PALLADIUM PUZZLE RESOLVED

Abstract

IN JANUARY, JAPANESE CHEMists published a startling report: They claimed to have synthesized a complex that contained palladium(VI), a high oxidation state not seen before nor expected in this metal. The complex contained a central Pd, presumed to be Pd(VI), surrounded by six silicon atoms. This was highly unexpected because silicon isn't thought of as an electronegative ligand [ Science , 295, 308 (2002); C&EN, Jan. 14, page 8]. However, Yale University chemistry professor Robert H. Crabtree, who wrote a perspective accompanying the report, and the Japanese group, which included Shigeru Shimada at the National Institute of Advanced Industrial Science & Technology in Tsukuba, entertained an alternate scenario. Two pairs of the silicon atoms were close enough together to possibly form sigma bonds with which the central Pd might be interacting. Although this would assign the Pd an oxidation state of II, not VI, the structure would still be unprecedented. Now two independent theoretical ...