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

The ditertiary arsine (CH3)2AsCH2CH(C(CH3)3)CD2As(CH3)2 (L–L) forms 'tetrahedral' (L–L)Ni(CO)2 and square planar (L–L)NiOC(CF3)2C(CF3)2O. 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)′PtbipyCl2 and (L–L)2′PtCl2 and their palladium analogs ((L–L)′ = H2NCH2CH(C(CH3)3)CD2NH2) also have their chelate rings in locked chair conformations. This results in the identification of isomers in the case of (L–L)2′M2+. The 3JH–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 3JPt–H couplings indicate changes in the puckering about the N … N axis.