Ein neuer Weg zu cyclopentadienyl-substituierten Diethylaminocarbin-Komplexen des Wolframs / A New Route to Cyclopentadienyl-Substituted Diethylaminocarbyne Complexes of Tungsten

Abstract

We have developed a new, large scale, high yield synthesis of cyclopentadienyl-substituted tungsten diethylaminocarbyne complexes. In the first step an almost quantitative conversion of (η5-C5H5)W(CO)3I (1) and (η5-C5Me5)W(CO)3I (2) using EtNC and Me3NO occurs to give an isomeric mixture of cis and trans (η5-C5H5)W(CO)2(EtNC)I (3 a, 3b) and cis and trans (η5-C5Me5)W(CO)2(EtNC)I (4a, 4b), respectively. The isomeric mixtures of 3a and 3b and 4a and 4b are then quantitatively transformed with sodium powder in THF into the highly reactive, anionic isocyanide complexes Na[η(5-C5H5)W(CO)2(EtNC)] (5) and Na[(η5-C5Me5)W(CO)2(EtNC)] (6). Finally, alkylation of the strong nucleophiles 5 and 6 with Et3OBF4 occurs on the isocyanide nitrogen and yields the low-valent tungsten diethylaminocarbyne complexes (η5-C5H5)(CO)2W≡CNEt2 (7) and (η5-C5Me5)(CO)2W≡CNEt2 (8). Oxidative decarbonylation of 7 and 8 with iodine in CH2C12 gives the high-valent tungsten compounds (η5-C5H5)(I)2(CO)W≡CNEt2 (9) and (η5-C5Me5)(I)2(CO)W≡CNEt2 (10). 9 and 10 are subsequently converted with one equivalent of EtNC and TlPF6 into the cationic carbyne complexes [(η5-C5H5)(I)(EtNC)(CO)W≡CNEt2]PF6 (11) and [(η5-C5Me5)(I)(EtNC)(CO)W≡CNEt2]PF6 (12). Advantages of this route to low- and high-valent tungsten diethylaminocarbyne complexes are discussed in comparison to the classical Fischer procedure using the carbyne complex trans-I(CO)4W≡CNEt2 as precursor.