LAUSR

Abstract Six rhenium(I) complexes are structurally compared, with regards to steric and electronic influences induced by the different β-diketone (benzoylacetone – Benzac, trifluoroacetylacetone – Tfaa and hexafluoroacetylacetone – Hfaa) and phosphine ligands (cyclohexyldiphenyl phosphine – PPh2Cy and dicyclohexylphenyl phosphine – PPhCy2). The complexes fac-[Re(Benzac)(CO)3(PPh2Cy)] (2), fac-[Re(Benzac)(CO)3(PPhCy2)] (3), fac-[Re(Tfaa)(CO)3(PPh2Cy)] (5), fac-[Re(Tfaa)(CO)3(PPhCy2)] (6), fac-[Re(Hfaa)(CO)3(PPh2Cy)] (8) and fac-[Re(Hfaa)(CO)3(PPhCy2)] (9) were synthesized by using the ‘2 + 1’ mixed ligand approach and characterized by means of IR, UV–Vis, 1H, 13C and 31P NMR and also X-ray diffraction, clearly showing the increase in the carbonyl stretching frequencies and downfield shifts in the 31P NMR as the fluoro atoms on the ligand backbone increases. The Tolman angles for the coordinated phosphine ligands are: 2 = 134.77°; 3 molecule A = 146.81°; 5 = 134.46°; 6 = 146.05°; 8 = 136.68° and 9 = 146.22°, illustrating the change in steric bulk as the cyclohexyl ligands on the phosphine ligands increase. A direct link is noted between the Re–P distances (2.4906(6) A for 2, 2.5213(17) A for 3 molecule A, 2.4865(16) A for 5, 2.5372(15) A for 6, 2.4906(14) A for 8 and 2.5365(16) A for 9), O,O′-bidentate ligand bite angles, O4–Re–O5, (85.12(6)° for 2, 83.34(13)° for 3 molecule A, 84.91(12)° for 5, 83.53(12)° for 6, 84.54(11)° for 8 and 83.7(2)° for 9) and the calculated dihedral angles (3.677(1)° for 2, 12.521(1)° for 3 molecule A, 1.489(7)° for 5, 12.463(11)° for 6, 2.940(7)° for 8 and 11.747(6)° for 9). The dihedral angle is calculated between the equatorial plane (Re1, C1, O1, C2, O2, O4, C5, C6, C7, O5) and the plane through Re1, O4, C5, C6, C7, O5. Dihedral angles of approximately four times larger are observed in complexes with coordinated PPhCy2 ligands compared to the PPh2Cy containing analogues, indicating the steric effect induced on the bidentate ligand by the extra cyclohexyl substituent on the PPhCy2 ligand.