A Strongly Ambiphilic Ferrocene-Based Cyclic (Alkyl)(amino)carbene - Specific Decomposition to an Enamine by a 1,2-Phenyl Shift.

The recently described crystalline cyclic (alkyl)(amino)carbene with a 1,1'-ferrocenylene (fc) backbone fc(CPh-C-NMes) (A, Mes=mesityl) is highly reactive due to its particularly pronounced ambiphilicity and is thermally not stable in solution due to an intramolecular insertion of the divalent carbon atom into a methyl C-H bond of the Mes substituent. The closely related congener fc(CPh-C-N-p-CH-tBu) (1) cannot undergo such an insertion reaction. Nevertheless, 1 is too short-lived for isolation due to a rapid 1,2-shift of a phenyl group, furnishing the isomeric cyclic enamine fc[C(Ph)=C(Ph)-N-p-CH-tBu] (1') in a specific decomposition process unprecedented for CAACs.

A bromo(boryloxy) silylene and its heavier analogues.

A N-heterocylic boryloxy ligand equipped with bulky diazaboryl -substituents is used to synthesize divalent and dicoordinate group 14 compounds which represent the first examples of acyclic halo(boryloxy) tetrylenes. The bromo(boryloxy) silylene reacts swiftly with benzophenone to a siloxindane.

A complete series of N-heterocyclic tetrylenes (Si-Pb) with a 1,1'-ferrocenediyl backbone enabled by 1,3,2-diazaborolyl -substituents.

The use of bulky 1,3,2-diazaborolyl -substituents has allowed the synthesis of the complete series of ferrocene-based N-heterocyclic tetrylenes fc[(N{B})E] (fc = 1,1'-ferrocenediyl, {B} = (HCNCH-2,6-Pr)B, E = Si-Pb). The silylene fc[(N{B})Si] is inert towards NH, CO or NO under ambient conditions and thus significantly less reactive than the -aryl homologue fc[(NCH-2,6-Pr)Si]. In accord with its higher reactivity, computational results indicate a more pronounced ambiphilicity of fc[(NCH-2,6-Pr)Si].

Ferrocene-Based N-Heterocyclic Plumbylenes [Fe{(η -C H )NSiMe R} Pb:]: Influence of the Steric Demand of the N-Substituents on Their Dimerization via C-H Activation with Pb.

Ferrocene-based N-heterocyclic plumbylenes fc[(NSiMe R) Pb:] (1; fc=1,1'-ferrocenylene) are easily accessible by transamination from [(Me Si) N] Pb and the corresponding 1,1'-diaminoferrocene derivatives fc(NHSiMe R) . They may form unconventional dimers 2 by a process, which causes the cleavage of a cyclopentadienyl C-H bond and the formation of a Pb-C and an N-H bond. The monomer-dimer equilibrium (2 1⇆2) has been addressed experimentally and computationally.

Planar-chiral 1,1'-diaminoferrocenes.

Planar-chiral homologues of 1,1'-diaminoferrocene, which bear a single additional substituent adjacent to one of the amino groups, are prepared as racemic mixtures in a few steps and in good yields from ferrocene. Various substituents relevant to steric shielding, coordination and further functionalisation are used, giving access to ferrocene-based planar-chiral diimines and diamines as well as stable N-heterocyclic carbenes and tetrylenes by transformations analogous to procedures established for 1,1'-diaminoferrocene.

Reactive Dimerization of an N-Heterocyclic Plumbylene: C-H Activation with Pb.

The N-heterocyclic plumbylene [Fe{(η -C H )NSiMe } Pb:] 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 Pb insertion into a cyclopentadienyl C-H bond, but is best described as an electrophilic substitution. The bulkier plumbylene [Fe{(η -C H )NSitBuMe } Pb:] shows no dimerization, but compensates its electrophilicity by the formation of an intramolecular Fe-Pb bond.

New Stable and Persistent Acyclic Diaminocarbenes.

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.