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

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 C2v 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.