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The introduction of heteroatoms into conjugated organic molecules is an important strategy to tune their reactivity and physical properties. In this realm triazabutadienes (TBDs) of the general from R2C=N-N=NR' are an interesting class of compounds, however, general synthetic protocols for their generation are limited. Based on the serendipitous finding that the sterically encumbered azide Mes*N3 (Mes* = 2,4,6-tBu3C6H2) reacted with PMe3 in the presence of an aromatic aldehyde to form a TBD, we now report on the "Azide-Wittig" reaction. This azide-Wittig reaction is shown to be a versatile tool for the synthesis of a variety of TBDs, tolerating a wide range of aldehydes and organic azides as coupling partners. The preference for azide-Wittig, rather than aza-Wittig reactivity was rationalized using computational methods. This study shows how kinetic control can significantly alter the reaction pathway, thereby switching from an aza-Wittig to an azide-Wittig regime., (© 2024 Wiley‐VCH GmbH.)

Biradicals are important intermediates in the formation and breaking of a chemical bond. Their use as molecular switches is of particular interest. Much less is known about tetraradicals, which can, for example, consist of two biradical(oid) units. Here we report the synthesis of the first persistent phosphorus-centred tetraradical bound to a transition metal fragment. Starting from a zirconocene complex, rac-(ebthi)ZrCl 2 (rac-(ebthi)=1,2-ethylene-1,10-bis(η 5 -tetrahydroindenyl), two cyclo-1,3-diphospha-pentane-1,3-diyls were successfully introduced, which finally led to the isolation of a deep green zirconcene-bridged bis(biradicaloid) complex (5) that can act as a double molecular switch. Under the influence of light (570 nm), this tetraradical forms a transannular bond in each of the two five-membered biradical units, leading to the formation of housane 5 h. Upon irradiation at 415 nm, the reverse reaction is observed, fully recovering tetraradical 5. Through single-crystal-to-single-crystal transformation, both stable species of the molecular switch could be structurally characterised using SCXRD. The switching under the influence of light and the activation of molecular hydrogen were analysed in solution using NMR and UV spectroscopy. It was found that the addition of one or two equivalents of molecular hydrogen can be switched on and off by light., (© 2024 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

The synthesis of group 4 metal 1-metallacyclobuta-2,3-dienes as organometallic analogues of elusive 1,2-cyclobutadiene has so far been limited to SiMe 3 substituted examples. We present the synthesis of two Ph substituted dilithiated ligand precursors for the preparation of four new 1-metallacyclobuta-2,3-dienes [rac-(ebthi)M] (M=Ti, Zr; ebthi=1,2-ethylene-1,10-bis(η 5 -tetrahydroindenyl)). The organolithium compounds [Li 2 (RC 3 Ph)] (1 b: R=Ph, 1 c: R=SiMe 3 ) as well as the metallacycles of the general formula [rac-(ebthi)M(R 1 C 3 R 2 )] (2 b: M=Ti, R 1 =R 2 =Ph, 2 c: M=Ti, R 1 =Ph, R 2 =SiMe 3 ; 3 b: M=Zr, R 1 =R 2 =Ph; 3 c: M=Zr, R 1 =Ph, R 2 =SiMe 3 ) were fully characterised. Single crystal X-ray diffraction and quantum chemical bond analysis of the Ti and Zr complexes reveal ligand influence on the biradicaloid character of the titanocene complexes. X-band EPR spectroscopy of structurally similar Ti complexes [rac-(ebthi)Ti(Me 3 SiC 3 SiMe 3 )] (2 a), 2 b, and 2 c was carried out to evaluate the accessibility of an EPR active triplet state. Cyclic voltammetry shows that introduction of Ph groups renders the complexes easier to reduce. 13 C CPMAS NMR analysis provides insights into the cause of the low field shift of the resonances of metal-bonded carbon atoms and provides evidence of the absence of the β-C-Ti interaction., (© 2024 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

The conversion of CO 2 into multicarbon (C 2+ ) compounds by reductive homocoupling offers the possibility to transform renewable energy into chemical energy carriers and thereby create "carbon-neutral" fuels or other valuable products. Most available studies have employed heterogeneous metallic catalysts, but the use of molecular catalysts is still underexplored. However, several studies have already demonstrated the great potential of the molecular approach, namely, the possibility to gain a deep mechanistic understanding and a more precise control of the product selectivity. This Minireview summarizes recent progress in both the thermo- and electrochemical reductive homocoupling of CO 2 toward C 2+ products mediated by molecular catalysts. In addition, reductive CO homocoupling is discussed as a model for the further conversion of intermediates obtained from CO 2 reduction, which may serve as a source of inspiration for developing novel molecular catalysts in the future., (© 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Dehydropolymerisation of methylamine borane (H 3 B⋅NMeH 2 ) using the well-known iron amido complex [(PNP)Fe(H)(CO)] (PNP=N(CH 2 CH 2 PiPr 2 ) 2 ) (1) gives poly(aminoborane)s by a chain-growth mechanism. In toluene, rapid dehydrogenation of H 3 B⋅NMeH 2 following first-order behaviour as a limiting case of a more general underlying Michaelis-Menten kinetics is observed, forming aminoborane H 2 B=NMeH, which selectively couples to give high-molecular-weight poly(aminoborane)s (H 2 BNMeH) n and only traces of borazine (HBNMe) 3 by depolymerisation after full conversion. Based on a series of comparative experiments using structurally related Fe catalysts and dimethylamine borane (H 3 B⋅NMe 2 H) polymer formation is proposed to occur by nucleophilic chain growth as reported earlier computationally and experimentally. A silyl functionalised primary borane H 3 B⋅N(CH 2 SiMe 3 )H 2 was studied in homo- and co-dehydropolymerisation reactions to give the first examples for Si containing poly(aminoborane)s., (© 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

The thermodynamics of halogen bonding of a series of isostructural Group 10 metal pincer fluoride complexes of the type [(3,5-R 2 - tBu POCOP tBu )MF] (3,5-R 2 - tBu POCOP tBu =κ 3 -C 6 HR 2 -2,6-(OPtBu 2 ) 2 with R=H, tBu, COOMe; M=Ni, Pd, Pt) and iodopentafluorobenzene was investigated. Based on NMR experiments at different temperatures, all complexes 1-tBu (R=tBu, M=Ni), 2-H (R=H, M=Pd), 2-tBu (R=tBu, M=Pd), 2-COOMe (R=COOMe, M=Pd) and 3-tBu (R=tBu, M=Pt) form strong halogen bonds with Pd complexes showing significantly stronger binding to iodopentafluorobenzene. Structural and computational analysis of a model adduct of complex 2-tBu with 1,4-diiodotetrafluorobenzene as well as of structures of iodopentafluorobenzene in toluene solution shows that formation of a type I contact occurs., (© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

The reaction of the allene precursor Li 2 (Me 3 SiC 3 SiMe 3 ) with [Cp 2 ZrCl 2 ] (Cp=cyclopentadienyl) was examined. The selective formation of hitherto unknown linear, allene-bridged dizirconocene complexes [(Cp 2 ZrCl) 2 {-μ-(Me 3 Si)C 3 (SiMe 3 )-}] and [(Cp 2 Zr) 2 {-μ-(Me 3 Si)C 3 (SiMe 3 )-} 2 ] was observed. Upon σ coordination of the allenediyl unit to {Cp 2 Zr}, pyrophoric Li 2 (Me 3 SiC 3 SiMe 3 ) is tamed stepwise to yield a surprisingly robust 1,5-dizirconacyclooctatetra-2,3,6,7-ene with cumulated double bonds. This complex is unexpectedly inert against moisture, air, water and acetone. Surprisingly, it degrades under MS conditions to give the highly strained 1-zirconacyclobuta-2,3-diene. All compounds isolated have been fully characterised and the molecular structures are discussed. The stability and reactivity of these complexes are rationalised by DFT computations., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Coordination of the alkyl-substituted alkynes Me 3 SiC 2 CH 2 R (1: R=SiMe 3 ; 2: R=N(SiMe 3 ) 2 ) to titanocene centres [Cp' 2 Ti] (Cp'=Cp, Cp*) yields stable alkyne complexes of the type Cp' 2 Ti(η 2 -Me 3 SiC 2 CH 2 R) (3: Cp'=Cp, R=SiMe 3 ; 5: Cp'=Cp, R=N(SiMe 3 ) 2 ; 6: Cp'=Cp*, R=SiMe 3 ) that are not prone to alkyne/allene isomerisation. When reacting alkyne 2 with Cp * 2 TiCl 2 and Mg formation of the complex Cp* 2 Ti(III)(η 3 -Me 3 SiC 2 CH 2 ) (7) which displays a propargylic unit coordinated to the Ti III centre takes place. All complexes were fully characterised, the molecular structures for 5, 6, and 7 are discussed., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A mixed decamethyltitanocene(III) isonitrile alkynyl complex (7) was synthesized by the sequential introduction of the isonitrile and alkynyl ligands. Direct synthesis results in the formation of the diamagnetic decamethyltitanocene bis(isonitrile) (2) and bis(alkynyl) (3) complexes. Compound 7 undergoes disproportionation at room temperature to give 2 and 3. All complexes were fully characterized by IR, NMR, and EPR spectroscopy, and mass spectrometry. Molecular structures for complexes 2 and 7 are reported. The stability and reactivity of these complexes are rationalized by DFT computations., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A study of visible-light-driven hydrogen production using a multicomponent system consisting of different boron dipyrromethene (BODIPY) dyes, triethylamine and [{Pd(PPh3)Cl2}2] from THF/water mixtures is presented. A trio of meso-mesityl BODIPY dyes display the best activities and long-term stabilities of more than ten days with the 2,6-diiodo derivative showing the best performance., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Nanocomposites based on molybdenum disulfide (MoS2 ) and different carbon modifications are intensively investigated in several areas of applications due to their intriguing optical and electrical properties. Addition of a third element may enhance the functionality and application areas of such nanocomposites. Herein, we present a facile synthetic approach based on directed thermal decomposition of (Ph4 P)2 MoS4 generating MoS2 nanocomposites containing carbon and phosphorous. Decomposition at 250 °C yields a composite material with significantly enlarged MoS2 interlayer distances caused by in situ formation of Ph3 PS bonded to the MoS2 slabs through MoS bonds and (Ph4 P)2 S molecules in the van der Waals gap, as was evidenced by (31) P solid-state NMR spectroscopy. Visible-light-driven hydrogen generation demonstrates a high catalytic performance of the materials., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A detailed mechanism of hydrogen production by reduction of water with decamethyltitanocene triflate [Cp*2 Ti(III) (OTf)] has been derived for the first time, based on a comprehensive in situ spectroscopic study including EPR and ATR-FTIR spectroscopy supported by DFT calculations. It is demonstrated that two H2 O molecules coordinate to [Cp*2 Ti(III) (OTf)] subsequently forming [Cp2 *Ti(III) (H2 O)(OTf)] and [Cp*Ti(III) (H2 O)2 (OTf)]. Triflate stabilizes the water ligands by hydrogen bonding. Liberation of hydrogen proceeds only from the diaqua complex [Cp*Ti(III) (H2 O)2 (OTf)] and involves, most probably, abstraction and recombination of two H atoms from two molecules of [Cp*Ti(III) (H2 O)2 (OTf)] in close vicinity, which is driven by the formation of a strong covalent TiOH bond in the resulting final product [Cp*2 Ti(IV) (OTf)(OH)]., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The synthesis of a series of ansa-titanocene dichlorides [Cp'2TiCl2] (Cp' = bridged η(5)-tetramethylcyclopentadienyl) and the corresponding titanocene bis(trimethylsilyl)acetylene complexes [Cp'2Ti(η(2)-Me3SiC2SiMe3)] is described. The ethanediyl-bridged complexes [C2H4(C5Me4)2TiCl2] (2-Cl2) and [C2H4(C5Me4)2Ti(η(2)-Me3SiC2SiMe3)] (2-btmsa; btmsa = η(2)-Me3SiC2SiMe3) can be obtained from the hitherto unknown calcocenophane complex [C2H4(C5Me4)2Ca(THF)2] (1). Furthermore, a heterodiatomic bridging unit containing both, a dimethylsilyl and a methylene group was introduced to yield the ansa-titanocene dichloride [Me2SiCH2(C5Me4)2TiCl2] (3-Cl2) and the bis(trimethylsilyl)acetylene complex [Me2SiCH2(C5Me4)2Ti(η(2)-Me3SiC2SiMe3)] (3-btmsa). Besides, tetramethyldisilyl- and dimethylsilyl-bridged metallocene complexes (structural motif 4 and 5, respectively) were prepared. All ansa-titanocene alkyne complexes were reacted with stoichiometric amounts of water; the hydrolysis products were isolated as model complexes for the investigation of the elemental steps of overall water splitting. Compounds 1, 2-btmsa, 2-(OH)2, 3-Cl2, 3-btmsa, 4-(OH)2, 3-alkenyl and 5-alkenyl were characterised by X-ray diffraction analysis., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Visible-light-driven photocatalysis is currently attracting a great deal of attention because of its potential application in solar water splitting. However, the development of efficient and durable catalyst systems is still a challenging problem. In Ru dye-sensitised TiO(2) nanopowders, catalyst performances are found to decline as a result of poor bonding of the dye molecule to the TiO(2) surface and subsequent detachment and self-aggregation of the dye. Our strategy to improve the stability of the dye-TiO(2) interface is the encapsulation of the dye/TiO(2) assembly in an amino-group-containing polyallylamine layer anchored to TiO(2). A low-pressure pulsed microwave discharge plasma polymerization process was employed to coat a commercial anatase nanopowder with a thin polyallylamine layer to nanoconfine the adsorbed dye molecules. Electron microscopy and UV/Vis spectroscopy was carried out to characterise the resulting encapsulated nanostructures. The long-term stability of the new nanomaterial as the photoactive component of a water reduction catalyst system for H(2) evolution investigated in a slurry reactor under visible-light irradiation showed stable evolution rates over a period of several days., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Water reduction systems that use a bis-cyclometalated Ir(III) photosensitiser (PS) along with homogeneous Pd complexes as a source of in-situ-formed colloidal Pd as the water reducing complex (WRC) and triethylamine (TEA) as the sacrificial electron donor were tested and characterised with respect to their photocatalytic H(2) production performance. It was confirmed that substitution of the 2-(pyridin-2-yl)benzen-1-ide (pyb) ligand in the well-known system [Ir(pyb)(2)(bpy)](+) (bpy=2,2'-bipyridine) by the fluorinated cyclometalating ligand 5-fluoro-2-(5-methylpyridin-2-yl)benzen-1-ide (Fmpyb) tremendously enhanced the H(2) production rate. Moreover, variation of the bidentate N^N ligand bpy by alkyl substitution in the 4,4'-position resulted in an increase in the H(2) production yield by a factor of three. The incident-photon-to-hydrogen-efficiency could be enhanced from 2.6 to 12.3%. Furthermore, a new dinuclear Co complex was used as a reduction catalyst and showed up to 760 turnovers after 20 h. A detailed study of the concentration impact of all components in the photoredox system was performed. DFT calculations were used to aid the explanation of the findings., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The reaction of different metallocene fragments [Cp(2)M] (Cp=η(5)-cyclopentadienyl, M=Ti, Zr) with diferrocenylacetylene and 1,4-diferrocenylbuta-1,3-diyne is described. The titanocene complexes form the highly strained three- and five-membered ring systems [Cp(2)Ti(η(2)-FcC(2)Fc)] (1) and [Cp(2)Ti(η(4)-FcC(4)Fc)](2) (Fc=[Fe(η(5)-C(5)H(4))(η(5)-C(5)H(5))]) by addition of the appropriate alkyne or diyne to Cp(2)Ti. Zirconocene precursors react with diferrocenyl- and ferrocenylphenylacetylene under C-C bond coupling to yield the metallacyclopentadienes [Cp(2)Zr(C(4)Fc(4))](3) and [Cp(2)Zr(C(4)Fc(2)Ph(2))](5), respectively. The exchange of the zirconocene unit in 3 by hydrogen atoms opens the route to the super-crowded ferrocenyl-substituted compound tetraferrocenylbutadiene (4). On the other hand, the reaction of 1,4-diferrocenylbuta-1,3-diyne with zirconocene complexes afforded a cleavage of the central C-C bond, and thus, dinuclear [{Cp(2)Zr(μ-η(1):η(2)-C≡CFc)}(2)] (6) that consists of two zirconocene acetylide groups was formed. Most of the complexes were characterized by single-crystal X-ray crystallography, showing attractive multinuclear molecules. The redox properties of 3, 5, and 6 were studied by cyclic voltammetry. Upon oxidation to 3(n+), 5(n+), and 6(n+) (n=1-3), decomposition occured with in situ formation of new species. The follow-up products from 3 and 5 possess two or four reversible redox events pointing to butadiene-based molecules. However, the dinuclear complex 6 afforded ethynylferrocene under the measurement conditions., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A study regarding coordination chemistry of the bis(diphenylphosphino)amide ligand Ph(2) P-N-PPh(2) at Group 4 metallocenes is presented herein. Coordination of N,N-bis(diphenylphosphino)amine (1) to [(Cp(2) TiCl)(2) ] (Cp=η(5) -cyclopentadienyl) generated [Cp(2) Ti(Cl)P(Ph(2) )N(H)PPh(2) ] (2). The heterometallacyclic complex [Cp(2) Ti(κ(2) -P,P-Ph(2) P-N-PPh(2) )] (3 Ti) can be prepared by reaction of 2 with n-butyllithium as well as from the reaction of the known titanocene-alkyne complex [Cp(2) Ti(η(2) -Me(3) SiC(2) SiMe(3) )] with the amine 1. Reactions of the lithium amide [(thf)(3) Li{N(PPh(2) )(2) }] with [Cp(2) MCl(2) ] (M=Zr, Hf) yielded the corresponding zirconocene and hafnocene complexes [Cp(2) M(Cl){κ(2) -N,P-N(PPh(2) )(2) }] (4 Zr and 4 Hf). Reduction of 4 Zr with magnesium gave the highly strained heterometallacycle [Cp(2) Zr(κ(2) -P,P-Ph(2) P-N-PPh(2) )] (3 Zr). Complexes 2, 3 Ti, 4 Hf, and 3 Zr were characterized by X-ray crystallography. The structures and bondings of all complexes were investigated by DFT calculations., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Teamwork: A new intermolecular heterobimetallic system for photocatalytic water reduction, consisting of a photosensitizer of the type [Ru(bpy)(2)(L)](PF(6))(2) (L=bidentate ligand), a dichloro palladium complex PdCl(2)(L) serving as the water reduction catalyst, and triethyl amine as electron donor, is presented. Variations of the ligand as well as of the palladium source results in a significant improvement of the performance of the catalyst system., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)