Fluoro-Germanium (IV) Cations with Neutral Co-Ligands—Synthesis, Properties and Comparison with Neutral GeF4 Adducts

The reaction of [GeF4L2], L = dmso (Me2SO), dmf (Me2NCHO), py (pyridine), pyNO (pyridine-N-oxide), OPPh3, OPMe3, with Me3SiO3SCF3 (TMSOTf) and monodentate ligands, L, in a 1:1:1 molar ratio in anhydrous CH2Cl2 formed the monocations [GeF3L3][OTf]. These rare trifluoro-germanium (IV) cations were characterised by microanalysis, IR, 1H, 19F{1H} and, where appropriate, 31P{1H} NMR spectroscopy. The 19F{1H} NMR data show that in CH3NO2 solution the complexes exist as a mixture of mer and fac isomers, with the mer isomer invariably having the higher abundance. The X-ray structure of mer-[GeF3(OPPh3)3][OTf] is also reported. The attempts to remove a second fluoride using a further equivalent of TMSOTf and L were mostly unsuccessful, although a mixture of [GeF2(OAsPh3)4][OTf]2 and [GeF3(OAsPh3)3][OTf] was obtained using excess TMSOTf and OAsPh3. The reaction of [GeF4(MeCN)2] with TMSOTf in CH2Cl2 solution, followed by the addition of 2,2′:6′,2”-terpyridine (terpy) formed mer-[GeF3(terpy)][OTf], whilst a similar reaction with 1,4,7-trimethyl-1,4,7-triazacyclononane (Me3-tacn) in MeCN solution produced fac-[GeF3(Me3-tacn)][OTf]. Dicationic complexes bearing the GeF22+ fragment were isolated using the tetra-aza macrocycles, 1,4,7,10-tetramethyl-1,4,7,10-tetra-azacyclododecane (Me4-cyclen) and 1,4,8,11-tetramethyl-1,4,8,11-tetra-azacyclotetradecane (Me4-cyclam), which reacted with [GeF4(MeCN)2] and two equivalents of TMSOTf to cleanly form the dicationic difluoride salts, cis-[GeF2(Me4-cyclen)][OTf]2 and trans-[GeF2(Me4-cyclam)][OTf]2. The 19F{1H} NMR spectroscopy shows that in CH3NO2 solution there are four stereoisomers present for trans-[GeF2(Me4-cyclam)][OTf]2, whereas the smaller ring-size of Me4-cyclen accounts for the formation of only cis-[GeF2(Me4-cyclen)][OTf], and is confirmed crystallographically. New spectroscopic data are also reported for [GeF4(L)2] (L = dmso, dmf and pyNO). Density functional theory calculations were used to probe the effect on the bonding as fluoride ligands were sequentially removed from the germanium centre in the OPMe3 complexes.

Tin(IV) fluoride complexes with neutral phosphine coordination and comparisons with hard N- and O-donor ligands

The reactions of trans-[SnF₄(PMe₃)₂] with one, two or three equivalents of Me₃SiO₃SCF₃ (TMSOTF), respectively, in anhydrous CH₂Cl₂ form six-coordinate [SnF_4-n(PMe₃)₂(OTf)_n] (n = 1-3), which have been characterised by microanalysis, IR and multinuclear NMR (¹H, ¹⁹F{¹H}, ³¹P{¹H} and ¹¹⁹Sn) spectroscopy. The crystal structure of [SnF₃(PMe₃)₂(OTf)] reveals the three fluorines are in a mer-arrangement with mutually trans PMe₃ ligands. The multinuclear NMR spectra confirm this structure is retained in solution, and show that [SnF₂(PMe₃)₂(OTf)₂] has trans-phosphines, while [SnF(PMe₃)₂(OTf)₃] has trans PMe₃ groups and hence mer-triflate ligands. The [SnF_4-n(PMe₃)₂(OTf)_n] are unstable in solution and the decomposition products include [Me₃PF]⁺ and the tin(II) complexes [Sn(PMe₃)₂(OTf)₂] and [Sn₃F₅(OTf)], both of the latter identified by their crystal structures. The reaction of trans-[SnF₄(PⁱPr₃)₂] containing the bulkier phosphine, with one and two equivalents of TMSOTf produced unstable mono- and bis-triflates, which the NMR data also suggest contain weakly coordinated triflate, [SnF₃(PⁱPr₃)₂(OTf)] and [SnF₂(PⁱPr₃)₂(OTf)₂], again with axial phosphines, although some OTf dissociation from the former to give [SnF₃(PⁱPr₃)₂]⁺ may occur in solution at room temperature. The new phosphine complexes of SnF₄, trans-[SnF₄(PⁱPr₃)₂] and (cis) [SnF₄(κ²-triphos)] (triphos = CH₃C(CH₂PPh₂)₃) have also been fully characterised, including the crystal structure of [SnF₄(κ²-triphos)]. Attempts to promote P₃-coordination by further treatment of this complex with TMSOTf were unsuccessful. The [SnF₄(L)₂] (L = dmso, py, pyNO, DMF, OPPh₃) complexes, which exist as mixtures of cis and trans isomers, react with one equivalent of TMSOTf, followed by addition of one equivalent of L, to form the ionic [SnF₃(L)₃][OTf] complexes, which were characterised by microanalysis, IR and multinuclear NMR spectroscopy. In nitromethane solution they are a mixture of mer and fac isomers based upon multinuclear NMR data (¹H, ¹⁹F{¹H}, ¹¹⁹Sn). Reaction of [SnF₄(OPPh₃)₂] with two equivalents of TMSOTf and further OPPh₃ produced [SnF₂(OPPh₃)₄][OTf]₂, which is a mixture of cis and trans isomers in solution. The crystal structure of [SnF₂(OPPh₃)₄][OTf]₂ confirms the trans isomer in the solid state, with the triflate ionic. These complexes are rare examples of fluorotin(IV) cations with neutral monodentate ligands.

Neutral and cationic phosphine and arsine complexes of tin(iv) halides: synthesis, properties, structures and anion influence

The reaction of trans-[SnCl₄(PR₃)₂] (R = Me or Et) with trimethylsilyltriflate (TMSOTf) in CH₂Cl₂ solution substitutes one chloride to form [SnCl₃(PR₃)₂(OTf)]; addition of excess TMSOTf does not substitute further chlorides. The complexes have been fully characterised by microanalysis, IR and multinuclear NMR (¹H, ¹³C{¹H}, ¹⁹F{¹H}, ³¹P{¹H}, ¹¹⁹Sn) spectroscopy. The crystal structure of [SnCl₃(PMe₃)₂(OTf)] revealed mer-chlorines and trans-phosphines. In contrast, trans-[SnBr₄(PR₃)₂], [SnCl₄{Et₂P(CH₂)₂PEt₂}], [SnCl₄{o-C₆H₄(PMe₂)₂}] and [SnCl₄{o-C₆H₄(AsMe₂)₂}] did not react with TMSOTf in CH₂Cl₂ solution even after 3 days. The arsine complexes, [SnX₄(AsEt₃)₂] (X = Cl, Br), were confirmed as trans-isomers by similar spectroscopic and structural studies, while attempts to isolate [SnI₄(AsEt₃)₂] were unsuccessful and reaction of SnX₄ with SbR₃ (R = Et, ⁱPr) resulted in reduction to SnX₂ and formation of R₃SbX₂. trans-[SnCl₄(AsEt₃)₂] is converted by TMSOTf into [SnCl₃(AsEt₃)₂(OTf)], whose X-ray structure reveals the same geometry found in the phosphine analogues, with the triflate coordinated. The salts, [SnCl₃(PEt₃)₂][AlCl₄] and [SnCl₂(PEt₃)₂][AlCl₄]₂ were made by treatment of [SnCl₄(PEt₃)₂] with one and two mol. equivalents, respectively, of AlCl₃ in anhydrous CH₂Cl₂, whereas reaction of [SnCl₄(AsEt₃)₂] with AlCl₃ produced a mixture including Et₃AsCl₂ and [Et₃AsCl][Sn(AsEt₃)Cl₅] (the latter identified crystallographically). In contrast, using Na[BAr^F] (BAr^F = [B{3,5-(CF₃)₂C₆H₃}₄]^-) produced [SnCl₃(PEt₃)₂][BAr^F] and also allowed clean isolation of the arsine analogue, [SnCl₃(AsEt₃)₂][BAr^F]. [SnCl₄{o-C₆H₄(PMe₂)₂}] also reacts with AlCl₃ in CH₂Cl₂ to form [SnCl₃{o-C₆H₄(PMe₂)₂}][AlCl₄] and [SnCl₂{o-C₆H₄(PMe₂)₂}][AlCl₄]₂. Multinuclear NMR spectroscopy on the [AlCl₄]^- salts show that δ³¹P and δ¹¹⁹Sn move progressively to high frequency on conversion from the neutral complex to the mono- and the di-cations, whilst ¹J(¹¹⁹Sn-³¹P) follow the trend: [SnCl₃{o-C₆H₄(PMe₂)₂}]⁺ > [SnCl₄{o-C₆H₄(PMe₂)₂}] > [SnCl₂{o-C₆H₄(PMe₂)₂}]²⁺. DFT studies on selected complexes show only small changes in ligand geometries and bond lengths between the halide and triflate complexes, consistent with the X-ray crystallographic data reported and the HOMO and LUMO energies are relatively unperturbed upon the introduction of (coordinated) triflate, whereas the energies of both are ca. 4 eV lower in the cationic species and reveal significant hybridisation across the pnictine ligands.

Synthesis, characterization and mass-spectrometric analysis of [LSn(IV)F4−x]x+ salts [L = tris ((1-ethyl-benzoimidazol-2-yl)methyl)amine, x = 1–4]

A series of cationic tin fluoride complexes has been synthesized by successive fluoride abstraction from SnF₄ with TMSOTf in the presence of the tetradentate nitrogen donor BIMEt₃.

Liquid coordination complexes of Lewis acidic metal chlorides: Lewis acidity and insights into speciation

Lewis acidic, liquid coordination complexes (LCCs) were synthesised from metal chlorides and trioctylphosphine or trioctylphosphine oxide.

Phosphine complexes of lone pair bearing Lewis acceptors

An overview of the synthesis, structures and reaction chemistry of coordination complexes featuring an acceptor with at least one lone pair and at least one phosphine donor is presented. One or more examples of complexes have been structurally-characterized for the majority of p-block elements but few are known for most elements. The unusual condition of a p-block element centre accommodating a lone pair of electrons and offering a low energy LUMO gives the element centre the potential to behave as both a Lewis acid and a Lewis Base. The structural diversity and reactivity of the phosphine complexes highlights new directions in main group chemistry and by comparison with transition metal coordination chemistry, the featured complexes demonstrate significant configurational and stereochemical flexibility. Ligand exchange, oxidation and reduction chemistry at the lone pair bearing acceptor centre reveals unusual reactivity and an interesting class of ligands and inorganic reagents, with new possibilities for catalysis or small molecule activation.

Coordination complexes of bismuth triflates with tetrahydrofuran and diphosphine ligands

The reaction of CH3OSO2CF3 (MeOTf) with BiBr3 in tetrahydrofuran (THF) yields (THF)2BiBr2(OTf) (1), which is converted to (dmpe)BiBr2(OTf) (2Br) upon displacement of the THF ligands with bis(dimethylphosphino)ethane (dmpe). The chloride derivatives (dmpe)BiCl2(OTf) (2Cl) and (dmpe)BiCl(OTf)2 (3) are obtained from the reaction of BiCl3 and dmpe with 1 and 2 equiv of Me3SiOSO2CF3 (TMSOTf), respectively. The complexes readily decompose in solution to give elemental bismuth and a mixture of products. The solid-state structures reveal dimeric units bridged by both triflate O-S-O interactions and weak Bi-X-Bi interactions (X = Cl, Br). Comparison of the solid-state structures illustrates that both cis and trans configurations of halides are possible in complexes of the form L2BiX2(OTf), depending upon the denticity of the ligand. The experimentally observed configurations are consistent with minima calculated at the MP2 level for the triflate-free cations in the gas phase. Examination of the MP2-calculated electronic structure of 3 reveals the presence of low-lying π-type orbitals that may result in Z-type ligand activity. However, the attempted coordination of 3 with the electron-rich metal center in K2PdCl4, via metal-to-ligand back-donation, leads instead to halide abstraction, giving [(dmpe)2Pd][(CH3CN)2Bi2Cl6(OTf)2] (8). The anion in 8 consists of two octahedral bismuth environments bridged along one edge by two triflate anions. The results illustrate new coordination chemistry for bismuth.