Flexible Coordination of Diphosphine Ligands Leading to cis and trans Pd(0), Pd(II), and Rh(I) Complexes

A series of diphosphine ligands iPr2P–C6H4–X–C6H4–PiPr2 (for ligand L1, X = CH2; for ligand L2, X = CH2CH2) was investigated to determine the preference for cis/trans coordination to palladium(0), palladium­(II), and rhodium­(I). Increasing the length of the bridging alkyl backbone from one to two carbons changes the geometry of the resulting palladium­(II) complexes, with L1 coordinating preferentially cis, while L2 coordinates in a trans fashion. Coordination to Pd(0) leads to L1Pd­(dba) and L2Pd­(dba), in which both ligands accommodate a P–M–P angle close to 120°. L2 was found to coordinate cis in a rhodium­(I) complex ([L2Rh­(nbd)]­[BF4], where nbd = norbornadiene).