Aminotroponiminate Research Articles

ATI Stabilized Germylene Cation as a Cyanosilylation Catalyst for Aldehydes and Ketones.

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. Further, DFT calculations reveal a pronounced charge localization at the germanium atom of compound 2, leading to its superior catalytic performance.

Sulfinyl-aminotroponiminates: alkali- (Li, Na, K) and heavy-metal (Bi) complexes.

The installation of electron-withdrawing functional groups at the carbocyclic backbone of aminotroponiminate (ATI) ligands is a versatile method for influencing the electronic properties of the resulting ATI complexes. We report here Li, Na, and K salts of an ATI ligand with a phenylsulfinyl substituent in the backbone. It is demonstrated that the sulfinyl group actively contributes to the coordination chemistry of these complexes, effectively competing with neutral donor ligands such as thf or pyridine in the solid state (XRD), in solution (DOSY NMR spectroscopy), and in the gas phase (DFT). The impact of the phenylsulfinyl group on the redox properties of the complexes have been investigated and access to sodium sodiate species through ligand-induced disproportionation has been studied. Transfer of the ATI ligand to the heavy p-block element bismuth has been demonstrated. Analytical techniques applied in this work include multinuclear and DOSY NMR spectroscopy, cyclic voltammetry, DFT calculations, and single-crystal X-ray diffraction analysis.

Stannylene cyanide and its use as a cyanosilylation catalyst.

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.

Aminotroponiminates: Impact of the NO2 Functional Group on Coordination, Isomerisation, and Backbone Substitution.

Aminotroponiminate (ATI) ligands are a versatile class of redox‐active and potentially cooperative ligands with a rich coordination chemistry that have consequently found a wide range of applications in synthesis and catalysis. While backbone substitution of these ligands has been investigated in some detail, the impact of electron‐withdrawing groups on the coordination chemistry and reactivity of ATIs has been little investigated. We report here Li, Na, and K salts of an ATI ligand with a nitro‐substituent in the backbone. It is demonstrated that the NO2 group actively contributes to the coordination chemistry of these complexes, effectively competing with the N,N‐binding pocket as a coordination site. This results in an unprecedented E/Z isomerisation of an ATI imino group and culminates in the isolation of the first “naked” (i. e., without directional bonding to a metal atom) ATI anion. Reactions of sodium ATIs with silver(I) and tritylium salts gave the first N,N‐coordinated silver ATI complexes and unprecedented backbone substitution reactions. Analytical techniques applied in this work include multinuclear (VT‐)NMR spectroscopy, single‐crystal X‐ray diffraction analysis, and DFT calculations.

Cationic Bismuth Aminotroponiminates: Charge Controls Redox Properties.

The behavior of the redox‐active aminotroponiminate (ATI) ligand in the coordination sphere of bismuth has been investigated in neutral and cationic compounds, [Bi(ATI)3] and [Bi(ATI)2Ln][A] (L=neutral ligand; n=0, 1; A=counteranion). Their coordination chemistry in solution and in the solid state has been analyzed through (variable‐temperature) NMR spectroscopy, line‐shape analysis, and single‐crystal X‐ray diffraction analyses, and their Lewis acidity has been evaluated by using the Gutmann–Beckett method (and modifications thereof). Cyclic voltammetry, in combination with DFT calculations, indicates that switching between ligand‐ and metal‐centered redox events is possible by altering the charge of the compounds from 0 in neutral species to +1 in cationic compounds. This adds important facets to the rich redox chemistry of ATIs and to the redox chemistry of bismuth compounds, which is, so far, largely unexplored.

Synthesis of Lewis Acidic, Aromatic Aminotroponiminate Zinc Complexes for the Ring-Opening Polymerization of Cyclic Esters

Three novel aminotroponiminate (ATI) zinc complexes I-III (I = [(Ph2)ATI]Zn-N(SiMe3)2, II = [(C6H3-2,6-C2H5/Ph)ATI]Zn-N(SiMe3)2, and III = [(C6H3-2,6-CH(CH3)2/Ph)ATI]Zn-N(SiMe3)2) were synthesized and tested in the ring-opening polymerization of the lactones β- rac-butyrolactone (BBL) and rac-lactide (LA). The ligands, with two of them literature unknown, were readily obtained via a three-step synthesis from tropolone. Forming a five-membered metallacycle with zinc, the complexes were further structurally examined via single-crystal X-ray analysis and compared with that of the established, 6-ringed β-diiminate (BDI) complex IV ([CH(CMeNPh)2]Zn-N(SiMe3)2). The influence of the varying metallacycle ring size on the polymerization was evaluated. In situ IR measurements indicate a higher catalytic activity of the novel ATI complexes I-III for BBL compared with the BDI system IV. The activity and degree of control were further improved by an in situ generated alkoxy initiating group generated after the addition of 2-propanol. An enhanced initiator efficiency allowed the synthesis of polymers with controlled molecular weights and narrow polydispersities. Furthermore, II and III exhibited a high activity in the ring-opening polymerization of rac-LA. Hereby, reaction time and initiator efficiency could also be optimized at a higher temperature or by the addition of 2-propanol.

Sodium Aminotroponiminates: Ligand‐Induced Disproportionation, Mixed‐Metal Compounds, and Exceptional Activity in Polymerization Catalysis

AbstractSodium complexes of aminotroponiminate (ATI) ligands have been reacted with a range of neutral donor ligands. Upon addition of crown ethers, they undergo an unusual ligand‐induced disproportionation reaction with formation of [Na(ATI)2]− sodiate complex anions. The same structural motif has also been found in the first well‐defined mixed‐metal ATI complexes, which have been accessed starting from monometallic sodium and potassium species. The mixed‐metal compounds confirm the possibility of ATIs to act as ditopic ligands. Using the polymerization of ϵ‐caprolactone as a model system, structure‐reactivity‐relationships in sodium and mixed‐metal ATI compounds have been studied by comparing the reactivity of [Na(ATI)] and [Na(ATI)2]− structural motifs. These studies revealed trends in the catalyst activity depending on the nuclearity of the complex and the substitution pattern at the ATI ligand. Exceptionally high activities were obtained for dinuclear sodium sodiates of type [Na(crown)2][Na(ATI)2], making them the most active alkali metal initiators for this reaction. The organometallic and polymeric compounds presented in this work have been characterized by techniques including (VT‐)NMR spectroscopy, single‐crystal X‐ray diffraction, gel permeation chromatography, mass spectrometry, and DFT calculations.

Aminotroponiminatosilathio- and Siloxygermylenes: Reactivity Comparison

Aminotroponiminate (ATI) ligand stabilized silathiogermylene [(Bui2ATI)GeSSiMe3] (11) and siloxygermylenes [(Bui2ATI)GeOSiR3] (R = Me 2, Ph 3) react differently with the same reagents, i.e., N-methylmorpholine-N-oxide (nmmo), diironnonacarbonyl, and elemental sulfur/selenium. Whereas silathiogermylene 11 afforded the first O-silylthionogermaester [(Bui2ATI)Ge(S)OSiMe3] (1) in its reaction with nmmo involving 1,3-silyl migration, siloxygermylenes 2 and 3 reacted with the same to give 1,3-dioxadigermetanes [{(Bui2ATI)Ge(O)OSiR3}2] (R = Me 14 and Ph 4, respectively) as dimerized products. Similarly, in the reaction with diironnonacarbonyl, compound 3 behaved in the anticipated way and led to its complex with irontetracarbonyl [(Bui2ATI)Ge(Fe(CO)4)OSiPh3] (5), but compound 11 did not offer the desired complex. Further, unlike compound 11, compounds 2 and 3 afford the anticipated O-silylthiono- and selenogermaesters [(Bui2ATI)Ge(E)OSiR3] (E = S; R = Me 1, Ph 7; E = Se; R = Me 6, Ph 8) when treated with element...

Use of thio and seleno germanones as ligands: silver(I) halide complexes with Ge═E→Ag-I (E = S, Se) moieties and chalcogen-dependent argentophilic interaction.

The potential of thio and seleno germanones [LPhGe═E] (L = aminotroponiminate (ATI) ligand, E = S 3, Se 4) to function as ligands has been demonstrated through the isolation of their silver(I) iodide complexes [{(t-Bu)2ATIGe(E)Ph}2(Ag2I2)] (E = S 5, Se 6) with a planar and discrete Ag2I2 core. Compounds 5 and 6 possess the hitherto unknown Ge═E→Ag-I moieties and the crystallographic data reveals the presence of a strong argentophilic interaction (2.950(1) Å) in complex 6, but is inconclusive in complex 5 (3.470(1) Å). Using theoretical studies, proof for the presence and absence of argentophilic interactions in complexes 6 and 5 was obtained, respectively. Further, it is disclosed that the donor ability of the chalcogen atoms in the Ge═E→Ag-I moieties dictate the Ag···Ag interaction in these complexes.

Germylene cyanide complex: a reagent for the activation of aldehydes with catalytic significance.

The first example of a germanium(II) cyanide complex [GeCN(L)] (2) (L=aminotroponiminate (ATI)) has been synthesized through a novel and relatively benign route that involves the reaction of a digermylene oxide [(L)Ge-O-Ge(L)] (1) with trimethylsilylcyanide (TMSCN). Interestingly, compound 2 activates several aldehydes (RCHO) at room temperature and results in the corresponding cyanogermylated products [RC{OGe(L)}(CN)H] (R=H 3, iPr 4, tBu 5, CH(Ph)Me 6). Reaction of one of the cyanogermylated products (4) with TMSCN affords the cyanosilylated product [(iPr)C(OSiMe3 )(CN)H] (7) along with [GeCN(L)] quantitatively, and insinuates the possible utility of [GeCN(L)] as a catalyst for the cyanosilylation reactions of aldehydes with TMSCN. Accordingly, the quantitative formation of several cyanosilylated products [RC(OSiMe3 )(CN)H] (7-9) in the reaction between RCHO and TMSCN by using 1 mol % of [GeCN(L)] as a catalyst is also reported for the first time.

Are ligand-stabilized carboxylic acid derivatives with Ge═Te bonds isolable?

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.

Digermylene Oxide Complexes: Facile Synthesis and Reactivity

A simple heating of aminotroponiminate (ATI) ligand stabilized germylene monochlorides [(R)2ATIGeCl] (R = t-Bu 1, i-Bu 2) with an excess of potassium hydroxide in toluene resulted in the first ATI ligand stabilized digermylene oxides [{(R)2ATIGe}2O] (R = t-Bu 3, i-Bu 4), respectively. Reaction of compound 3 with elemental sulfur and selenium gave the first germaacid anhydride complexes [{(t-Bu)2ATIGe(E)}2O] (E = S 5, Se 6) with (S)Ge-O-Ge(S) and (Se)Ge-O-Ge(Se) moieties, respectively. The digermylene oxide complexes 3 and 4 and germaacid anhydride complexes 5 and 6 were characterized by multinuclear NMR spectroscopy and single-crystal X-ray diffraction analysis. In its (77)Se NMR spectrum, compound 6 showed a resonance at -78.9 ppm. The Ge-O-Ge bond angles in compounds 5 and 6 are 178.66(2)° and 179.81(2)°, respectively. To understand further the bonding features, DFT calculations followed by MO, AIM, and NBO analysis were carried out on compounds 3, 5, and 6. The computed Wiberg bond indices of Ge-O bonds are slightly less than 0.5 in all the aforementioned compounds, and the same for the Ge═E bonds in compounds 5 and 6 are close to 1.4.

Aminotroponiminatogermaacid Halides with a Ge(E)X Moiety (E = S, Se; X = F, Cl)

Fluorination of aminotroponiminate (ATI) ligand-stabilized germylene monochloride [(t-Bu)(2)ATI]GeCl (1) with CsF gave the aminotroponiminatogermylene monofluoride [(t-Bu)(2)ATI]GeF (2). Oxidative addition reaction of compound 2 with elemental sulfur and selenium led to isolation of the corresponding germathioacid fluoride [(t-Bu)(2)ATI]Ge(S)F (3) and germaselenoacid fluoride [(t-Bu)(2)ATI]Ge(Se)F (4), respectively. Similarly, reaction of aminotroponiminatogermylene monochloride [(i-Bu)(2)ATI]GeCl (9) with elemental sulfur and selenium gave the aminotroponiminatogermathioacid chloride [(i-Bu)(2)ATI]Ge(S)Cl (11) and aminotroponiminatogermaselenoacid chloride [(i-Bu)(2)ATI]Ge(Se)Cl (12), respectively. Compound 9 has been prepared through a multistep synthetic route starting from 2-(tosyloxy)tropone 5. All compounds (2-4 and 6-12) were characterized through the multinuclear NMR spectroscopy, and single-crystal X-ray diffraction studies were performed on compounds 2, 4, and 8-12. The germaselenoacid halide complexes 4 and 12 showed doublet (-142.37 ppm) and singlet (-213.13 ppm) resonances in their (77)Se NMR spectra, respectively. Germylene monohalide complexes 2 and 9 have a germanium center in distorted trigonal pyramidal geometry, whereas a distorted tetrahedral geometry is seen around the germanium center in germaacid halide complexes 4, 11, and 12. The length of the Ge═E bond in germathioacid chloride (11) and germaselenoacid halide (4 and 12) complexes is 2.065(1) and 2.194(av) Å, respectively. Theoretical studies (based on the DFT methods) on complexes 4, 11, and 12 reveal the nature of the Ge═E multiple bond in these germaacid halide complexes with computed Wiberg bond indices (WBI) being 1.480, 1.508, and 1.541, respectively.

Germaester Complexes with a Ge(E)Ot-Bu Moiety (E = S or Se)

Although germanium analogues of ketones, carboxylic acids, acid halides, and amides are known, an example of a germaester complex is still missing. Therefore, the first examples of germathioesters [(R)2ATI]Ge(S)Ot-Bu (R = t-Bu 5 and R = i-Bu 6) and germaselenoesters [(R)2ATI]Ge(Se)Ot-Bu (R = t-Bu 7 and R = i-Bu 8) stabilized through aminotroponiminate (ATI) ligands are reported here. Aminotroponiminatogermylene alkoxides [(t-Bu)2ATI]GeOt-Bu (3) and [(i-Bu)2ATI]GeOt-Bu (4) serve as starting materials for the synthesis of the aforementioned ester complexes. Compounds 5–8 were characterized by multinuclear NMR spectroscopic and single-crystal X-ray diffraction studies in the liquid and solid state, respectively. 77Se NMR spectra of compounds 7 and 8 showed a singlet resonance at −77.76 and −285.10 ppm, respectively. The germanium center in compounds 5–8 adopts a distorted tetrahedral geometry. The average Ge═S and Ge═Se bond lengths in germathioester (5 and 6) and germaselenoester (7 and 8) complexes are 2.0...

Investigation of silver salt metathesis: preparation of cationic germanium(II) and Tin(II) complexes, and silver adducts containing unsupported silver-germanium and silver-tin bonds.

Syntheses of halide derivatives of germanium(II) and tin(II) aminotroponiminate (ATI) complexes and their silver salt metathesis reactions have been investigated. The treatment of GeCl(2) x (1,4-dioxane), SnCl(2), or SnI(2) with [(n-Pr)(2)ATI]Li in a 1:1 molar ratio affords the corresponding germanium(II) or tin(II) halide complex [(n-Pr)(2)ATI]MX (where [(n-Pr)(2)ATI](-) = N-(n-propyl)-2-(n-propylamino)troponiminate; M = Ge or Sn; X = Cl or I). As usually expected, [(n-Pr)(2)ATI]GeCl and [(n-Pr)(2)ATI]SnCl undergo rapid metathesis with CF(3)SO(3)Ag, leading to trifluoromethanesulfonate salts, [[(n-Pr)(2)ATI]Ge][SO(3)CF(3)] and [[(n-Pr)(2)ATI]Sn][SO(3)CF(3)], and silver chloride. However, when the silver source [HB(3,5-(CF(3))(2)Pz)(3)]Ag(eta(2)-toluene) is used, rather than undergoing metathesis, very stable 1:1 adducts [HB(3,5-(CF(3))(2)Pz)(3)]Ag<--Ge(Cl)[(n-Pr)(2)ATI] and [HB(3,5-(CF(3))(2)Pz)(3)]Ag<--Sn(Cl)[(n-Pr)(2)ATI] are formed (where [HB(3,5-(CF(3))(2)Pz)(3)](-) = hydrotris(3,5-bis(trifluoromethyl)pyrazolyl)borate). The use of the iodide derivative [(n-Pr)(2)ATI]SnI did not change the outcome either. All new compounds have been characterized by multinuclear NMR spectroscopy and X-ray crystallography. The Ag-Ge and Ag-Sn bond distances of [HB(3,5-(CF(3))(2)Pz)(3)]Ag<-- Ge(Cl)[(n-Pr)(2)ATI], [HB(3,5-(CF(3))(2)Pz)(3)]Ag<--Sn(Cl)[(n-Pr)(2)ATI], and [HB(3,5-(CF(3))(2)Pz)(3)]Ag<--Sn(I)[(n-Pr)(2)ATI] are 2.4142(6), 2.5863(6), and 2.5880(10) A, respectively. A convenient route to [(n-Pr)(2)ATI]H is also reported.