Lithium Complexes Derived of Benzylphosphines: Synthesis, Characterization and Evaluation in the ROP of rac-Lactide and ε-Caprolactone.

A series of lithium complexes ([Ph2P(o-C6H4-CH2Li·TMEDA)] (1-Li), [PhP(o-C6H4-CH3)(o-C6H4-CH2Li·TMEDA)] (2-Li), [PhP(o-C6H4-CH2Li·TMEDA)2] (2-Li2) and [P(o-C6H4-CH2Li·TMEDA)3] (3-Li3)) was prepared from mono-, di- and tri-benzylphosphines and varying amounts of nBuLi and was characterized extensively by IR and ¹H, 7Li, 13C and 31P NMR spectroscopy. The molecular structures of complexes 1-Li and 2-Li were determined by single-crystal X-ray diffraction studies. The two complexes have monomeric structures in the solid state comprising seesaw lithium atoms. In each case, the ligand exhibits an asymmetric C-C η²-coordination mode and an intramolecular P-Li bond interaction. Theoretical calculations at Density functional theory (DFT) level M06/6111+G(2d,p) show that indeed a P-Li bond is established which can be explained as the P lone pair (sp1.26) being partially delocalized on an available sp² orbital on Li (sp2.04) and additional bonding contribution of the phosphorous atom to Li stems from further delocalization of a σ P-C orbital into the sp² orbital on Li. The observed short contact distances between an aromatic ipso carbon and Li in the crystal structures of 1-Li and 2-Li are explained as due to the interaction of a σ C-Li orbital into the π* orbital of a C-C aromatic bond. Preliminary tests show compounds 1-Li, 2-Li, 2-Li2 and 3-Li3 are active catalysts in the solvent free ring-opening polymerization (ROP) of ε-caprolactone (ε-CL) and rac-lactide (rac-LA). High conversions to polycaprolactones were obtained in short periods of time: 1-6 min at 25 °C. Additionally, all four lithium complexes behave as moderately good initiators for the ROP of rac-LA showing high conversions to polylactides at 140 °C in one hour.

Calix[4]arenes of aluminum and gallium with benzimidazolyl ligands: steric control of the conformation via substitution on the ligand.

Complexes [bzimAlR(2)](4) [bzim = benzimidazolate; R = Et (2), (i)Bu (3)], [mbzimAlR(2)](4) [mbzim = 2-methylbenzimidazolate; R = Et (6), (i)Bu (7)], [dmbzimAlR(2)](4) [dmbzim = 5,6-dimethylbenzimidazolate; R = Me (9), Et (10), (i)Bu (11)], and [tmbzimAlR(2)](4) [tmbzim = 2,5,6-trimethylbenzimidazolate; R = Me (12), Et (13), (i)Bu (14)] have been prepared via alkane elimination and coordinative self-assembly upon the reaction of benzimidazole ligands with aluminum alkyls in benzene, toluene, or xylene. Characterization of the complexes was achieved by spectroscopic methods, microanalysis, and X-ray crystallography of 2, 7, 10, 11, 13, and 14. The complexes reported herein and the aluminum and gallium analogues 1, 4, 5, and 8 reported in a previous paper (1) are predominantly tetranuclear aggregates related to calix[4]arenes in which the benzimidazolyl ligands bind two metal atoms in a η(1):η(1) fashion. X-ray crystallography demonstrates that modulation of the conformation adopted by these metallacalix[4]arenes is achieved by proper substitution on the C atom at the 2 position of the benzimidazolyl ligand. An H substituent for 1, 2, 4, 10, and 11 favors a chair conformation with a small cavity and approximate C(2h) symmetry, while a CH(3) substituent for 5, 7, 8, 13, and 14 introduces enough repulsion to switch the conformation to a 1,3-alternate or double cone with a concomitant larger cavity and approximate C(2v) symmetry.

Steric control of conformation in self-assembly metallacalix[4]arenes derived from AlMe3 or GaMe3 with benzimidazolyl ligands.

Metallacalix[4]arenes [bzimAlMe(2)](4) (1), [bzimGaMe(2)](4) (2), [mbzimAlMe(2)](4) (3) and [mbzimGaMe(2)](4) (4) were obtained by self-assembly. The larger cavity of 3 and 4 allows them to function as hosts of benzene molecules.

Aluminium complexes derived from tridentate thioetherbis(phenolate) ligands and their activity in Diels-Alder catalysis.

Organoaluminium(III) thioetherbis(phenolate) complexes derived from 2,2-thiobis(4,6-diterbuthylphenolate) (Stdiol) and 2,2-thiobis(4,6-dimethylphenolate) (Smdiol) were prepared by reaction of AlMe3 with the diol proligands LH2 (SmdiolH2, StdiolH2). Monomeric complexes of general formulae [LAlR(L)] (L = Stdiol, R = Me, L = THF (1); L = Stdiol, R = Me, L = Et2O (2); L = Stdiol, R = iBu, L = THF) (3); L = Smdiol, R = Me, L = THF (4); L = Smdiol, R = iBu, L = THF (5)) and [LAlCl(THF)] (L = Stdiol (6); L = Smdiol (7)) were obtained when the reactions were performed in THF or Et2O in hexane or toluene, species of formulae [(L2Al)AlR2] (L = Stdiol, R = Me (8); L = Stdiol, R = iBu (9); L = Smdiol, R = Me (10)) were formed as evidenced by spectroscopic methods. Crystals suitable for X-ray diffraction studies were obtained for 2, 3, 4, 6, 8, 9 and 10. In these cases the sulfur atom coordinates to the aluminium center with Al-S bond lengths between 2.43-2.75 A adopting boat-boat conformations. Compounds 1, 3, 4, and 8 were tested in the catalytic Diels-Alder cycloaddition reaction between methacrolein and cyclopentadiene showing excellent regioselectivities with good conversion yields.

Dichloro and alkylchloro gallium derivatives of dichalcogenoimidodiphosphinate ligands: isolation of a spirogallium cation.

Dichloro and chloromethyl Ga(III) complexes of general formulae [XClGa-eta2-{R2P(E)NP(E'R'2-E,E'}](X = Cl, R, R'= Ph, E, E'= O (1), S (2), Se (3); R = Ph, R'= OEt, E = O, E'= S (4); R = Me, R'= Ph, E, E'= S (5) and X = Me, E, E'= O (6), S (7), Se (8)) were synthesised by either metathesis reactions between GaCl3 and the potassium salt of the ligand (X = Cl) or by methane eliminations from in situ prepared GaMe2Cl and the protonated ligands LH (X = Me). Redistribution reaction of (3) in either CDCl3 or THF afforded the solvent-free tetracoordinate gallium spirocycle cation [Ga-{eta2-{Ph2P(Se)NP(Se)Ph2-Se,Se'})2]+ (9+). The molecular structures of complexes 2, 4, 5, 7 and 9(+) show non-planar gallacycle rings.