American Chemical Society
om900631j_si_002.cif (399.31 kB)

Lanthanide-Induced Diinsertion of Isocyanates into the N−H Bond: Synthesis, Structure, and Reactivity of Organolanthanides Containing Diureido Ligands

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posted on 2009-11-09, 00:00 authored by Yan Sun, Zhengxing Zhang, Xu Wang, Xiaoqing Li, Linhong Weng, Xigeng Zhou
Treatment of [Cp2LnNHPy]2 (Py = 2-pyridyl) (1) with 4-nitrophenyl isocyanate gives the unexpected complexes Cp2Ln[η21-PyNCON(C6H4NO2-4)CONHC6H4NO2-4] (Ln = Yb (5a), Er (5b)) as the main product regardless of the equivalency of isocyanate reagent employed. The more bulky isocyanate (2,6-iPr2C6H3NCO) also undergoes double insertion into 1, affording Cp2Ln[η21-PyNCON(C6H3iPr2-2,6)CONHC6H3iPr2-2,6] (Ln = Yb (6a), Er (6b)). Reaction of 1 with 4 equiv of ClCH2CH2CH2NCO affords Cp2Ln[η21-PyNCON(CH2CH2CH2Cl)CONH(CH2)3Cl] (Ln = Yb (7a), Er (7b)) in good yields. Moreover, [(C5H4Me)2LnNHPy]2 (Ln = Yb (2a), Er (2b), Y (2c)) are also reactive toward isocyanate diinsertion, giving (C5H4Me)2Ln[η21-PyNCON(Ph)CONHPh] (Ln = Yb (8a), Er (8b), Y (8c)) in almost quantitative yields. Furthermore, it is found that the presence of electron-withdrawing and electron-donating substituents on the pyridyl ring does not appear to alter the product selectivity and yields. The diinsertion of PhNCO into [Cp2LnNHPyMe]2 (PyMe = 4-methyl-2-pyridyl) (3) and [Cp2LnNHPyCl]2 (PyCl = 5-chloro-2-pyridyl) (4) leads to the formation of Cp2Ln[η21-PyMeNCON(Ph)CONHPh] (Ln = Er (9a), Y (9b)) and Cp2Ln[η21-PyClNCON(Ph)CONHPh] (Ln = Yb (10a), Er (10b), Y (10c)), respectively. In addition, the monoinsertion intermediate Cp2Yb[η2-N(Py)CONHC6H3iPr2-2,6](HMPA) (11·HMPA) can be trapped during this diinsertion process by adding HMPA. Interestingly, the mixed diinsertion complex Cp2Yb[η21-PyNCON(C6H3iPr2-2,6)CONHPh] (12) can be prepared by allowing 2,6-iPr2C6H3NCO to react first with PyNH2 and then with Cp3Yb followed by inserting with PhNCO or by the reaction of 11 with PhNCO. On the other hand, treatment of 6a with excess PhNCO leads to the replacement of 2,6-iPr2C6H3NCO units inserted into the N−H bond by PhNCO molecules, wherein the newly formed ligand has been structurally characterized in its protonated form PyNHCON(Ph)CONHPh (13). Similarly, PyNHCON(C6H3iPr2-2,6)CONHC6H3iPr2-2,6 (14) could also be obtained by reaction of Cp2Yb[PyNCON(Ph)CONHPh] with excess 2,6-iPr2C6H3NCO followed by hydrolysis. All the complexes were characterized by spectroscopic analysis. The structures of compounds 514 are also determined through X-ray single-crystal diffraction analysis.