Substitution reactions of a heterodimetallic molybdenum-manganese complex

The reactions of [MoMn(μ-C₅H₄PPh₂)(CO)₇] 1 with phosphines and with isonitriles have been studied. Less bulky phosphines give derivatives of 1 of the type [MoMn(μ-C₅H₄PPh₂)(CO)₆L], which are monosubstituted at the manganese atom [L = PPh₂H 2a, PPh₂Me 2b, PPhMe₂ 2c or P(OMe)₃ 2f] whereas more bulky phosphines substitute only at the molybdenum atom (L = PPh₃ 3a). Phosphines of intermediate bulk give both types of derivative depending on the reaction conditions (L = PPh₂Et 2e or 3b, PPh₂CH=CH₂ 2d or 3c). Disubstituted derivatives, [MoMn(μ-C₅H₄PPh₂)(CO)₅L ₂] [L = PPh₂Me 4a, PPh₂CH=CH₂ 4b or P(OMe)₃ 4c], obtained by reaction of 1 with excess of the appropriate ligand, have one substituent on the manganese and one on the molybdenum atom. Isonitriles give derivatives [MoMn(μ-C₅H₄PPh₂)(CO)₆L] (L = CNCH₂Ph 2g or CNBu^t 2h) which are monosubstituted at the manganese atom but in a different position to the phosphine derivatives 2a-2f. Thermolysis of the diphenylphosphine derivative 2a gives [MoMn(μ-C₅H₄PPh₂)(μ-H)(μ-PPh ₂) (CO)₅] 5a and thermolysis of either one of the vinylphosphine derivatives 2d or 3c gives a complex [MoMn(μ-C₅H₄PPh₂)(μ-PPh ₂CH=CH₂)(CO)₅] 6 in which the vinylphosphine ligand is bonded through phosphorus to manganese and through the vinyl group to the molybdenum atom. Hydrogenation of 6 gives 3b in a reaction which involves a transfer of the co-ordination of the vinylphosphine phosphorus atom from manganese to molybdenum. Addition reactions of 6 with CO and P(OMe)₃ involve a similar transfer to give [MoMn(μ-C₅H₄PPh₂)(CO)₆(PPh ₂CH=CH₂)] 3c and [MoMn(μ-C₅H₄PPh₂)(CO)₅(PPh ₂CH=CH₂){P(OMe)₃}] 7 respectively. The structures of [MoMn(μ-C₅H₄PPh₂)(CO)₆(PPh ₂Et)] 3b and [MoMn(μ-C₅H₄PPh₂)(μ-H)(μ-PPh ₂) (CO)₅] 5a have been determined by X-ray analysis.