Roland W. Kunz

Chemistry of PdII complexes containing both BINAP (2′2′-bis(diphenylphosphino)binaphthyl) and a η3-pinene or -allyl ligand. NMR studies on [Pd(η3-C10H15){S(−)BINAP}] (CF3SO3). The crystal structure of [Pd(η3-C10H15)(4,4′-dimethylbipyridine)](CF3SO3)

Abstract One and two-dimensional 1H, 13C and 31P NMR studies on palladium(II) complexes containing η3-C10H15 or η3-C4H7 allyl and S(−)BINAP ligands are reported. Details of the three-dimensional solution structure for [Pd(η3C10H15) {S(−)BINAP}(CF3SO3) based on 1H-2D NOESY and molecular modelling calculations are presented. The structure for the model β-pinene allyl complex [Pd(η3-C10H15)(4,4′-dimethylbipyridine)]CF3SO3) has been determined by an X-ray diffraction study, which reveals that the CH2 terminal allyl carbon is significantly displaced from the N-Pd-N plane.

Desulfurization of 4-Nitro-N,2-diphenyl-3-(phenylamino)isothiazol- 5(2H)-imine: Formation of a 3-Imino-2-nitroprop-2-enamidine

The course of the desulfurization reaction of 4-nitro-N,2-diphenyl-3-(phenylamino)isothiazol-5(2H)-imine (3) is investigated and the formation of the unstable 3-imino-2-nitroprop-2-enamidine (A) as intermediate is discussed. Addition of amines and thiophenol to the reaction mixture yielded the amidine derivatives 5 and the thioimidate 6, respectively, via nucleophilic addition of the respective reagent to A (Scheme 2). Benzoic acid and thiobenzoic acid afforded the amide 7 and the thioamide 8, respectively, as secondary products of the expected adducts 7a and 8a (Schemes 3 and 4). The presence of (benzylidene)(methyl)amine in the reaction mixture of the desulfurization of 3 led to the 1,2,4-oxadiazole derivative 10, together with the quinoxaline N-oxide 4 as a minor product. Reaction mechanisms involving an intermediate ketene imine and participation of the NO2 group in the reaction leading to 1,2,4-oxadiazole 10 are proposed. Ab initio calculations of model structures for the nitroketene imine were performed and the results correlated with the experimental results. The structures of 8 and 10 were established by X-ray crystal-structure analysis.

On the structure of [η4-2,5-bis(trimethylsilyl)cyclopentadienone](η5-cyclopentadienyl)cobalt

X-ray diffraction study has been carried out on [η 4 -bis(trimethylsilyl)cyclopentadienone](η 5 -cyclopentadienyl)cobalt (I), the first example of a (η 4 -cyclopentadienone)(η 5 -cyclopentadienyl)cobalt complex with only two substituents on the cyclopentadienone ring. Complex I crystallizes in space group P 2 1 / c with four molecules in the unit cell and lattice parameters a 6.5259(5), b 12.2378(9), c 21.8397(15) A and β 90.442(7)°. Extended Huckel MO calculations are discussed for a simpler model, namely the parent cyclopentadienone complex (III).

13C chemical shifts in the aryl complexes PdX(p-RC6H4)(TMEDA). Is the PdX(TMEDA) fragment a substantial π-donor?

A series of aryl complexes of the form PdX(p‐RC6H4)(TMEDA)(1, R=OMe, Me, H, CO2Me, CN, NO2, TMEDA=tetramethylethylenediamine, X=Br, I) were prepared, together with the derivatives PdI(C6F5)(TMEDA) and PdI(2‐Me‐C6H4)(TMEDA). Their 13C NMR spectra were recorded and showed that (i) the ipso carbon, C‐1, with δ=107.6–162.0, is always shifted to higher frequencies, relative to the model organic compound HC6H4R, (ii) C‐1 is markedly affected by the nature of the p‐R substituent, with electron‐withdrawing groups producing high‐frequency shifts, (iii) there is a linear correlation between δC‐1 and the Hammett constant σp+ with a correlation coefficient R=0.998 and (iv) there is no compelling evidence for a large π−donor effect from palladium into the aryl ring. Screening constants for C‐1 in a series of phenyllithium compounds, p‐RC6H4Li, were calculated. There is an excellent correlation (R=0.972) of ΔδC‐1 for 1 with ΔσC‐1 for p‐RC6H4Li. Copyright

1,4-Diacyl-3-acylamino-5-aryl-4,5-dihydro-1H-1,2,4-triazoles: Ring closure products of aromatic carbaldehyde (diaminomethylene) hydrazones with acylating agents

SummaryTreatment of aromatic carbaldehyde (diaminomethylene)hydrazones1 with hot acetic anhydride or benzoyl chloride affords 1,4-diacyl-3-acylamino-5-aryl-4,5-dihydro-1H-1,2,4-triazoles2. In contrast, a new type of 0,N-acetal with an 1,2,4-triazole substructure (3) is obtained from 4-pyridine-carbaldehyde (diaminomethylene)hydrazone (li) by using a similar reaction procedure. The structures of all novel compounds were confirmed by spectroscopic data (1H and13C NMR, MS, IR); some representative compounds were also studied by X-ray analysis.ZusammenfassungDie Umsetzung von aromatischen Aldehyde-diaminomethylene-hydrazonen1 mit heißem Essigsäureanhydrid oder Benzoylchloride liefert 1,4-Diacyl-3-acylamino-5-aryl-4,5-dihydro-1H-1,2,4-triazole2. Im Gegensatz dazu erhält man aus 4-Pyridinaldehyd-diaminomethylenhydrazon (li) unter den gleichen Reaktionsbedingungen einen neuen O,N-Acetaltyp mit einer 1,2,4-Triazoleinheit. Die Struktur sämtlicher neuer Produkte wurde durch spektroskopische Daten (1H- und13C-NMR, MS, IR) unterstützt; einige repräsentative Vertreter wurden zusätzlich mittles Röntgenstrukturanalyse untersucht.

Platinum (II) complexes with four ligating phosphorus atoms. Crystal and molecular structure of [Pt(PEt3)4] (ClO4)2. Discussion of electronic spectra of planar and tetrahedrally distorted PtP4 chromophores

Abstract The crystal and molecular structure of [Pt-(PEt3)4](ClO4)2 has been determine by X-ray diffraction. The compound crystallizes in the orthorhombic space group Pbca with cell constants a = 26.839(4) A b = 13.762(3) A, c = 19.568(6) A, z = 8. The structure was solved by the heavy-atom-method and refined to a final R-value of 0.053 As a consequence of ligand repulsion the expected square-planar PtP4 coordination exhibits a strong tetrahedral distortion. The PPtPtrans angle are 150.3° and 150.9°, respectively (instead of 180° for a square-planar structure). The PtP bond lengths of 2.33 A to 2.35 A are similar to those found in other platinum(II) compounds containing phosphine ligands in trans-position. Electronic spectra of the cations [Pt(PR3)4]2+ (R = Me, Et) have been discussed and compared with those of the related ions [Pt(R2PCh2CH2PR2)2]2+, which have recently [1] been shown to be planar. SCCC-EHMO calculations have been carried out for various geometries of the PtP4 chromophore in order to support the band assignments.

13 C Studies of Phosphorus Containing Complexes

Although 31P NMR offers the chemist the most direct approach to the study of the phosphorus-metal interaction, information concerning chemical transformations at more remote centers in the molecule can not be monitored as readily. An obvious solution to this problem involves the NMR study of other nuclei within the carbon skeleton of the ligand and of course 13C and 1H NMR techniques are well suited for this purpose. The study of a second nucleus is valuable not only because it may provide a unique method by which a particular problem can be approached, but also because the second study can provide confirmation of a hypothesis stemming from the first study. This is useful since occasionally an NMR study of nucleus B can lead to a completely different conclusion than that which would be drawn from a study of nucleus A alone [221]. In view of the enormity of the existing 1H literature we have chosen to limit our few comments to the 13C studies of some phosphorus complexes. Further we have divided these results into two categories: the first concerns the 13C characteristics of the phosphorus ligands themselves and the second the 13C parameters of other ligands in phosphorus complexes.

Formation of Unusual Products from the Acid-Catalyzed Reaction of Azulenes with Dimethyl Acetylenedicarboxylate

The reaction of guaiazulene (4) and dimethyl acetylenedicarboxylate (ADM) in tetralin or toluene, catalyzed by 5 mol-% of trifluoroacetic acid (TFA) at ambient temperature, leads to the formation of the corresponding heptalene-4,5-dicarboxylate 6 and a guaiazulenyl-substituted 2,2a,4a,8b-tetrahydrocyclopent[cd]azulene derivative 7 beside the expected guaiazulenyl-substituted ethenedicarboxylates (E)-5 and (Z)-5 as main products (Scheme 2). The structure of 7 was unequivocally established by an X-ray crystal-structure analysis (Fig. 1). Precursor of 7 must be the 2a,4a-dihydrocyclopent[cd]azulene-3,4-dicarboxylate 9 which reacts, under TFA catalysis, with a second molecule of 4 (Scheme 3). No formation of products of type 7 has been observed in the TFA-catalyzed reaction of 4,6,8-trimethyl- and 1,4,6,8-tetramethylazulene (13 and 16, respectively) and ADM (Scheme 4). On the other hand, the TFA-catalyzed reaction of azulene (18) itself and ADM at ambient temperature gives rise to a whole variety of new products (Scheme 5), the major part of which is derived from dimethyl 2a,4a-dihydrocyclopent[cd]azulene-3,4-dicarboxylate (25) as the main intermediate (Scheme 6). Nevertheless, for the formation of the 2a,4a,6,8b-tetrahydrocyclobut[a]azulene derivatives (E)-24a and (E)-24b, a corresponding 2a,8b-dihydro precursor 29 has to be postulated as crucial intermediate (Scheme 8).

Motivation and Methodology

For almost a quarter of a century the words “nuclear magnetic resonance” were synonymous with proton measurements. During this period the literature abounded with a seemingly infinite variety of 1H NMR studies concerned primarily with carbon chemistry. Occasionally a “novel” nucleus was studied and, even in those early days, the potential offered by 13C, 14N, 31P and 19F was clearly recognized. Despite the allure, the technical difficulties involved in measuring some of these nuclei were far from trivial. Small magnetic moments and low natural abundance in combination with spin-spin coupling from other nuclei, mostly protons, resulted in a signal-to-noise problem whose severity effectively excluded the study of metal complexes with unfavorable solubility characteristics. The first important breakthrough came with the advent of broad band 1H-decoupling. For example, the featureless broad 31P resonance associated with the commonly used ligand triphenyl phosphine is converted to a sharp, more readily observed singlet when wide-band decoupling is employed (see Fig. 1). Despite this improvement investigation of more interesting molecules, such as catalytically active complexes was forced to await the development of Fourier Transform methods since only with relatively rapid signal averaging methods could sufficient signal-to-noise ratios be achieved.

Typische Modelle und Programme

Die Krafte zwischen Partikeln konnen in vier Kategorien eingeteilt werden: a) Gravitation, b) Elektromagnetismus, c) starke und d) schwache Krafte.