Pyramidal Dicationic Ge(II) Complexes with Homoleptic Neutral Pnictine Coordination: A Combined Experimental and Density Functional Theory Study

Synthesis, spectroscopic and structural properties of Sn(II) and Pb(II) triflate complexes with soft phosphine and arsine coordination

Reaction of the divalent M(OTf)₂ (M = Sn, Pb; OTf = CF₃SO₃) with soft phosphine and arsine ligands, L, where L = o-C₆H₄(ER₂)₂ (E = P, R = Me or Ph; E = As, R = Me), MeC(CH₂ER₂)₃ (E = P, R = Ph; E = As, R = Me), PhP(CH₂CH₂PPh₂)₂ or P(CH₂CH₂PPh₂)₃, affords complexes of stoichiometry M(L)(OTf)₂ as white powders, which have been characterised via elemental analysis, ¹H, ¹⁹F{¹H}, ³¹P{¹H} and ¹¹⁹Sn NMR spectroscopy, with the expected ³¹P-¹¹⁹Sn and ³¹P-²⁰⁷Pb couplings clearly evident. The crystal structures of nine of these pnictine complexes are reported, in each case revealing retention of one or both OTf anions, which gives rise to a diverse range of coordination environments including monomers, as well as varying degrees of oligomerisation to form weakly associated (OTf-bridged) dimers, trimers and polymers. ¹⁹F{¹H} NMR spectra indicate that the OTf is essentially anionic (dissociated) in solution. Anion metathesis of [M(OTf)₂{MeC(CH₂PPh₂)₃}] with Na[BAr^F] (BAr^F = B{3,5-(CF₃)₂C₆H₃}₄) yields the corresponding [M{MeC(CH₂PPh₂)₃}][BAr^F]₂ salts, the crystal structures of all three (M = Ge, Sn, Pb) reveal pyramidal dications with discrete [BAr^F]^- anions providing charge balance. Density functional theory (DFT) calculations on these [M{MeC(CH₂PPh₂)₃}]²⁺ (M = Ge, Sn, Pb) dications using the B3LYP-D3 functional show the presence of a directional lone pair, which is a mixture of valence s and p_z character, with the valence p-orbital character decreasing down group 14. Natural bond orbital (NBO) analysis also shows that the natural charge at the metal centre increases and the charge on the P centre decreases upon going down group 14.

Structural Diversity in Divalent Group 14 Triflate Complexes Involving Endocyclic Thia-Macrocyclic Coordination

A highly unusual series of M(II) (M = Ge, Sn, Pb) complexes with endocyclic thioether macrocyclic coordination and with coordination numbers ranging from three to nine have been prepared by the reaction of [9]aneS₃ (1,4,7-trithiacyclononane), [12]aneS₄ (1,4,7,10-tetrathiacyclododecane), or [24]aneS₈ (1,4,7,10,13,16,19,22-octathiacyclotetracosane) with M(OTf)₂ (M = Sn and Pb; OTf = CF₃SO₃^-) or with GeCl₂·dioxane and 2 mol equiv of TMSOTf (Me₃SiO₃SCF₃) in a mixture of anhydrous CH₂Cl₂ and MeCN. The isolated bulk products are characterized by ¹H, ¹³C{¹H}, ¹⁹F{¹H}, and ¹¹⁹Sn{¹H} NMR and IR spectroscopy, high-resolution ESI⁺ MS, and microanalytical data. Crystal structures are also reported for [M(L)][OTf]₂ (M = Ge, Sn, Pb; L = [9]aneS₃, [12]aneS₄) and for [M([24]aneS₈)][OTf]₂ (M = Sn, Pb). In all cases, the ligand is bound in an endocyclic fashion, but the coordination environment and number are highly dependent on the group 14 ion, the macrocyclic ring size, and the number of S-donor atoms it presents. Solution NMR spectroscopic data suggest that the metal-macrocycle coordination is retained in solution but that the triflate anions are extensively dissociated on the NMR timescale. Density functional theory calculations on the [M([9]aneS₃)]²⁺ and [M([12]aneS₄)]²⁺ (M = Ge, Sn, Pb) dications reveal that the HOMO is centered on the group 14 atom as a directional "lone pair"; it also retains a significant amount of positive charge.

Self-assembly of [Sn(OPMe3)3(CF3SO3)2]6 metallocyclic Sn(ii) hexamer stacks with CF3-lined channel interiors

The preparation, spectroscopic and structural characterisation of a [Sn(OPMe3)3(CF3SO3)2]6, a Sn(ii)-based metallocyclic hexamer, containing hydrophobic CF3-lined 8.0 Å diameter channels is reported.

Neutral and cationic germanium(IV) fluoride complexes with phosphine coordination - synthesis, spectroscopy and structures

The neutral complexes trans-[GeF₄(PⁱPr₃)₂] and [GeF₄(κ²-L)] (L = CH₃C(CH₂PPh₂)₃ or P(CH₂CH₂PPh₂)₃) are obtained from [GeF₄(MeCN)₂] and the ligand in CH₂Cl₂. Treatment of [GeF₄(PMe₃)₂] with n equivalents of TMSOTf (Me₃SiO₃SCF₃) leads to formation of the series [GeF_4-n(PMe₃)₂(OTf)_n] (n = 1, 2, 3), each of which contains six-coordinate Ge(IV) with trans PMe₃ ligands and X-ray structural data confirm that the OTf groups interact with Ge(IV) to varying degrees. Unexpectedly, [GeF₃(PMe₃)₂(OTf)] undergoes reductive defluorination in solution, forming the Ge(II) complex, [Ge(PMe₃)₃][OTf]₂ (and [FPMe₃]⁺). The bulkier PⁱPr₃ leads to formation of the ionic [GeF₃(ⁱPr₃P)₂][OTf], containing a [GeF₃(ⁱPr₃P)₂]⁺ cation. [GeF₄{o-C₆H₄(PMe₂)₂}], containing the cis-chelating diphosphine, also reacts with n equivalents of TMSOTf to generate [GeF_4-n{o-C₆H₄(PMe₂)₂}(OTf)_n] (n = 1, 2, 3). As for the PMe₃ system, the trifluoride, [GeF₃{o-C₆H₄(PMe₂)₂}(OTf)], is unstable to reductive defluorination in solution, producing the pyramidal Ge(II) complex [Ge{(o-C₆H₄(PMe₂)₂}(OTf)][OTf], whose crystal structure has been determined. The [GeF₃{Ph₂P(CH₂)₂PPh₂}(OTf)] and [GeF₂{Ph₂P(CH₂)₂PPh₂}(OTf)₂], obtained similarly from the parent tetrafluoride complex, are poorly soluble, however their structures were confirmed crystallographically. The complexes in this work have been characterised via variable temperature ¹H, ¹⁹F{¹H} and ³¹P{¹H} NMR studies in solution, IR spectroscopy and microanalysis and through single crystal X-ray analysis of representative examples across each series. Trends in the NMR and structural parameters are also discussed.