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Treatment of TaCIH2(PMe3)4 with CO or oxidation of [Ta(CO)61-with TaC15 in diethyl ether-PMe3 solutions provides TaCI(C0)3(PMe3)3, a capped trigonal prismatic complex whose structure has been determined by X-ray diffraction; bromo and iodo analogues have been isolated by oxidation of [Ta(CO)61-with Br2 or l2 in diethyl ether-PMe3 solutions.

Recently there has been considerable interest in the structure and chemistry of cluster compounds of the main group elements[l] as well as the corresponding clusters of the transition elements[2].In our laboratories, we have established the fluxional nature in solution of the naked metal anionic clusters Sn,_,Pb:-( x = 0 to 9) by the use of "%n and 20'Pb nmrE3-J. These clusters are formed when alloys of composition Na-Sn-Pb are maintained in contact with anhydrous ethylenediamine (en) for an extended period of time. We now wish to report that these clusters may also be generated by constant current electrolysis.We have observed that deposition of sodium from an en solution 0.1 M in NaI at either a lead or tin cathode leads to the formation of the Pb$-and Snzclusters, respectively. The lead cluster appears rapidly and quantitatively with current, whereas the dissolution of the tin cluster from the electrode surface is considerably slower. If the electrolytic cell and its contents are allowed to stand after conclusion of current passage, the concentration of the Sn:-cluster increases continuously for several days.Examination of the catholyte solutions by either "'Pb or l19Sn nmr after removal of an aliquot from the cells at various electrolysis times always reveals the same species, ie, PbG-or Snf-. Although other cluster species have been observed when Na-Pb or Na-Sn alloys of varying compositions have been extracted with en, notably Sn$-141, Sn:-[S]and Pb:-[S], the electrolytic methodapparently produces the nine atom clusters excIusively regardless of the electrolyte concentration or the current density.In a typical experiment, a current density of 10 ma/cm' (Hi-Tek potentiostat) is passed between a clean tin cathode and a Pt-gauze anode in an all glass H-cell, the two electrode compartments separated by a glass frit. The solution is 0.1 MNaI in en. Aliquots of the catholyte solution examined by llgSn nmr gave a quintet of intensity ratio 0.045:0.311:1.ooO:0.311:0.045 in excellent agreement with that predicted for a fluxional nine atom tin ciuster[3 Furthermore, the chemical shift and 119Sn-L' 4 Sn coupling constants agree within experim-* Present address: T6G 2G2. t To whom correspondence should be addressed. ental error with those values obtained previously[3]. In a classic paper, Zintl and Kaiser[6] were able to produce Pb$-by electrolytic reduction of a lead cathode in NH ,(f). Surprisingly, they observed that a tin cathode remained passive to Sn",-formation and only plated out metallic sodium which gave the typical blue solution of the active metal. Our present study in en provides a more convenient solvent system which appears to give important new dimensions to electrolytic production of naked metal clusters. In the present situation, tin passivity is obviously diminished. For this reason a variety of other metals as well as alloys are currently under investigation. For instance, it is observed that reduction of Na+ at a Pb-Sn (1: 1 mole ratio) alloy electrode produces all species in the series S+,_,Pb:-(x...

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