Cyclorhenated compounds derived from 1,4-diaryl-1-azabutadienes: preparation, structures and reactions

Article abstract of DOI:10.1016/j.jorganchem.2009.09.033

PhCH₂Re(CO)₅ reacted with 1,4-diaryl-1-azabutadienes to give cyclometallated (η²-(C,N)-azabutadiene)Re(CO)₄ (4) together with the substituted derivatives (η¹-(N)-azabutadiene)(η²-(C,N)-azab

Full text of DOI:10.1016/j.jorganchem.2009.09.033

Journal of Organometallic Chemistry 695 (2010) 96–102
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Cyclorhenated compounds derived from 1,4-diaryl-1-azabutadienes:
preparation, structures and reactions
*
Toshie Asamizu, Jaime L. Nielsen, Brian K. Nicholson
Chemistry Department, School of Science and Engineering, University of Waikato, Private Bag 3105, Hamilton 3240, New Zealand
a r t i c l e i n f o
a b s t r a c t
Article history:
PhCH2Re(CO)5 reacted with 1,4-diaryl-1-azabutadienes to give cyclometallated (
g
2-(C,N)-azabutadi-
2-(C,N)-azabutadi-
ene)Re(CO)4 (4) together with the substituted derivatives (
g
1-(N)-azabutadiene)(
g
Received 31 July 2009
Received in revised form 21 September
2009
Accepted 24 September 2009
Available online 3 October 2009
ene)Re(CO)3 (6 and 7) The substituted product was shown by NMR and X-ray crystal structure
analysis to be an inseparable mixture of isomers differing in the conformation of the
1-ligand about
the N@C bond—trans for (6) and cis for (7). Reaction of the mixture of 6 and 7 from 1,4-diphenyl-1-
azabutadiene with phenyl acetylene gave
5-(1,2,4-triphenyl-1-aza-cyclohexadienyl)Re(CO)3.
Ó 2009 Elsevier B.V. All rights reserved.
g
g
Keywords:
Cyclometallation
Rhenium
Azabutadiene
Cis/trans isomerisation
Crystal structures
Azacyclohexadienyl
1. Introduction
lisation under the cyclometallation conditions. In situ reactions of
the putative 3 as it formed, with alkynes or alkenes, gave products
consistent with initial cyclomanganation [3]. Homrighausen et al.
have reported some complexes of type 3 from an indirect route [4].
Cyclometallation reactions are well-established for many of the
metals in the periodic table, especially where the metallation has
occurred at an aromatic carbon atom [1]. However examples
involving cyclometallation of sp2 carbon atoms from non-aromatic
substrates are much less common. We have previously described
the preparations of cyclomanganated species from enones (chal-
cones), 1, and shown that their reactivity differs from that of cyclo-
manganated acyl-arenes [2]. As an extension of this work we
investigated the manganese chemistry of related azabutadienes,
2 [3].
O
R
N
R'
R
R'
N
M
(CO)4
Mn(CO)3
(5)
(3 M = Mn)
(4 M = Re)
R'
Cyclorhenation reactions are comparatively unexplored [5], but we
reasoned that the increased Re–C bond strength (compared to Mn–
C) might slow CO-insertion so that the cyclorhenated azabutadiene
4 might be able to be isolated. This proved to be the case, though
with some unanticipated complications, as detailed below.
R
R
N
R'
O
(2)
Mn
(CO)4
(1)
2. Experimental
Although we were unable to isolate the expected cyclomanganated
compound 3, it was assumed to be an intermediate for the final
product of the reaction, the
2.1. General
g
4-pyrrolinonyl complex 5. It appears
that first-formed 3 underwent spontaneous CO-insertion and cyc-
Solvents were dried and deoxygenated on a PureSolv PS-SD-5
purification system.
PhCH2Re(CO)5 was prepared from PhCH2Br and Na[Re(CO)5] as
for PhCH2Mn(CO)5 [6]. The azabutadienes 2a–c were prepared
* Corresponding author. Fax: +64 7 838 4219.
E-mail address: b.nicholson@waikato.ac.nz (B.K. Nicholson).
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.09.033

T. Asamizu et al. / Journal of Organometallic Chemistry 695 (2010) 96–102
97
from the appropriate aromatic amines and cinnamaldehydes, using
the method of Knolker [7], and were characterised by NMR and
ESI-MS. ESI-MS were measured on a Fisons Platform II or a Bruker
MicrOTOF spectrometer, using MeOH as solvent. NaOMe was
added to aid ionisation [8]. 1H and 13C NMR spectra were recorded
on Bruker AC300 or AC400 spectrometers using CDCl3 as solvent.
Assignments used standard DEPT, HSQC and HMBC procedures.
Only selected data are given below, with full tables of assignments
deposited as Supplementary material. The numbering system used
for NMR assignments is:
120.7/122.7 (C-5). ESI-MS: (MeOH/NaOMe, +ve ion) m/z 707.137
([M+Na]+, C33H25N2NaO3Re, calcd. 707.132).
2.2.2.2. From the reaction with 1-(p-fluorophenyl)-4-phenyl-1-
azabutadiene 2b. Compound 4b, yellow crystals, 15%, mp 145 °C.
Anal. Calc. for C19H11FN1O4Re: C, 43.68; H, 2.12; N, 2.68. Found:
C, 44.40; H, 2.13; N, 2.70%. mC„O (CH2Cl2) 2092 (w), 1995 (s),
1983(vs), 1936 (m) cmÀ1
.
NMR: 1H (300 MHz, CDCl3): d 7.23 (d 3J 2.32 Hz, H-2), 8.23 (d, 3J
2.32 Hz, H-3); 13C: 191.4 (CO trans to N), 191.0 (CO trans to C),
187.4 (trans COs), 219.5 (C-1), 178.0 (C-3), 136.9 (C-2). ESI-MS:
(MeOH/NaOMe, Àve ion) m/z 553 [M+OMe]À.
H
H
Compounds 6b/7b, red crystals (mixture of plates and needles),
77%. Anal. Calc. C33H23F2N2O3Re: C, 55.07; H, 3.22; N, 3.89. Found:
C, 55.07; H, 3.07; N, 3.91%. mC„O (hexane) 2003 (s), 1899, 1892 (s)
C2 C3
N
C11
C21 C1
cmÀ1 1H NMR (300 MHz, CDCl3) d (6b/7b, ratio ca 2:1) 6.25/7.11
.
Re(CO)3
(m, H-5), 7.00/7.00 (d, H-6), 7.25/7.08 (d, H-2), 8.15/7.86 (d, H-4),
8.35/8.11 (d, H-3); 13C NMR: d (6b/7b) 200.5/199.9 (C-1), 176.4/
176.0 (C-3), 172.7/174.8 (C-4), 148.4/150.1 (C-6), 135.3/135.9 (C-
2), 120.6/122.9 (C-5).
H
N
C31
C5 C4
ESI-MS: (MeOH/NaOMe, +ve ion) m/z 742 ([M+Na]+, (Àve ion)
m/z 750 ([M+OMe]À).
C41 C6
H
H
2.2.2.3. From the reaction with 1-(p-tolyl)-4-(dimethylaminophenyl)-
1-azabutadiene 2c. Compound 4c, orange crystals, 32%, mp 210 °C.
Anal. Calc. C22H19N2O4Re: C, 47.05; H, 3.41; N, 4.99. Found: C,
47.51; H, 3.53; N, 4.92%. mC„O (CH2Cl2) 2089 (w), 1989 (s),
1974(s), 1926 (w) cmÀ1. NMR: 1H (300 MHz, CDCl3): d 7.25 (d 3J
2.52 Hz, H-2), 8.16 (d, 3J 2.52 Hz, H-3); 13C: 192.6 (CO trans to N),
191.4 (CO trans to C), 188.2 (trans COs), 217.0 (C-1), 176.7 (C-3),
133.8 (C-2). ESI-MS: (MeOH/NaOMe, +ve ion) m/z 584 [M+Na]+,
562 [M+H]+; (Àve ion) m/z 592 [M+OMe]À.
2.2. Syntheses
2.2.1. General reaction of PhCH2Re(CO)5 with azabutadienes 2
In nitrogen-flushed Schlenk flask, the azabutadiene
a
2
(0.22 mmol) was added to a solution of PhCH2Re(CO)5 (94 mg,
0.23 mmol) in distilled heptane (20 mL). With continuous stirring,
the clear yellow reaction solution was heated in an oil bath at 95–
100 °C. As soon as the temperature reached 95 °C, the mixture
turned red. Aliquots were removed for monitoring of mCO bands
by infrared spectroscopy and the reaction was continued until
the starting material was consumed (4–7 h). The resulting red
solution with some red precipitate was cooled and the solvent
was evaporated under vacuum. The residue was chromatographed
on silica plates, eluting with CH2Cl2/petroleum spirits (2:3). This
gave strong yellow and orange bands. These were extracted and
crystallised separately from CH2Cl2/petroleum spirits at À20 °C,
providing 4 as yellow, and 6/7 as red, crystals from the yellow
and orange bands, respectively.
Compounds 6c/7c, red crystals (mixture of blocks and needles),
77%. Anal. Calc. for C39H39N4O3Re: C, 58.70; H, 4.93; N, 7.02. Found:
C, 58.88; H, 4.94; N, 7.01%. mC„O (hexane) 2003 (s), 1899, 1892 (s)
cmÀ1. 1H NMR (300 MHz, CDCl3) d (6c/7c, ratio ca1:2) 6.02/6.98 (m,
H-5), 6.82/6.81 (d, H-6), 7.24/7.04 (d, H-2), 8.00/7.74 (d, H-4), 8.30/
8.05 (d, H-3); 13C NMR: d (6c/7c) 201.8/201.1 (C-1), 175.1/174.6 (C-
3), 171.7/174.1 (C-4), 147.7/150.3 (C-6), 132.1/132.7 (C-2), 116.1/
123.7 (C-5).
ESI-MS: (MeOH/NaOMe, +ve ion) m/z 821.243 ([M+Na]+, calcd.
for C39H39N4NaO3Re 821.243).
2.2.3. Reactions of cyclometallated 6a/7a
2.2.3.1. With CO. A sample of the mixed isomers 6a and 7a was dis-
solved in CH2Cl2 and stirred for 24 h under an atmosphere of CO.
An IR spectrum showed only bands arising from the starting com-
plex, with no sign of the formation of any tetracarbonyl 4a.
2.2.2. Characterisation of cyclorhenated compounds
2.2.2.1. From the reaction with 1,4-diphenyl-1-azabutadiene
2a. Compound 4a, yellow crystals, 29%, mp 169–171 °C. Anal. Calc.
for C19H12N1O4Re: C, 45.23; H, 2.40; N, 2.78. Found: C, 45.45; H,
2.2.3.2. With p-methoxyphenyl isonitrile. p-Methoxyphenyl isoni-
trile (0.19 g 1.43 mmol) was added to a solution of 6a/7a (0.19 g,
0.28 mmol) in heptane (15 mL). The mixture was heated in an oil
bath at 100–105 °C for 5 h. After removal of solvent, the residue
was chromatographed on silica plates, eluting with CH2Cl2/petro-
leum spirits (1:1). The main orange band (Rf 0.7) was collected
and recrystallisation from CH2Cl2/petroleum spirits gave red crys-
2.30; N, 2.87%. mC„O (hexane) 2091 (w), 1990 (s), 1948 (m) cmÀ1
.
NMR: 1H (300 MHz, CDCl3): d 7.24 (d 3J 2.26 Hz, H-2), 8.26 (d, 3J
2.26 Hz, H-3); 13C: 191.7 (CO trans to N), 191.1 (CO trans to C),
187.5 (trans COs), 218.5 (C-1), 177.9 (C-3), 137.0 (C-2). ESI-MS:
(MeOH, +ve ion) m/z 505 [M+H]+; (MeOH/NaOMe, Àve ion) m/z
535 [M+OMe]À).
tals of the isonitrile derivative 8 (0.136 g, 80%). mC„O (CH2Cl2) 2009
Compounds 6a/7a, red crystals, 56%, [mixture of 6a (as blocks)
and 7a (as needles) determined by X-ray crystallography, see be-
low]. Anal. Calc. for C33H25N2O3Re: C, 57.97; H, 3.69; N, 4.10.
Found: C, 57.23; H, 3.81; N, 3.97%. mC„O (hexane) 2008 (s), 1913,
(s), 1939 (m), 1904 (m) cmÀ1. NMR (CDCl3): 1H d 7.20 (d 3J 2.3 Hz)
H-2; 8.27 (d 3J 2.3 Hz) H-3. 13C d 135.6 (C-2); 176.3 (C-3); 225.2 (C-
1). ESI-MS: (MeOH, +ve ion) m/z 632 [M+Na]+; 610 [M+H]+;
(MeOH/NaOMe, Àve ion) m/z 640 [M+OMe]À.
1897 (s) cmÀ1 1H NMR (300 MHz, CDCl3) d (6a/7a, ratio ca
.
1.0:0.3) 6.25/6.87 (m, H-5), 6.98/6.98 (d 3J 15.6 Hz, H-6), 7.28/
7.10 (d, 3J 2.3 Hz, H-2), 8.17/7.88 (d, 3J 9.9 Hz, H-4), 8.40/8.15 (d,
3J 2.3 Hz, H-3); 13C NMR: d (6a/7a) 200.7/200.1 (C-1), 176.3/176.0
(C-3), 171.8/174.6 (C-4), 147.6/150.4 (C-6), 135.3/135.9 (C-2),
2.2.3.3. With phenyl acetylene. PhCCH (0.11 mL, 1.00 mmol) was
added to a solution of 6a/7a (0.21 g, 0.31 mmol) in heptane
(15 mL). The mixture was heated in an oil bath at 95–100 °C for
2.5 h. Solvent was removed and the residue chromatographed with

98
T. Asamizu et al. / Journal of Organometallic Chemistry 695 (2010) 96–102
CH2Cl2/petroleum spirits (7:5). The main yellow band (Rf 0.9) was
spectrometry data, and also from the mCO bands which conformed
to the usual pattern found for cis-L2M(CO)4 species. An X-ray crys-
tal structure determination confirmed this assignment. As shown
in Fig. 1 the azabutadiene has formed a five-membered cyclomet-
allated group, coordinated through the N atom and the deproto-
nated C(1) atom.
The ring is essentially planar, with the peripheral phenyl rings
twisted out of the ring plane to avoid contact with the adjacent
CO ligands. The Re–C and Re–N distances are essentially equal
[2.188(2) and 2.185(2) Å], and are close to the values found in cyc-
lorhenated species involving aryl metallation [5]. Coordination has
increased the C(1)–C(2) and C(3)–N(1) distances, and decreased
the C(2)–C(3) distance compared to the equivalent differences in
uncomplexed azabutadienes, consistent with increased delocalisa-
tion around the metallocyclic ring. The Re–CO distances increase in
the order Re–CO (trans to N(1)) > Re–CO (trans to C(1)) > Re–CO
(trans to CO), reflecting the trans influence of the opposing species.
The second product of the reaction was intensely red. The crys-
tallised material gave mass spectra and analytical data that indi-
cated that two moles of the azabutadiene had been incorporated
removed and recrystallised from CH2Cl2/petroleum spirits to give
yellow plates of the
g
5-azacyclohexadienyl complex 9 (32 mg,
18%). mC„O (CH2Cl2) 2026 (s), 1949 (m), 1935 (m) cmÀ1. NMR
(CDCl3): 1H d 5.26 (d, 3J 4.1 Hz) H-4; 5.83 (d 3J 4.0 Hz) H-5; 6.63
(s) H-7. 13C d 57.2 (C-4); 93.9 (C-5); 101.0 (C-6); 90.7 (C-7);
79.8 (C-8). ESI-MS: (MeOH, +ve ion) m/z 601 [M+Na]+; 308
[MÀRe(CO)3]+; (MeOH/NaOMe, Àve ion) m/z 610 [M+OMe]À, 578
[MÀH]À. The compound was fully characterised by an X-ray crystal
structure determination.
2.3. X-ray crystallography
X-ray intensity data for compounds 4a, 6a, 7a, 6b and 9 were
obtained from a Bruker APEX II CCD diffractometer, and were pro-
cessed using standard software. Crystal data and refinement de-
tails are summarised in Table 1. Corrections for absorption were
carried out using SADABS [9]. The structures were solved and refined
using the SHELX programs [10], operating under WINGX [11]. All H
atoms were included in calculated positions. Disorder of the C1/
N1 atoms was possible for structures 4, 6a and 7a with the 1,4-
diphenylazabutadiene ligand, but in each case refinement with
assignment of atom type reversed gave significantly higher R val-
ues and disparate Ueq values [e.g. for 6a the Ueq values were N(1)
0.019 and C(1) 0.016 as assigned, N(1) 0.009 and C(1) 0.027 when
reversed]. The ordered assignment was also supported from an
analysis of the Re–CO distances, which consistently gave shorter
values for those trans to N (average 1.927 Å) than those trans to
C (average 1.952 Å) consistent with the different trans-influences.
into the product, and the mCO bands were indicative of a fac-Re(CO)3
group. A block-shaped crystal was selected and the structure was
determined by X-ray crystallography as 6a, as shown in Fig. 2a.
The molecule is a derivative of the cyclometallated compound 4,
where one of the axial CO ligands has been replaced by a second
azabutadiene group acting as a simple two-electron donor via
the imine-N atom. This has had only a minor effect on the rest of
the molecule with bond parameters of the metallocyclic ring
essentially unchanged. The Re–N(2) distance of 2.238(2) Å is longer
than Re–N(1), (2.186(2) Å), indicating a stronger coordination of
the imine nitrogen when it is part of the metallocyclic ring.
The NMR data of the apparently pure red product were unex-
pectedly complicated and it was noted that the crystals were of
two distinct forms – blocks and needles. Since the IR, elemental
analysis and mass spectrometric data indicated a single compound
it was initially assumed that these were polymorphs, however an
X-ray determination on the needle crystals showed that it was
actually a different isomer 7a. This is illustrated in Fig. 2b, and dif-
3. Results and discussion
3.1. Reactions of PhCH2Re(CO)5 with 1,4-azabutadienes
The overall reactions are summarised in Scheme 1.
When a mixture of 1,4-diphenyl-1-azabutadiene and PhCH2Re-
(CO)5 was heated under reflux in heptane, the resulting red mix-
ture provided two major products after chromatography. The first
of these was yellow and was characterised as the cyclorhenated
complex 4a, the rhenium analogue of the implicated manganese
metallocycle 3a that could not be isolated in the previous investi-
gation [3]. This was apparent from the microanalytical and mass
fers in the geometry of the
g
1-azabutadiene ligand about the C@N
bond, which is trans for 6a but cis for 7a. This difference has had
little effect on the parameters for the rest of the molecule. The
Re–N(2) bond for the cis isomer, 2.188(2) Å, is shorter than the
Table 1
Crystal data and refinement details for 4a, 6a, 7a, 6b and 9.
4a
6a
7a
6b
9
Formula
Mr
C19H12NO4Re
504.50
C33H25N2O3Re
683.75
C33H25N2O3Re
683.75
C33H23F2N2O3Re
719.73
C26H18NO3Re
578.61
T (K)
93(2)
84(2)
93(2)
97(2)
83(2)
Crystal system
Space group
a (Å)
b(Å)
c(Å)
Monoclinic
P21/c
Monoclinic
P21/c
Monoclinic
P21/c
Orthorhombic
Pbca
13.8048(3)
14.8172(3)
27.0507(6)
Monoclinic
C2/c
12.4902(3)
17.5205(4)
8.1233(2)
106.365(1)
1705.64(7)
4
12.0281(2)
14.4460(2)
15.7868(2)
97.690(1)
2718.41(7)
4
9.3259(3)
10.0899(3)
29.4933(9)
95.066(1)
2764.40(15)
4
22.3672(8)
10.9716(4)
17.0784(6)
93.127(1)
4184.9(3)
8
b (°)
V (Å3)
Z
5533.2(2)
8
1.728
4.44
Dc (g cmÀ3
)
1.965
7.15
1.671
4.51
1.643
4.43
1.837
5.84
l
(mmÀ1
)
Size (mm3)
F (0 0 0)
0.30 Â 0.25 Â 0.15
028 Â 0.28 Â 0.12
0.26 Â 0.22 Â 0.02
0.43 Â 0.37 Â 0.34
0.40 Â 0.18 Â 0.15
960
1344
1040
2816
2240
hmax (°)
35
26
34
28
32
Reflections collected
39 116
15 836
45 919
60 010
13 176
Tmax,
Unique reflections
Parameters
0.413, 0.223
6436 (Rint 0.027)
226
0.413, 0.292
5543 (Rint 0.024)
368
0.917, 0.392
9871 (Rint 0.032)
352
0.313, 0.251
6693 (Rint 0.0317)
370
0.475, 0.204
6166 (Rint 0.0274)
280
min
R1 [I > 2
r
(I)]
0.0163
0.0215
0.0312
0.0207
0.0273
wR2 (all data)
0.0379
1.073
0.0530
1.087
0.0607
1.261
0.0549
1.080
0.0515
1.015
GOF on F2

T. Asamizu et al. / Journal of Organometallic Chemistry 695 (2010) 96–102
99
PhCH2M(CO)5
R
N
R'
R
N
R'
M
(CO)4
2a R = R' = Ph
2b R = Ph R' = C6H4F-p
2c R = C6H4NMe2-p R' = C6H4Me-p
(3 M = Mn)
(4 M = Re)
M = Re
R
M = Mn
O
R'
N
R
R
R
R'
N
R'
N
Re
(CO)3
Mn(CO)3
(6)
R'
(5)
N
R
N
R'
Re
(CO)3
(7)
Scheme 1.
Fig. 1. The structure of the cyclometallated azabutadiene complex 4. Selected bond lengths (Å): Re–C(1) 2.1877(16); Re–N(1) 2.1825(15); C(1)–C(2) 1.343(2); C(2)–C(3)
1.427(3); N(1)–C(3) 1.319(2).
Re–N(2) bond to the trans-
gesting a stronger donor bond in this case.
g
1-azabutadiene in 6a, 2.238(2) Å, sug-
of isomers there was one set of corresponding doublets at 7.28
and 8.40, and another at 7.10 and 8.15, with relative intensities
ca 3:1. The sample used was made up of more block-shaped crys-
tals than needles, so the more intense pair of doublets was as-
signed to the trans isomer 6a and the latter pair to the cis one,
7a. The two forms cannot be distinguished from their IR spectra,
the mCO bands are not significantly different in spectra obtained
from the distinct single crystal forms using a microscope attach-
ment for the spectrometer.
The same reactions were carried out using the substituted
aryl azabutadienes 2b or 2c. For reactions with a PhCH2Re(CO)5:
azabutadiene ratio of 1:1, mixtures of the yellow cyclometallat-
ed-Re(CO)4 complexes 4b or 4c with the red substituted Re(CO)3
species 6b/7b or 6c/7c were obtained. The time needed for com-
There appear to be no previous reports of a cis-azabutadiene
acting as an g1 ligand from amongst many studies describing
g
1-trans-azabutadiene complexes [12]. The normal synthesis of
azabutadienes gives >96% of the trans form [13], so the formation
of significant amounts of 7a in the reaction implicates a metal-
induced isomerisation about the C@N bond. An NMR study of
azabutadienes showed that lanthanide ions could induce trans–
cis isomerisation, but no complexes were isolated [13]. The forma-
tion of a cis isomer for 7a is presumably driven by steric factors; in
6a the trans-geometry about the C@N bond directs the rest of the
ligand so that it lies close to the substituents on the metallocyclic
ring (Fig. 2a) whereas the cis geometry in 7a allows the ligand to
fold away from the rest of the complex (Fig. 2b).
plete disappearance of the mCO bands of PhCH2Re(CO)5 was approx-
Although the two isomers cannot be separated by chromatogra-
phy, the relative amounts could be assessed from their NMR spec-
tra. For the unsubstituted complex 4 the 1H NMR spectrum shows
two doublets at d 7.24 and 8.26 (3JHH = 2.26 Hz) which can be as-
signed to H-2 and H-3, respectively. In the spectra of the mixture
imately seven hours for 2b but only three hours for 2c. This is
possibly because of the effects of the electron-withdrawing F ver-
sus the electron-releasing Me on the basicity of the N atom, but
more examples would be needed to be sure this was the main
contributor.

100
T. Asamizu et al. / Journal of Organometallic Chemistry 695 (2010) 96–102
Fig. 2. The two isomers of the substituted complex, with trans (6a) and cis (6b)
g
1-azabutadiene ligands. Selected bond lengths (Å) for 6a [6b] are: Re–C(1) 2.187(3)
[2.178(2)]; Re–N(1) 2.186(2) [2.183(2)]; Re–N(2) 2.238(2) [2.188(2)]; C(1)–C(2) 1.352(4) [1.346(4)]; C(2)–C(3) 1.423(4) [1.423(4)]; C(4)–C(5) 1.437(4) 1.443(3)]; C(5)–C(6)
1.342(4) [1.341(3)]; N(1)–C(3) 1.313(4) [1.315(4)]; N(2)–C(4) 1.295(4) [1.294(3)].
Recrystallisation of the red compounds again gave two distinct
forms of crystals for the substituted compounds, and a complex 1H
NMR spectrum, showing that two isomers were also being formed
with these azabutadienes. An X-ray crystal structure analysis of a
block-shaped crystal from the reaction with the p-fluorophenyl
azabutadiene showed it was the trans isomer 6b, so the needles
that co-formed were assumed to be the cis form, as with the
unsubstituted species. The structure of 6b is illustrated in Fig. 3
and confirms that it is a direct analogue of 6a. The presence of
the fluoro group has no significant effect on the structural param-
eters, with even the relative conformations of the aryl rings being
such that the two structures are essentially superimposable de-
spite being in different space groups with different crystal packing
interactions.
7a. For the trans isomers the H-3 and H-2 signals of the cyclomet-
allated azabutadiene were doublets at 8.30–8.40 and 7.24–
3
7.28, respectively, with JHH coupling of 2.2–2.4 Hz, while for
the cis isomers these signals were ꢀ0.2 ppm upfield at 8.05–
8.15 and 7.04–7.10 ppm, respectively. For the
g
1-azabutadiene,
the H-4 signal was 8.00–8.17 for the trans isomers and 7.74–
3
7.86 for the cis ones with JHH ꢀ10 Hz. The largest difference
was for H-5 which was 6.02–6.24 for the trans isomers and
6.87–7.11 for the cis. 13C shifts were less useful for distinguishing
the two forms, with the largest difference being for C-5 which ap-
peared at 116–120 ppm for the trans and ꢀ123 ppm for the cis
forms.
Interestingly, the NMR data indicated that the trans isomers
6a or 6b were favoured over 7a or 7b, but that the cis form 7c
dominated over trans 6c with the methyl-substituted azabutadi-
ene, possibly indicating a more facile isomerisation of azabutadi-
ene 2c.
For 6b/7b and 6c/7c the 1H NMR spectra could be used to
distinguish the two isomers, by comparison with the chemical
shifts for the H-2, H-3, H-4 and H-5 protons established for 6a/

T. Asamizu et al. / Journal of Organometallic Chemistry 695 (2010) 96–102
101
Fig. 3. The structure of 6b. Bond lengths (Å) include: Re–C(1) 2.183(2); Re–N(1) 2.186(2); Re–N(2) 2.238(2).
3.2. Some reactions of the cyclorhenated complexes
1-azabutadiene ligand
from 6a/7a. When a solution was stirred under one atmosphere
of CO for 24 h there was no change observed. However with p-
methoxyphenyl isonitrile, displacement of the ligand was observed
in heptane at ca 100 °C, giving the substituted cyclorhenated spe-
cies 8 in reasonable yield.
The reaction of 6a/7a with phenyl acetylene was investigated. This
led to the isolation of an
5-azacyclohexadienyl-rhenium complex
g
Attempts were made to displace the
g
9, which was structurally characterised since no azacyclohexadie-
nyl examples have been described before for rhenium. The struc-
ture is illustrated in Fig. 4. The crystals are isomorphous with the
manganese example reported earlier [3]. The C(4)–C(8) atoms are
essentially planar, forming a dihedral angle with the C(4)–N(1)–
C(8) plane of 48.7° (50° for the Mn analogue). The Re–C distances
range from 2.271 to 2.344 Å with an average of 2.304 Å, 0.16 Å
longer than the average for the manganese compound (2.146 Å).
The difference between the average M–CO bonds is 0.13 Å for the
Re and Mn analogues, so bonding appears very similar in the two
species with the differences arising simply from the increased
atomic radius. When compared with a (cyclohexadienyl)Re(CO)3
complex [14], the average Re–Cring bonds are 0.033 Å shorter, and
the Re–CO bonds are 0.062 Å longer, for the azacyclohexadienyl
Ph
Ph
N
Ph
N
Ph
Ph
Re
(CO)3
p-MeOC6H4NC
Re(CO)3
(8)
(9)
Fig. 4. The structure of 9. Selected bond lengths (Å): Re–C(4) 2.298(3); Re–C(5) 2.271(3); Re–C(6) 2.329(3); Re–C(7) 2.276(3); Re–C(8) 2.344(3); N(1)–C(4) 1.450(4); N(1)–
C(8) 1.462(3); N(1)–C(11) 1.417(4).

102
T. Asamizu et al. / Journal of Organometallic Chemistry 695 (2010) 96–102
complex 9, suggesting the heterocyclic ring is a better p-acceptor
Appendix A. Supplementary material
ligand.
The manganese analogue of 9 was prepared from an in situ
reaction of PhCH2Mn(CO)5, diphenylazabutadiene and PhCCH and
was assumed to involve the intermediacy of the cyclometallated
compound 1, which was not directly observed [3]. The isolation
of the rhenium complex 9 from a cyclometallated precursor
under comparable conditions supports this previously suggested
pathway.
CCDC 742573, 742574, 742575, 742576 and 742577 contain the
supplementary crystallographic data for this paper. These data can
be obtained free of charge from The Cambridge Crystallographic
Data Centre via http://www.ccdc.cam.ac.uk/data_request/cif. Sup-
plementary data associated with this article can be found, in the
online version, at doi:10.1016/j.jorganchem.2009.09.033.
References
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We thank Dr. Tania Groutso, University of Auckland for collec-
tion of X-ray intensity data. Professor Lyndsay Main is thanked
for assistance with NMR assignments, and Dr Michael Mucalo for
IR measurements on single crystals.