From Neutral to Ionic Species: Syntheses and X-ray Crystallographic and Multinuclear NMR Spectroscopic Studies of Li center dot center dot center dot P(SiMe3)-PtBu2 and Its Solvent Complexes

Li(THF)(3)P(SiMe3)-PtBu2 (1, THF = tetrahydrofuran) has been prepared by the reaction of (Me3Si)(2)P-PtBu2 with n-butyllithium in THF and isolated in good yields. Compound 1 eliminates THF in vacuo to yield the dimeric [Li(THF)P(SiMe3)-PtBu2](2) (2). By metalation of H(SiMe3)P-PtBu2 with n-butyllithium in hexane, the solvent-free derivative [Li(Me3Si)P-PtBu2](4) (3) has been prepared. Compounds 1-3 form the ionic species [Li(TMEDA)(2)](+)[(Me3Si)P-PtBu2](-) [4, TMEDA = Me2N(CH2)(2)NMe2] and [Li(12-crown-4)(2)](+)[(SiMe3)P-PtBu2](-) (5) with TMEDA and 12-crown-4, respectively, in solution. The molecular structures of 1-5 were established by single-crystal X-ray diffraction. Compound 3 forms a cyclic tetramer with a flat butterfly geometry. Extensive solution NMR spectroscopic investigations have shown that all species except for 3 exist in the same form in solution as in the solid state. Moreover, multinuclear variable-temperature NMR studies showed that 2 is involved in a rapid conversion between conformers at 298 K, which can be slowed down on the NMR timescale at 183 K.