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The complex [{1,3-[2,6-(i-Pr)2-C6H3N]2(CH2)3}2ThCl][Li(THF)4] (1), containing two chelating amides, was prepared via straightforward halogen replacement of ThCl4(DME) with dilithium salt of 1,3-[2,6-(i-Pr)2-C6H3NH]2(CH2)3. Attempts to reduce this species were carried out with K(naphthalenide), affording an intermediate dark colored solution that slowly discolored and yielded colorless crystals of the tetravalent metallacyclic complex [{1,3-[2,6-(i-Pr)2-C6H3N]2(CH2)3}{1,3-[2-(i-Pr)-6-(CH2CHCH2)C6H3N]2 (CH2)3}Th][Li(DME)3] (2). In this species, one hydrogen atom of one neighboring ligand methyl group was eliminated to form a metallacyclic structure.

Reduction of the homopletic (ArO)4Th (1;Ar = 2,6-Ph2Ph) afforded different products, depending on the reaction conditions used in carrying out the reduction. Reduction with K(naphthalene) in DME afforded the doubly ortho-metalated product [(μ-OAr)K2][(μ-2-Ph,6-C6H4)2Th(OAr)](μ-OAr)[K(DME)2] (2), while treatment with finely dispersed K in toluene and in the presence of a stoichiometric amount of DME afforded, after treatment with a solution of 18-crown-6 in THF, {[Th(OAr)4(OH)THF][K(18-crown-6)(THF)2]}·C7H8 (3). The presence of a terminally bonded OH group in 3 is probably the result of solvent cleavage.

Treatment of the 2,6-diiminopyridine ligand 2,6-{[2,6-(i-Pr)2C6H3]N&dbd;C(CH3)}2(C5H3N) with 2 equiv of Me3SiCH2Li afforded the corresponding {[2,6-{[2,6-(i-Pr)2C6H3]N-C&dbd;(CH2)}2(C5H3N)]^2- (1) dianion via deprotonation of the two methyl groups attached to the two imine functions. Reaction of 1 with NdCl3(THF)3 yielded {[2,6-{[2,6-(i-Pr)2C6H3]N-C&dbd;(CH2)}2(C5H3N)]Nd(THF)}(μ-Cl)2[Li(THF)2]·0.5(hexane) (2a), whose recrystallization from DME gave the corresponding ionic {[2,6-{[2,6-(i-Pr)2C6H3]N-C&dbd;(CH2)}2(C5H3N)]NdCl2(DME)}{Li(DME)3](2b). With the exception of the reaction with (allyl)MgBr, which proceeded readily with 2b to form the allyl derivative {[2,6-{[2,6-(i-Pr)2C6H3]N-C&dbd;(CH2)}2(C5H3N)]Nd(η³-C3H5)Br}{Li(DME)3} (3), compounds 2a,b are not suitable starting substrates for further alkylation reactions. A viable synthetic strategy for the preparation of alkyl derivatives of 2 consisted instead of the pretreatment of NdCl3(THF)3 with RLi [R = Me3SiCH2, CH3] at low T followed by treatment with either the diimine ligand or 1. According to this procedure, the terminally bound alkyl derivative [2,6-{[2,6-(i-Pr)2C6H3]N-C&dbd;(CH2)}2(C5H3N)]Nd[CH2Si (CH3)3](THF) (4) was prepared and subsequently crystallographically characterized. The same synthetic procedure with MeLi afforded {[2,6-{[2,6-(i-Pr)2C6H3]N-C&dbd;(CH2)}2(C5H3N)]Nd}(μ-CH3)2[Li(THF)2] (5) and {[2,6-{[2,6-(i-Pr)2C6H3]N-C&dbd;(CH2)}2(C5H3N)]Nd}(μ-Cl)(μ-X)[Li (THF)2] (6) [X = Cl 53%, Me 47%] depending on the MeLi/Nd ratio. Both 5 and 6 as well as 2a are potent catalysts for the cis-polymerization of butadiene.

The transamination reaction of Sm{N(SiMe3)2}2(THF)2 with two dipyrrole ligands of formula RR‘C(α-C4H3NH)2 (R = R‘ = Et; R = Me, R‘ = Ph) has been examined. The reactions in THF and under N2 gave two similar tetranuclear dinitrogen complexes, {[Et2C(α-C4H3N)2Sm}4(THF)2](μ-N2)·2THF and [{[(C6H5)(CH3)C(α-C4H3N)2]Sm}4(DME)2](μ-N2), 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(α-C4H3N)2]Sm}8(THF)4·4THF. In the case of the reaction with the methylphenyldipyrrolylmethane ligand under N2, the unprecedented hexanuclear mixed-valence Sm^II/Sm^III cluster [([(C6H5)(CH3)C(α-C4H3N)2][(C6H5)(CH3)C(α-C4H3N)(β-C4H3N)]{[(C6H5)(CH3)C]2(α-C4H3N)2(α,α‘-C4H2N)}Sm3)(THF)3]2, containing tripyrrolide, “N-confused”, and regular dipyrrolide ligands was serendipitously formed by reaction with the impurities contained in the nonpurified ligand.

Reaction of the dipotassium salt of the dipyrrolide dianion [1,1-(2-C4H3N)2C6H10]^2- with FeCl2(THF)1.5 afforded the tetranuclear [μ,η⁵-{[1,1-(2-C4H3N)2C6H10]2Fe}Fe]2 (1) cluster containing two diamagnetic ferrous links π-bonded to two pyrrolyl rings of two ligands and closely reminiscent of a ferrocenoid-type arrangement. Reaction of the dianionic metalate {[[1,1-(2-C4H3N)2C6H10]2Co][K(THF)]2}n with FeCl2(THF)1.5 also afforded the corresponding [μ,η⁵-{[1,1-(2-C4H3N)2C6H10]2Co}Fe]2 nearly isostructural with 1. This indicates that the two ferrous links provide the driving force for assembling the two clusters, although the two structures are labile and may be disrupted by simple treatment with pyridine.

The reactions of [N(SiMe3)2]2Sm(THF)2 with three similar tetradentate pyrrole-based Schiff base ligands yielded three very different complexes. In two cases, an increase in the oxidation state was obtained via either ligand reductive coupling or disproportionation. The presence of a methyl substituent at the imine carbon atom instead prevented metal oxidation and afforded the first divalent samarium imine complex.

Reaction of VCl3(THF)3 with 3 equiv of the potassium salt of acetylpyrrole, K[α-(CH3CO)C4H3N], afforded the dinuclear {V2[K(THF)]2[CH3CO(C4H3N)]2}[(C4H3N)C(O)CH2C(C4H3N)(CH3)O]2 (1), where four acetylpyrrolide anions from two vanadium moieties have undergone an aldol condensation. The two pyrrolyl−acetylacetonate units so generated work as tetradentate binucleating ligands holding together the dinuclear structure. A similar reaction carried out on the divalent [V2Cl3(THF)6]2[Zn2Cl6] salt afforded the dinuclear and trivalent {VK(THF)[(C4H3N)C(O)CH3]}2[(C4H3N)(CH3)(O)CC(O)(CH3)(C4H3N)]·0.5(toluene) (2), where two acetylpyrrolide ligands, one per vanadium atom, have undergone a reductive coupling to form a pinacol. Even in this case the dipyrrolylpinacol works as a tetradentate binucleating ligand holding together the dinuclear frame. Attempts to perform the same reaction on another V(II) salt such as VCl2(TMEDA)2 (TMEDA = N,N,N‘,N‘-tetramethylethylenediamine) afforded instead the corresponding divalent derivative V(TMEDA)[(C4H3N)C(O)CH3]2 (3), where the acetylpyrrolide anions remained intact. Both 1 and 2 are potent olefin copolymerization catalysts upon activation with diethyl aluminum chloride, while 3 displays low but not negligible activity.

The reactivity of the pentavalent dipyrrolide complex {[Ph2C(C4H3N)2]2TaCl2}{Li(THF)4}·2THF was investigated. While an isostructral dimethyl derivative was readily prepared by treatment with MeLi, reaction with NaHBEt3 gave a major reorganization, affording a mixture of [Ph2C(C4H3N)2]Ta[(1,4-η¹:η¹-2,3-η²-C6H7PhC(C4H3N)2][Na(OEt2)] and [Ph2C(C4H3N)2]3Ta[Na(OEt2)]2·(OEt2). The first complex arises from partial hydrogenation of one of the ligand phenyl rings performed by an intermediate Ta hydride. In the second case, ligand scrambling occurred along with reduction of the metal center.

Reaction of CrCl3(THF)3 with 3 equiv of R−M [R = Me3CCH2 (a), Me3SiCH2 (b)] afforded either the previously reported tetravalent homoleptic R4Cr (1a, b) [M = MgCl] or the unprecedented divalent and tetranuclear homoleptic [R2Cr]4 (2b) [M = Li]. Both types of compounds display a remarkable chemical inertness toward proton transfer agents but readily react with ethylene.

The reactions of SmI2(THF)2 and YbI2(THF)2 with the alkali-metal salts of 2,5-dimethylpyrrole, or the reaction of SmCl3(THF)3 and YbCl3(THF)3 with the same ligands followed by reduction with the appropriate alkali metals, led to the formation of divalent mono- and polynuclear complexes. Structural analysis of these complexes indicated that the bonding mode adopted by the ligand depends on the nature of the alkali-metal cation retained in the structure.

The dinuclear and trivalent complex {[(Me3Si)NCH2CH2]2N(Me3Si)}2V2(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 {[(Me3Si)NCH2CH2]2N(Me3Si)}V(CH3)(pyridine) (2). However, reaction of 1 with Me2AlCl, AlMe3, or PMAO-IP yields the tetrametallic species {[(Me3Si)NCH2CH2]2N(Me3Si)}2V2(μ-Cl)2(AlMe2)2 (3), where the central core of 1 was preserved except for the vanadium centers, which were reduced to the divalent state. The two Me2Al 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 AlCl3 resulted in disproportionation forming the tetravalent complex {[(Me3Si)NCH2CH2]2N(Me3Si)}VCl2AlCl3 (4) and the pentanuclear mixed-valent V(II)/V(III) species [(AlCl2){[(Me3Si)NCH2CH2]2N(Me3Si)}V]2[(μ-Cl)6V]·(toluene)2 (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.

The reaction of YbI2(THF)2 with diphenyldipyrrolylmethanide leads to a complex reaction from which an octameric divalent Yb macrocyclic complex, [diphenyldipyrromethanediyl-Yb]8, was obtained as a major product. A tetrameric cyclic Yb(II)-oxo complex, [(diphenyldipyrrolylmethanediyl)Yb]4[(K(THF)3]2(μ-O)·2(THF), arising from solvent deoxygenation and a monomeric Yb(III) complex, Yb(diphenyldipyrrolylmethanediyl)3[K(THF)]3, were also isolated as byproducts of a complex reaction.