Synthesis And Characterization Of Bridged Bis(Phenolate) Lanthanide(Ⅱ) Complexes And Their Reaction Activity

A series of lanthanide（Ⅱ） complexes supported by two kinds of N-heterocycle bridged bis（phenolato） ligands were synthesized and well characterized. The redox reaction of lanthanide（Ⅱ） complexes with carbodiimides、diazadienes were studied. The catalytic activity of lanthanide（Ⅱ） complexes in guanylation of amines with carbodiimides, amination of carbodiimides with terminal alkynes, respectively, was tested. The main results obtained are as follows:1. Reaction of [ONNO]¹H₂ and [ONNO]²H₂ with equivalent Ln[N（SiMe₃）₂]₂（THF）₂ respectively, afforded the corresponding lanthanide（Ⅱ） complexes [ONNO]12Yb2 1 ,[ONNO]₂Yb（THF）₃ 2 ,[ONNO]₂²Eu2（THF） 24. The reaction of [ONNO]²H₂ with Yb[N（SiMe₃）₂]₂（TMEDA） in 1:1 molar ratio afforded the lanthanide（Ⅱ） complex [ONNO]₂²Yb2 7. All these complexes were well characterized including X-ray diffraction, IR spectroscopy, elemental analysis and 1H NMR for 1、2 and 7.2. Redox reaction of complex 2 and complex 7 with carbodiimides was examined. The reaction of complex 2 with carbodiimide in THF led to hydroxyl bridged complex [ONNO]₂²Yb2（OH）₂ 4, we still obtained the complex 4 in toluene for the same reaction. Taking into account the role of THF coordination of complex 2, so we synthesized complex 7. The reaction of complex 7 with carbodiimides afforded corresponding bridged lanthanide carbene complexes [（ONNO）₂Yb]₂（iPr-NCN-iPr）·C7H8 3 and [（ONNO）₂Yb]₂（Cy-NCN-Cy）·C7H8 5,carbodiimide works as two electron oxidant in the reaction. We first found that the reaction of piperazidine-bridged bis（phenolato） lanthanide（Ⅱ） complex 2 with carbodiimide led to ring opening of THF, and afforded a hydroxyl bridged complex.3. we examined the reactivity of bridged lanthanide carbene complexes. Reaction of complex 3 with PhNCO in 1:6 molar ratio afforded the complex [（ONNO）₂Yb]₂（PhNCO）₂（PhN） 11 and compound C₂₉H₂₉N₅O₄·10. Reaction of complex 8 with PhNCO in 1:6 molar ratio afforded the complex [（ONNO）₄Yb]₂（PhNCO）₂（PhN）·9 and compound·10. This result indicated that PhNCO could inserted into the Ln-N of bridged lanthanide carbene complexes, and released the carbene carbon which reacted with PhNCO immediately leading to compound 10. We presumed the reaction mechanism. Meanwhile, the reaction of complex 3 with CO2 was examined, complex of （ONNO）₂YbO2C（iPr）N=C[（iPr）HN]₂C=N（iPr）O2CYb（ONNO）₂（THF）₂ 12 was isolated in THF/hexane. It has not reported as so far that insetion of CO2 makes the further transformation.4. Reaction of [ONNO]3H2 with Yb[N（SiMe₃）₂]₂（THF）₂ in 1:1 molar ratio afforded the complex [ONNO]3Yb（DME）（THF） 13. Reaction of complex 13 with carbodiimide in THF led to the complex [ONNO]32Yb2（MeO）₂ 14. To THF solution of [ONNO]3Yb, which was synthesized by the reaction of Yb[N（SiMe₃）₂]₂（THF）₂ with [ONNO]3H2 in 1:1 molar ratio in situ, was added equivalent carbodiimide, affording the complex [ONNO]3Yb[μ-（iPr）NCHN（iPr）] 15. The reaction of Yb[N（SiMe₃）₂]₂（TMEDA） with [ONNO]3H2 in toluene, followed by addition of an equivalent carbodiimide, afforded the complex {[ONNO]3Yb}2[μ-（iPr）NCN（iPr）] 16. It has not reported as so far that the reaction pathway of lanthanide（Ⅱ） complex with carbodiimide is affected by solvents. We presumed the free radical reaction mechanism for the above reaction.5. We synthesized the first Sm（Ⅱ） complex, which represents the first example of the molecular structure of samarium （Ⅱ） complexes supported by heteroatom bridged bis（phenolate） ligand, and the unexpected reactivity of the divalent samarium complex [（ONNO）₂Sm]m（THF）n formed in situ to carbodiimides was examined. Reaction of [ONNO]²H₂ with Sm[N（SiMe₃）₂]₂（THF）₂ in a 1:1 molar ratio, followed by addition of two equivalent of HMPA afforded a tetrametallic Sm（Ⅱ） complex [[ONNO]₂4Sm4（hmpa）8 17. Reaction of [（ONNO）₂Sm]m（THF）n formed in stiu with iPrNCNiPr led to the complex （ONNO）₂Sm{（NiPr）₂CC（NiPr）₂}Sm（ONNO）₂ 18, Reaction of [（ONNO）₂Sm]m（THF）n formed in stiu with CyNCNCy afforded [（ONNO）₂Sm]₂（Cy-NCN-Cy） 19. Obviously, CyNCNCy in the present case works as a two-electron oxidant to react with two equivalent of Sm（Ⅱ） complex, while in the above case iPrNCNiPr acts as a one-electron oxidant to react with one equivalent of Sm（Ⅱ） complex. We first found that carbodiimide reacted with the same samarium（Ⅱ） complex led to different product.6. Guanylation of amines with carbodiimides catalyzed by lanthanide（Ⅱ） complexes was studied. Sm[N（SiMe₃）₂]₂（THF）₂ was then chosen as the precatalyst for the guanylation of various primary aromatic amines with carbodiimides under solvent free condition. The reaction was not influenced by either electron-withdrawing or electron-donating substituents at the phenyl group. The reactions with secondary aliphatic amines also went smoothly at 80℃, even though secondary amines are generally less active than primary amines. We isolated the intermediate product sucessfully, so we presumed the reaction mechanism.7. Amination of carbodiimides with terminal alkynes catalyzed by lanthanide（Ⅱ） complexes was examined. Addition of terminal alkynes to carbodiimides catalyzed by lanthanide（Ⅱ） complexes I-V went smoothly at 80℃. The active sequence was observed: Yb < Eu < Sm for metals, and -MeC5H4 < -OAr < -N（TMS）₂ for ligands. Sm[N（SiMe₃）₂]₂（THF）₂ was then chosen as the precatalyst for the amination of various terminal alkynes with carbodiimides in THF. The reaction was not influenced by either electron-withdrawing or electron-donating substituents at the phenyl group. We isolated the intermediate product sucessfully, so we presumed the reaction mechanism.8. Reaction of non-cyclopentadienyl lanthanide（Ⅱ） complexes with diazadienes was first examined. Reaction of （ONNO）12Yb2 and （ONO）5Yb（THF）₃ with iPr₂C₆H₃N=CHCH=NC₆H₃ⁱPr₂ respectively, afforded the corresponding complexes （ONNO）12Yb2（ iPr₂C₆H₃NCH=CHNC₆H₃ⁱPr₂） 20 and （ONO）52Yb2（ iPr₂C₆H₃NCH=CHNC₆H₃ⁱPr₂） 21. To study coordination and redox properties of diazadienes , the reaction of （ONNO）₂Yb（THF）₃ with iPr₂C₆H₃N=C（Me）C（Me）=NC₆H₃ⁱPr₂ was examined, and afforded the complex （ONNO）₂Yb（ONNO）₂Yb（iPr₂C₆H₃NC（Me）=C（Me）NC₆H₃ⁱPr₂） 22. They had different reaction pathway because of different structure of diazadienes, but they all worked as a two-electron oxidant to react with two molecules of lanthanide（Ⅱ） complexes. To examined the influence of central metal, reaction of Sm（Ⅱ） complex and Eu（Ⅱ） complex with diazadienes was carried out respectively. The corresponding complexes of （ONNO）₂Sm^Ⅲ（iPr₂C₆H₃NCHCHNC₆H₃ⁱPr₂–·） 23 and （ONNO）₂EuIII（iPr₂C₆H₃NCHCHNC₆H₃ⁱPr₂–·） 25 were isolated, in which diazadiene acts as a one-electron oxidant to react with one molecule of Sm（Ⅱ） complex and Eu（Ⅱ） complex. It’s worthy to note that complexes 20、21、22、23 are stable in THF, and complex 25 is instable in THF,this result indicate that stability of the reaction products is influenced by the central metals.