The N‐heterocyclic plumbylene [Fe{(η5‐C5H4)NSiMe3}2Pb:] is in equilibrium with an unprecedented dimer in solution, whose formation involves the cleavage of a strong C−H bond and concomitant formation of a Pb−C and an N−H bond. According to a mechanistic DFT assessment, dimer formation does not involve direct PbII insertion into a cyclopentadienyl C−H bond, but is best described as an electrophilic substitution. The bulkier plumbylene [Fe{(η5‐C5H4)NSitBuMe2}2Pb:] shows no dimerization, but compensates its electrophilicity by the formation of an intramolecular Fe−Pb bond.

The portfolio of acyclic diaminocarbenes (ADACs) has been substantially expanded, owing to the synthesis of eleven new formamidinium salts, mostly of the type [(iPr2N)CH(NRR')][PF6], for use as immediate carbene precursors. The corresponding ADACs (iPr2N)C(NRR') were sufficiently stable for isolation in the case of NRR' = 2-methylpiperidino (13), 3-methylpiperidino (14), 4-methylpiperidino (15), morpholino (17) and NiPrPh (20), but had to be trapped in situ in the case of NRR' = 2,2,6,6-tetramethylpiperidino (12) and NiPrMe (19). The tetraaryl-substituted ADACs (Ph2N)2C (22) and (Ph2N)C[N(C6F5)2] (24) also could only be generated and trapped in situ. Trapping with elemental selenium was particularly efficient, affording the corresponding selenourea derivative in all cases, whereas trapping with [{Rh(μ-Cl)(cod)}2] did not work for 12 and 24. The (77)Se NMR chemical shifts, δ((77)Se), of the selenourea compounds derived from the new ADACs lie in the range 450-760 ppm, which indicates a much higher electrophilicity and π-accepting capability of ADACs in comparison with NHCs, which typically exhibit δ((77)Se)<200 ppm. The extreme low-field shift of 758 ppm observed for 12Se can be rationalised by the results of DFT calculations, which revealed that ADAC 12 has a minimum energy conformation with the 2,2,6,6-tetramethylpiperidino unit perpendicular to the N2C plane, which suppresses the π donation of this amino group and causes an unusually low LUMO energy and high electrophilicity.

Planar-chiral homologues of the important synthon 1,1′-diaminoferrocene, which bear a single additional substituent adjacent to an amino group, are efficiently synthesised on a gram scale.

The reactivity of ferrocene-based N-heterocyclic tetrylenes [{Fe(η 5 À C 5 H 4 À NSitBuMe 2 ) 2 }E] (E = Ge, Sn, Pb) towards mesityl azide (MesN 3 ) is compared with that of PPh 2functionalised congeners exhibiting two possible reaction sites, namely the E II and P III atom. For E = Ge and Sn the reaction occurs at the E II atom, leading to the formation of N 2 and an E IV =NMes unit. The germanimines are sufficiently stable for isolation. The stannanimines furnish follow-up products, either by [2 + 3] cycloaddition with MesN 3 or, in the PPh 2 -substituted case, by NMes transfer from the Sn IV to the P III atom. Whereas [{Fe(η 5 À C 5 H 4 À NSitBuMe 2 ) 2 }Pb] and other diaminoplumbylenes studied are inert even under forcing conditions, the PPh 2 -substituted congener forms an addition product with MesN 3 , thus showing a behaviour similar to that of frustrated Lewis pairs. The germylenes of this study afford copper(I) complexes with CuCl, including the first structurally characterised linear dicoordinate halogenido complex [CuX(L)] with a heavier tetrylene ligand L.