TRINUCLEAR COMPLEXES WITH PT(2)M(MU(3)-S) GROUPS AND THE EASE OF INVERSION AT SULFUR

The binuclear platinum complex [Pt-2(mu-S)(mu-dppm)(mu(1)-dppm)(2)]) ( 1), dppm=Ph(2)PCH(2)PPh(2), can act as a tridentate ligand in forming homonuclear and heteronuclear cluster cations. Thus, 1 reacted with sq uare planar complexes of formula [PtClRT(2)], L(2)=(SMe(2))(2) or 1,5- cyclooctadiene (cod), to form the corresponding trinuclear clusters [P t(3)R(mu(3)-S)(mu-dPPm)(3)]Cl-+(-) (R=Me (2), Ph (3), CH2Cl (4), Cl (5 )), with [PdCl2,(PhCN)(2)] to form [Pt2PdCl(mu(3)-S)(mu-dppm)(3)][Cl] (6), with [Rh(mu-Cl)(CO)(2)](2) or [Ir(mu-Cl)(CO)(3)](2) to form [Pt(2 )M(CO)(mu(3)-S)(mu-dppm)(3)][Cl] (M=Rh (7), Ir (8)), with the d(10) me tal compounds CuCl, AgNO3, and [AuCl(SMe(2))] to give [Pt(2)M,M(mu(3)- S)(mu-dppm)(3)](+)) (M=Cu (9), Ag (10), Au (11)), and with Hg(NO3)(2) to yield [Pt(2)M(mu(3)-SMe)(CO)(mu-dppm)(3)](2+). Complexes 7 and 8 ea ch reached with excess iodomethane to yield [Pt(2)M(mu(3)-SMe)(CO)(mu- dppm)(3)]I-2 (M=Rh (16), Ir (17)) and with AgBF4 to give [Pt-2(mu(3)-S )(CO)(mu(3)-AgCl)(mu-dppm)(3)]BF4 (M=Rh (19), Ir (20)). The complexes 2-8 are shown to be fluxional with respect to inversion at sulfur, whe reas 9-12 are not; the inversion has a lower activation energy for 7 a nd 8 than for 2-6 and this is attributed to stabilization of the plana r transition state by the carbonyl ligand. The structure of 11 has bee n confirmed by an X-ray structure determination.