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Novel methyl complexes [Pd(Me)(N‐N‐N)]X (N‐N‐N = flexible or rigid terdentate nitrogen ligand, X = Cl, SO3CF3, BAr′4) have been synthesized and fully characterized. All complexes readily underwent insertion of carbon monoxide resulting in the quantitative formation of complexes [Pd{C(O)Me}(N‐N‐N)]X [X = Cl (1d–6d), BAr′4 (1e–6e)]. Subsequently, complexes 2e–6e underwent quantitative insertion of norbornadiene, resulting in complexes [Pd{C7H8C(O)Me}(N‐N‐N)]BAr′4 (2f–6f). Unexpectedly, these complexes, including even those containing rigid terdentate nitrogen ligands, possess a structure in which the nitrogen ligand is coordinated in a bidentate fashion. A kinetic study of the reaction of norbornadiene with complexes 1e–6e revealed that the reactivity of complexes 1e–6e toward norbornadiene increases with increasing rigidity of the terdentate ligand, i.e. with increasing strain in the PdN3 moiety, which indicates that insertion very likely occurs via a mechanism involving nitrogen dissociation. This is fully supported by ab initio MO calculations on CO and ethylene insertion into carbon–palladium bonds of cationic model systems containing a rigid terdentate nitrogen ligand, which showed that the lowest‐energy pathway for both insertion reactions consists of substitution of one of the distal nitrogen atoms of the rigid terdentate nitrogen ligand by the substrate, followed by a rate‐determining migratory insertion of the substrate into the carbon–palladium bond.

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The versatile carbene‐like chemistry of electrophilic phosphinidene complexes (R−P=MLn) with C=C, C≡C, C=X, and C≡X (X = N, O, S, Si, and P) bonds and aromatics is discussed.

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