Synthesis of chelating trimethylsiloxy diisonitrile ligands and their rhodium(1) complexes. Crystal and molecular structure of [Rh(t-BuDiNC)2]BPh4·1.5CH3CN (DiNC = chelating bidentate isonitrile ligand)

An X-ray crystallographic study, the first of a complex containing a chelating bidentate isonitrile (DiNC) ligand, reveals that [Rh(t-BuDiNC)2]BPh4·1.5CH3CN crystallizes as a “slipped-stacked” face-to-face dimer of two approximately planar [Rh(t-BuDiNC)2]+ cations with a Rh-Rh distance of 3.384 A, and an angle of 22.7° between the stacking axis and the RhRh vector. The syntheses of two new bidentate isonitrile ligands, SiNC-2 and SiNC-3 are also described. These ligands contain bulky trimethylsiloxy groups ortho to each isonitrile group and differ only in that the SiNC-3 ligand contains an additional CH2 unit in its backbone. Each reacts with [Rh(COD)Cl]2 to afford, after metathesis with KPF6, a complex of the empirical formula [Rh(SiNC-n)2]PF6. Spectroscopic results suggest the SiNC-2 complex is dinuclear, with four SiNC-2 ligands bridging the two rhodium atoms. The SiNC-3 complex is mononuclear, but unlike most other mononuclear [Rh(CNR)4]+ complexes, shows no tendency to self-associate in solution. The different structures of these two complexes and the solution behavior of the SiNC-3 complex are attributed to the bulkiness of the trimethylsiloxy groups.