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Reaction of the pro-ligand α,α,α',α'-tetra(3,5-di-tert-butyl-2-hydroxyphenyl-p-)xylene-para-tetraphenol (p-L(1)H4) with two equivalents of [NbCl5] in refluxing toluene afforded, after work-up, the complex {[NbCl3(NCMe)]2(μ-p-L(1))}·6MeCN (1·6MeCN). When the reaction was conducted in the presence of excess ethanol, the orange complex {[NbCl2(OEt)(NCMe)]2(μ-p-L(1))}·3½MeCN·0.614toluene (2·3½MeCN·0.614toluene) was formed. A similar reaction using [TaCl5] afforded the yellow complex {[TaCl2(OEt)(NCMe)]2(μ-p-L(1))}·5MeCN (3·5MeCN). In the case of the meta pro-ligand, namely α,α,α',α'tetra(3,5-di-tert-butyl-2-hydroxyphenyl-m-)xylene-meta-tetraphenol (m-L(2)H4) only the use of [Nb(O)Cl3(NCMe)2] led to the isolation of crystalline material, namely the orange bis-chelate complex {[Nb(NCMe)Cl(m-L(2)H2)2]}·3½MeCN (4·3½MeCN) or {[Nb(NCMe)Cl(m-L(2)H2)2]}·5MeCN (4·5MeCN). The molecular structures of 1-4 and the tetraphenols L(1)H4 and m-L(2)H4·2MeCN have been determined. Complexes 1-4 have been screened as pre-catalysts for the ring opening polymerization of ε-caprolactone, both with and without benzyl alcohol or solvent present, and at various temperatures; conversion rates were mostly excellent (>96%) with good control either at >100 °C over 20 h (in toluene) or 1 h (neat).

(S)-1-(Methylaminocarbonyl)-3-phenylpropanaminium chloride (S2 x HCl), C10H15N2O+ x Cl-, crystallizes in the orthorhombic space group P2(1)2(1)2(1) with a single formula unit per asymmetric unit. (5R/S)-5-benzyl-2,2,3-trimethyl-4-oxoimidazolidin-1-ium chloride (R3 and S3), C13H19N2O+ x Cl-, crystallize in the same space group as S2 x HCl but contain three symmetry-independent formula units. (R/S)-5-benzyl-2,2,3-trimethyl-4-oxoimidazolidin-1-ium chloride monohydrate (R4 and S4), C13H19N2O+ x Cl- x H2O, crystallize in the space group P2(1) with a single formula unit per asymmetric unit. Calculations at the B3LYP/6-31G(d,p) and B3LYP/6-311G(d,p) levels of the conformational energies of the cation in R3, S3, R4 and S4 indicate that the ideal gas-phase global energy minimum conformation is not observed in the solid state. Rather, the effects of hydrogen-bonding and van der Waals interactions in the crystal structure cause the molecules to adopt higher-energy conformations, which correspond to local minima in the molecular potential energy surface.

We describe the synthesis and structures of the first tantalum-containing nitride-chlorides, Ba(3)Ta(3)N(6)Cl and Ba(15)Ta(15)N(33)Cl(4), and the structurally related Ba(3)Si(3)N(5)OCl, and their relationship with a theoretical silaceous framework.