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Herein, we present that the radicals [Ph3PC(Me)EMes2]˙ (2Si and 2Ge) can be generated from the α-silylated and α-germylated phosphorus ylides Ph3PC(Me)E(Cl)Mes2 (1Si and 1Ge) through one-electron reduction with Jones' dimer (MesNacNacMg)2 in benzene. Although isolation of the free radicals was not possible, the products of the intramolecular addition of the radicals to a phenyl substituent of the phosphorus moiety, followed by subsequent reaction with 2Si or 2Ge to the isolated species 3Si and 3Ge, respectively, were observed. This transformation witnesses a dearomative 1,4-addition of tetryl radical species to the phenyl scaffold in a stereoselective anti-fashion. [ABSTRACT FROM AUTHOR]

The overall neutral α-borylated phosphorus ylide Ph3PC(Me)BEt2 behaves like a polar borataalkene and can act as acyclic, ambiphilic π-type ligand with L- and Z-type functionalities side by side. In the complexes [MX{η2-Ph3PC(Me)BEt2}] (M = Cu, (Ag), Au; X = Cl, NTf2), the bonding is dominated by the highly nucleophilic ylidic carbon atom (L-type ligand). The Lewis acidic boron atom furnishes nonetheless a small but significant bonding contribution (Z-type ligand). [ABSTRACT FROM AUTHOR]

We herein report on the synthesis of biphenylenes substituted with a pyridine (N), a phosphine (P) and a carbene (C′) donor as well as a carbene donor with additional pyridine in the lateral position. We describe the synthesis and structures of derived gold(I) complexes, which we tried to use for the synthesis of non-palindromic [(C^C^D)AuIII] pincer complexes by means of an intramolecular oxidative addition of the strained biphenylene ring. However, the anticipated formation of gold(III) complexes failed due to kinetic and thermodynamic reasons, which we extensively investigated by quantum chemical calculations. Furthermore, we shed light on the oxidative addition of biphenylene to two different gold(I) systems reported in the literature. Our comprehensive quantum-chemical analysis is complemented by NMR experiments. [ABSTRACT FROM AUTHOR]

A highly luminescent non-palindromic [(C^C^N)Pd] pincer complex forms upon reacting pyridine-substituted 2,2′-diiodo-biphenyl with [Pd(PPh3)4]. This case study establishes for the first time that the title compound is formed via a double oxidative addition – comproportionation sequence. DFT and TDDFT calculations complement mechanistic and photophysical characterizations. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Very high activities were observed in the redox-induced hydroamination of alkynes by employing a redox-active gold(i) complex featuring an electron-deficient, terphenyl-substituted phosphonite-based ligand. The hydroamination proceeds roughly two-fold faster with the in situ oxidized catalysts than with their reduced form. [ABSTRACT FROM AUTHOR]

The activation of the C≡N moiety in the redox-active metalloligand [CpRu{κ3Npz-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 RuII-IrIII 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 IrIII 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 E0½ = 0.36 V, which was attributed to the RuII/RuIII redox couple, while two irreversible reduction processes were observed at very negative potentials and have been assigned to the stepwise reduction of IrIII to IrI. First efforts to elucidate the reaction mechanism have also been performed. [ABSTRACT FROM AUTHOR]

Heavy analogues of hydrocarbons intrigue chemists for a number of reasons, not least because they are often fundamentally different from their carbon counterparts and have remained a challenge for both experimentalists and theoreticians for a long time. The appealing properties of [1.1.1]propellanes of group 14 consisting of inverted tetrahedral bridgehead atoms can mainly be attributed to the particular bonding between the latter. More than 20 years after the first member of this family has been published, several contributions to this area have impressively extended the spectrum of these so-called main-group biradicaloids. Still in its infancy, further perspectives for these “non-classical” molecules are now arising. In this tutorial review, early findings and recent developments in this area are presented. Particular attention is drawn on the relationship of unusual structures and unusual reactivities of main-group element compounds in general and in particular of heavy propellane scaffolds of group 14. [ABSTRACT FROM AUTHOR]

The reaction conditions for the synthesis [Si2(Mepz)6] (1) and [Si(Mepz)4] (4) have been investigated in detail in order to obtain suitable precursor compounds for the synthesis of the hitherto unknown Janus-headligand tris(3,5-dimethylpyrazolyl)silanide ([Si(Mepz)3]−, MeTpsd). Within the monomeric lithium salt [Li(thf)(MeTpsd)] (5), the ambidentate silanide ligand is bound in a κ3N-fashion to the Li cation, featuring an uncoordinated, anionic silicon bridgehead. Treatment of the silanide with various electrophiles such as Me3SiCl, Me3SnCl and Ph3SnCl gave in each case the expected salt metathesis reaction with the formation of Si–Si and Si–Sn bonds, respectively. The products [Me3Si–Si(Mepz)3] (6) and [Me3Sn–Si(Mepz)3] (7) and [Ph3Sn–Si(Mepz)3] (8) are the first backbone-funtionalized derivatives originating from the tris(pyrazolyl)silanide. Overall, it could be concluded that the anionic ligand backbone of MeTpsd is much more accessible for electrophiles compared to the carbon analogue ([C(Mepz)3]−, MeTpmd). [ABSTRACT FROM AUTHOR]

In this communication we present the experimental charge density distribution in [Mg{(pz*)3C}2] (1), (pz* = 3,5-dimethylpyrazolyl), containing two non-coordinating sp3carbanionic lone-pairs. [ABSTRACT FROM AUTHOR]

We report on the utility of multifunctional, κ1Si:κ3S-coordinated tris(methimazolyl)silanide ligands [Si(mtMe)3]−for the stabilisation of a triangulopalladium cluster [Pd3{Si(mtMe)3}2] (3) consisting of very unusual μ3-capping SiR3donors. Differences to the corresponding platinum chemistry were supported by NMR spectroscopy and DFT calculations. [ABSTRACT FROM AUTHOR]

A straightforward natural abundance 2D HMQC NMR experiment between lithium-7 and nitrogen-15 is reported; this fast, reliable and routinely implementable method represents a powerful spectroscopic tool to study complex structures or intermediate species in solution, in particular those containing nitrogen-lithium bonds. [ABSTRACT FROM AUTHOR]

Herein, we present that the radicals [Ph 3 PC(Me)EMes 2 ]˙ (2Si and 2Ge) can be generated from the α-silylated and α-germylated phosphorus ylides Ph 3 PC(Me)E(Cl)Mes 2 (1Si and 1Ge) through one-electron reduction with Jones' dimer ( Mes NacNacMg) 2 in benzene. Although isolation of the free radicals was not possible, the products of the intramolecular addition of the radicals to a phenyl substituent of the phosphorus moiety, followed by subsequent reaction with 2Si or 2Ge to the isolated species 3Si and 3Ge, respectively, were observed. This transformation witnesses a dearomative 1,4-addition of tetryl radical species to the phenyl scaffold in a stereoselective anti -fashion.

The synthesis, characterisation and reactivity of new phosphine-functionalised tris(pyrazolyl)methane ligands (TpmPR 2 , 2a-c, with R = Ph, nBu, iPr) are presented. The reaction of 2a-c with [Rh(CO) 2 Cl] 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 ][PF 6 ] (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)Cl 2 ], 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.

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.

The heterolytic splitting of hydrogen by two types of [2.2]paracyclophane derived bisphosphines (1, 2a and 2b) in combination with tris(pentafluorophenyl)borane (3) at room temperature is described. The corresponding frustrated Lewis pairs (FLPs) exhibit different behavior in the activation of hydrogen. This results from diverse steric and electronic properties of the bisphosphines. The reactivity of the frustrated Lewis pairs was exploited in the first diastereoselective domino hydrosilylation/hydrogenation reaction catalyzed by FLPs.

We report the synthesis and properties of alkynyl-functionalised and -bridged bicyclo[1.1.1]pentane derivatives consisting of the heavier group 14 elements silicon and tin.

In this communication we present the experimental charge density distribution in [Mg{(pz*)(3)C}(2)] (1), (pz* = 3,5-dimethylpyrazolyl), containing two non-coordinating sp(3) carbanionic lone-pairs.

We report on the utility of multifunctional, κ(1)Si:κ(3)S-coordinated tris(methimazolyl)silanide ligands [Si(mt(Me))(3)](-) for the stabilisation of a triangulo palladium cluster [Pd(3){Si(mt(Me))(3)}(2)] (3) consisting of very unusual μ(3)-capping SiR(3) donors. Differences to the corresponding platinum chemistry were supported by NMR spectroscopy and DFT calculations.

The reaction conditions for the synthesis [Si(2)((Me)pz)(6)] (1) and [Si((Me)pz)(4)] (4) have been investigated in detail in order to obtain suitable precursor compounds for the synthesis of the hitherto unknown Janus-head ligand tris(3,5-dimethylpyrazolyl)silanide ([Si((Me)pz)(3)](-), (Me)Tpsd). Within the monomeric lithium salt [Li(thf)((Me)Tpsd)] (5), the ambidentate silanide ligand is bound in a kappa(3)N-fashion to the Li cation, featuring an uncoordinated, anionic silicon bridgehead. Treatment of the silanide with various electrophiles such as Me(3)SiCl, Me(3)SnCl and Ph(3)SnCl gave in each case the expected salt metathesis reaction with the formation of Si-Si and Si-Sn bonds, respectively. The products [Me(3)Si-Si((Me)pz)(3)] (6) and [Me(3)Sn-Si((Me)pz)(3)] (7) and [Ph(3)Sn-Si((Me)pz)(3)] (8) are the first backbone-functionalized derivatives originating from the tris(pyrazolyl)silanide. Overall, it could be concluded that the anionic ligand backbone of (Me)Tpsd is much more accessible for electrophiles compared to the carbon analogue ([C((Me)pz)(3)](-), (Me)Tpmd).

Two equivalents of 3,5-bis(trifluoromethyl)pyrazole or 5-methyl-3-(trifluoromethyl)pyrazole react with [Ge{N(SiMe(3))(2)}(2)] to give dimeric homoleptic germanium(ii) compounds [{Ge(3,5-RR'pz)(2)}(2)] (R = R' = CF(3) (1); R = Me, R' = CF(3) (2)), which provide cationic triply pz-bridged cages of the general formula [Ge(mu(2)-3,5-RR'pz)(3)Ge](+)[OTf](-) (R = R' = CF(3) (3); R = Me, R' = CF(3) (4)) upon treatment with one equivalent of triflic acid (HOTf, HSO(3)CF(3)). The compounds were studied using the pulsed field gradient spin-echo (PGSE) NMR technique and (19)F,(1)H-HOESY NMR methods. Single crystal X-ray structure determinations of all compounds are reported. The results obtained are verified by density functional theory calculations.

A straightforward natural abundance 2D HMQC NMR experiment between lithium-7 and nitrogen-15 is reported; this fast, reliable and routinely implementable method represents a powerful spectroscopic tool to study complex structures or intermediate species in solution, in particular those containing nitrogen-lithium bonds.

Multifunctional ligands with podand topology provide intrinsically well-defined coordination geometries. Several subgroups of multidentate ligand systems comprising dual functionality have been developed so far. Recent advances made in this research area reflect its topicality. Work on metal complexes of ambiphilic ligands consisting of Lewis-acidic Group 13 element bridgehead atoms and additional donor functionalities is in the current focus of interest. The intrinsic topology of tetradentate ligands may introduce a fascinating reactivity and interesting electronic properties to the metal complexes. Janus-head type ligands are very promising candidates for the preparation of multimetallic complexes.

Tris(pyrazolyl)methanides, [C(3,5-R2pz)3]-, contain an unassociated tetrahedral carbanionic centre in the bridgehead position. In addition to nitrogen donor centres for transition metal coordination, an accessible reactive site for further manipulations is available in the backbone of the ligand. The coordination variability of the ambidental C-/N ligand [C(3,5-Me2pz)3]- was elucidated by investigating its coinage metal complexes. Two principle coordination modes were found for complexes of general formula [LMPR3] (with M = Cu(I), Ag(I), Au(I); L =[C(3,5-Me2pz)3]-; R = Ph, OMe). While for Cu(I) (2,3) and Ag(I) (4) complexes the anionic ligand acts as a face-capping, six electron N3-donor, gold(I) (5) is coordinated by the bridging carbanion yielding a two coordinate Au(I) complex comprising a covalent Au-C bond. The complexes featuring the kappa3-coordinated N3-donor ligand were investigated by 31P CP (MAS) NMR in the solid state.

A combination of the rigid bis(5H-dibenzo[a,d]cyclohepten-5-yl)amine (trop(2)NH) and 5-amino-5H-dibenzo[a,d]cycloheptene (tropNH(2)) ligand allowed the synthesis of the stable pentacoordinated 18 electron amine olefin rhodium(i) complex [Rh(trop(2)NH)(tropNH(2))]O(3)SCF(3)(); this complex can be cleanly deprotonated [pK(a)(DMSO) = 20.6(1)] to the corresponding amide [Rh(trop(2)N)(tropNH(2))](6) which is reversibly oxidised at -0.466 V (vs. Fc/Fc(+)). The coordinated NH bond strength in is estimated to be 379 +/- 10 kJ mol(-1).