TRANSITION-METAL CARBYNE COMPLEXES .99. SYNTHESIS AND X-RAY STRUCTURE OF (ETA-5-C5ME5) (CO)2MO=CNET2, 1ST LOW-VALENCY DIETHYLAMINOCARBYNE COMPLEX OF MOLYBDENUM WITH A PENTAMETHYLCYCLOPENTADIENYL LIGAND

Activation of the ethylisocyanide ligand for an electrophilic attack at nitrogen is induced in Na[(eta-5-C5Me5)(CO)2Mo(EtNC)] (2) by the electron rich Mo0 center. Thus complex 2, which is quantitatively obtained by reduction of cis, trans-(eta-5-C5Me5)Mo(CO)2(EtNC)I (1a, 1b) with two equivalents of Na, reacts with Et3OBF4 in THF to give as the major product (eta-5-C5Me5)(CO)2Mo = CNEt2 (3). A minor product, the iminoacyl complex (eta-5-C5Me5)(CO)2Mo[eta-2-C(NEt)Et] (4) is also obtained in this reaction. Formation of 4 is explained by a concomitant attack of the electrophile Et3OBF4 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 (pi-arene)(CO)2M = CNR2 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 beta = 102.34(3)-degrees 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 pi interaction of the diethylaminogroup with the carbyne carbon. Moreover the amino plane of the carbyne ligand and the mirror plane of the (eta-5-C5Me5)(CO)2Mo fragment are almost perpendicular to each other.