Neutral and Cationic Alkylmanganese(II) Complexes Containing 2,6‐Bisiminopyridine Ligands

Manganese alkyl complexes stabilised by 2,6‐bis( N , N ′‐2,6‐diisopropyl‐phenyl)acetaldiminopyridine ( i Pr BIP) have been selectively prepared by reacting suitable alkylmanganese(II) precursors, such as homoleptic dialkyls [(MnR 2 ) n ] or the corresponding THF adducts [{MnR 2 (thf)} 2 ] with the mentioned ligand. For R=CH 2 CMe 2 Ph or CH 2 Ph, formally Mn I derivatives are produced, in which one of the two R groups migrates to the 4‐position of the central pyridine ring in the i Pr BIP ligand. In contrast, a true dialkyl complex [MnR 2 ( i Pr BIP)] can be isolated for R=CH 2 SiMe 3 . In solution, this compound slowly evolves to the corresponding Mn I monoalkyl derivative. A detailed study of this reaction provides insights on its mechanism, showing that it proceeds through successive alkyl migrations, followed by spontaneous dehydrogenation. Protonation of [Mn(CH 2 SiMe 3 ) 2 ( i Pr BIP)] with the pyridinium salt [H(Py) 2 ][BAr′ 4 ] (Ar′=3,5‐C 6 H 3 (CF 3 ) 2 ) leads to the cationic species [Mn(CH 2 SiMe 3 )(Py)( i Pr BIP)] + . Alternatively, the same complex can be produced by reaction of the pyridine complex [{Mn(CH 2 SiMe 3 ) 2 (Py)} 2 ] with the protonated ligand salt [H i Pr BIP] + [BAr′ 4 ] − . This last reaction allows the synthesis of analogous cationic alkylmanganese(II) derivatives, when precursors of type [MnR 2 ( i Pr BIP)] are not available. Treatment of these neutral and cationic i Pr BIP alkylmanganese derivatives with a range of typical co‐catalysts (modified methylaluminoxane (MMAO), B(C 6 F 5 ) 3 , trimethyl or triisobutylaluminum) does not lead to active ethylene polymerisation catalysts.