No abstract

Reactions of Pd(PPh 3 ) 4 with P(dE)(N i Pr 2 )(naph) (6, E ) S; 7, E ) O) (naph ) 1,8-naphthylene) having a strained four-membered P(V)-phosphacycle gave dimeric complexes [Pd{κ 2 P,C-µ 2 -PE-P(dE)(N i Pr 2 )(naph)}(PPh 3 )] 2 (9, E ) S; 10, E ) O), in which a Pd metal has been inserted into a P-C bond of the phosphacycle to form a phosphapalladacycle having a P(V) donor, and the two phosphapalladacycle units have been mutually bridged with EdP groups, as confirmed by X-ray structure analysis for thermodynamically more stable racemic isomers 9a and 10a. The meso-to-racemic isomerization observed for the simultaneously formed meso isomer 9b, and probably also for the corresponding meso isomer 10b, indicated partial dissociation of 9 and 10 taking place to their monomer units in solution, which were actually trapped as [Pd{κ 2 P,C-P(dE)(N i Pr 2 )(naph)}(dppe)] by treatment with bidentate dppe (dppe ) 1,2-bis(diphenylphosphino)ethane). On the other hand, a similar treatment of 9a with monodentate PMe 3 and PEt 2 Ph resulted in a trivial substitution of both PPh 3 ligands to give dimeric PMe 3 and PEt 2 Ph analogues of 9a, respectively. 10a was found to react with O 2 to form an unprecedented oxidation product, [Pd{κ 2 P,O-µ 2 -PO-PO(dO)(N i Pr 2 )(naph)}(PPh 3 )] 2 , 17, in which an oxygen atom has been inserted into each P(V)-Pd bond. 9a and 10a exhibited moderate catalytic activities for a Heck reaction between PhI and styrene. The mercury test indicated that metallic Pd nanoparticles released from 9a and 10a would be practical catalysts.