End Road, London E.l Chromium(1V) tetra-alkoxides Cr(OR), (R = t-alkyl) and Cr(OSiEt,), have been prepared and their reactions studied. Variable-temperature magnetic susceptibilities, electronic and infrared spectra, electron spin resonance, and mass spectra have been measured for Cr(OBut), and the results are discussed in terms of a distorted tetrahedral Cr04 unit.QUADRIVALENT chromium compounds are comparatively rare. Apart from the halides CrX, (X = F, C1, Br),, and M1CrF5 and M1,CrF6 (M = K, Rb, Cs),, and the mixed oxides Mn4Cr06 and MI13Cr0, (M = Sr, Ba) which are complex, the volatile blue solid C ~( O B U ~) , ~ is the best authenticated quadrivalent chromium compound. We now report the preparation of more chromium(1v) alkoxides together with details of their physicochemical properties.Prefiarative Methods. -Chromium t etra-tertiary butoxide has been prepared by the following methods: (i) the action of di-t-butyl peroxide on dibenzenechromium; (ii) alcoholysis of Cr(NEt,),;5 (iii) oxidation of cr(Ol31.1~)~ in the presence of ButOH by various reagents [e.g. But,O,, CrO,(OBut),, Pb(OAc),, Br,, or OJ ; 5 (iv) from the reaction of CrC13,3THF with NaOBut and cuprous chloride; and (v) the addition of cuprous chloride to a suspension of LiCr(OBut), in refluxing tetrahydrofuran.' A number of pure tetra-t-alkoxides were prepared [mainly by method (ii)] and their physical properties are listed in Table 1. They are all blue liquids or low-melting solids which can be distilled i n vacuo. Molecular-weight determinations (cryoscopic in cyclohexane) showed that they were monomeric and 1
