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

Dalton Transactions Pub Date: 2010-10-06 DOI: 10.1039/C0DT00771D

Abstract

Reaction of {Li(THF)Ar′MnI2}2 (Ar′ = C6H3-2,6-(C6H2-2,6-iPr3)2) with LiAr′, LiC[triple bond, length as m-dash]CR (R = tBu or Ph), or (C6H2-2,4,6-iPr3)MgBr(THF)2 afforded the diaryl MnAr′2 (1), the alkynyl salts Ar′Mn(C[triple bond, length as m-dash]CtBu)4{Li(THF)}3 (2) and Ar′Mn(C[triple bond, length as m-dash]CPh)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 LitBu gave complex Ar*MntBu (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.

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