Studies of rheniumtricarbonyl complexes of tripodal pyridyl-based ligands

Article abstract of DOI:10.1016/j.ica.2009.11.039

The reaction of N-benzoyl and N-acetyl tris(pyridin-2-yl)methylamine 1b and 1c (LH = tpmbaH and tpmaaH) with [Re(CO)₅Br] has been investigated and shown to proceed via the initial formation of a cationic rheniumtricarbonyl complex [(LH)Re(CO)

Full text of DOI:10.1016/j.ica.2009.11.039

Inorganica Chimica Acta 363 (2010) 1186–1194
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Studies of rheniumtricarbonyl complexes of tripodal pyridyl-based ligands
*
D. Vaughan Griffiths , Mohamad J. Al-Jeboori, Phillip J. Arnold, Yuen-Ki Cheong,
Philip Duncanson, Majid Motevalli
School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London E1 4NS, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 2 June 2009
Received in revised form 19 November 2009
Accepted 29 November 2009
Available online 4 December 2009
The reaction of N-benzoyl and N-acetyl tris(pyridin-2-yl)methylamine 1b and 1c (LH = tpmbaH and
tpmaaH) with [Re(CO)5Br] has been investigated and shown to proceed via the initial formation of a cat-
ionic rheniumtricarbonyl complex [(LH)Re(CO)3]Br in which coordination of the ligand occurs via the
three pyridine rings. For tpmbaH 1b, but not tpmaaH 1c, this initial complex 2b readily undergoes the
loss of HBr to give a neutral octahedral complex 4b [(L)Re(CO)3] where coordination occurs via two of
the pyridine rings and the deprotonated amide nitrogen. The 1H NMR spectrum of the latter complex
4b is very unusual in that at room temperature the signals for the 3-H protons on the coordinated pyr-
idine rings are not visible due to extreme broadening of these resonances. Comparison with the analo-
gous complex 7 from N-benzoyl bis(pyridin-2-yl)methylamine 6b (bpmbaH) confirms that this is due
to rotation of the uncoordinated pyridine ring. The structure of the cationic complex 3d [(LH)Re(CO)3]Br
formed from N-benzyl tris(pyridin-2-yl)methylamine 1d (bz-tpmaH) is also discussed. The crystal struc-
tures of complexes [(tpmba)Re(CO)3] 4b, [(bz-tpmaH)Re(CO)3]Br 3d and [(bpmba)Re(CO)3] 7 have been
determined. In all complexes the coordination geometry around Re is distorted octahedral with a fac-
{Re(CO)3}+ core.
Dedicated to Prof. Jonathan R. Dilworth.
Keywords:
Rheniumtricarbonyl
Tripodal ligands
Temperature dependent NMR
Bis(pyridyl)methylamine
Tris(pyridyl)methylamine
X-ray crystal structures
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
1a X = NH2
N
We have previously reported the synthesis and use of the
tris(pyridin-2-yl)methylamine ligand system, tpmaH 1a, in the
context of trying to develop a model for the so-called ‘Type 2’
centre in copper-based nitrite reductases [1,2]. The concept here
was to use the primary amine group in the ligand 1a as a means
of immobilising it onto an appropriate support or for connecting
it to a second metal centre while still permitting coordination of
the copper(II) via the three pyridine ring nitrogens. Fortunately,
although the parent ligand 1a was able to exhibit a range of
coordination behaviours arising from the presence of four poten-
tial donor sites in this ligand system, it had proved possible to
restrict coordination to only the pyridyl rings by acylation of
the primary amino group. Thus, for example, while the parent li-
gand 1a was able to form complexes (i) via the three pyridine
nitrogens, as in [Cu(SO4)(tmpaH)(H2O)]ꢀ3H2O, (ii) via two of the
pyridine nitrogens and the amino group, as in [Cu(tmpaH)2][BF4],
or (iii) as a bidentate ligand, as in [Cu(tmpaH)3][BF4], the copper
1b X = NHCOPh
1c X = NHCOMe
1d X = NHCH2Ph
1e X = OH
N
X
N
More recently we have investigated whether the potentially
bifunctional ligand system 1a might have possible applications
in radiopharmaceutical imaging and therapy agents. The develop-
ment of convenient methods for forming rhenium(I)tricarbonyl
complexes [3] in aqueous media using nitrogen-containing li-
gands has renewed interest in such ligands for use in nuclear
medicine. We were interested to see if tripodal ligand systems
based on 1a could form rheniumtricarbonyl complexes with the
ligand coordinated in the required facial manner as in 2a thus
permitting derivatisation of the amine group to gain the required
biodistribution. However, in our initial studies [4] we concluded
that this might be problematic. The reaction of rheniumpentacar-
bonyl bromide [Re(CO)5Br] with the ligand system 1a had led to
the isolation of the cationic complex [(tpmaH)Re(CO)3]Br 3a, in
which coordination to the ligand system 1a had occurred
through two of its pyridyl nitrogen atoms and the primary amino
group. Furthermore, attempts to encourage coordination of the
rhenium through the three pyridyl nitrogens by using the N-ben-
zoylated system 1b (tpmbaH) had been unsuccessful, leading to
the isolation of a neutral complex [(tpmba)Re(CO)3] 4b in which
complexes of the corresponding N-acylated ligands
1
(X = NHCOR) showed only coordination through the three pyri-
dine nitrogen atoms [1,2].
* Corresponding author. Tel.: +44 (0)20 7882 5389; fax: +44 (0)20 7882 7427.
E-mail address: d.v.griffiths@qmul.ac.uk (D.V. Griffiths).
0020-1693/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2009.11.039

D.V. Griffiths et al. / Inorganica Chimica Acta 363 (2010) 1186–1194
1187
coordination occurs through only two of the pyridyl nitrogens
and a deprotonated amide nitrogen.
chloride to give 1b and 6b, respectively, while acetylation of the
trispyridyl parent system 1a was achieved with acetic anhydride
to give 1c. N-Benzylation of the trispyridyl ligand 1a to give 1d
was achieved by the in situ reduction of the initially formed ben-
zylimide using benzaldehyde and sodium borohydride.
3'
N
N
H
X
H
H
N
N
3
3
X
Y
6a R = H
6b R = COPh
N
N
N
N
N
N
N
NHR
Re(CO)3 Br
Re(CO)3 Br
Re(CO)3
2a X = NH2
3a X = NH2
4b Y = NCOPh
4c Y = NCOMe
4e Y = O
2.2. Complex formation
2b X = NHCOPh
2c X = NHCOMe
2e X = OH
3d X = NHCH2Ph
2.2.1. Formation of ionic complex [(tpmbaH)Re(CO)3]Br (2b)
We have now established that by using appropriate reactant
concentrations, and with toluene as the solvent, it is possible to
get [Re(CO)5Br] to react with tpmbaH 1b, to form a limited quan-
tity of the cationic complex [(tpmbaH)Re(CO)3]Br 2b, in which
coordination occurs via the three pyridine nitrogen atoms. To
achieve this, the temperature of the reaction mixture was slowly
increased until the [Re(CO)5Br] was seen to dissolve and then at
ca. 100 °C a small quantity of a dark coloured material was seen
to precipitate from the solution. This crude solid was then ex-
tracted into DCM and isolated as a yellow powder which mass
spectrometry showed had a molecular ion consistent with the for-
mation of the cationic complex [(tpmbaH)Re(CO)3]Br 2b. More-
over, the 13C NMR spectrum of this complex confirmed the
symmetrical nature of the structure with respect to the coordina-
tion of the pyridine rings since only one set of resonances for these
three rings was observed. It is interesting to note that this NMR
spectrum also showed that one of the carbonyl ligand resonances
was to slightly higher field of the other two. Since the NMR signals
for the chelate portion of the molecule indicates a symmetrical
magnetic environment with respect to the three pyridine rings this
suggest the differential effect on the carbonyl ligands does not
arise from the chelate system. In the absence of other obvious
explanations we cannot exclude the effect being due to the influ-
ence of the counterion.
In contrast, a recent paper [5] reported that the coordination of
the related tris(pyridin-2-yl)methanol ligand system 1e (tmpOH)
with [Re(CO)5Br] led to the formation of three complexes: (i) a
cationic complex [(tmpOH)Re(CO)3]Br 2e in which the tripodal li-
gand was coordinated in a facial manner through the three pyr-
idine nitrogen atoms; (ii) a neutral complex [(tmpO)Re(CO)3] 4e
in which coordination occurs via two pyridine nitrogen atoms
and the deprotonated hydroxyl group, and (iii) a binuclear com-
plex [Re(CO)3(tmpO)Re(CO)3Br] 5. It was suggested that the last
complex 5 had been formed from the reaction of the neutral
complex 4e with further Re(CO)5Br, with the oxygen atom of
the deprotonated ligand system bridging the two rhenium
centres.
Although the relative quantities of the three complexes were
not indicated, the fact that the first two complexes 2e and 4e were
found to co-crystallise, giving crystals suitable for X-ray diffraction
studies, suggests they were both formed in significant quantities.
Whether formation of the neutral complex [(tmpO)Re(CO)3] 4e fol-
lows the initial formation of the cationic complex [(tmpOH)Re-
(CO)3]Br 2e was not investigated. However, it was noted that these
two complexes could be separated by column chromatography and
the pure complexes characterised. This implies that the cationic
complex 2e was stable under these conditions.
The report of the formation of a stable cationic rheniumtricar-
bonyl complex of a tris(pyridin-2-yl)methane ligand system coor-
dinated through the three pyridine nitrogen atoms, led us to
reinvestigate whether under appropriate conditions a similar cat-
ionic complex 2b might be formed using the tpmbaH ligand sys-
tem 1b. We also wanted to establish whether such a cationic
complex might be the precursor of the neutral complex [(tpmba)R-
e(CO)3] 4b we had previously isolated. This initial objective led us
to study more widely the impact that the N-substituent on the
amino group in the tris(pyridin-2-yl)methylamine ligand has on
the structure and stability of the complexes formed. Work was also
undertaken to try to rationalise some interesting temperature
dependent features observed in the solution state NMR spectra of
some of the complexes.
2.2.2. Formation of neutral complex [(tpmba)Re(CO)3] (4b)
Of more significance is the observation that efforts to recrystal-
lise the ionic complex 2b, to prepare a sample of this material suit-
able for X-ray diffraction, led to loss of hydrogen bromide and the
formation of crystals of the neutral complex [(tpmba)Re(CO)3] 4b.
The X-ray crystal structure of this neutral product is shown in
Fig. 1 and related data are shown in Tables 1 and 2 (see also Appen-
dix A). This clearly suggests that tpmbaH 1b, initially coordinates
to the rhenium via its three pyridine rings to give the cationic com-
plex 2b but that this product is not particularly stable in solution
and readily rearranges to give a complex that undergoes elimina-
tion of hydrogen bromide to give the neutral complex 4b. If more
dilute reaction conditions or higher reaction temperatures are
used, as in our original study, the initially formed complex 2b does
not precipitate until after it has undergone rearrangement and loss
of hydrogen bromide to give 4b.
2. Results and discussion
2.1. Ligand synthesis
2.2.3. NMR studies of complex [(tpmba)Re(CO)3] (4b)
The ligand systems used in our study were prepared from
bis(pyridin-2-yl)methylamine 6a (bpmaH) which can be prepared
either from 2-aminomethylpyridine, as we have previously re-
ported [6,7], or by reducing the oxime formed from the reaction
of hydroxylamine with bis(pyridin-2-yl)ketone [8]. Conversion of
the bispyridyl ligand 6a to the trispyridyl parent system 1a was
achieved by quenching the carbanion formed from 6a and n-butyl
lithium with 2-chloropyridine. N-Benzoylation of the ligand sys-
tems 1a and 6a was achieved using benzoic anhydride and benzoyl
As expected the NMR spectra of complex 4b showed the chem-
ical shifts of the non-coordinated pyridine ring to be significantly
different from those of the two coordinated rings which, as ex-
pected, were magnetically equivalent. However, more careful anal-
ysis of the 1H NMR spectrum failed to locate any signals that could
be attributed to the 3-H protons on the two coordinated pyridine
rings (Fig. 2a). Integration of the signals in the aromatic region of
the spectrum also failed to provide any evidence for the presence
of these resonances.

1188
D.V. Griffiths et al. / Inorganica Chimica Acta 363 (2010) 1186–1194
3'
N
H
O4
C15
C9
N4
H
H
C21
O2
C11
C7
N3
3
C20
3
C10
C8
PhCO.N
N
N
N2
C2
C1
Re(CO)3
O1
Re1
N1
C3
O3
Fig. 1. X-ray structure of 4b.
Table 1
Crystal refinement data.
Complex
[(tpmba)Re(CO)3] 4b
[(bz-tpmaH)Re(CO)3]ꢁBr+ 3d
[(bpmba)Re(CO)3] 7
Formula
Mr (Da)
T (K)
Crystal system
Space group
a (Å)
C26H17N4O4Re
635.64
160(2)
monoclinic
P21/n
21.567(4)
12.180(6)
8.691(7)
C26H20BrN4O3ReꢀCHCl3
821.94
120(2)
orthorhombic
Pbca
C21H14N3O4Reꢀ1/4C2H5N
569.32
120(2)
triclinic
ꢀ
P1
15.3818(3)
19.1013(5)
19.2623(6)
90
10.7023(1)
12.8618(2)
15.0542(1)
109.990(1)
b (Å)
c (Å)
a
(°)
90
b (°)
95.01(4)
90
95.392(1)
c
(°)
90
2274(2)
1.856 (4)
5.385
0.40 ꢂ 0.20 ꢂ 0.10
ꢁ25/25, ꢁ4/14, 0/10
4350
3990 (0.0117)
3523
0.6150 and 0.2219
3990/0/304
1.076
90
5659.5(3)
1.929 (8)
6.026
0.14 ꢂ 0.08 ꢂ 0.03
ꢁ14/19, ꢁ22/24, ꢁ21/25
33 824
6468 (0.0634)
4888
0.8399 and 0.4858
6468/0/360
1.155
91.556(1)
1934.86(4)
1.954 (4)
6.316
0.48 ꢂ 0.30 ꢂ 0.18
ꢁ13/13, ꢁ16/16, ꢁ19/19
40 952
8865 (0.0373)
8280
0.3960 and 0.1515
8865/0/541
1.113
V (Å3)
DCalc (g cmꢁ3) (Z)
lMo (mmꢁ1
)
Crystal size (mm3)
Index ranges for h, k, l
Number of reflections collected
Number of reflections unique (Rint
Number of reflections observed
Tmax/min
)
Data/restraints/parameters
Goodness-of-fit (GOF)
R1, wR2 [I > 2
r
(I)]
0.0195, 0.0480
0.0280, 0.0514
0.696 and ꢁ0.998
0.0494, 0.0899
0.0769, 0.102
0.966 and ꢁ0.944
0.0237, 0.0553
0.0264, 0.0563
0.750 and ꢁ1.935
(all data)
Largest differences in peak and hole (e Åꢁ3
)
A clue to help explain this behaviour came from the 13C NMR
spectrum of the complex 4b acquired at 300 K at 100.6 MHz. Under
these conditions substantial broadening of some of the carbon res-
onance associated with the coordinated pyridine rings was ob-
served suggesting the presence of an NMR exchange process.
Thus, the resonance for the C-3 carbons in the coordinated pyridine
rings could be observed as a broad resonance spreading from dc
123.5 to 125.5 ppm while that for the same resonance in the unco-
ordinated pyridine ring remained sharp. The presence of an NMR
exchange process was confirmed by acquiring both the 1H and
13C NMR spectra of complex 4b in d6-DMSO at higher tempera-
tures. At 341 K this caused the broad resonances in the 13C NMR
spectrum to sharpen and at 371 K a broad signal became visible
in the 270 MHz 1H NMR spectrum at ca. dH 8.4 corresponding to
the two 3-H protons (Fig. 2b). The dramatic broadening of these
3-H proton resonances at 321 K and the relatively modest broaden-
ing of that for the 6-H protons on the coordinated rings, illustrated
in Fig. 2a, points to the origin of these effects as being due to the
rotation of the uncoordinated pyridine ring. Whether the particu-
larly large effect observed in this case is a consequence only of
the anisotropy arising from the ring current of the uncoordinated
pyridine ring, or whether the non-symmetrical nature of the aro-
matic ring is also contributing, is at present unclear. Clearly the
rotating pyridine ring will ensure that the 3-H positions on the
coordinated pyridines will experience the alternating effects of
the nitrogen lone pair and the 30-H proton increasing the range
of magnetic environments experienced during one rotation of the
uncoordinated pyridine ring. Further synthetic work, involving
the replacement of the uncoordinated pyridine ring by a benzene
ring, is underway to try to establish this.

D.V. Griffiths et al. / Inorganica Chimica Acta 363 (2010) 1186–1194
1189
Table 2
Selected bond lengths (Å), bond angles (°) and torsion angles (°) for complexes.
[(tpmba)Re(CO)3]
[(bz-tpmaH)Re(CO)3]Br
[(bpmba)Re(CO)3]
4b
3d
Molecule 7A
Molecule 7B
Bond lengths (Å)
C(1)–Re(1)
C(2)–Re(1)
C(3)–Re(1)
N(1)–Re(1)
N(2)–Re(1)
N(3)–Re(1)
C(1)–O(1)
C(2)–O(2)
C(3)–O(3)
C(9)–N(3)
C(20)–N(3)
1.931(4)
1.920(4)
1.912(4)
2.196(3)
2.158(3)
2.164(3)
1.147(5)
1.155(5)
1.154(5)
1.482(4)
1.361(5)
C(1)–Re(1)
C(2)–Re(1)
C(3)–Re(1)
N(1)–Re(1)
N(2)–Re(1)
N(3)–Re(1)
C(1)–O(1)
C(2)–O(2)
C(3)–O(3)
C(4)–N(1)
C(20)–N(1)
1.910(7)
C(1A)–Re(1A)
C(2A)–Re(1A)
C(3A)–Re(1A)
N(1A)–Re(1A)
N(2A)–Re(1A)
N(3A)–Re(1A)
C(1A)–O(1A)
C(2A)–O(2A)
C(3A)–O(3A)
C(9A)–N(3A)
C(15A)–N(3A)
1.923(3)
1.919(3)
1.908(3)
2.186(3)
2.200(3)
2.156(3)
1.154(4)
1.155(4)
1.167(4)
1.472(4)
1.347(4)
C(1B)–Re(1B)
C(2B)–Re(1B)
C(3B)–Re(1B)
N(1B)–Re(1B)
N(2B)–Re(1B)
N(3B)–Re(1B)
C(1B)–O(1B)
C(2B)–O(2B)
C(3B)–O(3B)
C(9B)–N(3B)
C(15B)–N(3B)
1.922(3)
1.921(4)
1.920(3)
2.179(3)
2.195(3)
2.157(3)
1.152(4)
1.146(4)
1.150(4)
1.474(4)
1.344(4)
1.935(8)
1.939(8)
2.211(5)
2.187(5)
2.182(6)
1.153(9)
1.149(9)
1.140(9)
1.531(8)
1.495(8)
Bond angles (°)
C(3)–Re(1)–C(2)
C(3)–Re(1)–C(1)
C(2)–Re(1)–C(1)
C(3)–Re(1)–N(2)
C(2)–Re(1)–N(2)
C(1)–Re(1)–N(2)
C(3)–Re(1)–N(3)
C(2)–Re(1)–N(3)
C(1)–Re(1)–N(3)
C(3)–Re(1)–N(1)
C(2)–Re(1)–N(1)
C(1)–Re(1)–N(1)
N(2)–Re(1)–N(3)
N(2)–Re(1)–N(1)
N(3)–Re(1)–N(1)
C9–N3–C20
90.35(16)
87.08(16)
91.95(16)
97.33(14)
91.91(14)
174.12(14)
167.47(14)
99.53(13)
100.17(14)
95.84(15)
171.38(13)
94.34(14)
74.80(11)
81.38(11)
73.57(11)
113.6(3)
C(1)–Re(1)–C(2)
C(1)–Re(1)–C(3)
C(2)–Re(1)–C(3)
C(1)–Re(1)–N(3)
C(2)–Re(1)–N(3)
C(3)–Re(1)–N(3)
C(1)–Re(1)–N(2)
C(2)–Re(1)–N(2)
C(3)–Re(1)–N(2)
C(1)–Re(1)–N(1)
C(2)–Re(1)–N(1)
C(3)–Re(1)–N(1)
N(3)–Re(1)–N(2)
N(3)–Re(1)–N(1)
N(2)–Re(1)–N(1)
84.7(3)
86.8(3)
87.4(3)
98.1(3)
97.3(3)
173.5(3)
99.3(3)
175.6(3)
94.8(2)
169.5(3)
102.6(3)
100.9(3)
80.3(2)
73.7(2)
73.2(2)
C(3A)–Re(1A)–C(2A)
C(3A)–Re(1A)–C(1A)
C(2A)–Re(1A)–C(1A)
C(3A)–Re(1A)–N(3A)
C(2A)–Re(1A)–N(3A)
C(1A)–Re(1A)–N(3A)
C(3A)–Re(1A)–N(1A)
C(2A)–Re(1A)–N(1A)
C(1A)–Re(1A)–N(1A)
C(3A)–Re(1A)–N(2A)
C(2A)–Re(1A)–N(2A)
C(1A)–Re(1A)–N(2A)
N(3A)–Re(1A)–N(1A)
N(3A)–Re(1A)–N(2A)
N(1A)–Re(1A)–N(2A)
C(9A)–N(3A)–C(15A)
90.04(14)
88.58(14)
90.30(14)
96.96(12)
101.16(12)
167.23(12)
171.64(12)
92.42(11)
99.38(12)
95.55(12)
173.22(11)
93.66(12)
74.73(10)
74.41(10)
81.51(10)
114.2(3)
C(3B)–Re(1B)–C(2B)
C(3B)–Re(1B)–C(1B)
C(2B)–Re(1B)–C(1B)
C(3B)–Re(1B)–N(3B)
C(2B)–Re(1B)–N(3B)
C(1B)–Re(1B)–N(3B)
C(3B)–Re(1B)–N(1B)
C(2B)–Re(1B)–N(1B)
C(1B)–Re(1B)–N(1B)
C(3B)–Re(1B)–N(2B)
C(2B)–Re(1B)–N(2B)
C(1B)–Re(1B)–N(2B)
N(3B)–Re(1B)–N(1B)
N(3B)–Re(1B)–N(2B)
N(1B)–Re(1B)–N(2B)
C(9B)–N(3B)–C(15B)
89.50(15)
90.66(14)
88.50(14)
98.08(12)
101.91(12)
166.40(12)
172.44(12)
91.95(12)
96.79(12)
96.43(13)
173.32(12)
94.50(12)
74.36(10)
74.26(10)
81.77(10)
115.2(3)
Torsion angles (°)
O4–C20–N3–Re(1)
O4–C20–N3–C9
120.2(3)
ꢁ3.9(3)
O(4A)–C(15A)–N(3A)–Re(1A)
O(4A)–C(15A)–N(3A)–C(9A)
142.1(3)
ꢁ1.0(4)
O(4B)–C(15B)–N(3B)–Re(1B)
O(4B)–C(15B)–N(3B)–C(9B)
ꢁ152.1(3)
ꢁ4.4(5)
5-Hx2, 5’-H,4”-H,3”/5”-H
(b) at 371 K
2“/6”-H
4‘-H
6-Hx2
4-Hx2
3‘-H
6‘-H
3-Hx2
(a) at 321 K
δH ppm
9.00
8.50
8.00
7.50
Fig. 2. A 270 MHz 1H NMR spectra of 4b in d6-DMSO at 321 and 371 K.
2.2.4. Formation of neutral complex [(bpmba)Re(CO)3] (7)
To confirm that the dramatic broadening observed in the NMR
spectrum of [(tpmba)Re(CO)3] 4b was due to the uncoordinated
pyridine ring, the corresponding bispyridyl complex [(bpmba)Re-
(CO)3] 7 was prepared by heating N-[bis(pyridin-2-yl)methyl]benz-
amide system bpmbaH 6b with [Re(CO)5Br] in DMF over an
extended period. As expected, its NMR spectra (see Section 4)
showed none of the broadening observed in the spectra of the cor-
responding trispyridyl system 4b.
H
H
3
3
NCOPh
N
N
Re(CO)3
7

1190
D.V. Griffiths et al. / Inorganica Chimica Acta 363 (2010) 1186–1194
To ensure it was appropriate to compare the structure of
It is interesting to note that the 1H NMR spectra of the acetylated
complex 2c also showed significant temperature dependent
broadening of the signals for the 3-H and 4-H pyridine protons,
unlike the corresponding signals in the N-benzoylated complex
2b which were sharp at room temperature. Satisfactory NMR
data for the acetylated complex 2c could therefore only be ob-
tained at higher temperatures where the resonances were signif-
icantly sharper. The fact that the 3-H and 4-H pyridine proton
resonances were most affected by this broadening points to the
origin of this effect being the adjacent uncoordinated amide
group. However, restricted rotation around the bond to the acet-
amide group cannot explain the residual broadening of the car-
bonyl ligand resonance observed in the 13C NMR spectrum of
2c at 363 K where the set of carbon resonances for the three pyr-
idine rings are now sharp. To explain the selective broadening of
the rhenium carbonyl resonances requires the presence of an
effect analogous to that mentioned earlier which produced mag-
netically non-equivalent carbonyl ligands in the N-benzoylated
complex 2b.
the trispyridyl complex 4b with that of the bispyridyl complex 7
the X-ray structure of the latter complex was also determined. In
the solid state the bispyridyl complex exists in two forms 7A and
7B within the same crystal. These differ in the orientation of the
benzoyl group relative to the rhenium centre and probably arise
because of the presence of a solvent molecule within the unit cell.
The X-ray structure of the 7A form of this compound is shown in
Fig. 3 and related data for both structures 7A and 7B are shown
in Tables 1 and 2 (see also Appendix A). These X-ray data shows
that the portion of the ligand system containing the benzamide
unit has a similar conformation in both 7A and 4b with little differ-
ence in the dihedral angle of the benzoyl carbonyl group with re-
spect to the N3–C9 bond [ꢁ1.1(4)° vs. ꢁ3.9 (3)°;
D
/ 2.8(7)°] or
C–N–C
in the C–N3–C bond angle [114.2(3)° vs. 113.6(3)°;
D
0.6(6)°]. This therefore strongly supports the conclusion that the
broadening of the 3-H proton resonances in 4b is due to rotation
of the uncoordinated pyridine ring.
However, the observation that the ortho-protons of the benzoyl
group in the trispyridyl system 4b are more than 0.25 ppm down-
field of the corresponding resonances in the analogous bispyridyl
complex 7 cannot be attributed to their interaction with the rotat-
ing uncoordinated pyridine ring since these ortho-proton reso-
nances in 4b remain relatively sharp even when the 3-H protons
on the coordinated pyridine rings suffer extreme broadening
(Fig. 2a). This suggests that despite the similarity in the conforma-
tion of the amide portion of the molecule in both complexes there
must be a significant change in the relative positions of the phenyl
ring in the benzoyl groups and the nearby carbonyl ligands on the
metal centre. This difference becomes readily apparent when the
dihedral angles of the benzoyl carbonyl group with respect to the
N3–Re bond are compared in 7A and 4b [142.1(3)° vs. 120.2(3)°;
2.2.6. Formation of ionic complex [(bz-tpmaH)Re(CO)3]Br (3d)
Since, as we reportedearlier[4], theunsubstituted tris(pyridin-2-
yl)methylamine 1a also forms a complex [(tpmaH)Re(CO)3]Br 3a
that has an uncoordinated pyridine ring, we were interested to
investigate whether the presence of a benzyl substituent on the ami-
no group in this type of complex would also result in some restricted
rotation of the uncoordinated pyridine ring. As expected the analo-
gous N-benzyl-substituted tris(pyridin-2-yl)methylamine ligand
system 1d (bz-tpmaH) reacted with [Re(CO)5Br] to give the complex
[(bz-tpmaH)Re(CO)3]Br 3d, whose X-ray structure is shown in Fig. 4.
Related crystallographic data are also shown in Tables 1 and 2 (see
also Appendix A). An interesting feature in the 1H NMR spectrum
of this compound is the observation that the N–H proton shows sig-
nificant coupling to one of the benzyl protons (J = 8 Hz) but not the
other suggesting that the dihedral angle to the latter benzyl proton
is approaching 90°. This, together with the narrow chemical shift
range observed for the phenyl protons, suggests the preference for
the approximately staggered conformation along the N1–C20 bond
observed in the crystalline state is still maintained in solution, keep-
ing the phenyl ring well away from the pyridine rings. However, the
asymmetry arising from the orientation of the benzyl group results
in the three pyridine rings having quite different chemical shifts
particularly for the 3-H positions [dH (d6-DMSO, 300 K) 7.68, 8.17
and 8.80 ppm]. The effects of slow rotation of the uncoordinated
pyridine ring are also again apparent with substantial broadening
of the lowest field 3-H resonance although the relative orientations
of the coordinated pyridine rings means that only one of them is
significantly affected in this system.
D
/ 21.9(6)°].
2.2.5. Formation of cationic complex [(tpmaaH)Re(CO)3]Br (2c)
To try to assess whether the bulk of the benzoyl group had a
significant impact on the rate of rotation of the uncoordinated
ring we prepared the analogous N-acetylated tris(pyridin-2-
yl)methylamine ligand system 1c (tpmaaH), with the intention
of preparing the corresponding neutral [(tpmaa)Re(CO)3]
complex 4c. However, reaction of tpmaaH 1c with [Re(CO)5Br]
resulted in the formation of the cationic complex [(tpmaaH)Re-
(CO)3]Br 2c, with coordination via the three pyridine nitrogen
atoms rather than the expected neutral compound 4c. Further-
more, this complex proved to be much more stable than the cor-
responding N-benzoylated complex 2b and showed no tendency
to undergo rearrangement to the neutral complex 4c even after
heating in a solution of dimethylformamide at 110 °C for 16 h.
O4a
C16a
H
H
O
C7a
N3a
C15a
C2a
C9a
C8a
3
3
Ph
N
O2a
N
N
N1a
Re(CO)3
C11a
C10a
Re1a
C1a
C3a
N2a
O3a
O1a
Fig. 3. X-ray structure of 7A.

D.V. Griffiths et al. / Inorganica Chimica Acta 363 (2010) 1186–1194
1191
Cl1
Cl3
C27
Cl2
N4
C15
N
C20
N1
C4
N3
PhCH2
C11
C10
C6
N
H
N
N
O2
C3
C2
C5
Re(CO)3 Br
O3
Re1
N2
C1
O1
Br1
Fig. 4. X-ray structure of 3dꢀCHCl3.
Efforts were also made to investigate the extent to which the
N-substituent on the ligand affected the ease of rotation of the
uncoordinated pyridine ring, although as previously noted the
N-acetylated complex 4c, was not formed on reaction of the
N-acetylated ligand 1c with [Re(CO)5Br]. The N-benzylated ligand
1d, on the other hand, behaved like the parent ligand 1a forming
a cationic complex [(LH)Re(CO)3]Br 3d with [Re(CO)5Br] in which
one pyridine ring remained uncoordinated and where coordination
to the rhenium occurs via two of the pyridine rings and the NH of
the benzylamine portion of the ligand. However, while this cationic
complex 3d showed temperature dependent broadening effects in
its NMR spectra arising from the presence of a slowly rotating
uncoordinated pyridine ring, only one of the 3-H protons on the
coordinated pyridine rings exhibited substantial broadening and
the significant chemical shift differences observed between the
two coordinated pyridine rings highlighted the non-symmetrical
nature of this complex. It was therefore not possible to draw con-
clusions from a comparison of NMR spectra of the complexes 3d
and 4b.
It is interesting to note that while complex 2c did not contain an
uncoordinated pyridine ring it did still show temperature depen-
dent behaviour due to rotation of the uncoordinated amide group.
However, the origin of an additional effect causing selective broad-
ening of the carbonyl ligand carbon resonance in this compound
and magnetic non-equivalence of the carbonyl ligands in the anal-
ogous complex 2b is less clear and merits further investigation.
The X-ray molecular structures of several of the complexes
were also determined and it is worth noting that the neutral com-
plexes 4b and 7, and the cationic complex 3d show a number of
features in common. The overall structures around the Re centre
in all three cases can be described as a distorted octahedral coordi-
nation sphere comprising three carbonyl ligands linearly coordi-
nated in fac geometry, two pyridyl groups and either an amine
group, as in 3d, or an amide group, as in 4b and 7. The Re–CO bond
distances are similar of those observed in related examples [10].
The Re–N amide bond distances of 2.164(3) Å for complex 4b
and 2.156(3) and 2.157(3) Å for molecules 7A and 7B, respectively,
are typical of deprotonated nitrogen atoms bound to Re(I) atom.
The approximately planar geometry about the N atom in the coor-
dinated amide units is also indicative of the expected sp2 hybrid-
isation of the nitrogen with donation of a nitrogen lone pair to
the metal. Other Re–N distances are unremarkable, and typical of
Re(I)-complexes with such donors [11]. It is worth noting that in
3. Conclusion
The reactions of several N-substituted tris(pyridin-2-yl)methyl-
amine ligands with [Re(CO)5Br] have been investigated and the N-
substituent has been shown to have a significant impact on the
nature and stability of the complexes formed.
1a Z = H
1b Z = COPh
1c Z = COMe
1d Z = CH2Ph
N
N
NH
Z
N
Thus both the N-benzoylated and N-acetylated tris(pyridin-2-
yl)methylamine ligand systems, tpmbaH 1b and tpmaaH 1c reacted
with [Re(CO)5Br] with the initial formation of the corresponding
cationic rheniumtricarbonyl complexes 2b and 2c [(LH)Re(CO)3]Br,
where LH = tpmbaH and tpmaaH, respectively] in which coordina-
tion of the ligand occurs via the three pyridine rings. However, of
these two complexes only the tpmbaH complex 2b was found to
undergo loss of HBr on heating to give a neutral octahedral complex
[(L)Re(CO)3] 4b in which coordination occurs via two of the pyri-
dine rings and the deprotonated amide nitrogen. This difference
in behaviour would correlate with the relative acidities of the
amide protons in the initial ligand since the benzamide 1b is likely
to be more acidic than the corresponding acetamide 1c [9].
The 1H NMR spectra of the complexes also showed some inter-
esting features. Thus, for example, the neutral complex 4b run at or
slightly above room temperatures are very unusual in that the sig-
nals for the 3-H protons on the coordinated pyridine rings are not
visible due to extreme broadening of these resonances. These res-
onances did become visible at higher temperature but even at
371 K they were still very broad. Since such broadening was not
observed in the 1H NMR spectra of the related bispyridyl complex
7, where the uncoordinated pyridine ring present in 4b has been
replaced by a hydrogen atom, we were able to conclude that the
broadening effect observed in 4b was due to slow rotation of the
uncoordinated pyridine ring. The extreme nature of this broaden-
ing is thought to be due in part to the non-symmetrical nature of
the rotating heterocyclic ring increasing the difference in magnetic
field experienced by the 3-H protons during one rotation of the
uncoordinated pyridine ring.

1192
D.V. Griffiths et al. / Inorganica Chimica Acta 363 (2010) 1186–1194
complex 3d there is a strong hydrogen bond (N1–H1ꢀꢀꢀBr1) to Br1
as well as two ‘weak’ hydrogen bonds to adjacent molecules. In
the other complexes too there are ‘weak’ hydrogen bonds some
of which could affect the conformations of the molecules.
4.2.2. N-[1,1,1-Tris(pyridin-2-yl)methyl]benzamide, tpmbaH (1b)
Benzoic anhydride (0.28 g, 1.24 mmol) was added to a solution
of tpmaH 1a (0.25 g, 0.95 mmol) in dichloromethane (2 cm3) and
the mixture was stirred at room temperature for 24 h. Dichloro-
methane (20 cm3) was then added and the solution washed first
with saturated aqueous sodium bicarbonate (2 ꢂ 20 cm3) and then
water (2 ꢂ 20 cm3). The organic phase was dried (MgSO4), filtered
and the volatile components removed under reduced pressure.
Recrystallisation of the residue from a mixture of dichloromethane
and pentane gave the tpmbaH 1b (0.18 g, 52%) as yellow crystals,
m.p. 233–234 °C. 1H NMR (270 MHz, CDCl3): d (ppm) 7.10–7.17
(3H, m, 5-H), 7.41–7.51 (3H, m, 4-H), 7.59–7.64 (6H, m, 3-H, 30/
50-H and 40-H), 8.00 (2H, dd, J 7 and 2, 20/60-H), 8.53 (3H, br d, J
As expected the IR spectra of the rheniumtricarbonyl complexes
showed strong bands in the region of 2029–1872 cmꢁ1 consistent
with the presence of the fac-{Re(CO)3}+ core [12], whilst those
complexes based on amide containing ligand systems, such as
2b, 2c, 4b and 7, exhibited an additional strong absorption in the
region 1692–1589 cmꢁ1, corresponding to the
m(C@O) of the amide
group. Relative to their corresponding pyridyl ligands, complexes
4b and 7 showed the previously reported shift to lower wavenum-
ber of these carbonyl absorptions together with the loss of the N–H
bands (at 3338 and 3420 cmꢁ1, respectively) resulting from the
coordination and deprotonation of the amide group to the rhenium
[13,14]. Changes were also observed in the pyridine bands on coor-
dination. However, while the band around 1587 cmꢁ1 in the li-
gands 1b, 1c and 6b clearly moved to higher wavenumber in the
cationic complexes 2b and 2c (1595 and 1599 cmꢁ1) we can only
speculate that a similar effect was observed in the IR spectra of
the complexes 4b and 7 since the presence of the amide carbonyl
band around 1590–1600 cmꢁ1 prevented us from observing any
underlying bands in this region. Other bands in the region 1450–
1600 cmꢁ1 arising from the pyridine rings showed a reduction in
value on coordination to the rhenium.
5, 6-H). 13C NMR (67.9 MHz, CDCl3): d (ppm) 70.9 (
a-C), 122.3
(C-5), 124.7 (C-3), 127.5 (C-30/50), 128.8 (C-20/60), 131.6 (C-40),
134.9 (C-10), 136.2 (C-4), 148.0 (C-6), 161.0 (C-2), 165.5 (C@O). Se-
lected IR (KBr)/cmꢁ1: 3338 (NH), 1658 (C@O), 1587, 1570, 1507
and 1486 (pyr). MS-ESI (m/z) 367 (M+H+. C23H19N4O requires 367).
4.2.3. N-[1,1,1-Tris(pyridin-2-yl)methyl]acetamide, tpmaaH (1c)
A mixture of tpmaH 1a (300 mg, 1.2 mmol) and acetic anhy-
dride (3 cm3) was heated to 50 °C and stirred at this temperature
for 3 h. After cooling, water (50 cm3) was added and the solution
adjusted to pH 8 by the addition of sodium bicarbonate. The aque-
ous mixture was then extracted with DCM (3 ꢂ 25 cm3). The com-
bined organic extracts were dried (MgSO4), filtered and solvent
evaporated under reduced pressure (30 °C at 15 mm Hg) to leave
a yellow waxy solid. Recrystallisation of this product from a
DCM/hexane mixture gave the tpmaaH 1c (250 mg, 71%) as a pale
yellow powder, m.p. 153 °C, Anal. Calc. for C18H16N4O: C, 71.0; H,
5.3; N, 18.4. Found: C, 71.0; H, 5.2; N, 18.5%. 1H NMR (270 MHz,
CDCl3): d (ppm) 2.24 (3H, s, Me), 7.20 (3H, ddd, J 6, 5 and 2, 5-
H), 7.63–7.67 (3H, m, 4-H), 7.69 (3H, td, J 8 and 2, 3-H), 8.59 (3H,
d, J 5, 6-H), 9.40 (1H, br s, NH). 13C NMR (67.9 MHz, CDCl3): d
Further work on how the choice of the N-substituent on the pri-
mary amino group can affect the nature of the complexes formed
from [Re(CO)5Br] with bis- and tris(pyridin-2-yl)methylamine
based tripodal ligand systems will be discussed in a subsequent
publication.
4. Experimental
(ppm) 24.1 (Me), 70.7 (
a-C), 122.0, (C-5), 124.4 (C-3), 136.0 (C-
4.1. General details
4), 147.8 (C-6), 160.8 (C-2), 168.7 (C@O). Selected IR (ATR)/cmꢁ1
:
NMR (1H, 13C, COSY, 13C–1H correlated) spectra were recorded
on JEOL EX-270 and Bruker AMX400, AV400 and AV600
spectrometers. 1H NMR spectra in CDCl3 are referenced to TMS,
those in d4-MeOD to the residual CD2H signal at dH 3.31 ppm and
those in d6-DMSO to the residual CD2H signal at dH 2.50 ppm
unless otherwise indicated. 13C NMR spectra are referenced to
the solvent resonance, i.e. CDCl3 at dC 77.23 ppm, d4-MeOD at dC
49.15 ppm or d6-DMSO at dC 39.51 ppm unless otherwise indi-
cated. J values are given in Hz. IR spectra were recorded from
4000 to 400 cmꢁ1 as KBr discs or with ATR using a Shimadzu
FTIR-8300 spectrophotometer and selected bands are reported be-
low. TLC was performed with alumina backed silica gel 60 F254
eluting with the solvent system used for the column chromatogra-
phy unless otherwise stated and the plates were visualised under
UV light or developed in an iodine tank. Column chromatography
3273 (NH), 1667 (C@O), 1587, 1568), 1494 and 1465 (pyr). MS-EI
(m/z) 304.1324 (M+, C18H16N4O requires 304.1324).
4.2.4. N-Benzyl-1,1,1-tris(pyridin-2-yl)methylamine, bz-tpmaH (1d)
A
mixture of tpmaH 1d (270 mg, 1 mmol), benzaldehyde
(110 mg, 1.1 mmol) and methanol (5 cm3) was heated under reflux
for 4 h and then cooled. Sodium borohydride (100 mg 2.7 mmol)
was then added to the stirred solution in small portions. After
2 h the methanol was evaporated under reduced pressure (40–
45 °C at 15 mm Hg) and water (25 cm3) was added to the residue.
This mixture was then extracted with DCM (2 ꢂ 25 cm3). The com-
bined organic layers were dried (MgSO4), filtered and solvent re-
moved under reduced pressure to leave an orange coloured oil.
Chromatography on silica gel eluting with a DCM/MeOH (95:5)
mixture gave the required product 1d (53 mg, 14%) as a yellow
oil, Rf = 0.25. 1H NMR (270 MHz, CDCl3): d (ppm) 3.45 (2H, s,
NCH2), 7.12 (3H, ddd, J 7, 5 and 1, 5-H), 7.23 (1H, tt, J 7 and 1.5,
40-H), 7.29 (2H, m, 30/50-H), 7.36 (2H, m, 20/60-H), 7.60 (3H, ddd, J
8, 7 and 2, 4-H), 7.69 (3H, dt, J 8 and 1, 3-H), 8.60 (3H, ddd, J 5, 2
and 1, 6-H). 13C NMR (67.9 MHz, CDCl3): d (ppm) 48.2 (NCH2),
used silica gel with particle size 33–50 lm and was purchased
from BDH. Rheniumpentacarbonyl bromide [Re(CO)5Br] was pur-
chased from Strem Chemicals UK. All other materials were pur-
chased from Sigma–Aldrich Ltd.
74.3 (a
-C), 121.8 (C-5), 124.2 (C-3), 126.8 (C-40), 128.3 (C-20/60),
4.2. Ligand synthesis
128.4 (C-30/50), 136.1 (C-4), 141.1 (C-10), 148.5 (C-6), 163.3 (C-2).
4.2.1. 1,1,1-Tris(pyridin-2-yl)methylamine, tpmaH (1a)
4.2.5. N-[Bis(pyridin-2-yl)methyl]benzamide, bpmbaH (6b)
Ligand 1a was prepared as previously described [1], m.p. 98 °C.
1H NMR (270 MHz, CDCl3): d (ppm) 2.35 (2H, br s, NH2), 7.15 (3H,
ddd, J 7.4, 4.8 and 1.0, 5-H), 7.36 (3H, ddd, J 8.0, 1.0 and 0.9, 3-H),
7.61 (3H, ddd, J 8.0, 7.4 and 1.9, 4-H), 8.57 (3H, ddd, J 4.8, 1.9 and
A solution of benzoyl chloride (450 mg, 3.2 mmol) in DCM
(5 cm3) was added dropwise, over a period of 5 min, to a stirred
solution of bpmaH 6a (550 mg, 3 mmol) and triethylamine
(350 mg, 3.3 mmol) in DCM (10 cm3) cooled in an ice bath. The
cooling bath was then removed and stirring was continued for a
further 2 h. The resulting solution was washed with water
0.9, 6-H). 13C NMR (67.9 MHz, CDCl3): d (ppm) 70.2 (
a-C), 121.8 (C-
5), 123.0 (C-3), 136.2 (C-4), 148.7 (C-6), 165.0 (C-2).

D.V. Griffiths et al. / Inorganica Chimica Acta 363 (2010) 1186–1194
1193
(15 ml ꢂ 2), dried (MgSO4), filtered and volatile components re-
moved by warming under reduced pressure to leave a brown solid.
Recrystallisation of this residue from a hexane/DCM mixture gave
the product 6b (650 mg, 75%) as fawn coloured crystals, m.p. 159–
162 °C. 1H NMR (270 MHz, CDCl3): d (ppm) 6.40 (1H, d, J 6.5, CH),
7.15 (2H, ddd, J 7.5, 5.0 and 1.0, 5-H), 7.40–7.52 (5H, m, 3-H2, 30/
40/50-H), 7.64 (2H, td, J 7.5 and 2.0, 4-H), 7.96 (2H, dd, J 7.5 and 2,
20/60-H), 8.57 (2H, dm, J 5.0, 6-H), 8.78 (1H, br d, J 6.5, NH). 13C
NMR (67.9 MHz, CDCl3): d (ppm) 59.5 (CH), 122.4 (C-3), 122.7 (C-
5), 127.4 (C-20/60), 128.6 (C-30/50), 131.7 (C-40), 134.4 (C-10), 137.0
(C-4), 149.4 (C-2), 159.1 (C-6), 166.6 (C@O). Selected IR (ATR)/
cmꢁ1: 3420 (NH), 1654 (C@O), 1586, 1572, 1507 and 1464 (pyr).
MS-EI (m/z) 289 (M+, C18H15N3O requires 289).
by filtration, washed with a petroleum ether (b.p. 40–60 °C)
(5 cm3) and dried. The complex [(tpmaaH)Re(CO)3]Br 2c (120 mg,
69%) was isolated as a fawn coloured powder, m.p. > 250 °C. 1H
NMR (400 MHz, d6-DMSO, 363 K): d (ppm) 2.56 (3H, s, CH3), 7.60
(3H, dd, J 7 and 6, 5-H), 8.26 (3H, t, J 7, 4-H), 8.31 (3H, br s, 3-H),
9.20 (3H, d, J 6, 6-H), 9.99 (1H, s, NH). 13C NMR (100.63 MHz, d6-
DMSO at 363 K): d (ppm) 23.5 (Me), 72.5 (a-C), 124.7 (br, C-3),
125.3 (C-5), 141.5 (C-4), 154.0 (C-2), 156.1(C-6), 172.3 (C@O),
194.3 (br, CO). Selected IR (ATR)/cmꢁ1: 2029 and 1908(br) (CO),
1692 (C@O), 1599, 1510, 1467 and 1439 (pyr). MS-ESI (m/z) 574
(M–Br+. C21H16N4O4Re+ requires 574).
A sample of the complex 2c was dissolved in DMF (2 cm3) and
the solution heated at 105–110 °C for 16 h. After cooling, the sol-
vent was removed in vacuo (60 °C at 0.10 mm Hg) to leave a brown
solid which gave a similar 1H NMR spectrum to that of the original
complex. The slow evaporation of a solution of this compound in
acetone gave crystals suitable for X-ray diffraction studies, which
confirmed the compound was still 2c [16].
4.3. Synthesis of rhenium complexes
4.3.1. [(tpmbaH)Re(CO)3]Br (2b) and [(tpmba)Re(CO)3] (4b)
A mixture of [Re(CO)5Br] (105 mg, 0.26 mmol), tpmbaH 1b
(107 mg, 0.29 mmol) and toluene (5 cm3) was slowly heated.
When the reaction mixture reached ca. 100 °C, a black tarry mate-
rial formed which was filtered off and extracted with dichloro-
methane (10 cm3). This DCM solution was filtered and then
evaporated to dryness to give [(tpmbaH)Re(CO)3]Br 2b (21 mg,
8%) as a yellow powder, m.p. > 250 °C. 1H NMR (400 MHz, CDCl3):
d (ppm) 7.19 (1H, s, CH), 7.46 (3H, dd, J 7 and 5, 5-H), 7.50 (2H, t,
J 7.8, 30/50-H), 7.55–7.61 (4H, m, 3-H3 and 40-H), 7.86 (3H, td, J
7.8, 1.5, 4-H), 7.95 (2H, dd, J 7.8 and 1, 20/60-H), 9.07 (3H, d, J 5,
6-H), 10.4 (1H, s, NH). 13C NMR (100.63 MHz, CDCl3): d (ppm)
61.8 (C–NH), 123.5 (C-5), 124.8 (C-3), 127.6 (C-30/50), 129.3 (C-20/
60), 132.5 (C-10), 133.3 (C-40), 141.7 (C-4), 146.7 (C-6), 158.0 (C-
2), 166.2 (C@O), 186.5 (CO), 186.7 (ꢂ2)(CO). Selected IR (KBr)/
cmꢁ1: 2021, 1911(br) (CO), 1665 (C@O), 1595, 1508, 1466 and
1437 (pyr). MS-ESI (m/z) 637.0886 (M–Br+. C26H18N4O3Re requires
637.0881).
4.3.3. [(bz-tpmaH)Re(CO)3]Br (3d)
A mixture of bz-tpmaH 1d (53 mg, 0.15 mmol), [Re(CO)5Br]
(61 mg 0.15 mmol) and dry toluene (1 cm3) was heated at 100 °C
for 16 h. The precipitated solid was collected by filtration, washed
with petroleum ether (b.p. 40–60 °C) (10 cm3) and then dried. The
complex [(bz-tpma)Re(CO)3]Br 3d was isolated as a yellow powder
(95 mg, 90%), m.p. > 250 °C. 1H NMR (600 MHz, d6-DMSO, 300 K): d
(ppm) 3.46 (1H, d, J 12, CHPh), 3.56 (1H, dd, J 12 and 8, CHPh), 7.28
(5H, br s, Ph), 7.60 (1H, m, 5-H), 7.62 (1H, m, 5-H), 7.68 (1H, d, J 8,
3-H) 7.73 (1H, dd, J 7 and 5, 50-H), 8.15–8.18 (2H, m, 4-H, 30-H),
8.21 (1H, td, J 7.8 and 1.2, 40-H), 8.28 (1H, td, J 8 and 1, 4-H), 8.80
(1H, br s, 3-H), 8.92 (1H, d, J 5, 60-H), 9.14 (1H, br d, J 5, 6-H), 9.17
(1H, d, J 5.5, 6-H). 13C NMR (100.63 MHz, d6-DMSO, 363 K):
d (ppm) 53.3 (CH2), 81.3 (a-C), 124.6 (C-5), 125.1 (C-3), 125.2
Attempts to grow crystals of the [(tpmbaH)Re(CO)3]Br 2b for X-
ray analysis, by slow evaporation of an acetonitrile solution, gave
yellow crystals that were shown by X-ray diffraction to be the rear-
rangement product [(tpmba)Re(CO)3] 4b. Further heating (reflux,
16 h) of the original reaction mixture after removal of the 2b also
resulted in the formation of 4b. After cooling this solution the yel-
low solid formed was filtered off, washed with DCM (10 cm3) and
recrystallised from acetonitrile. The complex 4b (48 mg, 32%) was
isolated as a yellow crystalline compound, m.p. > 250 °C suitable
for X-ray diffraction studies (see Appendix A). Anal. Calc. for
C26H17BrN4O4Re: C, 49.13; H, 2.70; N, 8.81. Found: C, 49.10; H,
2.67; N, 8.80%. 1H NMR (270 MHz, d6-DMSO, 321 K): d (ppm)
7.27–7.45 (6H, m, 5-H2, 50-H, 400-H, 300/500-H), 7.62 (1H, d, J 8, 30-
H), 7.73–7.81 (3H, m, 40-H and 200/600-H), 8.01 (2H, t, J 8, 4-H),
8.84 (1H, ddd, J 5, 2 and 1, 60-H), 8.90 (2H, br d, J 5.0, 6-H), 3-H res-
onances absent (Fig. 2a); 1H NMR (270 MHz, d6-DMSO, 371 K): d
(ppm) 7.25–7.43 (6H, m, 300/500-H, 400-H, 5-H2 and 50-H), 7.62 (1H,
d, J 7.7, 30-H), 7.70–7.80 (3H, m, 200/600-H and 40-H), 7.98 (2H, t, J
7.7, 4-H2), 8.39 (2H, br s, 3-H2), 8.83 (1H, d, J 5, 60-H), 8.87 (2H,
d, J 5, 6-H2) (Fig. 2b), X0 refers to non-coordinated pyridine ring
and X00 to Ph ring. 13C NMR (100.63 MHz, d6-DMSO, 341 K): d
(ppm) 79.5 (C), 121.9 (C-50), 122.2 (C-30), 123.8 (C-5), 124.4 (br,
C-3), 126.9 (C-300/500), 128.6 (C-200/600), 129.6 (C-400), 137.0 (C-40),
139.7 (C-4), 140.3 (C-100), 146.8 (C-60), 153.0 (C-6), 161.8 (C-20),
163.4 (br, C-2), 176.5 (C@O), 197.6–197.8 (br, CO)[15]. Selected
IR (KBr)/cmꢁ1: 2012, 1898 and 1881 (CO), 1601 (C@O), 1573,
1472 and 1457 (pyr).
(C-5), 125.3 (C-5), 125.9 (C-3), 127.4 (C-400), 127.6 (C-200/600), 127.9
(C-300/500), 128.9 (C-3), 134.9 (C-100), 137.8 (C-4), 140.3 (C-4), 140.8
(C-4), 148.3 (C-6), 152.6 (C-2), 153.8 (C-6), 154.4 (C-6), 155.7
(C-2), 159.1 (C-2), 194.4 (CO), 195.8 (CO), 196.5 (CO) [15]; where
X0 refers to non-coordinated pyridine ring and X00 to Ph ring.
Selected IR (ATR)/cmꢁ1: 2020, 1920 and 1904 (CO), 1605, 1585,
1473 and 1448 (pyr). MS-ESI (m/z) 623.1068 (M–Br+.
C26H20N4O3Re+ requires 623.1088).
Crystals of 3d suitable for X-ray diffraction studies were ob-
tained by the slow evaporation of a solution of the complex in chlo-
roform (see Appendix A).
4.3.4. [(bpmba)Re(CO)3] (7)
A mixture of bpmbaH 6 (R = COPh) (87 mgs, 30 mmol), [Re-
(CO)5Br] (115 mg, 0.28 mmol) and DMF (8 cm3) was heated at
118 °C for 48 h. Volatile components were removed from the
reaction mixture (70 °C at 10 mm Hg) and the residue recrystal-
lised from acetonitrile to give the pure [(bpmba)Re(CO)3] 7
(82 mg, 52%) as pale yellow crystals, m.p. > 250 °C. 1H NMR
(400 MHz, d6-DMSO): d (ppm) 7.25 (1H, s, CH), 7.27 (2H, m, 30/
50-H), 7.32 (1H, tt, J 7 and 1.5, 40-H), 7.39 (2H, ddd, J 7.6, 5.5
and 1.4, 5-H), 7.49 (2H, dd, J 7 and 1.5, 20/60-H), 8.10 (2H, td, J
7.6 and 1.7, 4-H), 8.17 (2H, br d, J 7.6, 3-H), 8.88 (2H, br d, J
5.5, 6-H). 13C NMR (100.63 MHz, d6-DMSO): d (ppm) 70.6 (
a-
CH), 122.9 (C-3), 124.4 (C-5), 127.1 (C-30/5), 127.9 (C-20/60),
128.9 (C-40), 141.1 (C-4), 141.4 (C-10), 153.9 (C-6), 161.0 (C-2),
175.8 (C@O), 197.7 (CO), 198.6 (ꢂ2)(CO). Selected IR (ATR):
2010, 1872(br) (CO), 1589 (C@O), 1556, 1466 and 1446 (pyr).
These crystals proved suitable for X-ray crystallography (see
Appendix A).
4.3.2. [(tpmaaH)Re(CO)3]Br (2c)
A mixture of tpmaaH 1c (78 mg, 0.26 mmol), [Re(CO)5Br]
(101 mg, 0.25 mmol) and toluene (2 cm3) was heated at 100–
105 °C for 16 h. After cooling, the precipitated solid was collected

1194
D.V. Griffiths et al. / Inorganica Chimica Acta 363 (2010) 1186–1194
4.4. X-ray structure determination
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X scans (1.0° increments, 20 s expo-
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drawing the molecules. WINGX [28] was used to prepare material
for publication.
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Acknowledgements
The authors would like to thank both the EPSRC UK National
Crystallographic Service at Southampton and the EPSRC National
Mass Spectrometry Service Centre (NMSSC) at Swansea for their
help with the acquisition of some of the data presented.
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Appendix A. Supplementary material
CCDC 733188, 733187 and 733189 contain the supplementary
crystallographic data for this paper. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif. Supplementary data
associated with this article can be found, in the online version, at
doi:10.1016/j.ica.2009.11.039.
[28] L.J. Farrugia, WINGX: A Program for Crystal Structure Analysis, University of
Glasgow, 1998.