Synthesis, X-ray studies, spectroscopic characterization and DFT calculations of p-tolylimido rhenium(V) complexes bearing an imidazole-based ligand

Article abstract of DOI:10.1016/j.poly.2010.10.002

Novel p-tolylimido rhenium(V) complexes [Re(p-NC₆H ₄CH₃)X₂(hpb)(PPh₃)] and [Re(p-NC₆H₄CH₃)(hpb)₂(PPh ₃)]X (X = Cl, Br) have been obtained in the

Full text of DOI:10.1016/j.poly.2010.10.002

Polyhedron 30 (2011) 142–153
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Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis, X-ray studies, spectroscopic characterization and DFT calculations
of p-tolylimido rhenium(V) complexes bearing an imidazole-based ligand
⇑
B. Machura , M. Wolff, I. Gryca
Department of Crystallography, Institute of Chemistry, University of Silesia, 9th Szkolna St., 40-006 Katowice, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
Novel p-tolylimido rhenium(V) complexes [Re(p-NC6H4CH3)X2(hpb)(PPh3)] and [Re(p-NC6H4CH3)(hpb)2-
(PPh3)]X (X = Cl, Br) have been obtained in the reactions of [Re(p-NC6H4CH3)X3(PPh3)2] with 2-(2-
hydroxyphenyl)-1H-benzimidazole (Hhpb). The compounds were identified by elemental analysis IR,
UV–Vis spectroscopy and X-ray crystallography. The electronic structures of the complex [Re(p-NC6H4-
CH3)Cl2(hpb)(PPh3)] and the cation [Re(p-NC6H4CH3)(hpb)2(PPh3)]+ have been calculated with the
density functional theory (DFT) method. Additional information about binding in the [Re(p-NC6H4CH3)-
Cl2(hpb)(PPh3)] and [Re(p-NC6H4CH3)(hpb)2(PPh3)]+ has been obtained by NBO analysis. The electronic
spectra of [Re(p-NC6H4CH3)Cl2(hpb)(PPh3)] and [Re(p-NC6H4CH3)(hpb)2(PPh3)]Cl were investigated at
the TDDFT level employing B3LYP functional in combination with LANL2DZ.
Received 2 September 2010
Accepted 1 October 2010
Available online 20 October 2010
Keywords:
Rhenium imido complexes
2-(2-Hydroxyphenyl)-1H-benzimidazole
X-ray
Electronic structure
DFT and TDDFT calculations
NBO analysis
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
Previously, we investigated the reactivity of oxorhenium(V)
species [ReOX3(EPh3)2] (X = Cl or Br; E = As, P) towards 2-(2-
Imidazole and its derivatives are an important class of heterocy-
cle with N-donor atoms, which can be excellent organic ligands to
generate various complexes upon ligation. The imidazole ring pos-
sesses two adjacent nucleophilic sites and its steric and electronic
properties can be modified by the substituents of the heterocyclic
ring. As a monodentate ligand it coordinates to the metal ion via
the pyridine-type nitrogen. The pyrrole-type nitrogen (N–H) is
usually involved in hydrogen bond formation with available hydro-
gen acceptor and/or hydrogen donor sites. In many cases these
hydrogen bonds dictate interesting molecular packing and
arrangements in the solid state. On the other hand, the imidazolate
anion can function as a bridge ligand through both nitrogens
affording polynuclear complexes of intriguing structural diversi-
ties, properties and reactivities, not found for mononuclear com-
plexes [1–5]. Furthermore the imidazole ring is an essential
metal binding site in metalloproteins, therefore complexes con-
taining imidazole-derived ligands are important in the context of
biomimetic models [6–10].
hydroxyphenyl)-1H-benzimidazole (Hhpb). The 2-(2-hydroxy-
phenyl)-1H-benzimidazole has been shown to bind to rhenium(V)
as a chelate, and the reactions [ReOX3(PPh3)2] with Hhpb lead to
the formation of cis and trans stereoisomers of [ReOX2(hmb-
zim)(PPh3)]. The disubstituted [ReO(OMe)(hpb)2]ꢀMeCN complex
has been isolated from the reaction of [ReOX3(PPh3)2] with ligand
excess in a mixture of acetonitrile and methanol [13].
As an extension of this work, we decided to examine the reac-
tivity of the related imido complexes [Re(p-NC6H4CH3)X3(PPh3)2]
(X = Cl, Br) towards 2-(2-hydroxyphenyl)-1H-benzimidazole (Hhpb;
Scheme 1).
The complexes containing NR2ꢁ ligand have this advantage over
oxocomplexes that the incorporation of functional groups in the
organic moiety R may facilitate the linking of the rhenium(V) imi-
do complex to biologically relevant molecules. In addition, the
incorporation of the Re = N–R core would allow the modification
of the organic substituent R to manipulate the biodistribution of
the radiopharmaceutical.
Here we present the structural and spectral properties of
trans-[Re(p-NC6H4CH3)X2(hpb)(PPh3)] and [Re(p-NC6H4CH3)(hpb)2-
(PPh3)]X (X = Cl, Br). The experimental studies on the imido
rhenium complexes have been accompanied computationally by
the density functional theory (DFT) and time-dependent DFT
calculations [14,15]. Additional information about bonding
between the rhenium atom and imido ligand in trans-[Re(p-
NC6H4CH3)Cl2(hpb)(PPh3)] and [Re(p-NC6H4CH3)(hpb)2(PPh3)]+
has been obtained by NBO analysis.
Due to the favourable nuclear properties of 186Re and 188Re
nuclides
(
186Re: 1.07 MeV b-emitter, t1/2 90 h) and 188Re:
2.12 MeV b-emitter, t1/2 17 h) in radionuclide therapy, chemistry
of oxo and imido rhenium complexes with imidazole-derived li-
gands arouses particular interest [11,12].
⇑
Corresponding author.
E-mail address: basia@ich.us.edu.pl (B. Machura).
0277-5387/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2010.10.002

B. Machura et al. / Polyhedron 30 (2011) 142–153
143
Anal. Calc. for C38H3Cl2N3OPRe: C, 54.74; H, 3.75; N, 5.04.
Found: C, 54.55; H, 3.67; N, 5.15%. 1H NMR (400 MHz; DMSO-d6)
d = 13.82 (1H, N–H), 8.04 (d, 1H), 7.65 (d, 1H), 7.53 (t, 1H), 7.42–
7.32 (m, 8H), 7.28–7.18 (m, 4H), 7.14 (d, 1H), 7.07 (t, 1H), 7.03–
6.90 (m, 4H), 6.84 (d, 1H), 6.73 (t, 1H), 6.65 (d, 1H), 6.51 (t, 1H),
6.83 (d, 1H), 5.59 (d, 1H), 2.14 (s, 3H).
Scheme 1. Structure of Hhpb ligand.
2.3. Preparation of [Re(p-NC6H4CH3)Br2(hpb)(PPh3)] (2)
2. Experimental
A procedure similar to that for 1 was used with [Re(p-NC6H4-
CH3)Br3(PPh3)2] (0.50 g, 0.47 mmol) and Hhpb (0.11 g, 0.52 mmol).
Green crystals of 2 were collected in 75%.
2.1. General procedure
All the reagents used to the synthesis were commercially avail-
able and were used without further purification. The complexes
[Re(p-NC6H4CH3)X3(PPh3)2] (X = Cl, Br) were prepared according
to the literature methods [16].
IR spectra were recorded on a Nicolet Magna 560 spectropho-
tometer in the spectral range 4000–400 cmꢁ1 with the samples in
form of KBr pellets. Electronic spectra were measured on a spectro-
photometer Lab Alliance UV–Vis 8500 in the range 1100–180 nm.
Elemental analyses (C, H, N) were performed on a Perkin–Elmer
CHN-2400 analyzer. 1H NMR spectrum was obtained in DMSO-d6
using Bruker Avance 400 spectrometer.
Anal. Calc. for C38H3Br2N3OPRe: C, 49.47; H, 3.39; N, 4.55.
Found: C, 49.68; H, 3.29; N, 4.49%.
1H NMR (400 MHz; DMSO-d6) d = 13.71 (1H, N–H), 8.06 (d, 1H),
7.83–7.72 (m, 5H), 7.69–7.52 (m, 4H), 7.51–7.41 (m, 7H), 7.36
(d, 1H), 7.30 (t, 1H), 7.18 (t, 2H), 7.12 (d, 2H), 7.09 (t, 2H), 6.96
(t, 1H), 5.99(d, 1H), 2.121 (s, 3H). UV–Vis of 2 (CH3CN; kmax [nm]
(e
; [dm3 molꢁ1 cmꢁ1]): 675.2 (290), 326.8 (13600), 297.8 (17900),
206.8 (70050).
2.4. Preparation of [Re(p-NC6H4CH3)(hpb)2(PPh3)]Cl (3)
2.2. Preparation of [Re(p-NC6H4CH3)Cl2(hpb)(PPh3)] (1)
[Re(p-NC6H4CH3)Cl3(PPh3)2] (0.50 g, 0.54 mmol) was added to
2-(2-hydroxyphenyl)-1H-benzimidazole (0.50 g, 2.38 mmol) in
methanol (80 ml) and the reaction mixture was refluxed for 12 h.
The resulting solution was reduced in volume to ꢂ10 ml and
allowed to cool to room temperature. Green crystalline precipitate
was filtered off and dried in the air. Yield 70%. X-ray quality
crystals of [Re(p-NC6H4CH3)(hpb)2(PPh3)]Cl were obtained by slow
recrystallization from methanol.
[Re(p-NC6H4CH3)Cl3(PPh3)2] (0.50 g, 0.54 mmol) was added to
2-(2-hydroxyphenyl)-1H-benzimidazole (0.12 g, 0.57 mmol) in
acetonitrile (80 ml) and the reaction mixture was refluxed for
6 h. The resulting solution was reduced in volume to ꢂ10 ml and
allowed to cool to room temperature. A green crystalline precipi-
tate was filtered off and dried in the air. Yield 80%. X-ray quality
crystals of trans-[Re(p-NC6H4CH3)Cl2(hpb)(PPh3)] were obtained
by slow recrystallization from an acetonitrile.
Anal. Calc. for C51H40N5O2PClRe: C, 60.80; H, 4.00; N, 6.95.
Found: C, 60.46; H, 3.92; N, 6.89%.
Table 1
Crystal data and structure refinement for 1, 2, 3 and 4.
1
2
3
4
Empirical formula
Formula weight
Temperature
Wavelength (Å)
Crystal system
Space group
C
38H31Cl2N3OPRe
C38H31Br2N3OPRe
922.65
293.0(2)
0.71073
monoclinic
P21/n
C51H40N5O2PClRe
1007.50
293.0(2)
0.71073
orthorhombic
Pna21
C51H40BrN5O2PRe
1051.96
293.0(2)
0.71073
orthorhombic
Pna21
833.73
293.0(2)
0.71073
orthorhombic
Pbca
Unit cell dimensions (Å), (°)
a (Å)
b (Å)
11.095(2)
17.170(3)
10.096(2)
15.682(3)
b = 96.71(3)°
21.653(4)
3404.6(12)
4
1.800
5.999
1792
21.254(4)
10.124(2)
21.220(4)
10.136(2)
c (Å)
V (Å)
35.531(7)
6769(2)
8
1.636
3.831
20.177(4)
4341.3(15)
4
1.541
2.945
20.196(4)
4344.0(15)
4
1.608
3.802
Z
Dcalc (mg/m3)
Absorption coefficient (mmꢁ1
F(0 0 0)
)
3296
2016
2088
Crystal size (mm)
h Range for data collection (°)
Index ranges
0.032 ꢃ 0.060 ꢃ 0.112
3.30–25.00
ꢁ13 6 h 6 13
ꢁ20 6 k 6 20
ꢁ42 6 l 6 38
34541
0.031 ꢃ 0.136 ꢃ 0.260
0.072 ꢃ 0.218 ꢃ 0.520
3.51–25.00
ꢁ25 6 h 6 22
ꢁ12 6 k 6 11
ꢁ23 6 l 6 18
19985
0.157ꢃ0.288 ꢃ 0.588
3.43–25.05
ꢁ25 6 h 6 25
ꢁ12 6 k 6 12
ꢁ24 6 l 6 23
20767
3.50
ꢁ12 6 h 6 12
ꢁ18 6 k 6 18
ꢁ25 6 l 6 24
31635
Reflections collected
Independent reflections
Completeness to 2h = 25°
Minimum and maximum transmission
Data/restraints/parameters
Goodness-of-fit on F2
5949 (Rint = 0.0404)
99.8%
0.546 and 1.000
5949/0/416
1.066
5965 (Rint = 0.0492)
99.7%
0.126 and 1.000
5965/0/416
1.037
6794 (Rint = 0.0528)
99.7%
0.316 and 1.000
6794/1/551
1.021
7572 (Rint = 0.0403)
99.6%
0.426 and 1.000
7572/1/551
1.015
Final R indices [I > 2
r
(I)]
R1 = 0.0285
wR2 = 0.0488
R1 = 0.0442
wR2 = 0.0515
R1 = 0.0314
wR2 = 0.0583
R1 = 0.0526
wR2 = 0.0630
R1 = 0.0376
wR2 = 0.0961
R1 = 0.0482
wR2 = 0.1000
0.018(9)
R1 = 0.0405
wR2 = 0.1212
R1 = 0.0475
wR2 = 0.1237
0.006(10)
R indices (all data)
Absolute structure parameter
Largest difference in peak and hole [e Åꢁ3
]
0.581 and ꢁ1.255
0.872 and ꢁ0.718
1.494 and ꢁ1.060
0.923 and ꢁ2.292
*
H.D. Flack, Acta Crystallogr., Sect. A 39 (1983) 876.

144
B. Machura et al. / Polyhedron 30 (2011) 142–153
1H NMR (400 MHz; DMSO-d6) d = 13.70 (2H, N–H), 8.07 (t, 3H),
7.85–7.70(m, 9H), 7.51–7.41 (m, 14H), 7.40–7.28 (m, 2H), 7.22–
7.04 (m, 5H), 6.96 (t, 1H), 5.98 (d, 1H), 2.21 (s, 3H).
in a closed-shell singlet (S = 1) states without any symmetry
restrictions with the DFT method using the hybrid B3LYP func-
tional of GAUSSIAN-03 [19–21]. The calculations were performed
using ECP LANL2DZ basis set [22] with an additional d and f
function with the exponent
a = 0.3811 and a = 2.033 [23] for
2.5. Preparation of [Re(p-NC6H4CH3)(hpb)2(PPh3)]Br (4)
rhenium and the standard 6-31G basis set for other atoms. For
chlorine, oxygen, nitrogen and phosphorous atoms, diffuse and
polarization functions were added [24–29]. All vibrations in the
calculated vibrational spectra of [Re(p-NC6H4CH3)Cl2(hpb)(PPh3)]
and [Re(p-NC6H4CH3)(hpb)2(PPh3)]+ were real thus the geometries
correspond to true energy minima.
The electronic spectra of [Re(p-NC6H4CH3)Cl2(hpb)(PPh3)] and
[Re(p-NC6H4CH3)(hpb)2(PPh3)]+ were calculated with the TDDFT
method [30], and the solvent effect was simulated using the
polarizable continuum model with the integral equation formalism
(IEF-PCM) [31–34].
A procedure similar to that for 3 was used with [Re(p-
NC6H4CH3)Br3(PPh3)2] (0.50 g, 0.47 mmol) and Hhpb (0.50 g,
2.38 mmol). Green crystals of 2 were collected in 75%.
Anal. Calc. for C51H40N5O2PBrRe: C, 58.23; H, 3.83; N, 6.66.
Found: C, 58.39; H, 3.76; N, 6.74%. 1H NMR (400 MHz; DMSO-d6)
d = 13.72 (2H, N–H), 8.07 (t, 3H), 7.90–7.70(m, 9H), 7.71–7.43 (m,
14H), 7.41–7.27 (m, 2H), 7.27–7.00 (m, 5H), 6.96 (t, 1H), 5.98 (d,
1H), 2.21 (s, 3H).
UV–Vis of 4 (CH3CN; kmax [nm] (e
; [dm3 molꢁ1 cmꢁ1]): 604.2
(515), 370.0 (2270), 313.0 (2125), 295.0 (8920), 202.2 (38150).
Natural bond orbital (NBO) calculations were performed with
the NBO code [35] included in Gaussian03.
2.6. Crystal structures determination and refinement
The X-ray intensity data of 1, 2, 3 and 4 were collected on a
Gemini A Ultra diffractometer equipped with Atlas CCD detector
4. Results and discussion
and graphite monochromated Mo K
a radiation (k = 0.71073 Å)
4.1. Preparation
at room temperature. Details concerning crystal data and refine-
ment are given in Table 1. Lorentz, polarization and empirical
absorption correction using spherical harmonics implemented in
The imido complexes [Re(p-NC6H4CH3)X2(hpb)(PPh3)] (X = Cl,
Br) were prepared in good yield by a route analogous to that used
for the synthesis of the [ReOX2(hpb)(PPh3)2], namely by ligand
exchange reactions starting from the [Re(p-NC6H4CH3)X3(PPh3)2]
complexes and 2-(2-hydroxyphenyl)-1H-benzimidazole (Hhpb) in
molar ratio 1:1: the disubstituted imido compounds [Re(p-NC6H4-
CH3)(hpb)2(PPh3)]X have been isolated from the reactions of
[Re(p-NC6H4CH3)X2(hpb)(PPh3)] with an excess of Hhpb in metha-
nol (Scheme 2). Similar to the related oxocompounds methanol
favour formation of the disubstituted complexes.
SCALE
3 ABSPACK scaling algorithm [17] were applied. The structures
were solved by the Patterson method and subsequently com-
pleted by the difference Fourier recycling. All the non-hydrogen
atoms were refined anisotropically using full-matrix, least-
squares technique. The hydrogen atoms were treated as ‘‘riding’’
on their parent carbon atoms and assigned isotropic temperature
factors equal 1.2 (non-methyl) and 1.5 (methyl) times the value
of equivalent temperature factor of the parent atom. The methyl
groups were allowed to rotate about their local threefold axis.
SHELXS97 and SHELXL97 [18] programs were used for all the calcula-
tions. Atomic scattering factors were those incorporated in the
computer programs.
As the imido core NR2ꢁ is isoelectronic to the O2ꢁꢀ moiety, a
short comparison with the Re(V) oxocompounds deserves com-
ment. The complexes [Re(p-NC6H4CH3)X3(PPh3)2] are related to
the oxocompounds [ReOX3(PPh3)2], which have proven to be
useful precursors in the synthesis of Re(V) oxocompounds incorpo-
rating N,O-donor chelate ligands [13,36–39]. Our studies have
shown that the [Re(p-NC6H4CH3)X3(PPh3)2] compounds easily
react with 2-(2-hydroxyphenyl)-1H-benzimidazole to give mono-
substituted [Re(p-NC6H4CH3)X2(hpb)(PPh3)] complexes with trans-X,X
3. Computational details
The gas phase ground state geometries of [Re(p-NC6H4CH3)Cl2-
(hpb)(PPh3)] and [Re(p-NC6H4CH3)(hpb)2(PPh3)]+ were optimized
[Re(p-NC6H4CH3)X3(PPh3)]
+
+
Hhpb (excess)
in MeOH
Hhpb (1:1)
in MeCN
trans-[Re(p-NC6H4CH3)X2(hpb)(PPh3)]
[Re(p-NC6H4CH3)(hpb)2(PPh3)]X
Scheme 2.
[ReOX3(PPh3)]
+
+
Hhpb (excess)
in MeOH/MeCN
Hhpb (1:1)
in MeCN
cis-[ReOX2(hpb)(PPh3)]
and
[ReO(OMe)(hpb)2] MeCN
trans-[ReOX2(hpb)(PPh3)]
Scheme 3.

B. Machura et al. / Polyhedron 30 (2011) 142–153
145
arrangement of the halide ions and disubstituted [Re(p-NC6-
H4CH3)(hpb)2(PPh3)]X compounds. This contrasts with the ex-
change reactions performed with oxocompounds [ReOX3(PPh3)2].
The reactions of [ReOX3(PPh3)2] with 2-(2-hydroxyphenyl)-1H-
benzimidazole in molar ratio 1:1 yield a mixture of cis and trans
stereoisomers of [ReOX2(hpb)(PPh3)], whereas the reactions of
[ReOX3(PPh3)2] with an excess 2-(2-hydroxyphenyl)-1H-benzi-
midazole lead to [ReO(OMe)(hpb)2]ꢀMeCN [13] (Scheme 3).
confirmed for [ReCl2(APO)(PPh3)] and [ReOCl2(DPO)(PPh3)]-
(APOH = 4-anilino-3-penten-2-one; DPOH = 4-[2,6-dimethylanili-
no]-3-penten-2-one) [39]. A mixture of cis and trans stereoisomers
[ReOX2(N–O)(PPh3)] was also isolated from the reactions of
[ReOX3(PPh3)2] with 2-(20-hydroxyphenyl)-2-benzothiazole, but
cis-halide isomer [ReOX2(N–O)(PPh3)] was a main product in these
reactions [38]. The imido rhenium complexes incorporating uni-
negative N,O-donor chelate ligands have been studied rarely
[40,41]. However, the trans-X,X arrangement of halide ions seems
to be favoured in the [Re(NAr)X2(N–O)(PPh3)] compounds, proba-
bly due to presence of more bulky imido ligand.
The majority of the known [ReOX2(O–N)(PPh3)] structures has
halide ligands in cis geometry. The trans-X,X conformation is far
more rarely in this type of complexes, and it has been previously
Fig. 1. The experimental and calculated (non-scaled) vibrational spectra of 1.
Fig. 2. The experimental and calculated (non-scaled) vibrational spectra of 3.

146
B. Machura et al. / Polyhedron 30 (2011) 142–153
Table 2
Short intra- and intermolecular contacts detected in 1, 2, 3 and 4 complexes.
D–Hꢀ ꢀ ꢀA
D–H [Å]
Hꢀ ꢀ ꢀA [Å]
Dꢀ ꢀ ꢀA [Å]
D–Hꢀ ꢀ ꢀA [°]
1
N(3)–H(3N)ꢀ ꢀ ꢀCl(2)_$1
C(2)–H(2)ꢀ ꢀ ꢀCl(2)
C(16)–H(16)ꢀ ꢀ ꢀCl(1)_$2
0.86
0.93
0.93
2.41
2.63
2.83
3.177(3)
3.354(4)
3.499(5)
149.2
135.1
130.2
2
N(3)–H(3N)ꢀ ꢀ ꢀBr(1)#3
C(27)–H(27)ꢀ ꢀ ꢀN(1)
C(38)–H(38)ꢀ ꢀ ꢀN(3)
0.86
0.93
0.93
2.59
2.48
2.59
3.370(4)
3.204(7)
2.899(7)
150.8
134.2
100.2
3
N(3)–H(3N)ꢀ ꢀ ꢀCl(1)_$4
N(5)–H(5N)ꢀ ꢀ ꢀCl(1)
C(8)–H(8)ꢀ ꢀ ꢀO(1)
C(8)–H(8)ꢀ ꢀ ꢀO(2)
C(17)–H(17)ꢀ ꢀ ꢀCl(1)_$5
C(27)–H(27)ꢀ ꢀ ꢀN(4)
C(38)–H(38)ꢀ ꢀ ꢀN(3)
C(40)–H(40)ꢀ ꢀ ꢀN(1)
C(51)–H(51)ꢀ ꢀ ꢀN(5)
0.86
0.86
0.93
0.93
0.93
0.93
0.93
0.93
0.93
2.29
2.23
2.43
2.52
2.73
2.48
2.55
2.52
2.62
3.092(7)
3.039(7)
156.2
156.2
119.6
135.8
154.4
123.3
99.9
3.000(10)
3.254(10)
3.590(10)
3.089(10)
2.862(12)
3.133(11)
2.919(11)
123.7
99.6
4
N(3)–H(3N)ꢀ ꢀ ꢀBr(1)_$6
N(5)–H(5N)ꢀ ꢀ ꢀBr(1)
C(11)–H(11)ꢀ ꢀ ꢀBr(1)_$7
C(14)–H(14)ꢀ ꢀ ꢀO(1)
C(14)–H(14)ꢀ ꢀ ꢀO(2)
C(27)–H(27)ꢀ ꢀ ꢀN(4)
C(40)–H(40)ꢀ ꢀ ꢀN(1)
C(51)–H(51)ꢀ ꢀ ꢀN(5)
0.86
0.86
0.93
0.93
0.93
0.93
0.93
0.93
2.27
2.23
2.71
2.41
2.52
2.51
2.53
2.58
3.073(7)
3.024(8)
155.9
153.6
156.3
120.3
135.8
120.6
123.2
100.1
3.578(11)
2.992(11)
3.256(11)
3.092(11)
3.134(12)
2.889(12)
Fig. 3. The molecular structure of 1. Displacement ellipsoids are drawn at 50%
probability.
Symmetry transformations used to generate equivalent atoms: #1: 1 ꢁ x, ꢁy, ꢁz;
#2: 1/2 ꢁ x, ꢁ1/2 + y, z; #3: 1 ꢁ x, ꢁy, 2 ꢁ z; #4: ꢁ1/2 + x, 1/2 ꢁ y, z; #5: 1 ꢁ x, ꢁy,
ꢁ1/2 + z; #6: ꢁ1/2 + x, 3/2 ꢁ y, z; #7: 1 ꢁ x, 2 ꢁ y, ꢁ1/2 + z.
1
4.2. IR spectra and H NMR
Characteristic bands corresponding to the m(CN), m(C@C) modes
of the hpbꢁ ligand appear in the range 1630–1530 cmꢁ1, and a
band in the range 3450–3200 cmꢁ1 confirms the presence N–H
group in the coordinated hpbꢁ ligand of the examined complexes
[42]. Similar to the other related imido complexes it is extremely
difficult to identify the Re-NC6H4CH3 stretches in the IR spectra
of 1, 2, 3 and 4, as they may be mixed with mC
@ and mP–C modes
N
of PPh3 and hpbꢁ ligands [43–50].
The experimental vibrational spectra of 1 and 3 are compared to
the calculated (non-scaled) ones (Figs. 1 and 2). The calculated
m
(Re-NC6H4CH3) frequencies appear at 1402, 1044 and
1026 cmꢁ1 for 1 and 1407, 1043 and 1024 cmꢁ1 for 3.
In the 1H NMR spectra of 1, 2, 3 and 4 the region containing sig-
nals from aromatic protons of triphenylphosphine, p-tolylimido
and hpbꢁ ligands (8.10–5.50 ppm) is accompanied by distinctive
signals corresponding the alkyl protons of the p-tolylimido ion
(2.25–2.10 ppm) and N–H protons (13.85–13.65 ppm). Owing to
the overlapping of the signals of the aromatic protons of the tri-
phenylphosphine, p-tolylimido and hpbꢁ, the aromatic region of
the 1H NMR spectra of 1, 2, 3 and 4 is difficult to identify.
The lack of paramagnetic broadening or shifts of resonances in
the 1H NMR spectra of [Re(p-NC6H4CH3)X2(hpb)(PPh3)] and
[Re(p-NC6H4CH3)(hpb)2(PPh3)]Xꢀ(X = Cl, Br) confirms diamagne-
tism of the complexes.
Fig. 4. The molecular structure of 3. Displacement ellipsoids are drawn at 50%
probability. Hydrogen atoms are omitted for clarity.
molecules into dimers, whereas the complex molecules of 3 and
4 are linked into zig-zag chains by N–Hꢀ ꢀ ꢀX hydrogen bonds. Addi-
tionally, in all the structures exist short C–Hꢀ ꢀ ꢀO, C–Hꢀ ꢀ ꢀN and C–
Hꢀ ꢀ ꢀX interactions, which can be considered as weak or very weak
hydrogen bonds [51,52].
The molecular structures of 1 and 3 are shown in Figs. 3 and 4,
respectively. The selected bond lengths and angles of 1, 2, 3 and 4
are collected in Tables 3–6.
4.4. [Re(p-NC6H4CH3)X2(hpb)(PPh3)] complexes
4.3. Crystal structures
The complexes [Re(p-NC6H4CH3)X2(hpb)(PPh3)] (X = Cl, Br)
show octahedral geometry about the central rhenium atom de-
fined by the p-methylphenylimido group, two halide ions, the
phosphorus atom of PPh3 molecule, and the bidentate N,O atom
donors of the hpbꢁ ligand. The ligands cis to the p-methylpheny-
limido group are bowed slightly away from p-NC6H4CH3 moiety
The crystallographic data of 1, 2, 3 and 4 are summarized in Ta-
ble 1. The intra- and intermolecular contacts detected in the 1, 2, 3
and 4 are listed in Table 2. In all the structures the pyrrole-type
nitrogen (N–H) is involved in hydrogen bond formation. The med-
ium strength N–Hꢀ ꢀ ꢀX hydrogen bonds of 1 and 2 links complex

B. Machura et al. / Polyhedron 30 (2011) 142–153
147
Table 3
The experimental and optimized bond lengths (Å) and angles (°) for 1.
Table 6
The experimental bond lengths (Å) and angles (°) for 4.
Bond
lengths
Experimental Opti- Bond
mized angles
Experi-
mental
Opti-
mized
Bond lengths
Experimental
Bond angles
Experimental
Re(1)–N(1)
Re(1)–O(2)
Re(1)–O(1)
Re(1)–N(4)
Re(1)–N(2)
Re(1)–P(1)
1.735(6)
1.995(6)
2.023(6)
2.116(7)
2.138(7)
2.459(2)
N(1)–Re(1)–O(2)
N(1)–Re(1)–O(1)
O(2)–Re(1)–O(1)
N(1)–Re(1)–N(4)
O(2)–Re(1)–N(4)
O(1)–Re(1)–N(4)
N(1)–Re(1)–N(2)
O(2)–Re(1)–N(2)
O(1)–Re(1)–N(2)
N(4)–Re(1)–N(2)
N(1)–Re(1)–P(1)
O(2)–Re(1)–P(1)
O(1)–Re(1)–P(1)
N(4)–Re(1)–P(1)
N(2)–Re(1)–P(1)
Re(1)–N(1)–C(19)
174.2(3)
94.7(3)
87.0(2)
96.2(3)
82.5(2)
168.6(2)
98.8(3)
86.9(2)
86.4(2)
88.7(3)
Re(1)–N(1) 1.731(3)
Re(1)–O(1) 1.970(3)
Re(1)–N(2) 2.145(3)
Re(1)–Cl(1) 2.3747(10)
Re(1)–P(1) 2.4477(11)
Re(1)–Cl(2) 2.4747(10)
1.733 N(1)–Re(1)–O(1) 169.34(13) 170.18
2.008 N(1)–Re(1)–N(2) 95.81(13)
2.139 O(1)–Re(1)–N(2) 80.80(11)
2.472 N(1)–Re(1)–Cl(1) 100.12(11) 100.33
2.508 O(1)–Re(1)–Cl(1) 89.90(8)
2.521 N(2)–Re(1)–Cl(1) 87.96(9)
101.01
81.71
89.22
86.61
91.87
85.79
167.07
89.95
88.36
82.43
85.27
169.10
96.38
166.30
N(1)–Re(1)–P(1)
O(1)–Re(1)–P(1)
N(2)–Re(1)–P(1)
Cl(1)–Re(1)–P(1) 87.94(4)
N(1)–Re(1)–Cl(2) 88.91(11)
O(1)–Re(1)–Cl(2) 80.92(8)
N(2)–Re(1)–Cl(2) 88.29(9)
Cl(1)–Re(1)–Cl(2) 170.53(4)
P(1)–Re(1)–Cl(2) 93.87(4)
Re(1)–N(1)–C(19) 164.6(3)
96.79(11)
87.13(8)
167.26(8)
89.8(2)
84.66(17)
88.17(17)
95.18(18)
170.13(19)
173.3(6)
to some extent due to accessible p-donation from rhenium to tri-
Table 4
The experimental bond lengths (Å) and angles (°) for 2.
phenylphosphine molecule. The multiple bonding imido ligand
and narrow bite angle of the chelating ligand contribute to clear
distortions of the pseudooctahedral environment of Re center in
the [Re(p-NC6H4CH3)X2(hpb)(PPh3)] complexes. In 1 and 2 the
Re(1) atom is displaced respectively 0.2187(9), 0.1850(10) Å from
the plane formed by the two halogen, one nitrogen and one phos-
phorous atoms (plane A), 0.0544(1), 0.0363(12) Å from the plane
formed the two halogen, one nitrogen and one oxygen atoms
(plane B) and 0.0506(14), 0.0037(19) Å from the plane formed by
two nitrogen, one oxygen and one phosphorous atoms (plane C).
Least squares plane A is inclined at 89.00(7)°, 86.38(7)° to plane
B and at 89.56(6)°, 89.29(8)°, to plane C; planes B and C are inclined
at 88.19(5)°, 88.67(7)° respectively as above.
The Re(1)–N(1)–C(19) bond angle in the structures [Re(p-
NC6H4CH3)X2(hpb)(PPh3)] (164.6(3)° for 1 and 174.30(34)° for
2) agrees with the linear coordination mode of the arylimido li-
gands, ant it reaches a smaller value for the chloride compound.
The Re–N(1) bond lengths of [Re(p-NC6H4CH3)X2(hpb)(PPh3)]
(1.731(3) Å for 1 and 1.713(4) Å for 2) fall in the range 1.67–
1.74 Å typical of mononuclear complexes of rhenium(V) having
[Re„NR]3+ core, and confirm the presence of a triple bond
Re„N [43–50]. The interatomic distances between the rhenium
atom and the oxygen atom of hpbꢁ ligand in 1 and 2 structures
are somewhat shorter than an ideal single Re–O bond length (ca.
2.04 Å) [53], indicating small delocalization in the RN„Re–O
unit.
Bond lengths
Experimental
Bond angles
Experimental
Re(1)–N(1)
Re(1)–O(1)
Re(1)–N(2)
Re(1)–P(1)
Re(1)–Br(2)
Re(1)–Br(1)
1.713(4)
1.968(3)
2.146(4)
2.4408(12)
2.5696(9)
2.5782(9)
N(1)–Re(1)–O(1)
N(1)–Re(1)–N(2)
O(1)–Re(1)–N(2)
N(1)–Re(1)–P(1)
O(1)–Re(1)–P(1)
N(2)–Re(1)–P(1)
N(1)–Re(1)–Br(2)
O(1)–Re(1)–Br(2)
N(2)–Re(1)–Br(2)
P(1)–Re(1)–Br(2)
N(1)–Re(1)–Br(1)
O(1)–Re(1)–Br(1)
N(2)–Re(1)–Br(1)
P(1)–Re(1)–Br(1)
Br(2)–Re(1)–Br(1)
Re(1)–N(1)–C(19)
173.37(15)
103.65(15)
82.11(14)
89.07(12)
85.30(10)
167.12(11)
90.86(13)
86.26(13)
85.89(12)
96.05(4)
95.32(13)
88.29(13)
85.82(12)
91.08(4)
170.64(2)
174.30(34)
Table 5
The selected experimental and optimized bond lengths (Å) and angles (°) for 3.
Bond
lengths
Experi-
mental
Opti-
mized
Bond angles
Experi-
mental
Opti-
mized
Re(1)–N(1)
Re(1)–O(2)
Re(1)–O(1)
Re(1)–N(4)
Re(1)–N(2)
Re(1)–P(1)
1.742(6)
1.997(5)
2.036(5)
2.121(6)
2.144(6)
2.460(2)
1.733
2.028
2.042
2.176
2.161
2.544
N(1)–Re(1)–O(2)
N(1)–Re(1)–O(1)
O(2)–Re(1)–O(1)
N(1)–Re(1)–N(4)
O(2)–Re(1)–N(4)
O(1)–Re(1)–N(4)
N(1)–Re(1)–N(2)
O(2)–Re(1)–N(2)
O(1)–Re(1)–N(2)
N(4)–Re(1)–N(2)
N(1)–Re(1)–P(1)
O(2)–Re(1)–P(1)
O(1)–Re(1)–P(1)
N(4)–Re(1)–P(1)
N(2)–Re(1)–P(1)
173.8(3)
95.1(2)
173.66
97.05
87.62
94.67
80.71
168.28
99.72
84.89
85.30
92.55
89.67
86.44
85.24
95.04
167.42
177.34
86.7(2)
96.7(3)
82.0(2)
The Re–P and Re–Cl bond distances fall within the normal range
in six-coordinate rhenium complexes [54].
167.7(2)
98.1(3)
4.5. [Re(p-NC6H4CH3)(hpb)2(PPh3)]X complexes
87.9(2)
85.6(2)
89.2(2)
90.1(2)
The asymmetric unit of
3 and 4 contains the cation
[Re(p-NC6H4CH3)(hpb)2(PPh3)]+ and halide ion. The cation
84.05(16)
88.71(15)
94.83(17)
170.45(16)
Table 7
Atomic charges from the Natural Population Analysis (NPA) for 1 and 3.
Re(1)–N(1)–C(19) 172.0(6)
Complex
1
3
Re(1)
O(1)
O(2)
Cl(1)
Cl(2)
P(1)
N(1)
N(2)
N(4)
0.785
ꢁ0.690
0.517
ꢁ0.637
to minimize steric congestion around the rhenium atom. The ha-
lide ions of [Re(p-NC6H4CH3)X2(hpb)(PPh3)] are arranged in trans
geometry. The oxygen atom of hbpꢁ chalate ligand occupies trans
position to the 4-methylphenylimido ion, and the triphenylphos-
ꢁ0.633
ꢁ0.469
ꢁ0.511
1.413
1.502
ꢁ0.334
ꢁ0.260
ꢁ0.486
ꢁ0.495
phine molecule with their
p-acidity adopts cis position with
ꢁ0.524
respect to the almost linear RN„Re–O unit. Consequently, the
RN„Re–O core with multiply bonded imido ligand is stabilized

148
B. Machura et al. / Polyhedron 30 (2011) 142–153
[Re(p-NC6H4CH3)(hpb)2(PPh3)]+ has a distorted octahedral configu-
ration with two bidentate hbpꢁ ligands, p-methylphenylimido
group and triphenylphosphine molecule. Likewise in 1 and 2, the
cis-location of PPh3 molecule in relation to the linear RN„Re–O
unit in [Re(p-NC6H4CH3)(hpb)2(PPh3)]+ is governed by electronic
influence of the multiply bonded ligand, which forces the metal
nonbonding d electrons to lie in the plane perpendicular to the
Re„NR bond axis. In 3 and 4 the Re(1) atom is displaced respec-
tively 0.0107(30), 0.0109(31) Å from the plane formed by the
two oxygen and two nitrogen atoms (plane A), 0.1862(26),
0.1824(29) Å from the plane formed the two nitrogen, one phos-
phorous and one oxygen atoms (plane B) and 0.0375(26),
0.0360(28) Å from the plane formed by two nitrogen, one oxygen
and one phosphorous atoms (plane C). Least squares plane A is
π*(PPh3), dz2
π*(PPh3)
L+6
L+5
L+4
-1.00
-2.00
-3.00
-4.00
-5.00
-6.00
-7.00
2
2
dx
L+3
-y
π*(hpb), dxy
L+2
dxz, π*(p-tol), π*(hpb),
dxz, π*(p-tol)
L+1
LUMO
d
xy, π(Cl)
HOMO
H-1
π(hpb)
(hpb)
H-2
H-3
H-4
(hpb), π(p-tol), dxz, π(Cl)
π(hpb), π(p-tol), dxy, π(Cl), (PPh3)
Fig. 5. The energy (eV), character and some contours of the unoccupied molecular orbitals of [Re(p-NC6H4CH3)Cl2(hpb)(PPh3)]. Positive values of the orbital contour are
represented in blue (0.04 au) and negative values – in yellow (ꢁ0.04 au). (For interpretation of the references to colour in this figure legend, the reader is referred to the web
version of this article.)

B. Machura et al. / Polyhedron 30 (2011) 142–153
149
inclined at 89.30(12)°, 88.72(13)° to plane B and at 89.10(15)°,
88.58(16)°, to plane C; planes B and C are inclined at 88.26(13)°,
88.39(14)° respectively as above.
bond in trans position to the benzimidazole, indicating small delo-
calization in the RN„Re–O unit.
Similar to the [Re(p-NC6H4CH3)X2(hpb)(PPh3)] complexes, the
Re(1)–N(1)–C(19) bond angles in the structures [Re(p-
NC6H4CH3)(hpb)2(PPh3)]X (172.0(6)° for 3 and 173.3(6)° for 4)
agree with the linear coordination mode of the arylimido ligands,
and the Re–N(1) bond lengths (1.742(6) Å for 3 and 1.735(6) Å
for 4) fall in the range typical of mononuclear complexes of rhe-
nium(V) having [Re„NR]3+ core [43–50].
For both complexes the interatomic distance between the rhe-
nium atom and the oxygen atom of hpbꢁ in trans position to the
p-methylphenylimido anion is somewhat shorter than the Re–O
4.6. Geometry optimisations, charge distributions, electronic structures
and NBO analyses
To get an insight in the electronic structures and bonding prop-
erties of the complex [Re(p-NC6H4CH3)Cl2(hpb)(PPh3)] and the
cation [Re(p-NC6H4CH3)(hpb)2(PPh3)]+, the calculations in the
DFT method were carried out. Before the calculations of the
electronic structures of the studied compounds, their geometries
were optimized in singlet states using the DFT method with
the B3LYP functional. The optimized geometric parameters of
π*(PPh3)
L+6
L+5
-1.00
2
2
π*(PPh3), dx
;
-y
L+4
π*(hpb)
L+3
L+2
-2.00
-3.00
-4.00
-5.00
-6.00
-7.00
dxz, π*(p-tol), π*(hpb)
dxz, π*(p-tol), π*(hpb)
L+1
LUMO
dxy,
π(hpb)
HOMO
π(hpb)
H-1
H-2
π(hpb), dxy,
(hpb), π(p-tol), dyz
π(hpb)
H-3
H-4
Fig. 6. The energy (eV), character and some contours of the unoccupied molecular orbitals of [Re(p-NC6H4CH3)(hpb)2(PPh3)]+. Positive values of the orbital contour are
represented in blue (0.04 au) and negative values – in yellow (ꢁ0.04 au). (For interpretation of the references to colour in this figure legend, the reader is referred to the web
version of this article.)

150
B. Machura et al. / Polyhedron 30 (2011) 142–153
Table 8
The occupancy and composition of the calculated natural bond orbitals (NBOs) between the rhenium and the p-tolylimido ligand for [Re(p-NC6H4CH3)Cl2(hpb)(PPh3)] and [Re(p-
NC6H4CH3)(hpb)2(PPh3)]+.
BD
Occupancy
Composition of NBO
0.488 (sp0.01d3.11 Re + 0.873 (sp0.81
0.608 (d)Re + 0.794 (p)N
0.663 (d)Re + 0.748 (p)N
BDa
Occupancy
[Re(p-NC6H4CH3)Cl2(hpb)(PPh3)]
Re–N(p-tol)
Re–N(p-tol)
Re–N(p-tol)
[Re(p-NC6H4CH3)(hpb)2(PPh3)]+
1.96
1.96
1.92
)
)
N
0.873 (sp0.01d3.11
)
Re ꢁ 0.488 (sp0.81
)
N
0.30
0.29
0.28
0.779 (d)Re ꢁ 0.627 (p)N
0.748 (d)Re ꢁ 0.664 (p)N
Re–N(p-tol)
Re–N(p-tol)
1.97
1.92
0.623 (d)Re + 0.783 (p)O
0.655 (d)Re + 0.755 (p)O
0.783 (d)Re ꢁ 0.623 (p)O
0.755 (d)Re ꢁ 0.655 (p)O
0.20
0.32
BD denotes 2-center bond.
a
Denotes antibond NBO.
1.60
Table 9
Stabilization energies associated with delocalisation from the nitrogen imido lone
pair orbital of [Re(p-NC6H4CH3)(hpb)2(PPh3)]+.
Donor orbital
(sp1.25
Occupancy of
donor orbital
Acceptor orbital
*
DEij [kcal/mol]
1.20
0.80
0.40
0.00
)
N1
1.516
LP (2)Re1 [(d)Re
]
269.52
99.01
LP (3)Re1 [(sp0.30d0.51
) ]
Re
*
[Re(p-NC6H4CH3)Cl2(hpb)(PPh3)] and [Re(p-NC6H4CH3)(hpb)2(PPh3)]+
are given in Tables 3 and 5. In general, the predicted bond lengths
and angles are in agreement with the values based upon the X-ray
crystal structure data, and the general trends observed in the
experimental data are well reproduced in the calculations. The
largest differences are found for the Re–Cl and Re–P bond dis-
tances. It may come from the basis sets which are approximated
to a certain extent or may indicate the influence of the crystal
packing on the values of the experimental bond lengths. The theo-
retical calculations do not consider the effects of chemical
environment.
400.00
800.00
Fig. 7. The experimental (black) and calculated (red) electronic absorption spectra
of 1. (For interpretation of the references to colour in this figure legend, the reader is
referred to the web version of this article.)
Table 7 presents the atomic charges from the Natural Popula-
tion Analysis (NPA) for 1 and 3. The calculated charge on the Re
atom in the disubstituted complex is less positive in comparison
with the mono-substituted one. However, the both values are con-
siderable lower than the formal charge +5. The populations of the
dxy, dxz, dyz, d2 ꢁ y2 and dz2 rhenium orbitals are following: 1.039,
x
1.889, 0.951, 0.941 and 0.969 for 1 and 1.296, 1.471, 0.824, 1.070
and 0.915 for 3. This data suggest that the donation from ligands
to dRe orbitals plays a key role in the electronic structure of the
examined complexes. There are large positive charges on the P
atoms, and the charges on the chloride and oxygen atom of hpbꢁ
are significantly smaller than ꢁ1.
The [Re(p-NC6H4CH3)Cl2(hpb)(PPh3)] and the cation [Re(p-
NC6H4CH3)(hpb)2(PPh3)]+ are closed-shell structures. Their partial
molecular orbital diagrams with the several highest occupied and
lowest unoccupied molecular orbital contours are presented in
Figs. 5 and 6, respectively.
The highest occupied MO of [Re(p-NC6H4CH3)Cl2(hpb)(PPh3)] is
comprised of rhenium dxy and porbitals of chloride ions in antibond-
ing arrangement. The remaining four d-type orbitals of rhenium are
found among unoccupied MOs. It confirms d2 configuration of the
rhenium atoms in the [Re(p-NC6H4CH3)X2(hpb)(PPh3)] complexes.
The LUMO and LUMO + 1 are predominately localized on the rhe-
nium atom (dxz and dyz orbitals) with significant contribution of
the p nitrogen orbitals of the imido ligand. To large extent these
p
*
orbitals can be ascribed as
p
Re„NR orbitals. The rhenium–nitrogen
interaction in 1 can be described as a triple bond. Assuming that rhe-
nium uses its six valence orbitals, 5d2x ꢁ y2, 5dz2, 6s, 6px, 6py and 6pz to
form
r-bonds with the six ligands, empty 5dxz and 5dyz orbitals are
Fig. 8. The experimental (black) and calculated (red) electronic absorption spectra
of 3. (For interpretation of the references to colour in this figure legend, the reader is
referred to the web version of this article.)
available to overlap with 2px and 2py orbitals on the imido nitrogen
to form an effective triple bond as -anti-bonding rhenium–imido
p

B. Machura et al. / Polyhedron 30 (2011) 142–153
151
molecular orbitals. The dx2 ꢁ y2 and d2z rhenium orbital contributes to
the LUMO + 3 and LUMO + 6, respectively. The value of the energy
separation between the highest occupied molecular orbital and
the lowest unoccupied molecular orbital equals to 3.09 eV.
stabilization energy
is estimated by the second-order perturbative as:
D
Eij (kcal/mol) associated with delocalization
2
D
Eij ¼ qjðFði; jÞ Þ=ðej
ꢁ
ei
Þ
ð3Þ
The highest occupied MO of the cation [Re(p-NC6H4CH3)-
where qi is the donor orbital occupancy, ei
(orbital energies) and F(i,j) is the off-diagonal NBO Fock matrix
element [55].
For complex [Re(p-NC6H4CH3)Cl2(hpb)(PPh3)] three Re–NR
natural bond orbitals were detected. The Re–N bond orbital of
,
e
j are diagonal elements
(hpb)2(PPh3)]+ is comprised of rhenium dxy and
p
orbitals of hpbꢁ
ligands. Similar to the monosubstituted complex, the LUMO and
LUMO + 1 can be ascribed as -anti-bonding rhenium–imido
molecular orbitals. Among the lowest unoccupied MOs of[Re(p-
p
NC6H4CH3)(hpb)2(PPh3)]+, the largest numbers constitute
p orbitals
r
-character is strongly polarized towards the nitrogen atom, and
the s and p nitrogen orbitals and s and d rhenium orbitals take part
in the bond formation. The Re–N bond orbitals of -character are
of the hpbꢁ and PPh3ligand. The dx2 ꢁ y2 and d2z rhenium orbital con-
tributes to the higher unoccupied MO. The HOMO–LUMO gap of
[Re(p-NC6H4CH3)(hpb)2(PPh3)]+ is equal to 2.93 eV.
p
results of overlapping of the empty dxy and dyz rhenium orbitals
with the occupied px and pz orbitals of the deprotonated nitrogen
of the imido ligand. For the cation [Re(p-NC6H4CH3)(hpb)2(PPh3)]+
only two Re–NR natural bond orbitals were confirmed by NBO
analysis. As the detected natural Re–N bond orbitals of [Re(p-
NC6H4CH3)(hpb)2(PPh3)]+ are composed of the p oxygen and d rhe-
The nature of the rhenium–imido ligand interaction in [Re(p-
NC6H4CH3)Cl2(hpb)(PPh3)] and [Re(p-NC6H4CH3)(hpb)2(PPh3)]+
has been also studied by NBO analysis. The occupancy and compo-
sition of the calculated Re–NR natural bond orbitals (NBOs) are
given in Table 8. Each natural bond orbital (NBO)
rAB can be writ-
ten in terms of two directed valence hybrids (NHOs) hA and hB on
atoms A and B:
nium orbitals, it can be assumed that both are of
p character. Not
detected Re–N bond has predominantly ionic character, similar as
r
Re–N bond orbital in [ReCl4(MeCN)2] [56]. Strong delocalization of
the lone pair localized on the imido nitrogen atom into non-Lewis
rhenium orbitals (Table 9) confirms this interpretation.
rAB ¼ cAhA þ cAhB
ð1Þ
where cA and cB are polarization coefficients. Each valence bonding
NBO must in turn be paired with a corresponding valence anti-
bonding NBO:
4.7. Electronic spectra
rꢄAB ¼ cBhA ꢁ cAhB
ð2Þ
The experimental and calculated electronic spectra of 1 and 3
are presented in Figs. 7 and 8, respectively. Each calculated transi-
2
to complete the span of the valence space. The Lewis-type (donor)
NBOs are thereby complemented by the non-Lewis-type (acceptor)
NBOs that are formally empty in an idealized Lewis picture. The
interactions between ‘filled’ (donor) Lewis-type NBOs and ‘empty’
(acceptor) non-Lewis NBOs lead to loss of occupancy from the
localized NBOs of the idealized Lewis structure into the empty
non-Lewis orbitals, and they are referred to as ‘delocalization’
corrections to the zeroth-order natural Lewis structure. The
tion for 1 and 3 is represented by a gaussian function y ¼ ceꢁbx
with the height (c) equal to the oscillator strength and b equal to
0.04 nmꢁ2. The TD-DFT results obtained by using B3LYP in combi-
nation with the LANL2DZ basis set are in good agreement with the
experimental spectra.
Tables 10 and 11 present the most important electronic transi-
tions calculated with the TDDFT method assigned to the observed
absorption bands of 1 and 3, respectively. For the high energy part
Table 10
The energy and molar absorption coefficients of experimental absorption bands and the electronic transitions calculated with the TDDFT method for [Re(p-
NC6H4CH3)Cl2(hpb)(PPh3)].
The most important orbital excitations
Character
k [nm]
E [eV]
f
Experimental
K[nm](E [eV])e
H ? L
H ? L + 1
d/
p
(Cl) ? d/
(Cl) ? d/
p
*(p-tol)
670.2
564.6
476.7
425.8
389.5
364.2
355.3
351.8
350.7
339.7
333.9
1.85
2.20
2.60
2.91
3.18
3.40
3.49
3.52
3.54
3.65
3.71
0.0005
0.0003
0.0059
0.0010
0.0619
0.0708
0.0303
0.0348
0.1818
0.1576
0.0496
731.4 (1.70) 90
d/p
p*(p-tol)/p*(hpb)
H ꢁ 1 ? L
p
(hpb) ? d/
d/ (Cl) ? d
(hpb) ? d/
(hpb)/
(Cl) ?
(PPh3) ? d/
d/ (Cl) ? *(hpb)/d
(hpb)/ (p-tol)/ (PPh3)/
(hpb) ? d/ *(p-tol)/ *(hpb)
(hpb) ? *(hpb)/d
p
*(p-tol)
323.1 (3.84) 25500
H ? L + 3
p
H ꢁ 1 ? L + 1
p
p
p
*(p-tol)/p*(hpb)
H ꢁ 3 ? L
p
(p-tol)/
*(hpb)/d
*(p-tol)
p(Cl)/d ? d/p*(p-tol)
H ? L + 2
d/p
p
H ꢁ 5 ? L
p
p
H ? L + 2
p
p
H ꢁ 4 ? L
p
p
p
p
p
p
p
p
p
p
p
p
p
p
p
p
p
p
p
p
p(Cl)/d ? d/p*(p-tol)
H ꢁ 2 ? L + 1
H ꢁ 1 ? L + 2
H ꢁ 7 ? L
p
p
p
(PPh3) ? d/
(PPh3) ? d/
(PPh3) ? d/
(hpb) ? d
(hpb) ? d/
(hpb) ? d
(Cl)/
(p-tol)/
(hpb) ?
(hpb)/ (p-tol)/
(Cl) ? d/ *(p-tol)/
(Cl)/ (hpb)/d ? d/
(PPh3) ?
(PPh3) ?
(hpb)/
p
p
p
*(p-tol)
*(p-tol)
*(p-tol)/
328.3
315.3
312.1
311.1
308.7
3.78
3.93
3.97
3.99
4.02
0.0432
0.0390
0.1506
0.0451
0.3369
H ꢁ 8 ? L
294.7 (4.21) 31870
H ꢁ 5 ? L + 1
H ꢁ 1 ? L + 3
H ꢁ 2 ? L + 1
H ꢁ 1 ? L + 3
H ꢁ 12 ? L
H ꢁ 10 ? L
H ꢁ 2 ? L + 2
H ꢁ 3 ? L + 2
H ꢁ 15 ? L + 1
H ꢁ 18 ? L + 1
H ꢁ 5 ? L + 5
H ꢁ 8 ? L + 4
H ꢁ 4 ? L + 5
p
*(hpb)
p*(p-tol)/p
*(hpb)
p
(p-tol)/
(Cl) ? d/
(hpb)/d
(Cl)/d ?
*(hpb)
*(p-tol)/
p(hpb) ? d/
p
*(p-tol)
303.7
4.08
0.0519
p
p
*(p-tol)
p
277.2
273.0
247.9
230.3
229.9
225.3
4.47
4.54
5.00
5.38
5.39
5.50
0.1797
0.0516
0.0304
0.0376
0.0453
0.0388
p
p
p
*(hpb)/d
p
p
p
215.9 (5.74) 110110
p
p*(hpb)
p
p
*(PPh3)
*(PPh3)
p(p-tol)/
p(PPh3)/
p
(Cl)/d ? p*(PPh3)
e
– molar absorption coefficient [dm3 molꢁ1 cmꢁ1]; f – oscillator strength; H – highest occupied molecular orbital; L – lowest unoccupied molecular orbital.

152
B. Machura et al. / Polyhedron 30 (2011) 142–153
Table 11
The energy and molar absorption coefficients of experimental absorption bands and the electronic transitions calculated with the TDDFT method for [Re(p-
NC6H4CH3)(hpb)2(PPh3)]Cl.
The most important orbital excitations
Character
k [nm]
E [eV]
f
Experimental
K
[nm](E [eV])
e
H ? L
H ? L + 1
d/
d/
p
(hpb) ? d/
p
*(p-tol)
687.2
581.5
461.6
437.9
405.1
388.2
381.7
370.9
365.2
344.2
330.3
327.3
326.8
313.8
312.2
1.81
2.13
2.69
2.83
3.06
3.19
3.25
3.34
3.39
3.60
3.75
3.79
3.79
3.95
3.97
0.0042
0.0047
0.0249
0.1238
0.0201
0.0213
0.0838
0.1065
0.0765
0.0308
0.0566
0.0901
0.2371
0.0308
0.0422
585.8 (2.12) 500
p(hpb) ? d/
p
*(p-tol)/p*(hpbi)
H ꢁ 1 ? L
p
p
p
(hpb) ? d/
(hpb)/d ? d/
(hpb) ? d/
p*(p-tol)
330.8 (3.75) 5100
H ꢁ 2 ? L
p
*(p-tol)
H ꢁ 1 ? L + 1
H ? L + 2
p*(p-tol)/
p*(hpb)
p*(hpb)
p*(hpbi)
d/
d/
p
p
(hpb) ?
(hpb) ?
H ? L + 3
H ꢁ 3 ? L
p
p
p
p
p
p
(hpb)/
(hpb) ? d/
(PPh3)/ (hpb) ? d/
(p-tol)/ (PPh3)/ (hpb) ? d/
(hpb) ?
(hpb) ?
p
(p-tol)/d ? d/
p*(p-tol)
H ꢁ 4 ? L
p*(p-tol)
H ꢁ 6 ? L
p
p
p*(p-tol)
H ꢁ 8 ? L
p
p
*(p-tol)
315.2 (3.93) 8900
H ꢁ 1 ? L + 2
H ꢁ 1 ? L + 3
H ꢁ 2 ? L + 2
H ꢁ 5 ? L + 1
H ꢁ 2 ? L + 2
H ? L + 6
p
p
*(hpb)
*(hpb)
d/
p(hpb) ?
p
p
p
p
p
*(hpb)
*(p-tol)/
*(hpb)
*(PPh3)
*(hpb)
p
p
(hpb) ? d/
(hpb)/d ?
p*(hpbi)
d/
p(hpb) ?
309.2
306.4
4.01
4.05
0.0394
0.0376
H ꢁ 2 ? L + 3
H ꢁ 11 ? L
H ꢁ 2 ? L + 3
H ꢁ 6 ? L + 1
H ꢁ 8 ? L + 1
H ꢁ 1 ? L + 4
H ꢁ 3 ? L + 2
H ꢁ 4 ? L + 2
H ꢁ 3 ? L + 3
H ꢁ 2 ? L + 4
H ꢁ 4 ? L + 3
H ꢁ 2 ? L + 4
H ? L + 8
p
p
p
p
p
p
p
p
p
p
p
p
(hpb)/d ?
(PPh3) ? d/
(hpb)/d ?
(PPh3)/
(p-tol)/
(hpb) ?
(hpb)/ (p-tol) ?
(hpb) ? *(hpb)
(hpb)/ (p-tol) ?
(hpb)/d ?
(hpb) ? *(hpb)
(hpb)/d ?
p
*(p-tol)
p*(hpb)
p
p
(hpb) ? d/
(PPh3)/ (hpb) ? d/
*(PPh3)
p*(p-tol)/
p
p
*(hpbi)
*(p-tol)/p*(hpbi)
302.8
298.9
294.3
285.7
282.5
280.4
277.4
276.8
272.1
4.09
4.15
4.21
4.34
4.39
4.42
4.47
4.48
4.56
0.0343
0.0655
0.0302
0.1253
0.0690
0.1191
0.0436
0.0437
0.0318
296.8 (4.18) 9100
p
p
p
p
*(hpb)
p
p
p
*(hpb)
p*(PPh3)
p
p
p
p
*(PPh3)
*(p-tol)
*(hpb)
d/
d/
p
p
(hpb) ?
(hpb) ?
H ? L + 13
H ꢁ 7 ? L + 2
p
(PPh3)/
p
p
(hpb) ?
p
*(hpb)
265.6
4.67
0.0347
H ? L + 9
d/ (hpb) ?
p*(hpb)
H ꢁ 9 ? L + 3
H ꢁ 9 ? L + 3
H ꢁ 16 ? L + 1
H ? L + 15
H ? L + 16
H ꢁ 3 ? L + 6
p
p
p
d/
d/
(PPh3) ?
(PPh3) ?
(hpb) ? d/
p
p
p
p
p
*(hpb)
*(hpb)
*(p-tol)/
*(hpb)
*(hpb)
248.6
248.0
245.8
244.5
242.7
239.7
4.99
5.00
5.04
5.07
5.11
5.17
0.0587
0.0600
0.0540
0.0385
0.0359
0.0612
201.6 (6.15) 35500
p
*(hpbi)
p
p
(hpb) ?
(hpb) ?
p
(hpb)/
p
(p-tol) ?
p
*(PPh3)
e
– molar absorption coefficient [dm3 molꢁ1 cmꢁ1]; f – oscillator strength; H – highest occupied molecular orbital; L – lowest unoccupied molecular orbital.
of the spectrum, only transitions with oscillator strengths larger
than 0.030 are listed in Tables 10 and 11. The assignment of the
calculated orbital excitations to the experimental bands was based
on an overview of the contour plots and relative energy to the
occupied and unoccupied orbitals involved in the electronic
transitions.
(Ligand–Metal Charge Transfer; LMCT) and
p
(Cl)/
p
(p-tol)/
p
(PPh3)/
p
(hpb) ? *(p-tol)/p*(hpb) (Ligand–Ligand Charge Transfer; LLCT)
p
transitions. The absorption band at 215.9 nm is attributed to the
Ligand–Ligand Charge Transfer and interligand (IL) transitions.
4.9. Electronic spectrum of 3
Likewise for 1, the longest wavelength experimental band of 3
may be attributed to the transition of d ? d character or may be seen
as a delocalized MLLCT (Metal–Ligand-to-Ligand CT) transitions.
The transitions leading to the experimental band at 330.8 nm
4.8. Electronic spectrum of 1
The longest wavelength experimental band of 1 at 731.4 nm
originates in the HOMO ? LUMO and HOMO ? LUMO + 1 transi-
tions. As it can be seen from the Fig. 5, the HOMO is composed of
can be seen as mixed
p
(hpbi) ? dRe (Ligand–Metal Charge Transfer;
*(p-tol)/ *(hpbi) (Metal–Ligand Charge Transfer;
(hpbi) ? *(p-tol)/ *(hpbi) ( Ligand–Ligand Charge
LMCT), dRe
LMCT) and
?
p
p
p
p
p
p
chloride orbitals and dxy rhenium atomic orbital, the LUMO
p
and LUMO + 1 are delocalized on central ion and
orbitals of the 4-methylphenylimido ligand with small contribution
of
-anti-bonding orbitals of the hpbꢁ. Accordingly, the transition at
p-anti-bonding
Transfer; LLCT) transitions. The absorption bands at 296.8 and
201.6 nm result mainly fromLigand–Ligand Charge Transfer and int-
erligand (IL) transitions.
p
731.4 nm can be seen as a delocalized MLLCT (Metal–Ligand-to-Li-
gand CT) transition. On the other hand, considering that the molec-
ular orbitals involved in the electronic transitions assigned to the
longest wavelength experimental band comprise mainly rhenium
5d atomic orbitals, the HOMO ? LUMO and HOMO ? LUMO + 1
transitions may be ascribed as transitions of d ? d character. The
longest wavelength experimental band of 2 is blue shifted and more
intense in comparison with 1 (see Section 2).
5. Conclusions
The reactivity of [Re(p-NC6H4CH3)Cl3(PPh3)2] (X = Cl, Br) towards
2-(2-hydroxyphenyl)-1H-benzimidazole has been examined and
compared with the related exchange reactions performed with
oxocompounds [ReOX3(PPh3)2]. Novel rhenium(V) imidocomplex-
es trans-[Re(p-NC6H4CH3)X2(hpb)(PPh3)] and [Re(p-NC6H4CH3)-
(hpb)2(PPh3)]X (X = Cl, Br) have been obtained and characterized
The transitions assigned to the experimental bands at 323.1 and
294.7 nm can be seen as mixed p(Cl)/p(p-tol)/p(PPh3)/p(hpb) ? Re

B. Machura et al. / Polyhedron 30 (2011) 142–153
153
structurallyand spectroscopically. In all of them the hpbꢁ ion is coor-
dinated in a chelate way via N- and O-donor atoms, and the PPh3
molecule is cis-located in relation to the Re„N moiety, which forces
the metal nonbonding d electrons to lie in the plane perpendicular to
the M„N bond axis. The X-ray studies and NBO analysis confirm a
linear coordination mode of the p-NC6H4CH3 ligand and triple bond
between the rhenium and the imido ligand.
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