Antimony(i) → Pd(ii) complexes with the (μ-Sb)Pd2 coordination framework

Palladium(II) and Platinum(II) Bis(Stibinidene) Complexes with Intramolecular Hydrogen-Bond Enforced Geometries

The coordination capability of two N,C,N pincer coordinated stibinidenes, i. e. bis(imino)- [2,6-(DippN=CH)2C6H3]Sb (1) or imino-amino- [2-(DippN=CH)-6-(DippNHCH2)C6H3]Sb (2) toward palladium(II) and platinum(II) centers was examined. In the course of this study, seven new square-planar bis(stibinidene) complexes were synthesized and characterized by NMR, IR, Raman, UV-vis spectroscopy and single crystal (sc)-X-ray diffraction analysis. In all cases, both stibinidene ligands 1 or 2 adopt trans positions, but differ significantly in the torsion angle describing mutual orientation of aromatic rings of the stibinidenes along the Sb-Pd/Pt-Sb axes. Furthermore, majority of complexes form isomers in solution most probably due to a hindered rotation around Sb-Pd/Pt bonds caused by bulkiness of 1 and 2. This phenomenon also seems to be influenced by the absence/presence of a pendant -CH2NH- group in 1/2 that is able to form intramolecular hydrogen bonds with the adjacent chlorine atom(s) attached to the metal centers. The whole problem was subjected to a theoretical study focusing on the role of hydrogen bonds in structure architecture of the complexes. To describe the UV-vis spectra of these highly coloured complexes, TD-DFT calculations were employed. These outline differences between the stibinidene ligands, the transition metals as well as between the charge of the complexes (neutral or anionic).

Phosphine-Stabilized Pnictinidenes

The reaction of the intramolecular germylene‐phosphine Lewis pair (o‐PPh₂)C₆H₄GeAr* (1) with Group 15 element trichlorides ECl₃ (E=P, As, Sb) was investigated. After oxidative addition, the resulting compounds (o‐PPh₂)C₆H₄(Ar*)Ge(Cl)ECl₂ (2: E=P, 3: E=As, 4: E=Sb) were reduced by using sodium metal or LiHBEt₃. The molecular structures of the phosphine‐stabilized phosphinidene (o‐PPh₂)C₆H₄(Ar*)Ge(Cl)P (5), arsinidene (o‐PPh₂)C₆H₄(Ar*)Ge(Cl)As (6) and stibinidene (o‐PPh₂)C₆H₄(Ar*)Ge(Cl)Sb (7) are presented; they feature a two‐coordinate low‐valent Group 15 element. After chloride abstraction, a cyclic germaphosphene [(o‐PPh₂)C₆H₄(Ar*)GeP] [B(C₆H₃(CF₃)₂)₄] (8) was isolated. The ³¹P NMR data of the germaphosphene were compared with literature examples and analyzed by quantum chemical calculations. The phosphinidene was treated with [iBu₂AlH]₂, and the product of an Al−H addition to the low‐valent phosphorus atom (o‐PPh₂)C₆H₄(Ar*)Ge(H)P(H)Al(C₄H₉)₂ (9) was characterized.

Low-Valent, Multiply Bonded, Trigonal-Planar Sb Complex: Rational Syntheses, Dual Acidic/Basic Properties, and Unexpected Semiconducting Characteristics

A 4-center, 6π-conjugated, multiply bonded trigonal-planar complex, [Sb{Cr(CO)₅}₃]^- (1), was synthesized via the hydride abstraction of [HSb{Cr(CO)₅}₃]^2- (1-H) with HBF₄·H₂O, with the release of high yields of H₂. The oxidation state of the Sb atom in [Et₄N][1] was well-defined as 0, which was evidenced by X-ray photoelectron spectroscopy and X-ray absorption near-edge structure. The distinct color-structure relationship of this low-valent Sb complex 1 toward a wide range of organic solvents was demonstrated, as interpreted by time-dependent density functional theory calculations, allowing the trigonal-planar 1 and the tetrahedral solvent adducts to be probed, revealing the dual acid/base properties of the Sb center. In addition, 1 showed pronounced electrophilicity toward anionic and neutral nucleophiles, even with solvent molecules, to produce tetrahedral complexes [(Nu)Sb{Cr(CO)₅}₃]^n- [1-Nu; n = 2, Nu = H, F, Cl, Br, I, OH; n = 1, Nu = PEt₃, PPh₃, N,N-dimethylformamide (DMF), acetonitrile (MeCN)]. On the contrary, the Fe/Cr hydride complex [HSb{Fe(CO)₄}{Cr(CO)₅}₂]^2- (2-H) was obtained by treating 1 with [HFe(CO)₄]^-. Upon hydride abstraction of 2-H with HBF₄·H₂O or [CPh₃][BF₄], a multiply bonded Fe/Cr trigonal-planar complex, [Sb{Fe(CO)₄}{Cr(CO)₅}₂]^- (2), was produced in which the oxidation coupling Sb₂-containing complexes [Sb₂Cr₄Fe₂(CO)₂₈]^2- (3-Cr) and [HSb₂Cr₃Fe₂(CO)₂₃]^- (3-H) were yielded as final products. Complex 3-Cr exhibited dual Lewis acid/base properties via hydridation and protonation reactions, to form 2-H or 3-H, respectively. Surprisingly, [Et₄N][1] possessed a low energy gap of 1.13 eV with an electrical conductivity in the range of (1.10-2.77) × 10^-6 S·cm^-1, showing that [Et₄N][1] was a low-energy-gap semiconductor. The crystal packing, crystal indexing, and density of states results of [Et₄N][1] further confirmed the efficient through-space conduction pathway via the intermolecular Sb···O(carbonyl) and O(carbonyl)···O(carbonyl) interactions of the 1D anionic zigzag chain of 1.

(N),C,N-Coordinated Heavier Group 13-15 Compounds: Synthesis, Structure and Applications

The aim of this review is to summarize recent achievements in the field of (N),C,N-coordinated group 13-15 compounds not only regarding their synthesis and structure, but mainly focusing on their potential applications. Relevant compounds contain various types of N-coordinating ligands built up on an ortho-(di)substituted phenyl platform. Thus, group 13 and 14 derivatives were used as single-source precursors for the deposition of semiconducting thin films, as building blocks for the preparation of high-molecular polymers with remarkable optical and chemical properties or as compounds with interesting reactivity in hydrometallation processes. Group 15 derivatives function as catalysts in the Mannich reaction, in the allylation of aldehydes or activation of CO₂ . They were used as transmetallation reagents in transition metal catalysed coupling reactions. The univalent species serve as ligands for transition metals, activate alkynes or alkenes and are utilized as catalysts in the transfer hydrogenation of azo-compounds.

(2-Pyridyloxy)arsines as ligands in transition metal chemistry: a stepwise As(iii) → As(ii) → As(i) reduction

Neutral inherently tri- and tetradentate ligands of the type Ph_3-xAs(PyO)_x (x = 2 (1), 3 (2)) have been synthesized and characterized. Reaction of 1 with [RuCl₂(PPh₃)₃] affords complex [PhAs(μ-PyO)₂RuCl₂(PPh₃)] (3), whereas 2 and [RuCl₂(PPh₃)₃] react with formation of [As(μ-PyO)₂RuCl(PPh₃)₂] (5) and [Ph₃P(PyO)]Cl (6). Treatment of complex 5 with [AuCl(tht)] (tht = tetrahydrothiophene) results in liberation of tht and formation of [AuCl(As(PyO)₂)RuCl(PPh₃)₂] (7), featuring an (Au-As-Ru) core. For compounds 3, 5, and 7 the As-Ru and As-Au bond situation has been investigated using NBO, AIM and ELF analysis, allowing the assignment of pronounced canonical forms of σ-(As^III→Ru^II) to 3, σ-(As^II-Ru^I) to 5 and σ-(Au^I←As^I→Ru^II) to 7.

PSb+P Ligand: Platform for a Stibenium to Transition-Metal Interaction

The coordination chemistry of cationic divalent pnictogen ligands, such as nitrenium and phosphenium, has been well-explored in recent years. However, corresponding studies of a heavier congener, stibenium ion, are rare. To better facilitate a Sb⁺-metal interaction, a tridentate P-Sb⁺-P ligand with two phosphine buttresses was designed and synthesized, and its coordination chemistry toward late transition metals was investigated. The stibenium ligand was delivered as an activated P(SbCl)P-AgOTf complex (2) that releases AgCl and the P-Sb⁺-P ligand upon the treatment with transition metals. Reacting 2 with Rh(I) and Ir(I) metals yielded the anticipated stibenium-transition-metal complexes [(Rh(COD)Cl)₂(μ-PSb⁺P)] OTf ([3][OTf]) and [(Ir(COD)Cl)₂(μ-PSb⁺P)] OTf ([4][OTf]). The M-Sb⁺-M bridging structure was confirmed by single-crystal X-ray crystallography, and the bonding situation was examined computationally. Theoretical studies revealed the presence of three-center delocalized M-Sb⁺-M bonding interactions in [3][OTf] and [4][OTf].