Phosphine-nitrile ligands: the molecular structure of cis-2-diphenylphosphino-1-cyanocyclopentane and studies of the donor/acceptor properties of this and related ligands

Article abstract of DOI:10.1016/0022-328X(94)87068-3

The cis and trans isomers of the previously reported 2-diphenylphosphino-1-cyanocyclo-pentane and -cyclohexane have been separated, and three 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 Ph2PC5H8CN isomer with the more-shielded 31P chemical shift proved it to be the cis isomer.A prominent feature observed for the structure is that the CN group is directed toward the phosphorus lone pair.Van der Waals and molecular mechanics calculations have suggested that the corresponding trans isomer has a structure in which the CN group is in general directed away from the phosphorus lone pair.Cone angle calculations based on the X-ray structure and calculated geometries of both cis and trans Ph2C5H8CN as well as the analogous Ph2C5H8(R) (R=H, CH3) have provided values between 150 deg and 173 deg with the cis isomers having larger angles than the trans.Nonaqueous titrations have been used to determine pK_a values for the three cycloalkane-nitrile phosphines, and values between 2.44 and 2.52 have been obtained.IR and NMR studies of the Ni(CO)3L complexes of these three ligands have been completed, and the results indicate that these ligands are similar in effect to PhP(OR)2.Both Pd^II and Pt^II complexes (all trans geometries) of these ligands have been obtained, and the P-N chelates (Pd) of the corresponding methyl imino ethers (from trans Ph2C5H8CN and Ph2PC6H10CN) have also been isolated. Key words: Phosphine-nitrile ligands; Nickel; Palladium; Platinum; Hindered (bulky) ligands; Molecular mechanics