Antimony β-diketonates and alkoxide/β-diketonates: remarkable formation of a 3,4-dihydro-2H-pyran ring by coupling of 1,1,1,5,5,5-hexafluoro-2,4-pentanedione ligands

Homoleptic antimony(III) β-diketonates Sb(thd)3 (Hthd = 2,2,6,6-tetramethyl-3,5-heptanedione) and Sb(fod)3 (Hfod = 2,2-dimethyl-6,6,7,7,8,8,8-heptafluoro-3,5-heptanedione) have been synthesised from Sb(OEt)3 and three equivalents of the appropriate ligand. Both compounds have been characterised crystallographically and are monomeric with pseudo seven-coordination at antimony, where each ligand chelates the metal in an anisobidentate manner. Attempts to prepare Sb(hfac)3 (Hhfac = 1,1,1,5,5,5-hexafluoro-2,4-pentanedione) by the same route generated a compound of formula [(EtO)Sb(hfac)2]2 but in which the two β-diketonate ligands have combined to produce a functionalised 3,4-dihydro-2H-pyran ring; the dimer arises from a bridging ethoxy group. Heteroleptic (EtO)Sb(thd)2 has also been synthesised and crystallographically characterised as a monomeric structure in which the ethoxy group is terminal. In addition, Sb(OEt)2(fod) and Sb(OEt)4(thd) have been prepared for comparison.