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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.

The synthesis of a new trisbenzylsilanephosphine P{(o-CHCH)SiMeH} (1) is shown to proceed with high yields from P(o-tolyl). Compound 1 coordinates to the Rh and Ir dimers [MCl(COD)] (M = Rh, Ir) in a tetradentate or tridentate fashion, depending on the strict exclusion of water. The dimeric compounds [ClM(SiMeCH-o-CH)P(o-CH-CHSiMeH)], 2Rh and 2Ir, feature a tetradentate coordination of the starting ligand with P and two Si atoms as well as a non-classical agostic Si-H group. The presence of adventitious water in the solvents leads to the formation of two new complexes [(μ-Cl)M(SiMeCH-o-CH)P(o-CH-CHSiMeOSiMeCH-o-CH-)P(SiMeCH-o-CH)], 3Rh and 3Ir, which feature a siloxane bridge through Si-H bond breaking in 2. Reaction of [RhCl(COD)] with the bisbenzylsilanephosphine PhP{(o-CHCH)SiMeH} leads to the formation of compound 4Rh which features also a dimeric structure with the SiPSi ligand coordinated through the two silicon atoms, one of which occupies the apical position of a square-pyramidal geometry in the solid state, while the second is disposed equatorially trans to π-donor Cl. Finally, bidentate coordination of a PSi ligand is achieved by reaction of [RhCl(COD)] with PhP{(o-CHCH)SiMeH} which leads to the monometallic species [RhCl(SiMeCH-o-CH-PPh)], 5Rh, incorporating two chelating PSi ligands and maintaining a Cl ligand.

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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.

A series of Al(III) chloride [LAl-Cl]; Al(III) alkoxide [LAl-OR] 2 ; and Zn(II) [LZn] 2 complexes with Schiff base ligands were obtained. 1 H NMR and X-ray diffraction studies indicate that [LAl-Cl] complexes have C s symmetry and the Al center is penta-coordinated. The Al(III) alkoxide complex [L 5 Al-O i Pr] 2 is a dimer bridged by O i Pr − with the Al center in a distorted octahedral environment. Zn complexes [LZn] 2 are double helix dimers with tetra-coordinated Zn centers. The catalytic activity for the ring-opening polymerization of rac-lactide was evaluated. The best activity in this series is shown by the aluminium chloride complex with a flexible three-carbon bridge; more flexible four-carbon bridges lower the activity.

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