Low valent chromium complexes bearing N,O-chelating pyridyl-enolate ligands [OC(But)(=2-CHN5H3Me-x)]– (x=3–6)

Treatment of [CrCl2(THF)](THF = tetrahydrofuran) with the sodium salt of HOC(But)(2-CH2NC5H3Me-x)2(x= 6) in refluxing THF results in fragmentation of the L2X (L = neutral donor, X = anionic donor) ligand to afford the square planar bis(pyridyl-enolate) chromium(II) complex [Cr {OC(But)(=2-CHNC5H3Me-6)}2](1) and the by-product trans-[CrCl2(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(But)(=2-CHNC5H3Me-6)}3](3). Similar use of the sodium salts of HOC(But)(2-CH2NC5H3Me-x)2(x= 3–5) also results in ligand fragmentation but gives solely the chromium(III)tris-chelated complexes [Cr{OC(But)(=2-CHNC5H3Me-x)}3][x= 3 (4), 4 (5), 5 (6)]. Surprisingly, prolonged heating in a sealed tube of a mixture of [CrCl2 (THF)] and the sodium salt of HOC(But)(2-CH2NC5H3Me-x)2(x= 6) in the presence of diphenylacetylene furnishes the bimetallic chromium(II) complex [ClCr{(µ-OC(But)(2-CH2NC5H3Me-6)2}CrCl](7), in which the two intact L2X 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.