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Solvent-free synthesis of bisferrocenylimines and their rhodium(I) complexes
Polyhedron 29 (2010) 1095–1101
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Solvent-free synthesis of bisferrocenylimines and their rhodium(I) complexes P.E. Kleyi *, C.W. McCleland, T.I.A. Gerber Department of Chemistry, Nelson Mandela Metropolitan University, P.O. Box 77000, Port Elizabeth 6031, South Africa
a r t i c l e
i n f o
Article history: Received 5 October 2009 Accepted 20 November 2009 Available online 27 November 2009 Keywords: Solvent-free Bisferrocenylimines Rhodium(I)
a b s t r a c t The solvent-free reaction of ferrocenecarboxaldehyde and diaminoalkanes under solvent-free conditions gave bisferrocenylimines (L) in excellent yields. Cationic rhodium(I) complexes with the formulation [Rh(COD)(L)]ClO4 were prepared by the reaction of [Rh(COD)Cl]2 with the bisferrocenylimines in the presence of silver perchlorate. The compounds were characterised by NMR, IR, MS and elemental analysis. The X-ray crystal structures of two rhodium(I) complexes are also reported. Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction The discovery and characterisation of ferrocene in the early 1950s [1] led to an explosion of interest in d-block metal–carbon bonds and stimulated the development of organometallic chemistry [2–6]. Ferrocene derivatives are extremely versatile, since they can be used in a variety of functions, such as in the synthesis of non-linear optical materials, organometallic complexes, and in catalysis [7–10]. The preparation of bisferrocenylimines has usually been performed under homogeneous conditions in the presence of classical solvents [11–14]. Unfortunately, the methods employed usually required prolonged heating of the reaction mixture under reflux in high boiling solvents [11,12], and also required expensive catalysts [13]. Cationic Rh(I) complexes of bisferrocenylimines have been investigated for their catalytic activity in olefin polymerisation reactions [15]. Some 1,10 -bisferrocenylimines have been prepared and used for the synthesis of cyclopalladated complexes [11]. As an extension to our previous studies [16,17], we report here the solvent-free synthesis of bisferrocenylimines. 2. Results and discussion 2.1. Synthesis and characterisation of bisferrocenylimines The solvent-free mixing and grinding of two mole equivalents of ferrocenecarboxaldehyde with the appropriate diaminoalkane gave the corresponding bisferrocenylimines in excellent yields (Scheme 1). * Corresponding author. Tel.: +27 415042278; fax: +27 415044236. E-mail address: [email protected] (P.E. Kleyi). 0277-5387/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.poly.2009.11.017
On grinding the mixture of reagents, a melt was obtained which eventually solidified at room temperature. However, for prf the melt obtained only gradually solidified at room temperature, after the removal of water formed during the condensation. Compounds etf [13,15] and prf [13] have been reported elsewhere; however, they are reported here for the first time under solvent-free conditions. The solidified melts were initially analysed by infrared (IR) spectroscopy using a potassium bromide disc. Infrared analysis showed the disappearance of the carbonyl (C@O) band (at approximately 1700 cm1) and the appearance of the strong imine (C@N) band at 1646 cm1. The solidified melts were ultimately recrystallized from a minimum amount of cold anhydrous methanol to provide a pure product. 1 H NMR spectra of all the bisferrocenylimines showed proton signals in the region d 8.1–8.2 ppm which are indicative of the presence of the imine (CH@N) protons. While etf, prf, hef and ocf exhibited one singlet for the imine protons, buf showed two singlets at d 8.23 and 8.22 ppm. This indicates that the two imines protons of buf are chemically inequivalent. 1H NMR spectra of the compounds L were expected to possess some similarities, since the only difference in their molecular structures was the length of the alkyl chain of the diamines. A singlet was observed at d 3.78 ppm for etf, indicative of the four protons for the two CH2 groups. Compound prf has an additional CH2 group in the b-position and exhibited a triplet at d 3.56 and a multiplet at d 2.03 ppm due to the four protons of the two terminal (a) CH2 groups and two protons of the middle (b) CH2 group, respectively. As expected, buf, with four CH2 groups, exhibited a triplet at d 3.7 ppm due to the protons on the terminal (a) CH2 groups and a multiplet at d 1.71 ppm due to the protons on the middle (b) CH2 groups. Three signals were observed for hef; a triplet at d 3.45 ppm for the protons on the terminal (a) CH2 groups and two multiplets at d 1.66 and 1.44 ppm for the protons on the
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CHO
2
Fe
N Grind
(CH2)
CH
H2N(CH2)xNH2
x
Fe
N CH Fe
x = 2: x = 3: x = 4: x = 6: x = 8:
etf prf buf hef ocf
Scheme 1. Solvent-free synthesis of bisferrocenylimines.
Table 1 Chemical shifts for protons on the CH2 groups directly bonded to nitrogen atoms. Compound L
Chemical shift d (ppm)
etf prf buf hef ocf
3.78 3.56 3.47 3.45 3.42
inner (b) CH2 groups and the middle (c) CH2 groups, respectively. An interesting scenario was observed with ocf, where instead of four signals that would have been expected, only three were observed. A triplet at d 3.42 ppm, due to the protons on the terminal (a) CH2 groups, a multiplet at d 1.62 ppm for the inner (b) CH2 groups, and a singlet at d 1.30 ppm for the protons on the four middle CH2 groups were observed. This suggested that the deshielding effect of the nitrogen groups became less pronounced as the length of the alkyl chain increased. The substituted cyclopentadienyl ring of the ferrocene moiety for all the compounds was represented by two pseudotriplets and a very intense singlet for the unsubstituted cyclopentadienyl ring. For all the compounds L, the chemical shifts of the protons on the CH2 groups directly bonded to the nitrogen groups were expected to be very similar. However, this was not the case and the results are summarised in Table 1. This table shows that the proton signals are shifted to lower frequencies (less deshielding) as the length of the alkyl chains increased. This effect could be attributed to the increase in the distance from the second electronegative N atom. A significant change was observed between etf and prf, as well as prf and buf, while there was less change from buf to hef to ocf. Additionally, for prf–ocf, these protons appeared as triplets, indicating some vicinal proton–proton coupling. For etf a singlet was observed showing that there was no vicinal coupling between the neighbouring protons. 13 C NMR spectra for all compounds showed signals for the imine carbons in the region d 160–163 ppm. The observed carbon signals for all the compounds were as expected. Compound etf exhibited a single signal at d 62.80 ppm for two CH2 groups, while for prf two signals were observed at d 59.25 and 32.90 ppm, representing the carbons directly bonded to nitrogen groups and the middle carbons, respectively. Compounds buf, hef and ocf exhibited two, three and four signals, respectively, in the expected chemical shift regions for the CH2 groups. All the compounds are stable in the solid state at room temperature and in air, while they showed some degree of instability in solution [12]. Attempts to perform the same reactions using acetylferrocene were unsuccessful, even after heating the reaction mixtures up to 65 °C. The inability of acetylferrocene to react is attributed to the steric hindrance of the methyl group. 2.2. Synthesis of cationic rhodium(I) complexes The rhodium(I) compounds [Rh(COD)(L)]ClO4 were synthesized by a literature procedure as illustrated in Scheme 2 [15]. A solution
of silver perchlorate in acetone was added to a solution of [Rh(COD)Cl]2 in acetone. On precipitation of silver chloride, a solvated complex of general formula [Rh(COD)(acetone)2]ClO4 was formed [15,18]. The addition of a bisferrocenylimine ligand resulted in the formation of a cationic complex by the displacement of the coordinated solvent from the rhodium coordination sphere. The complexes 1, 2 and 3 were obtained in low to excellent yields by redissolving the residue, after concentration of solvent, in dichloromethane and precipitating them by the addition of diethyl ether. The complexes were further purified by recrystallization. Compound 2 was produced in the highest yield, 84%, whereas 1 was obtained in the lowest yield, 32%. This effect was attributed to the stability of the six-membered ring formed by the bidentate ligand prf with the metal centre, compared to the five- and sevenmembered rings formed by etf and buf, respectively. Attempts to prepare complexes with hef, and ocf were unsuccessful. 1 H NMR chemical shifts of the imine (CH@N) proton for 2 and 3 were observed in the expected region while, for 1 the peak was shifted to a lower frequency. This effect has also been observed by Lee et al. [15]. The signal in 1 moved from d 8.17 ppm in the free ligand to d 7.42 ppm in the complex, while in 2 and 3 it was observed at d 8.31 and d 8.22 ppm, respectively. In the ferrocene region, a sharp singlet was observed at d 4.37 and 4.07 ppm for 1 and 2, respectively, and it was assigned to the unsubstituted cyclopentadienyl ring. Two singlets at d 4.73 and 4.80 ppm for 1 were assigned to the substituted cyclopentadienyl ring. The substituted cyclopentadienyl ring signals for 2 were observed at d 4.23 and 4.72 ppm. The appearance of additional signals in the ferrocene region of 3 complicated the assignments. Two sharp and equally intense singlets were observed at d 4.26 and 4.14 ppm, and are assigned to the unsubstituted cyclopentadienyl rings. This suggests that the cyclopentadienyl rings are chemically inequivalent due to the trans orientation of one imine (C21–C9–N1–C10 = 179.2°), and the cis orientation of the other imine (C41–C14–N2–C13 = 2.54°), something that was not observed in 1 and 2. The origin of this cis–trans orientation is unclear. Other signals could not be assigned due to the complexity of the signals in the region. Initially, it was thought that the extra signals were due to the presence of impurities. However, the signals remained even after several recrystallizations. The COD ligand exhibited the expected patterns, giving rise to a singlet due to CH@CH protons at d 4.16 ppm, a multiplet d 2.64 ppm and a doublet d 2.09 ppm due to CH2 protons, for 1. For 2 and 3 the CH@CH proton signal was split into two singlets at d 5.48 and 5.39 ppm and 6.11 and 5.65 ppm, respectively. The CH2 signals were observed in the expected region for both 2 and 3. 13C NMR showed the C@N signals in the expected region: d 168.48, 170.44 and 170.39 ppm for 1, 2 and 3, respectively. The ferrocene signals for 1 and 2 were observed in the expected region while the same problem as with the 1H NMR was experienced for 3. The COD signals were also observed in the expected region for all complexes. IR spectra of all the compounds showed that the v(C@N) stretching signals have moved to lower frequencies.
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Cl Rh
+
Rh
2 AgClO4
acetone
[Rh(COD)(acetone)2]ClO4 + AgCl (s)
Cl 2L
x = 2: [1] = 3: [2] = 4: [3]
N
(CH2)
CH Fe
x
N CH Fe
Rh
ClO4
Scheme 2. Procedure for the synthesis of rhodium(I) compounds.
Table 2 Crystal data and structure refinement of 2 and 3. 2
3
Empirical formula Formula weight Temperature (K) Wavelength (Å) Crystal system Space group
C33H38ClFe2N2O4Rh 776.71 113(2) 0.71073 triclinic P1
C34H40ClFe2N2O4Rh 790.74 173(2) 0.71073 monoclinic P21/c
Unit cell dimensions a (Å) b (Å) c (Å) a () b () c () Volume (Å3) Z Calculated density (Mg/m3) Reflections collected/unique Goodness-of-fit (GOF) on F2 Final R indices (R1, wR2) R indices (all data) (R1, wR2)
12.0890(2) 16.5931(2) 17.5512(3) 67.8240(10) 72.9460(10) 72.3860(10) 3042.77(8) 4 1.696 70435/11534 1.023 0.0456, 0.0875 0.0758, 0.0987
12.983(3) 13.536(2) 17.729(4) 90 92.580(7) 90 3112.6(11) 4 1.687 48758/5716 1.034 0.0611, 0.0934 0.1324, 0.1119
Fig. 1. ORTEP drawing of 2.
2.3. X-ray crystallography Crystals of 2 and 3 suitable for X-ray crystallographic analysis were obtained by the slow diffusion of diethyl ether into a solution of the complex in dichloromethane. Complex 2 crystallized in a tri with Z = 4 and contains two molecules (strucclinic space group P 1 tural isomers) in the asymmetric unit. Complex 3 crystallized in the monoclinic space group P21/c with Z = 4 (Table 2). The ORTEP drawings shown in Figs. 1 and 2 confirm the molecular structures of 2 (structural isomer 2A) and 3. The bond lengths, angles, torsion angles and other parameters are given in Tables 3 and 4 for 2 and 3, respectively. The rhodium atom is placed in an essentially square planar geometry defined by the two nitrogen atoms of the diimine ligand and the two C@C double bonds of the COD ligand. The six-membered ring formed in 2, by the rhodium atom, the two nitrogen atoms of the ligand and the three carbon atoms of the alkyl chain separating the two nitrogen atoms is in a chair conformation. The chair conformation is the lowest energy state that a six-membered ring can be found in, which explains the reason for 2 being obtained in excellent yields. The Rh(1A)–N(1A) and Rh(1A)–N(2A) bond distances for molecule 2A are 2.077(4) and 2.095(4) Å, respectively. For molecule 2B, the Rh(1B)–N(2B) and Rh(1B)–N(1B) the bond distances are 2.076(4) and 2.088(4) Å, respectively. The bond distances Rh(1A)–C(2A),
Fig. 2. ORTEP drawing of 3.
Rh(1A)–C(6A), Rh(1A)–C(1A) and Rh(1A)–C(5A) for molecule 2A, are 2.144(4), 2.150(5), 2.152(4) and 2.158(4) Å, respectively. On the other hand, for molecule 2B the bond distances
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Table 3 Selected bond distances and angles of 2. Molecule A
Molecule B
Rh(1A)–N(1A) Rh(1A)–N(2A) Rh(1A)–C(2A) Rh(1A)–C(6A) Rh(1A)–C(5A) Rh(1A)–C(2B) N(1A)–C(9A) N(2A)–C(13A) N(1A)–(Rh(1A)–N(2A) N(1A)–(Rh(1A)–C(2A) N(2A)–(Rh(1A)–C(2A) N(1A)–(Rh(1A)–C(6A) N(2A)–(Rh(1A)–N(6A) C(2A)–(Rh(1A)–N(CA) N(2A)–Rh(1A)–N(2A)–C(9A) C(2A)–Rh(1A)–N(1A)–C(9A) C(6A)–Rh(1A)–N(1A)–C(9A) C(1A)–Rh(1A)–N(1A)–C(9A)
2.077(4) 2.095(4) 2.144(4) 2.150(5) 2.152(4) 2.158(4) 1.294(6) 1.277(5) 85.92(14) 92.34(16) 171.25(16) 154.73(17) 89.01(16) 96.11(18) 112.4(4) 59.0(4) 168.7(4) 96.7(4)
Table 4 Selected bond distances and angles of 3. Bond distances Rh(1)–N(1) Rh(1)–N(1) Rh(1)–C(6) Rh(1)–C(2) Rh(1)–C(5) Rh(1)–C(1) N(1)–C(9) N(1)–C(10) N(2)–C(14) N(2)–C(13) C(9)–C(21) C(10)–C(11) C(11)–C(12) C(12)–C(13) C(14)–C(41)
Bond angles 2.089(5) 2.105(5) 2.135(6) 2.146(6) 2.150(6) 2.165(6) 1.283(7) 1.478(7) 1.289(7) 1.473(7) 1.450(8) 1.512(8) 1.522(8) 1.522(8) 1.470(8)
N(1)–Rh(1)–N(2) N(1)–Rh(1)–C(6) N(2)–Rh(1)–C(6) N(1)–Rh(1)–C(2) N(2)–Rh(1)–C(2) C(6)–Rh(1)–C(2) N(1)–Rh(1)–C(5) N(2)–Rh(1)–C(5) C(6)–Rh(1)–C(5) C(2)–Rh(1)–C(5) C(10)–(11)–C(12) C(13)–C(12)–C(11) C(25)–C(21)–C(22) C(25)–C(21)–C(9) C(22)–C(21)–C(9)
89.04(18) 158.7(2)) 92.9(2) 89.7(2) 153.2(2) 97.8(2) 163.6(2) 91.8(2) 37.6(2) 82.2(2) 116.1(5) 114.7(5) 106.6(6) 130.7(6) 122.4(6)
Rh(1B)–C(2B), Rh(1B)–C(5B), Rh(1B)–C(6B) and Rh(1B)–C(1B) are 2.130(4), 2.143(4), 2.144(4) and 2.171(4) Å, respectively. In complex 3, the Rh(1)–N(1) and Rh(1)–N(2) bond distances are 2.089(5) and 2.105(5) Å and are slightly longer than those for 2. The Rh(1)–C(6), Rh(1)–C(2), Rh(1)–C(5) and Rh(1)–C(1) distances are 2.135(6), 2.146(6), 2.150(6) and 2.165(6) Å, respectively. The bite angle N(1)–Rh(1)–N(2) of 89.0(2)° is much close to the ideal 90° a square planar complex. 2.4. Electronic spectroscopy The UV–Vis spectra of the bisferrocenylimines and their rhodium(I) complexes were obtained in dichloromethane solution. Spectral comparisons with unsubstituted ferrocene as a reference were also made. Ferrocene exhibits two bands at wavelengths of kmax 326 and 442 nm, which have been assigned to 1A2g ? 1E2g and 1A1g ? 1E1g ligand field d–d transitions [19]. The ferrocenyl bands in compounds L were observed at longer wavelengths kmax (Fig. 3(top)), largely due to conjugation with the CH@N bond. Bathochromic shifts are anticipated where conjugation increases in length. Some absorption bands due to p ? p* and n ? p* transitions of the imine groups CH@N in L were also observed at wavelengths lower than 300 nm. The extinction coefficients of the compounds L were higher for the band at lower wavelengths and lower for the band at higher wavelengths than that of ferrocene. In comparison with the free ligands, spectra of complexes 1–3 exhibited an extra band at kmax 350, 382 and 383 nm, respectively
Rh(1B)–N(2B) Rh(1B)–N(1B) Rh(1B)–C(2B) Rh(1B)–C(5B) Rh(1B)–C(6B) Rh(1B)–C(1B) N(1B)–C(9B) N(2B)–C(13B) N(2B)–(Rh(1B)–N(1B) N(2B)–(Rh(1B)–C(2B) N(1B)–(Rh(1B)–C(2B) N(2B)–(Rh(1B)–C(5A) N(1B)–(Rh(1B)–C(5A) C(2B)–(Rh(1B)–C(5A) N(2B)–Rh(1B)–N(1B)–C(9B) C(2B)–Rh(1B)–N(1B)–C(9B) C(5B)–Rh(1B)–N(1B)–C(9B) C(6B)–Rh(1B)–N(1B)–C(9B)
2.076(4) 2.088(4) 2.130(4) 2.143(4) 2.144(4) 2.171(4) 1.289(6) 1.286(6) 85.06(14) 162.39(16) 95.29(16) 95.04(16) 174.44(16) 82.94(18) 112.8(4) 49.6(4) 21.5(19) 163.7(4)
(Fig. 3(bottom)). Moreover, the bands that were observed in the free ligands etf, prf and buf shifted to higher wavelengths, after coordination to rhodium(I). Both these bands at lower wavelengths appeared as shoulders in the complexes. 2.5. Cyclic voltammetry The observed redox behaviour of the compounds was compared with that of ferrocene as a standard. Ferrocene exhibits a one-electron reversible wave with E1/2 at 90.5 mV. The bisferrocenylimines exhibited a positive shift in potential indicating that these compounds became more difficult to oxidise (Table 5). These shifts can be attributed to the presence of the CH@N bond in close proximity to the ferrocene group, resulting in a reduced electron density at the metal centre. The rhodium(I) complexes exhibited positive shifts in potential, implying that the complexes became more resistant to oxidation than their corresponding free ligands (Table 5). 3. Experimental 3.1. Purification procedures All reagents and solvents were purified using standard purification and drying methods [20]. Ferrocenecarboxaldehyde, silver tetrafluoroborate and the chloro-(1,5-cyclooctadiene)rhodium(I) dimer were purchased from Sigma Aldrich. All other common laboratory chemicals were obtained locally and were used without further purification. 3.2. Instrumentation Melting points were determined on an Electrothermal IA 900 series digital melting point apparatus and were uncorrected. NMR spectra were recorded on a Bruker DPX (300 MHz) spectrometer at ambient temperatures. 1H NMR spectra were referenced against the deuterated solvent (CDCl3: d 7.28) and the values reported relative to tetramethylsilane (TMS: d 0.00). 13C NMR spectra were similarly referenced internally to the solvent resonance (CDCl3: d 77.0) with values reported relative to tetramethylsilane (TMS: d 0.00). Infrared spectra were recorded on a DigiLab FTS 3100 Excalibur HE series, running DigiLab Resolution 4.0 software with solid samples prepared as potassium bromide (KBr) disks. Microanalyses were obtained on a Carlo Erba EA 1108 elemental analyser at the
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Fig. 3. UV–Vis spectra of L (top) and 1–3.
Table 5 Half-wave potentials of compounds L and 1–3. Compound
Epa (mV)
Epc (mV)
E1/2 (mV)
Ferrocene etf prf buf hef ocf 1 2 3
140 243 246 243 238 242 413 388 372
41 124 167 171 168 163 342 300 261
90.5 133.5 206.5 207 203 202.5 327.5 344 316.5
University of Cape Town. Fast atomic bombardment (FAB) and high resolution (EI) mass spectra were recorded on a micromass autoTof mass spectrometer at the Witwatersrand University in South Africa. UV–Vis spectra were recorded on a Hewlett Packard 8452A diode array spectrometer in dichloromethane (103 M) with a cell width of 1 cm.
Cyclic voltammograms were obtained on a BAS 100B electrochemical analyser with a three-electrode system using Ag/AgNO3 (0.01 M) as a reference electrode, platinum wire as the auxiliary electrode and platinum disc as the working electrode. Samples (103 M) were prepared and run under nitrogen at ambient temperatures, in acetonitrile with tetrabutylammonium perchlorate (0.1 M) as a background electrolyte. The scan rate used was 100 mV s1. Solutions were saturated with nitrogen by bubbling for 10 min prior to each run. The system gave ferrocene E1/ 2 = 90.5 mV. X-ray crystal intensity data were collected on a Nonius KappaCCD diffractometer using graphite monchromated Mo Ka radiation at the University of Cape Town. Temperature was controlled by an Oxford Cryostream cooling system (Oxford Cryostat). The strategy for the data collections was evaluated using the Bruker Nonius ‘‘Collect” program [21]. Data were scaled and reduced using DENZO-SMN software [21]. The empirical absorption correction utlilized the program SADABS, and the structure was solved by direct methods and refined by full-matrix least-squares with the program 2 SHELXL-97, refining on F [22,23]. Packing diagrams were produced
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using the program PovRay and graphic interface X-seed [24]. All the non-H atoms, except C(29B), C(30B) and C(33B), were refined anisotropically. These ferrocenyl carbons exhibit high thermal motions with Uiso between 0.06356 and 0.09921, and were treated isotropically. 3.3. Synthesis of bisferrocenylimines 3.3.1. General procedure Ferrocenecarboxaldehyde (2 mol equivalents) and the diamine (1 mol equivalent) were added to a Pyrex tube fitted with glass ground joint. The two compounds were ground together at room temperature (ca. 25 °C) using a glass rod. The tube was then placed under a high vacuum pump overnight. The products were obtained as yellow to orange solids after recrystallization from cold anhydrous methanol. 3.3.1.1. N,N0 -ethylenebis(ferrocenylmethylidene)imine (etf). Ferrocenecarboxaldehyde (360 mg, 1.68 mmol) and ethylenediamine (50 mg, 0.84 mmol). The product was obtained as a yellow solid (380 mg, 99%). M.p. 147–150 °C; 1H NMR (CDCl3): 8.18 (2H, s, N@CH), 4.63 (4H, t, J = 1.8, C5H4), 4.30 (4H, t, J = 1.8, C5H4), 4.16 (10H, s, C5H5), 3.78 (4H, s, 2 CH2); 13C NMR (CDCl3): 162.74, 80.85, 70.75, 69.52, 68.86, 62.80; IR (KBr): 3113, 3071, 2917, 2897, 2832, 1782, 1705, 1643, 1462, 1412, 1381, 1327, 1281, 1246, 1215, 1211, 1103, 1049, 1011, 961, 891, 822, 768, 644, 594, 517, 486, 475, 436, 401; m/z (EI): 453 (29%), 452 ([M+], 80%), 321 (13%), 256 (31%), 241 (22%), 227 (19%) 226 (63%), 213 (92%), 199 (27%), 186 (14%), 160 (14%), 121 (63%), 69 (21%), 56 (16%), 43 (11%), 41(11%), 32 (32%), 30 (11%), 28 (100%); MW, 452.15076. Found: MW, 452.06%. 3.3.1.2. N,N0 -propylenebis(ferrocenylmethylidene)imine (prf). Ferrocenecarboxaldehyde (200 mg, 0.93 mmol) and 1,3-diaminopropane (41 mg, 0.55 mmol). The product was obtained as an orange solid (204 mg, 94%). M.p. 127–129 °C; 1H NMR (CDCl3) 8.18 (2H, s, N@CH), 4.67 (4H, t, J = 1.8, C5H4), 4.39 (4H, t, J = 1.8, C5H4), 4.21 (10H, s, C5H5), 3.56 (4H, t, J = 7.0, 2 CH2), 2.03 (2H, m, CH2); 13C NMR (CDCl3) 160.57, 81.88, 70.28, 69.25, 68.64, 59.25, 32.90; IR (KBr) 3108, 3066, 2929, 2946, 2866, 2823, 1640, 1470, 1449, 1323, 1243, 1105, 1004, 823, 544; m/z (EI) 467 (24%), 466 ([M+], 100%), 401 (30%), 335 (56%), 255 (55%), 254 (38%), 253 (30%), 241 (24%), 240 (60%), 233 (26%), 227 (62%), 226 (24%), 225 (21%), 212 (36%), 199 (38%), 186 (52%), 129 (25%), 120 (90%), 56 (52%), 39 (28%); Anal. Calc. for C25H26N2Fe2: C, 64.41; H, 5.62; N, 6.01; MW, 466.18. Found: C, 63.15; H, 5.82; N, 5.75; MW, 466.08%. 3.3.1.3. N,N0 -butylenebis(ferrocenylmethylidene)imine (buf). Ferrocenecarboxaldehyde (200 mg, 0.93 mmol) and 1,4-diaminobutane (44 mg, 0.50 mmol). The product was isolated as an orange solid (207 mg, 92%). M.p. 152–154 °C; 1H NMR (CDCl3) 8.19 (1H, s, CH@N), 8.16 (1H, s, CH@N) 4.65 (2H, t, J = 1.8, C5H4), 4.36 (2H, t, J = 1.7, C5H4), 4.19 (10H, s, C5H5), 3.47 (4H, t, J = 7.0, 2 CH2), 1.71 (4H, m, 2 CH2); 13C NMR (CDCl3) 160.29, 81.08, 70.69, 69.47, 68.78, 62.07, 29.09; IR(KBr) 3071, 2930, 2860, 2814, 2364, 1644, 1470, 1439, 1407, 1381, 1369, 1324, 1244, 1104, 1041, 1020, 1001, 962, 930, 819; m/z (EI) 481 (5%), 480 ([M+], 13%), 284 (15%), 268 (23%), 267 (100%), 213 (15%), 199 (17%), 121 (50%), 56 (18%), 55 (15%), 44 (25%), 43 (34%), 41 (26%), 39 (22%), 30 (67%), 28 (61%), 27 (20%). Anal. Calc.1 for C26H28N2Fe2: C, 65.03; H, 5.88; N, 5.83; MW, 480.20. Found: C, 64.51; H, 6.05; N, 5.74; MW, 480.10%. 1 The tendency for the C and N content to be too low and H too high could be due to the presence of traces of water. This also applies to compounds hef, ocf and 3.
3.3.1.4. N,N0 -hexylenebis(ferrocenylmethylidene)imine (hef). Ferrocenecarboxaldehyde (100 mg, 0.47 mmol) and 1,6-diaminohexane (24 mg, 0.23 mmol). The product was isolated as a light yellow solid (109 mg, 94%). M.p. 109–111 °C; 1H NMR (CDCl3) 8.16 (2H, s, CH@N), 4.65 (4H, t, J = 1.8, C5H4), 4.36 (4H, t, J = 1.8, C5H4), 4.19 (10H, s, C5H5), 3.45 (4H, t, J = 6.2, 2 CH2), 1.66 (4H, m, 2 CH2), 1.44 (4H, m, 2 CH2); 13C NMR (CDCl3) 161.08, 81.96, 70.67, 69.46, 68.78, 62.30, 31.32, 27.61; IR (KBr) 3099, 2935, 2862, 2822, 1646, 1468, 1454, 1409, 1381, 1351, 1326, 1243, 1204, 1164, 1103, 1063, 1051, 1038, 1004, 957, 936, 876, 865, 846, 826, 807; m/z (EI) 509 (15%), 508 ([M+], 41%), 312 (20%), 296 (19%), 295 (71%), 214 (23%), 213 (26%), 199 (27%), 186 (30%), 121 (100%), 56 (34%), 55 (22%), 43 (24%), 41 (39%), 39 (41%), 30 (27%), 28 (49%), 27 (33%). Anal. Calc. for C28H32N2Fe2: C, 66.17; H, 6.35; N, 5.51; MW, 508.26. Found: C, 64.31; H, 6.46; H, 5.40; MW, 508.13%. 3.3.1.5. N,N0 -octylenebis(ferrocenylmethylidene)imine (ocf). Ferrocenecarboxaldehyde (200 mg, 0.93 mmol) and 1,8-diaminooctane (239 mg, 0.47 mmol). The product was obtained as a yellow solid (231 mg, 97 %). M.p. 97–100 °C; 1H NMR (CDCl3) 8.15 (2H, s, N@CH), 4.65 (4H, t, J = 1.8, C5H4), 4.36 (4H, t, J = 1.8, C5H4), 4.19 (10H, s, C5H5) 3.42 (4H, t, J = 6.6, 2 CH2), 1.62 (4H, m, 2 CH2), 1.40 (8H, s, 4 CH2); 13C NMR (CDCl3) 161.00, 81.13, 70.66, 69.46, 68.78, 62.35, 31.33, 29.84, 27.73; IR (KBr) 3065, 2923, 2848, 2819, 1646, 1612, 1494, 1471, 1371, 1327, 1243, 1106, 1043, 1022, 1001, 950, 824, 768, 725, 545; m/z (EI) 537 (29%), 536 ([M+],100%), 471 (20%), 341 (14%), 340 (79%), 268 (19%), 226 (15%), 213 (19%), 199 (26%), 186 (15%), 121 (49%), 55 (16%), 43 (14%), 30 (43%). Anal. Calc. for C30H36N2Fe2: C, 67.19; H, 6.77; N, 5.22; MW, 536.31. Found: C, 65.23; H, 7.19; N, 5.59; MW, 536.16%. 3.4. Synthesis of cationic rhodium(I) complexes 3.4.1. General procedure Silver perchlorate (0.23 mmol) in acetone (2 cm3) was added to a solution of the chloro-(1,5-cyclooctadiene)rhodium dimer (0.11 mmol) in acetone (30 cm3). After removal of the precipitated AgCl, the reaction mixture was heated under reflux for 30 min. The reaction mixture was treated with bisferrocenylimine (0.23 mmol) in toluene (20 cm3) and the resultant dark red solution was left to stir at room temperature (ca. 25 °C) for 3 h. Solvents were removed in vacuo and the dark red solid was recrystallized from a dichloromethane/hexane mixture. The products were obtained as dark red to orange solids. 3.4.1.1. [Rh(COD)(etf)]ClO4 (1). N,N0 -ethylenebis(ferrocenylmethylidene)imine (104 mg, 0.23 mmol) in toluene (20 cm3). The complex was obtained as a dark red solid (27 mg, 32%). M.p. 215 °C (decomp) (lit. 192 °C, decomp.); 1H NMR (CDCl3) 7.43 (2H, s, N@CH), 4.80 (4H, t, J = 1.7, C5H4), 4.73 (4H, t, J = 1.8, C5H4), 4.37 (10H, s, C5H5), 4.16 (4H, s, COD-CH), 3.85 (4H, s, CH2), 2.64 (4H, br-s, COD-CH2), 2.09 (4H, d, J = 7.5, COD-CH2); 13C NMR (CDCl3) 168.48, 84.65, 84.49, 74.71, 73.23, 70.68, 57.01, 30.55; IR (KBr); 3249, 2951, 2886, 2836, 1612, 1447, 1412, 1377, 1259, 1219, 1098, 1102, 954, 825, 733, 622, 479; m/z (FAB) 665 ([M++2], 3%), 663 ([M+], 29%), 553 (3%), 489 (2%), 453 (9%), 333 (3%), 308 (18%), 289 (16%), 233 (4%), 154 (100). MW, 663.06. Found: MW, 662.70%. 3.4.1.2. [Rh(COD)(prf)]ClO4 (2). N,N0 -propylenebis(ferrocenylmethylidene)imine (107 mg, 0.23 mmol) in toluene (20 cm3). The complex was obtained as a reddish orange solid (72 mg, 84%). M.p. 220 °C (decomp.); 1H NMR 8.31 (2H, s, N@CH), 5.49 (2H, s, COD-CH), 5.39 (2H, s, COD-CH), 4.72 (4H, s, C5H4), 4.68 (4H, s, 2 CH2), 4.23 (4H, s, C5H4), 4.17 (2H, m, CH2), 4.07 (10H, s,
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C5H5), 2.59 (4H, br-s, COD-CH2), 1.97 (4H, d, J = 7.7, COD-CH2) 13C NMR (CDCl3) 170.44, 77.62, 75.61, 73.41, 70.51, 70.28, 65.04, 30.89, 30.55; IR (KBr) 3106, 2933, 2852, 1624, 1457, 1411, 1373, 1331, 1253, 1093, 1052, 998, 897, 829, 622; m/z (FAB) 677 ([M+], 11%), 675 (2%), 567 (2%), 467 (5%), 424 (3%), 347 (2%), 307 (18%), 289 (17%), 242 (2%), 154 (100%). Anal. Calc. for C33H38N2Fe2Rh: C, 51.03; H, 4.93; N, 3.61; MW, 677.26. Found: C, 50.27; H, 4.59; N, 3.48; MW, 676.7%.
Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: [email protected]
3.4.1.3. [Rh(COD)(buf)]ClO4 (3). N,N0 -butylenebis(ferrocenlmethylidene)imine (111 mg, 0.23 mmol). The complex was obtained as an orange solid (68.3 mg, 70%). M.p. 228 °C (decomp.); 1H NMR (CDCl3) 8.23 (1H, s, CH@N), 8.22 (1H, s, CH@N) 6.11 (2H, s, CODCH), 5.65 (2H, s, COD-CH), 4.14 (5H, s, C5H5), 4.12 (5H, s, C5H5), 2.62 (4H, m, COD-CH2), 1.79 (4H, s, COD-CH2), other signals could not be assigned properly; 13C NMR (CDCl3) 170.53, 170.35, 84.58, 75.63, 73.74, 73.90, 73.33, 70.04, 69.96, 69.78, 66.46, 58.02, 29.29, 28.73; IR (KBr) 3101, 3013, 2926, 2882, 2838, 1620, 1454, 1436, 1414, 1375, 1331, 1256, 1146, 1103, 1046, 1002, 967, 830, 624, 506, 483; m/z (FAB) 693 ([M++2], 9%) 691 ([M+], 65%), 581 (7%), 495 (4%), 481 (6%), 396 (5%), 345 (3%), 307 (21%), 289 (20%), 233 (7%), 154 (100%). Anal. Calc. for C34H40N2Fe2Rh: C, 51.64; H, 5.10; N, 3.54; MW, 691.09. Found: C, 51.46; H, 5.43; N, 3.31; MW, 690.70%.
References
4. Conclusions
Acknowledgements We are thankful to the Nelson Mandela Metropolitan University (NMMU) and the National Research Foundation (NRF) for financial assistance.
[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14]
Solvent-free synthesis and characterisation of bisferrocenylimines was achieved. The solvent-free approach was simple, fast and gave excellent yields at room temperature. UV–Vis spectra and cyclic voltammograms of rhodium(I) complexes confirmed coordination of the ligands. The structures of the complexes were successfully determined by X-ray crystallography, with 2 having a cis configuration and 3 a cis–trans configuration. Supplementary data CCDC 735149 and 735150 contain the supplementary crystallographic data for complex 2 and 3. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road,
[15] [16] [17] [18] [19] [20]
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Solvent-free synthesis of bisferrocenylimines and their rhodium(I) complexes P.E. Kleyi *, C.W. McCleland, T.I.A. Gerber Department of Chemistry, Nelson Mandela Metropolitan University, P.O. Box 77000, Port Elizabeth 6031, South Africa
a r t i c l e
i n f o
Article history: Received 5 October 2009 Accepted 20 November 2009 Available online 27 November 2009 Keywords: Solvent-free Bisferrocenylimines Rhodium(I)
a b s t r a c t The solvent-free reaction of ferrocenecarboxaldehyde and diaminoalkanes under solvent-free conditions gave bisferrocenylimines (L) in excellent yields. Cationic rhodium(I) complexes with the formulation [Rh(COD)(L)]ClO4 were prepared by the reaction of [Rh(COD)Cl]2 with the bisferrocenylimines in the presence of silver perchlorate. The compounds were characterised by NMR, IR, MS and elemental analysis. The X-ray crystal structures of two rhodium(I) complexes are also reported. Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction The discovery and characterisation of ferrocene in the early 1950s [1] led to an explosion of interest in d-block metal–carbon bonds and stimulated the development of organometallic chemistry [2–6]. Ferrocene derivatives are extremely versatile, since they can be used in a variety of functions, such as in the synthesis of non-linear optical materials, organometallic complexes, and in catalysis [7–10]. The preparation of bisferrocenylimines has usually been performed under homogeneous conditions in the presence of classical solvents [11–14]. Unfortunately, the methods employed usually required prolonged heating of the reaction mixture under reflux in high boiling solvents [11,12], and also required expensive catalysts [13]. Cationic Rh(I) complexes of bisferrocenylimines have been investigated for their catalytic activity in olefin polymerisation reactions [15]. Some 1,10 -bisferrocenylimines have been prepared and used for the synthesis of cyclopalladated complexes [11]. As an extension to our previous studies [16,17], we report here the solvent-free synthesis of bisferrocenylimines. 2. Results and discussion 2.1. Synthesis and characterisation of bisferrocenylimines The solvent-free mixing and grinding of two mole equivalents of ferrocenecarboxaldehyde with the appropriate diaminoalkane gave the corresponding bisferrocenylimines in excellent yields (Scheme 1). * Corresponding author. Tel.: +27 415042278; fax: +27 415044236. E-mail address: [email protected] (P.E. Kleyi). 0277-5387/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.poly.2009.11.017
On grinding the mixture of reagents, a melt was obtained which eventually solidified at room temperature. However, for prf the melt obtained only gradually solidified at room temperature, after the removal of water formed during the condensation. Compounds etf [13,15] and prf [13] have been reported elsewhere; however, they are reported here for the first time under solvent-free conditions. The solidified melts were initially analysed by infrared (IR) spectroscopy using a potassium bromide disc. Infrared analysis showed the disappearance of the carbonyl (C@O) band (at approximately 1700 cm1) and the appearance of the strong imine (C@N) band at 1646 cm1. The solidified melts were ultimately recrystallized from a minimum amount of cold anhydrous methanol to provide a pure product. 1 H NMR spectra of all the bisferrocenylimines showed proton signals in the region d 8.1–8.2 ppm which are indicative of the presence of the imine (CH@N) protons. While etf, prf, hef and ocf exhibited one singlet for the imine protons, buf showed two singlets at d 8.23 and 8.22 ppm. This indicates that the two imines protons of buf are chemically inequivalent. 1H NMR spectra of the compounds L were expected to possess some similarities, since the only difference in their molecular structures was the length of the alkyl chain of the diamines. A singlet was observed at d 3.78 ppm for etf, indicative of the four protons for the two CH2 groups. Compound prf has an additional CH2 group in the b-position and exhibited a triplet at d 3.56 and a multiplet at d 2.03 ppm due to the four protons of the two terminal (a) CH2 groups and two protons of the middle (b) CH2 group, respectively. As expected, buf, with four CH2 groups, exhibited a triplet at d 3.7 ppm due to the protons on the terminal (a) CH2 groups and a multiplet at d 1.71 ppm due to the protons on the middle (b) CH2 groups. Three signals were observed for hef; a triplet at d 3.45 ppm for the protons on the terminal (a) CH2 groups and two multiplets at d 1.66 and 1.44 ppm for the protons on the
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CHO
2
Fe
N Grind
(CH2)
CH
H2N(CH2)xNH2
x
Fe
N CH Fe
x = 2: x = 3: x = 4: x = 6: x = 8:
etf prf buf hef ocf
Scheme 1. Solvent-free synthesis of bisferrocenylimines.
Table 1 Chemical shifts for protons on the CH2 groups directly bonded to nitrogen atoms. Compound L
Chemical shift d (ppm)
etf prf buf hef ocf
3.78 3.56 3.47 3.45 3.42
inner (b) CH2 groups and the middle (c) CH2 groups, respectively. An interesting scenario was observed with ocf, where instead of four signals that would have been expected, only three were observed. A triplet at d 3.42 ppm, due to the protons on the terminal (a) CH2 groups, a multiplet at d 1.62 ppm for the inner (b) CH2 groups, and a singlet at d 1.30 ppm for the protons on the four middle CH2 groups were observed. This suggested that the deshielding effect of the nitrogen groups became less pronounced as the length of the alkyl chain increased. The substituted cyclopentadienyl ring of the ferrocene moiety for all the compounds was represented by two pseudotriplets and a very intense singlet for the unsubstituted cyclopentadienyl ring. For all the compounds L, the chemical shifts of the protons on the CH2 groups directly bonded to the nitrogen groups were expected to be very similar. However, this was not the case and the results are summarised in Table 1. This table shows that the proton signals are shifted to lower frequencies (less deshielding) as the length of the alkyl chains increased. This effect could be attributed to the increase in the distance from the second electronegative N atom. A significant change was observed between etf and prf, as well as prf and buf, while there was less change from buf to hef to ocf. Additionally, for prf–ocf, these protons appeared as triplets, indicating some vicinal proton–proton coupling. For etf a singlet was observed showing that there was no vicinal coupling between the neighbouring protons. 13 C NMR spectra for all compounds showed signals for the imine carbons in the region d 160–163 ppm. The observed carbon signals for all the compounds were as expected. Compound etf exhibited a single signal at d 62.80 ppm for two CH2 groups, while for prf two signals were observed at d 59.25 and 32.90 ppm, representing the carbons directly bonded to nitrogen groups and the middle carbons, respectively. Compounds buf, hef and ocf exhibited two, three and four signals, respectively, in the expected chemical shift regions for the CH2 groups. All the compounds are stable in the solid state at room temperature and in air, while they showed some degree of instability in solution [12]. Attempts to perform the same reactions using acetylferrocene were unsuccessful, even after heating the reaction mixtures up to 65 °C. The inability of acetylferrocene to react is attributed to the steric hindrance of the methyl group. 2.2. Synthesis of cationic rhodium(I) complexes The rhodium(I) compounds [Rh(COD)(L)]ClO4 were synthesized by a literature procedure as illustrated in Scheme 2 [15]. A solution
of silver perchlorate in acetone was added to a solution of [Rh(COD)Cl]2 in acetone. On precipitation of silver chloride, a solvated complex of general formula [Rh(COD)(acetone)2]ClO4 was formed [15,18]. The addition of a bisferrocenylimine ligand resulted in the formation of a cationic complex by the displacement of the coordinated solvent from the rhodium coordination sphere. The complexes 1, 2 and 3 were obtained in low to excellent yields by redissolving the residue, after concentration of solvent, in dichloromethane and precipitating them by the addition of diethyl ether. The complexes were further purified by recrystallization. Compound 2 was produced in the highest yield, 84%, whereas 1 was obtained in the lowest yield, 32%. This effect was attributed to the stability of the six-membered ring formed by the bidentate ligand prf with the metal centre, compared to the five- and sevenmembered rings formed by etf and buf, respectively. Attempts to prepare complexes with hef, and ocf were unsuccessful. 1 H NMR chemical shifts of the imine (CH@N) proton for 2 and 3 were observed in the expected region while, for 1 the peak was shifted to a lower frequency. This effect has also been observed by Lee et al. [15]. The signal in 1 moved from d 8.17 ppm in the free ligand to d 7.42 ppm in the complex, while in 2 and 3 it was observed at d 8.31 and d 8.22 ppm, respectively. In the ferrocene region, a sharp singlet was observed at d 4.37 and 4.07 ppm for 1 and 2, respectively, and it was assigned to the unsubstituted cyclopentadienyl ring. Two singlets at d 4.73 and 4.80 ppm for 1 were assigned to the substituted cyclopentadienyl ring. The substituted cyclopentadienyl ring signals for 2 were observed at d 4.23 and 4.72 ppm. The appearance of additional signals in the ferrocene region of 3 complicated the assignments. Two sharp and equally intense singlets were observed at d 4.26 and 4.14 ppm, and are assigned to the unsubstituted cyclopentadienyl rings. This suggests that the cyclopentadienyl rings are chemically inequivalent due to the trans orientation of one imine (C21–C9–N1–C10 = 179.2°), and the cis orientation of the other imine (C41–C14–N2–C13 = 2.54°), something that was not observed in 1 and 2. The origin of this cis–trans orientation is unclear. Other signals could not be assigned due to the complexity of the signals in the region. Initially, it was thought that the extra signals were due to the presence of impurities. However, the signals remained even after several recrystallizations. The COD ligand exhibited the expected patterns, giving rise to a singlet due to CH@CH protons at d 4.16 ppm, a multiplet d 2.64 ppm and a doublet d 2.09 ppm due to CH2 protons, for 1. For 2 and 3 the CH@CH proton signal was split into two singlets at d 5.48 and 5.39 ppm and 6.11 and 5.65 ppm, respectively. The CH2 signals were observed in the expected region for both 2 and 3. 13C NMR showed the C@N signals in the expected region: d 168.48, 170.44 and 170.39 ppm for 1, 2 and 3, respectively. The ferrocene signals for 1 and 2 were observed in the expected region while the same problem as with the 1H NMR was experienced for 3. The COD signals were also observed in the expected region for all complexes. IR spectra of all the compounds showed that the v(C@N) stretching signals have moved to lower frequencies.
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Cl Rh
+
Rh
2 AgClO4
acetone
[Rh(COD)(acetone)2]ClO4 + AgCl (s)
Cl 2L
x = 2: [1] = 3: [2] = 4: [3]
N
(CH2)
CH Fe
x
N CH Fe
Rh
ClO4
Scheme 2. Procedure for the synthesis of rhodium(I) compounds.
Table 2 Crystal data and structure refinement of 2 and 3. 2
3
Empirical formula Formula weight Temperature (K) Wavelength (Å) Crystal system Space group
C33H38ClFe2N2O4Rh 776.71 113(2) 0.71073 triclinic P1
C34H40ClFe2N2O4Rh 790.74 173(2) 0.71073 monoclinic P21/c
Unit cell dimensions a (Å) b (Å) c (Å) a () b () c () Volume (Å3) Z Calculated density (Mg/m3) Reflections collected/unique Goodness-of-fit (GOF) on F2 Final R indices (R1, wR2) R indices (all data) (R1, wR2)
12.0890(2) 16.5931(2) 17.5512(3) 67.8240(10) 72.9460(10) 72.3860(10) 3042.77(8) 4 1.696 70435/11534 1.023 0.0456, 0.0875 0.0758, 0.0987
12.983(3) 13.536(2) 17.729(4) 90 92.580(7) 90 3112.6(11) 4 1.687 48758/5716 1.034 0.0611, 0.0934 0.1324, 0.1119
Fig. 1. ORTEP drawing of 2.
2.3. X-ray crystallography Crystals of 2 and 3 suitable for X-ray crystallographic analysis were obtained by the slow diffusion of diethyl ether into a solution of the complex in dichloromethane. Complex 2 crystallized in a tri with Z = 4 and contains two molecules (strucclinic space group P 1 tural isomers) in the asymmetric unit. Complex 3 crystallized in the monoclinic space group P21/c with Z = 4 (Table 2). The ORTEP drawings shown in Figs. 1 and 2 confirm the molecular structures of 2 (structural isomer 2A) and 3. The bond lengths, angles, torsion angles and other parameters are given in Tables 3 and 4 for 2 and 3, respectively. The rhodium atom is placed in an essentially square planar geometry defined by the two nitrogen atoms of the diimine ligand and the two C@C double bonds of the COD ligand. The six-membered ring formed in 2, by the rhodium atom, the two nitrogen atoms of the ligand and the three carbon atoms of the alkyl chain separating the two nitrogen atoms is in a chair conformation. The chair conformation is the lowest energy state that a six-membered ring can be found in, which explains the reason for 2 being obtained in excellent yields. The Rh(1A)–N(1A) and Rh(1A)–N(2A) bond distances for molecule 2A are 2.077(4) and 2.095(4) Å, respectively. For molecule 2B, the Rh(1B)–N(2B) and Rh(1B)–N(1B) the bond distances are 2.076(4) and 2.088(4) Å, respectively. The bond distances Rh(1A)–C(2A),
Fig. 2. ORTEP drawing of 3.
Rh(1A)–C(6A), Rh(1A)–C(1A) and Rh(1A)–C(5A) for molecule 2A, are 2.144(4), 2.150(5), 2.152(4) and 2.158(4) Å, respectively. On the other hand, for molecule 2B the bond distances
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Table 3 Selected bond distances and angles of 2. Molecule A
Molecule B
Rh(1A)–N(1A) Rh(1A)–N(2A) Rh(1A)–C(2A) Rh(1A)–C(6A) Rh(1A)–C(5A) Rh(1A)–C(2B) N(1A)–C(9A) N(2A)–C(13A) N(1A)–(Rh(1A)–N(2A) N(1A)–(Rh(1A)–C(2A) N(2A)–(Rh(1A)–C(2A) N(1A)–(Rh(1A)–C(6A) N(2A)–(Rh(1A)–N(6A) C(2A)–(Rh(1A)–N(CA) N(2A)–Rh(1A)–N(2A)–C(9A) C(2A)–Rh(1A)–N(1A)–C(9A) C(6A)–Rh(1A)–N(1A)–C(9A) C(1A)–Rh(1A)–N(1A)–C(9A)
2.077(4) 2.095(4) 2.144(4) 2.150(5) 2.152(4) 2.158(4) 1.294(6) 1.277(5) 85.92(14) 92.34(16) 171.25(16) 154.73(17) 89.01(16) 96.11(18) 112.4(4) 59.0(4) 168.7(4) 96.7(4)
Table 4 Selected bond distances and angles of 3. Bond distances Rh(1)–N(1) Rh(1)–N(1) Rh(1)–C(6) Rh(1)–C(2) Rh(1)–C(5) Rh(1)–C(1) N(1)–C(9) N(1)–C(10) N(2)–C(14) N(2)–C(13) C(9)–C(21) C(10)–C(11) C(11)–C(12) C(12)–C(13) C(14)–C(41)
Bond angles 2.089(5) 2.105(5) 2.135(6) 2.146(6) 2.150(6) 2.165(6) 1.283(7) 1.478(7) 1.289(7) 1.473(7) 1.450(8) 1.512(8) 1.522(8) 1.522(8) 1.470(8)
N(1)–Rh(1)–N(2) N(1)–Rh(1)–C(6) N(2)–Rh(1)–C(6) N(1)–Rh(1)–C(2) N(2)–Rh(1)–C(2) C(6)–Rh(1)–C(2) N(1)–Rh(1)–C(5) N(2)–Rh(1)–C(5) C(6)–Rh(1)–C(5) C(2)–Rh(1)–C(5) C(10)–(11)–C(12) C(13)–C(12)–C(11) C(25)–C(21)–C(22) C(25)–C(21)–C(9) C(22)–C(21)–C(9)
89.04(18) 158.7(2)) 92.9(2) 89.7(2) 153.2(2) 97.8(2) 163.6(2) 91.8(2) 37.6(2) 82.2(2) 116.1(5) 114.7(5) 106.6(6) 130.7(6) 122.4(6)
Rh(1B)–C(2B), Rh(1B)–C(5B), Rh(1B)–C(6B) and Rh(1B)–C(1B) are 2.130(4), 2.143(4), 2.144(4) and 2.171(4) Å, respectively. In complex 3, the Rh(1)–N(1) and Rh(1)–N(2) bond distances are 2.089(5) and 2.105(5) Å and are slightly longer than those for 2. The Rh(1)–C(6), Rh(1)–C(2), Rh(1)–C(5) and Rh(1)–C(1) distances are 2.135(6), 2.146(6), 2.150(6) and 2.165(6) Å, respectively. The bite angle N(1)–Rh(1)–N(2) of 89.0(2)° is much close to the ideal 90° a square planar complex. 2.4. Electronic spectroscopy The UV–Vis spectra of the bisferrocenylimines and their rhodium(I) complexes were obtained in dichloromethane solution. Spectral comparisons with unsubstituted ferrocene as a reference were also made. Ferrocene exhibits two bands at wavelengths of kmax 326 and 442 nm, which have been assigned to 1A2g ? 1E2g and 1A1g ? 1E1g ligand field d–d transitions [19]. The ferrocenyl bands in compounds L were observed at longer wavelengths kmax (Fig. 3(top)), largely due to conjugation with the CH@N bond. Bathochromic shifts are anticipated where conjugation increases in length. Some absorption bands due to p ? p* and n ? p* transitions of the imine groups CH@N in L were also observed at wavelengths lower than 300 nm. The extinction coefficients of the compounds L were higher for the band at lower wavelengths and lower for the band at higher wavelengths than that of ferrocene. In comparison with the free ligands, spectra of complexes 1–3 exhibited an extra band at kmax 350, 382 and 383 nm, respectively
Rh(1B)–N(2B) Rh(1B)–N(1B) Rh(1B)–C(2B) Rh(1B)–C(5B) Rh(1B)–C(6B) Rh(1B)–C(1B) N(1B)–C(9B) N(2B)–C(13B) N(2B)–(Rh(1B)–N(1B) N(2B)–(Rh(1B)–C(2B) N(1B)–(Rh(1B)–C(2B) N(2B)–(Rh(1B)–C(5A) N(1B)–(Rh(1B)–C(5A) C(2B)–(Rh(1B)–C(5A) N(2B)–Rh(1B)–N(1B)–C(9B) C(2B)–Rh(1B)–N(1B)–C(9B) C(5B)–Rh(1B)–N(1B)–C(9B) C(6B)–Rh(1B)–N(1B)–C(9B)
2.076(4) 2.088(4) 2.130(4) 2.143(4) 2.144(4) 2.171(4) 1.289(6) 1.286(6) 85.06(14) 162.39(16) 95.29(16) 95.04(16) 174.44(16) 82.94(18) 112.8(4) 49.6(4) 21.5(19) 163.7(4)
(Fig. 3(bottom)). Moreover, the bands that were observed in the free ligands etf, prf and buf shifted to higher wavelengths, after coordination to rhodium(I). Both these bands at lower wavelengths appeared as shoulders in the complexes. 2.5. Cyclic voltammetry The observed redox behaviour of the compounds was compared with that of ferrocene as a standard. Ferrocene exhibits a one-electron reversible wave with E1/2 at 90.5 mV. The bisferrocenylimines exhibited a positive shift in potential indicating that these compounds became more difficult to oxidise (Table 5). These shifts can be attributed to the presence of the CH@N bond in close proximity to the ferrocene group, resulting in a reduced electron density at the metal centre. The rhodium(I) complexes exhibited positive shifts in potential, implying that the complexes became more resistant to oxidation than their corresponding free ligands (Table 5). 3. Experimental 3.1. Purification procedures All reagents and solvents were purified using standard purification and drying methods [20]. Ferrocenecarboxaldehyde, silver tetrafluoroborate and the chloro-(1,5-cyclooctadiene)rhodium(I) dimer were purchased from Sigma Aldrich. All other common laboratory chemicals were obtained locally and were used without further purification. 3.2. Instrumentation Melting points were determined on an Electrothermal IA 900 series digital melting point apparatus and were uncorrected. NMR spectra were recorded on a Bruker DPX (300 MHz) spectrometer at ambient temperatures. 1H NMR spectra were referenced against the deuterated solvent (CDCl3: d 7.28) and the values reported relative to tetramethylsilane (TMS: d 0.00). 13C NMR spectra were similarly referenced internally to the solvent resonance (CDCl3: d 77.0) with values reported relative to tetramethylsilane (TMS: d 0.00). Infrared spectra were recorded on a DigiLab FTS 3100 Excalibur HE series, running DigiLab Resolution 4.0 software with solid samples prepared as potassium bromide (KBr) disks. Microanalyses were obtained on a Carlo Erba EA 1108 elemental analyser at the
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Fig. 3. UV–Vis spectra of L (top) and 1–3.
Table 5 Half-wave potentials of compounds L and 1–3. Compound
Epa (mV)
Epc (mV)
E1/2 (mV)
Ferrocene etf prf buf hef ocf 1 2 3
140 243 246 243 238 242 413 388 372
41 124 167 171 168 163 342 300 261
90.5 133.5 206.5 207 203 202.5 327.5 344 316.5
University of Cape Town. Fast atomic bombardment (FAB) and high resolution (EI) mass spectra were recorded on a micromass autoTof mass spectrometer at the Witwatersrand University in South Africa. UV–Vis spectra were recorded on a Hewlett Packard 8452A diode array spectrometer in dichloromethane (103 M) with a cell width of 1 cm.
Cyclic voltammograms were obtained on a BAS 100B electrochemical analyser with a three-electrode system using Ag/AgNO3 (0.01 M) as a reference electrode, platinum wire as the auxiliary electrode and platinum disc as the working electrode. Samples (103 M) were prepared and run under nitrogen at ambient temperatures, in acetonitrile with tetrabutylammonium perchlorate (0.1 M) as a background electrolyte. The scan rate used was 100 mV s1. Solutions were saturated with nitrogen by bubbling for 10 min prior to each run. The system gave ferrocene E1/ 2 = 90.5 mV. X-ray crystal intensity data were collected on a Nonius KappaCCD diffractometer using graphite monchromated Mo Ka radiation at the University of Cape Town. Temperature was controlled by an Oxford Cryostream cooling system (Oxford Cryostat). The strategy for the data collections was evaluated using the Bruker Nonius ‘‘Collect” program [21]. Data were scaled and reduced using DENZO-SMN software [21]. The empirical absorption correction utlilized the program SADABS, and the structure was solved by direct methods and refined by full-matrix least-squares with the program 2 SHELXL-97, refining on F [22,23]. Packing diagrams were produced
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using the program PovRay and graphic interface X-seed [24]. All the non-H atoms, except C(29B), C(30B) and C(33B), were refined anisotropically. These ferrocenyl carbons exhibit high thermal motions with Uiso between 0.06356 and 0.09921, and were treated isotropically. 3.3. Synthesis of bisferrocenylimines 3.3.1. General procedure Ferrocenecarboxaldehyde (2 mol equivalents) and the diamine (1 mol equivalent) were added to a Pyrex tube fitted with glass ground joint. The two compounds were ground together at room temperature (ca. 25 °C) using a glass rod. The tube was then placed under a high vacuum pump overnight. The products were obtained as yellow to orange solids after recrystallization from cold anhydrous methanol. 3.3.1.1. N,N0 -ethylenebis(ferrocenylmethylidene)imine (etf). Ferrocenecarboxaldehyde (360 mg, 1.68 mmol) and ethylenediamine (50 mg, 0.84 mmol). The product was obtained as a yellow solid (380 mg, 99%). M.p. 147–150 °C; 1H NMR (CDCl3): 8.18 (2H, s, N@CH), 4.63 (4H, t, J = 1.8, C5H4), 4.30 (4H, t, J = 1.8, C5H4), 4.16 (10H, s, C5H5), 3.78 (4H, s, 2 CH2); 13C NMR (CDCl3): 162.74, 80.85, 70.75, 69.52, 68.86, 62.80; IR (KBr): 3113, 3071, 2917, 2897, 2832, 1782, 1705, 1643, 1462, 1412, 1381, 1327, 1281, 1246, 1215, 1211, 1103, 1049, 1011, 961, 891, 822, 768, 644, 594, 517, 486, 475, 436, 401; m/z (EI): 453 (29%), 452 ([M+], 80%), 321 (13%), 256 (31%), 241 (22%), 227 (19%) 226 (63%), 213 (92%), 199 (27%), 186 (14%), 160 (14%), 121 (63%), 69 (21%), 56 (16%), 43 (11%), 41(11%), 32 (32%), 30 (11%), 28 (100%); MW, 452.15076. Found: MW, 452.06%. 3.3.1.2. N,N0 -propylenebis(ferrocenylmethylidene)imine (prf). Ferrocenecarboxaldehyde (200 mg, 0.93 mmol) and 1,3-diaminopropane (41 mg, 0.55 mmol). The product was obtained as an orange solid (204 mg, 94%). M.p. 127–129 °C; 1H NMR (CDCl3) 8.18 (2H, s, N@CH), 4.67 (4H, t, J = 1.8, C5H4), 4.39 (4H, t, J = 1.8, C5H4), 4.21 (10H, s, C5H5), 3.56 (4H, t, J = 7.0, 2 CH2), 2.03 (2H, m, CH2); 13C NMR (CDCl3) 160.57, 81.88, 70.28, 69.25, 68.64, 59.25, 32.90; IR (KBr) 3108, 3066, 2929, 2946, 2866, 2823, 1640, 1470, 1449, 1323, 1243, 1105, 1004, 823, 544; m/z (EI) 467 (24%), 466 ([M+], 100%), 401 (30%), 335 (56%), 255 (55%), 254 (38%), 253 (30%), 241 (24%), 240 (60%), 233 (26%), 227 (62%), 226 (24%), 225 (21%), 212 (36%), 199 (38%), 186 (52%), 129 (25%), 120 (90%), 56 (52%), 39 (28%); Anal. Calc. for C25H26N2Fe2: C, 64.41; H, 5.62; N, 6.01; MW, 466.18. Found: C, 63.15; H, 5.82; N, 5.75; MW, 466.08%. 3.3.1.3. N,N0 -butylenebis(ferrocenylmethylidene)imine (buf). Ferrocenecarboxaldehyde (200 mg, 0.93 mmol) and 1,4-diaminobutane (44 mg, 0.50 mmol). The product was isolated as an orange solid (207 mg, 92%). M.p. 152–154 °C; 1H NMR (CDCl3) 8.19 (1H, s, CH@N), 8.16 (1H, s, CH@N) 4.65 (2H, t, J = 1.8, C5H4), 4.36 (2H, t, J = 1.7, C5H4), 4.19 (10H, s, C5H5), 3.47 (4H, t, J = 7.0, 2 CH2), 1.71 (4H, m, 2 CH2); 13C NMR (CDCl3) 160.29, 81.08, 70.69, 69.47, 68.78, 62.07, 29.09; IR(KBr) 3071, 2930, 2860, 2814, 2364, 1644, 1470, 1439, 1407, 1381, 1369, 1324, 1244, 1104, 1041, 1020, 1001, 962, 930, 819; m/z (EI) 481 (5%), 480 ([M+], 13%), 284 (15%), 268 (23%), 267 (100%), 213 (15%), 199 (17%), 121 (50%), 56 (18%), 55 (15%), 44 (25%), 43 (34%), 41 (26%), 39 (22%), 30 (67%), 28 (61%), 27 (20%). Anal. Calc.1 for C26H28N2Fe2: C, 65.03; H, 5.88; N, 5.83; MW, 480.20. Found: C, 64.51; H, 6.05; N, 5.74; MW, 480.10%. 1 The tendency for the C and N content to be too low and H too high could be due to the presence of traces of water. This also applies to compounds hef, ocf and 3.
3.3.1.4. N,N0 -hexylenebis(ferrocenylmethylidene)imine (hef). Ferrocenecarboxaldehyde (100 mg, 0.47 mmol) and 1,6-diaminohexane (24 mg, 0.23 mmol). The product was isolated as a light yellow solid (109 mg, 94%). M.p. 109–111 °C; 1H NMR (CDCl3) 8.16 (2H, s, CH@N), 4.65 (4H, t, J = 1.8, C5H4), 4.36 (4H, t, J = 1.8, C5H4), 4.19 (10H, s, C5H5), 3.45 (4H, t, J = 6.2, 2 CH2), 1.66 (4H, m, 2 CH2), 1.44 (4H, m, 2 CH2); 13C NMR (CDCl3) 161.08, 81.96, 70.67, 69.46, 68.78, 62.30, 31.32, 27.61; IR (KBr) 3099, 2935, 2862, 2822, 1646, 1468, 1454, 1409, 1381, 1351, 1326, 1243, 1204, 1164, 1103, 1063, 1051, 1038, 1004, 957, 936, 876, 865, 846, 826, 807; m/z (EI) 509 (15%), 508 ([M+], 41%), 312 (20%), 296 (19%), 295 (71%), 214 (23%), 213 (26%), 199 (27%), 186 (30%), 121 (100%), 56 (34%), 55 (22%), 43 (24%), 41 (39%), 39 (41%), 30 (27%), 28 (49%), 27 (33%). Anal. Calc. for C28H32N2Fe2: C, 66.17; H, 6.35; N, 5.51; MW, 508.26. Found: C, 64.31; H, 6.46; H, 5.40; MW, 508.13%. 3.3.1.5. N,N0 -octylenebis(ferrocenylmethylidene)imine (ocf). Ferrocenecarboxaldehyde (200 mg, 0.93 mmol) and 1,8-diaminooctane (239 mg, 0.47 mmol). The product was obtained as a yellow solid (231 mg, 97 %). M.p. 97–100 °C; 1H NMR (CDCl3) 8.15 (2H, s, N@CH), 4.65 (4H, t, J = 1.8, C5H4), 4.36 (4H, t, J = 1.8, C5H4), 4.19 (10H, s, C5H5) 3.42 (4H, t, J = 6.6, 2 CH2), 1.62 (4H, m, 2 CH2), 1.40 (8H, s, 4 CH2); 13C NMR (CDCl3) 161.00, 81.13, 70.66, 69.46, 68.78, 62.35, 31.33, 29.84, 27.73; IR (KBr) 3065, 2923, 2848, 2819, 1646, 1612, 1494, 1471, 1371, 1327, 1243, 1106, 1043, 1022, 1001, 950, 824, 768, 725, 545; m/z (EI) 537 (29%), 536 ([M+],100%), 471 (20%), 341 (14%), 340 (79%), 268 (19%), 226 (15%), 213 (19%), 199 (26%), 186 (15%), 121 (49%), 55 (16%), 43 (14%), 30 (43%). Anal. Calc. for C30H36N2Fe2: C, 67.19; H, 6.77; N, 5.22; MW, 536.31. Found: C, 65.23; H, 7.19; N, 5.59; MW, 536.16%. 3.4. Synthesis of cationic rhodium(I) complexes 3.4.1. General procedure Silver perchlorate (0.23 mmol) in acetone (2 cm3) was added to a solution of the chloro-(1,5-cyclooctadiene)rhodium dimer (0.11 mmol) in acetone (30 cm3). After removal of the precipitated AgCl, the reaction mixture was heated under reflux for 30 min. The reaction mixture was treated with bisferrocenylimine (0.23 mmol) in toluene (20 cm3) and the resultant dark red solution was left to stir at room temperature (ca. 25 °C) for 3 h. Solvents were removed in vacuo and the dark red solid was recrystallized from a dichloromethane/hexane mixture. The products were obtained as dark red to orange solids. 3.4.1.1. [Rh(COD)(etf)]ClO4 (1). N,N0 -ethylenebis(ferrocenylmethylidene)imine (104 mg, 0.23 mmol) in toluene (20 cm3). The complex was obtained as a dark red solid (27 mg, 32%). M.p. 215 °C (decomp) (lit. 192 °C, decomp.); 1H NMR (CDCl3) 7.43 (2H, s, N@CH), 4.80 (4H, t, J = 1.7, C5H4), 4.73 (4H, t, J = 1.8, C5H4), 4.37 (10H, s, C5H5), 4.16 (4H, s, COD-CH), 3.85 (4H, s, CH2), 2.64 (4H, br-s, COD-CH2), 2.09 (4H, d, J = 7.5, COD-CH2); 13C NMR (CDCl3) 168.48, 84.65, 84.49, 74.71, 73.23, 70.68, 57.01, 30.55; IR (KBr); 3249, 2951, 2886, 2836, 1612, 1447, 1412, 1377, 1259, 1219, 1098, 1102, 954, 825, 733, 622, 479; m/z (FAB) 665 ([M++2], 3%), 663 ([M+], 29%), 553 (3%), 489 (2%), 453 (9%), 333 (3%), 308 (18%), 289 (16%), 233 (4%), 154 (100). MW, 663.06. Found: MW, 662.70%. 3.4.1.2. [Rh(COD)(prf)]ClO4 (2). N,N0 -propylenebis(ferrocenylmethylidene)imine (107 mg, 0.23 mmol) in toluene (20 cm3). The complex was obtained as a reddish orange solid (72 mg, 84%). M.p. 220 °C (decomp.); 1H NMR 8.31 (2H, s, N@CH), 5.49 (2H, s, COD-CH), 5.39 (2H, s, COD-CH), 4.72 (4H, s, C5H4), 4.68 (4H, s, 2 CH2), 4.23 (4H, s, C5H4), 4.17 (2H, m, CH2), 4.07 (10H, s,
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C5H5), 2.59 (4H, br-s, COD-CH2), 1.97 (4H, d, J = 7.7, COD-CH2) 13C NMR (CDCl3) 170.44, 77.62, 75.61, 73.41, 70.51, 70.28, 65.04, 30.89, 30.55; IR (KBr) 3106, 2933, 2852, 1624, 1457, 1411, 1373, 1331, 1253, 1093, 1052, 998, 897, 829, 622; m/z (FAB) 677 ([M+], 11%), 675 (2%), 567 (2%), 467 (5%), 424 (3%), 347 (2%), 307 (18%), 289 (17%), 242 (2%), 154 (100%). Anal. Calc. for C33H38N2Fe2Rh: C, 51.03; H, 4.93; N, 3.61; MW, 677.26. Found: C, 50.27; H, 4.59; N, 3.48; MW, 676.7%.
Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: [email protected]
3.4.1.3. [Rh(COD)(buf)]ClO4 (3). N,N0 -butylenebis(ferrocenlmethylidene)imine (111 mg, 0.23 mmol). The complex was obtained as an orange solid (68.3 mg, 70%). M.p. 228 °C (decomp.); 1H NMR (CDCl3) 8.23 (1H, s, CH@N), 8.22 (1H, s, CH@N) 6.11 (2H, s, CODCH), 5.65 (2H, s, COD-CH), 4.14 (5H, s, C5H5), 4.12 (5H, s, C5H5), 2.62 (4H, m, COD-CH2), 1.79 (4H, s, COD-CH2), other signals could not be assigned properly; 13C NMR (CDCl3) 170.53, 170.35, 84.58, 75.63, 73.74, 73.90, 73.33, 70.04, 69.96, 69.78, 66.46, 58.02, 29.29, 28.73; IR (KBr) 3101, 3013, 2926, 2882, 2838, 1620, 1454, 1436, 1414, 1375, 1331, 1256, 1146, 1103, 1046, 1002, 967, 830, 624, 506, 483; m/z (FAB) 693 ([M++2], 9%) 691 ([M+], 65%), 581 (7%), 495 (4%), 481 (6%), 396 (5%), 345 (3%), 307 (21%), 289 (20%), 233 (7%), 154 (100%). Anal. Calc. for C34H40N2Fe2Rh: C, 51.64; H, 5.10; N, 3.54; MW, 691.09. Found: C, 51.46; H, 5.43; N, 3.31; MW, 690.70%.
References
4. Conclusions
Acknowledgements We are thankful to the Nelson Mandela Metropolitan University (NMMU) and the National Research Foundation (NRF) for financial assistance.
[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14]
Solvent-free synthesis and characterisation of bisferrocenylimines was achieved. The solvent-free approach was simple, fast and gave excellent yields at room temperature. UV–Vis spectra and cyclic voltammograms of rhodium(I) complexes confirmed coordination of the ligands. The structures of the complexes were successfully determined by X-ray crystallography, with 2 having a cis configuration and 3 a cis–trans configuration. Supplementary data CCDC 735149 and 735150 contain the supplementary crystallographic data for complex 2 and 3. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road,
[15] [16] [17] [18] [19] [20]
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