Chromium(II) complexes bearing 2,6-substituted N,N '-diarylformamidinate ligands

The synthesis, isolation and characterisation of several new chromium(II) c omplexes of the N,N'-bis(2,6-xylyl)formamidinate ligand (DXylF) has been un dertaken. The structure of three such complexes, namely Cr(DXylF)(2), 1, Cr -2(mu-Cl)(2)(DXylF)(2)(THF)(2), 2, and Cr-2(Ac)(2)(DXylF)(2)(THF)(2), 3, ha ve been determined by X-ray crystallography. It has been shown that the ste ric demands of the 2,6-xylyl group effectively discourage the formation of the homoleptic paddlewheel structure Cr-2(DXylF)(4): instead, the mononucle ar (but stoichiometrically equivalent) complex Cr(DXylF)(2), 1 was obtained . It is likely that the unusual dichromium dichloride-bridged intermediate 2 also owes its stability to the presence of such bulky substituents. Altho ugh this complex does not possess a significant metal-metal bonding interac tion [Cr-Cr=2.612(1) Angstrom], it has however, proven to be a useful start ing material for the preparation of the novel quadruply bonded dichromium m ixed acetate-formamidinate complex 3 [Cr-Cr (avg)= 2.339(7) Angstrom]. In b oth 2 and 3, the 2,6-xylyl groups force the formamidinate ligands to oppose one another contrary to the trans effect. In addition, it was found that c ompound 3 can be accessed from the chromium acetate starting material and, for comparison, an attempt was also made to prepare the N,N-bis(o-anisyl)fo rmamidinate ((DPhF)-F-OMe) analogue. With the formamidinates occupying posi tions cis to one another and with the absence of axially coordinated THF li gands, the molecular structure of the resultant Cr-2(Ac)(2)((DPhF)-F-OMe)(2 ), 4 [Cr-Cr=2.037(1) Angstrom], is different from that of 3.