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

A divalent calix-tetrapyrrole Sm complex, {[(−CH2−)5]4-calix-tetrapyrrole}Sm(THF)[Li(THF)]2[Li(THF)2](μ3-Cl) (1), reacts with dinitrogen to reversibly form the labile dinuclear
complex [{[(−CH2−)5]4-calix-tetrapyrrole}Sm[Li(THF)]3(μ3-Cl)]2(μ2-N2)·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 [{[(−CH2−)5]4-calix-tetrapyrrole}2Sm3Li2](μ3-N2)[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 {[(−CH2−)5]4-calix-tetrapyrrole}[Li(THF)]4 (6) and of the
trivalent {[(−CH2−)5]4-calix-tetrapyrrole}Sm(Cl){[Li(THF)]3(μ3-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,
{[(−CH2−)5]4-calix-tetrapyrrole}Sm(THF)Li2[Li(THF)](μ3-OCHCH2) (3). This species contains an enolate fragment in the molecular backbone and shows no reactivity with N2.
Recrystallization of 3 from THF did not eliminate the enolate fragment but afforded instead
another divalent complex, {[(−CH2−)5]4-calix-tetrapyrrole}Sm(THF)2{Li[Li(THF)]2}(μ3-OCHCH2)·THF (4), also unreactive toward N2. Finally a slow THF deoxygenation process
occurs during the formation of 2 and 5, affording a dinuclear trivalent oxo derivative
[{[(−CH2−)5]4-calix-tetrapyrrole}Sm[Li(THF)]3(μ3-Cl)]2(μ-O) (8).