Co-ordination chemistry of the [Re(NO)2(PR3)2]+ fragment: crystallographic and computational studies†

Abstract

The cationic complexes [Re(NO)₂(PCy₃)₂]⁺ I⁺ and [Re(NO)₂(PR₃)₂L]⁺ [L = CO, R = Cy III⁺; L = C₆H₅CHO, R = Cy IV⁺; L = ONRe(NO)(PR₃)₂H, R = ⁱPr V⁺] have been synthesized and their structures determined. The counter ion in all cases is [B{3,5-(F₃C)₂C₆H₃}₄]^–. Complex I⁺ adopts the C_2v butterfly geometry, whereas III⁺ takes on a trigonal bipyramidal (TBP) co-ordination. In IV⁺ and V⁺ one of the nitrosyl ligands is strongly bent, and a shape analysis suggests that the co-ordination geometry of the [Re(NO)₂(PR₃)₂L]⁺ core is best described as tetragonal pyramidal (TP). A computational study based on density functional theory showed how steric effects due to the ligand L induce the NO bend, and subsequently lead to the change in co-ordination from TBP to TP. Examination of a series of model compounds [Re(NO)₂(PH₃)₂L]⁺ showed further how the π donor and acceptor properties of the ligand L are reflected in the P–Re–P and N–Re–N angles of the complexes.