| In this paper, we focused on the study of the activation of carbodiimide and transformation with amine to guanidinate group by the bulky lanthanide tris(phenoxide)s Ln(OAr1)3(THF)2 (Ln = Y and Yb; Ar1= [2,6-(tBu)2-4-MeC6H2]). Three carbodiimide coordinated complexes were isolated, and the corresponding monoguanylate complexes were also isolated and structurally characterized. The catalytic activity of Ln(OAr1)3(THF)2 for guanylation of amines with carbodiimide were tested. The main results obtained are as follows:1. Treatment of Y(OAr1)3(THF)2 (Ar1= [2,6-(tBu)2-4-MeC6H2] Ln = Y,Yb) with N,N'-diisopropylcarbodiimide (iPrNCNiPr) in a molar ratio of 1:2 in toluene afforded the carbodiimide coordinated complexes (Ar1O)3Y(iPrNCNiPr) (1) and (Ar1O)3Yb(iPrNCNiPr) (2). Complexes 1 and 2 were structurally characterized.2. Treatment of Y(OAr1)3(THF)2 with N,N'-dicyclohexylcarbodiimide (CyNCNCy) in a molar ratio of 1:1 afforded the corresponding complex (Ar1O)3Y(CyNCNCy) (3). Complex 3 has also been structurally characterized.3. The analogous reactions using the less bulky complexes, Y(OAr2)3(THF)2 (Ar2= [2,6-(iPr)2C6H3]) and Y(OAr3)3(THF)2 (Ar3= [2,6-Me2C6H3]), did not occur, indicating that the steric effect of lanthanide tris(phenoxide)s has a remarkable influence on this reaction.4. Treatment of complexes 1 and 2, respectively, with 4-Chloroaniline in a molar ratio of 1:1, afforded the corresponding monoguanidinate complexes (Ar1O)2Y[(4-Cl-C6H4N)C(NHiPr)NiPr](THF) (4) and (Ar1O)2Yb[(4-Cl-C6H4N)C(NHiPr)NiPr](THF) (5) in high yield. Both complexes were structurally characterized.5. Further study revealed that complexes 4 and 5 can also be synthesized in high yield by the reaction of Y(OAr1)3(THF)2 with iPrNCNiPr and 4-Cl-C6H4NH2 at a 1:1:1 molar ratio in toluene in one pot synthesis. Neither the less bulky aryloxides, Y(OAr2)3(THF)2, nor Y(OAr3)3(THF)2 could react with iPrNCNiPr and 4-Cl-C6H4NH2. This result indicated the formation of carbodiimide coordinated complexes was a crucial step for their further transformation with amine to guanidinate group.6. Treatment of complex 1 with excess 2-Methoxyaniline at room temperature in toluene yielded the amine complex by amine protonolysis of the resulting guanidinate species. Complex 6 was structurally characterized.7. Both Y(OAr1)3(THF)2 and complex 4 can serve as novel catalysts for guanylation of amines with carbodiimides to substituted guanidines. The results indicate that complex 4 is a reaction intermediate in the process of guanylation of amines with carbodiimides to substituted guanidines by Y(OAr1)3(THF)2 as a precatalyst. The catalytic system with complex Y(OAr1)3(THF)2 showed a wide range of substituents. |
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