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) Å; Ag–Te 2.7676(7)–2.8104(8) Å. 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 Å 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.