A wide-bite-angle diphosphorin ligand I (Q = P) was designed and prepd., which exhibits structural features for a preferred formation of trans complexes. Acetylation of 1,1':2',1''-terphenyl by AcCl/AlCl3 gave 4,4''-diacetyl-1,1':2',1''-terphenyl, which upon condensation with 1,3-diphenyl-2-propen-1-one and HBF4Et2O gave bis-pyrylium salt I2BF4 (3, Q = O+). Reaction of 3 with P(SiMe3)3 gave the bis-phosphorin I (4, Q = P). Due to the linear orientation of the lone-pair electrons of the phosphorus donors in combination with an appropriate P-P distance, trans coordination toward a Rh center was obsd. and the corresponding [LRh(CO)I] (L = 4) complex could be characterized crystallog. Although typical reactivities usually obsd. for trans complexes were found, reaction of the diphosphorin 4 with the cis-enforcing precursor [Rh(nbd)2]BF4 did result in the formation of several species at low temp., to which cis-structures were attributed.
Müller, C., Freixa, Z., Lutz, M., Spek, A. L., Vogt, D., & Leeuwen, van, P. W. N. M. (2008). Wide-bite-angle diphosphinines: design, synthesis, and coordination properties. Organometallics, 27(5), 834-838. https://doi.org/10.1021/om7003546