Borabenzene metal complexes bonding

All borabenzene-metal complexes investigated structurally so far show very similar patterns for the ligand geometry (Table I) and for the metal-ligand bonding (Table II) only the cobalt complex 6 deserves separate consideration (see below). 

The bonding situation in borabenzene-metal complexes has been treated by several authors and with varying methods and intentions (38-41). The complexes are partitioned in boratabenzene ions and positive complex fragments or metal ions. The tt MO s of the C5H5BR ligand (Fig. 2) may... 

Borabenzene metal complexes, like their cyclopentadienyl counterparts, are not readily amenable to breaking of the metal-ligand bond. Such bond breaking will occur more easily in complexes with antibonding electrons. By fortuitous chance the cobaltocene route to borabenzene chemistry (Section V,A) provided 19-e complexes with the useful property of inherently weakened metal-ligand bonds. Thus most of this section centers on the reactivity of Co(C5H5BMe)2 (7) and Co(CsH5BPh)2 (13). 

---