This talk will focus on the chemistry of coordinatively unsaturated, cationic early metal alkylidyne complexes and the study of their potential application as catalysts for alkyne metathesis. In particular, this study is centered around the tantalum systems Ta(?5-C5(CH3)5)(CC6H5)(P(CH3)2Cl and Ta(?5-C5H5)(CC6H5)(P(CH3)2Cl, described by Schrock et al.1 We have attempted the synthesis of electrophilic species of these species by halide abstraction using the sodium salts of the weakly coordinating anions [HCB11Cl11]- and [B(3,5-C6H3(CF3)2)4]-.Upon abstraction of chloride, a mixture of cationic species can be observed. Two of the components are two isomeric products of cyclometallation of one of the P(CH3)3 ligands. One of such isomers is the alkylidene [Ta(?5-C5(CH3)5)(CHC6H5)(P(CH3)3)(CH2P(CH3)2)][BuCB11Cl11] (1  ), which was characterized by X-ray crystallography. Another component of this mixture is the cation [Ta(?5-C5H5)(CC6H5)(P(CH3)3]+ (2  ), which is the product of redistribution of the P(CH3)3 ligands. When such mixture was treated with excess P(CH3)3, only 2  can be observed by 1H and 31P NMR. When the mixture of cations is treated with 3-hexyne, the corresponding cationic tantalacyclobutadiene [Ta(?5-C5(CH3)5)(CHC6H5)(P(CH3)3)(CH2P(CH3)2)][HCB11Cl11] (3 ) is formed cleanly. This compound was isolated and characterized by NMR spectroscopy and X-ray crystallography. To the best of our knowledge, this compound represents the first example of an isolated and crystallographically characterized tantalum metallacyclobutadiene .                                                                                                                                    (1)                                                                                                                                      (3) References1. Messerle, L. W.; Jennische, P.; Schrock, R. R.; Stucky, G. J. Am. Chem. Soc. 1980  , 102, 6744.

Chemistry of coordinatively unsaturated tantalum alkylidynes

247th National Meeting (2014)

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