The cation cluster of heavier group 14 elements: a free germyl cation with trishomoaromaticity

The heavier group 14 element cation cluster compound, [(tBu3Si)6Ge10I]+.TTFPB- (3+. TTFPB-; TTFPB- = tetrakis(2,3,5,6-tetrafluorophenyl)borate), was unexpectedly obtained by thermolysis of in situ prepared iodocyclotrigermene, (tBu3Si)3Ge3I, in toluene in the presence of KI and K+.TTFPB-. The molecular structure of 3+.TTFPB- has been unambiguously determined by X-ray crystallography, showing that 3+ is a free germyl cation. The three "naked" cationic germanium atoms in the framework constitute a three-center two-electron (3c-2e) bond with a trishomocyclotrigermenylium character, which is well-supported by a theoretical calculation on the model compound Ge10H7+.     

Halogen-Substituted Cyclotrigermenes: The π(Ge = Ge)-σ*(Ge–X) Interaction and a Unique Dynamic Behavior

Abstract

The halogen-substituted cyclotrigermenes (^tBu₃Si)₃Ge₃X (X = F, Cl, Br, I) (2) were synthesized by the reaction of tris(tri-tert-butylsilyl)cyclotrigermenylium tetrakis(2,3,5,6-tetrafluorophenyl)borate) (1 ⁺?TTFPB^?) with potassium halides (KF, KCl, KBr, KI). Intramolecular halogen migration over the three-membered ring skeleton was observed in the solution.

GRAPHICAL ABSTRACT     

Iron complexes of (e)- and (z)-1,2-dichlorodisilenes

Novel disilene-iron complexes [(E)- (1E) and (Z)-(eta2-R3SiClSi=SiClSiR3)Fe(CO)4 (1Z), SiR3 = tBu2MeSi] were synthesized by the reaction of the corresponding tetrachlorodisilane with an excess amount of K2Fe(CO)4, and the structures of 1E and 1Z were determined by X-ray crystallography. These complexes constitute not only the first transition-metal complexes with E,Z-isomerism but also the first complexes with halogen-substituted disilene ligands. The initial formation of 1Z during the synthetic reaction and the slow one-way isomerization of 1Z to 1E are rationalized by the intervention of the corresponding silylene complex (R3SiCl2Si)(R3Si)Si=Fe(CO)4.     

Ab initio Study on Formation Mechanism of Spiro-Si-Heterocyclic Ring Compound Involving Ge from H2Ge=Si: and Formaldehyde

H₂Ge=Si: and its derivatives (X₂Ge=Si:, X=H, Me, F, Cl, Br, Ph, Ar,…) are new species. Its cycloaddition reactions are new area for the study of silylene chemistry. The cycloaddition reaction mechanism of singlet H₂Ge=Si: and formaldehyde has been investigated with the MP2/aug-cc-pVDZ method. From the potential energy profile, it could be predicted that the reaction has one dominant reaction pathway. The reaction rule is that two reactants firstly form a four-membered Ge-heterocyclic ring silylene through the [2+2] cycloaddition reaction. Because of the 3p unoccupied orbital of Si: atom in the four-membered Ge-heterocyclic ring silylene and the π orbital of formaldehyde forming a π→p donor-acceptor bond, the four-membered Ge-heterocyclic ring silylene further combines with formaldehyde to form an intermediate. Because the Si: atom in the intermediate undergoes sp³ hybridization after transition state, then the intermediate isomerizes to a spiro-Si-heterocyclic ring compound involving Ge via a transition state. The result indicates the laws of cycloaddition reaction between H₂Ge=Si: or its derivatives (X₂Ge=Si:, X=H, Me, F, Cl, Br, Ph, Ar,…) and asymmetric π-bonded compounds are significant for the synthesis of small-ring involving Si and Ge and spiro-Si-heterocyclic ring compounds involving Ge.     

Mechanism of abstraction reactions of dimetallenes (R2X=XR2; X = C, Si, Ge, Sn, Pb) with halocarbons: a theoretical study

Potential energy surfaces for the abstraction reactions of dimetallenes with halocarbons have been studied using density functional theory (B3LYP). Five dimetallene species, (SiH(3))(2)X=X(SiH(3))(2), where X = C, Si, Ge, Sn, and Pb, have been chosen in this work as model reactants. The present theoretical investigations suggest that the relative dimetallenic reactivity increases in the order C=C < Si=Si < Ge=Ge < Sn=Sn < Pb=Pb. That is to say, for halocarbon abstractions there is a very clear trend toward lower activation barriers and more exothermic reactions on going from C to Pb. Moreover, for a given dimetallene, the overall barrier heights are determined to be in the order CF(4) > CCl(4) > CBr(4) > CI(4). That is, the heavier the halogen atom (Y), the more facile its abstraction from CY(4). Halogen abstraction is always predicted to be much faster than the abstraction of a CY(3) group irrespective of the dimetallene or halocarbon involved. Our model conclusions are consistent with some available experimental findings. Furthermore, both a configuration mixing model based on the work of Pross and Shaik and bonding dissociation energies can be used to rationalize the computational results. These results allow a number of predictions to be made.     

Reactions of iridium hydride pincer complexes with dioxygen: new dioxygen complexes and reversible O2 binding

The reaction of molecular oxygen with iridium pincer hydride complexes, ((tBu)PCP)Ir(H)(X) [(tBu)PCP = kappa(3)-C(6)H(3)(CH(2)P(t)Bu(2))(2), X = Ph, H, CCPh], results in O(2) induced reductive elimination and formation of the novel dioxygen complexes ((tBu)PCP)Ir(O(2))(n) [n = 1 (), 2 ()].     

Vibrational spectra and ab initio analysis of tert-butyl, trimethylsilyl, trimethylgermyl, trimethylstannyl, and trimethylplumbyl derivatives of 3,3-dimethylcyclopropene X. Some regularities

The changes in the vibrational frequencies of 1-tert-butyl and 1,2-di-tert-butyl derivatives of 3,3-dimethylcyclopropene brought about by substitution of the central carbon atom (X) of the tert-butyl moieties by Si, Ge, Sn, or Pb atoms are examined. The most important decrease in the vibrational frequencies implicating the X(CH(3))(3) moieties is noted for substitution of X=C by Si. The substitutions of Si by Ge or Ge by Sn or Sn by Pb are not accompanied by the pronounced frequency shifts observed for the C-->Si transition. An explanation is given for trends in these vibrational frequencies for the transitions X=C-->Si-->Ge-->Sn-->Pb. It is concluded that there are lower limiting values of the vibrational frequencies of a molecular moiety which are approached when the mass of its isovalent atom is increased. This leads to the formation of cluster regions in the vibrational spectra for the frequencies of the SnC(3) and PbC(3) moieties.     

Computational studies on stable triplet states of heteroacetylenes and the effects of halogen substituents

This paper describes theoretical studies of halogen-substituted heteroacetylenes (XCMY, M = Si and Ge; X, Y = H, Cl and F) performed at the QCISD(T)/6-311G//QCISD/6-31G level of theory. The electronegative halogen substituents destabilize the singlet state such that the triplet state tends to become favorable. The triplet state has the bifunctional electronic structure of a triplet carbene joined to a heavy singlet carbene. We found that the substituents effectively reduce the energy of the donor-acceptor interactions (E(D-A)) between the two in-plane lone pairs of electrons of the singlet state; therefore, the remaining pi bond is less favorable energetically than the triplet state with a sigma bond. A related phenomenon occurs for the homonuclear heavy acetylenes in singlets in which the lead compound RPbPbR switches to a Pb-Pb sigma bond from the pi bonds observed for the lighter acetylenes.     

A novel type of phosphide: synthesis and X-ray crystal structure analysis of (tBu3Si)3P4Li3

The tetraphosphides (tBu3Si)3P4M3 (M = Li, Na) and (tBu2PhSi)3P4Na3 have been synthesized in high yield from the reaction of 3 equivalents of the silanides tBu3SiM (M = Li, Na) and tBu2PhSiNa with P4 in benzene. (tBu3Si)3P4M3 (M = Li, Na) are transformed into the unsaturated triphosphides (tBu3Si)2P3M (M = Li, Na) and tBu3SiPM2 in tetrahydrofuran at ambient temperature.     

Three-coordinate Co(I) provides access to unsaturated dihydrido-Co(III) and seven-coordinate Co(V)

The three-coordinate, T-shaped Co(I) complex, PNPCo (PNP = [(tBu2PCH2SiMe2)2N-], is readily synthesized by magnesium reduction of divalent PNPCoCl. Triplet (S = 1) PNPCo is coordinatively and electronically unsaturated and undergoes a thermally reversible oxidative addition reaction with H2, producing trivalent PNPCo(H)2. In contrast, the reaction with excess primary silane PhSiH3 quantitatively generates the base-stabilized silylene Co(V) compound {kappa2-tBu2PCH2Me2SiNSiMe2CH2tBu2P(H)Si=}Co(H)3(SiH2Ph)2.     

Si(SiMe3)3]3Ge9M(CO)3(-) (M=Cr, Mo, W): coordination chemistry with metalloid clusters

Very recently it was shown that the metalloid cluster compound {Ge(9)[Si(SiMe(3))(3)](3)}(-)1 can be used for subsequent reactions as the shielding of the cluster core is rather incomplete. So the reaction of 1 with Cr(CO)(3)(CH(3)CN)(3) leads to a cluster enlargement where the chromium atom is incorporated into the cluster core. Here further applications of 1 as a flexible ligand in coordination chemistry are presented where the reaction of 1 with Mo(CO)(3)(EtCN)(3) and W(CO)(3)(CH(3)CN)(3) leads to [(CO)(3)MoGe(9)R(3)](-)4 and [(CO)(3)WGe(9)R(3)](-)5 respectively (R = Si(SiMe(3))(3)), showing that 1 can indeed be used as a flexible ligand in coordination chemistry. Structural and electronic properties of the Ge(9)M clusters 4 and 5 are discussed as well as mechanistic aspects of their formation.     

Zur Reaktion eines Bis(amino)germylens mit Germaniumaziden: Abfangreaktionen von instabilen Germa-Iminen

Reaction of a Cyclic Bis(amino)germylene with Germaniumazides: Trapping-Reactions of Unstable Germa-Imines . The cyclic bis(amino)germylene 1 reacts with different germaniumazides of the type Me₂Si(NtBu)₂Ge(R)N₃ (R = Me ( 2 ), tBu ( 3 ), N(SiMe₃)₂ ( 4 ), R = N₃ ( 5 )). With the exception of 4 all azides lose dinitrogen when treated with 1 and the Ge^II center coordinates the α-nitrogen of the azide group. It seems to be reasonable to assume a transient germaimine (nitride) which is trapped by further reaction with the azide molecules 2 and 5 or by reaction with the solvent pyridine ( 3 ). In the case of 2 the germatetrazole [Me₂Si(NtBu)₂]GeN₄[Ge(NtBu)₂SiMe₂]₂ ( 6 ) is formed, the tetrazole nitrogens being exclusively substituted by germanium atoms (point symmetry of the molecule C_s(m)). When 1 is treated with 5 a tris(germa)amine [Me₂Si(NtBu)₂Ge(N₃)]₃N ( 8 ) is formed, which has an azide group attached to each Ge-atom. X-ray analysis reveals that the nine nitrogen atoms of the azide groups are coplanar with the trigonal planar Ge₃N moiety (crystallographic symmetry: 3/m). The reaction of 1 with 3 is very surprising: the pyridine in the product Me₂Si(NtBu)₂Ge(C₅H₄N)? N(H)Ge(tBu)(NtBu)₂SiMe₂ ( 7 ) is bonded via an α-carbon atom while the remaining hydrogen has added to the nitride-nitrogen. 6 crystallizes in the monoclinic system space group C2/m, a = 24.306(9), b = 10.933(6), c = 19.420(9) Å, β = 91.81(2)° and Z = 4. 7 crystallizes in the hexagonal system space group P6₃/m with a = b = 16.73(1), c = 11.006(8) Å, γ = 120° and Z = 2, and 8 crystallizes in the monoclinic system space group P2₁/n, a = 11.341(6), b = 26.086(9), c = 13.244(7) Å, β = 98. I2(2)° mit Z = 4.     

Building und Reaktionen des Phosphanyliden-Phosphorans (tBu)2P?P = PX(tBu)2 (X = Br,Cl)

Formation and Reaction of the Phosphanylidene-phosphorane (tBu)₂P? P = PX(tBu)₂ (X = Br, Cl) The formation of (tBu)₂P? P = P(Br)tBu₂ 1 from [(tBu)₂P]₂PLi and BrH₂C? CH₂Br begins with an exchange of Li against Br and is then determined by the migration of Br from the secondary P atom in [(tBu)₂P]₂PBr 6 to the primary P in 1 . Similarly, (tBu)₂P? P = PC1(tBu)₂ 2 is obtained starting from PCl₃ and LiP(tBu)₂. The formation of Phospanylidene—phosporane is not influenced by the choice o the halogene substituent, but the presence of the tBu groups is strongly required. (tBu)₂P? P(Li)? P(SiMe₃)₂ e. g., yields (tBu)₂P? P(br)? P(SiMe₃)₂ with BrH₂C? CH₂Br; however neither this nor (tBu)₂P? P(Cl)? P(SiMe₃)₂ do rearrange to a Phosphanylidene-phosphorane. The F₃C substituent could be neglected in this investigation as [(F₃C)₂P]₂P? SiMe₃ cannot be lithiated by means of BuLi. Compounds 1 and 2 display a charateristic temperature dependent behavior. While 1 at +20°C decomposes via the reactive intermediate (tBu)₂P? P to from the cyclophosphanes P₃[P(tBu)₂]₄, it gives crystals of [(tBu)₂P]₂P? p[P(tBu)₂]₂ at ?20°C (from a solution in toluene). Reacting 1 with tBuLi produces (tBu)₂P? P = P(H)tBu₂ 20 and (tBu)₂P? P(H)? P(tBu)₂ 14 . Initially, a transmetallation yield tBuBr and (tBu)₂ P? P=Pli(tBu)₂ 21 ,then LiBr and isobutene are eliminated and 20 is formed which can rearrange to produce 14 . Without the elimination of isobutene, 1 react with nBuLi to give 21 witch can be trapped with Me₃SiCl as (tBu)₂P? P(tBu)₂ 23 . The main product in in this reaction is however [(tBu)₂P]₂P? nBu 22 .     

The nature of halogen...halogen synthons: crystallographic and theoretical studies

A study of the halogen...halogen contacts in organic compounds using ab initio calculations and the results of previously reported crystallographic studies show that these interactions are controlled by electrostatics. These contacts can be represented by the geometric parameters of the C--X1...X2--C moieties (where theta1=C--X1...X2 and theta2=X1...X2--C; ri=X1...X2 distance). The distributions of the contacts within the sum of van der Waals radii (rvdW) versus thetai (theta1=theta2) show a maximum at theta approximately 150 degrees for X=Cl, Br, and I. This maximum is not seen in the distribution of F...F contacts. These results are in good agreement with our ab initio calculations. The theoretical results show that the position of the maximum depends on three factors: 1) The type of halogen atom, 2) the hybridization of the ipso carbon atom, and 3) the nature of the other atoms that are bonded to the ipso carbon atom apart from the halogen atom. Calculations show that the strength of these contacts decreases in the following order: I...I>Br...Br>Cl...Cl. Their relative strengths decrease as a function of the hybridization of the ipso carbon atom in the following order: sp2>sp>sp3. Attaching an electronegative atom to the carbon atom strengthens the halogen...halogen contacts. An electrostatic model is proposed based on two assumptions: 1) The presence of a positive electrostatic end cap on the halogen atom (except for fluorine) and 2) the electronic charge is anisotropically distributed around the halogen atom.     

Experimental and DFT study of the tautomeric behavior of cobalt-containing secondary phosphine oxides

New cobalt-containing secondary phosphine oxides [(mu-PPh(2)CH(2)PPh(2))Co(2)(CO)(4){mu,eta-PhC[triple chemical bond]CP(==O)(H)(R)}] (8 a: R=tBu; 8 b: R=Ph) were prepared by reaction of secondary phosphine oxides PhC[triple chemical bond]CP- (==O)(H)(R) (6 a: R=tBu; 6 b: R=Ph) with dppm-bridged dicobalt complex [(mu-PPh(2)CH(2)PPh(2))Co(2)(CO)(6)] (2). The molecular structures of 8 a and 8 b were determined by single-crystal X-ray diffraction. Although palladium-catalyzed Heck reactions employing 8 b as ligand gave satisfying results, 8 a performed poorly in the same reaction. Judging from these results, a tautomeric equilibrium between 8 b and its isomeric form [(mu-PPh(2)CH(2)PPh(2))Co(2)(CO)(4){mu,eta-PhC[triple chemical bond]CP(OH)(Ph)}] 8 b' indeed takes place, but it is unlikely between 8 a and [(mu-PPh(2)CH(2)PPh(2))Co(2)(CO)(4){mu,eta-PhC[triple chemical bond]CP(OH)(tBu)}] (8 a'). The DFT studies demonstrated that reasonable activation energies for the tautomeric conversions can be achieved only via a bimolecular pathway. Since a tBu group is much larger than a Ph group, the conversion is presumably only feasible in the case of 8 bright harpoon over left harpoon8 b', but not in the case of 8 aright harpoon over left harpoon8 a'. Another cobalt-containing phosphine, namely, [(mu-PPh(2)CH(2)PPh(2))Co(2)(CO)(4){mu,eta-PhC[triple chemical bond]CP(NEt(2))(tBu)}] (7 a), and its oxidation product [(mu-PPh(2)CH(2)PPh(2))Co(2)(CO)(4){mu,eta-PhC[triple chemical bond]CP(==O)(NEt(2))(tBu)}] 7 a' were prepared from the reaction of PhC[triple chemical bond]CP(NEt(2))(tBu) (5 a) with 2. The molecular structures of 7 a and 7 a' were determined by single-crystal X-ray diffraction. The phosphorus atom is surrounded by substituents in a tetrahedral environment. A P--N single bond (1.676(3) A) is observed in the molecular structure of 7 a. Heck reactions employing 7 a/Pd(OAc)(2) as catalyst system exhibited efficiency comparable to that of 8 a/Pd(OAc)(2).     

Vibrational spectra and ab initio analysis of tert-butyl, trimethylsilyl, and trimethylgermyl derivatives of 3,3-dimethylcyclopropene. VI: Application of observed trends to stannyl derivatives

The effects of substitution of X = C by Si or Ge in X(CH(3))(3) moieties attached to the formal double bond of 3,3-dimethylcyclopropene are examined. Regularities in observed trends of vibrational frequencies implicating the moieties containing the X atom, as the X atomic mass is increased, are extrapolated to X = Sn. The results of this extrapolation made it possible to assign the known experimental vibrational frequencies of 3,3-dimethyl-1-(trimethylstannyl)cyclopropene and 3,3-dimethyl-1,2-bis(trimethylstannyl)cyclopropene.     

Theoretical investigation of paramagnetic group 13 diazabutadiene radicals: insights into the prediction and interpretation of EPR spectroscopy parameters

The electronic structures and the spin density distributions of the group 13 1,4-diaza(1,3)butadiene (DAB) radicals [(R-DAB)2M]*, [(R-DAB)MX2] and {[(R-DAB)MX]2}** (M = Al, Ga, In; X = F, Cl, Br, I; R = H, Me, tBu, Ph) are studied using density functional theory at both non-relativistic and relativistic levels of theory. The calculations demonstrate that all systems share a qualitatively similar electronic structure and are primarily ligand centred pi-radicals. The calculated metal, nitrogen and hydrogen hyperfine couplings are found to be independent of the identity of the R-group and the halogen atom. They are, however, dependent on the geometry and oxidation state of the metal centre. Both observed trends contrast what has previously been deduced from the interpretation of experimental EPR and ENDOR spectra. Good agreement between the calculated and experimentally determined hyperfine coupling constants is found only for some of the studied systems. Instances where significant discrepancies between the calculated and experimental values exist can be attributed to the tendency of these systems toward complex solution behaviour, which results in differences between the solid state and solution structures of certain complexes. A careful re-evaluation of the experimental data as well as calculated reaction energies lends strong support to this hypothesis. However, further studies are needed before the identity of some of the studied radical species in solution can be unambiguously determined.     

Cyclic and polycyclic tellurium-tin and tellurium-lead compounds--synthesis, structures and thermal decomposition

The miscellaneously substituted silyltellanes tBu(2)PhSiTeSiMe(3) (1) and (Me(3)Si)(3)SiTeSiMe(3) were used to synthesize the cyclic tin(II) and lead(II) tellurolates [(tBu(2)PhSiTe)(4)M(2)] (M = Sn (2), Pb (3)), [tBu(2)PhSiTePbC(SiMe(3))(3)](2) (4) and the uncommon cluster compound [{(Me(3)Si)(3)SiTe}(4)Te(2)Sn(4)] (5).     

Interactions of a Mn atom with halogen atoms and stability of its half-filled 3d-shell

Using density functional theory with hybrid exchange-correlation potential, we have calculated the geometrical and electronic structure, relative stability, and electron affinities of MnX(n) compounds (n = 1-6) formed by a Mn atom and halogen atoms X = F, Cl, and Br. Our objective is to examine the extent to which the Mn-X interactions are similar and to elucidate if/how the half-filled 3d-shell of a Mn atom participates in chemical bonding as the number of halogen atoms increases. While the highest oxidation number of the Mn atom in fluorides is considered to be +4, the maximum number of halogen atoms that can be chemically attached in the MnX(n)(-) anions is 6 for X = F, 5 for X = Cl, and 4 for X = Br. The MnCl(n) and MnBr(n) neutrals are superhalogens for n ≥ 3, while the superhalogen behavior of MnF(n) begins with n = 4. These results are explained to be due to the way different halogen atoms interact with the 3d electrons of Mn atom.