Synthesis, Structure, and Hydroamination Kinetics of (2,2‘-Diaryldipyrrolylmethane)- and Bis(2-arylpyrrolyl)titanium Complexes

Abstract

The trifluoroacetic acid catalyzed reaction of acetone and 2-arylpyrroles results in the formation of 2,9-diaryl-5,5-dimethyldipyrrolylmethanes. Ligands bearing 3,5-(CF3)2C6H3 (H2dmpm3,5-CF3) and mesityl (H2dmpmmes) arenes were prepared in 72% and 68% yields using this procedure. The new dipyrrolylmethanes react with Ti(NMe2)4 to form Ti(NMe2)2(dmpm3,5-CF3) and Ti(NMe2)2(dmpmmes) in 92% and 30% yields, respectively. The solid-state structures of these complexes are quite similar to that of the sterically smaller 5,5-dimethyldipyrrolylmethane complex Ti(NMe2)2(dmpm) with one η5- and one η1-pyrrolyl; however, the substituted derivatives display much lower barriers to pyrrolyl conformational exchange, as judged by VT 1H NMR spectroscopy. Also synthesized were bis(pyrrolyl) complexes without the methylene connector. Reactions of 2-arylpyrroles where the aryl group was 3,5-(CF3)2C6H3, mesityl, 4-(CF3)C6H4, and p-tolyl generated Ti(NMe2)2(pyrr3,5-CF3)2, Ti(NMe2)2(pyrrmes)2, Ti(NMe2)2(pyrr4-CF3)2, and Ti(NMe2)2(...