Facile construction of the guanidine substituent or guanidinate anionic ligand through addition of the adjacent amino group to carbodiimide

Abstract

The reaction of N,N′-dicyclohexylcarbodiimide (DCCI) with [Cp₂Yb(o-H₂NC₆H₄S)]₂ (Cp = C₅H₅) (1) forms the monomer product Cp₂Yb[SC₆H₄NC(NHCy)₂] (2), indicating that the adjacent NH₂group can add to the CN double bonds of carbodiimide to construct a neutral guanidine group. When DCCI reacts with [Cp₂Y(o-H₂NC₆H₄S)]₂·2THF (4), a dimer product [CpY(μ-η²:η¹-SC₆H₄NC(NHCy)NCy)(THF)]₂ (5) was isolated, through the amino group addition and cyclopentadienyl elimination. Interestingly, on treatment of 4 with one or two equivalent of ⁱPrNCNⁱPr at the same conditions gave an amino group partial addition product CpY(THF)[μ-η²:η¹-SC₆H₄NC(NHⁱPr)NⁱPr)](μ-η²:η¹-SC₆H₄NH₂)YCp₂·THF (6), where only one NH₂group can add to the CN double bonds of carbodiimide molecule, another one is remained. However, when we extended this reaction to the gadolinium complex, a novel co-crystalline compound {Cp₂Gd[SC₆H₄NC(NHCy)₂]}·{CpGd(THF)[μ-η²:η¹-SC₆H₄NC(NHCy)NCy)][μ-η²:η¹-SC₆H₄NH₂]GdCp₂·THF} (8) was obtained from the reaction of [Cp₂Gd(o-H₂NC₆H₄S)]₂ (7) with DCCI. In order to investigate the sequence of addition and the elimination of the cyclopentadienyl group, a deprotonation reaction of the addition product has also been studied. Reaction of CpYb[SC₆H₄NC(NHⁱPr)₂]₂(THF) (9), formed by reaction of Cp₃Yb with two equivalent of o-aminothiophenol, and subsequently with 2 equiv. of ⁱPrNCNⁱPr, with one equiv. of Cp₃Yb gave a cyclopentadienyl elimination product [CpYb(μ-η²:η¹-SC₆H₄NC(NHⁱPr)NⁱPr)(THF)]₂ (3). This result reveals that addition of the NH₂group to carbodiimide is prior to the elimination of cyclopentadienyl group. All of new compounds have been characterized by elemental analysis and spectroscopic properties. The solid-state structures of complexes 2, and 5–9 were determined by single-crystal X-ray diffraction.