Butatrienylidene synthesis

The synthesis introduced by Bruce et al. starts from butadiynyl lithium [14]. The addition of HBF4 to solutions of buta-l,3-diynyl ruthenium complex 3 was proposed to afford the butatrienylidene cation 4 by protonation of the terminal carbon atom of the butadiynyl ligand. Complex 4 could neither be isolated nor spectroscopically detected. It readily decomposed by reaction with even traces of water in the air by nucleophilic attack of H2O on the cationic center (Scheme 3.2). 

Scheme 3.4 Synthesis of the first binuclear butatrienylidene complexes by addition of electrophiles to butadiyndiyi diiron...

Rearrangement reactions have turned out to be very convenient and the most used methods for the synthesis of butatrienylidene complexes. 1,4-H shift reactions have been used by Bruce et al. [19, 20] and Winter et al. (e.g.. Scheme 3.6) [21, 22] for generating butatrienylidene ruthenium complexes. Analogously, a butatrienylidene iron complex tvas obtained from [Cp (dppe)Fe-Cl] (dppe = Ph2PCH2CH2PPh2), Mc3Si-C = CC = CH, and NaBPh4 in methanol via 1,4-H shift (Scheme 3.7) [23, 24]. 

Scheme 3.8 Synthesis of the first isolable neutral butatrienylidene complex.

This unusual reactivity was subsequently extended to a broad variety of allylic and propargylic amines, in combination with other ruthenium(II) metal fragments, allowing the isolation of aminoaUenylidene complexes 33-35 [47-49] (Fig. 6). In addition, the synthesis of the thio-allenylidene [44] and seleno-aUenylidene [50] derivatives 36 from the in situ generated butatrienylidene Zran.s - RuCI (=C=C=C=CH2)(L2)2] (L2 = dppm, dppe) and the corresponding aUyl sulfides... 

The use of the enol triflate HC=C-C(OTf)=CPh2 that contains an excellent leaving group at the C(7) carbon was the key to the successful synthesis of the more elusive butatrienylidene derivative, [IrCl(C=C=C=CPh2) (PPr 3)2] 606, which was reported by Ilg and Werner in 2000. ... 

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