Preparation and properties of cyclic and open-chain Sb/N-donor ligands

Abstract

The preparations of both open-chain and cyclic mixed-donor Sb/N ligands, MeN(CH₂-2-C₆H₄)₂SbMe (1), MeN(CH₂-2-C₆H₄SbMe₂)₂ (2), CH₂{CH₂N(Me)CH₂-2-C₆H₄SbMe₂}₂ (3) and CH₂{CH₂N(Me)CH₂-2-C₆H₄}₂SbMe (4), are described via reaction of chlorostibines with dilithio-reagents, and their spectroscopic properties established. Air-stable stibonium derivatives of (3) and (4) have been isolated by treatment of the compounds with excess MeI, which leads to quaternisation at the Sb atoms exclusively. A crystal structure of a bis(stibonium) derivative of (3), [CH₂{CH₂N(Me)CH₂-2-C₆H₄SbMe₃}₂]I₂, reveals hypervalency at Sb through long-range Sb⋯N interactions (ca. 2.87 Å), giving pseudo-five-membered rings fused to the aromatic rings, and distorted trigonal bipyramidal coordination at Sb. The coordinating properties of compounds (1) to (4) have been investigated through their reactions with Cu(I), Mn(I), Mo(0) and Pt(IV) reagents, and for (1) and (4) by reaction with Fe(0), giving [Fe(CO)₄(L)]. The spectroscopic data (IR, ¹H, ¹³C{¹H}, ⁵⁵Mn, ⁶³Cu, ⁹⁵Mo and ¹⁹⁵Pt NMR), mass spectrometry and microanalyses for this series of complexes confirm that coordination occurs via the Sb donor atoms in all cases, with N-coordination only present in fac-[Mn(CO)₃(2)](CF₃SO₃). Crystal structures of [Cu(2)₂]BF₄, [Mo(CO)₄(2)] and [PtMe₃I(2)] confirm the coordination modes, showing (2) functioning as a wide-angle bidentate distibine. The structures also show the amine N-donor atoms in the complexes are involved in a hypervalent Sb⋯N interaction (ca. 3.0 Å) with one of the coordinated Sb atoms in each ligand, leading to significant differences in the conformations of the carbon backbones linking the Sb and N atoms. Reaction of Na₃[RhCl₆]·12H₂O with one mol equiv. of (2), (3) or (4) leads to the bis-ligand complex [RhCl₂(2)₂]Cl and the 1 : 1 Rh : L complexes [RhCl₂(3)]Cl and [RhCl₃(4)], both of which involve coordination via the Sb and N donor atoms.