P n ‐Liganden mit maximaler Elektronendonorfähigkeit, 7. Dreikomponentenreaktion von P 4 ‐Phosphor mit [Cp x Rh(CO) 2 ] in Gegenwart von [Cr(CO) 5 THF] oder [CpMn(CO) 2 THF]. – Eine Methode zum Studium des Transformationsweges vom P 4 ‐Tetraeder zum planaren cyclo ‐P 4 ‐Liganden

P n Ligands with Maximum Electron‐Donor Capacity, 7. – Three‐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 Herrn Professor Gerhard Fritz zum 75. Geburtstag gewidmet. The reaction of P 4 with [Cp x Rh(CO) 2 ] (Cp x = Cp′, Cp′′; Cp′ = η 5 ‐C 5 H 4 t Bu, Cp′′ = η 5 ‐C 5 H 3 t Bu 2 ‐1,3) in the presence of [Cr(CO) 5 THF] leads to [Cp x Rh(CO)(η 1:1 ‐P 4 ){Cr(CO) 5 } 4 ] ( 1a, b ), [Cp′′Rh(η 4 ‐P 4 ){Cr(CO) 5 } 3 ] ( 2b ), and [Cp′Rh(η 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)(μ‐CO) 2 ] ( 4 ) is formed. An X‐ray structure determination of [Cp x Rh(CO)(η 1:1 ‐P 4 ){Cr(CO) 5 } 4 ] ( 1 ) and [Cp′Rh(η 4 ‐P 4 )‐{Cr(CO) 5 } 4 ] ( 3a ) indicates a stepwise (PP) bond cleavage as the transformation pathway from the P 4 tetrahedron to the cyclo ‐P 4 ligand by passing a bicyclotetraphosphane. In the cyclo ‐P 4 ligand complex 3a all P atoms are able to coordinate to [Cr(CO) 5 ] groups. However, in [Cp′′Rh(η 4 ‐P 4 ){Cr(CO) 5 } 3 ] ( 2b ) the additional t Bu group at the Cp x ligand sterically influences the coordination behavior of the P atoms, and only three of them are able to coordinate to [Cr(CO) 5 ] units. In these syntheses the [Cr(CO) 5 ] moieties promote the reaction and stabilise intermediates along the reaction pathway. Variable‐temperature 31 P{ 1 H}‐NMR measurements indicate for 2b the freezing of the Cp′′ rotation at low temperature and reveals a Δ G   ≠ c(at the coalescence temperature) of 36 kJ mol −1 . Surprisingly, in [(Cp′′RhCO)(CpMnCO)(μ‐CO) 2 ]‐( Rh‐Mn ) ( 4 ) the Cp x ligands are cis ‐oriented whereas in [(Cp*RhCO)(CpMnCO)(μ‐CO) 2 ]( Rh‐Mn ) a trans arrangement is observed. This 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.