Reactivity of [(C5Me5)Fe(C5H4BBr2)] and [(OC)3Mn(C5H4BBr2)] toward Et3SiH: Facile Access to [(OC)3Mn(C5H4BH2)]2 and to Boron-Bridged Dinuclear Organometallics

The reaction of (FeBBr2)-B-# with 2 equiv of Et3SiH gives the boron-bridged din uclear species (Fe2BBr)-B-# with concomitant liberation of B2H6 (Fe-# = (C5Me5)Fe(C5H4)). The transformation is slow (48 h) but nevertheless provides yields of > 85%. Fc(2)(#)BBr can conveniently be converted into the aminoborane (Fe2BNMe2)-B-# by treatment with Me3SiNMe2. For an X-ray crystal structure analysis, (Fe2BNMe2)-B-#, was hydrolyzed to the bonnie acid (Fe2BOH)-B-#. A cross-coupling experiment using Et3SiH and an equimolar mixture of FeBBr2 and (Fe2BBr2)-B-# led to the formation of the mixed product Fc(Fc(#))BBr with high selectivity (Fe = (C5H5)Fe(C5H4)). Similar to the case for Fc(2)(#)BBr, Cym(2)BBr can be prepared from CymBBr(2) and Et3SiH (Cym = (OC)(3)Mn(C5H4)). In contrast to FcBH(2), which exists only as transient intermediate on the way to Fc(2)BH, CymBH(2) is an isolable species. The compound was synthesized from a concentrated toluene solution of CymBBr(2) and excess neat Et3SiH at -78 degrees C and forms B-H-B-bridged dimers (CymBH(2)), in the solid state (X-ray crystallography). Our reactivity studies indicate that the Et3SiH-induced coupling reaction of derivatives LnM(C5H4BBr2) is fastest for electron-rich cyclopentadienyl complexes. Addition of NMe2Et to (CymBH(2))(2) affords the monomeric amine adduct CymBH(2)(NMe2Et). The reaction of (CymBH(2))(2) with HCC'Bu in a stoichiometric ratio of 1:4 (or slightly higher) results in a mixture of products from which the dinuclear hydroboration product (CymB(C(H)=C(H)'Bu))(2)C(H) C(H)(2)'Bu could be isolated and structurally characterized. To obtain the divinylborane CymB(C(H)=C(H)'Bu)(2) in high yield and pure form, (CymBH(2))(2) has to be dissolved in excess neat HCC'Bu.