ELECTRON-RICH ISOCYANIDE-SUBSTITUTED DIETHYLAMINOCARBYNE COMPLEXES OF TUNGSTEN WITH PENTAMETHYLCYCLOPENTADIENYL LIGANDS

Two high yield synthetic routes to the electron-rich diethylaminocarbyne complex Cp*(CO) (EtNC)W = CNEt2 (5) are described starting from a mixture of the W(II) isomers cis- and trans-Cp*W(CO)2(EtNC)I (1a,1b) (Cp* = eta-5-C5Me5). The first route begins with the oxidative decarbonylation of 1a/1b with I2 to give the W(IV) complex Cp*W(CO)(EtNC)(I)3 (2). Reductive elimination of two iodide ligands in 2 by Na/Hg in the presence of EtNC yields subsequently a mixture of the W(II) isomers cis- and trans-Cp*W(CO)(EtNC)2I (3a,3b). A minor product, trans-Cp*W(CO)(EtNC)2(HgI3) (3b'), the HgI2-adduct of 3b is also formed in this reaction. The isomeric mixture 3a/3b is further reduced with Na to the W-degrees isocyanide metallate Na[Cp*W(CO)(EtNC)2] (4), which is finally ethylated at one isocyanide nitrogen with Et3OBF4 to give 5. The second route is based upon a recently reported method for the high yield transformation of 1a/1b to Cp*(Br)2(CO)W = CNEt2 (8). This procedure involves reduction of 1a/1b to the W-degrees isocyanide metallate Na[Cp*W(CO)2(EtNC)] (6) followed by ethylation of 6 to give the diethylaminocarbyne complex Cp*(CO)2W = CNEt2 (7) and oxidation of 7 with Br2. Reductive elimination of the bromide ligands in the resulting diethylaminocarbyne complex 8 by Na/Hg in the presence of EtNC gives finally 5. Using the second route, other electron rich diethylaminocarbyne complexes such as Cp*(CO)(RNC)W = CNEt2 (9: R = Me; 10: R = (t)Bu) and Cp*(CO)(PMe3)W = CNEt2 (11) can be prepared. All new complexes have been fully characterized.