Functionalized Keggin- and Dawson-Type Cyclopentadienyltitanium Heteropolytungstate Anions: Small, Individually Distinguishable Labels for Conventional Transmission Elactron Microscopy. 1. Synthesis

Article abstract of DOI:10.1021/ja00285a012

With an eye toward the development of a new series of small, highly electron dense labels for electron microscopy, we have synthesized several cyclopentadienyltitanium-substituted Keggin- and Dawson-type heteropolytungstate (HPT) ions that bear reactive organic groups on the Cp ring suitable for selective attachment to macromolecular sites.R-Cp-Ti(NMe2)3 derivatives 5a-f were prepared and then inserted into the Keggin defect HPT anion PW11O39^7- 7 to give TBA salts 10a-e.The major byproduct was shown to be oxotitanium compound 14.Ion exchange of 10a-d over acidic Al2O3 gave the corresponding moderately water soluble TMA salts 11.Conventional ion exchange then gave the corresponding water soluble K⁺ salts 13 and heteropoly acids 12.Amine 10e underwent methathetical exchange with Cs2B10Br10 and then ion exchange to give 12e and 13e, from which 11e was prepared.In the Dawson series, a suspension of HPT defect anion 16 in DMF was allowed to react with benzene solutions of 5c,e,f, giving, after anion exchange on acidic alumina, the corresponding TMA salts 17a-c which were then converted into K⁺ salts 18a-c.Oxotitanium HPT 21 was the major byproduct.Reaction 16 with potassium bis(oxalato)oxotitanium(IV) also led to 21, confirming the structure assignment.The new HPTs were characterized by elemental analysis of their TMA salts and by 1H, 31P, and 183W NMR spectroscopy on the water soluble K⁺ salts.