Dinuclear Rh(I) complex with 2,7-bis(diphenylphosphino)-1,8-naphthyridine: Synthesis, structure, and dynamic property

Reaction of [RhCl(cod)]2 with 2,7-bis(diphenylphosphino)-1,8-naphthyridine (dpnapy) and 2,6-xylyl isocyanide (XylNC) in the presence of NH4PF6 afforded the dirhodium(I) complex, [Rh2(μ-dpnapy)2(XylNC)4](PF6)2 (5), and similar procedures using [MCl2(cod)] (M = Pt, Pd) resulted in the formation of [Pt2(μ-dpnapy)2(XylNC)4](PF6)4 (6) and [Pd2Cl2(μ-dpnapy)2(XylNC)2](PF6)2 (7). Complexes 5–7 were characterized by elemental analysis, IR, UV–Vis, 1H and 31P{1H} NMR, and ESI mass spectroscopic techniques, to involve a small and rigid d8 {M2(μ-dpnapy)2} metallomacrocycle. Complex 5 readily incorporated a silver(I) ion into the macrocycle to afford [Rh2Ag(μ-dpnapy)2(XylNC)4](PF6)3 (8) which was characterized by X-ray crystallography. The Ag(I) ion is trapped by two trans N atoms of dpnapy ligands, resulting in an asymmetric Rh–Ag⋯Rh structure, determined as a disordered model in the crystal structure, and however, in a CH2Cl2 solution, a dynamic interconversion of the two Ag-trapped sites was observed with low-temperature NMR studies, which was further supported by DFT molecular orbital calculations. When an acetonitrile solution of complex 5 was treated over a droplet of mercury(0), the polymeric compound formulated as {[Rh(μ-dpnapy)(XylNC)2](PF6)}n (9) was isolated as yellow single crystals, which were revealed by X-ray crystallography to consist of C6 helical rods along c axis with a pitch of 33.5 Å (rise of unit = 5.6 Å) and a diameter of 20.64 Å.