Element-TM Bond Formation

The first reaction to give a structurally authenticated RE-TM bonded complex was the stJt elimination reaction of [LuClCpjfthf)] and Na[RuCp(CO)2], reported by Beletskaya and coworkers in 1990, 

After these initial results, no further studies describing direct f-element-transition metal bonds were published for almost 20 years. This period of silence ended in 2008, when Kempe et al. showed alkane elimination iyide infra) to be a successful tool for the preparation of bismetallocenes [Cp REReCp ] (RE=Y, Yb) [12]. Within the series of reports following this finding, salt elimination still proved to be the potentially most versatile way of preparing RE/An-TM bonds. Divalent ytterbium was found to form two metal-metal bonds within the compounds [(thf)2Yb(ReCp2)2] and [(py )3Yb RuCp(CO)2 2l (py = d-tert-butylpyridine). 

One of the limitations of the salt elimination strategy is the need for a polar solvent such as the commonly used tetrahydrofuran that promotes the reactions by providing at least partial solubility for the salt-like transition metalates. As was shown in detail for a Re-Lu system (vide infra), the stabUity of the bimetallic species may be low in ethers, sometimes leading to complete decomposition. 

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