A Monometallic Rh(III) Tetraphosphine Complex: Reductive Activation of CH₂Cl₂ and Selective Meso to Racemic Tetraphosphine Ligand Isomerization

The first Rh complex with an η4-coordinated rac-et,ph-P4 ligand [et,ph-P4 = (Et2PCH2CH2)(Ph)PCH2P(Ph)(CH2CH2PEt2)] has been synthesized by reacting [Rh(nbd)2]BF4 with meso- or rac-et,ph-P4 in dichloromethane. The reaction occurs fairly rapidly at room temperature to form [rac-RhCl2(η4-et,ph-P4)]+ in high yields, regardless of whether one starts with mixed or even pure meso-et,ph-P4 ligand. This unusual and highly selective metal assisted isomerization of the meso-et,ph-P4 ligand to its rac-et,ph-P4 disastereomer will be discussed.