Butatrienylidene Complex Synthesis

The nucleophilicity of the terminal carbon atom of butadiynyl ligands was also used later by Dixneuf et al. for the generation of a related phenylbutatrienylidene 

Neither of these complexes was isolable. Nevertheless, they were stable enough to be used in reactions, predominantly with nucleophiles (see Section 3.4.1). 

A bis(trimethylstannyl)-substituted butatrienylidene complex (17) related to 13 (R = R = Me) was formed in the reaction of cydoheptatrienyl(methylcyclopentadie-nyl)manganese with Me3SnC = C-C = CSnMc3 and dmpe. Complex 17 was obtained 

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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.

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). 

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... 

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