Publications

Catalysis using low-valent main-group compounds is usually done under inert conditions; no example of such catalysis has been doable entirely in ambient conditions until now. This aspect is addressed in this work through an air- and water-stable germylene cation [DPMGe][(OH)B(C6F5)3] (2) (DPM=dipyrromethene); it efficiently catalyzes aldehyde and ketone hydrosilylations under ambient conditions. Detailed theoretical studies reveal that compound 2’s stability is bolstered by the interaction between the anion and germanium's frontier orbitals. However, the detachment of the anion (in the solution) alters the capability of compound 2 to render exceptional catalytic efficiency. Compound 2 was synthesized under ambient conditions by the equimolar reaction of DPMGeOH (1) with B(C6F5)3.

The aminotroponiminate (ATI) ligand stabilized germylene cation [(i-Bu)2ATIGe][B(C6F5)4] (2) is found to be an efficient low-valent main-group catalyst for the cyanosilylation of aldehydes and ketones (ATI = aminotroponiminate). It was synthesized by reacting [(i-Bu)2ATIGeCl] (1) with Na[B(C6F5)4]. The catalytic cyanosilylation of diverse aliphatic and aromatic carbonyl compounds (aldehydes and ketones) using 0.075−0.75 mol% of compound 2 was completed within 5−45 min. The catalytic efficiency seen with aliphatic aldehydes was around 15,800 h−1, making compound 2 a capable low-valent main-group catalyst for the aldehyde and ketone cyanosilylation reactions.

Low-valent main group compounds that fluoresce in the solid-state were previously unknown. To address this, we investigated room-temperature photoluminescence from a series of crystals of germylenes 3–8 in this article; they exhibited emissions nearly reaching the NIR. Germylene carboxylates (3–8) were synthesized by reacting dipyrromethene stabilized germylene pyrrolide (2) with carboxylic acids such as acetic acid, trifluoroacetic acid, benzoic acid, p-cyanobenzoic acid, p-nitrobenzoic acid, and acetylsalicylic acid.

The possibility of using aza-dipyrromethene (a-DPM) ligands to stabilize compounds containing low-valent main group elements is demonstrated through the isolation of germylenes, a-DPM(p-tol)GeCl (2), a-DPM(Naph)GeCl (6), and a-DPM(Naph)GeN(TMS)2 (7) (tol=tolyl, Naph=naphthyl). Because of the presence of the a-DPM ligand, these germylenes exhibit an absorption maximum at around 640 nm, a highly red-shifted value previously unknown for germylenes.

Two routes can offer the first stannylene cyanide [(L)SnCN] (5); the substitution reaction of either stannylene amide [(i-Bu)2ATISnN(SiMe3)2] (3) or stannylene pyrrolide [(i-Bu)2ATISn(NC4H4)] (4) using an excess of trimethylsilyl cyanide (L = aminotroponiminate (ATI)). Using 0.1–2.0 mol% of compound 5, catalytic cyanosilylation of a variety of aliphatic and aromatic aldehydes was achieved at rt−50 °C in 0.33–2.0 h. The mechanism of this catalytic reaction is authenticated by the isolation of a structurally characterized intermediate.

The paper describes the synthesis of stable germacarbonyl compounds under ambient conditions using dipyrromethene ligand stabilization. These compounds have Ge=E bonds (E = S, Se) and can react with copper(I) halides, forming stable copper(I) complexes. Selective binding to specific halides was observed.

This chapter provides a comprehensive overview of the vast and rapidly growing field of organometallic chemistry of germanium. It covers various compounds involving germanium atoms, including those with single and multiple bonds to elements and metals across the periodic table. Polymers containing germanium in their main chains are also discussed. The chapter highlights the importance of germylenes, germanium (I) compounds, and germylones in low-valent germanium chemistry. The focus of the chapter is on the synthesis and reactivity of these compounds over the past fifteen years.

The biological applications of germylenes remain unrealized owing to their unstable nature. We report the isolation of air-, water-, and culture-medium-stable germylene DPMGeOH (3; DPM=dipyrromethene ligand) and its potential biological application. Compound 3 exhibits antiproliferative effects comparable to that of cisplatin in human cancer cells. The cytotoxicity of compound 3 on normal epithelial cells is minimal and is similar to that of the currently used anticancer drugs. These findings provide a framework for a plethora of biological studies using germylenes and have important implications for low-valent main-group chemistry.

This manuscript presents the synthesis and characterization of germylene-stabilized cadmium complexes and novel germylene zinc complexes using aminotroponiminate ligands. The reactions also resulted in the formation of glutathione and germaselenone-stabilized zinc complexes. Interconversions between monomeric and dimeric zinc/cadmium complexes are demonstrated. The compounds are characterized by NMR spectroscopy and X-ray diffraction studies, with ab initio calculations used to understand the bonding in the germylene cadmium complexes.

The first examples of aminotroponiminatogermylene stabilized Ru(II) complexes 1 and 2 are synthesized and characterized.
Using complex 2, the hitherto unknown reactivity of N-heterocyclic germylene (NHGe) stabilized Ru(II) complexes is addressed.
The reaction of complex 2 with H2O and Me3SiCl gave NHGe stabilized Ru(II) complexes 3 and 1, respectively.
In the reaction of complex 2 with SnCl2, a bimetallic complex 4 is isolated.

New compounds including germaacid chloride, germaester, and N-germaacyl pyrrole are reported. Germaacid chloride reacts to form germaynone, germaester, and germanone compounds. Germaester and germaacid chloride can interconvert. Reaction of N-germaacyl pyrrole with thiophenol produces a germaacyl thioester. Attempted syntheses of germaamides and germacarboxylic acids are also discussed.

Well-defined germylene cations [(i-Bu)2ATI]GeOTf (4) and [(i-Bu)2ATIGe][GaCl4] (5) are isolated, and the catalytic utility of compound 4 for the hydroboration of a variety of aldehydes and ketones is reported (ATI = aminotroponiminate).

A triflatostannylene [L†Sn(II)][OTf] (2) is reported here as an efficient catalyst with low-valent main-group element for the hydroboration of aldehydes and ketones (L† = aminotroponate). Using 0.025–0.25 mol% of compound 2, hydroboration of various aldehydes and ketones is accomplished in 0.13–1.25 h at room temperature; the aliphatic aldehydes show an impressive TOF of around 30 000 h−1. DFT calculations are performed to explore the mechanistic aspects of this reaction suggesting that the reaction proceeds via a stepwise pathway with hydridostannylene [L†Sn(II)H] (2a) as the active catalyst and the H atom transfer from the Sn–H bond to the carbonyl carbon being the rate determining step.

Germylene transition-metal complexes: The difference in the coordination behavior of pseudohalogenogermylenes [(iBu)2ATI]GeY (Y=NCO 4, NCS 5) and the corresponding halogenogermylenes [(iBu)2ATI]GeX (X=F 1, Cl 2, Br 3) towards group 6 metal carbonyls cis-[M(CO)4(COD)] (M=Mo, W) is demonstrated (ATI=aminotroponiminate).

​The ability of a platinum compound to act as a catalyst for the cyanosilylation of carbonyl compounds is demonstrated through a well-defined germylene stabilized Pt(II) dicyanide, trans-{(iBu)2ATIGe(iPr)}2Pt(CN)2.

A structurally characterized cationic aluminium complex [(AT)Al(DMAP)]+[OTf]− (3) stabilized through a relatively nonbulky aminotroponate (AT) ligand is reported (DMAP = 4-(dimethylamino)pyridine). This compound was found to work as an excellent mononuclear main-group catalyst of the cyanosilylation of a variety of aldehydes and ketones. Loadings of 1 to 2 mol% of this catalyst consumed these substrates in just 5 to 30 min at room temperature.

Complexes of germanone containing formal Ge=O→M bonds (M=Zn, B, Ge, Sn) were synthesized from a germanium μ-oxo dimer, circumventing the need to prepare synthetically challenging germanones. The complexes were spectroscopically and structurally characterized. LA= Lewis acid.

The halogen exchange reaction of germylene monochloride and germachalcogenoacid chlorides did not occur. Germanium compounds with Ge-N bonds reacted with Me3SiBr/CN to form various derivatives. The reactivity difference between Ge-Cl and Ge-N bonds was analyzed theoretically.

Use of a substituted digermylene oxide as a ligand has been demonstrated through the isolation of a series of group 11 metal(I) iodide complexes. Accordingly, the reactions of digermylene oxide [{(i-Bu)2ATIGe}2O] (ATI = aminotroponiminate) (1) with CuI under different conditions afforded [({(i-Bu)2ATIGe}2O)2(Cu4I4)] (2) with a Cu4I4 octahedral core, [({(i-Bu)2ATIGe}2O)2(Cu3I3)] (3) with a Cu3I3 core, and [{(i-Bu)2ATIGe}2O(Cu2I2)(C5H5N)2] (4) with a butterfly-type Cu2I2 core. The reactions of compound 1 with AgI and AuI produced [({(i-Bu)2ATIGe}2O)2(Ag4I4)] (5) with a Ag4I4 octahedral core and [{(i-Bu)2ATIGe}2O(Au2I2)] (6) with a Au2I2 core, respectively. The presence of metallophilic interactions in these compounds is shown through the single-crystal X-ray diffraction and atom-in-molecule (AIM) studies. Preliminary photophysical studies on compound 6 are also carried out.

A structurally characterized cationic aluminium complex [(AT)Al(DMAP)]+[OTf]− (3) stabilized through a relatively nonbulky aminotroponate (AT) ligand is reported (DMAP = 4-(dimethylamino)pyridine). This compound was found to work as an excellent mononuclear main-group catalyst of the cyanosilylation of a variety of aldehydes and ketones. Loadings of 1 to 2 mol% of this catalyst consumed these substrates in just 5 to 30 min at room temperature.

Silathiogermylene and siloxygermylenes react differently with various reagents. Silathiogermylene forms O-silylthionogermaester, while siloxygermylenes form dimerized products 1,3-dioxadigermetanes. Siloxygermylene also forms complex with irontetracarbonyl. Silathiogermylene does not yield the desired complex. O-silylthiono- and selenogermaesters are obtained from siloxygermylenes when treated with elemental sulfur and selenium. Reactions of these germaesters with methanol and nmmo are also investigated.

A novel silathiogermylene [Bui2(ATI)GeSSiMe3] (2) containing a reactive Ge(II)-SSiMe3 moiety showed an unusual reaction when treated with elemental selenium and sulfur to afford the germaacid anhydrides [{Bui2(ATI)Ge(Se)}2Se] (3) and [{Bui2(ATI)Ge(S)}2S] (4) in excellent yields, respectively. This single-step conversion of compound 2 to compounds 3 and 4 involves condensation along with insertion and oxidative addition reactions and such reactivity of a germylene with elemental chalcogens is observed for the first time.

A well-defined dipyrrinatogermylene monochloride 1 that is stable in water is reported. Surprisingly, it reacts with cesium fluoride under ambient conditions without any decomposition and affords the water stable dipyrrinatogermylene monofluoride, 2. The presence of a dipyrrinate ligand in compounds 1 and 2 provides fluorescence property to these germylenes.

The stability of ligand-stabilized carboxylic acid derivatives (such as esters, amides, anhydrides, and acid halides) with terminal Ge═Te bonds is highly questionable as there is no report on such compounds. Nevertheless, we are able to isolate germatelluroester [LGe(Te)Ot-Bu] (4), germatelluroamide [LGe(Te)N(SiMe3)2] (5), and germatelluroacid anhydride [LGe(Te)OGe(Te)L] (6) complexes (L = aminotroponiminate (ATI)) as stable species. Consequently, the synthetic details, structural characterization, and UV–vis spectroscopic and theoretical studies on them are reported for the first time.

The reaction of aminotroponiminato(chloro)germylene with CuI yielded copper(I) iodide complexes with tetrameric, monomeric, and dimeric CuI cores. Interconversions between the complexes and conversion of one complex to another were observed. The compounds were characterized by NMR spectroscopy and X-ray diffraction. The Ge(II)-Cu(I) bond lengths in the complexes were determined.

Reaction of a digermylene oxide complex [(L)GeOGe(L)] (1) with trimethylsilylcyanide (TMSCN) gave the first germylene monocyanide [GeCN(L)] (2) (L=aminotroponiminate). Compound 2 catalyzes the cyanosilylation of aldehydes by using TMSCN and has become the first isolable and structurally characterized germylene to act as a catalyst.

The reaction of aminotroponiminato(chloro)germylene with CuI yielded copper(I) iodide complexes with tetrameric, monomeric, and dimeric CuI cores. Interconversions between the complexes and conversion of one complex to another were observed. The compounds were characterized by NMR spectroscopy and X-ray diffraction. The Ge(II)-Cu(I) bond lengths in the complexes were determined.

Reaction of a digermylene oxide complex [(L)GeOGe(L)] (1) with trimethylsilylcyanide (TMSCN) gave the first germylene monocyanide [GeCN(L)] (2) (L=aminotroponiminate). Compound 2 catalyzes the cyanosilylation of aldehydes by using TMSCN and has become the first isolable and structurally characterized germylene to act as a catalyst.

Fluorination of germylene monochloride yielded germylene monofluoride. Reaction with sulfur and selenium produced germathioacid and germaselenoacid fluorides. Similar reactions with a different germylene monochloride led to germathioacid and germaselenoacid chlorides. The compounds were characterized using NMR and X-ray analysis. Resonances at −142.37 ppm and −213.13 ppm were observed in the 77Se NMR spectra of germaselenoacid complexes. Ge═E bond lengths were 2.065(1) Å for germathioacid chloride and 2.194 Å (average) for germaselenoacid halides. Theoretical studies indicated Ge═E multiple bonding with computed Wiberg bond indices of 1.480, 1.508, and 1.541 for the respective complexes.

The first examples of germathioesters and germaselenoesters stabilized by aminotroponiminate ligands are reported. Starting from aminotroponiminatogermylene alkoxides, the ester complexes were synthesized. Characterization was done using NMR spectroscopy and X-ray diffraction studies. Resonances at −77.76 ppm and −285.10 ppm were observed in the 77Se NMR spectra of germaselenoesters. The germanium center in the complexes adopts a distorted tetrahedral geometry. The average Ge═S and Ge═Se bond lengths in germathioester and germaselenoester complexes are 2.078 Å and 2.219 Å, respectively.

By means of a two-step synthetic route, aminotroponimine [(t-Bu)2ATI]H (3) with a tert-butyl substituent on the nitrogen atoms has been synthesized from 2-(tosyloxy)tropone. Lithiation of 3 with n-BuLi in THF afforded the lithium salt [(t-Bu)2ATI]Li·(THF)2 (4). Reaction of 4 with GeCl2·(1,4-dioxane) resulted in the germylene monochloride complex [(t-Bu)2ATI]GeCl (5). Treatment of 5 with the lithium derivative of ethynyl ferrocene [(C5H5)Fe(C5H4)C≡CH] (6) and phenyl acetylene (C6H5C≡CH) (7) gave the corresponding alkynyl germylene complexes [(t-Bu)2ATI]GeC≡C(C5H4)Fe(C5H5) (8) and [(t-Bu)2ATI]GeC≡CC6H5 (9), respectively. Compounds 3, 4, 5, 8, and 9 have been characterized by elemental analysis and various spectroscopic (multinuclear NMR, mass, and IR) techniques. Further confirmation came from the single-crystal X-ray structural studies on all these compounds. The structure of the alkynyl germylenes reveals the presence of a slightly bent Ge(II)−C≡C moiety [bond angle in 8 168.4(3)° and 9 170.8(2)°].