Proton-induzierte Kopplung eines tert-Butylisonitril-mit einem Phenylcarbin-Liganden am Wolfram / Proton-Induced Coupling of one tert-Butylisonitrile with one Phenylcarbyne Ligand at Tungsten

Abstract

A good entry to highly substituted phenylcarbyne complexes of tungsten containing tert-butyl-isonitrile ligands is provided via Br(CO)2(pic)2W≡CC6H5 (1) (pic: γ-picoline). The first step includes the replacement of the picoline ligands in 1 by t-BuNC in refluxing CH2Cl2 to give Br(CO)2(t-BuNC)2 W≡CC6H5 (2) in high yield. Complex 2 is then transformed with excess t-BuNC in toluene at 90°C to the carbonyl free carbyne complex trans-Br(t-BuNC)4W≡CC6H5 (3). The monocarbonyl substituted analogue of 3, Br(CO)(t-BuNC)3W≡CC6H5 (4), is observed by IR spectroscopy as an intermediate of this reaction. Its preparation is achieved by the CoCl2 catalyzed decarbonylation of 2 in the presence of one equivalent of t-BuNC. trans-Br(t-BuNC)4W≡CC6H5 (3) and the analogous iodocompound trans-I(t-BuNC)4W≡CC6H5 (5) react with HX (X = Br, I) to give respectively, Br2(t-BuNC)3W[(t-Bu)HN—C≡C—C6H5] (6) and I2(t-BuNC)3W[(t-Bu)HN—C≡C—C6H5] (7) in high yield. Complexes 6 and 7 contain a 4e-donor acetylene ligand resulting from the proton induced coupling of one tert-butylisonitrile with the phenylcarbyne ligand at the tungsten center. The reaction of complex 4 with HBr leads also to the coupling product Br2(CO)(t-BuNC)2W[(t-Bu)HN—C≡C—C6H5] (8), the carbonyl containing analogue of 6, in low yield. With one equivalent of t-BuNC and TlPF6 compounds 6 and 7 are converted to the cationic complexes [Br(t-BuNC)4W[(t-Bu)HN—C≡C—C6H5]]+PF6 - (9) and [I(t-BuNC)4W[(t-Bu)HN—C≡C—C6H5]]+PF6 - (10) respectively. The analogous chloro compound [Cl(t-BuNC)4W[(t-Bu)HN—C≡C—C6H5]]+PF6- (11) is obtained by halogen exchange from 10 and PPN+Cl-. The composition and structure of the new complexes 3, 4, and 6—11 have been determined by elemental analyses, IR, 1H NMR, 13C NMR and mass spectra.