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

Treatment of [CP(2)LnNHPy](2) (Py = 2-pyridyl) (1) with 4-nitrophenyl isocyanate gives the unexpected complexes Cp(2)Ln[eta(2):eta(1)-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-(Pr2C6H3NCO)-Pr-i) also undergoes double insertion into 1, affording Cp(2)Ln[eta(2):eta(1)- PyNCON((C6H3Pr2)-Pr-i-2,6)(CONHC6H3Pr2)-Pr-i-2,6] (Ln = Yb (6a), Er (6b)). Reaction of 1 with 4 equiv of ClCH2CH2CH2NCO affords Cp(2)Ln[eta(2):eta(1)-PyNCON(CH2CH2CH2Cl)CONH(CH2)(3)Cl] (Ln = Yb (7a), Er (7b)) in good yields. Moreover, [(C5H4Me)(2)LnNHPy](2) (Ln = Yb (2a), Er (2b), Y (2c)) are also reactive toward isocyanate diinsertion, giving (C(5)H(4)Me(2)Ln[eta(2):eta(1)-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 [Cp(2)LnNHPy(Me)](2) (Py-Me = 4-methyl-2-pyridyl) (3) and [CP(2)LnNHPy(Cl)](2) (Py-Cl = 5-chloro-2-pyridyl) (4) leads to the formation of Cp(2)Ln[eta(2)-eta(1)-(PyNCON)-N-Me(Ph)CONHPh] (Ln = Er (9a), Y (9b)) and Cp(2)Ln[eta(2):eta(1)-(PyNCON)-N-Cl(Ph)CONHP] (Ln = Yb (10a), Er (10b), Y (10c)), respectively. In addition, the monoinsertion intermediate Cp2Yb[eta(2)-N(Py)(CONHC6H3Pr2)-Pr-i-2,6](HMPA) (11 . HMPA) can be trapped during this diinsertion process by adding HMPA. Interestingly, the mixed diinsertion complex Cp2Yb[eta(2):eta(1)- PyNCON((C6H3Pr2)-Pr-i-2,6)CONHPh] (12) can be prepared by allowing 2,6-(Pr2C6H3NCO)-Pr-i 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-(Pr2C6H3NCO)-Pr-i 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((C6H3Pr2)-Pr-i-2,6)(CONHC6H3Pr2)-Pr-i-2,6 (14) could also be obtained by reaction of CP2Yb[PyNCON(Ph)CONHPh] with excess 2,6-(Pr2C6H3NCO)-Pr-i followed by hydrolysis. All the complexes were characterized by spectroscopic analysis. The structures of compounds 5-14 are also determined through X-ray single-crystal diffraction analysis.