Selenium complexes dimeric

Although selenium derivatives of gold occur less frequently than sulfur ones, the presence of Au- Se intermolecular weak interactions has also been reported in a number of selenium complexes. For example, the cations of the tetranuclear complex [Se(AuPPh3)4](CF3S03)2 [40] are paired across symmetry centers to form loose dimers via an [Au- -Se]2 unit (Figure 5.21), which resembles the supramolecular motif usually found in sulfur compounds of gold. The intermolecular Au---Se... 

YbSe". With (Me3Si)2N]3M (M = La, Ce) and (Me3Si)SiSeH, 3-coordinate monomers result in toluene but the Y derivative occurs in solution as a selenium bridged dimer. The La, Sm and Yb(III) derivatives complex with 2 moles of THF100. 

The reaction of dabco (l,4-diazobicyclo[2.2.2]octane) with Me2Cd yields a 1 1 adduct 197, which adopts a linear polymeric structure (Figure 34).255 The cadmium atom is coordinated by two dabco units and two methyl carbon atoms giving rise to a distorted tetrahedral environment. Finally, the organocadmium adduct 198 (Figure 35) has been isolated from the reaction of Me2Cd with Cd[(SeP-/-Pr2)2N]2.256 The solid-state structure consists of dimeric units where each methylcadmium unit is coordinated to three selenium atoms. The geometry about the cadmium center is tetrahedral with a Cd-C distance of 2.16 A, which is comparable to that observed in other cadmium alkyl complexes. 

Here the residual affinity of the two selenium atoms serves to hold the two molecules together in an additive complex from which two molecules of C-ethylacetylacetone are eliminated, leaving a molecule of the dimeric selenium acetylacetone. 

There is an isolated example in which phosphine selenides and tellurides transfer selenium or tellurium to unsaturated lanthanide complexes to form bridging dimers [263]. 

Examples for square planar complexes of Se(II) and Te(II) with other sulfur and selenium donor ligands such as thio- and selenocarbamates are given (e.g., in 29,165, 205). When triarylphosphane ligands were introduced as two-electron donors by the reaction of triarylphosphane selenide with Br2, T-shaped Ar3PSeBr2 with the Br ligands in trans positions was prepared (435). Possibly, the molecules are dimerized via bromine bridges as in Se2(tmtu)2Br4 (445). 

Cyclooctaselenadiazole in the presence of the CpCo source [CoCp(PPh3)2] eliminates Nj in refluxing toluene to give a similar type of ligand bonded to a dimeric CpCo framework (75). In the presence of [CoCp(PPh3)2], elemental selenium adds to bicyclic selenadiazoles and thus affords the first diselenolene complexes without electron-withdrawing substituents (52-54) (76). 

The tungsten complex 509j leads to a dimer containing an M—M bond, 511 (2S6). The selenium and tellurium Iron carbonyl compounds (512)... 

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