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Eight new cis-methylplatinum(II) derivatives of the type DIARSPt(CH3)X (DIARS abbreviates o-phenylenebis(dimethylarsine), where X is an anionic substituent, and [DIARSPt(CH3)L]+PFti-, where L is a neutral ligand, have been prepared. Data derived from the I3C n.m.r. spectra of these complexes are discussed and compared with data derived from the ' H n.m.r. spectra of the complexes. Comparisons with the 13C n.m.r. parameters obtained from related series of trans-methylplatinum(I1) derivatives reveal marked differences between the n.m.r. cis-and trm~s-influences. It appears that the n.m.r. cisinfluence may in part be related to a ligand's "steric bulk".On a prepart huit nouveaux derives cis-mCthylplatine du type DIARS-Pt(CH3)X (DIARS etant I'abrCviation de o-phknylenebis (dimithylarsine)), oh X est un substituant du type anionique, et du type [DIARSPt(CH,)L] +PFti-, oh Lest un coordinat neutre. On discute et I'on compare les donnees obtenues a partir des spectres r.m.n. du 13C de ces complexes avec celles obtenues a partir des spectres r.m.n. du 'H des complexes. La comparaison de ces donnCes avec les parameters obtenus de la r.m.n. d u 13C d'une sCrie parente de derives trans-mCthylplatine(I1) a montre que I'influence des formes cis et trans sur les spectres r.m.n. etait tres differente. I1 semble que I'influence de la forme cis sur les spectres r.m.n., soit imputable, en partie, a un encombrement stkrique du coordinat.[Traduit par le journal]Can. J. Chem., 52, 570 (1974) Introduction While nuclear magnetic resonance studies of transition metal derivatives have vielded substantial information concerning the trans-influence (2), investigations (3, 4) of the n.m.r. cis-influence have been generally unrewarding. Our examination of series of trans-phenylplatinum(I1) (1) and trans-methylplatinum(11) (5, 6) complexes has indicated that I3C n.m.r. is an extremely powerful technique for the study of bonding in these and related derivatives. Thus, it appeared that the cis-influence might also be conveniently and successfully examined by 13C n.m.r. Accordingly, we have synthesized a number of new cis-methylplatinum(I1) complexes of the type DIARSPt(CH,)X (where X is an anionic substituent) and [DIARSPt(CH3)L]+PF6-(where L is a neutral ligand). We have specifically chosen the chelating ditertiary arsine DIARS-(0-phenylenebis(dimethy1arsine) in order to preclude cis-trans isomerization in solution. In addition, we have selected the cis ligands L to encompass a wide range of the trans-influence, which some workers believe parallels a ligand's cis-influence.The n.m.r. parameters of the platinum-methyl,

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