Preparation of methylhydrazine and methyldiazene complexes of molybdenum and tungsten

Article abstract of DOI:10.1016/j.poly.2012.03.004

Nitrosyl complexes [M(CO)₃(NO)L₂]BPh₄ (2, 5) [M = Mo, W; L = PPh(OEt)₂, PPh₂OEt] were prepared by allowing carbonyl compounds M(CO)₄L₂ (1, 4) to react with NOPF₆ in CH₂Cl₂. Dicarbonyl complex [W(CO) ₂(NO){PPh(OEt)₂}₃]BPh₄ (7) was also prepared by reacting W(CO)₃[PPh(OEt)₂]₃ (6) with NOPF₆. Treatment of nitrosyl complexes 2, 5 with [NEt ₄]Br gave bromide derivative [MBr(CO)₂(NO)L ₂]BPh₄ (3). Hydrazine complexes [M(CO)(RNHNH ₂)(NO)L₃]BPh₄ (8, 9, 10) (R = H, CH ₃) were prepared by allowing nitrosyl complexes 2, 5 to react with hydrazine RNHNH₂ in CH₂Cl₂. Reaction of methylhydrazine complexes [M(CO)(CH₃NHNH₂)(NO)L ₃]BPh₄ (8, 10) with Pb(OAc)₄ at -30°C resulted in selective oxidation of hydrazine, affording the corresponding methyldiazene derivatives [M(CO)(CH₃NNH)(NO)L₃]BPh ₄ (11, 12). The complexes were characterised spectroscopically (IR and NMR), and a geometry in solution was also established.

Full text of DOI:10.1016/j.poly.2012.03.004

Polyhedron 38 (2012) 162–168
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Preparation of methylhydrazine and methyldiazene complexes
of molybdenum and tungsten
⇑
Gabriele Albertin , Stefano Antoniutti, Chiara Girardi
Dipartimento di Scienze Molecolari e Nanosistemi, Università Ca’ Foscari Venezia, Dorsoduro 2137, 30123 Venezia, Italy
a r t i c l e i n f o
a b s t r a c t
Article history:
Nitrosyl complexes [M(CO)3(NO)L2]BPh4 (2, 5) [M = Mo, W; L = PPh(OEt)2, PPh2OEt] were prepared by
allowing carbonyl compounds M(CO)4L2 (1, 4) to react with NOPF6 in CH2Cl2. Dicarbonyl complex
[W(CO)2(NO){PPh(OEt)2}3]BPh4 (7) was also prepared by reacting W(CO)3[PPh(OEt)2]3 (6) with NOPF6.
Treatment of nitrosyl complexes 2, 5 with [NEt4]Br gave bromide derivative [MBr(CO)2(NO)L2]BPh4 (3).
Hydrazine complexes [M(CO)(RNHNH2)(NO)L3]BPh4 (8, 9, 10) (R = H, CH3) were prepared by allowing
nitrosyl complexes 2, 5 to react with hydrazine RNHNH2 in CH2Cl2. Reaction of methylhydrazine com-
plexes [M(CO)(CH3NHNH2)(NO)L3]BPh4 (8, 10) with Pb(OAc)4 at À30 °C resulted in selective oxidation
of hydrazine, affording the corresponding methyldiazene derivatives [M(CO)(CH3N@NH)(NO)L3]BPh4
(11, 12). The complexes were characterised spectroscopically (IR and NMR), and a geometry in solution
was also established.
Received 23 January 2012
Accepted 2 March 2012
Available online 16 March 2012
Keywords:
Carbonyl and nitrosyl complexes
Methylhydrazine
Methyldiazene
Phosphonite and phosphinite ligands
Molybdenum and tungsten
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
We have now extended these studies to molybdenum and tung-
sten and report here the synthesis and reactivity of hydrazine com-
The chemistry of transition-metal coordinated hydrazine and
substituted hydrazines continues to be studied, primarily for its
relevance in the nitrogen fixation process [1,2] and also for the rich
and varied chemistry shown by the metal bond hydrazine system
[3–6].
plexes of these metals, stabilised by phosphonite and phosphinite
ligands.
2. Experimental
Hydrazine may behave either as a mono (
ligand or as a bridging group ( ) between two metal fragments [3–
g )
1) or bidentate (g2
2.1. General comments
l
6]. Coordinated hydrazine can be selectively oxidised to 1,2-dia-
zene [2] or, alternatively, reduced to ammonia [1,7,8]. Hydrazine
has also been shown to be a substrate of nitrogenase and has been
trapped as an intermediate during enzyme turnover [9].
A number of hydrazine complexes were thus prepared for sev-
eral central metals, with different types of supporting ligands
including tertiary phosphines, carbonyl, and cyclopentadienyl [3–
6]. Less attention has been paid to phosphites and for molybdenum
[10] – a metal present in nitrogenase – no hydrazine complex sta-
bilised by phosphonite or phosphinite as supporting ligand has
ever been reported.
All synthetic work was carried out under Ar using standard
Schlenk techniques or an inert atmosphere dry-box. All solvents
were dried over appropriate drying agents, degassed on a vacuum
line, and distilled into vacuum-tight storage flasks. Mo(CO)6 and
W(CO)6 were STREM products, used as received. Phosphines
PPh(OEt)2 and PPh2OEt were prepared by the method of Rabino-
witz and Pellon [13]. Hydrazines C6H5NHNH2 and CH3NHNH2 were
Aldrich products and were used as received. Hydrazine NH2NH2
was prepared by decomposition of hydrazine cyanurate (Fluka) fol-
lowing the reported method [14]. High-grade (99.99%) lead(IV)
acetate was purchased from Aldrich. Other reagents were pur-
chased from commercial sources in the highest available purity
and used as received. Infrared spectra (KBr pellets) were recorded
on Perkin-Elmer Spectrum-One FT-IR spectrophotometer. NMR
spectra (1H, 31P, 13C) were obtained on AVANCE 300 Bruker spec-
trometer (300 MHz) at temperatures between +20 and À80 °C, un-
less otherwise noted. 1H and 13C{1H} spectra are referred to
internal tetramethylsilane; 31P{1H} chemical shifts are reported
with respect to 85% H3PO4, with downfield shifts considered
positive. J values are given in Hz. COSY, HMQC and HMBC NMR
We have been interested for several years in the chemistry of
diazo complexes of transition metals and have reported the syn-
thesis and reactivity of mono- and bis(hydrazine) complexes of
Mn and Fe triads with phosphite ligands, of the type
+
[M(RNHNH2)(CO)nL5Àn
]
(M = Mn, Re; n = 2,3), [MH(RNHNH2)L4]+
and [M(RNHNH2)2L4]2+ (M = Fe, Ru, Os; L = phosphites) [11,12].
⇑
Corresponding author.
E-mail address: albertin@unive.it (G. Albertin).
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2012.03.004

G. Albertin et al. / Polyhedron 38 (2012) 162–168
163
experiments were performed with standard programs. iNMR soft-
ware package [15] was used to treat NMR data. The conductivity
of 10À3 mol dmÀ3 solutions of the complexes in CH3NO2 at 25 °C
was measured on a Radiometer CDM 83. Elemental analyses were
determined in the Microanalytical Laboratory of the Dipartimento
di Scienze Farmaceutiche, University of Padova (Italy).
31P{1H} NMR (CD2Cl2, 25 °C) d: A2 spin syst, 161.7 (s) ppm. Anal.
Calc. for C22H30BrMoNO7P2 (658.27): C, 40.14; H, 4.59; N, 2.13.
Found: C, 40.29; H, 4.42; N, 2.00%. 3b: IR (KBr pellet)
(s), 1916 (m); NO: 1622 (s); (Nujol mull) CO: 1972 (s); mNO
1624 (s) cmÀ1
mCO: 1967
m
m
:
.
1H NMR (CD2Cl2, 25 °C) d: 7.75, 7.47 (m, 20H, Ph),
3.91 (m, 4H, CH2), 1.29 (t, 6H, CH3) ppm. 31P{1H} NMR (CD2Cl2,
25 °C) d: A2 spin syst, 131.1 (s) ppm. Anal. Calc. for C30H30BrMo-
NO5P2 (722.35): C, 49.88; H, 4.19; N, 1.94. Found: C, 49.66; H,
4.32; N, 2.05%.
2.2. Synthesis of precursor complexes
Complexes Mo(CO)4(pip)2 (pip = piperidine) and W(CO)3
(CH3CN)3 were prepared following the previously reported meth-
ods [16,17].
2.3.4. W(CO)4[PPh(OEt)2]2 (4a)
An excess of PPh(OEt)2 (0.59 mL g, 2.98 mmol) was added to a
solution of W(CO)6 (0.5 g, 1.42 mmol) in toluene (80 mL) and the
reaction mixture was irradiated at room temperature for 15 min
in a Pyrex Schlenk-flask using a standard 125-W medium-pressure
mercury arc lamp. The solvent was removed under reduced pres-
sure to give an oil which was triturated with ethanol (2 mL). The
white solid which slowly separated out was filtered and crystal-
2.3. Synthesis of complexes
2.3.1. Mo(CO)4L2 (1) [L = PPh(OEt)2 (a), PPh2OEt (b)]
An excess of the appropriate phosphite (12 mmol) was added to
a solution of Mo(CO)4(pip)2 (1.5 g, 3.97 mmol) in toluene (40 mL)
and the reaction mixture was refluxed for 2 h. The solvent was re-
moved under reduced pressure to give an oil which was triturated
with ethanol (3 mL). A yellow solid slowly separated out which
was filtered and crystallised from ethanol; Yield: 75%. 1a: IR (KBr
lised from ethanol; Yield: 25%. IR (KBr pellet)
mCO: 1920 (m),
1887 (s); (Nujol mull)
m
CO: 1898 (s) cmÀ1 1H NMR (CD2Cl2,
.
25 °C) d: 7.61, 7.44 (m, 10H, Ph), 3.97, 3.81 (m, 8H, CH2), 1.32 (t,
12H, CH3) ppm. 31P{1H} NMR (CD2Cl2, 25 °C) d: A2 spin syst,
pellet)
m
CO: 1921 (m), 1893 (s); (Nujol mull)
m
CO: 1897 (s) cmÀ1
.
156.3 (s) ppm, J
= 363.0 Hz. Anal. Calc. for C24H30O8P2W
W
31P183
1H NMR (CD2Cl2, 25 °C) d: 7.63–7.36 (m, 10H, Ph), 3.99, 3.82 (m,
8H, CH2), 1.31 (t, 12H, CH3) ppm. 31P{1H} NMR (CD2Cl2, 25 °C) d:
A2 spin syst, 184.2 (s) ppm. Anal. Calc. for C24H30MoO8P2
(604.38): C, 47.69; H, 5.00. Found: C, 47.48; H, 5.13%. 1b: IR (KBr
(692.28): C, 41.64; H, 4.37. Found: C, 41.51; H, 4.28%.
2.3.5. [W(CO)3(NO){PPh(OEt)2}2]BPh4 (5a)
A slight excess of solid NOPF6 (0.14 g, 0.79 mmol) was added
to a solution of W(CO)4[PPh(OEt)2]4 (4a) (0.50 g, 0.72 mmol) in
dichloromethane (10 mL) and the reaction mixture was stirred at
room temperature for 60 min. The solvent was removed under re-
duced pressure to leave an oil which was triturated with ethanol
(2 mL) containing an excess of NaBPh4 (0.49 g, 1.44 mmol). A yellow
solid slowly separated out from the solution, which was filtered and
crystallised from dichloromethane and ethanol; Yield: 80%. IR (KBr
pellet) m .
CO: 1900 (s) cmÀ1 1H NMR [(CD3)2CO, 25 °C] d: 7.67, 7.48
(m, 20H, Ph), 3.75 (m, 4H, CH2), 1.27 (t, 6H, CH3) ppm. 31P{1H}
NMR [(CD3)2CO, 25 °C] d: A2 spin syst, 152.3 (s) ppm. Anal. Calc.
for C32H30MoO6P2 (668.46): C, 57.50; H, 4.52. Found: C, 57.72; H,
4.65%.
2.3.2. [Mo(CO)3(NO)L2]BPh4 (2) [L = PPh(OEt)2 (a), PPh2OEt (b)]
A slight excess of solid NOPF6 (0.16 g, 0.91 mmol) was added to
a solution of the appropriate complex Mo(CO)4L2 (1) (0.83 mmol)
in dichloromethane (15 mL). The reaction mixture was stirred at
room temperature for 90 min and then the solvent removed under
reduced pressure. The oil obtained was treated with ethanol (2 mL)
containing an excess of NaBPh4 (0.565 g, 1.65 mmol). A yellow so-
lid slowly separated out which was filtered and crystallised from
pellet) mCO: 2096 (m), 2025, 2001 (s); m .
NO: 1734 (s) cmÀ1 1H NMR
(CD2Cl2, 25 °C) d: 7.62, 7.31, 7.02, 6.87 (m, 30H, Ph), 3.98, 3.93
(qnt, 8H, CH2), 1.40, 1.39 (t, 12H, CH3) ppm. 31P{1H} NMR (CD2Cl2,
25 °C) d: AB spin syst, dA 139.4, dB 131.8 ppm, JAB = 37.0,
J
= 358.0, J
= 242.8 Hz. KM = 53.5 OÀ1 molÀ1 cm2. Anal.
31PA183
W
31PB183
W
Calc. for C47H50BNO8P2W (1013.50): C, 55.70; H, 4.97; N, 1.38.
Found: C, 55.56; H, 5.08; N, 1.29%.
dichloromethane and ethanol; Yield: 80%. 2a: IR (KBr pellet) mCO
:
2108 (m), 2039, 2016 (s);
m
NO: 1739 (s) cmÀ1 1H NMR (CD2Cl2,
.
2.3.6. W(CO)3[PPh(OEt)2]3 (6a)
25 °C) d: 7.70–6.88 (m, 30H, Ph), 3.97, 3.92 (qnt, 8H, CH2), 1.39,
1.38 (t, 12H, CH3) ppm. 31P{1H} NMR (CD2Cl2, 25 °C) d: AB spin syst,
dA 157.2, dB 142.9 ppm, JAB = 43.0 Hz. KM = 51.7 OÀ1 molÀ1 cm2.
Anal. Calc. for C47H50BMoNO8P2 (925.60): C, 60.99; H, 5.44; N,
An excess of PPh(OEt)2 (1.52 mL, 7.67 mmol) was added to a
solution of W(CO)3(CH3CN)3 (1 g, 2.56 mmol) in dichloromethane
(20 mL) and the reaction mixture was refluxed for 2 h. The solvent
was removed under reduced pressure to give an oil which was
triturated with ethanol (2 mL). A dark-blue solid separated out,
which was filtered and crystallised from ethanol; Yield: 55%. IR
1.51. Found: C, 60.76; H, 5.32; N, 1.59%. 2b: IR (KBr pellet) mCO
:
2106 (m), 2037, 2010 (s);
m
NO: 1747 (s) cmÀ1 1H NMR (CD2Cl2,
.
25 °C) d: 7.70–6.86 (m, 40H, Ph), 3.58, 3.49 (qnt, 4H, CH2), 1.15,
1.13 (t, 6H, CH3) ppm. 31P{1H} NMR (CD2Cl2, 25 °C) d: AB spin syst,
dA 129.4, dB 115.6 ppm, JAB = 82.0 Hz. KM = 54.8 OÀ1 molÀ1 cm2.
Anal. Calc. for C55H50BMoNO6P2 (989.69): C, 66.75; H, 5.09; N,
1.42. Found: C, 66.59; H, 5.21; N, 1.53%.
(KBr pellet) m .
CO: 1974 (m), 1893, 1862 (s) cmÀ1 1H NMR (CD2Cl2,
25 °C) d: 7.70–7.25 (m, 15H, Ph), 3.98, 3.83, 3.67 (m, 12H, CH2),
1.33, 1.27 (t, 18H, CH3) ppm. 31P{1H} NMR (CD2Cl2, 25 °C) d: A2B
spin syst, dA 156.3, dB 154.4 ppm, JAB = 25.8,
J
= 363.4,
W
31PA183
J
W = 317.3 Hz. Anal. Calc. for C33H45O9P3W (862.47): C,
31PB183
45.96; H, 5.26. Found: C, 45.74; H, 5.37%.
2.3.3. MoBr(CO)2(NO)L2 (3) [L = PPh(OEt)2 (a), PPh2OEt (b)]
An equimolar amount of solid [NEt4]Br (0.173 g, 0.82 mmol)
was added to a solution of the appropriate complex [Mo(CO)3(-
NO)L2]BPh4 (2) (0.82 mmol) in dichloromethane (10 mL) and the
reaction mixture was stirred at room temperature for 4 h. The sol-
vent was removed under reduced pressure leaving an oil which
was treated with ethanol (2 mL). A yellow solid separated out from
the resulting stirring solution, which was filtered and crystallised
from dichloromethane and ethanol; Yield: 75%. 3a: IR (KBr pellet)
2.3.7. [W(CO)2(NO){PPh(OEt)2}3]BPh4 (7a)
A slight excess of solid NOPF6 (0.112 g, 0.64 mmol) was added
solution of complex W(CO)3[PPh(OEt)2]3 (6a) (0.50 g,
to
a
0.58 mmol) in dichloromethane (15 mL) and the reaction mixture
was stirred at room temperature for 60 min. The solvent was re-
moved under reduced pressure leaving an oil which was treated
with ethanol (2 mL) containing an excess of NaBPh4 (0.60 g,
1.75 mmol). A yellow solid slowly separated out which was filtered
and crystallised from dichloromethane and ethanol; Yield: 90%. IR
m
CO: 1993 (s);
m .
NO: 1635 (s) cmÀ1 1H NMR (CD2Cl2, 25 °C) d: 7.74–
6.38 (m, 10H, Ph), 4.16, 3.99 (m, 8H, CH2), 1.35 (t, 12H, CH3) ppm.
(KBr pellet)
mCO: 2037, 1970 (s); m .
NO: 1694 (s) cmÀ1 1H NMR

164
G. Albertin et al. / Polyhedron 38 (2012) 162–168
(CD2Cl2, 25 °C) d: 7.60–6.87 (m, 35H, Ph), 3.90, 3.80 (m, 12H, CH2),
1.35, 1.34 (t, 18H, CH3) ppm. 31P{1H} NMR (CD2Cl2, 25 °C) d: A2B
Yield: 35%. IR (KBr pellet)
mNH: 3328, 3272 (m); mCO: 1963 (s);
m
NO: 1648 (s) cmÀ1 1H NMR (CD2Cl2, 25 °C) d: 7.65–6.87 (m, 35H,
.
spin syst, dA 144.8, dB 134.2 ppm, JAB = 40.5,
J
= 359.4,
Ph), 4.06, 3.89 (m, 12H, CH2), 2.29 (br, 2H, NH2), 1.86 (m, 1H,
NH), 1.58 (d, 3H, CH3N, JHH = 4 Hz), 1.42, 1.38, 1.35 (t, 18H, CH3
phos) ppm. 31P{1H} NMR (CD2Cl2, 25 °C) d: A2B spin syst, dA
156.5, dB 156.0 ppm, JAB = 28.2 Hz. KM = 55.1 OÀ1 molÀ1 cm2. Anal.
Calc. for C56H71BN3O8P3W (1201.75): C, 55.97; H, 5.95; N, 3.50.
Found: C, 55.76; H, 5.83; N, 3.61%.
31PA183
W
J
W = 239.8 Hz. 13C{1H} NMR (CD2Cl2, 25 °C) d: 205.9 (dt, CO,
31PB183
JCP = 9.8, JCP = 17.4 Hz), 165–122 (m, Ph), 65.9 (d), 64.4 (t) (CH2),
16.4 (t, CH3) ppm. KM = 53.6 OÀ1 molÀ1 cm2. Anal. Calc. for
C56H65BNO9P3W (1183.69): C, 56.82; H, 5.53; N, 1.18. Found: C,
56.58; H, 5.40; N, 1.26%.
2.3.8. [Mo(CO)(CH3NHNH2)(NO)L3]BPh4 (8) [L = PPh(OEt)2 (a),
PPh2OEt (b)]
2.3.11. [Mo(CO)(CH3N@NH)(NO)L3]BPh4 (11) [L = PPh(OEt)2 (a),
PPh2OEt (b)]
An excess of methylhydrazine CH3NHNH2 (144 lL, 2.70 mmol)
A solid sample of the appropriate methylhydrazine complex
[Mo(CO)(CH3NHNH2)(NO)L3]BPh4 (8) (0.16 mmol) was placed in
a 25-mL three-necked round-bottomed flask fitted with a solid-
addition side-arm containing a slight excess of Pb(OAc)4 (80 mg,
0.18 mmol). Dichloromethane (10 mL) was added, the solution
cooled to À30 °C and lead acetate added portion wise to the cold
stirring solution over 20–30 min. The reaction mixture was al-
lowed to reach 0 °C and stirred for 15 min and then the solvent re-
moved under reduced pressure. The oil obtained was treated with
ethanol (2 mL) containing a slight excess of NaBPh4 (68 mg,
0.20 mmol). An orange solid slowly separated out from the result-
ing solution, which was filtered and crystallised from dichloro-
was added to a solution of the appropriate complex [Mo(CO)3(-
NO)L2]BPh4 (2) (0.54 mmol) in dichloromethane (15 mL) and the
reaction mixture was stirred at room temperature for 2 h. The sol-
vent was removed under reduced pressure leaving an oil which
was treated with ethanol (2 mL) containing an excess of NaBPh4
(0.55 g, 1.62 mmol). A yellow solid separated out from the result-
ing solution, which was filtered and crystallised from dichloro-
methane and ethanol; Yield: 45%. 8a: IR (KBr pellet)
mNH: 3334,
3277 (m); CO: 1977 (s);
m
m
NO: 1658 (s) cmÀ1 1H NMR (CD2Cl2,
.
25 °C) d: 7.51, 7.33 (m, 35H, Ph), 4.05, 3.95 (m, 12H, CH2), 2.17
(br, 2H, NH2), 1.90 (m, 1H, NH), 1.64 (d, 3H, CH3N, JHH = 4 Hz),
1.42, 1.41, 1.39 (t, 18H, CH3 phos) ppm. 31P{1H} NMR (CD2Cl2,
25 °C) d: A2B spin syst, dA 173.7, dB 169.2 ppm, JAB = 37.3 Hz.
13C{1H} NMR (CD2Cl2, 25 °C) d: 219.5 (dt, CO, JCP = 50.6,
JCP = 11.3 Hz), 165–122 (m, Ph), 64.2 (m, CH2), 43.3 (s, CH3N),
16.7 (m, CH3 phos) ppm. KM = 49.5 OÀ1 molÀ1 cm2. Anal. Calc. for
methane and ethanol; Yield: 65%. 11a: IR (KBr pellet)
mCO: 1987
(s);
m
NO: 1661 (s) cmÀ1 1H NMR (CD2Cl2, 25 °C) d: 11.06 (s, br,
.
1H, NH), 7.55–6.84 (m, 35H, Ph), 4.16, 4.01, 3.89 (m, 12H, CH2),
2.57 (q, 3H, CH3N), 1.46, 1.40, 1.39 (t, 18H, CH3 phos) ppm.
31P{1H} NMR (CD2Cl2, 25 °C) d: A2B spin syst, dA 174.6, dB
170.7 ppm, JAB = 35.5 Hz. KM = 52.9 OÀ1 molÀ1 cm2. Anal. Calc. for
C
56H71BMoN3O8P3 (1113.85): C, 60.39; H, 6.42; N, 3.77. Found: C,
60.20; H, 6.28; N, 3.91%. 8b: IR (KBr pellet) NH: 3323, 3255 (m);
CO: 1983 (s);
NO: 1629 (s) cmÀ1 1H NMR (CD2Cl2, 25 °C) d:
m
C
56H69BMoN3O8P3 (1111.83): C, 60.49; H, 6.26; N, 3.78. Found: C,
60.25; H, 6.15; N, 3.91%. 11b: IR (KBr pellet) CO: 1982 (s); mNO
1633 (s) cmÀ1 1H NMR (CD2Cl2, 25 °C) d: 10.44 (s, br, 1H, NH),
m
m
.
m
:
7.55–6.88 (m, 50H, Ph), 3.55 (m), 3.30 (qnt) (6H, CH2),
1.75 (m, br, 2H, NH2), 1.58 (br, 1H, NH), 1.34 (d, 3H, CH3N,
JHH = 4 Hz), 0.94, 0.64 (t, 9H, CH3 phos) ppm. 31P{1H} NMR (CD2Cl2,
25 °C) d: A2B spin syst, dA 142.4, dB 139.4 ppm, JAB = 32.0 Hz.
KM = 54.1 OÀ1 molÀ1 cm2. Anal. Calc. for C68H71BMoN3O5P3
(1209.98): C, 67.50; H, 5.91; N, 3.47. Found: C, 67.32; H, 5.77; N,
3.33%.
.
7.79–7.86 (m, 50H, Ph), 3.43 (m), 3.34 (qnt) (6H, CH2), 2.21 (q,
3H, CH3N), 0.87, 0.63 (t, 9H, CH3 phos) ppm. 31P{1H} NMR (CD2Cl2,
25 °C) d: A2B spin syst, dA 143.8, dB 140.9 ppm, JAB = 31.0 Hz.
KM = 54.4 OÀ1 molÀ1 cm2. Anal. Calc. for C68H69BMoN3O5P3
(1207.96): C, 67.61; H, 5.76; N, 3.48. Found: C, 67.44, H 5.89, N
3.37%.
2.3.9. [Mo(CO)(NH2NH2)(NO){PPh(OEt)2}3]BPh4 (9a)
2.3.12. [W(CO)(CH3N@NH)(NO){PPh(OEt)2}3]BPh4 (12a)
A slight excess of hydrazine NH2NH2 (7.6
lL, 0.24 mmol) was
This complex was prepared exactly like the related molybdenum
compounds 11 and crystallised from dichloromethane and ethanol;
added to solution of [Mo(CO)3(NO){PPh(OEt)2}2]BPh4 (2a)
a
Yield: 70%. IR (KBr pellet) mCO: 1960 (s); m
NO: 1648 (s) cmÀ1. 1H NMR
(0.20 g, 0.22 mmol) in dichloromethane (10 mL) and the reaction
mixture was stirred at room temperature for 2 h. The solvent was
removed under reduced pressure leaving an oil which was treated
with ethanol (2 mL) containing an excess of NaBPh4 (0.144 g,
0.42 mmol). A yellow solid slowly separated out from the resulting
solution, which was filtered and crystallised from dichloromethane
(CD2Cl2, 25 °C) d: 12.13 (s, br, 1H, NH), 7.70–6.86 (m, 35H, Ph), 4.10,
3.87 (m, 12H, CH2), 2.18 (q, 3H, CH3N), 1.36, 1.34, 1.30 (t, 18H, CH3
phos) ppm. 31P{1H} NMR (CD2Cl2, 25 °C) d: A2B spin syst, dA 155.0, dB
149.5 ppm, JAB = 30.1 Hz. KM = 50.7 OÀ1 molÀ1 cm2. Anal. Calc. for
C56H69BN3O8P3W (1199.73): C, 56.06; H, 5.80; N, 3.50. Found: C,
and ethanol; Yield: 15%. IR (KBr pellet)
mNH: 3338, 3278, 3255 (m);
55.87; H, 5.72; N, 3.37%.
mCO: 1978 (s);
m
NO: 1651 (s) cmÀ1 1H NMR (CD2Cl2, 25 °C) d: 7.52–
.
6.84 (m, 35H, Ph), 4.10–3.85 (m, 12H, CH2), 2.30 (m, 2H, Mo-NH2),
1.55 (m, 2H, N-NH2), 1.38, 1.36, 1.34 (t, 18H, CH3 phos) ppm.
31P{1H} NMR (CD2Cl2, 25 °C) d: A2B spin syst, dA 172.7, dB
168.8 ppm, JAB = 37.3 Hz. KM = 53.4 OÀ1 molÀ1 cm2. Anal. Calc. for
3. Results and discussion
3.1. Preparation of precursor complexes
C
55H69BMoN3O8P3 (1099.82): C, 60.06; H, 6.32; N, 3.82. Found: C,
Mixed-ligands complexes Mo(CO)4L2 with carbonyl and phos-
phine were prepared by substituting piperidine ligands in the com-
pound Mo(CO)4(pip)2, as shown in Scheme 1.
Complexes 1 were isolated in good yields as stable yellow solids
and characterised by analytical and spectroscopic data (IR and
NMR). Trans geometry I in solution was also established (Chart 1).
59.84; H, 6.45; N, 3.70%.
2.3.10. [W(CO)(CH3NHNH2)(NO){PPh(OEt)2}3]BPh4 (10a)
An excess of methylhydrazine CH3NHNH2 (26 lL, 0.49 mmol)
was added to a solution of complex [W(CO)3(NO){PPh(OEt)2}2]BPh4
(5a) (0.100 g, 0.1 mmol) in dichloromethane (15 mL) and the reac-
tion mixture was stirred at room temperature for 3 h. The solvent
was removed under reduced pressure to give an oil which was
treated with ethanol (2 mL) containing an excess of NaBPh4
(68 mg, 0.20 mmol). An orange solid slowly separated out which
was filtered and crystallised from dichloromethane and ethanol;
Scheme 1. pip = piperidine; L = PPh(OEt)2 (a), PPh2OEt (b).

G. Albertin et al. / Polyhedron 38 (2012) 162–168
165
L
with the metal centre in a formal oxidation state of zero [Mo(0)]. In
the temperature range +20 to À80 °C, the 31P{1H} NMR spectra of
complexes 2 appear as AB quartets, which can be simulated with
the parameters reported in Section 2 and suggesting the magnetic
non-equivalence of the two phosphines. On the basis of these data,
mer–cis geometry II (Scheme 2) may be proposed for nitrosyl com-
plexes 2.
OC
OC
CO
CO
Mo
L
( I ) 1
The IR spectrum of MoBr(CO)2(NO)[PPh(OEt)2]2 (3a) shows only
one mCO band at 1993 cmÀ1 indicating a mutually trans position of
the two carbonyl ligands. One strong band at 1635 cmÀ1, attrib-
uted to the mNO of the nitrosyl ligand, is also present. Instead, the
IR spectrum of the related complex MoBr(CO)2(NO)(PPh2OEt)2
(3b) shows, in KBr, two mCO bands, one strong at 1967 and one of
medium intensity at 1916 cmÀ1. A strong band at 1622 cmÀ1 of
the nitrosyl ligand is also present. However, in Nujol, the spectrum
shows only one strong mCO band at 1972 cmÀ1, suggesting the
mutually trans position of the two carbonyl ligands. In the temper-
ature range +20 to À80 °C, the 31P{1H} NMR spectrum is a sharp
singlet suggesting the magnetic equivalence of the two phospho-
nite ligands. The 1H NMR spectrum also suggests a mutually trans
position of the two phosphines, based on the complicated multi-
plets at 4.16 and 3.99 ppm, for 3a, and at 3.91 ppm, for 3b, of the
methylene protons of the substituents, due to virtual coupling
[23] of two phosphorus atoms in a mutually trans position. On
the basis of these data, trans–trans geometry III (Chart 2) may be
proposed for phenyldiethoxyphosphine derivatives 3.
Chart 1.
The IR spectrum of complex Mo(CO)4(PPh2OEt)2 (1b) shows
only one mCO band at 1900 cmÀ1 (KBr), indicating a trans arrange-
ment of the ligands [18], as in geometry I. Instead, the related com-
plex Mo(CO)4[PPh(OEt)2]2 (1a) shows, in KBr, two mCO bands, one of
medium intensity at 1921 and one strong at 1893 cmÀ1, which
may suggest a mutually cis position of the two groups. However,
in Nujol mull, the spectra show only one strong band at
1897 cmÀ1 suggesting, in this case too, a trans arrangement of
the ligands. The 31P{1H} NMR spectra of both carbonyls 1 support
geometry I, showing a sharp singlet at 184.2 ppm, for 1a, and at
152.3 ppm, for 1b, due to the two magnetically equivalent phos-
phine ligands.
Carbonyl complexes Mo(CO)4L2 (1) react with NOPF6 in CH2Cl2
to give cationic nitrosyl derivatives [Mo(CO)3(NO)L2]+ (2), which
À
were isolated as BPh4 salts and characterised (Scheme 2).
The reaction proceeds with substitution of one carbonyl ligand
by NO+ affording the mixed-ligand nitrosyl derivatives 2. Treat-
ment of these complexes with [NEt4]Br in CH2Cl2 gives the bro-
mo-nitrosyl derivatives MoBr(CO)2(NO)L2 (3), which were
isolated in good yield and characterised. Bromide substitutes one
carbonyl ligand in 2, yielding the neutral complex 3 (Scheme 3).
Related triphenylphosphine complexes Mo(CO)4(PPh3)2 have
been reported [19] to give MoF2(NO)2(PPh3)2 by treatment with
NOPF6, whereas the dinitrosyl complex MoBr2(NO)2(PPh3)2 was
obtained in the presence of NOPF6 and [NBu4]Br. The tris(phos-
phine) complexes MoX(CO)(NO)(PMePh2)3 were also described
[20].
Tungsten bis(phosphonite) complex W(CO)4[PPh(OEt)2]2 (4)
was prepared by photochemical substitution of carbonyls by
phosphonites in W(CO)6, as shown in Scheme 4.
Treatment of compound W(CO)4[PPh(OEt)2]2 (4) with NOPF6 in
CH2Cl2 gave the cationic nitrosyl complex [W(CO)3(NO){P-
Ph(OEt)2}2]+ (5), which was separated as tetraphenylborate salt
and characterised (Scheme 5).
The reaction proceeds with substitution of one carbonyl ligand,
yielding the tricarbonyl-nitrosyl derivative 5. A similar reaction
L
The new nitrosyl complexes [Mo(CO)3(NO)L2]BPh4 (2) and
MoBr(CO)2(NO)L2 (3) were separated as yellow solids, stable in
air and in solution of polar solvents, where they behave as either
1:1 (2) or non-electrolytes (3) [21]. Analytical and spectroscopic
data (IR, NMR) support the proposed formulations and geometries
in solution were also established. The IR spectra of nitrosyl com-
plexes [Mo(CO)3(NO)L2]BPh4 (2) show three mCO bands – one of
medium intensity and two strong – suggesting a mer arrangement
of the three carbonyl ligands. The spectra also show one strong
absorption at 1739 (2a) and 1747 cmÀ1 (2b) attributed to the mNO
of the nitrosyl ligand. By comparison with literature data [22],
OC
Br
NO
CO
Mo
L
( III ) 3
Chart 2.
PPh(OEt)2
the value of the
m
NO also suggest the presence of a linear NO+ group,
OC
OC
CO
W
exc. PPh(OEt)2
W(CO)6
hν
CO
+
PPh(OEt)2
NO
OC
OC
L
( IV ) 4
NOPF6
CH2Cl2
Mo
Mo(CO)4L2
1
CO
Scheme 4.
L
( II ) 2
+
L
NO
W
Scheme 2. L = PPh(OEt)2 (a), PPh2OEt (b).
OC
OC
CO
CO
OC
OC
L
NOPF6
CH2Cl2
W
CO
[NEt4]Br
CH2Cl2
L
L
[Mo(CO)3(NO)L2]+
MoBr(CO)2(NO)L2
4
( V ) 5
2
3
Scheme 3. L = PPh(OEt)2 (a), PPh2OEt (b).
Scheme 5. L = PPh(OEt)2.

166
G. Albertin et al. / Polyhedron 38 (2012) 162–168
[19] was observed in the related complex W(CO)4(PPh3)2 [24],
yielding the cation [W(CO)3(NO)(PPh3)2]+.
different from the third. On the basis of these data, mer geometry
VI may be proposed for complex 6.
New tungsten complexes 4 and 5 were isolated as white (4) or
yellow (5) solids, stable in air and in solution of polar organic sol-
vents, where they behave as either non-electrolyte (4) or 1:1 elec-
trolytes (5) [21]. Analytical and spectroscopic data support the
proposed formulation and a geometry in solution was also estab-
lished. The IR spectrum in KBr of the tetracarbonyl complex
W(CO)4[PPh(OEt)2]2 (4) shows one strong mCO band at 1887 cmÀ1
and one of medium intensity at 1920 cmÀ1. However, in Nujol, only
one strong mCO band at 1898 cmÀ1 was observed, suggesting trans
geometry IV for the compound [18]. The 31P NMR spectrum shows
a sharp singlet at 156.7 ppm, with the characteristic satellites due
The IR spectrum of the nitrosyl complex [W(CO)2(NO)
{PPh(OEt)2}3]BPh4 (7) shows two mCO bands, at 2037 and
1970 cmÀ1, indicating a mutually cis position of the two carbonyl
ligands. A strong absorption at 1694 cmÀ1 is also present, due to
the mNO of the nitrosyl group. The 31P NMR spectrum appears as
an A2B multiplet, which can be simulated with the parameters re-
ported in the Section 2 and indicating that two phosphines are
magnetically equivalent and different from the third. As the 13C
NMR spectrum shows only one multiplet (doublet of triplets) in
the carbonyl carbon region at 205.9 ppm, due to the magnetic
equivalence of the two CO ligands, fac–cis geometry VII is proposed
in solution for the nitrosyl derivative 7.
to coupling with 183W (J
W = 363.0 Hz), indicating the magnetic
31P183
equivalence of the two phosphines, as expected for IV-type
geometry.
3.2. Preparation and reactivity of hydrazine complexes
The IR spectrum of the tricarbonyl-nitrosyl complex
[W(CO)3(NO){PPh(OEt)2}2]BPh4 (5) shows three mCO bands – one
of medium intensity and two strong – suggesting mer arrangement
of the three carbonyl ligands. The spectrum also shows a strong
band at 1734 cmÀ1, attributed to the mNO of the nitrosyl group. In
the temperature range between +20 and À80 °C, the 31P NMR spec-
trum is an AB quartet, which can be simulated with the parameters
reported in the Section 2 and indicating that the two phosphines
are not magnetically equivalent. On the basis of these data, mer–
cis geometry V may be proposed for the nitrosyl complex 5.
Tricarbonyl complex W(CO)3[PPh(OEt)2]3 (6) was prepared by
substituting the nitrile ligands with phosphonites in the acetoni-
trile precursor W(CO)3(CH3CN)3, as shown in Scheme 6.
The phosphine complex [25] W(CO)3[PPh(OEt)2]3 (6) reacts
with NOPF6 in CH2Cl2 to give the nitrosyl derivative [W(CO)2(N-
O){PPh(OEt)2}3]+ (7), which was isolated as BPh4 salt and charac-
terised (Scheme 7).
All carbonyl complexes of molybdenum and tungsten 1–7 were
reacted with hydrazine, in an attempt to prepare RNHNH2 deriva-
tives. The results showed that only cationic nitrosyl complexes
[M(CO)3(NO)L2]BPh4 (2, 5) (M = Mo, W) react with hydrazines
RNHNH2 to give the related complexes [M(CO)(RNHNH2)(-
NO)L3]BPh4 (8–10), which were isolated in the solid state and char-
acterised (Scheme 8).
The other complexes, 1, 3, 4, 6 and 7, do not react with hydra-
zines at room temperature and the starting complexes were recov-
ered unchanged even after some days of reaction. Instead, in reflux
conditions only some decompositions were observed and no
hydrazine complexes could be obtained.
The reaction of tricarbonyl species 2 and 5 with hydrazines is
rather surprising, because it does not involve the simple substitu-
tion of one ligand with hydrazine, but is followed by a redistribu-
tion of ligands between the molecules, yielding the probably more
stable tris(phosphine) complexes [M(CO)(RNHNH2)(NO)L3]BPh4
(8–10).
It is worth noting that only with methylhydrazine were both
Mo and W complexes obtained as solids in moderate yields,
whereas with phenylhydrazine no derivative was separated in
pure form. At room temperature, the reaction with PhNHNH2
was very slow, but reflux conditions caused only decomposition,
preventing the separation of phenylhydrazine derivatives. Instead,
hydrazine NH2NH2 gives the stable molybdenum complex 9a in
low yield, and only a mixture of products, which were not sepa-
rated, was obtained with tungsten.
The new complexes 6 and 7 were separated as green (6) or yel-
low (7) solids stable in air and in solution of polar organic solvents
where they behave as either non-electrolyte (6) or 1:1 electrolyte
(7) [21]. Analytical and spectroscopic data (IR, NMR) support the
proposed formulation and allows geometry in solution to be pro-
posed. In the mCO region, the IR spectrum of tricarbonyl compound
W(CO)3[PPh(OEt)2]3 (6) shows one band of medium intensity and
two strong ones, suggesting mer arrangement of the three carbonyl
ligands. The 31P NMR spectrum appears as an A2B multiplet, which
can be simulated with the parameters reported in the Section 2 and
indicating that two phosphines are magnetically equivalent and
The new hydrazine complexes 8–10 were isolated as yellow sol-
ids, stable in air and in solution of polar organic solvents, where
they behave as 1:1 electrolytes [21]. The elemental analysis and
spectroscopic data (IR, NMR) support the proposed formulation.
The IR spectra of methylhydrazine complexes 8 and 10 show three
bands of medium intensity between 3334 and 3255 cmÀ1 attrib-
uted to the mNH of the hydrazine ligand. The spectra also show
one strong band at 1983–1963 cmÀ1, attributed to the mCO of the
carbonyl group, and a strong one at 1663–1629 cmÀ1 due to the
mNO of the nitrosyl ligand. Beside the signals of the phosphines
and BPh4 anion, the 1H NMR spectra of [M(CO)(CH3NHNH2)
(NO)L3]BPh4 (8, 10) show one slightly broad multiplet at 2.29–
1.75 ppm, attributed to the metal-bonded NH2 group, and one
multiplet at 1.90–1.58 ppm, due to the NH moiety of the hydrazine
ligand. In the spectra, a doublet at 1.64–1.34 ppm is also present
PPh(OEt)2
OC
OC
PPh(OEt)2
exc. PPh(OEt)2
reflux
W
W(CO)3(CH3CN)3
CO
PPh(OEt)2
( VI ) 6
Scheme 6.
+
PPh(OEt)2
PPh(OEt)2
PPh(OEt)2
OC
OC
OC
OC
PPh(OEt)2
NOPF6
CH2Cl2
W
W
CO
PPh(OEt)2
exc. RNHNH2
-
-
[M(CO)3(NO)L2]+BPh4
[M(CO)(RNHNH2)(NO)L3]+BPh4
PPh(OEt)2
NO
CH2Cl2
2, 5
8–10
6
( VII ) 7
Scheme 8. M = Mo (8, 9), W (10); L = PPh(OEt)2 (a), PPh2OEt (b); R = CH3 (8, 10), H
(9).
Scheme 7.

G. Albertin et al. / Polyhedron 38 (2012) 162–168
167
+
+
+
L
L
L
L
NO
L
NH2NHCH3
NO
L
NH2NHCH3
CO
M
M
M
OC
NH2NHCH3
OC
ON
L
L
L
VIII
IX
X
Chart 3.
and was attributed to the methyl substituent of the CH3NHNH2
ligand. These attributions were supported by integrations of the
proton signals, 1H–1H and 1H–31P decoupling and COSY experi-
ments, which strongly support the presence of the hydrazine
ligand. In the temperature range between +20 and À80 °C, the
31P NMR spectra are A2B multiplets, indicating that two phos-
phines are magnetically equivalent and different from the third.
However, spectroscopic data alone do not allow us to decide
unambiguously between the three geometries of Chart 3 for meth-
ylhydrazine complexes 8 and 10.
moiety at 1.55 ppm. The 31P NMR spectrum was an A2B multiplet,
indicating that two phosphites are magnetically equivalent and
different from the third. However, like methylhydrazine complexes
8 and 10, the spectroscopic data do not allow us to decide between
the three geometries of Chart 3.
Reactivity studies on hydrazine complexes [M(CO)(RNHNH2)(-
NO)L3]BPh4 (8–10) towards oxidation reaction were undertaken
and the results are summarised in Scheme 9.
Methylhydrazine complexes [M(CO)(CH3NHNH2)(NO)L3]BPh4
(8, 10) react with Pb(OAc)4 at À30 °C to give methyldiazene deriv-
atives [M(CO)(CH3N@NH)(NO)L3]BPh4 (11, 12), which were iso-
lated as solids and characterised. The reaction proceeds with
selective oxidation of the coordinated methylhydrazine to methyl-
diazene, which turned out to be stable and could be isolated.
Instead, the related hydrazine complex [Mo(CO)(NH2NH2)(-
NO){PPh(OEt)2}3]BPh4 (9a) reacts with Pb(OAc)4 at À30 °C with a
colour change of the solution, but no stable product was isolated.
The new diazene complexes 11 and 12 were isolated as yellow-
orange solids, stable in air and in solution of polar organic solvents,
where they behave as 1:1 electrolytes [21]. The analytical and
spectroscopic data (IR, NMR) support the proposed formulation.
Diagnostic for the presence of the methyldiazene moiety are 1H
NMR spectra, which show the characteristic signal [3] of the dia-
zene hydrogen atom at 12.13–10.44 ppm. The spectra also showed
a quartet at 2.57–2.18 ppm and was attributed – by decoupling and
COSY experiments – to the methyl substituent of the diazene li-
gand CH3N@NH. The multiplicity of this signal was due both to
the H-H coupling with the diazene NH proton (see Fig. 1b) and to
‘‘long range’’ H-P coupling with the phosphorus nuclei of only
two phosphines (see Fig. 1c). Coupling with the third phosphine
is probably small and was not observed.
Unfortunately, any attempt to determine the crystal structure
by X-ray diffraction studies failed, owing to the poor quality of
the crystals obtained, and therefore no geometry can reasonably
be proposed.
The IR spectrum of hydrazine complex [Mo(CO)(NH2NH2)
(NO){PPh(OEt)2}3]BPh4 (9a) shows one mCO band at 1978 cmÀ1
,
one mNO at 1651 cmÀ1 and three medium intensity absorptions at
3338, 3278, 3255 cmÀ1, attributed to the mNH of the hydrazine
ligand. However, its presence is confirmed by the 1H NMR
spectrum, which shows a broad multiplet at 2.30 ppm, due to the
metal-bonded NH2 group, and the multiplet of the end-on NH2
Pb(OAc)4
–30 °C, CH2Cl2
[M(CO)(CH3NHNH2)(NO)L3]+
[M(CO)(CH3N=NH)(NO)L3]+
8, 10
11, 12
Scheme 9. M = Mo (11), W (12); L = PPh(OEt)2 (a), PPh2OEt (b).
The IR spectra show the expected strong bands due to the mCO at
1987–1960 cmÀ1 and to the mNO at 1661–1633 cmÀ1, whereas the
31P NMR spectra was an A2B multiplet, suggesting the magnetic
equivalence of two phosphines, different from the third. However,
these spectroscopic data do not allow us to decide between the
three geometries of Chart 4, although 1H NMR spectra of methyl-
diazene complexes may suggest XI-type geometry.
4. Conclusions
In this paper we prove that hydrazine complexes of molybde-
num and tungsten, stabilised by phosphonite and phosphinite
L ligands, can be prepared with nitrosyl compounds [M(CO)3
(NO)L2]BPh4 as precursors. Among the properties shown by these
Fig. 1. 1H NMR spectra of complex 11a in CD2Cl2 at 298 K, signals of the HN@NCH3
moiety: (a) 1H spectrum; (b) 1H{31P} spectrum; (c) 1H with homodecoupling at
11.06 d; (d) 1H with homodecoupling at 2.57 d.
+
+
+
L
L
L
H
CH3
H
CH3
L
NO
N
L
N
N
L
N
N
M
M
M
OC
N
OC
NO
ON
CO
L
L
L
H
CH3
XI
XII
XIII
Chart 4.

168
G. Albertin et al. / Polyhedron 38 (2012) 162–168
(c) R.R. Schrock, T.E. Glassman, M.G. Vale, J. Am. Chem. Soc. 113 (1991) 725;
(d) D. Shaown, Z. Nianyong, W. Xintao, L. Jiaxi, Inorg. Chem. 31 (1992) 2847;
(e) G. Barrado, D. Miguel, V. Riera, S. García-Granda, J. Organomet. Chem. 489
(1992) 129;
hydrazine complexes is easy oxidation with Pb(OAc)4, yielding
methyldiazene derivatives.
(f) M.R. Smith III, T.-Y. Cheng, G.L. Hillhouse, Inorg. Chem. 31 (1992) 1535;
(g) P.E. Mosier, C.G. Kim, D. Coucouvanis, Inorg. Chem. 32 (1993) 2620.
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Acknowledgment
The financial support of MIUR (Rome)-PRIN 2009 is gratefully
acknowledged. We thank Mrs. Daniela Baldan for her technical
assistance.
(b) G. Albertin, S. Antoniutti, A. Bacchi, E. Bordignon, F. Miani, G. Pelizzi, Inorg.
Chem. 39 (2000) 3283;
(c) G. Albertin, S. Antoniutti, E. Bordignon, P. Perinello, J. Organomet. Chem.
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