Synthesis of (E)-2-chlorovinyltellurium trichloride and (E,E)-bis(2-chlorovinyl) ditelluride

The reaction of tellurium tetrachloride with acetylene in CCl₄ at atmospheric pressure and ambient temperature affords earlier unknown (E)-2-chlorovinyltellurium trichloride in 30% yield, whose reduction with sodium bisulfite gives (E,E)-bis(2-chlorovinyl) ditelluride in 64% yield.     

Transient Dipnictyl Analogues of Acrylamides,R−E=E′−CONR2, and a Related Diphosphadigalletane from Na[OCP] and (R2N)2ECl (E,E′=P,As, Ga)

The reaction of Na[OCP] with (R₂N)₂ECl (E=P or As; R=alkyl) granted direct access to transient amine-substituted diphospha- and arsaphospha-acrylamide analogues, (R₂N)E=P(CONR₂) 1 . Their facile formation allowed for a comprehensive reactivity study. Dimerization yielded the four-membered rings (R₂N)₂E₂P₂(CONR₂)₂, whereas in the presence of excess Na[OCP], a stepwise [2+2] cycloaddition occured, leading to the sodium salts of carboxotripnictides [(R₂N)EP₂CO(CONR₂)]⁻. These salts served as a reservoir of 1 , either by extrusion of Na[OCP] or by reaction with the appropriate (R₂N)₂ECl, giving the [4+2]-cycloaddition products (R₂N)EP(C₆H₁₀)(CONR₂) in the presence of 2,3-dimethylbutadiene. The formal conjugate addition product K[(tBuO)(R₂N)PP(CONR₂)] was obtained by reaction of Na[(R₂N)PP₂CO(CONR₂)] with tBuOK. In addition, a rare diphosphadigalletane with a ladder-type (R₂N)₂Ga₂P₂(CONR₂)₂ core was isolated from the reaction of Na[OCP] with (R₂N)₂GaCl (R=alkyl). The unprecedented pnictogenyl carboxamide compounds were thoroughly characterized, including single-crystal X-ray structure determinations, and mechanisms for their formation were investigated by DFT calculations.     

Linking of CuI Units by Tetrahedral Mo2E2 Complexes (E=P,As)

The reaction of [Cp₂Mo₂(CO)₄(μ,η^2:2-E₂)] ( A : E=P, B : E=As, Cp=C₅H₅) with the WCA-containing Cu^I salts ([Cu(CH₃CN)₄][Al{OC(CF₃)₃}₄] (CuTEF, C ), [Cu(CH₃CN)₄][BF₄] ( D ) and [Cu(CH₃CN)_3.5][FAl{OC₆F₁₀(C₆F₅)}₃] (CuFAl, E )) affords seven unprecedented coordination compounds. Depending on the E₂ ligand complex, the counter anion of the copper salt and the stoichiometry, four dinuclear copper dimers and three trinuclear copper compounds are accessible. The latter complexes reveal first linear Cu₃ arrays linked by E₂ units (E=P, As) coordinated in an η^2:1:1 coordination mode. All compounds were characterized by X-ray crystallography, NMR and IR spectroscopy, mass spectrometry and elemental analysis. To define the nature of the Cu⋅⋅⋅Cu⋅⋅⋅Cu interactions, DFT calculations were performed.     

Fixation and Release of Intact E4 Tetrahedra (E=P,As)

By the reaction of [NacnacCuCH₃CN] with white phosphorus (P₄) and yellow arsenic (As₄), the stabilization and enclosure of the intact E₄ tetrahedra are realized and the disubstituted complexes [(NacnacCu)₂(μ,η^2:2‐E₄)] ( 1 a : E=P, 1 b : E=As) are formed. The mono‐substituted complex [NacnacCu(η²‐P₄)] ( 2 ), was detected by the exchange reaction of 1 a with P₄ and was only isolated using low‐temperature work‐up. All products were comprehensively spectroscopically and crystallographically characterized. The bonding situation in the products as intact E₄ units (E=P, As) was confirmed by theory and was experimentally proven by the pyridine promoted release of the bridging E₄ tetrahedra in 1 .     

Structural and theoretical studies of (E,E)-benzaldehyde azine and its rhenium(IV) complex

The azine bridged dicatechol ligand (E,E)-benzaldehyde azine (H₄L) was fully characterized by X-ray analysis. The reaction of [ReCl₆]²⁻ with this compound was studied and the novel Re(IV) complex (HNEt₃)(NBu₄)[ReCl₄(H₂L)] was prepared and characterized. The structure and spectroscopy of the compound H₄L and its Re(IV) complex were studied experimentally and by means of density functional calculations.     

Unprecedented Bonding Situation in Viable E2(NHBMe)2 (E=Be,Mg; NHBMe=(HCNMe)2B) Complexes: Neutral E2 Forms a Single E−E Covalent Bond

Is it possible to facilitate the formation of a genuine Be?Be or Mg?Mg single bond for the E₂ species while it is in its neutral state? So far, (NHC^R)Be?Be(NHC^R) (R=H, Me, Ph) have been reported where Be₂ is in ¹Δ_g excited state imposing a formal Be?Be bond order of two. Herein, we present the formation of a single E?E (E=Be, Mg) covalent bond in E₂(NHB^Me)₂ (E=Be, Mg; NHB^Me=(HCN^Me)₂B) complexes where E₂ is in ³∑_u⁺ excited state having (nσ_g⁺)²(nσ_u⁺)¹((n+1)σ_g⁺)¹ (n=2 for Be and n=4 for Mg) valence electron configuration and it forms electron‐shared bonding with two NHB^Me radicals. The effects of bonding with nσ_u⁺ and (n+1)σ_g⁺ orbitals will cancel each other, providing the former E?E bond order as one. Be₂(NHB^Me)₂ complex is thermochemically stable with respect to possible dissociation channels at room temperature, whereas the two exergonic channels, Mg₂(NHB^Me)₂ → Mg + Mg(NHB^Me)₂ and Mg₂(NHB^Me)₂ → Mg₂ + (NHB^Me)₂, are kinetically inhibited by a free energy barrier of 15.7 and 18.7 kcal mol^?1, respectively, which would likely to be further enhanced in cases of bulkier substituents attached to the NHB ligands. Therefore, the title complexes are first viable systems which feature a neutral E₂ moiety with a single E?E covalent bond.     

Unprecedented Bonding Situation in Viable E2(NHBMe)2 (E=Be,Mg; NHBMe=(HCNMe)2B) Complexes: Neutral E2 Forms a Single E−E Covalent Bond

Is it possible to facilitate the formation of a genuine Be?Be or Mg?Mg single bond for the E₂ species while it is in its neutral state? So far, (NHC^R)Be?Be(NHC^R) (R=H, Me, Ph) have been reported where Be₂ is in ¹Δ_g excited state imposing a formal Be?Be bond order of two. Herein, we present the formation of a single E?E (E=Be, Mg) covalent bond in E₂(NHB^Me)₂ (E=Be, Mg; NHB^Me=(HCN^Me)₂B) complexes where E₂ is in ³∑_u⁺ excited state having (nσ_g⁺)²(nσ_u⁺)¹((n+1)σ_g⁺)¹ (n=2 for Be and n=4 for Mg) valence electron configuration and it forms electron‐shared bonding with two NHB^Me radicals. The effects of bonding with nσ_u⁺ and (n+1)σ_g⁺ orbitals will cancel each other, providing the former E?E bond order as one. Be₂(NHB^Me)₂ complex is thermochemically stable with respect to possible dissociation channels at room temperature, whereas the two exergonic channels, Mg₂(NHB^Me)₂ → Mg + Mg(NHB^Me)₂ and Mg₂(NHB^Me)₂ → Mg₂ + (NHB^Me)₂, are kinetically inhibited by a free energy barrier of 15.7 and 18.7 kcal mol^?1, respectively, which would likely to be further enhanced in cases of bulkier substituents attached to the NHB ligands. Therefore, the title complexes are first viable systems which feature a neutral E₂ moiety with a single E?E covalent bond.     

Heterometall-Komplexe mit E6-Liganden (E = P,As)

Heterometallic Complexes with E₆ Ligands (E = P, As) The reaction of [Cp*Co(μ-CO)]₂ 1 with the sandwich complexes [Cp*Fe(η⁵-E₅)] 2 a: E = P, 2 b: E = As in decalin at 190°C affords besides [CpCo₂E₄] 4: E = P, 7: E = As and [CpFe₂P₄] 5 the trinuclear complexes [(Cp*Fe)₂(Cp*Co)(μ-η²-P₂)(μ₃-η^1:2:1-P₂)₂] 3 as well as [(Cp*Fe)₂(Cp*Co)(μ₃-η^2:2:2-As₃)₂] 6 . With [Mo(CO)₅(thf)] 3 and 6 form in a build-up reaction the tetranuclear clusters [(Cp*Fe)₂(Cp*Co)E₆{Mo(CO)₃}] 10: E = P, 11: E = As. 3, 6 and 11 have been further characterized by an X-ray crystal structure determination.     

THE CHEMISTRY OF (ECN)2 (E = S,Se) AND RELATED COMPOUNDS

The psuedohalogens (ECN)₂ (E = S, Se) have been prepared by reaction of AgNCS with bromine and AgNCSe with iodine respectively. (SCN)₂ spontaneously polymerises to give polythiocyanogen a polymer of unknown structure with empirical formula (SCN)_x. A series of late transition metal complexes bearing the ambidentate psuedohalide ligands (ECN) (E = S, Se) have been synthesised. In addition we have prepared a series of late transition metal complexes of the cyanodithioimidocarbonate ion [C₂N₂S₂]^2? and the first transition metal complexes of the cyanodiselenocarbonate ion [C₂N₂Se₂]^2?.     

Synthesis and redox behaviour of the chalcogenocarbonyl dianions [(E)C(PPh(2)S)(2)](2-): formation and structures of chalcogen-chalcogen bonded dimers and a novel selone

The lithium salts of the chalcogenocarbonyl dianions [(E)C(PPh₂S)₂]^2? (E=S ( 4 b ), Se ( 4 c )) were produced through the reactions between Li₂[C(PPh₂S)₂] and elemental chalcogens in the presence of tetramethylethylenediamine (TMEDA). The solid‐state structure of {[Li(TMEDA)]₂[(Se)C(PPh₂S)₂]}—[{Li(TMEDA)}₂ 4 c ]—was shown to be bicyclic with the Li⁺ cations bis‐S,Se‐chelated by the dianionic ligand. One‐electron oxidation of the dianions 4 b and 4 c with iodine afforded the diamagnetic complexes {[Li(TMEDA)]₂[(SPh₂P)₂CEEC(PPh₂S)₂]} ([Li(TMEDA)]₂ 7 b (E=S), [Li(TMEDA)]₂ 7 c (E=Se)), which are formally dimers of the radical anions [(E)C(PPh₂S)₂]^{? .} (E=S ( 5 b ), Se ( 5 c )) with elongated central E? E bonds. Two‐electron oxidation of the selenium‐containing dianion 4 c with I₂ yielded the LiI adduct of a neutral selone {[Li(TMEDA)][I(Se)C(PPh₂S)₂]}—[{LiI(TMEDA)} 6 c ]—whereas the analogous reaction with 4 b resulted in the formation of 7 b followed by protonation to give {[Li(TMEDA)][(SPh₂P)₂CSS(H)C(PPh₂S)₂]}—[Li(TMEDA)] 8 b . Attempts to identify the transient radicals 5 b and 5 c by EPR spectroscopy in conjunction with DFT calculations of the electronic structures of these paramagnetic species and their dimers are also described. The crystal structures of [{Li(TMEDA)}₂ 4 c ], [{LiI(TMEDA)} 6 c ] ? C₇H₈, [Li(TMEDA)]₂ 7 b? (CH₂Cl₂)_0.33, [Li(THF)₂]₂ 7 b , [Li(TMEDA)]₂ 7 c , [Li(TMEDA)] 8 b? (CH₂Cl₂)₂ and [Li([12]crown‐4)₂] 8 b were determined and salient structural features are discussed.     

Five-, six- and eight-membered ring organosilicon chalcogenides of the types Z2(SiMe2)2E (Z = Me2Si, H2C; E = S, Se, Te), Z(SiMe2E)2MR2 (Z = Me2Si, H2C, O; E = S, Se, Te; M = Si, Ge, Sn, R = Me, Ph) and (SiMe2ZSiMe2E)2 (Z = Me2Si, H2C; E = S, Se)

Reactions of ClMe₂Si–Z–SiMe₂Cl (Z = SiMe₂ (1a), CH₂ (1c), O (1e)) with Li₂E (E = S, Se) yielded eight-membered ring compounds (SiMe₂ZSiMe₂E)₂ (3a–d) as well as acyclic oligomers (SiMe₂ZSiMe₂E)_x of different chain lengths. If 1:1 molar mixtures of 1a, 1c or 1e and a diorganodichlorosilane, -germane or -stannane (R₂MCl₂) are reacted with Li₂E (E = S, Se, Te), six-membered ring compounds Z(SiMe₂E)₂MR₂ (4a–7g) are formed exclusively. Five-membered rings Z₂(SiMe₂)₂E (Z = SiMe₂ (8a–c), CH₂ (9a–c); E = S, Se, Te) are obtained starting from the tetrasilane ClMe₂Si–(SiMe₂)₂–SiMe₂Cl (1b) or the disilylethane ClMe₂Si–(CH₂)₂–SiMe₂Cl (1d) by treatment with Li₂E. All products were characterized by multinuclear NMR spectroscopy (¹H, ¹³C, ²⁹Si, ¹¹⁹Sn, ⁷⁷Se, ¹²⁵Te, including coupling constants) and the effects of the different ring sizes towards NMR chemical shifts are discussed.     

Perfluormethyl-Element-Liganden. IX.. Synthese und Eigenschaften von (CF3)2EMn(CO)5 (E = P,As)

Preparation and Properties of (CF₃)₂EMn(CO)₅ (E ? P, As) The complexes (CF₃)₂EMn(CO)₅ (E ? P, As) are formed by the reaction of E₂(CF₃)₄ with HMn(CO)₅. They can be converted quantitatively to the binuclear compounds [Mn(CO)₄E(CF₃)₂]₂ in a thermal (E ? P) or photochemical (E ? P, As) process. u. v. irradiation of a 1:1 mixture gives the mixed derivative Mn₂(CO)₈As(CF₃)₂P(CF₃)₂ together with the symmetrical systems. The Mn? E bond is less reactive with HBr and Me₃SnBr than the M? E bond in derivatives of the type Me₃ME(CF₃)₂ (M ? Si, Ge, Sn; Me ? CH₃). The terminal (CF₃)₂E groups are found to be strong π-acceptor ligands.     

Bond stretching and redox behavior in coinage metal complexes of the dichalcogenide dianions [(SPh2P)2CEEC(PPh2S)2]2- (E=S, Se): diradical character of the dinuclear copper(I) complex (E=S)

The metathetical reactions of a) [Li(tmeda)]₂[(S)C(PPh₂S)₂] (Li₂? 3 c ) with CuCl₂ and b) [Li(tmeda)]₂[(SPh₂P)₂CSSC(PPh₂S)₂] (Li₂? 4 c ) with two equivalents of CuCl both afford the binuclear Cu^I complex {Cu₂[(SPh₂P)₂CSSC(PPh₂S)₂]} ( 5 c ). The elongated (C)S? S(C) bond (ca. 2.54 and 2.72 Å) of the dianionic ligand observed in the solid‐state structure of 5 c indicate the presence of diradical character as supported by theoretical analyses. The treatment of [Li(tmeda)]₂[(SPh₂P)₂CSeSeC(PPh₂S)₂] (Li₂? 4 b ) and Li₂? 4 c with AgOSO₂CF₃ produce the analogous Ag^I derivatives, {Ag₂[(SPh₂P)₂CEEC(PPh₂S)₂]} ( 6 b , E=Se; 6 c , E=S), respectively. The diselenide complex 6 b exhibits notably weaker Ag? Se(C) bonds than the corresponding contacts in the Cu^I congeners, and the ³¹P NMR data suggest a possible isomerization in solution. In contrast to the metathesis observed for Cu^I and Ag^I reagents, the reactions of Li₂? 4 b and Li₂? 4 c with Au(CO)Cl involve a redox process in which the dimeric dichalcogenide ligands are reduced to the corresponding monomeric dianions, [(E)C(PPh₂S)₂]^2? ( 3 b , E=Se; 3 c , E=S), and one of the gold centers is oxidized to generate the mixed‐valent Au^I/Au^III complexes, {Au[(E)C(PPh₂S)₂]}₂ ( 7 b , E=Se; 7 c , E=S), with relatively strong aurophilic Au^I???Au^III interactions. The new compounds 5 c , 6 b , c and 7 b , c are characterized in solution by NMR spectroscopy and in the solid state by X‐ray crystallography ( 5 c , 6 b , 7 b and 7 c ) and by Raman spectroscopy ( 5 c and 6 c ). The UV‐visible spectra of coinage metal complexes of the type 5 , 6 and 7 are discussed in the light of results from theoretical analyses using time‐dependent density functional theory.     

E4 Transfer (E=P,As) to Ni Complexes

The use of [Cp′′₂Zr(η^1:1-E₄)] (E=P ( 1 a ), As ( 1 b ), Cp′′=1,3-di-tert-butyl-cyclopentadienyl) as phosphorus or arsenic source, respectively, gives access to novel stable polypnictogen transition metal complexes at ambient temperatures. The reaction of 1 a/1 b with [Cp^RNiBr]₂ (Cp^R=Cp^Bn (1,2,3,4,5-pentabenzyl-cyclopentadienyl), Cp′′′ (1,2,4-tri-tert-butyl-cyclopentadienyl)) was studied, to yield novel complexes depending on steric effects and stoichiometric ratios. Besides the transfer of the complete E_n unit, a degradation as well as aggregation can be observed. Thus, the prismane derivatives [(Cp′′′Ni)₂(μ,η^3:3-E₄)] ( 2 a (E=P); 2 b (E=As)) or the arsenic containing cubane [(Cp′′′Ni)₃(μ₃-As)(As₄)] ( 5 ) are formed. Furthermore, the bromine bridged cubanes of the type [(Cp^RNi)₃{Ni(μ-Br)}(μ₃-E)₄]₂ (Cp^R=Cp′′′: 6 a (E=P), 6 b (E=As), Cp^R=Cp^Bn: 8 a (E=P), 8 b (E=As)) can be isolated. Here, a stepwise transfer of E_n units is possible, with a cyclo-E₄²⁻ ligand being introduced and unprecedented triple-decker compounds of the type [{(Cp^RNi)₃Ni(μ₃-E)₄}₂(μ,η^4:4-E′₄)] (Cp^R=Cp^Bn, Cp′′′; E/E′=P, As) are obtained.     

Reaction Mechanism of the Symmetry‐Forbidden [2+2] Addition of Ethylene and Acetylene to Amido‐Substituted Digermynes and Distannynes Ph2NEENPh2, (E=Ge,Sn): A Theoretical Study

Quantum chemical calculations of reaction mechanisms for the formal [2+2] addition of ethylene and acetylene to the amido‐substituted digermyne and distannyne Ph₂N?EE?NPh₂ (E=Ge, Sn) have been carried out by using density functional theory at the BP86/def2‐TZVPP level. The nature and bonding situations were studied with the NBO method and with the charge and energy decomposition analysis EDA‐NOCV. The addition of ethylene to Ph₂N?EE?NPh₂ takes place through an initial [2+1] addition to one metal atom and consecutive rearrangement to four‐membered cyclic species, which feature a weak E?E bond. Rotation about the C?C bond with concomitant rupture of the E?E bond leads to the 1,2‐disubstituted ethanes, which have terminal E(NPh₂) groups. The overall reaction Ph₂N?EE?NPh₂+C₂H₄→(Ph₂N)E?C₂H₄?E(NPh₂) has very low activation barriers and is slightly exergonic for E=Ge but slightly endergonic for E=Sn. The analysis of the electronic structure shows that there is charge donation of nearly one electron to the ethylene moiety already in the first part of the reaction. The energy partitioning analysis suggests that the HOMO(Ph₂N?EE?NPh₂)→LUMO(C₂H₄) interaction has a similar strength as the HOMO(C₂H₄)→LUMO(Ph₂N?EE?NPh₂) interaction. The [2+2] addition of acetylene to Ph₂N?EE?NPh₂ also takes place through an initial [2+1] approach, which eventually leads to 1,2‐disubstituted olefins (Ph₂N)E?C₂H₂?E(NPh₂). The formation of the energetically lowest lying conformations of cis‐(Ph₂N)E?C₂H₂?E(NPh₂), which occurs with very low activation barriers, is clearly exergonic for the germanium and the tin compound. The trans‐coordinated isomers of (Ph₂N)E?C₂H₂?E(NPh₂) are slightly lower in energy than the cis form but they are separated by a substantial energy barrier for the rotation about the C?C bond. The energy decomposition analysis indicates that the initial reaction takes place under formation of electron‐sharing bonds between triplet fragments rather than HOMO–LUMO interactions.     

Transition‐Metal Complexes [(PMe3)2Cl2M(E)] and [(PMe3)2(CO)2M(E)] with Naked Group 14 Atoms (E=C–Sn) as Ligands; Part 1: Parent Compounds

The equilibrium geometries and bond dissociation energies of 16‐valence‐electron(VE) complexes [(PMe₃)₂Cl₂M(E)] and 18‐VE complexes [(PMe₃)₂(CO)₂M(E)] with M=Fe, Ru, Os and E=C, Si, Ge, Sn were calculated by using density functional theory at the BP86/TZ2P level. The nature of the M? E bond was analyzed with the NBO charge decomposition analysis and the EDA energy‐decomposition analysis. The theoretical results predict that the heavier Group 14 complexes [(PMe₃)₂Cl₂M(E)] and [(PMe₃)₂(CO)₂M(E)] with E=Si, Ge, Sn have C_2v equilibrium geometries in which the PMe₃ ligands are in the axial positions. The complexes have strong M? E bonds which are slightly stronger in the 16‐VE species 1ME than in the 18‐VE complexes 2ME . The calculated bond dissociation energies show that the M? E bonds become weaker in both series in the order C>Si>Ge>Sn; the bond strength increases in the order Fe<Ru<Os for 1ME , whereas a U‐shaped trend Ru<Os<Fe is found for 2ME . The M? E bonding analysis suggests that the 16‐VE complexes 1ME have two electron‐sharing bonds with σ and π symmetry and one donor–acceptor π bond like the carbon complex. Thus, the bonding situation is intermediate between a typical Fischer complex and a Schrock complex. In contrast, the 18‐VE complexes 2ME have donor–acceptor bonds, as suggested by the Dewar–Chatt–Duncanson model, with one M←E σ donor bond and two M→E π‐acceptor bonds, which are not degenerate. The shape of the frontier orbitals reveals that the HOMO?2 σ MO and the LUMO and LUMO+1 π* MOs of 1ME are very similar to the frontier orbitals of CO.     

Transition‐Metal Complexes [(PMe3)2Cl2M(E)] and [(PMe3)2(CO)2M(E)] with Naked Group 14 Atoms (E=C–Sn) as Ligands; Part 2: Complexation with W(CO)5

Density functional calculations at the BP86/TZ2P level were carried out to understand the ligand properties of the 16‐valence‐electron(VE) Group 14 complexes [(PMe₃)₂Cl₂M(E)] ( 1ME ) and the 18‐VE Group 14 complexes [(PMe₃)₂(CO)₂M(E)] ( 2ME ; M=Fe, Ru, Os; E=C, Si, Ge, Sn) in complexation with W(CO)₅. Calculations were also carried out for the complexes (CO)₅W–EO. The complexes [(PMe₃)₂Cl₂M(E)] and [(PMe₃)₂(CO)₂M(E)] bind strongly to W(CO)₅ yielding the adducts 1ME–W(CO)₅ and 2ME–W(CO)₅ , which have C_2v equilibrium geometries. The bond strengths of the heavier Group 14 ligands 1ME (E=Si–Sn) are uniformly larger, by about 6–7 kcal mol^?1, than those of the respective EO ligand in (CO)₅W‐EO, while the carbon complexes 1MC–W(CO)₅ have comparable bond dissociation energies (BDE) to CO. The heavier 18‐VE ligands 2ME (E=Si–Sn) are about 23–25 kcal mol^?1 more strongly bonded than the associated EO ligand, while the BDE of 2MC is about 17–21 kcal mol^?1 larger than that of CO. Analysis of the bonding with an energy‐decomposition scheme reveals that 1ME is isolobal with EO and that the nature of the bonding in 1ME–W(CO)₅ is very similar to that in (CO)₅W–EO. The ligands 1ME are slightly weaker π acceptors than EO while the π‐acceptor strength of 2ME is even lower.     

Alternativ-Liganden. XXVI [1]. M(CO)4L-Komplexe (M  Cr,Mo, W) der Chelatliganden Me2ESiMe2(CH2)2E′Me2 (Me  CH3; E  P,As; E′  N,P, As)

Alternative Ligands. XXVI. M(CO)₄ L-Complexes (M ? Cr, Mo, W) of the Chelating Ligands Me₂ESiMe₂(CH₂)₂E′ Me₂ (Me ? CH₃; E ? P, As; E′ ? N, P, As) The reaction of M(CO)₄NBD (NBD = norbornadiene; M ? Cr, Mo, W) with the ligands Me₂ESiMe₂(CH₂)₂E′ Me₂ yields the chelate complexes (CO)₄M[Me₂ESiMe₂]) for E,E′ ? P, As, but not for E and /or E′ ? N. The NSi group is not suited for coordination because of strong (p-d)π-interaction. In the case of the ligands with E ? P or As and E′ ? N chelate complexes can be detected in the reaction mixture, but isolable products are complexes with two ligands coordinated via the E donor group. The new compounds are characterized by analytical and spectroscopic (IR, NMR, MS) investigations. The spectroscopic data are also used to deduce the coordinating properties of the ligands. X-ray diffraction studies of the molybdenum complexes (CO)₄Mo[Me₂ESiMe₂(CH₂)₂AsMe ₂] (E ? P, As) in accord with the observed coordination effects show only small differences between SiE and CE donor functions. Attempts to use the ligands Me₂ESiMe₂(CH₂)₂AsMe₂ (E ? P, As) for the preparation of Fe(CO)₃L complexes result in the fission of the SiE bonds and the formation of the binuclear systems Fe₂(CO)₆(EMe₂)₂ (E ? P, As) together with the disilane derivative [Me₂Si(CH₂)₂AsMe₂]₂.     

Total synthesis of resolvin E2

Resolvin E2 (2) was synthesized stereoselectively using the C1-8 and C15-20 aldehydes 6 and 9, which were connected to the C9-14 fragment by using Wittig reactions. The aldehyde 6 was prepared from the γ-silyl alcohol (S)-20 by a sequence of reactions involving ozonolysis, oxidation with NaIO₄, and the Wittig reaction of the resulting aldehyde with Ph₃PCHCHO, whereas the aldehyde 9 was synthesized from the corresponding γ-silyl alcohol through epoxidation, reaction with Et₂AlCN, and reduction with DIBAL-H.     

Photochemical reactions. 137th communication. Preparation and photolysis of (E/Z)-7-methyl-β-ionone

The title compounds (E/Z)- 7 were prepared in 66% overall yield by reaction of β-ionone ((E)-( 1 ) with lithium dimethylcuprate, trapping of the intermediate enolate with benzeneselenenyl bromide and oxidation with H₂O₂. Analogously, (E/Z)-7-methyl-α-inone ((E/Z)- 12 ) was obtained in 65% yield from α-ionone ((E)- 11 ). ¹n, π^*- Excitation (λ > 347 nm, pentane) of (E)-7 causes rapid (E/Z)-isomerization and subsequent reaction of (Z)- 7 to 15 (66%). The formation of 15 is explained by twisting of the dienone chromophore due to repulsive interaction of the 7-CH₃-group with the CH₃-groups of the cyclohexene ring. On the other hand, irradiation λ > 347 nm, Et₂O) of (E)- 7 in the presence of acid leads to (Z)- 7 (5%) and to the novel compound 16 (88%).