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Mono- and dinuclear rhenium(I) compounds with bidentate benzimidazole chelators
Mono- and Dinuclear Rhenium(I) compounds with bidentate benzimidazole chelators Irvin N. Booysen, Muhammed B. Ismail, Orde Q. Munro PII: DOI: Reference:
S1387-7003(13)00074-9 doi: 10.1016/j.inoche.2013.01.032 INOCHE 4985
To appear in:
Inorganic Chemistry Communications
Received date: Accepted date:
7 December 2012 29 January 2013
Please cite this article as: Irvin N. Booysen, Muhammed B. Ismail, Orde Q. Munro, Mono- and Dinuclear Rhenium(I) compounds with bidentate benzimidazole chelators, Inorganic Chemistry Communications (2013), doi: 10.1016/j.inoche.2013.01.032
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ACCEPTED MANUSCRIPT Mono- and Dinuclear Rhenium(I) compounds with bidentate benzimidazole chelators
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Irvin N. Booysen,,* Muhammed B. Ismail and Orde Q. Munro* University of Kwazulu-Natal, School of Chemistry and Physics, Private Bag X01, Scottsville 3209,
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Pietermaritzburg, South Africa. E-mail: [email protected]; [email protected]. Tel: (+27) 33 260 5326.
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Fax: (+27) 33 260 5009
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Abstract:
A mononuclear rhenium(I) complex, fac-[Re(CO)3(bzch)Cl] (1), where bzch = 2benzimidazole-4H-chromen-4-one, was isolated from the equimolar reaction between the The
1:2
molar
ratio
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[Re(CO)5Cl].
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Schiff base ligand 2-(2-aminophenyliminomethyl)-4H-chromen-4-one (H2pch) and reactions
between
[Re(CO)5Cl]
and
N-(2-
hydroxybenzylidene)-benzimidazole (Hbzp) afforded a dinuclear rhenium(I) compound,
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(μ-bzp)2[Re(CO)3]2 (2). These new rhenium(I) compounds were characterized by NMR, UVvis, IR, and emission spectroscopy, as well as conductance measurements and single crystal X-ray diffraction. The emission spectra for 1 in dichloromethane were well-resolved and could be deconvoluted into three main bands. The emission spectra for 2 were red-shifted by > 140 nm and markedly broadened relative to those of 1. Keywords:
Rhenium(I),
Benzimidazole,
Bidentate,
X-ray
Structure,
Spectral
Characterization
A current design concept for exploring new metallodrug candidates is the attachment of biologically active moieties to 186/188Re radionuclides for the development of target-specific radiopharmaceuticals [1]. Exploring the coordination chemistry of rhenium is critical for discovering novel target-specific rhenium radiopharmaceuticals as the biodistribution of a radiopharmaceutical is highly dependent on its stability and geometry. 1
ACCEPTED MANUSCRIPT Uracil derivatives (e.g. 5-fluorouracil and uracil mustard) are well-established anticancer agents [2] and we have reported the isolation of rhenium(I/V) compounds containing the uracil analogue 5,6-diamino-1,3-dimethyl uracil and its Schiff base derivatives [3]. For
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example, the cationic complex salt trans-[ReV(ddd)(Hduo)(PPh3)2]I, where H2ddd = 5,6diamino-1,3-dimethyl uracil, may be isolated from the reaction of cis-[ReVO2I(PPh3)2] and (N-(2-hydroxybenzylidene)-5-amino-1,3-dimethyl
uracil)
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H3duo
[4].
Mononuclear
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rhenium(I) compounds of 6-amino-1,3-dimethyl-5-nitrosouracil (DANU) are known to exhibit antiproliferative properties [5]. In addition, DANU has been utilized as a precursor
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for the synthesis of azines and diazines, which afforded mononuclear and dinuclear rhenium (I) complexes, respectively, with the former displaying optimal anticancer activity
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against human tumour cell lines [6].
In this paper, we explore the coordination behaviour of Schiff base ligands
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containing chromone (H2pch, 2-(2-aminophenyliminomethyl)-4H-chromen-4-one) and benzimidazole (Hbzp, N-(2-hydroxybenzylidene)-benzimidazole) moieties towards the fac-
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[ReI(CO)3]+ core. The choice of these heterocyclic ligands is governed by their diverse
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medicinal applications and relevance in biological systems: chromones function as secondary metabolites [7], while benzimidazoles are aryl analogues of imidazoles which are ubiquitous in peptides and proteins as the amino acid histidine [8]. Novel mononuclear fac-[Re(CO)3(bzch)Cl], (1), and dinuclear μ-(bzp)2[Re(CO)3]2, (2), compounds have been isolated and characterized. Interestingly, upon coordination of H2pch to the fac-[ReI(CO)3]+ core, intra-ligand cyclization occurred between the amino nitrogen atom and the Schiff base carbon atom to afford a benzimidazole moiety, bzch. The ligand H2pch was obtained from the equimolar condensation reaction of 1,2-diaminobezene with 4-oxo-4H-chromene3-carbaldehyde; condensation of 2-aminobenzimidazole with salicylaldehyde afforded Hbzp. The bzp and bzch chelators coordinated to the metal centre as monoanionic bidentate and neutral bidentate moieties, respectively. Their metal compounds were characterized by UV–vis, IR and NMR spectroscopy, conductance measurements, and single crystal X-ray diffraction [9, 10].
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The IR spectra of 1 and 2 are dominated by strong absorptions due to the facial carbonyl co-ligands. For 2, the Schiff base vibration is at a lower frequency (1686 cm-1)
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compared to the free ligand Hbzp (1691 cm-1). However, for 1 no strong absorption is found between 1650 and 1700 cm-1 due to ν(C=N), indicating that the H2pch Schiff base
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ligand cyclized to form bzch [ν(C=N) for the free H2pch is found at 1640 cm-1]. The
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appearance of new C-N vibrational bands for 1 (at 1557 and 1569 cm-1) indicates the formation of the benzimidazole moiety and these bands are common to 2 (at 1581 cm-1 and
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1606 cm-1). Three distinctive vibrations for the chromone moiety of 1 are observed in the 1600-1640 cm-1 region for the ketone and ether functional groups. Well-resolved signals were observed in the 1H NMR spectra of both 1 and 2 illustrating the diamagnetic nature of the complexes. For 2, non-distinguishable proton signals were observed for the two bzp chelators due to their chemical equivalence. Coordination of the bzp ligand was affirmed by the shift of the aromatic signals in the proton spectrum of 2 relative to the free ligand and the disappearance of the phenolic proton, which is observed at 12.03 ppm in the proton NMR spectrum of Hpzb. Furthermore, the Schiff base protons experience a considerable downfield shift to 8.78 ppm compared to the free ligand at 9.33 ppm. Cyclization of H2pch led to the replacement of the one-proton singlet at 10.23 ppm due to the Schiff base and broad singlets of the amino protons at 8.13 ppm (found in the proton spectrum of H2pch) with a broad singlet at 14.12 ppm, which we assign to the imidazole N–H proton of bzch.
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ACCEPTED MANUSCRIPT Electronic transitions common to both the free ligands and their respective complexes were observed in the 280-340 nm region of their UV-vis spectra in DCM (dichloromethane) and are assigned as intra-ligand -* transitions. Metal-to-ligand charge
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transfer (MLCT) bands ( values between 4500 and 5500 M-1 cm-1) were observed at 394 nm (for 1) and 437 nm (for 2) as shown in Fig. S1 (Supporting Information). Although the
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low-intensity d-d bands for 1 (transitions 1A1g 1T1g and 1A1g 1T2g for pseudo-
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octahedral low-spin d6 ions) were broad and not well resolved, the absorption envelope reached a maximum at 547 nm and was partially overlapped with the more intense MLCT
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band. The d-d transitions were not detectable for 2, presumably due their overlap with the more intense MLCT and -* bands of the complex.
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The emission spectra of 1 and 2 were studied in distilled DCM with previously described equipment and procedures [11]. Using the MLCT band wavelengths as excitation
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energies (394 nm for 1 and 437 nm for 2), several intense emission bands were observed
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between 450–550 nm for 1 and 540–750 nm for 2. As shown in Fig. 1(a), three main emission bands could be deconvoluted for 1 in ambient DCM (containing dissolved oxygen)
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with emission maxima [and relative band areas] at 461.4(8) [24%], 495.2(5) [30%], and 539(1) nm [47%]. From Fig. 1(b), deoxygenation of the solution (by degassing with dry nitrogen for 5 min) significantly changes the spectrum; the first two bands exhibit a blue shift of ca. 7 nm and the second and third bands broaden. The emission band maxima [and relative areas] for 1 in a deoxygenated solution of DCM were: 454.5(7) [24%], 488(1) [45%], and 537(2) nm [31%]. The shortest wavelength band therefore remains unaffected by the presence of triplet oxygen in solution, while significant intensity enhancement for band 2 (with concomitant intensity loss for band 3) is observed. Since the absence of dissolved 3O2 favours enhanced emission intensity from a triplet excited state (due to less efficient quenching), this simple experiment enables identification of the multiplicity of an emitting state [12]. On this basis, we tentatively assign band 1 to a singlet emitting state (possibly an intraligand, 1IL, * emission [13]). Band 2 may be tentatively assigned to a triplet emitting state (either 3MLCT or 3IL), while band 3 could be the longer-wavelength vibrational overtone of band 2, or possibly due to a second emissive triplet state (as might be implied by the intensity ratio of bands 2 and 3, which changes with [3O2]). Clearly, 4
ACCEPTED MANUSCRIPT variable temperature time-resolved fluorescence studies (beyond the scope of the present communication) will be required to fully delineate the excited states of 1. That said, the presence of emissive singlet (1IL) and triplet (3MLCT) states for complexes analogous to 1
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of the fac-[ReI(CO)3]+ core has been firmly established by rigorous DFT (density functional theory) calculations of the excited and ground states of [Re(CO)3(dpphen)Cl], where
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dppphen = 4,7-diphenyl-1,10-phenanthroline [14]. The emission spectra for 2 were red-
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shifted (by ca. 148 nm) relative to those of 1 and markedly broader, as reflected by a roughly two-fold increase (on average) for the band widths of the constituent bands and
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the absence of any uniquely discernible “peaks” in the spectrum (Fig. S2). The low conductivity values recorded for 1 and 2, [8.71 and 15.87 ohm–1 cm–2 mol–1]
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confirm that both complexes are non-electrolytes in DMF and are therefore neutral and do not undergo ligand exchange with the solvent during the timeframe of the conductivity
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measurements. Note that negligible exchange is expected based on the fact that the ligands chelate the metal ion and the low-spin d6 Re(I) electron configuration is kinetically inert
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[15].
Structure of fac-[Re(CO)3(bzch)Cl] (1): Complex 1 exhibits a distorted octahedral geometry with the equatorial plane occupied by the chelating ligand and a pair of cis-carbonyl co-ligands; the axial sites are occupied by the third carbonyl ligand and the chloride ion (Fig. 2). The distortion from ideal octahedral symmetry is mainly brought about by the 6-membered chelate ring, which affords a bite angle [O(1)-Re(1)-N(1) = 82.23(6)°], substantially smaller than the idealized equatorial plane angles of 90° [16]. This phenomenon induces deviation from linearity for the trans angles: O(1)-Re(1)-C(18) = 173.09(8)°, N(1)-Re(1)-C(19) = 171.49(7)° and Cl(1)-Re(1)C(17) = 175.97(6)°. Predominately, the bond distances that constitute the coordination sphere are comparable with those found in the literature. For example, the Re(1)-N(1) [2.179(2) Å] bond length of 1 is comparable to the Re-Nimidazole bond length of 2.154(3) Å found in fac5
ACCEPTED MANUSCRIPT [Re(CO)3(bidz)]Br {bidz = bis-2(2-(1-methylimidazolyl)methyl)amine} [17]. In addition, the average Re-CO bond distance [1.910 Å] falls within the average range [1.900(2) – 1.928(2) Å] observed in the literature for mononuclear rhenium(I) complexes [18]. The rhenium(I)
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reported in the literature [Re(1)-O(1) = 2.137(2) Å] [19].
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to ketonic oxygen bond distance of 1 is also consistent with similar interaction distances
Within the chelator, the chromone and benzimidazole moieties are bridged by a C-C
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[C(1)-C(8) = 1.461(3) Å] single bond which allows the chromone moiety to be slightly out of plane (by 6.8°) with respect to the benzimidazole moiety. The metal centre is virtually
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aligned with the equatorial plane. However, the ligand forms dihedral angles of 19.1° (for the chromone plane) and 19.2° (for the benzimidazole plane) with the equatorial plane.
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The carbons within the C(8)-C(9) [1.367(3) Å] bond are sp2 hybridized and are similar to the delocalized π-bonds found within the C(10) to C(16) and C(2) to C(7) phenyl rings. A
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longer C-N bond length was found for C(1)-N(2) [1.358(3) Å] in comparison to C(1)-N(1) [1.335(3) Å] which confirms that the latter is a localized double bond. The C(12)-O(1)
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[1.254(3) Å] is a double C=O bond since it has a longer bond distance than the average
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triple bond distance [1.154(3) Å] for the carbon monoxides. The extended structure of 1 is characterized by intermolecular hydrogen-bonding involving the benzimidazole N–H donor of one molecule and the axial chloride ligand of a neighbouring molecule, leading to the formation of centrosymmetric H-bonded dimers (Fig. S3). The N–H···Cl angle, H···Cl, and N···Cl distances measure 159, 2.32 Å, and 3.1575(19) Å, respectively. The co-crystallized toluene solvent molecule of 1 -stacks over the imidazole and chromone ring systems (Table S1 and Fig. S4) and is canted by 8.9 and 1.2 relative to the imidazole and chromone ring planes, respectively (interplanar spacing, ca. 3.1–3.3 Å). The chelating ligands within the H-bonded dimer of 1 are, furthermore, -stacked in backto-back fashion (Fig. S4). The centres of gravity of the interacting imidazole rings within the dimer are separated by 4.4927(12) Å with an interplanar separation of 3.15 Å and slippage (lateral displacement) of 3.20 Å.
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ACCEPTED MANUSCRIPT Structure of (μ-bzp)2[Re(CO)3]22(OEt2) (2): The dinuclear compound 2 crystallizes as the bis(diethylether) solvate, triclinic space
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group P-1 [20], and has crystallographically-required inversion symmetry (Fig. 3). The imine-phenoxide moiety of the ligand forms a 6-membere chelate ring with one Re(I) ion;
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the benzimidazole ring is oriented in a near-orthogonal plane (dihedral angle, 77. 8(1)) to the chelate ring and thus binds in the usual monodentate fashion to the second Re(I) ion,
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thereby effectively bridging the two metal centres. As found for 1, the 6-membered chelate ring of 2 exhibits a bite angle [O(1)-Re(1)-N(3) = 84.37(6)˚] which significantly deviates
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from the ideal octahedral value of 90°. This leads to non-linear axial [C(15)-Re(1)-N(1) = 174.38(8)˚] and equatorial [C(16)-Re(1)-N(3) = 175.38(8)˚ and C(17)-Re(1)-O(1) =
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177.19(7)˚] bond angles. The constrained bite angle also causes the C(1)-N(3)-C(8) bond angle [115.4(2)°] to be smaller than the theoretical value of 120° for a bridging sp2
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hybridized nitrogen atom [i.e. N(3)], but the C(8)-N(3) [1.307(3) Å] bond length is typical of
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a Schiff base imino functional group coordinated to a Re(I) metal atom [21]. A centralized 8-membered chelate ring is formed by coordination of the respective metal centers to the
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neutral benzimidazole nitrogen atoms and results in a common Re-Nimidazole bond length of 2.225(2) Å; this distance is shorter than that found in 1 and, within 1 of the upper bound of the literature range [2.106(3) – 2.223(3) Å] [22]. The remaining rhenium coordination bonds [Re(1)-O(1) = 2.092(1) Å and Re(1)N(3) =2.183(2) Å] are consistent with literature values, e.g. the ‘2+1’ complex fac[Re(CO)3(Hons)(H2no)] {Hons = 2-(2-(methylthio)benzylideneimino)phenol, H2no = 2aminophenol} has a similar rhenium(I) to phenolate bond [Re-O = 2.107(4) Å] [23], while the complex salt fac-[Re(CO)3(tris)]Br {tris = tri-(2-benzylimine)} has an average Schiff base imino coordination bond of 2.152(2) Å [24]. Shorter C-N bond distances are found within the benzimidazole ring of 2 [C(1)-N(1) = 1.327(3) Å and C(1)-N(2) = 1.351(2) Å] compared to 1, which implies that the N(1) atom (for 2) acts as a weaker σ-donor, consistent with the longer rhenium to imidazole nitrogen [Re-Nimidazole = 2.225(2) Å] bond lengths compared to 1 [Re(1)-N(1) = 2.179(2) Å]. Finally, each dinuclear complex is hydrogen bonded to two diethylether solvent molecules via the benzimidazole N–H groups
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ACCEPTED MANUSCRIPT (Fig. S5). The N2–H2···O5 angle, H2···O5, and N2···O5 distances measure 15, 1.93 Å, and 2.735(3) Å, respectively. One significant intermolecular -stacking interaction between adjacent dinuclear complexes is noteworthy (Fig. S6, Table S2). This involves the edges of
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the phenoxide rings (C12, C13) whose centres of gravity are separated by 5.3821(12) Å,
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giving a below-normal interplanar spacing of 2.75 Å and slippage (lateral shift) of 4.63 Å.
Figure Captions:
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Fig. 1. Deconvoluted emission spectra for 1 (Voigt functions) recorded at 295 K. (a) Spectrum in ambient (O2-containing) CH2Cl2. Band 1: max-EM, 461.4(8) nm; HWHM, 21(2) nm; height, 6.7(9) × 10band 2: max-EM, 495.2(5) nm; HWHM, 21(6) nm; height, 8.5(6) × 10-3; band 3: max-EM, 539(1) nm;
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3;
HWHM, 10(1) nm; height, 7.7(8) × 10-3; correlation coefficient, R2 = 0.996. (b) Spectrum in deoxygenated CH2Cl2. Band 1: max-EM, 454.5(7) nm; HWHM, 20(2) nm; height, 6.9(9) × 10-3; band 2:
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max-EM, 488(1) nm; HWHM, 30(6) nm; height, 8.6(7) × 10-3; band 3: max-EM, 537(2) nm; HWHM,
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19(3) nm; height, 4.6(7) × 10-3; correlation coefficient, R2 = 0.999. Both spectra are backgroundcorrected and normalized (areas = 1). The spectral deconvolution is empirical, employing the
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minimum number of bands that fit the spectral envelope. The number of theoretically possible main emissive states could well be different.
Fig. 2. Thermal ellipsoid diagram (50% probability surfaces) and atom numbering scheme of the Xray structure of fac-[Re(CO)3(bzch)Cl] (1). Bonds are shown as cylinders and hydrogen atoms are rendered as spheres of arbitrary radii. Selected bond lengths (Å) and angles (°): Re(1)-C(19) 1.929(2), Re(1)-C(18) 1.898(2), Re(1)-C(17) 1.904(2), Re(1)-Cl(1) 2.492(6), Re(1)-O(1) 2.137(2), Re(1)-N(1) 2.179(2), C(8)-C(9) 1.367(3), N(2)-C(1) 1.358(3), C(1)-N(1) 1.335(3), C(12)-O(1) 1.254(3), C(18)-O(4) 1.157(3), C(19)-O(5) 1.150(3), C(17)-O(3) 1.154(3), C(1)-C(8) 1.461(3), C(19)-Re(1)-N(1) 171.49(7), C(17)-Re(1)-Cl(1) 175.97(6), O(1)-Re(1)-C(18) 173.09(8), N(1)Re(1)-O(1) 82.23(6).
Fig. 3. Thermal ellipsoid diagram (50% probability surfaces) and atom numbering scheme (symmetry unique half) of the X-ray structure of (μ-bzp)2[Re(CO)3]2 (2). Selected bond lengths (Å) 8
ACCEPTED MANUSCRIPT and angles (°): Re(1)-C(15) 1.918(2), Re(1)-C(16) 1.932(2), Re(1)-C(17) 1.903(2), Re(1)-N(1) 2.225(2), Re(1)-N(3) 2.183(2), Re(1)-O(1) 2.092(1), N(3)-C(8) 1.307(3), N(2)-C(1) 1.351(2), N(1)C(1) 1.327(3), C(16)-Re(1)-N(3) 175.38(8), C(15)-Re(1)-N(1) 174.38(8), C(17)-Re(1)-O(1)
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177.19(7), O(1)-Re(1)-N(3) 84.37(6), C(8)-N(3)-C(1) 115.4(2).
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Acknowledgements:
We are grateful to the University of KwaZulu-Natal and the National Research Foundation
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of South Africa for financial support.
Supporting Information:
at
www.ccdc.cam.ac.uk/conts/retrieving.html
[or
from
the
Cambridge
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charge
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CCDC- contains crystallographic data for this article. These data can be obtained free of Crystallographic Data Centre (CCDC), 12 Union Road, Cambridge CB21EZ, UK; Fax:
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+44(0)1223-336033; Email: [email protected]]. Fig. S1 (electronic absorption spectra for 1 and 2); Fig S2, deconvoluted emission spectra for 2.
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N.A. Illán-Cabeza, A.R. Garcıá-Garcıá, M.N. Moreno-Carretero, J.M. Martínez-Martos, M.J. Ramírez-Expósito, J. Inorg. Biochem. 99 (2005) 1637.
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Equimolar amounts of H2pch (0.0731 g; 0.277 mmol) and [Re(CO)5Cl] (0.1006 g,
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0.227 mmol) in 20 cm3 toluene were heated at reflux for 1 h in a nitrogen atmosphere. Slow evaporation of the mother liquor afforded yellow rhombic shaped crystals suitable for X-ray analysis. Yield = 73%; M.P. = 277 - 278 ˚C;
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Conductivity (DMF, 10-3 M) = 8.71 ohm-1cm-2mol-1; IR (νmax/cm-1): ν(N-H) 3225,
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3165, 3012 (w), ν(C≡O) 2027, 1912, 1862 (vs), ν(C=O) 1635 (m), ν(O-C-O) 1618, 1606 (m), ν(C-N)Heterocyclic 1569, 1557 (s); 1H NMR (295K/ppm): 14.23 (br, s, 1H,
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NH), 9.73 (s, 1H, H9), 8.45 (d, 1H, H6), 8.24 (d, 1H, H3), 8.05-7.91 (m, 2H, H15, H16), 7.79-7.65 (m, 2H, H13, H14), 7.53 (d, 2H, H4, H5), 5.27-5.15 (m, 5H, H2s, H3s, H4s, H5s, H6s), 3.13 (s, 3H, C7s-H3); UV-Vis (DMF, λmax (ε, M-1cm-1)): 303 (54529), 394 (4320), 547 (1077). [10]
A mixture of Hbzp (0.1314 g; 0.554 mmol) and [Re(CO)5Cl] (0.1006 g; 0.277 mmol) in toluene (20 cm3) was heated in a nitrogen atmosphere under reflux for 4 hours. The resultant light yellow solution was allowed to cool to room temperature, and the orange precipitate was filtered by gravity. Evaporation of the filtrate yielded exquisite, orange, parallelogram-shaped crystals. Yield = 78%; M.P. > 350 ˚C; Conductivity (DMF, 10-3 M) = 15.87 ohm-1cm-2mol-1; IR (νmax/cm-1): ν(N-H) 3180 (w), ν(C≡O) 2018, 1884 (vs), ν(C=N)Schiff Base 1686 (s), ν(C-N)Heterocyclic 1606, 1581 (s); 1H NMR (295K/ppm): 13.50 (s, 2H, N-H2, N-H2’), 8.78 (s, 2H, H8, H8’), 8.53 (d, 2H, H3, H3’), 7.51 (d, 2H, H6, H6’), 7.33 – 7.44 (m, 8H, H4, H4’, H5, H5’, H10, H10’,
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ACCEPTED MANUSCRIPT H12, H12’), 6.88 (d, 2H, H13, H13’), 6.46 (t, 2H, H11, H11’); UV-Vis (DMF, λmax (ε, M1cm-1)):
281 (12736), 329 (4703), 437 (5120).
J.S. Field, C.R. Wilson, O.Q. Munro, Inorg. Chim. Acta 374 (2011) 197.
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Crystallographic data for 1, C19H10ClN2O5ReC7H8: monoclinic; space group P21/n;
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[16]
a = 12.3734(5), b = 11.7176(5), c = 16.1453(7) Å, β = 91.970(2)°; V = 2339.47(2)
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Å3; Z = 4; Dc = 1.87 Mg/m3; μ = 5.350 mm-1; data/restraints/parameters
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17072/0/321; GOOF = 1.106; final R indices [I>2σ(I)]: R1 = 0.038, wR2 = 0.0817. Z.R. Tshentu, T.I.A. Gerber, R. Walmsley, P. Mayer, Polyhedron 27 (2008) 406.
[18]
T. Jin, G. Li, X. Zhou, J. Zuo, Inorg. Chem. Comm. 14 (2011) 1944.
[19]
N.A. Illan-Cabeza, A.R. Garcia-Garcia, M.N. Moreno-Carretero, Inorg. Chim. Acta 366
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[17]
(2011) 262; B. Machura, R. Kruszynsk, J. Organomet. Chem. 692 (2007) 4161. [20]
Crystallographic data for 2, C21H20N3O5Re: triclinic; space group Pī; a = 10.2572(5), b = 10.5903(5), c = 10.6681(5) Å, α = 91.510(2), β = 117.698(2), γ = 98.091(2)°; V = 1010.25(13)
Å3;
Z
=
1;
Dc
=
1.91
Mg/m3;
μ
=
6.053
mm-1;
data/restraints/parameters 5782/0/277; GOOF = 1.134; final R indices [I>2σ(I)]: R1 = 0.0147, wR2 = 0.0360. [21]
A.
Brink,
H.G.
Visser,
A.
Roodt,
Polyhedron
(2012),
http://dx.doi.org/10.1016/j.poly.2012.08.059. [22]
T.I.A. Gerber, K.C. Potgieter, P. Mayer, Inorg. Chem. Comm. 14 (2011) 1115; R.F. Vitor, S. Alves, J.D.G. Correia, A. Paulo, I. Santos, J. Organomet. Chem. 689 (2004) 4764; R. Czerwieniec, A. Kapturkiewicz, J. Lipkowski, J. Nowacki, Inorg. Chim. Acta 358 (2005) 2701.
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ACCEPTED MANUSCRIPT [23]
T.I.A. Gerber, R. Betz, I.N. Booysen, K.C. Potgieter, P. Mayer, Polyhedron 30 (2011) 1739. K. Potgieter, P. Mayer, T. Gerber, N. Yumata, E. Hosten, I. Booysen, R. Betz, M.
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Ismail, B. van Brecht, Polyhedron 49 (2012) 67.
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[24]
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Figure 1
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Figure 2
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Figure 3
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Graphical Abstract
The coordination behaviour of Schiff base ligands containing chromone (H2pch, 2-(2and
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aminophenyliminomethyl)-4H-chromen-4-one)
benzimidazole
(Hbzp,
N-(2-
hydroxybenzylidene)-benzimidazole) moieties towards the fac-[ReI(CO)3]+ core are
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explored. Novel mononuclear fac-[Re(CO)3(bzch)Cl], (1), and dinuclear μ-(bzp)2[Re(CO)3]2, (2), compounds have been isolated and characterized.
16
ACCEPTED MANUSCRIPT Highlights
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Novel mono- and dinuclear rhenium(I) compounds
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Schiff base ligands containing chromone and benzimidazole moieties respectively
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Three distinct emission bands
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Crystallographically-required inversion symmetry
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S1387-7003(13)00074-9 doi: 10.1016/j.inoche.2013.01.032 INOCHE 4985
To appear in:
Inorganic Chemistry Communications
Received date: Accepted date:
7 December 2012 29 January 2013
Please cite this article as: Irvin N. Booysen, Muhammed B. Ismail, Orde Q. Munro, Mono- and Dinuclear Rhenium(I) compounds with bidentate benzimidazole chelators, Inorganic Chemistry Communications (2013), doi: 10.1016/j.inoche.2013.01.032
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Mono- and Dinuclear Rhenium(I) compounds with bidentate benzimidazole chelators
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Irvin N. Booysen,,* Muhammed B. Ismail and Orde Q. Munro* University of Kwazulu-Natal, School of Chemistry and Physics, Private Bag X01, Scottsville 3209,
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Pietermaritzburg, South Africa. E-mail: [email protected]; [email protected]. Tel: (+27) 33 260 5326.
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Fax: (+27) 33 260 5009
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Abstract:
A mononuclear rhenium(I) complex, fac-[Re(CO)3(bzch)Cl] (1), where bzch = 2benzimidazole-4H-chromen-4-one, was isolated from the equimolar reaction between the The
1:2
molar
ratio
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[Re(CO)5Cl].
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Schiff base ligand 2-(2-aminophenyliminomethyl)-4H-chromen-4-one (H2pch) and reactions
between
[Re(CO)5Cl]
and
N-(2-
hydroxybenzylidene)-benzimidazole (Hbzp) afforded a dinuclear rhenium(I) compound,
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(μ-bzp)2[Re(CO)3]2 (2). These new rhenium(I) compounds were characterized by NMR, UVvis, IR, and emission spectroscopy, as well as conductance measurements and single crystal X-ray diffraction. The emission spectra for 1 in dichloromethane were well-resolved and could be deconvoluted into three main bands. The emission spectra for 2 were red-shifted by > 140 nm and markedly broadened relative to those of 1. Keywords:
Rhenium(I),
Benzimidazole,
Bidentate,
X-ray
Structure,
Spectral
Characterization
A current design concept for exploring new metallodrug candidates is the attachment of biologically active moieties to 186/188Re radionuclides for the development of target-specific radiopharmaceuticals [1]. Exploring the coordination chemistry of rhenium is critical for discovering novel target-specific rhenium radiopharmaceuticals as the biodistribution of a radiopharmaceutical is highly dependent on its stability and geometry. 1
ACCEPTED MANUSCRIPT Uracil derivatives (e.g. 5-fluorouracil and uracil mustard) are well-established anticancer agents [2] and we have reported the isolation of rhenium(I/V) compounds containing the uracil analogue 5,6-diamino-1,3-dimethyl uracil and its Schiff base derivatives [3]. For
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example, the cationic complex salt trans-[ReV(ddd)(Hduo)(PPh3)2]I, where H2ddd = 5,6diamino-1,3-dimethyl uracil, may be isolated from the reaction of cis-[ReVO2I(PPh3)2] and (N-(2-hydroxybenzylidene)-5-amino-1,3-dimethyl
uracil)
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H3duo
[4].
Mononuclear
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rhenium(I) compounds of 6-amino-1,3-dimethyl-5-nitrosouracil (DANU) are known to exhibit antiproliferative properties [5]. In addition, DANU has been utilized as a precursor
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for the synthesis of azines and diazines, which afforded mononuclear and dinuclear rhenium (I) complexes, respectively, with the former displaying optimal anticancer activity
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against human tumour cell lines [6].
In this paper, we explore the coordination behaviour of Schiff base ligands
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containing chromone (H2pch, 2-(2-aminophenyliminomethyl)-4H-chromen-4-one) and benzimidazole (Hbzp, N-(2-hydroxybenzylidene)-benzimidazole) moieties towards the fac-
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[ReI(CO)3]+ core. The choice of these heterocyclic ligands is governed by their diverse
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medicinal applications and relevance in biological systems: chromones function as secondary metabolites [7], while benzimidazoles are aryl analogues of imidazoles which are ubiquitous in peptides and proteins as the amino acid histidine [8]. Novel mononuclear fac-[Re(CO)3(bzch)Cl], (1), and dinuclear μ-(bzp)2[Re(CO)3]2, (2), compounds have been isolated and characterized. Interestingly, upon coordination of H2pch to the fac-[ReI(CO)3]+ core, intra-ligand cyclization occurred between the amino nitrogen atom and the Schiff base carbon atom to afford a benzimidazole moiety, bzch. The ligand H2pch was obtained from the equimolar condensation reaction of 1,2-diaminobezene with 4-oxo-4H-chromene3-carbaldehyde; condensation of 2-aminobenzimidazole with salicylaldehyde afforded Hbzp. The bzp and bzch chelators coordinated to the metal centre as monoanionic bidentate and neutral bidentate moieties, respectively. Their metal compounds were characterized by UV–vis, IR and NMR spectroscopy, conductance measurements, and single crystal X-ray diffraction [9, 10].
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The IR spectra of 1 and 2 are dominated by strong absorptions due to the facial carbonyl co-ligands. For 2, the Schiff base vibration is at a lower frequency (1686 cm-1)
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compared to the free ligand Hbzp (1691 cm-1). However, for 1 no strong absorption is found between 1650 and 1700 cm-1 due to ν(C=N), indicating that the H2pch Schiff base
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ligand cyclized to form bzch [ν(C=N) for the free H2pch is found at 1640 cm-1]. The
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appearance of new C-N vibrational bands for 1 (at 1557 and 1569 cm-1) indicates the formation of the benzimidazole moiety and these bands are common to 2 (at 1581 cm-1 and
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1606 cm-1). Three distinctive vibrations for the chromone moiety of 1 are observed in the 1600-1640 cm-1 region for the ketone and ether functional groups. Well-resolved signals were observed in the 1H NMR spectra of both 1 and 2 illustrating the diamagnetic nature of the complexes. For 2, non-distinguishable proton signals were observed for the two bzp chelators due to their chemical equivalence. Coordination of the bzp ligand was affirmed by the shift of the aromatic signals in the proton spectrum of 2 relative to the free ligand and the disappearance of the phenolic proton, which is observed at 12.03 ppm in the proton NMR spectrum of Hpzb. Furthermore, the Schiff base protons experience a considerable downfield shift to 8.78 ppm compared to the free ligand at 9.33 ppm. Cyclization of H2pch led to the replacement of the one-proton singlet at 10.23 ppm due to the Schiff base and broad singlets of the amino protons at 8.13 ppm (found in the proton spectrum of H2pch) with a broad singlet at 14.12 ppm, which we assign to the imidazole N–H proton of bzch.
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ACCEPTED MANUSCRIPT Electronic transitions common to both the free ligands and their respective complexes were observed in the 280-340 nm region of their UV-vis spectra in DCM (dichloromethane) and are assigned as intra-ligand -* transitions. Metal-to-ligand charge
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transfer (MLCT) bands ( values between 4500 and 5500 M-1 cm-1) were observed at 394 nm (for 1) and 437 nm (for 2) as shown in Fig. S1 (Supporting Information). Although the
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low-intensity d-d bands for 1 (transitions 1A1g 1T1g and 1A1g 1T2g for pseudo-
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octahedral low-spin d6 ions) were broad and not well resolved, the absorption envelope reached a maximum at 547 nm and was partially overlapped with the more intense MLCT
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band. The d-d transitions were not detectable for 2, presumably due their overlap with the more intense MLCT and -* bands of the complex.
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The emission spectra of 1 and 2 were studied in distilled DCM with previously described equipment and procedures [11]. Using the MLCT band wavelengths as excitation
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energies (394 nm for 1 and 437 nm for 2), several intense emission bands were observed
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between 450–550 nm for 1 and 540–750 nm for 2. As shown in Fig. 1(a), three main emission bands could be deconvoluted for 1 in ambient DCM (containing dissolved oxygen)
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with emission maxima [and relative band areas] at 461.4(8) [24%], 495.2(5) [30%], and 539(1) nm [47%]. From Fig. 1(b), deoxygenation of the solution (by degassing with dry nitrogen for 5 min) significantly changes the spectrum; the first two bands exhibit a blue shift of ca. 7 nm and the second and third bands broaden. The emission band maxima [and relative areas] for 1 in a deoxygenated solution of DCM were: 454.5(7) [24%], 488(1) [45%], and 537(2) nm [31%]. The shortest wavelength band therefore remains unaffected by the presence of triplet oxygen in solution, while significant intensity enhancement for band 2 (with concomitant intensity loss for band 3) is observed. Since the absence of dissolved 3O2 favours enhanced emission intensity from a triplet excited state (due to less efficient quenching), this simple experiment enables identification of the multiplicity of an emitting state [12]. On this basis, we tentatively assign band 1 to a singlet emitting state (possibly an intraligand, 1IL, * emission [13]). Band 2 may be tentatively assigned to a triplet emitting state (either 3MLCT or 3IL), while band 3 could be the longer-wavelength vibrational overtone of band 2, or possibly due to a second emissive triplet state (as might be implied by the intensity ratio of bands 2 and 3, which changes with [3O2]). Clearly, 4
ACCEPTED MANUSCRIPT variable temperature time-resolved fluorescence studies (beyond the scope of the present communication) will be required to fully delineate the excited states of 1. That said, the presence of emissive singlet (1IL) and triplet (3MLCT) states for complexes analogous to 1
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of the fac-[ReI(CO)3]+ core has been firmly established by rigorous DFT (density functional theory) calculations of the excited and ground states of [Re(CO)3(dpphen)Cl], where
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dppphen = 4,7-diphenyl-1,10-phenanthroline [14]. The emission spectra for 2 were red-
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shifted (by ca. 148 nm) relative to those of 1 and markedly broader, as reflected by a roughly two-fold increase (on average) for the band widths of the constituent bands and
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the absence of any uniquely discernible “peaks” in the spectrum (Fig. S2). The low conductivity values recorded for 1 and 2, [8.71 and 15.87 ohm–1 cm–2 mol–1]
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confirm that both complexes are non-electrolytes in DMF and are therefore neutral and do not undergo ligand exchange with the solvent during the timeframe of the conductivity
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measurements. Note that negligible exchange is expected based on the fact that the ligands chelate the metal ion and the low-spin d6 Re(I) electron configuration is kinetically inert
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[15].
Structure of fac-[Re(CO)3(bzch)Cl] (1): Complex 1 exhibits a distorted octahedral geometry with the equatorial plane occupied by the chelating ligand and a pair of cis-carbonyl co-ligands; the axial sites are occupied by the third carbonyl ligand and the chloride ion (Fig. 2). The distortion from ideal octahedral symmetry is mainly brought about by the 6-membered chelate ring, which affords a bite angle [O(1)-Re(1)-N(1) = 82.23(6)°], substantially smaller than the idealized equatorial plane angles of 90° [16]. This phenomenon induces deviation from linearity for the trans angles: O(1)-Re(1)-C(18) = 173.09(8)°, N(1)-Re(1)-C(19) = 171.49(7)° and Cl(1)-Re(1)C(17) = 175.97(6)°. Predominately, the bond distances that constitute the coordination sphere are comparable with those found in the literature. For example, the Re(1)-N(1) [2.179(2) Å] bond length of 1 is comparable to the Re-Nimidazole bond length of 2.154(3) Å found in fac5
ACCEPTED MANUSCRIPT [Re(CO)3(bidz)]Br {bidz = bis-2(2-(1-methylimidazolyl)methyl)amine} [17]. In addition, the average Re-CO bond distance [1.910 Å] falls within the average range [1.900(2) – 1.928(2) Å] observed in the literature for mononuclear rhenium(I) complexes [18]. The rhenium(I)
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reported in the literature [Re(1)-O(1) = 2.137(2) Å] [19].
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to ketonic oxygen bond distance of 1 is also consistent with similar interaction distances
Within the chelator, the chromone and benzimidazole moieties are bridged by a C-C
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[C(1)-C(8) = 1.461(3) Å] single bond which allows the chromone moiety to be slightly out of plane (by 6.8°) with respect to the benzimidazole moiety. The metal centre is virtually
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aligned with the equatorial plane. However, the ligand forms dihedral angles of 19.1° (for the chromone plane) and 19.2° (for the benzimidazole plane) with the equatorial plane.
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The carbons within the C(8)-C(9) [1.367(3) Å] bond are sp2 hybridized and are similar to the delocalized π-bonds found within the C(10) to C(16) and C(2) to C(7) phenyl rings. A
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longer C-N bond length was found for C(1)-N(2) [1.358(3) Å] in comparison to C(1)-N(1) [1.335(3) Å] which confirms that the latter is a localized double bond. The C(12)-O(1)
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[1.254(3) Å] is a double C=O bond since it has a longer bond distance than the average
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triple bond distance [1.154(3) Å] for the carbon monoxides. The extended structure of 1 is characterized by intermolecular hydrogen-bonding involving the benzimidazole N–H donor of one molecule and the axial chloride ligand of a neighbouring molecule, leading to the formation of centrosymmetric H-bonded dimers (Fig. S3). The N–H···Cl angle, H···Cl, and N···Cl distances measure 159, 2.32 Å, and 3.1575(19) Å, respectively. The co-crystallized toluene solvent molecule of 1 -stacks over the imidazole and chromone ring systems (Table S1 and Fig. S4) and is canted by 8.9 and 1.2 relative to the imidazole and chromone ring planes, respectively (interplanar spacing, ca. 3.1–3.3 Å). The chelating ligands within the H-bonded dimer of 1 are, furthermore, -stacked in backto-back fashion (Fig. S4). The centres of gravity of the interacting imidazole rings within the dimer are separated by 4.4927(12) Å with an interplanar separation of 3.15 Å and slippage (lateral displacement) of 3.20 Å.
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ACCEPTED MANUSCRIPT Structure of (μ-bzp)2[Re(CO)3]22(OEt2) (2): The dinuclear compound 2 crystallizes as the bis(diethylether) solvate, triclinic space
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group P-1 [20], and has crystallographically-required inversion symmetry (Fig. 3). The imine-phenoxide moiety of the ligand forms a 6-membere chelate ring with one Re(I) ion;
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the benzimidazole ring is oriented in a near-orthogonal plane (dihedral angle, 77. 8(1)) to the chelate ring and thus binds in the usual monodentate fashion to the second Re(I) ion,
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thereby effectively bridging the two metal centres. As found for 1, the 6-membered chelate ring of 2 exhibits a bite angle [O(1)-Re(1)-N(3) = 84.37(6)˚] which significantly deviates
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from the ideal octahedral value of 90°. This leads to non-linear axial [C(15)-Re(1)-N(1) = 174.38(8)˚] and equatorial [C(16)-Re(1)-N(3) = 175.38(8)˚ and C(17)-Re(1)-O(1) =
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177.19(7)˚] bond angles. The constrained bite angle also causes the C(1)-N(3)-C(8) bond angle [115.4(2)°] to be smaller than the theoretical value of 120° for a bridging sp2
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hybridized nitrogen atom [i.e. N(3)], but the C(8)-N(3) [1.307(3) Å] bond length is typical of
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a Schiff base imino functional group coordinated to a Re(I) metal atom [21]. A centralized 8-membered chelate ring is formed by coordination of the respective metal centers to the
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neutral benzimidazole nitrogen atoms and results in a common Re-Nimidazole bond length of 2.225(2) Å; this distance is shorter than that found in 1 and, within 1 of the upper bound of the literature range [2.106(3) – 2.223(3) Å] [22]. The remaining rhenium coordination bonds [Re(1)-O(1) = 2.092(1) Å and Re(1)N(3) =2.183(2) Å] are consistent with literature values, e.g. the ‘2+1’ complex fac[Re(CO)3(Hons)(H2no)] {Hons = 2-(2-(methylthio)benzylideneimino)phenol, H2no = 2aminophenol} has a similar rhenium(I) to phenolate bond [Re-O = 2.107(4) Å] [23], while the complex salt fac-[Re(CO)3(tris)]Br {tris = tri-(2-benzylimine)} has an average Schiff base imino coordination bond of 2.152(2) Å [24]. Shorter C-N bond distances are found within the benzimidazole ring of 2 [C(1)-N(1) = 1.327(3) Å and C(1)-N(2) = 1.351(2) Å] compared to 1, which implies that the N(1) atom (for 2) acts as a weaker σ-donor, consistent with the longer rhenium to imidazole nitrogen [Re-Nimidazole = 2.225(2) Å] bond lengths compared to 1 [Re(1)-N(1) = 2.179(2) Å]. Finally, each dinuclear complex is hydrogen bonded to two diethylether solvent molecules via the benzimidazole N–H groups
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ACCEPTED MANUSCRIPT (Fig. S5). The N2–H2···O5 angle, H2···O5, and N2···O5 distances measure 15, 1.93 Å, and 2.735(3) Å, respectively. One significant intermolecular -stacking interaction between adjacent dinuclear complexes is noteworthy (Fig. S6, Table S2). This involves the edges of
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the phenoxide rings (C12, C13) whose centres of gravity are separated by 5.3821(12) Å,
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giving a below-normal interplanar spacing of 2.75 Å and slippage (lateral shift) of 4.63 Å.
Figure Captions:
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Fig. 1. Deconvoluted emission spectra for 1 (Voigt functions) recorded at 295 K. (a) Spectrum in ambient (O2-containing) CH2Cl2. Band 1: max-EM, 461.4(8) nm; HWHM, 21(2) nm; height, 6.7(9) × 10band 2: max-EM, 495.2(5) nm; HWHM, 21(6) nm; height, 8.5(6) × 10-3; band 3: max-EM, 539(1) nm;
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3;
HWHM, 10(1) nm; height, 7.7(8) × 10-3; correlation coefficient, R2 = 0.996. (b) Spectrum in deoxygenated CH2Cl2. Band 1: max-EM, 454.5(7) nm; HWHM, 20(2) nm; height, 6.9(9) × 10-3; band 2:
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max-EM, 488(1) nm; HWHM, 30(6) nm; height, 8.6(7) × 10-3; band 3: max-EM, 537(2) nm; HWHM,
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19(3) nm; height, 4.6(7) × 10-3; correlation coefficient, R2 = 0.999. Both spectra are backgroundcorrected and normalized (areas = 1). The spectral deconvolution is empirical, employing the
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minimum number of bands that fit the spectral envelope. The number of theoretically possible main emissive states could well be different.
Fig. 2. Thermal ellipsoid diagram (50% probability surfaces) and atom numbering scheme of the Xray structure of fac-[Re(CO)3(bzch)Cl] (1). Bonds are shown as cylinders and hydrogen atoms are rendered as spheres of arbitrary radii. Selected bond lengths (Å) and angles (°): Re(1)-C(19) 1.929(2), Re(1)-C(18) 1.898(2), Re(1)-C(17) 1.904(2), Re(1)-Cl(1) 2.492(6), Re(1)-O(1) 2.137(2), Re(1)-N(1) 2.179(2), C(8)-C(9) 1.367(3), N(2)-C(1) 1.358(3), C(1)-N(1) 1.335(3), C(12)-O(1) 1.254(3), C(18)-O(4) 1.157(3), C(19)-O(5) 1.150(3), C(17)-O(3) 1.154(3), C(1)-C(8) 1.461(3), C(19)-Re(1)-N(1) 171.49(7), C(17)-Re(1)-Cl(1) 175.97(6), O(1)-Re(1)-C(18) 173.09(8), N(1)Re(1)-O(1) 82.23(6).
Fig. 3. Thermal ellipsoid diagram (50% probability surfaces) and atom numbering scheme (symmetry unique half) of the X-ray structure of (μ-bzp)2[Re(CO)3]2 (2). Selected bond lengths (Å) 8
ACCEPTED MANUSCRIPT and angles (°): Re(1)-C(15) 1.918(2), Re(1)-C(16) 1.932(2), Re(1)-C(17) 1.903(2), Re(1)-N(1) 2.225(2), Re(1)-N(3) 2.183(2), Re(1)-O(1) 2.092(1), N(3)-C(8) 1.307(3), N(2)-C(1) 1.351(2), N(1)C(1) 1.327(3), C(16)-Re(1)-N(3) 175.38(8), C(15)-Re(1)-N(1) 174.38(8), C(17)-Re(1)-O(1)
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177.19(7), O(1)-Re(1)-N(3) 84.37(6), C(8)-N(3)-C(1) 115.4(2).
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Acknowledgements:
We are grateful to the University of KwaZulu-Natal and the National Research Foundation
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of South Africa for financial support.
Supporting Information:
at
www.ccdc.cam.ac.uk/conts/retrieving.html
[or
from
the
Cambridge
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charge
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CCDC- contains crystallographic data for this article. These data can be obtained free of Crystallographic Data Centre (CCDC), 12 Union Road, Cambridge CB21EZ, UK; Fax:
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+44(0)1223-336033; Email: [email protected]]. Fig. S1 (electronic absorption spectra for 1 and 2); Fig S2, deconvoluted emission spectra for 2.
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Equimolar amounts of H2pch (0.0731 g; 0.277 mmol) and [Re(CO)5Cl] (0.1006 g,
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0.227 mmol) in 20 cm3 toluene were heated at reflux for 1 h in a nitrogen atmosphere. Slow evaporation of the mother liquor afforded yellow rhombic shaped crystals suitable for X-ray analysis. Yield = 73%; M.P. = 277 - 278 ˚C;
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Conductivity (DMF, 10-3 M) = 8.71 ohm-1cm-2mol-1; IR (νmax/cm-1): ν(N-H) 3225,
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3165, 3012 (w), ν(C≡O) 2027, 1912, 1862 (vs), ν(C=O) 1635 (m), ν(O-C-O) 1618, 1606 (m), ν(C-N)Heterocyclic 1569, 1557 (s); 1H NMR (295K/ppm): 14.23 (br, s, 1H,
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NH), 9.73 (s, 1H, H9), 8.45 (d, 1H, H6), 8.24 (d, 1H, H3), 8.05-7.91 (m, 2H, H15, H16), 7.79-7.65 (m, 2H, H13, H14), 7.53 (d, 2H, H4, H5), 5.27-5.15 (m, 5H, H2s, H3s, H4s, H5s, H6s), 3.13 (s, 3H, C7s-H3); UV-Vis (DMF, λmax (ε, M-1cm-1)): 303 (54529), 394 (4320), 547 (1077). [10]
A mixture of Hbzp (0.1314 g; 0.554 mmol) and [Re(CO)5Cl] (0.1006 g; 0.277 mmol) in toluene (20 cm3) was heated in a nitrogen atmosphere under reflux for 4 hours. The resultant light yellow solution was allowed to cool to room temperature, and the orange precipitate was filtered by gravity. Evaporation of the filtrate yielded exquisite, orange, parallelogram-shaped crystals. Yield = 78%; M.P. > 350 ˚C; Conductivity (DMF, 10-3 M) = 15.87 ohm-1cm-2mol-1; IR (νmax/cm-1): ν(N-H) 3180 (w), ν(C≡O) 2018, 1884 (vs), ν(C=N)Schiff Base 1686 (s), ν(C-N)Heterocyclic 1606, 1581 (s); 1H NMR (295K/ppm): 13.50 (s, 2H, N-H2, N-H2’), 8.78 (s, 2H, H8, H8’), 8.53 (d, 2H, H3, H3’), 7.51 (d, 2H, H6, H6’), 7.33 – 7.44 (m, 8H, H4, H4’, H5, H5’, H10, H10’,
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ACCEPTED MANUSCRIPT H12, H12’), 6.88 (d, 2H, H13, H13’), 6.46 (t, 2H, H11, H11’); UV-Vis (DMF, λmax (ε, M1cm-1)):
281 (12736), 329 (4703), 437 (5120).
J.S. Field, C.R. Wilson, O.Q. Munro, Inorg. Chim. Acta 374 (2011) 197.
[12]
L. Wei, J. W. Babich, W. Ouellette, J. Zubieta, Inorg. Chem. 45 (2006) 3057.
[13]
G. Li, T. Jin, L. Sun, J. Qin, D. Wen, J. Zuo, X. You, J. Organomet. Chem. 696 (2011)
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[11]
B. Machura, M. Wolff, M. Jaworska, P. Lodowski, E. Benoist, C. Carrayon, N. Saffon,
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[14]
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3076.
R. Kruszynski, Z. Mazurak, J. Organomet. Chem. 696 (2011) 3068. R. Alberto, R. Schibli, R. Waibel, U. Abram, A.P. Schubiger, Coord. Chem. Rev. 190–
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[15]
192 (1999) 901.
Crystallographic data for 1, C19H10ClN2O5ReC7H8: monoclinic; space group P21/n;
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[16]
a = 12.3734(5), b = 11.7176(5), c = 16.1453(7) Å, β = 91.970(2)°; V = 2339.47(2)
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Å3; Z = 4; Dc = 1.87 Mg/m3; μ = 5.350 mm-1; data/restraints/parameters
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17072/0/321; GOOF = 1.106; final R indices [I>2σ(I)]: R1 = 0.038, wR2 = 0.0817. Z.R. Tshentu, T.I.A. Gerber, R. Walmsley, P. Mayer, Polyhedron 27 (2008) 406.
[18]
T. Jin, G. Li, X. Zhou, J. Zuo, Inorg. Chem. Comm. 14 (2011) 1944.
[19]
N.A. Illan-Cabeza, A.R. Garcia-Garcia, M.N. Moreno-Carretero, Inorg. Chim. Acta 366
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[17]
(2011) 262; B. Machura, R. Kruszynsk, J. Organomet. Chem. 692 (2007) 4161. [20]
Crystallographic data for 2, C21H20N3O5Re: triclinic; space group Pī; a = 10.2572(5), b = 10.5903(5), c = 10.6681(5) Å, α = 91.510(2), β = 117.698(2), γ = 98.091(2)°; V = 1010.25(13)
Å3;
Z
=
1;
Dc
=
1.91
Mg/m3;
μ
=
6.053
mm-1;
data/restraints/parameters 5782/0/277; GOOF = 1.134; final R indices [I>2σ(I)]: R1 = 0.0147, wR2 = 0.0360. [21]
A.
Brink,
H.G.
Visser,
A.
Roodt,
Polyhedron
(2012),
http://dx.doi.org/10.1016/j.poly.2012.08.059. [22]
T.I.A. Gerber, K.C. Potgieter, P. Mayer, Inorg. Chem. Comm. 14 (2011) 1115; R.F. Vitor, S. Alves, J.D.G. Correia, A. Paulo, I. Santos, J. Organomet. Chem. 689 (2004) 4764; R. Czerwieniec, A. Kapturkiewicz, J. Lipkowski, J. Nowacki, Inorg. Chim. Acta 358 (2005) 2701.
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ACCEPTED MANUSCRIPT [23]
T.I.A. Gerber, R. Betz, I.N. Booysen, K.C. Potgieter, P. Mayer, Polyhedron 30 (2011) 1739. K. Potgieter, P. Mayer, T. Gerber, N. Yumata, E. Hosten, I. Booysen, R. Betz, M.
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Ismail, B. van Brecht, Polyhedron 49 (2012) 67.
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[24]
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Figure 1
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Figure 2
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Figure 3
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Graphical Abstract
The coordination behaviour of Schiff base ligands containing chromone (H2pch, 2-(2and
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aminophenyliminomethyl)-4H-chromen-4-one)
benzimidazole
(Hbzp,
N-(2-
hydroxybenzylidene)-benzimidazole) moieties towards the fac-[ReI(CO)3]+ core are
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explored. Novel mononuclear fac-[Re(CO)3(bzch)Cl], (1), and dinuclear μ-(bzp)2[Re(CO)3]2, (2), compounds have been isolated and characterized.
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ACCEPTED MANUSCRIPT Highlights
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Novel mono- and dinuclear rhenium(I) compounds
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Schiff base ligands containing chromone and benzimidazole moieties respectively
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Three distinct emission bands
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Crystallographically-required inversion symmetry
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