Preparation and reactivity of hydrazine complexes of rhenium: Synthesis of 1,2-diazene (NH=NH) and methyleneimine (CH2=NH) derivatives

Article abstract of DOI:10.1002/ejic.200300155

The hydrazine complexes [Re(RNHNH₂)(CO)_nP _5-n]BPh₄ [R = H, CH₃, Ar; n = 1-4; P = P(OEt)₃, PPh(OEt)₂, PPh₂OEt] were prepared by allowing the hydride species [ReH(CO)_nP_5-n] to react first with a Bronsted acid and then with hydrazine. The reaction of either [Re(NH₂NH₂)(CO)_nP_5-n]BPh ₄ or [Re(ArNHNH₂)(CO)_nP_5-n]BPh ₄ with Pb(OAC)₄ at -40 °C proceeds with the selective oxidation of the hydrazine ligand to yield either [Re(NH=NH)(CO) _nP_5-n]BPh₄ or [Re(ArN=NH)(CO)_nP _5-n]BPh₄. The oxidation of [Re-(CH₃NHNH ₂)(CO)ⁿP_5-n]BPh₄ (n = 1, 2) with Pb(OAc)₄ at -40 °C gives both [Re(CH₃N=NH)(CO) _nP_5-n]BPh₄ and [Re(_η-NH=CH ₂)(CO)_nP_5-n]BPh₄. Reduction reactions of both hydrazine and diazene complexes with Zn amalgam were also studied and yielded ammonia in moderate yield (20-25%). ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003).

Full text of DOI:10.1002/ejic.200300155

FULL PAPER
Preparation and Reactivity of Hydrazine Complexes of Rhenium: Synthesis of
1,2-Diazene (NH؍NH) and Methyleneimine (CH2؍NH) Derivatives
Gabriele Albertin,*[a] Stefano Antoniutti,[a] and Maria Teresa Giorgi[a]
Keywords: Hydrazine / N ligands / Oxidation / Rhenium
The hydrazine complexes [Re(RNHNH2)(CO)nP5−n]BPh4 [R =
(CH3NHNH2)(CO)nP5−n]BPh4 (n = 1, 2) with Pb(OAc)4 at
H, CH3, Ar; n = 1−4; P = P(OEt)3, PPh(OEt)2, PPh2OEt] were −40 °C gives both [Re(CH3N=NH)(CO)nP5−n]BPh4 and
prepared by allowing the hydride species [ReH(CO)nP5−n] to
react first with a Brønsted acid and then with hydrazine.
The reaction of either [Re(NH2NH2)(CO)nP5−n]BPh4 or
[Re(ArNHNH2)(CO)nP5−n]BPh4 with Pb(OAc)4 at −40 °C
proceeds with the selective oxidation of the hydrazine
ligand to yield either [Re(NH=NH)(CO)nP5−n]BPh4 or
[Re(ArN=NH)(CO)nP5−n]BPh4. The oxidation of [Re-
[Re(η1-NH=CH2)(CO)nP5−n]BPh4. Reduction reactions of both
hydrazine and diazene complexes with Zn amalgam were
also studied and yielded ammonia in moderate yield
(20−25%).
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2003)
Introduction
paring hydrazine complexes and studying their reactivity to-
ward oxidizing and reducing reagents in an attempt to test
whether the rhenium fragments are able to stabilize diazene
species. The results of these studies, which include the syn-
thesis of stable 1,2-diazene complexes and the unpre-
cedented methyleneimine (CH2ϭNH) derivatives, are re-
ported here. A preliminary paper on part of this work has
previously been published.[12]
Complexes containing partially reduced dinitrogen mol-
ecules such as hydrazine (RNHNH2), hydrazido
(RNHNH), diazene (RNϭNH), and diazenido (RN2) as li-
gands continue to be studied not only for their relationship
with the nitrogen-fixation process intermediates, but also
because their properties lead us to consider this class of
compounds as having an identity and chemistry of their
own,[1Ϫ3] with potentially interesting developments.
The hydrazine complexes are the least studied[1,2] among
these diazo species even though NH2NH2 has been shown
to be a substrate[4] as well as a product of functioning nitro-
genase and has been isolated by quenching the enzyme.[5]
Furthermore, rhenium complexes containing NH2NH2 or
substituted hydrazine RNHNH2 are very rare and include,
apart from the pioneering work on [Re(NCO)-
(CO)2(NH2NH2)P2] (P ϭ tertiary phosphane),[6] only two
Results and Discussion
Preparation of Hydrazine Complexes
The hydrazine complexes [Re(RNHNH2)(CO)nP5Ϫn]-
BPh4 (1Ϫ8) were prepared by reacting the hydride species
[ReH(CO)nP5Ϫn] first with an equimolar amount of a
Brønsted acid (CF3SO3H or HBF4) and then with an excess
of hydrazine, as shown in Scheme 1.
papers,[7,8]
one
on
[ReCp*Me3(NH2NH2)]CF3SO3
Treatment of the hydrides [ReH(CO)nP5Ϫn] with the
Brønsted acid CF3SO3H or HBF4 (HY) gives the dihydro-
(Cp* ϭ pentamethylcyclopentadienyl) and [Re(NH2NH2)-
(CO)3(PPh3)2]CF3SO3, and another on the substituted-
hydrazine complex [ReCl2(PPh3)2{NNC(O)Ph}{H2NNHC-
(S)Ph}].[9]
We have previously reported the synthesis and reactivity
of mono- and bis(hydrazine) complexes of the iron triad[10]
and manganese[11] of the type [MH(RNHNH2)P4]BPh4,
[M(RNHNH2)2P4](BPh4)2 (M ϭ Fe, Ru, Os) and
[Mn(RNHNH2)(CO)nP5Ϫn]BPh4 (P ϭ phosphites). We have
now extended these studies to rhenium with the aim of pre-
gen-containing
cationic
complexes
[Re(η2-
H2)(CO)nP5Ϫn]ϩ,[13] which are thermally unstable and easily
lose H2 yielding either the neutral ReY(CO)nP5Ϫn species,
containing the labile YϪ ligand, or the coordinatively un-
saturated [Re(CO)nP5Ϫn
ϩ
]
cations. Reaction of these inter-
mediates with an excess of hydrazine gives the final deriva-
ϩ
tives [Re(RNHNH2)(CO)nP5Ϫn
]
(1Ϫ8), which were iso-
Ϫ
lated as their BPh4 salts and characterised. 1,1-Dimeth-
ylhydrazine reacts with these rhenium intermediates giving
the final derivatives [Re{(CH3)2NNH2}(CO)nP5Ϫn]BPh4 (1e
and 3e).
[a]
`
Dipartimento di Chimica, Universita CaЈ Foscari di Venezia,
Dorsoduro 2137, 30123 Venezia, Italy
Fax: (internat.) ϩ39-041/234-8917
E-mail: albertin@unive.it
Good analytical data were obtained for all the hydrazine
complexes 1Ϫ8, which are white or pale-yellow solids,
Eur. J. Inorg. Chem. 2003, 2855Ϫ2866
DOI: 10.1002/ejic.200300155
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2855

G. Albertin, S. Antoniutti, M. T. Giorgi
FULL PAPER
31P{1H} NMR spectra display either an A2B- or an AB2-
type coupling pattern, suggesting the magnetic equivalence
of two P atoms, different from the third. On this basis a fac
geometry (II) may be proposed for the dicarbonyl deriva-
tives.
In the temperature range between ϩ30 and Ϫ80 °C, the
31P NMR spectra of the tricarbonyl compounds 5Ϫ7 show
a sharp singlet, in agreement with two magnetically equiva-
lent phosphane ligands. The IR spectra show three ν(CO)
bands, two strong and one of medium intensity, suggesting
a mer arrangement of the carbonyl ligands. On this basis,
a mer-trans geometry (III) in solution may be reasonably
proposed for the tricarbonyl derivatives.
Finally, the presence of four ν(CO) bands in the carbonyl
region of its IR spectrum strongly suggests a cis geometry
(IV) for the tetracarbonyl derivative [Re(NH2NH2)-
(CO)4(PPh2OEt)]ϩ (8).
Oxidation Reactions
The hydrazine complexes [Re(NH2NH2)(CO)nP5Ϫn]BPh4
react with Pb(OAc)4 at Ϫ40 °C to give the 1,2-diazene de-
rivatives [Re(NHϭNH)(CO)nP5Ϫn]BPh4, which were iso-
lated in the solid state and characterised (Scheme 2).
Scheme 1. P ϭ P(OEt)3 (1, 2, 5), PPh(OEt)2 (3, 6), PPh2OEt (4, 7,
8); Y ϭ CF3SO3Ϫ, BF4Ϫ; R ϭ H (a), CH3 (b), C6H5 (c), 4-
NO2C6H4 (d); (CH3)2NNH2 (e)
stable in air and in solution in polar organic solvents, where
they behave as 1:1 electrolytes.[14] The IR and NMR spec-
troscopic data (Table 1) support the proposed formulation
and allow a geometry in solution to be established.
The presence of a hydrazine ligand in the complexes is
confirmed by the IR spectra, which show the characteristic
ν(NH) bands between 3366 and 3202 cmϪ1. In some com-
plexes the δ(NH2) absorption at 1624Ϫ1611 cmϪ1 is also
1
observed. Furthermore, the H NMR spectra confirm the
presence of the hydrazine ligand, showing the characteristic
NH and NH2 signals, which were clearly assigned by accu-
rate integration and homodecoupling experiments, and are
reported in Table 1. The spectra also show that, in the case
of the NH2NH2 complexes, two NH2 proton signals are
present, thus excluding the formation of a dimeric complex
with an NH2NH2 bridging ligand.
Scheme 2
The reaction proceeds with the selective oxidation of the
In the temperature range between ϩ30 and Ϫ80 °C the hydrazine ligand to 1,2-diazene, which is stabilized by coor-
31P NMR spectra of the monocarbonyl complexes 1 show dination to all the [Re(CO)nP5Ϫn] (n ϭ 1, 2, 3) fragments,
a sharp singlet suggesting a mutual trans position (ge- thus allowing the complexes to be isolated. The use of a
ometry I) of the carbonyl and hydrazine ligands. This is temperature below Ϫ30 °C during the reaction course is
confirmed by the IR spectra, which show the ν(CO) band crucial for a successful synthesis, as is crystallisation of the
at 1887Ϫ1888 cmϪ1
.
products at 0 °C. If these temperatures are not maintained,
The IR spectra of the dicarbonyl complexes 2Ϫ4 show large amounts of decomposition products are obtained that
two strong bands in the ν(CO) region indicating the mutual contain only traces of the diazene complexes. In pure form,
cis position of the two carbonyl ligands. The 13C NMR however, the NHϭNH compounds 9Ϫ14 are stable at room
spectra also indicate that the two CO groups are magneti- temperature both as a solid and in solution in polar organic
cally equivalent, showing only one multiplet for 2b in the solvents, where they behave as 1:1 electrolytes.[14] Analytical
carbonyl carbon region at δ ϭ 194.2 ppm. Furthermore, the and spectroscopic data (Table 1) support the proposed for-
2856
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2003, 2855Ϫ2866

Hydrazine Complexes of Rhenium
FULL PAPER
Table 1. Selected IR and NMR spectroscopic data for rhenium complexes
Compound
IR[a]
Assgnt 1H NMR[b][c]
Assgnt
Spin
system δ (J/Hz)
31P{1H} NMR[b] [d]
ν˜, cmϪ1
δ (J/Hz)
[Re(NH2NH2)(CO){P(OEt)3}4]BPh4 (1a)
3366m
3313m
3283w
3218m
1887s
ν(NH) 4.45 (br. m)
4.07 (m)
ReNH2
CH2
CH3
A4
118.1 (s)
1.30 (t)
ν(CO)
[Re(C6H5NHNH2)(CO){P(OEt)3}4]BPh4 (1c)
[Re{(CH3)2NNH2}(CO){P(OEt)3}4]BPh4 (1e)
[Re(CH3NHNH2)(CO)2{P(OEt)3}3]BPh4 (2b)[e]
3341m
3285m
1888s
1611m
3327w
3283m
1887s
ν(NH) 6.22 (br. t)
5.16 (br. m)
NH
ReNH2
CH2
CH3
ReNH2
CH2
(CH3)2N
CH3
ReNH2
NH
A4
117.8 (s)
116.7 (s)
ν(CO)
4.08 (m)
δ(NH2) 1.31 (t)
ν(NH) 4.24 (br)
4.06 (m)
A4
ν(CO)
2.39 (s)
1.29 (t)
3325m
3285m
3213w
1982s
ν(NH) 4.44 (br)
3.36 (br)
A2B
δA ϭ 114.7
δB ϭ 113.3
JAB ϭ 49
4.13 (m)
CH2
ν(CO)
2.59 (d, JH,H ϭ 6) CH3N
1902s
1.38 (t)
1.34 (t)
CH3
[Re(NH2NH2)(CO)2{PPh(OEt)2}3]BPh4 (3a)
[Re(CH3NHNH2)(CO)2{PPh(OEt)2}3]BPh4 (3b)
[Re(C6H5NHNH2)(CO)2{PPh(OEt)2}3]BPh4 (3c)
3357w
3298m
3262w
3219w
1999s
1905s
3335w
3289w
3276m
1989s
1905s
ν(NH) 3.55 (br. m)
3.90 (m)
ReNH2
CH2
NH2
AB2
AB2
AB2
AB2
AB2
AB2
AB2
δA ϭ 139.3
δB ϭ 136.4
JAB ϭ 35
2.71 (br)
1.35 (t)
CH3
ν(CO)
1.33 (t)
1.31 (t)
ν(NH) 3.27 (br. m)
3.93 (m)
ReNH2
CH2
NH
δA ϭ 139.4
δB ϭ 137.1
JAB ϭ 35
2.27 (m)
ν(CO)
1.79 (d, JH,H ϭ 6) CH3N
1.38 (t)
1.32 (t)
ν(NH) 4.87 (br. t)
CH3
3354w
3268m
1982s
1905s
1617m
NH
ReNH2
CH2
δA ϭ 139.9
δB ϭ 136.6
JAB ϭ 35
4.04 (br. m)
ν(CO)
3.88 (m)
1.31 (t)
CH3
δ(NH2) 1.30 (t)
1.27 (t)
ν(NH) 6.13 (m)
6.10 (m)
[Re(4-NO2C6H4NHNH2)(CO)2{PPh(OEt)2}3]BPh4 (3d) 3295m
ReNH2
NH
CH2
δA ϭ 144.4
δB ϭ 144.1
JAB ϭ 40
3276w
1986s
1894s
ν(CO)
4.10Ϫ3.80 (m)
1.39 (t)
1.32 (t)
1.25 (t)
CH3
[Re{(CH3)2NNH2}(CO)2{PPh(OEt)2}3]BPh4 (3e)
[Re(NH2NH2)(CO)2(PPh2OEt)3]BPh4 (4a)
[Re(CH3NHNH2)(CO)2(PPh2OEt)3]BPh4 (4b)
3299w
3262w
1980s
1868s
ν(NH) 4.05Ϫ3.80 (m)
CH2
δA ϭ 138.7
δB ϭ 135.1
JAB ϭ 38
3.74 (m)
ReNH2
(CH3)2N
CH3
ν(CO)
2.05 (s)
1.37 (t)
1.35 (t)
1.28 (t)
3358m
3290m
3271w
3224w
1970s
ν(NH) 3.69 (br. m)
3.60Ϫ3.30 (m)
2.60 (br. t)
ReNH2
CH2
NH2
δA ϭ 113.4
δB ϭ 109.1
JAB ϭ 30
0.99 (t)
CH3
ν(CO)
0.63 (t)
1872s
3332m
3262m
1970s
ν(NH) 3.80Ϫ3.15 (m)
CH2
ReNH2
NH
δA ϭ 113.7
δB ϭ 109.4
JAB ϭ 30
2.97 (m)
ν(CO)
2.04 (m)
1881s
1.61 (d, JH,H ϭ 6) CH3N
0.97 (t)
0.62 (t)
CH3
Eur. J. Inorg. Chem. 2003, 2855Ϫ2866
www.eurjic.org
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2857

G. Albertin, S. Antoniutti, M. T. Giorgi
FULL PAPER
Table 1 (Continued)
Compound
IR[a]
Assgnt 1H NMR[b][c]
Assgnt
Spin
system δ (J/Hz)
31P{1H} NMR[b] [d]
ν˜, cmϪ1
δ (J/Hz)
[Re(NH2NH2)(CO)3{P(OEt)3}2]BPh4 (5a)
3347w ν(NH) 4.11 (m)
CH2
ReNH2
NH2
A2
110.9 (s)
3261m
3223w
3.47 (br. m)
2.83 (br. m)
111.3 (s)[f]
2076m ν(CO) 1.38 (t)
1971s
CH3
1947s
1612m δ(NH2)
3348m ν(NH) 3.97 (m)
[Re(NH2NH2)(CO)3{PPh(OEt)2}2]BPh4 (6a)
CH2
A2
132.3 (s)
3287m
3268w
3219m
3.22 (br. m)
2.57 (br. t)
1.38 (t)
ReNH2
NH2
CH3
2072w ν(CO)
1968s
1944s
1624m δ(NH2)
[Re(4-NO2C6H4NHNH2)(CO)3{PPh(OEt)2}2]BPh4 (6d) 3285m ν(NH) 6.30 (m)
NH
ReNH2
CH2
A2
133.0 (s)
107.1 (s)
3270sh
3230w
6.24 (m)
4.10 (m)
2084w ν(CO) 1.42 (t)
1984s
1938s
CH3
[Re(NH2NH2)(CO)3(PPh2OEt)2]BPh4 (7a)
3354m ν(NH) 3.61 (m)
CH2
A2
3281w
3267m
3217w
3.43 (br. m)
2.67 (br. t)
1.16 (t)
ReNH2
NH2
CH3
2075w ν(CO)
1970s
1933s
[Re(CH3NHNH2)(CO)3(PPh2OEt)2]BPh4 (7b)
[Re(NH2NH2)(CO)4(PPh2OEt)]BPh4 (8a)
3322w ν(NH) 3.76 (br. m)
3263m 3.68 (m)
2076m ν(CO) 2.77 (m)
ReNH2
CH2
NH
CH3N
CH3
CH2
ReNH2
NH2
CH3
A2
A
109.0 (s)
102.9 (s)
1969s
1926s
1.97 (d, JH,H ϭ 6)
1.21 (t)
3328w ν(NH) 3.58 (qnt)
3282w
3267w
3202m
2.31 (m)
1.94 (br. t)
1.18 (t)
2113m ν(CO)
2024sh
2009s
1975s
1614m δ(NH2)
[Re(NHϭNH)(CO){P(OEt)3}4]BPh4 (9a)
1887s
ν(CO) A4XY spin syst.
δX ϭ 16.70
δY ϭ 15.84
JXY ϭ 33.0
JAX ϭ 1.26
JAY ϭ 2.86
4.06 (m)
NHϭNH A4
ReNH
NϭNH
CH2
123.6 (s)
123.4 (s)[f]
CH3
1.32 (t)
[Re(C6H5NϭNH)(CO){P(OEt)3}4]BPh4 (9c)
[Re(CH3NϭNH)(CO)2{P(OEt)3}3]BPh4 (10b)[g]
1899s
ν(CO) 14.39 (qnt, JPH ϭ 4) NH
A4
116.8 (s)
4.08 (m)
1.27 (t)
CH2
CH3
1992s
1911s
ν(CO) 15.86 (br. s)
4.10 (m)
ReNH
CH2
A2B[f] δA ϭ 114.1
δB ϭ 111.3
4.44 (d)
1.36 (t)
ν(CO) 13.82 (br. s)
4.05 (m)
ϭNCH3
CH3
ReNH
CH2
JAB ϭ 48.3
[Re(η1-NHϭCH2)(CO)2{P(OEt)3}3]BPh4 (10*b)[h]
2002s
1915s
A2B[f] δA ϭ 120.9
δB ϭ 118.7
3.75 (q)
1.31 (t)
NϭCH2
CH3
JAB ϭ 47.8
2858
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Eur. J. Inorg. Chem. 2003, 2855Ϫ2866

Hydrazine Complexes of Rhenium
FULL PAPER
Table 1 (Continued)
Compound
IR[a]
Assgnt 1H NMR[b][c]
Assgnt
Spin
system δ (J/Hz)
31P{1H} NMR[b] [d]
ν˜, cmϪ1
δ (J/Hz)
[Re(NHϭNH)(CO)2{PPh(OEt)2}3]BPh4 (11a)
1998s
1906s
ν(CO) A2B2XY spin syst. NHϭNH A2B
δA ϭ 142.8
δB ϭ 140.0
JAB ϭ 35
δX ϭ 16.07
δY ϭ 15.28
JXY ϭ 33.3
JAX ϭ 2.15
JAY ϭ 3.15
JBX ϭ 1.15
JBY ϭ 1.45
3.92 (m)
ReNH
NϭNH
CH2
CH3
1.38 (t)
1.35 (t)
1.33 (t)
[Re(CH3NϭNH)(CO)2{PPh(OEt)2}3]BPh4 (11b)
and
1992s
1911s
ν(CO) 15.94 (br. s)
12.08 (br. s)
4.29 (d)
NϭNH
CϭNH
ϭNCH3
CH2
AB2
AB2
142Ϫ140 (m)
135Ϫ132 (m)
[Re(η1-NHϭCH2)(CO)2{PPh(OEt)2}3]BPh4 (11*b)
3.90 (m)
3.70 (m)
1.35 (m)
NϭCH2
CH3
[Re(C6H5NϭNH)(CO)2{PPh(OEt)2}3]BPh4 (11c)
[Re(NHϭNH)(CO)2(PPh2OEt)3]BPh4 (12a)
1970s
1887s
ν(CO) 12.22 (d)
3.35 (m)
NH
CH2
CH3
AB2
δA ϭ 113.2
δB ϭ 108.6
JAB ϭ 28
0.84 (t)
0.67 (t)
1972s
1887s
ν(CO) AB2XY spin syst. NHϭNH AB2
δA ϭ 113.5
δB ϭ 109.1
JAB ϭ 30
δX ϭ 15.31
δY ϭ 14.42
JXY ϭ 33.5
JAX ϭ 2.38
JAY ϭ 3.74
JBX ϭ 1.16
JBY ϭ 1.88
3.45 (m)
ReNH
NϭNH
CH2
CH3
0.99 (t)
0.64 (t)
[Re(NHϭNH)(CO)3{PPh(OEt)2}2]BPh4 (13a)
2071w ν(CO) A2XY spin syst.
NHϭNH A2
ReNH
NϭNH
131.0 (s)
1969s
1944s
δX ϭ 13.03
δY ϭ 11.89
JXY ϭ 26.5
JAX ϭ 2.4
JAY ϭ 1.3
3.88 (m)
131.6 (s)[f]
CH2
CH3
1.30 (t)
[Re(4-NO2C6H4NϭNH)(CO)3{PPh{OEt)2}2]BPh4 (13d) 2076m ν(CO) 13.14 (br)
NH
CH2
CH3
NHϭNH A2
ReNH
NϭNH
A2
133.5 (s)
110.8 (s)
1982s
1951s
4.10 (m)
1.43 (t)
[Re(NHϭNH)(CO)3(PPh2OEt)2]BPh4 (14a)
2069w ν(CO) A2XY spin syst.
1967s
1940s
δX ϭ 13.16
δY ϭ 12.40
JXY ϭ 26.6
JAX ϭ 2.20
JAY ϭ 1.04
3.48 (m)
CH2
CH3
CH2
CH3N
NH2
CH3
1.14 (t)
3329m ν(NH) 4.04 (m)
[Re(CH3NH2)(CO)2{P(OEt)3}3]BPh4 (15)[i]
A2B
δA ϭ 172.1
δB ϭ 171.3
JAB ϭ 49
3283m
2005s
1894s
2.73 (t)
ν(CO) 2.65 (br)
1.37 (t)
1.32 (t)
[a]
[b]
[c]
In KBr. In CD2Cl2 at 25 °C, unless otherwise noted. Phenyl proton resonances are omitted. [d] Positive shift downfield from 85%
H3PO4. [e] 13C{1H} NMR (2b): δ ϭ 194.2 (m) CO, 165Ϫ122 (m) Ph, 62.9 (m) CH2, 44.6 (s) CH3N, 16.3 (m) CH3 ppm. At Ϫ80 °C.
[f]
[g]
13C{1H} NMR (10b): δ ϭ 196.2 (m) CO, 165Ϫ120 (m) Ph, 71.7 (s) CH3Nϭ, 62.7 (m) CH2, 16.3 (m) CH3 ppm. [h] 13C{1H} NMR (10*
b): δ ϭ 194.7 (m) CO, 165Ϫ122 (m) Ph, 67.8 (s) NϭCH2, 62.4 (m) CH2, 16.1 (m) CH3 ppm. [i] 13C{1H} NMR (15): δ ϭ 194.2 (m) CO,
165Ϫ122 (m) Ph, 62.8 (m) CH2, 38.5 (br. s) CH3N, 16.3 (s) CH3 ppm.
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G. Albertin, S. Antoniutti, M. T. Giorgi
FULL PAPER
mulation and a geometry in solution can also be established lated manganese complexes [Mn(NH2NH2)(CO)nP5Ϫn]BPh4
from the IR and NMR spectroscopic data.
also react with Pb(OAc)4,[11] but give only thermally un-
Diagnostic evidence for the presence of the NHϭNH li- stable diazene complexes, which cannot be isolated.
1
gand are the H NMR spectra, which show a multiplet of
The arylhydrazine complexes [Re(ArNHNH2)(CO)n-
the type shown in Figure 1 in the high-frequency region, P5Ϫn]BPh4 also react with Pb(OAc)4 to give the correspond-
which can reasonably be attributed to the H1 and H2 pro- ing aryldiazene complexes [Re(ArNϭNH)(CO)nP5Ϫn]BPh4,
tons of the diazene ligand coupled to the phosphorus nu- which were isolated and characterised (Scheme 3).
cleus of the phosphane. This multiplet, in fact, can easily
be simulated by using A2XY, AB2XY or A4XY models (X,
Y ϭ H), with the parameters reported in Table 1. The value
3
of JH,H was found to fall in the range 35Ϫ27 Hz, suggest-
ing a probable trans-NHϭNH geometry of the ligand.[16a]
1
Figure 1. Observed (bottom) and calculated (top) H NMR spec-
trum in the diazene region of [Re(NHϭNH)(CO)3(PPh2O-
Scheme 3
Et)2]BPh4 (14a), in CD2Cl2 at 25 °C; the simulated spectrum was
obtained using the parameters reported in Table 1
These complexes are yellow or orange solids that are
IR and NMR spectroscopic data support the geometry stable in air and in solution in polar organic solvents, where
shown in Scheme 2 for the diazene complexes 9Ϫ14, which they behave as 1:1 electrolytes.[14] Analytical and spectro-
proves to be the same as that of the related hydrazine pre- scopic data (Table 1) confirm the proposed formulation.
cursors. The oxidation of the NH2NH2 ligand does not Furthermore, the spectroscopic data of complex 9c are
change the geometry of the complexes, and a trans ge- identical to those of samples we have previously prepared
ometry is proposed for the monocarbonyl complex 9a on by reacting the ReH(CO)P4 hydride with a phenyldiazon-
the basis of the sharp singlet present in the 31P NMR spec- ium cation;[18] this feature strongly supports the proposed
trum. A fac structure is proposed for the dicarbonyl com- formulation. Moreover, this result highlights that stable ar-
plexes 11a and 12a, as their IR spectra show two ν(CO) yldiazene complexes of rhenium can be prepared following
bands, while an AB2 multiplet appears in the 31P NMR two different methods, which involve the oxidation of a co-
spectra. Finally, the presence of three ν(CO) bands, one me- ordinated arylhydrazine, in one case, and the insertion of
dium and two strong, in the IR spectra of the tricarbonyl an aryldiazonium cation into the ReϪH bond of the appro-
complexes 13a and 14a, and only one sharp singlet in the priate hydride complex, in the other.
31P NMR spectra, suggest a mer-trans geometry for the
complexes.
The presence of the aryldiazene ligand in complexes 9c,
11c and 13d is confirmed by the H NMR spectra, which
1
The stabilization of the very reactive molecule NHϭNH show the characteristic high-frequency signal of the ArNϭ
by coordination to a transition metal has been achieved in NH ligand. The IR and NMR spectra also allow a ge-
a few cases, mainly in bimetallic complexes containing a µ- ometry in solution to be established (Scheme 3). Apart from
NHϭNH ligand.[15] Stable derivatives containing a mono- the trans geometry of the monocarbonyl complex 9c,[18]
a
dentate diazene have been reported,[16] but they are rather mer-cis arrangement of the ligands, like that of the related
rare and include only one example for rhenium.[17] The use compound [Re(C6H5NϭNH)(CO)2(PPh2OEt)3]BPh4,[18]
of a mixed-ligand phosphite-carbonyl Re(CO)nP5Ϫn frag- can be proposed for the carbonyl complex 11c. The IR spec-
ment allows new examples of the stabilization of monodent- tra, in fact, show two ν(CO) bands, while an AB2 multiplet
ate diazene to be achieved. It should be noted that the re- is observed in the 31P NMR spectrum.
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Hydrazine Complexes of Rhenium
FULL PAPER
In the temperature range between ϩ20 and Ϫ80 °C the protons, in agreement with the proposed assignment. In the
31P NMR spectrum of the tricarbonyl compound 13d ap- temperature range between ϩ20 and Ϫ80 °C the 31P NMR
pears as a sharp singlet, while the IR spectrum shows one spectrum appears as an A2B multiplet indicating that two
medium-intensity and two strong bands in the ν(CO) re- of the phosphites are magnetically equivalent and different
gion. On this basis, a mer-trans geometry for the complex from the third. On the basis of these data a fac geometry
can be proposed.
(Scheme 4) can reasonably be proposed.
Surprisingly, the reaction of methylhydrazine complexes
A similar fac geometry can also be proposed for the
with an equimolar amount of Pb(OAc)4 gives a mixture of methyldiazene derivative 10b on the basis of the presence
ϩ
methyldiazene [Re(CH3NϭNH)(CO)nP5Ϫn
]
and methyl- of two ν(CO) bands in the IR spectrum and only one mul-
ϩ
eneimine [Re(η1-NHϭCH2)(CO)nP5Ϫn
]
derivatives, which tiplet for the carbonyl carbon atoms at δ ϭ 196.2 ppm in
were separated and characterised (Scheme 4).
the 13C NMR spectrum, indicating the magnetic equival-
ence of the two cis carbonyl ligands. A singlet at δ ϭ
71.7 ppm is also present in the 13C NMR spectrum; it was
attributed, with the help of an HMQC experiment, to the
methyl carbon atom of the CH3NϭNH ligand. The pres-
1
ence of this ligand is confirmed by the H NMR spectrum,
which shows the characteristic diazene signal at δ ϭ
15.86 ppm and the methyl protons as a doublet at δ ϭ
4.44 ppm. The 31P NMR spectrum appears as an A2B mul-
tiplet, in agreement with the proposed geometry.
The results on the oxidation of methylhydrazine com-
plexes seem to indicate that the formation of an η1-NHϭ
CH2 ligand is general for the [Re(CO)nP5Ϫn] [n ϭ 1, 2; P ϭ
P(OEt)3,
PPh(OEt)2]
fragments
containing
the
CH3NHNH2 ligand, but appears to be specific for
Pb(OAc)4, as attempts to carry out the reaction with other
oxidants like MnO2 or H2O2 were unsuccessful. Further-
more, while oxidation of a coordinated hydrazine to the re-
lated diazene is a known reaction, the formation of the
methyleneimine molecule in the reaction of methylhydra-
zine with Pb(OAc)4 is completely new and involves the
cleavage of the NϪN bond.[19] Finally, it is worth noting
that methyleneimine is a very reactive molecule which has
never been isolated since it is unstable above Ϫ80 °C in the
Scheme 4
The two monocarbonyl complexes 9b and 9*b were free state.[20] It has been detected in outer space,[21] and has
characterised not only spectroscopically (IR and NMR been proposed as a possible precursor[22] of the simplest α-
spectroscopic data) but also by two X-ray crystal structure amino acid glycine. As a ligand, it has been found in only
determinations. These structures were reported in a prelimi- one case, through π-coordination to an osmium centre,[23]
nary communication[12] and will not be discussed further.
and no other report has been found on this molecule, which
The dicarbonyl complexes 10b and 10*b, containing the displays a simple constitution and structure and whose
P(OEt)3 ligand, can be separated by fractional crystallis- chemical properties are still unknown.
ation or by the Pasteur method, obtaining the methyldiaz-
We have also investigated the products of the oxidation
ene (10b) and the methyleneimine (10*b) species as white of methylhydrazine complexes in order to establish a stoi-
microcrystalline solids, while the related PPh(OEt)2 deriva- chiometry and/or a possible reaction path. In the reaction
tives 11b and 11*b were characterised spectroscopically as mixture we have unambiguously identified, beside the
a mixture of the two species. The presence of the CH2ϭNH methyldiazene complexes 9b and 10b and the methyleneim-
ligand in 10*b is confirmed by the 1H NMR spectrum, ine complexes 9*b and 10b*, only acetic acid, dinitrogen
which shows the NH signal at δ ϭ 13.82 ppm and the two and traces of NH3. Both the NMR spectra and GC analysis
inequivalent CH2 protons as an AB quadruplet at δ ϭ of the reaction mixture also revealed the presence of other
3.75 ppm. The IR spectra show two strong bands at 2002 species, but all were present in very small amounts and were
and 1915 cmϪ1 attributed to two CO ligands in a mutually not identified.
cis position. These two carbonyls are also magnetically
The oxidation of methylhydrazine to methyldiazene by
equivalent, since the 13C NMR spectrum shows only one Pb(OAc)4 probably proceeds to give acetic acid and lead()
multiplet at δ ϭ 194.7 ppm for the carbonyl carbon atoms. acetate (Scheme 5) and should involve the loss of two hy-
A singlet at δ ϭ 67.8 ppm is also present in the 13C NMR drogen atoms and two electrons with cleavage of two NϪH
spectrum and is attributed to the methylene carbon atom bonds to give the final methyldiazene species. The forma-
of the CH2ϭNH ligand. A 1H, 13C HMQC experiment cor- tion of the coordinated methyleneimine, however, seems to
relates this signal with that at δ ϭ 3.75 ppm for the ϭCH2 be much more complicated and should involve the cleavage
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G. Albertin, S. Antoniutti, M. T. Giorgi
FULL PAPER
of one NϪN and one CϪH bond (Scheme 6), with the loss
The complex was isolated as its BPh4 salt and character-
of fragments such as H or NH2 to give the final species. ised in the usual way (Table 1). The IR spectrum shows two
However, the lack of identified reaction products, as well as strong ν(CO) bands at 2005 and 1894 cmϪ1 due to two car-
of any intermediates, does not allow us to determinate bonyls in a mutually cis position. Two absorptions of me-
either the stoichiometry or to propose a path for the reac- dium intensity are also present at 3329 and 3283 cmϪ1, at-
tion.
tributed to ν(NH) of the methylamine ligand. The presence
of this ligand is confirmed by the 1H NMR spectrum,
which shows a triplet at δ ϭ 2.73 ppm for the CH3 group
and a broad signal at δ ϭ 2.65 ppm for the NH2 group
of the CH3NH2 ligand. The 13C NMR spectrum further
supports the proposed formulation for the complex and
indicates that the two CO ligands are magnetically equiva-
lent, showing only one multiplet at δ ϭ 194.2 ppm for the
carbonyl carbon atom. In the temperature range between
ϩ20 and Ϫ80 °C, the 31P NMR spectrum appears as an
A2B multiplet indicating that two of the phosphanes are
magnetically equivalent and different from the third. On the
basis of these data, a fac geometry can be proposed for our
methylamine complex 15.
Scheme 5
The reaction of this complex with Pb(OAc)4 was studied
extensively in an attempt to prepare a methyleneimine com-
plex by selective oxidation of the CH3NH2 ligand. Unfortu-
nately, the reaction does not proceed under any conditions
[at Ϫ40 or at ϩ20 °C, with an equimolar or an excess
amount of Pb(OAc)4; Scheme 8], and the starting amine
complex was recovered almost quantitatively. The coordi-
nated methylamine does not react with Pb(OAc)4 and this
reaction, therefore, cannot be used to prepare methyleneim-
ine complexes. Until a new method can be found, only the
reaction of coordinated methylhydrazine can give a stable
complex containing methyleneimine as a unidentate ligand,
even though it is formed as a mixture.
Scheme 6
In light of the reagent and the η1-NHϭCH2 species
formed, an N1 to N2 shift in the coordination of the meth-
ylhydrazine followed by NϪN and CϪH bond cleavage
with loss of NH3 and formation of the methyleneimine li-
gand may be hypothesized. The presence of only traces of
NH3 in the reaction mixture, however, seems to exclude
such a mechanism in which the Pb(OAc)4 does not behave
as an oxidant, but only as a catalyst.
Further studies on other metal complexes will, therefore,
be required to shed light on the mechanism of this new re-
action.
Scheme 8
The stabilization of the methyleneimine molecule by co-
ordination to appropriate metal fragments prompted us to
attempt to prepare similar η1-NHϭCH2 complexes follow-
ing a different method involving, for example, the reaction
of a methylamine (CH3NH2) derivative with Pb(OAc)4.
Reduction Reactions
The hydrazine complexes [Re(NH2NH2)(CO)2P3]BPh4
[P ϭ PPh(OEt)2 and PPh2OEt] are reduced by zinc amal-
gam in tetrahydrofuran (THF) in the presence of 2,6-luti-
dine hydrochloride (Lu·HCl) to give NH3 in about a
20Ϫ25% yield (Table 2). The reaction was carried out at
room temperature under argon and found to be relatively
slow, with the formation of NH3 in appreciable amounts
after 24 h. The conversion is, however, rather low and the
addition of free NH2NH2 does not increase the conversion
into NH3, thus excluding any catalytic involvement of the
rhenium complexes. Also, the related 1,2-diazene complex
[Re(NHϭNH)(CO)2{PPh(OEt)2}3]BPh4 is reduced by zinc
amalgam to give NH3 but, as expected, with a lower yield
(about 7%) than the hydrazine precursors. Instead, a rela-
tively high conversion (about 27%) was observed with the
methylhydrazine complex [Re(CH3NHNH2)(CO)2{PPh-
(OEt)2}3]BPh4 and this result may be connected with the
The
synthesis
of
the
precursor
complex
[Re(CH3NH2)(CO)2{P(OEt)3}3]BPh4 (15) was achieved by
reacting the hydride complex [ReH(CO)2{P(OEt)3}3] first
with triflic acid and then with an excess of CH3NH2, as
shown in Scheme 7.
Scheme 7. P ϭ P(OEt)3
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Hydrazine Complexes of Rhenium
FULL PAPER
Table 2. Reduction reactions of hydrazine, methylhydrazine and diazene complexes to give ammonia
(mol)[a]
Time (h)
Conv. (%)
[a][b]
Compd
Mol
NH3
[Re(NH2NH2)(CO)2{PPh(OEt)2}3]BPh4 (3a)
[Re(NH2NH2)(CO)2{PPh(OEt)2}3]BPh4 (3a)
[Re(NH2NH2)(CO)2{PPh2OEt}3]BPh4 (4a)
[Re(CH3NHNH2)(CO)2{PPh(OEt)2}3]BPh4 (3b)
[Re(NHϭNH)(CO)2{PPh(OEt)2}3]BPh4 (11a)
[Re(NH2NH2)(CO)2{PPh(OEt)2}3]BPh4 (3a)[c]
Zn(Hg)/Lut·HCl
1.82·10Ϫ4
9.25·10Ϫ5
8.87·10Ϫ5
1.20·10Ϫ4
7.17·10Ϫ5
9.33·10Ϫ5
1.81·10Ϫ5
3.71·10Ϫ5
4.41·10Ϫ5
3.18·10Ϫ5
0.97·10Ϫ5
2.26·10Ϫ4
2.6·10Ϫ6
23
48
72
26
48
96
24
24
5
20
25
27
7
12
NH2NH2/Zn(Hg)/Lut·HCl
1.02·10Ϫ4 [d]
3.1·10Ϫ6
1.5
[a] At 25 °C. [b] Mean value from two or three experiments. [c] Containing added NH2NH2 (9.4·10Ϫ4 mol, ratio 10:1). [d] Mol of NH2NH2.
zines CH3NHNH2, C6H5NHNH2, 4-NO2C6H4NHNH2, and
(CH3)2NNH2 are Aldrich products and were used as received. High
purity (99.99%) Pb(OAc)4 is an Aldrich product was used as re-
ceived. Hydrazine (NH2NH2) was prepared by decomposition of
hydrazine cyanurate (Fluka) following the reported method.[25]
Other reagents were purchased from commercial sources in the
highest available purity and used as received. Infrared spectra were
recorded on a Nicolet Magna 750 FT-IR spectrophotometer. NMR
spectra (1H, 31P, 13C) were obtained on Bruker AC200 or Bruker
observed easy cleavage of the NϪN bond of methylhydra-
zine bonded to [Re(CO)2P3] or [Re(CO)P4] fragments. In
the presence of Pb(OAc)4, in fact, the methyleneimine spec-
ies [Re]η1-NHϭCH2 is formed, whereas ammonia is ob-
tained with Zn amalgam and Lut·HCl; in both cases cleav-
age of the NϪN bond of the coordinated methylhydrazine
takes place.
Although these data must be considered as preliminary
results, they indicate that both hydrazine and diazene mol-
AVANCE 300 spectrometers at temperatures varying between Ϫ90
1
ecules bonded to the [Re(CO)2P3] fragment can be reduced and ϩ30 °C, unless otherwise noted. H spectra are referenced to
internal tetramethylsilane, while 31P{1H} chemical shifts are re-
to ammonia by zinc amalgam, and this seems to be an
ported with respect to 85% H3PO4, with downfield shifts con-
interesting observation in organometallic diazo chemistry.
sidered positive. The SwaN-MR software package[26] was used in
treating the NMR spectroscopic data. The conductivities of 10Ϫ3
 solutions of the complexes in CH3NO2 at 25 °C were measured
with a Radiometer CDM 83 instrument.
Conclusions
In this contribution we have shown that a series of
hydrazine complexes of rhenium of the type
[Re(RNHNH2)(CO)nP5Ϫn]BPh4 can easily be prepared
from precursor ReH(CO)nP5Ϫn hydrides. Among the
properties shown by these complexes we can highlight the
reaction of the methylhydrazine species with Pb(OAc)4,
which gives the unprecedented methyleneimine derivative
[Re(η1-NHϭCH2)(CO)nP5Ϫn]BPh4 as well as the methyldi-
azene derivative [Re(CH3NϭNH)(CO)nP5Ϫn]BPh4. Also,
1,2-diazene can be stabilized by the Re(CO)nP5Ϫn fragment,
allowing stable [Re(NHϭNH)(CO)nP5Ϫn]BPh4 complexes
to be obtained through the selective oxidation of the hydra-
zine precursors with Pb(OAc)4. Finally, reduction of hydra-
zine and diazene complexes with zinc amalgam in the pres-
ence of Lu·HCl was also tested and found to give NH3 in
low yield.
Synthesis of Complexes: The hydrides [ReH(CO)nP5Ϫn] [n ϭ 1Ϫ4;
P ϭ P(OEt)3, PPh(OEt)2, PPh2OEt] were prepared following the
method reported previously.[13]
[Re(NH2NH2)(CO){P(OEt)3}4]BPh4 (1a) and [Re{(CH3)2NNH2}
(CO){P(OEt)3}4]BPh4 (1e): An equimolar amount of CF3SO3H
(0.2 mmol, 18 µL) was added to a solution of the hydride
[ReH(CO){P(OEt)3}4] (0.2 mmol, 196 mg) in 8 mL of CH2Cl2 co-
oled to Ϫ196 °C, and the reaction mixture warmed to room tem-
perature and stirred for about 1 h. An excess of the appropriate
hydrazine (0.6 mmol) was added to the resulting solution which
was stirred for a time varying between 3 (1a) and 24 (1e) h and
then the solvent was removed under reduced pressure. The oil ob-
tained was triturated with 3 mL of ethanol containing an excess of
NaBPh4 (0.4 mmol, 137 mg). Upon cooling of the resulting solu-
tion to Ϫ25 °C, a white solid separated out which was filtered off
and recrystallised from CH2Cl2 (3 mL) and ethanol (3 mL); yield
between 80% (1a) and 15% (1e).
1a: C49H84BN2O13P4Re (1230.11): calcd. C 47.84, H 6.88, N 2.28;
found C 47.58, H 6.94, N 2.20. ΛM ϭ 55.4 ΩϪ1 molϪ1 cm2
1e: C51H88BN2O13P4Re (1258.17): calcd. C 48.69, H 7.05, N 2.23;
found C 48.92, H 7.24, N 2.08. ΛM ϭ 58.6 ΩϪ1 molϪ1 cm2.
Experimental Section
General: All synthetic work was carried out under an inert atmos-
phere (Ar, N2) using standard Schlenk techniques or a Vacuum [Re(C6H5NHNH2)(CO){P(OEt)3}4]BPh4 (1c): An equimolar
Atmosphere dry-box. Once isolated, the complexes were found to
be relatively stable in air, but were stored under an inert atmosphere
at Ϫ25 °C. All solvents were dried over appropriate drying agents,
degassed on a vacuum line and distilled into vacuum-tight storage
amount of HBF4·Et2O (0.2 mmol, 28 µL) was added to a solution
of the hydride [ReH(CO){P(OEt)3}4] (0.2 mmol, 176 mg) in 5 mL
of CH2Cl2 cooled to Ϫ196 °C, and the reaction mixture warmed
to room temperature and stirred for 1 h. An excess of C6H5NHNH2
flasks. Re2(CO)8 was a Pressure Chem. (USA) product, and used (0.6 mmol, 60 µL) was added to the resulting solution, which was
as received. Triethylphosphite P(OEt)3 (Aldrich) was purified by
distillation under nitrogen, while PPh(OEt)2 and PPh2OEt were
prepared by the method of Rabinowitz and Pellon.[24] The hydra-
stirred for about 150 min, and then the solvent was removed under
reduced pressure. The oil obtained was treated with ethanol (3 mL),
and then an excess of NaBPh4 (0.4 mmol, 137 mg) in 3 mL of etha-
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G. Albertin, S. Antoniutti, M. T. Giorgi
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nol was added. A white solid slowly separated out which was fil-
under reduced pressure to give a yellow oil, which was triturated
tered off and recrystallised from CH2Cl2 (2 mL) and ethanol with ethanol containing an excess of NaBPh4 (0.4 mmol, 137 mg).
(2 mL); yield Ն40%. C55H88BN2O13P4Re (1306.21): calcd. C 50.57, Upon cooling of the resulting solution to Ϫ25 °C a white solid
H 6.79, N 2.14; found C 50.49, H 6.87, N 2.10. ΛM ϭ 55.8 ΩϪ1
separated out, which was filtered off and recrystallised from
CH2Cl2 and ethanol; yield between 55 and 80%.
5a: Yield Ն 55% C39H54BN2O9P2Re (953.82): calcd. C 49.11, H
5.71, N 2.94; found C 48.94, H 5.80, N 3.02. ΛM ϭ 56.6 ΩϪ1
molϪ1 cm2.
6a: Yield Ն 65% C48H56BN2O7P2Re (1031.94): calcd. C 55.87, H
5.47, N 2.71; found C 55.74, H 5.55, N 2.79. ΛM ϭ 54.8 ΩϪ1
molϪ1 cm2.
6d: Yield Ն 80% C53H57BN3O9P2Re (1139.01): calcd. C 55.89, H
5.04, N 3.69; found C 55.71, H 5.18, N 3.59. ΛM ϭ 51.6 ΩϪ1
molϪ1 cm2.
7a: Yield Ն 60% C55H54BN2O5P2Re (1082.00): calcd. C 61.05, H
5.03, N 2.59; found C 61.23, H 5.15, N 2.68. ΛM ϭ 60.2 ΩϪ1
molϪ1 cm2.
molϪ1 cm2.
[Re(CH3NHNH2)(CO)2{P(OEt)3}3]BPh4 (2b): An equimolar
amount of HBF4·Et2O (0.2 mmol, 28 µL) was added to a solution
of [ReH(CO)2{P(OEt)3}3] (0.2 mmol, 143 mg) in 5 mL of CH2Cl2
cooled to Ϫ196 °C, and the reaction mixture warmed to room tem-
perature and stirred for 1 h. An excess of methylhydrazine
(0.3 mmol, 16 µL) was added to the resulting solution which was
stirred for 3 h and then the solvents evaporated to dryness. The oil
obtained was treated with ethanol (2 mL) containing an excess of
NaBPh4 (0.4 mmol, 137 mg). Upon cooling the resulting solution
to Ϫ25 °C a white solid slowly separated out which was filtered off
and recrystallised from CH2Cl2 (2 mL) and ethanol (2 mL); yield
Ն65%. C45H71BN2O11P3Re (1105.99): calcd. C 48.87, H 6.47, N
2.53; found C 48.80, H 6.55, N 2.48. ΛM ϭ 50.8 ΩϪ1 molϪ1 cm2.
7b: Yield Ն 70% C56H56BN2O5P2Re (1096.03): calcd. C 61.37, H
5.15, N 2.56; found C 61.19, H 5.25, N 2.62. ΛM ϭ 57.4 ΩϪ1
molϪ1 cm2.
[Re(RNHNH2)(CO)2P3]BPh4 3, 4 [R ؍ H a, CH3 b, 4-NO2C6H4 d;
P ؍ PPh(OEt)2 3, PPh2OEt 4]: These complexes were prepared
similarly to 1 by reacting the appropriate hydride ReH(CO)2P3
(0.2 mmol) first with an equimolar amount of CF3SO3H and then
with an excess (0.6 mmol) of the appropriate hydrazine. The reac-
tion time was 20 h for 3a, 3b, 4a and 24 h for 3d and 4b; yields
between 60 and 80%.
[Re(NH2NH2)(CO)4(PPh2OEt)]BPh4 (8a): This complex was pre-
pared similarly to complexes 5a, 6a and 7a; yield approx. 65%.
C42H39BN2O5PRe (879.76): calcd. C 57.34, H 4.47, N 3.18; found
C 57.13, H 4.50, N 3.10. ΛM ϭ 57.0 ΩϪ1 molϪ1 cm2.
[Re(NH؍NH)(CO){P(OEt)3}4]BPh4 (9a): A solid sample of the
hydrazine complex [Re(NH2NH2)(CO){P(OEt)3}4]BPh4 (1a;
0.1 mmol, 123 mg) was placed in a three-necked 25-mL round-bot-
tomed flask fitted with a solid-addition sidearm containing a slight
excess of Pb(OAc)4 (0.12 mmol, 53 mg). Dichloromethane (10 mL)
was added, the solution cooled to Ϫ40 °C and the Pb(OAc)4 added
portionwise over 20Ϫ30 min to the cold stirring solution. The solu-
tion was then warmed to 0 °C, stirred for 15 min and the solvent
removed under reduced pressure. The oil obtained was treated at 0
°C with ethanol (2 mL) containing an excess of NaBPh4 (0.2 mmol,
68 mg) and the white solid separated was filtered off and recrystal-
lised at 0 °C from CH2Cl2 (2 mL) and ethanol (2 mL); yield approx.
45%. C49H82BN2O13P4Re (1228.10): calcd. C 47.92, H 6.73, N 2.28;
found C 48.01, H 6.77, N 2.19. ΛM ϭ 54.8 ΩϪ1 molϪ1 cm2.
3a: Yield Ն 60% C56H69BN2O8P3Re (1188.10): calcd. C 56.61, H
5.85, N 2.36; found C 56.43, H 5.89, N 2.28. ΛM ϭ 58.9 ΩϪ1
molϪ1 cm2.
3b: Yield Ն 70% C57H71BN2O8P3Re (1202.13): calcd. C 56.95, H
5.95, N 2.33; found C 57.11, H 6.03, N 2.20. ΛM ϭ 58.1 ΩϪ1
molϪ1 cm2.
3d: Yield Ն 80% C62H72BN3O10P3Re (1309.20): calcd. C 56.88, H
5.54, N 3.21; found C 56.95, H 5.62, N 3.17.. ΛM ϭ 49.3 ΩϪ1
molϪ1 cm2.
4a: Yield Ն 75% C68H69BN2O5P3Re (1284.23): calcd. C 63.60, H
5.42, N 2.18; found C 63.46, H 5.51, N 2.15. ΛM ϭ 49.4 ΩϪ1
molϪ1 cm2.
4b: Yield Ն 65% C69H71BN2O5P3Re (1298.26): calcd. C 63.84, H
5.51, N 2.16; found C 63.66, H 5.59, N 2.20. ΛM ϭ 60.0 ΩϪ1
molϪ1 cm2.
[Re(C6H5N؍NH)(CO){P(OEt)3}4]BPh4 (9c): This complex was
prepared by oxidation of the corresponding hydrazine derivatives
with Pb(OAc)4 at low temperature (Ϫ40 °C) following the method
used for the related 1,2-diazene derivative 9a; yield approx. 55%.
C55H86BN2O13P4Re (1304.20): calcd. C 50.65, H 6.65, N 2.15;
found C 50.43, H 6.70, N 2.09. ΛM ϭ 52.8 ΩϪ1 molϪ1 cm2.
[Re(C6H5NHNH2)(CO)2{PPh(OEt)2}3]BPh4 (3c): This complex
was prepared similarly to 2b by treating [ReH(CO)2{PPh(OEt)2}3]
(0.2 mmol) first with an equimolar mount of HBF4·Et2O and then
with an excess of C6H5NHNH2. The reaction time was 150 min;
yield approx. 40%. C62H73BN2O8P3Re (1264.20): calcd. C 58.91,
H 5.82, N 2.22; found C 59.05, H 5.90, N 2.27. ΛM ϭ 51.3 ΩϪ1
molϪ1 cm2.
[Re(CH3N؍NH)(CO)2{P(OEt)3}3]BPh4 (10b) and [Re(η1-NH؍
CH2)(CO)2{P(OEt)3}3]BPh4
(10*b):
A
sample
of
[Re(CH3NHNH2)(CO)2{P(OEt)3}3]BPh4 (2b; 200 mg, 0.18 mmol)
was placed in a three-necked 25-mL round-bottomed flask fitted
with a solid-addition sidearm containing Pb(OAc)4 (0.18 mmol,
80 mg). Dichloromethane (8 mL) was added, the solution cooled
to Ϫ40 °C and the Pb(OAc)4 added portionwise over 10Ϫ20 min
to the cold stirring solution. The solution was then warmed to 0
°C, stirred for 10 min, and the solvent removed under reduced
pressure. The oil obtained was treated at 0 °C with ethanol (2 mL)
containing an excess of NaBPh4 (0.2 mmol, 68 mg). A white solid
slowly separated out, which was filtered and crystallised frac-
[Re{(CH3)2NNH2)(CO)2{PPh(OEt)2}3]BPh4 (3e): This compound
was also prepared similarly to complexes 3 and 4 using CF3SO3H
as the protonating agent, but in this case a large excess of
(CH3)2NNH2 was used; yield approx. 75%. C58H73BN2O8P3Re
(1216.15): calcd. C 57.28, H 6.05, N 2.30; found C 57.37, H 6.12,
N 2.28. ΛM ϭ 49.5 ΩϪ1 molϪ1 cm2.
[Re(RNHNH2)(CO)3P2]BPh4 5؊7 [R ؍ H a, CH3 b, 4-NO2C6H4
d; P ؍ P(OEt)3 5, PPh(OEt)2 6, PPh2OEt 7]: An equimolar mount
of CF3SO3H (0.2 mmol, 18 µL) was added to a solution of the
appropriate hydride ReH(CO)3P2 (0.2 mmol) in 7 mL of CH2Cl2 tionally to separate the two complexes. A typical separation in-
cooled to Ϫ196 °C, and the reaction mixture warmed to room tem- volved the slow cooling from ϩ25 to Ϫ25 °C of a saturated solution
perature and stirred for 1 h. An excess of the appropriate hydrazine of the complexes prepared by adding 10 mL of ethanol to the white
(0.6 mmol) was added and the resulting solution was stirred for 3
solid and enough CH2Cl2 to obtain a saturated solution at room
h for 5a, 6a, 7a; 8 h for 6d and 15 h for 7b. The solvent was removed
temperature. The first crystals obtained were 10b, and the second
2864
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Eur. J. Inorg. Chem. 2003, 2855Ϫ2866

Hydrazine Complexes of Rhenium
FULL PAPER
a mixture, which was further recrystallised. Upon further cooling,
white microcrystals of 10*b were obtained. Pure samples of 10b
and 10*b were also obtained by Pasteur separation of the crystals
obtained by cooling a saturated solution of the reaction product in
ethanol/CH2Cl2; yield: 38% for 10b and 25% for 10*b
10b: C45H69BN2O11P3Re (1103.98): calcd. C 48.96, H 6.30, N 2.54;
found C 49.11, H 6.23, N 2.43. ΛM ϭ 51.1 ΩϪ1 molϪ1 cm2.
10*b: C45H68BNO11P3Re (1088.96): calcd. C 49.63, H 6.29, N 1.29;
found C 49.45, H 6.37, N 1.35. ΛM ϭ 58.9 ΩϪ1 molϪ1 cm2.
a 10-fold excess of Zn (20 mmol), as 2% zinc amalgam, to a solu-
tion of the appropriate diazo complex (about 0.1 mmol) in 10 mL
of THF. A 16-fold excess of lutidine hydrochloride in 10 mL of
THF was then added to the reaction mixture, which was stirred at
room temperature under an argon atmosphere for a reaction time
varying from 23 to 96 h. An excess of hydrochloric acid (1 mL of
1  solution in Et2O) was added to the reaction mixture, which
was stirred for 1 h. The solvent was then removed under reduced
pressure. The solid obtained was treated with five 5-mL portions
of H2O and, after filtration, ammonia from the solution was
quantified by the indophenol method.[27]
[Re(CH3N؍NH)(CO)2{PPh(OEt)2}3]BPh4 (11b) and [Re(η1-NH؍
CH2)(CO)2{PPh(OEt)2}3]BPh4 (11*b): These complexes were also
prepared by oxidation of the methylhydrazine complex
[Re(CH3NHNH2)(CO)2{PPh(OEt)2}3]BPh4 (3b) with Pb(OAc)4 at
Ϫ40 °C following exactly the same method as used for the synthesis
of 10b and 10*b. The reaction afforded a mixture of the two species
which, in this case, could not be separated. The IR and NMR spec-
troscopic data, however, confirm the formation of both the methyl-
diazene (11b) and methyleneimine (11*b) derivatives.
Acknowledgments
The financial support of MIUR (Rome) Programmi di Ricerca
Scientifica di Rilevante Interesse Nazionale, COFIN 2002-2003 is
gratefully acknowledged. We thank Daniela Baldan for technical
assistance.
[Re(NH؍NH)(CO)2P3]BPh4 [P ؍ PPh(OEt)2 11a, PPh2OEt 12a]:
These complexes were prepared by oxidation of the hydrazine pre-
cursors [Re(NH2NH2)(CO)2P3]BPh4 (3a, 4a) with Pb(OAc)4 at Ϫ40
°C following the method used for the related compound 9a; yield
between 40 and 55%.
11a: C56H67BN2O8P3Re (1186.09): calcd. C 56.71, H 5.69, N 2.36;
found C 56.58, H 5.73, N 2.29. ΛM ϭ 59.2 ΩϪ1 molϪ1 cm2.
12a: C68H67BN2O5P3Re (1282.22): calcd. C 63.70, H 5.27, N 2.18;
found C 63.56, H 5.33, N 2.08. ΛM ϭ 57.7 ΩϪ1 molϪ1 cm2.
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added to a solution of [ReH(CO)2{P(OEt)3}3] (200 mg, 0.27 mmol)
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N 1.29. ΛM ϭ 58.5 ΩϪ1 molϪ1 cm2.
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Eur. J. Inorg. Chem. 2003, 2855Ϫ2866
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 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2865

G. Albertin, S. Antoniutti, M. T. Giorgi
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2866
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2003, 2855Ϫ2866