Versatile Zirconium Reductants and Carbon–Carbon Coupling Agents Selectively Accessible from the 2:1 Molar Aggregate of n‐Butyllithium and Zirconium(IV) Salts

Abstract

In the original article,1 the following changes should be applied: (i) On page 3527 of the original article in the 2nd column, the 4th paragraph composed of 17 lines should be replaced by the following paragraph: Given the demonstrated versatility of the zirconium reagents discussed here, one might wonder how the titanium and hafnium derivatives compare with those of zirconium. First, with reagents of the type nBu2MCl2, the zirconium analog is readily prepared and sufficiently stable to serve as a hydrozirconating agent for diverse π-bonded substrates (cf. supra). The titanium counterpart, nBu2TiCl2, is difficult to generate, because it decomposes too readily into TiCl2, and the hafnium hydride, nBu2HfCl2, is much too stable to serve as a source of HfCl2 and thus functions as an alternative hydride to nBu2ZrH2, albeit twice as expensive. As to the accessible epimetallating agents, TiCl2 or ZrCl2 in THF, prior work with aromatic aldehyde reduction dimerizations has led us to conclude that they were comparable in their selectivity.[16] But this present study and a subsequent doctoral dissertation33 have compelled us to correct this misconception. The interaction of a 1:1 molar ratio of ZrCl2 and benzaldehyde (4) on a 2.0 millimolar scale, according to the procedure described on p. 3529, 1st column, 1st paragraph, led upon workup solely to rac-1,2-diphenyl-1,2-ethanediol (7). No trace of the meso isomer 8 of 7 nor any benzyl alcohol (6) was detected. Recently, the corresponding interaction of a 1:1 molar ratio of TiCl2 and 4 was undertaken and reported in Wei Liu's doctoral dissertation with 13C NMR and TLC analyses as follows: rac-1,2-diphenyl-1,2-ethanediol (7; 54 %), the meso isomer (8; 25 %) benzyl alcohol (6; 15 %) and benzaldehyde (4; at least 6%, because some 4 could well have been oxidized and lost during workup). From this experiment, reproduced about 10 times in this study, it is evident that ZrCl2 is far more selective in producing the rac-diol and in favoring the diol over benzyl alcohol. The reaction mechanisms leading to this differing array of products cannot yet be depicted, but these results have immediate value in the synthesis of geminal diols. (ii) Reference [33] of the original article will have its text changed to the new ref.33 These changes in the original manuscript are necessary, because the 4th paragraph in the 2nd column on page 3527 of the original article was inaccurate and ambiguous in the wording. The new paragraph and its more accurate and clear wording stem from the completed doctoral dissertation of Wei Liu (now cited in reference [33]). The Authors