Stabilisation of carbonyl free amidinato-manganese(ii) hydride complexes: “masked” sources of manganese(i) in organometallic synthesis

Abstract

Reaction of the amidinato-manganese(II) bromide complex, [{(κ²-N,N′-Piso)Mn(μ-Br)}₃(THF)₂] (Piso = [(DipN)₂CBu^t]⁻, Dip = 2,6-diisopropylphenyl), with K[BHEt₃] affords the first example of a structurally authenticated amidinato-manganese(II) hydride complex, [{(N-,η³-arene-Piso)Mn(μ-H)₂}₂], via a process which involves a change in the amidinate coordination mode. Treatment of the bulkier precursor complex, [{(Piso′′)Mn(μ-Br)}_n] (Piso′′ = [(Dip′′N)₂CBu^t]⁻, Dip′′ = C₆H₂Prⁱ₂(CPh₃)-2,6,4), with K[BHEt₃] did not lead to an isolable manganese hydride complex, but its reaction with the magnesium(I) complex, [{(^MesNacnac)Mg}₂] (^MesNacnac = [(MesNCMe)₂CH]⁻, Mes = mesityl), did. This reaction presumably proceeds via a reactive manganese(I) intermediate, which abstracts hydrogen from a reaction component to give [{(κ²-N,N′-Piso′′)Mn(μ-H)}₃]. A comparison of the reactivities of [{(N-,η³-arene-Piso)Mn(μ-H)₂}₂] and the isomorphous manganese(I) complex, [{(N-,η³-arene-Piso)Mn}₂], toward CO, O₂ and N₂O was carried out. Reactions with the manganese(I) and manganese(II) species gave identical results, namely the formation of the manganese(I) carbonyl complex, [(κ²-N,N′-Piso)Mn(CO)₄] (reactions with CO), and the manganese(III)-μ-oxo complex, [{(κ²-N,N′-Piso)Mn(μ-O)}₂] (reactions with O₂ and N₂O). These results indicate that [{(N-,η³-arene-Piso)Mn(μ-H)₂}₂] can act as a “masked” source of an amidinato-manganese(I) fragment in synthetic transformations.