Jörg Sundermeyer

Enhanced lithium transference numbers in ionic liquid electrolytes.

Ion transport processes in mixtures of N-butyl- N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide (BMP-TFSI) and lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI) were characterized by ac impedance spectroscopy and pulsed field gradient NMR. Molar ratios x = n Li-TFSI/( n Li-TFSI + n BMP-TFSI) up to 0.377 could be achieved without crystallization. From the bulk ionic conductivity and the individual diffusion coefficients of cations and anions we calculate the Haven ratio and the apparent lithium transference number. Although the Haven ratio exhibits typical values for ionic liquid electrolytes, the maximal apparent lithium transference number is higher than found in other recent studies on ionic liquid electrolytes containing lithium ions. On the basis of these results we discuss strategies for further improving the lithium transference number of such electrolytes.

Peroxomolybdenum Complexes as Epoxidation Catalysts in Biphasic Hydrogen Peroxide Activation: Raman Spectroscopic Studies and Density Functional Calculations

Density functional calcula- tions and Raman spectroscopic data were correlated with the unique cata- lytic epoxidation activity of peroxomo- lybdenum complexes (MoO(O2)2(O- ER3)) (EaN, P, As; Ra n-dodecyl) in a biphasic chloroform - 1-octene/aque- ous hydrogen peroxide system. Crystal structure determinations on (MoO(O2)2(OPtBu3)(OCMe2)) and two complexes containing chelating hemila- bile ether - phosphane oxide and ether - arsane oxide ligands (MoO(O2)2- {iPr2E(O)CH2CH2OCH3}) (Ea P, As) are reported. A mechanistic study with these model complexes reveals the im- portance of free coordination sites for peroxide activation. Calculations and Raman spectroscopic data indicate the tendency of coordinatively unsaturated species (MoO(O2)2(L)) to dimerize in noncoordinating solvents. The catalytic activity in the presence of water as competing ligand could be correlated with the calculated proton affinity of the ligands OER3 (Ra N, P, As). Elucida- tion of the vibrational behavior of the structurally characterized peroxo com- plexes was supported by normal-coordi- nate analyses.

Spectroscopic and Computational Studies of an End-on Bound Superoxo-Cu(II) Complex: Geometric and Electronic Factors that Determine the Ground State

A variety of techniques including absorption, magnetic circular dichroism (MCD), variable-temperature, variable-field MCD (VTVH-MCD), and resonance Raman (rR) spectroscopies are combined with density functional theory (DFT) calculations to elucidate the electronic structure of the end-on (η(1)) bound superoxo-Cu(II) complex [TMG(3)trenCuO(2)](+) (where TMG(3)tren is 1,1,1-tris[2-[N(2)-(1,1,3,3-tetramethylguanidino)]ethyl]amine). The spectral features of [TMG(3)trenCuO(2)](+) are assigned, including the first definitive assignment of a superoxo intraligand transition in a metal-superoxo complex, and a detailed description of end-on superoxo-Cu(II) bonding is developed. The lack of overlap between the two magnetic orbitals of [TMG(3)trenCuO(2)](+) eliminates antiferromagnetic coupling between the copper(II) and the superoxide, while the significant superoxo π*(σ) character of the copper dz(2) orbital leads to its ferromagnetically coupled, triplet, ground state.

Complexes of Manganese, Iron, Zinc, and Molybdenum with a Superbasic Tris(guanidine) Derivative of Tris(2-ethylamino)amine (Tren) as a Tripod Ligand

The synthesis of the novel tripod ligand N[CH2CH2N=C(NMe2)2]3, based on the tris(2-ethylamino)amine (tren) backbone and having a set of three superbasic tetramethylguanidine (TMG) donor atoms instead of the primary amine functionalities, is described. This ligand has been prepared by treating tren with the Vilsmeyer salt [(Me2N)2CCl]Cl in the presence of triethylamine as an auxiliary base and NaOH. Complexes of manganese(II), iron(II), and zinc(II) as biologically relevant transition metal ions as well as of molybdenum(0) have been synthesized and spectroscopically and structurally characterized. The electrochemical properties of selected complexes have been studied.

Höhervalente derivate der d-metall-säuren X. Imidokomplexe des fünf- und vierwertigen niobs und tantals mit halbsandwich- und metallocen- struktur☆☆☆

Abstract The halfsandwich complexes [(η-C 5 R 5 )Nb(N t Bu)Cl 2 ](R  H ( 1 ), Me ( 2 )) and [(η 5 -C 5 R 5 )Ta(N t Bu)Cl 2 ] (R  H ( 4 ), Me ( 5 )) are synthezised by reacting the precursors (η 5 -C 5 R 5 )MCl 4 with t BuNH 2 in the presence of bases such as t BuNH 2 , LiNH t Bu and LiN t Bu(SiMe 3 ). These complexes are starting material for the preparation of the corresponding methyl complexes [(η 5 -C 5 Me 5 )M(N t Bu)(CH 3 ) 2 ] (M  Nb ( 3 ), Ta ( 6 )), and of d o - niobocene imido complexes [(η 5 -C 5 H 5 ) 2 Nb(N t Bu)Cl] ( 7 ) and [(η 5 -C 5 H 5 )(η 5 -C 5 Me 5 )Nb(N tBu Cl] ( 8 ), or d o -tantalocene imido complexes [(η 5 -C 5 H 5 ) 2 Ta(N t Bu)Cl] ( 9 ) and [(η 5 -C 5 H 5 )(η 5 - C 5 Me 5 ) Ta(N t Bu)Cl] ( 10 ), respectively. The most efficient synthesis for 7 and 9 makes use of the reaction of readily available pyridin imido complexes [M(N t Bu)Cl 3 (py) 2 ] (M  Nb, Ta) with NaC 5 H 5 . With methyllithium 7 and 9 are converted into methyl complexes [(η 5 -C 5 H 5 ) 2 M(N t Bu)CH 3 ] (M  Nb ( 11 ), Ta ( 12 )). The one-electron reduction of 1 and 4 leads to diamagnetic dinuclear complexes with bridging imido ligands [(η 5 -C 5 H 5 )Nb(μ-N t Bu)Cl 2 ( 1 3) and [(η 5 -C 5 H 5 ) Ta(μ-N t Bu)Cl 2 ( 14 ). Similarly, the reduction of d o -niobocene imido complex 7 results in the formation of a dinuclear complex [(η 5 -C 5 H 5 ) 2 Nb(N t Bu)] 2 ( 15 ) with spin coupling of both d 1 -metal centres.

A new synthetic pathway to the second and third generation of superbasic bisphosphazene proton sponges: the run for the best chelating ligand for a proton.

We present the up to now strongest chelating neutral pincer ligand for the simplest electrophile of chemistry, the proton. Two novel bisphosphazene proton sponges, 1,8-bis(trispyrrolidinophosphazenyl)naphthalene (TPPN) and its higher homologue P2-TPPN, were obtained via a Staudinger reaction and investigated concerning their structural features and basic properties by experimental and computational means. They exhibit experimental pK(BH)(+) values in acetonitrile of 32.3 and 42.1, respectively, exceeding the existing basicitiy record for proton sponges by more than 10 orders of magnitude. We show that Schwesingers concept of homologization of phosphazene bases and Alders concept of proton chelation in a constrained geometry regime of basic centers can be combined in the design of highly basic nonionic superbases of pincer type.

Olefin Epoxidation with Transition Metal η2-Peroxo Complexes: The Control of Reactivity

The activation energies for olefin epoxidation with Mimoun-type η2-peroxo complexes have been calculated using density functional methods. Six degrees of freedom of the complex [MOL(O2)(OER3)] and the olefin CH2CHR′ have been systematically modified. The calculations were based on the assumptions that the reaction follows a concerted oxygen-transfer mechanism suggested by Sharpless and that a peroxo oxygen atom trans to the phosphane oxide ligand is transferred. This was recently proved for the epoxidation of ethylene with the parent complex [MoO(O2)2{OP(CH3)3}]. It has been found that the diperoxotungsten complexes (M = W; L = O2) are more reactive than the diperoxomolybdenum complexes (M = Mo; L = O2). The activation barriers for the monoperoxomolybdenum complexes (M = Mo; L = O) are significantly higher than the barriers for the corresponding diperoxo complexes (M = Mo; L = O2), whereas equal activation energies have been predicted for both tungsten compounds (M = W; L = O2 and O). The influence of the pnicogen oxide OER3 on epoxidation activity is comparably small, while electron-releasing substituents R′ at the C=C bond reduce the activation barrier. The transition states for the epoxidation of alkenes with conjugated double bonds show a large extent of asymmetry, with the C−O bond at the terminal carbon atom being formed first. Additional ligands L′ coordinating to the metal center inhibit oxygen transfer. The results are in agreement with an electrophilic attack of the oxidant on the C=C double bond.

Highly active Cr(III) catalysts for the reaction of CO2 with epoxides

This paper describes the synthesis and characterization of [Cr(babhq)OAcF(EtOH)] (OAcF− = CF3CO2−) as well as the application of the complex as the catalyst in the reaction of CO2 with epoxides. While cyclic propylene-carbonate was obtained as the sole product when propylene oxide was used as epoxide, alternating polycarbonate was obtained with cyclohexene oxide. Following the course of the reaction with in situ IR spectroscopy revealed that a direct pathway to the formation of cyclic carbonate prevails in the case of propylene oxide whereas the polycarbonate obtained from cyclohexene oxide is prone to degradation to cyclic carbonate. The differences in chemoselectivity are rationalised on the basis of the propensity of the ligand to adopt a podand-like structural motif allowing for an inner-sphere mechanism.

Synthesis and structure of a series of new haloaryl imido complexes of molybdenum

Abstract The synthesis of a series of mono- and bis-haloarylimido molybdenum(VI) complexes is described. Two methods of introducing the electron poor imido functionality are employed, first the condensation of substituted anilines with Na2MoO4 in the presence of Me3SiCl/NEt3, secondly the sulfinyl amine metathesis with [Mo(O)2Cl2(dme)] (1). The latter method works even in cases, when the first one does not work. Crystal structures of three complexes [Mo(NC6F5)(O)Cl2(dme)] (2a), [Mo(N-2,6-Cl2C6H3)2Cl2(dme)] (3b) and [Mo(N-2,4,6-Br3C6H2)2Cl2(dme)] (4) are reported. The unusually small MoNC(Ar) angle of 149.1(5)° has been found in the structure of 4.

Oxidation of diphosphazane-bridged derivatives of diruthenium nonacarbonyl by silver(I) salts in protic solvents: synthesis, structural characterization and protonation of the adduct [Ru2{µ-η2-OC(O)}(CO)4{µ-(RO)2PN(Et)P(OR)2}2](R = Me or Pri) involving a novel mode of co-ordination of carbon dioxide

Treatment of [Ru2(µ-CO)(CO)4{µ-(RO)2PN(Et)P(OR)2}2](R = Me or Pri) with AgSbF6 in methanol, ethanol or tetrahydrofuran–water resulted in the formation of the solvento species [Ru2(CO)5(R′OH){µ-(RO)2PN(Et)P(OR)2}2][SbF6]2 which is isolable for R′= H but which spontaneously deprotonates to the alkoxycarbonyl-bridged derivative [Ru2{µ-η2-OC(OR′)}(CO)4{µ-(RO)2PN(Et)P(OR)2}2]SbF6 for R′= Me or Et. The aqua species [Ru2(CO)5(H2O){µ-(RO)2PN(Et)P(OR)2}2][SbF6]2 was readily deprotonated in consecutive steps by appropriate bases to afford respectively the hydroxycarbonyl-bridged species [Ru2{µ-η2-OC(OH)}(CO)4{µ-(RO)2PN(Et)P(OR)2}2]SbF6 and the adduct [Ru2{µ-η2-OC(O)}(CO)4{µ-(RO)2PN(Et)P(OR)2}2] in which the carbon dioxide molecule adopts a novel bridging co-ordination mode; this deprotonation is reversible and treatment of the latter with HBF4·OEt2 leads to stepwise regeneration of the aqua species. The co-ordinated water molecule in [Ru2(CO)5(H2O){µ-(PriO)2PN(Et)P(OPri)2}2][SbF6]2 was readily displaced by acids HA derived from conjugate bases with potential co-ordinating properties such as thiolate ions R″S–(R″= H or Ph) or carboxylate ions R‴CO2–(R‴= H, Me, Ph or CF3), to produce monocationic pentacarbonyl species of the type [Ru2A(CO)5{µ-(PriO)2PN(Et)P(OPri)2}2]SbF6; detection of an intermediate, presumably [Ru2(CO)5(HA){µ-(PriO)2PN(Et)P(OPri)2}2][SbF6]2, was possible for HA = HCO2H and MeCO2H. The sulfido derivatives [Ru2(SR″)(CO)5{µ-(PriO)2PN(Et)P(OPri)2}2]SbF6(R″= H or Ph) rapidly decarbonylate in solution to afford the tetracarbonyl products [Ru2(µ-SR″)(CO)4{µ-(PriO)2PN(Et)P(OPri)2}2]SbF6 in which the sulfido group bridges the two ruthenium atoms. On the other hand the carboxylato derivatives [Ru2{OC(O)R‴}(CO)5{µ-(PriO)2PN(Et)P(OPri)2}2]SbF6(R‴= H, Me, Ph or CF3) are stable to decarbonylation in solution at room or elevated temperatures but can be decarbonylated to the carboxylato-bridged products [Ru2{µ-η2-OC(R‴)O}(CO)4{µ-(PriO)2PN(Et)P(OPri)2}2]SbF6 by irradiation with ultraviolet light. The water molecule in [Ru2(CO)5(H2O){µ-(PriO)2PN(Et)P(OPri)2}2][SbF6]2 was also readily displaced by the conjugate bases of the above acids HA, but in contrast to that observed for the carboxylic acids R‴CO2H (R‴= H, Me or Ph), reaction of the aqua species with the corresponding carboxylate ions R‴CO2– led to direct formation of the carboxylato-bridged species [Ru2{µ-η2-OC(R‴)O}(CO)4{µ-(PriO)2PN(Et)P(OPri)2}2]SbF6. Possible mechanisms for the formation of the various products are discussed as are the structures of [Ru2(CO)5(H2O){µ-(PriO)2PN(Et)P(OPri)2}2][SbF6]2·OCMe2, [Ru2{µ-η2-OC(OEt)}(CO)4{µ-(MeO)2PN(Et)P(OMe)2}2]SbF6, [Ru2{µ-η2-OC(Me)O}(CO)4{µ-(PriO)2PN(Et)P(OPri)2}2]PF6 and [Ru2{µ-η2-OC(O)}(CO)4{µ-(PriO)2PN(Et)P(OPri)2}2], established X-ray crystallographically.