Chromium(II) complexes bearing 2-substituted N,N′-diarylformamidinate ligands

Abstract

A study regarding the interaction of several ortho ring-substituted N,N′-diarylformamidinate ligands (DPh^XF, X = Me, OMe, Cl and Br) with the Cr₂⁴⁺ moiety has been undertaken. X-Ray diffraction and spectroscopic data have shown that while all of these ligands form the well-known paddlewheel type complex Cr₂(DPh^XF)₄, 1 [X = Me, OMe, Cl and Br; Cr–Cr = 1.925(1), 2.140(2), 2.208(2) and 2.272(2) Å, respectively], two of them form highly unusual A-frame type complexes with short Cr–Cr bonds, and the smallest M–X–M angle ever reported in an A-frame structure. These are Cr₂(μ-Cl)(DPh^XF)₃, 2 [X = Cl and Br; Cr–Cr = 1.940(1) and 1.940(2) Å, respectively]. For some of the paddlewheel complexes, the elongation of the metal–metal bond distance out of the ‘super-short’ range (Cr–Cr > 2.00 Å) has been attributed to the presence of axial interactions between two of the ortho substituents and the Cr₂⁴⁺ moiety.