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Featured researches published by Burgert Blom.


Journal of the American Chemical Society | 2013

Electron-Rich N-Heterocyclic Silylene (NHSi)–Iron Complexes: Synthesis, Structures, and Catalytic Ability of an Isolable Hydridosilylene–Iron Complex

Burgert Blom; Stephan Enthaler; Shigeyoshi Inoue; Elisabeth Irran; Matthias Driess

The first electron-rich N-heterocyclic silylene (NHSi)-iron(0) complexes are reported. The synthesis of the starting complex is accomplished by reaction of the electron-rich Fe(0) precursor [(dmpe)2Fe(PMe3)] 1 (dmpe =1,2-bis(dimethylphosphino)ethane) with the N-heterocyclic chlorosilylene LSiCl (L = PhC(N(t)Bu)2) 2 to give, via Me3P elimination, the corresponding iron complex [(dmpe)2Fe(←:Si(Cl)L)] 3. Reaction of in situ generated 3 with MeLi afforded [(dmpe)2Fe(←:Si(Me)L)] 4 under salt metathesis reaction, while its reaction with Li[BHEt3] yielded [(dmpe)2Fe(←:Si(H)L)] 5, a rare example of an isolable Si(II) hydride complex and the first such example for iron. All complexes were fully characterized by spectroscopic means and by single-crystal X-ray diffraction analyses. DFT calculations further characterizing the bonding situation between the Si(II) and Fe(0) centers were also carried out, whereby multiple bonding character is detected in all cases (Wiberg Bond Index >1). For the first time, the catalytic activity of a Si(II) hydride complex was investigated. Complex 5 was used as a precatalyst for the hydrosilylation of a variety of ketones in the presence of (EtO)3SiH as a hydridosilane source. In most cases excellent conversions to the corresponding alcohols were obtained after workup. The reaction pathway presumably involves a ketone-assisted 1,2-hydride transfer from the Si(II) to Fe(0) center, as a key elementary step, resulting in a betaine-like silyliumylidene intermediate. The appearance of the latter intermediate is supported by DFT calculations, and a mechanistic proposal for the catalytic process is presented.


Inorganic chemistry frontiers | 2014

N-heterocyclic silylene complexes in catalysis: new frontiers in an emerging field

Burgert Blom; Daniel Gallego; Matthias Driess

The present account is a review of all N-heterocyclic silylene (NHSi) transition metal complexes that have been employed in catalytic transformations, reported up to the present time (2013). NHSi transition metal complexes now enjoy indefatigable attention since their facile isolation was realised by the report of the first isolable NHSis by West and Denk in 1994. Despite considerable research activity since then, in comparison to ubiquitous N-heterocyclic carbene (NHC) complexes, NHSi complexes are still comparatively rare. Accordingly, in comparison to the plethora of reports associated with NHC complexes, implicated in catalytic processes, only scant examples exist for NHSi complexes. Some of these reports include Heck or Suzuki type coupling, alkyne cyclotrimerisation, ketone hydrosilylation, amide reduction or Sonogashira cross-coupling reactions, and are discussed in detail here. These endeavours pave the way for new families of catalysts based on NHSis and highlight the potential future applications of these emerging and rather unexplored complexes in novel catalytic processes.


Journal of the American Chemical Society | 2013

A Fragile Zwitterionic Phosphasilene as a Transfer Agent of the Elusive Parent Phosphinidene (:PH)

Kerstin Hansen; Tibor Szilvási; Burgert Blom; Shigeyoshi Inoue; Jan Dirk Epping; Matthias Driess

The simplest parent phosphinidene, :PH (1), has been observed only in the gas phase or low temperature matrices and has escaped rigorous characterization because of its high reactivity. Its liberation and transfer to an unsaturated organic molecule in solution has now been accomplished by taking advantage of the facile homolytic bond cleavage of the fragile Si═P bond of the first zwitterionic phosphasilene LSi=PH (8) (L = CH[(C═CH2)CMe(NAr)2]; Ar = 2,6-(i)Pr2C6H3). The latter bears two highly localized lone pairs on the phosphorus atom due to the LSi═PH ↔ LSi(+)-PH(-) resonance structures. Strikingly, the dissociation of 8 in hydrocarbon solutions occurs even at room temperature, affording the N-heterocyclic silylene LSi: (9) and 1, which leads to oligomeric [PH]n clusters in the absence of a trapping agent. However, in the presence of an N-heterocyclic carbene as an unsaturated organic substrate, the fragile phosphasilene 8 acts as a :PH transfer reagent, resulting in the formation of silylene 9 and phosphaalkene 11 bearing a terminal PH moiety.


Chemistry: A European Journal | 2012

Facile access to silicon-functionalized bis-silylene titanium(II) complexes.

Burgert Blom; Matthias Driess; Daniel Gallego; Shigeyoshi Inoue

A series of unprecedented bis-silylene titanium(II) complexes of the type [(η(5)-C(5)H(5))(2)Ti(LSiX)(2)] (L=PhC(NtBu)(2); X=Cl, CH(3), H) has been prepared using a phosphane elimination strategy. Treatment of the [(η(5)-C(5)H(5))(2)Ti(PMe(3))(2)] precursor (1) with two molar equivalents of the N-heterocyclic chlorosilylene LSiCl (2), results in [(η(5)-C(5)H(5))(2)Ti(LSiCl)(2)] (3) with concomitant PMe(3) elimination. The presence of a Si-Cl bond in 3 enabled further functionalization at the silicon(II) center. Accordingly, a salt metathesis reaction of 3 with two equivalents of MeLi results in [(η(5)-C(5)H(5))(2)Ti(LSiMe)(2)] (4). Similarly, the reaction of 3 with two equivalents of LiBHEt(3) results in [(η(5)-C(5)H(5))(2)Ti(LSiH)(2)] (5), which represents the first example of a bis-(hydridosilylene) metal complex. All complexes were fully characterized and the structures of 3 and 4 elucidated by single-crystal X-ray diffraction analysis. DFT calculations of complexes 3-5 were also carried out to assess the nature of the titanium-silicon bonds. Two σ and one π-type molecular orbital, delocalized over the Si-Ti-Si framework, are observed.


Angewandte Chemie | 2015

Synthesis of Mixed Silylene–Carbene Chelate Ligands from N‐Heterocyclic Silylcarbenes Mediated by Nickel

Gengwen Tan; Stephan Enthaler; Shigeyoshi Inoue; Burgert Blom; Matthias Driess

The Ni(II) -mediated tautomerization of the N-heterocyclic hydrosilylcarbene L(2) Si(H)(CH2 )NHC 1, where L(2) =CH(CCH2 )(CMe)(NAr)2 , Ar=2,6-iPr2 C6 H3 ; NHC=3,4,5-trimethylimidazol-2-yliden-6-yl, leads to the first N-heterocyclic silylene (NHSi)-carbene (NHC) chelate ligand in the dibromo nickel(II) complex [L(1) Si:(CH2 )(NHC)NiBr2 ] 2 (L(1) =CH(MeCNAr)2 ). Reduction of 2 with KC8 in the presence of PMe3 as an auxiliary ligand afforded, depending on the reaction time, the N-heterocyclic silyl-NHC bromo Ni(II) complex [L(2) Si(CH2 )NHCNiBr(PMe3 )] 3 and the unique Ni(0) complex [η(2) (Si-H){L(2) Si(H)(CH2 )NHC}Ni(PMe3 )2 ] 4 featuring an agostic SiH→Ni bonding interaction. When 1,2-bis(dimethylphosphino)ethane (DMPE) was employed as an exogenous ligand, the first NHSi-NHC chelate-ligand-stabilized Ni(0) complex [L(1) Si:(CH2 )NHCNi(dmpe)] 5 could be isolated. Moreover, the dicarbonyl Ni(0) complex 6, [L(1) Si:(CH2 )NHCNi(CO)2 ], is easily accessible by the reduction of 2 with K(BHEt3 ) under a CO atmosphere. The complexes were spectroscopically and structurally characterized. Furthermore, complex 2 can serve as an efficient precatalyst for Kumada-Corriu-type cross-coupling reactions.


Archive | 2013

Recent Advances in Silylene Chemistry: Small Molecule Activation En-Route Towards Metal-Free Catalysis

Burgert Blom; Matthias Driess

Previously only known as fleeting, transient laboratory curiosities in the 1960s, silylenes (species of the general type: SiIIR′R″ where R′ and R″ are any σ or π-bonded substituents, homo or heteroleptic) are now one of the most rigorously investigated classes of compounds in contemporary chemistry. The breakthroughs came in 1986 when Jutzi and co-workers isolated Cp* 2Si: (Cp* = η5-C5Me5), the first isolable Si(II) compound, and later in 1994 with the discovery of the first N-heterocyclic silylene by West and Denk, heralding the beginning of a bourgeoning era in low-valent silicon chemistry. Since these and other key discoveries, massive advances have been made in understanding and elucidating the nature of these reactive compounds, and their ability, for example, to activate small molecules, or behave as ligands in transition metal complexes which can perform a variety of catalytic or stoichiometric transformations. In this chapter, recent advances in silylene chemistry will be presented, with a particular focus on developments in the last 10 years approximately. A key emphasis will rest on the reactivity of isolable silylenes, including their coordination towards metals, with respect to small molecule bond activation, and potential catalytic transformations. Although metal-coordinated silylene complexes have been shown to be catalytically useful in a variety of transformations, metal-free catalysis with silylenes is still a target.


Australian Journal of Chemistry | 2013

N-Heterocyclic Silylene (NHSi) Rhodium and Iridium Complexes: Synthesis, Structure, Reactivity, and Catalytic Ability

Miriam Stoelzel; Carsten Präsang; Burgert Blom; Matthias Driess

Reaction of the zwitterionic N-heterocyclic silylene (NHSi) 1 L′Si: (L′ = [HC(CMeNAr)(C(CH2)NAr)], Ar = 2,6-iPr2C6H3) with HCl at low temperatures affords the kinetically stable 1,4-addition product of 1, LSiCl (L = [HC(CMeNAr)2], Ar = 2,6-iPr2C6H3) (9a), which upon reaction with [Rh(Cl)cod]2 and [Ir(Cl)cod]2 (cod = 1,5-cyclooctadiene) selectively affords the NHSi complexes [L(Cl)Si:→Rh(Cl)cod] (10a) and [L(Cl)Si:→Ir(Cl)cod] (10b), respectively. The latter were employed as pre-catalysts in the catalytic reduction of amides in the presence of silanes. Remarkably, they show strikingly different activities and selectivities. While complex 10a yields selectively the C–O cleavage product, 10b affords both cleavage products (C–O and C–N). Moreover, the total conversion of the catalytic amide reduction with 10b is significantly higher than the conversion with a benchmark system [Ir(Cl)cod]2 highlighting the enhanced catalytic activity afforded by the coordination of the NHSi ligand. Introducing the hydride source Li[HBEt3] into the catalytic reactions retards the catalyst performance due to a competitive decomposition pathway. This appears to occur via a H-shift onto the cod ligand with concomitant liberation of cyclooctene, which is also presented. The different reactivity of 10a and 10b towards nucleophiles such as MeLi is also discussed. The reaction of 10a with MeLi affords an intractable array of products, while the reaction of 10b with one equivalent of MeLi selectively affords [L(Cl)Si:→Ir(CH3)cod] (14) with selective methylation at the Ir centre. The analogous reaction with two equivalents of 10b affords the double methylated product [L(CH3)Si:→Ir(CH3)cod] (15).


Journal of the American Chemical Society | 2014

An elusive hydridoaluminum(I) complex for facile C-H and C-O bond activation of ethers and access to its isolable hydridogallium(I) analogue: syntheses, structures, and theoretical studies.

Gengwen Tan; Tibor Szilvási; Shigeyoshi Inoue; Burgert Blom; Matthias Driess

The reaction of AlBr3 with 1 molar equiv of the chelating bis(N-heterocyclic carbene) ligand bis(N-Dipp-imidazole-2-ylidene)methylene (bisNHC, 1) affords [(bisNHC)AlBr2](+)Br(-) (2) as an ion pair in high yield, representing the first example of a bisNHC-Al(III) complex. Debromination of the latter with 1 molar equiv of K2Fe(CO)4 in tetrahydrofuran (THF) furnishes smoothly, in a redox reaction, the (bisNHC)(Br)Al[Fe(CO)4] complex 3, in which the Al(I) center is stabilized by the Fe(CO)4 moiety through Al(I):→Fe(0) coordination. Strikingly, the Br/H ligand exchange reactions of 3 using potassium hydride as a hydride source in THF or tetrahydropyran (THP) do not yield the anticipated hydridoaluminum(I) complex (bisNHC)Al(H)[Fe(CO)4] (4a) but instead lead to (bisNHC)Al(2-cyclo-OC4H7)[Fe(CO)4] (4) and (bisNHC)Al(2-cyclo-OC5H9)[Fe(CO)4] (5), respectively. The latter are generated via C-H bond activation at the α-carbon positions of THF and THP, respectively, in good yields with concomitant elimination of dihydrogen. This is the first example whereby a low-valent main-group hydrido complex facilitates metalation of sp(3) C-H bonds. Interestingly, when K[BHR3] (R = Et, sBu) is employed as a hydride source to react with 3 in THF, the reaction affords (bisNHC)Al(OnBu)[Fe(CO)4] (6) as the sole product through C-O bond activation and ring opening of THF. The mechanisms for these novel C-H and C-O bond activations mediated by the elusive hydridoaluminum(I) complex 4a were elucidated by density functional theory (DFT) calculations. In contrast, the analogous hydridogallium(I) complex (bisNHC)Ga(H)[Fe(CO)4] (9) can be obtained directly in high yield by the reaction of the (bisNHC)Ga(Cl)[Fe(CO)4] precursor 8 with 1 molar equiv of K[BHR3] (R = Et, sBu) in THF at room temperature. The isolation of 9 and its inertness toward cyclic ethers might be attributed to the higher electronegativity of gallium versus aluminum. The stronger Ga(I)-H bond, in turn, hampers α-C-H metalation or C-O bond cleavage in cyclic ethers, the latter of which is supported by DFT calculations.


Chemistry: A European Journal | 2015

From an Isolable Acyclic Phosphinosilylene Adduct to Donor-Stabilized Si=E Compounds (E=O, S, Se).

Kerstin Hansen; Tibor Szilvási; Burgert Blom; Elisabeth Irran; Matthias Driess

Reaction of the arylchlorosilylene-NHC adduct ArSi(NHC)Cl [Ar=2,6-Trip2C6H3; NHC=(MeC)2(NMe)2C:] 1 with one molar equiv of lithium diphenylphosphanide affords the first stable NHC-stabilized acyclic phosphinosilylene adduct 2 (ArSi(NHC)PPh2), which could be structurally characterized. Compound 2, when reacted with one molar equiv selenium and sulfur, affords the silanechalcogenones 4 a and 4 b (ArSi(NHC)(=E)PPh2, 4 a: E=Se, 4 b: E=S), respectively. Conversion of 2 with an excess of Se and S, through additional insertion of one chalcogen atom into the Si=P bond, leads to 3 a and 3 b (ArSi(NHC)(=E)-E-P(=E)Ph2, 3 a: E=Se, 3 b: E=S), respectively. Additionally, the exposure of 2 to N2O or CO2 yielded the isolable NHC-stabilized silanone 4 c, Ar(NHC)(Ph2P)Si=O.


Angewandte Chemie | 2015

Biomimetic [2Fe-2S] clusters with extensively delocalized mixed-valence iron centers.

Shenglai Yao; Florian Meier; Nils Lindenmaier; Robert Rudolph; Burgert Blom; Mario Adelhardt; Jörg Sutter; Stefan Mebs; Michael Haumann; Karsten Meyer; Martin Kaupp; Matthias Driess

A complete series of biomimetic [2Fe-2S] clusters, [(L(Dep) Fe)2 (μ-S)2 ] (3, L(Dep) =CH[CMeN(2,6-Et2 C6 H3 )]2 ), [(L(Dep) Fe)2 (μ-S)2 K] (4), [(L(Dep) Fe)2 (μ-S)2 ][Bu4 N] (5, Bu=n-butyl), and [(L(Dep) Fe)2 (μ-S)2 K2 ] (6), could be synthesized and characterized. The all-ferric [2Fe-2S] cluster 3 is readily accessible through the reaction of [(L(Dep) Fe)2 (μ-H)2 ] (2) with elemental sulfur. The chemical reduction of 3 with one molar equivalent of elemental potassium affords the contact ion pair K(+) [2Fe-2S](-) (4) as a one-dimensional coordination polymer, which in turn reacts with [Bu4 N]Cl to afford the separate ion pair [Bu4 N](+) [2Fe-2S](-) (5). Further reduction of 4 with potassium furnishes the super-reduced all-ferrous [2Fe-2S] cluster 6. Remarkably, complexes 4 and 5 are [2Fe-2S] clusters with extensively delocalized Fe(2+) Fe(3+) pairs as evidenced by (57) Fe Mössbauer, X-ray absorption and emission spectroscopy (XAS, XES) and in accordance with DFT calculations.

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Matthias Driess

Technical University of Berlin

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Gengwen Tan

Technical University of Berlin

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Tibor Szilvási

University of Wisconsin-Madison

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Daniel Gallego

Technical University of Berlin

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Shigeyoshi Inoue

Technical University of Berlin

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Kerstin Hansen

Technical University of Berlin

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Elisabeth Irran

Technical University of Berlin

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Stephan Enthaler

Technical University of Berlin

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Florian Meier

Technical University of Berlin

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Jan Dirk Epping

Technical University of Berlin

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