Cryptands, alkali metal derivatives

Stable dianionic derivatives of the Ti carbonyl complex [Ti(CO)6]2 have been synthesized, isolated, and characterized.1045 The [Ti(CO)6]2 ion was obtained via reductive carbonylation of Ti(CO)3(DMPE)2 or TiCl4(DME) by KCioHg in the presence of a crown ether or cryptand.1045 An octahedral environment about Ti in [K(cryptand 2.2.2)l2[Ti(CO)6] was confirmed both in solution by the observation of a septet resonance in the 49Ti NMR spectrum for the 13CO complex and cry stallographically.1046 Related complexes with weakly solvated alkali metal cations readily decomposed.1047... 

Neutral Ti(CO)6 is an extremely unstable compound which decomposed even below -220 °C, as shown by matrix isolation spectroscopy [165]. The much more stable phosphine derivatives Ti(CO)3(dmpe)2, Ti(CO)5(dmpe), Ti(CO)5(PMe3)2, Ti(CO)4(PMe3)3 have been isolated [166-168]. In contrast, the dianionic salt [Ti(CO)6] (53) is thermally much more stable and decomposes only above 200 C. Complex 53 was obtained by reductive carbonylation of Ti(CO)3(dmpe)2 by alkali metal naphthalenides in the presence of cryptand [169]. Carbonylation of 79 also produces 53 [170]. The naph-thalenide-assisted reductive carbonylation of the zirconium tetrachloride afforded the zirconium analog [Zr(CO)6] (54) [171], which was also derived by carbonylation of the tris(diene) dianion 45 [150]. One anion [R3Sn] effectively stabilizes Ti(CO)e as an air stable monoanionic salt, [R3SnTi(CO)J [172]. 

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