Synthesis and Characterization of Cyclotetraphosphato Complexes of Rh(I), Ir(I), Ru(II), and Pd(II)

The cyclotetraphosphate ion (P4O124-) as a PPN (PPN =
(PPh3)2N+) salt reacts with [MCl(cod)]2 (M = Rh, Ir; cod = 1,5-cyclooctadiene) to give the dinuclear complexes (PPN)2[{M(cod)}2(P4O12)], in which the two metal moieties are situated trans to
each other with respect to the P4O4 ring in the solid state. In
solution, however, these complexes exist as mixtures of trans and
cis isomers. On the other hand, the P4O124- ion reacts with 4
equiv of [Rh(cod)(MeCN)x]+ cation to give the tetranuclear complex
[{Rh(cod)}4(P4O12)], where the four Rh(cod) fragments are bound
to the P4O12 platform alternately on both sides of the P4O4 ring.
Dinuclear P4O12 complexes of ruthenium and palladium are also
synthesized.