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 reactions. Deoxygenation of carbonyl-containing substrates is effected by both the W(CO) 5 complex, which reductively couples benzaldehyde, and the HgCl 2 complex, which converts benzaldehyde to ␣,␣-dichlorotoluene. Metal coordination appears to decrease the tendency of the dihydrophosphete to undergo electrocyclic ring opening to the corresponding 1-phosphabutadiene, and the HgCl 2 complex reacts with dimethyl acetylenedicarboxylate to afford a cyclopentadienyl ylide containing an intact dihydrophosphete unit. By reducing the nucleophilicity of the dihydrophosphete and/or the availability of the highly nucleophilic uncoordinated dihydrophosphete, coordination to HgCl 2 and W(CO) 5 makes accessible new mechanistic pathways. Dihydrooxaphosphinines, although unavailable through the reactions of the dihydrophosphete, may be synthesized by exploitation of the reactivity of organotitanium metallacycles.