In spite of the considerable number of dinitrogen complexes reported since the discovery of the first example of dinitrogen fixation in [ R u ( N H~)~]~+ 30 years ago,' the chemistry of Nz still remains in its infancy. However, new perspectives for the metalpromoted activation fixation of dinitrogen are opening up, as has been recently seen in both the reversible dinitrogen activation operated by the lithium countercation of an anionic Zr(II1) complex2 and the considerable reduction of NZ performed by electron deficient low-valent early transition metals.3 In thelatter case, the variety of bonding modes of dinitrogen associated with these systems4 has been carefully investigated and r a t i~n a l i z e d .~~Low-valent lanthanides, and in particular Sm(II), are potentially good systems for studying the coordination/reduction of dinitrogen.5 Samarocene dinitrogen complex (Cp*2Sm)z(N,) provides a puzzling example where the strikingly short N-N distance: which suggests minimal N2 reduction, is in contrast to the side-on bonding mode. Unfortunately low-valent lanthanides are rare and, besides the bis(cyclopentadieny1) systems,' limited to a very few examples.* To date, ( C P *~S~)~ ( N , ) remains the sole case of coordination of dinitrogen in the lanthanide series.We describe in this paper the preparation of a low-valent Sm macrocyclic complex and its reaction with dinitrogen to form a (1) (a) Allen, A. D.; Senoff, C. V. (4) (a) Fryzuk, M. D.; Haddad, T. S.; Mylvaganam, M.; McConville, D. H.; Rettig, S. J. Scheme 1 (lXF),Li!OEPG) Sm N, Li, / ' -L i SmCI,(THF), t (OEPG)Li,(THF), -% Ar "green crystals" + / < / h i Sm 1 (THF),L~~OEPG~tetralithium hydrazide salt. The choice of the porphyrinogen tetraanion as a spectator ligand was 2-fold. First, we were interested in studying the behavior of the highly reactive Sm(I1) center in a coordination environment sterically and electronically more flexible than that provided by two cyclopentadienyl rings. Second, the alkali cations, easily retained by the porphyrinogen ligand,lob-c may play an important role in promoting molecular activation processes at the Sm(I1) center. The reduction of the mixture obtained from the reaction of SmC13(THF)3 with the colorless tetralithium salt of octaethylporphyrinogen (OEPG)9 (OEPG)L&(THF)410 under argon may be conveniently carried out in a one-pot preparation forming a gold yellow complex.ll The subsequent reduction with 1 equiv of metallic lithium proceeds at room temperature in THF under argon to yield a deep-green, extremely air-sensitive crystalline material (Scheme 1). While the extreme air-sensitivity of this species in combination with easy loss of volatile components has prevented formula determination by elemental analysis, recrystallization of this complex from THF under nitrogen yielded moderately air-stable orange-red crystals of [ (THF)zLi(OEPG)-The formation of 1 is a perfectly reproducible process, and it can be achieved both by slow recrystallization of the green solid from a dilute THF solution under N2 (5% yield) and by ex...

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Reaction of Li 4 (thf) 4 (oepg) (oepg = octaethylporphyrinogen with YCl 3 (thf) 3.5 affords the first yttrium porphyrinogen complex [Li(thf) 2 ](oepg)Y(µ-OEt)Li(thf)] 1 via intermediate cleavage of thf, subsequent reaction with alkyl and hydride sources leads to the formation of the demetallated dienolate salt of the macrocycle [(oepg)(thfLi) 4 ][(thf)LiOCH=CH 2 ] 2 2.