Capítulo 2: Solución Propuesta
2.4 Definición del procedimiento
2.4.9. Etapa 2: Definir y especificar las características de calidad en uso a evaluar
4.2.1: Synthesis and characterisation o f quinoline functionalised Rh(I) NHC complexes.
The use o f free carbene route by deprotonation o f the imidazolium salts with strong base, which was expected to produce the corresponding free carbene, was not successful presumably because o f interference from deprotonation o f benzylic methylene protons [17]. Therefore,A all the Rh(I) NHC complexes presented in this work were prepared from the A g1(NHC) complexes presented in chapter 3. Treatment o f [Rh(COD)Cl]2 with the methylene bridged quinoline functionalised Ag*(NHC) com plexes in dichloromethane at ambient temperature
1 2 3
-C h a p te r F o u r: R h(I) and Ir(I) complexes o f quinoline functionalised ligands
gave the desired rhodium carbene complexes as yellow solids in good yield after work up as shown in Scheme 4.1 below. All the prepared rhodium complexes were characterised by 'H N M R , 13C N M R and mass spectroscopy, elemental analysis and X- ray crystallography. The 13C NM R data for the coordinating carbene carbons for com plexes 4.20, 4.22, 4.23 and 4.24 appear at 5 values of
181.60, 180.38, 178.66 and 183.45ppm respectively, suggesting the formation o f the Rh-C bond which are in the usual range for other Rh(I)-NHC complexes [18,
19, 20-22]. The carbenic carbon in complex 4.21 was not observed in the 13C NMR spectrum. The !H N M R shifts corresponding to the protons o f the quinoline ring are essentially sim ilar to those o f the silver complexes from which they were made, indicating that the quinoline nitrogen donor remains uncoordinated. Furthermore, lH N M R spectra show diasterotopic protons for the CH2 linker ( 5 = 6.5 and 5.6 for com plex 4.20, 6.5 and 6.1 for complex 4.21, 6.5 and 5.75 for complex 4.22, 6.5 and 5.6 for complex 4.23 and 6.5 and 5.8 for complex 4.24) which suggests that this group is out o f the coordination plane o f the molecule thus reducing its symmetry.
R
[Rh(COD)CI].
DCM, r. tem p.
3.36: R = Me, X = Cl 4.20: R = Me
3.37: R = Mes, X = Cl 4.21: R = Mes
3.38: R = iPr, X = I 4.22: R = iPr
3.39: R = n-Bu, X = I 4.23: R =
n-Bu
3.41: R =QuinCH2, X = Cl 4.24: R
-QuinCH2
Chapter Four: Rh(I) and Ir(I) complexes o f quinoline functionalised ligands
Elemental analysis results for complex 4.20 were satisfactory but no reasonable data could be obtained from the mass spectrum. Suitable crystals for X-ray single crystal diffraction were obtained from a DCM/ n-pentane solution at ambient temperature. The detailed solid state coordination sphere around the rhodium centre of complex 4.20 is confirmed by the X- ray crystal structural analysis. The complete molecular structure of complex 4.20 is depicted in Figure 4. 3 below. Selected bond distances and bond angles are listed in table 4.1
C 2 2 C 21
V
\
C 15
Rh1
I C 1 0 C11
\ f c ®____C 9 ^ > — —■
H iF 1 ^ — - v \
& — ^
< \ ✓ ''ce*— N3 C14 cis
C 5
ci:
C 1 4 C 1 3
Figure 4.3: ORTEP projection o f complex 4.20 excluding hydrogen atoms for clarity,showing atom labelling scheme.
Table 4.1: Selected bond lengths (A) and bond angles (°) of 4.20
Cl - N1 1.356(6) C 16 - Rh 1 2.126(5) N l- C l- Rhl 131.4 (4) C l-R h l 2.028(5) C 19 - Rh 1 2.206(5) C l-R h l-C ll 87.99(14) Cl -N 2 1.362(7) R h l- C ll 2.386(13) N2- C5- C6 113.90(4) N 2-C 3 1.394(9) C20- Rhl 2.233(6) Cl-Rhl-C15 92.00(2) C15 -Rhl 2.123(5) N 1 -C 1 -N 2 103.8(4) C1-N2- C3 111.00(4)
The structural arrangement o f complex 4.20 shows that the molecular geometry around the rhodium ion is a square planar arrangement with two coordination
1 2 5
-C hap ter Four: R h(l) and Ir(I) com plexes o f quinoline functionalised ligands
sites occupied by carbene and chloride in a cis fashion. The distances of Rh- C(COD) trans to the carbene donor appear to be longer than those in the cis arrangement, suggesting that the a-donor nature of the diaminocarbene is stronger than that of the chloride. No major deviations were observed in the bond lengths and bond angles o f complex 4.20 compared with those reported in the literature [23-25].
The *H NMR shifts for complex 4.21 corresponding to the protons of the quinoline ring are essentially similar to those of the silver complexes from which they were made, indicating that the quinoline nitrogen donor remains uncoordinated with the carbenic carbon not observed in the ,3C NMR spectrum.
The high resolution MS measurement were consistent with the proposed formulation with [M- Cl]+ observed at M/z = 538.18 Da (100% intensity).
Crystals suitable for X-ray crystallography were obtained for complex 4.21 by diffusion of n- pentane into the DCM solution o f the compound enabling elucidation of the solid state structure as depicted in Figure 4.4. Selected bond distances and bond angles are listed in table 4.2
Figure 4.4: ORTEP projection o f complex 4.21 excluding hydrogen atoms for clarity showing atom labelling scheme.
C30
c i y / ' o n 4
C6
Chapter Four: Rh(I) and Ir(I) com p lexes o f quinoline functionalised ligands
Table 4.2: Selected bond lengths
(A)
and bond angles (°) of 4.21.Cl - N1 1.355(5) C24 - Rhl 2.179(4) N l-C l-R hl 130.8(4) Cl - Rhl 2.045(5) C27- Rhl 2.123(4) C l-R hl- Cll 87.67(11) C l- N2 1.355(5) R h l-C ll 2.3865(9) C 1-N 1-C 4 124.3(3) N 2 -C 3 1.379(9) C 2 8 - Rhl 2.112(4) Cl - Rhl-C28 94.63(2) C23 -Rhl 2.202(4) N1-C1-N 2 103.7(3) C24-Rhl-Cll 90.55(14)
Elemental analysis o f complex 4.21 returned satisfactory results. There are no significant deviations in terms o f the bond lengths and bond angles of complex 4.21 with complex 4.20 and all are within the range reported in the literature [ 20-22, 23,].
Complex 4.22 was characterised by spectroscopic analysis, elemental analysis and X- ray crystallography. The lH NMR spectrum for complex 4.22 displays similar pattern with that of complexes 4.20 and 4.21. The synthesis of complex was confirmed by l3C NMR, which reveals Rh-C resonance at a a value of 180.38 ppm. The high resolution MS measurement was consistent with the proposed formulation with [M- Cl]+ observed at M/z = 462.14 Da (100%
intensity) and elemental analysis results were in agreement with the proposed formulation. Crystals suitable for X-ray structural determination were obtained by diffusion of n-pentane into the saturated DCM solution of the compound and Ortep crystal structure is as depicted in Figure 4.5. Selected bond distances and bond angles are listed in table 4.3.
1 2 7
-C hapter Four: Rh(I) and Ir(I) com plexes o f q uin olin e functionalised ligands
*— C14I
C 13
Figure 4.5: ORTEP projection of complex 4.22 excluding hydrogen atoms for clarity showing atom labelling scheme.
The geometry of rhodium in complex 4.22 is square planar and the parameters in terms of bond distances and internal angles in the complex are consistent the reported values [23].
Table 4.3: Selected bond lengths (A) and bond angles (°) o f 4.22.
C l - N l 1.343(6) C l 9 -Rhl 2.127(5) N l-C l-R h l 129.7(4) C l-R h l 2.037(5) C22- Rhl 2.213(5) C l-R h l-C ll 89.2467(13) C1-N2 1.345(6) R hl-C ll 2.3755(13) C1-N1-C4 125.0(4) N2-C3 1.369(7) C3- Rhl 2.226(5) C l-R hl-C 19 93.10(2) C18- Rhl 2.113(5) N1-C1-N2 104.7(4) C23-Rhl-Cll 94.52(17)
High resolution MS of complex 4.23 displays a cluster of peak M/z = 476.16 Da (100% intensity) assignable to the [M-C1]+ and th e elemental analysis gave results consistent with the formulation of the complex.
C hap ter Four: Rh(I) and Ir(I) com plexes o f quinoline functionalised ligands
C21
Figure 4.6: ORTEP projection of complex 4.23 excluding hydrogen atoms for clarity, showing atom labelling scheme.
Table 4.4: Selected bond lengths (A) and bond angles (°) of 4.23.
C l- N l 1.355(5) C l 9 -Rhl 2.114(4) N 1 -C l -Rhl 126.4 (3) C l-R hl 2.032(4) C 2 2 -R h l 2.197(4) C l-R h l-C ll 88.03(11) C1-N2 1.368(5) R h l-C ll 2.3786(10) C3-N1-C14 123.7(3) N1-C3 1.387(5) C23 -R hl 2.208(4) C l-R hl-C 18 90.62(15) C18-Rhl 2.097(4) N 1-C 1-N 2 103.8(3) C l-R hl-C 22
163.07(15)
1 2 9
-C hap ter Four: Rh(I) and Ir(I) com plexes o f quinoline functionalised ligands
Figure 4.7: ORTEP projection o f complex 4.24 excluding hydrogen atoms for clarity, showing atom labelling scheme.
Table 4.5: Selected bond lengths
(A)
and bond angles (°) of 4.24.C11-N12 1.358(3) Rhl-C3 2.105(3) Cl 1-Rhl - C12 87.46(7) C ll-R h l 2.016(3) Rhl-C4 2.121(3) Cl 1- Rhl- C8 167.02(10)
Rhl-C12 2.3794(7) C11-N26 1.358(3) C ll- R h l- C 3 92.99(10)
Rhl-C8 2.230(3) Cl 1-N12 -C13 125.20(2)
Rhl-C7 2.196(2) N12-C11-N26 103.7(2)
C3-Rhl-C12 157.31(8)
Due to variations in the steric bulk around the carbene carbon there was the need to compare the structure o f all the rhodium(I) carbene complexes 4.20-4.24. In doing so two planes were chosen to calculate the inter planer angles. The planes chosen are the NHC consisting o f the five atoms in the heterocycle carbene ring and the rhodium coordination plane consisting of Cl-Rhl-C12. The inter planer angles and other important angles are listed in Table 4.6 below.
C h ap ter Four: Rh(I) and Ir(I) com plexes o f quinoline functionalised ligands
Table 4.6: Bond angles (°) for compounds 4.20- 4.24 of rhodium complexes of general formula [Rh(Cod)Cl(NHC)]
Compound G(interplaner angle)
N1-C1-N2 C l-R hl-C ll C lR h l-(C18-C19)
4.20 76.87 103.80(4) 87.99(14) 165.30(2)
4.21 76.77 103.70(3) 87.67(11) 165.92(11)
4.22 80.31 104.70(4) 89.25(3) 159.6(2)
4.23 76.49 103.80(3) 88.03(11) 163.07(15)
4.24 82.69 103.70(2) 87.46(7) 167.02(10)
From the table presented above, the main structural features of these compounds are:
A distorted square planar geometry with Cl-Rh-L angles within the range of 87.46-89.25°, the highest being observed in compound 4.22.
An average value o f 76.71° inter planar angles for compounds 4.20, 4.21 and 4.23, 80.31° for 4.22 and 82.69° for 4.24 , thus orientation of the NHC with respect to the coordination approaches perpendicular probably to reduce steric interactions.
The N1-C1-N2 angle o f 103.70° observed around the carbene carbon in all complexes. Only 4.22 slightly differ with a value of 104.70°.
Cl-Rhl-(Cod) angles for the complexes ranges from 159.6(2)- 167.02(10)°, with the highest being observed in 4.24, a significant variation from the normal square planar(180°).
Some important bond distances are listed in Table 4.7 in order to see the variations in the complexes.
131
-C h ap ter Four: Rh(I) and Ir(I) com plexes o f quinoline functionalised ligands
Table 4.7: Other bond distances
(A)
for complexes of general formula [Rh(Cod)Cl(NHC)]Compound Rh-C Rh-Cl N l-C l
Rh-(C15-C16)
Rh-(C19-C20)
4.20 2.028(5) 2.386(13) 1.336(6) 2,123(5) 2.206(5)
4.21 2.045(5) 2.387(9) 1.355(5) 2.112(4) 2.202(4)
4.22 2.037(5) 2.377(13) 1.343(6) 2.113(5) 2.213(5)
4.23 2.032(4) 2.379(10) 1.355(5) 2.114(4) 2.197(4)
4.24 2.0163(3) 2.379(7) 1.358(3) 2.121(3) 2.105(3)
-The distances between Rh and the NHC ligands are shorter than distances between Rh and the Cod, owing to the strong electron donating ability of NHCs.
- There is no significant difference in the C-N bond distance of NHCs, with an average value o f 1.35
A
(Table 4.7), this indicates a degree o f C-N double character. This parameter may vary depending on the degree of back donation from Rh to the NHC (more back donation decreases the push mesomeric effect in the NHC and increases the C-N distance), based on these observations, it can be deduced that all the complexes display the same level of back donation. Similarly, from Table 4.6 the Nl-Ccarbene-N2 angles (103.95° on average) are very close.The chelation of quinN AC-R toward the rhodium centre was achieved by the treatment of 4.20 and 4.24 with an equimolar amount AgBF4, leading to chloride abstraction and ligand substitution o f chloride by the quinoline nitrogen. All of the *H NMR signals o f the quinoline hydrogen atoms in 4.25 are shifted downfield relative to those in the non chelated rhodium complex 4.20 indicating chelation of the qiunN AC-R ligand. The ]H NMR data for the non chelated complex 4.20 and that o f the corresponding chelated complex 4.25 are 8= 8.10 (d, 1H, quin-H), 8.00 (d, 1H, quin-H), 7.75 (d, 1H, quin-H), 7.70 (t, 2H, quin- H), 7.45 (t, 1H, quin-H), 6.80 (s, 2H, C H H C ), 6.50 (d, 1H, C ^ W e r ) , 5.60 (d, 1H, C H 2iinker), 5.00 (m, 2H, C O D ), 4.10 (s, 3H, C H 3), 3.40 (m, 1H, C O D ), 3.20 (m, 1H, C O D ), 2.30 (m, 4H, C O D ), 1.90 (m, 4H, C O D ) and 8 8.75 (d, 1H,
quin-C h ap ter Four: Rh(I) and Ir(I) com plexes o f quinoline functionalised ligands
H), 8.25 (d, 1H, quin-H), 8.10 (d, 1H, quin-H), 7.85 (t, 2H, quin-H), 7.60 (d, 2H, CHHC, quin-H), 6.65 (s, 1H , CHHC), 6.25 (d, 1H, C H 2iinker), 6.05 (d, 1H, C H 2i,nker), 5.50 (m, 1H, COD), 4.70 (m, 1H, COD), 4.40 (m, 2H, COD),4.10 (m, 1H, COD), 3.65 (s, 3H, CH3), 2.80 (m, 1H, COD), 2.40 (m, 4H, COD), 2.10 (m, 2H, COD) respectively. High resolution MS o f complex 4.25 displays a cluster of peak M/z = 434.1117 Da (100% intensity) assignable to the [M- BF4]+.
Elemental analysis gave unacceptable results probably because of contamination from silver halides which were difficult to remove.,3C NMR spectrum for complex 4.25 could not be obtained because the complex is not soluble in most solvents. Suitable crystals for X-ray crystallography were not obtained for complex 4.25. Complex 4.26 was not characterised because it is insoluble in most solvents such as DCM, acetonitrile and methylene chloride. The use of DMSO did help solve the problem o f solubility but the JH NMR spectra of both chelated and non chelated rhodium complexes are essentially similar possibly due to competitive coordination o f DMSO. Elemental analysis returned a slightly low percentage o f carbon presumably due contamination from silver halide.
RhX I
DCM f = \
A gB F 4
1 hr.
A gBF,
4.20: R = Me 4.24: R = QiunCH2
4.25: R = Me 4.26: R = QiunCH2
Scheme 4.2: Synthesis o f chelated quinoline functionalised Rh(I) NHC complexes.
1 3 3
-C h a p te r Four: Rh(I) and Ir(I) com plexes o f quinoline functionalised ligands