Papers by Dennis Rottschäfer
Angewandte Chemie International Edition
Dalton Transactions
The installation of electron-withdrawing functional groups at the carbocyclic backbone of aminotr... more 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...
Angewandte Chemie
Das 1,4-Diarsinin-1,4-diid [(ADC Ph)As] 2 (5) (ADC Ph = {C(DippN)} 2 CPh, Dipp = 2,6-iPr 2 C 6 H ... more Das 1,4-Diarsinin-1,4-diid [(ADC Ph)As] 2 (5) (ADC Ph = {C(DippN)} 2 CPh, Dipp = 2,6-iPr 2 C 6 H 3) mit einem planaren C 4 As 2-Ring, der an zwei 1,3-Imidazol-Ringen anelliert ist, wurde als roter, kristalliner Feststoff isoliert. Verbindung 5, die formal einen 8p-Elektronen-C 4 As 2-Ring enthält, ist antiaromatisch und geht eine 2e-Oxidation mit AgOTf ein, die zum aromatischen 6p-Elektronen-System [(ADC Ph)As] 2-(OTf) 2 (6) führt.
Chemistry – A European Journal, 2021
Metalloradicals are key species in synthesis, catalysis, and bioinorganic chemistry. Herein, two ... more Metalloradicals are key species in synthesis, catalysis, and bioinorganic chemistry. Herein, two iron radical cation complexes (3-E)GaCl 4 [(3-E)C + = [{(IPr)-C(Ph)E} 2 Fe(CO) 3 ]C + , E = P or As; IPr = C{(NDipp)CH} 2 , Dipp = 2,6-iPr 2 C 6 H 3 ] are reported as crystalline solids. Treatment of the divinyldipnictenes {(IPr)C(Ph)E} 2 (1-E) with Fe 2 (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 (h 3-EEC vinyl) fashion and functions as a 4e donor ligand. Complexes 2-E undergo 1e oxidation with GaCl 3 to yield (3-E)GaCl 4. Spin density analysis revealed that the unpaired electron in (3-E)C + is mainly located on the Fe (52-64 %) and vinylic C (30-36 %) atoms. Further 1e oxidation of (3-E)GaCl 4 leads to unprecedented h 3-EEC vinyl to h 3-EC vinyl C Ph coordination shuttling to form the dications (4-E)(GaCl 4) 2. Supporting information and the ORCID identification number(s) for the author(s) of this article can be found under:
Angewandte Chemie International Edition, 2021
1,4-Diarsinine-1,4-diide compound [(ADC Ph)As] 2 (5) (ADC Ph = {C(DippN)} 2 CPh, Dipp = 2,6-iPr 2... more 1,4-Diarsinine-1,4-diide compound [(ADC Ph)As] 2 (5) (ADC Ph = {C(DippN)} 2 CPh, Dipp = 2,6-iPr 2 C 6 H 3) with a planar C 4 As 2 ring fused between two 1,3-imidazole scaffolds has been isolated as a red crystalline solid. Compound 5, formally comprising an 8p-electron C 4 As 2 ring, is antiaromatic and undergoes 2e-oxidation with AgOTf to form the 6pelectron aromatic system [(ADC Ph)As] 2 (OTf) 2 (6). Benzene derivatives containing heavier main-group elements (E) in an unsaturated C 6Àn E n ring are highly appealing synthetic targets because of their intriguing electronic structure, reactivity, and physical properties. [1] The close resemblance between benzene (C 6 H 6) and pyridine (C 5 H 5 N) is wellknown, the stability of heavy heteroarenes C 5 H 5 E, however, decreases according to E = P > As > Sb > Bi. [2] This is because of the weak C=E p-interaction, making these species highly reactive. The first breakthrough was made by Märkl in 1966 with the isolation of 2,4,6-Ph 3 C 5 H 2 P. [3] Over the years numerous stable compounds featuring one or more phosphorus atoms in a six-membered unsaturated ring have been reported. [4] In contrast, analogous stable arsenic (as well as Sb and Bi) species remained extremely rare. [5] In 1971, Ashe reported the parent arsabenzene I (Figure 1), [4f] while in 1969, Jutzi [6] and Bickelhaupt [7] independently described the synthesis of 9-arsaanthracene II. In 2001, [8] Ashe and co-workers also reported 1-arsanaphthalenes III. While I was found to be
Angewandte Chemie International Edition, 2021
Chemistry – A European Journal, 2021
Herein, we report the first 1,4-diphosphinine-1,4diide compound [(ADC Ph)P] 2 (5-Ph)(ADC Ph = PhC... more Herein, we report the first 1,4-diphosphinine-1,4diide compound [(ADC Ph)P] 2 (5-Ph)(ADC Ph = PhC{(NDipp)C} 2 ; Dipp = 2,6-iPr 2 C 6 H 3)d erived from an anionic dicarbene (ADC Ph)a sared crystalline solid. Compound 5-Ph containing a1 6 p-electronp lanarf used-tricyclic ring system was obtained by the 4e reduction of [(ADC Ph)PCl 2 ] 2 (4-Ph)w ith Mg (or KC 8)i naquantitative yield. Experimental and computational results imply that the central 8p-electronsC 4 P 2 ring of 5-Ph,w hich is fused between two 6p-electronsC 3 N 2 aromat-[a] Dr.
The Journal of Organic Chemistry, 2020
Phosphinidene complexes of a general formula RPM(CO) n (R = an alkyl or aryl group; M = a transit... more Phosphinidene complexes of a 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 so far a challenge. Herein, we report the first terminal phosphinidene complexes [{(NHC)C(Ph)}P]Fe(CO) 4 (NHC = IPr = C{(NDipp)CH} 2 , 3; Me-IPr = C{(NDipp)CMe} 2 , 4; Dipp = 2,6-iPr 2 C 6 H 3 ; NHC = N-heterocyclic carbene) as red crystalline solids containing a π-donor N-heterocyclic vinyl (NHV) substituent at the phosphorus atom. Calculations reveal the donor-acceptor type bonding between phosphorus and iron atoms in 3 and 4. The P→Fe donation represents ~70 % whereas the Fe→P π-back donation corresponds to ~15 % of the orbital interaction. The phosphorus atom in 3 and 4 carries +0.65e and +0.64e charge, respectively, indicating an electrophilic character of the phosphinidene {(NHC)C(Ph)}P moiety. Accordingly, 3 reacts with an NHC nucleophile (IMe 4) to yield the Lewis adduct [{(NHC)C(Ph)}P(IMe 4)]Fe(CO) 4 (5) (IMe 4 = :C(NMeCMe) 2). The coordination of an electron-rich NHC (IMe 4) to the phosphorus atom in 5 precludes the π-electron density transfer from the NHV to the phosphorus atom. Thus, the C IPr-C Vinyl and C Vinyl-P bonds of 5 become respectively shorter and longer compared to those of 3.
Organometallics, 2020
Imidazole-based mesoionic carbenes (iMICs) are a very promising class of carbon-donor ligands in ... more Imidazole-based mesoionic carbenes (iMICs) are a very promising class of carbon-donor ligands in synthesis and catalysis. However, a systematic study of the quantification of stereoelectronic properties of iMICs is lacking. This is most likely due to the absence of rational synthetic routes to suitable iMIC compounds. Herein, we report the synthesis of the appropriate phosphinidene (iMIC Ar)PPh (iMIC Ar = :CCH(NDipp) 2 CAr; Ar = Ph (5a), DMP (5b); DMP = 4-Me 2 NC 6 H 4 ; Dipp = 2,6-iPr 2 C 6 H 3), selenium (iMIC Ar)Se (Ar = Ph (6a), DMP (6b)), and nickel carbonyl compounds (iMIC Ar)Ni(CO) 3 (Ar = Ph (7a), DMP (7b)). The π-accepting property of iMIC Ar (Ar = Ph (2a), DMP (2b)) has been evaluated by 31 P and 77 Se NMR spectroscopic analyses of 5 and 6, respectively. The overall donor property of 2 has been assessed by determining the Tolman electronic parameter (TEP) of 7. Studies suggest that iMIC Ar (2) are stronger σ donors and weaker π acceptors compared to classical N-heterocyclic carbenes (NHCs). The steric profile of iMIC Ar (2) has been obtained by calculating the percentage buried volume (%V bur) for (iMIC Ar)CuX (Ar = Ph, X = I (8a); Ar = DMP, X = Br (8b)).
Chemical Communications, 2020
The first C5-protonated 1,3-imidazole-based mesoionic carbene (iMICBp) has been isolated and char... more The first C5-protonated 1,3-imidazole-based mesoionic carbene (iMICBp) has been isolated and characterized by single-crystal X-ray diffraction.
Chemical Communications, 2019
The synthesis and characterization of the crystalline diphosphene radical cations [P2]+˙ and dica... more The synthesis and characterization of the crystalline diphosphene radical cations [P2]+˙ and dications [P2]2+featuring a π-conjugated C2P2C2-framework have been reported (Dipp = 2,6- iPr2C6H3).
Chemistry – A European Journal, 2019
The olefinic C-H bond functionalization of (NHC)CHPh (NHC = IPr = C{(NAr)CH}c2 1; SIPr = C{(NAr)C... more The olefinic C-H bond functionalization of (NHC)CHPh (NHC = IPr = C{(NAr)CH}c2 1; SIPr = C{(NAr)CH2}2 2; Ar = 2,6-iPr2C6H3) 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. While the P=P bond lengths of 5 (2.062(1) Å) and 6 (2.055(1) Å) are comparable with those of the known diphosphenes (2.02-2.08 Å), the C-P bond lengths of 5 (1.785(1) Å) and 6 (1.797(1) Å) are, however, considerably shorter than a C(sp2)-P single bond length (1.85 Å), indicating a considerable π-conjugation between C=C and P=P moieties. The HOMO-LUMO energy gap for 5 (4.15 eV) and 6 (4.52 eV) is strikingly small and thus the narrowest among the diphosphenes (> 4.93 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]2Se 8 with an intact P-P bond.
Chemistry – A European Journal, 2019
Para-quinodimethane (pQDM) is a fundamental structural component in many p-conjugated organic mol... more Para-quinodimethane (pQDM) is a fundamental structural component in many p-conjugated organic molecules and materials. The incorporation of phosphorus atom into p-conjugated frameworks offers unique opportunities for controlling the properties of derived species. A phosphorus analogue of p-quinodimethane (pQDM), (IPrC) 2 P 4 [5, IPr = C{N(Ar)CH 2 } 2 ; Ar= 2,6-iPr 2 C 6 H 3 ] featuring a planar P 4 ring, was readily accessible by KC 8-reduction of (IPrC)(PCl 2) 2 (2). Base-mediated CÀH functionalization of IPrCH 2 (1) with PCl 3 afforded 2. The formation of 5 was expected to occur through a dimerization of the transient 3H-diphosphirene (IPrC)P 2 (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 (P 4). The formation of and VI and P 4 suggested the formal diphosphorus (P 2) elimination from 5. Indeed, photolysis of a mixture of 1,3-cyclohexadiene (CHD) and 5 led to the formation of P 2-entrapped product (CHD) 2 P 2 (6). The compound 5 represents the first organophosphorus species that functions as a P 2 source.
Chemistry - A European Journal, 2018
Twofold CC cross-coupling of N-heterocyclic carbenes (NHCs) (SIPr = C{NAr}2CH2CH2,1; IPr = C{NAr}... more Twofold CC cross-coupling of N-heterocyclic carbenes (NHCs) (SIPr = C{NAr}2CH2CH2,1; IPr = C{NAr}2CHCH, 2; Me-IPr = C{NAr)}2CMeCMe, 3; Ar = 2,6-iPr2C6H3) with 4,4ʹʹ-diiodo-p-terphenyl under Ni-catalysis furnished [(SIPr)2(C6H4)3](I)2 (4), [(IPr)2(C6H4)3](I)2 (5), and [(Me-IPr)2(C6H4)3](I)2 (6). Two electron reduction of 4-6 with KC8 readily afforded NHC-analogues of Müller's hydrocarbon (MH), [(SIPr)2(C6H4)3] (7), [(IPr)2(C6H4)3] (8), and [(Me-IPr)2(C6H4)3] (9), respectively, as highly colored crystalline solids. Quantum chemical calculations suggest the singlet ground state for 7-9 with a vertical singlet-triplet energy gap ∆ES-T of-7.24 to-7.60 kcal/mol, which is significantly lower compared to that of the NHC-analogues of Thiele's (TH) and Chichibabin's (CH) (18-38 kcal/mol) 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 to 0.4), suggesting the open-shell singlet character of 7-9.
Chemical science, Jan 14, 2018
The direct double carbenylation of 1,4-diiodobenzene and 4,4'-dibromobiphenyl with a classica... more The direct double carbenylation of 1,4-diiodobenzene and 4,4'-dibromobiphenyl with a classical N-heterocyclic carbene, SIPr () (SIPr = :C{(2,6-iPrCH)}CHCH), by means of nickel catalysis gives rise to 1,3-imidazolinium salts [(SIPr)(CH)(SIPr)](I) () and [(SIPr)(CH)(SIPr)](Br) () as off-white solids. Two-electron reduction of and with KC cleanly yields Kekulé diradicaloid compounds [(SIPr)(CH)(SIPr)] () and [(SIPr)(CH)(SIPr)] (), respectively, as crystalline solids. Structural parameters and DFT as well as CASSCF calculations suggest the closed-shell singlet ground state for and . Calculations reveal a very low singlet-triplet energy gap Δ for (10.7 kcal mol), while Δ for (29.1 kcal mol) is rather large.
Angewandte Chemie (International ed. in English), Jan 16, 2018
One-electron reduction of C2-arylated 1,3-imidazoli(ni)um salts (IPr )Br (Ar=Ph, 3 a; 4-DMP, 3 b;... more One-electron reduction of C2-arylated 1,3-imidazoli(ni)um salts (IPr )Br (Ar=Ph, 3 a; 4-DMP, 3 b; 4-DMP=4-Me NC H ) and (SIPr )I (Ar=Ph, 4 a; 4-Tol, 4 b) derived from classical NHCs (IPr=:C{N(2,6-iPr C H )} CHCH, 1; SIPr=:C{N(2,6-iPr C H )} CH CH , 2) gave radicals [(IPr )] (Ar=Ph, 5 a; 4-DMP, 5 b) and [(SIPr )] (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.
Angewandte Chemie (International ed. in English), Jan 18, 2018
Stable N-heterocyclic carbene analogues of Thiele and Chichibabin hydrocarbons, [(IPr)(C H )(IPr)... more Stable N-heterocyclic carbene analogues of Thiele and Chichibabin hydrocarbons, [(IPr)(C H )(IPr)] and [(IPr)(C H ) (IPr)] (4 and 5, respectively; IPr=C{N(2,6-iPr C H )} CHCH), are reported. In a nickel-catalyzed double carbenylation of 1,4-Br C H and 4,4'-Br (C H ) with IPr (1), [(IPr)(C H )(IPr)](Br) (2) and [(IPr)(C H ) (IPr)](Br) (3) were generated, which respectively afforded 4 and 5 as crystalline solids upon reduction with KC . Experimental and computational studies support the semiquinoidal nature of 5 with a small singlet-triplet energy gap ΔE of 10.7 kcal mol , whereas 4 features more quinoidal character with a rather large ΔE of 25.6 kcal mol . In view of the low ΔE , 4 and 5 may be described as biradicaloids. Moreover, 5 has considerable (41 %) diradical character.
Dalton Transactions, 2017
The NHC ligand of the complex 3-W undergoes normal-to-abnormal rearrangement on treatment with Cs... more The NHC ligand of the complex 3-W undergoes normal-to-abnormal rearrangement on treatment with CsOH and yields the aNHC-complex 6-W, which is found to be 13.5 kcal mol−1 less stable than its normal counterpart.
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Papers by Dennis Rottschäfer