Low valent chromium complexes bearing N,O-chelating pyridylenolate ligands [OC(Bu~t)(=2-CHN_5H_3Me-x)]~- (x = 3-6)

摘要

Treatment of [CrCl_2(THF)](THF = tetrahydrofuran) with the sodium salt of HOC(Bu~t)(2-CH_2NC_5H_3Me-x)_2(x= 6) in refluxing THF results in fragmentation of the L_2X (L = neutral donor, X = anionic donor) ligand to afford the square planar bis(pyridyl-enolate) chromium(II) complex [Cr{OC(Bu~t)(=2-CHNC_5H_3Me-6)}_2] (1) and the by-product trans-[CrCl_2(2,6-dimethylpyridine)_2] (2). On prolonged heating in refluxing toluene, oxidation of 1 occurs yielding the octahedral tris(pyridyl-enolate) chromium(III) complex [Cr{OC(Bu~t)(2-CHNC_5H_3Me-6)}_3](3). Similar use of the sodium salts of HOC(Bu~t)(2-CH_2NC_5H_3Me-x)_2 (x = 3-5) also results in ligand fragmentation but gives solely the chromium(III)tris-chelated complexes [Cr{OC(Bu~t)(=2-CHNC_5H_3Me-x)}_3][x = 3 (4), 4 (5), 5 (6)]. Surprisingly, prolonged heating in a sealed tube of a mixture of [CrCl_2(THF)] and the sodium salt of HOC(Bu~t)(2-CH_2NC_5H_3Me-x)_2(x = 6) in the presence of diphenylacetylene furnishes the bimetallic chromium(II) complex [ClCr{(μ-OC(Bu~t)(2-CH_2NC_5H_3Me-6)_2}CrCl] (7), in which the two intact L_2X ligands bridge the Cr-Cr vector (2.92 A), one acting as a bidentate ligand and the other as a tridentate ligand. Single crystal X-ray diffraction studies have been performed on 1, 2, 3, 6 and 7.