TRANSITION-METAL CARBYNE COMPLEXES .48. N-ALKYLATION OF AN ETHYLISOCYANIDE LIGAND TO MOLYBDENUM(0) - SYNTHESIS AND OXIDATION REACTIONS OF PRELIMINARY CYCLOPENDADIENYL SUBSTITUTED MOLYBDENUM DIETHYLAMINOCARBYNE COMPLEXES

A large scale, high yield synthesis of the first cyclopentadienyl-substituted diethylaminocarbyne complexes of molybdenum has been developed starting from (η5-C5H5)Mo(CO)3I (1). In the first step of the synthetic procedure 1 is quantitatively transformed with EtNC in CH2Cl2 into an isomeric mixture of cis- and trans-(η5-C5H5)Mo(CO)2(EtNC)I (2a, 2b). The isomers 2a and 2b are then quantitatively reduced with sodium powder to the zerovalent molybdenum complex Na[(η5-C5H5)Mo(CO)2(EtNC)] (3). The ethylisocyanide ligand in 3 is susceptible to electrophilic attack at nitrogen. Thus reaction of 3 with Et3OBF4 gives as the major product, the low valent diethylaminocarbyne complex (η5-C5H5)(CO)2MoCNEt2 (4). A minor product, the η2-iminoacyl complex (η5-C5H5)(CO)2Mo[η2-C(NEt)Et] (5), is also formed in this reaction via electrophilic attack on the electron rich metal center of 3. Compounds 4 and 5 are separated by column chromatography and isolated as yellow and red, microcrystalline solids in 60 and 8% yield respectively. Oxidative decarbonylation of 4 with I2 and Br2 leads to the high valent diethylaminocarbyne complexes (η5-C5H5)(I)2(CO)MoCNEt2 (6) and (η5-C5H5)(Br)2-(CO)MoCNEt2 (7), isolated as thermally stable, black and purple solids in quantitative yield. Composition and structure of the complexes 2a-7 were determined by total elemental analyses, IR, 1H NMR and 13C NMR spectra and the spectral data compared with the analogous tungsten compounds. © 1990.