P−B Adducts of 3,4‐Dimethyl‐1‐phosphaferrocene with Bromoboranes

The crystalline adducts FcP−BBr 3 ( 2 ) and FcP−BBr 2 Fc ( 3 ), which are very rare examples of P ‐bonded complexes between phosphaferrocene and a main‐group metal atom, were obtained by the reaction of 3,4‐dimethyl‐1‐phosphaferrocene (FcP) with BBr 3 and FcBBr 2 (Fc: ferrocenyl). According to X‐ray crystallography, the Fe−P bond length in 2 is 0.085 Å shorter than in the parent phosphaferrocene. All structural changes resulting from P−B acid−base pairing follow the same qualitative trend, but are significantly larger than those occurring from the formation of transition metal complexes of phosphaferrocene. In contrast to 2 , NMR spectroscopy reveals 3 to be almost completely dissociated in CDCl 3 solution at room temperature. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)