| Abstract
| - Tantalum-alkyne complexes with the general formula TaCl3(R1C⋮CR2)(dme) (1a, R1 =R2 = Et; 1b, R1 = R2 = n-C5H11; 1c, R1 = Ph, R2 = Me; 1d, R1 = R2 = Ph; DME = 1,2-dimethoxyethane) were synthesized by treatment of the corresponding alkynes with a low-valent tantalum derived by reduction of tantalum pentachloride with zinc powder in a mixedsolvent of toluene and DME. The DME ligand can be replaced by 2 equiv of pyridine toafford the corresponding dipyridine complexes TaCl3(R1C⋮CR2)(py)2 (2a, R1 = R2 = Et; 2b,R1 = R2 = n-C5H11; 2c, R1 = Ph, R2 = Me; 2d, R1 = R2 = Ph). Additionally, the reaction of1a with the bidentate nitrogen ligands bipyridine and N,N,N‘,N‘-tetramethyethylenediamine(= TMEDA) gave TaCl3(EtC⋮CEt)(bipy) (3) and TaCl3(EtC⋮CEt)(tmeda) (4), respectively.The η2- and 4e-coordination mode of an alkyne with a large contribution of a metalacyclopropene canonical structure was revealed by spectroscopic methods (NMR and IR) andcrystallographic analyses of 1a, 1c, 2a, and 4. The reactivies of the tantalum-3-hexynecomplexes 1a, 2a, 3, and 4 toward 3-phenylpropanal were investigated. Only the pyridinecomplex 2a reacted with a stoichiometric amount of the aldehyde to afford the correspondingallylic alcohol in 77% yield upon hydrolysis. The reaction proceeded via an oxatantalacyclopentene species.
- The series of new tantalum-η2-alkyne complexes TaCl3(R1C⋮CR2)L2 (L2 = DME, Bipy, and TMEDA; L = Py) were prepared and characterized by 1H and 13C{1H} NMR spectroscopy and single-crystal X-ray structure analysis. Only the bis(pyridine) complex 2 (R = Et) reacted with a stoichiometric amount of the 3-phenylpropanol to afford the corresponding allylic alcohol upon hydrolysis.
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