1166834-03-2Relevant academic research and scientific papers
A new stable CNHCCHCNHCN-heterocyclic dicarbene ligand: Its mono- and dinuclear Ir(i) and Ir(i)-Rh(i) complexes
Raynal, Matthieu,Cazin, Catherine S. J.,Vallee, Christophe,Olivier-Bourbigou, Helene,Braunstein, Pierre
experimental part, p. 3824 - 3832 (2009/09/26)
The ligand [(1,3-phenylene)bis(methylene)]bis(1-ethyl-imidazol-2-ylidene) (2) (abbreviated as EtCNHCCHCNHC with CH = central aromatic ring, = CH2 spacer) has been synthesised, and isolated, by deprotonation of [(1,3-phenylene)bis(methylene)]bis(1-ethyl- imidazolium) dichloride, Et(CHimid.CHCH imid.)Cl2 (1) with LiN(SiMe3)2. This new, remarkably stable NHC dicarbene ligand is quantitatively protonated with HBr to form [(1,3-phenylene)bis(methylene)]bis(1-ethyl-imidazolium) dibromide Et(CHimid.CHCHimid.)Br2 (3) and reprotonated slowly enough in MeOH to allow observation of the monoprotonated intermediate 4. Dicarbene 2 reacts with S8 to give the dithione compound [(1,3-phenylene)bis(methylene)]bis(1-ethyl-imidazol-2-thione) Et[(SC)CH(CS)] (6). Reaction of 2 with [IrCl(CO)(PPh 3)2] and [Ir(μ-Cl)(cod)]2 yielded the mononuclear [Ir(CO)(PPh3)2Et(CH imid.CHCNHC)(PF6)](PF6) (8) and [IrCl(cod)Et(CHimid.CHCNHC)](PF6) (10) complexes, respectively, and the dinuclear complexes [{Ir(CO)(PPh 3)2}2Et(μ-CNHCCHC NHC)](PF6)2 (7) and [{IrCl(cod)} 2Et(μ-CNHCCHCNHC)] (9), respectively, in which 2 acts as a bridging, non-pincer type ligand. Only one other Ir(i) complex has been reported before containing a C NHCCHCNHC ligand. The structures of 6 and 9 were determined by X-ray diffraction and depict different conformations of the (1,3-phenylene)bis(methylene) (or xylylene) moiety. The mononuclear Ir complex 9 reacted smoothly with [Rh(μ-Cl)(cod)]2 and Cs2CO 3 to generate a rare example of a heteronuclear NHC complex, [IrRhCl2(cod)2Et(μ-CNHCCHC NHC)] (11).
