Dinitrogen Labile Coordination versus Four-Electron Reduction, THF Cleavage, and Fragmentation Promoted by a (calix-tetrapyrrole)Sm(II) Complex

Abstract

A divalent calix-tetrapyrrole Sm complex, {[(−CH 2 −) 5 ] 4 -calix-tetrapyrrole}Sm(THF)[Li(THF)] 2 [Li(THF) 2 ](μ 3 -Cl) ( 1 ), reacts with dinitrogen to reversibly form the labile dinuclear complex [{[(−CH 2 −) 5 ] 4 -calix-tetrapyrrole}Sm[Li(THF)] 3 (μ 3 -Cl)] 2 (μ 2 -N 2 )·2THF ( 2 ). Further attack on 2 by two additional molecules of 1 afforded four-electron reduction of the coordinated dinitrogen and formation of the novel trinuclear dinitrogen complex [{[(−CH 2 −) 5 ] 4 -calix-tetrapyrrole} 2 Sm 3 Li 2 ](μ 3 -N 2 )[Li(THF) 2 ]·THF ( 5 ). The formation of this species, where one calix-tetrapyrrole ligand was abstracted from one of the three samarium centers, is accompanied by formation of {[(−CH 2 −) 5 ] 4 -calix-tetrapyrrole}[Li(THF)] 4 ( 6 ) and of the trivalent {[(−CH 2 −) 5 ] 4 -calix-tetrapyrrole}Sm(Cl){[Li(THF)] 3 (μ 3 -Cl)} ( 7 ). A THF degradation reaction occurs in parallel to the dinitrogen fixation process. During the formation of 2, complex 1 also reacts with THF to afford another mononuclear divalent Sm complex, {[(−CH 2 −) 5 ] 4 -calix-tetrapyrrole}Sm(THF)Li 2 [Li(THF)](μ 3 -OCH CH 2 ) ( 3 ). This species contains an enolate fragment in the molecular backbone and shows no reactivity with N 2 . Recrystallization of 3 from THF did not eliminate the enolate fragment but afforded instead another divalent complex, {[(−CH 2 −) 5 ] 4 -calix-tetrapyrrole}Sm(THF) 2 {Li[Li(THF)] 2 }(μ 3 -OCH CH 2 )·THF ( 4 ), also unreactive toward N 2 . Finally a slow THF deoxygenation process occurs during the formation of 2 and 5, affording a dinuclear trivalent oxo derivative [{[(−CH 2 −) 5 ] 4 -calix-tetrapyrrole}Sm[Li(THF)] 3 (μ 3 -Cl)] 2 (μ-O) ( 8 ).