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

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)-kappa Y-2,C)PdCl(PR3)], by insertion of FcNC into the Pd-C bond of cyclopalladated precursors [(YCH2C6H4-kappa Y-2,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)-kappa Y-2,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 (sigma-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)-kappa N-2,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 Br & oslash;nsted acids.

Automated summary

This research reports the reactivity of isocyanoferrocene and its reactions with palladium compounds to form imidoyl complexes. The structures and properties of these imidoyl complexes were characterized experimentally, and their bonding situations were described using computational methods. In addition, an unexpected reductive elimination product was observed, and its formation mechanism was analyzed.