PADDLE-WHEEL TRIS(CYCLOPENTADIENYL)TIN(II) AND TRIS(CYCLOPENTADIENYL)LEAD(II) COMPLEXES - SYNTHESES, STRUCTURES, AND MODEL MO CALCULATIONS

Nucleophilic addition reactions of cyclopentadienide anions (Cp-) to b is(cyclopentadienyl)-tin(II) and -lead(II) produces complexes containi ng ''paddle-wheel'' [(eta(5)-Cp)(3)E](-)(CP = C5H5; E = Sn, Pb) anions . Thus, the heavy main-group metals act as Lewis acids rather than as bases. The syntheses and X-ray structures of four such complexes, [(et a(5)-Cp)(2)Sn(mu-Cp)-NaPMDETA] (1;PMDETA = H2](2)NCH3),[Mg(THF)(6)](2)[(eta(3)-Cp)(3)Sn-](2) (2), [(eta(5)-Cp)(2)Pb(mu-Cp)NaPMDETA] (3), an d [Mg(THF)(6)](2+)[(eta(3)-Cp)(3)Pb-](2) (4), are reported. The monome ric complexes 1 and 3 are essentially isostructural and contain trigon al-planar (eta(5)-Cp)(3)E units linked, through bridging mu-eta(5)-Cp ligands, to NaPMDETA(+) cations in their molecular structures. Ab init io MO calculations have been used to probe the structures and charge d istributions of the [(eta(5)-Cp)(3)E](-) anions in these complexes. Th ese show that the natures of the species are highly dependent on the e xtent of alkali- or alkaline-earth-metal cation solvation. Thus, where as unsolvated [(eta(5)-Cp)(2)E(mu-Cp)Na](E = Sn, Pb) are loose-contact complexes of [Cp2E] and [CpNa], [(eta(3)-Cp)(3)E](-) species are best formulated as triorganometal anions, Solid-state magic angle spinning (MAS) Sn-119 and C-13 NMR spectroscopic studies are in broad agreemen t with the model ab initio calculations and illustrate that in [(eta(5 )-Cp)(2)Sn(mu-Cp)NaPMDETA], in which partial solvation of the Na+ coor dination sphere occurs, the electronic situation approaches that in [C p2Sn].