PHOSPHINE-NITRILE LIGANDS - THE MOLECULAR-STRUCTURE OF CIS-2-DIPHENYLPHOSPHINO-1-CYANOCYCLOPENTANE AND STUDIES OF THE DONOR ACCEPTOR PROPERTIES OF THIS AND RELATED LIGANDS/

The cis and trans isomers of the previously reported 2-diphenylphosphi no-1 -cyanocyclo-pentane and -cyclohexane have been separated, and thr ee of the four isomers have been obtained (both isomers of the former and one of the latter) as pure samples. An X-ray study of the Ph(2)PC( 5)H(8)CN isomer with the more-shielded P-31 chemical shift proved it t o be the cis isomer. A prominent feature observed for the structure is that the CN group is directed toward the phosphorus lone pair. Van de r Waals,and molecular mechanics calculations have suggested that the c orresponding trans isomer has a structure in which the CN group is in general directed away from the phosphorus lone pair. Cone angle calcul ations based on the X-ray structure and calculated geometries of both cia and trans Ph(2)C(5)H(8)CN as well as the analogous Ph(2)C(5)H(8)(R ) (R = H, CH3) have provided values between 150 degrees and 173 degree s with the cis isomers having larger angles than the trans. Nonaqueous titrations have been used to determine pK(a) values for the three cyc loalkane-nitrile phosphines, and values between 2.44 and 2.52 have bee n obtained. IR and NMR studies of the Ni(CO)(3)L complexes of these th ree ligands have been completed, and the results indicate that these l igands are similar in effect to PhP(OR)(2). Both Pd-II and Pt-II compl exes (all trans geometries) of these ligands have been obtained, and t he P-N chelates (Pd) of the corresponding methyl imino ethers (from tr ans Ph(2)C(5)H(8)CN and Ph(2)PC(6)H(10)CN) have also been isolated.