Chromium borazine complex

One of the most fascinating developments in borazine chemistry has been the recent isolation of hexaalkylborazine chromiumtricarbonyl complexes. A reaction was observed when hexamethylborazine was reacted Mo(CO)e but no definite products could be isolated 1S8>. However, with extremely pure starting materials using (CO)3Cr(CHaCN)3 or (CO)3(NH3)3Cr as reactants, the preparation of a borazine-metal complex has been effected iss.ieo). Solvents other than dioxane did not lead to the desired product, and it has been suggested that the reaction proceeds via a dioxane-chromium tricarbonyl complex. The reaction appears to proceed by altering the existing equilibria, indicated in the reaction as depicted in Eq. (43). 

A number of (substituted borazine)chromium tricarbonyl complexes have been prepared. 0 The chief change in the vibrational spectrum of the ligand upon complexation is a decrease in the wavenumbers of the band associated with B—N stretching, e.g. in (Me3N3B3Me2Ph)Cr(CO)3 this is at 1371 cm , compared to 1423 cm-1 in the free ligand. 

In retrospect, it is ironic to it that when I met Ernst Schumacher in 1969 (he was then Professor at the University of Bern in Switzerland) we did not talk about the experiments he did at Zurich in the same building where I was at that time. Instead, his interest focussed on our work on borazine transition metal compounds and we discussed in some detail whether it would be possible to incorporate metal atoms like chromium or molybdenum between the layers of hexagonal boron nitride (BN) in a similar way as it can be done with graphite. In the course of these discussions I did not mention that, after I had moved to Zurich, we had begun to investigate the reactivity of nickelocene towards both nucleophilic and electrophilic substrates. The reason was that we were still at the beginning, and while we had been able to prepare a series of monocyclopentadienyl nickel complexes from Ni(C5H5)2 and Lewis bases, our attempts to obtain alkyl- or acyl-substituted nickelocenes by the Friedel-Crafts reaction failed. 

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