Trialkylstibine Complexes of Boron, Aluminum, Gallium, and Indium Trihalides: Synthesis, Properties, and Bonding

Ligand-stabilized heteronuclear diatomics of group 13 and 15

A theoretical investigation of ligand-stabilized MX diatomics (M = group 13, X = group 15 element) with N-heterocyclic carbene (NHC) ligands has been carried out to assess bonding and electronic structure. Binding of two ligands in the form L-MX-L is generally preferred over binding of a single ligand as L-MX or MX-L. Binding of carbene donor ligands is predicted to be thermodynamically favorable for all the systems, and is very favorable for the lighter group 15 systems (nitrogen and phosphorus). Detailed analysis of the bonding in these complexes has been carried out with energy decomposition analysis (EDA). In all cases, the carbene to boron and carbene to nitrogen bonding is described as an electron-sharing double bond with both σ and π bonding interactions. For the heavier elements, bonding to C (except for PC interactions) is best described as a donor-acceptor σ single bond.

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.

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.