Fused in the same molecule! An N-heterocyclic carbene and a diphosphine are generated and used in the modular synthesis of a variety of target heterometallic complexes. The experimental approach involves formation of a unique 4,5-bis(diphenylphosphino)-1,3-dimethyl-imidazolium salt, simply by starting from 1-methylimidazole (see scheme; M(1) = Cr, Mn; M(2) = Au, Rh, Pd; LiHMDS = LiN(SiMe(3))(2)).

Diphosphino-functionalized 1,3-dialkylimidazolium salts react with KOH affording amine/formamide open-chain products, which fully revert to the imidazolium cation by treatment with a variety of acids or are converted to 2-imidazolones by noncatalyzed intramolecular dehydrogenative C-N coupling, a process that is modulated by coordination of the phosphino functionalities to transition metals.

Simply using 1-methylimidazole as the starting material, the functionalized ionic liquid 1,3-dimethyl-4-(diphenylphosphino)imidazolium triflate ([3]OTf) has been prepared, from which the corresponding 4-phosphinosubstituted N-heterocyclic carbene 4 was generated. The coordination capability of 3 and 4 toward a variety of transition-metal centers has been studied, as well as their electron-donor character through an evaluation of the TEP parameter. 3 behaves as a cationic phosphine ligand, whereas 4 shows a strong preference to coordinate to transition metals through the carbene carbon atom, leading to the obtention of mononuclear complexes with a free phosphine arm which act as metalloligands, allowing for the modular formation of homo-and heterodinuclear transition-metal complexes. ■ INTRODUCTION1,3-Dialkylimidazolium salts are currently receiving a great deal of attention, owing to their use as ionic liquids for novel media in organic synthesis and catalysis 1 and as precursors of Nheterocyclic carbenes (NHCs). 2 Recently, imidazolium salts containing functional groups have been used for task-specific applications, 3 such as separation of CO 2 from gas streams, 4 supports for organic synthesis, 5 extraction of metal ions, 6 construction of nanostructures, 7 and ion conductive materials. 8 Particularly, phosphino-functionalized imidazolium salts, most of them containing the phosphino group connected to a nitrogen atom of the imidazolium cycle through a carbon spacer, have been extensively employed in the formation of chelating or pincer NHC-phosphine ligands 9 and as ionophilic phosphines for ionic-liquid biphasic catalysis. 10 In recent pioneering works, the groups of Bertrand 11 and Gates 12 have described the synthesis of 4-phosphino-substituted 1,3-diarylimidazol-2-ylidenes and proved their suitability for the synthesis of several dimetallic transition-metal complexes. 13 Subsequently our group managed to isolate 4,5-diphosphinosubstituted imidazolium salts and use them for generating mixed diphosphine-NHC ligands. 14,15 In related studies, 4-phosphorylimidazolium and 4,5-bis(phosphoryl)imidazolium salts have also been prepared, some of them being remarkable examples of room-temperature ionic liquids, as well as their corresponding NHC-transition-metal complexes. 16 In this paper we describe the synthesis of the functionalized ionic liquid 1,3-dimethyl-4-(diphenylphosphino)imidazolium triflate ([3]OTf; Figure 1), which contains one of the simplest imidazolium scaffolds, and the study of its properties and coordination capabilities together with those of the corresponding NHC derivative. A comparison has been made with its isomer 1,3-dimethyl-2-(diphenylphosphino)imidazolium triflate ([2]OTf) as well as with the parent unsubstituted imidazolium salt ([1]OTf).