Methanide-type complexes

In the reactions with phosphonio-a-methoxycarbonyl-alkanides, the products of type 261 derived from 1,3-cycloaddition can rearrange to the tautomeric lif-pyrazolo-triazole (87MI2). The reaction of 3-diazopyra-zoles and 3-diazoindazole with acyl-substituted phosphonium ylides led to pyrazolo-triazine and indazolo-triazine derivatives 266 instead of the expected triazole compounds (8IJHC675). In this case, the ylides, which can exist as phosphonium enolates, possess nucleophilic and electrophilic centers in a /8-relationship, giving [7 + 2] or [11 -I- 2]cycloaddition reactions. With dimethylsulfonio-a-aroyl-methanides, very complex, temperature-dependent mixtures were obtained, in some cases with sulfur retention (87MI3). 

Furthermore, in contrast to P-diketiminato ligands, the methanide group of bis-(phosphinimino)methanides can be deprotonated again to give bis(phosphinimino)-methandiides which act as dianionic A, A-ligand systems. As shown by Cavell et al., this ligand forms a pincer carbene-type complex with samarium, which exhibits a... 

In summary, the tendency is obvious for the formation of the oxycarbides of the rare earth elements La, Ce, Pr and Nd form the carbide-oxides RjOjCj or C 02C2 of an acetyhde nature and with complex crystal structures, while the smaller rare earth elements Sm, Dy, Ho, Lu, Y and Sc form the fee methanide-type carbide-oxides, M-(C,0, ). 

Sarsfield reported the only three known examples of uranyl bis(imino-phosphorano)-methanides reported to date.52,53 Treatment of the tris-THF adduct of anhydrous uranyl dichloride with one molar equivalent of 2 resulted in the isolation of dimeric 101 when the recrystallisation was carried out in dichloromethane, but monomeric 102 when recrystallised from THF. Both 101 and 102, when treated with two and one equivalents, respectively, of potassium bis(trimethylsilyl)amide afford 103. Complexes 101-103 all exhibit uranyl-methanide contacts in the solid state and these represent noteable examples of out-of-equatorial-plane uranyl coordination. A DFT study concluded that the methanide centre coordinates to the uranyl centre with an orbital of p-type character by a highly polarised cr-type interaction. 

---