N-Heterocyclic carbene adducts of the parent arsinidene (AsH) were prepared by two different synthetic routes, either by reaction of As(SiMe) with 2,2-difluoroimidazolines followed by desilylation or by reaction of [Na(dioxane)][AsCO] with imidazolium chlorides.

The synthesis and characterization of the first parent phosphanylalane and phosphanylgallane stabilized only by a Lewis base (LB) are reported. The corresponding substituted compounds, such as IDipp⋅GaH2PCy2 (1) (IDipp=1,3‐bis(2,6‐diisopropylphenyl)‐imidazolin‐2‐ylidene) were obtained by the reaction of LiPCy2 with IDipp⋅GaH2Cl. However, the LB‐stabilized parent compounds IDipp⋅GaH2PH2 (3) and IDipp⋅AlH2PH2 (4) were prepared via a salt metathesis of LiPH2⋅DME with IDipp⋅E′H2Cl (E′=Ga, Al) or by H2‐elimination reactions of IDipp⋅E′H3 (E′=Ga, Al) and PH3, respectively. The compounds could be isolated as crystalline solids and completely characterized. Supporting DFT computations gave insight into the reaction pathways as well as into the stability of these compounds with respect to their decomposition behavior.

The recent crystallization of the neuropeptide Y Y 1 receptor (Y 1 R) in complex with the argininamide-type Y 1 R selective antagonist UR-MK299 (2) opened up a new approach toward structure-based design of nonpeptidic Y 1 R ligands. We designed novel fluorescent probes showing excellent Y 1 R selectivity and, in contrast to previously described fluorescent Y 1 R ligands, considerably higher (∼100-fold) binding affinity. This was achieved through the attachment of different fluorescent dyes to the diphenylacetyl moiety in 2 via an amine-functionalized linker. The fluorescent ligands exhibited picomolar Y 1 R binding affinities (pK i values of 9.36−9.95) and proved to be Y 1 R antagonists, as validated in a Fura-2 calcium assay. The versatile applicability of the probes as tool compounds was demonstrated by flow cytometry-and fluorescence anisotropy-based Y 1 R binding studies (saturation and competition binding and association and dissociation kinetics) as well as by widefield and total internal reflection fluorescence (TIRF) microscopy of live tumor cells, revealing that fluorescence was mainly localized at the plasma membrane.

The synthesis and characterization of the unprecedented compounds IDipp⋅E′H2AsH2 (E′=Al, Ga; IDipp=1,3‐bis(2,6‐diisopropylphenyl)imidazolin‐2‐ylidene) are reported, the first monomeric, parent representatives of an arsanylalane and arsanylgallane, respectively, stabilized only by a LB (LB=Lewis Base). They are prepared by a salt metathesis reaction of KAsH2 with IDipp⋅E′H2Cl (E′=Al, Ga). The H2‐elimination pathway through the reaction of AsH3 with IDipp⋅E′H3 (E′=Al, Ga) was found to be a possible synthetic route with some disadvantages compared to the salt metathesis reaction. The corresponding organo‐substituted compounds IDipp⋅GaH2AsPh2 (1) and IDipp⋅AlH2AsPh2 (2) were obtained by the reaction of KAsPh2 with IDipp⋅E′H2Cl (E′=Al, Ga). The novel branched parent compounds IDipp⋅E′H(EH2)2 (E′=Al, Ga; E=P, As) were synthesized by salt metathesis reactions starting from IDipp⋅E′HCl2 (E′=Al, Ga). Supporting DFT computations give insight into the different synthetic pathways and the stability of the products.