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

Treatment of [Cp₂LnNHPy]₂ (Py = 2-pyridyl) (1) with 4-nitrophenyl isocyanate gives the unexpected complexes Cp₂Ln[η²:η¹-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[η²:η¹-PyNCON(C₆H₃ⁱPr₂-2,6)CONHC₆H₃ⁱPr₂-2,6] (Ln = Yb (6a), Er (6b)). Reaction of 1 with 4 equiv of ClCH₂CH₂CH₂NCO affords Cp₂Ln[η²:η¹-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[η²:η¹-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 [Cp₂LnNHPy^Me]₂ (Py^Me = 4-methyl-2-pyridyl) (3) and [Cp₂LnNHPy^Cl]₂ (Py^Cl = 5-chloro-2-pyridyl) (4) leads to the formation of Cp₂Ln[η²:η¹-Py^MeNCON(Ph)CONHPh] (Ln = Er (9a), Y (9b)) and Cp₂Ln[η²:η¹-Py^ClNCON(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[η²:η¹-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 5−14 are also determined through X-ray single-crystal diffraction analysis.