Germylene Research Articles

Donor/acceptor stabilization of Ge(ii) dihydride

A combined donor/acceptor approach is presented for the stabilization of the parent germylene, :GeH2.

Structures and Suzuki-Coupling of N-Heterocyclic Carbene Complexes of PdII with Coordinated Solvent and PPh3

A series of mononuclear N,N-heterocyclic carbene (NNHC) complexes of PdII with mixed ligands of 1,3-dibenzylbenzimidazoly-2-ylidene and solvate (dimethyl sulfoxide, CH3CN, N,N-dimethylformamide, and pyridine) or PPh3 were prepared and characterized by X-ray single-crystal diffraction analysis. They are more active in the Suzuki–Miyaura coupling of selected aryl bromides than their N,S-heterocyclic carbene (NSHC) analogues.

Complexes of four-membered group 13 metal(I) N-heterocyclic carbene analogues with platinum(II) fragments

A series of fluorinated bis(aryl)platinum(II) complexes, cis-[Pt(Ar(f))2(1,5-C6H10)] (Ar(f) = p-C6HF4, p-C6(OMe)F4 or C6H2F(3-)2,4,6) were reacted with the four-membered gallium(I) or indium(I) heterocycles, [:E{[N(Ar)]2CN(C6H11)2}] (E = Ga or In, Ar = C6H3Pr(i)(2-)2,6) under various stoichiometries. These yielded either the 2:1 complexes, cis-[Pt(Ar(f))2{Ga{[N(Ar)]2CN(C6H11)2}}2], trans-[Pt(C6H2F(3-)2,4,6)2{Ga{[N(Ar)]2CN(C6H11)2}}2] and trans-[Pt(Ar(f))2{In{[N(Ar)]2CN(C6H11)2}}2], or the 3:1 complexes, trans-[Pt(Ar(f))2{In{[N(Ar)]2CN(C6H11)2}}3] (Ar(f) = p-C6HF4 or p-C6(OMe)F4), all of which were crystallographically characterised. The differing outcomes of these reactions are explained in terms of the lesser nucleophilicity and greater electrophilicity of the indium heterocycle relative to its gallium counterpart. In the solid state, and in solution, the 3:1 indium complexes exhibit strong intramolecular In...F interactions which are indicative of their heterocyclic ligands displaying rare examples of "Lewis amphoteric" behaviour. An unusual platinum(0) complex in which the indium(I) heterocycle acts as a mu3-bridging ligand, [{Pt(norbornene)}3{mu3-In{[N(Ar)]2CN(C6H11)2}}2], was also prepared and structurally authenticated.

Mono‐ and Bidentate Benzannulated N‐Heterocyclic Germylenes, Stannylenes and Plumbylenes

AbstractThe current state of the chemistry of mono‐ and bidentate N‐heterocyclic germylenes, stannylenes, plumbylenes, and related compounds is reviewed with special emphasis placed on benzannulated derivatives. The preparation, electronic structure, aggregation behaviour, and the coordination chemistry of the free benzannulated carbene analogues and their adducts with Lewis bases and complexes with transition metals are discussed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

(5,10,15,20-Tetraphenylporphyrinato-κ4 N)(2,2,2-trifluoro-1-phenylethylidene-κC 1)ruthenium(II): a stable fluorinated alkylidene complex of a ruthenium(II) porphyrin

In the title compound, [Ru(C44H28N4)(C8H5F3)], the fluorin­ated alkyl­idene group is bound to a five-coordinate Ru atom, which is located toward the carbene C atom, 0.3301 (5)Å from the least-squares plane of the C20N4 porphyrin core. The Ru=C bond is tilted slightly from the normal to the C20N4 least-squares plane due to steric repulsion between the porphyrinate ligand and the bulky trifluoro­methyl group. The Ru=C bond length of 1.838 (2) Å is comparable with those in bis­(subsituted phen­yl)carbene analogs.

Application of Terminal Electrophilic Phosphinidene Complexes

Phosphinidenes are phosphorus analogues of carbenes in which phosphorus is monovalent with an incomplete octet of electrons. Phosphinidene complexes readily react with alkenes, whereas free phosphinidenes do not react with alkenes. This indicates that the coordination of these unstable phosphorus compounds [¹] with metallic species enhances their stability as well as reactivity by increasing the electrophilicity of the phosphorus atom. A number of precursors like phosphiranes, [²] phospholenes, [²] norbornadienes, [³] 2H-azaphosphirene [4] and phosphirene [5] metal complexes are known to generate terminal phosphinidene complexes in situ via their thermal or photochemical decomposition. These phosphinidene complexes are short-lived intermediates and their existence is proved by trapping them with substituted alkenes, [6] acetylenes, [7] and organic nitriles [8] via cycloaddition reactions resulting in the formation of a variety of P-heterocycles. Recently, insertion of phosphinidene complexes into carbon-halogen bonds has been established, [9-¹¹] which affords a number of novel organophosphorus compounds.

Monomeric Boron and Tin(II) Heterocyclic Derivatives of 1,8‐Diaminonaphthalenes: Synthesis, Characterization and X‐ray Structures

AbstractThe reaction of the diaminonaphthalene dilithium salt(THF)2Li2[(NSiMe3)2C10H6] with BX3 (X = Cl, Br) in hexane provides the monomeric compounds BX[(NSiMe3)2C10H6] [3 (X = Cl), 4 (X = Br)] with a tricoordinate boron atom. Attempts to reduce 3 and 4 with lithium, sodium, potassium or sodium/potassium alloy with the intention to isolate a boranide resembling a carbene were unsuccessful. However, the diaminonaphthalene dilithium salt (THF)2Li2[(NSi‐iPr3)2C10H6] (2) reacts with SnCl2 in THF to provide the carbene analog 5. Compounds 2, 3 and 5 were characterized by single‐crystal X‐ray structure analysis. The structures of 3 and 5 show the naphthalene backbone to be nearly planar, while the heterocycles in 3 and 5 containing boron and tin atoms, respectively, have torsion angles (3: 30.06°; 5: 37.27°) with respect to the naphthalene plane. The boron atom has a trigonal‐planar environment, and the stannylene tin–nitrogen bonds form a very acute N–Sn–N angle of 92.2°.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

New Routes for the Functionalization of P4

New Routes for the Functionalization of P₄

Organoiron compounds derived from the indium ‘carbene analogues’, [In{N(Ar)C(Me)}2CH] (Ar = dipp = 2,6-iPr2C6H3; = Mes = 2,4,6-Me3C6H2)

Oxidative insertion of the In(I) 'carbene analogues', [In{N(Dipp)C(Me))2CH] (Ar = Dipp = 2,6-iPr2C6H3; Ar = Mes = 2,4,6-Me3C6H2) into the Fe-I bond of [CpFe(CO)2I] occurred cleanly and under mild conditions to yield the In(III) compounds [CH((CH3)2CN-2,6-iPr2C6H3)2In(I)FeCp(CO)2] and [CH( (CH3)2CN-2,4,6-Me3C6H3)2In(I)FeCp(CO)2], which have been fully characterised in solution and the solid state. Attempts to abstract the iodide anion from [CH( (CH3)2CN-2,6-iPr2C6H3)2In(I)FeCp(CO)2] to form cationic species containing a coordinated indium diyl were unsuccessful and resulted in a complex mixture of products from which two ionic species were isolated. Neither cation was found to contain indium by X-ray crystallographic analysis. These observations were indicative of ill-defined decomposition pathways as have been noted by previous workers. A further attempt to form a cationic iron species containing a coordinated [In(N(Dipp)C(Me) )2CH] fragment resulted in oxidation of the iron centre from Fe(II) to Fe(III), with deposition of indium metal, and the isolation of a cationic Fe(III) beta-diketiminate complex.

Synthesis and structure of two new (guanidinate)boron dichlorides and their attempted conversion to boron(i) derivatives

To test the feasibility of the guanidinate architecture for the support of boron(i) carbene analogues the energy gap between the singlet and triplet states of the model compound, [Me(2)NC{N(Ph)}(2)B:] (), has been probed by both DFT and second order Møller-Plesset (MP2) methods. The singlet state is calculated to be more stable than the triplet state by between 6.0 and 10.1 kcal mol(-1). The new (guanidinate)boron dichlorides [Ph(2)NC{N(Mes)(2)]BCl(2) () and [Ph(2)NC{N(Dipp)(2)]BCl(2) () have been prepared and characterized by single-crystal X-ray diffraction. Attempts to reduce and to the corresponding boron(i) species were not successful.

The 6π, phosphide-stabilised stannylene dianion [C6H4P2Sn]2−; the first member of a new class of Arduengo-type carbene analogues

Dilithiation of 1,2-(PH2)2C6H4 with nBuLi followed by reaction with Sn(NMe2)2 in the presence of the Lewis base donor tmeda [Me2NCH2CH2NMe2] gives [(C6H4P2Sn)(Li.tmeda)2] , containing the phosphide-stabilised, 6pi stannylene dianion [C6H4P2Sn]2-.

Electronic Structures of Main-Group Carbene Analogues

The electronic structures of 15 group 13-16 carbene analogues are analyzed using various quantum chemical methods and compared to the data obtained for the parent N-heterocyclic carbene (NHC), imidazol-2-ylidene. The results of this study present a uniform analysis of the similarities and differences in the electronic structures of p-block main-group carbene analogues. Though all systems are formally isovalent, the theoretical analyses unambiguously indicate that their electronic structures run the gamut from C=C localized (group 13) to C=N localized (group 16) via intermediate, more delocalized, systems. In particular, neither the stibenium ion nor any of the chalcogenium dications is a direct analogue of imidazol-2-ylidene as they all contain two lone pairs of electrons around the divalent main-group center, instead of the expected one. The reason behind the gradual change in the electronic structure of main-group analogues of imidazol-2-ylidene was traced to the total charge of the systems, which changes from anionic to dicationic when moving from left to right in the periodic table. Results from theoretical analyses of aromaticity show that all group 13-16 analogues of imidazol-2-ylidene display some degree of aromatic character. The heavier group 13 anions benefit the least from pi-electron delocalization, whereas the cationic group 15 systems are on par with the parent carbon system and display only slightly less aromatic character than cyclopentadienide, a true 6pi-electron aromatic species. The sigma-donor and pi-acceptor ability of the different main-group carbene analogues are also evaluated.

A Theoretical Study on the Mechanism of Boron Metathesis

The mechanism of the boron metathesis reaction of the transition-metal-aminoborylene complex Cp(CO)(2)FeBN(CH(3))(2+) (8) with EX, where EX = H(3)PO (9ap), H(3)AsO (9bp), H(3)PS (9aq), H(3)AsS (9bq), CH(3)CHCH(2) (9cr), (NH(2))(2)CCH(2) (9dr), H(2)CO (9ep), and (NH(2))(2)CO (9dp) is investigated at the B3LYP/LANL2DZ level. The analysis of bonding and charge distribution shows that the Fe-borylene complex (8) is a Fischer-type carbene analogue. The attack of the olefin takes place at the metal end of the M=C bond of the metal-carbene complex in olefin metathesis and proceeds via [2 + 2] cycloaddition, while in boron metathesis, the initial attack of the substrates takes place at the positively charged B atom of the Fe-borylene complex and forms the preferred acyclic intermediate. The energetics of boron metathesis is comparable to that of the olefin metathesis. Substrates that are polar and a have low-lying sigma* molecular orbital (weak sigma bond) prefer the boron metathesis reaction. The relative stability of the metathesis products is controlled by the strength of the Fe-E and B-X bonds of the products 13 and 14, respectively. We have also investigated the possibility of a beta-hydride-transfer reaction in the Fe-borylene complex.

Oxidative Addition Reactions of Alkyl Halides with the Group 13 Carbene Analogue [In{N(Dipp)C(Me)}2CH] (Dipp = 2,6-iPr2C6H3)

Reactions of the well-defined two-coordinate indium "carbene analogue" [In{N(Dipp)-C(Me)}2CH] (Dipp=2,6-iPr2C6H3) have been studied. Reactions of MeI, iPrI, and tBuI with [In{N(Dipp)C(Me)}2CH] formed by the in situ reaction of InI, [K{N(SiMe3)2}], and the iminoenamine ligand precursor successfully yielded the oxidative addition products [InRI{N(Dipp)C(Me)}2CH] (R=Me, iPr, tBu). The results of NMR investigations, which indicated the formation of a series of four-coordinate indium(III) complexes in C6D6 solution, were confirmed in the solid-state by single-crystal X-ray diffraction. Similar reactions employing alkyl bromides were unsuccessful and resulted in the isolation of the corresponding iodides, apparently by metathesis of the bromide oxidative addition product with KI formed during the initial InI metathesis. Reactions of isolated samples of [In{N(Dipp)C(Me)}2CH] with iPrBr and tBuBr, however, were straightforward and resulted in the successful isolation of the analogous iso-propyl and tert-butyl indium(III) bromide complexes. These were also fully characterized by 1H and 13C NMR and single-crystal X-ray diffraction experiments. In contrast, no reaction was observed between [In{N(Dipp)-C(Me)}2CH] and aryl halides or alkyl chlorides.

The reactivity of an anionic gallium N-heterocyclic carbene analogue with a solution stable digermene

The reaction of the anionic gallium(I) N-heterocyclic carbene (NHC) analogue 3 with the solution stable digermene 5 results in the formation of the gallium NHC – germylene complex 8. The gallium NHC – germylene complex 8 was derivatized with CH3I and (CH3)3SiCl.Key words: digermene, carbene analogue, germylene, gallium(I).

Investigations into the preparation of groups 13–15 N-heterocyclic carbene analogues

Attempts have been made to prepare a variety of groups 13–15 N-heterocyclic carbenoid systems. The work in group 13 led to two structurally characterized, paramagnetic gallium(III) heterocycles, [I 2Ga{[N(R)C(Me)] 2}], R = C 6 H 3 Pr 2 i - 2 , 6 ( Ar ) or C 6H 3(C 6H 4Bu t -4) 2-2,6. Reduction of the former gave the anionic gallium(I) heterocyclic complex, [K(tmeda)][:Ga{[N(Ar)C(Me)] 2}], which was oxidatively coupled, affording the structurally characterized digallane(4), [Ga{[N(Ar)C(Me)] 2}] 2. From group 14, the new germanium(IV) heterocycle, [Cl 2Ge{[N(Ar)C(H)] 2}], and the N-heterocyclic germylene, [:Ge{[N(Ar)C(H)] 2}], have been prepared and fully characterized. Attempts to prepare N-heterocyclic silylene, phosphenium and arsenium compounds were unsuccessful and led instead to the silyl, phosphino and arsino-substituted ene-amines, [(Cl n E) 2{μ-[N(Ar)C(H)] 2}], E = Si, n = 3; E = P or As, n = 2.

4‐Valence Electron Reactive Intermediates and the Philicity of Charged Carbene Analogues

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Preparation of organometallic uracil-analogue Fischer carbene complexes: Comparative study of conventional heating vs microwave irradiation

Mono and disubstituted ureas react with alkynyl Fischer carbene complexes to give mono and di N, N-substituted organometallic uracil analogues. An optimization of the process using different starting metal carbene complexes and variously substituted ureas under conventional heating (with and without solvent) and microwave irradiation techniques is reported. The synthesis of the metal–carbene analog of the commercially available dimethyl uracil is reported.

Theoretical Designs for Neutral Five-Membered Carbene Analogues of the Group 13 Elements: A New Target for Synthesis

Potential energy surfaces for the chemical reactions of neutral five-membered group 13 carbenoids have been studied using density functional theory (B3LYP/LANL2DZ). Five five-membered group 13 carbenoid species, HCMeP(PhN)2X, where X = B, Al, Ga, In, and Tl, have been chosen as model reactants in this work. Also, three kinds of chemical reaction, C-H bond insertion, alkene cycloaddition, and dimerization, have been used to study the chemical reactivities of these group 13 carbenoids. Our present theoretical work predicts that the larger the angleNXN bond angle in the neutral five-membered group 13 carbenoid, the smaller the singlet-triplet splitting, the lower the activation barrier, and, in turn, the more rapid are its various chemical reactions. Moreover, the theoretical investigations suggest that the relative carbenoidic reactivity decreases in the order B > Al > Ga > In > Tl. That is, the heavier the group 13 atom (X), the more stable is its carbenoid with respect to chemical reactions. As a result, we predict that the neutral five-membered group 13 carbenoids (X = Al, Ga, In, and Tl) should be stable, readily synthesized, and isolated at room temperature. Furthermore, the neutral five-membered group 13 carbenoid singlet-triplet energy splitting, as described in the configuration mixing model attributed to the work of Pross and Shaik, can be used as a diagnostic tool to predict their reactivities. The results obtained allow a number of predictions to be made.

Extending the Series: Synthesis and Characterization of a Dicationic N-Heterocyclic Selenium Carbene Analogue

The room-temperature reaction between the Dipp2DAB ligand, SnCl2, and SeCl4 results in the quantitative formation of a dicationic N-heterocyclic "carbenoid". This represents the first example of a chalcogenium dication that mimics the ubiquitous Arduengo-type carbenes; however, the electronic structure is significantly different.