Event-by-event fluctuations of the Kaon-to-Pion ratio in central Pb+Pb collisions at 158 GeV per nucleon

We present the first measurement of fluctuations from event to event in the production of strange particles in collisions of heavy nuclei. The ratio of charged kaons to charged pions is determined for individual central Pb+Pb collisions. After accounting for the fluctuations due to detector resolution and finite number statistics we derive an upper limit on genuine nonstatistical fluctuations, which could be related to a first- or second-order QCD phase transition. Such fluctuations are shown to be very small.     

Trapping of Terminal Platinapolyynes by Copper(I) Catalyzed Click Cycloadditions; Probes of Labile Intermediates in Syntheses of Complexes with Extended sp Carbon Chains,and Crystallographic Studies

The silylated hexatriynyl complex trans-(C₆F₅)(p-tol₃P)₂Pt(C≡C)₃SiEt₃ ( PtC₆TES ) is converted in situ to PtC₆H (wet n-Bu₄N⁺ F⁻, THF) and cross coupled with the diyne H(C≡C)₂SiEt₃ ( HC₄TES ; CuCl/TMEDA, O₂) to give PtC₁₀TES (71 %). This sequence is repeated twice to afford PtC₁₄TES (65 %) and then PtC₁₈TES (27 %). An analogous series of reactions starting with PtC₈TES gives PtC₁₂TES (60 %), then PtC₁₆TES (43 %), and then PtC₂₀TES (17 %). Similar cross couplings with H(C≡C)₂Si(i-Pr)₃ ( HC₄TIPS ) give PtC₁₂TIPS (68 %), PtC₁₄TIPS (68 %), and PtC₁₆TIPS (34 %). The trialkylsilyl species (up to PtC₁₈TES ) are converted to 3+2 “click” cycloadducts or 1,4-disubstituted 1,2,3-triazoles trans-(C₆F₅)(p-tol₃P)₂Pt(C≡C)_n-1C=CHN(CH₂C₆H₅)N=N (29–92 % after workups). The most general procedure involves generating the terminal polyynes PtC _x H (wet n-Bu₄N⁺ F⁻, THF) in the presence of benzyl azide in DMF and aqueous CuSO₄/ascorbic acid. All of the preceding complexes are crystallographically characterized and the structural and spectroscopic properties analyzed as a function of chain length. Two pseudopolymorphs of PtC₂₀TES are obtained, both of which feature molecules with parallel sp carbon chains in a pairwise head/tail packing motif with extensive sp/sp van der Waals contacts.     

Highly bulky and electron-rich terminal ruthenium phosphido complexes: new donor ligands for palladium-catalyzed suzuki cross-couplings

Secondary phosphine complexes of the formula [(eta(5)-C(5)H(5))Ru(L)(2)(PHR(2))](+) BAr(F)(-) are prepared from cationic ruthenium N(2) complexes and PHR(2) (R = Ph (a), t-Bu (b), Cy (c)). Additions of t-BuOK or NaN(SiMe(3))(2) give the phosphido complexes (eta(5)-C(5)H(5))Ru(L)(2)(PR(2)) ((L)(2) = (PEt(3))(2) (5a-c), depe (6a,b)) in high NMR yields. These rapidly oxidize in air to give isolable RuP(=O)R(2) species. Complex 5a is more basic than the rhenium analogue (eta(5)-C(5)H(5))Re(NO)(PPh(3))(PPh(2)), and 6b is more basic than P-t-Bu(3). Complexes 5a-c and 6b are effective ligands for palladium-catalyzed Suzuki reactions. The catalyst from 6b is nearly as reactive as that from the benchmark ligand P-t-Bu(3).     

Thermodynamic Enantioface-Binding Selectivities of Monosubstituted Alkenes to a Highly Discriminating Chiral Transition -Metal Lewis Acid; equilibration of diastereoisomeric (cyclopentadienyl)(alkene)(nitrosyl)(triphenylphosphine)rhenium complexes ([Re(η5–C5H5)(CH2 = CHR)(NO) (PPh3)]+BF)

Reactions of monosubstituted alkenes RCH = CH₂ and [Re(η⁵–C₅H₅)(CH₂Cl₂) (NO)(PPh₃)]⁺BF give complexes ([Re(η⁵–C₅H₅))(CH₂?CHR)(NO) (PPh₃)]⁺BF ( 1a–g ) in 63–99% yields as mixtures of (RS,SR)- and (RR,SS)-diastereoisomers ( 1a (R = Me), 66:34; 1b (R = Pr), 63:37; 1c (R = PhCH₂), 70:30; 1d (R = Ph), 75:25; 1e (R = i-Pr), 64:36; 1f (R = t-Bu), 84:16; 1g (R = Me₃Si), 69:31; Scheme 2). These differ in the C?C enantioface bound to the chiral Re fragment. In most cases, the analogous reactions of RCH?CH₂ and [Re(η⁵–C₅H₅) (C₆H₅Cl)(NO)(PPh₃)]⁺ BF give comparable results. When 1a – e , g are heated in PhCl at 95–100°, equilibration to 96:4, 97:3, 97:3, 90:10, > 99:< 1, and > 99:< 1 (RS,SR)/(RR,SS) mixtures occurs (79–99% recoveries; Tables 1 and 2). Thus, thermodynamic enantioface-binding selectivities are much higher than kinetic binding selectivities. This phenomenon is analyzed in detail. A crystal structure of (RS,SR)- 1e (monoclinic, P2₁/c, a = 10.256(1) Å. b = 17.191(1) Å, c = 16.191(1) Å, β = 101.04(1)°, Z = 4) shows that the Re–C(1)–C(2) plane (see Fig.2) is nearly coincident with the Re–P bond (angle 15°), and that the i-Pr group is ‘syn’ to the nitrosyl ligand.     

Ionic Transformations in Extremely Nonpolar Fluorous Media: Easily Recoverable Phase‐Transfer Catalysts for Halide‐Substitution Reactions

Solutions of the fluorous alkyl halides R_f8(CH₂)_mX (R_fn=(CF₂)_n?1CF₃; m=2, 3; X=Cl, Br, I) in perfluoromethylcyclohexane or perfluoromethyldecalin are inert towards solid or aqueous NaCl, NaBr, KI, KCN, and NaOAc. However, halide substitution occurs in the presence of fluorous phosphonium salts (R_f8(CH₂)₂)(R_f6(CH₂)₂)₃P⁺X^? (X=I ( 1 ), Br ( 3 )) and (R_f8(CH₂)₂)₄P⁺I^? (10 mol %), which are soluble in the fluorous solvents under the reaction conditions (76–100 °C). Stoichiometric reactions of a) 1 with R_f8(CH₂)₂Br and b) 3 with R_f8(CH₂)₂I were conducted under homogenous conditions in perfluoromethyldecalin at 100 °C and yielded the same R_f8(CH₂)₂I/R_f8(CH₂)₂Br equilibrium ratio (≈60:40). This shows that ionic displacements can take place in extremely nonpolar fluorous phases and suggests a classical phase‐transfer mechanism for the catalyzed reactions. Interestingly, the nonfluorous salt (CH₃(CH₂)₁₁)(CH₃(CH₂)₇)₃P⁺I^? ( 4 ) also catalyzes halide substitutions, but under triphasic conditions with 4 suspended between the lower fluorous and upper aqueous layers. NMR experiments established very low solubilities in both phases, which suggests interfacial catalysis. Catalyst 1 is easily recycled, optimally by simple precipitation onto teflon tape.     

Three-fold intramolecular ring-closing metatheses involving square-planar platinum complexes with cis-phosphorus donor ligands: syntheses, structures, and properties of parachute-like complexes

Reactions of the phosphite and phosphine complexes cis-PtCl 2((PX(CH2)mCH=CH2)3)2 (X/m = O/3, O/4, O/5, -/5, -/6) with Grubbs' catalyst, followed by hydrogenations, yield cis-PtCl2(P(X(CH2)(2m+2)X)3P) (6-40%). Crystal structures establish parachute-like motifs in which one X(CH2)(2 m+2)X bridge lies roughly in the platinum coordination plane, and the others lie above and below.