A Nuclear Magnetic Resonance Study of the Conformation of Six-membered Chelate Rings in Four-coordinate Complexes

The ditertiary arsine (CH 3 ) 2 AsCH 2 CH(C(CH 3 ) 3 )CD 2 As(CH 3 ) 2 (L–L) forms 'tetrahedral' (L–L)Ni(CO) 2 and square planar (L–L)NiOC(CF 3 ) 2 C(CF 3 ) 2 O. In both complexes the conformations of the chelate rings are locked with the t-butyl groups equatorial. The dihedral angles are very similar in spite of the anticipated differences in angles at the central atom. The square planar complexes (L–L)′PtbipyCl 2 and (L–L) 2 ′PtCl 2 and their palladium analogs ((L–L)′ = H 2 NCH 2 CH(C(CH 3 ) 3 )CD 2 NH 2 ) also have their chelate rings in locked chair conformations. This results in the identification of isomers in the case of (L–L) 2 ′M 2+ . The 3 J H–H couplings indicate that the dihedral angles are similar in the group VIII complexes with a degree of puckering which could be less than in related complexes of L–L. The 3 J Pt–H couplings indicate changes in the puckering about the N … N axis.