P-31 NMR and X-ray crystallographic study of atropisomerism in cis-tetracarbonylmolybdenum(0) and cis-dichloroplatinum (II) complexes of (+/-)-6,6 '-[[1,1 '-biphenyl]-2,2 '-diylbis(oxy)]bis(dibenzo[d,f]-1,3,2] dioxaphosphepin) and (+/-)-6,6 '-[[1,1 '-binaphthyl]-2,2 '-diylbis(oxy)]bis(dibenzo[d,f][1,3,2]dioxaphosphepin) ligands

Both cis-tetracarbonylmolybdenum(0) and cis-dichloroplatinum(II) complexes of {(+/-)-6,6'-[[1,1'-biphenyl]-2,2'-diylbis(oxy)]bis(dibenzo [d,f][1,3,2]d ioxaphosphepin)}, 1, and {(+/-)-6,6'-[[1,1'-binaphthyl]-2,2'-diylbis(oxy)]b is(dibenzo[d,f][1,3,2]dioxaphosphepin)} 2, have been prepared. Atropisomeri sm of the ligands in these complexes has been investigated by variable-temp erature P-31{H-1} NMR spectroscopy. These studies demonstrate that all thre e diastereomers are pre sent in solutions of the cis-tetracarbonylmolybdenu m(0) complexes of both ligands in the slow exchange region, although the di stribution of the diastereomers is strongly dependent on the nature of the ligand. The conformations proposed for the major complexes in solution are consistent with the solid-state conformations of the complexes, as determin ed by X-ray crystallography. Only two species are present in solutions of t he cis-dichloroplatinum(II) complexes, and surprisingly, both appear to hav e the R*R*S*(S*S*R*) configuration. The different conformations of the R*R* S*(S*S*R*) disatereomers may arise from different interplanar angles of the biaryl group in the nine-membered chelate ring.