Anukul Jana

A Germanium(II) Hydride as an Effective Reagent for Hydrogermylation Reactions

Herein we report on the reactivity of the stable germanium(II) hydride LGeH (L = CH{(CMe)(2,6-iPr(2)C(6)H(3)N)}(2)) (2), which contains a low-valent germanium atom. 2 is prepared from the corresponding germanium(II) chloride LGeCl (1) using H(3)Al x NMe(3) or K[HB(iBu)(3)] in toluene. The reaction of 2 with carbon dioxide in toluene at room temperature affords a germanium(II) ester of formic acid, LGe-O-C(O)H (3), which is formed by insertion of the carbon dioxide into the germylene hydrogen bond. 2 also reacts with alkynes at room temperature to give the first germanium(II)-substituted alkenes (4, 5, and 6). These two reaction types have in common the fact that the hydrogen and germylene from LGeH are transferred to an unsaturated bond: the carbon-oxygen double bond (C=O) in the former case and the carbon-carbon triple bond (C[triple bond]C) in the latter. Moreover, the reaction of 2 with elemental sulfur in toluene at room temperature leads to the germanium dithiocarboxylic acid analogue LGe(S)SH (7). Compound 7 is formed by the unprecedented insertion of elemental sulfur into the germylene hydrogen bond and oxidative addition of elemental sulfur to the germanium(II) atom. This leads to the formal conversion of the GeH hydride to a SH proton. Compounds 3-7 were investigated by microanalysis, multinuclear NMR spectroscopy, and single-crystal X-ray structural analyses.

A remarkable base-stabilized bis(silylene) with a silicon(I)-silicon(I) bond.

Double and triple covalent bonds are ubiquitous in carbon chemistry and have been studied for more than two centuries but were unusual with its congener in the periodic table, silicon. Initial attempts to synthesize such compounds were unsuccessful, resulting in the formation of polymeric substances. This situation changed when West and co-workers in 1981 synthesized a compound containing a Si Si double bond (R2Si=SiR2, R = Me3C6H2), in which each Si atom has a formal oxidation state of + II. Key to the discovery of stable compounds containing Si Si double bonds was the protection of the double bonds by bulky substituents, which provide kinetic stability. Apeloig et al. showed that silylene has a singlet ground state, and the B1 triplet state lies significantly higher in energy. Moreover, recent calculations indicate that the energy difference between the singlet and triplet states of silylene is around 18–21 kcalmol . This singlet–triplet energy difference of the silylene fragments is the main reason for the weakness of the Si=Si double bond. This now generally accepted model originated from Carter, Goddard, Malrieu, and Trinquier (CGMT), who described the doublebond topology as being a function of the energy difference between the singlet and the triplet state of the carbene-like fragments formally constituting the double bond. Compounds with double-bonded silicon are established and have been studied in detail during the last decade. In 2004, Sekiguchi and co-workers as well as Wiberg et al. were successful in isolating compounds containing Si Si triple bonds (RSi SiR; R = Si(iPr){CH(SiMe3)2}2 and R = SiMe(SitBu3)2) in which the formal oxidation state of Si is + I. [7] Subsequently, Robinson and co-workers synthesized two compounds, one with a Si Si single bond having formal oxidation state + I and another with a Si Si double bond in which the formal oxidation state of Si is 0 (RClSi SiClR and RSi=SiR, R = 1,3-bis-(2,6-diisopropylphenyl)imidazol-2-ylidene). In addition to disilenes and disilynes, a number of other unusual stable compounds with low-coordinate Si atoms have been described. To our knowledge, only one compound consisting of a Si Si single bond and a lone pair of electrons on each Si atom was reported to date. The compound was stabilized by an N-heterocyclic carbene, and one chlorine atom was attached to each silicon center making the formal oxidation state of the silicon atoms + I. This situation is unique, because each Si center which features a lone pair of electrons is simultaneously involved in bonding. These two attributes are usually associated with extreme instability. In view of this chemistry, we became interested in synthesizing a compound with a Si Si single bond stabilized by a monoanionic ligand, thus avoiding the lone pair of electrons taking part in any bonding. We were recently successful in using an amidinate ligand with tBu substituents on the nitrogen atoms to stabilize heteroleptic silylenes and a Ge dimer. It seems that such a ligand might also stabilize a Si compound with a Si Si single bond. Our preliminary results in this direction are reported herein. The reaction of tert-butylcarbodiimide with one equivalent of PhLi in diethyl ether and subsequent treatment with SiCl4 afforded [PhC(NtBu)2]SiCl3 (1, Scheme 1). Compound 1

Selective aromatic C-F and C-H bond activation with silylenes of different coordinate silicon.

Herein we report on the reaction of stable two-coordinate silylene, L(1)Si [L(1) = CH{(C=CH(2))(CMe)(2,6-iPr(2)C(6)H(3)N)(2)}] (1) and three-coordinate silylene (Lewis base stabilized silylene), L(2)SiCl [L(2) = PhC(NtBu)(2)] (2) with aromatic compounds containing C-F and C-H bonds. The reaction of 1 and 2 with hexafluorobenzene (C(6)F(6)) affords the silicon(IV) fluorides, L(1)SiF(C(6)F(5)) (3) and L(2)SiFCl(C(6)F(5)) (4), respectively. The reaction proceeds through the unprecedented oxidative addition of one of the C-F bonds to the silicon(II) center without any additional catalyst. When 1 and 2 are treated with octafluorotoluene (C(6)F(5)CF(3)), pentafluoropyridine (C(5)F(5)N) regioselective C-F bond activation occurs leading to the formation of L(1)SiF(4-C(6)F(4)CF(3)) (5), L(1)SiF(4-C(5)F(4)N) (6), L(2)SiFCl(4-C(6)F(4)CF(3)) (7), and L(2)SiFCl(4-C(5)F(4)N) (8), respectively. More interestingly, compounds 1 and 2 react with pentafluorobenzene (C(6)F(5)H) under formation of silicon(IV) hydride L(1)SiH(C(6)F(5)) (9) by chemoselective C-H bond activation, in the latter case producing silicon(IV) fluoride L(2)SiFCl(4-C(6)F(4)H) (10) by chemo- as well as regioselective C-F bond activation. Furthermore, the reaction of 1 with 1,3,5-trifluorobenzene (1,3,5-C(6)F(3)H(3)) leads to the chemoselective formation of silicon(IV) hydride L(1)SiH(1,3,5-C(6)F(3)H(2)) (11). The formation of compounds 9 and 11 occurs via oxidative addition of the aromatic C-H bond to the silicon(II) center instead of C-F bond activation. All reported reactions proceed without any additional catalyst. Compounds 3, 4, 5, 6, 7, 8, 9, 10, and 11 were investigated by microanalysis and multinuclear NMR spectroscopy and compounds 3, 7, 8, and 9 additionally by single crystal X-ray structural analyses.

A base-stabilized silylene with a tricoordinate silicon atom as a ligand for a metal complex.

Treatment of base stabilized silylene [PhC(NtBu)(2)]SiOtBu (1) with a tricoordinate silicon atom and diiron nonacarbonyl [Fe(2)(CO)(9)] in tetrahydrofuran led to the formation of {[PhC(NtBu)(2)]SiOtBu}Fe(CO)(4) (2), the first stable metal complex derived from a base-stabilized tricoordinate silylene ligand. The solid-state structure and bonding situation of 2 were investigated with single-crystal X-ray diffraction and quantum chemical calculations.

Reactions of tin(II) hydride species with unsaturated molecules.

SnH2 has been prepared and characterized in an argon matrix. At elevated temperature, SnH2 changed to an insoluble solid of unknown structure. Terphenyl and bdiketiminate ligands have been used for the preparation of substituted tin(II) hydrides. The terphenyl derivatives exist in the solid state as dimeric structures, whereas the bdiketiminate species incorporates a terminal tin(II) hydride with very weak intermolecular interactions. Until recently, reactions of organotin hydrides were based on tin(IV) precursors. Diand triorganotin hydrides, of composition R2SnH2 and R3SnH, with a formal oxidation state of Sn IV

Facile access of stable divalent tin compounds with terminal methyl, amide, fluoride, and iodide substituents.

The stable beta-diketiminate tin(II) complexes LSnX [L = HC(CMeNAr)2, Ar = 2,6-iPr2C6H3] with terminal methyl, amide, fluoride, and iodide (X = Me, N(SiMe3)2, F, I) are described. LSnMe (2) is synthesized by salt metathesis reaction of LSnCl (1) with MeLi and can be isolated in the form of yellow crystals in 88% yield. Compound LSnN(SiMe3)2 (3) was obtained by treatment of LH with 2 equiv of KN(SiMe3)2 in THF followed by adding 1 equiv of SnCl2. Reaction of 2 and 3 respectively with Me3SnF in toluene provided the tin(II)fluoride LSnF (4) with a terminal fluorine as colorless crystals in 85% yield. 4 is highly soluble in common organic solvents. The reaction of LLi(OEt2) with 1 equiv of SnI2 in diethyl ether afforded the LSnI (5). Compounds 2, 3, 4, and 5 were characterized by microanalysis, multinuclear NMR spectroscopy, and X-ray structural analysis. Single crystal X-ray structural analyses indicate that all the compounds (2, 3, 4, 5) are monomeric and the tin center resides in a trigonal-pyramidal environment.

Hydrostannylation of Ketones and Alkynes with LSnH [L = HC(CMeNAr)2, Ar=2,6-iPr2C6H3]

The reactions of the stable beta-diketiminate tin(II) hydride LSnH [L = HC(CMeNAr)(2), Ar = 2,6-iPr(2)C(6)H(3)] with different ketones (Ph(2)CO, 2-Py(2)CO, cyPr(2)CO, and 2-C(4)H(3)SCOCF(3)) generated a variety of tin(II) alkoxides (1-4) in high yield. The activated terminal alkynes (HC[triple bond]CCO(2)R, R = Me, Et) react with LSnH to yield the tin(II) substituted terminal alkenes (5-6) instead of dihydrogen elimination although the Sn-H and C-H bonds are differently polarized. Furthermore, LSnH reacts with disubstituted alkyne (RO(2)CC[triple bond]CCO(2)R, R = Et, tBu) in toluene at room temperature to form the stannylene substituted internal alkenes (7-8). Compounds 1-8 were characterized by microanalysis and multinuclear NMR spectroscopy. Moreover compounds 3, 4, 5, and 7 were characterized by X-ray crystallography, and the resulting structures confirmed the monomeric nature, in which the tin centers reside in a trigonal-pyramidal environment.

Heavier Alkaline Earth Metal Borohydride Complexes Stabilized by β-Diketiminate Ligand

The reaction of KB[sec-Bu](3)H with calcium iodide [LCa(mu-I).thf](2)] (1) and strontium iodide [LSr(mu-I).thf](2) (2) yields calcium trisec-butylborohydride LCaB(sec-Bu)(3)H.thf (3) and strontium trisec-butylborohydride LSrB(sec-Bu)(3)H.thf (4) (L = CH(CMe2,6-iPr(2)C(6)H(3)N)(2)), respectively. Compounds 2, 3, and 4 were characterized by multinuclear NMR spectroscopy, mass spectrometry, elemental analysis, and single crystal X-ray analysis, whereas 1 was characterized without X-ray structural analysis. Compounds 3 and 4 are monomeric in the solid state with a hydride ligation between the metal and boron centers.

Pentafluoropyridine as a fluorinating reagent for preparing a hydrocarbon soluble β-diketiminatolead(II) monofluoride

A well-designed method for the preparation of a β-diketiminatolead(II) monofluoride has been developed using LPbNMe(2) (L = [CH{C(Me)(2,6-iPr(2)C(6)H(3)N)}(2)]) and pentafluoropyridine (C(5)F(5)N). The resulting LPbF was used for the synthesis of amidinatosilicon(II) monofluoride. Moreover the activation of a ketone was observed when the LPbF was treated with PhCOCF(3).

End-on nitrogen insertion of a diazo compound into a germanium (II) hydrogen bond and a comparable reaction with diethyl azodicarboxylate

A happy ending: The germanium(II) hydride [LGeH], where L = [HC{(CMe)(2,6-iPr(2)C(6)H(3)N)}(2)], reacts with a diazoalkane to form the hydrazone derivative (see picture). The reaction proceeds through the unprecedented end-on nitrogen insertion of the diazo compound.