What Determines the Lewis Acidity of a Bismuthane? Towards Bi-Based FLPs.

Aiming at intramolecular frustrated Lewis pairs (FLPs) based on soft Lewis acidic bismuth centers, a phosphine function was combined with a dichloridobismuthane unit on a phenylene backbone utilizing a scrambling approach. The reaction between two equivalents of BiCl and (o-(PhP)CH)Bi yielded (o-(PhP)CH)BiCl(THF), the structure of which indicated BiP interactions and thus a pronounced Lewis acidity at the bismuth center that was confirmed by the Gutmann-Beckett method. However, the system turned out to be insufficient to be utilized for FLP reactivity.

Appropriation of group II metals: synthesis and characterisation of the first alkaline earth metal supported transition metal carbonite complexes.

Nickel carbonite complexes supported by alkaline earth metals have been accessed salt-metathesis of the corresponding alkali metal precursors. The new complexes undergo Schlenk-like exchange reactions in solution which have been investigated by NMR spectroscopy. Also their reactivity towards epoxides and carbon monoxide was studied.

Controlling the Activation at Ni-CO Moieties through Lewis Acid Interactions in the Second Coordination Sphere.

Nickel complexes with a two-electron reduced CO ligand (CO , "carbonite") are investigated with regard to the influence alkali metal (AM) ions have as Lewis acids on the activation of the CO entity. For this purpose complexes with Ni(CO)AM (AM=Li, Na, K) moieties were accessed via deprotonation of nickel-formate compounds with (AM)N(Pr). It was found that not only the nature of the AM ions in vicinity to CO affect the activation, but also the number and the ligation of a given AM.

A high-spin alkylperoxo-iron(iii) complex with -anionic ligands: implications for the superoxide reductase mechanism.

The NO macrocycle of the 12-TMCO ligand stabilizes a high spin ( = 5/2) [Fe(12-TMCO)(OOBu)Cl] (3-Cl) species in the reaction of [Fe(12-TMCO)(OTf)] (1-(OTf)) with -butylhydroperoxide (BuOOH) in the presence of tetraethylammonium chloride (NEtCl) in acetonitrile at -20 °C. In the absence of NEtCl the oxo-iron(iv) complex 2 [Fe(12-TMCO)(O)(CHCN)] is formed, which can be further converted to 3-Cl by adding NEtCl and BuOOH. The role of the -chloride ligand in the stabilization of the Fe-OOBu moiety can be extended to other anions including the thiolate ligand relevant to the enzyme superoxide reductase (SOR).

A New Thiolate-Bound Dimanganese Cluster as a Structural and Functional Model for Class Ib Ribonucleotide Reductases.

In class Ib ribonucleotide reductases (RNRs) a dimanganese(II) cluster activates superoxide (O ⋅ ) rather than dioxygen (O ), to access a high valent Mn -O -Mn species, responsible for the oxidation of tyrosine to tyrosyl radical. In a biomimetic approach, we report the synthesis of a thiolate-bound dimanganese complex [Mn (BPMT)(OAc) ](ClO) (BPMT=(2,6-bis{[bis(2-pyridylmethyl)amino]methyl}-4-methylthiophenolate) (1) and its reaction with O ⋅ to form a [(BPMT)MnO Mn] complex 2. Resonance Raman investigation revealed the presence of an O-O bond in 2, while EPR analysis displayed a 16-line S =1/2 signal at g=2 typically associated with a Mn Mn core, as detected in class Ib RNRs.

Evidence of Sulfur Non-Innocence in [Co (dithiacyclam)] -Mediated Catalytic Oxygen Reduction Reactions.

In many metalloenzymes, sulfur-containing ligands participate in catalytic processes, mainly via the involvement in electron transfer reactions. In a biomimetic approach, we now demonstrate the implication of S-ligation in cobalt mediated oxygen reduction reactions (ORR). A comparative study between the catalytic ORR capabilities of the four-nitrogen bound [Co(cyclam)] (1; cyclam=1,5,8,11-tetraaza-cyclotetradecane) and the S-containing analog [Co(S N -cyclam)] (2; S N -cyclam=1,8-dithia-5,11-diaza-cyclotetradecane) reveals improved catalytic performance once the chalcogen is introduced in the Co coordination sphere.

A strained intramolecular P/Al-FLP and its reactivity toward allene.

FLPs featuring aluminum-phosphane interactions, spring-loaded by a rigid biphenylene linker, have been accessed through a route where trimethyltin units at phosphane-functionalized organic backbones are exchanged by an AlCl moiety. Upon contact with substrates like CO these are readily bound by the Al/P site with release of strain. The system could also be utilized for a unique reactivity, namely the activation of allene.

Reactivity of Xantphos-Type Rhodium Complexes Towards SF : SF Versus SF Complex Generation.

S-F-bond activation of sulfur tetrafluoride at [Rh(Cl)( xanPOP)] (1; xanPOP=9,9-dimethyl-4,5-bis-(di-tert-butylphosphino)-xanthene) led to the formation of the cationic complex [Rh(F)(Cl)(SF )( xanPOP)][SF ] (2 a) together with trans-[Rh(Cl)(F) ( xanPOP)] (3) and cis-[Rh(Cl) (F)( xanPOP)] (4) which both could also be obtained by the reaction of SF Cl with 1. In contrast to that, the conversion of SF at the methyl complex [Rh(Me)( xanPOP)] (5) gave the isolable and room-temperature stable cationic λ -trifluorosulfanyl complex [Rh(Me)(SF )( xanPOP)][SF ] (6). Treatment of 6 with the Lewis acids BF or AsF produced the dicationic difluorosulfanyl complex [Rh(Me)(SF )( xanPOP)][BF ] (8 a) or [Rh(Me)(SF )( xanPOP)][AsF ] (8 b), respectively.

Synthesis of Intramolecular P/Al-Based Frustrated Lewis Pairs via Aluminum-Tin-Exchange and their Reactivity toward CO.

Frustrated Lewis pairs (FLPs) composed of acidic alane and basic phosphane functions, separated by a xanthene linker, can be prepared through the corresponding Me Sn derivative and methyl aluminum compounds with elimination of Me Sn. This way MeClAl-, Cl Al- and (C F ) Al- moieties could be introduced and the resulting FLPs are stabilized by a further equivalent of the alane precursors. In contact with the FLPs CO is bound via the C atom at the phosphane functions and the two O atoms at the Al centers.

The influence of secondary interactions on the [Ni(O)] mediated aldehyde oxidation reactions.

A rate enhancement of one to two orders of magnitude can be obtained in the aldehyde deformylation reactions by replacing the -N(CH) groups of [Ni(O)(Me[12]aneN)] (Me[12]aneN = 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane) and [Ni(O)(Me[13]aneN)] (Me[13]aneN = 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclotridecane) complexes by -NH in [Ni(O)([12]aneN)] (2; [12]aneN = 1,4,7,10-tetraazacyclododecane) and [Ni(O)([13]aneN)] (4; [13]aneN = 1,4,7,10-tetraazacyclotridecane). Based on detailed spectroscopic, reaction-kinetics and theoretical investigations, the higher reactivities of 2 and 4 are attributed to the changes in the secondary-sphere interactions between the [Ni(O)] and [12]aneN or [13]aneN moieties, which open up an alternative electrophilic pathway for the aldehyde oxidation reaction. Identification of primary kinetic isotope effects on the reactivity and stability of 2 when the -NH groups of the [12]aneN ligand are deuterated may also suggest the presence of secondary interaction between the -NH groups of [12]aneN and [Ni(O)] moieties, although, such interactions are not obvious in the DFT calculated optimized structure at the employed level of theory.

A rare isostructural series of 3d-4f cyanido-bridged heterometallic squares obtained by assembling [Fe{HB(pz)}(CN)] and Ln ions: synthesis, X-ray structure and cryomagnetic study.

A new series of cyanido-bridged {FeLn} neutral molecular squares of general formula [Fe{HB(pz)}(CN)(μ-CN)Ln(NO)(pyim)(PhPO)]·2CHCN [Ln = Ce (1), Pr (2), Nd (3), Gd (4), Tb (5), Dy (6) and Er (7); {HB(pz)} = hydrotris(pyrazolyl)borate, pyim = 2-(1-imidazol-2-yl)pyridine and PhPO = triphenylphosphine oxide] were obtained by reacting the low-spin [Fe{HB(pz)}(CN)] species with the preformed [Ln(pyim)(NO)(pyim)(PhPO)] complex anions (generated by mixing the nitrate salt of each Ln(III) ion with pyim and PhPO molecules). Single-crystal X-ray diffraction studies show that 1-7 are isostructural compounds that crystallize in the triclinic 1̄ space group. Their crystal structures consist of centrosymmetric cyanido-bridged {FeLn} molecular squares where two [Fe{HB(pz)}(CN)] units adopt bis-monodentate coordination modes towards two [Ln(pyim)(NO)(pyim)(PhPO)] moieties.

Secondary Phosphine Oxide Functionalized Gold Clusters and Their Application in Photoelectrocatalytic Hydrogenation Reactions.

Ligands in ligand-protected metal clusters play a crucial role, not only because of their interaction with the metal core, but also because of the functionality they provide to the cluster. Here, we report the utilization of secondary phosphine oxide (SPO), as a new family of functional ligands, for the preparation of an undecagold cluster . Different from the commonly used phosphine ligand (i.

Transformation of Formazanate at Nickel(II) Centers to Give a Singly Reduced Nickel Complex with Azoiminate Radical Ligands and Its Reactivity toward Dioxygen.

The heteroleptic (formazanato)nickel bromide complex LNi(μ-Br)NiL [LH = Mes-NH-N═C(-tol)-N═N-Mes] has been prepared by deprotonation of LH with NaH followed by reaction with NiBr(dme). Treatment of this complex with KC led to transformation of the formazanate into azoiminate ligands via N-N bond cleavage and the simultaneous release of aniline. At the same time, the potentially resulting intermediate complex L'Ni [L' = HN═C(-tol)-N═N-Mes] was reduced by one additional electron, which is delocalized across the π system and the metal center.

Structural Determination of an Unusual Cu -Porphyrin-π-Bond in a Hetero-Pacman Cu-Zn-Complex.

The synthesis and characterization of a hetero-dinuclear compound is presented, in which a copper(I) trishistidine type coordination unit is positioned directly above a zinc porphyrin unit. The close distance between the two coordination fragments is secured by a rigid xanthene backbone, and a unique (intramolecular) copper porphyrin-π-bond was determined for the first time in the molecular structure. This structural motif was further analyzed by temperature-dependent NMR studies: In solution at room temperature the coordinative bond fluctuates, while it can be frozen at low temperatures.

Electron transfer within β-diketiminato nickel bromide and cobaltocene redox couples activating CO.

Reduction of β-diketiminato nickel(ii) complexes (LtBuNiII) to the corresponding nickel(i) compounds does not require alkali metal compounds but can also be performed with the milder cobaltocenes. LtBuNiBr and Cp2Co have rather similar redox potentials, so that the equilibrium with the corresponding electron transfer compound [LtBuNiIBr][Cp2CoIII] (ETC) clearly lies on the side of the starting materials. Still, the ETC portion can be used to activate CO2 yielding a mononuclear nickel(ii) carbonate complex and ETC can be isolated almost quantitatively from the solutions through crystallisation.

Selective Transformation of Nickel-Bound Formate to CO or C-C Coupling Products Triggered by Deprotonation and Steered by Alkali-Metal Ions.

The complexes [L Ni(OCO-κ O,C)]M [N(SiMe ) ] (M=Li, Na, K), synthesized by deprotonation of a nickel formate complex [L NiOOCH] with the corresponding amides M[N(SiMe ) ], feature a Ni -CO core surrounded by Lewis-acidic cations (M ) and the influence of the latter on the behavior and reactivity was studied. The results point to a decrease of CO activation within the series Li, Na, and K, which is also reflected in the reactivity with Me SiOTf leading to the liberation of CO and formation of a Ni-OSiMe complex. Furthermore, in case of K , the {[K [N(SiMe ) ] } shell around the Ni-CO entity was shown to have a large impact on its stabilization and behavior.