RESUMO
When bismuth atoms are incorporated into cyclic organic systems, this commonly goes along with strained or distorted molecular geometries, which can be exploited to modulate the physical and chemical properties of these compounds. In six-membered heterocycles, bismuth atoms are often accompanied by oxygen, sulfur or nitrogen as a second hetero-element. In this work, we present the first examples of six-membered rings, in which two CH units are replaced by BiX moieties (X=Cl, Br, I), resulting in dihydro-anthracene analogs. Their behavior in chemically reversible reduction reactions is explored, aiming at the generation of dibisma-anthracene (bismanthrene). Heterometallic compounds (Bi/Fe, Bi/Mn) are introduced as potential bismanthrene surrogates, as supported by bismanthrene-transfer to selenium. Analytical techniques used to investigate the reported compounds include NMR spectroscopy, high-resolution mass spectrometry, single-crystal X-ray diffraction analyses, and DFT calculations.
RESUMO
The first series of 9-bisma-10-pnictatriptycenes Bi(C6H4)3Pn (2-Pn, Pn = P-Bi; see graphic) has been synthesized in a two-step procedure via suitable tris(2-bromophenyl)pnictanes 1-Pn and characterized in solution as well as in the solid state. DFT calculations suggest preferential interactions between 2-Pn and soft Lewis acids via the lighter pnictogen donor atom. Experimental studies demonstrate that even the weakest Lewis base in the series of 2-Pn, namely the dibismatriptycene 2-Bi, interacts with Lewis acidic [BiMe2(SbF6)] in solution. Analytical techniques include (VT-)NMR spectroscopy, DOSY NMR spectroscopy, high-resolution mass spectrometry, single-crystal X-ray diffraction analyses, and DFT calculations.
RESUMO
The first 1,4-distibabenzene-1,4-diide compound [(ADC)Sb]2 (5) based on an anionic dicarbene (ADC) (ADC=PhC{N(Dipp)C}2 , Dipp=2,6-iPr2 C6 H3 ) is reported as a bordeaux-red solid. Compound 5, featuring a central six-membered C4 Sb2 ring with formally SbI atoms may be regarded as a base-stabilized cyclic bis-stibinidene in which each of the Sb atoms bears two lone-pairs of electrons. 5 undergoes 2 e-oxidation with Ph3 C[B(C6 F5 )4 ] to afford [(ADC)Sb]2 [B(C6 F5 )4 ]2 (6) as a brick-red solid. Each of the Sb atoms of 6 has an unpaired electron and a lone-pair. The broken-symmetry open-shell singlet diradical solution for (6)2+ is calculated to be 2.13â kcal mol-1 more stable than the closed-shell singlet. The diradical character of (6)2+ according to SS-CASSCF (state-specific complete active space self-consistent field) and UHF (unrestricted Hartree-Fock) methods amounts to 36 % and 39 %, respectively. Treatments of 6 with (PhE)2 yield [(ADC)Sb(EPh)]2 [B(C6 F5 )4 ]2 (7-E) (E=S or Se). Reaction of 5 with (cod)Mo(CO)4 affords [(ADC)Sb]2 Mo(CO)4 (8).
RESUMO
Herein, the first stable anions K[SIPrBp ] (4 a-K) and K[IPrBp ] (4 b-K) (SIPrBp =BpC{N(Dipp)CH2 }2 , IPrBp =BpC{N(Dipp)CH}2 ; Bp=4-PhC6 H4 ; Dipp=2,6-iPr2 C6 H3 ) derived from classical N-heterocyclic carbenes (NHCs) (i.e. SIPr and IPr) have been isolated as violet crystalline solids. 4 a-K and 4 b-K are prepared by KC8 reduction of the neutral radicals [SIPrBp ] (3 a) and [IPrBp ] (3 b), respectively. The radicals 3 a and 3 b as well as [Me-IPrBp ] 3 c (Me-IPrBp =BpC{N(Dipp)CMe}2 ) are accessible as crystalline solids on treatment of the respective 1,3-imidazoli(ni)um bromides (SIPrBp )Br (2 a), (IPrBp )Br (2 b), and (Me-IPrBp )Br (2 c) with KC8 . The cyclic voltammograms of 2 a-2 c exhibit two one-electron reversible redox processes in -0.5 to -2.5â V region that correspond to the radicals 3 a-3 c and the anions (4 a-4 c)- . Computational calculations suggest a closed-shell singlet ground state for (4 a-4 c)- with the singlet-triplet energy gap of 17-24â kcal mol-1 .
RESUMO
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.
Assuntos
Iminas , Dióxido de Nitrogênio , Cristalografia por Raios X , Ligantes , Tropolona/análogos & derivadosRESUMO
Herein, we report the first 1,4-diphosphinine-1,4-diide compound [(ADCPh )P]2 (5-Ph) (ADCPh =PhC{(NDipp)C}2 ; Dipp=2,6-iPr2 C6 H3 ) derived from an anionic dicarbene (ADCPh ) as a red crystalline solid. Compound 5-Ph containing a 16π-electron planar fused-tricyclic ring system was obtained by the 4e reduction of [(ADCPh )PCl2 ]2 (4-Ph) with Mg (or KC8 ) in a quantitative yield. Experimental and computational results imply that the central 8π-electrons C4 P2 ring of 5-Ph, which is fused between two 6π-electrons C3 N2 aromatic rings, is antiaromatic. Thus, each of the phosphorus atoms of 5-Ph has two electron-lone-pairs, one in a p-type orbital is in conjugation with the C=C bonds of the C4 P2 ring, while the second resides in a σ-symmetric orbital. This can be shown with the gold complex [(ADCPh )P(AuCl)2 ]2 (6-Ph) obtained by reacting 5-Ph with (Me2 S)AuCl. A mixture of 5-Ph and 4-Ph undergoes comproportionation in the presence of MgCl2 to form the intermediate oxidation state compound [(ADCAr )P]2 (MgCl4 ) (7-Ph), which is an aromatic species.
RESUMO
Metalloradicals are key species in synthesis, catalysis, and bioinorganic chemistry. Herein, two iron radical cation complexes (3-E)GaCl4 [(3-E).+ = [{(IPr)C(Ph)E}2 Fe(CO)3 ].+ , E = P or As; IPr = C{(NDipp)CH}2 , Dipp = 2,6-iPr2 C6 H3 ] are reported as crystalline solids. Treatment of the divinyldipnictenes {(IPr)C(Ph)E}2 (1-E) with Fe2 (CO)9 affords [{(IPr)C(Ph)E}2 Fe(CO)3 ] (2-E), in which 1-E binds to the Fe atom in an allylic (η3 -EECvinyl ) fashion and functions as a 4e donor ligand. Complexes 2-E undergo 1e oxidation with GaCl3 to yield (3-E)GaCl4 . Spin density analysis revealed that the unpaired electron in (3-E).+ is mainly located on the Fe (52-64 %) and vinylic C (30-36 %) atoms. Further 1e oxidation of (3-E)GaCl4 leads to unprecedented η3 -EECvinyl to η3 -ECvinyl CPh coordination shuttling to form the dications (4-E)(GaCl4 )2 .
RESUMO
1,4-Diarsinine-1,4-diide compound [(ADCPh )As]2 (5) (ADCPh ={C(DippN)}2 CPh, Dipp=2,6-iPr2 C6 H3 ) with a planar C4 As2 ring fused between two 1,3-imidazole scaffolds has been isolated as a red crystalline solid. Compound 5, formally comprising an 8π-electron C4 As2 ring, is antiaromatic and undergoes 2e-oxidation with AgOTf to form the 6π-electron aromatic system [(ADCPh )As]2 (OTf)2 (6).
RESUMO
The first SnI diradical [(ADCPh )Sn]2 (4) based on an anionic dicarbene (ADCPh ={CN(Dipp)}2 CPh; Dipp=2,6-iPr2 C6 H3 ) scaffold has been isolated as a green crystalline solid by KC8 reduction of the corresponding bis-chlorostannylene [(ADCPh )SnCl]2 (3). The six-membered C4 Sn2 -ring of 4 containing six π-electrons shows a diatropic ring current, thus 4 may also be regarded as the first 1,4-distannabenzene derivative. DFT calculations suggest an open-shell singlet (OS) ground state of 4 with a remarkably small singlet-triplet energy gap (ΔEOS-T =4.4â kcal mol-1 ), which is consistent with CASSCF (ΔES-T =6.6â kcal mol-1 and diradical character y=37 %) calculations. The diradical 4 splits H2 at room temperature to yield the bis-hydridostannylene [(ADCPh )SnH]2 (5). Further reactivity of 4 has been studied with PhSeSePh and MeOTf.
RESUMO
Phosphinidene complexes of the general formula RPM(CO)n (R = an alkyl or aryl group; M = a transition metal) are electrophilic and thermally unstable. Thus, the isolation of these elusive species for structural elucidations remains a challenge. Herein, we report the first terminal phosphinidene complexes [{(NHC)C(Ph)}P]Fe(CO)4 [NHC = IPr = C{(NDipp)CH}2 for 3; Me-IPr = C{(NDipp)CMe}2 for 4; Dipp = 2,6-iPr2C6H3; NHC = N-heterocyclic carbene] as red crystalline solids containing a π-donor N-heterocyclic vinyl (NHV) substituent at the phosphorus atom. Calculations reveal donor-acceptor type bonding between phosphorus and iron atoms in 3 and 4. The P â Fe donation represents â¼70% of the orbital interaction, whereas the Fe â P π-back-donation corresponds to â¼15% of the orbital interaction. The phosphorus atoms in 3 and 4 carry charges of +0.65e and +0.64e, respectively, indicating the electrophilic character of the phosphinidene {(NHC)C(Ph)}P moiety. Accordingly, 3 reacts with an NHC nucleophile (IMe4) to yield the Lewis adduct [{(NHC)C(Ph)}P(IMe4)]Fe(CO)4 (5) [IMe4 = C(NMeCMe)2]. The coordination of an electron-rich NHC (IMe4) to the phosphorus atom in 5 precludes the π-electron density transfer from the NHV to the phosphorus atom. Thus, the CIPr-Cvinyl and Cvinyl-P bonds of 5 become shorter and longer, respectively, compared to those of 3.
RESUMO
Para-quinodimethane (pQDM) is a fundamental structural component in many π-conjugated organic molecules and materials. The incorporation of phosphorus atom into π-conjugated frameworks offers unique opportunities for controlling the properties of derived species. A phosphorus analogue of p-quinodimethane (pQDM), (IPrC)2 P4 [5, IPr=C{N(Ar)CH2 }2 ; Ar=2,6-iPr2 C6 H3 ] featuring a planar P4 ring, was readily accessible by KC8 -reduction of (IPrC)(PCl2 )2 (2). Base-mediated C-H functionalization of IPrCH2 (1) with PCl3 afforded 2. The formation of 5 was expected to occur through a dimerization of the transient 3H-diphosphirene (IPrC)P2 (4), which was theoretically suggested to have an intermediate diradical character. Compound 5 underwent photo-induced ring-contraction reaction to form the singlet diradicaloid (IPrCP)2 VI and white phosphorus (P4 ). The formation of and VI and P4 suggested the formal diphosphorus (P2 ) elimination from 5. Indeed, photolysis of a mixture of 1,3-cyclohexadiene (CHD) and 5 led to the formation of P2 -entrapped product (CHD)2 P2 (6). The compound 5 represents the first organophosphorus species that functions as a P2 source.
RESUMO
The olefinic C-H bond functionalization of (NHC)CHPh (NHC=IPr=C{(NAr)CH}2 1; SIPr=C{(NAr)CH2 }2 2; Ar=2,6-iPr2 C6 H3 ), derived from classical N-heterocyclic carbenes (NHCs), with PCl3 affords the dichlorovinylphosphanes {(NHC)C(Ph)}PCl2 (NHC=IPr 3, SIPr 4). Two-electron reduction of 3 and 4 with magnesium leads to the formation of the divinyldiphosphenes [{(NHC)C(Ph)}P]2 (NHC=IPr 5, SIPr 6) as crystalline solids. Unlike literature-known diphosphenes, which are mostly yellow or orange, 5 is a green whereas 6 is a purple solid. Although the P=P bond lengths of 5 (2.062(1)) and 6 (2.055(1)â Å) are comparable to those of the known diphosphenes (2.02-2.08â Å), the C-P bond lengths of 5 (1.785(1)) and 6 (1.797(1)â Å) are, however, considerably shorter than a C sp 2 -P single bond length (1.85â Å), indicating a considerable π-conjugation between C=C and P=P moieties. The HOMO-LUMO energy gap for 5 (4.15) and 6 (4.52â eV) is strikingly small and thus the narrowest among the diphosphenes (>4.93â eV) reported as yet. Consequently, 5 readily undergoes P=P bond cleavage at room temperature on treatment with sulfur to form the unique dithiophosphorane {(IPr)C(Ph)}P(S)2 7. Interestingly, reaction of 5 with selenium gives the selenadiphosphirane [{(IPr)C(Ph)}P]2 Se 8 with an intact P-P bond.
RESUMO
The synthesis, structure, and reactivity of the first silylene-functionalized N-heterocyclic carbene (Si-NHC), {(L1 )Si}(L2 ), (3) (L1 =PhC(NtBu)2 , L2 =CCH(CNAr)2 C:, Ar=2,6-diisopropylphenyl) are reported. The ditopic carbanionic-NHC (dc-NHC), [Li(L2 )]∞ (1) reacts with the monochlorosilylene (L1 )SiCl (2) to afford 3. The HOMO of 3 is the silylene lone-pair orbital, whereas the HOMO-1 is located at the carbene carbon atom. Both SiII and CII functionalities of 3 undergo reactions with chalcogens to give heavier ketone derivatives {(L1 )Si(E)}L2 (E) (E=S, 4; Se, 5; and Te, 6). Compounds 4-6 feature a highly polarized Siδ+ -Eδ- bond with a formal charge of -0.72 (4), -0.64 (5), and -0.50â e (6) on the E atom. The Wiberg bond indices of 1.64 (4), 1.66 (5), and 1.63 (6) for the Si-E bond however indicate a moderate pπ -pπ interaction between Si and E atoms. Compound 3 functions as a reducing agent and induces disproportionation of Si2 Cl6 to yield the silyl-functionalized NHC, {(L1 )SiCl2 }(L2 ) (7). Treatment of 3 with HSiCl3 leads to the formation of the silyl-functionalized imidazolium salt [{(L1 )SiCl2 }(L2 H)]Cl (8). The silylene moiety of 3 readily forms the iridium-silylene complex [{(L2 )(L1 )Si}Ir(cod)Cl] (9) featuring a free NHC ligand on treatment with [Ir(cod)(µ-Cl)]2 .
RESUMO
Two-fold C-C cross-coupling of N-heterocyclic carbenes [NHCs; SIPr=C(NArCH2 )2 , 1; IPr=C(NArCH)2 , 2; Me-IPr=C(NArCMe)2 , 3; Ar=2,6-iPr2 C6 H3 ] with 4,4''-diiodo-p-terphenyl under Ni catalysis furnished [(SIPr)(C6 H4 )3 (SIPr)](I)2 (4), [(IPr)(C6 H4 )3 (IPr)](I)2 (5), and [(Me-IPr)(C6 H4 )3 (Me-IPr)](I)2 (6). Two-electron reduction of 4-6 with KC8 readily afforded NHC analogues of Müller's hydrocarbon (MH), [(SIPr)(C6 H4 )3 (SIPr)] (7), [(IPr)(C6 H4 )3 (IPr)] (8), and [(Me-IPr)(C6 H4 )3 (Me-IPr)] (9), respectively, as highly colored crystalline solids. Quantum chemical calculations suggested that the singlet ground state for 7-9 possesses a vertical singlet-triplet energy gap ΔES-T of -7.24 to -7.60â kcal mol-1 , which is significantly lower compared to that of the NHC analogues of Thiele's (TH) and Chichibabin's (CH) (18-38â kcal mol-1 ) hydrocarbons. Importantly, the calculated diradical character (y) of 7-9 (y≈0.6) is considerably higher compared to that of the related TH and CH (y=0.1-0.4), suggesting the open-shell singlet character of 7-9.
RESUMO
The first C5-protonated abnormal N-heterocyclic carbene (aNHC), PhC{N(2,6-iPr2 C6 H3 )}2 CHC: (4) is readily accessible by C4-deprotonation of [ArC{N(2,6-iPr2 C6 H3 )}2 CHCH]X (3 a-X) (Ar=Ph, X=Br or I) with a base. The aNHC 4 is stable at 298â K in [D8 ]THF solution and has been spectroscopically characterized. The facile availability of 4 enables the synthesis of a series of main-group compounds as well as transition-metal complexes featuring a new phosphorus-aNHC hybrid ligand. Double deprotonation of [ArC{N(2,6-iPr2 C6 H3 )}2 CHCH]X (Ar=Ph, 3 a-X (X=Br or I); 4-Tol, 3 b-Br; 4-DMP, 3 c-Br; Tol=MeC6 H4 , DMP=Me2 NC6 H4 ) with nBuLi yields the C4,C5-ditopic carbanionic aNHCs, [ArC{N(2,6-iPr2 C6 H3 )}2 (C:)2 ]Li(THF)n (Ar=Ph, 13 a; 4-Tol, 13 b; 4-DMP, 13 c), which on treatment with Ph2 PCl affords cationic vicinal bisphosphine derivatives [ArC{N(2,6-iPr2 C6 H3 )}2 {C(PPh2 }2 ]X (Ar=Ph, 14 a-X, X=Br or I; 4-Tol, 14 b-Br; 4-DMP, 14 c-Br).
RESUMO
Stable N-heterocyclic carbene analogues of Thiele and Chichibabin hydrocarbons, [(IPr)(C6 H4 )(IPr)] and [(IPr)(C6 H4 )2 (IPr)] (4 and 5, respectively; IPr=C{N(2,6-iPr2 C6 H3 )}2 CHCH), are reported. In a nickel-catalyzed double carbenylation of 1,4-Br2 C6 H4 and 4,4'-Br2 (C6 H4 )2 with IPr (1), [(IPr)(C6 H4 )(IPr)](Br)2 (2) and [(IPr)(C6 H4 )2 (IPr)](Br)2 (3) were generated, which respectively afforded 4 and 5 as crystalline solids upon reduction with KC8 . Experimental and computational studies support the semiquinoidal nature of 5 with a small singlet-triplet energy gap ΔES-T of 10.7â kcal mol-1 , whereas 4 features more quinoidal character with a rather large ΔES-T of 25.6â kcal mol-1 . In view of the low ΔES-T , 4 and 5 may be described as biradicaloids. Moreover, 5 has considerable (41 %) diradical character.
RESUMO
One-electron reduction of C2-arylated 1,3-imidazoli(ni)um salts (IPrAr )Br (Ar=Ph, 3 a; 4-DMP, 3 b; 4-DMP=4-Me2 NC6 H4 ) and (SIPrAr )I (Ar=Ph, 4 a; 4-Tol, 4 b) derived from classical NHCs (IPr=:C{N(2,6-iPr2 C6 H3 )}2 CHCH, 1; SIPr=:C{N(2,6-iPr2 C6 H3 )}2 CH2 CH2 , 2) gave radicals [(IPrAr )]. (Ar=Ph, 5 a; 4-DMP, 5 b) and [(SIPrAr )]. (Ar=Ph, 6 a; 4-Tol, 6 b). Each of 5 a,b and 6 a,b exhibited a doublet EPR signal, a characteristic of monoradical species. The first solid-state characterization of NHC-derived carbon-centered radicals 6 a,b by single-crystal X-ray diffraction is reported. DFT calculations indicate that the unpaired electron is mainly located at the original carbene carbon atom and stabilized by partial delocalization over the adjacent aryl group.
RESUMO
Four-membered biradicaloid compounds containing a N2 E2 (E=main group element) framework have been thoroughly investigated; however, the synthesis of stable analogues with a C2 P2 skeleton remains a challenge. Base-mediated double C-H functionalization of IPr=CH2 (1) (IPr=C[N(2,6-iPr2 -C6 H3 )CH]2 ) with PCl3 affords [{(IPr)CP}2 Cl]Cl (2) as a royal blue solid. Treatment of 2 with KC8 yields the stable phosphorus biradicaloid [(IPr)CP]2 (3) featuring a four-membered C2 P2 ring. Compound 3 is diamagnetic and shows sharp and temperature-independent NMR resonances, revealing its singlet biradicaloid nature. The stability of 3 is attributed to the σ- and π-electron-donating property of the N-heterocyclic vinylidene [(IPr)C] group.
RESUMO
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.
RESUMO
The first C5-protonated 1,3-imidazol-based mesoionic carbene iMICBp (2) (iMICBp = :C{CH(NDipp)2C(Bp)}; Dipp = 2,6-iPr2C6H3; Bp = 4-PhC6H4) has been reported as a crystalline solid. Spectroscopic, X-ray diffraction, and computational studies clearly support the carbenic nature of 2, which has been further corroborated by its reactions with Ni(CO)4, (Me2S)AuCl, white phosphorus, and CO2.