P-N LIGANDS WITH MAXIMUM ELECTRON-DONOR C APACITY .7. 3-COMPONENT REACTION OF P-4-PHOSPHORUS WITH [CP(X)RH(CO)(2)] IN THE PRESENCE OF [CR(CO)(5)THF] OR [CPMN(CO)(2)THF] - A METHOD OF STUDYING THE PATHWAY FROM TETRAHEDRAL P-4 TO THE PLANAR CYCLO-P-4 LIGAND

The reaction of P-4 with [Cp(x)Rh(CO)(2)] (Cp(x) = Cp', Cp ''; Cp' = e ta(5)-C(5)H(4)tBU, Cp '' = eta(5)-C(5)H(3)tBu(2)-1,3) in the presence of [Cr(CO)(5)THF] leads to [Cp(x)Rh(CO)(eta(1:1)-P-4)(Cr(CO)(5))(4)] ( 1a, b), [Cp '' Rh(eta(4)-P-4)(Cr(CO)(5))(3)] (2b), and [Cp'Rh(eta(4)-P -4){Cr(CO)(5)}(4)] (3a). In the corresponding reaction with [CpMn-(CO) (2)THF] no P-4 takes part, and [(Cp '' RhCO)(CpMnCO)(mu-CO)(2)] (4) is formed. An X-ray structure determination of [Cp(x)Rh(Co)(eta(1:1)-P-4 ){Cr(CO)(5)}(4)] (1) and [Cp'Rh(eta(4)-P-4)-(Cr(CO)(5))(4)] (3a) indic ates a stepwise (PP) bond cleavage as the transformation pathway from the P-4 tetrahedron to the cyclo-P-4 ligand by passing a bicyclotetrap hosphane. In the cyclo-P-4 ligand complex 3a all P atoms are able to c oordinate to [Cr(CO)(5)] groups. However, in [Cp '' Rh(eta(4)-P-4)(Cr( CO)(5))(3)] (2b) the additional tBu group at the Cp(x) ligand sterical ly influences the coordination behavior of the P atoms, and only three of them are able to coordinate to [Cr(CO)(5)] units. In these synthes es the [Cr(CO)(5)] moieties promote the reaction and stabilise interme diates along the reaction pathway. Variable-temperature P-31{H-1}-NMR measurements indicate for 2b the freezing of the Cp '' rotation at low temperature and reveals a Delta G(c)(not equal) (at the coalescence t emperature) of 36 kJ mol(-1). Surprisingly, in [(Cp '' RhCO)(CpMnCO)(m u-CO)(2)](Rh-Mn) (4) the Cp(x) ligands are cis-oriented whereas in [(C pRhCO)(CpMnCO)(mu-CO)(2)]-(Rh-Mn) a trans arrangement is observed. Th is indicates the unusual behavior of the Cp '' ligand as a ''rod'' and not as an ''enlarged disk'' like Cp in the crystal lattice of these compounds.