“…More recently, we have described the synthesis of Z-arene-molybdenum complexes, such as [(Z-C 6 H 5 R)Mo(Z-C 3 H 5 ){Ph 2 PXHC(O)R 0 -k 2 P,O}]-[PF 6 ] (R ¼ H, Me; R 0 ¼ Ph, NPh 2 , Me; X ¼ N, C). 22,23 In these complexes, the P,O ligands act either as P-monodentate phosphine or as a P,O-chelate, whereas O-monocoordination, which may have been anticipated owing to the relatively hard nature of molybdenum vs. late transition metals, was not observed. Although ligands with carbonyl functions (ketones, [24][25][26] amides, 27,28 acids/esters 29,30 ) are known to coordinate readily to groups 5 and 6 metals, there has been no example reported, to the best of our knowledge, when a phosphine donor is also present in the ligand.…”