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⁻

Abstract

Cr 2 (CO) 8 (NO) 2 (1) has been prepared and characterized, and the crystal structure determined, along with that of the related salt Cr 2 (CO) 9 NO − monoanion (2) as the CH 2 Cl 2 -solvated PPN + salt (where PPN + denotes the (PPh 3 ) 2 N + monocation). Both 1 and 2 possess a metal–metal bonded structure analogous to that of Mn 2 (CO) 10 and the electronically equivalent Cr 2 (CO) 10 2− dianion. Although Cr 2 (CO) 8 (NO) 2 (1) is slowly formed in poor yield from Cr(CO) 4 NO − and Cr(CO) 4 NOBr, 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) 4 NO − 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 Mn 2 (CO) 10 . Key words: chromium nitrosyl, chromium carbonyl, X-ray crystal structure, metalate anion, metal–metal dimer.