Germylene Complexes Research Articles

An Isolable Bis(silylene)-Stabilized Germylone and Its Reactivity.

The first zerovalent germanium complex ("germylone") 3, [SiII(Xant)SiII]Ge0, stabilized by a chelating bis(N-heterocyclic silylene)xanthene donor ligand 1 was successfully synthesized via the dechlorination of the corresponding {[SiII(Xant)SiII]GeCl}+Cl- complex 2 with KC8; it was structurally and spectroscopically characterized, and also studied by density functional theory (DFT) calculations. Natural bond orbital (NBO) analysis of 3 unambiguously exhibits two lone pairs of electrons (one σ-type lone-pair and one 3p(Ge) lone-pair) on the zerovalent Ge atom. This is why the Ge atom can form the corresponding mono- and bis-AlBr3 Ge → Al Lewis adducts [SiII(Xant)SiII]Ge(AlBr3) 4 and [SiII(Xant)SiII]Ge(AlBr3)2 5, respectively. Due to the electron-rich character of the Ge0 atom, the germylone 3 displayed quite unusual reactivities. Thus, the reaction of 3 with 9-borabicyclo[3.3.1]nonane (9-BBN) as a potential Lewis acid furnished the first boryl(silyl)germylene complex 6, possessing a heteroallylic B···Ge···Si π-conjugation. When 3 was allowed to react with Ni(cod)2 (cod = 1,5-cyclooctadiene), the unique {[SiII(Xant)SiII]GeI}2NiII complex with a three-membered ring Ge2Ni-metallacycle was obtained via reductive coupling of two Ge0 atoms on the Ni center. Moreover, 3 was suitable to form a frustrated Lewis pair (FLP) with BPh3, which was capable of heterolytic H2 cleavage at 1 atm and room temperature, representing, for the first time, that a metallylone could be applied in FLP chemistry.

Nickel as a Lewis Base in a T‐Shaped Nickel(0) Germylene Complex Incorporating a Flexible Bis(NHC) Ligand

AbstractFlexible, chelating bis(NHC) ligand 2, able to accommodate both cis‐ and trans‐coordination modes, was used to synthesize (2)Ni(η2‐cod), 3. In reaction with GeCl2, it produced (2)NiGeCl2, 4, featuring a T‐shaped Ni0 and a pyramidal Ge center. Complex 4 could also be prepared from [(2)GeCl]Cl, 5, and Ni(cod)2, in a reaction that formally involved Ni–Ge transmetalation, followed by coordination of the extruded GeCl2 moiety to Ni. A computational analysis showed that 4 possesses considerable multiconfigurational character and the Ni→Ge bond is formed through σ‐donation from the Ni 4s, 4p, and 3d orbitals to Ge. (NHC)2Ni(cod) complexes 9 and 10, as well as (NHC)2GeCl2 derivative 11, incorporating ligands that cannot accommodate a wide bite angle, failed to produce isolable Ni–Ge complexes. The isolation of (2)Ni(η2‐Py), 12, provides further evidence for the reluctance of the (2)Ni0 fragment to act as a σ‐Lewis acid.

Nickel as a Lewis Base in a T-Shaped Nickel(0) Germylene Complex Incorporating a Flexible Bis(NHC) Ligand.

Flexible, chelating bis(NHC) ligand 2, able to accommodate both cis- and trans-coordination modes, was used to synthesize (2)Ni(η2 -cod), 3. In reaction with GeCl2 , it produced (2)NiGeCl2 , 4, featuring a T-shaped Ni0 and a pyramidal Ge center. Complex 4 could also be prepared from [(2)GeCl]Cl, 5, and Ni(cod)2 , in a reaction that formally involved Ni-Ge transmetalation, followed by coordination of the extruded GeCl2 moiety to Ni. A computational analysis showed that 4 possesses considerable multiconfigurational character and the Ni→Ge bond is formed through σ-donation from the Ni 4s, 4p, and 3d orbitals to Ge. (NHC)2 Ni(cod) complexes 9 and 10, as well as (NHC)2 GeCl2 derivative 11, incorporating ligands that cannot accommodate a wide bite angle, failed to produce isolable Ni-Ge complexes. The isolation of (2)Ni(η2 -Py), 12, provides further evidence for the reluctance of the (2)Ni0 fragment to act as a σ-Lewis acid.

Synthesis, characterisation and cytotoxicity studies of ruthenium arene complexes bearing trichlorogermyl ligands

The synthesis of five half sandwich ruthenium(II) trichlorogermyl complexes of the type [(η6-Arene)Ru(PR3)Cl(GeCl3)] (PR3 = Phosphane and phosphite ligands; Arene = p-cymene or C6H5-OC2H4OH) is reported: [(η6-p-cymene)Ru(P(OMe)3)Cl(GeCl3)] (1), [(η6-p-cymene)Ru(P(OPh)3)Cl(GeCl3)] (2), [(η6-p-cymene)Ru(PPh3)Cl(GeCl3)] (3), [(η6-p-cymene)Ru(pta)Cl(GeCl3)] (pta = 1,3,5-triaza-7-phosphaadamantane) (4) and [(η6-C6H5-OC2H4OH)Ru(pta)Cl(GeCl3)] (5). The nature of the η6-arene and phosphane ligand was varied and the complexes have been prepared by facile insertion of GeCl2 (from GeCl2.(dioxane)) into the Ru-Cl bonds of the respective easily accessible precursor complexes [(η6-Arene)Ru(PR3)Cl2]. The complexes were fully spectroscopically characterized by 1H, 13C{1H} and 31P{1H} NMR spectroscopy, UV-Vis, ATR-IR, HRMS (ESI) and their thermal behavior elucidated by TGA. Their cytotoxicity to human ovarian carcinoma (A2780) and non-tumorigenic human embryonic kidney HEK293 cell lines is also reported, and represents the first cytotoxic investigations of Ru(II) germyl complexes to date. The first DFT studies (B3LYP; basis set 6-31+G(d,p) for H, C, O, P, Cl, N, and Ge atoms and DGDZVP for Ru atom) on trichlorogermyl ruthenium complexes were carried out on complex 2 and 5 in order to gain insights into the bonding situation between Ru and Ge and are reported.

β‐Diketiminato–Germylene Complexes of Carbonyl Ruthenium: Synthesis, Structure, and Reactivity

The reaction of the β‐diketiminatochlorogermylene L(Cl)Ge {1, L = HC[C(Me)N‐2,6‐iPr2C6H3]2} with Ru3(CO)12 in molar ratios of 3:1 or 6:1 led to the Ge2Ru complex [L(Cl)Ge]2Ru(CO)3 (3). A speculative GeRu intermediate, L(Cl)GeRu(CO)4, was detected when the reaction was monitored by 1H NMR spectroscopy at elevated temperatures. The formation of this intermediate was supported by similar monitoring of the reaction of L(PhC≡C)Ge (2) with Ru3(CO)12 by 1H NMR spectroscopy and the isolation of a mixture of L(PhC≡C)GeRu(CO)4 (4) and [L(R)Ge]2Ru(CO)3 (5) from this reaction in a molar ratio of 3:1 as well as the clean formation of 5 from such a reaction in a 6:1 molar ratio. Complex 3 reacted with LiHBEt3 through an unusual Cl/Et metathesis to give L(Et)GeRu(CO)4 (6). However, the reaction of 3 with LiN(SiMe3)2 resulted in the base‐assisted dehydrochlorination involving one methyl group of each L ligand backbone and the chlorine atom at the Ge center to yield [L′Ge]2Ru(CO)3 {7, L′ = HC[C(Me)N‐2,6‐iPr2C6H3][C(CH2)N‐2,6‐iPr2C6H3]}. The further reaction of 7 with a stoichiometric amount of H2O afforded L(HO)GeRu(CO)4 (8) through a 1,4‐dipolar addition across the L′Ge functionality. In addition, the reaction of 3 with I2 occurred through an oxidative addition at the Ru center to generate L(Cl)GeRuI2(CO)3 (10).

NHC-induced conversion of a W–Ge double bond into the triple bond through formation of W–Ge single and double bonded intermediates

Reaction of hydrido(hydrogermylene) complex Cp*(CO)2(H)W=Ge(H)(Tsi) (1, Tsi = C(SiMe3)3) with 1 equiv of MeIMe (MeIMe = 1,3-dimethyl-4,5-dimethylimidazol-2-ylidene) immediately afforded NHC-stabilized germylene complex Cp*(CO)2(H)WGe(H)(MeIMe)(Tsi) (2) that has a zwitterionic, W–Ge single-bonded structure. Complex 2 was thermally unstable and intramolecular proton-transfer followed by hydride-transfer to the NHC-unit occurred slowly at room temperature to give anionic germylene complex [Cp*(CO)2W=Ge(H)(Tsi)][HMeIMe] ([3][HMeIMe]) first and subsequently germylyne complex Cp*(CO)2W≡Ge(Tsi) (4) and H2MeIMe. Although [3][HMeIMe] was too unstable to be isolated, the salt of bulkier [HMeIiPr]+, [Cp*(CO)2W=Ge(H)(Tsi)][HMeIiPr] ([3][HMeIiPr]), was thermally more stable and was isolated and fully characterized.

Coordination Chemistry of [E(Idipp)]2+Ligands (E = Ge, Sn): Metal Germylidyne [Cp*(CO)2W≡Ge(Idipp)]+and Metallotetrylene [Cp*(CO)3W–E(Idipp)]+Cations

The synthesis and full characterization of the NHC-stabilized tungstenochlorostannylene [Cp*(CO)3W–SnCl(Idipp)] (1Sn), the NHC-stabilized chlorogermylidyne complex [Cp*(CO)2W═GeCl(Idipp)] (2), the tungsten germylidyne complex salt [Cp*(CO)2W≡Ge(Idipp)][B(C6H3-3,5-(CF3)2)4] (3), and the cationic metallostannylene [Cp*(CO)3W–Sn(Idipp)][Al(OC(CF3)3)4] (4Sn) are reported (Idipp = 2,3-dihydro-1,3-bis(2,6-diisopropylphenyl)-1H-imidazol-2-ylidene, Cp* = η5-C5Me5). Metathetical exchange of SnCl2(Idipp) with Li[Cp*W(CO)3] afforded selectively 1Sn. Photolytic decarbonylation of the Ge analogue [Cp*(CO)3W–GeCl(Idipp)] (1Ge) afforded the NHC-stabilized chlorogermylidyne complex (2), featuring a trigonal-planar coordinated germanium center and a W–Ge double bond (W–Ge 2.3496(5) Å). Chloride abstraction from 2 with Na[B(C6H3-3,5-(CF3)2)4] yielded the germylidyne complex salt 3, which contains an almost linear W–Ge–C1 linkage (angle at Ge = 168.7(1)°) and a W–Ge triple bond (2.2813(4) Å). Chloride elimination from 1Ge afforded the tungstenogermylene salt [Cp*(CO)3W–Ge(Idipp)][B(C6H3-3,5-(CF3)2)4] (4Ge), which in contrast to 1Ge could not be decarbonylated to form 3 despite the less strongly bound carbonyl ligands. The tin compounds 1Sn and 4Sn did not afford products bearing multiple W–Sn bonds. Treatment of 4Ge with Me2NC≡CNMe2 yielded unexpectedly the neutral germyl complex 5 containing a pendant 1-germabicyclo-[3,2,0]-hepta-2,5-diene ligand instead of the anticipated [2 + 1]-cycloaddition product at the Ge-center.

Activation of CS2 and COS at a Rhodium(I) Germyl Complex: Generation of CS and Carbido Complexes

Treatment of the germyl complex [Rh(GePh3)(PEt3)3] (1) with CS2 afforded the rhodium thiocarbonyl complex trans‐[Rh(SGePh3)(CS)(PEt3)2] (2) by phosphine dissociation and C–S bond activation. The analogous reaction with COS gave the structurally related carbonyl complex trans‐[Rh(SGePh3)(CO)(PEt3)2] (3). Low‐temperature NMR measurements revealed initial formation of the intermediates mer‐[Rh(GePh3)(η2‐CS2)(PEt3)3] (4) and mer‐[Rh(GePh3)(η2‐COS)(PEt3)3] (5). Reactions of 2 towards CO and HCl led to the replacement of the thiocarbonyl or germylthiolato ligand yielding complex 3 and trans‐[Rh(Cl)(CS)(PEt3)2] (6), respectively. The germylthiolato complex trans‐[Rh(SGePh3)(CS)(PEt3)2] (2) reacted with the boryl complex [Rh(Bpin)(PEt3)3] (7; pin = pinacolato) to afford the rhodium µ‐carbido complex trans,trans‐[{Rh(SBpin)(PEt3)2}(µ‐C){Rh(SGePh3)(PEt3)2}] (8). Complex 8 is not stable in solution and rearranges to form the symmetrical µ‐carbido complexes trans,trans‐[Rh2(µ‐C)(SGePh3)2(PEt3)4] (9) and trans,trans‐[Rh2(µ‐C)(SBpin)2(PEt3)4] (10). The molecular structures of 2 and 9 were determined by X‐ray crystallography.

An iron germylene complex having Fe-H and Ge-H bonds: synthesis, structure and reactivity.

A base-free iron germylene complex Cp*(CO)(H)Fe[double bond, length as m-dash]GeH{C(SiMe3)3} (1) was synthesised by abstraction of pyridine from a germyl complex Cp*(CO)(py)FeGeH2{C(SiMe3)3} (2), which was prepared by treatment of Cp*Fe(CO)(py)(Me) with H3GeC(SiMe3)3. X-ray crystallographic analysis revealed that 1 has an Fe-Ge bond that is the shortest among those ever reported. Reactivity of 1 toward several polar unsaturated organic compounds was investigated. Complex 1 underwent stoichiometric hydrogermylation of carbonyl compounds such as ketones, aldehydes and isocyanates (RNCO) at room temperature. In contrast, the reactions of 1 with isothiocyanates (RNCS) resulted in clean cleavage of the C[double bond, length as m-dash]S double bonds.

Platinum Complexes Bearing a Tripodal Germyl Ligand

The reaction of the germane [Ge(H)(2‐C6H4PPh2)3] (1) and the platinum precursor complex [Pt(nbe)3] (nbe = norbornene) gave a racemic mixture of the germyl complex [Pt(nor){Ge(2‐C6H4PPh2)3}] (2; nor = exo‐2‐norbornyl, exo‐2‐bicyclo[2.2.1]heptyl). Mechanistic studies showed that the hydrido complex [Pt(H){Ge(2‐C6H4PPh2)3}] (3) is not formed as an intermediate during the formation of 2. Further studies revealed that in contrast to the chlorido complex [Pt(Cl){Ge(2‐C6H4PPh2)3}] (4), the methyl compound [Pt(CH3){Ge(2‐C6H4PPh2)3}] (5) is an efficient starting compound for accessing cationic platinum species. Complex 5 was converted into the triflato complex [Pt(OTf){Ge(2‐C6H4PPh2)3}] (6) as well as the complexes [Pt(L){Ge(2‐C6H4PPh2)3}][B{3,5‐C6H3(CF3)2}4] [L = thf (7), toluene (8), CH2Cl2 (9), PPh3 (10)].

A Systematic Study of Structure and E-H Bond Activation Chemistry by Sterically Encumbered Germylene Complexes.

A series of new germylene compounds has been synthesized offering systematic variation in the σ- and π-capabilities of the α-substituent and differing levels of reactivity towards E-H bond activation (E=H, B, C, N, Si, Ge). Chloride metathesis utilizing [(terphenyl)GeCl] proves to be an effective synthetic route to complexes of the type [(terphenyl)Ge(ERn )] (1-6: ERn =NHDipp, CH(SiMe3 )2 , P(SiMe3 )2 , Si(SiMe3 )3 or B(NDippCH)2 ; terphenyl=C6 H3 Mes2 -2,6=Ar(Mes) or C6 H3 Dipp2 -2,6=Ar(Dipp) ; Dipp=C6 H3 iPr2 -2,6, Mes=C6 H2 Me3 -2,4,6), while the related complex [{(Me3 Si)2 N}Ge{B(NDippCH)2 }] (8) can be accessed by an amide/boryl exchange route. Metrical parameters have been probed by X-ray crystallography, and are consistent with widening angles at the metal centre as more bulky and/or more electropositive substituents are employed. Thus, the widest germylene units (θ>110°) are found to be associated with strongly σ-donating boryl or silyl ancillary donors. HOMO-LUMO gaps for the new germylene complexes have been appraised by DFT calculations. The aryl(boryl)-germylene system [Ar(Mes) Ge{B(NDippCH)2 }] (6-Mes), which features a wide C-Ge-B angle (110.4(1)°) and (albeit relatively weak) ancillary π-acceptor capabilities, has the smallest HOMO-LUMO gap (119 kJ mol(-1) ). These features result in 6-Mes being remarkably reactive, undergoing facile intramolecular C-H activation involving one of the mesityl ortho-methyl groups. The related aryl(silyl)-germylene system, [Ar(Mes) Ge{Si(SiMe3 )3 }] (5-Mes) has a marginally wider HOMO-LUMO gap (134 kJ mol(-1) ), rendering it less labile towards decomposition, yet reactive enough to oxidatively cleave H2 and NH3 to give the corresponding dihydride and (amido)hydride. Mixed aryl/alkyl, aryl/amido and aryl/phosphido complexes are unreactive, but amido/boryl complex 8 is competent for the activation of E-H bonds (E=H, B, Si) to give hydrido, boryl and silyl products. The results of these reactivity studies imply that the use of the very strongly σ-donating boryl or silyl substituents is an effective strategy for rendering metallylene complexes competent for E-H bond activation.

Synthesis of a rhodium(i) germyl complex: a useful tool for C-H and C-F bond activation reactions.

The dihydrido germyl complex cis,fac-[Rh(GePh3)(H)2(PEt3)3] (2) was synthesized by an oxidative addition of HGePh3 at [Rh(H)(PEt3)3] (1). Treatment of 2 with neohexene generated the rhodium(i) germyl complex [Rh(GePh3)(PEt3)3] (3). Alternatively, treatment of the methyl complex [Rh(CH3)(PEt3)3] (4) with HGePh3 furnished at room temperature also 3. Low-temperature NMR measurements revealed an initial formation of the oxidative addition product fac-[Rh(GePh3)(H)(CH3)(PEt3)3] (5), which transforms into the intermediate complex [Rh(GePh3)(H)(CH3)(PEt3)2] (6) by dissociation of a triethylphosphine ligand. The reductive elimination of methane and coordination of PEt3 afforded the germyl complex 3. Treatment of 3 with CO gave the biscarbonyl complex [Rh(GePh3)(CO)2(PEt3)2] (7). The molecular structures of the complexes 2, 3 and 7 were determined by X-ray crystallography. The germyl complex 3 reacted with 2,3,5,6-tetrafluoropyridine or pentafluorobenzene to furnish the C-H activation products [Rh(4-C5NF4)(PEt3)3] (8) and [Rh(C6F5)(PEt3)3] (9), respectively. The reaction of 3 with hexafluorobenzene or perfluorotoluene gave selectively the C-F activation products 9 and [Rh(4-C6F4CF3)(PEt3)3] (10). Treatment of 3 with pentafluoropyridine resulted in the formation of the C-F activation products 8 and [Rh(2-C5NF4)(PEt3)3] (11) in a 1 : 10 ratio. The two isomeric activation compounds [Rh{(E)-CF[double bond, length as m-dash]CF(CF3)}(PEt3)3] (12) and [Rh{(Z)-CF[double bond, length as m-dash]CF(CF3)}(PEt3)3] (13) were obtained in a 3 : 1 ratio by reaction of 3 with hexafluoropropene. On exposure to oxygen the highly air sensitive complex 12 reacts to yield the peroxido-bridged dirhodium complex [Rh{(E)-CF[double bond, length as m-dash]CF(CF3)}(μ-κ(1):η(2)-O2)(PEt3)2]2 (14). The molecular structure of 14 was determined by X-ray crystallography.

Competing reaction pathways of 3,3,3-trifluoropropene at rhodium hydrido, silyl and germyl complexes: C-F bond activation versus hydrogermylation.

The reaction of the silyl complex [Rh{Si(OEt)3}(PEt3)3] (1) with 3,3,3-trifluoropropene afforded the rhodium complex [Rh(CH2CHCF3){Si(OEt)3}(PEt3)2] (2) which features a bonded fluorinated olefin. In contrast the rhodium hydrido complex [Rh(H)(PEt3)3] (3) yielded on treatment with 3,3,3-trifluoropropene in the presence of a base the fluorido complex [Rh(F)(PEt3)3] (4) together with 1,1-difluoro-1-propene by C-F bond activation. At low temperature the intermediate fac-[Rh(H)(CH2CHCF3)(PEt3)3] (5) was detected by NMR spectroscopy. The germyl complex [Rh(GePh3)(PEt3)3] (6) reacted also with 3,3,3-trifluoropropene by C-F bond activation affording again the fluorido complex [Rh(F)(PEt3)3] (4) as well as the (3,3-difluoroallyl)triphenylgermane 7. The catalytic hydrogermylation of 3,3,3-trifluoropropene in the presence of various germanium hydrides under mild conditions was developed by employing complex 6 as a catalyst. The molecular structures of both germane derivatives (3,3-difluoroallyl)triphenylgermane 7 and 1,1,1-trifluoropropane-3-triphenylgermane 8 were determined by X-ray crystallography.

Alkaline-Earth-Metal-Induced Liberation of Rare Allotropes of Elemental Silicon and Germanium from N-Heterocyclic Metallylenes.

The synthesis and striking reactivity of the unprecedented N-heterocyclic silylene and germylene ("metallylene") alkaline-earth metal (Ae) complexes of the type [(η(5)-C5Me5)2Ae←:E(N(t)BuCH)2] (3, 4, and 7-9; Ae = Ca, E = Ge 3; Ae = Sr, E = Ge 4; Ae = Sr, E = Si 7; Ae = Ba, E = Si 8; Ae = Ba, E = Ge 9) are reported. All complexes have been characterized by spectroscopic means, and their bonding situations investigated by density functional theory (DFT) methods. Single-crystal X-ray diffraction analyses of examples revealed relatively long Si-Ae and Ge-Ae distances, respectively, indicative of weak E:→Ae (E = Si, Ge) dative bonds, further supported by the calculated Wiberg bond indices , which are rather low in all cases (∼0.5). Unexpectedly, the complexes undergo facile transformation to 1,4-diazabuta-1,3-diene Ae metal complexes of the type [(η(5)-C5Me5)2Ae(κ(2)-{N(t)Bu═CHCH═N(t)Bu})] (Ae = Sr 10, Ae = Ba 11) or in the case of calcium to the dinuclear complex [(η(5)-C5Me5)2Ca←:N((t)Bu)═CHCH═((t)Bu)N:→Ca(η(5)-C5Me5)2] (12) under concomitant liberation of elemental silicon and germanium. The formation of elemental silicon and germanium is proven by inductively coupled plasma atomic emission spectroscopy, transmission electron microscopy, selected area electron diffraction, and energy dispersive X-ray spectroscopy. Notably, the decomposition of the Si(II)→Ba complex 8 produces allo-silicon, a rare allotropic form of elemental silicon. Similarly, the analogous Ge(II)→Ba complex 9, upon decomposition, forms tetragonal germanium, a dense and rare allotrope of elemental germanium. The energetics of this unprecedented alkaline-earth-metal-induced liberation of elemental silicon and germanium was additionally studied by DFT methods, revealing that the transformations are pronouncedly exergonic and considerably larger for the N-heterocyclic germylene complexes than those of the corresponding silicon analogues.

A Ruthenium Dihydrogen Germylene Complex and the Catalytic Synthesis of Digermoxane

A germylene complex with a labile η2-H2 coligand, [RuH2(═GePh2)(η2-H2)(PCy3)2] (2), was isolated in very good yield from the reaction of the bis(dihydrogen) complex [RuH2(η2-H2)2(PCy3)2] (1) with Ph2GeH2. The hydrolytic synthesis of 1,1,3,3-tetraphenyldigermoxane, (HPh2Ge)2O, was catalyzed by 2, 1, and the tricyclopentylphosphine analogue 1Cyp. Coordination of digermoxane by ruthenium led to a complex best formulated as [RuH2({η2-H-GePh2}2O)(PCy3)2] on the basis of X-ray, NMR, IR, and DFT studies.

Can Low‐Valent Germanium Chemistry Be Practiced Under Ambient Conditions? A Tale of a Water‐Stable Yet Reactive Germylene Monochloride Complex

A germylene monochloride complex ((DPM)GeCl, 1) that is water stable was isolated for the first time. Interestingly, it reacts with cesium fluoride under ambient conditions (non-inert atmosphere and water-containing solvent) to afford water stable germylene monofluoride complex ((DPM)GeF, 2). Due to the usage of DPM (dipyrrinate) ligand, germylene monohalides 1 and 2 show fluorescence in the visible region at 555 and 538 nm, respectively. Compounds 1 and 2 are the first fluorescent germylene complexes and were characterized by multinuclear NMR spectroscopy. The structure of compound 1 was also proved by single crystal X-ray diffraction studies.

Interconversion of η3-H2SiRR′ σ-Complexes and 16-Electron Silylene Complexes via Reversible H–H or C–H Elimination

Solid samples of η(3)-silane complexes [PhBP(Ph)3]RuH(η(3)-H2SiRR') (R,R' = Et2, 1a; PhMe, 1b; Ph2, 1c, MeMes, 1d) decompose when exposed to dynamic vacuum. Gas-phase H2/D2 exchange between isolated, solid samples of 1c-d3 and 1c indicate that a reversible elimination of H2 is the first step in the irreversible decomposition. An efficient solution-phase trap for hydrogen, the 16-electron ruthenium benzyl complex [PhBP(Ph)3]Ru[η(3)-CH2(3,5-Me2C6H3)] (3) reacts quantitatively with H2 in benzene via elimination of mesitylene to form the η(5)-cyclohexadienyl complex [PhBP(Ph)3]Ru(η(5)-C6H7) (4). This H2 trapping reaction was utilized to drive forward and quantify the elimination of H2 from 1b,d in solution, which resulted in the decomposition of 1b,d to form 4 and several organosilicon products that could not be identified. Reaction of {[PhBP(Ph)3]Ru(μ-Cl)}2 (2) with (THF)2Li(SiHMes2) forms a new η(3)-H2Si species [PhBP(Ph)3]Ru[CH2(2-(η(3)-H2SiMes)-3,5-Me2C6H2)] (5) which reacts with H2 to form the η(3)-H2SiMes2 complex [PhBP(Ph)3]RuH(η(3)-H2SiMes2) (1e). Complex 1e was identified by NMR spectroscopy prior to its decomposition by elimination of Mes2SiH2 to form 4. DFT calculations indicate that an isomer of 5, the 16-electron silylene complex [PhBP(Ph)3]Ru(μ-H)(═SiMes2), is only 2 kcal/mol higher in energy than 5. Treatment of 5 with XylNC (Xyl = 2,6-dimethylphenyl) resulted in trapping of [PhBP(Ph)3]Ru(μ-H)(═SiMes2) to form the 18-electron silylene complex [PhBP(Ph)3]Ru(CNXyl)(μ-H)(═SiMes2) (6). A closely related germylene complex [PhBP(Ph)3]Ru[CN(2,6-diphenyl-4-MeC6H2)](H)(═GeH(t)Bu) (8) was prepared from reaction of (t)BuGeH3 with the benzyl complex [PhBP(Ph)3]Ru[CN(2,6-diphenyl-4-MeC6H2)][η(1)-CH2(3,5-Me2C6H3)] (7). Single crystal XRD analysis indicated that unlike for 6, the hydride ligand in 8 is a terminal hydride that does not engage in 3c-2e Ru-H → Ge bonding. Complex 1b is an effective precatalyst for the catalytic Ge-H dehydrocoupling of (t)BuGeH3 to form ((t)BuGeH2)2 (85% yield) and H2.

Synthesis, Structure, and Reactivity of Tungsten Acetylide–Germylene Complexes

The novel acetylide–germylene complexes Cp*(CO)2W(GePh2)(CCR) (7a, R = SiMe3; 7b, R = CMe3) were synthesized by the reactions of Cp*(CO)2W(NCMe)Me with Ph2HGeC≡CR (R = SiMe3, CMe3). X-ray crystal analysis of 7a revealed significantly increased germylene–tungsten and decreased germylene–acetylide interactions in comparison to the corresponding interactions in the previously reported acetylide–silylene complex Cp*(CO)2W(SiPh2)(CCSiMe3) (1). Complexes 7a,b reacted with acetone to give the six-membered cyclic vinylidene complexes Cp*(CO)2W═C═C(R)CMe2OGePh2 (8a, R = SiMe3; 8b, R = CMe3) by acetone insertion reaction, similar to the case of 1 affording Cp*(CO)2W═C═C(SiMe3)CMe2OSiPh2 (2). In the presence of 4-(dimethylamino)pyridine (DMAP), complexes 8a,b gave trans- and cis-DMAP-stabilized germylene acetylide complexes Cp*(CO)2W(GePh2·DMAP)(CCR) (trans- and cis-9a, R = SiMe3; trans- and cis-9b, R = CMe3) and acetone, showing a reactivity different from that of the silicon analogue 2. Complexes cis-9a,b were isolated as crystals from the reaction of 7a,b with DMAP and formed mixtures with trans-9a,b in solutions, respectively. A mixture of cis- and trans-9a reacted with acetone to form an equilibrium mixture with 8a and DMAP. The reactivity of 7a,b toward Me3COH was also investigated to reveal the formation of the vinylidene complexes Cp*(CO)2W{GePh2(OCMe3)}═C═CHR (10a, R = SiMe3; 10b, R = CMe3); 10a is equilibrated with 7a and Me3COH, whereas 10b is further converted to the carbyne complex Cp*(CO)2W≡CCH(CMe3){GePh2(OCMe3)} (11).

Preparation and reactivity of germyl complexes of ruthenium and osmium stabilised by cyclopentadienyl, indenyl and tris(pyrazolyl)borate fragments

Half-sandwich trichlorogermyl complexes Ru(GeCl3)(η5-C5H5)(PPh3)L (1) and Ru(GeCl3)(η5-C9H7)(PPh3)L (2) [L = P(OMe)3 (a), P(OEt)3 (b) and PPh(OEt)2 (c)] were prepared by allowing chloro compounds RuCl(η5-C5H5)(PPh3)L and RuCl(η5-C9H7)(PPh3)L to react with an excess of GeCl2·dioxane in ethanol. Treatment of trichlorogermyl complexes 1 and 2 with LiAlH4 in THF yielded trihydridogermyl derivatives Ru(GeH3)(η5-C5H5)(PPh3)L (3) and Ru(GeH3)(η5-C9H7)(PPh3)L (4). Instead, reaction of trichlorogermyl complexes 1 and 2 with NaBH4 in ethanol afforded triethoxygermyl complexes Ru[Ge(OEt)3](η5-C5H5)(PPh3)L (5) and Ru[Ge(OEt)3](η5-C9H7)(PPh3)L (6). Trichlorogermyl complexes with the tris(pyrazolyl)borate ligand M(GeCl3)(Tp)(PPh3)L [M = Ru (7), Os (10)] were prepared by reacting chloro compounds MCl(Tp)(PPh3)L with an excess of GeCl2·dioxane. Depending on metal centre, nature of phosphite and experimental conditions, the reaction of trichlorogermyl complexes 7 and 10 with LiAlH4 or NaBH4 afforded trihydridogermyl M(GeH3)(Tp)(PPh3)L (8, 12) and triethoxygermyl derivatives M[Ge(OEt)3](Tp)(PPh3)L (9, 11). The complexes were characterised by IR and multinuclear NMR spectroscopy and by X-ray crystal structure determination of 3a.

Coordination Chemistry of Disilylated Germylenes with Group 4 Metallocenes

Reaction of the PEt3 adduct of a disilylated five-membered cyclic germylene with group 4 metallocene dichlorides in the presence of magnesium led to the formation of the respective germylene metallocene phosphine complexes of titanium, zirconium, and hafnium. Attempts to react the related NHC adduct of a disilylated four-membered cyclic germylene under the same conditions with Cp2TiCl2 did not give the expected germylene NHC titanocene complex. This complex was, however, obtained in the reaction of Cp2Ti(btmsa) with the NHC germylene adduct. A computational analysis of the structure of the group 4 metallocene germylene complexes revealed the multiple-bond character of the M–Ge(II) linkage, which can be rationalized with the classical σ-donor/π-acceptor interaction. The strength of the M–Ge(II) bond increases descending group 4.