Diazo complexes of rhenium: Preparations and crystal structures of the bis(dinitrogen), [Re(N2)2{PPh(OEt)2}4][BPh4] and methyldiazenido [ReCl(CH3N2)(CH3NHNH2){PPh(OEt)2}3][BPh4] derivatives

Article abstract of DOI:10.1021/ic990970r

Depending on experimental conditions and the nature of the hydrazine, the reactions of ReCl₃P₃ [P = PPh(OEt)₂] with RNHNH₂ (R = H, CH₃, (t)Bu) afford the bis(dinitrogen) [Re(N₂)₂P₄]⁺ (2⁺), dinitrogen ReClN₂P₄ (3), and methyldiazenido [ReCl(CH₃N₂)(CH₃NHNH₂)P₃]⁺ (1⁺) derivatives. In contrast, reactions of ReCl₃P₃ [P = PPh(OEt)₂, PPh₂OEt] with arylhydrazines ArNHNH₂ (Ar = Ph, p-tolyl) give the aryldiazenido cations [ReCl(ArN₂)(ArNHNH₂)P₃]⁺ (4⁺) and [ReCl(ArN₂)P₄]⁺ (7⁺) and the bis(aryldiazenido) cations [Re(ArN₂)₂P₃]⁺ (5⁺, 6⁺). These complexes were characterized spectroscopically (IR; ¹H and ³¹P NMR), and the BPh⁴ complexes 1, 2, and 7 were characterized crystallographically. The methyldiazenido derivative [ReCl(CH₃N₂)(CH₃NHNH₂){PPh(OEt)₂}₃][BPh₄] (1) crystallizes in space group P1 with a = 15.396(5) A, b = 16.986(5) A, c = 11.560(5) A, α = 93.96(5)°, β = 93.99(5)°, γ = 93.09(5)°, and Z = 2 and contains a singly bent CH₃N₂, group bonded to an octahedral central metal. One methylhydrazine ligand, one Cl^- trans to the CH₃N₂, and three PPh(OEt)₂ ligands complete the coordination. The complex [Re(N₂)₂{PPh(OEt)₂}₄][BPh₄] (2) crystallizes in space group Pbaa with a = 23.008(5) A, b = 23.367(5) A, c = 12.863(3) A, and Z = 4. The structure displays octahedral coordination with two end-on N₂ ligands in mutually trans positions. [ReCl(PhN₂){PPh(OEt)₂}₄][BPh₄] (7) crystallizes in space group P2₁/n with a = 19.613(5) A, b = 20.101(5) A, c = 19.918(5) A, β = 115.12(2)°, and Z = 4. The structure shows a singly bent phenyldiazenido group trans to the Cl^- ligand in an octahedral environment. The dinitrogen complex ReClN₂P₄ (3) reacts with CF₃SO₃CH₃ to give the unstable methyldiazenido derivative [ReCl(CH₃N₂)P₄][BPh₄]. Reaction of the methylhydrazine complex [ReCl(CH₃N₂)(CH₃NHNH₂)P₃][BPh₄] (1) with Pb(OAc)₄ at -30 °C results in selective oxidation of the hydrazine, affording the corresponding methyldiazene derivative [ReCl(CH₃N=NH)(CH₃N₂)P₃][BPh₄] (8). In contrast, treatment with Pb(OAc)₄ of the related arylhydrazines [ReCl(ArN₂)(ArNHNH₂)P₃][BPh₄] (4) [P = PPh(OEt)₂] gives the bis(aryldiazenido) complexes [Re(ArN₂)₂P₃][BPh₄] (5). Possible protonation reactions of Bronsted acids HX with all diazenides, 1, 4, 5, 6, and 8, were investigated and found to proceed only in the cases of the bis(aryldiazenido) complexes 5 and 6, affording, with HCl, the octahedral [ReCl(ArN=NH)(ArN₂)P₃][BPh₄] or [ReCl{Ar(H)NN}(ArN₂)P₃][BPh₄] (10) (Ar = Ph; P = PPh₂OEt) derivative.

Full text of DOI:10.1021/ic990970r

Inorg. Chem. 2000, 39, 3283-3293
3283
Diazo Complexes of Rhenium: Preparations and Crystal Structures of the Bis(dinitrogen),
[Re(N2)2{PPh(OEt)2}4][BPh4] and Methyldiazenido
[ReCl(CH3N2)(CH3NHNH2){PPh(OEt)2}3][BPh4] Derivatives
Gabriele Albertin,*,† Stefano Antoniutti,† Alessia Bacchi,‡ Emilio Bordignon,†
Francesca Miani,† and Giancarlo Pelizzi‡
Dipartimento di Chimica, Universita` Ca’Foscari di Venezia, Dorsoduro 2137, 30123 Venezia, Italy, and
Dipartimento di Chimica Generale ed Inorganica, Chimica Analitica, Chimica Fisica, Centro CNR di
Strutturistica Diffrattometrica, Universita` di Parma,Viale delle Scienze, 43100 Parma, Italy
ReceiVed August 11, 1999
Depending on experimental conditions and the nature of the hydrazine, the reactions of ReCl3P3 [P ) PPh(OEt)2]
t
with RNHNH2 (R ) H, CH3, Bu) afford the bis(dinitrogen) [Re(N2)2P4]+ (2+), dinitrogen ReClN2P4 (3), and
methyldiazenido [ReCl(CH3N2)(CH3NHNH2)P3]+ (1+) derivatives. In contrast, reactions of ReCl3P3 [P ) PPh-
(OEt)2, PPh2OEt] with arylhydrazines ArNHNH2 (Ar ) Ph, p-tolyl) give the aryldiazenido cations [ReCl(ArN2)-
(ArNHNH2)P3]+ (4+) and [ReCl(ArN2)P4]+ (7+) and the bis(aryldiazenido) cations [Re(ArN2)2P3]+ (5+, 6+). These
complexes were characterized spectroscopically (IR; 1H and 31P NMR), and the BPh4 complexes 1, 2, and 7 were
characterized crystallographically. The methyldiazenido derivative [ReCl(CH3N2)(CH3NHNH2){PPh(OEt)2}3][BPh4]
(1) crystallizes in space group P1h with a ) 15.396(5) Å, b ) 16.986(5) Å, c ) 11.560(5) Å, R ) 93.96(5)°, â
) 93.99(5)°, γ ) 93.09(5)°, and Z ) 2 and contains a singly bent CH3N2, group bonded to an octahedral central
metal. One methylhydrazine ligand, one Cl- trans to the CH3N2, and three PPh(OEt)2 ligands complete the
coordination. The complex [Re(N2)2{PPh(OEt)2}4][BPh4] (2) crystallizes in space group Pbaa with a ) 23.008-
(5) Å, b ) 23.367(5) Å, c ) 12.863(3) Å, and Z ) 4. The structure displays octahedral coordination with two
end-on N2 ligands in mutually trans positions. [ReCl(PhN2){PPh(OEt)2}4][BPh4] (7) crystallizes in space group
P21/n with a ) 19.613(5) Å, b ) 20.101(5) Å, c ) 19.918(5) Å, â ) 115.12(2)°, and Z ) 4. The structure shows
a singly bent phenyldiazenido group trans to the Cl- ligand in an octahedral environment. The dinitrogen complex
ReClN2P4 (3) reacts with CF3SO3CH3 to give the unstable methyldiazenido derivative [ReCl(CH3N2)P4][BPh4].
Reaction of the methylhydrazine complex [ReCl(CH3N2)(CH3NHNH2)P3][BPh4] (1) with Pb(OAc)4 at -30 °C
results in selective oxidation of the hydrazine, affording the corresponding methyldiazene derivative [ReCl(CH3Nd
NH)(CH3N2)P3][BPh4] (8). In contrast, treatment with Pb(OAc)4 of the related arylhydrazines [ReCl(ArN2)-
(ArNHNH2)P3][BPh4] (4) [P ) PPh(OEt)2] gives the bis(aryldiazenido) complexes [Re(ArN2)2P3][BPh4] (5).
Possible protonation reactions of Brønsted acids HX with all diazenides, 1, 4, 5, 6, and 8, were investigated and
found to proceed only in the cases of the bis(aryldiazenido) complexes 5 and 6, affording, with HCl, the octahedral
[ReCl(ArNdNH)(ArN2)P3][BPh4] or [ReCl{Ar(H)NN}(ArN2)P3][BPh4] (10) (Ar ) Ph; P ) PPh2OEt) derivative.
Introduction
the aim of obtaining insight into N2 binding and activation
through metal complexation.
Complexes containing partially reduced dinitrogen ligands
such as diazene, NHdNH, diazenides, RNtN+, or hydrazide,
NHNH2-, were also prepared and studied as models for the
intermediates of N2 reduction.21-24 The goal of these studies
Dinitrogen complexes1-3 are an important class of compounds
which continue to attract interest because of their relevance to
nitrogen fixation processes.4-11 A number of N2 complexes have
been synthesized,1-3,12-20 and several studies on their chemical,
electronic, and structural properties have been carried out, with
† Universita` Ca’Foscari di Venezia.
(13) Nishibayashi, Y.; Iwai, S.; Hidai, M. J. Am. Chem. Soc. 1998, 120,
10559.
‡ Universita` di Parma.
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120, 5836.
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CRC: Boca Raton, FL, 1997.
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10.1021/ic990970r CCC: $19.00 © 2000 American Chemical Society
Published on Web 07/01/2000

3284 Inorganic Chemistry, Vol. 39, No. 15, 2000
Albertin et al.
on diazo complexes was not only to provide insight into the N2
fixation mechanism and the nature of the intermediate but also
to design a dinitrogen reduction process operating under mild
conditions. Development of synthetic methods for obtaining
organonitrogen compounds directly from N2 as the nitrogen
source under mild conditions was a further target of these
studies. Despite the number of research studies, none of these
goals have yet been achieved, but it is generally believed that
systematic in-depth studies on dinitrogen and diazo transition
metal complexes will soon lead to the activation of N2 and its
exploitation to produce NH3 under milder conditions than those
of the Haber-Bosch process.
(PR3)49 (Cp ) η5-C5H5, Cp* ) η5-C5Me5), have been reported.
Except for ReCl(PPhMe2)4(µ-N2)MoCl4(OMe)50 and Tp(CO)2-
Re(µ-N2)Re(CO)2Tp (Tp ) hydridotris(pyrazolyl)borate),51 the
reported compounds are all mononuclear and are often obtained
by reactions of aryldiazenido [Re]-N2COPh and [Re]-N2Ar
species. They contain only one molecule of N2; bis(dinitrogen)-
rhenium derivatives are still without precedent.
Diazo complexes of rhenium are also known21-24 and mainly
include aryldiazenide species,52-62 as hydrazine63-65 and
diazene66-70 complexes are rather rare. No example of a
methyldiazenido complex has ever been reported.
New studies on diazo complexes of rhenium are therefore of
interest not only for their importance in nitrogen fixation
processes, but also because of their diverse reactivity modes
and structural properties.21-24,52-70 This paper reports a sys-
tematic investigation of reactions of ReCl3P3 complexes with
hydrazines that afford a series of new diazo derivatives.
As part of our contribution25-33 to this field, we report here
the syntheses, crystal structures and reactivity studies both of
the first bis(dinitrogen) complexes of rhenium and of other diazo
derivatives, including a rare example of a methyldiazenido
complex.
(Dinitrogen)rhenium complexes with tertiary phosphine and
carbonyl groups as ancillary ligands, of the types ReX(N2)P4,34,35
ReX(CO)2(N2)P2,35,36 ReX(N2)(P-P)2,34,35,37 [ReCl(N2)(P-P)2]-
[FeCl4],38 and Re(S2CNR2)(N2)(PPhMe2)339 (X ) Cl-, Br-, H-;
P ) monodentate phosphine; P-P ) bidentate phosphine),40-44
and with cyclopentadienyl groups as ligands, of the types CpRe-
(CO)2(N2),45,46 Cp*Re(CO)2(N2),47,48 and Cp*Re(CO)(N2)-
Experimental Section
General Materials and Procedures. All synthetic work was carried
out under an appropriate atmosphere (Ar, N2) using standard Schlenk
techniques or a vacuum atmosphere drybox. Once isolated, the
complexes were found to be relatively stable in air but were nevertheless
stored under an inert atmosphere at -25 °C. All solvents were dried
over appropriate drying agents, degassed on a vacuum line, and distilled
into vacuum-tight storage flasks. Metallic rhenium was a Chempur
(Heraeus) product, used as received. Phosphines PPh(OEt)2 and the
PPh2OEt were prepared by the method of Rabinowitz and Pellon.71
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Hydrazines CH3NHNH2, BuNHNH2‚HCl, PhNHNH2, and NH2NH2‚
H2O were Aldrich products, used as received. The compound p-tol
NHNH2 (p-tol ) p-tolyl) was prepared by treating under nitrogen the
corresponding RNHNH2‚HCl salt with a slight excess of NaOH in
aqueous solution. A solid separated out which, after 15 min of stirring,
was filtered off, washed with water, and dried over P2O5 under vacuum
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Diazo Complexes of Rhenium
Inorganic Chemistry, Vol. 39, No. 15, 2000 3285
for 24 h. The product was stored under nitrogen at -25 °C. Hydrazine,
NH2NH2, was prepared by decomposition of hydrazine cyanurate
(Fluka) following the reported method.72 A solution of HCl (0.1 M) in
Et2O was prepared by treating Me3SiCl with CH3OH. 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) were obtained
on a Bruker AC200 spectrometer at temperatures between -90 and
+30 °C, unless otherwise noted. 1H spectra are referred to internal
tetramethylsilane; 31P{1H} chemical shifts are reported with respect to
85% H3PO4, with downfield shifts considered positive. The SwaN-
MR software package73 was used to treat NMR data. The conductivities
of 10-3 M solutions of the complexes in CH3NO2 at 25 °C were
measured with a Radiometer CDM 83 instrument.
(probably the hydrazinium salt) that separated out from the resulting
solution was filtered off and discarded. The solution was cooled to
-25 °C. After 24 h, an orange solid appeared. This was filtered off
and crystallized from a mixture of CH2Cl2 (3 mL) and ethanol (5 mL);
yield g60%. Anal. Calcd for C66H78BClN4O6P3Re, 4a: C, 58.77; H,
5.83; N, 4.15; Cl, 2.63. Found: C, 58.61; H, 5.70; N, 4.29; Cl, 2.70.
ΛM ) 56.2 Ω1- mol-1 cm2. Anal. Calcd for C68H82BClN4O6P3Re, 4b:
C, 59.32; H, 6.00; N, 4.07; Cl, 2.57. Found: C, 59.41; H, 5.92; N,
4.14; Cl, 2.68. ΛM ) 54.9 Ω1- mol-1 cm2.
[Re(ArN2)2P3][BPh4] (5, 6) [P ) PPh(OEt)2, Ar ) Ph (5a); P )
PPh(OEt)2, Ar ) p-tol (5b); PPh2OEt, Ar ) Ph (6)]. An excess of
the appropriate arylhydrazine ArNHNH2 (11.3 mmol) was added to a
suspension of ReCl3P3 (1.13 mmol) in 20 mL of ethanol, and the
reaction mixture was refluxed for about 1 h. The solvent was removed
under reduced pressure, giving an oil, which was treated with ethanol
(5 mL) containing an excess of NaBPh4 (1.5 g, 4.5 mmol). The white
solid (probably the hydrazinium salt) that separated out from the
resulting solution was filtered off and discarded. An orange solid
appeared after the remaining solution was cooled to -25 °C. This was
filtered off and crystallized from a mixture of CH2Cl2 (3 mL) and
ethanol (5 mL); yield g45%. Anal. Calcd for C66H75BN4O6P3Re, 5a:
Syntheses of the Complexes. The compounds ReCl3P3 [P ) PPh-
(OEt)2, PPh2OEt] were prepared as previously reported.74
[ReCl(CH3N2)(CH3NHNH2){PPh(OEt)2}3][BPh4] (1). To a suspen-
sion of ReCl3[PPh(OEt)2]3 (1 g, 1.13 mmol) in 15 mL of ethanol under
an argon atmosphere were added first an excess of methylhydrazine
(0.6 mL, 11.3 mmol) and then an excess of NEt3 (1.57 mL, 11.3 mmol),
and the reaction mixture was stirred for about 2 h. The solvent was
removed under reduced pressure, giving a brown oil, which was treated
with 5 mL of ethanol. The addition of an excess of NaBPh4 (2.33 g,
6.8 mmol) in 3 mL of ethanol to the resulting solution caused the
separation of a yellow solid, from which compound 1 was extracted
with three 4-mL portions of CH2Cl2. The extracts were evaporated to
dryness, giving an oil, which was crystallized from ethanol; yield g40%.
Anal. Calcd for C56H74BClN4O6P3Re: C, 54.92; H, 6.09; N, 4.57; Cl,
2.89. Found: C, 54.84; H, 5.89; N, 4.49; Cl, 2.89. ΛM ) 60.8 Ω-1
mol-1 cm2.
[Re(N2)2{PPh(OEt)2}4][BPh4] (2). A 25-mL three-necked round-
bottomed flask was charged with 1 g (1.13 mmol) of ReCl3[PPh(OEt)2]3
and 15 mL of ethanol under a dinitrogen atmosphere. First an excess
of methylhydrazine (0.6 mL, 11.3 mmol), then an excess of NEt3 (1.57
mL, 11.3 mmol), and last a slight excess of free PPh(OEt)2 (0.44 mL,
2.26 mmol) were added, and the reaction mixture, was stirred for about
90 min. The solvent was removed under reduced pressure, giving an
oil, which was treated with ethanol (7 mL) containing an excess of
NaBPh4 (2.33 g, 6.8 mmol). A yellow solid slowly separated out from
the resulting solution, which was treated with four 3-mL portions of
CH2Cl2 to extract the rhenium complexes that were formed. The extracts
were evaporated to dryness, giving an oil, which was triturated with
ethanol until a solid separated out. This solid was a mixture of
methyldiazenido 1, bis(dinitrogen) 2, and traces of ReCl(N2)P4 (3), from
which 2 was separated by repeated fractional crystallization from
ethanol; yield g15%. Anal. Calcd for C64H80BN4O8P4Re: C, 56.76;
H, 5.95; N, 4.14. Found: C, 56.69; H, 5.95; N, 4.02. ΛM ) 58.2 Ω1-
mol-1 cm2.
ReCl(N2)[PPh(OEt)2]4 (3). To a suspension of ReCl3[PPh(OEt)2]3
(1 g, 1.13 mmol) in 15 mL of ethanol under a dinitrogen atmosphere
were added first an excess of tBuNHNH2‚HCl (1.4 g, 11.3 mmol), then
an excess of NEt3 (3.14 mL, 22.6 mmol), and last a slight excess of
PPh(OEt)2 (0.4 mL, 2 mmol). The reaction mixture was refluxed for
30 min, and the solvent was then removed under reduced pressure,
giving an oil, which was treated with ethanol (5 mL). A pale-yellow
solid slowly separated out after vigorous stirring of the resulting solution
and was collected and crystallized from ethanol; yield g40%. Anal.
Calcd for C40H60ClN2O8P4Re: C, 46.09; H, 5.80; N, 2.69; Cl, 3.40.
Found: C, 45.90; H, 5.83; N, 2.60; Cl, 3.21.
[ReCl(ArN2)(ArNHNH2){PPh(OEt)2}3][BPh4] (4) [Ar ) Ph (4a),
p-tolyl (4b)]. An excess of the appropriate hydrazine ArNHNH2 (11.3
mmol) was added to a suspension of ReCl3[PPh(OEt)2]3 (1 g, 1.13
mmol) in 20 mL of ethanol, and the reaction mixture was stirred at
room temperature for 2 h. The solvent was removed under reduced
pressure, giving an oil, which was treated with ethanol (5 mL)
containing an excess of NaBPh4 (1.54 g, 4.5 mmol). The white solid
C, 60.50; H, 5.77; N, 4.28. Found: C, 60.51; H, 5.74; N, 4.29. ΛM
)
57.9 Ω1- mol-1 cm2. Anal. Calcd for C68H79BN4O6P3Re, 5b: C, 61.03;
H, 5.95; N, 4.19. Found: C, 61.16; H, 5.94; N, 4.21. ΛM ) 56.0 Ω1-
mol-1 cm2. Anal. Calcd for C78H75BN4O3P3Re, 6: C, 66.61; H, 5.38;
N, 3.98. Found: C, 66.51; H, 5.54; N, 4.19. ΛM ) 58.5 Ω1- mol-1
cm2.
[ReCl(PhN2){PPh(OEt)2}4][BPh4] (7). To a suspension of ReCl3-
[PPh(OEt)2]3 (1 g, 1.13 mmol) in 20 mL of ethanol were added first
an excess of PPh(OEt)2 (0.79 mL, 4 mmol) and then an excess of
phenylhydrazine (1.15 mL, 11.3 mmol), and the reaction mixture was
refluxed for 1 h. The solvent was removed under reduced pressure,
giving an oil, which was treated with ethanol (5 mL) containing an
excess of NaBPh4 (1.54 g, 4.5 mmol). The white solid (probably the
hydrazinium salt) that slowly separated out from the resulting solution
was filtered off and discarded. An orange solid appeared after the
remaining solution was cooled to -25 °C. This was filtered off and
crystallized from ethanol; yield g60%. Anal. Calcd for C70H85-
BClN2O8P4Re: C, 58.43; H, 5.95; N, 1.95; Cl, 2.46. Found: C, 58.64;
H, 6.09; N, 2.07; Cl, 2.68. ΛM ) 60.7 Ω1- mol-1 cm2.
[ReCl(CH3NdNH)(CH3N2){PPh(OEt)2}3][BPh4] (8). A sample of
[ReCl(CH3N2)(CH3NHNH2){PPh(OEt)2}3][BPh4] (1) (0.10 g, 0.082
mmol) was placed in a 25-mL three-necked round-bottomed flask fitted
with a solids-addition sidearm containing an equimolar amount of Pb-
(OAc)4 (36 mg, 0.082 mmol). Dichloromethane (10 mL) was added,
the resulting solution was cooled to -30 °C, and Pb(OAc)4 was added
portionwise over 30-40 min to the cold stirred solution. The reaction
mixture was brought to 0 °C, and the solvent was removed under
reduced pressure to give an oil. The addition at 0 °C of cold ethanol (2
mL) containing an excess of NaBPh4 (55 mg, 0.16 mmol) caused the
precipitation of a yellow-orange solid, which was filtered off and
crystallized at 0 °C from a mixture of CH2Cl2 (1 mL) and ethanol (3
mL); yield g65%. Anal. Calcd for C56H72BClN4O6P3Re: C, 55.02; H,
5.94; N, 4.58; Cl, 2.90. Found: C, 55.17; H, 5.86; N, 4.44; Cl, 3.01.
ΛM ) 53.6 Ω1- mol-1 cm2.
[ReCl(PhNdNH)(PhN2)(PPh2OEt)3][BPh4] (10). To a solution of
[Re(PhN2)2(PPh2OEt)3][BPh4] (6) (0.10 g, 0.071 mmol) in 10 mL of
CH2Cl2, cooled to -196 °C, was added a slight excess of HCl (0.078
mmol, 0.78 mL of a 0.1 M solution in diethyl ether), and the reaction
mixture, brought to room temperature, was stirred for about 2 h. The
solvent was removed under reduced pressure, giving an oil, which was
triturated with 3 mL of ethanol containing an excess of NaBPh4 (68
mg, 0.20 mmol). The red-brown solid that slowly precipitated out from
the resulting solution was filtered off and crystallized from ethanol;
yield g70%. Anal. Calcd for C78H76BClN4O3P3Re: C, 64.93; H, 5.31;
N, 3.88; Cl, 2.46. Found: C, 64.81; H, 5.42; N, 3.76; Cl, 2.59. ΛM
)
49.7 Ω1- mol-1 cm2.
X-ray Crystal Structure Determinations. Crystals suitable for
X-ray diffraction analysis were obtained for compounds 1, 2, and 7 by
slow cooling of saturated solutions of the complexes in ethanol.
Diffraction data for all compounds were acquired at room temperature
(72) Nachbaur, E.; Leiseder, G. Monatsh. Chem. 1971, 102, 1718.
(73) Balacco, G. J. Chem. Inf. Comput. Sci. 1994, 34, 1235.
(74) Garcia-Fonta´n, S.; Marchi, A.; Marvelli, L.; Rossi, R.; Antoniutti, S.;
Albertin, G. J. Chem. Soc., Dalton Trans. 1996, 2779.

3286 Inorganic Chemistry, Vol. 39, No. 15, 2000
Albertin et al.
Table 1. Crystal Data and Structure Refinement Details for [ReCl(CH3N2)(CH3NHNH2){PPh(OEt)2}3][BPh4] (1), [Re(N2)2{PPh(OEt)2}4][BPh4]
(2), and [ReCl(PhN2){PPh(OEt)2}4][BPh4] (7)
1
2
7
formula
fw
C56H74BClN4O6P3Re
1224.61
C64H80BN4O8P4Re
1354.26
C70H85BClN2O8P4Re
1254.64
crystal dimensions (mm)
temp (k)
wavelength (Å)
crystal system, space group
color
0.9 × 0.8 × 0.2
1 × 0.3 × 0.3
0.9 × 0.3 × 0.2
293(2)
293(2)
293(2)
0.710 69
triclinic, P1h
orange
0.710 69
orthorhombic, Pbaa
yellow
0.710 69
monoclinic, P21/n
red
unit cell dimensions (Å; deg)
a ) 15.396(5),
b ) 16.986(5),
c ) 11.560(5)
R ) 93.96(5),
â ) 93.99(5),
γ ) 93.09(5)
3003(2)
a ) 23.008(5),
b ) 23.367(5),
c ) 12.863(3)
a ) 19.613(5),
b ) 20.101(5),
c ) 19.918(5);
â ) 115.12(2)
volume (Å3)
6916(3)
4, 1.301
1.901
7110(3)
4, 1.344
1.889
Z, calcd density (Mg/m3)
2, 1.354
2.196
abs coeff (mm-1
)
max/min transmission factors
θ range for data collection (deg)
no. of collected/unique reflns
no. od unique obsd reflns [I > 2σ(I)]
no. of data/restraints/parameters
goodness-of-fit on F2
1.000/0.861
3-30
1.000/0.442
3-30
1.000/0.796
3-28
17 456/17 456
12 407
19 904/10 103 [R(int) ) 0.0826]
16 450/16 450
7496
3846
17 456/2/679
0.889
0.0340, 0.0661
10 103/22/406
0.920
0.0463, 0.1047
16 450/0/800
1.030
0.0414, 0.0768
final R1, wR2 indicesa [I > 2σ(I)]
2
2
a R1 ) ∑(|Fo| - |Fc|)/∑|Fo|, wR2 ) {∑[w(Fo - Fc2)2]/∑[w(Fo )2]}1/2
.
on a Philips PW100 diffractometer using Mo KR (λ ) 0.710 73 Å)
radiation, a graphite monochromator, and θ/2θ scans. In each case,
the intensity of one standard reflection was monitored every 100
measurements, and intensity decay corrections were found to be
necessary for 1 and 2. Empirical ψ-scan corrections for absorption
effects were applied in all cases. The intensity data were processed
with peak-profile procedures and corrected for Lorentz and polarization
effects. Table 1 lists the most important details of the data collections
and structure refinements for the compounds. In all cases, phase
problems were solved by direct methods, using SIR97,75 which allowed
all non-hydrogen atoms to be retrieved. For 1, it was necessary to
consider the P1 space group to solve the phase problem, although
intensity statistics indicated centrosymmetric structure. The structure
showed the presence of the center of symmetry, and refinement was
carried out in the P1h space group. Neutral-atomic scattering factors
were employed, those for non-hydrogen atoms being corrected for
anomalous dispersion. Structures were successively refined on F2 by a
full-matrix least-squares program using SHELXL97.76 In the last stages
of refinement, anisotropic displacement parameters were used for all
non-hydrogen atoms. In general, the substituents on the phosphites
showed considerable anisotropic motion, and in one case, 1, one atom
appeared in two positions. Hydrogen atoms were introduced into
calculated positions, riding on their carrier atoms, with the exception
of hydrazine hydrogens in 1, which were located on a difference Fourier
map and refined isotropically, with restraints on bonding geometry.
For 2 and 7, isolated systems of residual peaks with significant
electronic density were found and were introduced into the final
refinements as disordered solvent molecules. Nevertheless, the final
maps still revealed spurious features. In 2, one of the two coordination
sites for N2 ligands (N1-N2) had a sausage-like electronic density and
the N1-N2 distance refined to the extremely short value of 0.7 Å.
This indicated substitutional disorder between N2 and Cl- due to
contamination77 of 2 with the mono(dinitrogen) complex ReCl(N2)-
[PPh(OEt)2]4 (3), obtained together with 2 from the reaction of ReCl3-
[PPh(OEt)2]3 with hydrazine (see below). The complementary site
occupancies of N2 and Cl- were consequently refined (for stoichiometric
consistence, the same occupancies were assigned to N2 and BPh4-),
and convergence was achieved by restraining the N1-N2 distance to
1.03 Å and that of Re-Cl to 2.52 Å, in agreement with average
literature values, and by applying rigid-bond and similar thermal motion
restraints for N2 and Cl-. The final amount of chloride was 9%. The
second dinitrogen site (N3-N4) was not involved in disorder and was
refined independently, with rigid-bond restraints on the thermal
anisotropic parameters.
Electronic density maps were examined with the XtalView pro-
gram,78 running on a Silicon Graphics workstation. The final geometries
were analyzed with the PARST97 program,79 and the drawings of the
structures were made with ZORTEP.80 All calculations were performed
on a Digital Alpha 255 computer at the Centro di Studio per la
Strutturistica Diffrattometrica del CNR in Parma. Besides those of the
original literature, data for comparison with other compounds were
retrieved and analyzed by the software packages of the Cambridge
Structural Database.81 Complete lists of final atomic fractional coor-
dinates, atomic displacement parameters, and bond distances and angles
are deposited in CIF format as Supporting Information.
Results and Discussion
The outcomes of the reactions of the trichlororhenium
complexes ReCl3P3 with hydrazines depend on the experimental
conditions and the natures of the reagents, as shown in Schemes
1 and 2.
Under an argon atmosphere, the ReCl3P3 complex reacted
with methylhydrazine to give the methyldiazenido [ReCl-
(CH3N2)(CH3NHNH2)P3]+ derivative 1+, which was isolated
as its BPh4 salt and characterized (eq 1). In contrast, under a
dinitrogen atmosphere, the reaction proceeded to give both
methyldiazenido 1 and bis(dinitrogen) [Re(N2)2P4][BPh4] (2)
complexes, which were separated by fractional crystallization
and characterized (eq 2). These results indicate that the N2 ligand
comes from the atmosphere of the reaction and is not due to
(78) McRee, D. E. XtalView, Release 3.2; The Scripps Research Institute,
La Jolla, CA, 1997.
(79) Nardelli, M. PARST97, updated version of PARST95. J. Appl.
Crystallogr. 1995, 28, 659.
(75) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A.; Burla,
M. C.; Polidori, G.; Camalli, M. J. Appl. Crystallogr. 1994, 27, 435.
(76) Sheldrick G. M. SHELXL97: Program for Structure Refinement;
University of Goettingen: Goettingen, Germany, 1997.
(80) Zsolnai, L.; Pritzkow, H. ZORTEP: ORTEP Original Program
Modified for PC; University of Heidelberg: Heidelberg, Germany,
1994.
(81) Allen, F. H.; Kennard, O. Cambridge Structural Database. Chem. Des.
Autom. News 1993, 8, 1, 31-37.
(77) Davis, B. R.; Ibers, J. A. Inorg. Chem. 1971, 10, 578.

Diazo Complexes of Rhenium
Inorganic Chemistry, Vol. 39, No. 15, 2000 3287
Scheme 1
that protons are liberated in the reaction course, as expected
for the formation of the methyldiazenido ligand, CH3NtN, in
1 from the reaction of ReCl3P3 with CH3NHNH2.
(1)
(2)
Rhenium(V) complexes of the type ReOCl3P2 (P ) tertiary
phosphine) are reported to react with arylhydrazines,52,54,82-84
affording mono- or bis(aryldiazenido) (ReCl2(N2COPh)P2 or
ReCl(ArN2)2P2) derivatives. The use of methylhydrazine with
Re(III) ReCl3P3 starting materials allows both the first bis-
(dinitrogen) and the first methyldiazenido-methylhydrazine
complexes, 1 and 2, to be prepared. However, to test the
influence of the ancillary ligands on these reactions, other studies
are in progress on ReCl3P3 complexes containing both tertiary
phosphine, PR3, and phosphite, P(OR)3, which will be the
subject of a forthcoming paper.
Bis(dinitrogen) complex 2 was also obtained by treating
ReCl3P3 complexes either with hydrazine at 25 °C or with
methylhydrazine at reflux, but in these cases, the mono-
(dinitrogen) complex ReCl(N2)P4 (3) (eq 3) was also formed
and had to be separated from 2 by fractional crystallization. In
contrast, only the mono(dinitrogen) compound ReCl(N2)P4 (3)
was produced upon reacting ReCl3P3 complexes with tert-
butylhydrazine (eq 4), and it was isolated in good yield and
characterized.
(3)
(4)
No dinitrogen complex was obtained after treating ReCl3P3
complexes with arylhydrazines (Scheme 2), aryldiazenido
derivatives 4-6 being the only products. . At room temperature,
in fact, the ReCl3P3 complexes reacted with arylhydrazines to
give aryldiazenido [ReCl(ArN2)(ArNHNH2)P3]+ (4+) cations (eq
5), while under reflux, the reactions proceeded to give bis-
(aryldiazenido) [Re(ArN2)2P3]+ (5+, 6+) derivatives (eq 6). Last,
treatment of an ReCl3P3 complex with an excess of an
arylhydrazine at reflux in the presence of free phosphite PPh-
(OEt)2 afforded the [ReCl(ArN2)P4]+ (7+) cation (eq 7), which
Scheme 2
(5)
(6)
(7)
-
was isolated as its BPh4 salt and characterized.
Good analytical data were obtained for all rhenium complexes
1-7. They are air-stable diamagnetic solids and are soluble in
organic polar solvents in which they (except 3) behave as 1:1
electrolytes.85 The IR and NMR data (Table 2) support the
proposed formulations.
At 3325-3205 cm-1, the IR spectrum of methyldiazenido
complex 1 shows three bands of weak intensity due to the ν-
(NH2) and ν(NH) of the methylhydrazine ligand and a medium-
intensity absorption at 1714 cm-1 attributed to ν(NN) of the
methyldiazenido ligand. This value, falling above 1600 cm-1
,
degradation of methyldiazenido complex 1 or the dinitrogen
formed by decomposition of the oxidation product of CH3-
NHNH2. The reduction of the central metal from Re(III) to Re-
(I) probably involves the methylhydrazine, whose oxidation
product can liberate N2, affording the dinitrogen complex. In
the raw product of the reaction carried out under argon, traces
of dinitrogen complex 2 were observed, but it was only when
the reaction was conducted under N2 that a reasonable amount
of 2 was obtained.
Addition of free phosphite ligand PPh(OEt)2 and varying
amounts of NEt3 to the reaction mixture only resulted in a slight
variation of the ratio between 1 and 2 (eq 2), with an increase
in bis(dinitrogen) complex 2 in the presence of PPh(OEt)2 and
an excess of NEt3. We also attempted to isolate some intermedi-
ates, to collect information on the reaction path and the nature
of the intermediate rhenium fragment which binds N2, but the
solids isolated at the initial stage of the reaction or with the use
of a low CH3NHNH2:Re ratio contained a mixture of paramag-
netic species, preventing any clear identification. However, in
the final reaction product, we always observed a white solid
identified as the ammonium salt [NHEt3][BPh4], which indicated
also indicates a singly bent diazenido ligand,86 formally present
as CH3N2+, with the central metal in an oxidation state of I.
The X-ray structure confirms this assignment (Figure 1). In the
NMR proton spectra, the methylhydrazine shows the NH2 and
NH groups as broad multiplets at 5.74 and 3.28 ppm, respec-
tively, and the methyl substituent as a doublet at 2.61 ppm.
These assignments were confirmed by integration data and
homodecoupling experiments. In the temperature range between
+30 and -80 °C, the 31P{1H} NMR spectrum of 1 appears as
an AB2 multiplet, indicating that two phosphines are magneti-
cally equivalent and different from the third. The spectroscopic
data, however, do not allow a geometry in solution for 1 to be
unambiguously assigned, since I, Ia, and Ib (Chart 1) equally
fit both IR and NMR data.
(82) Dilworth, J. R.; Harrison, S. A.; Walton, D. R. M.; Schweda, E. Inorg.
Chem. 1985, 24, 2594.
(83) Nicholson, T.; Lombardi, P.; Zubieta, J. Polyhedron 1987, 6, 1577.
(84) Chatt, J.; Dilworth, J. R.; Leigh, G. J.; Gupta, V. D. J. Chem. Soc. A
1971, 2631.
(85) Geary, W. J. Coord. Chem. ReV. 1971, 7, 81.
(86) Haymore, B. L.; Ibers, J. A. Inorg. Chem. 1975, 14, 3060.

3288 Inorganic Chemistry, Vol. 39, No. 15, 2000
Albertin et al.
Table 2. Selected IR and NMR Data for the Rhenium Complexes
compound
1H NMRb,c
(ppm; J, Hz)
spin 31P{1H} NMRb,d
no.
formula
IRa (cm-1
)
assgnt
assgnt
NH2
NH
CH2
CH3N2
CH3NH
syst
(ppm; J, Hz)
1
[ReCl(CH3N2)(CH3NHNH2){PPh(OEt)2}3][BPh4]
3325 w
3287 m
3205 w
1714 s
ν(NH) 5.74 m, br
3.28 m
4.15-3.50 m
ν(N2) 3.16 s
2.61 d
AB2 δA ) 130.5
δB ) 121.0
JAB ) 22
JHH ) 6.2
1.33, 1.29, 1.21 t CH3
2
3
[Re(N2)2{PPh(OEt)2}4][BPh4]
[ReCl(N2){PPh(OEt)2}4]
2094 s
2027 s
ν(N2) 3.69 m
CH2
CH3
CH2
CH3
NH2
NH
A4
A4
130.3 s
129.0 s
1.26 t
ν(N2) 3.96, 3.64 m
1.19 t
4a [ReCl(C6H5N2)(C6H5NHNH2){PPh(OEt)2}3][BPh4]
3354 w
3287 m
3214 w
1653 s
ν(NH) 6.57 br
AB2 δA ) 131.2
δB ) 118.7
5.89 t, br
4.00, 3.65 m
CH2
JAB ) 22
ν(N2) 1.22, 1.19, 1.12 t CH3
4b [ReCl(4-CH3C6H4N2)(4-CH3C6H4NHNH2){PPh(OEt)2}3][BPh4] 3353 w
ν(NH) 6.53 br
NH2
NH
AB2 δA ) 133.5
δB ) 123.2
3288 m
3219 w
1653 s
5.78 t, br
4.10-3.60 m
CH2
CH3C6H4
JAB ) 22
ν(N2) 2.44, 2.33 s
1.23, 1.19, 1.13 t CH3
g
5a {Re(C6H5N2)2{PPh(OEt)2}3][BPh4]
1642 m
1616 s
ν(N2) 3.58 m
CH2
AB2 δA ) 143.5
1.26, 1.23, 1.06 t CH3
δB ) 123.5
JAB ) 15
5b [Re(4-CH3C6H4N2)2{PPh(OEt)2}3][BPh4]f
1635 m
1617 s
ν(N2) 3.70 m
2.52 s
CH2
CH3C6H4
AB2 δA ) 144.3
δB ) 125.2
1.27, 1.22, 1.06 t CH3
JAB ) 15
6
[Re(C6H5N2)2(PPh2OEt)3][BPh4]f
1653 sh
1620 s
ν(N2) 3.37 m
CH2
CH3
AB2 δA ) 125.3
δB ) 104.0
0.72 t
JAB ) 12
7
8
[ReCl(C6H5N2){PPh(OEt)2}4][BPh4]f
1662 s
1695 s
ν(N2) 3.69 m
1.22 t
CH2
CH3
NH
CH2
A4
118.6 s
134-105 me
[ReCl(CH3NdNH)(CH3N2){PPh(OEt)2}3][BPh4]
ν(N2) 15.89 d, br
AB2 δA ) 129.0
δB ) 119.6
3.90 m
3.34 s
4.05 s
CH3N2
CH3NdNH
JAB ) 26
10 [ReCl(C6H5NdNH)(C6H5N2)(PPh2OEt)3][BPh4]
1670 s
AB2 δA ) 105.6
δB ) 93.0
JAB ) 20
a In KBr. b In CD2Cl2 at 25 °C. c Phenyl proton resonances are omitted. d Positive shift downfield from 85% H3PO4. e At -90 °C. f In (CD3)2CO.
g At -30 °C.
Chart 1
Methyldiazenido complexes are rather rare87-92 and have
often been obtained by reactions of diazomethane with transition
metal hydrides. The use of methylhydrazine with ReCl3[PPh-
(OEt)2]3 allowed us to synthesize the first complex containing
both a methyldiazenido and a methylhydrazine ligand bonded
to the same central metal.
Closely related to the methyldiazenido complex 1 are the
aryldiazenido-arylhydrazine complexes [ReCl(ArN2)(ArNHNH2)-
P3][BPh4] (4), which were obtained with the phenyl (4a) and
p-tolyl (4b) substituents at the diazo groups (Scheme 2).
Figure 1. Perspective view of the crystal structure of the cation [ReCl-
(CH3N2)(CH3NHNH2){PPh(OEt)2}3]+ (1+), with thermal ellipsoids
drawn at the 50% probability level. The ethyl and phenyl groups of
the phosphites are omitted for clarity. The network of intramolecular
hydrogen bonds between methylhydrazine and ethoxy groups is
represented as dashed bonds.
(87) Herrmann, W. A. Angew. Chem., Int. Ed. Engl. 1975, 14, 355.
(88) Herrmann, W. A.; Ziegler, M. L.; Weidenhammer, K. Angew. Chem.,
Int. Ed. Engl. 1976, 15, 368.
(89) Hillhouse, G. L.; Haymore, B. L.; Herrmann, W. A. Inorg. Chem.
1979, 18, 2423.
(90) Turney, T. W. Inorg. Chim. Acta 1982, 64, L141.
(91) Day, V. W.; George, T. A.; Iske, S. D. A. J. Am. Chem. Soc. 1975,
97, 4127.
The solid-state structure (Figure 1) shows that the halide Cl-
+
is in a trans position with respect to the good π-acceptor CH3N2
group, and it is therefore probable that such geometry (type I)
is also preserved in solution.
(92) Tatsumi, T.; Hidai, M.; Uchida, Y. Inorg. Chem. 1975, 14, 2530.

Diazo Complexes of Rhenium
Inorganic Chemistry, Vol. 39, No. 15, 2000 3289
Figure 2. Perspective view of the crystal structure of the cation [Re-
(N2)2{PPh(OEt)2}4]+ (2+), with thermal ellipsoids drawn at the 50%
probability level. The ethyl and phenyl groups of the phosphites are
omitted for clarity. Substitutional disorder between N1-N2 (91%) and
Cl (9%) is not shown. The cation has 2-fold crystallographic symmetry.
Figure 3. Perspective view of the crystal structure of the cation [ReCl-
(PhN2){PPh(OEt)2}4]+ (7+), with thermal ellipsoids drawn at the 50%
probability level. The ethyl and phenyl groups of the phosphites are
omitted for clarity.
trogen) 2 and the new mono(dinitrogen) 3 rhenium derivatives
to be prepared.
The spectroscopic data (Table 2) support the proposed
formulation for 4 and suggest the presence of a singly bent
aryldiazenido ligand (ν(N2) at 1653 cm-1) formally present as
ArN2+ bonded to a Re(I) central metal.86 However, the IR and
NMR data (AB2 multiplet in the 31P{1H} NMR spectra) do not
allow us to assign a geometry among the three shown in Chart
1, although, by analogy with the related methyldiazenido
compound 1, we tentatively propose structure I for our aryl-
The NMR data for the aryldiazenido [ReCl(PhN2)P4]+ cation
7+ indicate temperature-dependent behavior in solution. The
broad singlet appearing at 118 ppm in the 31P NMR spectrum
at 25 °C does change as temperature falls and resolves into a
complicated multiplet at -90 °C. This result implies the
presence of inequivalent phosphorus nuclei and, in contrast with
the trans structure observed in the solid state, suggests a cis
diazenido derivatives 4, with the Cl- and ArN2 ligands in
+
+
arrangement for the Cl- and ArN2 ligands. However, the 31P
mutually trans positions.
spectra may also be interpreted on the basis of a trans geometry,
in which the four PPh(OEt)2 ligands are made inequivalent by
the different arrangement of the phenyl and ethoxy groups of
one phosphite with respect to the other. Examples of inequiva-
lent phosphorus nuclei in octahedral complexes containing four
PPhMe2 or PPh(OEt)2 ligands in a plane were recently reported
The IR spectrum of the bis(dinitrogen) complex [Re(N2)2-
{PPh(OEt)2}4][BPh4] (2) shows only one strong ν(N2) band93
at 2094 cm-1, suggesting mutually trans positions for the two
dinitrogen ligands (geometry II, Scheme 1). This is confirmed
by the 31P{1H} NMR spectra which, between +30 and -80
°C, display only one sharp singlet near 130 ppm. A similar trans
geometry was observed in the solid state (Figure 2).
for [IrCl2(PPhMe2)4]ClO4,101 FeHCl[PPh(OEt)2]4,102 and MnH-
103
(CO)[PPh(OEt)2]4
derivatives. Taking into account these
The mono(dinitrogen) complex ReClN2[PPh(OEt)2]4 (3) also
shows ν(N2) as a sharp strong band at 2027 cm-1 whereas,
between +30 and -90 °C, the 31P{1H} NMR spectra show a
sharp singlet, suggesting mutually trans positions for the Cl-
ligand and the dinitrogen ligand (geometry III, Scheme 1).
Mononuclear complexes containing two dinitrogen ligands
are scarce1-7 and include the well-known Mo and W complexes
M(N2)2(P-P)2 and M(N2)2P4 (P, P-P ) mono-, bidentate
phosphine)94-99 and the Na[V(N2)2(Me2PCH2CH2PMe2)] com-
pound,100 the related rhenium bis(dinitrogen) derivatives being
unknown. The use of methylhydrazine as a reducing agent for
the Re(III) complex ReCl3[PPh(OEt)2]3 allows both bis(dini-
precedents and the crystal structure shown in Figure 3, discussed
below, we find that the trans octahedral geometry VII (Scheme
2) may also be proposed in solution for the [ReCl(PhN2){PPh-
(OEt)2}4][BPh4] compound (7). A singly bent aryldiazenido
+
PhN2 ligand is also present in the complex, fitting the ν(N2)
value of 1662 cm-1 observed in the IR spectra.
The bis(aryldiazenido) [Re(ArN2)2P3][BPh4] derivatives (5,
6) show two medium-intensity ν(N2) bands at 1653-1616 cm-1
,
indicating the mutually cis positions of the two ArN2 ligands.
The absorption values also indicate a singly bent coordination
for both aryldiazenido ligands, which are therefore formally
+
bonded as ArN2 to a metal center, resulting in the formal
oxidation state of -I [Re(-I)]. Between +30 and -80 °C, the
31P{1H} NMR spectra of complexes 5 and 6 appear as AB2
multiplets, indicating that two phosphites are magnetically
equivalent and different from the third. However, the IR and
NMR data do not allow us unambiguously to assign a geometry
in solution to the compounds, since both geometries V and VI
(Chart 2) fit the spectroscopic data.
(93) Nakamoto, K. Infrared Spectra of Inorganic and Coordination
Compounds; Wiley: New York, 1970.
(94) Hidai, M.; Tominari, K.; Uchida, Y. J. Am. Chem. Soc. 1972, 94,
110.
(95) Chatt, J.; Pearman, A. J.; Richards, R. L. J. Chem. Soc., Dalton Trans.
1977, 2139.
(96) Carmona, E.; Marin, J. M.; Poveda, M. L.; Atwood, J. L.; Rogers, R.
D. J. Am. Chem. Soc. 1983, 105, 3014.
(97) Dadkhah, H.; Dilworth, J. R.; Faiman, K.; Kan, C. T.; Richards, R.
L.; Hughes, D. L. J. Chem. Soc., Dalton Trans. 1985, 1523.
(98) Anderson, S. N.; Richards, R. L.; Hughes, D. L. J. Chem. Soc., Dalton
Trans. 1986, 245.
(101) Deeming, A. J.; Doherty, S.; Marshall, J. E.; Powell, N. I. J. Chem.
Soc., Chem. Commun. 1989, 1351.
(99) George, T. A.; De Bord, J. R. D.; Kaul, B. B.; Pickett, C. J.; Rose, D.
J. Inorg. Chem. 1992, 31, 1295.
(100) Rehder, D.; Woitha, C.; Priebsch, W.; Gailus, H. J. Chem. Soc.,
Dalton Trans. 1992, 364.
(102) Albertin, G.; Antoniutti, S.; Bordignon, E. J. Organomet. Chem. 1996,
513, 147.
(103) Albertin, G.; Antoniutti, S.; Bettiol, M.; Bordignon, E.; Busatto, F.
Organometallics 1997, 16, 4959.

3290 Inorganic Chemistry, Vol. 39, No. 15, 2000
Albertin et al.
Table 3. Selected Bond Distances (Å) and Angles (deg), with
Chart 2
Esd’s in Parentheses
[ReCl(CH3N2)(CH3NHNH2){PPh(OEt)2}3][BPh4] (1)
Distances
Re-Cl
Re-P1
Re-P2
Re-P3
Re-N1
Re-N3
P1-O1
P1-O2
2.438(1)
P2-O3
P2-O4
P3-O5
P3-O6
N1-N2
N2-C32
N3-N4
N4-C1
1.610(2)
1.593(3)
1.610(2)
1.602(2)
1.199(4)
1.431(6)
1.445(4)
1.480(6)
2.362(1)
2.406(1)
2.412(1)
1.817(3)
2.235(3)
1.601(2)
1.601(2)
As comparisons with the data reported for other pentacoor-
dinate aryldiazenido complexes whose X-ray structures are
known21-25,104 indicate that singly bent aryldiazenido ligands
generally occupy equatorial positions in bipyramidal geometries,
we tentatively propose cis geometry V for our bis(aryldiazenido)
complexes 5 and 6.
Angles
Cl-Re-P1
Cl-Re-P2
Cl-Re-P3
Cl-Re-N1
Cl-Re-N3
P1-Re-P2
P1-Re-P3
P1-Re-N1
P1-Re-N3
P2-Re-P3
P2-Re-N1
P2-Re-N3
P3-Re-N1
92.86(3)
89.38(3)
86.66(3)
175.66(9)
80.65(7)
91.78(4)
94.97(3)
91.14(9)
173.47(8)
172.33(4)
92.17(8)
87.45(7)
91.34(8)
P3-Re-N3
N1-Re-N3
Re-P1-O1
Re-P1-O2
Re-P2-O3
Re-P2-O4
Re-P3-O5
Re-P3-O6
Re-N1-N2
N1-N2-C32
Re-N3-N4
N3-N4-C1
85.43(8)
95.4(1)
119.37(9)
112.38(9)
105.10(9)
121.19(9)
106.67(9)
126.00(9)
173.3(3)
125.0(3)
115.6(2)
108.8(3)
X-ray Crystal Structures. In the cationic complex [ReCl-
(CH3N2)(CH3NHNH2){PPh(OEt)2}3]+ (1+), the metal coordi-
nates one methyldiazenido, N1-N2-C32, and one methylhy-
drazine, N3-N4-C1, molecule; octahedral coordination is
completed by a chloride, trans to the methyldiazenido ligand,
and three phosphites (Figure 1). Table 3 lists relevant geometric
features of 1+. The structure is completed by a BPh4 coun-
-
teranion. This is the first known crystal structure of a rhenium
complex containing either an NNCH3 or an NH2NHCH3 ligand.
The diazenido fragment shows a linear arrangement around N1
(Re-N1-N2 ) 173.3(3)°) and an sp2 geometry around N2
(N1-N2-C32 ) 125.0(3)°). This suggests a marked double-
bond character for the Re-N and N-N bonds, as indicated by
the very short bond distances Re-N1 ) 1.817(3) and N1-N2
) 1.199(4) Å, explained by π back-donation from the metal to
the ligand, fitting the geometry found for dicarbonyl(η5-
cyclopentadienyl)(methyldiazenido)tungsten89 (W-N ) 1.850,
N-N ) 1.281 Å; W-N-N ) 173, N-N-C ) 116°). The
situation is different when the diazenido group is protonated,
as in trans,trans-dicarbonyl(methylhydrazine)nitrosylbis(triphen-
ylphosphine)tungsten hexafluorophosphate,105 where the bond
geometry is bent around the metal-nitrogen bond and the
increase in bond strength is shifted toward the terminal methyl
(W-N ) 2.215, N-N ) 1.330, N-C ) 1.336 Å; W-N-N )
117, N-N-C ) 119°). These two complexes89,105 are the only
other structurally known compounds containing the NNCH3
ligand. The mode of coordination of the diazenido ligand
influences the Re-Cl bond, situated trans to N1, which is longer
(2.438(1) Å) than the mean distance found for terminal chlorides
in octahedral Re complexes (2.391 Å). The methylhydrazine
molecule, N3-N4-C1, is coordinated to rhenium by a typical
σ single bond via the terminal -NH2 group, with a bonding
geometry similar to that observed for trans-carbonyl(methyl-
hydrazine)bis(triphenylphosphine)rhodium perchlorate106 (N-N
) 1.454, N-C ) 1.459 Å; Rh-N-N ) 110, N-N-C ) 113°),
the only other structurally known metal complex containing this
ligand. The Re-N3 and N-N bond lengths agree with those
found for similar systems. The coordination of phosphites in 1
is an interesting example of the influence that nonbonding
interactions may have on the bonding of metal complexes. It
has been shown that these effects can induce distortions of up
to 0.02 Å and 1-2° in coordination geometry; among others,
“second-order effects” have been described, which affect bond
[Re(N2)2{PPh(OEt)2}4][BPh4] (2)
Distances
Re-N3
Re-N1
Re-P2
Re-Cl
1.970(9)
2.025(7)
2.434(1)
2.44(2)
Re-P1
N1-N2
N3-N4
2.445(2)
1.022(2)
1.09(1)
Angles
N3-Re-N1
N3-Re-P2
N1-Re-P2
N3-Re-P2′
N1-Re-P2′
P2-Re-P2′
N3-Re-P1′
N1-Re-P1′
P2-Re-P1′
180
P2′-Re-P1′
N3-Re-P1
N1-Re-P1
P2-Re-P1
P2′-Re-P1
P1′-Re-P1
Re-N1-N2
Re-N3-N4
90.02(5)
93.25(4)
86.75(4)
90.03(5)
89.72(5)
173.50(9)
180
92.22(4)
87.78(4)
92.22(4)
87.78(4)
175.56(8)
93.25(4)
86.75(4)
89.72(5)
180
[ReCl(PhN2)]{PPh(OEt)2}4][BPh4] (7)
Distances
Re-P1
Re-P2
Re-P3
Re-P4
2.441(2)
2.448(2)
2.440(2)
2.462(2)
Re-Cl
Re-N1
N1-N2
N2-C1
2.437(2)
1.799(6)
1.220(7)
1.44(1)
Angles
P1-Re-P2
P1-Re-P3
P1-Re-P4
P1-Re-Cl
P1-Re-N1
P2-Re-P3
P2-Re-P4
P2-Re-Cl
P2-Re-N1
85.73(7)
168.76(7)
92.78(7)
84.72(7)
97.2(2)
P3-Re-P4
P3-Re-Cl
P3-Re-N1
P4-Re-Cl
P4-Re-N1
Cl-Re-N1
Re-N1-N2
N1-N2-C1
86.94(7)
84.05(7)
93.9(2)
89.32(7)
86.6(2)
175.5(2)
170.9(6)
125.8(7)
94.90(7)
177.55(7)
92.48(7)
91.7(2)
lengths by deforming bond angles.107 In compound 1, the
distance Re-P1 ) 2.362(1) Å, trans to N3, is comparable to
those observed for 2 and 7 (see below). The distances Re-P2
) 2.406(1) Å and Re-P3 ) 2.412(1) Å are significantly longer,
due to a system of strong intramolecular hydrogen bonds
between the hydrazine NH groups and the ethoxy substituents
carried by P2 and P3: N3-H1‚‚‚O3 (N3‚‚‚O3 ) 2.855(4) Å,
N3-H1‚‚‚O3 ) 102(2)°), N3-H2‚‚‚O5 (N3‚‚‚O5 ) 2.807(4)
Å, N3-H‚‚‚O5 ) 130(3)°), N4-H‚‚‚O3 (N3‚‚‚O3 ) 3.165(4)
(104) Albertin, G.; Antoniutti, S.; Pelizzi, G.; Vitali, F.; Bordignon, E. J.
Am. Chem. Soc. 1986, 108, 6627.
(105) Smith, M. R., III; Keys, R. L.; Hillhouse, G. L.; Rheingold, A. L. J.
Am. Chem. Soc. 1989, 111, 8312.
(106) Davies, C. J.; Dodd, I. M.; Harding, M. M.; Heaton, B. T.; Jacob,
C.; Ratnam, J. J. Chem. Soc., Dalton Trans. 1994, 787.
(107) Mart`ın, A. M.; Orpen, A. G. J. Am. Chem. Soc. 1996, 118, 1464.

Diazo Complexes of Rhenium
Inorganic Chemistry, Vol. 39, No. 15, 2000 3291
ever, ours is the first case in which the metal is coordinated to
two N2 molecules. The Re-N and N-N distances tend to be
anticorrelated, according to a possible π back-donation from
Re d occupied orbitals to the π* LUMO of N2. The extreme
cases are mer-tris(dimethylphenylphosphine)(dinitrogen-N)-
(diphenyldithiophosphinato-S)(methyl isocyanide)rhenium108
(Re-N ) 1.828, N-N ) 1.128 Å; Re-N-N ) 174°), in which
back-donation is significant, and tetrakis(diethylphenylphos-
phine)(dinitrogen-N)hydridorhenium109 (Re-N ) 2.055, N-N
) 1.018 Å; Re-N-N ) 180°), in which the N-N distance,
trans to H-, is apparently shorter than the N2 internuclear
distance in the gas phase (1.0976 Å). Compound 2 falls in the
intermediate range, typical of complexes in which the dinitrogen
is bonded trans to a chloride or a PMe3 ligand.
-
The asymmetric unit also contains half of a BPh4 counter-
anion, with the B atom lying on a crystallographic 2-fold axis;
crystal packing does not show any other important features
except for van der Waals interactions.
Figure 4. Complete sketch of the cation [Re(N2)2{PPh(OEt)2}4]+ (2+),
showing the arrangement of phenyl groups around coordination site
N1-N2.
In the cation [ReCl(PhN2){PPh(OEt)2]4]+ (7+), rhenium is
bonded to a phenyldiazenido group, trans to a chloride ligand,
and four phosphites complete the octahedral coordination (Figure
3). The crystal structure is completed by a BPh4- anion. Table
3 lists the most important bonding parameters for the cation.
Comparison between the bonding situations of the diazenido
ligands in 1 and 7 shows that replacement of the methyl
substituent in the former with a phenyl group in the latter slightly
shortens the Re-N bond (1.817(3) and 1.799(5) Å, respectively)
and lengthens the N-N bond (1.199(4) and 1.220(7) Å,
respectively), according to the greater π-acceptor capability of
the phenyldiazenido with respect to the methyldiazenido ligand.89
As already observed for 1, the geometry of the diazenido group
is essentially linear on N1 (Re-N1-N2 ) 170.9(6)°) and bent
on N2 (N1-N2-C1 ) 125.8(7)°). The Re-Cl distance (2.437-
(2) Å) is the same as that in 1, indicating similar trans effects
of the two diazenido ligands, and the Re-P bonds clearly
resemble those observed in 2, where bonding is not perturbed
by intramolecular hydrogen bonds. The phenyl group is slightly
rotated around the N2-C1 bond (N1-N2-C1-C6 ) -17-
(1)°), allowing optimization of the intramolecular interaction
C6-H‚‚‚O3 (C6‚‚‚O3 ) 3.440(8) Å, C6-H‚‚‚O3 ) 170.0(5)°).
Other nonnegligible intramolecular interactions involving dif-
ferent phosphites may partially account for the temperature-
dependent behavior observed in the solution 31P NMR spectrum,
which indicates that the four phosphites are not magnetically
equivalent; i.e., their free rotation around the Re-P bonds is
somewhat hindered. In the solid state, the substituents on the P
atoms are differently oriented and the shortest contacts observed
are C12-H‚‚‚N2 (C‚‚‚N ) 3.22(1) Å, C-H‚‚‚N ) 118.4(5)°),
C19-H‚‚‚Cl (C‚‚‚Cl ) 3.39(1) Å, C-H‚‚‚Cl ) 122.4(5)°), and
C39-H‚‚‚O1 (C‚‚‚O ) 3.10(1) Å, C-H‚‚‚O ) 135.6(6)°),
where C12 belongs to the phenyl at P1, C19 is bonded to O4,
and C39 is bonded to O8.
Å, N4-H‚‚‚O3 ) 135(5)°). The same effect was observed in
the complex bis(hydrazine)tetrakis(triethoxyphosphine)osmium
bis(tetraphenylborate),26 where a network of intramolecular
hydrogen bonds induced a lengthening of about 0.06 Å in the
Os-P distances. These interactions cause the bending of the
phosphite toward N3 (P2-Re-N3 ) 87.45(7), P3-Re-N3 )
85.43(8), Re-P2-O3 ) 105.10(9), Re-P3-O5 ) 106.67(9)°),
slightly hindering the overlap of bonding orbitals between Re
and P and producing the elongation of the Re-P bonds.
The complex cation [Re(N2)2{PPh(OEt)2}4]+ (2+) shows C2
point group symmetry, the metal and the two dinitrogen
molecules being collinear on a crystallographic 2-fold axis along
z (Figure 2). The geometry around the metal is completed by
four phosphite groups, symmetrically related in pairs, giving
octahedral coordination. Table 3 lists principal bond distances
and angles for the complex. The overall geometry of the cation
is close to C4 symmetry, the two independent phosphites being
related by a pseudo-4-fold axis coinciding with the crystal-
lographic 2-fold axis along z, and the cell constants simulate a
tetragonal setting. The octahedral geometry is highly regular in
the equatorial plane containing the P atoms, and it is slightly
distorted along the z axis, as the angles P-Re-N3 are 93.25-
(4) and 92.22(4)° for P1 and P2, respectively. The bending of
the phosphites toward N1-N2 is related to the peculiar
arrangement of the ethoxy and phenyl groups, shown in Figure
4. The aromatic moieties define a 4-fold corolla around N1-
N2, with the torsion angles N1-Re-P-C ) 26.3(3) and 15.3-
(3)° for P1 and P2, respectively, and with a dihedral angle of
85° between the two independent rings C1-C6 and C11-C16.
The ethoxy groups surround the N3-N4 molecule on the other
side of the complex. A cavity with a volume of about 134 Å3
is located on the molecular 2-fold axis, centered about 3.1 Å
from N4, and contains approximately 5 electrons. This blurry
electronic density has been explained in terms of a disordered
solvent, whose loss might be the cause of the crystal decay
observed during X-ray exposure. As mentioned in the Experi-
mental Section, the coordination site of the molecule N1-N2
is partially occupied by a chloride anion and this prevents
satisfactory definition of local bonding geometry. The distances
Re-N3 ) 1.970(9) Å and N3-N4 ) 1.09(1) Å agree with other
values observed for dinitrogen complexes of rhenium.
In the crystallographic literature, 15 cases of rhenium
complexes with phenyldiazenido ligands are known, containing
different substituents on the aromatic ring. In only one case
(bis(1,2-bis(dimethylphosphino)ethane)bis((4-chlorophenyl)dia-
zenido)rhenium(III) hexafluorophosphate)55 is the coordination
bent (Re-N-N ) 147 and 149° for two independent ligands,
acting as 1-electron donors); the geometry is generally linear
(108) Pombeiro, A. J. L.; Hitchcock, P. B.; Richards, R. L. J. Chem. Soc.,
Dalton Trans. 1987, 319.
(109) Chiu, K. W.; Howard, C. G.; Rzepa, H. S.; Sheppard, R. N.;
Wilkinson, G.; Galas, A. M. R.; Hursthouse, M. B. Polyhedron 1982,
1, 441.
A search of the Cambridge Crystallographic Database81
(October 1998 release) revealed that 13 other molecules
containing the Re-NdN system are structurally known. How-

3292 Inorganic Chemistry, Vol. 39, No. 15, 2000
Albertin et al.
Scheme 3
Scheme 4
in the remaining molecules, with Re-N-N angles ranging from
159 to 178°. In all cases, the N-N-C angles range from 116
to 126°.
Reactivity. The new dinitrogen complexes [Re(N2)2P4][BPh4]
(2) and ReCl(N2)P4 (3) are very stable, both as solids and in
solution, and the N2 group cannot easily be substituted by
ligands such as CO or phosphite even after long reaction times.
For example, bis(dinitrogen) complex 2 showed no substitution
of N2 after 24 h of reaction with CO (1 atm) at room
temperature. Protonation with HBF4 or CF3SO3H and methy-
lation with CF3SO3CH3 were also investigated and found to
cause decomposition of compound 2, with loss of N2. However,
in the case of ReCl(N2)P4 (3), while protonation resulted in
decomposition, methylation with CF3SO3CH3 proceeded slowly
to give a rather unstable compound, which was isolated as a
BPh4- salt and whose IR and NMR data support its formulation
as the methyldiazenido derivative [ReCl(CH3N2)P4][BPh4] (eq
8). The IR spectrum shows a medium-intensity band at 1739
drazido(2-), NN(H)CH3, ligand26,82,111 formed by oxidation of
the methylhydrazine molecule. A doublet due to the coupling
with the NH proton should in fact be present for the CH3 signal
of a NN(H)CH3 ligand, with the NH signal at a lower frequency
than 15 ppm (11-12 ppm), as observed for other methylhy-
drazido(2-) complexes.82,111,112
The infrared spectrum of 8 shows the νN2 band of the
methyldiazenido ligand at 1695 cm-1 whereas, between -80
and +30 °C, the 31P{1H} NMR spectra display an AB2 multiplet.
These spectroscopic data (IR and NMR) fit the proposed
structure (VIII), which is based on the hypothesis that oxidation
of CH3NHNH2 does not change the geometry from that of
precursor 1 to that of the final diazene derivative 8.
Methyldiazene complexes are rare,26,105,113 and no examples
are reported for rhenium. The easy oxidation of 1 with Pb(OAc)4
allows the synthesis of the first complex containing both one
methyldiazene and one methyldiazenido ligand bonded to the
same central metal.
Arylhydrazine-aryldiazenido complexes 4 also react with Pb-
(OAc)4 at -30 °C to give, after workup, red-orange solids,
which turn out to be the bis(aryldiazenido) [Re(ArN2)2P3][BPh4]
derivatives (5) and not the expected [ReCl(ArNdNH)(ArN2)-
P3][BPh4] complexes. However, this result is not completely
surprising, taking into account the known properties of aryl-
diazene complexes,21-25,28,29,32,33,104 which can easily be depro-
tonated to give the corresponding aryldiazenido derivatives. On
this basis, it is plausible to hypothesize the path shown in
Scheme 4 for the formation of the bis(aryldiazenido) complexes
5 from the oxidation of complexes 4.
(8)
cm-1, attributed to νN2 of the CH3N2 group formed by
1
methylation of the N2 ligand. In the H NMR spectrum, the
singlet of the methyl substituent appears at 3.12 ppm, but in
the 31P{1H} NMR spectrum, a multiplet appears, indicating a
cis arrangement for the Cl- and CH3N2 ligands. In contrast to
the related [ReCl(CH3N2)(CH3NHNH2)P3][BPh4] (1) complex,
the new methyldiazenido [ReCl(CH3N2)P4]+ cation is unstable,
both as a solid and in solution, and this prevents its complete
characterization. However, the spectroscopic data and the
precedent of compound 1 strongly support the formation of a
methyldiazenido species by electrophilic attack110 of CH3 on
+
the coordinate N2 molecule in 3.
The methylhydrazine ligand in the [ReCl(CH3N2)(CH3-
NHNH2)P3][BPh4] (1) complex was selectively oxidized by Pb-
(OAc)4 at low temperature to give the corresponding methyl-
diazene derivative [ReCl(CH3NdNH)(CH3N2)P3][BPh4] (8),
which was isolated in good yield and characterized (Scheme
3).
In fact, in this case too, reactions of complexes 4 with Pb-
(OAc)4 probably give the aryldiazene-aryldiazenido cations
[9]+, which can lose the diazene proton to give intermediates
[A], each containing two aryldiazenido ligands, one singly bent
(ArN2+) and one doubly bent (ArN2-). The deprotonating agent
may be the acetate ion present in the reaction mixtures. Upon
Complex 8 is an orange-yellow stable solid, which is also
stable in solutions of polar organic solvents, where it behaves
as a 1:1 electrolyte.85 Analytical and spectroscopic data (Table
2) support the proposed formulation. In particular, the presence
-
+
rearrangement of ArN2 to ArN2 and concurrent formal
reduction of the central metal to Re(-I), the bis(aryldiazenido)
complexes are formed and probably lose one ligand to reach
the more stable 18-electron configuration, as in 5. Although
the intermediates [9]+ were not detected in these reactions, the
closely related complex [ReCl(PhNdNH)(PhN2)(PPh2OEt)3]-
[BPh4] (10) can be obtained by protonation of [Re(PhN2)2(PPh2-
1
of the diazene ligand is confirmed by the H NMR spectrum,
which shows the characteristic NH signal as a broad doublet at
15.89 ppm. The spectrum also contains two singlets at 4.05 and
at 3.34 ppm, attributed to the methyl substituents of the CH3Nd
NH and CH3N2 ligands, respectively. The sharp singlet at 4.05
ppm and the rather high frequency of the NH proton signal
(15.89 ppm) also seem to exclude the presence of a methylhy-
(111) Barrientos-Penna, C. F.; Campana, C. F.; Einstein, F. W. B.; Jones,
T.; Sutton, D.; Tracey, A. S. Inorg. Chem. 1984, 23, 363.
(112) Albertin, G.; Antoniutti, S.; Bacchi, A.; Bordignon, E.; Giorgi, M.
T.; Pelizzi, G. Manuscript in preparation.
(110) Diamantis, A. A.; Chatt, J.; Heath, G. A.; Hooper, N. E.; Leigh, G.
J. J. Chem. Soc., Dalton Trans. 1977, 688.
(113) Ackerman, M. N. Inorg. Chem. 1971, 10, 272.

Diazo Complexes of Rhenium
Inorganic Chemistry, Vol. 39, No. 15, 2000 3293
Scheme 5
protonated, affording an aryldiazene, ArNdNH, or an arylhy-
drazido(2-), Ar(H)NN, derivative of type 10a or 10b, respec-
tively. However, the observed spectroscopic properties are not
sufficient to distinguish between the two possible protonation
sites on the aryldiazenide ligand, and the absence of any X-ray
structure prevents conclusive assignment of the geometry. The
IR spectrum shows a νN2 absorption of the aryldiazenido ligand
1
at 1670 cm-1, whereas the H NMR spectrum shows an NH
signal due to the ArNdNH or Ar(H)NN ligand present as a
broad doublet at 14.20 ppm. Two phosphines, magnetically
equivalent and different from the third, are also present in the
complex, as indicated by the AB2 multiplet observed in the 31P-
{1H} NMR spectrum. The ν(N2) adsorption at 1670 cm-1 also
OEt)3][BPh4] (6) with HCl (see below). The subsequent
treatment of 10 with NEt3 gives back the bis(aryldiazenido)
complex 6, thus strongly supporting the path shown in Scheme
4.
These results prompted us to treat the methyldiazene complex
[ReCl(CH3NdNH)(CH3N2){PPh(OEt)2}3][BPh4] (8) with an
excess of NEt3 in an attempt to prepare a bis(methyldiazenido)
[Re(CH3N2)2P3][BPh4] complex related to 5 (eq 9). However,
+
indicates a singly bent ArN2 ligand. On this basis, the
aryldiazene [ReCl(ArNdNH)(ArN2)P3]+ (10a+) should contain
a formal Re(I) central metal and the arylhydrazide(2-) [ReCl-
{Ar(H)NN}(ArN2)P3]+ (10b+) a formal Re(III), indicating that
the protonation reaction of a singly bent aryldiazenido ligand
in [Re(ArN2)2P3]+ (6+) results in 2 e- or 4 e- oxidation of the
central metal.
This feature may also explain the lack of reactivity toward
acid of all the mono(aryldiazenido) Re(I) complexes 1, 4, 7,
and 8, whose probable reluctance to give rhenium complexes
in a high oxidation state (III or V) prevents protonation from
taking place.
(9)
in this case, no reaction occurred and starting complex 8
was recovered unchanged after 24 h at 25 °C. This result
was rather unexpected but may be explained as being due to
the absence of acidity in methyldiazene in contrast to the
properties of the related aryldiazene. However, as previously
reported results21-25,28,29,31-33,104 indicate that deprotonation of
a diazene is often closely linked to one rearrangement, one
reduction and the dissociation of one ligand (see Scheme 4),
the lack of reactivity of 8 toward a base may be related to the
whole sequence of reactions and not only to the low acidity of
the diazene. Furthermore, the properties of the final aryldiaz-
enido compounds can also influence the deprotonation reactions,
and the nonreactivity of 8 may also be due to a reluctance to
form a bis(methyldiazenido) Re(-I) derivative. In any case, the
natures of the substituents on the NN groups in these diazene
and diazenido rhenium complexes seem to be significant in
determining their chemical properties.
Aryldiazenido complexes are reported to react with Brønsted
acids to give the corresponding aryldiazene derivatives,21-33 and
we therefore tested this type of reaction using HCl, CF3SO3H,
and CF3COOH, for both the methyldiazenido complexes 1 and
8 and the aryldiazenido complexes 4-7 derivatives. Results
show that only bis(aryldiazenido) complexes 5 and 6 react with
strong acids to give new derivatives of the type 10, which, in
the case of the reaction with HCl, was isolated in the solid state
and characterized (Scheme 5).
Conclusions
This paper reports some new aspects of the diazo chemistry
of rhenium. In particular, the syntheses of both the unprec-
edented bis(dinitrogen) [Re(N2)2P4][BPh4] (2) and methyldia-
zenido [ReCl(CH3N2)(CH3NHNH2)P3][BPh4] (1) derivatives
were easily achieved using methylhydrazine as the reducing
agent for the trichloro Re(III) complex ReCl3P3. Diazo com-
plexes such as the mono(dinitrogen) ReCl(N2)P4 (3), the bis-
(aryldiazenido) [Re(ArN2)2P3][BPh4], and the mono(aryldiaz-
enido) [ReCl(ArN2)(ArNHNH2)P3][BPh4] and [ReCl(ArN2)P4]-
[BPh4] derivatives were prepared. The first structural parameters
for both bis(dinitrogen) 2 and methyldiazenido-methylhydra-
zine 1 complexes of rhenium were also obtained. Reactivity
studies carried out on these new complexes highlighted their
interesting properties, including selective oxidation of the
methylhydrazine ligand in 1 by lead tetraacetate to give the
corresponding methyldiazene derivative [ReCl(CH3NdNH)-
(CH3N2){PPh(OEt)2}3][BPh4] (8). The methylation reaction of
the dinitrogen ligand in 3, affording an unstable species
characterized as methyldiazenido [ReCl(CH3N2)P4]+, was also
detected.
Acknowledgment. The financial support of MURST (Rome)
is gratefully acknowledged. We thank Dr. G. Balacco (Menarini
Ricerche S.p.A.) for the use of his NMR software SwaN-MR
and D. Baldan for technical assistance.
The other mono(diazenido) complexes 1, 8, 4 and 7 do not
react toward protonation (as ascertained by NMR) and may be
isolated unchanged even after treatment with excess acid.
The new compound 10 is an air-stable orange solid that is
diamagnetic and behaves as a 1:1 electrolyte. Its spectroscopic
data indicate that only one aryldiazenido ligand in 6 is
Supporting Information Available: X-ray crystallographic files,
in CIF format, for the structure determinations of complexes 1, 2, and
7. This material is available free of charge via the Internet at
http://pubs.acs.org.
IC990970R