Cationic diphosphaferrocene gallium dichloride complexes

Abstract

The octaethyldiphosphaferrocene ligand 1 reacts with gallium trichloride at room temperature to afford the cationic complex [(1)GaCl₂]⁺[GaCl₄]⁻. To definitely establish the formula of 2, which could not be crystallized, the synthesis of the corresponding complex incorporating the octa(n-propyl)diphosphaferrocene ligand 6 was carried out. Preparation of ligand 6 was achieved via a three-step sequence. In a first step the tetra(n-propyl)zirconacyclopentadiene 3 was synthesized from dichlorozirconocene, 4-octyne and butyllithium. Reaction of 3 with 1 equiv. of PCl₃ affords the 1-P-chloro-2,3,4,5-tetra(n-propyl)phosphole 4, which is subsequently converted to the corresponding tetra(n-propyl)phospholide anion 5 through reaction with lithium metal. Reaction of 5 with half an equivalent of FeCl₂ yields ligand 6. The formulation of 6 was ascertained by an X-ray crystal structure, which reveals that the ligand adopts a C_i conformation. Reaction of an equimolar amount of 6 with GaCl₃ affords the [(6)GaCl₂]⁺[GaCl₄]⁻ complex 7, which was successfully characterized by X-ray crystallography. In 7, the diphosphaferrocene ligand acts as a chelate and the overall geometry around gallium is tetrahedral. Theoretical calculations carried out using the BP86 functional indicate that the bonding of the diphosphaferrocene ligand to the [GaCl₂]⁺ fragment involves the lone pairs on the phosphorus atoms and a contribution of the P–Fe bond.