PROTON-INDUCED COUPLING OF A TERT-BUTYLISOCYANIDE WITH A DIETHYLAMINOCARBYNE TO YIELD AN ALKYNE LIGAND AT A SINGLE TUNGSTEN CENTER

The tert-butylisocyanide substituted diethylaminocarbyne complex I(CO)2(t-BuNC)2 WCNEt2 (1) reacts with one equivalent of HI in CH2Cl2 at room temperature to yield a mixture of complexes (I)2(CO)2(t-BuNC)W[η2-(t-Bu)HN-CC-NEt2] (2), major product, and (I)2(CO)(t-BuNC)2W[η2-(t-Bu)HN-CC-NEt2](3), minor product, separable by column chromatography on silica. The exclusive preparation of compound 3 can be achieved by treating I(CO)(t-BuNC)3 WCNEt2 (4) with one equivalent of HI in CH2Cl2 at room temperature. Complexes 2 and 3 contain a 4e-donor alkyne ligand resulting from the proton-induced coupling of one tert-butylisocyanide with the diethylaminocarbyne ligand at a single tungsten centre. Both complexes react with t-BuNC in refluxing CH2Cl2 to give quantitatively the cationic alkyne complex [I(CO)(t-BuNC)3W[η2-(t-Bu)HN-CC-NEt2]]+I- (5). Thermal decarbonylation of this complex in toluene in the presence of t-BuNC at 90°C leads to the carbonyl-free alkyne complex [I(t-BuNC)4W[η2-(t-Bu)HN-CC-NEt2]]+I- (6). The ionic nature of 5 and 6 has been confirmed by comparison of their conductivity data in 1,2-dichloroethane with NR4+X - salts (R = alkyl ; X = PF6, Br, I). The composition and structure of the alkyne complexes 2, 3, 5 and 6 have been determined by total elemental analyses, IR, 1H NMR and 13C NMR spectroscopies and mass spectrometry. The spectroscopic results indicate a substantial bond delocalization and a hindered rotation of the diethylamino-group in the alkyne ligand. The barrier to this rotation is calculated to be ca 13.9-15.3 kcal mol-1 for compounds 2, 3, 5 and 6. © 1990.