Serendipitous isolation of the first example of a mixed-valence samarium tripyrrole complex

The transamination reaction of Sm{N(SiMe3)(2)}(2)(THF)(2) with two dipyrrole ligands of formula RR'C(alpha-C4H3NH)(2) (R = R' = Et; R = Me, R' = Ph) has been examined. The reactions in THF and under N-2 gave two similar tetranuclear dinitrogen complexes, {[Et2C(alpha-C4H3N)(2)-Sm}(4)(THF)(2)](mu-N-2)(.)2THF and [{[(C6H5)(CH3)C(alpha-C4H3N)(2)]Sm}(4)(DME)(2)](mu-N-2), where the dinitrogen unit has undergone a four-electron reduction via cooperative attack of four divalent samarium atoms and remained coordinated both side-on and end-on between the four coplanar metal centers. The same reaction carried out with diethyldipyrrolylmethane under an argon atmosphere afforded the divalent samarium macrocyclic cluster {[Et2C(alpha-C4H3N)(2)]-Sm}(8)(THF)(4)(.)4THF. In the case of the reaction with the methylphenyldipyrrolylmethane ligand under N-2, the unprecedented hexanuclear mixed-valence Sm-II/Sm-III cluster [([(C6H5)-(CH3)C(alpha-C4H3N)(2)][(C6H5)(CH3)C(alpha-C4H3N)(beta-C4H3N)]{[(C6H5)(CH3)C](2)(alpha-C4H3N)(2)(alpha,alpha' -C4H2N)}- Sm-3)(THF)(3)](2), containing tripyrrolide, "N-confused", and regular dipyrrolide ligands was serendipitously formed by reaction with the impurities contained in the nonpurified ligand.