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Abstract: The isolation and full characterisation of a series of cationic metal–carbonyl complexes bearing an N‐heterocyclic carbene stabilised phosphorus(I) ligand are reported. Specifically, the mononuclear coordination complexes [LM(CO)5][BPh4] (M=Cr, Mo, W), [LFe(CO)4][BPh4] and the dinuclear complexes [LMn2(CO)8][BPh4] and [LCo2(CO)6][BPh4], in which L=[bis(1,3,4,5‐tetramethylimidazol‐2‐ylidene)phosphanide]+, have all been isolated in the solid state and structurally confirmed by single‐crystal X‐ray diffraction. The dicationic platinum complex trans‐[L2PtCl2][BPh4]2 is also reported and fully characterised. The donor ability of [L]+ has been assessed by IR spectroscopy of its metal–carbonyl complexes and by using DFT calculations. The results suggest that [L]+ is a weak π‐acceptor with moderate donor strength and thus it bridges the gap that exists between phosphines and amines in terms of ligand properties. Collectively, these molecules represent the first crystallographically characterised cationic metal–carbonyl derivatives of a PI‐centred ligand and are a rare collection of cationic metal–carbonyl complexes. [ABSTRACT FROM AUTHOR]

Craftily crowned: The treatment of crown ether GeII dications with water or ammonia produces the stable complexes [([15]crown‐5)Ge⋅OH2][OTf]2 (see picture; Ge orange, O red, F green, S yellow, H blue) and [([15]crown‐5)Ge⋅NH3][OTf]2. The OH and NH hydrogen atoms are rendered more acidic in these compounds. [ABSTRACT FROM AUTHOR]

A series of tin(II) triflate and chloride salts in which the cations are complexed by either cyclic or acyclic polyether ligands and which have well-characterized single-crystal X-ray structures are investigated using a variety of experimental and computational techniques. Mössbauer spectroscopy illustrates that the triflate salts tend to have valence electrons with higher s-character, and solid-state NMR spectroscopy reveals marked differences between superficially similar triflate and chloride salts. Cyclic voltammetry investigations of the triflate salts corroborate the results of the Mössbauer and NMR spectroscopy and reveal substantial steric and electronic effects for the different polyether ligands. MP2 and DFT calculations provide insight into the effects of ligands and substituents on the stability and reactivity of the low-valent metal atom. Overall, the investigations reveal the existence of more substantial binding between tin and chlorine in comparison to the triflate substituent and provide a rationale for the considerably increased reactivity of the chloride salts. [ABSTRACT FROM AUTHOR]

The treatment of the soluble indium(I) salt [In([18]crown-6)][O_{3}SCF_{3}] with several potassium salts of the form [K][A] results in the release of the indium(I) cation from the crown ether and the production of salts of [K([18]crown-6)]^{+} and uncomplexed [In]^{+}. [ABSTRACT FROM AUTHOR]

Salts containing the decamethylmetallocenium cations, [(C5Me5)2M]+ (or Cp*2M+) of the group 13 “metals” B, Al and Ga have been prepared using a variety of synthetic routes. Precursor molecules of the type Cp*2MX (X = Cl, Br, Me) exhibit structural features that vary significantly depending on the size and electronegativity of the central atom. While salt metathesis, halide abstraction and methanide abstraction methods represent viable routes for the preparation of salts of Cp*2B+ and Cp*2Al+, acidolysis of a Cp* group from Cp*3Ga is the most reliable method for the synthesis of the analogous gallium cation. Gallocenium cations are less stable than either of the lighter congeneric cations since they prove to be susceptible to decomposition reactions involving the “back-transfer” of ligands from the counter anion. Density functional theory (DFT) calculations revealed that, whereas Cp*2Ga+ is predicted to adopt a molecular structure more similar to that of Cp*2B+, the electronic structure of the gallium cation bears a greater resemblance to that of Cp*2Al+. [ABSTRACT FROM AUTHOR]

The cover picture illustrates the relative π‐acidity of two classes of N‐heterocyclic carbenes that have been employed to stabilize the usually very reactive P+ ion. The background depicts the packing structure of the tetraphenylborate salt of a cation featuring a P+ ion that is ligated by two 1,4‐diisopropyl‐1,2,4‐triazol‐5‐ylidene (TAZ) groups (P atoms are gold, N atoms are blue, B atoms are red, C atoms are grey). Direct comparisons of the chemical and physical properties of salts of the cations featuring TAZ ligands and those of analogous PI cations stabilized by 1,3‐diisopropylimidazol‐2‐ylidene (IMID) ligands were made using X‐ray crystallography, NMR spectroscopy and computational calculations. The data reveal a larger degree of π‐bonding across the C‐P‐C fragment in the case of the TAZ‐stabilized PI cations that is attributable to the greater π‐accepting ability of the TAZ group. More details are discussed in the article by Elnajjar et al. on pp. 1251 ff. [ABSTRACT FROM AUTHOR]

At 173 K, the structure of the acyclic `triphosphenium' salt 1,1,1,3,3,3-hexa­phenyl­triphosphenium tetra­chloro­aluminate dichloro­methane hemisolvate, [(Ph3P)2P][AlCl4]·0.5CH2Cl2, contains two cations, two anions and one solvent mol­ecule in the asymmetric unit. There are no unusually short anion–cation distances and the structures of the ions are comparable to those that have been reported previously. [ABSTRACT FROM AUTHOR]

In the structure of cobaltocenium trifluoro­methane­sulfonate [systematic name: bis­(η5-cyclo­penta­dien­yl)cobalt(III) tri­fluoro­methane­sulfonate], [Co(C5H5)2](CF3O3S) or [CoCp2][OTf], the asymmetric unit contains three independent anions, together with two full and two half-cations. Two of the cations reside on crystallographic inversion centers. [ABSTRACT FROM AUTHOR]

Phosphines are traditionally considered as Lewis bases or ligands in transition metal and main group complexes. Despite their electron-rich (lone pair-bearing) nature, an extensive coordination chemistry for Lewis acidic phosphorus centers is being developed; such chemistry provides a new synthetic approach for phosphorus-element bond formation, leading to new types of structures and modes of bonding. Complexes of Ph2P+ with a variety of donor elements (P, N, C) give experimentally short donor-acceptor bond lengths, when compared to other cationic phosphorus Lewis acid complexes. We have calculated that the energy of the lowest unoccupied molecular orbital (LUMO) in Ph2P+ is lower than that of (Me2N)2P+, which partially explains the greater exothermicity of reactions of donors with the diaryl acceptor. Furthermore, the energies required to distort the diphenylphosphenium cation from its ground-state geometry are significantly smaller than those of the diamido cations and, thus, enhance the exothermicity of donor coordination. These computational data, in conjunction with evidence from experimental solid-state structures, indicate that Ph2P+ is a significantly better Lewis acid relative to the more common diaminophosphenium analogues (R2N)2P+ and are used to elucidate the nature of the bonding in donor-phosphenium complexes. [ABSTRACT FROM AUTHOR]