Chelate-bridged enolates

Figure 4.2 Bimetallic chelate-bridged ester enolate complex.

A related enolate complex [Na Pr 2PC(H)=C(0)Ph ]4 has been prepared by deprotonation of the ketone Pr PCH2C(0)Ph with NaN (SiMes)2 170). In the solid state this complex adopts a cubane-type structure with a Na404 core. Each ligand bridges opposite edges of the cube, forming a five-membered chelate ring at each sodium. The Na-P distance in this complex of 2.852(2) A is short in comparison to other similar contacts. 

A dinuclear Pt complex with chelating tris( -tolyl)phosphine and bridging chloro ligands has been converted into a neutral PPhs-coordinated complex 548 and then into cationic complexes containing phosphonium-substituted enolate ligands (549, Scheme 76). Reaction with phosphorus ylides produces 550 and 551. 

The Cobalt Triad.— The first methylene-bridged binuclear cobalt complex [Ck)2O-CO)0i-CH2)(C5Mes)2] has been obtained by treatment of C0CI2 with lithium pentamethylcyclopentadienide and the lithium enolate of acetaldehyde (Li+CHaCHO-). The novel transannular electron-rich olefin (35) reacts with f RhCl(cod) 2] to form the chelating c -dicarbenerhodium(i) salt (36) [X=RhCla-... 

The chemical shifts at 5 18.1 and 5 19.1 (strongly chelated enolic proton of intramolecular hydrogen bridge) and at 5 4.12 (methine proton of the 2-methyl-... 

---