Tin(ii) fluoridevs.tin(ii) chloride – a comparison of their coordination chemistry with neutral ligands

Abstract

Reaction of SnF₂ in MeOH with the appropriate neutral N- or O-donor ligands produces [SnF(2,2′-bipy)]₂SnF₆, [SnF(1,10-phen)]₂SnF₄ and [SnF₂(L)] L = Me₃PO, dmso or pyNO). The X-ray structures of [SnF(2,2′-bipy)]₂SnF₆, [SnF(1,10-phen)]₂SnF₄ and [SnF₂(dmso)], reveal trigonal pyramidal Sn(II) cores with longer fluorine bridges completing distorted 5- or 6-coordination. Attempts to prepare SnF₂ adducts with various phosphine or diphosphine ligands in MeCN failed, whilst in CH₂Cl₂ solution complex reactions involving the solvent occurred. The NHC, 1,3-(2,6-di-isopropylphenyl)imidazol-2-ylidene (IDiPP) and SnF₂ produced the imidazolium salt, [IDiPPH]SnF₃, the crystal structure of which revealed the first example of a discrete trifluorostannate(II) ion. In contrast, diphosphine complexes of tin(II) chloride formed readily, including [SnCl₂{Me₂P(CH₂)₂PMe₂}], [SnCl₂{o-C₆H₄(PMe₂)₂}], [SnCl₂{o-C₆H₄(PPh₂)₂}] and [(SnCl₂)₂(μ-Ph₂P(CH₂)₂PPh₂)], which were characterised by X-ray crystallography. The structures of [SnCl₂{Me₂P(CH₂)₂PMe₂}] and [SnCl₂{o-C₆H₄(PMe₂)₂}] reveal chloride-bridged dimers, but [SnCl₂{o-C₆H₄(PPh₂)₂}], although also dimeric, has very asymmetric diphosphine coordination best described as κ¹. The structures of [(SnCl₂)₂(μ-Ph₂P(CH₂)₂PPh₂)] and of [SnCl{o-C₆H₄(AsMe₂)₂}]SnCl₃ reveal trigonal pyramidal cores, but with longer Sn⋯Cl bridges affording polymeric structures. The synthesis of [SnCl₂(R₃EO)₂] (R = Ph, E = P or As; and R = Me, E = P) are also reported, along with the structure of [SnCl₂(Me₃PO)₂], which contains distorted tetragonal pyramidal Sn(II) coordination. X-ray structures are also reported for [(PMe₃)₂CH₂][SnCl₃]₂ and [Ph₂P(H)(CH₂)₂P(H)Ph₂][SnCl₃]₂, obtained as by-products from the attempts to synthesise phosphine complexes, as well as [(o-C₆H₄(PMe₂)₂CH₂]I₂. All complexes were characterised by microanalysis, IR and multinuclear NMR spectroscopy (¹H, ¹⁹F{¹H}, ³¹P{¹H } and, where solubility allowed, ¹¹⁹Sn). Comparisons are drawn with corresponding Sn(IV) and Ge(II) complexes.