Low-temperature 13C Research Articles

Seven-co-ordinate dibromo complexes of molybdenum(II) and tungsten(II) derived from [MBr2(CO)3(NCMe)2]. Crystal structures of the isostructural complexes [WX2(CO)3(NCMe)(SBPh3)]·Ch2Cl2(X = Br or I)

Reaction of the complexes fac-[M(CO)3(NCMe)3](M = Mo or W)(prepared in situ) with an equimolar quantity of Br2 at –78 °C afforded high yields of the seven-co-ordinate complexes [MBr2(CO)3(NCMe)2]. The reaction of these complexes with an equimolar amount of L (L = PPh3, AsPh3 or SbPh3) in CH2Cl2 at room temperature gave the new mixed-ligand complexes [MBr2(CO)3(NCMe)L]. The molecular structure of [WBr2(CO)3(NCMe)(SbPh3)]·CH2Cl2 and its diiodo analogue [WI2(CO)3(NCMe)(SbPh3)]·CH2Cl2 have been crystallographically determined. Crystals of the former are monoclinic of space group P21/c, a= 8.302(3), b= 26.199(3), c= 13.020(4)A, β= 97.53(2)°, Z= 4. Crystals of the latter are also monoclinic of space group P21/c, a= 8.450(2), b= 25.941 (6), c= 13.042(4)A, β= 96.47(2)°, Z= 4. The two complexes are isostructural and can best be described as distorted capped trigonal prismatic with one triangular face having three carbonyl ligands and the other triangular face having X(2), Sb and N. The X(1 ) atom caps the rectangular face defined by C(1), X(2), N and C(3). The low-temperature (–6O °C, CDCl3)13C NMR spectrum of [WI2(CO)3(NCMe)(SbPh3)]·CH2Cl2 was obtained and correlated with the solid-state structure. Reaction of [WBr2(CO)3(NCMe)2] with 2 equivalents of AsPh3 in CH2Cl2 at room temperature gave [WBr2(CO)3(AsPh3)2].

Remarkable dynamic NMR spectra and properties of a sterically congested cis-1,2-diarylcyclobutane

Dimethyl 2.2′-dichloro-6,6′-dimethoxy-β-truxinate 2 displays in solution, by 1H NMR spectroscopy, a mixture of two conformers: a meso conformer and a racemic conformer. The other possible meso conformer may be present in a small amount in solution. The NMR parameters of these conformers were extracted from their low-temperature static 1H and 13C spectra. The conformers interconvert mainly by a mechanism involving rotation of one aryl group at a time. Activation parameters of the same dynamic process were obtained by band-shape simulations from four different regions of the variable-temperature 1H spectra. In one spectral region, rate constants in excess of 106 s–1 were recorded.

Six- and seven-co-ordinate complexes of molybdenum(II) and tungsten(II) with thioether ligands. Crystal structures of [WI2(CO)3{4-MeC6H4S(CH2)2SC6H4Me-4}] and [WI2(CO)2{MeS(CH2)2S(CH2)2SMe-S,S′,S″}

Reaction of [MI2(CO)3(NCMe)2](M = Mo or W) with a slight excess of RS(CH2)2SR (R = Ph, 4-MeC6H4 or 4-FC6H4) in CH2Cl2 at room temperature gave [MI2(CO)3{RS(CH2)2SR}]. The molecular structure of [WI2(CO)3{4-MeC6H4S(CH2)2SC6H4Me-4}] has been determined by X-ray crystallography. It shows that the tungsten has essentially capped-octahedral geometry with a carbonyl ligand in the unique capping position. Low-temperature 13C NMR studies on the tungsten complexes suggest that their structures in solution are similar to the solid-state structure found. Reaction of [WI2(CO)3(NCMe)2] with 2 equivalents of PhS(CH2)2SPh in CH2Cl2 afforded [WI(CO)3{PhS(CH2)2SPh-S}{PhS(CH2)2SPh-S,S′}]I which was reduced by LiBun to cis-[W(CO)2{PhS(CH2)2SPh-S.S′}2]. Equimolar quantities of [MI2(CO)3(NCMe)2](M = Mo or W) and MeS(CH2)2S(CH2)2SMe reacted in CH2Cl2 to give [MoI2(CO)2{MeS(CH2)2S(CH2)2SMe-S,S″,S″}] and [WI2(CO)3{MeS(CH2)2S(CH2)2SMe-S,S″}]. The latter was converted in CHCl3 into [WI2(CO)2{MeS(CH2)2S(CH2)2SMe-S,S″,S″}], the molecular structure of which is essentially a capped octahedron with a carbonyl ligand in the unique capping position.

Infrared, Raman and NMR spectra, conformational stability, and ab initio calculations of divinylmethoxyborane

The infrared spectra (4000–50 cm −1) of gaseous and solid divinylmethoxyborane, (CH 2=CH) 2BOCH 3, as well as the Raman spectra (3500–20 cm −1) of the liquid and solid have been recorded. Qualitative depolarization values have been obtained from the Raman spectrum of the liquid. All normal modes, except the torsions, have been assigned based on infrared band contours, depolarization values, group frequencies, and normal coordinate calculations. From a comparison of the spectra in the fluid and solid states, it is concluded that the molecule exists predominantly in a single conformation in all physical states. Frequencies and potential energy distributions for the normal modes have been calculated with the 3–21G basis set. A comparison of these calculated frequencies to the observed spectra is consistent with the predominant form having a “planar” heavy atom skeleton with C s , symmetry. From the variable low temperature 13C NMR data, a barrier to rotation about the B-O bond of 10.1 ± 0.1 kcal mol −1 has been determined, which is in excellent agreement with a barrier of 8.5 kcal mol"1 obtained from ab initio calculations. Structural parameters, conformational stability, and barriers to internal rotation have been obtained from ab initio Hartree-Fock gradient calculations employing both the 3–21G and 6–31G * basis sets. The results are compared to the corresponding data for some similar organoboranes.

Cis-Cyclohexano-9-crown-3 ether. Solid state and low-temperature solution stereochemistry as determined by X-ray crystallography and nuclear magnetic resonance spectroscopy

The X-ray crystal structure of the title material has been determined at −130 °C. Low-temperature 1H1H COSY, 13C1H HETCOR, and DEPT 13C NMR spectra have been recorded, which permit unambiguous assignments of all carbon resonances when ring inversion is slow on the NMR timescale. The limiting low-temperature solution phase 13C spectrum has many common features with the solid phase 13C CPMAS spectrum recorded at 300 K. Spectra for the 7,10-tetra-deuterio derivative have also been obtained and substituent influences on 13C shieldings are discussed in detail.

High-resolution solid-state 13C and 29Si NMR investigations of the dynamic properties of tetrakis(trimethylsilyl)silane

High-resolution solid-state 13C and 29Si NMR spectroscopy have been used to investigate the dynamic properties of tetrakis(trimethylsilyl)silane (TTMSS) as a function of temperature; from the temperature dependence of the spectra, it is clear that TTMSS is not useful as a chemical shift reference material below ca. 238K, but the spectral changes associated with the phase transition at this temperature nevertheless provide a precise method for controlling temperature calibration in low-temperature solid-state 13C NMR studies.

Tetraphenyl sulfurane: first detection as intermediate in the reactions of triphenylsulfonium salt and diphenyl sulfoxide with phenyllithium by low temperature 1H and 13C nmr

Direct evidence for the formation of tetraphenyl sulfurane was presented in the reactions of triphenylsulfonium hexafluorophosphate and diphenyl sulfoxide with phenyllithium by 1H, 13C, and CH-COSY NMR studies at low temperature.

Synthesis, structure, and stability of the zinc complex of the dimethyl ester of meso-2,3-dimercaptosuccinic acid.

The dimethyl ester of meso-2,3-dimercaptosuccinic acid (meso-DiMeDMSA) reacts with Zn2+ ions to form protonated and polynuclear complexes. The species [Zn2L3H]- and [Zn2L3]2- are formed at pH values between 3 and 6.5 and have overall formation constants of 10(37.53) and 10(32.52), respectively, whereas the mononuclear complex [ZnL2]2- is formed at physiological pH and has a formation constant of 10(18.06). The mononuclear complex was synthesized and isolated as an ion association complex with the tetramethylammonium ion, [(Me)4N]2[Zn(DiMeDMSA)2], and its structure in solution was determined by low-temperature 1H and 13C NMR spectroscopy. In this structure the Zn2+ ion is tetrahedrally coordinated to four thiolate groups from two meso-DiMeDMSA molecules.

Silver(I) complexes with aryldithiocarboxylates and triphenylphosphine. Crystal and molecular structure of the dinuclear complex [{Ag(S 2C- p-tolyl)PPh 3} 2] and NMR investigation of the mononuclear compounds [{Ag(S 2CAr)(PPh 3} 2] in solution

1H, 13C, 31P NMR spectra are reported for the complexes [Ag(S 2CAr)(PPh 3) 2] (Ar=phenyl, o-tolyl, p-tolyl). In solution at room temperature these species are partially dissociated and the phosphine undergoes fast exchange. 31P NMR parameters were obtained from low temperature spectra, 13C and 1H data from room temperature spectra. Overall examination of the spectra shows that no stable species with more than two triphenylphosphine molecules coordinated to one silver atom is detectable, that in phenyl and p-tolyl derivatives the dithiocarboxylato group prefers to be coplanar with the aromatic ring also in solution and that in the AgS 2CAr bonding the covalent character is rather poor. The monophosphine derivatives [{Ag(S 2CAr)PPh 3} 2] (Ar= o-tolyl, p-tolyl) present incongruent solubility. For the complex with Ar= p-tolyl X-ray diffraction methods show an unusual molecular structure, consisting of centrosymmetric species [{Ag(CS 2- p-tolyl)PPh 3} 2], in which the dithioarylate ligand is tridentate; while S(1) bridges two metal centres (2.631(2) and 2.692(3) Å), S(2) is only bonded to one silver atom (2.657(2) Å). Phosphorus atoms from triphenylphosphine (AgP = 2.392(2) Å) complete the distorted tetrahedral arrangement of the silver atoms. The crystals are triclinic, space group P 1 , with a=11.744(3), b=10.862(2), c=9.831(2) Å, α=106.90(2), β=96.51(2), γ=74.54(2)° and Z=1. A total of 3206 symmetry independent reflections above background was measured at room temperature and the structure, solved by Patterson and Fourier methods, was refined by full matrix least-squares to R=0.050.

Nucleophilic addition to η 6-arenetricarbonylmanganese cations—the role of intermediates in the reactions with phosphines

The structures of adducts of phosphines (e.g. PEt 3) with the η 6-arenetricarbonylmanganese cations [(η 6-XYC 6H 4)Mn(CO) 3] + (Ia, X = Y = H; Ib, X = Me, Y = H; Ic, X = Cl, Y = H; Id, X = Cl, Y = p-Me) in acetone have been determined by low-temperature 1H and 13C NMR spectroscopy. In all cases regiospecific exo addition occurs at the arene ring with formation of η 5-cyclohexadienylphosphoniumtricarbonylmanganese cations [(η 5-XYC 6H 4PEt 3)Mn(CO) 3] + with Ib giving meta addition only (IIb) and Ic and Id forming both meta and ortho adducts (IIc, IIIc, and IId, IIId, respectively). Increase in temperature reverses the equilibria for IIa and IIb with formation of [(arene)Mn(CO) 2(PEt 3)] + whereas IIc, IIIc and IId, IIId form fac-Mn(CO) 3(PEt 3) 2Cl involving direct attack by the PEt 3 at the chlorine-bearing ring carbon atom rather than through a metal-hydride intermediate.

Tricyclohexylphosphinecarbondisulphide seven-coordinate complexes of molybdenum(II) and tungsten(II)

The complexes [MI 2(CO) 3(NCMe) 2] (M = Mo or W) react with one equivalent of S 2CPCy 3 in CH 2Cl 2 to afford the new seven-coordinate complexes [MI 2(CO) 3(S 2CPCy 3)]. Reaction of [MI 2(CO) 3(NCMe) 2] (M = Mo or W), with two equivalents of S 2CPCy 3 afford the new dicationic complexes [M(CO) 2(S 2CPCy 3) 2]2I in good yield. The dicationic nature [W(CO) 3(S 2CPCy 3) 2]2I was confirmed by the formation of the complex [W(CO) 3(S 2CPCy 3) 2][BPh 4] 2 by iodide exchange with Na[BPh 4]. Further reaction in situ of [M(CO) 3(S 2CPCy 3) 2]2I with one equivalent of S 2CPCy 3 afforded the tris ligand complex [W(CO) 3(S 2CPCy 3) 3]2I. The reaction of [W(CO) 3(S 2CPCy 3) 3]2I with Na[BPh 4] in acetonitrile gave [W(CO) 3(S 2CPCy 3) 3][BPh 4] 2, which confirmed the dicationic nature of [W(CO) 3(S 2CPCy 3) 3]2I. The mixed ligand complexes [MI(CO) 3(PPh 3)(S 2CPCy 3)]I (M = Mo or W) and [WI(CO) 3L(S 2CPCy 3)]I (L = P(OPh) 3, AsPh 3 or SbPh 3) were synthesised by reaction of [MI 2(CO) 3-(NCMe) 2] with an equimolar quantity of L in CH 2Cl 2 followed by an in situ reaction with one equivalent of S 2CPCy 3. The cationic nature of [MI(CO) 3(PPh 3)(S 2CPCy 3)]I was confirmed by iodide exchange with Na[BF 4] to afford the complexes [MI(CO) 3(PPh 3)(S 2CPCy 3)][BF 4]. The reaction of two equivalents of [WI 2(CO) 3(NCMe)(PPh 3)] with S 2CPCy 3 afforded the ligand-bridged complex [W 2I 4(CO) 6(PPh 3) 2(μ-S 2CPCy 3)]. Treatment of [WI 2(CO) 3(NCMe) 2] with two equivalents of PPh 3 followed by an in situ reaction with one equivalent of S 2CPCy 3 afforded the dicationic complex [W(CO) 3(PPh 3) 2(S 2CPCy 3)]2I. The ionic nature of the complex was confirmed by iodide exchange with Na[BPh 4] to give [W(CO) 3(PPh 3) 2(S 2CPCy 3)][BPh 4] 2. Treatment of [W(CO) 3(PPh 3) 2(S 2CPCy 3)]2I with one further equivalent of S 2CPCy 3 afforded the complex [W(CO) 3(PPh 3) 2(S 2CPCy 3)]2I. The low temperature 13C NMR spectra (carbonyl region) of several-coordinate complexes are interpreted to suggest likely structures for these compounds.

An NMR study of some seven-coordinate organophosphine carbonyl iodide derivatives of molybdenum(II) and tungsten(II)

The seven-coordinate complexes [MI 2(CO) 3L 2] (M = Mo, L = PMe 2Ph; M = W, L = PMe 2Ph, PMePh 2 or PPh 3) have been studied by variable temperature 31P-{ 1H} NMR spectroscopy; a fluxional process is observed and activation energies (Δ G ≠# = 52–57 kJ mol −1) have been calculated from coalescence temperatures. Low temperature 13C-{ 1H} and 31P-{ 1H} spectra suggest that the lowest energy configuration of [WI 2(CO) 3(PMe 2Ph) 2] is based on that of a carbonyl ligand face-capped octahedron with overall Cs symmetry with the PMe 2Ph ligands trans, and the two remaining carbonyl ligands presumably cis.

Conformational properties of cyclic pentaalkoxy phosphoranes: Apical-equatorial attachment and nonchair conformation of the phosphorus-containing six-membered ring

A series of phosphoranes with pentacovalent phosphorus contained in a 1,3,2-dioxaphosphorinane ring have been studied by 1H NMR. One compound was investigated by low-temperature 13C NMR and another by X-ray crystallography. Although the 1H NMR parameters observed are time-averaged, the coupling constants can be accounted for if the phosphoranes have the six-membered ring attached apical–equatorial to phosphorus and occupy in solution rapidly isomerizing boat or slightly twisted boat conformations similar to that found in the X-ray study.

Evidence for intermediate π-complexes in the addition of trialkylsilyl and trialkylstannylcuprates to β, β-unsaturated enones

Low temperature 13C NMR spectra of solutions generated during the addition of metallocuprates (PhMe 2Si) 3CuLi 2, PhMe 2Si(Me)Cu(CN)Li 2, (Me 3Sn) 3CuLi 2 and Me 3Sn(Me)Cu(CN)Li 2 to cyclohex-2-en-1-one suggest that these reactions proceed initially via unstable lithium coordinated copper(I)-olefin π-complexes. Workup of these reactions results in exclusive delivery of R 3Si or R 3Sn moiety in a 1,4-manner.

Seven-coordinate acetylacetonato, hexafluoroacetylacetonato and benzoylacetylacetonato complexes of molybdenum(II) and tungsten(II)

The complexes [MI 2(CO) 3(NCMe) 2] (M = Mo or W) react in CH 2Cl 2 with one or two equivalents of PPh 3 to give [MI 2(CO) 3(NCMe)(PPh 3)] or [MI 2(CO) 3(PPh 3) 2], which when reacted, in situ, with one equivalent of Na[ L L ] [ L L = acetylacetonato (acac), hexafluoroacetylacetonato (hfacac) or benzoylacetylacetonato (bzacac)] give the seven-coordinate complexes [MI(CO) 3(PPh 3)( L L )] and [MI(CO) 2(PPh 3) 2( L L )], respectively. The low temperature 13C NMR spectra of selected complexes are interpreted to suggest the likely structures of these compounds.

Reactions of the seven-co-ordinate complexes [MI2(CO)3(NCMe)2] and [MI2(CO)3(NCMe)L](M = Mo or W; L = PPh3, AsPh3 or SbPh3) with dithiocarbamate ligands

The complexes [MI2(CO)3(NCMe)2](M = Mo or W) react with 1 equivalent of Na[S2CN(CH2Ph)2] eventually to give the iodo-bridged dimers [{M(µ-I)(CO)3[S2CN(CH2Ph)2]}2]. The reaction of [MI2(CO)3(NCMe)2] with 1 equivalent of L (L = PPh3, AsPh3 or SbPh3) gave [MI2(CO)3(NCMe)L] which when treated in situ with Na[S2CNR2](R = Me, Et or CH2Ph) afforded [Ml(CO)3L(S2CNR2)]. The complexes [Mol(CO)3L(S2CNR2)] prepared as described above when treated in situ with 1 equivalent of [S2CNR2]– generally give the mixed-ligand oxides [Mo2O3(S2CNR2)2(S2CNR'2)2]. The complexes [WI(CO)3(PPh3)(S2CNR2)](R = Me, Et or CH2Ph) when treated in situ with Na[S2CNR'2] afforded [W(CO)2(PPh3)(S2CNR2)(S2CNR'2)](R = Me, R′= Et; R = Me, R′= CH2Ph; R = Et, R′= CH2Ph), whereas reaction with the AsPh3 and SbPh3 complexes in an analogous manner gave [W(CO)3(S2CNR2)(S2CNR′2)] in low yield. Reaction of [Mol2(CO)3(NCMe)2] with 2 equivalents of Na[S2CNEt2]·3H2O gave the previously reported oxide compound [Mo2O3(S2CNEt2)4], whereas [WI2(CO)3(NCMe)2] reacts to give [W(CO)3(S2CNEt2)2]. Two equivalents of Na[S2CN(CH2Ph)2] react with [Mol2(CO)3(NCMe)L] to give for L = PPh3 and AsPh3 the oxides [Mo2O3{S2CN(CH2Ph)2}4] and the seven-co-ordinate complex [Mo(CO)2(SbPh3){S2CN(CH2Ph)2}2] for L = SbPh3. The complexes [W(CO)2L{S2CN(CH2Ph)2}2](L = PPh3, AsPh3 or SbPh3) were prepared in an analogous manner. Low-temperature 13C NMR spectra are interpreted to suggest the likely stereochemistry of several of these complexes.

Triphenylphosphineoxide and triphenylphosphinesulfide seven-coordinate complexes of molybdenum(II) and tungsten(II)

The complexes [MI 2(CO) 3(NCMe) 2] (MMo or W) react with one equivalent of OPPh 3 in CH 2Cl 2 at room temperature to rapidly afford the iodo-bridged dimers [M(μ-I)I(CO) 3(OPPh 3)] 2 in good yield. By contrast reaction of equimolar quantities of SPPh 3 and [MI 2(CO) 3(NCMe) 2] react in CH 2Cl 2 at room temperature to give the monoacetonitrile monomers [MI 2(CO) 3(NCMe)(SPPh 3)]. The monomers [MI 2(CO) 3(NCMe)(SPPh 3)] dimerise very slowly on stirring at room temperature in CH 2Cl 2 for 24 h to eventually give the iodo-bridged dimers [M(μ-I)I(CO) 3(SPPh 3)] 2. The molybdenum iodo-bridged compound [Mo(μ-I)I(CO) 3(OPPh 3)] 2 reacts with two equivalents of L (LPPh 3, AsPh 3 or P(OPh) 3) to rapidly give the bridged cleaved products [MoI 2(CO) 3L(OPPh 3)]. The monoacetonitrile complexes [MI 2(CO) 3(NCMe)(SPPh 3)] react in situ with an equimolar quantity of [NBu n 4]I in CH 2Cl 2 at room temperature to give the expected anionic compounds [NBu n 4][MI 3(CO) 3(SPPh 3)] in good yield. The bis- acetonitrile compounds [MI 2(CO) 3(NCMe) 2] react with two equivalents of L (LOPPh 3 or SPPh 3) in CH 2Cl 2 to afford the bis-ligand compounds [MI 2- (CO) 3L 2] in high yield. However, one equivalent of L (LOPPh 3 or SPPh 3) reacts with [MI 2(CO) 3L 2] to give the monocationic complexes [MI(CO) 3L 3]I. The ionic nature of these complexes was confirmed by the formulation of the complex [MoI(CO) 3- (SPPh 3) 3][BPh 4] by iodide exchange with Na[BPh 4]. The reaction of [MI 2(CO) 3L 2] with two equivalents of L (LOPPh 3 (for MW only) or SPPh 3) give the dicationic compounds [M(CO) 3L 4]2I. The bis- tetraphenylborate complex [Mo(CO) 3(SPPh 3) 4]- [BPh 4] 2 was also prepared in the normal manner. Three equivalents of OPPh 3 react with [MI 2(CO) 3- (OPPh 3) 2] to give the dicarbonyl compounds [M(CO) 2(OPPh 3) 5]2I in high yield. The mixed ligand complexes [MI 2(CO) 3L′L] (MMo or W; LOPPh 3 or SPPh 3; L′PPh 3, AsPh 3 or SbPh 3) were synthesized by reaction of [MI 2(CO) 3(NCMe) 2] with an equimolar quantity of L′ in CH 2Cl 2, followed by an in situ reaction with one equivalent of L. The triphenylphosphine complex [MoI 2(CO) 3(PPh 3)- (OPPh 3)] on stirring in CH 2Cl 2 for 18 h gave the anionic complex [PPh 3H][MoI 3(CO) 3(OPPh 3)]. Low temperature 13C NMR spectra (carbonyl region) for several seven-coordinate complexes are interpreted to suggest structures for these compounds.

Molecular recognition of oxygen-containing substrates with mad

The binding behaviors of Lewis acidic MAD for various oxygen-containing substrates have been studied by low-temperature 13C NMR analysis. Amides were found to more strongly coordinate to MAD than to aldehydes, esters, or ketones, while coordination of ethereal oxygens was rather weak.

13C NMR and Raman investigation of an intramolecular interaction between a zinc atom and a carbon—carbon triple bond in dihexyn-4-ylzinc

Procedures to make the novel compounds of type [CH3CC(CH2)n]2M (M = Hg, Zn and n = 3, 4) are described. The influence of the donor species on the 13C NMR and Raman spectra of these compounds was examined. The low-temperature 13C NMR spectra of hexyn-4-yl derivatives have been recorded. The presence of a relatively strong intramolecular ground state interaction between the zinc atom and the carbon—carbon triple bond in dihexyn-4-ylzinc has been confirmed.

Barriers to rotation about the C(O)N bond in tricarbonylchromium complexes of aromatic N,N-dialkylamides

The variable-temperature 1H NMR spectra of tricarbonylchromium complexes of five aromatic N,N-dialkylamides have been recorded to determine the barrier to amide rotation. Low-temperature 13C NMR spectra have also been recorded in some cases to support conclusions concerning the stereochemistry of the investigated compounds. Complexation of the arene ring causes a considerable modification of the stereodynamics of the amide molecule. The origin of the observed effects is discussed.