Coordination chemistry of the main group elements with phosphine, arsine and stibine ligands

Beyond transition block metals: exploring the reactivity of phosphine PTA and its oxide [PTA(O)] towards gallium(iii)

The water-soluble cage-like phosphine PTA (1,3,5-triaza-7-phosphaadamantane) and its phosphine oxide derivative [PTA(O)] (1,3,5-triaza-7-phosphaadamantane-7-oxide) were used to explore their reactivity towards two gallium(iii)-halide precursors, namely GaCl3 and GaI3, for the first time. By using various reaction conditions, a series of N-mono-protonated phosphine salts with [GaCl4]- or [I]- as counterions were obtained in all cases, while the formation of coordinated Ga-PTA and Ga-[PTA(O)] complexes was not observed. All compounds were characterized in solution using multinuclear NMR spectroscopy (1H, 13C{1H}, 31P{1H} and 71Ga) and in the solid state using FT-IR spectroscopy and X-ray crystal diffraction. The new Ga-phosphine salts resulted stable and highly soluble in aqueous solution at room temperature. Density functional theory (DFT) calculations were also performed to further rationalize the coordination features of PTA with Ga3+ metal ion, highlighting that the phosphorus-gallium bond is about twice weaker than the phosphorus-metal bond commonly established by PTA with transition metals such as gold. Furthermore, the mono-protonation of PTA (or [PTA(O)]) makes the formation of ionic gallium-PTA coordination complexes thermodynamically unstable, as confirmed experimentally by the formation of Ga-phosphine salts reported herein.

Probing Homogeneous Catalysts and Precatalysts in Solution by Exchange-Mediated Overhauser Dynamic Nuclear Polarization NMR

Triphenylphosphine (PPh3) is a ubiquitous ligand in organometallic chemistry that has been shown to give enhanced 31P NMR signals at high magnetic field via a scalar-dominated Overhauser effect dynamic nuclear polarization (OE DNP). However, PPh3 can only be polarized via DNP in the free form, while the coordinated form is DNP-inactive. Here, we demonstrate the possibility of enhancing the 31P NMR signals of coordinated PPh3 in metal complexes in solution at room temperature by combining Overhauser effect DNP and chemical exchange between the free and coordinated PPh3 forms. With this method, we successfully obtain 31P DNP enhancements of up to 2 orders of magnitude for the PPh3 ligands in Rh(I), Ru(II), Pd(II), and Pt(II) complexes, and we show that the DNP enhancements can be used to determine the activation energy of the ligand exchange reaction.

Electrocatalytic Reduction of CO2 and H2O with Zn(II) Complexes Through Metal-Ligand Cooperation

Air and water-stable zinc (II) complexes of neutral pincer bis(diphenylphosphino)-2,6-di(amino)pyridine ("PN3P") ligands are reported. These compounds, [Zn(κ2-2,6-{Ph2PNR}2(NC5H3))Br2] (R=Me, 1; R=H, 2), were shown to be capable of electrocatalytic reduction of CO2 at -2.3 V vs. Fc+/0 to selectively yield CO in mixed water/acetonitrile solutions. These complexes also electrocatalytically generate H2 from water in acetonitrile solutions, at the same potential, with Faradaic efficiencies of up to 90 %. DFT computations support a proposed mechanism involving the first reduction of 1 or 2 occurring at the PN3P ligand. Furthermore, computational analysis suggested a mechanism involving metal-ligand cooperation of a Lewis acidic Zn(II) and a basic ligand.

The Narrow Synthetic Window for Highly Homogenous InP Quantum Dots toward Narrow Red Emission

Low-toxicity InP-based quantum dots (QDs) exhibit potential for replacing Cd/Pb-containing QDs in the visible and near-infrared regions. Despite advancements, further improvement relies on synthesizing homogeneous InP QDs to achieve a high color purity. In a commonly employed two-step "seed-mediated" synthetic approach, we demonstrate the high sensitivity of InP seed sizes and size distribution to the quantities of trioctylphosphine (TOP) and tris(trimethylsilyl)phosphine [(TMS)3P], attributed to the process of "self-focusing of size distribution" and enhanced reactivity of In-oleate through coordination with TOP. During growth, the processes of size focusing and defocusing are modulated by the accumulation of oleic acid and TOP molecules, as well as the amount of (TMS)3P in the growth precursor, which may relate to the dissolution process of InP magic size clusters. Through precise control, the best valley/depth ratio of InP QDs was 0.52 at the first absorption peak at 571 nm, resulting in luminescence with a full width at half-maximum of 35 at 620 nm with an absolute photoluminescence quantum yield around 90% after heteroepitaxial growth with ZnSe and ZnS shells.

Carbon-Phosphorus Ligands with Extreme Donating Character

Carbeniophosphines [R2 C+ -PR2 ] and phosphonium ylides [R3 P+ -CR2 - ] are two complementary classes of carbon-phosphorus based ligands defined by their unique donor properties. Indeed, while carbeniophosphines are electron-poor P-ligands due to the positioning of a positive charge near the coordinating P-atom, phosphonium ylides are electron-rich C-ligands due to the presence of a negatively charged coordinating C-atom. Based on this knowledge, this account summarizes our recent contribution on these two classes of carbon-phosphorus ligands, and in particular the strategies developed to lower the donor character of carbeniophosphines and enhance that of phosphonium ylides. This led us to design, at both extremities of the donating scale, extremely electron-poor P-ligands exemplified by imidazoliophosphonites [R2 C+ -P(OR)2 ] and dicarbeniophosphines [(R2 C+ )2 -PR], and extremely electron-rich C-ligands illustrated by pincer architectures exhibiting several phosphonium ylide donor extremities. In the context of carbon-phosphorus analogy, the closely related cases of ligands where the C-atom of a NHC ligand is in close proximity of two positive charges, and that of a phosphonium ylide coordinated through its P-atom are also discussed. An overview of the synthetic methods, coordinating properties, general reactivity and electronic structure of all these C,P-based species is presented here.

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.

Diantimony Complexes [CpR 2 Mo2 (CO)4 (μ,η2 -Sb2 )] (CpR =C5 H5 , C5 H4 t Bu) as Unexpected Ligands Stabilizing Silver(I)n (n=1-4) Monomers, Dimers and Chains

Synthesis and reactivity of transition metal compounds bearing "naked" pnictogen atoms is an active research area with remarkable bonding patterns observed in the formed compounds. Within this field, intense investigations on the coordination behavior of complexes possessing P_n and As_n (2≤n≤5) moieties have been conducted. However, studies on heavier analogues have been ignored so far due to arduous challenges related to low yields and moderate air stability. Herein, we present the first in-depth study addressing the reactivity of organometallic complexes containing Sb-donor atoms with several Ag^I salts. These reactions afforded twelve unprecedented aggregates as monomers, dimers as well as three- and four-membered chains of Ag^I ions claimed in the literature to be inaccessible. Interatomic distances as well as computational evidence obtained with help of several different methods suggest the presence of Ag⋅⋅⋅Ag interactions in all complexes containing more than one Ag^I ion.

Beyond phosphorus: synthesis, reactivity, coordination behaviour and catalytic properties of 1,1'-bis(diphenylstibino)ferrocene

Compared to their widely studied phosphine counterparts, ferrocene stibines have received only marginal attention thus far. This paper describes the synthesis of 1,1'-bis(diphenylstibino)ferrocene (1*), which is an antimony analogue of the ubiquitous dppf, and our investigations into the reactivity and coordination behaviour of this compound. Thus, distibine 1 was oxidised to stiboranes fc(SbPh₂X₂)₂ (X = Cl, 2*; F, 6*; fc = ferrocene-1,1'-diyl) and to stibine-stiborane Ph₂SbfcSbPh₂F₂ (5*). Compounds 2 and 6 were easily hydrolysed to produce ferrocenophanes fc[SbPh₂XOSbPh₂X] (X = Cl, 3*; F, 7*). Removing the halogen from 3 with silver(I) salts afforded the corresponding ferrocenophanes with O-bound oxyanions, fc[SbPh₂ZOSbPh₂Z] (Z = NO₃, 4a*; ClO₄, 4b*), which were alternatively prepared from 2 and also converted back to 2 by adding a chloride source. Through investigations into the coordination behaviour of distibine 1, the following compounds were isolated and characterised: [(μ-ClO₄)₂{Ag(1-κ²Sb,Sb')}₂] (8*), [Ag(1-κ²Sb,Sb')₂]X (X = ClO₄, 9a; SbF₆, 9b*), [(μ(Sb,Sb')-1){(arene)MCl₂}₂] (10*, 11*) and [(arene)MCl(1-κ²Sb,Sb')][PF₆] (12*, 13*; 10, 12: M/arene = Ru/η⁶-p-cymene, 11, 13; Rh/η⁵-C₅Me₅), [(η⁵-C₅Me₅)RuCl(1-κ²Sb,Sb')] (14), [MCl₂(1-κ²Sb,Sb')] (M = Pd, 15*; Pt, 16*), [Pd(1-κ²Sb,Sb')₂]X₂ (X = BF₄, 17a; SbF₆, 17b*), [Pd(η²-ma)(1-κ²Sb,Sb')] (18*; ma = maleic anhydride), [(μ(Sb,Sb')-1)(AuCl)₂] (19*), and [Au(1-κ²Sb,Sb')₂]X (X = AuCl₂, 20a*; SbF₆, 20b*). Inspection of the structural parameters suggested that complexes featuring 1 exhibit less sterically strained structures than their dppf analogues due to longer M-Sb and Sb-C bonds, which reduce crowding around the ligated metal centre. Cyclic voltammetry and DFT calculations revealed that the primary electrochemical oxidation of 1 is reversible and occurs at the ferrocene unit. Based on preliminary catalytic tests in Suzuki-Miyaura biaryl coupling, Pd-1 complexes exhibited a lower efficiency than their respective Pd-dppf analogues. (An asterisk indicates that the crystal structure has been determined.).

Neutral and Cationic Complexes of Silicon(IV) Halides with Phosphine Ligands

The reaction of SiI₄ and PMe₃ in n-hexane produced the yellow salt, [SiI₃(PMe₃)₂]I, confirmed from its X-ray structure, containing a trigonal bipyramidal cation with trans-phosphines. This contrasts with the six-coordination found in (the known) trans-[SiX₄(PMe₃)₂] (X = Cl, Br) complexes. The diphosphines o-C₆H₄(PMe₂)₂ and Et₂P(CH₂)₂PEt₂ form six-coordinate cis-[SiI₄(diphosphine)], which were also characterized by X-ray crystallography, multinuclear NMR, and IR spectroscopy. Reaction of trans-[SiX₄(PMe₃)₂] (X = Cl, Br) with Na[BAr^F] (BAr^F = [B{3,5-(CF₃)₂C₆H₃}₄]) produced five-coordinate [SiX₃(PMe₃)₂][BAr^F], but while Me₃SiO₃SCF₃ also abstracted chloride from trans-[SiCl₄(PMe₃)₂], the reaction products were six-coordinate complexes [SiCl₃(PMe₃)₂(OTf)] and [SiCl₂(PMe₃)₂(OTf)₂] with the triflate coordinated. X-ray crystal structures were obtained for [SiCl₃(PMe₃)₂][BAr^F] and [SiCl₂(PMe₃)₂(OTf)₂]. The charge distribution across the silicon species was also examined by natural bond orbital (NBO) analyses of the computed density functional theory (DFT) wavefunctions. For the [SiX₄(PMe₃)₂] and [SiX₃(PMe₃)₂]⁺ complexes, the positive charge on Si decreases and the negative charge on X decreases going from X = F to X = I. Upon going from [SiX₄(PMe₃)₂] to [SiX₃(PMe₃)₂]⁺, i.e., removal of X^–, there is an increase in positive charge on Si and a decrease in negative charge on the X centers (except for the case X = F). The positive charge on P shows a slight decrease.

Unusual neutral and monocationic silicon(IV) iodide complexes with soft phosphine coordination are formed in hydrocarbon solvents, while treatment of [SiCl₄(PMe₃)₂] with NaBAr^F forms the [SiCl₃(PMe₃)₂]⁺ cation; the electronic structures of [SiX₄(PMe₃)₂] and [SiX₃(PMe₃)₂]⁺ (X = F, Cl, Br, I) are probed using DFT calculations.

Effects of Different Concentrations of Arsine on the Synthesis and Final Properties of Polypropylene

This article studies the effects of arsine on the synthesis and thermal degradation of 4 samples of virgin polypropylene (PP-virgin) and proposes reaction mechanisms that allow understanding of its behaviour. Different points are monitored during the polypropylene synthesis to perform TGA, DSC, FT-IR, RDX, and MFI analyses later. The content of AsH₃ in polypropylene varies between 0.05 and 4.73 ppm, and of arsenic in virgin PP residues between 0.001 and 4.32 ppm for PP0 and PP10, increasing in fluidity index from 3.0 to 24.51. The origin of thermo-oxidative degradation is explained by the reaction mechanisms of the Molecule AsH₃ with the active titanium center of the ZN catalyst and the subsequent oxidation to form radical complexes. OO-AsH-TiCl₄-MgCl₂ and (OO-as-OO)₂ -TiCl₄-MgCl₂, which, by radical reactions, give rise to the formation of functional groups aldehyde, ketone, alcohol, carboxylic acid, CO, CO₂, PP-Polyol, PP-Polyether, and PP-Isopropylethers. These species caused the TG and DTG curves to increase degradation peaks in pp samples.

Bisstibane-distibane conversion via consecutive single-electron oxidation and reduction reaction

peri-Substituted naphthalene complexes (Trip₂Pn)₂Naph (Pn = Sb 1, Bi 2) were synthesised and their redox behaviour investigated. Oxidation of 1 with [Fc][BAr^F] (BAr^F = B(C₆F₅)₄) yielded [(Trip₂Sb)(TripSb)Naph][BAr^F] (3) containing the stibane-coordinated stibenium cation [(Trip₂Sb)(TripSb)Naph]⁺. Subsequent reduction of 3 with KC₈ yielded distibane (TripSb)₂Naph (4). 1-4 were characterised by NMR (¹H, ¹³C) and IR spectroscopy as well as single-crystal X-ray diffraction (sc-XRD), while their electronic structures were analysed by quantum chemical computations.

Molecular Assemblies Offering Hydrogen-Bonding Cavities: Influence of Macrocyclic Cavity and Hydrogen Bonding on Dye Adsorption

This work presents a set of Hg macrocycles of amide-phosphine-based ligands offering H-bonding cavities of different dimensions. Such macrocycles are shown to selectively adsorb anionic dyes followed by neutral dyes as well as Prontosil, a biologically relevant antibiotic, within their cavities with the aid of H-bonding-assisted encapsulation. Kinetic experiments supported by spectroscopic and docking studies illustrate the importance of the cavity structure as well as H-bonds for the selective adsorption of dyes.

Synthesis, structure and reactivity with phosphines of Hg(II) ortho-cyano-aminothiophenolate complexes formed via C-S bond cleavage and dehydrogenation of 2-aminobenzothiazoles

Addition of 2-aminobenzothiazole (abt) and substituted derivatives to Hg(OAc)2 leads to the high yield formation of ortho-cyano-aminothiophenolate (ocap) complexes [Hg{SC6H3XN(C≡N)}]n (X = H, Me, Cl, Br, NO2) resulting from dehydrogenation...

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.

Synthetic and Structural Study of peri-Substituted Phosphine-Arsines

A series of phosphorus-arsenic peri-substituted acenaphthene species have been isolated and fully characterised, including single crystal X-ray diffraction. Reactions of EBr3 (E = P, As) with iPr2PAcenapLi (Acenap = acenaphthene-5,6-diyl) afforded the thermally stable peri-substitution supported donor-acceptor complexes, iPr2PAcenapEBr23 and 4. Both complexes show a strong P→E dative interaction, as observed by X-ray crystallography and 31P NMR spectroscopy. DFT calculations indicated the unusual As∙∙∙As contact (3.50 Å) observed in the solid state structure of 4 results from dispersion forces rather than metallic interactions. Incorporation of the excess AsBr3 in the crystal structure of 3 promotes the formation of the ion separated species [iPr2PAcenapAsBr]+Br- 5. A decomposition product 6 containing the rare [As6Br8]2- heterocubane dianion was isolated and characterised crystallographically. The reaction between iPr2PAcenapLi and EtAsI2 afforded tertiary arsine (BrAcenap)2AsEt 7, which was subsequently lithiated and reacted with PhPCl2 and Ph2PCl to afford cyclic PhP(Acenap)2AsEt 8 and acyclic EtAs(AcenapPPh2)2 9.

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.

Electrocatalytic reduction of CO2 to CO and HCO2- with Zn(II) complexes displaying cooperative ligand reduction

Air-stable zinc(II) pyridyl phosphine complexes, [Zn(κ²-2,6-{Ph₂PNMe}₂(NC₅H₃))Br₂] (1) and [Zn(κ²-2-{Ph₂PNMe}(NC₅H₃))Br₂] (2) are reported and 1 was capable of electrocatalytic reduction of CO₂ at -2.3 V vs. Fc^+/0 to yield CO/HCO₂H in mixed water/acetonitrile solutions. DFT computations support a proposed mechanism involving electron transfer reactions from a species with the anionic PN³P ligand ("L^-/Zn(II)").

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

An unusual series of Ge(II) dicationic species with homoleptic phosphine and arsine coordination, [Ge(L)][OTf]₂, L = 3 × PMe₃, triphos (MeC(CH₂PPh₂)₃), triars (MeC(CH₂AsMe₂)₃), or κ³-tetraphos (P(CH₂CH₂PPh₂)₃) (OTf^- = O₃SCF₃^-) have been prepared by reaction of [GeCl₂(dioxane)] with L and 2 mol equiv of Me₃SiOTf in anhydrous CH₂Cl₂ (or MeCN for L = triars, triphos). X-ray crystal structures are reported for [Ge(PMe₃)₃][OTf]₂, [Ge(triars)][OTf]₂, and [Ge(κ³-tetraphos)][OTf]₂, confirming homoleptic P₃- or As₃-coordination at Ge(II) in each case and with the discrete OTf^- anions providing a charge balance. The Ge-P/As bond lengths are significantly shorter than those in neutral germanium(II) dihalide complexes with diphosphine or diarsine coordination. Solution NMR spectroscopic data indicate that the complexes are labile in solution. Using excess AsMe₃ and [GeCl₂(dioxane)] gives only the neutral product, [Ge(AsMe₂)₂(OTf)₂], the crystal structure of which shows four coordination at Ge(II), via two As donor atoms and an O atom from two κ¹-OTf^- ligands; further weak, long-range intermolecular interactions give a chain polymer. The electronic structure of the [Ge(PMe₃)₃]²⁺ dication has been investigated using density functional theory (DFT) calculations. The computed geometrical parameters for this dication are in good agreement with the experimental X-ray crystallographic values in [Ge(PMe₃)₃][OTf]₂. The results also indicate that the pyramidal arrangement of the [Ge(PMe₃)₃]²⁺ (computed P-Ge-P angle 96.8° at the B3LYP-D3 level) arises from a balance between electronic energy (E_elec) contributions, which favor a lower P-Ge-P angle, and nuclear-nuclear contributions (E_nn), which favor a higher P-Ge-P angle, to the total energy (E_TOT). An Atoms in Molecules (AIM) analysis reveals that one reason why E_elec decreases as the P-Ge-P angle decreases is because of C···H and H···H interactions between atoms on different CH₃ groups. The stability of the [Ge(PMe₃)₃]²⁺ dication is enhanced by the distribution of a significant part of the positive charge on Ge²⁺ to the atomic centers of the PMe₃ ligands. Similar results were obtained for [Ge(AsMe₃)₃][OTf]₂, showing the tris-AsMe₃ complex to be less stable compared to the PMe₃ analogue. Related calculations were also performed for the neutral [Ge(PMe₃)₂(OTf)₂] and [Ge(AsMe₃)₂(OTf)₂] complexes.

Structural Evidence for Pnictogen-Centered Lewis Acidity in Cationic Platinum-Stibine Complexes Featuring Pendent Amino or Ammonium Groups

As part of our continuing interest in the chemistry of cationic antimony Lewis acids as ligands for late transition metals, we have now investigated the synthesis of platinum complexes featuring a triarylstibine ligand substituted by an o-[(dimethylamino)methyl]phenyl group referred to as Ar^N. More specifically, we describe the synthesis of the amino stibine ligand Ph₂SbAr^N (L) and its platinum dichloride complex [LPtCl]Cl which exists as a chloride salt and which shows weak coordination of the amino group to the antimony center. We also report the conversion of [LPtCl]Cl into a tricationic complex [LHPt(SMe₂)]³⁺ which has been isolated as a tris-triflate salt after reaction of [LPtCl]Cl with SMe₂, HOTf and AgOTf. Finally, we show that [LHPt(SMe₂)][OTf]₃ acts as a catalyst for the cyclization of 2-allyl-2-(2-propynyl)malonate.

Main Group Redox Catalysis of Organopnictogens: Vertical Periodic Trends and Emerging Opportunities in Group 15

A growing number of organopnictogen redox catalytic methods have emerged-especially within the past 10 years-that leverage the plentiful reversible two-electron redox chemistry within Group 15. The goal of this Perspective is to provide readers the context to understand the dramatic developments in organopnictogen catalysis over the past decade with an eye toward future development. An exposition of the fundamental differences in the atomic structure and bonding of the pnictogens, and thus the molecular electronic structure of organopnictogen compounds, is presented to establish the backdrop against which organopnictogen redox reactivity-and ultimately catalysis-is framed. A deep appreciation of these underlying periodic principles informs an understanding of the differing modes of organopnictogen redox catalysis and evokes the key challenges to the field moving forward. We close by addressing forward-looking directions likely to animate this area in the years to come. What new catalytic manifolds can be developed through creative catalyst and reaction design that take advantage of the intrinsic redox reactivity of the pnictogens to drive new discoveries in catalysis?

Structures and Chemical Bonding in Antimony(III) Bromide Complexes with Pyridine

Weakly or "partially" bonded molecules are an important link between the chemical and van der Waals interactions. Molecular structures of six new SbBr₃ -Py complexes in the solid state have been determined by single-crystal X-ray diffraction analysis. In all complexes all Sb atoms adopt a pseudo-octahedral coordination geometry which is completed by additional Sb⋅⋅⋅Br contacts shorter than the sum of the van der Waals radii, with Br-Sb⋅⋅⋅Br angles close to 180°. To reveal the nature of Sb-Br and Sb-N interactions, the DFT calculations were performed followed by the analysis of the electrostatic potentials, the orbital interactions and the topological analysis. Based on Natural Bond Orbital (NBO) analysis, the Sb-Br interactions range from the covalent bonds to the pnictogen bonds. A simple structural parameter, non-covalence criterion (NCC) is defined as a ratio of the atom-atom distance to the linear combination of sums of covalent and van der Waals radii. NCC correlates with E(2) values for Sb-N, Sb-Cl and Sb-Br bonds, and appears to be useful criterion for a preliminary evaluation of the bonding situation.

Trialkylphosphines Having a Bulky Phosphacyclopentane Backbone: Structural and Redox Properties Depending on the Exocyclic Alkyl Groups and EPR Observation of a Persistent Trialkylphosphine Radical Cation

Bulky phosphines and their redox properties have received increased attention in the view of useful auxiliary ligands for transition metal catalysts and Lewis-base components of frustrated Lewis pairs for chemical transformations. Herein we report the synthesis, structure, and properties of a series of trialkylphosphines 2R (R = methyl, ethyl, isopropyl, tert-butyl, 1-adamantyl) that possess the bulky 2,2,5,5-tetrakis(trimethylsilyl)-1-phosphacyclopentane as a structural backbone. Among these phosphines, 2Ad, which contains an adamantyl moiety, has a very large buried volume (%V_bur) for a trialkylphosphine (62.0) and shows a quasi-reversible oxidative wave at a lower oxidation potential (-0.12 V in CH₂Cl₂, vs ferrocene/ferrocenium couple) by cyclic voltammetry. The reaction of 2Ad with AgPF₆ afforded a cationic silver aquo complex [Ag(2Ad)(H₂O)]⁺[PF₆]^-, whereas the reaction with NOSbF₆ gave a persistent phosphine radical cation [2Ad]^•+. Based on the EPR spectra and DFT studies, the spin and positive charge of [2Ad]^•+ are localized on the phosphorus atom.

Tertiary Phosphine and Arsine Complexes of Phosphorus Pentafluoride: Synthesis, Properties, and Electronic Structures

The reaction of PMe₃ or PPh₃ with PF₅ in anhydrous CH₂Cl₂ or hexane forms the white, moisture-sensitive complexes [PF₅(PR₃)] (R = Me, Ph). Similar reactions involving the diphosphines o-C₆H₄(PR₂)₂ afford the complexes [PF₄{o-C₆H₄(PR₂)₂}][PF₆]. The X-ray structures of [PF₅(PR₃)] and [PF₄{o-C₆H₄(PMe₂)₂}][PF₆] show pseudo-octahedral fluorophosphorus centers. Multinuclear NMR spectra (¹H, ¹⁹F{¹H}, ³¹P{¹H}) show that in solution in CH₂Cl₂/CD₂Cl₂ the structures determined crystallographically are the only species present for [PF₅(PMe₃)] and [PF₄{o-C₆H₄(PMe₂)₂}][PF₆] but that [PF₅(PPh₃)] and [PF₄{o-C₆H₄(PPh₂)₂}][PF₆] exhibit reversible dissociation of the phosphine at ambient temperatures, although exchange slows at low temperatures. The complex ¹⁹F{¹H} and ³¹P{¹H} NMR spectra have been analyzed, including those of the cation [PF₄{o-C₆H₄(PMe₂)₂}]⁺, which is a second-order AA'XX'B₂M spin system. The unstable [PF₅(AsMe₃)], which decomposes in a few hours at ambient temperatures, has also been isolated and spectroscopically characterized; neither AsPh₃ nor SbEt₃ forms similar complexes. The electronic structures of the PF₅ complexes have been explored by DFT calculations. The DFT optimized geometries for [PF₅(PMe₃)], [PF₅(PPh₃)], and [PF₄{o-C₆H₄(PMe₂)₂}]⁺ are in good agreement with their respective crystal structure geometries. DFT calculations on the PF₅-L complexes reveal the P-L bond strength falls with L in the order PMe₃ > PPh₃ > AsMe₃, consistent with the experimentally observed stabilities, and in the PF₅-L complexes, electron transfer from L to PF₅ on forming these complexes also follows the order PMe₃ > PPh₃ ≈ AsMe₃.

Six-coordinate mononuclear dysprosium(iii) single-molecule magnets with the triphenylphosphine oxide ligand

Three rare octahedral mononuclear Dy^III complexes bearing triphenylphosphine oxide and halide ligands are reported. The Cl⁻ and Br⁻ analogues exhibit SMM behavior under a small dc field. Ab initio CASSCF calculations reveal a higher energy barrier for an analogous complex with iodides.

Sb- and Bi-based coordination polymers with N-donor ligands with and without lone-pair effects and their photoluminescence properties

Fifteen new sublimable Sb- and Bi-based chlorido, bromido and iodido coordination polymers (CPs) with linear bispyridyl ligands are presented in this work and compared in terms of their crystal structures and photoluminescence properties. The Sb-CPs occur in two structural motifs: 1∞[Sb2X6(L)2] (X: Cl (a), Br (b), I (c); L: 1,2-bis(4-pyridyl)ethylene (bpe) (1), 1,2-bis(4-pyridyl)ethane (bpa) (2), 4,4'-bipyridine (bipy) (X: Br, I; 3)) with two polymorphs showing negligible stereochemical demand of the lone-pair and 1∞[SbCl3(bipy)] (3a) featuring a stereochemically active lone pair with significant 5p-contribution at SbIII. This is accompanied by differences in the coordination polyhedra being octahedral for high s-character, whereas a high p-character of the lone pair results in a square pyramid as the coordination sphere. The Bi-CPs are represented by the general formula 1∞[Bi2X6(L)2] (X: Cl (a), Br (b), I (c); L: 1,2-bis(4-pyridyl)ethylene (bpe) (4), 1,2-bis(4-pyridyl)ethane (bpa) (5)) and thus show no significant 6p-character of the lone pairs. For examining the parallels and differences between the SbIII- and BiIII-CPs, both are compared in terms of structures and luminescence properties, as well as with related literature known CPs. Altogether, this comparison of structures and properties allows for gaining new insights into the photoluminescence mechanisms of the Sb and Bi-containing CPs. For the first time, distinct hints on the participation of inter-valence charge transfer transitions in E3+-pairs (E: Sb, Bi) were observed for the Sb- and Bi-containing coordination polymers constructed from N-donor 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.

Tailoring Cu+ for Ga3+ Cation Exchange in Cu2-xS and CuInS2 Nanocrystals by Controlling the Ga Precursor Chemistry

Nanoscale cation exchange (CE) has resulted in colloidal nanomaterials that are unattainable by direct synthesis methods. Aliovalent CE is complex and synthetically challenging because the exchange of an unequal number of host and guest cations is required to maintain charge balance. An approach to control aliovalent CE reactions is the use of a single reactant to both supply the guest cation and extract the host cation. Here, we study the application of GaCl₃-L complexes [L = trioctylphosphine (TOP), triphenylphosphite (TPP), diphenylphosphine (DPP)] as reactants in the exchange of Cu⁺ for Ga³⁺ in Cu_2-xS nanocrystals. We find that noncomplexed GaCl₃ etches the nanocrystals by S^2- extraction, whereas GaCl₃-TOP is unreactive. Successful exchange of Cu⁺ for Ga³⁺ is only possible when GaCl₃ is complexed with either TPP or DPP. This is attributed to the pivotal role of the Cu_2-xS-GaCl₃-L activated complex that forms at the surface of the nanocrystal at the onset of the CE reaction, which must be such that simultaneous Ga³⁺ insertion and Cu⁺ extraction can occur. This requisite is only met if GaCl₃ is bound to a phosphine ligand, with a moderate bond strength, to allow facile dissociation of the complex at the nanocrystal surface. The general validity of this mechanism is demonstrated by using GaCl₃-DPP to convert CuInS₂ into (Cu,Ga,In)S₂ nanocrystals, which increases the photoluminescence quantum yield 10-fold, while blue-shifting the photoluminescence into the NIR biological window. This highlights the general applicability of the mechanistic insights provided by our work.

Homo- and Copolymerization of Ethylene with Norbornene Catalyzed by Vanadium(III) Phosphine Complexes

Herein, we report the homo- and co-polymerization of ethylene (E) with norbornene (NB) catalyzed by vanadium(III) phosphine complexes of the type VCl₃(PMe_nPh_3-n)₂ [n = 2 (1a), 1 (1b)] and VCl₃(PR₃)₂ [R = phenyl (Ph, 1c), cyclohexyl (Cy, 1d), tert-butyl (tBu, 1e)]. In the presence of Et₂AlCl and Cl₃CCOOEt (ETA), 1a-1e exhibit good activities for the polymerization of ethylene, affording linear, semicrystalline PEs with a melting temperature of approximately 130 °C. Mainly alternating copolymers with high comonomer incorporation were obtained in the E/NB copolymerization. A relationship was found between the electronic and steric properties of the phosphine ligands and the catalytic performance. Overall, the presence of electron-withdrawing ligand substituents increases the productivity, complexes with aryl phosphine (weaker σ-donor character) exhibiting a higher (co)polymerization initiation rate than those with alkyl phosphines (stronger σ-donor character). Steric effects also seem to play a key role since 1d and 1e, having large size phosphines (PCy₃ θ = 170° and PtBu₃ θ = 182°, respectively) are more active than 1a (PMe₂Ph θ = 122°). In this case, the larger size of PtBu₃ and PCy₃ likely compensates for their higher donor strength compared to PMe₂Ph.

Oxidative addition of arsenic halides to platinum(0)

Reaction of AsCl3 with Pt(0) complexes [Pt(PCy3)2], [Pt(PCy3)(IMes)] and [Pt(IMes)2] (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) resulted in oxidative addition of As-Cl bonds at the Pt centres to form complexes of the form trans-[PtCl(AsCl2)L2]. Two of these compounds were characterised by X-ray diffraction, making them the first structurally characterised examples of AsX2 ligands (X = halogen). AsBr3 also underwent oxidative addition to [Pt(PCy3)2], forming trans-[PtBr(AsBr2)(PCy3)2] in situ, as judged by 31P NMR spectroscopy. This reaction was unselective, yielding several products, of which a Pt3As2 cluster could be identified by single-crystal X-ray diffraction.

Establishing the correlation between catalytic performance and N→Sb donor–acceptor interaction: systematic assessment of azastibocine halide derivatives as water tolerant Lewis acids

A series of organoantimony(iii) halide complexes with a tetrahydrodibenzo[c,f][1,5]azastibocine framework were synthesized and employed as water tolerant Lewis acid catalysts.