Über Polystannane. III. 1,2-Dichlortetramethyldistannan,eine Sn?Sn-verknüpfte helicale Bandstruktur [(…︁SnMe2?Cl…︁SnMe2?Cl…︁)∞]2

On Polystannanes. III. 1,2-Dichloro-tetramethyl-distannane. Forming a Sn? Sn-connected Helical Double Chain Structure [(…?SnMe₂Cl…?SnMe₂? Cl…?)_∞]₂ The crystal structure of the title compound has been determined at ?160°C and refined to R = 0.071 (bond lengths Sn? Sn 277.0(2), Sn? Cl 244.2(3) and 244.8(3), Sn? C 214(2) pm). Intermolecular Sn…?Cl connection (324.0(3) and 329.2(3) pm) results in a double chain structure. ¹¹⁹Sn-NMR spectra in CH₂Cl₂ and acetone exhibit a movable temperature dependent coordination of acetone at the distannane (¹J(¹¹⁹Sn? ¹¹⁹Sn) 8000 to 9000 Hz; appr. 5000 Hz in CH₂Cl₂).     

Highly diastereoselective 1,3-dipolar cycloaddition reactions of trans-2-methylene-1,3-dithiolane 1,3-dioxide with 3-oxidopyridinium and 3-oxidopyrylium betaines: a route to the tropane skeleton

The C2-symmetric vinyl sulfoxide, trans-2-methylene-1,3-dithiolane 1,3-dioxide, was found to react with a range of 3-oxidopyridinium betaines (bearing different substituents on nitrogen) in high yield and with total diastereoselectivity. A 2.3:1 mixture of regioisomers was formed with all of the 3-oxidopyridinium betaines but the ratio was found to change over prolonged periods of time due to reversibility of the minor regioisomer. 3-Oxidopyridinium betaines bearing methyl substituents at either the 2- or 6-position were also tested in the cycloaddition process. Improved regioselectivity (8:1) and again high diastereoselectivity were observed with the betaine having an additional substituent at the 2-position, but with betaines having a substituent in the 6-position although high regioselectivity was observed (9.9:1), the major isomer was formed with low diastereoselectivity (5.5:4.4). The origin of the regio- and diastereo-selectivity with all the betaines is discussed. Finally, the C2-symmetric vinyl sulfoxide, trans-2-methylene-1,3-dithiolane 1,3-dioxide was reacted with an oxidopyrylium betaine in moderate yield. Good regioselectivity and moderate diastereoselectivity were observed.     

Steric and electronic effects on the reactivity of rh and ir complexes containing P-S,P-P,and P-O ligands. Implications for the effects of chelate ligands in catalysis

Kinetic studies of the reactions of [M(CO)(L-L)I] [M = Rh, Ir; L-L = Ph(2)PCH(2)P(S)Ph(2) (dppms), Ph(2)PCH(2)CH(2)PPh(2) (dppe), and Ph(2)PCH(2)P(O)Ph(2) (dppmo)] with methyl iodide have been undertaken. All the chelate ligands promote oxidative addition of methyl iodide to the square planar M(I) centers, by factors of between 30 and 50 compared to the respective [M(CO)(2)I(2)](-) complexes, due to their good donor properties. Migratory CO insertion in [Rh(CO)(L-L)I(2)Me] leads to acetyl complexes [Rh(L-L)I(2)(COMe)] for which X-ray crystal structures were obtained for L-L = dppms (3a) and dppe (3b). Against the expectations of simple bonding arguments, methyl migration is faster by a factor of ca. 1500 for [Rh(CO)(dppms)I(2)Me] (2a) than for [Rh(CO)(dppe)I(2)Me] (2b). For M = Ir, alkyl iodide oxidative addition gives stable alkyl complexes [Ir(CO)(L-L)I(2)R]. Migratory insertion (induced at high temperature by CO pressure) was faster for [Ir(CO)(dppms)I(2)Me] (5a) than for its dppe analogue (5b). Reaction of methyl triflate with [Ir(CO)(dppms)I] (4a) yielded the dimer [[Ir(CO)(dppms)(mu-I)Me](2)](2+) (7), which was characterized crystallographically along with 5a and [Ir(CO)(dppms)I(2)Et] (6). Analysis of the X-ray crystal structures showed that the dppms ligand adopts a conformation which creates a sterically crowded pocket around the alkyl ligands of 5a, 6, and 7. It is proposed that this steric strain can be relieved by migratory insertion, to give a five-coordinate acetyl product in which the sterically crowded quadrants flank a vacant coordination site, exemplified by the crystal structure of 3a. Conformational analysis indicates similarity between M(dppms) and M(2)(mu-dppm) chelate structures, which have less flexibility than M(dppe) systems and therefore generate greater steric strain with the "axial" ligands in octahedral complexes. Ab initio calculations suggest an additional electronic contribution to the migratory insertion barrier, whereby a sulfur atom trans to CO stabilizes the transition state compared to systems with phosphorus trans to CO. The results represent a rare example of the quantification of ligand effects on individual steps from catalytic cycles, and are discussed in the context of catalytic methanol carbonylation. Implications for other catalytic reactions utilizing chelating diphosphines (e.g., CO/alkene copolymerization and alkene hydroformylation) are considered.     

Analysis of nonvolatile oxidation products of polypropylene. II. Process degradation

The nonvolatile products of polypropylene that has been process degraded in the melt by a Brabender torque rheometer have been quantitatively identified by infrared analysis and chemical reactions carried out on molded sheets. The molecular weight changes with degradation have been determined by gel-permeation chromatography (GPC). It was determined that there is only one functional group per chain scission instead of the two groups previously found for thermal oxidation in the solid state. The molecular weight distribution is similar, but the functional groups and the general scheme of oxidation differ slightly from those previously found for polyolefin oxidation carried out below the melting point. The functional group distribution differs from that determined in a process-degraded polyethylene sample.     

Synthesis and X-ray crystal structure analysis of Fe2(CO)6(μ3-S)2Pd(bipy)

The reaction of Fe₂(CO)₆(μ-S₂),1 withbis(dibenzylideneacetone)-palladium, Pd(dba)₂, in the presence of 2,2′-bipyridine yielded the new compound Fe₂(CO)₆(μ ₃-S)₂Pd(bipy),2 in good yield (66%). Compound2 was characterized by IR,¹H NMR and single-crystal X-ray diffraction analyses. Compound2 contains a Pd(bipy) group that has been inserted into the S-S bond of1. Crystal data for2: space group P2₁/n,a=10.019(2) Å,b=25.414(5) Å,c=7.714(2) Å,β=90.26(2)°,Z=4, 1436 reflections,R=0.023.     

Cluster synthesis 37—Platinum-ruthenium carbido-cluster complexes: The syntheses and structural characterizations of PtRu5(C)(CO)16, Pt2Ru5(C)(CO)13(COD)2, and Pt3Ru5(C)(CO)14(COD)2

From the reaction of [Ru₅(C)(CO)₁₄]^2– with Pt(COD)Cl₂, COD=1, 5 cyclooctadiene, the new platinum-ruthenium carbido cluster complex PtRu₅ (C)(CO)₁₄(COD),1, was obtained in 41% yield. When1 was allowed to react with carbon monoxide (25°C/1 atm), the new complex PtRu₅(C)(CO)₁₆,2, was obtained almost quantitatively (97% yield). Compound2 was characterized by IR and single-crystal X-ray diffraction analysis. The six metal atoms are arranged in the form of an octahedron with the carbide ligand located in the center. Compound1 is believed to have a similar structure to2 except for a COD ligand coordinated to the platinum atom. When activated by treatment with Me₃NO, compound2 reacts with Pt(COD)₂ at 25°C to yield two higher nuclearity cluster complexes, Pt₂Ru₅C(CO)₁₃(COD)₂.3, and Pt₃Ru₅C(CO)₁₄(COD)₂,4. The structure of3 is similar to that of1, but contains a Pt(COD) grouping capping one Ru₃ triangle of the PtRu₅ octahedron. The structure of4 consists of a PtRu₅ octahedron with two Pt(COD) capping groups, one on an Ru₃ triangle and the other on a PtRu₂ triangle of the octahedron. Crystal data: for2, space group=P2₁/n,a=9.341 (2) Å,b=14.957 (3) Å,c=36.80 (1) Å, =90.38 (2) °,Z=8, 4034 reflections,R=0.030, for3, space group=P2₁/c,a=14.998 (3) Å,b=10.288 (3) Å,c=26.581 (7) Å, =102.75 (2) °,Z=4, 2917 reflections,R=0.028. for4, space group=P2₁/n,a=13.412 (4) Å,b=16.252 (4) Å,c=20.107 (4) Å, =106.13 (2) °,Z=4, 2745 reflections,R=0.032.     

Cluster chemistry. 85. Addition of a gold acetylide to an Ru5 cluster. X-ray structure of AuRu5(μ5-C2PPh2)(μ-C2Ph)(μ-PPh2)(CO)13(PPh3)

The reaction between Ru₅(₅-C₂PPh₂)(-PPh₂)(CO)₁₃ and Au(C₂Ph)(PPh₃) afforded AuRu₅(₅-C₂PPh₂)(-C₂Ph)(-PPh₂)(CO)₁₃ (PPh₃), in which the Ru₅ cluster has a scorpion geometry; the Au(PPh₃) group bridges one of the Ru-Ru bonds of the Ru₃ triangle, while the C₂Ph group bridges one of the tail Ru-Ru vectors.For Part 84, see Ref. 1.     

Xanthobilirubic acid and its amides. Synthesis,spectroscopy, and solution structures

Xanthobilirubic acid, 5-[1,5-didehydro-3-ethyl-4-methyl-5-oxo-2H-pyrrol-2-ylidene)methyl]-2,4-dimethyl-1H-pyrrol-3-propanoic acid, its methyl ester, amide, N-methylamide and dimethylamide, and kryptopyrromethenone have been synthesized and characterized spectroscopically. In d₆-DMSO solution all pyrromethenones were monomeric, with lactam and pyrrole N-Hs H-bonded to solvent. In deuteriochloroform, the pyrromethenones preferred a dimeric form, with intramolecular H-bonding between the lactam C = 0 of one unit and the lactam and pyrrole N-Hs of the second.