Übergangsmetall-carbin-komplexe XCVIII. N-Alkylierung eines ethylisocyanid-liganden am molybdän(0); Synthese und oxidationsreaktionen erster cyclopentadienyl-substituierter molybdän-diethylaminocarbin-komplexe

Abstract

A large scale, high yield synthesis of the first cyclopentadienyl-substituted diethylaminocarbyne complexes of molybdenum has been developed starting from (η 5-C 5H 5)Mo(CO) 3I ( 1). In the first step of the synthetic procedure 1 is quantitatively transformed with EtNC in CH 2Cl 2 into an isomeric mixture of cis- and trans-(η 5-C 5H 5)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[(η 5-C 5H 5)Mo(CO) 2(EtNC)] ( 3). The ethylisocyanide ligand in 3 is susceptible to electrophilic attack at nitrogen. Thus reaction of 3 with Et 3OBF 4 gives as the major product, the low valent diethylaminocarbyne complex (η 5-C 5H 5)(CO) 2MoCNEt 2 ( 4). A minor product, the η 2-iminoacyl complex (η 5-C 5H 5)(CO) 2Mo[η 2-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 I 2 and Br 2 leads to the high valent diethylaminocarbyne complexes (η 5-C 5H 5)(I) 2(CO)MoCNEt 2 ( 6) and (η 5-C 5H 5)(Br) 2-(CO)MoCNEt 2 ( 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.