Vanadium-Promoted Aldol Condensation and Pinacolic Coupling of Acetylpyrrole:  Formation of Two New Potent Dinuclear Catalysts for Olefin Copolymerization

Abstract

Reaction of VCl 3 (THF) 3 with 3 equiv of the potassium salt of acetylpyrrole, K[α-(CH 3 CO)C 4 H 3 N], afforded the dinuclear {V 2 [K(THF)] 2 [CH 3 CO(C 4 H 3 N)] 2 }[(C 4 H 3 N)C(O)CH 2 C(C 4 H 3 N)(CH 3 )O] 2 ( 1 ), where four acetylpyrrolide anions from two vanadium moieties have undergone an aldol condensation. The two pyrrolyl−acetylacetonate units so generated work as tetradentate binucleating ligands holding together the dinuclear structure. A similar reaction carried out on the divalent [V 2 Cl 3 (THF) 6 ] 2 [Zn 2 Cl 6 ] salt afforded the dinuclear and trivalent {VK(THF)[(C 4 H 3 N)C(O)CH 3 ]} 2 [(C 4 H 3 N)(CH 3 )(O)CC(O)(CH 3 )(C 4 H 3 N)]·0.5(toluene) ( 2 ), where two acetylpyrrolide ligands, one per vanadium atom, have undergone a reductive coupling to form a pinacol. Even in this case the dipyrrolylpinacol works as a tetradentate binucleating ligand holding together the dinuclear frame. Attempts to perform the same reaction on another V(II) salt such as VCl 2 (TMEDA) 2 (TMEDA = N, N, N ‘, N ‘-tetramethylethylenediamine) afforded instead the corresponding divalent derivative V(TMEDA)[(C 4 H 3 N)C(O)CH 3 ] 2 ( 3 ), where the acetylpyrrolide anions remained intact. Both 1 and 2 are potent olefin copolymerization catalysts upon activation with diethyl aluminum chloride, while 3 displays low but not negligible activity.