Synthesis and structure of trans-HfCl4(OEt2)2 and cis-ReCl4(OEt2)2, and computational studies of Group 4 to Group 7 MCl4(OEt2)2 isomer preferences (M = Zr, Hf, Nb, Ta, Mo, W, Re)

Abstract

The bis(diethyl ether) adducts of early transition metal chlorides, MCl₄(OEt₂)₂, serve as excellent precursors for complex inorganic and organometallic compounds due to the lability of the coordinated ethers. Previously reported MCl₄(OEt₂)₂ (M = Zr, Nb, Ta, Mo, W) complexes have crystallized with the ethers in a trans conformation, even though computational studies have predicted that compounds of the type MX₄L₂ should form cis isomers. Herein, we report the crystal structure of trans-HfCl₄(OEt₂)₂ and the synthesis and structure of cis-ReCl₄(OEt₂)₂. The report of the crystal structure of the Hf analog completes the Groups 4–6 2nd and 3rd row series and provides structural context regarding the trans preference and observations in M-Cl and M-O bond distances that are corroborated by Shannon’s ionic radii of the M(IV) cations. The isolation of the cis-Re analog provides the first structural example of a Group 7 MCl₄(OEt₂)₂ complex, as well as the first cis complex in the presented series. Computational studies were conducted to examine the cis/trans preferences across the entire series in the context of ionic radii, ligand hardness, and steric influence.