PBiP Pincer Complexes of Platinum, Palladium, and Iridium Featuring Metal–Metal Bonds Synthesized by Oxidative Addition of Bismuth–Halide Bonds

Combining geometric constraint and redox non-innocence within an ambiphilic PBiP pincer ligand

The synthesis of the first pincer ligand featuring a strictly T-shaped group 15 element and its coordination behaviour towards transition metals is described. The platform is itself derived from a trianionic redox non-innocent NNN scaffold. In addition to providing a rigid coordination environment to constrain a Bi centre in a T-shaped geometry to manipulate its frontier molecular orbital constitution, the NNN chelate displays highly covalent bonding towards the geometrically constrained Bi centre. The formation of intriguing ambiphilic Bi-M bonding interactions is demonstrated upon formation of a pincer complex as well as a multimetallic cluster. All compounds are comprehensively characterised by spectroscopic methods including X-ray Absorption Near Edge Structure (XANES) spectroscopy and complemented by DFT calculations.

Phosphine Ligand Binding and Catalytic Activity of Group 10-14 Heterobimetallic Complexes

Heterobimetallic complexes have attracted much interest due to their broad range of structures and reactivities as well as unique catalytic abilities. Additionally, these complexes can be utilized as single-source precursors for the synthesis of binary intermetallic compounds. An example is the family of bis(pyridine-2-thiolato)dichloro-germanium and tin complexes of group 10 metals (Pd and Pt). The reactivity of these heterobimetallic complexes is highly tunable through substitution of the group 14 element and the neutral ligand bound to the transition metal. Here, we study the binding energies of three different phosphorous-based ligands, PR₃ (R = Bu, Ph, and OPh) by density functional theory and restricted Hartree-Fock methods. The PR₃ ligand-binding energies follow the trend of PBu₃ > PPh₃ > P(OPh)₃, in agreement with their sigma-bonding ability. These results are confirmed by ligand exchange experiments monitored with ³¹P NMR spectroscopy, in which a weaker binding PR₃ ligand is replaced with a stronger one. Furthermore, we demonstrate that the heterobimetallic complexes are active catalysts in the Negishi coupling reaction, where stronger binding PR₃ ligands inhibit access to an active site at the metal center. Similar strategies could be applied to other complexes to better understand their ligand-binding energetics and predict their reactivity as both precursors and catalysts.

Bismuth species in the coordination sphere of transition metals: synthesis, bonding, coordination chemistry, and reactivity of molecular complexes

This contribution is focused on bismuth species in the coordination sphere of transition metals. In molecular transition metal complexes, three types of Bi-M bonding are considered, namely dative Bi→M interactions (with Bi acting as a donor), dative Bi←M interactions (with Bi acting as an acceptor) and covalent Bi-M interactions (M = transition metal). Synthetic routes to all three classes of compounds are outlined, the Bi-M bonding situation is discussed, trends in the geometric parameters and in the coordination chemistry of the compounds are addressed, and common spectroscopic properties are summarized. As an important part of this contribution, the reactivity of bismuth species in the coordination sphere of transition metal complexes in stoichiometric and catalytic reactions is highlighted.

Oxidative addition of Bi-C bonds to Pt(0): reaction of Pt(PEt3)3 with cyclic organobismuth compounds

The reaction of cyclic organobismuth compounds, 12-phenyl- and 12-chloro-5,6,7,12-tetrahydrodibenz[c,f][1,5]azabismocines, with Pt(PEt3)3 was examined. Oxidative addition of the exocyclic Bi-C bond to Pt(0) selectively took place in the reaction of the 12-phenyl derivative. Oxidative addition of the exocyclic Bi-Cl bond reversibly took place and was kinetically preferred, while endocyclic Bi-C bond oxidative addition products were thermodynamically favored and became the final products in the reaction of 12-chloro derivatives. These results demonstrate the oxidative addition of a Bi-C bond to a transition metal complex for the first time.

Trivalent Antimony as L-, X-, and Z-Type Ligand: The Full Set of Possible Coordination Modes in Pt-Sb Bonds

In the course of our investigations of the coordination chemistry of trivalent antimony (Sb) compounds, we studied heteronuclear complexes formed in reactions of the compounds RSb(pyS)₂ (R = pyS, Ph; pyS^- = pyridine-2-thiolate) with [Pt(PPh₃)₄], i.e., complexes [(R)Sb(μ-pyS)₂Pt(PPh₃)] (R = pyS, 1; R = Ph, 2). The reaction of 1 with o-chloranil proceeds cleanly with elimination of 2,2'-dipyridyl disulfide and formation of the salt [(PPh₃)Pt(μ-pyS)₂Sb(μ-pyS)₂Pt(PPh₃)]⁺[Sb(C₆Cl₄O₂)₂]^- (3^III), which features the cation 3⁺. The charge-neutral, unsymmetrically substituted compound [(PPh₃)Pt(μ-pyS)₂Sb(μ-pyS)₂Pt(κS-pyS)] (4) can be accessed by the reaction of 3⁺ with LipyS. The oxidation of 2 with o-chloranil furnishes the complex [(κ-O,O-C₆Cl₄O₂)PhSb(μ-pyS)₂Pt(PPh₃)] (5). The oxidation of 1 with PhICl₂ afforded the paddlewheel-shaped complex [Sb(μ-pyS)₄PtCl] (6). Moreover, compound 6 was obtained by the reaction of Sb(pyS)₃ with [PtCl(pyS)(PPh₃)]. The polarization of Pt-Sb bonds of compounds 1-6 was investigated by natural localized molecular orbital (NLMO) calculations, which suggest X-type ligand character (covalent Pt-Sb bonds) for 1 and 2, whereas the Sb ligand of 6 reflects Z-type character (dative Pt→Sb bonds). In 3⁺, 4, and 5, high contributions of the reverse, i.e., L-type (dative Pt←Sb bonds), were observed. In conjunction with the results of NLMO analyses, ¹²¹Sb Mössbauer spectroscopy proves that complexes 1-6 represent essentially trivalent Sb complexes with either a free lone pair (LP) at the Sb atom (1, 2, and 6) or LP character involved in L-type Pt←Sb coordination (3⁺, 4, and 5).

Combined experimental and theoretical studies towards mutual osmium-bismuth donor/acceptor bonding

Osmium(ii) PNP pincer complexes bearing a hemilabile pyridyl-pyrazolide (PyrPz) ligand have been synthesised, and their reactivity towards Lewis acidic bismuth compounds has been examined. Reactions with BiCl3 resulted in chlorine-atom-transfer to give an osmium(iii) species. Reactions with cationic bismuth species led to adduct formation through N → Bi bond formation via the PyrPz ligand. Theoretical analyses revealed that steric interactions hamper Os → Bi bond formation and indicate that such interactions are possible upon reducing the steric profile around the osmium atom. Analytical techniques include NMR, IR, and EPR spectroscopy, cyclic voltammetry, elemental analysis and DFT calculations.

Ionic-caged heterometallic bismuth-platinum complex exhibiting electrocatalytic CO2 reduction

An air-stable heterometallic Bi-Pt complex with the formula [BiPt(SAc)5]n (1; SAc = thioacetate) was synthesized. The crystal structure, natural bond orbital (NBO) and local orbital locator (LOL) analyses, localized orbital bonding analysis (LOBA), and X-ray absorption fine structure (XAFS) measurements were used to confirm the existence of Bi-Pt bonding and an ionic cage of O atoms surrounding the Bi ion. From the cyclic voltammetry (CV) and controlled potential electrolysis (CPE) experiments, 1 in tetrahydrofuran reduced CO2 to CO, with a faradaic efficiency (FE) of 92% and a turnover frequency (TOF) of 8 s-1 after 30 min of CPE at -0.79 V vs. NHE. The proposed mechanism includes an energetically favored pathway via the ionic cage, which is supported by the results of DFT calculations and reflectance infrared spectroelectrochemistry data.

Synthesis and structures of gallaarsenes LGaAsGa(X)L featuring a Ga-As double bond

Three equivalents of LGa {L = HC[C(Me)N(2,6-i-Pr₂C₆H₃)]₂} react with AsX₃ (X = Cl, Br) by insertion into two As-X bonds, followed by the elimination of LGaX₂ and formation of LGaAsGa(Cl)L (1) and LGaAsGa(Br)L (2). According to single crystal X-ray analysis, 1 and 2 each exhibit one Ga-As single bond and one Ga-As double bond. The π-bonding contribution (9.71 kcal mol^-11 and 9.44 kcal mol^-12) was proved by variable temperature (VT) ¹H NMR spectroscopy, while the electronic structure of 1' was studied by quantum chemical calculations.

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.

Key factors in pincer ligand design

This tutorial review analyses the reasons of success of pincer ligands.

Bismuthanes as Hemilabile Donors in an O2 -Activating Palladium(0) Complex

A xanthene-based bismuthane/phosphane chelating ligand has been accessed that has enabled the synthesis of a palladium(0) bismuthane complex. The bismuthane donor proved to be hemilabile as it switched to a dangling position upon addition of O₂ that gave a palladium(II) peroxide complex. Unlike the corresponding 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene (Xantphos) palladium peroxide, the bismuth analogue could be employed for catalytic phosphane oxidation and oxidative phenol coupling.

Synthesis and Oxidation of a Paddlewheel-Shaped Rhodium/Antimony Complex Featuring Pyridine-2-Thiolate Ligands

The paddlewheel-shaped complex [Sb(μ-pyS)₄ Rh]₂ (1) (pyS^- = 2-S-C₅ H₄ N^- ) was synthesized from [Rh(pyS)(cod)]₂ (cod=1,5-cyclooctadiene) and Sb(pyS)₃ . Upon oxidation with ONMe₃ , the complex [(μ-O)Sb(μ-pyS)₃ Rh(κ² -pyS)]₂ (2) is formed. Both 1 and 2 form dimers and feature short Rh-Sb bonds and bridging pyS ligands. ¹²¹ Sb Mössbauer spectro- scopy and computational studies were employed to elucidate the Rh-Sb bonding in 1 and 2. Both covalent (Rh-Sb, X-type Sb ligand) and dative (Rh→Sb, Z-type; Rh←Sb L-type Sb ligand) interactions have to be considered for the description of their bonding situations.

Structure and dynamic NMR behavior of rhodium complexes supported by Lewis acidic group 13 metallatranes

Z-type complexes featuring Rh → Al and Rh → Ga interactions show distorted Rh centers and fluxionality on the NMR timescale.