Disodiation of Primary Phosphanes and Arsanes

Ab initio calculations (MP2/6-31G ) of the parent compound of 8 revealed that the most stable arrangement of the dimer adopts Dih symmetry (Fig. 5). Interestingly, the four Li ions and the two phosphorus centers constitute an octahedral skeleton with relatively short Li-Li and Li-P distances of 2.645 and 2.458 A, respectively. Charge analysis (22) undoubtedly supports the electrostatic bonding model for this system because of the high net charges of the natural atomic orbitals (NBO) at Li (+0.768) and P (-1.583), while NBO-Lewis resonance structures support stabilization through delocalization (Fig. 5). 

Synthesis of Lithium-Deficient Mixed-Valent Clusters 

Reaction of the phosphane la and the arsane 2a with freshly sublimed BuLi in the molar ratio of 1 2 in toluene as solvent at —80°C 

The electrostatically favored cation (Li) and anion (RE) arrangement implies the presence of two different E-, Si- and Li sorts, which has been established by solution and solid-state NMR spectroscopy. The electronic structures of the mixed-valent pnictides 10 and 11 have been simply described as electron-deficient clusters with delocalized framework electrons. Formally the latter consist of two low-valent anediyl moieties RE and eight andiides (RE)2- (E = P, As). The relatively large E-E distances of 4 A exclude the occurrence of localized E-E bonds. However, delocalization of the cluster valence electrons is achieved without Li-Li bonds via Li-mediated multiple bonding. Evidence for this has been seen in the NMR spectra (31P, 7Li, 29Si), which are in accordance with the electron delocalization model (see later discussion). 

The synthesis of crystalline disodium derivatives of primary phos-phanes and arsanes turned out to be more difficult than that of dilithium compounds. The reaction of NaN(SiMe3)2 with 2c led, as in its lithiation with BuLi, under redox reaction (H2 elimination, As-As bond formation) to the Na2As6 dimer 12 (Eq. 5). The latter has been 

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