Synthesis, structural characterisation and reactivity of molybdenum half-sandwich complexes containing keto- and amido-phosphines

The keto-functionalised N-pyrrolyl phosphine ligand PPh2NC4H3{C(O)CH3-2}. L-1 reacts with [MoCl(CO)(3)(eta(5)-C5R5)] (R = H, Me) to give [MOCl(CO)(2)(L-1-kappa(1)P)(eta(5)-C5R5)] (R = H 1a; Me 1b). The phosphine ligands PPh2CH2C(O)Ph (L-2) and Pph(2)CH(2)C(O)NPh2 (L-3) react with [MoCl(CO)(3)(eta(5)-C5R5)] in an analogous manner to give the compounds [MoCl(CO)(2)(L-kappa(1)P)(eta(5)-C5R5)] (L = L-2, R=H 2a, Me 2b; L=L-3, R = H 3a, Me 3b). Compounds 1-3 react with AgBF4 to give [MO(CO)2(L-kappa(2) P,O)(eta(5) -C5R5)]BF4 (L = L-1, R = H 4a, Me 4b; L = L-2, R = H 5a, Me 5b; L = L-3, R = H 6a, Me 6b) following displacement of chloride. The X-ray crystal structure of 4a revealed a lengthening of both Mo-P and C=O bonds on co-ordination of the keto group. The lability of the co-ordinated keto or amido group has been assessed by addition of a range of phosphines to compounds 4-6. Compound 4a reacts with PMe3, PMe2Ph and PMePh2 to give [Mo(CO)(2)(L-1-kappa(1)P)(L)(eta(5)-C5H5)]BF4 (L = PMe3 7a; PMe2Ph 7b; PMePh2 7c) but does not react with PPh3, 5a reacts with PMe2Ph, PMePh2 and PPh3 to give [MO(CO)(2)(L-2-kappa(1)P)(L)(eta(5)- C5H5)]BF4 (L = PMe2Ph 8b; PMePh2 8c; PPh3 8d), and 6a reacts with PMe3, PMe2Ph, PMePh2 and PPh3 to give [Mo(CO)(2)(L-3- kappa(1)P)(L)(eta(5) -C5H5)]BF4 (L = PMe3 10a; PMe2Ph 10b; PMePh2 10c; PPh3 10d). No reaction was observed for the pentamethylcyclopentadienyl compounds 4b-6b with PMe3, PMe2Ph, PMePh2 or PPh3. These results are consistent with the displacement of the co-ordinated oxygen atom being influenced by the steric properties of the P,O-ligand, with PPh3 displacing the keto group from L 2 but not from the bulkier Lt. In the reaction of [Mo(CO)(2)(L-2-kappa(2)P,O)(eta(5) -C5H5)]BF4 (5a) with PMe3 the phosphine does not displace the keto group, instead it acts as a base, with the only observed molybdenum-containing product being the enolate compound [Mo(CO)(2){PPh2CH=C(O)Ph-kappa(2)P,O}(eta(5) -C5H5)]9, Compound 9 can also be formed from the reaction of 2a with BuLi or NEt3, and a single crystal X-ray analysis has confirmed the enolate structure. (C) 2002 Elsevier Science B.V. All rights reserved.