Two-coordinate, Homoleptic Manganese(II) Primary Terphenyl Amido Complexes: The Effects of Secondary Coordination on Geometry and Lewis Base Complexation


The synthesis and characterization of the mononuclear manganese primary amido complex Mn{N(H)Ar#}2 (1), its Lewis base adducts Mn{N(H)Ar#}2(L) (Ar# = C6H 3-2,6-(C6H2-2,4,6-Me3)2; L = THF (2), and C5H5N (3)), and Mn{N(H)Ar*} 2 (4) (Ar* = C6H3-2,6-(C 6H2-2,4,6-iPr3)2) are described. Complex 1 was prepared by the reaction of MnCl2 with two equivalents of LiN(H)Ar# in benzene. X-Ray crystallography showed that it had a quasi-two-coordinate strongly bent geometry with Mn-N = 1.979(3) Å, N-Mn-N = 138.19(9)°and secondary Mn⋯C(aryl ring) interactions. In contrast, complex 4, which was prepared by the same route as 1, has an almost linear geometry with a wide N-Mn-N angle of 176.1(2)°. The complexes 1 and 4 are the first structurally characterized homoleptic primary amido derivatives of manganese. Complex 1 did not react with THF or pyridine, but its THF complex 2 could be formed by the reaction of MnI2(THF) 2 with two equivalents of LiN(H)Ar#. Similarly, complex 3 was prepared either by the direct reaction of MnCl2 with LiN(H)Ar# in hexanes in the presence of pyridine, or by reaction of the THF complex 2 with excess pyridine. Attempts to form Lewis base complexes of 4 by similar routes led to the recovery of unreacted 4. The results suggested that reaction with Lewis bases is prevented by secondary interactions (1) or steric effects (4). Magnetic studies show that the manganese(ii) ions in 1-4 have high spin configurations with S = and small zero-field splittings, D, of ca.±1.5 to ±3 cm-1.




National Science Foundation (U.S.)

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Manganese compounds
X-ray crystallography

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Article - Journal

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