Metal-mediated conversion of methylcycloarsoxane (CH3AsO)(n) to macrocyclic octa- and decanuclear ligands - Trigonal bipyramidal coordination of trivalent arsenic

Reaction of cyclo-(CH3AsO)(n) with MCl3 . x H2O in acetonitrile at 100 degr ees C affords [MCl2(cyclo-(CH3AsO)(8))] [M = Ru (1), M = Os (2)] in which c yclooctamers (CH3AsO)(8) are stabilised in a (KAs1,3.5,7)-As-4 binding mode in the equatorial coordination sphere of the Group 8 metals. In contrast t reatment of K2PtCl4 with alternatively AgNO3 os Ag2CO3 and cyclo-(CH3AsO)(n ) at 100 degrees C in the same solvent leads to the formation of respective ly octa- or decanuclear cagelike Ligands in [Pt-2{[cyclo-(As[CH3]OAs[NC(O)C H3]O)(2)](2)} (3) and [Pt-2{[{CH3C(O)N}(2)As-5(CH3)(5)O-4](2)}] (4) by meta l-assisted reactions between cyclo-(CH3AsO)(n) and acetonitrile. lambda(5)- As-III atoms in these complexes participate in square-planar Pt-II coordina tion and themselves exhibit distorted trigonal bipyramidal coordination geo metries.