Cyclic (alkyl)(amino)carbenes with a six-membered backbone were prepared. Compared to their five-membered analogues, they feature increased % V and enhanced donor and acceptor properties, as evidenced by the observed n → π* transition trailing into the visible region. The high ambiphilic character even allows for the intramolecular insertion of the carbene into an unactivated C(sp)-H bond. When used as ligands, they outcompete the five-membered analogues in the palladium-mediated α-arylation of ketones with aryl chlorides.

A straightforward strategy allows for the synthesis of storable bicyclic (alkyl)(amino)carbenes (BICAACs), which feature enhanced σ-donating and π-accepting properties compared to monocyclic (alkyl)(amino)carbenes (CAACs). Due to the bicyclo[2.2.2]octane skeleton, the steric environment around the carbene center is different from that of CAACs and similar to that observed in classical N-heterocyclic carbenes. The different electronic properties of BICAACs as compared to CAACs allow for ligand exchange reactions not only at a metal center, but also at main group elements.

Selenium NMR has become a standard tool for scaling the p-accepting character of carbenes. Herein, we highlight that non-classical hydrogen bonding (NCHB), likely resulting from hyperconjugation, can play a significant role in the carbene-selenium 77 Se NMR chemical shift, thus triggering a non-linear behavior of the Se-Scale.

The reaction of cyclic di(amido)- and (alkyl)(amino)-carbenes with white phosphorus in benzene afford P8 clusters supported by four carbenes, or a novel type of carbene-P4 adduct.

The tin(II) hydride [ArSn(μ-H)](Ar = CH-2,6(CH-2,4,6-Pr)) (1a) reacts with 2 equiv of ethylene or t-butylethylene at ca. 25 °C to yield Sn(Ar)R(R = ethyl or t-butylethyl), which exist either as a symmetric distannene Ar(R)SnSn(R)Ar (2a or 5a) or an unsymmetric stannylstannylene ArSnSnRAr (3a). In contrast, the less crowded Sn(II) hydride [ArSn(μ-H)] (Ar = CH-2,6(CH-2,6-Pr)) (1b) reacts with excess ethylene to give Ar(CHCH)Sn(CHCH)Sn(CHCH)(CHCH)Ar (4) featuring five ethylene equivalents, one of which is dehydrogenated to an vinyl, -CH═CH, group. The Ar isomers of 2a and 3a, i.e., [ArSn(CH)] (2b) and ArSnSn(CH)Ar (3b) are obtained by reaction of [ArSn(μ-Cl)] with EtLi or EtMgBr. The isomeric pairs 2a and 3a are separated by crystallization at different temperatures. Variable-temperature H NMR spectroscopy indicates fast ethyl group exchange between Ar(CH)SnSn(CH)Ar (Ar = Ar (2a) or Ar (2b)) and ArSnSn(CH)Ar (Ar = Ar (3a) or Ar (3b)) with ΔG = 14.2 ± 0.65 kcal mol for 2a/3a and 14.8 ± 0.36 kcal mol for 2b/3b. The bulkier distannenes [ArSn(CHCHBu)] (Ar = Ar (5a) or Ar (5b)), obtained from 1a or 1b and t-butylethylene, dissociate to ArSnCHCHBu monomers in solution. At lower temperature, they interconvert with their stannylstannylene isomers with parameters K = 4.09 ± 0.16 for 5a and 6.38 ± 0.41 for 5b and ΔG = -1.81 ± 0.19 kcal mol for 5a and -1.0 ± 0.03 kcal mol for 5b at 298 K. The 1:1 reaction of 1a or 1b with 5a or 5b yields the unknown monohydrido species SnRHAr which has the structure ArSn-Sn(H)(CHCHBu)Ar (6a) or the monohydrido bridged ArS n(μ-H)S n(CHCHBu)Ar (6b). The latter represents the first structural characterization of a monohydrido bridged isomer of a ditetrelene.

By utilizing stable carbenes with low-lying LUMOs, coupling with the stable nucleophilic diaminocyclopropenylidene was achieved. This reaction resulted in the formation of two new and rare examples of a bent allene as well as the isolation of the first carbene-carbene heterodimer.

Reactions of the Sn(II) hydrides [ArSn(μ-H)] (1) (Ar = Ar (1a), Ar (1b); Ar = CH-2,6-(CH-2,6-Pr), Ar = CH-2,6-(CH-2,4,6-Pr)) with norbornene (NB) or norbornadiene (NBD) readily generate the bicyclic alkyl-/alkenyl-substituted stannylenes, ArSn(norbornyl) (2a or 2b) and ArSn(norbornenyl) (3a or 3b), respectively. Heating a toluene solution of 3a or 3b at reflux afforded the rearranged species ArSn(3-tricyclo[2.2.1.0]heptane) (4a or 4b), in which the norbornenyl ligand is transformed into a nortricyclyl group. H NMR studies of the reactions of 4a or 4b with tert-butylethylene indicated the existence of an apparently unique reversible β-hydride elimination from the bicyclic substituted aryl/alkyl stannylenes 2a or 2b and 3a or 3b. Mechanistic studies indicated that the transformation of 3a or 3b into 4a or 4b occurs via a β-hydride elimination of 1a or 1b to regenerate NBD. Kinetic studies showed that the conversion of 3a or 3b to 4a or 4b is first order. The rate constant k for the conversion of 3a into 3b was determined to be 3.33 × 10 min, with an activation energy E of 16.4 ± 0.7 kcal mol.

The reactions of heavier group 14 element alkyne analogues (EAr iPr4 )2 (E = Ge, Sn; Ar iPr4 = C6H3-2,6-(C6H3-2,6-i Pr2)2) with the group 6 transition metal carbonyls M(CO)6 (M = Cr, Mo, W)under UV irradiation resulted in the cleavage of the E-E bond and the formation of complexes {Ar iPr4 EM(CO)4}2 (1-6) that were characterized by single crystal X-ray diffraction as well as by IR and multinuclear NMR spectroscopies. Single crystal X-ray structural analyses of 1-6 showed that the complexes have a nearly planar rhomboid M2E2 core with three-coordinate group 14 atoms. The coordination geometry at the group 6 metals is distorted octahedral formed by four carbonyl groups as well as two bridging EAr iPr4 units. IR spectroscopic data suggest that the EAr iPr4 units are not very efficient -acceptors, but the investigation of E-M metal-metal interactions in 1-6 with computational methods revealed the importance of both σ-and -type contributions to bonding. The mechanism for the insertion of transition metal carbonyls into E-E bonds in (EAr iPr4 )2 was also probed computationally.2