Transition metal complexes of 1,3-dihydrobenzo[c]tellurophene: synthesis, spectroscopy and crystal structures

Abstract

Reaction of 1,3-dihydrobenzo[c]tellurophene (L) with [Cu(MeCN)4]PF6 or AgBF4 yielded [CuL4]PF6 and [AgL4]BF4 respectively, which adopt distorted tetrahedral structures at the metal centre, with the tellurophene ligated via a Te-based lone pair, Cu–Te 2.587(2)–2.596(2) A; Ag–Te 2.7676(7)–2.8104(8) A. With palladium(II) and platinum(II) chlorides the neutral species [PdCl2L2] and [PtCl2L2] were formed readily. Infrared, 125Te-{1H} and 195Pt NMR spectroscopic studies showed that the former is the trans isomer, whereas the latter is the cis isomer. The 125Te-{1H} NMR spectra showed that in solution [RhCl3L3] is a mixture of mer and fac isomers in approximately 3∶2 ratio, whereas RuCl3 reacted with L in EtOH and hypophosphorous acid to give trans-[RuCl2L4] exclusively. The carbonyl derivatives fac-[MnCl(CO)3L2], [Mo(CO)5L], cis-[Mo(CO)4L2] and fac-[Mo(CO)3L3] have also been characterised through IR spectroscopy, 1H, 13C-{1H}, 55Mn, 95Mo and 125Te-{1H} NMR spectroscopy. For the molybdenum species δ(95Mo) and δ(125Te-{1H}) shift to high frequency with increasing substitution of the carbonyl ligands. The crystal structure of [Mo(CO)4L2] confirms the cis geometry and shows the Mo–CO bond lengths trans to L are about 0.10 A shorter than those trans to CO. The 1H NMR spectra of these complexes typically reveal AB quartets for the methylene protons, indicative of co-ordination through a Te-based lone pair in each case. The 125Te-{1H} NMR studies reveal a high frequency co-ordination shift except for the copper and silver species which show δ(125Te-{1H}) to low frequency of that for free L.