes
of molybdenum, trans-[Mo(N2)(NCNR2)(dppe)2] (R ) Me,
2a, or Et, 2b), and studied their protic reactions, what has
also allowed a comparison between the behaviors of the
cyanamide and dinitrogen (as well as of nitrile) ligands
activated by a common metal center. In particular, the first
electrophilic addition has been achieved to the cyano group
of a cyanamide ligand which, however, behaves as a weaker
base than dinitrogen and an organonitrile. The electrophilic
addition reaction (which has previously been observed for
nitriles,22-29 isocyanides,30-41 cyanide,32,34,41-46 alkyne-
derived species,38-41,47-53 or phosphaalkynes47,54,55 when
ligating the above or a related N2-binding phosphinic
transition metal center) has thus been extended for the first
time to cyanamide ligands.
Results and Discussion
Mixed Dinitrogen-Organocyanamide Complexes. Treat-
ment of a THF solution of the dinitrogen complex trans-
[Mo(N2)2(dppe)2] (1, dppe ) Ph2PCH2CH2PPh2), at room
temperature, with an excess (10-fold molar ratio) of the
appropriate organocyanamide, NtCNR2 (R ) Me or Et),
leads to the formation [reaction i, Scheme 1] of the
corresponding monocyanamide complexes trans-[Mo(N2)-
(NCNR2)(dppe)2] (R ) Me, 2a, or Et, 2b) which have been
isolated, after ca. 3 h, in high yield (ca. 80-85%), as a brick
(2a) or dark red (2b) solid. These complexes represent the
first mixed dinitrogen-cyanamide complexes of molybde-
num and relate to the dinitrogen-organonitrile compounds
trans-[Mo(N2)(NCR)(dppe)2] (R ) alkyl or aryl) prepared
by Hidai et al.56 by an identical route. The mixed rhenium
mer-[ReCl(N2)(NCNR2)(PMePh2)3] complexes have already
been prepared,57 but their reactions have not yet been
reported.
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Complexes 2 have strong IR bands assigned to ν(NtN)
at ca. 1900 cm-1 and to ν(NtC) at ca. 2190 cm-1. The
former value is slightly lower than that, 1975 cm-1, displayed
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2158 Inorganic Chemistry, Vol. 42, No. 6, 2003

Mo(0) Dinitrogen-Organocyanamide Complexes
dinitrogen and cyanamide ligands which present linear
coordinations.
The Mo-N bond length for the N2 ligand, 1.994(4) Å, is
comparable with that, 2.014(5) Å,58 of the bis(dinitrogen)
complex trans-[Mo(N2)2(dppe)2], 1, but marginally shorter
than those for the mixed carbonyl complexes trans-
[Mo(N2)(CO)(dppe)2], 2.068(12) Å,59 and trans-[Mo(N2)-
(CO){(PhCH2)2CH2CH2P(CH2Ph)2}2], 2.090(3) Å,60 in ac-
cord with the strong competition of CO for the metal dπ
electron density. The Mo-N distance for the NCNEt2 li-
gand, 2.151(4) Å, is identical to that, 2.168(6) Å,61 in
t
[Mo2(OCH2 Bu)6(µ-C4Me4)(NCNEt2)]. The NtN and NtC
bond lengths, 1.084(8) and 1.142(8) Å, respectively, are
similar to those of the free ligands [1.0976(1) Å62 for N2
and 1.1609(16) Å63a for the related dimethylcyanamide,
NCNMe2].
The N atom of the amide group, N(4), has a trigonal planar
geometry [the N(4), C(27), C(29), C(31) and N(3) atoms
are coplanar] rather than a pyramidal one, indicating a
significant contribution of the canonical form (a).
Figure 1. Molecular structure of the complex trans-[Mo(N2)(NCNEt)2-
(dppe)2], 2b, with ellipsoids at the 30% probability level.
Table 1. Selected Bond Distances (Å) and Angles (deg) for the
Complex trans-[Mo(N2)(NCNEt2)(dppe)2], 2ba
Mo-N(1)
1.994(4)
2.151(4)
N(3)-Mo-P(1)
N(3)-Mo-P(2)
N(3)-Mo-P(3)
N(3)-Mo-P(4)
P(1)-Mo-P(2)
84.04(12)
85.53(12)
102.19(12)
90.34(12)
80.85(5)
96.63(5)
80.07(5)
102.98(5)
173.14(5)
174.07(5)
177.4(5)
173.1(5)
178.0(7)
122.1(7)
112.4(10)
122.2(7)
114.1(10)
115.8(8)
Mo-N(3)
Mo-P(1)
2.4479(14)
2.4361(15)
2.4393(14)
2.4601(16)
1.084(8)
Mo-P(2)
The trigonal planar geometry has also been reported for
other complexes such as [Cr(NCNEt2)(CO)5],64 trans-
[Fe(NCNEt2)2(depe)2][BF4]2 (depe ) Et2PCH2CH2PEt2),65
trans-[Pt(CF3)(NCNEt2)(PPh3)2][BF4],66 or cis-[Pt(NCNEt2)2-
(PPh3)2][BF4]2,15 whereas the pyramidal one is displayed by
mer-[ReCl2(NCNEt2)(PMePh2)3]67 and by the uncoordinated
NCNMe2.63
Mo-P(3)
Mo-P(4)
P(2)-Mo-P(3)
N(1)-N(2)
P(3)-Mo-P(4)
N(3)-C(31)
C(31)-N(4)
N(4)-C(27)
C(27)-C(28)
N(4)-C(29)
C(29)-C(30)
N(1)-Mo-N(3)
N(1)-Mo-P(1)
N(1)-Mo-P(2)
N(1)-Mo-P(3)
N(1)-Mo-P(4)
1.142(8)
1.334(9)
P(1)-Mo-P(4)
P(1)-Mo-P(3)
1.423(14)
1.418(18)
1.419(14)
1.396(18)
173.37(18)
89.99(13)
96.39(13)
83.93(13)
88.18(13)
P(2)-Mo-P(4)
Mo-N(1)-N(2)
Mo-N(3)-C(31)
N(3)-C(31)-N(4)
C(31)-N(4)-C(27)
N(4)-C(27)-C(28)
C(31)-N(4)-C(29)
N(4)-C(29)-C(30)
C(27)-N(4)-C(29)
Hydrazide(2-) and Amidoazavinylidene Complexes.
Treatment of a THF solution of the mixed dinitrogen-
cyanamide complexes trans-[Mo(N2)(NCNR2)(dppe)2] (R )
Me 2a or Et 2b), at low temperature (-60 °C), with HBF4
(a diluted diethyl ether solution [Et2OH][BF4] added drop-
wise, ca. 4.5 molar ratio of acid relative to the complex),
a esd’s in parentheses.
by the parent bis(dinitrogen) complex 1, and the latter,
ν(NtC), is shifted to a lower wavenumber (by ca. 25 cm-1)
in comparison with that exhibited by the free organocyan-
amide, as a result of the strong π-electron releasing ability
of the electron-rich Mo(0) site. Complexes 2 are unstable in
air and also commonly undergo significant decomposition
in solution, even under N2, which precludes a reliablecol-
lection of NMR data in the usual deuterated solvents. In
agreement with the lability of the N2 ligand, their FAB+-
MS spectra, run in nitrobenzyl alcohol matrixes, do not show
the corresponding molecular ions ([M+]), although the
fragments derived from loss of N2, i.e., [M - N2]+, are
clearly observed at m/z 964 (2a) or 992 (2b).
(58) Uchida, T.; Uchida, Y.; Hidai, M.; Kodama, T. Acta Crystallogr., Sect.
B 1975, 31, 1197.
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Y. J. Am. Chem. Soc. 1978, 100, 4447.
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33, 5219.
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Organometallics 1986, 5, 602. (b) Chisholm, M. H.; Huffman, J. C.;
Marchant, N. S. Polyhedron 1988, 7, 919.
(62) Stoicheff, B. P. Can. J. Phys. 1954, 82, 630.
(63) (a) Khaikin, L. S.; Vilkov, L. V.; Andrutskaya, L. G.; Zenkin, A. A.
J. Mol. Struct. 1975, 29, 171. (b) Li, Y. S.; Durig, J. R. J. Mol. Struct.
1973, 16, 433.
(64) (a) Ohnet, M.-N.; Spasojevic´-de Bire´, A.; Dao, N. Q.; Schweiss, P.;
Braden, M.; Fischer, H.; Reindl, D. J. Chem. Soc., Dalton Trans. 1995,
665. (b) Fischer, E. O.; Kleine, W.; Schubert, U.; Neugebauer, D. J.
Organomet. Chem. 1978, 149, C40.
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Henderson, R. A.; Evans, D. J.; Benetollo, F.; Bombieri, G.; Michelin,
R. A. Inorg. Chim. Acta 1999, 291, 39.
(66) Guedes da Silva, M. F. C.; Branco, E. M. P. R. P.; Wang, Y.; Frau´sto
da Silva, J. J R.; Pombeiro, A. J. L.; Bertani, R.; Michelin, R. A.;
Mozzon, M.; Benetollo, F.; Bombieri, G. J. Organomet. Chem. 1995,
490, 89.
Their formulation was authenticated by a single-crystal
X-ray diffraction analysis of diethylcyanamide complex 2b
whose molecular structure is depicted in Figure 1, and
selected bond lengths and angles are listed in Table 1. The
Mo atom exhibits octahedral-type coordination, with the four
P atoms in the equatorial positions, whereas the apical
positions are occupied by the terminal N atoms of the trans
(67) Costa, M. T. A. R. S.; Frau´sto da Silva, J. J R.; Pombeiro, A. J. L.;
Michelin, R. A.; Bombieri, G.; Benetollo, F. Inorg. Chim. Acta 1998,
280, 308.
Inorganic Chemistry, Vol. 42, No. 6, 2003 2159

Cunha et al.
resulted [reaction ii, Scheme 1] in the formation of a pale
green precipitate of the corresponding hydrazide(2-) prod-
ucts trans-[Mo(NNH2)(NCNR2)(dppe)2][BF4]2 (R ) Me, 3a,
or Et, 3b), which were isolated in good yield (ca. 62-66%).
significant lability, being readily displaced by fluoride, at
least in FAB conditions. Interestingly, this behavior is
consistent with that observed in solution (see in a following
paragraph).
The reaction is related to the known68 protonation at one
of the N2 ligands in trans-[M(N2)2(dppe)2] (M ) Mo or W)
to give, on loss of the other N2 and metal fluorination, the
hydrazide(2-) products [MF(NNH2)(dppe)2][BF4], but in the
case of complexes 2, the stronger coordination ability of the
organocyanamide, in comparison with dinitrogen, allows its
retention in the metal coordination sphere. To the best of
our knowledge, there are only two more examples in the
literature of isolated hydrazide(2-) complexes which result
from protonation of coordinated N2 to NNH2(2-) occurring
without loss of a ligand: trans-[M(NNH2)(NCnPr)(dppe)2]-
[HSO4]2 (M ) Mo or W)69a and fac-[Mo(NNH2){PhP-
(CH2CH2PPh2)2}(Me2PCH2PMe2)][CF3SO3]2.69b In the present
case, the protonation of N2 at complexes 2 to yield
NNH2(2-) in 3 with resulting metal oxidation leads to a
significant increase (by ca. 40 cm-1) of the IR ν(NtC) of
the organocyanamide ligand [2231 (3a) or 2225 (3b) cm-1]
which becomes even higher (by ca. 15 cm-1) than the value
of the corresponding free species. This indicates that, in
contrast to complexes 2 of Mo(0), in the Mo(IV) complexes
3 the organocyanamide ligand behaves as a predominant
σ-donor and not as an effective π-acceptor.
The formation of complexes 3 involves â-protonation at
the N2 ligand in the mixed dinitrogen-organocyanamide
parent complexes 2. Hence, the commonly inert N2 ligand
is more susceptible to protonation than the organocyanamide
co-ligand in compounds 2, and the proton addition occurs
selectively at the former. Although a similar reaction was
reported69a between trans-[M(N2)(NCnPr)(dppe)2] (M ) Mo
or W) and H2SO4 to give [M(NNH2)(NCnPr)(dppe)2][HSO4]2,
these behaviors contrast sharply with those observed28,29 for
the reactions of HBF4, HCl, or HBr with the series trans-
[M(N2)(NCR)(dppe)2] (HBF4: M ) Mo, R ) Ph, C6H4Me-
p, C6H4OMe-p, Me;28 M ) W, R ) Me.29 HCl: M ) Mo
or W, R ) Ph, C6H4Me-p, C6H4OMe-p, Me.28 HBr: M )
Mo, R ) Ph, C6H4Me-p, C6H4OMe-p, Me28) in which the
organonitrile undergoes double protonation at the cyano-
carbon, with formation, on N2 loss, of the imido-complexes
trans-[MX(NCH2R)(dppe)2]+ (X ) F, Cl, or Br). Therefore,
although such protonations appear to depend on the nature
of the acid, the reactions with HBF4 suggest that those ligands
can be ordered as follows according to their Bro¨nsted
basicity: NCR > N2 > NCNR2. The ligating organocyan-
amides appear to behave as the weakest bases despite the
strong overall (resonance/inductive) electron-donor character
of the NR2 group. Although this character could enhance
the nucleophilicity of the adjacent cyano-group, the effect
appears to be transmitted to the metal (see above form a),
thus promoting its π-electron release to the N2 ligand which
is in trans position to the cyanamide.
In complexes 3, the hydrazide(2-) ligand is clearly
detected by its strong IR band at 1618 cm-1 due to δ(NH2),
and the ν(NH2) medium intensity bands in the 3418-3237
cm-1 range. Particularly, the presence of the bending mode
is consistent with both hydrogen atoms attached to the same
1
nitrogen atom. In their H NMR spectra (CD2Cl2), broad
Nevertheless, the organocyanamide in complexes 2 is also
activated toward protonation and treatment of a THF solution
of 2a or 2b, at low temperature (-80 °C), with Ag[BF4],
followed by diethyl ether addition, affords [reaction iii,
Scheme 1] trans-[MoF(NCHNR2)(dppe)2][BF4]2 (R ) Me
4a or Et 4b) which were isolated in a considerable yield
(ca. 65%) as a greenish yellow (4a) or dark yellow (4b) solid.
To the best of our knowledge, these products present the
previously unknown amidoazavinylidene (or amidomethylene-
amide) ligand NdCHNR2 (R ) Me or Et) formally derived
from protonation at the cyano-C atom of the organocyan-
amide, an unprecedented reaction of this species which, thus,
is shown to be susceptible to protonation similarly to an
organonitrile (NCR) when activated by the electron-rich
metal center in the described28,29 trans-[M(N2)(NCR)(dppe)2]
(M ) Mo or W) complexes. This type of reaction was first
reported22-24 for trans- or cis-[ReCl(NCR)(dppe)2] which,
on reaction with HBF4, generate the azavinylidene (or meth-
yleneamide) complexes trans- or cis-[ReCl(NCHR)(dppe)2]-
[BF4], and parallels the behavior observed for other unsat-
urated species, such as isocyanides,30-41 vinylidenes,49 or
phenylallene,48,52,53 ligating the {ReCl(dppe)2} or {M(dppe)2}
(M ) Mo or W) metal sites.
resonances at δ 7.00 (3a) or 6.83 (3b), which disappear upon
deuteriation, are assigned to NNH2. In fact, these shifts
support the hydrazide formulation, NNH2, rather than the
diazene one, NHNH, for which the NH protons resonance
should occur as two distinct multiplets at significantly lower
fields;70 furthermore, ready H/D exchange upon addition of
D2O is a common feature for several hydrazide(2-)
complexes.68a The expected 1H and 13C NMR resonances of
the organocyanamides have also been unambiguously identi-
fied, and, e.g., for 3a, the methyl-protons resonance occurs
as a singlet at δ 2.02 whereas the cyano-carbon resonance
is a singlet at δ 130.02 (or 129.72 for 3b).
In the FAB+-MS spectra of complexes 3, the molecular
ions ([M+]) are not detected, but the fragments derived from
NNH2 loss [M - NNH2]+ [m/z 964 (3a) or 992 (3b)] and
metal fluorination [M - NNH2 + F]+ [m/z 983 (3a) or 1011
(3b)] are clearly observed with the expected isotopic patterns.
These observations suggest that the NNH2 ligand exhibits a
(68) (a) Chatt, J.; Pearman, A. J.; Richards, R. L. J. Chem. Soc., Dalton
Trans. 1976, 1520. (b) Hidai, M.; Kodama, T.; Sato, M.; Harakawa,
M.; Uchida, Y. Inorg. Chem. 1976, 15, 2694.
(69) (a) Chatt, J.; Leigh, G. J.; Neukomm, H.; Pickett, C. J.; Stanley, D.
R. J. Chem. Soc., Dalton Trans. 1980, 121. (b) George, T. A.; Ma,
L.; Shailh, S. N.; Tisdale, R. C.; Zubieta, J. Inorg. Chem. 1990, 29,
4789.
The formation of complexes 4a or 4b by reaction of the
Mo(0) complexes 2a or 2b with Ag[BF4] involves metal
oxidation by Ag+, with resulting loss of the labile N2 ligand,
(70) Smith, M. R., III; Cheng, T.-Y.; Hillhouse, G. L. J. Am. Chem. Soc.
1993, 115, 8638.
2160 Inorganic Chemistry, Vol. 42, No. 6, 2003

Mo(0) Dinitrogen-Organocyanamide Complexes
nucleophilic attack by [BF4]- at the metal leading to
fluorination, and protonation of the ligating NCNR2 which
occurs even without the deliberate addition of an acid. Traces
of moisture in the solvents used and/or in the hygroscopic
silver salt conceivably constitute the proton source, although
a radical process (involving the THF solvent as the hydrogen
source) cannot be ruled out. Preliminary cyclic voltammetric
experiments, at low temperature, in dried [NBu4][BF4]/THF
show that complexes 4a or 4b are only formed upon
oxidation of the corresponding 2a or 2b parent complexes.
The protonation occurs selectively at the ligated cyano-group
rather than at the amide part of the NCNR2 ligand, being
consistent with the relevance of the activating role of the
metal on the former group and also with the shown VB form
(a) with a positive charge localized at the amide N atom.
Complexes 4 are also formed by slow spontaneous
decomposition in CHCl3 or CH2Cl2 solution of the corre-
sponding hydrazide(2-) compounds trans-[Mo(NNH2)-
(NCNR2)(dppe)2][BF4]2, 3a or 3b, with formal loss of N2H2
and addition of “HF” [reaction iv, Scheme 1], thus somehow
paralleling the behavior of the latter complexes in FAB+-
MS conditions (see previous description). This conversion
was monitored by 1H and 31P-{1H} NMR in CDCl3 and also
accounts for the isolation (in greater amounts for extended
reaction times) of 4a and 4b from the mother liquor in the
synthesis of 3a or 3b by reaction of HBF4 with trans-
[Mo(N2)(NCNR2)(dppe)2], 2a or 2b. The 3 f 4 conversion
also leads to the formation of ammonia and hydrazine (molar
yields of ca. 8.5 and 2.5%, respectively, relative to the metal
or to NNH2), the formation of ammonia being highly
promoted (above 40% yield) by the addition of a catalytic
amount of HBF4 (0.10 HBF4/complex molar ratio).
Reaction iv (Scheme 1) can alternatively be viewed as
formally involving an intramolecular prototropic shift from
the ligating NNH2(2-) to the cyanamide ligand, followed
by displacement of the resulting diazenide (NNH-) by
fluoride. However, the driving forces are not clearly envis-
aged for these processes which, moreover, do not appear to
have a precedent, although a proton transfer between â-
ketonitrile species has been reported27,28 for the {Mo(dppe)2}
metal center, on treatment of trans-[Mo(N2)2(dppe)2], 1, with
an excess of NtCCH2COR to afford the (alkyleneamido)-
(nitrile-enolato) complexes trans-[Mo(NCHCH2COR)-
(NCCHCOR)(dppe)2] which further convert into nitride
products. Hence, the mode of conversion of the NNH2 ligand
in complexes 3 into N2H4 and NH3 could not be elucidated.
Decomposition reactions of hydrazide(2-) ligands have
been reported only scantly and are not yet well understood.
They are dependent on a variety of factors and can lead
namely to hydride ligands (with N2 loss)69b or, in an acid
catalyzed process, to bridging hydrazide(3-), (N-NH)3-,
or bridging hydrazide(4-), (N-N)4-, ligands.71
as a hybrid of the canonical forms (b) and (c), corresponding
to formal 3- or 5-electron donors (the latter with an imido
character) and conferring the 16- or 18-electron configuration
to the metal center, respectively.
The methylene-carbon NCHNR2 resonance, in the 13C-
{1H} NMR spectra, is a singlet at δ 162.54 (4a) or 162.32
(4b), which splits in the expected doublet (JCH ≈ 200 Hz)
in the 1H-undecoupled spectra and falls within the chemical
shift range, δ 157-169, known72 for the amidinium species
[H(R1)NC(R2)dNR3(R4)]+. The other carbon nuclei of the
NCHNR2 ligands resonate as expected, e.g., for 4a as two
singlets, in the 13C-{1H} NMR spectra, at δ 44.27 and 37.64,
which, in the 1H-undecoupled spectra, split into quartets (JCH
≈ 145 Hz). The nonequivalency of the two R groups (also
1
observed in the H NMR spectra, as well as for 4b) in the
NCHNR2 ligand indicate some restricted rotation of the
amide group around the CsNR2 bond, suggesting a signifi-
cant contribution of the VB form (c) with a CdNR2 double
bond character. Formamidinium ions, [H(R1)NCHdNR2(R3)]+,
also exhibit a restricted rotation around the CdN bond.72
In the 1H NMR spectra, although the NCHNR2 resonance
1
was not clearly identified, H-13C HETCOR experiments
allowed its unambiguous identification at δ 7.29 (4a) or 7.37
(4b), i.e., comparable with those commonly observed72 for
the formyl CHdN proton resonance of formamidinium ions
(δ 7.43-8.43) or of formamidines R1NdCHNR2(R3) (δ
7.13-7.61).
IR data also corroborate the shown conjugated representa-
tion of the amidoazavinylidene ligands. In fact, the very
strong band (KBr pellet) at 1616 (4a) or 1586 (4b) cm-1
falls in the commonly observed range (1658-1582 cm-1)72
for ν(NdC) of conjugated amidines, whereas no band that
could be assigned to this stretching mode was exhibited by
other phosphinic compounds22,27,73 with nonconjugated aza-
vinylidene ligands, NCHR (R ) alkyl or aryl). In addition,
the medium/strong bands at 1330 (4a) or 1319 (4b) cm-1
can tentatively be assigned to ν(MoN) since these wave-
numbers are close to those known (1300-1100 cm-1)74 for
metal-imide vibrations.
The presence of the fluoride ligand in complexes 4 was
proved by the typical doublet (2JPF ≈ 38 Hz) resonance (δ
ca. -104) shown by the 31P-{1H} NMR spectra and the
quintet resonance, with an identical coupling constant, in the
19F NMR spectra, observed at δ -38.81 (4a) or -37.20 (4b).
The molecular ions for both complexes were detected in their
FAB+-MS spectra [m/z ) 984 (4a) or 1012 (4b)].
In complexes 4a and 4b, the amidoazavinylidene ligands
1
have been clearly identified by 13C and H NMR and IR
(72) Ha¨felinger, G. In The Chemistry of Amidines and Imidates; Patai, S.,
Ed.; John Wiley: London, U.K., 1975; Chapter 1.
(73) Barron, A. B.; Salt, J. E.; Wilkinson, G.; Motevalli, M.; Hursthouse,
M. B. J. Chem. Soc., Dalton Trans. 1987, 2947.
spectroscopies and can be represented, in a VB formalism,
(71) Glassman, T. E.; Vale, M. G.; Schrock, R. R. J. Am. Chem. Soc. 1992,
114, 8098.
(74) (a) Nugent, W. A. Coord. Chem. ReV. 1980, 31, 123. (b) Nugent, W.
A. Inorg. Chem. 1983, 22, 965 and references therein.
Inorganic Chemistry, Vol. 42, No. 6, 2003 2161

Cunha et al.
calibrated with CsI. The calculation of theoretical isotopic patterns
was performed by using a computer program78 taking into account
the natural abundance of the various isotopes. The m/z values were
calculated using the 98Mo isotope. The elemental analyses were
done by the Laborato´rio de Ana´lises of the Instituto Superior
Te´cnico.
Final Remarks
This study demonstrates that organocyanamides (NtCNR2)
are susceptible to activation toward electrophilic attack at
the cyano-group, upon coordination to a suitable transition
metal center, by achieving the first example of NC-
protonation of such ligands to produce the previously
unreported amidoazavinylidene (or amidomethyleneamide)
species, MdNdCHNR2. Hence, organocyanamides can
behave like organonitriles (NtCR) and dinitrogen, which,
when ligating the same or the isoelectronic metal sites
{M(dppe)2}n+ (n ) 0, M ) Mo or W; n ) 1, M ) Re), are
protonated to the corresponding azavinylidene (or methylene-
amide), MdNdCHR, or diazenide MdNdNH species.
However, the NR2 amide group confers to NCNR2 and
derived species distinct electronic properties from those of
the corresponding NCR and derivatives. In particular, the
organocyanamide ligands at the trans-{Mo(dppe)2} site
behave as weaker Bro¨nsted bases than NCR and N2 and
promote the activation (toward protonation) of N2 in trans
position. Moreover, the π-electron release of the amide group
favors the π-electron donor ability of the organocyanamides
and derived amidoazavinylidene ligands, enhancing the
formation of metal-nitrogen multiple bonds with imide
character. These features of organocyanamides deserve
further exploration, namely toward the search for novel
multiple metal-nitrogen bonded ligands and new forms of
reactivity.
Preparation of the Complexes. trans-[Mo(N2)(NCNR2)-
(dppe)2] (R ) Me, 2a, or Et, 2b). A THF solution (20 cm3) of
trans-[Mo(N2)2(dppe)2], 1, (0.100 g, 0.105 mmol) was treated with
the appropriate organocyanamide NCNR2 [85.0 µL, 1.05 mmol (R
) Me) or 124 µL, 1.06 mmol (R ) Et)] and stirred for ∼3-5 h,
at 25 °C, until dark red. Concentration in vacuo followed by slow
dropwise addition of n-pentane led to the precipitation of complex
2a or 2b as a microcrystalline brick (2a) or dark red (2b) solid
which was separated by filtration, washed with n-pentane, and dried
in vacuo (ca. 0.083 g, 80%, 2a, or ca. 0.090 g, 84%, 2b, yield).
One of the crystals of 2b was analyzed by X-ray diffraction. Once
isolated from the mother liquor, compounds 2a and 2b display a
pronounced instability even in the solid state and always have to
be handled under argon. Moreover, attempted recrystallization
resulted in partial decomposition. These difficulties prevented
reliable elemental analyses (ca. 2% C off the expected value).
Although in degassed C6D6 solutions their stability was sufficient
to collect 1H and 31P-{1H} NMR data, no valuable 13C NMR spectra
could be obtained due to decomposition during the required long
acquisition time. Low temperature 13C NMR studies were prevented
by the high freezing point of this solvent and by the low solubility
of the compounds in toluene at low temperature.
Complex 2a. IR (KBr pellet): 2190 [s, ν(NtC)], 1890 [vs,
ν(NtN)]. NMR (298 K): 1H (C6D6), δ 7.6-6.8 [m, 40 H, C6H5
(dppe)], 2.6-2.2 [m, 8 H, CH2 (dppe)], 1.49 [s, 6 H, NCN(CH3)2];
31P-{1H} (C6D6), δ -72.3 s. FAB+-MS: m/z 964 ([M - N2]+),
908 ([M - N2 - CNMe2]+).
Complex 2b. IR (KBr pellet): 2187 [m, ν(NtC)], 1910 [vs,
ν(NtN)]. NMR (298 K): 1H (C6D6), δ 7.6-6.8 [m, 40 H, C6H5
(dppe)], 2.45 [m, 4 H, CH2 (dppe)], 2.30 [m, 4 H, CH2 (dppe)],
1.84 [q, 4 H, JHH 7.2, NCN(CH2CH3)2], 0.26 [t, 6 H, JHH 7.2,
NCN(CH2CH3)2]; 31P-{1H} (C6D6), δ -72.2 s. FAB+-MS: m/z 992
([M - N2]+), 908 ([M - N2 - CNEt2]+).
trans-[Mo(NNH2)(NCNR2)(dppe)2][BF4]2 (R ) Me, 3a, or Et,
3b). To a stirred THF solution (20 cm3) of trans-[Mo(N2)(NCNR2)-
(dppe)2] [0.090 g, 0.091 mmol (2a) or 0.088 mmol (2b)], cooled
at -60 °C, was added dropwise a 1:11 diluted diethyl ether solution
of [Et2OH][BF4] 85% [0.650 cm3, 0.401 mmol (2a) or 0.620 cm3,
0.383 mmol (2b)]. The solution color turned greenish brown, and
after 1 h, the temperature was allowed to rise to -30 °C, leading
to the formation of a light green solid. After 4 h at -30 °C, with
stirring, the solution was allowed to reach room temperature, and
after 1 h at this temperature, the pale green solid of 3a or 3b was
separated by filtration, washed with diethyl ether, and dried in vacuo
[ca. 0.066 g, 62% yield (3a) or ca. 0.070 g, 66% yield (3b)].
Concentration of the mother liquor in vacuo and addition of Et2O
led to the precipitation of a mixture of 4a or 4b (see following
paragraphs) with trans-[MoFO(dppe)2][BF4], the latter identified
by comparing the IR and NMR (1H, 31P-{1H},and 19F) data with
those reported79 for the known compound.
Experimental Section
Generalities. Solvents were dried and degassed by standard
techniques. All reactions were performed under an inert atmosphere
(argon) which was also always used when handling the unstable
complexes 2a and 2b and the hygroscopic Ag[BF4] salt. trans-
[Mo(N2)2(dppe)2] was prepared according to a published method,75
and the other reagents were used as purchased (Aldrich). Hydra-
zine76 and ammonia77 tests were performed according to published
methods. All the preparations (see following paragraphs), including
those of compounds 4, have been repeated and gave reproducible
results.
Infrared spectra were recorded on a BioRad Excalibur FTS
3000MX FTIR spectrophotometer; wavenumbers are in cm-1
.
Abbreviations: vs ) strong, s ) strong, m ) medium, br ) broad.
NMR spectra were obtained on a Varian Unity 300 spectrometer;
δ values are in ppm relative to SiMe4 (1H or 13C), P(OMe)3 (31P),
or CFCl3 (19F). In the 13C NMR data, assignments and coupling
constants common to the 13C-{1H} NMR spectra are not repeated.
Coupling constants are in hertz. Abbreviations: s ) singlet, d )
doublet, t ) triplet, q ) quartet, qnt ) quintet, m ) complex
multiplet, br ) broad, dt ) doublet of triplets, dm ) doublet of
complex multiplets, tq ) triplet of quartets, tm ) triplet of complex
multiplets, qt ) quartet of triplets, qm ) quartet of complex
multiplets. The FAB-MS spectra were run on a Trio 2000 mass
spectrometer. The samples were dispersed in a 3-nitrobenzyl alcohol
(NBA) liquid matrix and then bombarded with an 8 keV (ca. 1.28
× 10-15 J) xenon fast atoms beam. Data system acquisition was
Complex 3a. IR (KBr pellet): 3416, 3321 and 3238 [m, br,
ν(NH2)], 2231 [vs, ν(NtC)], 1618 [s, δ(NH2)], 1150-1000 [vs,
(75) (a) George, T. A.; Noble, M. E. Inorg. Chem. 1978, 17, 1678. (b)
Archer, L. J.; George, T. A.; M. Noble, E. J. Chem. Educ. 1981, 58,
727.
(76) Watt, G. W.; Chrisp, J. D. Anal. Chem. 1952, 24, 2006.
(77) (a) Chaney, A. L.; Marbach, E. P. Clin. Chem. 1962, 8, 130. (b)
Weatherburn, M. W. Anal. Chem. 1967, 39, 971.
(78) Winter, M. Univ. Sheffield, U.K., http://www.shef.ac.uk/chemistry/
chemputer/isotopes.html.
(79) (a) Morris, R. H.; Sawyer, J. F.; Schweitzer, C. T.; Sella, A.
Organometallics 1989, 8, 2099. (b) Cotton, F. A.; Eglin, J. L.;
Wiesinger, K. J. Inorg. Chim. Acta 1992, 195, 11.
2162 Inorganic Chemistry, Vol. 42, No. 6, 2003

Mo(0) Dinitrogen-Organocyanamide Complexes
br, ν(BF)]. NMR (298 K): 1H (CD2Cl2), δ 7.51 [t, 4 H, JHH 7.2,
Hp (dppe)], 7.49 [t, 4 H, JHH 6.9, Hp′ (dppe)], [7.41 t, 8 H, JHH 7.3,
Hm (dppe)], 7.29 [t, 8 H, JHH 7.6, Hm′ (dppe)], 7.23 [m, 8 H, Ho
(dppe)], 7.00 (s, br, 2 H, disappears on addition of D2O, NNH2),
6.96 [m, 8 H, Ho′ (dppe)], 3.03 [m, 4 H, CH2 (dppe)], 2.81 [m, 4
H, CH2 (dppe)], 2.02 [s, 6 H, NCN(CH3)2]; 31P-{1H} (CD2Cl2), δ
-90.0 s; 13C-{1H} (CD2Cl2), δ 132.68 [qnt, virtual JCP 2.6, Co
(dppe)], 132.62 [qnt, virtual JCP 2.7, Co′ (dppe)], 131.90 [s, Cp
(dppe)], 131.73 [s, Cp′ (dppe)], 131.58 [qnt, virtual JCP 9.7, Ci
(dppe)], 130.85 [qnt, virtual JCP 9.7, Ci′ (dppe)], 130.05 [qnt, virtual
JCP 2.3, Cm (dppe)], 130.02 (s, NCNMe2), 129.84 [qnt, virtual JCP
2.2, Cm′ (dppe)], 39.11 [s, NCN(CH3)2], 27.21 [qnt, virtual JCP 9.7,
CH2 (dppe)]; 13C (CD2Cl2), δ 132.68 (dm, JCH 160.7), 132.62 (dm,
7.34 [t, 8 H, JHH 7.8, Hm (dppe)], 7.29 [cross-peak detected by
HETCOR, NCHNMe
2], 7.20 [t, 8 H, JHH 7.5, Hm′ (dppe)], 7.12
[m, 8 H, Ho′ (dppe)], 7.03 [m, 8 H, Ho (dppe)], 3.49 [m, 4 H, CH2
(dppe)], 3.17 [m, 4 H, CH2 (dppe)], 2.71 [s, 3 H, NCHN(CH3A)2],
B
0.62 [s, 3 H, NCHN(CH3 )2]; 31P-{1H} (CD2Cl2), δ -103.9 (d, JPF
37.5); 19F (CD2Cl2), δ -38.81 (qnt, 1 F, 2JFP 38.1, MoF-), -151.46
(s, 8 F, BF4-); 13C-{1H} (CD2Cl2), δ 162.54 [s, NCHNMe2], 132.88
[m, Co + Co′ (dppe)], 131.89 [s, Cp (dppe)], 130.95 [s, Cp′ (dppe)],
130.24 [qnt, virtual JCP 2.2, Cm (dppe)], 129.26 [qnt, virtual JCP
2.2, Cm′ (dppe)], 44.26 [s, NCHN(CH3A)2], 37.64 [s, NCHN-
(CH3 )2], 29.84 [qnt, virtual JCP 9.5, CH2 (dppe)]; 13C (CD2Cl2), δ
B
162.54 (d, JCH 200.8), 132.88 (dm, JCH 162.7), 131.89 (dt, JCH 163.5,
2JCH 7.3), 130.95 (dt, JCH 162.3, 2JCH 7.0), 130.24 (dm, JCH 163.0),
129.26 (dm, JCH 163.6), 44.26 (q, JCH 145.7), 37.64 (q, JCH 145.1),
29.84 (tm, JCH 131.5). FAB+-MS: m/z 984 ([M]+). FAB--MS: m/z
87 ([BF4]-). (Found: C, 56.2; H, 4.4; N, 2.0%. C55H55N2B2F9MoP4
requires C, 57.1; H, 4.8; N, 2.4%.)
J
CH 160.7), 131.90 (dt, JCH 162.9, 2JCH 6.8), 131.73 (dt, JCH 163.0,
2JCH 7.0), 131.58, 130.85, 130.05 (dm, JCH 163.0), 130.02, 129.84
(dm, JCH 163.0), 39.11 (q, JCH 143.2), 27.21 (tm, JCH 131.5). FAB+-
MS: m/z 983 ([M - NNH2 + F]+), 964 ([M - NNH2]+). FAB--
MS: m/z 87 ([BF4]-). (Found: C, 52.6; H, 4.7; N, 4.2%.
C55H56N4B2F8MoP4‚HBF4 requires C, 52.7; H, 4.6; N, 4.5%.)
Complex 3b. IR (KBr pellet): 3418, 3317 and 3237 [m, br,
ν(NH2)], 2225 [vs, ν(NtC)], 1618 [s, δ(NH2)], 1150-1000 [vs,
br, ν(BF)]. NMR (298 K): 1H (CD2Cl2), δ 7.52 [t, 4 H, JHH 6.9,
Hp (dppe)], 7.50 [t, 4 H, JHH 6.9, Hp′ (dppe)], 7.40 [t, 8 H, JHH 7.5,
Hm′ (dppe)], 7.30 [t, 8 H, JHH 7.2, Hm (dppe)], 7.16 [m, 8 H, Ho′
(dppe)], 6.99 [m, 8 H, Ho (dppe)], 6.83 (s, br, 2 H, disappears on
addition of D2O, NNH2), 3.00 [m, 4 H, CH2 (dppe)], 2.84 [m, 4 H,
CH2 (dppe)], 2.29 [q, 4 H, JHH 7.3, NCN(CH2CH3)2], 0.65 [t, 6 H,
Complex 4b. IR (KBr pellet): 1586 [vs, ν(NdC)], 1319 [s,
ν(MoN)], 1120-1000 [vs, br, ν(BF)]. NMR (298 K): 1H (CD2Cl2),
δ 7.53 [t, 4 H, JHH 7.3, Hp (dppe)], 7.41 [t, 4 H, JHH 7.2, Hp′ (dppe)],
7.37 [t, 9 H, JHH 7.3, Hm (dppe); buried under that triplet but its
cross-peak detected by HETCOR, NCHNEt2], 7.18 [t, 8 H, JHH
7.6, Hm′ (dppe)], 7.09 [m, 16 H, Ho + Ho′ (dppe)], 3.49 [m, 4 H,
A
CH2 (dppe)], 3.15 [q, 2 H, JHH 7.0, NCHN(CH2 CH3)2; buried under
that quartet but its cross-peak detected by HETCOR, 4 H, CH2
B
(dppe)], 1.33 [q, 2 H, JHH 7.3, NCHN(CH2 CH3)2], 0.90 [t, 3 H,
JHH 7.0, NCHN(CH2CH3A)2], -0.28 [t, 3 H, JHH 7.3, NCHN-
J
HH 7.3, NCN(CH2CH3)2]; 31P-{1H} (CD2Cl2), δ -90.8 s; 13C-{1H}
B
(CH2CH3 )2]; 31P-{1H} (CD2Cl2), δ -104.3 (d, JPF 37.4); 19F
(CD2Cl2), δ 132.68 [qnt, virtual JCP 2.7, Co (dppe)], 132.43 [qnt,
virtual JCP 2.8, Co′ (dppe)], 131.88 [s, Cp + Cp′ (dppe)], 131.45
[qnt, virtual JCP 9.7, Ci (dppe)], 130.93 [qnt, virtual JCP 9.7, Ci′
(dppe)], 130.08 [qnt, virtual JCP 2.2, Cm (dppe)], 129.93 [qnt, virtual
2
(CD2Cl2), δ -37.20 (qnt, 1 F, JFP 38.1, F-), -151.46 (s, 8 F,
BF4-); 13C-{1H} (CD2Cl2), δ 162.32 (s, NCHNEt2), 132.90 [qnt,
virtual JCP 2.7, Co (dppe)], 132.44 [qnt, virtual JCP 2.7, Co′ (dppe)],
132.28 [s, Cp (dppe)], 131.83 [s, Cp′ (dppe)], 130.38 [qnt, virtual
JCP 2.2, Cm′ (dppe)], 129.72 (s, NCNEt2), 45.01 [s, NCN(CH2CH3)2],
J
CP 2.1, Cm (dppe)], 129.25 [qnt, virtual JCP 2.3, Cm′ (dppe)], 48.56
27.01 [qnt, virtual JCP 9.8, CH2 (dppe)], 13.20 [s, NCN(CH2CH3)2];
B
[s, NCHN(CH2ACH3)2], 43.62 [s, NCHN(CH2 CH3)2], 29.68 [qnt,
13C (CD2Cl2), δ 132.68 (dm, JCH 165.0), 132.43 (dm, JCH 165.0),
virtual JCP 9.4, CH2 (dppe)], 13.28 [s, NCHN(CH2CH3A)2], 9.57
[s, NCHN(CH2CH3 )2]; 13C (CD2Cl2), δ 162.32 (d, JCH 200.2),
2
131.88 (dt, JCH 163.6, JCH 7.3), 131.45, 130.93, 130.08 (dm, JCH
B
165.4), 129.93 (dm, JCH 165.4), 129.72, 45.01 (tq, JCH 145.0, 2JCH
3.7), 27.01 (tm, JCH 134.6), 13.20 (qt, JCH 128.2, 2JCH 2.8). FAB+-
MS: m/z 1011 ([M - NNH2 + F] +), 992 ([M - NNH2]+). FAB--
MS: m/z 87 ([BF4]-). (Found: C, 56.4; H, 4.9; N, 4.0%.
C57H60N4B2F8MoP4‚1/4HBF4 requires C, 56.3; H, 5.0; N, 4.6%.)
trans-[MoF(NCHNR2)(dppe)2][BF4]2 (R ) Me, 4a, or Et, 4b).
A stirred THF solution (25 cm3) of trans-[Mo(N2)(NCNR2)(dppe)2]
[0.100 g, 0.101 mmol (2a) or 0.0981 mmol (2b)], cooled at -80
°C, was treated with a THF solution of Ag[BF4] [0.201 or 0.195
mmol (in the cases of 2a or 2b, respectively); 3.9 cm3 or 3.8 cm3,
accordingly, of a 0.0514 M solution]. There occurred an immediate
formation of a fine and dark precipitate of silver metal, and the
system was left with stirring for 2 h at -70 to -50 °C, then left to
warm to -30 °C (the solution color became greenish brown or
orangish brown, respectively) and maintained at this temperature
for ca. 2 h. It was then left to reach room temperature, and after 1
h, always with stirring, the solution was filtered through Celite and
concentrated in vacuo. Dropwise addition of diethyl ether resulted
in the precipitation of a greenish yellow or dark yellow solid of 4a
or 4b, respectively, which was separated by filtration, washed with
diethyl ether, and dried in vacuo [ca. 0.075 g, 64% yield (4a) or
0.076 g, 65% yield (4b)]. Complexes 4 are also formed upon slow
decomposition of the corresponding compounds 3 in solution (see
following paragraphs).
132.90 (dm, JCH 162.3), 132.44 (dm, JCH 161.8), 132.28 (dt, JCH
163.6, 2JCH 7.0), 131.83 (dt, JCH 163.6, 2JCH 7.0), 130.38 (dm, JCH
162.1), 129.25 (dm, JCH 163.7), 48.56 (tm, JCH 146.8), 43.62 (tm,
2
JCH 145.6), 29.68 (tm, JCH 135.2), 13.28 (qt, JCH 129.4, JCH 3.7),
9.57 (qt, JCH 129.6, 2JCH 3.7). FAB+-MS: m/z 1012 ([M]+). FAB--
MS: m/z 87 ([BF4]-). (Found: C, 57.0; H, 4.9; N, 2.0%.
C57H59N2B2F9MoP4 requires C, 57.8; H, 5.0; N, 2.4%.)
Conversion of the Hydrazide(2-) Complex 3b into the
Amidoazavinylidene Complex 4b. A CH2Cl2 (20 cm3) solution
of complex 3b (0.025 g, 0.021 mmol) was stirred at 23 °C and
regularly monitored by 31P-{1H} NMR and IR spectroscopies
(applied to 0.50 cm3 samples taken from that solution) until the
complete disappearance of the starting complex (45 days) upon
conversion into 4b (ca. 60% yield) as the main complex product.
The solution was then transferred to a separatory funnel, and the
water soluble nitrogen products were repeatedly extracted by 5 ×
20 cm3 portions of distilled and deionized water. The aqueous
extracts were added to a 100.0 cm3 volumetric flask, and aliquots
(5.00 cm3) of the final water solution were analyzed for hydrazine76
or ammonia77 by using standard spectrophotometric methods [molar
yields of 2.5% (hydrazine) or 8.5% (ammonia), relative to the
starting metal complex].
An identical procedure was also followed for monitoring the 3b
f 4b conversion in acidic media, by adding a catalytic amount
(0.10 acid/complex molar ratio) of [Et2OH][HBF4] to the starting
CH2Cl2 reaction solution. However, this procedure cannot be used
Complex 4a. IR (KBr pellet): 1616 [vs, ν(NdC)], 1330 [m,
ν(MoN)], 1120-1000 [vs, br, ν(BF)]. NMR (298 K): 1H (CD2Cl2),
δ 7.52 [t, 4 H, JHH 7.3, Hp (dppe)], 7.42 [t, 4 H, JHH 7.2, Hp′ (dppe)],
Inorganic Chemistry, Vol. 42, No. 6, 2003 2163

Cunha et al.
refinements were carried out with SHELXL-97.82 ORTEP repre-
sentations were performed using the PLATON99 program.83
Crystallographic data are summarized in Table 2, and selected bond
lengths and angles in Table 1.
Table 2. Crystalographic Data for trans-[Mo(N2)(NCNEt2)(dppe)2], 2b
chemical formula
fw
C57H58MoN4P4
1018.89
cryst syst
space group
orthorhombic
Pbca
a/Å
b/Å
14.545(3)
21.756(4)
31.881(6)
10088(3)
293
Acknowledgment. This work has been partially sup-
ported by the PRAXIS XXI and the POCTI Programs and
the Foundation for Science and Technology (FCT). We also
thank Prof. J. J. R. Frau´sto da Silva for general support, Prof.
Vitaly Belsky (L. Ya. Karpov Physico-Chemical Institute,
Moscow) for the X-ray diffraction analysis, Dr. M. Caˆndida
N. Vaz for the elemental analysis services (Instituto Superior
Te´cnico, Lisboa), and Mr. Indale´cio Marques (Centro de
Qu´ımica Estrutural, Complexo I, Instituto Superior Te´cnico)
for the FAB-MS spectra.
c/Å
V/Å3
T/K
Z
8
µ(Mo KR)/mm-1
total reflns collected
indep reflns
obsd reflns [I > 2σ(I)]
R indices (all data)
0.429
2879
2879 (Rint ) 0.0000)
2879
R1 ) 0.0230
wR2 ) 0.0582
R1 ) 0.0230
wR2 ) 0.0582
final R indices [I > 2σ(I)]
Supporting Information Available: CIF file giving positional
and thermal parameters, bond distances, and bond angles for 2b.
1H and 31P-{1H} NMR spectra for 2a and 2b. This material is
available free of charge via the Internet at http://pubs.acs.org.
for the preparation of 4b in view of its further decomposition in
acidic medium.
Crystal Structure Determination of trans-[Mo(N2)(NCNEt2)-
(dppe)2] 2b. Crystals of 2b were grown spontaneously at ca. -20
°C from the mother liquor resulting from the filtration step of the
synthesis of this complex. X-ray diffraction data were collected on
an Enraf-Nonius CAD4 diffractometer equipped with a â-mono-
chromator and using Mo KR radiation. All non-hydrogen atoms
were treated anisotropically. Hydrogen atoms were constrained to
have identical U. The PROFIT program80 was used for cell
refinement and data reduction. The structure was solved by direct
methods by using the SHELXS-97 package.81 The structure
IC026176E
(80) Strel’tsov, V. A.; Zavodnick, V. E. Kristallografia 1989, 34, 1369.
(81) Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, 46, 467.
(82) Sheldrick, G. M. SHELXL-97; University of Go¨ttingen: Go¨ttingen,
Germany, 1997.
(83) Spek, A. L. PLATON, version 240698; Utrecht University: Utrecht,
The Netherlands, 1980-1998.
2164 Inorganic Chemistry, Vol. 42, No. 6, 2003