13C NMR spectroscopy of [4.n.0] bicyclic compounds: Assignment of the ring junction configuration from ring junction configuration from ring junction 13C chemical shifts—application and limits

Several 6-methyl-9-carbamoyltetrahydro-4H-pyrido[1,2-α]pyrimidin-4-ones have been prepared using phosgene iminium chloride. These compounds can exist in equilibrium as the cis (3A) imine ? (3B) enamine ? trans (3C) imine. ¹H, ¹³C and ¹⁵N NMR prove that the cis- and trans-imine isomers are predominant in the equilibrium. ¹H NMR data reveal that the share of the 3B enamine form is negligible at measurable concentrations. The isomeric ratio 3A:3C is time dependent and can be monitored by measuring the CH₃? C-6 and (CH₃)₂N signals. The ¹³C NMR data show that doublets in the range 42–45 ppm for C-9 are only compatible with the imine forms 3A and 3C. The SCS values of the CH₃? C-6 and OCN(CH₃)₂ groups were calculated and used for identification of the cis and trans isomers. ¹⁵N NMR data show that the N-1 chemical shift of the imine is approximately ? 140 ppm for compound 3, whereas that of a fixed enamine is around ? 267.8. This provides additional support for the predominance of the imine tautomers in the equilibrium 3A ? 3B ? 3C. ¹⁵N data allow the stereoisomers 3A and 3C to be distinguished.     

Highly Stereoselective Photochemical Oxidative Addition Reactions. Preliminary Communication

Cyclometallated complexes of the type cis-bis(2-phenylpyridine)platinum(II) (C₂₂H₁₆N₂Pt) and cis-bis(2-(2′-thienyl)pyridine)platinum(II) (C₁₈H₁₂N₂S₂Pt) undergo thermal or photochemical oxidative addition (TOA or POA) reactions with a number of substrates. TOA (with CH₃I, CH₃CH₂I etc.) yield mixtures of several isomers which rearrange slowly (within ca. one week at room temperature) to one of the possible cis-isomers. CH₂Cl₂, CHCl₃, or (E)? ClCH?CHCl, e.g., do not react thermally. POA yield directly complexes of Pt(IV) with the halide and a σ-bonded C-atom in cis-position. The configuration, as assigned by extensive use of ¹H-NMR data, can be characterized for the two chelating ligands C …? N and C′ …? N′ by C,C′-cis; N,N′-cis and C(chelate), Cl-trans.     

Thermal isomerization of ruthenium hydride compounds containing asymmetric bidentate pyrrole‐imine ligands

A series of ruthenium hydride compounds containing substituted bidentate pyrrole‐imine ligands were synthesized and characterized. Reacting RuHCl(CO)(PPh₃)₃ with one equivalent of [C₄H₃NH(2‐CH=NR)] in ethanol in the presence of KOH gave compounds {RuH(CO)(PPh₃)₂[C₄H₃N(2‐CH=NR)]} where trans‐Py‐Ru‐H 1, R = CH₂CH₂C₆H₉; cis‐Py‐Ru‐H 2, R = Ph‐2‐Me; and cis‐Py‐Ru‐H 3, R = C₆H₁₁. Heating trans‐Py‐Ru‐H 1 in toluene at 70°C for 12 hr resulted a thermal conversion of the trans‐Py‐Ru‐H 1 into its cis form, {RuH(CO)(PPh₃)₂[C₄H₃N(2‐CH=NCH₂CH₂C₆H₉)]} (cis‐Py‐Ru‐H 1) in very high yield. The ¹H NMR spectra of trans‐Py‐Ru‐H 1, cis‐Py‐Ru‐H 2, cis‐Py‐Ru‐H 3, and cis‐Py‐Ru‐H 1 all show a typical triplet at ca. δ–11 for the hydride. The trans and cis form indicate the relative positions of pyrrole ring and hydride. The geometries of trans‐Py‐Ru‐H 1, cis‐Py‐Ru‐H 1, and cis‐Py‐Ru‐H 3 are relatively similar showing typical octahedral geometries with two PPh₃ fragments arranged in trans positions.     

Further Studies of CoIII(TIM) Mono-Alkynyl and Bis-Alkynyl Complexes

A new series of mono- and bis-alkynyl Co^III(TIM) complexes (TIM=2,3,9,10-tetramethyl-1,4,8,11-tetraazacyclotetradeca-1,3,8,10-tetraene) is reported herein. The trans-[Co(TIM)(C₂R)Cl]⁺ complexes were prepared from the reaction between trans-[Co(TIM)Cl₂]PF₆ and HC₂R (R=tri(isopropyl)silyl or TIPS ( 1 ), -C₆H₄-4-^tBu ( 2 ), -C₆H₄-4-NO₂ ( 3 a ), and N-mesityl-1,8-naphthalimide or NAP^Mes ( 4 a )) in the presence of Et₃N. The intermediate complexes of the type trans-[Co(TIM)(C₂R)(NCMe)](PF₆)(OTf), 3 b and 4 b , were obtained by treating 3 a and 4 a , respectively, with AgOTf in CH₃CN. Furthermore, bis-alkynyl trans-[Co(TIM)(C₂R)₂]PF₆ complexes, 3 c and 4 c , were generated following a second dehydrohalogenation reaction between 3 b and 4 b , respectively, and the appropriate HC₂R in the presence of Et₃N. These new complexes have been characterized using X-ray diffraction ( 2 , 3 a , 4 a , and 4 c ), IR, ¹H NMR, UV/Vis spectroscopy, fluorescent spectroscopy ( 4 c ), and cyclic voltammetry.     

Trägerfixierte Organometallkomplexe. VI. Charakterisierung und Reaktivität Polysiloxan-gebundener (Ether-phosphan)ruthenium(II)-Komplexe

Supported Organometallic Complexes. VI. Characterization und Reactivity of Polysiloxane-Bound (Ether-phosphane)ruthenium(II) Complexes The ligands PhP(R)CH₂D [R = (CH₃O)₃Si(CH₂)₃; D = CH₂OCH₃ ( 1b ); D = tetrahydrofuryl ( 1c ); D = 1,4-dioxanyl ( 1d )] have been used to synthesize (ether-phosphane)ruthenium(II) complexes, which have been copolymerized with Si(OEt)₄ to yield polysiloxane-bound complexes. The monomers cis,cis,trans-Cl₂Ru(CO)₂(P ～ O)₂ ( 3b ) and HRuCl(CO)(P ～ O)₃ ( 5b ) were treated with NaBH₄ to form cis,cis,trans-H₂Ru(CO)₂(P ～ O)₂ ( 4b ) and H₂Ru(CO)(P ～ O)₃ ( 6b ), respectively (P ～ O = η¹-P coordinated; = η²- coordinated). Addition of Si(OEt)₄ and water leads to a base catalyzed hydrolysis of the silicon alkoxy-functions and a precipitation of the immobilized counterparts 4b ′, 6b ′. The polysiloxane matrix resulting by this new sol gel route has been described under quantitative aspects by ²⁹Si CP-MAS NMR spectroscopy. 4b ′ reacts with carbon monoxide to form Ru(CO)₃(P ～ O)₂ ( 7b ′). Chelated polysiloxane-bound complexes Cl₂Ru( )₂ ( 9c ′, d ′) and Cl₂Ru( )(P ～ O)₂ ( 10b ′, c ′) have been synthesized by the reaction of 1b–c with Cl₂Ru(PPh₃)₃ ( 8 ) followed by a copolymerization with Si(OEt)₄. The polysiloxane-bound complexes 9c ′, d ′ and 10b ′, c ′ react with one equivalent of CO to give Cl₂Ru(CO)( )(P ～ O) ( 12b ′– d ′). Excess CO leads to the all-trans-complexes Cl₂Ru(CO)₂(P ～ O)₂ ( 14b ′– d ′), which are thermally isomerized to cis,cis,trans- 3b ′– d ′. The chemical shift anisotropy of ³¹P in crystalline Cl₂Ru( )₂ ( 9a , R = Ph, D = CH₂OCH₃) has been compared with polysiloxane-bound 9d ′ indicating a non-rigid behavior of the complexes in the matrix.     

Die Schwingungsspektren der isomeren Komplexe N,N′-Bis(dimethylgallium)-cis- und trans-N,N′-dimethyloxamideine kritische Analyse

Reaction of Ga(CH₃)₃ with N,N′-dimethyloxamide affords two isomeric N,N′-bis(dimethylgallium)-N,N′-dimethyloxamide complexes, characterized by crystal structure analysis as having cis-and trans-configuration with respect to the central oxamide CC bond and belonging to the point groups C_2v (cis) and C_2h (trans), respectively. Both isomers which are formed in varying ratio, depending upon the reaction conditions, have been isolated in pure form; their vibration spectra (IR/RE) are analyzed in detail in points of alternative behaviour, and are assigned in all bands, especially in the G-C and Ga-X frequency region. The assignment receives further confirmation from a comparison with the vibrational data of the homologous N,N′-bis(dimethylgallium)oxamide (cis/trans isomer mixture).     

Indolo[3,3a,4-gh]chinoline und 10a, 6a-Iminopropanoindolo[3,3a,4-gh] chinoline. Stereospezifische Synthesen und Umlagerungen. Teil I. 8. Mitteilung über synthetische Indolverbindungen

The stereospecific cyclization of derivatives of 1-benzyl-5-oxo-1,3,4,5-tetrahydrobenzo[cd]indole to trans-octahydroindolo[3,3a,4-gh]quinolines 3 and 4 is described. The trans methyl esters ( 4b and 4c ) were converted with BF₃/CH₃OH to the thermodynamically more stable cis-epimers 5 . The structures and stereochemistry of the products, deduced from chemical evidence and analysis of models, are compatible with the NMR. data.     

Triaziridine. 9. Mitteilung. Ringöffnungen von Triaziridinen

Triaziridines. Ring Openings of Triaziridines Eleven triaziridine derivatives were heated at 60° in CDCl₃ to obtain information on the tendency towards, resp. the resistance to, ring opening of the N₃-homocycle by thermolysis. Among these triaziridines, there are three which contain, as one of the substituents, a methoxycarbonyl group (ester derivatives 1 , 5 and 16 ), three a methyl group (methyl derivatives 18 , 24 , and 26 ), three an H-atom ( 14 , 27 , and 30 ), and two a negative charge ( 31 and 32 ). The other two substituents in each of these four classes of triaziridines are trans-located i-Pr groups ( 1 , 18 , 27 , and 31 ), cis-located i-Pr groups ( 5 , 24 , 14 , and 32 ), and a 1,3-cis-cyclopentylidene group ( 16 , 26 , and 30 ). As major products these mild thermolyses, we isolated : from the trans-ester 1 and from the annellated ester derivative 16 , the 1-acyl-azimines 2 and 17 , respectively, from the cis-ester 5 , the 3-acyl-triazene 4 , from the trans-methyl derivative 18 , the (E)-diazene 19 , and hexamine 21 , from the cis-methyl derivative 24 the 2-methylazimine 25 , both from the trans- and cis-H-derivatives 27 , and 14 , respectively, the H- triazene 13 and, finally, both from the trans-and cis-anion 31 and 32 , respectively – after protonation the H-triazene 13 and – after methylation – the methyl-triazene 33 . The same thermolysis of the annellated methyl and H-derivatives 26 and 30 , respestively, resulted only in decomposition. These results can be uniformly interpreted with a primary opening of the triaziridine ring by rupture of one of the two types of N? N bonds lending to azimines or triazenide anions. Some of the azimines were isolable, namely 2 , 17 , and 25 , and one was spectroscopically observable as an intermediate, namely 11 on the way to the triazene 4 . The other azimines are plausible intermediates to the isolated products, namely 15 on the way to 13 , and 22 on the way to 19 and 21 . The triazenide anion 28 is the evident intermediate on the way to 13 or to 33 . The annellated azimines are assumed not be formed from 26 and 30 , or then to be be decomposed under the conditions of their formation. We conclude that the triaziridine derivatives 1, 16 , and 18 underwent thermal ring opening between N(1) and N(2), while the derivatives 5 , 14 , 24 , 27 , 31 , and 32 were ruptured between N(2) and N(3); no conclusion was possible on the ring opening of the derivatives 26 and 30 . The predominant formation of the (Z)-azimine 2 from the trans-triaziridine 1 , and of the (E)-isomer 3 – among the two azimines – from the cis-triaziridine 5 suggests a stereospecificity in the triaziridine ring openings. This would, however, not be expected to be observable in the products from the other triaziridines, since both N? N bonds of the azimine 25 and of the anion 28 probably rotate rapidly and since the secondary trans formations of the other primary products are not able to retain configurational information.     

Synthesis,Structures, Ligand Substitution Reactions,and Electrochemistry of the Nitrile Complexes cis‐[Ru(dppm)2Cl(NCR)]+ PF6– (dppm = Bis(diphenylphosphino)methane,R = CH3, C2H5, tBu,Ph)

Isomerically pure nitrile complexes cis‐[Ru(dppm)₂Cl(NCR)]⁺ ( 2 a – d ) are formed upon chloride displacement from cis‐[Ru(dppm)₂Cl₂] ( 1 ) or, alternatively, by ligand substitution from the acetonitrile complex 2 a . This latter approach does also allow for the introduction of pyridine ( 3 a , b ), heptamethyldisilazane ( 4 ) or isonitrile ligands ( 5 ). All complexes are obtained as the configurationally stable cis‐isomers. Only cis‐[Ru(dppm)₂Cl(CN^tBu)]⁺ slowly isomerizes to the trans from. The solid state structures of the CH₃CN, C₂H₅CN and the trans‐^tBuNC complexes were established by X‐ray crystallography. Electrochemical investigations of the nitrile complexes 2 a – d show in addition to a chemically reversible one‐electron oxidation an irrversible reduction step. In CH₂Cl₂ solution, cis‐ and trans‐[Ru(dppm)₂Cl₂] have been identified as the final products of the electrochemically induced reaction sequence.     

Protonenresonanzuntersuchungen an Aminoboranen—II: Einflüsse von para-Phenylsubstituenten auf die Rotationsbarriere um die N?B-Bindung

The electronic influence of substituents on the free enthalpy of rotation around the N? B bond in aminoboranes was investigated in two series of compounds: (a) (CH₃)₂N?BCl (phenyl-p-X), containing the para-phenyl substituent at the boron atom, and (b) (p-X-phenyl)CH₃N?B(CH₃)₂, containing the para-phenyl substituent at the nitrogen atom of the N? B linkage (X = ? NR₂, ? OCH₃, ? C(CH₃)₃, ? Si(CH₃)₃, ? H, ? F, ? Cl, ? Br, ? I, ? CF₃ and ? NO₂). By comparing the rotational barriers in corresponding compounds of both series, a reverse effect of the substituents could be observed. Electron-withdrawing substituents in the para position of the phenyl ring increase the ΔG_c^≠ if the phenyl group is attached to the boron atom; on the other hand, a lower ΔG_c^≠ is observed if the phenyl ring is bonded to the nitrogen atom of the N? B system. Substitution of the phenyl ring with electron-donating substituents in the paraposition exerts the opposite effect. Within each series of compounds, the differences of ΔG_c^≠ values [δ(ΔG_c^≠) = ΔG_c^≠ (X) ? ΔG_c^≠ (X = H)] between substituted and unsubstituted compounds can be explained in terms of inductive and mesomeric effects of the ring substituents and can be correlated with the Hammett σ constant of each substituent. A comparison of the slopes of the plotted lines shows that the influence of the ring substituents is more pronounced in compounds with N-phenyl-p-X than in those with B-phenyl-p-X.     

Triaziridine. 6. Mitteilung. Substituententransformationen an Triaziridinen

Substituent Transformations on Triaziridines Several novel triaziridines were prepared by substituent transformations starting from the known dialkyl-triaziridine-carboxylates 1a – c , with the aim to study the influence of the substitution pattern on the properties of the triaziridine ring. The dialkyl-triaziridines 2a – c were obtained by (t-BuO^?)-mediated demethylation and decarboxylation and the dialkyl-triaziridine-methanols 4a – c by LiAlH₄ reduction. Further reduction of the tosylates of 4a , b with LiAlH₄ gave the methyl-dialkyl-triaziridines 3a , b . The dialkyl-triaziridines 2a , c could not be N-methylated directly with CH₃I, but the anions 10a , c , obtained from 2a, c with CH₃Li, yielded 3a , c . N-Methylation of 2a with (CH₃)₃OBF₄ did not afford 3a but rather the methyl-triaziridinium salt 11 . The dialkyl-triaziridine 2c has pK_a > 14, its protonated species < 2. A concept that the electron pairs on the triaziridine N-atoms are more strongly localized than on amine N-atoms explains (a) that the dialkyl-triaziridine 2c is hardly basic, (b) that the LiAlH₄ reductions of the esters 1 stop at the stage of the methanols 4 , and (c) that the methanols 4a , b do not cleave like aminomethanols.     

Conformation et spectrométrie de R.M.N.: II

The four isomeric 3-dimethylamino-trans-2-decalols-1,1,4,4-d₄ have been synthesised. Examination of PMR spectra of these compounds allows us to confirm the ‘flattened-chair’ conformation for the cis N(CH₃)₂^a OH^e isomer, whereas the remaining three conserve the double chair conformation. The same type of flattening is also observed in the case of the diaxial quaternary ammonium salt and is even more marked in the cis N(CH₃)₃^a OH^e isomer resulting in a ‘twist-chair’ conformation.     

IR and Raman spectroscopic study of the photopolymerization of Langmuir-Blodgett films of acetylenic acids

The UV induced photopolymerization of Langmuir-Blodgett films of lead salt of 2-docosynoic acid (CH₃(CH₂)₁₈C=CCOOH) is studied using IR and Raman spectroscopy. It is found that the films are a highly ordered system with trans-configuration of alkyl chains and a bridged complex generated between the carboxyl group and the lead ion. Based on a change in the absorption band intensity in the IR spectra corresponding to the triple bond vibration, the degree of polymerization depending on the irradiation time is determined. In the Raman spectra, a peak at ∼1635 cm⁻¹ appears during polymerization, which corresponds to the C=C double bond. The formation of conjugated double bonds in these systems is observed for the first time. During polymerization, methylene chains of molecules retain trans-configuration; the structural ordering of molecules in the film is observed.     

cis-trans-and Intramolecular enol-enolic equilibrium of β-ketoaldehydes

Tautomerism of aromatic β-ketoaldehydes p-XPhCOCH₂CHO ( 1 , X = NMe₂, OMe, Me, H, Br, NO₂), aliphatic β-ketoaldehydes and benzoylacetaldehyde RCOCH₂CHO ( 2 , R = Me, i-Bu, t-Bu, Ph), RCOCH(Me)CHO ( 3 , R = Me, Et, i-Pr) and methyl 2-formylpropionate MeOCOCH(Me)CHO ( 4 ) has been studied by the ¹H NMR technique. In basic solvents both cis- and trans-enol forms of these compounds co-exist. trans-Enolisation, which occurs exclusively at the formyl group, is most favoured in compound ( 4 ) and least favoured in compounds ( 1 ) and ( 2 ). The increasing electron-attracting property of the substituent X in the aromatic β-ketoaldehydes ( 1 ), as well as increasing solvent basicity in the series propanediol-1, 2-carbonate, acetone < dimethylformamide < dimethylacetamide < pyridine, also shifts the equilibrium towards the trans-enol form. The trans-enol form is absent in aprotic solvents of low basicity such as CCl₄, C₂HCl₃ and toluene. The thermodynamic parameters of the cis-trans-enol (C ? T) and cis-enol-enolic (C ? C') equilibria have been estimated from the temperature dependences. The transition from the cis-to the trans-enol form is accompanied by an entropy decrease of about 10 cal mol^?1 degree^?1. Nevertheless the trans-enol form is stabilised due to its lower enthalpy. The cis-trans-enol equilibrium is determined by the relative strength of the intramolecular hydrogen bond in the cis-enol form and the intermolecular hydrogen bonds with basic solvent molecules of the trans-enol form. The enthalpy difference of the two cis-enolic forms does not exceed 1.0 kcal/mol, in rough agreement with the data calculated by the CNDO/2 approximation. Polar solvents favour the hydroxymethyleneketone form (C) for both groups of compounds 2 and 3 . The content of the hydroxymethyleneketone form is about the same within series 2 where R = Me, i-Bu, Ph and is a little higher for the t-Bu derivative. A decrease of temperature only slightly shifts the equilibrium of compounds 1 and 2 to the hydroxymethyleneketone form, while in the case of 2-methyl-β-ketoaldehydes (3) this effect is markedly pronounced.     

Azimine. V.. Untersuchungen zur stereoisomerie an der N(2), N(3)-bindung von 2, 3-dialkyl-1-phthalimido-aziminen

Azimines. V. Investigation on the Stereoisomerism Around the N (2), N (3) Bond in 2, 3-Dialkyl-1-phthalimido-azimines 2, 3-(cis-1, 3-Cyclopentylene)-1-phthalimido-azimine ( 7 ) and isomerically pure (2 Z)- and (2 E)-2, 3-diisopropyl-1-phthalimido-azimine ( 9a and 9b ) were prepared by the addition of phthalimido-nitrene ( 1 ) to 2, 3-diazabicyclo [2.2.1]hept-2-ene ( 6 ) and to (E)- and (Z)-1, 1′-dimethylazoethane ( 8a and 8b ), respectively. Comparison of their UV. spectra with those of two stereoisomeric azimines of known configuration, namely (1 E, 2 Z)- and (1 Z, 2 E)-2, 3-dimethyl-1-phthalimido-azimine ( 5a and 5b ), reveals that 2, 3-dialkyl-1-phthalimido-azimines with (2 Z)-configuration are characterized by a shoulder at about 258 nm (? ≈? 14,000) and those with (2 E)-configuration by a maximum at 270–278 nm (? ≈? 10,000). The (2 E)-azimine 9b isomerizes under acid catalysis as well as thermally and photochemically into the more stable (2 Z)-isomer 9a . Under the last two conditions the isomerization is accompanied by a slower fragmentation with loss of nitrogen into N, N′-diisopropyl-N, N′-phthaloylhydrazine ( 4 , R = iso-C₃H₇). The same fragmentation was also observed on thermolysis and photolysis of the (2 Z)-isomer 9a . The kinetic parameters for the thermal isomerization of 9b (they fit first-order plots) and for the fragmentation of 9a and 9b were determined by ¹H-NMR. spectroscopy in benzene, trichloromethane and acetonitrile. In the photolysis of 9a or 9b the fragmentation is accompanied by dissociation into the azo compounds 8a or 8b and the nitrene 1 , the latter being subject to trapping by cyclohexene. With the azimine 7 , an analogous thermal fragmentation was observed to give N, N′-(cis-1, 3-cyclo-pentylene)-N, N′-phthaloylhydrazine ( 15 ), but more energetic conditions were required than with 9 . Photolysis of 7 led exclusively to dissociation into the azo compound 6 and the nitrene 1 , perhaps because the fragmentation of 7 is prevented by ring strain.     

Investigations on organoantimony compounds : XVII. Preparation and properties of heterocyclic trans-dichloro-β-diketonato-cis-diorganoantimony(V) compounds. Influence of stereochemistry on β-diketonate ligand exchange reactions in octahedral dichloro-β-diketonatodiorganoantimony(V) compounds

A series of heterocyclic trans-dichloro-β-diketonato-cis-diorganoantimony(V) compounds of the type R₂SbCl₂X (R₂ = (CH₂)₄, (CH₂)₅, o,o′−C₆H₄C₆H₄, o,o′−C₆H₄CH₂C₆H₄; X = Acac, Dpm) has been synthesized. The stereochemistry of these compounds has been deduced from PMR spectroscopic and molecular dipole moment data. Since the cis-dichloro-β-diketonato-trans-diorganoantimony(V) compounds R₂SbCl₂Acac (R = Me, Et, Ph) were known previously, a set of both cis- and trans-diorgano main group organometallic complexes has thus been made available, which allows a comparative study of the influence of stereochemistry on the strength of metal—ligand interactions in this type of octahedral d¹⁰ metal complex. β-Diketonate—ligand exchange reactions have been studied by PMR spectroscopy, and a marked influence of stereochemistry observed. trans-Dichloro-β-diketonato-cis-diorganoantimony(V) compounds undergo ligand exchange only slowly, if at all, whereas cis-dichloro-β-diketonato-trans-diorganoantimony(V) compounds react instantaneously. Both PMR chemical shift data and IR spectroscopic data point to the occurrence of a stronger antimony-β-diketonate interaction in trans-dichloro-β-diketonato-cis-diorganoantimony than in cis-dichloro-β-diketonato-trans-diorganoantimony compounds. This can be understood in terms of the hybridization of the antimony valence orbitals. The results are in line with the assumption that Sb---O bond rupture is the rate-determining step in β-diketonate ligand exchange.     

Coordination Chemistry of Highly Hemilabile Bidentate Sulfoxide N‐Heterocyclic Carbenes with Palladium(II)

Imidazolium salts, [RS(O)? CH₂(C₃H₃N₂)Mes]Cl (R=Me ( L1 a ), Ph ( L1 b )); Mes=mesityl), make convenient carbene precursors. Palladation of L1 a affords the monodentate dinuclear complex, [(PdCl₂{MeS(O)CH₂(C₃H₂N₂)Mes})₂] ( 2 a ), which is converted into trans‐[PdCl₂(NHC)₂] (trans‐ 4 a ; N‐heterocyclic carbene) with two rotamers in anti and syn configurations. Complex trans‐ 4 a can isomerize into cis‐ 4 a (anti) at reflux in acetonitrile. Abstraction of chlorides from 4 a or 4 b leads to the formation of a new dication: trans‐[Pd{RS(O)CH₂(C₃H₂N₂)Mes}₂](PF₆)₂ (R=Me ( 5 a ), Ph ( 5 b )). The X‐ray structure of 5 a provides evidence that the two bidentate SO? NHC ligands at palladium(II) are in square‐planar geometry. Two sulfoxides are sulfur‐ and oxygen‐bound, and constitute five‐ and six‐membered chelate rings with the metal center, respectively. In acetonitrile, complexes 5 a or 5 b spontaneously transform into cis‐[Pd(NHC)₂(NCMe)₂](PF₆)₂. Similar studies of thioether–NHCs have also been examined for comparison. The results indicate that sulfoxides are more labile than thioethers.     

Vanadium(II) alkyls. Synthesis and X-ray crystal structures of trans-VMe2(dmpe)2 and cis-V(CH2SiMe3) 2(dmpe)2

Treatment of the vanadium(II) tetrahydroborate complex trans-V(η¹-BH₄)₂(dmpe)₂ with (trimethylsilyl) methyllithium gives the new vanadium(II) alkyl cis-V(CH₂SiMe₃)₂(dmpe)₂, where dmpe is the chelating diphosphine 1,2-bis(dimethylphosphino)ethane. Interestingly, this complex could not be prepared from the chloride starting material VCl₂(dmpe)₂. The CH₂SiMe₃ complex has a magnetic moment of 3.8 μ_B, and has been characterized by ¹H NMR and EPR spectroscopy. The cis geometry of the CH₂SiMe₃ complex is somewhat unexpected, but in fact the structure can be rationalized on steric grounds. The X-ray crystal structure of cis-V(CH₂SiMe₃)₂(dmpe)₂ is described along with that of the related vanadium(II) alkyl complex trans-VMe₂(dmpe)₂. Comparisons of the bond distances and angles for VMe₂(dmpe) ₂, V---C = 2.310(5) Å, V---P = 2.455(5) Å, and P---V---P = 83.5(2)° with those of V(CH₂SiMe₃)₂(dmpe)₂, V---C = 2.253(3) Å, V---P = 2.551(1) Å, and P ---V---P = 79.37(3)° show differences due to the differing trans influences of alkyl and phosphine ligands, and due to steric crowding in latter molecule. The V---P bond distances also suggest that metal-phosphorus π-back bonding is important in these early transition metal systems. Crystal data for VMe₂(dmpe)₂ at 25°C: space group P2₁/n, with a = 9.041(1) Å, b = 12.815(2) Å, c = 9.905(2) Å, β = 93.20(1)°, V = 1145.8(5) ų, Z = 2, R_F = 0.106, and R_wF =0.127 for 74 variables and 728 data for which I 2.58 σ(I); crystal data for V(CH₂SiMe₃)₂(dmpe)₂ at −75°C: space group C2/c, with a = 9.652(4) Å, b = 17.958(5) Å, c = 18.524(4) Å, β = 102.07(3)°, V= 3140(3) ų, Z = 4, R_F = 0.033, and R_wF = 0.032 for 231 variables and 1946 data for which I 2.58 σ(I).     

Axial and Equatorial Substitution of Dimethylamine on Phosphorus in the 1,3,2-Oxazaphosphorinane Ring System: Structures of 2-Dimethylamino-Phenyl-2H-1,3,2-oxazaphosphorinane-2-Oxides

X-ray structures of trans-2-dimethylamino-5-phenyl-2H-1,3,2-oxazaphosphorinane-2-oxide, 5b , and trans-2-dimethylamino-6-phenyl-2H-1,3,2-oxazaphosphorinane-2-oxide, 6c , have been determined. These two compounds have been prepared in a straightforward manner by a reaction of cyclization of Mc₂NP(O)Cl₂ with the corresponding 3-amino-2-phenylpropanol and 3-amino-1-phenylpropanol, respectively, to produce (5b, 6b) and (5c, 6c) , and were separated into pure forms by chromatography. Crystal data of 5b : space group P_ccn, a = 10.675(5), b = 31.685(9), c = 7.217(3) Å, R = 0.065 for 1040 reflections. Crystal data of 6c: space group P-1, a = 9.803(6), b = 12.455(5), c = 12.690(2) Å, α = 114.11(2), β = 80.88(2), γ = 111.64(4)°, R = 0.035 for 3534 reflections. For the pair 5b and 6b , the slowly-migrating 5b is trans (Ph and P = O group trans) with the configuration of 2RS, 5RS, hence 6b is the cis isomer. For the pair 5c and 6c , the slowly migrating 6c is trans with the configuration of 2RS, 6SR; hence 5c is the cis isomer. In both X-ray structures the 1,3,2-oxazaphosphorinane rings are chair-like with the P-end essentially flattened. With a conformationally demanding 5-phenyl substituent, 5b has an axial Me₂N whereas with also a conformationally demanding 6-phenyl substituent, 6c has an equatorial Me₂N. For 6c , the exocyclic P-N bond has partial double bond character: the geometry about exocyclic N is planar. On the other hand, for 5b , the geometry about exocyclic N deviates considerably from planarity, the sum of the angles around N being 343.3°. In the crystalline state, the two crystallographically independent molecules of 6c are linked together in a hydrogen-bonded system involving the water molecule.     

14N NMR of amminecobalt(III) compounds

Directly detected ammine ¹⁴N NMR chemical shifts of 20 amminecobalt(III) compounds are reported. The coordination shifts, δ_CS = δ_coord ? δ_free, are in all cases negative and range from ?4.4 ppm for the trans ammine ligand in [Co(NH₃)₅(CH₃)]²⁺ to ?73.6 ppm for the trans ammine ligand in [Co(NH₃)₅(F)]²⁺. Among the ligands studied, the NO₂^? ligand is unique in that it exerts a significant cis influence. The regularity in trans or cis influences upon the ammine nitrogen chemical shifts provides a basis for assignments in cases where this cannot be deduced from intensity ratios. Copyright © 2003 John Wiley & Sons, Ltd.