620
Intrinsic Axial-Equatorial Chemical Shift Difference in the Conformational Analysis of Trisethylenediamine and Trispropylenediamine Complexes of Ruthenium (I1) , Cobalt (I11) , and Platinum (IV) James K . Beattie* and Lucille H. Novak Contribution from the Noyes Chemical Laboratory, Unicersity of Illinois, Urbana, Illinois 61801. Received June 25, 1970 Abstract: The proton magnetic resonance spectra of the N-deuterated trispropylenediamine complexes of Ru(II), Co(III), and Pt(1V) have been analyzed. The coupling constants indicate that the ligands are predominantly in one conformation with the methyl group equatorial. The chemical shift differences between the axial and equatorial methylene protons are 0.87, 0.33, and 0.13 ppm, respectively. These intrinsic chemical shift differences are considerably reduced by conformational averaging in the corresponding trisethylenediamine complexes, and the large differences among the metal ions account for the variety of spectra observed for the M(en)3 complexes. Evidence of scalar coupling between 5gcoand the equatorial proton in the propylenediamine complex is observed.
model to account for the nnir spectra of a series of N-deuterated M(en)3 complexes which have spin-paired d Gelectron configurations has recently been proposed.’ Spectra are available for the Pt(IV),2 CoRh(III),4 I I ~ I I I ) and , ~ R U ( I I ) ~complexes. The appearance of these vary enormously from a single narrow line for Pt(IV) (with satellites due t o coupling with l9;Pt) to a well-resolved AA’BB’ spectrum of 24 lines for Ru(I1). It was suggested that in all of the complexes there is rapid inversion between the two possible conformations, 6 and A, of each chelate ring.; In a fixed conformation of the chelate ring there is an axial and an equatorial proton on each carbon These are in different chemical environments and consequently have different chemical shifts. The two axial protons and the two equatorial protons are related by a CZsymmetry operation and all four protons are strongly coupled, resulting in an AA’BB’ nmr spectrum. On inversion from the 6 to X conforiiiation the axial and equatorial protons are interconverted. In an MenX4 complex there is no energy difference between the two conformations and each proton will spend an equal time in the axial and equatorial positions. Consequently, the average chemical shift of all of the protons will be the same and the nmr spectrum will consist of a single line. In the M(en), complexes there are free energy differences between the various possible configurations of chelate conformers about the metal ion. For Co(II1) these were estimated to be A(666) < A(S6X) < (A6XX) < R(XXX) for the A configuration of the three chelate rings around the metal ion.6 Further calculations, consideration of statistical effects, and experimental results7 obtained from separation of isomers of propylenediaminecobalt
A
(1) J. R. Gollogly, C. J. Hawkins, and J. IC. Beattie, Inorg. Cheni., in press. (2) J. K. Beattie and H. Elsbernd, J . A m e r . Chem. SOC.,92, 1946
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complexes indicate that the relative free energies are A(66X) < A(6XX)
