EFFECTS OF METAL COORDINATION ON THE REACTIVITY OF 1,3,4-TRIPHENYL-1,2-DIHYDROPHOSPHETE

Nucleophilicity dominates the reaction chemistry of 1,3,4-triphenyl-1, 2-dihydrophosphete even when it is coordinated to electrophilic metal centers, but coordination dramatically alters the course of its reacti ons. Deoxygenation of carbonyl-containing substrates is effected by bo th the W(CO)(5) complex, which reductively couples benzaldehyde, and t he HgCl2 complex, which converts benzaldehyde to alpha, alpha-dichloro toluene. Metal coordination appears to decrease the tendency of the di hydrophosphete to undergo electrocyclic ring opening to the correspond ing 1-phosphabutadiene, and the HgCl2 complex reacts with dimethyl ace tylenedicarboxylate to afford a cyclopentadienyl ylide containing an i ntact dihydrophosphete unit. By reducing the nucleophilicity of the di hydrophosphete and/or the availability of the highly nucleophilic unco ordinated dihydrophosphete, coordination to HgCl2 and W(CO)(5) makes a ccessible new mechanistic pathways. Dihydrooxaphosphinines, although u navailable through the reactions of the dihydrophosphete, may be synth esized by exploitation of the reactivity of organotitanium metallacycl es. (C) 1998 John Wiley & Sons, Inc.