Different Reductive Reactivities of SmCp2x(THF)n (Cpx = C5Me5 and C5H3tBu2) Samarocenes toward P2Ph4: THF Ring-Opening and Ligand-Exchange Pathways

The reduction of tetraphenyldiphosphine with two differently substituted samarocenes(II) proceeds via different pathways. With [SmCp*(2)(THF)(2)] (Cp* = eta(5)-C5Me5), the reaction had been known to result in the THF ring-opening product, [SmCp*(2)(O(CH2)(4)PPh2)], 3, owing to the instability of phosphido complex [SmCp*(2)(PPh2)] in the presence of THF. Complex 3 crystallizes from apolar solvents as dimeric or polymeric polymorph with butoxo-phosphine bridging ligands in both cases. In contrast, the phosphide [SmCp ''(2)(PPh2)] (Cp '' = eta(5)-1,3-(C5H3Bu2)-Bu-t), 5, is not prone to ring-opening owing to insufficient space in the Sm coordination sphere for a THF ligand. Product 5 is inevitably accompanied by homoleptic complex [SmCp ''(3)] 6 and dinuclear mixed-valent complex [(SmCp)-Cp-III ''(2)(mu-PPh2)(2)(SmCp)-Cp-II ''] 7 as the further products of redox transformations and ligand exchange The formation of 5-7 is rationalized by a sequence of initial coordination of one or two {(SmCp)-Cp-II ''(2)} fragments by P atoms and reductive elimination of PPh2 center dot or Cp ''center dot radicals. Further reaction with another equivalent of [SmCp ''(2)] results in the trapping the radicals and formation of all three products.