Germylene Complexes Research Articles

Cover Feature: Rhodium‐Mediated Dehydrogenation of Hydroboranes and Group 14 Compounds: Base‐Stabilized Silylene and Germylene Complexes vs. Transmetalation (Chem. Eur. J. 5/2024)

Cover Feature: Rhodium‐Mediated Dehydrogenation of Hydroboranes and Group 14 Compounds: Base‐Stabilized Silylene and Germylene Complexes vs. Transmetalation (Chem. Eur. J. 5/2024)

A neutral germanium-centred hard and soft lewis superacid and its unique reactivity towards hydrosilanes.

The germanium-centred Lewis superacid Ge(pinF)2 (1) was isolated as acetonitrile mono-adduct 1·MeCN and thoroughly characterized by NMR spectroscopy, X-ray crystallography and quantum chemical calculations. Ion abstraction and NMR experiments revealed the hard as well as soft Lewis superacidic nature of 1·MeCN. The title compound readily activates hydrosilanes such as Et3SiH, which is not feasible for its harder silicon homologue 2·MeCN, and even reacts with Et3SiF. The strongly coordinating acetonitrile could be abstracted by B(C6F5), giving the donor-free Ge(pinF)2 (1) and Si(pinF)2 (2) which are Lewis superacids. Unlike 1·MeCN, the donor-free 1 efficiently catalyses hydrosilylation of α-methylstyrene by Et3SiH. For this process, an inverse temperature dependence was observed, i.e. a complete conversion was achieved rapidly when the reaction was cooled to -35 °C, but the reaction stopped at elevated temperatures. Mechanistic investigations, including stoichiometric experiments and quantum chemical calculations, outlined the formation of germylene Ge(pinF) (3), which acts as the active catalyst. The germylene is formed by reductive elimination of the silylated pinacol from the hydrogermane intermediate, which is obtained by the initial reaction of 1 with Et3SiH. The inverse temperature dependence of the catalytic reaction could be explained by low entropy associated with the complexation of two cooperating germylenes and the substrates. With this example we introduce an in situ generated Lewis acidic germylene complex for catalytic hydrosilylation of olefins and again exemplify the great potential of main-group-element-based complexes in catalysis.

Synthesis and Characterization of Ruthenium Germyl Complexes with Various Substituents

Synthesis and Characterization of Ruthenium Germyl Complexes with Various Substituents

Rhodium-Mediated Dehydrogenation of Hydroboranes and Group 14 Compounds: Base-Stabilized Silylene and Germylene Complexes vs. Transmetalation.

Monocarbonyl rhodium complex LRh(CO), 1, which is stabilized by a pyrrole-based bis(phosphinimine) pincer ligand (L=κ3 -NNN'=2,5-[i Pr2 P=N(4-i PrC6 H4 )]2 -N'(C4 H2 )- ), serves as a versatile platform for the dehydrogenation of group 14 substrates. Reaction with primary and secondary silanes and germanes (MesSiH3 , Et2 SiH2 , Ph2 GeH2 , t BuGeH3 ; Mes=mesityl) liberates H2 and yields base-stabilized tetrylene compounds of the form κ2 -L(CO)Rh(ER2 ) (E=Si: R=Mes, H, 2; R=Et, 5; E=Ge: R=Ph, 6; R=t Bu, H, 8). The ":ER2 " fragment in these species bridges between the rhodium center and a phosphinimine donor. Preliminary reactions between pinacol (Pin) and κ2 -L(CO)Rh(ER2 ), E=Si, Ge, indicate that such complexes can serve as silylene and germylene synthons, releasing :ER2 and catalytically generating PinER2 . In contrast, combination of complex 1 and MesGeH3 does not yield the anticipated dehydrogenation product, but rather, transmetalation similar to that observed upon reaction between 1 and 3,5-dimethylphenylborane prevails.

Activation of heteroallenes by metal-substituted electron-rich tetrylenes

The metal-substituted germylene LGa(μ-Cl)GeDMP (L = HC[C(Me)NDipp]2, Dipp = 2,6-iPr2C6H3, DMP = 2,6-Mes2C6H3, Mes = 2,4,6-Me3C6H2) 1 reacts with CO2 with reductive decarbonylation and formation of the oxygen-bridged complex L(Cl)GaOGeDMP 2, which was also formed in the reaction of 1 with N2O. The CO2 reaction most likely proceeds via intermediate formation of a gallacarboxylate germylene complex as is observed in reactions of complex 1 with both ethyl isocyanate and N,N’-dicyclohexylcarbodiimide, yielding the corresponding heteroallenes insertion complexes L(Cl)Ga-[C(NEt)O]-GeDMP 3 and L(Cl)Ga-[C(NCy)2]-GeDMP 4. In addition, the gallanediyle stannylene adduct LGa-Sn[N(SiMe3)(Dipp)] 5 reacts with CO2 to form the gallacarboxylate tin complex L(Cl)Ga-(CO2)-Sn[N(Dipp)(SiMe3)] 6. Complexes 2–4 and 6 are characterized spectroscopically (1H, 13C, 119Sn (6), IR) and by single crystal X-ray diffraction (sc-XRD).

C–H and H–H Bond Activation by a Cationic Germylyne Complex

Reactivities of a cationic germylyne complex [Cp*(CO)2W≡Ge(IPr)](BAr4F) (1) [IPr = 1,3-bis(2,6-diisopropylphenyl)-1,3-dihydro-2H-imidazol-2-ylidene] toward several unsaturated organic substrates and dihydrogen were investigated. Complex 1 underwent activation of the formyl C–H bond of benzaldehyde and the ortho C–H bond of pyridine to afford base-stabilized germylene complexes, indicating that coordination of the heteroatom (O/N) of the substrates to the Lewis acidic Ge center facilitates the C–H bond activation on W. The reactions with alkenes resulted in the terminal C–H bond cleavage on Ge by coordination of the C═C double bond to W, giving η3-germaallyl complexes. The reactions with terminal alkynes, on the contrary, proceeded through no C–H bond cleavage to produce metallacyclopropenylgermylenes, which have an unprecedented bonding situation with a lone pair on Ge. Complex 1 also reacted with dihydrogen at room temperature to afford a dihydrido(dihydrogermyl) complex finally through a hydrido(hydrogermylene) complex. Characterization of these products including X-ray crystal diffraction study (XRD) and possible reaction mechanisms based on cooperative action at the W–Ge unsaturated bond platform are described.

π-Hole Tetrel Bonds—Lewis Acid Properties of Metallylenes

The MP2/aug-cc-pVTZ calculations were performed on the dihalometallylenes to indicate their Lewis acid and Lewis base sites. The results of the Cambridge Structural Database search show corresponding and related crystal structures where the tetrel center often possesses the configuration of a trigonal bipyramid or octahedron. The calculations were also carried out on dimers of dichlorogermylene and dibromogermylene and on complexes of these germylenes with one and two 1,4-dioxide molecules. The Ge⋯Cl, Ge⋯Br, and Ge⋯O interactions are analyzed. The Ge⋯O interactions in the above mentioned germylene complexes may be classified as the π-hole tetrel bonds. The MP2 calculations are supported by the results of the Quantum Theory of Atoms in Molecules (QTAIM) and the Natural Bond Orbital (NBO) approaches.

Dehydrogenative Double C-H Bond Activation in a Germylene-Rhodium Complex*.

Transition metal tetrylene complexes offer great opportunities for molecular cooperation due to the ambiphilic character of the group 14 element. Here we focus on the coordination of germylene [(ArMes2)2Ge :] (ArMes=C6H3‐2,6‐(C6H2‐2,4,6‐Me3)2) to [RhCl(COD)]2 (COD=1,5‐cyclooctadiene), which yields a neutral germyl complex in which the rhodium center exhibits both η 6‐ and η 2‐coordination to two mesityl rings in an unusual pincer‐type structure. Chloride abstraction from this species triggers a singular dehydrogenative double C−H bond activation across the Ge/Rh motif. We have isolated and fully characterized three rhodium‐germyl species associated to three C−H cleavage events along this process. The reaction mechanism has been further investigated by computational means, supporting the key cooperative action of rhodium and germanium centers.

Photodriven Elimination of Chlorine From Germanium and Platinum in a Dinuclear PtII→GeIV Complex

AbstractSearching for a connection between the two‐electron redox behavior of Group‐14 elements and their possible use as platforms for the photoreductive elimination of chlorine, we have studied the photochemistry of [(o‐(Ph2P)C6H4)2GeIVCl2]PtIICl2 and [(o‐(Ph2P)C6H4)2ClGeIII]PtIIICl3, two newly isolated isomeric complexes. These studies show that, in the presence of a chlorine trap, both isomers convert cleanly into the platinum germyl complex [(o‐(Ph2P)C6H4)2ClGeIII]PtICl with quantum yields of 1.7 % and 3.2 % for the GeIV–PtII and GeIII–PtIII isomers, respectively. Conversion of the GeIV–PtII isomer into the platinum germyl complex is a rare example of a light‐induced transition‐metal/main‐group‐element bond‐forming process. Finally, transient‐absorption‐spectroscopy studies carried out on the GeIII–PtIII isomer point to a ligand arene–Cl. charge‐transfer complex as an intermediate.

Photodriven Elimination of Chlorine From Germanium and Platinum in a Dinuclear PtII →GeIV Complex.

Searching for a connection between the two-electron redox behavior of Group-14 elements and their possible use as platforms for the photoreductive elimination of chlorine, we have studied the photochemistry of [(o-(Ph2 P)C6 H4 )2 GeIV Cl2 ]PtII Cl2 and [(o-(Ph2 P)C6 H4 )2 ClGeIII ]PtIII Cl3 , two newly isolated isomeric complexes. These studies show that, in the presence of a chlorine trap, both isomers convert cleanly into the platinum germyl complex [(o-(Ph2 P)C6 H4 )2 ClGeIII ]PtI Cl with quantum yields of 1.7 % and 3.2 % for the GeIV -PtII and GeIII -PtIII isomers, respectively. Conversion of the GeIV -PtII isomer into the platinum germyl complex is a rare example of a light-induced transition-metal/main-group-element bond-forming process. Finally, transient-absorption-spectroscopy studies carried out on the GeIII -PtIII isomer point to a ligand arene-Cl. charge-transfer complex as an intermediate.

Titanium Germylidenes

AbstractTwo novel 18‐electron titanium germylene complexes, Cp2Ti(L)=Ge[Si3(SiMetBu2)4] 3 b (L=Me3P) and 3 c (L=XylNC), were synthesized, isolated, and structurally characterized. The length of the titanium‐germanium bonds of 2.5387(3) Å and 2.5276(3) Å (in 3 b and 3 c, respectively) well match those expected for the double bond, which was further supported by the DFT study. Based on their structural characteristics, as well as their atomic charges calculations which revealed Ti(δ+)=Ge(δ−) bond polarization, both 3 b and 3 c are classified as the Schrock‐type titanium germylidenes, as the germanium analogues of the widely known titanium alkylidenes. By contrast, germylene complexes of the group 6 metals 8 a (M=Mo) and 8 b (M=W) are better described as Fischer‐type germylene complexes.

Synthesis of a Molybdenum Hydrido(hydrogermylene) Complex and Its Conversion to a Germylyne Complex: Another Route through Dehydrogenation with Nitriles

A molybdenum germylene complex having Mo–H and Ge–H bonds, Cp*(CO)2(H)Mo═Ge(H){C(SiMe3)3} (1), was synthesized by the reaction of a methyl molybdenum complex with a trihydrogermane and was converte...

A bis(silylene)-stabilized diphosphorus compound and its reactivity as a monophosphorus anion transfer reagent

In contrast to the well-established transition-metal-mediated activation of white phosphorus (P4), the metal-free direct functionalization of P4 has remained rare. The conversion of P4 into a reactive zero-valent diphosphorus compound (P2) has proven challenging to carry out without relying on metal reactivity. Herein, we describe the facile degradation of P4 mediated by two divalent silicon atoms in a bis(silylene) scaffold, resulting in a silylene-stabilized zero-valent P2 complex. The presence of two lone pairs of electrons on each P atom in the silylene-stabilized P2 complex enables a rich reactivity towards small molecules; reaction of the P2 species with CO2, water or a borane leads to the formation of P-C, P-H or P-B bonds, respectively. Notably, the P2 complex also serves as a single phosphorus anion (P-) transfer reagent towards metal carbonyls and a chlorogermylene compound, leading to the synthetically valuable phosphaketenide (PCO-) ligand and a phosphinidene germylene complex, respectively.

Coordination complexes of slight tetrylene with platinum(II)‐8‐hydroxyquinolines: Structure and bonding analysis

AbstractThe structure and bonding situation in platinum complexes containing slight tetrylene ligands [{PtCl‐C9H6NO}‐NHE] (Pt‐NHE) with E = C, Si, Ge were examined by DFT calculations with the levels are BP86/def2‐SVP and BP86/def2‐TZVPP. The predicted equilibrium structure of the ligands NHE in Pt‐NHE are bonded in distorted end‐on way to PtCl‐8‐hydroxyquinolines fragment with the bending angle, α, exhibits the biggest value in carbenes systems then slightly decrease from Pt‐NHC to Pt‐NHGe. Bond dissociation energies (BDEs), De (kcal.mol‐1), decrease from the carbene complex to the weaker bonded silylene and germylene manners. The BDE when considering dispersion correction at the BP86‐D3(BJ)/def2‐TZVPP level confirms that Pt‐E bond in Pt‐NHE belongs to the effect of the bulky group in slight tetrylene NHE and Pt(II)‐group fragment which makes the intrinsic Pt‐E bond strength decreases from carbene to germylene complexes. The hybridization of atoms E and Pt have large p characters while the hybridization of atom Pt has greater d character which lead to the Pt‐E bond possesses not only NHE→{PtCl‐C9H6NO} strong σ‐donation but also a significant contribution π‐donation NHE→{PtCl‐C9H6NO} and weak π‐backdonation metal‐ligand NHE←{PtCl‐C9H6NO} in complexes Pt‐NHE.

A Nickel Complex Containing a Pyramidalized, Ambiphilic Pincer Germylene Ligand.

Reaction of N-heterocyclic carbene (NHC)-stabilized PGeP-type germylene Ge{o-(PiPr2 )C6 H4 }2 ⋅Me IiPr (1) (Me IiPr=1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) with Ni(cod)2 gave pincer germylene complex Ni[Ge{o-(PiPr2 )C6 H4 }2 ](Me IiPr) (2), in which the Ge center of 2 is significantly pyramidalized. Theoretical calculation on 2 predicted the ambiphilicity of the germanium center, which was confirmed by reactivity studies. Thus, complex 2 reacted with both Lewis base Me IMe (Me IMe=1,3,4,5-tetramethylimidazol-2-ylidene) and Lewis acid BH3 ⋅SMe2 at the germanium center to afford the adducts Ni[Ge{o-(PiPr2 )C6 H4 }2 ⋅Me IMe](Me IiPr) (3) and Ni[Ge{o-(PiPr2 )C6 H4 }2 ⋅BH3 ](Me IiPr) (4), respectively. Furthermore, the former was slowly converted to dinuclear complex Ni2 [Ge{o-(PiPr2 )C6 H4 }2 ]2 (Me IMe)2 (5) at room temperature. Complex 5 can be regarded as a dimer of the Me IMe analog of 2 with a Ni-Ge-Ge-Ni linkage.

Synthesis and reactivity of germyl complex of Ruthenium(II)

Reaction of [RuCl(η5-C5Me5)L] and [RuCl(η5-C9H7)L] (L = 1,2-[bis(diphenyl) phosphanyloxy]-1,2-diphenylethane) with an excess of GeCl2·dioxane afforded the half-sandwich trichlorogermyl complexes [Ru(GeCl3)(η5-C5Me5)L] (1a) and [Ru(GeCl3)(η5-C9H7)L] (1b). Trihydridogermyl derivatives [Ru(GeH3)(Cp′)L] [Cp′ = η5-C5Me5 (2a), η5-C9H7 (2b)] were obtained by treating 1a and 1b with LiAlH4. Reaction of compound 1a with MeMgBr gave the monomethyl derivative [Ru(GeMeCl2)(η5-C5Me5)L] (3a) while the reaction between the complex 1b and MeMgBr yielded the trimethylgermyl derivative [Ru(GeMe3)(η5-C9H7)L] (3b). All the complexes present optical activity. The complexes were characterized spectroscopically and the X-ray crystal structure of [Ru(GeCl3)(η5-C5Me5)L] (1a) was determined.

A dipyrromethane-based diphosphane-germylene as precursor to tetrahedral copper(i) and T-shaped silver(i) and gold(i) PGeP pincer complexes.

A six-membered ring N-heterocyclic germylene flanked by two CH2PiPr2 groups, Ge(pyrmPiPr2)2CMe2 (1; (HpyrmPiPr2)2CMe2 = 5,5-dimethyl-1,9-bis(di-isopropylphosphanylmethyl)dipyrromethane), has been prepared in high yield. Upon treatment with group 11 metal precursors of the type [MCl(PPh3)]n (M = Cu (n = 4), Ag (n = 4), Au (n = 1)), germylene 1 easily forms a PGeP chloridogermyl ligand that is able to stabilize tetrahedral copper(i) and unusual T-shaped silver(i) and gold(i) PGeP pincer complexes, as has been demonstrated by the isolation of [Cu{κ3P,Ge,P-GeCl(pyrmPiPr2)2CMe2}(PPh3)] (2) and [M{κ3P,Ge,P-GeCl(pyrmPiPr2)2CMe2}] (M = Ag (3), Au (4)). Theoretical calculations have shown that the Ge-M bonds of these complexes are weak and that their strength decreases in the series 2 > 3 > 4.

A diamidinatogermylene as a Z-type ligand in a nickel(0) complex.

The reaction of the phosphine functionalized chlorogermylene 1 with Ni(COD)2 (COD = 1,5-cyclooctadiene) afforded the bis-chlorogermylene ligated nickel(0) complex 2 in high yield. The dechlorination reaction of 2 with elemental potassium serendipitously yielded the diamidinatogermylene nickel(0) complex 3. Single-crystal X-ray diffraction analysis reveals that the germanium center in 3 features a pyramidalized geometry, suggesting the germylene moiety in 3 acts as a Z-type ligand, which is further supported by theoretical calculations. Complex 3 represents the first example bearing a Z-type diaminogermylene ligand.

Activation of tetrafluoropropenes by rhodium(i) germyl and silyl complexes.

The reaction of the rhodium(i) complexes [Rh(E)(PEt3)3] (E = GePh3 (1), Si(OEt)3 (5)) with HFO-1234yf (2,3,3,3-tetrafluoropropene) afforded [Rh(F)(PEt3)3] (2) and the functionalized olefins Z-CF3CH[double bond, length as m-dash]CH(E) (E = GePh3 (4a), Si(OEt)3 (7)). Conceivable reaction pathways were assessed using DFT calculations. Reactions of [Rh(E)(PEt3)3] with HFO-1234ze (E-1,3,3,3-tetrafluoropropene) yielded the rhodium fluorido complex 2 and [Rh{(E)-CH[double bond, length as m-dash]CH(CF3)}(PEt3)3] (9) via two different reaction pathways. Using complexes 1 and 5 as catalysts, functionalized building blocks were obtained.

Reversible Carbene Insertion into a Ge-N Bond and Insights into CO and Carbene Substitution Reactions Involving Amidinatogermylenes and Fischer Carbene Complexes.

The formation of the five-membered-ring germylene complexes [M(CO)5 {Ge(tBu2 bzamC(OEt)Me)tBu}] (3M ; M=Cr, W), which occurs readily at room temperature from the germylene Ge(tBu2 bzam)tBu (1tBu ) and Fischer carbenes [M(CO)5 {C(OEt)Me}] (2M ; M=Cr, W), has been found to be reversible. Upon heating at 60 °C, complexes 3M undergo epimerization to an equilibrium mixture of 3M and 3'M . At that temperature, the chromium epimers (but not the tungsten ones) release CO to end in the mixed germylene-Fischer carbene complexes [Cr(CO)4 {C(OEt)Me}{Ge(tBu2 bzam)tBu}] (cis-4Cr and trans-4Cr ). The latter decompose at 120 °C to [Cr(CO)5 {Ge(tBu2 bzam)tBu}] (6Cr ). Because the formation of cis-4Cr and trans-4Cr from 3Cr or 3'Cr requires the presence of free 1tBu and 2Cr in the reaction solutions, the reactions of 1tBu with 2M to give 3M (and 3'M at 60 °C) should be reversible. This proposal has been proven by germylene-exchange crossover reactions in which free 1tBu and [M(CO)5 {Ge(tBu2 bzamC(OEt)Me)CH2 SiMe3 }] (5'M ; M=Cr, W) were formed when complexes 3M were treated at room temperature with the germylene Ge(tBu2 bzam)CH2 SiMe3 (1tmsm ). A clear differential behavior between N-heterocyclic carbenes (NHCs) and amidinatogermylenes (1tBu and 1tmsm ) in their reactivity against group 6 metal Fischer carbene complexes is demonstrated. The higher electron-donor capacity of amidinatogermylenes with respect to NHCs and the bias of the former to get involved in ring expansion processes are responsible for this differential behavior.