US EPA

7440377 

Journal Article 

Reactivity of the coordinated eta(2)-ketone in the tropocoronand complex [Hf(TC-3,5)(eta(2)-OC(CH2Ph)(2)]: N-C coupling, C-C coupling, and insertion into the C-O bond 

Scott, MJ; Lippard, SJ 

1998 

1 

Organometallics
ISSN: 0276-7333
EISSN: 1520-6041 

American Chemical Society 

17 

3 

466-474 

English 

10.1021/om971040n 

WOS:000071857700028 

The reactions of [Hf(TC-3,5)(η2-OC(CH2Ph)2)] (1) with a variety of substrates are described. Molecules containing conjugated terminal nitrogen atoms, specifically arylazides and diazoalkanes, insert into the metalloxirane unit in a 1,1-fashion to form four-membered chelate rings Hf-O-C-N via N-C coupling. Enones and phenyl-substituted ketones react by C-C, pinacolic-type coupling to give the 1,2-addition product of the ketone moiety across the metal-carbon bond, Hf-O-C-C-O. Reaction of 1 with simple ketones is notably more complex. With acetone, the product contains a six-membered Hf-O-C=C-C-O chelate ring, possibly derived by a β-hydrogen transfer from the η2-ketone to form the metal hydride, which reacts with substrate to achieve C-C coupling accompanied by loss of H2. Substrates containing nitro groups insert a single oxygen atom into the metalloxirane unit, forming an equivalent of nitrosoalkane or nitrosoarene. In the presence of nitrosoarenes, the resulting four-membered oxametallacycle can react further, undergoing a retro [2 + 2] cycloaddition to generate an unusual μ-η2:η2 nitrosoarene-bridged dinuclear species. Phenyl isocyanate attacks the C-O bond of the η2-ketone ligand in 1 giving rise to a coordinated carbamate, perhaps by means of a [2 + 2] cycloaddition. The products of the reactions were characterized by X-ray crystallography, and plausible mechanisms are suggested for all the coupling reactions.