Synthesis and reactivity of Pd(II) imidoyl complexes obtained by insertion of isocyanoferrocene into the Pd-C bonds of orthopalladated precursors

Abstract

While the multifaceted reactivity of organic isocyanides has been extensively demonstrated, that of their organometallic analogue, isocyanoferrocene (FcNC; Fc = ferrocenyl), has not yet been adequately explored. This contribution describes the syntheses of novel chelating Pd(II) imidoyl complexes, [(YCH₂C₆H₄C(NFc)-κ²Y,C)PdCl(PR₃)], by insertion of FcNC into the Pd-C bond of cyclopalladated precursors [(YCH₂C₆H₄-κ²Y,C)PdCl(PR₃)] (Y = Me₂N, MeS, R = Ph, Me). The imidoyl complexes underwent facile alkylation with [Me₃O][BF₄] to produce the cationic aminocarbene complexes [{YCH₂C₆H₄C(N(Me)Fc)-κ²Y,C}PdCl(PR₃)][BF₄]. All compounds were fully characterised using a combination of spectroscopic methods (NMR, FTIR and ESI MS), cyclic voltammetry and single-crystal X-ray crystallography. In addition, DFT calculations were used to describe the bonding in the two compound families. Analyses with intrinsic bond orbitals (IBOs) and the quantum theory of atoms in molecules (QTAIM) consistently pointed to the transformation of an X-type imidoyl C-ligand (σ-organyl) into an L-type carbene donor upon alkylation, which has only a minor structural consequence. Also reported is the unexpected conversion of the imidoyl complex [(Me₂NCH₂C₆H₄C(NFc)-κ²N,C)PdCl(PPh₃)] into (Z)-2,2-dimethyl-1-(ferrocenylimino)isoindolin-2-ium tetrafluoroborate as a reductive elimination product, which was induced by Lewis and Brønsted acids.