Terphenyl substituted derivatives of manganese(ii): distorted geometries and resistance to elimination

Abstract

Reaction of {Li(THF)Ar′MnI₂}₂ (Ar′ = C₆H₃-2,6-(C₆H₂-2,6-ⁱPr₃)₂) with LiAr′, LiCCR (R = ^tBu or Ph), or (C₆H₂-2,4,6-ⁱPr₃)MgBr(THF)₂ afforded the diaryl MnAr′₂ (1), the alkynyl salts Ar′Mn(CC^tBu)₄{Li(THF)}₃ (2) and Ar′Mn(CCPh)₃Li₃(THF)(Et₂O)₂(μ₃-I) (3), and the manganate salt {Li(THF)}Ar′Mn(μ-I)(C₆H₂-2,4,6-ⁱPr₃) (4), respectively. Complex 4 reacted with one equivalent of (C₆H₂-2,4,6-ⁱPr₃)MgBr(THF)₂ to afford the homoleptic dimer {Mn(C₆H₂-2,4,6-ⁱPr₃)(μ-C₆H₂-2,4,6-ⁱPr₃)}₂ (5), which resulted from the displacement of the bulkier Ar′ ligand in preference to the halogen. The reaction of the more crowded {Li(THF)Ar*MnI₂}₂ (Ar* = C₆H₃-2,6-(C₆H₂-2,4,6-ⁱPr₃)₂) with Li^tBu gave complex Ar*Mn^tBu (6). Complex 1 is a rare monomeric homoleptic two-coordinate diaryl Mn(II) complex; while 6 displays no tendency to eliminate β-hydrogens from the ^tBu group because of the stabilization supplied by Ar*. Compounds 2 and 3 have cubane frameworks, which are constructed from a manganese, three carbons from three acetylide ligands, three lithiums, each coordinated by a donor, plus either a carbon from a further acetylide ligand (2) or an iodide (3). The Mn(II) atom in 4 has an unusual distorted T-shaped geometry while the dimeric 5 features trigonal planar manganese coordination. The chloride substituted complex Li₂(THF)₃{Ar′MnCl₂}₂ (7), which has a structure very similar to that of {Li(THF)Ar′MnI₂}₂, was also prepared for use as a possible starting material. However, its generally lower solubility rendered it less useful than the iodo salt. Complexes 1–7 were characterized by X-ray crystallography and UV-vis spectroscopy. Magnetic studies of 2–4 and 6 showed that they have 3d⁵ high-spin configurations.