Reactions of manganese and rhenium complexes with organic azides: Preparation of tetraazabutadiene derivatives

Article abstract of DOI:10.1039/b613964g

Azide complexes M(RN₃)(CO)₃P₂BPh ₄ 1-3 M = Mn, Re; R = C₆H₅CH₂, 4-CH₃C₆H₄CH₂, C₆H ₅, 4-CH₃C₆

Full text of DOI:10.1039/b613964g

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www.rsc.org/dalton | Dalton Transactions
Reactions of manganese and rhenium complexes with organic azides:
preparation of tetraazabutadiene derivatives†
Gabriele Albertin,*a Stefano Antoniutti,a Alessia Bacchi,b Alessandro Celebrin,a Giancarlo Pelizzib and
Gianluigi Zanardoa
Received 26th September 2006, Accepted 11th December 2006
First published as an Advance Article on the web 9th January 2007
DOI: 10.1039/b613964g
Azide complexes [M(RN3)(CO)3P2]BPh4 1–3 [M = Mn, Re; R = C6H5CH2, 4-CH3C6H4CH2, C6H5,
4-CH3C6H4, C5H9; P = PPh(OEt)2, PPh2(OEt)] were prepared by allowing tricarbonyl MH(CO)3P2
hydride complexes to react first with Brønsted acid (HBF4, CF3SO3H) and then with organic azide in
2
the dark. In sunlight the reaction yielded tetraazabutadiene [M(g -1,4-R2N4)(CO)2P2]BPh4 4–6
1
=
complexes or, with benzyl azide, imine [M{g -NH C(H)Ar}(CO)3P2]BPh4 7 (Ar = C6H5, 4-CH3C6H4)
2
derivatives. Tetraazabutadiene [M(g -1,4-R2N4)(CO)2P2]BPh4 complexes were also prepared by reacting
dicarbonyl MH(CO)2P3 species first with Brønsted acid and then with an excess of organic azide.
Complexes were characterised spectroscopically (IR, 1H, 31P, 13C, 15N NMR data) and by the X-ray
2
crystal structure determination of complex [Re{g -1,4-(C6H5CH2)2N4}(CO)2{PPh(OEt)2}2]BPh4 (5a).
Strong evidence for coordination of the organic azide was obtained from the 15N NMR spectra of
labelled [M(C6H5CH215NN15N)(CO)3P2]BPh4 derivatives.
We are interested in the chemistry of diazo complexes and
Introduction
have reported several studies on the reactivity of manganese
and rhenium hydrides toward aryldiazonium cations,18 as well
as on the preparation and reactivity of hydrazine and diazene
derivatives.19 Now, as part of our continuing studies on the
chemistry of diazo and triazo complexes of transition metals,20
we focus attention on the reactivity of organic azides toward
manganese and rhenium complexes. The results, which include the
synthesis of the first tetraazabutadiene complexes of these metals,
as well as the unprecedented coordination of an organic azide on
Mn and Re fragments, are reported here.
The reactions of organic azides RN3 toward transition metal
complexes continue to be studied, not only for the rich and various
chemical reactivity shown, but also as a synthetic method for
1–17
=
obtaining imido M NR and 1,4-tetraazabutadiene derivatives.
1
This is because organoazide can g -coordinate to a metal
center to give, in some cases, stable and isolable complexes with
tantalum,7 vanadium8 and cobalt2 as metal centres. However,
unstable organoazide–metal intermediates, after extrusion of N2,
may yield a terminal metal–imide16 complex [M] NR, a common
=
final product from the reaction of organic azides with transition
metal complexes.2,3,7–9,11
=
=
Tetraazabutadiene [M]–(RN N–N NR) complexes are also
often prepared from the reaction of a metal fragment and an
excess of RN3, through a mechanism which probably involves the
[3 + 2] reaction of a metal–imido with the organic azide.1,4,5,9
Lastly, insertion of an azide into a metal–hydride bond to give
stable triazenide [M]–N(H)NNR complexes has been observed
in tungsten and hafnium complexes,10 and the insertion of RN3
into M–CO bonds to give isocyanate is also known.2a,15
Experimental
General comments
All synthetic work was carried out in an appropriate atmosphere
(Ar, N2) using standard Schlenk techniques or a vacuum atmo-
sphere dry-box. Once isolated, the complexes were found to be
relatively stable in air, but were stored in 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. Mn2(CO)10 and Re2(CO)10 were Pressure Chemical
Co. (USA) products, used as received. Phosphanes PPh(OEt)2
and PPh2(OEt) were prepared by the method of Rabinowitz
and Pellon.21 Alkyl22 and aryl23 azides were prepared following
methods previously reported. The labelled R15N3 azides (R =
C6H5CH2, 4-CH3C6H4CH2) were prepared following the same
method, by reacting Na[15NNN] (98% enriched, CIL) with the
appropriate alkyl bromide. Equimolar mixtures of R15NNN and
RNN15N were obtained. 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
or Perkin-Elmer Spectrum One FT-IR spectrophotometers. NMR
Reactivity with organic azides has been studied in several
fragments of both early and late transition metals, allowing the
synthesis of many imido and tetraazabutadiene complexes.1–16
Interesting intermediates have also been highlighted in these
reports. However, despite the number of publications, no data
on the reactivity of organic azide toward manganese and rhenium
complexes have yet been reported.
aDipartimento di Chimica, Universita` Ca’Foscari di Venezia, Dorsoduro,
2137, 30123, Venezia, Italy. E-mail: albertin@unive.it
bDipartimento di Chimica Generale ed Inorganica, Chimica Analitica,
Chimica Fisica, Universita` di Parma, Parco Area delle Scienze, 17/a, 43100,
Parma, Italy
† Electronic supplementary information (ESI) available: 15N NMR data
(Fig. S1–S4). See DOI: 10.1039/b613964g
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CH3 phos). 31P{ H} NMR (CD2Cl2, 25 ◦C) d: A2 spin system,
spectra (1H, 31P, 13C, 15N) were obtained on AC200 or AVANCE
1
300 Bruker spectrometers at temperatures between −90 and
186.8).
◦
1
+30 C, unless otherwise noted. H and 13C spectra are referred
[Re(RN3)(CO)3P2]BPh4 2, 3 [P = PPh(OEt)2 2, PPh2(OEt) 3;
R = C6H5CH2 a, 4-CH3C6H4CH2 b, C6H5 c, C5H9 (cyclopentyl) e].
These complexes were prepared exactly like the related manganese
derivatives 1 using a reaction time of 4 h with C6H5N3 and of 24 h
with the alkyl azides; yield 55 to 70% (2a: IR: mCO 2020 (w), 1965,
1950 (s) (KBr); 2021 (w), 1972, 1955 (s) (CH2Cl2) cm−1. 1H NMR
(CD2Cl2, 25 ◦C) d: 7.75–6.84 (m, 35 H, Ph), 4.52 (s, 2 H, CH2N3),
to internal tetramethylsilane; 31P{ H} chemical shifts are reported
1
with respect to 85% H3PO4, and 15N with respect to CH315NO2, in
both cases with downfield shifts considered positive. The COSY,
HMQC and HMBC NMR experiments were performed using
their standard programs. The SwaN-MR software package24 was
used to treat NMR data. The conductivity of 10−3 mol dm−3
solutions of the complexes in CH3NO2 at 25 ◦C were measured
with a Radiometer CDM 83.
1
3.95 (m, 8 H, CH2 phos), 1.30 (t, 12 H, CH3). 31P{ H} NMR
(CD2Cl2, 25 ◦C) d: A2 spin system, 136.4. KM/S cm2 mol−1 = 56.7.
Found: C, 57.79; H, 5.10; N, 3.81. C54H57BN3O7P2Re requires
C, 57.96; H, 5.13; N, 3.76%. 2c: IR: mCO 2040 (m), 1975, 1934
(s) (KBr); 2056 (m), 1983, 1943 (s) (CH2Cl2) cm−1. 1H NMR
(CD2Cl2, 25 ◦C) d: 7.51–6.86 (m, 35 H, Ph), 3.78 (m, 8 H, CH2),
Synthesis of complexes
The MH(CO)nP5−n [M = Mn, Re; n = 1, 2, 3; P = PPh(OEt)2,
PPh2(OEt)] hydride complexes were prepared following the known
method.25
1.32 (t, 12 H, CH3). 31P{ H} NMR (CD2Cl2, 25 ◦C) d: A2 spin
1
system, 135.9. KM/S cm2 mol−1 = 55.4. Found: C, 57.54; H, 4.96;
N, 3.73. C53H55BN3O7P2Re requires C, 57.61; H, 5.02; N, 3.80%.
2e: IR: mCO 2015 (m), 1962, 1950 (s) (KBr); 2018 (m), 1976, 1952
(s) (CH2Cl2) cm−1. 1H NMR (CD2Cl2, 25 ◦C) d: 7.50–6.89 (m, 30
H, Ph), 4.05 (m, 8 H, CH2), 3.79, 1.74 (m, 9 H, C5H9), 1.41 (t,
[Mn(RN3)(CO)3{PPh(OEt)2}2]BPh4 1 [R = C6H5CH2 a, 4-
CH3C6H4CH2 b, C6H5 c]. An equimolar amount of triflic acid
(0.37 mmol, 33 lL) was added to a frozen solution of the hydride
MnH(CO)3{PPh(OEt)2}2 (0.37 mmol, 200 mg) in 7 cm3 of CH2Cl2
cooled to −196 ◦C. The reaction mixture was brought to room
temperature, stirred for 1 h and then a slight excess of the
appropriate azide (0.44 mmol, 0.44 cm3 of 1 M solution in CH2Cl2)
was added. The solution was stirred at room temperature in the
dark, for about 3 h in the case of C6H5N3 and for 20 h with the
benzyl azides. The solvent was removed under reduced pressure
to give an oil which was treated with ethanol (1 cm3) containing a
slight excess of NaBPh4 (0.44 mmol, 151 mg). The slow addition of
diethyl ether to the resulting stirring solution caused the separation
of an orange solid which was filtered and crystallised from CH2Cl2
and diethyl ether; yield ≥60% (1a: IR (KBr): mCO 2016 (w), 1976,
12 H, CH3). 31P{ H} NMR (CD2Cl2, 25 ◦C) d: A2 spin system,
1
135.9. KM/S cm2 mol−1 = 53.5. Found: C, 56.77; H, 5.51; N,
3.75. C52H59BN3O7P2Re requires C, 56.93; H, 5.42; N, 3.83%. 3c:
IR: mCO 2069 (m), 1972, 1933 (s) (KBr); 2082 (w), 1981, 1942 (s)
(CH2Cl2) cm−1. H NMR (CD2Cl2, 25 ◦C) d: 7.50–6.84 (m, 45
1
1
H, Ph), 3.51 (m, 4 H, CH2), 1.15 (t, 6 H, CH3). 31P{ H} NMR
(CD2Cl2, 25 ◦C) d: A2 spin system, 110.5. KM/S cm2 mol−1 = 50.6.
Found: C, 62.57; H, 4.65; N, 3.64. C61H55BN3O5P2Re requires C,
62.67; H, 4.74; N, 3.59%).
[Re(C6H5CH215N3)(CO)3{PPh(OEt)2}2]BPh4 2a1. This com-
plex was prepared exactly like the related unlabelled compound 2a
using the C6H5CH215N3 azide as a reagent; yield ≥60% (IR (KBr):
◦
1
1955 (s) cm−1. H NMR (CD2Cl2, 25 C) d: 7.56–6.85 (m, 35 H,
Ph), 5.51 (s, 2 H, CH2N3), 3.86 (m, 8 H, CH2 phos), 1.31 (t,
◦
12 H, CH3). 31P{ H} NMR (CD2Cl2, 25 ◦C) d: A2 spin system,
1
mCO 2018 (w), 1967, 1948 (s) cm−1. H NMR (CD2Cl2, 25 C) d:
1
184.1. KM/S cm2 mol−1 = 54.9. Found: C, 65.42; H, 5.73; N,
4.34. C54H57BMnN3O7P2 requires C, 65.66; H, 5.82; N, 4.25%.
1b: IR: mCO 2020 (m), 1974, 1952 (s) (KBr); 2016 (m), 1979, 1959
(s) (CH2Cl2) cm−1. 1H NMR (CD2Cl2, 25 ◦C) d: 7.50–6.87 (m, 34
H, Ph), 5.49 (s, 2 H, CH2N3), 4.00 (m, 8 H, CH2 phos), 2.36 (s, 6 H,
7.72–6.84 (m, 35 H, Ph), 4.52 (s, 2 H, CH2N3), 3.95 (m, 8 H, CH2
◦
1
phos), 1.30 (t, 12 H, CH3). 31P{ H} NMR (CD2Cl2, 25 C) d: A2
spin system, 136.4).
[M(g2-1,4-R2N4)(CO)2P2]BPh4 4, 5, 6 [M = Mn 4, Re 5, 6; P =
PPh(OEt)2 4, 5, PPh2(OEt) 6; R = C6H5CH2 a, 4-CH3C6H4CH2
b]. An equimolar amount of HBF4·Et2O (0.25 mmol, 36 lL)
was added to a frozen solution of the appropriate MH(CO)2P3
(0.25 mmol) hydride complex in 7 cm3 of CH2Cl2 cooled to
−196 ◦C. The reaction mixture was brought to room temperature,
stirred for 1 h and then an excess of the benzyl azide (0.75 mmol,
0.75 cm3 of 1 M solution in CH2Cl2) was added. The solution
was exposed to sunlight and stirred at room temperature for 20 h.
The solvent was removed under reduced pressure to give an oil
which was triturated with ethanol (2 cm3) containing an excess of
NaBPh4 (0.50 mmol, 171 mg). A red-brown solid slowly separated
out from the resulting solution which was filtered and crystallised
from CH2Cl2 and ethanol; yield ≥65% (4a: IR: mCO 2004, 1949 (s)
1
CH3 p-tol), 1.35 (t, 12 H, CH3 phos). 31P{ H} NMR (CD2Cl2) d:
◦
◦
1
(25 C) A2 spin system, 186.8; (−70 C) 185.2 (s). 13C{ H} NMR
(CD2Cl2, 25 ◦C) d: 217.0 (t, JCP = 11 Hz, CO), 212.9 (t, JCP
=
20 Hz, CO), 165–122 (m, Ph), 72.2 (s, CH2N3), 64.3 (t, CH2 phos),
21.8 (s, CH3 p-tol), 16.3 (t, CH3 phos). KM/S cm2 mol−1 = 50.3.
Found: C, 65.78; H, 6.02; N, 4.31. C55H59BMnN3O7P2 requires
C, 65.94; H, 5.94; N, 4.19%. 1c: IR: mCO 2014 (m), 1978, 1939 (s)
(KBr); 2016 (m), 1986, 1947 (s) (CH2Cl2) cm−1. 1H NMR (CD2Cl2,
25 ◦C) d: 7.60–6.85 (m, 35 H, Ph), 3.82 (m, 8 H, CH2), 1.30 (t, 12
H, CH3). 31P{ H} NMR (CD2Cl2, −70 ◦C) d: A2 spin system,
1
183.9. KM/S cm2 mol−1 = 52.8. Found: C, 65.52; H, 5.60; N, 4.38.
C53H55BMnN3O7P2 requires C, 65.38; H, 5.69; N, 4.32%).
◦
[Mn(4-CH3C6H4CH215N3)(CO)3{PPh(OEt)2}2]BPh4 1b1. This
complex was prepared exactly like the related unlabelled com-
pound 1b using the 4-CH3C6H4CH215N3 azide as a reagent; yield
≥55% (IR (CH2Cl2): mCO 2020 (w), 1978, 1958 (s) cm−1. 1H NMR
(CD2Cl2, 25 ◦C) d: 7.50–6.90 (m, 34 H, Ph), 5.49 (s, 2 H, CH2N3),
4.06 (m, 8 H, CH2 phos), 2.37 (s, 3 H, CH3 p-tol), 1.35 (t, 12 H,
(KBr); 2018, 1960 (s) (CH2Cl2) cm−1. H NMR (CD2Cl2, 25 C)
1
d: 7.60–6.84 (m, 40 H, Ph), 5.53 (s, 4 H, CH2N), 3.64 (qnt, 8◦H,
1
CH2 phos), 1.27 (t, 12 H, CH3). 31P{ H} NMR (CD2Cl2, 25 C)
◦
1
d: A2 spin system, 167.0. 13C{ H} NMR (CD2Cl2, 25 C) d: 223.1
(t, JCP = 35.8 Hz, CO), 165–122 (m, Ph), 72.4 (s, CH2N), 65.9
(t, CH2 phos), 16.1 (t, CH3). KM/S cm2 mol−1 = 55.1. Found: C,
662 | Dalton Trans., 2007, 661–668
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67.51; H, 6.12; N, 5.20. C60H64BMnN4O6P2 requires C, 67.67; H,
6.06; N, 5.26%. 4b: IR: mCO 2014, 1956 (s) (KBr); 2017, 1960 (s)
(CH2Cl2) cm−1. 1H NMR (CD2Cl2, 25 ◦C) d: 7.60–6.82 (m, 38 H,
Ph), 5.50 (s, 4 H, CH2N), 3.66 (m, 8 H, CH2 phos), 2.37 (s, 6 H,
C60H64BMnN4O6P2 requires C, 67.67; H, 6.06; N, 5.26%. 5d: IR:
1
mCO 2015, 1947 (s) (KBr); 2023 (m), 1959 (s) (CH2Cl2) cm−1. H
NMR (CD2Cl2, 25 ◦C) d: 7.45–6.84 (m, 38 H, Ph), 3.69 (br, 8 H,
1
CH2), 2.48 (s, 6 H, CH3 p-tol), 1.20 (t, 12 H, CH3 phos). 31P{ H}
CH3 p-tol), 1.28 (t, 12 H, CH3 phos). 31P{ H} NMR (CD2Cl2,
NMR (CD2Cl2, 25 ◦C) d: A2 spin system, 116.3. KM/S cm2 mol−1
=
1
25 ◦C) d: A2 spin system, 167.2. KM/S cm2 mol−1 = 54.5. Found:
C, 68.21; H, 6.22; N, 5.05. C62H68BMnN4O6P2 requires C, 68.14;
H, 6.27; N, 5.13%. 5a: IR: mCO 2025, 1955 (s) (KBr); 2026, 1960
(s) (CH2Cl2) cm−1. 1H NMR (CD2Cl2, 25 ◦C) d: 7.60–6.84 (m, 40
H, Ph), 5.67 (s, 4 H, CH2N), 3.48, 3.37 (m,◦8 H, CH2 phos), 1.25
52.8. Found: C, 60.11; H, 5.46; N, 4.62. C60H64BN4O6P2Re requires
C, 60.25; H, 5.39; N, 4.68%. 6c: IR: mCO 2025, 1953 (s) (KBr); 2027,
1963 (s) (CH2Cl2) cm−1. 1H NMR (CD2Cl2, 25 ◦C) d: 7.50–6.84 (m,
1
50 H, Ph), 3.40 (qnt, 4 H, CH2), 1.06 (t, 6 H, CH3). 31P{ H} NMR
(CD2Cl2, 25 ◦C) d: A2 spin system, 95.9. KM/S cm2 mol−1 = 51.8.
Found: C, 64.23; H, 5.00; N, 4.64. C66H60BN4O4P2Re requires C,
64.34; H, 4.91; N, 4.55%).
1
(t, 12 H, CH3). 31P{ H} NMR (CD2Cl2, 25 C) d: A2 spin system,
◦
1
116.0. 13C{ H} NMR (CD2Cl2, 25 C) d: 199.4 (t, JCP = 18 Hz,
CO), 165–122 (m, Ph), 72.5 (s, CH2N), 65.5 (t, CH2 phos), 15.7 (t,
CH3). KM/S cm2 mol−1 = 53.9. Found: C, 60.08; H, 5.27; N, 4.76.
C60H64BN4O6P2Re requires C, 60.25; H, 5.39; N, 4.68%. 5b: IR:
mCO 2022, 1956 (s) (KBr); 2025, 1958 (s) (CH2Cl2) cm−1. 1H NMR
(CD2Cl2, 25 ◦C) d: 7.55–6.82 (m, 38 H, Ph), 5.52 (s, 4 H, CH2N),
3.42, 3.30 (m, 8 H, CH2 phos), 2.35 (s, 6 H,◦CH3 p-tol), 1.17 (t, 12
[M(g2-1,4-R215N4)(CO)2{PPh(OEt)2}2]BPh4 4a1, 5a1, 5b1 [M =
Mn 4, Re 5; R = C6H5CH2 a1, 4-CH3C6H4CH2 b1]. These com-
plexes were prepared exactly like the related unlabelled compounds
4a, 4b, 5b using the R15N3 azide as a reagent; yield ≥65% (4a1: IR:
mCO 2004, 1949 (s) (KBr); 2017, 1960 (s) (CH2Cl2) cm−1. 1H NMR
(CD2Cl2, 25 ◦C) d: 7.70–6.85 (m, 40 H, Ph), 5.56 (s, 4 H, CH2N),
1
H, CH3 phos). 31P{ H} NMR (CD2Cl2, 25 C) d: A2 spin system,
1
3.65 (m, br, 8 H, CH2 phos), 1.28 (t, 12 H, CH3). 31P{ H} NMR
◦
1
116.1. 13C{ H} NMR (CD2Cl2, 25 C) d: 199.6 (t, JCP = 17.4 Hz,
CO), 163–122 (m, Ph), 72.4 (s, CH2N), 65.4 (t, CH2 phos), 21.3 (s,
CH3 p-tol), 15.8 (t, CH3 phos). KM/S cm2 mol−1 = 52.6. Found:
C, 60.68; H, 5.65; N, 4.49. C62H68BN4O6P2Re requires C, 60.83;
H, 5.60; N, 4.58%. 6a: IR: mCO 2018, 1953 (s) (KBr); 2025, 1960
◦
1
(CD2Cl2, 25 C) d: A2 spin system, 168.0. 13C{ H} NMR (CD2Cl2,
25 ◦C) d: 223.1 (t, JCP = 35.8 Hz, CO), 165–122 (m, Ph), 72.4 (s,
CH2N), 65.9 (t, CH2 phos), 16.2 (t, CH3). 5a1: IR: mCO 2023, 1954
(s) (KBr); 2026, 1959 (s) (CH2Cl2) cm−1. 1H NMR (CD2Cl2, 25 ◦C)
d: 7.56–6.84 (m, 40 H, Ph), 5.67 (s, 4 H, CH2N), 3.48, 3.38 (m, 8 H,
(s) (CH2Cl2) cm−1. H NMR (CD2Cl2, 25 ◦C) d: 7.60–6.84 (m,
1
◦
CH2 phos), 1.23 (t, 12 H, CH3). 31P{ H} NMR (CD2Cl2, 25 C) d:
1
50 H, Ph), 5.58 (s, 4 H, CH2N), 3.39 (m, ◦4 H, CH2 phos), 1.21
◦
A2 spin system, 116.0. 13C{ H} NMR (CD2Cl2, 25 C) d: 199.5 (t,
JCP = 18.0 Hz, CO), 165–122 (m, Ph), 72.6 (s, CH2N), 65.5 (s, br,
CH2 phos), 15.8 (br, CH3). 5b1: IR: mCO 2022, 1955 (s) (KBr); 2025,
1
1
(t, 6 H, CH3). 31P{ H} NMR (CD2Cl2, 25 C) d: A2 spin system,
97.0. 13C{ H} NMR (CD2Cl2, 25 ◦C) d: 200.0 (t, JCP = 15 Hz,
1
CO), 165–122 (m, Ph), 72.7 (s, CH2N), 66.3 (t, CH2 phos), 15.8
(t, CH3). KM/S cm2 mol−1 = 56.6. Found: C, 64.64; H, 5.03; N,
4.54. C68H64BN4O4P2Re requires C, 64.81; H, 5.12; N, 4.45%. 6b:
1959 (s) (CH2Cl2) cm−1. H NMR (CD2Cl2, 25 ◦C) d: 7.60–6.83
1
(m, 38 H, Ph), 5.53 (s, 4 H, CH2N), 3.42, 3.30 (m, 8 H, CH2 phos),
1
2.36 (s, 6 H, CH3 p-tol), 1.18 (t, 12 H, CH3 phos). 31P{ H} NMR
1
IR: mCO 2021, 1959 ◦(s) (KBr); 2025, 1958 (s) (CH2Cl2) cm−1. H
(CD2Cl2, 25 ◦C) d: A2 spin system, 116.0).
NMR (CD2Cl2, 25 C) d: 7.60–6.87 (m, 48 H, Ph), 5.52 (s, 4 H,
CH2N), 3.34 (m, 4 H, CH2 phos), 2.23 (s, 6 H, CH3 p-tol), 1.17 (t,
=
[Re{ArC(H) NH)(CO)3{PPh(OEt)2}2]BPh4 7 [Ar = C6H5 a,
◦
1
6 H, CH3 phos). 31P{ H} NMR (CD2Cl2, 25 C) d: A2 spin system,
4-CH3C6H4 b]. An equimolar amount of triflic acid (0.37 mmol,
◦
95.9. 13C{ H} NMR (CD2Cl2, 25 C) d: 199.9 (t, JCP = 10.0 Hz,
CO), 165–122 (m, Ph), 72.4 (s, CH2N), 66.3 (t, CH2 phos), 21.2 (s,
CH3 p-tol), 15.7 (t, CH3 phos). KM/S cm2 mol−1 = 49.5. Found: C,
65.35; H, 5.23; N, 4.28. C70H68BN4O4P2Re requires C, 65.26; H,
5.32; N, 4.35%).
33 lL) was added to a frozen solution of the hydride
1
ReH(CO)3{PPh(OEt)2}2 (0.37 mmol, 250 mg) in 10 cm3 of CH2Cl2
cooled to −196 ◦C. The solution was brought to room temperature,
stirred for about 1 h and then a slight excess of the appropriate
azide, C6H5CH2N3 or 4-CH3C6H4CH2N3 (0.44 mmol, 0.44 cm3 of
1 M solution in CH2Cl2) was added. The reaction mixture was
stirred at room temperature in the presence of sunlight for about
24 h and then the solvent was removed under reduced pressure. The
oil obtained was treated with ethanol (2 cm3) containing an excess
of NaBPh4 (0.74 mmol, 250 mg). The resulting solution was stirred
for 1 h and then allowed to stand at −25 ◦C. White microcrystals
slowly separated out from the solution, which were filtered off and
crystallised from ethanol; yield ≥35% (7a: IR (KBr): mNH 3328 (m);
[M(g2-1,4-R2N4)(CO)2P2]BPh4 4, 5, 6 [M = Mn 4, Re 5, 6; P =
PPh(OEt)2 4, 5, PPh2(OEt) 6; R = C6H5 c, 4-CH3C6H4 d]. These
complexes were prepared as for the related aliphatic species 4a,
4b, 5a, etc., using a reaction time of 2 h; yield ≥75% (4c: IR: mCO
1
2021, 1966 (s) (KBr); 2021, 1967 (s) (CH2Cl2) cm−1. H NMR
(CD2Cl2, 25 ◦C) d: 7.59–6.88 (m, 40 H, Ph), 3.79 (qnt, 8 H,
CH2), 1.26 (t, 12 H, CH3). 31P{ H} NMR (CD2Cl2, 25 ◦C) d:
1
A2 spin system, 167.7. 13C{ H} NMR (CD2Cl2, 25 ◦C) d: 223.0
mCO 2070 (m), 1972, 1955 (s) cm−1. H NMR (CD2Cl2, 25 C) d:
◦
1
1
3
3
(t, JCP = 35.5 Hz, CO), 165–122 (m, Ph), 63.3 (d, CH2), 16.3 (d,
CH3). KM/S cm2 mol−1 = 55.3. Found: C, 67.27; H, 5.74; N, 5.49.
C58H60BMnN4O6P2 requires C, 67.19; H, 5.83; N, 5.40%. 4d: IR:
8.99 (d, 1 H, JHH = 15 Hz, NH), 7.97 (d, 1 H, JHH = 15 Hz,
=
CH), 7.50–6.85 (m, 35 H, Ph), 3.87 (m, 8 H, CH2), 1.35 (t,
12 H, CH3). 31P{ H} NMR (CD2Cl2, 25 ◦C) d: A2 spin system,
1
mCO 2003, 1948 (s) (KBr); 2016 (m), 1963 (s) (CH2Cl2) cm−1. H
132.6. 13C{ H} NMR (CD2Cl2, 25 ◦C) d: 189.6, 189.5 (t, JCP
=
1
1
NMR (CD2Cl2, 25 ◦C) d: 7.50–6.91 (m, 38 H, Ph), 4.09, 3.79 (br,
8 H, CH2), 2.50 (s, 6 H, CH3 p-tol), 1.46, 1.26 (t, 12 H, CH3
10.5 Hz, CO), 180.7 (s, CH), 165–122 (m, Ph), 64.2 (t, CH2),
16.3 (t, CH3). KM/S cm2 mol−1 = 54.4. Found: C, 59.57; H, 5.22;
N, 1.33. C54H57BNO7P2Re requires C, 59.45; H, 5.27; N, 1.28%.
7b: IR (KBr): mNH 3338 (m); mCO 2068 (w), 1971, 1938 (s) cm−1. 1H
=
◦
1
phos). 31P{ H} NMR (CD2Cl2, 25 C) d: A2 spin system, 168.6.
◦
13C{ H} NMR (CD2Cl2, 25 C) d: 222.3 (t, JCP = 35.4 Hz, CO),
165–122 (m, Ph), 66.1 (m, CH2), 21.5 (s, CH3 p-tol), 16.2 (t, CH3
phos). KM/S cm2 mol−1 = 50.7. Found: C, 67.46; H, 6.10; N, 5.18.
1
NMR (CD2Cl2, 25 ◦C) d: 8.95 (d, 1 H, NH), 7.95 (d, 1 H, JHH
=
=
15 Hz, CH), 7.53–5.85 (m, 34 H, Ph), 3.90 (m, 8 H, CH2), 2.39 (s,
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1
3 H, CH3 p-tol), 1.34 (t, 12 H, CH3 phos). 31P{ H} NMR (CD2Cl2,
Results and discussion
25 ◦C) d: A2 spin system, 134.4. KM/S cm2 mol−1 = 55.0. Found:
C, 59.64; H, 5.43; N, 1.21. C55H59BNO7P2Re requires C, 59.78; H,
5.38; N, 1.27%).
Reactions with organic azides
Depending on experimental conditions and the nature of the
organic azide, the reaction of hydride tricarbonyl MH(CO)3P2
complexes, first with Brønsted acid and then with organic azide,
[Re{C6H5C(H) 15NH}(CO)3{PPh(OEt)2}2]BPh4 7a1. This
gives azide [M(RN3)(CO)3P2]+ 1–3, tetraazabutadiene [M(g -1,4-
2
=
+
1
+
complex was prepared exactly like the related unlabelled
=
R2N4)(CO)2P2] 4–6 and imine [M{g -NH C(H)Ar}(CO)3P2] 7
compound 7a using the C6H5CH215N3 azide as a reagent; yield
derivatives, as shown in Scheme 1.
≥55% (IR (KBr): mNH 3323 (m); mCO 2068 (m), 1970, 1955 (s) cm−1.
◦
1
3
1H NMR (CD2Cl2, 25 C) d: 8.98 (dd, J
= 68 Hz, JHH
=
15
NH
15 Hz, 1 H, NH), 7.50–6.85 (m, 35 H, Ph), 7.97 (d, 3JHH = 15 Hz,
1 H, CH), 3.87 (m, 8 H, CH2), 1.34 (t, 12 H, CH3). 31P{ H} NMR
1
(CD2Cl2, 25 ◦C) d: A2X spin system, 132.4, JAX = 2.8 Hz).
Crystallographic analysis of
[Re{g2-1,4-(C6H5CH2)2N4}(CO)2{PPh(OEt)2}2]BPh4 5a
Data collection was performed on a SMART AXS 1000 CCD
˚
diffractometer with MoKa radiation (k = 0.71073 A), T =
293 K. Lorentz, polarisation, and absorption corrections were
applied.26 Structures solved by direct methods using SIR9727 and
refined by full-matrix least-squares on all F2 using SHELXL9728
implemented in the WingX package.29 Hydrogen atoms were
introduced in calculated positions. Anisotropic displacement
parameters were refined for all non-hydrogen atoms. Molecular
geometry has been analysed with PARST97,30 and extensive
use was made of the Cambridge Crystallographic Data Centre
packages31 (CSD 5.27, update May 2006). Table 1 summarises
crystal data and structure determination results.
Scheme 1 M = Mn 1, 4, Re 2, 3, 5, 6, 7; P = PPh(OEt)2 1, 2, 4, 5, 7,
CCDC reference number 622218.
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b613964g
PPh2(OEt) 3, 6; R = C6H5CH2 a, 4-CH3C6H4CH2 b, C6H5 c, 4-CH3C6H4
d, C5H9 e; Y = BF4−, CF3SO3
.
−
Instead, the reaction of hydride dicarbonyls MH(CO)2P3, first
with Brønsted acid and then with RN3, under any conditions gives
2
2
tetraazabutadiene [M(g -1,4-R2N4)(CO)2P2]+ 4–6 derivatives as fi-
Table 1 Crystal data and structure refinement for [Re{g -1,4-
(C6H5CH2)2N4}(CO)2{PPh(OEt)2}2]BPh4 5a
nal products, which were isolated as BPh4− salts and characterised
(Scheme 2).
Empirical formula
Formula weight
T/K
C60H64BN4O6P2Re
1196.10
293(2)
Triclinic
¯
P1
10.8658(7); 79.556(1)
16.388(1); 78.603(1)
17.404(1); 82.235(1)
2971.8(3)
Crystal system
Space group
◦
˚
a/A; a/◦
˚
b/A; b/◦
˚
c/A; c /
3
˚
Volume/A
Z
2
Density (calculated)/Mg m−3
Absorption coefficient/mm−1
F(000)
1.337
2.149
1220
1.89–27.13
Theta range for data collection/◦
Reflections collected
31672
Scheme 2 M = Mn 4, Re 5, 6; P = PPh(OEt)2 4, 5, PPh2(OEt) 6;
Independent reflections
Refinement method
12632 [R(int) = 0.0217]
Full-matrix least-squares on F2
12632/0/599
1.032
R1 = 0.0285, wR2 = 0.0814
R1 = 0.0378, wR2 = 0.0860
1.931; −0.484
−
R = C6H5CH2 a, 4-CH3C6H4CH2 b, C6H5 c, 4-CH3C6H4 d; Y = BF4
,
−
CF3SO3
.
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2r(I)]
R indices (all data)
Treatment of both MH(CO)3P2 and MH(CO)2P3 hydrides with
2
+
Brønsted acid gives dihydrogen [M(g -H2)(CO)nP5−n
]
cations
Largest DF maximum;
which slowly lose H2 yielding unsaturated [M(CO)3P2]+ and
[M(CO)2P3]+ cations.25,32 Reactions of tricarbonyl [M(CO)3P2]+
−3
˚
minimum/e A
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intermediates with equimolar amounts of organic azide in the
dark gives, after workup, white or pale yellow solids characterised
as azide [M(RN3)(CO)3P2]BPh4 1–3 derivatives (Scheme 1).
Surprisingly, carrying out the reaction in sunlight gave com-
pletely different results. In the presence of an excess of azide,
diene complexes 4–6 or, in the case of benzyl azides ArCH2N3,
1
+
=
leads to the formation of imine [M{g -NH C(H)Ar}(CO)3P2]
derivatives 7, through the 1,2-shift of one hydrogen atom.
For information on the reaction path and to decide between
the two proposed mechanisms of Scheme 3, we studied the
behaviour of azide [M(RN3)(CO)3P2]+ complexes, in an attempt
to isolate some intermediates like [A] and [B] or, at least, to
detect them in solution from the 15N NMR spectra of the labelled
[M(R15N3)(CO)3P2]+ precursors 1b1 and 2a1. Unfortunately, no
conclusive findings supported the presence of either a pentaco-
ordinate intermediate [A] or the amide [M(RN)(CO)3P2]+ species
[B], although their formation is plausible, and is in fact suggested
for [B] by several precedents:2,3,7–9,14,16 therefore, no hypothesis
may be made regarding the formation of either tetraazabutadiene
complexes 4–6 or imide derivatives 7. However, both paths of
Scheme 3 are reasonable and may also both be operating in the
presence of sunlight to give the final derivatives 4–7.
2
tetraazabutadiene [M(g -1,4-R2N4)(CO)2P2]+ 4–6 complexes were
obtained in good yield.35 Instead, when the azide and the
1
[M(CO)3P2]+ intermediate were reacted in a1:1ratio, imine [M{g -
+
NH C(H)Ar}(CO)3P2] 7 complexes are formed with benzyl36
=
C6H5CH2N3 and 4-CH3C6H4CH2N3 azides (ArCH2N3), which, in
the case of rhenium, were isolated as BPh4 salts and characterised.
In contrast with the results from tricarbonyls, the reaction of
dicarbonyl [M(CO)2P3]+ cations with RN3 (Scheme 2) did not
give stable azide complexes like 1–3, but only tetraazabutadiene
derivatives 4–6, which were separated and characterised. In
addition, high yields of tetraazabutadiene 4–6 were obtained using
an excess of RN3, although the same compounds also formed when
RN3 and dicarbonyl precursors are reacted in a 1 : 1 ratio. Lastly,
it was noted that the formation of tetraazabutadiene species is very
fast in sunlight, but rather slow in the dark.
The different behaviour of the dicarbonyl [M(CO)3P2]+ frag-
ment, compared with tricarbonyl [M(CO)2P3]+ in the reaction with
organic azides (Schemes 1 and 2), which allows the formation of
tetraazabutadiene without exposure to sunlight, may be due to
the easy dissociation of a P-ligand in the dicarbonyl complexes. In
fact, in this case an unstable azide [M(RN3)(CO)2P3]+ intermediate
may also be formed, which dissociates a P-ligand, giving a
pentacoordinate [M(RN3)(CO)2P2]+ intermediate. The further
reaction of this intermediate with free azide RN3 yields the final
tetraazabutadiene derivatives 4–6.
The influence of sunlight on the reactions of azides with metal
fragments is not altogether surprising, in view of the known
photochemical properties of the azide molecule.37
The results of Scheme 1 may be explained by taking into
account that the tricarbonyl [M(CO)3P2]+ fragment is able to
coordinate the azide, giving the related [M(RN3)(CO)3P2]+ 1–3
derivatives. This species is quite stable in the dark, and the coupling
reaction with another RN3 molecule to give the tetraazabutadiene
complexes is very slow, allowing the separation of azide complexes
1–3 in pure form. Instead, in the presence of sunlight, the
[M(RN3)(CO)3P2]+ complexes are unstable and give the imine
Characterisation of complexes
Azide [M(RN3)(CO)3P2]BPh4 complexes 1–3 are white (Mn)
or pale yellow (Re) solids, relatively stable in air and in
solutions of polar organic solvents, where they behave like
1 : 1 electrolytes.38 Analytical and spectroscopic data support the
proposed formulation. IR spectra show three bands in the mCO
region, one weak and two strong, suggesting a mer arrangement39
of the three carbonyl ligands. However, no band attributable to
the mN3 of the azide was observed in the spectra. This may be
due to overlapping with the strong, rather broad bands of the
carbonyls, which prevents observation of the mN3 absorption. The
presence of the organic azide as a ligand in the complex, however,
1
+
=
[M{g -NH C(H)Ar}(CO)3P2] 7 derivative or, in the presence of
excess RN3, tetraazabutadiene complexes 4–6.
It is reasonable to assume that exposure to sunlight of azide
[M(RN3)(CO)3P2]+ cations (Scheme 3) leads to the dissociation of
one carbonyl ligand, to give a pentacoordinate intermediate [A].
Reaction of this intermediate with an excess of azide yields the final
tetraazabutadiene complexes 4–6. However, exposure to sunlight
of azide cations 1–3 may also, after extrusion of N2, lead to the
formation of the imide [M(RN)(CO)3P2]+ intermediate [B]. This
species either undergoes reaction with RN3, giving tetraazabuta-
Scheme 3 M = Mn, Re; i = only with the benzyl ArCH2N3 azides.
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Table 2 15N NMR data for selected manganese and rhenium complexes
1
15N{ H} NMRa,b
Compound
d (J/Hz)
Assignment
1b1
2a1
4a1
5a1
5b1
7a1
[Mn(4-CH3C6H4CH215NN15N)(CO)3{PPh(OEt)2}2]BPh4
−69.5 s, −164.8 s
−26.8 s, −69.6 s
+82.4 m, +27.8 t
+53.6 t br, −26.7 s br
+54.1 s, −24.6 s
[Re(C6H5CH215NN15N)(CO)3{PPh(OEt)2}2]BPh4
2
[Mn{g -1,4-(C6H5CH2)215N4}(CO)2{PPh(OEt)2}2]BPh4
2
[Re{g -1,4-(C6H5CH2)215N4}(CO)2{PPh(OEt)2}2]BPh4
2
[Re{g -1,4-(4-CH3C6H4CH2)215N4}(CO)2{PPh(OEt)2}2]BPh4
1
15
1
[Re{g - NH C(H)C6H5}(CO)3{PPh(OEt)2}2]BPh4
−143.2 dt J
= 68, 2J
= 2.8)
NH
Nc, Na
=
15
NH
15 N31
P
C6H5CH215NNN + C6H5CH2NN15N
−166.5 s, −304.0 br
a In CD2Cl2 at 20 ◦C. b From CH315NO2.
is strongly supported by NMR spectroscopy, mainly by 15N data.
The H NMR spectra of aliphatic azides 1a, 1b, 2a show only
appear as sharp singlets, fitting the magnetic equivalence of the
two phosphane ligands. On the basis of these data and the mer
arrangement indicated by the IR spectra, a mer–trans geometry I
of the type shown in Scheme 1 can reasonably be proposed for our
azide derivatives.
1
one singlet between 4.5 and 5.5 ppm, attributed to the methylene
group ArCH2N3 of the ligand. This signal falls at various values
of chemical shift with respect to both the free azide and the
tetraazabutadiene derivatives, fitting the coordination of the azide
ligand. In the 13C NMR spectra of 1b, the signals of methylene
carbon resonances appear at 72.2 ppm and were correlated in
an HMQC experiment with the CH2 proton singlet at 5.49 ppm,
fitting the proposed assignment. In addition, the 15N NMR spectra
of the labelled [Mn(4-CH3C6H4CH215NN15N)(CO)3P2]BPh4 1b1
and [Re(C6H5CH215NN15N)(CO)3P2]BPh4 2a1 complexes (Table 2)
show two signals attributed to Na and Nc of the coordinate azide
(Fig. S2†). The presence of two signals at chemical shift values
different from those of the free R15NcNb15Na azide (Fig. S1†)
strongly supports the coordination of this intact molecule to the
metal center. Unfortunately, the absence of detectable coupling
between 15N and the methylene protons of the ArCH2 group on
one hand, and between 15N and the phosphorus nuclei of the
phosphanes on the other, prevents the attribution of the two signals
to Na and Nc.
2
The tetraazabutadiene [M(g -1,4-R2N4)(CO)2P2]+ 4–6 com-
plexes are orange (Mn) or red-brown (Re) solids, stable in air
and in solutions of polar organic solvents, where they behave like
1 : 1 electrolytes.38 Their formulation is supported by analytical and
spectroscopic data and by the X-ray crystal structure determina-
2
tion of the [Re{g -1,4-(C6H5CH2)2N4}(CO)2{PPh(OEt)2}2]BPh4
5a derivative. The molecular structure of the cation is shown
−
in Fig. 1, and a BPh4 anion completes the contents of the
asymmetric unit. Table 3 lists the main geometric features of the
complex cation. The six-coordinated metal has axially elongated
octahedral geometry, with the two phosphane ligands at the apices
˚
(Re1–P = 2.41 A) and the two carbonyl and tetraazabutadiene
bidentate ligands on the equatorial plane, with coordination
˚
distances ranging from 1.95 to 2.02 A. The overall geometry of
the complex suggests the presence of a pseudo-C2 axis, bisecting
the C1–Re1–C2 angle and passing through the metal and the
middle point of the N3–N4 bond. The tetraazabutadiene ligand
adopts an E conformation, with benzyl substituents oriented on
the opposite sides with respect to the five-membered chelation
Another question not clarified by spectroscopic data concerns
1
the coordination mode of the azide, which may be an g -terminal
1
2
[C], an g -diazoamino [D] or an g -olefinic [E] mode (Chart 1).
˚
ring, which is planar within 0.01 A. As regards angular defor-
mations of the coordination octahedron, the steric hindrance
of the tetraazabutadiene molecule forces the phosphane groups
Chart 1
The previously reported azide complexes of vanadium8 and
1
tantalum7 were shown to have g -terminal configuration [C] in
the solid state. The IR spectrum of the Cp2Ta(CH3)(N3C6H5)
1
complex7 shows strong absorption for the mN≡N of the g -
coordinated azide at 1730 cm−1. The absence of such a strong band
in the 1800–1700 cm−1 region in our azide complexes suggests an
1
g -diazoamino coordination mode [D], but the absence of any
X-ray crystal structure determination makes this proposal only
tentative.
Fig. 1 Perspective view and labelling scheme of the molecular structure of
2
[Re{g -1,4-(C6H5CH2)2N4}(CO)2{PPh(OEt)2}2]+ in 5a. Thermal ellipsoids
Lastly, it is worth noting that, in the temperature range between
are drawn at the 50% probability level. Phosphane substituents have been
omitted for clarity.
+20 and −80 ◦C, the 31P NMR spectra of all azide complexes 1–3
666 | Dalton Trans., 2007, 661–668
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◦
˚
Tetraazabutadiene complexes are known for several transition
metals, including Ni, Pd, Pt, Rh, Ir, Mo, W, Ru and Zr, and
were prepared following two different methods, involving either
Table 3 Most relevant bond lengths [A] and angles [ ] for 5a
Re(1)–C(1)
Re(1)–C(2)
Re(1)–N(1)
Re(1)–N(2)
Re(1)–P(2)
Re(1)–P(1)
1.954(4)
1.959(4)
2.017(3)
2.023(3)
2.4071(8)
2.4159(8)
N(1)–N(3)
N(1)–C(3)
N(2)–N(4)
N(2)–C(10)
N(3)–N(4)
1.332(4)
1.505(4)
1.330(4)
1.489(4)
1.308(4)
the reaction of a metal complex with an organic azide, or with
40
=
the tetraazenide dianion Li2[PhNN NNPh] as a reagent. The
use of mixed-ligand [M(CO)3P2]+ and [M(CO)2P3]+ cations with
phosphanes and carbonyls as precursors in the reaction with
organic azides allows the preparation of the first tetraazabutadiene
C(1)–Re(1)–C(2)
C(1)–Re(1)–N(1)
C(2)–Re(1)–N(1)
C(1)–Re(1)–N(2)
C(2)–Re(1)–N(2)
N(1)–Re(1)–N(2)
C(1)–Re(1)–P(2)
C(2)–Re(1)–P(2)
N(1)–Re(1)–P(2)
N(2)–Re(1)–P(2)
C(1)–Re(1)–P(1)
C(2)–Re(1)–P(1)
100.0(2)
163.5(1)
94.2(1)
95.1(1)
162.4(1)
72.4(1)
82.8(1)
81.5(1)
91.17(8)
109.55(8)
80.0(1)
83.3(1)
N(1)–Re(1)–P(1)
N(2)–Re(1)–P(1)
P(2)–Re(1)–P(1)
N(3)–N(1)–C(3)
N(3)–N(1)–Re(1)
C(3)–N(1)–Re(1)
N(4)–N(2)–C(10)
N(4)–N(2)–Re(1)
C(10)–N(2)–Re(1)
N(4)–N(3)–N(1)
N(3)–N(4)–N(2)
110.15(8)
90.54(8)
154.60(3)
109.6(3)
120.1(2)
130.3(2)
109.8(3)
119.7(2)
130.5(2)
113.6(3)
114.1(3)
derivatives of manganese and rhenium.
1
=
Imine [M{g -NH C(H)Ar}(CO)3P2]BPh4 complexes were ob-
tained in pure form only for rhenium41 complexes 7 and they
are stable both as solids and in solutions of polar organic
solvents, where they behave as 1 : 1 electrolytes.38 Analytical
and spectroscopic data support the proposed formulation for the
complexes.
The IR spectra of 7 show one band of medium intensity and
two strong bands in the mCO region, indicating the mer arrangement
of the three carbonyl ligands. A medium-intensity band at 3338–
3328 cm−1 is also present, and was attributed to the mNH of the
=
to bend away from it, as shown by the angle P1–Re1–P2 =
154.60 (3)◦, while the narrow N1–Re1–N2 bite angle (72.4(1)◦)
allows the opening of the opposite C1–Re1–C2 = 100.0(2)◦. The
tetraazabutadiene chelation ring is tilted by 16◦ relative to the
plane defined by Re1, C1, C2, due to the repulsion between the
tetraazabutadiene phenyl rings and the phosphane substituents.
imine ligand. However, the presence of the ArC(H) NH group is
confirmed by the H NMR spectra, which show a slightly broad
1
doublet at 8.99 ppm (7a) and 8.95 ppm (7b) (3JHH = 15 Hz),
attributed to the NH proton atom of the imine ligand. In the
COSY spectra, this doublet is correlated with another doublet
=
at 7.97–7.95 ppm, attributed to the CH methine proton of the
1
˚
In the tetraaza system, the central N3–N4 bond (1.308(4) A) is
imine group. Furthermore, the spectrum of the labelled [Re{g -
15
˚
=
shorter than the other two (1.332(4) and 1.330(4) A, respectively),
NH C(H)C6H5}(CO)3P2]BPh4 7a1 compound shows a doublet
1
of 68 Hz, due to 15NH
15
suggesting a certain electron density transfer towards N3–N4
from N1–N3 and N2–N4. A search on the 26 similar systems
containing a tetraazabutadiene ligand coordinated to a transition
metal contained in the Cambridge Structural Database,31 shows
that, on average, the central N–N bond is shorter than the lateral
of doublets at 8.98 ppm, with
J
NH
resonance, revealing the presence of the ArC(H) 15NH ligand.
Lastly, further support for the presence of the imine group comes
from the proton-coupled 15N NMR spectra of the labelled 7a1
(Table 2), which show a doublet of triplets at −143.2 ppm, with
=
1
2
˚
15
15 31
N P
ones by 0.08 A, in analogy with compound 5a.
J
of 68 Hz ( J
= 2.8 Hz) (Fig. S4†), as expected for a
NH
2
coordinated C6H5C(H) 15NH molecule.
=
The
IR
spectra
of
tetraazabutadiene
[M(g -1,4-
1
R2N4)(CO)2P2]BPh4 complexes 4–6 show two strong bands
in the mCO region between 2025 and 1948 cm−1, suggesting a
mutually cis position of the two carbonyl ligands. These CO
ligands are also magnetically equivalent, as indicated by the
presence, in the 13C NMR spectra, of only one triplet between 223
and 199 ppm for the carbonyl carbon resonances.
The 13C{ H} NMR spectra of imine complex 7a, besides the
signals of phosphane and the BPh4 anion, show two triplets at
189.6 and 189.5 ppm, attributed to carbonyl carbon resonances.
The intensity ratio of 2 : 1 of the signals also suggests that two
CO are magnetically equivalent and different from the third. A
singlet at 180.7 ppm also occurs, and was correlated in an HMQC
experiment with the proton signal at 7.97 ppm and attributed to
The 1H NMR spectra show the characteristic signals of P-
1
ligands and the R substituents of azides, whereas the 31P{ H}
the methine CH carbon resonance of the imine group.
=
◦
1
spectra appear as sharp singlets, fitting the magnetic equivalence
of the two P-ligands. On the basis of these data, a geometry of
type II (Schemes 1 and 2) in solution, like that observed in the
solid state, can reasonably be proposed for the tetraazabutadiene
4–6 complexes.
In the temperature range between +20 and −80 C, the 31P{ H}
1
=
NMR spectra of imine [Re{g -NH C(H)Ar}(CO)3P2]BPh4
7
complexes appear as sharp singlets, fitting the magnetic equiva-
lence of the two P-ligands. On the basis of these data, the mer–
trans geometry of III-type (Scheme 1) can reasonably be proposed
for imine derivatives.
We also prepared labelled complexes 4a1, 5a1, 5b1 from the
reaction of [M(CO)3P2]+ intermediates with R15N3 and recorded
the respective NMR spectra. Two signals were observed, at +53.6
and −26.7 ppm for rhenium 5a1 and at +82.4 and +27.8 ppm for
manganese 4a1 derivatives (Table 2). These signals, which appear
as slightly broad multiplets (Fig. S3†), do not allow unambiguous
Imine complexes of rhenium are rare,42,19b and generally ob-
tained from the reaction of free imine with appropriate metal
fragments. The reaction of the benzylazide ArCH2N3 with the
[Re(CO)3P2]+ fragment allows formation and stabilisation by
coordination of an elusive species such as the monosubstituted
=
15 31
15 15
determination of either J
or J
N, owing to the broadness
ArC(H) NH imine.
N
P
N
of the signals and small J values. The coupling between 15N nuclei
and methylene protons in the g -(ArCH2)215N4 ligand is also weak,
2
Conclusions
2
15
with values of J
within the width of the lines. These results,
therefore, prevent assignment of the 15N NMR signals to the
tetraazabutadiene derivatives.
NH
This paper reports an extensive study on the reactivity of
unsaturated [M(CO)3P2]+ and [M(CO)2P3]+ cations with organic
This journal is
The Royal Society of Chemistry 2007
Dalton Trans., 2007, 661–668 | 667
©

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azides, leading to the synthesis of the first examples of an azide
complex as well as of a tetraazabutadiene derivative of manganese
and rhenium. The structural parameters for a tetraazabutadiene
complex of rhenium are also described. Among the properties
shown by azide [M]–N3R complexes are the reaction with organic
azide, to give tetraazabutadiene derivatives and, in the case
of benzyl substituents, the formation of monosubstituted [M]–
Antoniutti and M. T. Giorgi, Eur. J. Inorg. Chem., 2003, 2855–2866;
(d) G. Albertin, S. Antoniutti, A. Bacchi, B. Fregolent and G. Pelizzi,
Eur. J. Inorg. Chem., 2004, 1922–1938.
20 For recent papers see: (a) G. Albertin, S. Antoniutti, M. Bedin, J.
Castro and S. Garcia-Fonta´n, Inorg. Chem., 2006, 45, 3816–3825;
(b) G. Albertin, S. Antoniutti, A. Bacchi, F. De Marchi and G. Pelizzi,
Inorg. Chem., 2005, 44, 8947–8954; (c) G. Albertin, S. Antoniutti, C.
Busato, J. Castro and S. Garcia-Fonta´n, Dalton Trans., 2005, 2641–
2649; (d) G. Albertin, S. Antoniutti, M. Bortoluzzi, J. Castro-Fojo and
S. Garcia-Fonta´n, Inorg. Chem., 2004, 43, 4511–4522; (e) G. Albertin,
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21 R. Rabinowitz and J. Pellon, J. Org. Chem., 1961, 26, 4623–4626.
22 S. G. Alvarez and M. T. Alvarez, Synthesis, 1997, 413–414.
23 R. O. Lindsay and C. F. H. Allen, Org. Synth., 1955, 3, 710–711.
24 G. Balacco, J. Chem. Inf. Comput. Sci., 1994, 34, 1235–1241.
25 (a) G. Albertin, S. Antoniutti, M. Bettiol, E. Bordignon and F. Busatto,
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26 (a) SAINT: SAX, Area Detector Integration, Siemens Analytical
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27 A. Altomare, M. C. Burla, M. Cavalli, G. Cascarano, C. Giacovazzo,
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=
N(H) C(H)Ar imine complexes.
Acknowledgements
The financial support of MIUR (Rome)-PRIN 2004 is gratefully
acknowledged. We thank Daniela Baldan for technical assistance.
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1
=
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668 | Dalton Trans., 2007, 661–668
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The Royal Society of Chemistry 2007
©