Synthese und Kristallstruktur der Spiro-Verbindung [(i-Pr)2P(S)NSiMe3]2SnCl2

Synthesis and Crystal Structure of the Spirocycle [(i-Pr)₂P(S)NSiMe₃]₂SnCl₂ The reaction of (i-Pr)₂P(S)N(SiMe₃)₂ ( 1 ) with SnCl₄ in 2:1 ratio yields under elimination of ClSiMe₃ the four-membered spirocycle [(i-Pr)₂P(S)NSiMe₃]₂SnCl₂ ( 2 ). The molecular structure of 2 was investigated by an X-ray structure analysis. Compound 2 crystallises in the monoclinic space group P2₁, Z = 2, a = 938.1(1), b = 1 424.1(2), c = 1 207.2(1) pm, β = 110.59(1)°, R = 2.05% for 4 102 reflexions. Compound 2 is a spirocycle with two Sn? N? P? S-rings joined at tin. The two rings are in cis-position.     

Application of unsymmetrical indirect covariance NMR methods to the computation of the (13)C <--> (15)N HSQC-IMPEACH and (13)C <--> (15)N HMBC-IMPEACH correlation spectra

Utilization of long-range (1)H--(15)N heteronuclear chemical shift correlation has continually grown in importance since the first applications were reported in 1995. More recently, indirect covariance NMR methods have been introduced followed by the development of unsymmetrical indirect covariance processing methods. The latter technique has been shown to allow the calculation of hyphenated 2D NMR data matrices from more readily acquired nonhyphenated 2D NMR spectra. We recently reported the use of unsymmetrical indirect covariance processing to combine (1)H--(13)C GHSQC and (1)H--(15)N GHMBC long-range spectra to yield a (13)C--(15)N HSQC-HMBC chemical shift correlation spectrum that could not be acquired in a reasonable period of time without resorting to (15)N-labeled molecules. We now report the unsymmetrical indirect covariance processing of (1)H--(13)C GHMBC and (1)H--(15)N IMPEACH spectra to afford a (13)C--(15)N HMBC-IMPEACH spectrum that has the potential to span as many as six to eight bonds. Correlations for carbon resonances long-range coupled to a protonated carbon in the (1)H--(13)C HMBC spectrum are transferred via the long-range (1)H--(15)N coupling pathway in the (1)H--(15)N IMPEACH spectrum to afford a much broader range of correlation possibilities in the (13)C--(15)N HMBC-IMPEACH correlation spectrum. The indole alkaloid vincamine is used as a model compound to illustrate the application of the method.     

Synthese und Kristallstruktur eines μ-Methylen-μ-hydrido-dialanats [R2Al(μ-CH2)(μ-H)AlR2]− (R = CH(SiMe3)2)

Synthesis and Crystal Structure of a μ-Methylene-μ-hydrido-dialanate [R₂Al(μ-CH₂)(μ-H)AlR₂]^? (R = CH(SiMe₃)₂) tert-Butyl lithium reacts with the recently synthesized methylene bridged dialuminium compound [(Me₃Si)₂CH]₂Al? CH₂? Al[CH(SiMe₃)₂]₂ 2 in the presence of TMEDA under β-elimination; the thereby formed hydride anion is bound in a chelating manner by both unsaturated aluminium atoms forming a 3c–2e–Al? H? Al bond. The crystal structure of the product shows two independent molecules differing only slightly in bond lengths and angles, but significantly in conformation. While one of the Al₂CH heterocycles deviates little from planarity with a rough C₂ symmetry for the whole anion, the other one is folded with an angle of 21.1° and the arrangement of the substituents is best described by C_s symmetry.     

Quantitative evaluation of d-pi interaction in copper(I) complexes and control of copper(I)-dioxygen reactivity

Crystal structures of the copper(I) complexes 1(X), 2, and 3 of a series of tridentate ligands L1(X), L2, and L3, respectively (L1(X): p-substituted derivatives of N,N-bis[2-(2-pyridyl)ethyl]-2-phenylethylamine; X=H, Me, OMe, Cl, NO(2); L2: N,N-bis[2-(2-pyridyl)ethyl]-2-methyl-2-phenylethylamine; L3: N,N-bis[2-(2-pyridyl)ethyl]-2,2-diphenylethylamine) were solved to demonstrate that all the copper(I) complexes involve an eta(2) copper-arene interaction with the phenyl ring of the ligand sidearm. The Cu(I) ion in each complex has a distorted tetrahedral geometry consisting of the three nitrogen atoms (one tertiary amine nitrogen atom and two pyridine nitrogen atoms) and C(1)-C(2) of the phenyl ring of ligand sidearm, whereby the Cu-C distances of the copper-arene interaction significantly depend on the para substituents. The existence of the copper-arene interaction in a nonpolar organic solvent (CH(2)Cl(2)) was demonstrated by the observation of an intense MLCT band around 290 nm, and the magnitude of the interaction was evaluated by detailed analysis of the (1)H and (13)C NMR spectra and the redox potentials E(1/2) of the copper ion, as well as by means of the ligand-exchange reaction between the phenyl ring and CH(3)CN as an external ligand. The thermodynamic parameters DeltaH(o) and DeltaS(o) for the ligand-exchange reaction with CH(3)CN afforded a quantitative measure for the energy difference of the copper-arene interaction in the series of copper(I) complexes. Density functional studies indicated that the copper(I)-arene interaction mainly consists of the interaction between the d(z(2) ) orbital of Cu(I) and a pi orbital of the phenyl ring. The copper(I) complexes 1(X) reacted with O(2) at -80 degrees C in CH(2)Cl(2) to give the corresponding (micro-eta(2):eta(2)-peroxo)dicopper(II) complexes 4, the formation rates k(obs) of which were significantly retarded by stronger d-pi interaction, while complexes 2 and 3, which exhibit the strongest d-pi interaction showed significantly lower reactivity toward O(2) under the same experimental conditions. Thus, the d-pi interaction has been demonstrated for the first time to affect the copper(I)-dioxygen reactivity, and represents a new aspect of ligand effects in copper(I)-dioxygen chemistry.     

Stepwise Degradation of Trifluoromethyl Platinum(II) Compounds

The action of moisture on the homoleptic organoplatinum(II) compound [NBu₄]₂[Pt(CF₃)₄] ( 1 ) gives rise to the carbonyl derivative [NBu₄][Pt(CF₃)₃(CO)] ( 2 ), which is itself moisture stable. However, treatment of compound 2 with HCl(aq) results in the formation of [NBu₄][cis‐Pt(CF₃)₂Cl(CO)] ( 3 ), which undergoes degradation of an additional CF₃ group by further treatment with HCl(aq) in large excess, affording [NBu₄][cis‐Pt(CF₃)Cl₂(CO)] ( 4 ). The carbonyl derivatives 2 – 4 are fairly stable species, in which the CO ligand, however, can be readily extruded by reaction with trimethylamine N‐oxide (ONMe₃). Thus, compound 2 reacts with ONMe₃ in the presence of a number of neutral or anionic ligands affording a series of singly or doubly charged derivatives with the general formulae [NBu₄][Pt(CF₃)₃(L)] [L=CNtBu ( 5 ), PPh₃ ( 6 ), P(o‐tolyl)₃ ( 7 ), tht ( 8 ; tht=tetrahydrothiophene)] and [NBu₄]₂[Pt(CF₃)₃X] [X=Cl ( 9 ), Br ( 10 ), I ( 11 )], respectively. Compound 2 also reacts with ONMe₃ and pyridin‐2‐thiol (C₅H₅NS) giving rise to the five‐membered metallacyclic derivative [NBu₄][Pt(CF₃)₂(CF₂NC₅H₄S‐κC,κS)] ( 12 ), which can be viewed as a difluorocarbene species stabilized by intramolecular base coordination. On the other hand, treatment of compound 3 with ONMe₃ in the presence of C₅H₅NS yields the four‐membered metallacyclic compound [NBu₄][Pt(CF₃)₂(NC₅H₄S‐κN,κS)] ( 13 ). The geometries of the metallacycles in compounds 12 and 13 are compared. In the absence of any additional ligand, compound 3 undergoes dimerization producing the dinuclear species [NBu₄]₂[{Pt(CF₃)₂}₂(μ‐Cl)₂] ( 14 ). Halide abstraction in the latter compound with AgClO₄ in THF yields the solvento compound cis‐[Pt(CF₃)₂(thf)₂] ( 15 ). The highly labile character of the THF ligands in compound 15 makes this species a convenient synthon of the “cis‐Pt(CF₃)₂” unit.     

Si?H and C?H Activation by Transition Metal Complexes: A Step Towards Isolable Alkane Complexes?

The recognition of the fundamental contributions by G. A. Olah on the elucidation of the structure of nonclassical carbocations, in the form of the award of the Nobel prize for chemistry, has recently emphasized the importance of electron-deficient bonds in the understanding of chemical bonding in organic chemistry. In the field of coordination chemistry, the formulation of electron-deficient bonds has been used for some time to describe nonclassical interactions between atoms. Traditional ligands in coordination chemistry such as amines and phosphanes bond to metal centers through their lone pair of electrons. Synergistic bonding effects dominate in the coordination of π-bonded ligands such as alkenes. In the mid-1980s the discovery of dihydrogen complexes having side-on coordination of H₂ gave fresh impetus to transition metal chemistry as well as to the understanding of the interaction of σ-coordinating ligands with transition metals. In the meantime, transiton metal complexes can be obtained with a variety of σ-coordinated X-H fragments, and their mode of bonding can be understood by a common and quite general model. The chemistry of σ-bound silane ligands is particularly varied and well-investigated. These silane ligands enable the investigation of a large range of σ-coordinated metal complex fragments up to complete oxidative addition with cleavage of the Si? H bond and formation of silyl(hydrido) complexes, which has thus also widened our general understanding of the bonding of other σ-bound ligands. Whilst there is a large range of isolable and stable H₂ and SiR₄ complexes available, there are no such alkane analogues known at present. Only when the C? H bond is part of a ligand that is already directly bonded to the transition metal center will the resulting chelate effect stabilize this agostic C-H-M interaction. The complexation of SiH₄, the simplest heavier homologue of CH₄, was achieved recently. This is a further step towards the understanding of the factors which govern σ-complexation of ligands at transition metal centers.     

Periphere Anbindung von Quecksilber(II)-iodid an dreikernige Molybdän-Schwefel-Dithiophosphinatocluster: [Mo3S4(R2PS2)4HgI2] (R = Et,Pr)

Peripheral Bonding of Mercury(II) Iodide to Trinuclear Molybdenum-Sulfur-Dithiophosphinato Clusters: [Mo₃S₄(R₂PS₂)₄HgI₂] (R = Et, Pr) Reaction of Mo₃S₄(R₂PS₂)₄ 1 (a : R = Et, b : R = Pr) with HgI₂ in THF yields the diamagnetic title complexes [Mo₃S₄(R₂PS₂)₄HgI₂] 3 . The crystal structure of [ 3a (H₂O)] · 2 CH₂Cl₂ shows the complexes to consist of a triangular array of Mo atoms which are bridged by μ₂? S atoms and capped by a μ₃? S atom. Each of the Mo atoms is chelated by a dithiophosphinato ligand Et₂PS₂^? and in addition two Mo atoms are bridged by a Et₂PS₂^? ligand while the H₂O molecule is bonded weakly to the third Mo atom. Thus, all Mo atoms reveal a distorted octahedral coordination sphere. HgI₂ is ?peripherally”? bonded to the cluster via two S atoms, one of which belongs to a chelating ligand and the other one to the bridging ligand. Space group P1 , lattice constants a = 12.157(2), b = 15.284(3), c = 16.049(3) Å, α = 115.56(1), β = 107.35(1), and γ = 94.62(1)°; Z = 2, d_calc = 2.23 mg/mm³; 4 236 observed reflections, R = 0.068. In organic solvents complexes 3 are strong electrolytes. VT-³¹P NMR data suggest a stepwise dissociation of 3 with formation of [Mo₃S₄(R₂PS₂)₃] ⁺[(R₂PS₂)HgI₂]^? and elimination of the bridging ligand from the cluster.     

Thermal redistribution reactions in crosslinked polysiloxanes

The thermolysis under argon of various polysiloxane resins containing D, T, D^H, or T^H units was investigated using thermogravimetric analysis combined with mass spectroscopy (TG/MS analysis) and solid-state ²⁹Si-NMR. Redistribution reactions involving the exchange of Si? C/Si? O bonds or Si? H/Si? O bonds were evidenced in addition to the exchange of Si? O/Si? O bonds reported to date. These reactions significantly modify the initial siloxane units and lead to an escape of volatile silanes or siloxanes. The exchange of Si? H/Si? O bonds takes place at lower temperatures (300°C) than the exchange of Si? C/Si? O bonds (500°C).     

BrO-H2O 及 HOBr-H2O复合物偶合方式的理论研究

在6-311++G(d,p)水平上采用四种方法讨论了两种BrO-H₂O和三种HOBr-H₂O复合物的构型性质。在两种BrO-H₂O复合物中，结合能为11.37–13.92 J/mol的复合物2 （电子态为²A′）最稳定，该复合物是通过BrO中的Br原子和水中的O原子结合的。三种HOBr-H₂O复合物中，复合物3和4的结合能约为16.30–21.32 J/mol，三种复合物的稳定顺序为：复合物3 ≈ 复合物4 > 复合物5。     

Rhodium(I) and rhodium(III) complexes formed by coordination and C-H activation of bulky functionalized phosphanes

The reaction of [[RhCl(C(8)H(14))(2)](2)] (2) with iPr(2)PCH(2)CH(2)C(6)H(5) (L(1)) led, via the isolated dimer [[RhCl(C(8)H(14))(L(1))](2)] (3), to a mixture of three products 4 a-c, of which the dinuclear complex [[RhCl(L(1))(2)](2)] (4 a) was characterized by Xray crystallography. The mixture of 4a-c reacts with CO, ethene, and phenylacetylene to give the square-planar compounds trans-[RhCl(L)(L(1))(2)] (L=CO (5), C(2)H(4) (6), C=CHPh (9)). The corresponding allenylidene(chloro) complex trans-[RhCl(=C=C=CPh(2))(L(1))(2)] (11), obtained from 4 a-c and HC triple bond CC(OH)Ph(2) via trans-[RhCl[=C=CHC(OH)Ph(2)](L(1))(2)] (10), could be converted stepwise to the related hydroxo, cationic aqua, and cationic acetone derivatives 12-14, respectively. Treatment of 2 and [[RhCl(C(2)H(4))(2)](2)] (7) with two equivalents of tBu(2)PCH(2)CH(2)C(6)H(5) (L(2)) gave the dimers [[RhCl(C(8)H(14))(L(2))](2)] (15) and [[RhCl(C(2)H(4))(L(2))](2)] (16), which both react with L(2) in the molar ratio of 1:2 to afford the five-coordinate aryl(hydrido)rhodium(III) complex [RhHCl(C(6)H(4)CH(2)CH(2)PtBu(2)-kappa(2)C,P)(L(2))] (17) by C-H activation. The course of the reactions of 17 with CO, H(2), PhC triple bond CH, HCl, and AgPF(6), leading to the compounds 19-21, 24, and 25 a, respectively, indicate that the coordinatively unsaturated isomer of 17 with the supposed composition [RhCl(L(2))(2)] is the reactive species. Labeling experiments using D(2), DCl, and PhC triple bond CD support this proposal. With either [Rh(C(8)H(14))(eta(6)-L(2)-kappaP]PF(6) or [Rh(C(2)H(4))(eta(6)-L(n)-kappaP]PF(6) (n=1 and 2) as the starting materials, the corresponding halfsandwich-type complexes 27, 28, and 32 were obtained. The nonchelating counterpart of the dihydrido compound 32 with the composition [RhH(2)(PiPr(3))(eta(6)-C(6)H(6))]PF(6) (35) was prepared stepwise from [Rh(C(2)H(4))(PiPr(3))(eta(6)-C(6)H(6))]PF(6) and H(2) in acetone via the tris(solvato) species [RhH(2)(PiPr(3))(acetone)(3)]PF(6) (34) as intermediate. The synthesis of the bis(chelate) complex [Rh(eta(4)-C(8)H(12))(C(6)H(5)OCH(2)CH(2)PtBu(2)-kappa(2)O,P)]BF(4) (39) is also described. Besides 4 a, the compounds 17, 25 a, and 39 have been characterized by Xray crystal structure analysis.     

Synthesis,spectral characterization,electrochemistry and catalytic activities of Cu(II) complexes of bifunctional tridentate Schiff bases containing O?N?O donors

Paramagnetic copper(II) complexes of the type [Cu(PPh₃)(L)] (where L = bifunctional tridentate Schiff bases) were synthesized from the reaction of anthranillic acid with salicylaldehyde (H₂L¹), 2‐hydroxy‐1‐naphthaldehyde (H₂L²), o‐hydroxyacetophenone (H₂L³) and o‐vanillin (H₂L⁴) with monomeric metal precursor [CuCl₂(PPh₃)₂]. The obtained complexes were characterized by elemental analysis, magnetic susceptility and spectroscopic methods (FT‐IR, UV–vis and EPR and cyclic voltammetry). EPR and redox potential studies have been carried out to elucidate the electronic structure, nature of metal–ligand bonding and electrochemical features. EPR spectra exhibit a four line pattern with nitrogen super‐hyperfine couplings originating from imine nitrogen atom. These planar complexes possess a significant amount of tetrahedral distortion leading to a pseudo‐square planar geometry, as is evidenced from EPR properties. Cyclic voltammograms of all the complexes display quasireversible oxidations, Cu(III)? Cu(II), in the range 0.31–0.45 V and reduction peaks, Cu(II)? Cu(I),in the range ?0.29 to ?0.36 V, involving a large geometrical change and irreversible. The observed redox potentials vary with respect to the size of the chelate ring of the Schiff base ligands. Further, the catalytic activity of all the complexes has been found to be high towards the oxidation of alcohols into aldehydes and ketones in the presence of N‐methylmorpholine‐N‐oxide as co‐oxidant. The formation of high valent Cu^IV?O oxo species as a catalytic intermediate is proposed for the catalytic process. Copyright © 2008 John Wiley & Sons, Ltd.     

Donorstabilisiertes Aluminium(I)-iodid

Donorstabilized Aluminium(I) Iodide A metastable solution of Al^I-iodide is formed by quenching of gaseous Al^I-iodide, formed from Al_(I) and HI_(g) at about 1000°C with a mixture of toluene/diethylether. Using triethylamine as donor and solvent crystalline (AlI · NEt₃)₄ 1 can be isolated: a planar Al₄ ring with an Al? Al distance of 265 pm is the most important structural feature in this first roomtemperature stable Al^I-Iodide.     

Methylene transfer from SnMe groups mediated by a rhodium(I) pincer complex: Sn-C, C-C, and C-H bond activation

The PCP-Rh(I) complex 1a based on the [1,3-phenylenebis(methylene)]bis(diisopropylphosphine) ligand reacts with [diazo(phenyl)methyl]trimethylstannane (2) at room temperature to give novel pincer-type phenyl(dimethylstannyl)methylene]hydrazinato complex 3a. The reaction sequence involves a unique combination of Sn-C bond cleavage, C-C bond formation, C-H activation and intramolecular deprotonation of a rhodium hydride intermediate, which results in methylene transfer from an SnMe group to the pincer system and PCP-chelate expansion. A methylene-transfer reaction was also demonstrated with tetramethyltin as the methylene source in the presence of KOC(CH(3))(3) at room temperature. The resulting unstable "chelate-expanded" Rh(I) complex [(C(10)H(5)(CH(2)PiPr(2))(2))(CH(2))Rh(L)] (L=N(2), THF; 4a) was isolated as its carbonyl derivative 5a. Heating 4a in benzene yielded an equimolar amount of toluene and 1a, which demonstrates the ability of the Rh(I) pincer complex to extract a methylene group from an unactivated alkyl tin substrate and transfer it, via C-C followed by C-H activation, to an arene. Use of fluorobenzene resulted in formation of fluorotoluene. Catalytic methylene-group transfer mediated by 1a was not possible, because of formation of o-xylylene complex 8 under the reaction conditions. Steric parameters play a decisive role in the reactivity with tin compounds; while iPrP derivative 1 a underwent facile reactions, tBuP complex 1b was inert.