A divalent calix-tetrapyrrole Sm complex, {[(-CH 2 -) 5 ] 4 -calix-tetrapyrrole}Sm(THF) [Li-(THF)] 2 [Li(THF) 2 ](µ 3 -Cl) (1), reacts with dinitrogen to reversibly form the labile dinuclear complex 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 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 {[(-CH 2 -) 5 ] 4 -calix-tetrapyrrole}[Li(THF)] 4 (6) and of the trivalent {[(-CH 2 -) 5 ] 4 -calix-tetrapyrrole}Sm(Cl){[Li(THF)] 3 (µ 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, {[(-CH 2 -) 5 ] 4 -calix-tetrapyrrole}Sm(THF)Li 2 [Li(THF)](µ 3 -OCHdCH 2 ) (3). This species contains an enolate fragment in the molecular backbone and shows no reactivity with N 2 . Recrystallization of 3 from THF did not eliminate the enolate fragment but afforded instead another divalent complex, {[(-CH 2 -) 5 ] 4 -calix-tetrapyrrole}Sm(THF) 2 {Li[Li(THF)] 2 }(µ 3 -OCHdCH 2 )‚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 [{[(-CH 2 -) 5 ] 4 -calix-tetrapyrrole}Sm[Li(THF)] 3 (µ 3 -Cl)] 2 (µ-O) (8).

The reaction of UX 3 (THF) 4 (X ) Cl, I) with the tetraanion of {[(-CH 2 -) 5 ] 4 -calix[4]-tetrapyrrole} gave different compounds depending on the uranium halide, the alkali-metal cation (Li vs K), the stoichiometric ratio of ligand to uranium, and the solvent used. Reaction of the potassium salt of the ligand with uranium iodide in THF and in the ratio 1:1 afforded the dinuclear, tetravalent species 1). The source of the bridging oxygen atom is a THF deoxygenation process. A reaction carried out under identical conditions but with the tetralithium salt of the calix[4]tetrapyrrole afforded instead intractable material unless a stoichiometric ratio of two ligands per uranium was employed. In this event, a new species, the dinuclear tetravalent species [{[(-CH 2 -) 5 ] 4 -calix[4]pyrrole}ULi(THF) 2 ] 2 ‚hexane (2), was isolated. In this complex, the β-C atom of one of the pyrrole rings of the macrocycle was deprotonated and metalated by uranium of a second identical unit, thus assembling the dinuclear structure. The reaction is not accompanied by loss of hydrogen gas, while the excess ligand is acting as a Brønsted base. An identical reaction carried out by using uranium trichloride afforded instead the mononuclear tetravalent species ({[(-CH 2 -) 5 ] 4 -calix[4]tetrapyrrole}ULi(OC 2 H 5 )(THF) 2 ) (3). In this compound one pyrrole ring was isomerized by shifting the attachment of the chain from the R-to the β-position. The LiOCH 2 CH 3 unit was generated by another pathway of THF fragmentation. Finally, a reaction carried out in dimethoxyethane with the purpose of preventing oxidative attack to the metal center, afforded the mononuclear trivalent complex [{[(-CH 2 -) 5 ] 4 -calix[4]tetrapyrrole}U(DME)][K(DME)] (4).

The dinuclear and trivalent complex {[(Me 3 Si)NCH 2 CH 2 ] 2 N(Me 3 Si)} 2 V 2 (µ-Cl) 2 (1) is the precursor to mono-and dinuclear alkyl derivatives that are thermally stable. For example, treatment with MeLi gives a stable methyl derivative, probably isostructural with 1, which upon further treatment with pyridine affords the mononuclear complex {[(Me 3 Si)NCH 2 -CH 2 ] 2 N(Me 3 Si)}V(CH 3 )(pyridine) (2). However, reaction of 1 with Me 2 AlCl, AlMe 3 , or PMAO-IP yields the tetrametallic species { 3), where the central core of 1 was preserved except for the vanadium centers, which were reduced to the divalent state. The two Me 2 Al residues remained coordinated to the amido ligand. The reduction of vanadium to the divalent state relates to the relatively short life of 1 as an ethylene polymerization catalyst. A similar reaction of 1 with AlCl 3 resulted in disproportionation forming the tetravalent complex {[(Me 3 Si)NCH 2 CH 2 ] 2 N(Me 3 Si)}VCl 2 AlCl 3 (4) and the pentanuclear mixed 5). The fact that complex 5 contains a divalent vanadium atom stripped of its ligand system indicates that two different reaction mechanisms are operating to reduce the vanadium center and that the differing Lewis acidity of the two aluminum species is the determining factor.

Trivalent methyl and vinyl samarium derivatives supported by the calix-tetrapyrrole ligand system (Et 8 -calix-pyrrole)(R)Sm(µ 3 -Cl)[Li(THF)] 2 [Li(THF) 2 ] [R ) Me (2a), CHdCH 2 (2b)] were prepared via reaction of (Et 8 -calix-pyrrole)(Cl)Sm[Li 2 (THF) 3 ] (1) with the corresponding organolithium reagent. Complex 2a reacts readily with H 2 at room temperature and atmospheric pressure to afford the corresponding samarium hydride (Et 8 -calix-pyrrole)(THF)-Sm[Li(THF)] 2 (µ 3 -H) (3). Complexes 2a and 3 are thermally robust. Conversely, the vinyl derivative 2b rapidly and spontaneously decomposes at room temperature to afford the Sm II derivative (Et 8 -calix-pyrrole)(THF)Sm[Li(THF)] 2 [Li(THF) 2 ](µ 3 -Cl) (4a).

Reaction of [(Me 3 Si)NdP(Ph) 2 C(H)P(Ph) 2 dN(SiMe 3 )]VCl 2 (1) with 2 equiv of MeLi yielded the corresponding trivalent vanadium derivative [(Me 3 Si)NdP(Ph) 2 C(H)P(Ph) 2 dN(SiMe 3 )]-VMe 2 (3). Subsequent hydrogenolysis afforded the dinuclear hydride complex {[(Me 3 Si)Nd P(Ph) 2 C(H)P(Ph) 2 dN(SiMe 3 )]V} 2 (µ-H) 2 ( 4), where reduction of the metal center to the divalent state had occurred. Hydrogenolysis of solutions of 1 previously treated with lower than stoichiometric amounts of MeLi afforded the two mixed-valent V(II)/V(III) hydrides 7). Hydrolysis of the divalent 4 afforded the trivalent and dinuclear {[(Me 3 Si)NdP(Ph) 2 C(H)P(Ph) 2 d(µ-N)]V(OSiMe 3 )} 2 (5), featuring migration of the Me 3 Si group from the N to the O atom of one incoming molecule of water.