Synthesis, Structure, and Reactivity of a Polynuclear Chromium Tetraanion, Tetrakis((μ3-methoxo)trlcarbony Ichromate (0))

Abstract

Reaction of Cr(CO)6 with excess hydroxide ion in refluxing methanol yields a polynuclear chromium tetraanion, [Cr4(CO)12(μ3-OCH3)4]4-, isolated as its R4N+ (R = Me, Et) salt. The X-ray structure of [Et4N]4[Cr4(CO)12(μ3-OCH3)4] has been determined; the crystals are orthorhombic, space group Fddd (D2h24), Z = 8, with unit cell dimensions a = 12.766 (4), b = 23.694 (7), and c = 38.601 (12) Å. The anion consists of a distorted cubic A4B4 (A = chromium, B = oxygen) arrangement with triply bridging μ3-methoxide groups and Cr(CO)3 units. A nonbonding Cr-Cr distance of 3.31 (6) Å (average) is consistent with a closed-shell metal configuration. Cr(CO)3(CH3CN)3 is formed as the exclusive product when [Cr4-(CO)12(μ3-OCH3)4]4- is treated with HCl in acetonitrile. Addition of the tetraanion to concentrated ammonium hydroxide quantitatively yields Cr(CO)3(NH3)3. © 1984, American Chemical Society. All rights reserved.