| Abstract
| - Free and ligand-stabilized substances containing metals in negative oxidation states are discussed and classified. Syntheses and properties of homoleptic carbonyl- and polyarenemetalates of the d-block elements are described. The latter are of particular interest as synthons for spin-paired atomic anions of transition metals.
- A brief history of substances containing s,p- and d-block metals in negative oxidation states is described. Aclassification of these species and discussions of formal oxidation state assignments for low-valent transition metalsin complexes are included, along with comments on the innocent and noninnocent character of ligands in metalates.Syntheses of highly reduced carbonyl complexes formally containing transition metals in their lowest known oxidationstates of III− and IV− are discussed. Atmospheric-pressure syntheses of early-transition-metal carbonyls involvingalkali-metal polyarene-mediated reductions of non-carbonyl precursors have been developed. In the absence ofcarbon monoxide, these reactions afford homoleptic polyarenemetalates, including the initial species containingthree aromatic hydrocarbons bound to one metal. In several instances, these metalates function as useful synthonsfor “naked” spin-paired atomic anions of transition metals.
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