Synthesis of N-allyl-2,3-dihydrobenzoxazol-2-ylidene complexes of chromium(0) and tungsten(0)

The reaction of 2-trimethyisiloxyphenyl isocyanide (1) with [M(CO)(5)(THF)] (M = Cr, W) gives the complexes [M(2-Me3SiO-C6H4NC)(CO)(5)] (2) (2a, M = C r; 2b, M = W). Hydrolysis of the Si-O bond leads to the formation of an equ ilibrium between complexes 3 (3a, M = Cr; 3b, M = W) with a 2-hydroxyphenyl isocyanide and complexes 4 (4a, M = Cr; 4b, M = W) with a 2,3-dihydrobenzo xazol-2-ylidene ligand. Deprotonation of mixtures 3/4 followed by alkylatio n with allyl bromide yields exclusively N-allyl-2,3-dihydrobenzoxazol-2-yli dene complexes (5) (5a, M=Cr; 5b, M=W). Thermally induced intramolecular su bstitution of one cis-carbonyl ligand in (N-allyl-2,3-dihydrobenzoxazol-2-y lidene) (5b) results in the formation of the alkene-carbene complex 6 incor porating an eta(2):eta(1)-(N-allyl-2,3-dihydrobenzoxazol-2-ylidene) ligand. The molecular structure of 5b is reported. (C) 1999 Elsevier Science S.A. All rights reserved.