Synthesis of (1R,1'S)- and (1S,1'S),(1R,1'R)-bis[1-(diphenylphosphino)ethyl]benzene derivatives and their cyclometalation reactions with platinum(II) compounds. The x-ray crystal structures of [2,6-bis[(diphenylphosphino)methyl]phenyl]chloropalladium(II), [(1R,1'S)-2,6-bis[1-(diphenylphosphino)ethyl]phenyl]chloroplatinum(II), and [(1R,1'R),(1S,1'S)-2,6-bis[1-(diphenylphosphino)ethyl]phenyl]chloroplatinum(II)