Ligand behavior of a (Z)-phosphazide (a 1,2,3,4 lambda(5)-triazaphosphinine) and of the corresponding phosphazene (a 1,2 lambda(5)-azaphosphete)

1,2,3,4 lambda(5)-Triazaphosphinine 1 reacts with PdCl2(PhCN)(2) and W(CO)(5)(THF) at room temperature, affording, according to P-31 NMR spectroscopy, eta(1)-triazaphosphinine complexes 3 and 5, which after elimination of dinitrogen give the bis(eta(1)-azaphosphete)palladium(II) complex 4 and (eta(1)-azaphosphete)W(CO)(5) complex 6, in 65% and 88% yield, respectively. Complex 4 can also be obtained in 90% yield by addition of PdCl2(PhCN)(2) to 1,2 lambda(5)-azaphosphete 2. Addition of cis-Mo(CO)(4)(pip)(2) to 1 leads to (eta(1)-triazaphosphinine)Mo(CO)(4)(pip) complex 7, which was isolated in 70% yield. In solution, at room temperature for 2 days, 7 transforms into to eta(1)-(five-membered cyclophosphazene)Mo(CO)(5) complex 9 in 45% yield. When 2 equiv of W(CO)(5)(pip) is added to 1, complex 10 featuring a five-membered cyclophosphazene bonded to W(CO)(5)(pip) via a hydrogen bond is isolated in 80% yield. 1,2 lambda(5)-Azaphosphete 2 reacts with piperidine, affording five-membered phosphazene ring 11 in 95% yield, which by subsequent treatment with Mo(CO)(5)(pip) and W(CO)(5)(pip) gives complexes 9 (75% yield) and 10 (83% yield), respectively. Schwartz's reagent reacts with 1, affording five-membered zirconacyclophosphazene 12 in 45% yield. Complexes 4, 7, 10, and 12 are characterized by single-crystal X-ray analyses. These results as a whole demonstrate that in contrast with (E)-phosphazides which behave as four-electron donors via the alpha- and gamma-nitrogen atoms and which are stabilized by complexation, (Z)-phosphazides, such as the 1,2,3,4 lambda(5)-triazaphosphinine 1, act as two-electron donors via the beta-nitrogen atom, and are destabilized by the metal with respect to nitrogen elimination.