High-oxidation-state neutral and cationic tantalum(IV) alkyl complexes that are stable toward beta-hydrogen and beta-methyl eliminations

The synthesis and solid-state structural characterization of a family of homoleptic and mixed dialkyl d1Ta(IV) complexes of the formula, (eta5-C5Me5)TaR1R2[N(i-Pr)C(Me)N(i-Pr)], where R1 = R2 = i-Bu (3), n-Bu (4), and Et (7), and R1 = Me, R2 = i-Bu (10), neopentyl (Np) (11), are reported, along with those for the cationic d1Ta(IV) complex, {(eta5-C5Me5)TaNp[N(i-Pr)C(Me)N(i-Pr)]}[B(C6F5)4] (12). All of the new compounds displayed a remarkably high degree of solution stability toward beta-hydrogen and beta-methyl eliminations/abstractions. Thermolysis of 3 in toluene at 80 degrees C for 18 h provided the Ta(IV) trimethylenemethane (TMM) complex 13.     

Steric effects in metathesis and reduction reactions of phosphinimines with catechol- and pinacolboranes

A series of catecholboryl-phosphinimide complexes with the general formula (mu-(R(3)PN)Bcat)(x)() (cat = O(2)C(6)H(4)) have been synthesized via associative metathetical reactions. For R = Et, n-Bu, Ph, and i-Pr and R(3) = n-Bu t-Bu(2) X-ray crystallography as well as solution NMR spectroscopy and reactivity studies reveal that these species are dimeric. In the case of R = t-Bu, the steric congestion results in the monomeric species, t-Bu(3)PNBcat. Similarly, reactions of R(t-Bu)(2)PNH (R = n-Bu, t-Bu) and i-Pr(3)PNH with pinacolborane (HBO(2)C(2)Me(4) = HBpin) led to the formation of n-Bu(t-Bu(2))PNBpin, t-Bu(3)PNBpin, and i-Pr(3)PNBpin. Analogous reactions of smaller phosphinimines R(3)PNH (R = Et or n-Bu) with pinacolborane (HBpin) generated free phosphine and the boron-containing product HN(Bpin)(2). In the related reactions of R(3)PNPh or R(3)PNAd (R = Et and n-Bu) and HBpin, the white crystalline solids PhHN(Bpin) or AdHN(Bpin) were isolated. HN(Bpin)(2) was also derived from the reaction of Et(3)PNSiMe(3) and HBpin. Kinetic studies showed this reaction is first order in both reagents with a rate constant of 1.3(7) x 10(-4) s(-1). A mechanism involving a 1:1 donor-acceptor interaction of the phosphinimine and borane affording reduction of the phosphinimine to phosphine with concurrent formation of borylamine is proposed. Computational studies were performed to probe the steric effects on these reactions of phosphinimine and borane. Model reactions involving t-Bu(3)PNH showed a lower activation barrier for protonolysis in comparison to phosphinimine reduction. In contrast, for the smaller phosphinimine H(3)PNH, the activation barriers for phosphinimine reduction are lower. The causes of these steric effects are considered.     

Direct addition of alcohols to organonitriles activated by ligation to a platinum(IV) center

Treatment of trans-[PtCl(4)(RCN)(2)] (R = Me, Et) with R'OH (R' = Me, Et, n-Pr, i-Pr, n-Bu) at 45 degrees C in all cases allowed the isolation of the trans-[PtCl(4)[(E)-NH=C(R)OR'](2)] imino ester complexes, while the reaction between cis-[PtCl(4)(RCN)(2)] and the least sterically hindered alcohols (methanol and ethanol) results in the formation of cis-[PtCl(4)[(E)-NH=C(R)OR'](2)] (R/R' = Me/Me) or trans-[PtCl(4)[(E)-NH=C(Et)OR'](2)] (R' = Me, Et), the latter being formed via thermal isomerization (ROH, reflux, 3 h) of the initially formed corresponding cis isomers. The reaction between alcohols R'OH and cis-[PtCl(4)(RCN)(2)] (R = Me, R' = Et, n-Pr, i-Pr, n-Bu; R = Et; R' = n-Pr, i-Pr, n-Bu), exhibiting greater R/R' steric congestion, allowed the isolation of cis-[PtCl(4)[(E)-NH=C(R)OR'][(Z)-NH=C(R)OR']] as the major products. The alcoholysis reactions of poorly soluble [PtCl(4)(RCN)(2)] (R = CH(2)Ph, Ph) performed under heterogeneous conditions, directly in the appropriate alcohol and for a prolonged time and, for R = Ph, with heating led to trans-[PtCl(4)[(E)-NH=C(R)OR'](2)] (R = CH(2)Ph, R' = Me, Et, n-Pr, i-Pr; R = Ph, R' = Me) isolated in moderate yields. In all of the cases, in contrast to platinum(II) systems, addition of R'OH to the organonitrile platinum(IV) complexes occurs under mild conditions and does not require a base as a catalyst. The formed isomerically pure (imino ester)Pt(IV) complexes can be reduced selectively, by Ph(3)P=CHCO(2)Me, to the corresponding isomers of (imino ester)Pt(II) species, exhibiting antitumor activity, without change in configuration of the imino ester ligands. Furthemore, the imino esters NH=C(R)OR' can be liberated from both platinum(IV) and platinum(II) complexes [PtCl(n)[H=C(R)OR'](2)] (n = 2, 4) by reaction with 1,2-bis(diphenylphosphino)ethane and pyridine, respectively. All of the prepared compounds were characterized by elemental analyses (C, H, N), FAB mass spectrometry, IR, and (1)H, (13)C[(1)H], and (195)Pt (metal complexes) NMR spectroscopies; the E and Z configurations of the imino ester ligands in solution were determined by observation of the nuclear Overhauser effect. X-ray structure determinations were performed for trans-[PtCl(4)[(E)-NH=C(Me)OEt](2)] (2), trans-[PtCl(4)[(E)-NH=C(Et)OEt](2)] (10), trans-[PtCl(4)[(E)-NH=C(Et)OPr-i](2)] (11), trans-[PtCl(4)[(E)-NH=C(Et)OPr-n](2)] (12), and cis-[PtCl(4)[(E)-NH=C(Et)OMe](2)] (14). Ab initio calculations have shown that the EE isomers are the most stable ones for both platinum(II) and platinum(IV) complexes, whereas the most stable configurations for the ZZ isomers are less stable than the respective EZ isomers, indicating an increase of the stability on moving from the ZZ to the EE configurations which is more pronounced for the Pt(IV) complexes than for the Pt(II) species.     

Substituent effects on Ni-S bond dissociation energies and kinetic stability of nickel arylthiolate complexes supported by a bis(phosphinite)-based pincer ligand

Pincer complexes of the type [2,6-(R(2)PO)(2)C(6)H(3)]NiSC(6)H(4)Z (R = Ph and i-Pr; Z = p-OCH(3), p-CH(3), H, p-Cl, and p-CF(3)) have been synthesized from [2,6-(R(2)PO)(2)C(6)H(3)]NiCl and sodium arylthiolate. X-ray structure determinations of these thiolate complexes have shown a somewhat constant Ni-S bond length (approx. 2.20 ?) but an almost unpredictable orientation of the thiolate ligand. Equilibrium constants for various thiolate exchange (between a nickel thiolate complex and a free thiol, or between two different nickel thiolate complexes) reactions have been measured. Evidently, the thiolate ligand with an electron-withdrawing substituent prefers to bond with "[2,6-(Ph(2)PO)(2)C(6)H(3)]Ni" rather than "[2,6-(i-Pr(2)PO)(2)C(6)H(3)]Ni", and bonds least favourably with hydrogen. The reactions of the thiolate complexes with halogenated compounds such as PhCH(2)Br, CH(3)I, CCl(4), and Ph(3)CCl have been examined and several mechanistic pathways have been explored.     

Substituent effects on chloro meso-tetra-ortho-alkylphenylporphinato iron catalyzed biomimetic oxidation of cyclohexane

Six sterically hindered chloro meso-tetra-ortho-alkylphenylporphinato irons (T(o-R)PPFe(HI)Cl, R = Me, Et, n-Pr, i-Pr, n-Bu, t-Bu) were synthesized and used to catalyze the monooxygenation of cyclohexane with PhIO. Both the yields of cyclohexanol and the relative rates of monooxygenation of cyclohexane catalyzed by T(o-R)PPFe(III)Cl were higher than those of TPPFe(III)Cl respectively. The order of the yields(%) of cyclohexanol and the rate of cyclohexanol formation in the monooxygenation of cyclohexane catalyzed by T(o-R)PPFe(III)Cl for the different substituents are: i-Pr(58) > Et(57) > n-Pr(52) > Me(51) > n-Bu(48) > t-Bu(46) > H(35) and i-Pr > Et > t-Bu > n-Pr > Me > n-Bu > H respectively. The special steric effect on the catalytic character of these different alkyl substituents in T(o-R )PPFe(III)Cl is proposed on the basis of the results.     

Zinc(II)/ketoxime system as a simple and efficient catalyst for hydrolysis of organonitriles

The hydrolysis of sterically hindered and unhindered alkyl nitriles, and also of benzyl and phenyl nitriles RCN (R = Me, CH(2)Cl, Et, n-Pr, i-Pr, n-Bu, t-Bu, p-MeOC(6)H(4)CH(2), Ph), to carboxamides is catalyzed by a novel system of superior simplicity consisting of cheap, widely commercially available, and rather environmentally friendly compounds, that is, a ZnX(2)/ketoxime combination, but it does not proceed at all with either the zinc salt or the ketoxime taken alone. The nature of the anion X(-) in the zinc salt (X = NO(3), Cl, CF(3)SO(3)) or of the ketoxime (Me(2)C=NOH, C(4)H(8)C=NOH, C(5)H(10)C=NOH) does not affect strongly the catalytic properties of the system, but the best results were obtained so far with a Zn(NO(3))(2).6H(2)O/2-propanone oxime molar ratio of 1:4; turnover numbers are typically above ca. 100 but reach as high as 1000 for p-MeOC(6)H(4)CH(2)C(=O)NH(2). The previously unknown structures of the two carboxamide products n-BuC(=O)NH(2) and p-MeOC(6)H(4)CH(2)C(=O)NH(2) were determined by X-ray diffraction studies. The complexes [ZnX(2)(R(2)C=NOH)(2)] (X = Cl, R(2) = 2Me, C(4)H(8), C(5)H(10); X = NO(3), R = C(4)H(8)), prepared by heating the appropriate zinc salts with 2 equiv of the ketoxime in acetone and characterized by C, H, N analyses, FAB-MS, (1)H and (13)C[(1)H] NMR spectroscopies, and also X-ray crystallography (for X = Cl, R(2) = 2Me; X = NO(3), R = C(4)H(8)), proved to be catalyst precursors in the conversions because the activity of these species is high only in the presence of 2 equiv of the ketoxime.     

Unusual reactions of [{micro-(phthalazine-N2:N3)}Fe2(micro-CO)(CO)6] with organolithium reagents. A novel coordination mode of 1,2-diazane diiron carbonyl compounds

[{Micro-(phthalazine-N2:N3)}Fe2(micro-CO)(CO)6](1) reacts with organolithium reagents, RLi (R = CH3, C6H5, p-CH3C6H4, p-CH3OC6H4, p-CF3C6H4, p-C6H5C6H4), followed by treatment with Me3SiCl to give the novel diiron carbonyl complexes with a saturated N-N six-membered diazane ring ligand, [{C6H4CH(R)NNCH2}Fe2(C=O)(CO)6](2, R = CH3; 3, R = C6H5; 4, R =p-CH3C6H4; 5, R =p-CH3OC6H4; 6, R =p-CF3C6H4; 7, R =p-C6H5C6H4). Compounds 4 and 5 were treated with [(NH4)2Ce(NO3)6] to afford the aryl-substituted phthalazine-coordinated diiron carbonyl compounds [(micro-{1-(p-CH3C6H4)-phthalazine-N2:N3})Fe2(micro-CO)(CO)6](8) and [(micro-{1-(p-CH3OC6H4)-phthalazine-N2:N3})Fe2(micro-CO)(CO)6](9), respectively. The structures of complexes 4 and 9 have been established by X-ray diffraction studies.     

二丁基锡磺酸酯催化酯交换合成碳酸二苯酯

研究了不同类型的酸催化剂对碳酸二甲酯与苯酚酯交换合成碳酸二苯酯的影响. 实验结果表明, 碳酸二甲酯与苯酚的酯交换反应是软碱(酚氧)亲硬酸(羰基碳)的反应; 硬Lewis酸比软Lewis酸、交界Lewis酸和Brönsted酸有更高的酯交换选择性. 将不同的磺基引入n-Bu₂SnO分子中, 制得一系列硬Lewis酸催化剂[n-Bu₂Sn(OH)OS(O)₂R(H₂O)]₂[R=p-NH₂C₆H₄(Ⅰ), p-CH₃C₆H₄(Ⅱ), C₆H₅(Ⅲ), p-ClC₆H₄(Ⅳ), Me(Ⅴ), CF₃(Ⅵ)]. 在酯交换反应中, 由于磺基的强吸电子效应增强了[n-Bu₂Sn(OH)OS(O)₂R(H₂O)]₂中Sn的Lewis酸性, 其催化活性比n-Bu₂SnO的高, 而且磺基上取代基的吸电子效应越强, 催化剂中Sn的Lewis酸性越强, 催化活性越高, 但取代基的吸电子效应过强会降低其对酯交换反应的选择性.     

W(CO)6-catalyzed oxidative carbonylation of primary amines to N,N'-disubstituted ureas in single or biphasic solvent systems. Optimization and functional group compatibility studies

Primary amines undergo carbonylation to N,N'-disubstituted ureas using W(CO)6 as the catalyst, I2 as the oxidant, and CO as the carbonyl source. Preparation of various N,N'-disubstituted ureas from aliphatic primary amines, RNH2 (R = n-Pr, n-Bu, i-Pr, sec-Bu, or t-Bu), was achieved in good to excellent yields. Studies of functional group compatibility using a series of substituted benzylamines demonstrated broad tolerance of functionality during the carbonylation reaction. Preparation of various N,N'-disubstituted ureas from substituted benzylamines, R-C6H4CH2NH2 (R = H, p-OCH3, p-CO2H, p-CO2Et, p-CH2OH, p-SCH3, p-vinyl, p-Cl, p-Br, m-I, p-NH2, p-NO2, or p-CN), was achieved in good yields. For many substituted benzylamines, yields of ureas were higher when a two-phase CH2Cl2/H2O solvent system was used.     

Novel tert-butyl-tris(3-hydrocarbylpyrazol-1-yl)borate ligands: synthesis, spectroscopic studies, and coordination chemistry

The lithium (1) and thallium (2) salts of five new tert-butyl-tris(3-hydrocarbylpyrazol-1-yl)borate ligands [t-BuTp(R)]- (R = H, a; Me, b; i-Pr, c; t-Bu, d; Ph, e) have been synthesized and characterized. Because of steric congestion at B, the reaction between t-BuBH3Li x 0.5 Et2O and excess 2,5-dimethylpyrazole Hpz(Me2) afforded the bis-pz(Me2) derivative, Tl[t-BuBH(3,5-Me2pz)2] (3) after metathesis with TlNO3. The compounds were characterized by elemental analysis and NMR spectroscopy. The Li salts 1a and 1c exhibit fluxional behavior on the NMR time scale in solution at room temperature. The solid-state 7Li and 11B NMR spectra of 1c suggest that this salt exists as a mixture of axial and equatorial isomers. The partial hydrolysis of 1d afforded the dimeric Li complex {Li[t-BuB(pz(t-Bu))2(mu-OH)]}2 (4). The crystal structure of 4 shows two Li cations encapsulated by the heteroscorpionate [t-BuB(OH)(3-t-Bupz)2]- ligands. A salt elimination reaction between FeCl2(THF)1.5 and 2 equiv of Li[t-BuTp(R)] (R = H, Me) followed by an in situ one-electron oxidation produced good yields of the homoleptic, paramagnetic low-spin iron(III) complexes [Fe(t-BuTp)2]PF6 (5) and [Fe(t-BuTp(Me))2]PF6 (6) that were characterized by elemental analyses, magnetic susceptibility measurements in solution and the solid phase, 1H NMR, high-resolution mass spectrometry, M?ssbauer spectroscopy, and single-crystal X-ray diffraction. The crystals are composed of discrete molecular units with the central Fe(III) ion in an almost perfectly octahedral coordination to six nitrogen atoms. Compound 5 has the shortest Fe-N bond lengths ever reported for [Fe(RTp(R)')2]+-type compounds.     

Alkylation of tricarbonylcyclohexadienyliron salts (1) with lithium alkyls

The salts $\text{1}$ (Y=H, OMe, Me) react with RLi(R=Me, n-Bu, i-Pr, t-Bu) in CH₂Cl₂ at low temperature to give $\text{2}$ and $\text{3}$ in excellent yields. Nucleophilic addition at the 1-position of $\text{1}$ (Y=OMe) has been observed for the first time.     

Phosphino imidazoles and imidazolium salts for Suzuki C-C coupling reactions

The consecutive syntheses of imidazoles 1-(4-X-C(6)H(4))-4,5-R(2)-(c)C(3)HN(2) (3a, X = Br, R = H; 3b, X = I, R = Me; 3c, X = H, R = Me; 5, X = Fc, R = H; 7, X = C≡CFc, R = H; 9, X = C(6)H(5), R = Me; Fc = Fe(η(5)-C(5)H(4))(η(5)-C(5)H(5))), phosphino imidazoles 1-(4-X-C(6)H(4))-2-PR'(2)-4,5-R(2)-(c)C(3)N(2) (11a-k; X = Br, I, Fc, FcC≡C, Ph; R = H, Me; R' = Ph, (c)C(6)H(11), (c)C(4)H(3)O), imidazolium salts [1-(4-X-C(6)H(4))-3-R'-4,5-R(2)-(c)C(3)HN(2)]I (16a; X = Br, R = H, R' = n-Bu; 16b, X = Br, R = H, R' = n-C(8)H(17); 16c, X = I, R = Me, R' = n-C(8)H(17), 16d, X = H, R = Me, R' = n-C(8)H(17)) and phosphino imidazolium salts [1-C(6)H(5)-2-PR'(2)-3-n-C(8)H(17)-4,5-Me(2)-(c)C(3)N(2)]PF(6) (17a, R' = C(6)H(5); 17b, R' = (c)C(6)H(11)) or [1-(4-P(C(6)H(5))(2)-C(6)H(4))-3-n-C(8)H(17)-4,5-Me(2)-(c)C(3)HN(2)]PF(6), (20) and their selenium derivatives 1-(4-X-C(6)H(4))-2-P([double bond, length as m-dash]Se)R'(2)-4,5-R(2)-(c)C(3)N(2) (11a-Se-f-Se; X = Br, I; R = H, Me; R' = C(6)H(5), (c)C(6)H(11), (c)C(4)H(3)O) are reported. The structures of 11a-Se and [(1-(4-Br-C(6)H(4))-(c)C(3)H(2)N(2)-3-n-Bu)(2)PdI(2)] (19) in the solid state were determined. Cyclovoltammetric measurements were performed with the ferrocenyl-containing molecules 5 and 7 showing reversible redox events at E(0) = 0.108 V (ΔE(p) = 0.114 V) (5) and E(0) = 0.183 V (ΔE(p) = 0.102 V) (7) indicating that 7 is more difficult to oxidise. Imidazole oxidation does not occur up to 1.3 V in dichloromethane using [(n-Bu)(4)N][B(C(6)F(5))(4)] as supporting electrolyte, whereas an irreversible reduction is observed between -1.2 - -1.5 V. The phosphino imidazoles 11a-k and the imidazolium salts 17a,b and 20, respectively, were applied in the Suzuki C-C cross-coupling of 2-bromo toluene with phenylboronic acid applying [Pd(OAc)(2)] as palladium source. Depending on the electronic character of 11a-k, 17a,b and 20 the catalytic performance of the in situ generated catalytic active species can be predicted. As assumed, more electron-rich phosphines with their higher donor capability show higher activity and productivity. Additionally, 11e was applied in the coupling of 4-chloro toluene with phenylboronic acid showing an excellent catalytic performance when compared to catalysts used by Fu, Beller and Buchwald. Furthermore, 11e is eligible for the synthesis of sterically hindered biaryls under mild reaction conditions. C-C Coupling reactions with the phosphino imidazolium salts 17b and 20 in ionic liquids [BMIM][PF(6)] and [BDMIM][BF(4)] were performed, showing less activity than in common organic solvents.     

Square-planar rhodium(I) complexes partnered with [arachno-6-SB(9)H(12)]- : a route toward the synthesis of new rhodathiaboranes and organometallic/thiaborane salts

Treatment of [RhCl(eta4-diene)]2 (diene = nbd, cod) with the N-heterocyclic ligands 2,2'-bipyridine (bpy), 4,4'-dimethyl-2,2'-bipyridine (Me2bpy), 1,10-phenanthroline (phen), and pyridine (py) followed by addition of Cs[arachno-6-SB9H12] affords the corresponding salts, [Rh(eta4-diene)(L2)][SB9H12] [diene = cod, L2 = bpy (1), Me2bpy (3), phen (5), (py)2 (7); diene = nbd, L2 = bpy (2), Me2bpy (4), phen (6), (py)2 (8)]. These compounds are characterized by NMR spectroscopy and mass spectrometry, and in addition, the cod-Rh species 1 and 3 are studied by X-ray diffraction analysis. These saltlike reagents are stable in the solid state, but in solution the rhodium(I) cations, [Rh(eta4-diene)(L2)]+, react with the polyhedral anion [SB9H12]- leading to a chemistry that is controlled by the d8 transition element chelates. The nbd-Rh(I) complexes react faster than the cod-Rh(I) counterparts, leading, depending on the conditions, to the synthesis of new rhodathiaboranes of general formulas [8,8-(L2)-nido-8,7-RhSB9H10] [L2 = bpy (9), Me2bpy (10), phen (11), (py)2 (12)] and [8,8-(L2)-8-(L')-nido-8,7-RhSB9H10] [L' = PPh3, L2 = bpy (13), Me2bpy (14), phen (15); L' = NCCH3, L2 = bpy (16), Me2bpy (17), phen (18)]. Compound 13 is characterized by X-ray diffraction analysis confirming the 11-vertex nido-structure of the rhodathiaborane analogues 14-18. In dichloromethane, 1 and 3 yield mixtures that contain the 11-vertex rhodathiaboranes 9 and 10 together with new species. In contrast, the cod-Rh(I) reagent 5 affords a single compound, which is proposed to be an organometallic rhodium complex bound exo-polyhedrally to the thiaborane cage. In the presence of H2(g) and stoichiometric amounts of PPh3, the cod-Rh(I) reagents, 1, 3, and 5, afford the salts [Rh(H)2(L2)(PPh3)2][SB9H12] [L2 = bpy (19), Me2bpy (20), phen (21)]. Similarly, in an atmosphere of CO(g) and in the presence of PPh3, compounds 1-6 afford [Rh(L2)(PPh3)2(CO)][SB9H12] (L2 = bpy (22), Me2bpy (23), phen (24)]. The structures of 19 and 24 are studied by X-ray diffraction analysis. The five-coordinate complexes [Rh(L2)(PPh3)2(CO)]+ undergo PPh3 exchange in a process that is characterized as dissociative. The observed differences in the reactivity of the nbd-Rh(I) salts versus the cod-Rh(I) analogues are rationalized on the basis of the higher kinetic lability of the nbd ligand and its faster hydrogenation relative to the cod diene.     

Facile Ni(II)/ketoxime-mediated conversion of organonitriles into imidoylamidine ligands. Synthesis of imidoylamidines and acetyl amides

Treatment of alkyl nitriles with NiX(2).6H(2)O (X = Cl, NO(3)) and 2-propanone oxime, followed by (X = Cl) addition of [i-Pr(4)N](NO(3)) for precipitation of the product, resulted in the formation of amidinium nitrates [RC([double bond]NH(2))NH(2)](NO(3)) (R = Me, Et, n-Pr). The reaction went to another direction with NiX(2).2H(2)O, i.e., the reaction between neat RCN (R = Me, Et, n-Pr, i-Pr, n-Bu, CH(2)Cl, CH(2)C(6)H(4)OMe-p) and NiCl(2).2H(2)O/2-propanone oxime (other ketoximes can also be used) gave the (imidoylamidine)Ni(II) complexes [Ni[N(H)[double bond]C(R)NHC(R)[double bond]NH](2)](2+) (1(2+)-7(2+)). The latter were isolated in good yields (65-91%) as the bis-chloride salts 1.Cl(2)-6.Cl(2) and the mixed salt 7.(Cl)(p-MeOC(6)H(4)CH(2)CO(2)). Remarkably, the latter transformation does not proceed at all if NiCl(2).2H(2)O or the ketoxime are taken alone. Liberation of imidoylamidines was performed for one alkyl-containing complex [2.Cl(2)] and one benzyl-containing complex [7.(Cl)(p-MeOC(6)H(4)CH(2)CO(2))], by (i) addition of HBF(4).Et(2)O to the acetonitrile solution of the complexes to yield [N(H)[double bond]C(R)NHC(R)[double bond]NH].2HBF(4) (R = Et 8 and R = CH(2)C(6)H(4)OMe-p 9) or (ii) substitution for ethanediamine (en) with following precipitation of the complex [Ni(en)(3)]Cl(2) with formation of free N(H)[double bond]C(R)NHC(R)[double bond]NH (R = Et 10 and R = CH(2)C(6)H(4)OMe-p 11). In contrast to the liberation in nonaqueous media, treatment of 2.Cl(2) and 7.(Cl)(p-MeOC(6)H(4)CH(2)CO(2)) with Na(2)EDTA.2H(2)O in water-methanol solutions led to substitution and hydrolysis to furnish the acyl amides [EtC([double bond]O)](2)NH (12) and [p-MeOC(6)H(4)CH(2)C([double bond]O)](2)NH (13). Alternatively, 12 and 13 were obtained by hydrolysis of 10 and 11 in water at pH ca. 8.5. It was shown that the oxime complexes trans-[NiCl(2)(C(4)H(8)C[double bond]NOH)(4)] (14) or cis-[Ni(O,O-NO(3))(2)(C(4)H(8)C[double bond]NOH)(2)] (15) can be intermediates in the formation of amidines and imidoylamidines. The sequence of the Ni(II)/oxime mediated formation of (imidoylamidine)Ni complexes and liberation (or hydrolytic liberation) of the ligands opens up a novel, facile and environmentally benign route to imidoylamidines and acyl amides.     

New triorganotin (IV) derivatives of dipeptides as models for metal-protein interactions: synthesis, structural characterization and biological studies

New non-electrolytic triorganotin(IV) derivatives of dipeptides with general formulae R3Sn(HL), where R = Ph and HL = monoanion of glycylisoleucine (H2L-1), valylvaline (H2L-2), alanylvaline (H2L-3), leucylalanine (H2L-4), leucylleucine (H2L-5); R = n-Bu and HL = monoanion of glycylisoleucine (H2L-1) and leucylalanine (H2L-4); and R = Me and HL = monoanion of leucylalanine (H2L-4) have been synthesized and characterized on the basis of infrared, multinuclear 1H, 13C and 119Sn NMR and 119Sn M?ssbauer spectroscopic studies. These investigations suggest that all the ligands in R3Sn(HL) act as monoanionic bidentates coordinating through the COO- and NH2 groups. The 119Sn M?ssbauer studies, together with the NMR data, indicate that, for these polymeric derivatives, the polyhedron around tin in R3Sn(HL) is a trigonal-bipyramid with the three organic groups in the equatorial positions, while the axial positions are occupied by a carboxylic oxygen and the amino nitrogen atom from the adjacent molecule. The anti-inflammatory and cardiovascular activities and toxicity of all these compounds have been determined. Four of the complexes have also been screened against some of the chosen bacterial and fungal strains. The Ph3Sn(IV) compounds exhibit better anti-inflammatory and cardiovascular activities in comparison to the Me3Sn(IV) and n-Bu3Sn(IV) analogues. n-Bu3Sn(Gly-Ile) and Ph3Sn(Ala-Val) exhibit good antibacterial activity against all the chosen strains.     

Lower homologues (methyl, ethyl) of diorganotin derivatives of germyl (substituted) propanoic acids: spectroscopic elucidations and biological studies

Some novel lower homologues of diorganotin derivatives of germyl substituted propanoic acids with general formula [Ar(3)GeCH(R(1))CH(R(2))COO](2)SnR(2)(3), where Ar = p-CH(3)C(6)H(4), C(6)H(5), R(1) = p-CH(3)C(6)H(4), p-CH(3)OC(6)H(4), o-CH(3)OC(6)H(4), C(6)H(5), R(2) = H, CH(3), R(3) = CH(3), C(2)H(5) have been prepared by the condensation reaction of dialkyltin oxide and triarylgermyl(substituted) propanoic acid in 1 : 2 M ratio, respectively, and were characterized by IR, multinuclear ((1)H, (13)C, (119)Sn) NMR, (119 m)Sn M?ssbauer spectroscopy. The synthesized compounds were also screened for their toxicity and possible antibacterial, antifungal activities and found some encouraging results.     

Heteronuclear rhodium, palladium, platinum, and gold organoimido complexes from dinuclear organoamido rhodium precursors

Treatment of the organoamido complexes [Rh(2)(mu-4-HNC(6)H(4)Me)(2)(L(2))(2)] (L(2) = 1,5-cyclooctadiene (cod), L = CO) with nBuLi gave solutions of the organoimido species [Li(2)Rh(2)(mu-4-NC(6)H(4)Me)(2)(L(2))(2)]. Further reaction of [Li(2)Rh(2)(mu-4-NC(6)H(4)Me)(2)(cod)(2)] with [Rh(2)(mu-Cl)(2)(cod)(2)] afforded the neutral tetranuclear complex [Rh(4)(mu-4-NC(6)H(4)Me)(2)(cod)(4)] (2), which rationalizes the direct syntheses of 2 from [Rh(2)(mu-Cl)(2)(cod)(2)] and Li(2)NC(6)H(4)Me. Reactions of [Li(2)Rh(2)(mu-4-NC(6)H(4)Me)(2)(CO)(4)] with chloro complexes such as [Rh(2)(mu-Cl)(2)(CO)(4)], [MCl(2)(cod)] (M = Pd, Pt), and [Ru(2)(mu-Cl)(2)Cl(2)(p-cymene)(2)] afforded the homo- and heterotrinuclear complexes PPN[Rh(3)(mu-4-NC(6)H(4)Me)(2)(CO)(6)] (5; PPN=bis(triphenylphosphine)iminium), [(CO)(4)Rh(2)(mu-4-NC(6)H(4)Me)(2)M(cod)] (M = Pd (6), Pt(7)) and [(CO)(4)Rh(2)(mu-4-NC(6)H(4)Me)(2)Ru(p-cymene)] (8), while the reaction with [AuCl(PPh(3))] gave the tetranuclear compound [(CO)(4)Rh(2)(mu--4-NC(6)H(4)Me)(2)[Au(PPh(3))](2)] (9). The structures of complexes 6, 8, and 9 were determined by X-ray diffraction studies. The anion of 5 reacts with [AuCl(PPh(3))] to give the butterfly cluster [[Rh(3)(mu-4-NC(6)H(4)Me)(2)(CO)(6)]Au(PPh(3))] (10), in which the Au atom is bonded to two rhodium atoms. Reaction of the anion of 5 with [Rh(cod)(NCMe)(2)](BF(4)) gave the tetranuclear complex [Rh(4)(mu-4-NC(6)H(4)Me)(2)(CO)(6)(cod)] (11) in which the Rh(cod) fragment is pi-bonded to one of the arene rings, while the reaction of the anion of 5 with [PdCl(2)(cod)] afforded the heterotrinuclear complex 6 through a metal exchange process.     

SHOP-type nickel complexes with alkyl substituents on phosphorus, synthesis and catalytic ethylene oligomerization

The beta-keto phosphorus ylides (n-Bu)3P=CHC(O)Ph 6, (t-Bu)2PhP=CHC(O)Ph 7, (t-Bu)Ph2P=CHC(O)Ph 8, (n-Bu)2PhP=CHC(O)Ph 9, (n-Bu)Ph2P=CHC(O)Ph 10, Me2PhP=CHC(O)Ph 11 and Ph3P=CHC(O)(o-OMe-C6H4) 12 have been synthesized in 80-96% yields. The Ni(II) complexes [NiPh{Ph2PCH...C(...O)(o-OMeC6H4)}(PPh3)] 13, [NiPh{Ph(t-Bu)PCHC(O)Ph}(PPh3)] 15, [NiPh{(n-Bu)2PCH...C(...O)Ph}(PPh3)] 16 and [NiPh{Ph(n-Bu)PCH...C(...O)Ph}(PPh3)] 17 have been prepared by reaction of equimolar amounts of [Ni(COD)2] and PPh3 with the beta-keto phosphorus ylides 12 or 8-10, respectively, and characterized by 1H and 31P{1H} NMR spectroscopy. NMR studies and the crystal structure determination of 13 indicated an interaction between the hydrogen atom of the C-H group alpha to phosphorus and the ether function. The complexes [NiPh{Ph2PCHC(O)Ph}(Py)] 18, [NiPh{Ph(t-Bu)PCHC(O)Ph}(Py)] 19, [NiPh{(n-Bu)2PCH...C(...O)Ph}(Py)] 20, [NiPh{Ph(n-Bu)PCH...C(...O)Ph}(Py)] 21 and [NiPh{Me2PCH...C(...O)Ph}(Py)] 22 have been isolated from the reactions of [Ni(COD)2] and an excess of pyridine with the -keto phosphorus ylides Ph3PCH=C(O)Ph 3 or 8-11, respectively, and characterized by 1H and 31P{1H} NMR spectroscopy. Ligands 3, 8, 10 and 12 have been used to prepare in situ oligomerization catalysts by reaction with one equiv. of [Ni(COD)2] and PPh3 under an ethylene pressure of 30 or 60 bar. The catalyst prepared in situ from 12, [Ni(COD)2] and PPh3 was the most active of the series with a TON of 12700 mol C2H4 (mol Ni)-1 under 30 bar ethylene. When the beta-keto phosphorus ylide 8 was reacted in situ with three equiv. of [Ni(COD)2] and one equiv. of PPh3 under 30 bar of ethylene, ethylene polymerization was observed with a TON of 5500 mol C2H4 (mol Ni)-1.     

Syntheses, Characterization, and Molecular Mechanics Calculations of Optically Active Silatrane Derivatives

A series of optically active silatrane derivatives, [Si{N(CHRCH(2)O)(CH(2)CH(2)O)(2)}X] (R = Me, i-Pr; X = Ph, OMe) has been synthesized by the reaction of optically active triethanolamine derivatives with XSi(OMe)(3), and characterized by (1)H NMR, (13)C NMR, (29)Si NMR, and mass spectroscopy, and the structures of six compounds have been determined by X-ray analysis. Molecular mechanics methods have also been employed to obtain the energy-minimized structures. The (29)Si NMR chemical shifts and the lengths of Si-N determined by X-ray analysis are sensitive to the bulkiness of the substituent (R). The Si-X bond lengths (X: trans position to nitrogen) do not appreciably differ from one another. The MM2 calculations indicated that the substituent exists in the equatorial position, and the results are in agreement with those of X-ray analysis and (1)H NMR spectroscopy. Crystallographic data: [R = H; X = OMe], C(7)H(15)NO(4)Si, orthorhombic, Pna2(1), a = 13.407(1) ?, b = 8.761(2) ?, c = 8.191(1) ?, Z = 4; [R = Me; X = OMe], C(8)H(17)NO(4)Si, orthorhombic, P2(1)2(1)2(1), a = 10.110(3) ?, b = 11.083(2) ?, c = 9.474(2) ?, Z = 4; [R = i-Pr; X = OMe], C(10)H(21)NO(4)Si, monoclinic, P2(1), a = 8.481(1) ?, b = 7.805(1) ?, c = 10.218(2) ?, beta = 111.31(1) degrees, Z = 2; [R = Me; X = Ph], C(13)H(19)NO(3)Si, orthorhombic, P2(1)2(1)2(1), a = 8.813(1) ?, b = 11.137(2) ?, c = 13.757(1) ?, Z = 4; [R = i-Pr; X = Ph], C(15)H(23)NO(3)Si, orthorhombic, P2(1)2(1)2(1), a = 8.365(1) ?, b = 13.538(2) ?, c = 13.841(2) ?, Z = 4.     

Proton transfer to nickel-thiolate complexes. 1. Protonation of [Ni(SC(6)H(4)R-4)(2)(Ph(2)PCH(2)CH(2)PPh(2))] (R = Me, MeO, H, Cl, or NO(2))

The kinetics of the equilibrium reaction between [Ni(SC(6)H(4)R-4)(2)(dppe)] (R= MeO, Me, H, Cl, or NO(2); dppe = Ph(2)PCH(2)CH(2)PPh(2)) and mixtures of [lutH](+) and lut (lut = 2,6-dimethylpyridine) in MeCN to form [Ni(SHC(6)H(4)R-4)(SC(6)H(4)R-4)(dppe)](+) have been studied using stopped-flow spectrophotometry. The kinetics for the reactions with R = MeO, Me, H, or Cl are consistent with a single-step equilibrium reaction. Investigation of the temperature dependence of the reactions shows that DeltaG = 13.6 +/- 0.3 kcal mol(-)(1) for all the derivatives but the values of DeltaH and DeltaS vary with R (R = MeO, DeltaH() = 8.5 kcal mol(-)(1), DeltaS = -16 cal K(-)(1) mol(-)(1); R = Me, DeltaH() = 10.8 kcal mol(-)(1), DeltaS = -9.5 cal K(-)(1) mol(-)(1); R = Cl, DeltaH = 23.7 kcal mol(-)(1), DeltaS = +33 cal K(-)(1) mol(-)(1)). With [Ni(SC(6)H(4)NO(2)-4)(2)(dppe)] a more complicated rate law is observed consistent with a mechanism in which initial hydrogen-bonding of [lutH](+) to the complex precedes intramolecular proton transfer. It seems likely that all the derivatives operate by this mechanism, but only with R = NO(2) (the most electron-withdrawing substituent) does the intramolecular proton transfer step become sufficiently slow to result in the change in kinetics. Studies with [lutD](+) show that the rates of proton transfer to [Ni(SC(6)H(4)R-4)(2)(dppe)] (R = Me or Cl) are associated with negligible kinetic isotope effect. The possible reasons for this are discussed. The rates of proton transfer to [Ni(SC(6)H(4)R-4)(2)(dppe)] vary with the 4-R-substituent, and the Hammett plot is markedly nonlinear. This unusual behavior is attributable to the electronic influence of R which affects the electron density at the sulfur.