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) (), its Lewis base adducts Mn{N(H)Ar(#)}(2)(L) (Ar(#) = C(6)H(3)-2,6-(C(6)H(2)-2,4,6-Me(3))(2); L = THF (), and C(5)H(5)N ()), and Mn{N(H)Ar*}(2) () (Ar* = C(6)H(3)-2,6-(C(6)H(2)-2,4,6-(i)Pr(3))(2)) are described. Complex was prepared by the reaction of MnCl(2) 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) A, N-Mn-N = 138.19(9) degrees and secondary MnC(aryl ring) interactions. In contrast, complex , which was prepared by the same route as , has an almost linear geometry with a wide N-Mn-N angle of 176.1(2) degrees . The complexes and are the first structurally characterized homoleptic primary amido derivatives of manganese. Complex did not react with THF or pyridine, but its THF complex could be formed by the reaction of MnI(2)(THF)(2) with two equivalents of LiN(H)Ar(#). Similarly, complex was prepared either by the direct reaction of MnCl(2) with LiN(H)Ar(#) in hexanes in the presence of pyridine, or by reaction of the THF complex with excess pyridine. Attempts to form Lewis base complexes of by similar routes led to the recovery of unreacted . The results suggested that reaction with Lewis bases is prevented by secondary interactions () or steric effects (). Magnetic studies show that the manganese(ii) ions in have high spin configurations with S = 5/2 and small zero-field splittings, D, of ca.+/-1.5 to +/-3 cm(-1).