Übergangsmetall-Carbin-Komplexe: XCIX. Synthese und röntgenstruktur von (η 5-C 5Me 5)(CO) 2MOCNEt 2, dem ersten niedervalenten Diethylaminocarbin-Komplex von Molybdän mit einem Pentamethylcyclopentadienyl-Liganden

Abstract

Activation of the ethylisocyanide ligand for an electrophilic attack at nitrogen is induced in Na[(η 5-C 5Me 5)(CO) 2Mo(EtNC)] ( 2) by the electron rich Mo 0 center. Thus complex 2, which is quantitatively obtained by reduction of cis, trans-(η 5-C 5Me 5)Mo(CO) 2(EtNC)I ( 1a, 1b) with two equivalents of Na, reacts with Et 3OBF 4 in THF to give as the major product (η 5-C 5Me 5(CO) 2MoCNEt 2 ( 3. A minor product, the iminoacyl complex (η 5-C 5Me 5)(CO) 2Mo[η 2-C(NEt)Et] ( 4) is also obtained in this reaction. Formation of 4 is explained by a concomitant attack of the electrophile Et 3OBF 4 on the metal center of 2 followed by a migratory insertion of the metal bonded ethyl group to the ethylisocyanide ligand. 3 represents the only hitherto known low valent molybdenum diethylaminocarbyne complex with a pentamethylcyclopentadienyl ligand and the first example in the class of the compounds (π-arene)(CO) 2MCNR 2 to be structurally characterized by a single X-ray crystallographic study. 3 crystallizes in the monoclinic space group P2 1/ c. The unit cell with a = 966.1(3), b = 1240.1(4), c = 1550.2(6) pm and β = 102.34(3)° contains four molecules. Striking features of the structure are the short C carbyneN bond distance (129.9(6) pm) and the planarity of the three bonds around the nitrogen atom indicating a strong π interaction of the diethylaminogroup with the carbyne carbon. Moreover the amino plane of the carbyne ligand and the mirror plane of the (η 5-C 5Me 5)(CO) 2Mo fragment are almost perpendicular to each other.