Gernot Boche

Metallophilic Interactions in Closed-Shell Copper(I) Compounds—A Theoretical Study

Cuprophilic interactions in neutral perpendicular model dimers of the type (CH3CuX)2 (X = OH2, NH3, SH2, PH3, N2, CO, CS, CNH, CNLi) were analyzed by ab initio quantumchemical methods. The basis set superposition error for the weakly interacting CH3CuX subunits is significant and is discussed in detail. A new correlation-consistent pseudopotential valence basis set for Cu. derived at the second-order Møller-Plesset level suppresses considerably the basis set superposition error in Cu-Cu interactions compared to the standard Hartree-Fock optimized valence basis set. This allowed the first accurate predictions of cuprophilicity, which has been the subject of considerable debate in the past. The dependence of the strength of cuprophilic interactions on the nature of the ligand X was addressed. The Cu-Cu interaction increases with increasing sigma-donor and pi-acceptor capability of the ligand and is approximately one-third of the well-documented aurophilic interactions. By fitting our potential-energy data to the Hershbach-Laurie equation, we determined a relation between the Cu-Cu bond length and the Cu-Cu force constant; this is important for future studies on vibrational behaviour. The role of relativistic effects on the structure and the interaction energy is also discussed. Finally we investigated cuprophilic interactions in (CH3Cu)4 as a model species for compounds isolated and characterized by X-ray diffraction.

The relation between ion pair structures and reactivities of lithium cuprates

From Li+ well-solvating solvents or complex ligands such as THF, [12]crown-4, amines etc., lithium cuprates R2CuLi(*LiX) crystallise in a solvent-separated ion pair (SSIP) structural type (e.g. 10). In contrast, solvents with little donor qualities for Li+ such as diethyl ether or dimethyl sulfide lead to solid-state structures of the contact ion pair (CIP) type (e.g. 11). 1H,6Li HOESY NMR investigations in solutions of R2CuLi(*LiX) (15, 16) are in agreement with these findings: in THF the SSIP 18 is strongly favoured in the equilibrium with the CIP 17, and in diethyl ether one observes essentially only the CIP 17. Salts LiX (X=CN, Cl, Br, I, SPh) have only a minor effect on the ion pair equilibrium. These structural investigations correspond perfectly with Bertzs logarithmic reactivity profiles (LRPs) of reactions of R2CuLi with enones in diethyl ether and THF: the faster reaction in diethyl ether is due to the predominance of the CIP 17 in this solvent, which is the reacting species; in THF only little CIP 17 is present in a fast equilibrium with the SSIP 18. A kinetic analysis of the LRPs quantifies these findings. Recent quantum-chemical studies are also in agreement with the CIP 17 being the reacting species. Thus a uniform picture of structure and reactivity of lithium cuprates emerges.

1,1′-Bis(N,N-dimethylamino)ferrocene,1,1′-bis(N,N-dimethylamino) cobaltocenium hexafluorophosphate and 1,1′-bis(N,N-dimethylamino)titanocene dichloride. Crystal structure of 1,1′-bis(N,N-dimethylamino)titanocene dichloride

Abstract A general method for the preparation of 1,1′-bis( N,N -dimethylamino)metallocenes is described, involving the reaction of N,N -dimethylamino-cyclopentadienyllithium ( 1 -Li) with metal chlorides. 1,1′-Bis( N,N -dimethylamino)ferrocene ( 2 ), 1,1′-bis( N,N -dimethylamino)cobaltocenium hexafluorophosphate ( 3 + PF 6 − ) and 1,1′-bis( N,N -dimethylamino)titanocene dichloride ( 4 ) have been synthesized in this way. The influence of the dimethylamino donor substituent has been studied by means of cyclic voltammetry. 1,1′-Bis( N,N -dimethylamino)ferrocene ( 2 ), e.g., has the most negative redox potential ( E o −0.23 V (SCE)) so far reported for a ferrocene derivative. The structure of 1,1-bis( N,N -dimethylamino)titanocene dichloride ( 4 ) has been determined by X-ray crystallography. It crystallizes in hexagonal plates with the space group C2/c ( Z = 4, a 1301.4, b 647.2, c 1828.5 pm, β 98.81°). The titanium atom does not lie exactly above the centres of the cyclopentadienyl rings, and the CN bond from the cyclopentadienyl ring carbon atom C(1) to the nitrogen atom of the dimethylamino group is very short (134.7 pm).

SN2 at nitrogen: The reaction of N-(4-cyanophenyl)-O-diphenylphosphinoylhydroxylamine with N.Methylaniline. A model for the reactions of ultimate carcinogens of aromatic amines with (bio) nucleophiles

The model reaction of 5 with 6 to give 7 and 8 (\t-90%) follows the SN2 mechanism. From this result and from product studies it is concluded that the reactions of the ultimate carcinogen 1 with 6 and deoxyguanosine (dG) (and hence d other ultimate carcinogens of aromatic amines with bionucleophiles) follow the same mechanism.

Primary amines via electrophilic amination of organometallic compounds with o-(diphenylphosphinyl)hydroxylamine

Abstract It is shown that O-(diphenylphosphinyl)hydroxylamine 4a transforms all kinds of “carbanions” into primary amines; best yields are received with “stabilized anions”, e.g. of the benzylic type.

Structure and Reactivity of Lithiated α‐Amino Nitriles

Investigations aimed at elucidating the structure of lithiated α-amino nitriles B have led to the identification of N-lithio α-amino nitrile anions as characteristic structural features. Their preparations, crystal structures, and solution structures under the reaction conditions, are described. X-ray crystal structure analyses of crystalline 3 and (S, S)-4 reveal the presence of dimeric aggregates B4 with Ci symmetry, held together by four-membered NLiNLi rings, coordinatively saturated at lithium by four THF ligands. The crystal structure of (S, S)-6 shows polymeric aggregation with dimeric subunits similar to those of 3 and (S, S)-4. The solution structure has been investigated by IR and Raman spectroscopy of 2, (S, S)-4 and (S, S)-6, by NMR spectroscopy of 3, (S, S)-5 and (S, S)-6, and by cryoscopic measurements of (S, S)-6 in THF. Trapping experiments complement the results. In THF, which constitutes the principal reaction medium, the lithiated amino nitriles B are found to exist as monomeric species B6 between −110 and +25°C. In less polar solvents, higher aggregation is presumed. NMR spectroscopic studies of 3 show that the favored orientations of the amine and phenyl groups are similar to their conformations in the solid state. In the light of the results obtained, a transition state is proposed to account for the relative topicity observed in the 1,4-additions of enantiopure lithiated α-amino nitriles (S, S)-4, (S, S)-5, and (S, S)-6 to Michael acceptors.

Die Kristallstrukturen eines Lower-order- und eines „Higher-order”-Cyanocuprates: [tBuCu(CN)Li(OEt2)2]∞ und [tBuCutBu{Li(thf)(pmdeta)2CN}]

Deutlich verschieden sind die Bindungsverhaltnisse in den Cyanocupraten 1 und 2, deren Kristallstrukturen jetzt bestimmt wurden (die Strichformeln unten zeigen die wesentlichen Strukturmerkmale). Demnach ist 1 ein Lower-order-Cyanocuprat des Typs RCu(CN)Li. Das Cuprat 2 des Typs R2Cu(CN)Li2 liegt nicht als „Higher-order”-Cyanocuprat mit einer Cu-CN-Bindung vor, sondern als Cyano-Gilman-Cuprat.

[Lithium tert‐butylperoxide]12: Crystal Structure of an Aggregated Oxenoid

The X-ray crystal structure of the dodecameric lithium tert-butylperoxide [2]12 is the first of an alkali or alkaline earth peroxide. It shows the lithium ion bridging the two oxygen atoms of the peroxide unit and a slight lenghtening of the O-O bond, in agreement with quantum-chemical calculations. A calculation for the model reaction of MeLi with LiOOH to give MeOLi and LiOH reveals the importance of Li bridging the O-O bond in the transition state of this reaction, as similarly discussed for many oxidation reactions of (transition-) metal peroxides. Preliminary theoretical studies of the O-O bond length (and thus of the oxenoid character) as a function of the aggregation of 2 disclose that increasing aggregation leads to stabilization of the charge at the anionic oxygen atom and thus to a reduction of the O-O bond length (oxenoid character). Related considerations of the effect of aggregation should also be valid for other lithium (organometallic) compounds and their structure and reactivity as well as other properties.

The positions of the hydrogen atoms in allyllithium and solvated allyllithium species. A MNDO study

Abstract In the MNDO geometry optimized structures of allyllithium and the solvated species C 3 H 5 Li·2H 2 O and C 3 H 5 Li·3H 2 O the allyl portions are distorted from planarity: the inner hydrogens H 1 and H 3 are strongly bent away from the lithium atom while the central hydrogen H 2 is only slightly bent towards lithium. This confirms earlier ab initio calculations on C 3 H 5 Li but disagrees with recent proposals, based on 1 H and 13 C NMR investigations of allyllithium in tetrahydrofuran, that H 2 is much more bent out of the plane of the carbon atoms than H 1 and H 3 . X-ray structural data for the distorted allyl moiety exist only in the case of (η 3 -C 3 H 5 ) 2 NiP(CH 3 ) 3 and C 6 H 8 Li 2 ·2TMEDA; they support the calculated data.

The Role of Ate Complexes in Halogen(Metalloid)–Metal Exchange Reactions: A Theoretical Study

Correlated electronic structure calculations predict that [(CH3)n+1X]− methyl ate anions, where X is an element of the main groups 14, 15, 16, or 17 up to Bi, possess widely varying stabilities that are governed by the electronegativities of their central atoms X. These stabilities correlate well with the propensities of the elements in question to undergo exchange with lithium and magnesium halide, except in the cases where steric hindrance in the transition states of the exchange reactions is important. These findings are nicely confirmed by calculations of the transition states [(CH3)2XLi]# (X = Cl, Br, I) and [(CH3)3SeLi]# of the corresponding degenerate exchange reactions CH3X (X = Cl, Br, I) + CH3Li and (CH3)2Se + CH3Li, respectively. The computed relative stabilities of the mixed [R–I–CH3]− ate anions of iodine (where R = phenyl, ethynyl, vinyl, ethyl, or cyclopropyl) are in excellent agreement with the experimentally observed equilibria of the corresponding lithium–iodine exchange reactions. The recent experimental observation of a highly stable α-iodine-substituted iodine ate complex as an intermediate in an iodine–magnesium bromide exchange reaction is also corroborated by our studies. Thus, the present calculations provide strong evidence for ate complexes being key intermediates in halogen(metalloid)–lithium(magnesium halide) exchange reactions.