Photolysis Of 2a Research Articles

Computational Study on the Mechanisms of Multiple Complexation of CO and Isonitrile Ligands to Boron.

The recent experimental realization of compound Tripp-B(CO)2 (denoted as 2a), where Tripp is 2,6-di(2,4,6-triisopropylphenyl)-phenyl), breaks through conventional knowledge that only transition metals can bind more than one CO to form multicarbonyl adducts. Compound 2a is stable in air but liberates CO under light. The B-CO bonds of 2a are considered to be similar to donor-acceptor bonds of transition metal complexes. To address the formation mechanism and chemical bonding of this novel type of boron compounds, we present a density functional theory study on the formation and photolysis of 2a and similar compounds. The results suggest that the formation of 2a is facile by three consecutive additions of CO to the terminal borylene metal complex, that is, the boron source of the synthesis. These CO additions can be practically accomplished via two different paths: CO direct addition and CO migration followed by addition. Such mechanisms can be excellently rationalized by the donor-acceptor bonding model of the terminal borylene complex, which in turn suggests that using donor-acceptor bonds for 2a is natural for understanding the mechanisms. Liberation of CO from 2a and its similar compounds has higher energy barriers at the ground states than that at the triplet states by 40 kcal/mol. These energy barriers explain the experimentally observed air stability and photolysis of these compounds. The results for the first time provide mechanistic insights for the unprecedented chemical processes; they allow evaluation of the applicability of donor-acceptor bonding in main-group compounds from the new perspective of chemical reactions.

Ultrafast Infrared and UV–Vis Studies of the Photochemistry of Methoxycarbonylphenyl Azides in Solution

The photochemistry of 4-methoxycarbonylphenyl azide (2a), 2-methoxycarbonylphenyl azide (3a), and 2-methoxy-6-methoxycarbonylphenyl azide (4a) were studied by ultrafast time-resolved infrared (IR) and UV-vis spectroscopies in solution. Singlet nitrenes and ketenimines were observed and characterized for all three azides. Isoxazole species 3g and 4g are generated after photolysis of 3a and 4a, respectively, in acetonitrile. Triplet nitrene 4e formation correlated with the decay of singlet nitrene 4b. The presence of water does not change the chemistry or kinetics of singlet nitrenes 2b and 3b, but leads to protonation of 4b to produce nitrenium ion 4f. Singlet nitrenes 2b and 3b have lifetimes of 2 ns and 400 ps, respectively, in solution at ambient temperature. The singlet nitrene 4b in acetonitrile has a lifetime of about 800 ps, and reacts with water with a rate constant of 1.9 × 10(8) L·mol(-1)·s(-1) at room temperature. These results indicate that a methoxycarbonyl group at either the para or ortho positions has little influence on the ISC rate, but that the presence of a 2-methoxy group dramatically accelerates the ISC rate relative to the unsubstituted phenylnitrene. An ortho-methoxy group highly stabilizes the corresponding nitrenium ion and favors its formation in aqueous solvents. This substituent has little influence on the ring-expansion rate. These results are consistent with theoretical calculations for the various intermediates and their transition states. Cyclization from the nitrene to the azirine intermediate is favored to proceed toward the electron-deficient ester group; however, the higher energy barrier is the ring-opening process, that is, azirine to ketenimine formation, rendering the formation of the ester-ketenimine (4d') to be less favorable than the isomeric MeO-ketenimine (4d).

Redox Isomerization of Allylic Alcohols Catalyzed by Osmium and Ruthenium Complexes Containing a Cyclopentadienyl Ligand with a Pendant Amine or Phosphoramidite Group: X-ray Structure of an η3-1-Hydroxyallyl-Metal-Hydride Intermediate

Complexes [MCl2(η6-p-cymene)]2 (M = Os (1a), Ru (1b)) react with Li(C5H4CH2CH2NHMe) (LiCpN) and KPF6 to give the sandwich derivatives [M(η5-CpN)(η6-p-cymene)]PF6 (M = Os (2a), Ru (2b)). Treatment of 2a and 2b with (2,2′-biphenol)PCl leads to [M(η5-CpP)(η6-p-cymene)]PF6 (M = Os (3a), Ru (3b); CpP = C5H4CH2CH2N(Me)P(2,2′-biphenol)). The photolysis of 2a, 2b, 3a, and 3b in acetonitrile produces the release of the p-cymene group and the coordination of the cyclopentadienyl pendant substituent to the metal center to afford [M(η5-C5,κ-N-CpN)(CH3CN)2]PF6 (M = Os (4a), Ru (4b)) and [M(η5-C5,κ-P-CpP)(CH3CN)2]PF6 (M = Os (5a), Ru (5b)). Complex 4a, which has been characterized by X-ray diffraction analysis, is a more efficient catalyst precursor than 4b for the redox isomerization of primary allylic alcohols, while the latter is more efficient than the former for the redox isomerization of secondary allylic alcohols. From the catalytic solutions containing 4a and 2-methyl-2-propen-1-ol, the η3-1-hydroxyallyl comple...

Isomeric Metamorphosis: Si3E (E = S, Se, and Te) Bicyclo[1.1.0]butane and Cyclobutene

Group 14 and 16 hybrid heavy bicyclo[1.1.0]butanes (tBu2MeSi)4Si3E (E = S, Se, and Te) 2a-c have been prepared by the [1 + 2] cycloaddition reaction of trisilirene 1 and the corresponding chalcogen. Bicyclo[1.1.0]butanes 2 have exceedingly short bridging Si-Si bonds (2.2616(19) A for 2b and 2.2771(13) A for 2c), a phenomenon explained by the important contribution of the trisilirene-chalcogen pi-complex character to the overall bonding of 2. Photolysis of 2a and 2b produced their valence isomers, the heavy cyclobutenes 3a and 3b, featuring flat four-membered Si3E rings and a planar geometry of the Si=Si double bond. The mechanism of such isomerization was studied using deuterium-labeled 2a-d6 to ascertain the preference of the pathway, involving the direct concerted symmetry-allowed transformation of bicyclo[1.1.0]butane 2 to cyclobutene 3.

2+2]-Cycloaddition and Subsequent meso/rac ansa-Metallocene Interconversion by Photolysis of a Bis(1,3-dialkenylcyclopentadienyl)zirconium Complex

6,6-Dimethylfulvene (5) was treated with acetone under basic conditions to yield 3-(1-methylethenyl)-6,6-dimethylfulvene (7). Deprotonation with LDA followed by transmetalation with 0.5 molar equiv of zirconium tetrachloride gave bis[1,3-di(1-methylethenyl)C5H3]zirconium dichloride (3a). Photolysis of 3a with Pyrex-filtered UV/vis light at ambient temperature led to a rapid intramolecular [2+2]-cycloaddition reaction to yield a 1:1 mixture of the meso- and rac-isomers of the corresponding singly cyclobutylene-bridged ansa-metallocene system 4a. Photolysis of this mixture with quartz-filtered UV light at −80 °C very slowly converted meso-4a to rac-4a. Over 2 days a 12:1 ratio of rac/meso-4a was achieved under these conditions.

Ring-opening reaction of phosphorus-bridged [1]ferrocenophane via ring slippage from eta(5)- to eta(1)-Cp.

A reaction mechanism was investigated for a ring-opening reaction of RP(E)-bridged [1]ferrocenophane, where RP(E) = PhP(S) (3a), PhP (3b), and MesP (3c) (Mes = 2,4,6-trimethylphenyl). Irradiation of UV-vis light in the presence of an excess amount of P(OMe)(3) transformed 3a to [Fe(PhP(S)(eta(5)-C(5)H(4))(eta(1)-C(5)H(4)))(P(OMe)(3))(2)] (4a), in which one of the two cyclopentadienyl (Cp) rings of 3a changed its coordination mode from eta(5) to eta(1) and vacant coordination sites thus formed on the iron center were occupied by two P(OMe)(3) ligands. The molecular structure of 4a was determined by X-ray analysis, in which eta(1)-Cp adopted a 1-Fe-2-P-1,3-cyclopentadiene structure. Under the same reaction conditions, 3b and 3c also gave similar ring-slipped products 4b and 4c, respectively. Photolysis of 3a using more strongly coordinating PMe(3) in place of P(OMe)(3) led to complete dissociation of a Cp ligand from the iron center to form [Fe(PhP(S)(eta(5)-C(5)H(4))(C(5)H(4)))(PMe(3))(3)] (5). The formation of the ring-slipped and -dissociated products on the photolysis of 3 strongly supports the view that photolytic ring-opening polymerization of 3 proceeds via an unprecedented Fe-Cp bond cleavage mechanism.

Ligand-Induced Conversion of π to σ C60−Metal Cluster Complexes: Full Characterization of the μ3-η1:η2:η1-C60 Bonding Mode

The reaction of Os3(CO)9(μ3-η2:η2:η2-C60) (1) with PhCH2NPPh3 in chlorobenzene affords the benzyl isocyanide substituted product Os3(CO)8(CNR)(μ3-η2:η2:η2-C60) (2a, R = CH2Ph) in 76% yield. Photolysis of 1 in the presence of an excess of benzyl isocyanide gives the isocyanide-inserted product Os3(CO)9(μ3-CNR)(μ3-η1:η2:η1-C60) (2b) in 11% yield. Thermal reaction of 2a with an excess of RNC in chlorobenzene at 80 °C produces two isocyanide-inserted, isomeric products, Os3(CO)8(CNR)(μ3-CNR)(μ3-η1:η2:η1-C60) (3a, 22%; 3b, 27%). The two isomers 3a and 3b can be selectively prepared by photolysis of 2a in the presence of excess isocyanide in 49% yield and by decarbonylation of 2b with Me3NO/MeCN and subsequent reaction with isocyanide in 56% yield, respectively. Compounds 2a,b and 3a,b have been characterized by microanalytical and spectroscopic methods. In particular, the sp3 carbons of M−C(C60) σ-interactions in μ3-η1:η2:η1-C60 complexes exhibit unique upfield resonances around 39 ppm in the 13C NMR spectra, compared to the π-bonded sp3 carbon resonances observed in the range of 95−65 ppm. The X-ray crystallographic studies for 2a,b and 3a,b reveal that μ3-η2:η2:η2-C60 ligands in 1 and 2a transform into new σ-type μ3-η1:η2:η1-C60 ligands in 2b and 3a,b by insertion of the isocyanide ligand concomitant with Os−Os bond cleavage, forming a bent triosmium framework. In compounds 2b and 3b, a boat-shaped 1,4-cyclohexadiene-like C6 ring in the C60 molecule is clearly observed and the M−C60 σ-bond distances (average 2.24 Å) are shorter than the π-bond lengths (average 2.41 Å). This study represents a novel ligand-induced conversion of π to σ C60−metal complexes.

Mononuclear (nitrido)iron(V) and (oxo)iron(IV) complexes via photolysis of [(cyclam-acetato)FeIII(N3)]+ and ozonolysis of [(cyclam-acetato)FeIII(O3SCF3)]+ in water/acetone mixtures.

Reaction of the monoanionic, pentacoordinate ligand lithium 1,4,8,11-tetraazacyclotetradecane-1-acetate, Li(cyclam-acetate), with FeCl3 yields, upon addition of KPF6, [(cyclam-acetato)FeCl]PF6 (1) as a red microcrystalline solid. Addition of excess NaN3 prior to addition of KPF6 yields the azide derivative [(cyclam-acetato)FeN3]PF6 (2a) as orange microcrystals. The X-ray crystal structure of the azide derivative has been determined as the tetraphenylborate salt (2b). Reaction of 1 with silver triflate yields [(cyclam-acetato)Fe(O3SCF3)]PF6 (3), which partially dissociates triflate in nondried solvents to yield a mixture of triflate and aqua bound species. Each of the iron(III) derivatives is low-spin (d5, S = 1/2) as determined by variable-temperature magnetic susceptibility measurements, Mössbauer and EPR spectroscopy. The low-spin iron(II) (d6, S = 0) complexes 1red and 2ared have been prepared by electrochemical and chemical methods and have been characterized by Mössbauer spectroscopy. Photolysis of 2a at 419 nm in frozen acetonitrile yields a nearly colorless species in approximately 80% conversion with an isomer shift delta = -0.04 mm/s and a quadrupole splitting delta EQ = -1.67 mm/s. A spin-Hamiltonian analysis of the magnetic Mössbauer spectra is consistent with an FeV ion (d3, S = 3/2). The proposed [(cyclam-acetato)FeV=N]+ results from the photooxidation of 2a via heterolytic N-N cleavage of coordinated azide. Photolysis of 2a in acetonitrile solution at -35 degrees C (300 nm) or 20 degrees C (Hg immersion lamp) results primarily in photoreduction via homolytic Fe-Nazide cleavage yielding FeII (d,6 S = 0) with an isomer shift delta = 0.56 mm/s and quadrupole splitting delta EQ = 0.54 mm/s. A minor product containing high-valent iron is suggested by Mössbauer spectroscopy and is proposed to originate from [((cyclam-acetato)Fe)2(mu-N)]2+ with a mixed-valent (FeIV(mu-N)FeIII))4+S = 1/2 core. Exposure of 3 to a stream of oxygen/ozone at low temperatures (-80 degrees C) in acetone/water results in a single oxidized product with an isomer shift delta = 0.01 mm/s and quadrupole splitting delta EQ = 1.37 mm/s. A spin-Hamiltonian analysis of the magnetic Mössbauer yields parameters similar to those of compound II of horseradish peroxidase which are consistent with an FeIV=O monomeric complex (S = 1).

Synthesis and structures of bis(silylene)iron complexes containing new six-membered chelate rings

Reaction of Cp′Fe(CO) 2SiMe 2SiMe 2Cl ( 1a: Cp′=η 5-C 5H 5 (Cp), 1b: Cp′=η 5-C 5Me 5 (Cp*)) with acetic acid in the presence of base (pyridine or Et 3N) afforded Cp′Fe(CO) 2SiMe 2SiMe 2OCOMe ( 2a: Cp′=Cp, 77%; 2b: Cp′=Cp*, 87%). Similarly, the reaction of 1b with 2-pyridone in the presence of Et 3N gave Cp*Fe(CO) 2SiMe 2SiMe 2O(2-C 5H 4N) ( 3, 43%). Photolysis of 2a, 2b, and 3 produced Cp′(CO)Fe{SiMe 2⋯OC(Me)O⋯SiMe 2} ( 4a: Cp′=Cp, 4b: Cp′=Cp*) and Cp*(CO)Fe{SiMe 2⋯O(2-C 5H 4N)⋯SiMe 2} ( 5) quantitatively, in which an acetoxy or 2-pyridyloxy group bridges two silylene ligands to form a six-membered chelate ring. 4a and 5 were structurally characterized by single-crystal X-ray diffraction experiments. All the FeSi bonds are significantly shorter than normal FeSi single bonds and are consistent with their unsaturated bond character. The six-membered chelate ring consists of two entirely different and delocalized unsaturated bond systems.

Conformational isomers of 1,2,5,6-tetrathiocins and the photoisomerization of a 1,2,5,6-tetrathiocin into a 1,2,3,6-tetrathiocin: X-ray structures of (C6X4S2)2 (X = F, Cl) and C6F4SSSC6F4S

The 1,2,5,6-tetrathiocins (C6X4S2)2 (3a, X = F; 3b, X = Cl) are obtained in high yields by the oxidation of the dithiols 1,2-C6X4(SH)2 (X = F, Cl) with I2 or SO2Cl2, respectively. In the solid state 3a has the C2h (chair) conformation and crystallizes in two different phases: alpha-(C6F4S2)2, monoclinic, P21/a, a = 9.351(2), b = 6.465(2), and c = 11.546(2) Å, ß = 95.60(1)°, V = 694.6(2) Å3, Z = 2; and ß-(C6F4S2)2, monoclinic, P21/c, a = 4.825(2), b = 11.302(2), and c = 12.453(2) Å, ß = 91.45(3)°, V = 678.8(3) Å3, Z = 2. By contrast, 3b displays a D2 (twist-boat) structure and crystallizes in the C2/c space group with a = 15.243(3), b = 8.703(2), and c = 27.010(14) Å, ß = 92.81(4)°, V = 3578(1) Å3, and Z = 8. The derivative 3a exists as an equilibrium mixture of two conformational isomers in toluene solution. The VT 19F NMR data afford the thermodynamic parameters H° = 9.9 ± 0.4 kJ mol-1 and S° = 14 ± 1 J K-1 mol-1. Density functional theory calculations for 3a indicate that the D2 conformation is lower in energy than the C2h isomer by 4.6 kJ mol-1. The photolysis of 3a in benzene promotes a transannular sulfur migration to give the 1,2,3,6-tetrathiocin, C6F4SSSC6F4S (6), which exists in a chair conformation with respect to antipodal sulfur atoms. Crystal structure of 6: orthorhombic, space group Pnma, a = 8.652(6), b = 19.084(4), and c = 8.301(6) Å, V = 1370.6(14) Å3, and Z = 4. The isomers 3a and 6 were also characterized by EI mass spectrometry, 19F NMR, FTIR, and Raman spectroscopies.Key words: tetrathiocins, conformational isomers, photoisomerization.

Photocycloaddition of 5,5-dimethyl-6-oxocyclohex-1-ene-1-carbonitrile to alkenes

While irradiation (350 nm) of the title cyanocyclohexenone 3a in the presence of 2,3-dimethylbut-2-ene affords hexahydroindeno-1,2-oxazole 6 selectively, photolysis of 3a in the presence of 2-methylbut-2-ene or isobutene gives mixtures of tricyclic 1,2-oxazoles and 2-oxobicyclooctane-1-carbonitriles, the product ratio oxazole/bicyclooctane decreasing with increasing I p of the alkene. The constitution of the photoproducts indicate that oxazoles and bicyclooctanes result from two isomeric triplet 1,4-biradicals, formed by addition of the less substituted C-atom of the alkene to either of the olefinic C-atoms of triplet 3a, respectively.

C-Centred chiral metal alkyls, [MR*(Cl)(η-C5H5)2], rac- and meso-[ZrR*2(η-C5H5 )2] [R* = CH(SiMe3)C6H4 Me-o], and their one-electron reductions; reaction of Li[CH(SiMe3)2](Me2NCH2CH 2NMe2) with [MCl2(η-C5H5)2] (M = Zr or Hf )

The chloro(alkyl)metallocenes [MR*(Cl)(η-C 5 H 5 ) 2 ] [R* = - CH(SiMe 3 )C 6 H 4 Me-o; M = Zr 1 or Hf 2] have been prepared from [MCl 2 (η-C 5 H 5 ) 2 ] and LiR*(tmen) (tmen = N,N,N′,N ′-tetramethylethane-1,2-diamine); further alkylation occurred only for M = Zr, affording rac-3a and meso-3b, [ZrR* 2 (η-C 5 H 5 ) 2 ]. In contrast, reaction of 2 equivalents of Li[CH(SiMe 3 ) 2 ](tmen) with [ZrCl 2 (η-C 5 H 5 ) 2 ] yielded an alkyl elimination product possessing µ-η 1 ∶η 5 -C 5 H 4 2- ligands. Compound 1 was reversibly reduced (E 1/2 red = -1.72 V vs. saturated calomel electrode, SCE) whereas 2, 3a or 3b were irreversibly reduced (E red = -2.12, -2.08, -2.00 V respectively vs. SCE). Thermolysis of 3b in toluene gave 3a (80 °C) or ‘Zr(C 10 H 8 )’ (120 °C). Photolysis of 3a or 3b at 20 °C in tetrahydrofuran (thf) yielded a 1∶1 mixture of 3a and 3b; a d 1 intermediate has been unambiguously identified as [ZrR*(η-C 5 H 5 ) 2 ]. Reduction of 1 (Na–Hg), or 3a and 3b (Na[C 10 H 8 ]), in thf also gave [ZrR*(η-C 5 H 5 ) 2 ] but this slowly transformed into [ZrR*(η-C 5 H 5 ) 2 (thf)], and 1 with Na[C 10 H 8 ] and PPh 3 gave [ZrR*(η-C 5 H 5 ) 2 (PPh 3 )]. Reduction of 1, 3a or 3b, or photolysis of 3a or 3b, in the presence of PMe 3 gave [ZrR*(η-C 5 H 5 ) 2 (PMe 3 )]. Crystal structure determinations showed a slightly more crowded metal environment in 2 than in 1, consistent with the view that dialkylation in 2 is limited on steric grounds; M–σ-C 2.359(4) (1), 2.322(8) (2), metal–centroid 2.22 (1), 2.21 (2), M–Cl 2.444(1) (1), 2.418(3) (2) A. The structure of 3a confirms the rac assignment, M–σ-C 2.37 4 A, metal–centroid 2.23, 2.24 A.

Imido and amido complexes of hydrotris(pyrazolyl)borate-rhenium

Rhenium(V) para-tolylimido complexes TpRe(NTol)X 2 (X = Cl ( 2a); I ( 2b)) are formed on refluxing the oxo derivatives TpRe(O)X 2 (X = Cl ( 1a); I ( 1b)) with para-toluidine (Tp = hydrotris(pyrazalyl)borate; Tol = para-tolyl). Reaction of 2a with ZnEt 2 in benzene gives the imido-ethyl complex TpRe(NTol)(Et)Cl (( 3) Et = CH 2CH 3), which was characterized by an X-ray crystal structure. Photolysis of 2a and 3 apparently lead to ReI and ReC bond homolysis, as in their oxo congeners, but the analogous photoproducts are not observed. Reaction of 1a with amines at ambient temperatures leads to the oxo-amido compounds TpReO(NRR′)Cl. Complexes with primary amido ligands, TpReO(NHR)Cl (R = Et ( 4); nPr ( 5); iPr ( 6)) exist as two isomers by 1H NMR. Similarly, NMR spectra of compounds with symmetrical amido ligands, TpReO(NR 2)Cl (R = H ( 7); Et ( 8); NR 2 = piperidyl ( 9)), show inequivalent substituents. These data indicate restricted rotation about the ReN amido bond. Based on the X-ray crystal structure of 8, the barrier to rotation is electronic as well as steric in origin.

Silicon−Carbon Unsaturated Compounds. 57. Photolysis of meso- and racemic-1,2-Diethyl-1,2-dimethyldiphenyldisilane, Direct Evidence for a Concerted 1,3-Silyl Shift to ortho-Carbon in the Phenyl Ring

meso- and racemic-1,2-diethyl-1,2-dimethyldiphenyldisilane (2a) and (2b) were synthesized respectively by hydrogenation of meso- and racemic-1,2-diethynyl-1,2-dimethyldiphenyldisilane in the presence of a IrCl(CO)(PPh3)2 catalyst. Irradiation of 2a with a low-pressure mercury lamp in the presence of isobutene in hexane proceeded with high diastereospecificity to give (R,S)- and (S,R)-2-(isobutylethylmethylsilyl)-1-(ethylmethylphenylsilyl)benzene in 77% yield. Similar irradiation of 2b with isobutene produced (R,R)- and (S,S)-isomer. The photolysis of 2a and 2b in the presence of 1,1-diphenylethylene also proceeded diastereospecifically to give the respective adducts. With 2,3-dimethylbutadiene, 2a and 2b produced the corresponding adducts, whose spectrometric analysis showed the presence of two diastereomers. Results on theoretical studies which were carried out using PhSiH2SiH3 as a model have also been reported.

Unusual reactivities of (μ-η 2:η 2-FPCCH)Co 2(CO) 6, the adducts of FPCCH to Co 2(CO) 8: photolysis, thermolysis and reduction with hydrosilanes giving polynuclear complexes, (CP) 2Fe 2Co 3(μ 5-CCH)(CO) 10, (μ-CHCH)[(−μ 3-C)Co 3(CO) 9] 2 and CpFeCo 3(μ-CCH 2)(CO) 9

The properties and reactivities of (μ-η 2:η 2-FPCCH)Co 2(CO) 6, ( 3) [the FPCCH adducts to Co 2(CO) 8: 3a (FP  Fp), 3b (FP  Fp★)] have been compared with those of alkyne adducts (μ-η 2:η 2-RCCR)Co 2(CO) 6 and the Ph analogue (μ-η 2:η 2-FpCCPh)Co 2(CO) 6 ( 5). Compound 3 has been shown to serve as a building block for polynuclear complexes. 13CO-labelling experiments on 3a and 5 have revealed an intramolecular exchange between the FECO and CoCO ligands. Photolysis of 3a, b produces pentanuclear clusters (CP) 2Fe 2CO 3(μ 5-CCH)(CO) 10 ( 11a, b), respectively, via an apparent addition reaction of a (CP)FeCo(CO) n , fragment to 3. On the other hand, thermolysis of 3a gives the Fe-free hexacobalt cluster compound (μ-CHCH)-[(-μ 3-C)Co 3(CO) 9] 2 ( 13) which consists of two alkylidyne tricobalt units linked by the CHCH bridge, whereas 3b is thermolyzed to give the FeCo dimer without the C 2H ligand, Cp★Fe(CO)(μ-CO) 2Co(CO) 3 ( 14), in addition to the photolysis product 11b. Reduction of 3 with hydrosilanes gives a mixture containing 1,2-disilylethylene ( 16) and the tetranuclear μ-vinylidene cluster CpFeCo 3(μ 4-CCH 2)(CO) 9 ( 12) formally by way of hydrosilylation and hydrometallation (with a HCo(CO) n species) of the C 2H ligand, respectively. In the case of the Pauson-Khand reaction and catalytic cyclotrimerization 3a exhibits reactivities similar to alkyne adducts to give the tricyclic cyclopentenone derivatives 18 (from norbornene and norbornadiene) and triphenylbenzenes, respectively.

2-Azoniaallenyliden-Komplexe des Mangans - Synthese, Struktur und Reaktivität

Cp(CO) 3Mn ( 1) reacts with [NC(R 1)R 2] − and [Et 3O]BF 4 to give alkylideneamino(ethoxy)carbene complexes, Cp(CO) 2MnC(OEt)NC(R 1)R 2 ( 3) [C(R 1)R 2  CPh 2 ( a), C(C 6H 4) 2O ( b), C(CMe 3) 2 ( c), C(CMe 3)Tol ( d), Tol = C 6H 4Me- p]. From 1, [NCPh 2] − and MeOSO 2F the complex Cp(CO) 2 MnC(OMe)NCPh 2 ( 4a) is obtained. The reaction of 1 with [NC( iPr)Ph] − and Me 3SiCl, however, yields an isocyanide complex, Cp(CO) 2MnC  NC(Ph)CMe 2 ( 7). Photolysis of 3a in THF in the presence of PTol 3 affords Cp(CO)(PTol 3)MnC(OEt)NCPh 2 ( 6a). According to the X-ray structure analysis of 4a the CNC fragment is strongly bent (CNC angle: 130.0(2)°) and both CN distances are significantly different. Alkoxide abstraction from 3a- c 4a and 6a by BF 3 gives 2-azoniaallenylidene complexes 13a- c and 14a, [Cp(CO)(R)Mn CNC(R 1)R 2]BF 4 [R  CO( 13), PTol 3 ( 14a)], respectively. The structure of 14a-BF 4 has also been determined by an X-ray diffraction analysis. The MnCNC fragment is almost linear and allows the formation of two orthogonal π-systems. Both CN distances differ significantly. The complexes are best described as hybrids of three resonance structures with that of the carbocationic structure beeing the main contributor. Accordingly, 13a-BF 4 adds a number of nucleophiles (OEt 2, PMe 3, H −, Me −, tBuSH, PHPh 2, PH 2Mes) at the terminal carbon of the MnCNC fragment to give, depending on the nucleophile, cationic or, after H + abstraction, neutral isocyanide complexes.

Alkylthio-substituierte Bis(benzol-1,2-dithiolato)zinkate, Benzol-1,2-dithiole und -1,2-dithiolate - Edukte f�r Dibenzo[c,g](1,2,5,6)tetrathiocine und Benzo[c](1,2,3)-trithiole; Untersuchungen zu Benzodithieten und ortho-Dithiobenzochinonen

Alkylthiosubstituted Bis(benzene-1,2-dithiolato)zincates, Benzene-1,2-dithioles, and -1,2-dithiolates – Educts for Dibenzo[c,g](1,2,5,6)tetrathiocins, and Benzo[c](1,2,3)trithioles; Investigations on Benzodithietes and ortho-Dithiobenzochinones Using benzenehexathiolate 1 it is possible to synthesize alkylthio-substituted benzo-1,3-dithiole-2-thiones 2, or -ones 3 and benzo-di(1,3-dithiole-2-thiones) 4, or -ones 5, resp., which were cleaved under basic conditions. The generated benzene-1,2-dithiolates 7 were isolated as benzene-dithiolato zincates 8, benzene-1,2-dithioles 11, and benzene-1-thiole-2-thiolates 10. Dibenzo[c,g](1,2,5,6)-tetrathiocins 9 were synthesized by oxidation of 7 or 8 in good yields. For the per(methylthio)-substituted tetrathiocin 9a the twist conformation was proved by x-ray structure analysis. The tetrathiocin 9a was probably formed via the orthodithiobenzoquinone 13a. Photolysis of 3a at room temperature in solution led to 9a and tetrakis(methylthio)benzo[c] (1,2,3)trithiole 12a as the main product, which was also formed by irradiation of 9a. The trithioles 12 were formed from 8 by reaction with sulfur dichloride. 12a was investigated by x-ray structure analysis. ortho-Dithiobenzoquinone 13c can be claimed as an intermediate upon irradiation of benzo-1,3-dithiol-2-one 3c in an argon matrix at 10 K. Depending on the wavelength the equilibrium lies either on the side of dithiobenzoquinone 13c or benzodithiete 14c. The same is true for system 15/16, which can be reached by flash vacuum pyrolysis of 3c.

Photochemistry of N ‐Phthaloyl α‐Amino Acid Esters: A New Approach to β,γ‐Unsaturated α‐Amino Acid, Dihydrobenzazepinedione, and Pyrrolizidinone Derivatives

The N-phthaloyl-α-amino acid methyl esters of 2-aminobutyric acid (2a), valine (2b), norvaline (2c), tert-leucine (2d), isoleucine (2e), allo-isoleucine (2f), leucine (2g), methionine (2h), alanine (2i), and phenylalanine (2k) were synthesized in enantiomerically pure form via the N-phthaloyl-α-amino acids (1a–k), and their photochemistry was studied. Except 2i and 2k, which proved to be photostable, all compounds were converted into three types of products, depending on the substitution pattern: a) isomerization products (derivatives of β,γ-unsaturated α-amino acids) 3a, b, c, and e, b) ring expansion products (benzazepinedione esters) 4a and c, and c) cyclization products (5d from the tert-leucine derivative 2d). High diastereoselectivities (d.r. > 95:5) were observed for all reactions except the transformations of the 2-aminobutyric acid derivative 2a. The absolute configuration of the α-stereogenic center was retained during photolysis, as proven for the isode-hydrovaline (type a product) 3b. PCC oxidation (to give 7b) and hydrogenation afforded 2b with an optical rotation comparable to the starting material. Treatment of 3b with an acid or a base led to epimerization (3b′) or isomerization of the C = C bond (6b), respectively. The diastereomeric dihydrobenz-azepinedione esters 4a, b were formed with d.r. = 33:67 (cis: trans) and in 60% yield during photolysis of 2a. The isoleucine derivative 2e, however, was converted into the cis isomer 4a with high diastereoselectivity (d.r. >95:5), whereas the corresponding allo substrate 2f was only converted into the trans-isomer 4b. Ethylene was extruded during irradiation of the latter substrates and during irradiation of the norvaline derivative 2c, whereas propene extrusion from the leucine derivative 2g led to the formation of the unsubstituted type b product 4c. The methionine derivative 1h was the only N-phthaloylamino acid which did not show photodecarboxylation, instead two ζ-hydrogen abstraction products were formed: the hydroxy acid 9h and the tetracyclic lactone 10h. The methionine ester 2h was only converted into the ring expansion products 11h, h′ presumably by a photo electron transfer step. The chronology of the double hydrogen transfer reaction (γ- followed by δ-H abstraction, leading to type a products) was determined by using the deuterium labeled compound (±)[3–D1]-2b.

Trifluormethylisocyanidkomplexe des chroms, molydäns und wolframs, hexakis(trifluormethylisocyanid)chrom

Tricarbonyl-tris(trifluoromethyl isocyanide)molybdenum ( 3a) and -tungsten ( 3b) are formed upon reaction of trifluoromethyl isocyanide ( 1) with tricarbonyl(η 6-cycloheptatrien)molydenum ( 2a) and -tungsten ( 2b), respectively. The NMR spectra indicate that these compounds are formed as the meridial isomers. Photolysis of 3a and 3b in the presence of 1 yields unseparable mixtures of the compounds (CO) x M(CNCF 3) 6− x . The homoleptic trifluoromethyl isocyanide complex hexakis(trifluoromethyl isocyanide)chromium ( 5) has been synthesized in low yields by reaction of tris(η 3-allyl)chromium ( 4) with 1. The yellow air-stable crystals of 5 possess a high vapour pressure at ambient temperature, and are thermally stable up to 180°C. The structure of 5 has been determined by an X-ray diffraction study.

Charakterisierung und photochemie von (dihalogenmethylen)sulfoxiden, XYCSO

Abstract Dihalogenomethylene sulfoxides (dihalogenosulfines) 2a – c were generated by flash vacuum pyrolysis of 2,2,4,4-tetrahalogeno-1,3-dithietane 1,3-dioxides 1a – c and trapping the pyrolysis products in argon at 10 K. At room temperature unstable difluorosulfine ( 2a ) and chlorofluorosulfine ( 2b ) were identified by i.r. spectroscopy, and the photochemistry of the sulfines was investigated. Chlorofluorosulfine ( 2b ) exists in two geometrical isomers. Photolysis of 2a leads to fragmentation to give CF 2 and SO, photolysis of the chlorine containing sulfines 2b and 2c to rearrangement to give the sulfenyl chlorides 6 and 8 . This is explained by different migratory tendencies of fluorine and chlorine and the stability of the CF bond.