Preparation of Cr2(CO)8(NO)2 and X-ray crystal structures of Cr2(CO)8(NO)2 and Cr2(CO)9NO−. Stereochemical comparisons to Cr2(CO)102−
Cr2(CO)8(NO)2 (1) has been prepared and characterized, and the crystal structure determined, along with that of the related salt Cr2(CO)9NO− monoanion (2) as the CH2Cl2-solvated PPN+ salt (where PPN+ denotes the (PPh3)2N+ monocation). Both 1 and 2 possess a metal–metal bonded structure analogous to that of Mn2(CO)10 and the electronically equivalent Cr2(CO)102− dianion. Although Cr2(CO)8(NO)2 (1) is slowly formed in poor yield from Cr(CO)4NO− and Cr(CO)4NOBr, it can be prepared in an almost quantitative yield by the one-electron oxidation of the monoanion with trityl hexafluorophosphate. The slowness of the former reaction makes Cr(CO)4NO− useful as a two-electron reductant of organohalide bonds. Triclinic crystals of 1 incorporate two distinct molecules in die [Formula: see text] space group, although the geometries of each are almost identical. Triclinic crystals of monoanion (2) also belong to the [Formula: see text] space group. The Cr—Cr bond length is 3.00–3.02 Å in 1 and 2.995 Å in 2, compared to 2.904 Å for the central Mn—Mn bond in Mn2(CO)10. Key words: chromium nitrosyl, chromium carbonyl, X-ray crystal structure, metalate anion, metal–metal dimer.