Tin(II) fluoride vs. tin(II) chloride--a comparison of their coordination chemistry with neutral ligands

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 κ(1). 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 ((1)H, (19)F{(1)H}, (31)P{(1)H } and, where solubility allowed, (119)Sn). Comparisons are drawn with corresponding Sn(IV) and Ge(II) complexes.