Novel Dihydridoruthenium(II) Complexes with Chelating Diphosphine Ligands, RuH2(CO) (diphosphine)(PPh3)(diphosphine = dppe, dppp, dppb, and dppf)

A cyclic tetramer of optically active spirosilane 1 was prepared as a new chiral molecular square with D4 symmetry by the Pd-catalyzed cross-coupling reaction, which shows a larger anisotropy factor g in the CD spectrum relative to a series of linear oligomers of 1.