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)

The X-ray structures of trans-HfCl4(OEt2)2 and cis-ReCl4(OEt2)2 are reported, thus completing the series of Groups 4–6 2nd and 3rd row MCl4(OEt2)2 complexes and presenting the first example of a Group 7 MCl4(OEt2)2 complex. The Re analog is also the first example of a cis isomer in the series. Computational studies were conducted to examine the cis/trans preference across the series in the context of ionic radii, ligand hardness, and steric influence. [Display omitted] 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.