Alkynylcarbyne complexes containing various tri- and bidentate ligands such as cyclopentadienide, tris(pyrazolyl)borate, bis(pyrazolyl)acetate and tmeda: synthesis and spectroscopic properties

The (alkynylcarbyne)tungsten complexes [L3(CO)2WCCCR] (3a,b–6a,b) [L3=hydro[tris(3,5-dimethylpyrazol-1-yl)]borato (Tp′, 3), hydro[tris(pyrazol-1-yl)]borato (Tp, 4), cyclopentadienyl (Cp, 5), bis(3,5-dimethylpyrazol-1-yl)acetato (bdmpza, 6); R=SiMe3 (a), Ph (b)] were prepared in a stepwise fashion from [W(CO)6] and Li[CCR], (CF3CO)2O and M[L3] (M=Na, K). The formation of 6a,b was highly selective, only complexes with a trans arrangement of the carboxylate group of bdmpza and the alkynylcarbyne ligand were detected. The reaction of [W(CO)6] with Li[CCR], C2O2Cl2 and tmeda afforded trans-[Cl(CO)2(tmeda)WCCCR] (7a,b). The electron-donating potential of the different tripodal ligands L3 was studied by IR- and 13C-NMR spectroscopy and compared to that of the ligand combination Cl/tmeda. The IR data suggest that in these complexes bdmpza is a weaker electron donor than Tp′ and Tp but displays stronger electron-donating abilities than Cp. The structures of 6b and 7b were established by X-ray structural analyses.