Harinath for their kind cooperation, guidance and encouragement which helped me in the completion of this project. I am very grateful to every research scholar in the Department of Chemistry IIT Hyderabad who all supported me and helped me a lot in collecting different information, recording the spectroscopic data because I completed my project within this limited time. I would like to thank the Department of Chemistry of -IIT Hyderabad for providing all possible laboratory and equipment facilities.
Finally, I salute all those who supported me in any way to complete the project. The thesis describes the functionalization of imidazoline-2-imine (1a, 1b and 1c) on exocyclic nitrogen (imine nitrogen) with phenyl isocyanate and chlorodiphenylphosphine. We prepared N-(1,3-di-tert-butylimidazol-2-ylidene)-N'-phenylurea 2a, N-(1,3-dimesitylimidazol-2-ylidene)-N'-phenylurea 2b, N-(1 ,3-bis-(2,6-diisopropylphenyl)imidazol-2-ylidene)-N'-phenylurea 2c ligands by reaction of imidazoline-2-imine with phenyl isocyanate at room temp.
To extend imidazolin-2-imine to the new imidazolin-2-ylidene-1,1-diphenylphosphinamine ligand family, we 1,3-dimesity imidazolin-2-ylidene-1,1-diphenylphosphinamine 3b and 1,3-bis -(2) prepared ,6-diisopropylphenyl)-imidazolin-2-ylidene-1,1-diphenylphosphinamine 3c ligands by reacting imidazolin-2-imine with chlorodiphenylphosphine in THF:CH2Cl2 mixture at ambient temperature. Reaction of 1,3-dimesitylimidazolin-2-ylidene-1,1-diphenylphosphinamine with H2O2, elemental sulfur, and selenium affords corresponding oxide, sulfide, and selenide derivatives, 1,3-dimesitylimidazolin-2-ylidene-P,P-dimenylphosphine sulfide 1 ,3-dimesitylimidazolin-2-ylidene-P,P-diphenylphosphinothioicamide 5b and 1,3-dimesitylimidazolin-2-ylidene-P,P-diphenylphosphinoselenoicamide 6b in good yield, respectively.
Introduction
Deprotonation of imidazoline-2-imine (ImNH) yields a monoanionic imidazoline-2-iminate ligand (ImN−) that can act as 2σ, 4π electron donors. The coordination chemistry of imidazoline-2-imine ligand with early to late transition metal, rare earth metals and transition metals in high oxidation state is known in the literature and has many applications in catalytic transformation 14, 15 such as olefin polymerization and metathesis reactions of alkenes, proved to be more active than the metallocene catalyst. Imidazolin-2-imine can be functionalized by changing the substituent on the imidazole nitrogen, on the olefin moiety and on the exocyclic imine nitrogen.
The monoanionic imidazolin-2-imine can act as a monodentate ligand (I), and by adding a substituent to the exocyclic imine nitrogen, this ligand can be changed from monodentate to bidentate, tridentate and bridging 16 (Figure 3). So far, many functionalized mono and bidentate imidazoline-2-imine ligands have been reported in the literature, some selected examples are shown in (Figure 4). Early to late transition metals and rare earths have already been reported for imidazolin-2-imine.
Only one report is known where imidazolin-2-imine was functionalized on the imine nitrogen of p-tolyisocyanate and thioisocyanate to prepare N-imidazol-2-ylidene-N'-p-tolylurea and thiourea ligands and metal complexes with titanium, nickel and palladium18. So far, there are only a few reports on nickel with functionalized imidazoline-2-imine, while the other transition metals are more explored18.
Aim of the project
Results and Discussion
Synthesis of N-(imidazol-2-ylidene)-N’-phenylureate ligand
The absorption for C=N bond stretching is well in the expected range cm-1. The imidazolium backbone protons of 2a resonate as a singlet in the 1H NMR spectrum at δ 6.22, a field shift from that of the imidazol-2-imine 1a (δ 5.94 ppm). The strong absorption band for N-H in the compound 1b and 1c is absent for compound 3b and 3c in the FT-IR spectra. In 1H NMR spectra, the imine proton of the imidazolin-2-imine ligand which was present in the range between 4.20 and 4.77 ppm for compound 3b and 3c is absent.
The olefinic protons present in the imidazolium ring in the case of both 3b and 3c are found to be identical to those of 1b and 1c at 6.28 ppm, respectively. In the case of 3c, the two 2,6-diisopropylphenyl rings on the N-substituted imidazoline ring are not coplanar and show two. NMR spectra of compound 3c show that only one signal is observed at 41.2 ppm, representing one phosphorus atom present in the molecule.
The angle C(1)-N(1)-P(1) is 124.58(17)o and probably deviates from linearity due to the steric packing between the phenyl groups over the phosphorus atom and the mesityl groups present in the imidazolium ring. A strong absorption band at 1260 cm-1 can be assigned as characteristic stretching of the P=O bond in the FT-IR spectra of compound 4b. Four o-methyl groups on mesityl are equivalent from the same chemical shift value in the range of 1.97 ppm.
In the 31P-{1H} NMR spectra, one signal is observed at 4.8 ppm, indicating that a phosphorus atom is present in the molecule. In the 31P {1H} NMR spectra observed a signal at 35.8 ppm, downshift compared to compound 4b. In the FT-IR spectra of compound 6b absorption at 965 cm-1 characteristic of P=Se bond stretching.
In the 31P-{1H} NMR spectra, one signal was observed at 25.7 ppm, field shift upward compared to compound 5b. However, hydrogen bonding was observed in the selenium compound between nitrogen N(1) and H(11c) of the mesityl substituent. A broad absorption peak of 200–400 nm in the solid-state UV–visible spectra of 2a and 2c was attributed to the π to π* transition of ligand.
In the solid state UV-visible spectra in the case of a strong absorption band of 7b observed at 550 nm, which is not observed in the compound due to strong field splitting of the ligand as nitrogen donor ligand coordinating with nickel(II). Hydrocarbon solvents (toluene and n-pentane) were distilled from LiAlH4 under nitrogen and stored in the glove box.
Synthesis of imidazolin-2-ylidene-1,1-diphenylphosphinamine ligand
Nickel Complexes
Recently the ligand has been introduced in transition metal chemistry, it is observed that the titanium compounds are highly active as polymerization catalysts26,27. Synthesis of bis-[N-(1,3-di-tert-butylimidazol-2-ylidene)-N'-phenyl-ureato]Ni(acac)2 7a can be achieved by treating 2a in THF with Ni(acac) The reaction mixture was kept under reflux for 3 days. We expected that a Ni-O bond present in Ni(acac)2 cleavage will occur to produce acetylacetonate by losing the N-H proton from the neutral ligand 2a to give the monoanionic form to coordinate with nickel ion on bi -dentate manner.
However, it was observed to our surprise that instead of Ni-O bond breakage, a hexacoordinated complex 7a is formed by coordination of two ligands 2a, to the Ni(acac)2. This can be attributed to the fact that N-H proton is not very acidic to provide monoanionic ligand. Due to extensiveness of the ligand, the exocyclic nitrogen of the imidazolin-2-imine fragment does not coordinate, instead of more electronegativity of oxygen, with its lone pair, easily proven by the low carbonyl stretching frequency in the metal complex than of the ligand 2a .
Compound 7a was recrystallized from CH2 Cl2 and crystallized in triclinic space group P-1 with one molecule per unit cell. In diaquabisacetylacetonatikkel(II), the acetylacetonate residue is planar with an average deviation of seven atoms from the least-squares plane of 0.04 Å. In other acetylacetonate fragments the nickel atom was not in the same plane, but 0.32 Å above it.
The solid state structure reveals hydrogen bonding interaction between N-H and acetylacetonate oxygen atoms, also between the carbonyl oxygen of the ligand and the CH3 proton, it is between O(1)-H(10a). We have done a separate reaction changing the substituent on the nitrogen of the imidazole ring from tertiary butyl to mesityl by maintaining the same reaction conditions, but the crystal structure shows that the C-N bond is broken due to the possible presence of some moisture and the amine coordinates with Ni (acac )2, the entire ligand is bound due to H-bonding interaction between carbonyl oxygen and benzene hydrogen (Scheme 10). Compound 7b was recrystallized from CH2Cl2 and crystallized in triclinic space group P-1 with one molecule per unit cell.
The coordination polyhedron of the complex 7b is formed by the chelation of four oxygen atoms of the two acetylacetonate ligand groups together with two nitrogen atoms of aniline. 13, the increase in absorption peak at 230 nm was observed, while for compound 7b it had not increased much. The solid-state UV–visible absorption spectra of 2a, 2c, 7a, and 7b were significantly different from that of the solution (Fig. 14).
Experimental
The solvent was evaporated in vacuo, and the residue was washed with n-pentane to give an orange solid and recrystallized from toluene. To a dry Schlenk (160 mg, 0.318 mmol) of 1,3-dimesethylimidazoline-2-iminediphenylphosphine dissolved in 4 mL of THF is added 0.1 mL of H2O2 and kept for 4 h at room temperature under stirring. The solvent is evaporated in vacuo and the crude product is purified by column chromatography and recrystallized from CH2Cl2/pentane at room temperature.
Synthesis of 1,3-dimesitylimidazolin-2-ylidene-P,P-diphenylphosphinoselenoicamide (6b): In a dry Schlenk (100 mg, 0.198 mmol) 1,3-dimesitylimidazolin-2-iminediphenylphosphine dissolved in 3 ml of toluene, to give the ( 18.76 mg, 0.396 mmol) elemental selenium was added and held at 90. The structure of compound 3b was freely optimized without any geometric constraints using density functional theory (B3LYP 6-311+G(2d,p)). The structure of compound 4b was freely optimized without any geometric constraints using density functional theory (B3LYP 6-311+G(2d,p)).
The structure of compound 5b was freely optimized without any geometric constraints using density functional theory (B3LYP 6-311+G(2d,p)). The structure of compound 6b was freely optimized without any geometric constraints using density functional theory (B3LYP 6-311+G(2d,p)).
Conclusion
Appendix
