Klaus Eichele

Rhodium pincer complexes of 2,2′-bis(diphenylphosphino)diphenylamine

Abstract The novel pincer ligand 2,2′-bis(diphenylphosphino)diphenylamine (1) has been synthesized by treatment of 2,2′-dibromodiphenylamine with n-butyl lithium and subsequent reaction with diphenylchlorophosphine. When ligand 1 is treated with RhCl3 hydrate the dinuclear complex 1a forms which can be converted into the square planar carbonyl complex 1c upon reduction with Na/Hg in the presence of CO. Depending on the reaction conditions two different complexes were isolated when 1 reacts with [(COE)2RhCl]2. In THF the hydrochloro complex 1b and with n-butyl lithium the COE complex 1d is generated. Interestingly, the formation of 1b represents a rare case of N–H oxidative addition to a late transition metal complex fragment. Compound 1c is observed upon reaction of the COE complex 1d with carbon monoxide. Quantum chemical calculations at different levels of theory are in good agreement with the experimental structure of 1c.

Construction of an internally B3N3-doped nanographene molecule

The synthesis of a hexa-peri-hexabenzocoronene (HBC) with a central borazine core is described. The solid-state structure of this BN-doped HBC (BN-HBC) is isotypic with that of the parent HBC. Scanning tunneling microscopy shows that BN-HBC lies flat on Au(111) in a two-dimensional pattern.

Supported organometallic complexes Part XXXV. Synthesis, characterization, and catalytic application of a new family of diamine(diphosphine)ruthenium(II) complexes

The novel diamine(dppp)ruthenium(II) complexes 3L1 � /3L12 have been obtained by reaction of equimolar amounts of Cl2Ru(dppp)2 (2) with the diamines L1 � /L12 in excellent yields. Within a few minutes one of the diphosphine ligands was quantitatively exchanged by the corresponding diamine. X-ray structural investigations of 3L1, 3L2, and 3L8 show triclinic unit cells with the space groups P/ ¯ 1 (3L1, 3L2) and P 1( 3L8). Whereas in solution all these complexes prefer a trans -RuCl2 configuration, in the solid state cis -(3L1, 3L2) and trans -isomers (3L8) were observed. With the exception of 3L5, 3L6, and 3L12 all mentioned ruthenium complexes are highly catalytically active in the hydrogenation of the a,b-unsaturated ketone trans -4-phenyl-3-butene-2one. In most cases the conversions and selectivities toward the formation of the unsaturated alcohol trans -4-phenyl-3-butene-2-ol were � /99% with high turnover frequencies (TOFs) under mild conditions. # 2002 Elsevier Science B.V. All rights reserved.

Asymmetric hydrogenation of an α,β-unsaturated ketone by diamine(ether–phosphine)ruthenium(II) complexes and lipase-catalyzed kinetic resolution: a consecutive approach

Abstract The RuCl2(η1-Ph2PCH2CH2OCH3)2(diamine) complexes 2L1–2L5 have been prepared in high yields from the reaction of equimolar amounts of RuCl2(η2-Ph2PCH2CH2OCH3)2 1 with various kinds of chelating diamines L1–L5 to form five-membered chelates with ruthenium. These novel ruthenium(II) complexes have been used as catalysts in the asymmetric hydrogenation of the prochiral ketone trans-4-phenyl-3-butene-2-one 3, using 2-propanol and different types of cocatalysts. Whereas complexes with achiral diamines afforded the racemic alcohols, complexes with chiral diamines (R,R or S,S) allowed the formation of the corresponding enantiomerically enriched secondary alcohol (S or R) with ee values of 45%. In order to obtain the secondary alcohol with ee of >99%, the kinetic resolution of enantiomerically enriched trans-4-phenyl-3-butene-2-ol 3 was performed in a consecutive approach using either the lipase-catalyzed enantioselective transesterification of the alcohol with isopropenyl acetate as the acyl donor in toluene or the enantioselective hydrolysis of the corresponding acetate in buffer. The determination of the enantiomeric excess (ee) of the resulting enantiomerically enriched secondary alcohols was performed by gas chromatography using heptakis(2,3-di-O-methyl-6-O-tert-butyldimethylsilyl)-β-cyclodextrin as the chiral stationary phase.

Supported organometallic complexes Part 34: synthesis and structures of an array of diamine(ether/phosphine)ruthenium(II) complexes and their application in the catalytic hydrogenation of trans-4-phenyl-3-butene-2-one

The novel diamine/bis(ether/phosphine)ruthenium(II) complexes Cl2Ru(h 1 -Ph2PCH2/CH2OCH3)2(diamine)2(3L1/3L11 )h ave been obtained by reaction of equimolar amounts of Cl2Ru(PS/O)2 (2) with the respective diamines L1/L11 in good yields. X-ray structural investigations of 3L2 and 3L8 show monoclinic unit cells with the space group P 21/c . The octahedrally coordinated ruthenium atoms have each two trans- chlorides and cis -phosphines which is in agreement with NMR studies in solution. With the exception of 3L4 all mentioned ruthenium complexes are highly catalytically active in the hydrogenation of the a,b-unsaturated ketone trans -4-phenyl-3-butene-2-one. In most cases the conversions and selectivities toward the formation of the unsaturated alcohol trans -4-phenyl-3-butene-2-ol were 100% with high turnover frequencies under mild conditions. # 2003 Elsevier Science B.V. All rights reserved.

B3N3 Borazine Substitution in Hexa-peri-Hexabenzocoronene: Computational Analysis and Scholl Reaction of Hexaphenylborazine

The doping of graphene molecules by borazine (B(3)N(3)) units may modify the electronic properties favorably. Therefore, the influence of the substitution of the central benzene ring of hexa-peri-hexabenzocoronene (HBC, C(42)H(18)) by an isoelectronic B(3)N(3) ring resulting in C(36)B(3)N(3)H(18) (B3N3HBC) is investigated by computational methods. For comparison, the isoelectronic and isosteric all-B/N molecule B(21)N(21)H(18) (termed BN) and its carbon derivative C(6)B(18)N(18)H(18) (C6BN), obtained by substitution of a central B(3)N(3) by a C(6) ring, are also studied. The substitution of C(6) in the HBC molecule by a B(3)N(3) unit results in a significant change of the computed IR vibrational spectrum between 1400 and 1600 cm(-1) due to the polarity of the borazine core. The properties of the BN molecule resemble those of hexagonal boron nitride, and substitution of the central B(3)N(3) ring by C(6) changes the computed IR vibrational spectrum only slightly. The allowed transitions to excited states associated with large oscillator strengths shift to higher energy upon going from HBC to B3N3HBC, but to lower energy upon going from BN to C6BN. The possibility of synthesis of B3N3HBC from hexaphenylborazine (HPB) using the Scholl reaction (CuCl(2)/AlCl(3) in CS(2)) is investigated. Rather than the desired B3N3HBC an insoluble and X-ray amorphous polymer P is obtained. Its analysis by IR and (11)B magic angle spinning NMR spectroscopy reveals the presence of borazine units. The changes in the (11)B quadrupolar coupling constant C(Q), asymmetry parameter η, and isotropic chemical shift δ(iso)((11)B) with respect to HPB are in agreement with a structural model that includes B3N3HBC-derived monomeric units in polymer P. This indicates that both intra- and intermolecular cyclodehydrogenation reactions take place during the Scholl reaction of HPB.

Methylaluminum‐Supported Rare‐Earth‐Metal Dihydrides

Compounds combining the large rare-earth-metal (Ln) centers with the smallest anionic ligand, H (hydrido), continue to pose challenging questions both in fundamental and applied chemistry. The inherent bonding properties in solid-state binary LnHx phases (e.g., causing metallic behavior) as well as in ligand-supported molecular counterparts (revealing unique cluster chemistry, see Supporting Information) have been the focus of extensive research. Moreover, heterobimetallic solid-state materials, such as Ni5LaHx, feature approved rechargeable battery components or, such as LnAlH6 (obtained from LnCl3 and NaAlH4 by the release of hydrogen), are discussed as intermediate-temperature hydrogen-storage materials. On the other hand, the quest for soluble molecular hydrides has triggered immense research efforts. In the meantime, mono and dihydrido derivatives “L2LnH” and “LLnH2” (L = monoanionic ligand), respectively, are assigned a crucial role in a variety of stoichiometric and catalytic transformations, whereas complexes of type [LnH3(Do)x] (Do = neutral donor ligand) are still elusive. While mono hydride complexes can exist as monomers, e.g., [(C5H2tBu3)2CeH], [4] dihydrido species “LLnH2”, carrying only one ancillary ligand per lanthanide center, tend to form polynuclear complexes (see Supporting Information) containing as few as two and up to six lanthanide metal centers. Several types of ancillary ligands have been employed in an effort to stabilize complexes of low nuclearity, including sterically demanding cyclopentadienyl derivatives such as C5Me4SiMe3 [6] tris(pyrazolyl)borato scorpionates, tetraazacycloamido, bis(phosphinophenyl)amido pincer, and pyridylamido ligands as well as chelating diamido ligands (see Supporting Information). However, the synthesis of a monomeric rare-earth-metal dihydride was not successful to date. The group of Takats used the sterically demanding hydrotris(3-tert-butyl-5-methylpyrazolyl)borato ligand (Tp) to stabilize Ln centers in species such as alkyls, carbenes, amides, halides, 13] or hydrides and was also able to obtain lanthanide dihydride complexes using the less-bulky dimethyl, diisopropyl, or unsubstituted derivative of the Tp ligand, but reported the formation of a mixture of products for the more bulky Tp ligand because of possible side reactions involving the ligand tertbutyl group. 15] Since tetrameric [(TpLnH2)4] as well as the other dihydride clusters reported were all synthesized from alkyl precursors by the addition of H2 or silanes, we tried to adopt a different route using HAlMe2 as hydride source. For example, this reaction pathway could yield the desired [TpLnH2] complex as a mononuclear species owing to the steric bulk of the ligand by a direct alkyl hydrido exchange generating trialkyl aluminum as byproduct or result in the formation of a bimetallic adduct complex. As use of the super-bulky tris(pyrazolyl)borato ligand Tp had enabled the isolation of soluble monomeric rareearth-metal dimethyl complexes we treated complex [TpLuMe2] with two equivalents of HAlMe2 in toluene at ambient temperature (Scheme 1). Formation of a precip-

Homoleptic Coinage Metal Compounds of Group(IV)heteroborates

This article describes the synthesis and characterization of the first silver complex with the germylene [GeB11H11](2-) and coinage metal complexes with the stannylene ligand [SnB11H11](2-). Starting materials like CuCl, AuCl(Me2S), and AgNO3 were used to give mononuclear (3 and 4), dinuclear (5), hexanuclear (6), and heptanuclear (7) coordination compounds: [Et4N]5[Cu(CH3CN)(SnB11H11)3] (3), [Et4N]5[Ag(SnB11H11)3] (4), [Et4N]6[{Au(SnB11H11)2}2] (5), [Et4N]6[{Ag(GeB11H11)}6] (6), and [Et4N]9[Ag7(SnB11H11)8] (7). In case of the oligonuclear compounds 5-7 silver and gold aggregation was observed under formation of metal-metal bonds. Furthermore, the germa-closo-dodecaborate is found in a hitherto unknown μ3-bridging coordination mode connecting three silver atoms. The new compounds were characterized by single crystal X-ray diffraction and in the case of 3-6 also by NMR spectroscopy and elemental analysis.

Bonding modes of stanna-closo-dodecaborate: η1(Sn) to η3(BH) rearrangement reactions in zwitterionic stanna-closo-dodecaborate ruthenium complexes

Reaction of the stanna-closo-dodecaborate salt [Bu3MeN]2[SnB11H11] with the dimeric ruthenium complex [Ru2(mu-Cl)3(triphos)2]Cl (triphos = {MeC(CH2PPh2)3}) in refluxing acetonitrile yields the zwitterionic compound [Ru(SnB11H11)(MeCN)2(triphos)] (4) which has been characterized by single-crystal X-ray diffraction analysis and solid-state NMR spectroscopy. Refluxing the zwitterion in acetone leads to an eta1(Sn) to eta3(BH) rearrangement with formation of [Ru(SnB1)H11)(triphos)] (5) whose structure has been confirmed by X-ray diffraction and multinuclear NMR spectroscopy in solution and in the solid state. Furthermore, two isomeric zwitterions fac- and mer-[Ru(SnB11H11)(dppb)(MeCN)3] (6a, 6b) and their rearrangement reactions as well as their NMR properties are described.

Neuartige elementorganische Sauerstoffsäuren des Phosphors und Schwefels [1]†

Die neuartige Imidazoliophosphonsaure Im—PO3H (7, Im = 2-{1, 3-diisopropyl-4, 5-dimethylimidazolio}) wird durch Hydrolyse des Phosphonylchlorids [Im-P(O)Cl2]Cl (6), das durch direkte Umsetzung des stabilen 2, 3-dihydro-1, 3-diisopropyl-4, 5-dimethylimidazol-2-ylidens (5) mit P(O)Cl3 zuganglich ist, erhalten. Die neuartige kationische Sulfonsaure [Im—SO3H]X ist als BF4- bzw. SbF6-Salz (11a, b) durch Umsetzung des Betains Im—SO3 (10) mit HBF4· Et2O bzw. HF/SbF5 zuganglich. Die Kristallstrukturen von 7 und 11b werden ermittelt und diskutiert. Novel Elementorganic Oxo-Acids of Phosphorus and Sulfur [1] The novel imidazoliophosphonate acid Im—PO3H (7, Im = 2-{1, 3-diisopropyl-4, 5-dimethylimidazolio}) is prepared through hydrolysis of the phosphonyl chloride [Im—P(O)Cl2]Cl (6) formed by the direct reaction of the stable 2, 3-dihydro-1, 3-diisopropyl-4, 5-dimethylimidazol-2-ylidene (5) with P(O)Cl3. The novel cat ionic sulfonic acid [Im—SO3H]X (11) is formed as its BF4 (11a) and SbF6 (11b) salt on treatment of the betaine Im—SO3 (10) with HBF4· Et2O or HF/SbF5. The crystal structures of 7 and 11b are reported and discussed.