Tetrametallic reduction of dinitrogen: formation of a tetranuclear samarium dinitrogen complex

The 1st example in which a four-electron dinitrogen redn. is achieved through the cooperative 1-electron oxidn. of four metal centers is presented. The reaction of [SmI2(THF)2] with one equiv. of diphenylmethyldipyrrolide dianion at room temp. under N2 yielded [{[μ-Ph2C(η1:η5-C4H3N)2]Sm}4(μ-η1:η1:η2:η2-N2)] (1). Complex 1 showed no sign of reversible coordination of dinitrogen and remained unchanged upon prolonged exposure to heat or vacuum. The four metal atoms arrange to form a slightly distorted lozenge, in the center of which is located a dinitrogen mol. that is coordinated side-on to two metal atoms and end-on to the other two metal atoms. The same reaction carried out under an Ar atm. afforded [{[μ-Ph2C(η1:η5-C4H3N)2]2[Sm(THF)]3}(μ3-I)][{[μ-Ph2C(η1:η5-C4H3N)2]Sm}5(μ5-I)] (2). The elimination of the formal SmI2 unit was achieved by reaction of 2 with KH under N2 and resulted in an immediate color change and concomitant release of H2 giving 1, Sm, and KI. Reaction of diphenylmethyldipyrrolide dianion in THF with [SmCl3(THF)3] followed by K metal and a catalytic amt. of naphthalene gave [{[μ-Ph2C(η1:η5-C4H3N)2]Sm}4(μ4-Cl){K(THF)2}] (3). The crystal and mol. structures of 1-3 were detd. by x-ray crystallog.