Synthesis of multiply-bonded dichromium complexes with a variety of formamidinate ligands

摘要

A series of dichromium tetraformamidinate complexes with (ArNCHNAr)~- where Ar is X_2C_6H_3 or XC_6H_4 and X is the remote substituent 3,5-Cl_2, 3,4-Cl, p-CF_3, m-CF_3, p-OCH_3 or m-OCH_3 has been synthesized, and the structures of four of the compounds determined by X-ray crystallography. The Cr-Cr bond distances of the complexes structurally characterized are 1.9072(110 A [Cr_2((p-ClC_6H_4N)_2CH)_4]. 1.9162(10) A [Cr_2((3,5-Cl_2C_6H_3N)_2CH_4], 1.9018((8) A [Cr_2((m-CF_3C_6H_4N)_2CH_4)], and 1.9178(11) A [Cr_2((m-OCH_3C_6H_4N)_2CH)_4]. ~1H NMR spectroscopy and electrochemistry were performed on the series. The diamagnetic anisotropy of the Cr-Cr bond was calculated from X-ray crystallographic and ~H NMR data and correlates with the Hammett constant of the formamidine ligands.