Synthesis and coordination chemistry of hybrid polydentate and halide-substituted stibines and bismuthines

Abstract

Halostibines and halobismuthines EMenX3-n (E = Sb, Bi; X = Cl, Br; n = 1, 2) display both Lewis acidic and Lewis basic characteristics. A series of adducts with neutral N- and O-donor ligands, [EMeX2(L)] (L = 2,2’-bipyridine, 1,10-phenanthroline, tetramethylethylenediamine) and [SbMeX2(L)2] (L = Ph3PO, Me3PO) were isolated and characterised by X-ray crystallography, 1H (and where appropriate 31P{1H}) NMR spectroscopy and microanalysis. Each complex is monomeric, displaying a distorted square pyramidal geometry around E, with two basal cis halides and the Me group apical. Combination of EMe2X with neutral ligands results in rearrangement at E to yield [EMeX2(L)] or [SbMeX2(L)2] once again as the isolable products. Reaction of SbMenBr3-n (n = 1, 2) with transition metal acceptors gives complexes in which the halostibines behave as Lewis bases. Examination of trends in the crystallographic and spectroscopic data of [M(CO)5(SbMenBr3-n)] (M = Cr, W; n = 1-3) from this work and the literature concluded that the halostibines have a significant ?-acceptor ability, which increases with increased halide substitution. Other transition metal complexes with L = SbMe2Br, [CpFe(CO)2(L)][BF4], [CpFe(CO)(L)2]Br (Cp = cyclopentadienyl) and [Mn(CO)6-n(L)n][CF3SO3] (n = 1, 3) were isolated and contain hypervalent, Sb···O, Sb···F or Sb···Br contacts between ions. Reaction of BiMe2Br with transition metal acceptors results in rearrangement at Bi; the only bismuthine complexes isolated contained the BiMe3 ligand.

The hybrid distibine S(CH2-2-C6H4SbMe2)2 and its methiodide [S(CH2-2-C6H4SbMe3)2][I]2 were synthesised and the X-ray structure of the latter determined. Systematic investigations into transition metal complexes of this and other hybrid distibine ligands were undertaken. These ligands coordinate in a bidentate bridging mode in the 1:2 complexes [{CpFe(CO)2}2(L)][BF4] (L = O{(CH2)2SbR2}2 (R = Me, Ph), MeN(CH2-2-C6H4SbMe2)2, S(CH2-2-C6H4SbMe2)2) and [{M(CO)5}2(L)] (M = Cr, W; L = O{(CH2)2SbR2}2 (R = Me, Ph)), a bidentate chelating mode in [M(CO)4(L)] (M = Cr, W; L = O{(CH2)2SbMe2}2, MeN(CH2-2-C6H4SbMe2)2) or a tridentate mode in [M(CO)3(S(CH2-2-C6H4SbMe2)2)] (M = Cr, Mo) and [Mn(CO)3(L)] [CF3SO3] (L = MeN(CH2-2-C6H4SbMe2)2, S(CH2-2-C6H4SbMe2)2). In the latter examples the central hetero-atom of the ligand is coordinated to the transition metal centre. In those cases where it is not, hypervalent interactions between this hetero-atom and one or both coordinated Sb atoms are sometimes, but not always, observed. Comparisons have been drawn with the chemistry of the corresponding hybrid dibismuthine ligands. The hybrid tristibine ligand N(CH2-2-C6H4SbMe2)3 was synthesised and preliminary investigations of its coordination chemistry carried out. It acts as a tridentate ligand via the three Sb donors in [Mn(CO)3(L)][CF3SO3] and [Cu4Br4(L)2], with the ligand fixed in a propeller-like conformation. In the latter, a Cu2Br4 core with a short Cu···Cu distance is observed. [Cu(L)] [BF4] was isolated, in which tetradentate coordination of the ligand has been proposed.

Transition metal complexes were characterised by 1H and 13C{1H} NMR spectroscopy and microanalysis, and where appropriate infrared and 55Mn or 63Cu NMR spectroscopies and mass spectrometry. The majority of these complexes have also been structurally characterised by single crystal X-ray diffraction.

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ORCID for Gillian Reid: orcid.org/0000-0001-5349-3468

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