Photoassisted adsorption of allylamine and 1-butene on H:Si(111) studied by surface vibrational spectroscopies

Ultraviolet photoassisted adsorption of terminally double-bonded molecules, allylamine (CH2=CH-CH2-NH2) and 1-butene (CH2=CH-CH2-CH3), on hydrogen-terminated silicon (111) surface was attempted to obtain adsorbates covalently terminating the surface Si atoms. The adsorption process was monitored by high-resolution electron energy loss spectroscopy, multiple internal infrared reflection-absorption spectroscopy, and Auger electron spectroscopy. Allylamine adsorbates emerged upon delivery of allylamine gas under ultraviolet irradiation. The N-H bonds in allylamine were evidenced to survive over the photoadsorption process by vibrational analysis and by the reaction with ketene. CH3- groups were detected at low coverage, indicating anchoring of the organic moieties by the secondary (sec-) type carbon atoms, which were taken over by the primary (n-) type with increasing coverage. C-D bonds were detected after deposition on deuterium-terminated Si(111) upon incorporation of Si-terminating H into the hydrocarbon part of adsorbates. In the case of 1-butene, not only the C=C end but also the CH3- end of a molecule might attach on Si, resulting in emergence of adsorbates composed of CH2 groups. The newly obtained adsorbates are prospective as a material applied for nanolithography, fine electrochemistry, and nano-biotechnology.     

An efficient photoinduced iodoperfluoroalkylation of carbon-carbon unsaturated compounds with perfluoroalkyl iodides

Dependent on the selection of the light sources employed, the photoinduced iodoperfluoroalkylation of a variety of unsaturated compounds takes place efficiently via a radical mechanism. Upon irradiation with a xenon lamp through Pyrex (hnu >300 nm), terminal alkenes (R-CH=CH2) and alkynes (R-C triple bond CH) undergo iodoperfluoroalkylation with perfluoroalkyl iodides (RF-I) regioselectively, providing R-CH(I)-CH2-RF and R-C(I)=CH-RF, respectively. In the case of terminal allenes (R-CH=C=CH2), the photoinduced iodoperfluoroalkylation occurs selectively at the terminal double bond, giving the corresponding beta-perfluoroalkylated vinylic iodides (R-CH=C(I)-CH2-RF) in good yields. The photoinitiated reaction of vinylcyclopropanes (c-C3H5-C(R)=CH2) with RF-I proceeds via the rearrangement of cyclopropylcarbinyl radical intermediates to the homoallylic radical intermediates, and the corresponding 1,5-iodoperfluoroalkylated products (I-(CH2)2CH=C(R)-CH2-RF) are obtained in high yields. Isocyanides (R-NC), as C-N unsaturated compounds, also undergo the xenon-lamp-irradiated iodoperfluoroalkylation to provide the corresponding 1,1-adducts (R-N=C(I)-RF) in good yields. Furthermore, the present photoinitiation procedure can be applied to the iodotrifluoromethylation of unsaturated compounds, when the xenon-lamp-irradiated reactions are conducted under the refluxing conditions of excess CF3-I.     

Why are proton transfers at carbon slow? Self-exchange reactions

When the quantum character of proton transfer is taken into account, the intrinsic slowness of self-exchange proton transfer at carbon appears as a result of its nonadiabatic character as opposed to the adiabatic character of proton transfer at oxygen and nitrogen. This difference is caused by the lesser polarity of C-H bonds as compared to that of O-H and N-H bonds. Besides solvent and heavy-atom intramolecular reorganizations, the kinetics of the reaction are consequently governed at the level of a pre-exponential term by proton tunneling through the barrier. These contrasting behaviors are illustrated by an analysis of the CH(3)H + (-)CH(3), H(2)O + OH(-), and (+)NH(4) + NH(3) self-exchange reactions. The effect of electron-withdrawing substituents and the case of cation radicals are discussed within the same framework taking the O(2)NCH(2)H + CH(2)=NO(2)(-) and (+.)H(2)NCH(2)H + (.)CH(2)NH(2) as examples. Illustrated by the CH(2)=CH-CH(2)H + (-)CH(2)-CH=CH(2) couple, it is shown that the "imbalanced character of the transition state" is related to heavy-atom intramolecular reorganization. Combination of these various effects is finally analyzed, taking the O(2)N-CH(2)=CH-CH(2)H + CH(2)=CH-CH=NO(2)(-) and (+.)H(2)N-CH(2)=CH-CH(2)H + (.)CH(2)-CH=CH(2)-NH(2) couples as examples.     

Manifestations of the Alder-Rickert reaction in the structures of bicyclo[2.2.2]octadiene and bicyclo[2.2.2]octene derivatives

The Alder-Rickert ethylene extrusion reaction manifests in the ground state structures of compounds 9-12 which contain the bicyclo[2.2.2]octadiene moiety and compounds 13, 14, and 17-20 which contain the bicyclo[2.2.2]octene moiety. A significant decrease of the 13C-13C one-bond coupling constants for the C-C bonds, which break in this fragmentation reaction, suggests lengthening, and hence weakening of these bonds. In the unsymmetrical systems these effects are also shown to be associated with strengthening of the CH2-CH2 bond, which is ultimately lost from the molecule as ethylene. Low-temperature crystal structures of compounds 9-12 and 16 provide evidence for similar crystal packing requirements of the CH2-CH2 and CH=CH moieties.     

Highly stable organic monolayers for reacting silicon with further functionalities: the effect of the C-C bond nearest the silicon surface

Crystalline Si(111) surfaces have been alkylated in a two-step chlorination/alkylation process using various organic molecules having similar backbones but differing in their C-C bond closest to the silicon surface (i.e., C-C vs C=C vs C[triple bond]C bonds). X-ray photoelectron spectroscopic (XPS) data show that functionalization of silicon surfaces with propenyl magnesium bromide (CH3-CH=CH-MgBr) organic molecules gives nearly full coverage of the silicon atop sites, as on methyl- and propynyl-terminated silicon surfaces. Propenyl-terminated silicon surface shows less surface oxidation and is more robust against solvent attacks when compared to methyl- and propynyl-terminated silicon surfaces. We also show a secondary functionalization process of propenyl-terminated silicon surface with 4'-[3-Trifluoromethyl-3H-diazirin-3-yl]-benzoic acid N-hydroxysuccinimide ester [TDBA-OSu] cross-linker. The Si-CH=CH-CH3 surfaces thus offer a means of attaching a variety of chemical moieties to a silicon surface through a short linking group, enabling applications in molecular electronics, energy conversion, catalysis, and sensing.     

Chemisorption of (CHx and C2Hy) hydrocarbons on Pt(111) clusters and surfaces from DFT studies

We used the B3LYP flavor of density functional theory (DFT) to study the chemisorption of all CH(x) and C(2)H(y) intermediates on the Pt(111) surface. The surface was modeled with the 35 atom Pt(14.13.8) cluster, which was found to be reliable for describing all adsorption sites. We find that these hydrocarbons all bind covalently (sigma-bonds) to the surface, in agreement with the studies by Kua and Goddard on small Pt clusters. In nearly every case the structure of the adsorbed hydrocarbon achieves a saturated configuration in which each C is almost tetrahedral with the missing H atoms replaced by covalent bonds to the surface Pt atoms. Thus, (Pt(3))CH prefers a mu(3) hollow site (fcc), (Pt(2))CH(2) prefers a mu(2) bridge site, and PtCH(3) prefers mu(1) on-top sites. Vinyl leads to (Pt(2))CH-CH(2)(Pt), which prefers a mu(3) hollow site (fcc). The only exceptions to this model are ethynyl (CCH), which binds as (Pt(2))C=CH(Pt), retaining a CC pi-bond while binding at a mu(3) hollow site (fcc), and HCCH, which binds as (Pt)HC=CH(Pt), retaining a pi bond that coordinates to a third atom of a mu(3) hollow site (fcc) to form an off center structure. These structures are in good agreement with available experimental data. For all species we calculated heats of formation (DeltaH(f)) to be used for considering various reaction pathways on Pt(111). For conditions of low coverage, the most strongly bound CH(x) species is methylidyne (CH, BE = 146.61 kcal/mol), and ethylidyne (CCH(3), BE = 134.83 kcal/mol) among the C(2)H(y) molecules. We find that the net bond energy is nearly proportional to the number of C-Pt bonds (48.80 kcal/mol per bond) with the average bond energy decreasing slightly with the number of C ligands.     

Density functional calculations on dissociation reactions of radical anions of 5-fluorouracil derivatives

Fragmentation reactions upon electron attachment to 5-fluorouracil with CH2R substituents at N1 have been evaluated by means of density functional calculations. The present results show that electron attachment to R = F, HC=O or CN derivatives follows a stepwise pathway with radical anions as intermediates. For these compounds, the most stable species formed is the pi radical anion which bears an unpaired spin density at the C6=C5-C4=O pi-conjugated system of the uracil ring. Cleavage of the N1-CH2R or N1CH2-R bond of these intermediates proceeds through the mixing of the pi and sigma states by means of proper geometrical fluctuations along the reaction coordinate. No sigma radical anion could be characterised on any of these sigma basal potential surfaces. A noticeable decrease in the activation energy for the N1-CH2R bond dissociation was observed for R = H-C=O or CN. Therefore, such derivatives with unsaturated groups positioned vicinal to the N1-C1' bond are identified as targets for the development of novel radiation-activated antitumour drugs. On the other hand, the electron transfer to the compounds with R = Cl, Br is dissociative, i.e. it occurs without the mediation of radical anions. For compounds with R = halides or R = NO2, the fragmentation of the N1CH2-R bond is the preferred dissociation pathway.     

Computational studies of carbon nanotube-hydrocarbon bond strengths at nanotube ends: effect of link heteroatom and hydrocarbon structure

Semiempirical and density functional electronic structure theory methods were used to study SWNT-X--R bond strengths, where the single-walled carbon nanotube (SWNT) had an armchair or zigzag structure, the link heteroatom X was O, N(H), or S and the hydrocarbon chain R was CH(2)CH(3), CH(OH)CH(3), CHCH(2), or CH(CF(3))CH(3). In all systems the hydrocarbon was bonded to the end of the nanotube. The SWNT-X--R bond (that is, the bond joining the link atom to the hydrocarbon) is more than 0.4 eV stronger for armchair than for zigzag nanotubes with the same diameters, irrespective of whether O, N, or S are used as link atoms or whether OH, C==C, or CF(3) groups are present in the hydrocarbon chain. This raises the possibility for selective manipulation of armchair/zigzag nanotubes using a variety of link atoms and hydrocarbon structures. The SWNT-O--CH(CF(3))CH(3) bond is weaker than the SWNT-O--CH(2)CH(3) bond (for both armchair and zigzag nanotubes), while inclusion of a double bond in the ethyl chain increases the bond strengths. Also, SWNT-S--CH(2)CH(3) and SWNT-N(H)--CH(2)CH(3) bonds are stronger than SWNT-O--CH(2)CH(3) bonds.     

Rate and mechanism of the reversible formation of cationic (eta3-allyl)-palladium complexes in the oxidative addition of allylic acetate to palladium(0) complexes ligated by diphosphanes

The oxidative addition of the allylic acetate, CH2=CH-CH2-OAc, to the palladium(o) complex [Pd0(P,P)], generated from the reaction of [Pd(dba)2, with one equivalent of P,P (P,P = dppb = 1,4-bis(diphenylphosphanyl)butane, and P,P = dppf = 1,1'-bis(diphenylphosphanyl)ferrocene), gives a cationic (eta3-allyl)palladium(II) complex, [(eta3-C3H5)Pd(P,P)+]. with AcO as the counter anion. This reaction is reversible and proceeds through two successive equilibria. The overall equilibrium constants have been determined in DMF. Compared with PPh3, the overall equilibrium lies more in favor of the cationic (eta3-allyl)palladium(II) complex when bidentate P,P ligands are considered in the order: dppb > dppf > PPh3. The reaction proceeds via a neutral intermediate complex [(eta2-CH=CH-CHCH2-OAc)Pd0(P,P)], which has been kinetically detected. The rate constants of the successive steps have been determined in DMF by UV spectroscopy and conductivity measurements. The overall complexation step of the Pd0 by the allylic acetate C=C bond is faster than the oxidative addition/ionization step which gives the cationic (eta3-allyl)palladium(II) complex.     

Unusual pathways for metal-assisted C[bond]C and C[bond]P coupling reactions using allenylidenerhodium complexes as precursors

The rhodium allenylidenes trans-[RhCl[[double bond]C[double bond]C[double bond]C(Ph)R](PiPr(3))(2)] [R = Ph (1), p-Tol (2)] react with NaC(5)H(5) to give the half-sandwich type complexes [(eta(5)-C(5)H(5))Rh[[double bond]C[double bond]C[double bond]C(Ph)R](PiPr(3))] (3, 4). The reaction of 1 with the Grignard reagent CH(2)[double bond]CHMgBr affords the eta(3)-pentatrienyl compound [Rh(eta(3)-CH(2)CHC[double bond]C[double bond]CPh(2))(PiPr(3))(2)] (6), which in the presence of CO rearranges to the eta(1)-pentatrienyl derivative trans-[Rh[eta(1)-C(CH[double bond]CH(2))[double bond]C[double bond]CPh(2)](CO)(PiPr(3))(2)] (7). Treatment of 7 with acetic acid generates the vinylallene CH(2)[double bond]CH[bond]CH[double bond]=C=CPh(2) (8). Compounds 1 and 2 react with HCl to give the five-coordinate allenylrhodium(III) complexes [RhCl(2)[CH[double bond]C[double bond]C(Ph)R](PiPr(3))(2)] (10, 11). An unusual [C(3) + C(2) + P] coupling process takes place upon treatment of 1 with terminal alkynes HC[triple bond]CR', leading to the formation of the eta(3)-allylic compounds [RhCl[eta(3)-anti-CH(PiPr(3))C(R')C[double bond]C[double bond]CPh(2)](PiPr(3))] [R' = Ph (12), p-Tol (13), SiMe(3) (14)]. From 12 and RMgBr the corresponding phenyl and vinyl rhodium(I) derivatives 15 and 16 have been obtained. The previously unknown unsaturated ylide iPr(3)PCHC(Ph)[double bond]C[double bond]C[double bond]CPh(2) (17) was generated from 12 and CO. A [C(3) + P] coupling process occurs on treatment of the rhodium allenylidenes 1, 2, and trans-[RhCl[[double bond]C[double bond]C[double bond]C(p-Anis)(2)](PiPr(3))(2)] (20) with either Cl(2) or PhICl(2), affording the ylide-rhodium(III) complexes [RhCl(3)[C(PiPr(3))C[double bond]C(R)R'](PiPr(3))] (21-23). The butatrienerhodium(I) compounds trans-[RhCl[eta(2)-H(2)C[double bond]C[double bond]C[double bond]C(R)R'](PiPr(3))(2)] (28-31) were prepared from 1, 20, and trans-[RhCl[[double bond]C[double bond]C[double bond]C(Ph)R](PiPr(3))(2)] [R = CF(3) (26), tBu (27)] and diazomethane; with the exception of 30 (R = CF(3), R' = Ph), they thermally rearrange to the isomers trans-[RhCl[eta(2)-H(2)C[double bond]C[double bond]C[double bond]C(R)R'](PiPr(3))(2)] (32, 33, and syn/anti-34). The new 1,1-disubstituted butatriene H(2)C[double bond]C[double bond]C[double bond]C(tBu)Ph (35) was generated either from 31 or 34 and CO. The iodo derivatives trans-[RhI(eta(2)-H(2)C[double bond]C[double bond]C[double bond]CR(2))(PiPr(3))(2)] [R = Ph (38), p-Anis (39)] were obtained by an unusual route from 1 or 20 and CH(3)I in the presence of KI. While the hydrogenation of 1 and 26 leads to the allenerhodium(I) complexes trans-[RhCl[eta(2)-H(2)C[double bond]C[double bond]C(Ph)R](PiPr(3))(2)] (40, 41), the thermolysis of 1 and 20 produces the rhodium(I) hexapentaenes trans-[RhCl(eta(2)-R(2)C[double bond]C[double bond]C[double bond]C[double bond]C[double bond]CR(2))(PiPr(3))(2)] (44, 45) via C-C coupling. The molecular structures of 3, 7, 12, 21, and 28 have been determined by X-ray crystallography.     

New iridacyclohexadienes and iridabenzenes by [2+2+1] cyclotrimerization of alkynes and facile interconversion between iridacyclohexadienes and iridabenzenes

Iridabenzenes [Ir[=CHCH=CHCH=C(CH2R)](CH3CN)2(PPh3)2]2+ (R=Ph 4 a, R=p-C6H4CH3 4 b) are obtained from the reactions of H+ with iridacyclohexadienes [Ir[-CH=CHCH=CHC(=CH-p-C6H4R')](CO)(PPh3)2]+ (R'=H 3 a, R'=CH3 3 b), which are prepared from [2+2+1] cyclotrimerization of alkynes in the reactions of [Ir(CH3CN)(CO)(PPh3)2]+ with HC[triple chemical bond]CH and HC[triple chemical bond]CR. Iridabenzenes 4 react with CO and CH3CN in the presence of NEt3 to give iridacyclohexadienes [Ir[-CH=CHCH=CHC(=CHR)](CO)2(PPh3)2]+ (6) and [Ir[-CH=CHCH=CHC(=CHR)](CH3CN)2(PPh3)2]+ (7), respectively. Iridacyclohexadienes 6 and 7 also convert to iridabenzenes 4 by the reactions with H+ in the presence of CH3CN. Alkynyl iridacyclohexadienes [Ir[-CH=CHCH=CHC(=CH-p-C6H4R')](-C[triple chemical bond]CH)(PPh3)2] (8) undergo a cleavage of C[triple chemical bond]C bond by H+/H2O to produce [Ir[-CH=CHCH=CHC(=CH-p-C6H4R')](-CH3)(CO)(PPh3)2] (10) via facile inter-conversion between iridacyclohexadienes and iridabenzenes.     

Metal coordination by sterically hindered heterocyclic ligands, including 2-vinylpyridine, assessed by investigation of cobaloximes

Structural and 1H NMR data have been obtained for cobaloximes with the bulkiest substituted pyridines reported so far. We have isolated in noncoordinating solvents the complexes CH3Co(DH)2L (methylcobaloxime, where DH = the monoanion of dimethylglyoxime) with L = sterically hindered N-donor ligands: quinoline, 4-CH3quinoline, 2,4-(CH3)2pyridine, and 2-R-pyridine (R = CH3, OCH3, CH2CH3, CH=CH2). We have found that the Co-N(ax) bond is very long in the structurally characterized complexes. In particular, CH3Co(DH)2(4-CH3quinoline) has a longer Co-N(ax) bond (2.193(3) A) than any reported for methylcobaloximes. The main cause of the long bonds is unambiguously identified as the steric bulk of L by the fairly linear relationship found for Co-N(ax) distance vs CCA (calculated cone angle, CCA, a computed measure of bulk) over an extensive series of methylcobaloximes. The linear relationship improves if L basicity (quantified by pKa) is taken into account. In anhydrous CDCl3 at 25 degrees C, all complexes except the 2-aminopyridine adduct exhibit 1H NMR spectra consistent with partial dissociation of L to form the methylcobaloxime dimer. 1H NMR experiments at -20 degrees C allowed us to assess qualitatively the relative binding ability of L as follows: 2,4-(CH3)2pyridine > 4-CH3quinoline approximately = quinoline approximately = 2-CH3pyridine > 2-CH3Opyridine > 2-CH3CH2pyridine > 2-CH2=CHpyridine. The broadness of the 1H NMR signals at 25 degrees C suggests a similar order for the ligand exchange rate. The lack of dissociation by 2-aminopyridine is attributed to an intramolecular hydrogen bond between the NH2 group and an oxime O atom. The weaker than expected binding of 2-vinylpyridine relative to the Co-N(ax) bond length is attributed to rotation of the 2-vinyl group required for this bulky ligand to bind to the metal center, a conclusion supported by pronounced changes in 2-vinylpyridine signals upon coordination.     

Detection of C-Si covalent bond in CH3 adsorbate formed by chemical reaction of CH3MgBr and H:Si(111)

High-resolution electron energy loss spectroscopy (HREELS) yielded evidence for the formation of single covalent bonds between Si(111) surface atoms and CH(3) groups from the reaction of CH(3)MgBr and hydrogen-terminated H:Si(111)(1 x 1). The vibration at 678 cm(-)(1), assigned to the C-Si bond, was isolated within the spectrum of CH(3) on deuterium-terminated D:Si(111)(1 x 1). The CH(3) groups were thermally stable at temperatures below 600 K. The C-Si bonds are essential for enhancing the usefulness of alkyl moieties, which will lead to a new prospective technology of nanoscale fabrication and biochemical application.     

Tin-based organo-Zintl ions: alkylation and alkenylation of Sn9(4-)

Reactions of nine-atom deltahedral clusters (Zintl ions) of tin, Sn 9 (4-), with alkyl chlorides, RCl (R = (t) Bu, (n) Bu, (s) Bu), and alkynes (Me3Si-C[triple bond]C-SiMe3, Ph-C[triple bond]CH) yielded the corresponding alkylated and alkenylated clusters [Sn 9-R] (3-). The triple bonds of the alkynes are hydrogenated to double bonds in the process. These are the first tin-based organo-Zintl ions, that is Zintl ions of tin that were subsequently functionalized with organic groups. They are analogous to the recently reported germanium-based derivatives. The (t) Bu-, vinyl-, and styrene-functionalized clusters [Sn 9- (t) Bu] (3-), [Sn 9-CH=CH 2] (3-), and [Sn 9-CH=CH-Ph] (3-), respectively, were structurally characterized in the solid state with [K(2,2,2-crypt)] (+) countercations and in solution by electrospray mass spectrometry. Crystal data: [K(2,2,2-crypt)] 3[Sn 9- (t) Bu].2py, triclinic, P1, a = 14.4259(3), b = 16.2725(4), and c = 22.5593(5) A, alpha = 86.092(1), beta = 78.952(1), and gamma = 65.114(1) degrees , V = 4714.48(7) A (3), Z = 2; [K(2,2,2-crypt)] 3[Sn 9-CH=CH 2].2py, triclinic, P-1, a = 15.6988(3), b = 17.4195(4), and c = 17.4432(4) A, alpha = 86.299(1), beta = 81.566(1), and gamma = 85.349(1) degrees , V = 4696.27(18) A (3), Z = 2; [K(2,2,2-crypt)] 3[Sn 9-CH=CH-Ph].tol.0.75py, monoclinic, C2/c, a = 38.5883(9), b = 23.3893(5), and c = 25.0192(5) A, beta = 120.269(1) degrees , V = 19502.6(7) A (3), Z = 8.     

C-H and P-C(Ph) activation competitive processes caused by interaction with the solvate [cis-Pt(C6F5)2(thf)2

The study of the reaction between the ethylene [Pt(eta-H2C = CH2)(PPh3)2] or alkyne [Pt(eta2-HC [triple bond] CR)(PPh3)2] (R = SiMe3 1, Bu(t) 2) complexes with [cis-Pt(C6F5)2(thf)2] (thf = tetrahydrofuran) has enabled us to observe the existence of competitive processes between the activation of a P-C(Ph) bond on the PPh3 ligand, to give the binuclear derivative [cis-(C6F5)2Pt(mu-Ph)(mu-PPh2)Pt(PPh3)] 3, and the activation of a C-H bond of the unsaturated group, to give the corresponding (mu-hydride)(mu-vinyl) [cis, cis-(PPh3)2Pt(mu-H)(mu-1kappaC(alpha):eta2-CH = CH2)Pt(C6F5)2] 4 or (mu-hydride)(mu-alkynyl) [cis,cis-(PPh3)2Pt(mu-H)(mu-1kappaC(alpha):eta2-C [triple bond]CR)Pt(C6F5)2] (R = SiMe3 5, Bu(t) 6) compounds, respectively. The monitoring of these reactions by NMR spectroscopy has allowed us to detect several intermediates, and to propose a mechanism for the C-H bond activation. In addition, the structures of the (muo-hydride)(mu-alkynyl) complex 5 and the unprecedented (mu-hydride)(mu-vinyl) derivative 4 have been obtained by X-ray crystallographic analyses.     

Study on Reaction of Tolylene Diisocyanate with Polyolefine Polyols

Polyurethane(PU) has been used widely. It is produced by polyisocyanate with polyol. There are many polyisocyanates and polyols. For polyols it is mainly concentrated on polyester and polyether, there is any study on polyolefine polyol. The paper mainly discuss it.By using tolylene diisocyanate(TDI,C6H4CH3(NCO)2) to react with hydroxyterminated polybutadiene(HTPB,HO-[-CH2-CH=CH-CH2-]n-OH,Mn=3805,) and hydroxy-terminated poly(butadiene-co-acrylonitrile)(HTBN, HO-[(-CH2-CH=CHCH2-)x-(-CHCN-CH2)y-]n-OH,Mn=2267), various NCO/OH equivalent ratio NCOterminated polyurethane(PU) prepolymers are synthesized.     

Acetylide-bridged organometallic oligomers via the photochemical metathesis of methyl-iron(II) complexes

The acetylido methyl iron(II) complexes, cis/trans-[Fe(dmpe)(2)(C[triple bond]CR)(CH(3))] (1) and trans-[Fe(depe)(2)(C[triple bond]CR)(CH(3))] (2) (dmpe = 1,2-dimethylphoshinoethane; depe = 1,2-diethylphosphinoethane), were synthesized by transmetalation from the corresponding alkyl halide complexes. Acetylido methyl iron(II) complexes were also formed by transmetalation from the chloride complexes, trans-[Fe(dmpe)(2)(C[triple bond]CR)(Cl)] or trans-[Fe(depe)(2)(C[triple bond]CR)(Cl)]. The structure of trans-[Fe(dmpe)(2)(C[triple bond]CC(6)H(5))(CH(3))] (1a) was determined by single-crystal X-ray diffraction. The methyl acetylido iron complexes, [Fe(dmpe)(2)(C[triple bond]CR)(CH(3))] (1), are thermally stable in the presence of acetylenes; however, under UV irradiation, methane is lost with the formation of a metal bisacetylide. Photochemical metathesis of cis- or trans-[Fe(dmpe)(2)(CH(3))(C[triple bond]CR)] (R = C(6)H(5) (1a), 4-C(6)H(4)OCH(3) (1b)) with terminal acetylenes was used to selectively synthesize unsymmetrically substituted iron(II) bisacetylide complexes of the type trans-[Fe(dmpe)(2)(C[triple bond]CR)(C[triple bond]CR')] [R = Ph, R' = Ph (6a), 4-CH(3)OC(6)H(4) (6b), (t)()Bu (6c), Si(CH(3))(3) (6d), (CH(2))(4)C[triple bond]CH (6e); R = 4-CH(3)OC(6)H(4), R' = 4-CH(3)OC(6)H(4), (6g), (t)()Bu (6h), (CH(2))(4)C[triple bond]CH (6i), adamantyl (6j)]. The structure of the unsymmetrical iron(II) bisacetylide complex trans-[Fe(dmpe)(2)(C[triple bond]CC(6)H(5))(C[triple bond]CC(6)H(4)OCH(3))] (6b) was determined by single-crystal X-ray diffraction. The photochemical metathesis of the bis-acetylene, 1,7-octadiyne, with trans-[Fe(dmpe)(2)(CH(3))(C[triple bond]CPh)] (1a), was utilized to synthesize the bridged binuclear species trans,trans-[(C(6)H(5)C[triple bond]C)Fe(dmpe)(2)(mu-C[triple bond]C(CH(2))(4)C[triple bond]C)Fe(dmpe)(2)(C[triple bond]CC(6)H(5))] (11). The trinuclear species trans,trans,trans-[(C(6)H(5)C[triple bond]C)Fe(dmpe)(2)(mu-C[triple bond]C(CH(2))(4)C[triple bond]C)Fe(dmpe)(2)(mu-C[triple bond]C(CH(2))(4)C[triple bond]C)Fe(dmpe)(2)(C[triple bond]CC(6)H(5))] (12) was synthesized by the photochemical reaction of Fe(dmpe)(2)(C[triple bond]CPh)(C[triple bond]C(CH(2))(4)C[triple bond]CH) (6e) with Fe(dmpe)(2)(CH(3))(2). Extended irradiation of the bisacetylide complexes with phenylacetylene resulted in insertion of the terminal alkyne into one of the metal acetylide bonds to give acetylide butenyne complexes. The structure of the acetylide butenyne complex, trans-[Fe(dmpe)(2)(C[triple bond]CC(6)H(4)OCH(3))(eta(1)-C(C(6)H(5))=CH(C[triple bond]CC(6)H(4)OCH(3)))] (9a) was determined by single-crystal X-ray diffraction.     

Crystal structures and 77Se NMR spectra of molybdenum(IV) areneselenolates having intramolecular NH...Se hydrogen bonds

Salts of the monooxomolybdenum(IV,V) areneselenolates having intramolecular NH...Se hydrogen bonds, [Mo(IV)O(Se-2-RCONHC6H4)4]2- (R = t-Bu, CH3, CF3) and [Mo(V)O(Se-2-t-BuCONHC6H4)4]-, were synthesized and characterized by 1H nuclear magnetic resonance (NMR), 77Se NMR, electron spin resonance (ESR), UV-visible spectra, X-ray analysis, and electrochemical measurements. 77Se-1H correlated spectroscopy (COSY) indicated a significant correlation between amide 1H and selenolate 77Se atoms through an NH...Se hydrogen bond with 1J(77Se-1H) = 5.4 Hz coupling. The hydrogen bonds contribute to the positive shift in the Mo(V)/Mo(IV) redox potential. In the crystal structure of (PPh4)2[Mo(IV)O(Se-2-CH3CONHC6H4)4], an NH...O=Mo hydrogen bond was found. Ab inito calculations support the presence of intramolecular NH...O=Mo and NH...Se hydrogen bonds.     

The synthesis, structure and dynamic behaviour of disubstituted alkenylphosphine derivatives of [Rh6(CO)16

A series of [Rh(6)(CO)(16)] substituted derivatives containing Ph(2)P(alkenyl) ligands has been synthesized starting from the [Rh(6)(CO)(16-x)(NCMe)(x)](x= 1, 2) clusters and Ph(2)P((CH(2))(n)CH=CH(2))(n= 2, 3) phosphines. It was shown that the terminal alkenyl substituents in these phosphines easily undergo isomerization in the coordination sphere of the hexarhodium complexes to give the allyl -CH(2)CH=C(H)R (R = Me and Et) fragments coordinated through the double bond of the rearranged organic moieties. The solid-state structure of two clusters, [Rh(6)(CO)(14)(mu2,kappa3-Ph(2)PCH(2)CH=C(H)CH(3))](4) and [Rh(6)(CO)(14)(mu2,kappa3-Ph(2)PCH(2)CH=C(H)CH(2)CH(3))](8), was established by X-ray crystallography. Solution structures of the products obtained were also characterized by IR and NMR ((1)H, (31)P, (1)H-(1)H COSY and (1)H-(1)H NOE) spectroscopy. It was shown that 4 and 8 exist in solution as mixtures of three isomers (A, B and C), which differ in the conformation of the coordinated allyl fragment. A similar (two species, A and B) equilibrium was found to occur in the solution of the [Rh(6)(CO)(14)(mu2,kappa3-Ph(2)PCH(2)CH=CH(2))](2) cluster. The dynamic behaviour of 2, 4 and 8[Rh(6)(CO)(14)(mu2,kappa3-Ph(2)PCH=CH(2))] has been studied using VT (31)P and (1)H-(1)H NOESY NMR spectroscopy, rate constants and activation parameters of the (A<-->B) isomerization processes were determined. It was shown that the most probable mechanism of this isomerization involves a dissociative [Rh6(CO)(14)(kappa1-Ph(2)P(alkenyl))] intermediate and re-coordination of the double bond to the same metal atom where the process started from. The conversion of the A and B species in and into the third isomer very likely occurs through the transfer of an allyl hydrogen atom onto the rhodium skeleton to give eventually cis conformation of the coordinated allyl fragment.     

Complete disassembly of carbon disulfide by a ditantalum complex

The side-on end-on dinitrogen complex [PhP(CH(2)SiMe(2)NPh)(2)Ta](μ-H)(2)(μ-η(2):η(1)-N(2)) reacts with CS(2) with complete cleavage of both C=S double bonds and the formation of [PhP(CH(2)SiMe(2)NPh)(2)Ta](μ-S)(2)(μ-CH(2)), which has two bridging sulfides and a bridging methylene unit. Further reaction with H(2) produces CH(4) and the disulfide complex.