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) (THF)](2)[Li(THF)(2)](mu (3)-Cl) (1), reacts with dinitrogen to reversibly form the labile dinuclear complex [{[(-CH2-)(5)](4)-calix-tetrapyrrole}Sm[Li(THF)](3)(mu (3)-Cl)](2)(mu (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 [{[(-CH2-)(5)](4)-calix-tetrapyrrole)(2)Sm3Li2](mu (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 {[(-CH2-)(5)](4)-calix-tetrapyrrole}[Li(THF)](4) (6) and of the trivalent {[(-CH2-)(5)](4)-calix-tetrapyrrole}Sm(Cl){[Li(THF)](3)(mu (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, {[(-CH2-)(5)](4)-calix-tetrapyrrole)Sm(THF)Li-2[Li(THF)](mu (3)-OCH=CH2) (3). This species contains an enolate fragment in the molecular backbone and shows no reactivity with Na 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)}(mu (3)-OCH=CH2). 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 [{[(-CH2-)(5)[(4)-calix-tetrapyrrole)Sm[Li(THF)](3)(mu (3)-Cl)](2)(mu -O) (8).