A series of new yttrium complexes supported by the bulky enediamido dianionic ligand DAB(2-) (DAB(2-) = (2,6-C(6)H(3)iPr(2))NC(Me)=C(Me)N(2,6-C(6)H(3)iPr(2))(2-)), that is, {DAB}Y(THF)(2)(mu-Cl)(2)Li(THF)(2) (1), {DAB}Y(OtBu)(THF)(DME) (2), and {{DAB}Y(BH(4))(2)}{Li(DME)(3)} (3), was synthesized by salt metathesis. The complexes were isolated after recrystallization in 73, 66, and 52% yield, respectively, and characterized in solution by NMR and in the solid state by single-crystal X-ray diffraction studies. In complex 1, the DAB(2-) ligand is bonded to the metal center via two covalent YN bonds, while in complexes 2 and 3 additional eta(2)-coordination of the C=C bond to the metal atom is observed, both in solution and in the solid state. The tert-butoxide and borohydride complexes 2 and 3 act as monoinitiators for the room temperature ring-opening polymerization of racemic lactide and beta-butyrolactone, providing atactic polymers with controlled molecular weights and relatively narrow polydispersities (M(w)/M(n) = 1.15-1.82). Effectively immortal ROP of lactide with as many as 50 equiv of isopropanol per metal center was performed using complex 2 as the catalyst.

Metalation of CpBn5H with PhCH2K (1:1 molar ratio) and subsequent reactions with 0.5 equiv of LnI2(THF) n (Ln = Yb, Sm, Eu, n = 2, 3) (THF, 30 °C, 1 h) afforded new lanthanoidocenes (CpBn5)2Ln (Ln = Yb (1), Sm (2), Eu (3)), which were isolated in reasonable yields. The X-ray diffraction studies revealed that the obtained complexes adopt the structures of bent sandwiches (CpCentr–Ln–CpCentr = 141.8–142.9°). Complexes 1–3 do not contain coordinated Lewis base molecules directly after recrystallization from toluene at ambient temperature; however they feature short contacts between Ln­(II) ions and o-carbon atoms of two pendant Ph groups. The reaction of equimolar amounts of YbI2(THF)2 and CpBn5K in DME afforded monocyclopentadienyl Yb­(II) complex [CpBn5Yb­(DME)­(μ-I)]2 (4). Complex 4 proved to be a centrosymmetric iodo-bridged dimer with trans-disposed cyclopentadienyl ligands, and no interactions of the Yb­(II) ion with pendant Ph groups were detected. Complexes 1–3 were inert toward Lewis bases (THF, DME, PMe3, TMEDA), small molecules (H2, SiH4, N2, CO), and molecules containing multiple C–C bonds (CH2CH2, PhCHCH2, trans-PhCHCHPh, cis-PhCHCHPh, CH2CH–CHCH2, Ph–CHCH–CHCH–Ph, PhCCPh, Me3SiCCSiMe3). Among compounds 1–3 only the samarium derivative 1 reacts with bipy and phenazine, affording SmIII complexes CpBn5 2Sm­(bipy–•) (5) and [(CpBn5)2Sm]2[μ-η3:η3-(C12H8N2)2–] (6). Complex 4 when illuminated with natural light undergoes redox reaction and in 72 h transforms into the mixed-valent compound {[CpBn5YbIIII2(μ-OMe)]2}2­{YbII(DME)3} (7), being a separated ion pair.

Metallacyclic neutral and ionic yttrium alkyl complexes coordinated by a dianionic ene-diamido ligand ([2,6-iPr2C6H3NC(Me)=C(Me)NC6H3iPr2-2,6] = L(1)) [L(1)]Y(CH2SiMe3)(THF)2 (2), {[L(1)]Y(CH2SiMe3)2}(-){Li(THF)4}(+) (3), [L(1)]Y(OEt2)(μ-Me)2Li(TMEDA) (4) were synthesized using a salt-metathesis approach starting from the related chloro complex [L(1)]Y(THF)2(μ-Cl)2Li(THF)2 (1) in 70, 85 and 72% yields respectively. The reactions of 2 with H2 or PhSiH3 afford the dimeric hydride {[L(1)]Y(THF)(μ-H)}2(μ-THF) (5) containing two μ-bridging hydrido and one μ-bridging THF ligands (91 and 85% yields). The X-ray studies of complexes 2, 3 and 5 revealed η(2)-coordination of the C=C fragment of an ene-diamido ligand to a Y cation. DFT calculations were carried out to give an insight into the metal-ligand bonding and especially the interaction between the metal and the ene-diamido ligand. The observed bonding of the ene-diamido fragment is found to reflect the acidity of the metal center in the complex that is partially overcome by a better donation from the double bond (better overlap with an empty d orbital at the yttrium center). The treatment of complex 4 with DME resulted in the C-O bond cleavage of DME and afforded a three nuclear methoxide oxide complex [{[L(1)]Y}3(μ(2)-OMe)3(μ(3)-O)](2-)[Li(DME)3](+)2 (6). Complexes 2, 3, 5 and 7 proved to be efficient precatalysts for the intermolecular hydrophosphination of styrene, 4-vinylpyridine, and 1-nonene with PhPH2 and Ph2PH as well as hydroamination of styrene and pyrrolidine.