Group 6 metal carbonyl complexes of cyclo-(P 5 Ph 5 )

Group 6 metal (Cr, Mo, W) carbonyl complexes react with cyclo-(P 5 Ph 5 ) to afford the phosphorus-rich complexes [Cr(CO) 5 {cyclo-(P 5 Ph 5 )-κP 1 }] (1), [{Cr(CO) 5 } 2 {μ-cyclo-(P 5 Ph 5 )-κP 1 ,P 3 }] (2), [M(CO) 4 {cyclo-(P 5 Ph 5 )-κP 1 ,P 3 }] (with M=Cr (3), Mo (4), W (exo-5, endo-5)) depending on the reaction conditions. Complexes 1-5 were characterised by 31 P{ 1 H} NMR and IR spectroscopy, elemental analysis, and X-ray crystallography. The cyclopentaphosphane remains intact and acts as monodentate (1), bridging (2) or bidentate (3-5) ligand. Compounds exo-5 and endo-5 are configurational isomers and essentially differ in the orientations adopted by the phenyl rings attached to the uncoordinated phosphorus atoms. The 31 P{ 1 H} NMR spectra show five multiplets for an ABCDE spin system. Theoretical calculations showed that exo-5 and endo-5 are practically isoenergetic, which is in good agreement with the observed equilibrium in solution between exo-5 and endo-5. The thermal properties of the complexes have also been evaluated.