Heterocubane

The potentially versatile ligating ability of trisimidometaphosphate anions is manifested in the formation of either dispirocyclic (13) or heterocubane (14) rhenium complexes from the reaction of [(Me3Si)2NP(=NSiMe3)2] with RefCOljCl [18, 19]. Both (13) and (14) contain the dianionic [(RN)2P(fi-NR)2P(NR)2] "... 

Cd thiolates and selenolates tend to form q-S- or q-Se-bridged dinuclear species, even with bulky organic groups, e.g., 2,4,6-tri-t-butylphenyl.317 318 With some ligand combinations, heterocubanes with Cd4S4 core or oligonuclear species derived from heterocubanes are formed.319,320... 

The coordination of the phosphine P(ft-Pr)2Ph to the Lewis acidic Ga center is essential for the synthesis of both compounds. In the absence of any Lewis base, the most likely reaction product would be the heterocubane [ClGaSbSi(/-Pr)3]4. However, in analogy to the results observed for reactions of heterocycles [R MER with Lewis bases, leading to base-stabilized monomeric compounds, both the formation of 84 and 85 can be explained by reaction of such a heterocubane intermediate with the phosphine base. According to the description of heterocycles as head-to-tail adducts, heterocubanes may be described as Lewis acid-base adducts between two four-membered rings as shown in Fig. 45. 

Reaction of the heterocubane cluster 14 (R = Ph) with (Cp Rhl2)2, a reagent that functions both as a Lewis acid (the metal center) and a Lewis base (the iodide ligands), generates the dirhodium complex 18. Complex 14 also adds to l,l-bis(diphenylphosphinoferrocene) to form the cyclic species 19.8... 

In yet another facet of heterocubane chemistry, 14 (R = Ph) has been found to react with Ag+ in acetonitrile to form the salt (MeCN)3Rh(C4H4B-Ph)+ BF4 20, which in turn combines with arenes to generate (arene)Rh(C4H4B-Ph)+ BF4- products.9 Under vacuum, 20 loses MeCN to form the polymer 21, the phenyl group migrating to the Rh center of a different fragment. 

Compound 667 adopts a rather unexpected structure in the solid state since the formation of a heterocubane-type structure, as was observed for [MeGaNR]4 (R = Bu 66 8 495 TMS 669496), [PhGaNPh]4 6 7 0 497 [MesGaNC6Fs]4... 

The heterocubanes each contain four-coordinate group 13/15 atoms and consequently show longer M-E bond distances than the monomeric and (base-free) heterocyclic derivatives with three-coordinate central atoms. Structure 677 is somewhat special since it contains five-coordinate In atoms due to the presence of thf donors. Consequently, the In-N bond distances differ more (213.6(5)—227.9(5) pm) than those of the base-free pentafluoro-phenyl analog 676501 (216.7( 1)—222.7( 1) pm). 

Fig. 3.5-8. Schematic drawing of the heterocubane type molecules E4X4R4.

Tab. 3.5-2. Selected structural parameters of E4X4 heterocubanes obtained from organo-element(l) compounds (E = Al, Ga, In, X = O, S, Se, Te) (distances in pm g represents the ratio of the angles EXE and XEX van der Waals radii Ga 190, In 190, O 150, S 180, Se 190,...

Tab. 3.5-3. Structurally characterized oxygen compounds of aluminum, gallium and indium (the heterocubane type compounds have been included in Table 3.5-2).

The metalation of trialkylsilylphosphane and -arsane with the alkaline earth metal bis[bis(trimethylsilyl)amides] of calcium, strontium, and barium yields the mixed phosphanides and phosphanediides as well as arsanides and arsanediides depending on the stoichiometry and the demand of the trialkylsily] substituents according to Scheme 3.6-11. The main feature is the M2E3 bipyramid with the metal atoms in apical positions. These cages are often interconnected via common faces (61, 63, 64, 65, 67, and 69). A substitution of the phosphanide substituents by other Lewis bases such as THF or benzonitrile is not possible for these compounds and, consequently, homoleptic phosphanediides and arsanediides with inner M4E4 heterocubane moieties are so far unknown for M = Ca, Sr, and Ba. In all these cases a further metalation to obtain homoleptic phosphanediides failed. 

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