Coinage metal complexes of tris(pyrazolyl)methanide [C(3,5-Me2pz)3]−: κ3-coordination vs. backbone functionalisation

A dianionic C3-symmetric scorpionate: synthesis and coordination chemistry

Introducing charges into ligand systems fine-tunes their electronic properties and influences the solubility of their metal complexes. Herein, we present a synthesis of a dianionic, C3-symmetric ligand combining three anionic N-donors tethered to a positively charged phosphonium center. The tris-skatylmethylphosphonium (TSMP) ligand, isolated in the form of its dipotassium salt TSMPK2, is the first dianionic homoscorpionate capable of metal exchange. The potassium cations in TSMPK2 are exchangeable for other metals, which results in rich coordination chemistry. Thus, the ligand displays a bridging μ2:κ2:κ1 coordination mode with trigonal planar Cu(i) centers in the tetrameric complex [(TSMP)Cu]44-. The κ3 mode is accessed upon addition of 1 equiv. of P(OEt)3 per Cu(i) to yield the tetrahedral monomeric complex [(TSMP)CuP(OEt)3]-. Both Fe(ii) and Ni(ii) in pyridine give octahedral high-spin κ3 complexes with composition (TSMP)M(Py)3 (M = Fe, Ni). Displacement of three pyridine ligands in (TSMP)Fe(Py)3 for a second equivalent of TSMP gives a high-spin pseudotetrahedral 2 : 1 complex [(TSMP)2Fe]2- with the ligands in κ2 coordination mode. The reduction in coordination number is likely due to electrostatic repulsion of the negatively-charged indolides as well as their weaker π-accepting character as compared to pyridine.

Phosphine-functionalised tris(pyrazolyl)methane ligands and their mono- and heterobimetallic complexes

The synthesis, characterisation and reactivity of new phosphine-functionalised tris(pyrazolyl)methane ligands (TpmPR₂, 2a-c, with R = Ph, nBu, iPr) are presented. The reaction of 2a-c with [Rh(CO)₂Cl]₂ furnished N,P-heterochelate carbonyl complexes (3a-c), which were used to quantify the donor abilities of the ligands via IR spectroscopy. The coordination flexibility was demonstrated by treating representative members of this new ligand class with [CpRu(acn)₃][PF₆] (acn = acetonitrile), [(tht)AuCl] (tht = tetrahydrothiophene) and [Pd(allyl)Cl]₂ providing either a N,N,P-heteroscorpionate complex (4) or the P-coordinated complexes (5,6) without any involvement of the pyrazolyl entities. With 2a and [Pd(cod)Cl₂], another P,N-heterochelate complex (7) was obtained, which served as a precursor for a heterobimetallic complex containing palladium and copper (8). Detailed NMR spectroscopic and X-ray crystallographic investigations have been performed on all new complexes.

Synthesis and reactivity at the Ir-MeTpm platform: from κ1-N coordination to κ3-N-based organometallic chemistry

Reaction of [Ir(μ-Cl)(COE)2]2 (COE = cis-cyclooctene) with tris(3,5-dimethylpyrazol-1-yl)methane (MeTpm) affords [IrCl(κ1-N-MeTpm)(COD)] (1) (COD = 1,5-cyclooctadiene). The formation of 1 implies the transfer dehydrogenation of a COE ligand to give COD and COA (cyclooctane). A mechanistic proposal based on DFT calculations that explains this iridium promoted process has been disclosed. Additionally, reactivity studies have allowed the preparation and characterization, including determination of the molecular structures of a number of iridium complexes with the MeTpm ligand in κ1, κ2 or κ3-N coordination modes. Moreover, the first example of an Ir-cyclooctyl complex featuring hydride and carbonyl ligands, whose solid state structure has been determined by X-ray diffraction methods, is reported.

A Redox-Switchable Germylene and its Ligating Properties in Selected Transition Metal Complexes

The synthesis, structure, and full characterization of a redox-switchable germylene based on a [3]ferrocenophane ligand arrangement, [Fc(NMes)₂ Ge] (4), is presented. The mesityl (Mes)-substituted title compound is readily available from Fc(NHMes)₂ (2) and Ge{N(SiMe₃ )₂ }₂ , or from the dilithiated, highly air- and moisture-sensitive compound Fc(NLiMes)₂ ⋅3 Et₂ O (3) and GeCl₂ . Cyclic voltammetry studies are provided for 4, confirming the above-mentioned view of a redox-switchable germylene metalloligand. Although several 1:1 Rh^I and Ir^I complexes of 4 (5-7) are cleanly formed in solution, all attempts to isolate them in pure form failed due to stability problems. However, crystalline solids of [Mo(κ¹ Ge-4)₂ (CO)₄ ] (8) and [W(κ¹ Ge-4)₂ (CO)₄ ] (9) were isolated and fully characterized by common spectroscopic techniques (8 by X-ray diffraction). DFT calculations were performed on a series of model compounds to elucidate a conceivable interplay between the metal atoms in neutral and cationic bimetallic complexes of the type [Rh(κ¹ E-qE)(CO)₂ Cl]^0/+ (qE=[Fc(NPh)₂ E] with E=C, Si, Ge). The bonding characteristics of the coordinated Fc-based metalloligands (qE/qE⁺ ) are strongly affected upon in silico oxidation of the calculated complexes. The calculated Tolman electronic parameter (TEP) significantly increases by approximately 20 cm^-1 (E=C) to 25 cm^-1 (E=Si, Ge) upon oxidation. The change in the ligand-donating abilities upon oxidation can mainly be attributed to Coulombic effects, whereas an orbital-based interaction appears to have only a minor influence.

Palladium complexes of ferrocene-based phosphine ligands as redox-switchable catalysts in Buchwald–Hartwig cross-coupling reactions

Redox-switchable catalysis: Palladium(ii) complexes of two differently substituted [1]phosphaferrocenophanes FcPR (R = Mes, biaryl) and of diphenylferrocenyl phosphine Ph₂PFc were applied in redox-switchable Buchwald–Hartwig cross-coupling reactions.

Electronic nature of zwitterionic alkali metal methanides, silanides and germanides - a combined experimental and computational approach

Zwitterionic group 14 complexes of the alkali metals of formula [E(SiMe₂OCH₂CH₂OMe)₃M], where E = C, Si or Ge and M = Li, Na or K, have been prepared, structurally characterized and their electronic nature was investigated by computational methods.

Zwitterionic group 14 complexes of the alkali metals of formula [C(SiMe₂OCH₂CH₂OMe)₃M], (M-1), [Si(SiMe₂OCH₂CH₂OMe)₃M], (M-2), [Ge(SiMe₂OCH₂CH₂OMe)₃M], (M-3), where M = Li, Na or K, have been prepared, structurally characterized and their electronic nature was investigated by computational methods. Zwitterions M-2 and M-3 were synthesized via reactions of [Si(SiMe₂OCH₂CH₂OMe)₄] (2) and [Ge(SiMe₂OCH₂CH₂OMe)₄] (3) with MOBu^t (M = Li, Na or K), resp., in almost quantitative yields, while M-1 were prepared from deprotonation of [HC(SiMe₂OCH₂CH₂OMe)₃] (1) with LiBu^t, NaCH₂Ph and KCH₂Ph, resp. X-ray crystallographic studies and DFT calculations in the gas-phase, including calculations of the NPA charges confirm the zwitterionic nature of these compounds, with the alkali metal cations being rigidly locked and charge separated from the anion by the internal OCH₂CH₂OMe donor groups. Natural bond orbital (NBO) analysis and the second order perturbation theory analysis of the NBOs reveal significant hyperconjugative interactions in M-1–M-3, primarily between the lone pair and the antibonding Si–O orbitals, the extent of which decreases in the order M-1 > M-2 > M-3. The experimental basicities and the calculated gas-phase basicities of M-1–M-3 reveal the zwitterionic alkali metal methanides M-1 to be significantly stronger bases than the analogous silanides M-2 and germanium M-3.

A structurally flexible triazolate-based metal–organic framework featuring coordinatively unsaturated copper(i) sites

A novel Cu^I-bistriazolate MOF showing reversible breathing behaviour is able to form a weak complex with carbon monoxide.

A metallacyclic alkyl-amido carbene complex (MCAAC)

The activation of the C≡N moiety in the redox-active metalloligand [CpRu{κ(3)N(pz)-1}][PF6] (2) (1: ambidentate hybrid ligand, N≡C-C(pz)3, with pz = pyrazolyl) was observed in the reaction with [Ir(cod)Cl]2 (cod = 1,5-cyclooctadiene). By performing detailed NMR spectroscopic and X-ray crystallographic investigations the product was found to be a bimetallic Ru(II)-Ir(III) complex of the composition [CpRu{μ-1}Ir(cod)Cl2][PF6] (3) consisting of a chemically modified ligand 1'. Most notably, the heterobimetallic complex 3 features an unprecedented metallacyclic alkyl-amido carbene (MCAAC) core structure, which is coordinated to an Ir(III) centre. Density functional theory (DFT) calculations as well as cyclic voltammetry (CV) studies were performed in an effort to establish the formal oxidation states of the metal atoms in 3. Indeed, a quasi-reversible oxidation wave was detected at E(1/2)(0) = 0.36 V, which was attributed to the Ru(II)/Ru(III) redox couple, while two irreversible reduction processes were observed at very negative potentials and have been assigned to the stepwise reduction of Ir(III) to Ir(I). First efforts to elucidate the reaction mechanism have also been performed.

Sodium, magnesium and zinc complexes of mono(phenolate) heteroscorpionate ligands

The reaction of bis(3,5-dimethylpyrazolyl)methylphenol N(2)O(Ar)H (1) with NaH in THF formed dimeric [Na(kappa(2)-N(2)O(Ar))(THF)](2) (2), which contains a kappa(2)(N,O)-bound bidentate N(2)O(Ar) ligand. The reaction of 1 with Mg(n)Bu(2) gave the four-coordinate monomeric butyl compound Mg(N(2)O(Ar))(n)Bu (3), whereas with (n)BuMgCl, a mixture of products was formed, including the six-coordinate homoleptic species Mg(N(2)O(Ar))(2) (4). The reaction of [Na(kappa(2)-N(2)O(Ar))(THF)](2) with (n)BuMgCl also gave 3, as did the redistribution reaction of Mg(n)Bu(2) with 4. The reaction of 1 with Mg{N(SiRMe(2))(2)}(2) afforded the four-coordinate amide derivatives Mg(N(2)O(Ar)){N(SiRMe(2))(2)} (R = Me (6) or H (7)), together with 4. The reactions of 1 with ZnMe(2) or Zn{N(SiMe(3))(2)}(2) gave the monomeric compounds Zn(N(2)O(Ar))Me (8) and Zn(N(2)O(Ar)){N(SiMe(3))(2)} (9), respectively. The reaction 9 of with HCl formed Zn(N(2)O(Ar))Cl (11), and subsequent addition of LiN(SiHMe(2))(2) to 11 led to Zn(N(2)O(Ar)){N(SiHMe(2))(2)} (12). The reaction of 1 with either Zn{N(SiMe(3))(2)}(2) or 9 gave Zn(N(2)O(Ar))(2). The compounds 2, 3, 4, 6, 8, 9 and 11 were crystallographically characterized. Compound was very active for the ring-opening polymerization (ROP) of epsilon-caprolactone (epsilon-CL) but the process was very poorly controlled as judged by the M(n) and polydispersity index of the polymer. Compounds 3, 8, 9 and 12 gave poor conversions to poly(epsilon-CL) over extended periods. N(2)O(Ar)H = 2,4-di-tert-butyl-6-(bis(3,5-dimethylpyrazolyl)methyl)phenol.