A series of (salen)tin(II) and (salen)tin(IV) complexes was synthesized. The (salen)tin(IV) complexes, (salen)SnX(2) (X = Br and I), were prepared in good yields via the direct oxidation reaction of (salen)tin(II) complexes with Br(2) or I(2). (Salen)SnX(2) successfully underwent the anion-exchange reaction with AgOTf (OTf = trifluoromethanesulfonate) to form (salen)Sn(OTf)(2) and (salen)Sn(X)(OTf) (X = Br). The (salen)Sn(OTf)(2) complex was easily converted to any of the dihalide (salen)SnX(2) compounds using halide salts. All complexes were fully characterized by (1)H NMR spectroscopy, mass spectrometry, and elemental analysis, while some were characterized by (13)C, (19)F, and (119)Sn NMR spectroscopy. Several crystal structures of (salen)tin(II) and (salen)tin(IV) were also determined. Finally, both (salen)tin(II) and (salen)tin(IV) complexes were shown to efficiently catalyze the formation of propylene carbonate from propylene oxide and CO(2). Of the series, (3,3',5,5'-Br(4)-salen)SnBr(2), 3i, was found to be the most effective catalyst (TOF = 524 h(-)(1)).

A series of µ-oxo-bis [(salen)iron (III)] complexes was prepared from the reaction of the corresponding salen ligands with FeCl 3 ‚6H 2 O in the presence of NEt 3 , and characterized by elemental analysis, infrared spectroscopy, and mass spectrometry. These air-stable complexes catalyzed the cyclopropanation of olefins with ethyl diazoacetate in good yields. The catalytic activity of these µ-oxo dimers, in the cyclopropanation of styrene, was examined as a function of the diamine backbone and the substituents in the 3,3′-and 5,5′-positions of the phenyl rings on the ligands. Solvent variation, catalyst loading, and styrene concentration were investigated to determine the optimal reaction conditions. The complex [Fe(3,3′,5,5′-t Bu 4 -salen)] 2 O (1d) was identified as the most efficient catalyst in the series, which successfully catalyzed the cyclopropanation not only of styrene but also of less reactive substrates such as R-methylstyrene, R-(trifluoromethyl)styrene, 1,1-diphenylethylene, methylenecyclohexane, and n-butyl vinyl ether and internal olefins such as trans-and cis--methylstyrene and ethylidenecyclohexane.

The cyclopropanation of various alkenes with different diazoester compounds was investigated using two different μ-oxo-bis[(salen)iron(III)] complexes, [Fe(3,3',5,5'-tBu4salen)]2O and [Fe(salen)]2O. Ethyl diazoacetate (EDA), tert-butyl diazoacetate (tBDA), and ethyl diazoacetoacetate (EDAA) were used with mono- and disubstituted terminal olefins (styrene and 1,1-diphenyl ethylene, respectively), internal olefin (trans-β-methyl styrene), and an electron-rich alkene (n-butyl vinyl ether). Moderate-to-good cyclopropanation yields were obtained for most substrates.