Utilizing Steric Bulk to Stabilize Molybdenum Aminogermylyne and Aminogermylene Complexes

Heavier tetrylene- and tetrylyne-transition metal chemistry: it's no carbon copy

Since the late 19th century, heavier tetrylene- and tetrylyne-transition metal chemistry has formed an important cornerstone in both main-group and organometallic chemistry alike. Driven by the success of carbene systems, significant efforts have gone towards the thorough understanding of the heavier group 14 derivatives, with examples now known from across the d-block. This now leads towards applications in cooperative bond activation, and moves ultimately towards well-defined catalytic systems. This review aims to summarise this vast field, from initial discoveries of tetrylene and tetrylyne complexes, to the most recent developments in reactivity and catalysis, as a platform to the future of this exciting, blossoming field.

Synthesis of Superbulky Amide Ligands by Addition of Polar Reagents to Sila-Imine

The chemistry of extremely bulky amide ligands is troubled by difficulties in deprotonation of the parent amine. As an alternative route to superbulky amide reagents, the addition of polar reagents to a sila-imine has been investigated. Attempts to synthesize the superbulky amide anion (tBu3Si)2N- by addition of tBuLi to tBu2Si=N(SitBu3) failed and gave tBu3Si(tBu2HSi)NLi and isobutene. Reaction of the sila-imine with KOtBu successfully led to tBu3Si[tBu2(tBuO)Si]NK which crystallized as a separated ion-pair. Reaction with the slightly bulkier KOAd (Ad=1-adamantyl) led in presence of THF to ether ring-opening. Reaction with tBuOH gave tBu3Si[tBu2(tBuO)Si]NH but this amine cannot be easily deprotonated. Reaction with (BDI*)MgnBu in presence of THF gave (BDI*)Mg+ ⋅ (THF)2 and the non-coordinating anion tBu3Si[tBu2(nBu)Si]N-; BDI*=ß-diketiminate ligand HC[C(tBu)N-DIPP]2, DIPP=2,6-diisopropylphenyl. Reaction of Mg(nBu)2 with tBu2Si=N(SitBu3) led to a Mg complex with one amide ligand: tBu3Si[tBu2(nBu)Si]N-. The other superbulky amide anion isomerized by internal deprotonation of a tBu-substituent to give a primary carbanion that is also coordinated to Mg. Although the amide-to-carbanion isomerization is highly contrathermodynamic, it allows for coordination of both anions to a single Mg center. The new bulky amides are rare cases of halogen-free weakly coordinating anions.

Synthesis of Cobalt-Tin and -Lead Tetrylidynes-Reactivity Study of the Triple Bond

Tetrylidynes [TbbSn≡Co(PMe3 )3 ] (1 a) and [TbbPb≡Co(PMe3 )3 ] (2) (Tbb=2,6-[CH(SiMe3 )2 ]2 -4-(t-Bu)C6 H2 ) are accessed for the first time via a substitution reaction between [Na(OEt2 )][Co(PMe3 )4 ] and [Li(thf)2 ][TbbEBr2 ] (E=Sn, Pb). Following an alternative procedure the stannylidyne [Ar*Sn≡Co(PMe3 )3 ] (1 b) was synthesized by hydrogen atom abstraction using AIBN from the paramagnetic hydride complex [Ar*SnH=Co(PMe3 )3 ] (4) (AIBN=azobis(isobutyronitrile)). The stannylidyne 1 a adds two equivalents of water to yield the dihydroxide [TbbSn(OH)2 CoH2 (PMe3 )3 ] (5). In reaction of the stannylidyne 1 a with CO2 a product of a redox reaction [TbbSn(CO3 )Co(CO)(PMe3 )3 ] (6) was isolated. Protonation of the tetrylidynes occurs at the cobalt atom to give the metalla-stanna vinyl cation [TbbSn=CoH(PMe3 )3 ][BArF 4 ] (7 a) [ArF =C6 H3 -3,5-(CF3 )2 ]. The analogous germanium and tin cations [Ar*E=CoH(PMe3 )3 ][BArF 4 ] (E=Ge 9, Sn 7 b) (Ar*=C6 H3 (2,6-Trip)2 , Trip=2,4,6-C6 H2 iPr3 ) were also obtained by oxidation of the paramagnetic complexes [Ar*EH=Co(PMe3 )3 ] (E=Ge 3, Sn 4), which were synthesized by substitution of a PMe3 ligand of [Co(PMe3 )4 ] by a hydridoylene (Ar*EH) unit.

The Electronic Nature of Cationic Group 10 Ylidyne Complexes

We report a broad theoretical study on [(PMe3)3MER]+ complexes, with M = Ni, Pd, Pt, E = C, Si, Ge, Sn, Pb, and R = ArMes, Tbb, (ArMes = 2,6-dimesitylphenyl; Tbb = C6H2-2,6-[CH(SiMe3)2]2-4-tBu). A few years ago, our group succeeded in obtaining heavier homologues of cationic group 10 carbyne complexes via halide abstraction of the tetrylidene complexes [(PMe3)3M=E(X)R] (X = Cl, Br) using a halide scavenger. The electronic structure and the M-E bonds of the [(PMe3)3MER]+ complexes were analyzed utilizing quantum-chemical tools, such as the Pipek–Mezey orbital localization method, the energy decomposition analysis (EDA), and the extended-transition state method with natural orbitals of chemical valence (ETS-NOCV). The carbyne, silylidyne complexes, and the germylidyne complex [(PMe3)3NiGeArMes]+ are suggested to be tetrylidyne complexes featuring donor–acceptor metal tetrel triple bonds, which are composed of two strong π(M→E) and one weaker σ(E→M) interaction. In comparison, the complexes with M = Pd, Pt; E = Sn, Pb; and R = ArMes are best described as metallotetrylenes and exhibit considerable M−E−C bending, a strong σ(M→E) bond, weakened M−E π-components, and lone pair density at the tetrel atoms. Furthermore, bond cleavage energy (BCE) and bond dissociation energy (BDE) reveal preferred splitting into [M(PMe3)3]+ and [ER] fragments for most complex cations in the range of 293.3–618.3 kJ·mol−1 and 230.4–461.6 kJ·mol−1, respectively. Finally, an extensive study of the potential energy hypersurface varying the M−E−C angle indicates the presence of isomers with M−E−C bond angles of around 95°. Interestingly, these isomers are energetically favored for M = Pd, Pt; E = Sn, Pb; and R = ArMes over the less-bent structures by 13–29 kJ·mol−1.

Group 6 germylidyne complexes in the gas phase by LIFDI and APCI mass spectrometry

Although showing fascinating chemical properties and reactivity in solution, heavier tetrelylidyne complexes with M≡E triple bonds have not been studied in the gas phase before due to their high sensitivity towards air and moisture. We selected four group 6 germylidyne complexes, [Cp(PMe₃)₂M≡GeAr^Mes] (M = Mo (1-Mo), W (1-W), Ar^Mes = 2,6-dimesitylphenyl) and [Tp'(CO)₂M≡GeAr^Mes] (M = Mo (2-Mo), W (2-W), Tp' = κ³-N,N',N''-hydridotris(3,5-dimethylpyrazolyl) borate), for a mass-spectrometric study. Liquid Injection Field Desorption Ionization (LIFDI) proved to be a well-suited technique to ionize these sensitive compounds as the spectra show the molecular ions as radical cations and only minor traces of fragmentation or degradation products. In addition, Atmospheric Pressure Chemical Ionization (APCI) connected to a high-resolving tandem mass spectrometer allowed us to study the gas-phase fragmentation behaviour of these compounds. The fragmentation patterns not only comprise the expected losses of phosphane or carbonyl ligands, respectively, but also indicate C-H bond activation by the electron-deficient metal centre. An enhanced reactivity of the tungsten species is visible in a preferred methyl abstraction in the phosphane complex 1-W compared to 1-Mo. Although degradation in solution before ionization obviously can destroy the M≡Ge triple bond, the cleavage of the M≡Ge bond upon gas-phase activation is not observed for the Mo species and only as a minor pathway for the W compounds, highlighting the high bonding energy between metal and tetrel.

Heavy metalla vinyl-cations show metal-Lewis acid cooperativity in reaction with small molecules (NH3, N2H4, H2O, H2)

Halide abstraction from tetrylidene complexes [TbbE(Br)IrH(PMe3)3] [E = Ge (1), Sn (2)] and [Ar*E(Cl)IrH(PMe3)3] gives the salts [TbbEIrH(PMe3)3][BArF 4] [E = Ge (3), Sn (4)] and [Ar*EIrH(PMe3)3][BArF 4] [E = Ge (3'), E = Sn (4')] (Tbb = 2,6-[CH(SiMe3)2]2-4-(t-Bu)C6H2, Ar* = 2,6-Trip2C6H3, Trip = 2,4,6-triisopropylphenyl). Bonding analysis suggests their most suitable description as metalla-tetrela vinyl cations with an Ir[double bond, length as m-dash]E double bond and a near linear coordination at the Ge/Sn atoms. Cationic complexes 3 and 4 oxidatively add NH3, N2H4, H2O, HCl, and H2 selectively to give: [TbbGe(NH2)IrH2(PMe3)3][BArF 4] (5), [TbbE(NHNH2)IrH2(PMe3)3][BArF 4] [E = Ge (7), Sn (8)], [TbbE(OH)IrH2(PMe3)3][BArF 4] [E = Ge (9), Sn (10)], [TbbE(Cl)IrH2(PMe3)3][BArF 4] [E = Ge (11a), Sn (12a)], [TbbGe(H)IrH2(PMe3)3][BArF 4] (13), [TbbSn(μ-H3)Ir(PMe3)3][BArF 4] (14), and [TbbSn(H)IrH2(PMe3)3][BArF 4] (15). 14 isomerizes to give 15via an 1,2-H shift reaction. Hydride addition to cation 3 gives a mixture of products [TbbGeHIrH(PMe3)3] (16) and [TbbGeIrH2(PMe3)3] (17) and a reversible 1,2-H shift between 16 and 17 was studied. In the tin case 4 the dihydride [TbbSnIrH2(PMe3)3] (18) was isolated exclusively. The PMe3 and PEt3 derivatives, 18 and [TbbSnIrH2(PEt3)3] (19), respectively, could also be synthesized in reaction of [TbbSnH2]- with the respective chloride [(R3P) n IrCl] (R = Me, n = 4; R = Et, n = 3). Reaction of complex 19 with CO gives the substitution product [TbbSnIrH2(CO)(PEt3)2] (20). Further reaction with CO results in hydrogen transfer from the iridium to the tin atom to give [TbbSnH2Ir(CO)2(PEt3)2] (21). The reversibility of this ligand induced reductive elimination transferring 20 to 21 is shown.

Accessing cationic tetrylene-nickel(0) systems featuring donor-acceptor E-Ni triple bonds (E = Ge, Sn)

We describe facile synthetic methods for accessing linear cationic tetrylene nickel(0) complexes [^SiiPDippE·Ni(PPh₃)₃]⁺ (E = Ge (4) and Sn (5); ^SiiPDipp = [(iPr₃Si)(Dipp)N]^-), which feature donor-acceptor E-Ni triple bonds. These species are readily accessed in a one-pot protocol, combining the bulky halo-tetrylenes ^SiiPDippECl (E = Ge (1) and Sn (2)), Ni(cod)₂, PPh₃, and Na[BAr^F₄]. Given the diamagnetic nature of 4 and 5, they each contain a formal zero-valent Ni centre, making the E-M triple bonds in these complexes unique compared to previously reported metal tetrylidyne complexes, which typically feature covalent/ionic bonding. In-depth computational analyses of these species further support triple bond character in their E-Ni interactions.

Geometrically Constrained Cationic Low-Coordinate Tetrylenes: Highly Lewis Acidic σ-Donor Ligands in Catalytic Systems

A novel non-innocent ligand class, namely cationic single-centre ambiphiles, is reported in the phosphine-functionalised cationic tetrylene Ni0 complexes, [PhR DippENi(PPh3 )3 ]+ (4 a/b (Ge) and 5 (Sn); PhR Dipp={[Ph2 PCH2 SiR2 ](Dipp)N}- ; R=Ph, i Pr; Dipp=2,6-i Pr2 C6 H3 ). The inherent electronic nature of low-coordinate tetryliumylidenes, combined with the geometrically constrained [N-E-Ni] bending angle enforced by the chelating phosphine arm in these complexes, leads to strongly electrophilic EII centres which readily bind nucleophiles, reversibly in the case of NH3 . Further, the GeII centre in 4 a/b readily abstracts the fluoride ion from [SbF6 ]- to form the fluoro-germylene complex PhR DippGe(F)Ni(PPh3 )3 9, despite this GeII centre simultaneously being a σ-donating ligand towards Ni0 . Alongside the observed catalytic ability of 4 and 5 in the hydrosilylation of alkynes and alkenes, this forms an exciting introduction to a multi-talented ligand class in cationic single-centre ambiphiles.

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 )2 Ge :] (ArMes =C6 H3 -2,6-(C6 H2 -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 η6 - and η2 -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.

On the edge of the steric repulsion and reactivity of bulky anilines; a case study of chloro(imino)phosphine synthesis

2-Benzhydryl-4-methyl-6-(1,1'-diphenyl-2-phenyl-ethyl)aniline was prepared by a three-step process. 2,6-Bis(benzhydryl)-4-methyl-aniline was protected by Schiff coupling, then benzylated and finally dealkylated by using hydrochloric acid and methanol. The resulting compound exhibits one of the highest buried volumes around the nitrogen atom of anilines prepared so far, but it reacts with phosphorus trichloride and triethylamine to give a monomeric chloro(imino)phosphine.

H2 and carbon-heteroatom bond activation mediated by polarized heterobimetallic complexes

The field of heterobimetallic chemistry has rapidly expanded over the last decade. In addition to their interesting structural features, heterobimetallic structures have been found to facilitate a range of stoichiometric bond activations and catalytic processes. The accompanying review summarizes advances in this area since January of 2010. The review encompasses well-characterized heterobimetallic complexes, with a particular focus on mechanistic details surrounding their reactivity applications.

Synthesis and Hydrogenation of Heavy Homologues of Rhodium Carbynes: [(Me3 P)2 (Ph3 P)Rh≡E-Ar*] (E=Sn, Pb)

Tetrylidynes [(Me3 P)2 (Ph3 P)Rh≡SnAr*] (10) and [(Me3 P)2 (Ph3 P)Rh≡PbAr*] (11) are accessed for the first time via dehydrogenation of dihydrides [(Ph3 P)2 RhH2 SnAr*] (3) and [(Ph3 P)2 RhH2 PbAr*] (7) (Ar*=2,6-Trip2 C6 H3 , Trip=2,4,6-triisopropylphenyl), respectively. Tin dihydride 3 was either synthesized in reaction of the dihydridostannate [Ar*SnH2 ]- with [(Ph3 P)3 RhCl] or via reaction between hydrides [(Ph3 P)3 RhH] and 1 / 2  [(Ar*SnH)2 ]. Homologous lead hydride [(Ph3 P)2 RhH2 PbAr*] (7) was synthesized analogously from [(Ph3 P)3 RhH] and 1 / 2  [(Ar*PbH)2 ]. Abstraction of hydrogen from 3 and 7 supported by styrene and trimethylphosphine addition yields tetrylidynes 10 and 11. Stannylidyne 10 was also characterized by 119 Sn Mössbauer spectroscopy. Hydrogenation of the triple bonds at room temperature with excess H2 gives the cis-dihydride [(Me3 P)2 (Ph3 P)RhH2 PbAr*] (12) and the tetrahydride [(Me3 P)2 (Ph3 P)RhH2 SnH2 Ar*] (14). Complex 14 eliminates spontaneously one equivalent of hydrogen at room temperature to give the dihydride [(Me3 P)2 (Ph3 P)RhH2 SnAr*] (13). Hydrogen addition and elimination at stannylene tin between complexes 13 and 14 is a reversible reaction at room temperature.

Metathetical Exchange between Metal-Metal Triple Bonds

The reaction of the molybdenum-molybdenum triple-bonded dimer (CO)₂CpMo≡MoCp(CO)₂ (Cp = η⁵-C₅H₅) with the triple-bonded dimetallynes Ar^iPr4MMAr^iPr4 or Ar^iPr6MMAr^iPr6 (Ar^iPr4 = C₆H₃-2,6-(C₆H₃-2,6-Prⁱ₂)₂, Ar^iPr6 = C₆H₃-2,6-(C₆H₂-2,4,6-Prⁱ₃)₂; M = Ge, Sn, or Pb) under mild conditions (≤80 °C, 1 bar) afforded Ar^iPr4M≡MoCp(CO)₂ or Ar^iPr6M≡MoCp(CO)₂ in moderate to excellent yields. The reactions represent the first isolable products from a metathesis of two metal-metal triple bonds. Analogous exchange reactions with the single-bonded (CO)₃CpMo-MoCp(CO)₃ gave ArM̈-MoCp(CO)₃ (Ar = Ar^iPr4 or Ar^iPr6; M = Sn or Pb). The products were characterized by NMR (¹H, ¹³C, ¹¹⁹Sn, or ²⁰⁷Pb), electronic, and IR spectroscopy and by X-ray crystallography.

A Stable N-Hetero-Rh-Metallacyclic Silylene

A cyclic (amino)metal-substituted dicoordinated silylene derivative has been synthesized and fully characterized. Of particular interest is that the N-hetero-Rh^I -metallacyclic silylene exhibits a distorted tetrahedral geometry around the rhodium atom and a considerably shortened Si-Rh bond (2.138 Å) compared to classical Si-Rh single bonds (ca. 2.30-2.35 Å). A theoretical investigation reveals that the geometrical deviation around the rhodium center from the classical square-planar to a tetrahedral geometry increases the π-donating and σ-accepting character of the rhodium atom, thereby efficiently stabilizing the silylene moiety.

Synthesis and Reactivity Studies of Amido-Substituted Germanium(I)/Tin(I) Dimers and Clusters

Three amide ligands of varying steric bulk and electronic properties were utilized to prepare a series of amido-germanium(II)/tin(II) halide compounds, (LEX)_n , (L= -N{B(DipNCH)₂ }(SiMe₃ ), ^TBo L; -N{B(DipNCH)₂ }(SiPh₃ ), ^PhBo L; -N(Dip)(tBu), ^DBu L; Dip=C₆ H₃ iPr₂ -2,6; E=Ge or Sn; X=Cl or Br; n=1 or 2). Reductions of these with a magnesium(I) dimer, {(^Mes Nacnac)Mg}₂ (^Mes Nacnac=[(MesNCMe)₂ CH]^- , Mes=mesityl), afforded singly bonded amido-digermynes (^TBo LGe-Ge^TBo L and ^PhBo LGe-Ge^PhBo L), and an amido-distannyne (^PhBo LSn-Sn^PhBo L), in addition to several low-valent, amido stabilized tetrel-tetrel bonded cluster compounds, (^DBu LGe)₄ , (^DBu LSn)₆ and Sn₅ (^TBo L)₄ . The nature of the products resulting from these reactions was largely dependent on the steric bulk of the amide ligand employed. Cluster (^DBu LGe)₄ possessed an unusual folded butterfly structure, the bonding and electronic of which were examined using DFT calculations. Reactions of the amido-germanium(I) compounds with H₂ were explored, and gave rise to the amido-digermene, ^TBo L(H)Ge=Ge(H)^TBo L and the cyclotetragermane, {^DBu L(H)Ge}₄ . Reactions of (^DBu LGe)₄ with a series of unsaturated small molecule substrates yielded ^DBu LGeOGe^DBu L, ^DBu LGe(μ-C₂ H₄ )₂ Ge^DBu L and ^DBu LGe(μ-1,4-C₆ H₈ )(μ-1,2-C₆ H₈ )Ge^DBu L. The latter results imply that (^DBu LGe)₄ can act as a masked source of the digermyne ^DBu LGeGe^DBu L in these reactions. All further reactivity studies indicated that the germanium(I) compounds exhibit a "transition-metal-like" behavior, which is closely related to that previously described for bulky digermynes and related compounds.

Redox transmetallation approaches to the synthesis of extremely bulky amido-lanthanoid(ii) and -calcium(ii) complexes

Redox transmetallation protolysis and direct redox transmetallation reactions have been employed to access a variety of extremely bulky amido-lanthanoid(ii), and related calcium(ii) complexes which cannot be prepared using classical salt metathesis pathways.

Triple bonds of niobium with silicon, germaniun and tin: the tetrylidyne complexes [(κ3-tmps)(CO)2Nb[triple bond, length as m-dash]E-R] (E = Si, Ge, Sn; tmps = MeSi(CH2PMe2)3; R = aryl)

A systematic, efficient approach to first complexes containing a triple bond between niobium and the elements silicon, germanium or tin is reported. The approach involves a metathetical exchange of the niobium-centered nucleophile (NMe4)[Nb(CO)4(κ2-tmps)] (1) (tmps = MeSi(CH2PMe2)3) with a suitable organotetrel(ii)halide. Compound 1 was obtained from (NMe4)[Nb(CO)6] and the triphosphane tmps by photodecarbonylation. Reaction of 1 with the disilene E-Tbb(Br)Si[double bond, length as m-dash]Si(Br)Tbb in the presence of 4-dimethylaminopyridine afforded selectively the red-brown silylidyne complex [(κ3-tmps)(CO)2Nb[triple bond, length as m-dash]Si-Tbb] (2-Si, Tbb = 4-tert-butyl-2,6-bis(bis(trimethylsilyl)methyl)phenyl). Similarly, treatment of 1 with E(ArMes)Cl (E = Ge, Sn; ArMes = 2,6-mesitylphenyl) afforded after elimination of (NMe4)Cl and two CO ligands the deep magenta colored germylidyne complex [(κ3-tmps)(CO)2Nb[triple bond, length as m-dash]Ge-ArMes] (3-Ge), and the deep violet, light-sensitive stannylidyne complex [(κ3-tmps)(CO)2Nb[triple bond, length as m-dash]Sn-ArMes] (3-Sn), respectively. Formation of 3-Sn proceeds via the niobiastannylene [(κ3-tmps)(CO)3Nb-SnArMes] (4-Sn), which was detected by IR and NMR spectroscopy. The niobium tetrylidyne complexes 2-Si, 3-Ge and 3-Sn were fully characterized and their solid-state structures determined by single-crystal X-ray diffraction studies. All complexes feature an almost linear tetrel coordination and the shortest Nb-E bond lengths (d(Nb-Si) = 232.7(2) pm; d(Nb-Ge) = 235.79(4) pm; d(Nb-Sn) = 253.3(1) pm) reported to date. Reaction of 3-Ge with a large excess of H2O afforded upon cleavage of the Nb-Ge triple bond the hydridogermanediol Ge(ArMes)H(OH)2. Photodecarbonylation of [CpNb(CO)4] (Cp = η5-C5H5) in the presence of Ge(ArMes)Cl afforded the red-orange chlorogermylidene complex [Cp(CO)3Nb[double bond, length as m-dash]Ge(ArMes)Cl] (5-Ge). The molecular structure of 5-Ge features an upright conformation of the germylidene ligand, a trigonal-planar coordinated Ge atom, and a Nb-Ge double bond length of 251.78(6) pm, which lies in-between the Nb-Ge triple bond length of 3-Ge (235.79(4) pm) and a Nb-Ge single bond length (267.3 pm). Cyclic voltammetric studies of 2-Si, 3-Ge, and 3-Sn reveal several electron-transfer steps. One-electron oxidation and reduction of the germylidyne complex of 3-Ge in THF are electrochemically reversible suggesting that both the radical cation and radical anion of 3-Ge are accessible species in solution.

Reaction Mechanism of the Hydrogermylation/Hydrostannylation of Unactivated Alkenes with Two-Coordinate E(II) Hydrides (E=Ge, Sn): A Theoretical Study

Quantum chemical calculations using density functional theory with the TPSS+D3(BJ) and M06-2X+D3(ABC) functionals have been carried out to understand the mechanisms of catalyst-free hydrogermylation/hydrostannylation reactions between the two-coordinate hydrido-tetrylenes :E(H)(L(+) ) (E=Ge or Sn, L(+) =N(Ar(+) )(SiiPr3 ); Ar(+) =C6 H2 {C(H)Ph2 }2 iPr-2,6,4) and a range of unactivated terminal (C2 H3 R, R=H, Ph, or tBu) and cyclic [(CH)2 (CH2 )2 (CH2 )n , n=1, 2, or 4] alkenes. The calculations suggest that the addition reactions of the germylenes and stannylenes to the cyclic and acyclic alkenes occur as one-step processes through formal [2+2] addition of the E-H fragment across the C-C π bond. The reactions have moderate barriers and are weakly exergonic. The steric bulk of the tetrylene amido groups has little influence on the activation barriers and on the reaction energies of the anti-Markovnikov pathway, but the Markovnikov addition is clearly disfavored by the size of the substituents. The addition of the tetrylenes to the cyclic alkenes is less exergonic than the addition to the terminal alkenes, which agrees with the experimentally observed reversibility of the former reactions. The hydrogermylation reactions have lower activation energies and are more exergonic than the stannylene addition. An energy decomposition analysis of the transition state for the hydrogermylation of cyclohexene shows that the reaction takes place with simultaneous formation of the Ge-C and (Ge)H-C' bonds. The dominant orbitals of the germylene are the σ-type lone pair MO of Ge, which serves as a donor orbital, and the vacant p(π) MO of Ge, which acts as acceptor orbital for the π* and π MOs of the olefin. Inspection of the transition states of some selected reactions suggests that the differences between the activation energies come from a delicate balance between the deformation energies of the interacting species and their interaction energies.

Extremely bulky amide ligands in main group chemistry

The development of extremely sterically demanding, monodentate amide ligands facilitates the isolation of main group species with new and highly reactive coordination modes. An outstanding feature of these ligands is the ability to tune their steric demands. Reactivity investigations highlight the potential for small molecule activation chemistry and catalysis for these compounds.

Stabilization of a two-coordinate, acyclic diaminosilylene (ADASi): completion of the series of isolable diaminotetrylenes, :E(NR2)2(E = group 14 element)

An extremely bulky boryl-amide ligand, [N(SiMe₃){B(DAB)}]⁻(TBoN; DAB = (DipNCH)₂, Dip = C₆H₃Prⁱ₂-2,6), has been developed and utilised in the preparation of the first isolable, two-coordinate acyclic diaminosilylene (ADASi),viz.:Si(TBoN)₂.

Two-coordinate terminal zinc hydride complexes: synthesis, structure and preliminary reactivity studies

The first examples of essentially two-coordinate, monomeric zinc hydride complexes have been stabilised by incorporation of “super bulky” amide ligands. Crystallographic studies show them to possess near linear N–Zn–H fragments (see picture).

Dispersion-Corrected Relativistic Density Functional Theory (DFT) Calculations of Structure and (119)Sn Mössbauer Parameters for M≡SnR Bonding in Filippou's Stannylidyne Complexes of Molybdenum and Tungsten

(119)Sn Mössbauer isomer shift (IS) and quadrupole splitting (ΔEQ) for M≡SnR bonding in metal-stannylidyne complexes trans-[Cl(PMe3)4Mo≡Sn-R] (1), trans-[Cl(PMe3)4W≡Sn-R] (2), trans-[Cl(dppe)2Mo≡Sn-R] (3), trans-[Cl(dppe)2W≡Sn-R] (4), [(dppe)2Mo≡Sn-R](+) (5), [(dppe)2W≡Sn-R](+) (6) (R = C6H3-2,6-Mes2) have been investigated for the first time. Calculations of optimized structures and (119)Sn Mössbauer parameters were carried out at the DFT/TPSS-D3(BJ)/TZVPP/ZORA level of theory. The calculated geometry parameters of stannylidyne complexes of molybdenum and tungsten (1-6) are in good agreement with experimental values of W-Sn and Sn-C bond distances. The calculated values of the isomer shift for the complexes (1-6) are almost same to the experimental values (within ±0.1 mm/s). Experimental values (ISexptl, 2.38-2.50 mm/s) and calculated values (IScalcd, 2.37-2.49 mm/s) of isomer shifts indicate that the oxidation state of tin in the studied complexes with M≡Sn-R bonding is Sn(II). The variations of ISexptl, as a function of Sn s electrons (Ns(Sn)), also exhibit a linear trend. (IS = 0.477Ns(Sn) - 1.888, R(2) = 0.9973). Calculated values of isomer shift (IScalcd) using the linear regression with the Ns(Sn) electron density are in excellent concord with the ISexptl.The calculated values of nuclear quadrupole splitting parameters (ΔEQ(calcd)) of (119)Sn using the relation ΔEQ(calcd) = (0.540 + 0.28) V are in agreement with the experimental values.

Two-coordinate group 14 element(ii) hydrides as reagents for the facile, and sometimes reversible, hydrogermylation/hydrostannylation of unactivated alkenes and alkynes

The ambient temperature hydrometallations of a variety of unactivated alkene and alkyne substrates using two-coordinate hydrido-tetrylenes, :E(H)(L^†) (E = Ge or Sn; L^† = extremely bulky amide), are reported.

Reactions of the solution stable, two-coordinate hydrido-tetrylenes, :E(H)(L^†) (E = Ge or Sn; L^† = –N(Ar^†)(SiPrⁱ₃); Ar^† = C₆H₂{C(H)Ph₂}₂Prⁱ-2,6,4), with a variety of unactivated cyclic and acyclic alkenes, and one internal alkyne, lead to the rapid and regiospecific hydrometallation of the unsaturated substrate at ambient temperature. The products of the reactions, [L^†E(C₂H₄R)] (E = Ge or Sn, R = H, Ph or Bu^t), [L^†E{CH(CH₂)₃(CH₂)_n}] (E = Ge, n = 1, 2 or 3; E = Sn, n = 1) and [L^†E{C(Ph) Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C(H)(Me)}], include the first structurally characterised examples of two-coordinate amido/alkyl germylenes and stannylenes. The cycloalkene hydrometallation reactions are cleanly reversible under ambient conditions, a process which computational and experimental van't Hoff analyses suggest proceeds via β-hydride elimination from the metal coordinated cycloalkyl ligand. Similarly, the reactions of :Ge(H)(L^†) with 1,5-cyclooctadiene and 2-methyl-2-butene, both likely proceed via β-hydride elimination processes, leading to the clean isomerisation of the alkene involved, and its subsequent hydrogermylation, to give [L^†Ge(2-cyclooctenyl)] and [L^†Ge{C₂H₄C(H)Me₂}], respectively. Reactions of [L^†GeEt] and [L^†Ge(C₅H₉)] with the protic reagents, HCl, NH₃ and EtOH, lead to oxidative addition to the germanium(ii) centre, and formation of the stable chiral germanium(iv) complexes, [L^†Ge(C₅H₉)(H)Cl] and [L^†Ge(Et)(H)R] (R = NH₂ or OEt). In contrast, related reactions between [L^†SnEt] and Bu^tOH or TEMPOH (TEMP = 2,2,6,6-tetramethylpiperidinyl) proceed via ethane elimination, affording the tin(ii) products, [L^†SnR] (R = OBu^t or OTEMP). In addition, the oxidation of [L^†Ge(C₆H₁₁)] and [L^†Sn(C₂H₄Bu^t)] with O₂ yields the oxo-bridged metal(iv) dimers, [{L^†(C₆H₁₁)Ge(μ-O)}₂] and [{L^†(Bu^tC₂H₄)Sn(μ-O)}₂], respectively.

Two-coordinate hydrido-germylenes

The first structurally characterised two-coordinate hydrido-germylenes, :Ge(H)L (L = -N(Ar){Si(OBu)}, Ar = C6H2{C(H)Ph2}2R-2,6,4; R = Pr(i) ((tBuO)L(†)), Me ((tBuO)L*)), have been prepared, and their dimerisation shown to be thermodynamically unfavourable, largely due to the extreme steric bulk of their amide ligands.

Utilisation of a lithium boryl as a reducing agent in low oxidation state group 15 chemistry: synthesis and characterisation of an amido-distibene and a boryl-dibismuthene

The first examples of an amido-distibene and a boryl dibismuthene (see picture) have been prepared by reaction of a lithium boryl complex with extremely bulky amido-group 15 dihalide precursor compounds.

Synthesis and characterization of extremely bulky amido-germanium(II) halide complexes

The extremely bulky aryl/silyl secondary amines, HN(Ar)(SiMe3), Ar = C6H2-i-Pr2(CPh3)-2,6,4 (LDipH), C6H2{C(H)Ph2}2-i-Pr-2,6,4 (L†H), or C6H2{C(H)Ph2}2-t-Bu-2,6,4 (Lt-BuH), have been synthesized via salt metathesis reactions between the appropriate lithium anilide complex and ClSiMe3. The related diaryl secondary amines, HN(Ar*)(R), Ar* = C6H2{C(H)Ph2}2Me-2,6,4 and R = C6H3Me2-3,5 (LMeH), C6H3(CF3)2-3,5 (LCF3H), or C6H2-i-Pr3-2,4,6 (LTripH), were prepared via palladium catalyzed cross-coupling reactions. Three of the amines were crystallographically characterized. Treatment of GeCl2·dioxane with 1 equiv. of each of the deprotonated amines led to the isolation of the amido-germanium(II) chloride complexes, [LGeCl] (L = L†, Lt-Bu, LCF3, or LTrip). Similarly, reaction of the known amido-digermyne, [L*Ge–GeL*] (L* = –N(Ar*)(SiMe3)), with I2 resulted in the oxidative cleavage of the Ge–Ge bond of the digermyne, and the formation of the first two-coordinate amido-germanium(II) iodide complex, [L*GeI]. Crystallographic characterization of [Lt-BuGeCl] and [L*GeI] revealed both to have similar monomeric structures. The compounds described in this study should prove useful as synthons for synthetic chemists working in the field of low oxidation state main group chemistry.

Reactions of a tungsten-germylyne complex with α,β-unsaturated ketones: complete cleavage of the W≡Ge bond and formation of two types of η3-germoxyallyl tungsten complexes

Germylyne complex Cp*(CO)2W≡Ge{C(SiMe3)3} (1) reacted with two molecules of RC(O)CH═CH2 (R = Me, Et) to give η(3)-allyl complexes, in which an oxagermacyclopentene framework was bound to an η(3)-allyl ligand through an oxygen atom. In the reaction with α-Me-substituted MeC(O)C(Me)═CH2, 1 reacted with only one molecule of the substrate to give another type of η(3)-allyl complex, in which a five-membered oxagermacyclopentenyl ring was coordinated to the W center in an η(3) fashion. Both reactions resulted in unprecedented complete cleavage of a W≡Ge triple bond.