Tridentate Crown Thioethers

Among crown thioethers 9S3 is unique in retaining its conformation on binding to a trigonal face of a metal. In effect, the enthalpic price for arranging the donor atoms for coordination is paid in the synthesis of the ligand. This retention of 

Comparison of the optical spectrum of [Cr(9S3)2] with those of other Cr(III) complexes shows that 9S3 generates a smaller ligand field splitting than comparable amine complexes (e.g., [Cr(9N3)2] ) [94]. This compound represents one of the first homoleptic thioether complexes of Cr it was prepared by heating Cr(C104)3 with 9S3 in the absence of a solvent. This extremely hazardous procedure cannot be recommended. The compound was characterized by elemental analysis and optical spectroscopy (Table 3). 

Reaction of CrClj 6H2O (in MeCN) or [CrCl3(THF)3] (in dioxane) with 9S3 gives [Cr(9S3)Cl3] as sparingly soluble blue-violet microcrystals [94]. Stirring of this complex with triflic acid results in replacement of chloride with triflate. Infrared spectroscopy establishes coordination of the triflate residues in the blue-green [Cr(9S3)(triflate)3] complex, but no structural data are available. 

Reaction of [Mn(CO)jX] (X = Cl, Br, I) with 9S3 in DMF gives the facially-coordinated [Mn(CO)3(9S3)]X as air- and water-stable yellow crystals (Eq. la) [95]. The complex crystallizes with three crystallographically independent cations per unit cell each cation has mirror symmetry. Carbon atoms in the 9S3 chain disorder to accommodate the mirror symmetry. Kinetic studies show that displacement of CO is zeroth-order in 9S3, consistent with a limiting dissociative mechanism in which loss of CO cis to X is the rate determining step. Upon treatment with 5 MHCl [Mn(CO)3(9S3)]+ expels one CO to give [Mn(CO)2(9S3)Cl] (Eq. lb), while treatment with NOBF4 oxidatively removes one CO to afford [Mn(CO)2(OH2)(9S3)] (Eq. Ic). 

Iron(III) perchlorate with excess 9S3 (which serves as reductant as well as ligand Eq. 2a) readily affords the pink cation [Fe(9S3)2] (which can also be made from 

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