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Propylene from ethylene and butene-2 THE METATHESIS PROCESS offers a way to make propylene from [C.sub.4] fractions, from ethylene or from a combination of these two. The manufacture of polymerization-grade [...]

Room-temperature ionic liquids are used as cosolvents in the palladium-catalyzed telomerization of butadiene with methanol. The basic catalyst is palladium(II) acetate with either triphenylphosphine or sodium diphenylphosphinobenzene-3-sulfonate (TPPMS), which was reacted with butadiene and methanol at 85 °C. It was found that the addition of several equivalents of 1,3-dialkylimidazolium salts per palladium leads to complete deactivation of the catalyst. It was suspected that the deactivation of the catalyst was due to the formation of highly stable palladium imidazolylidene complexes, but no direct evidence of this species was obtained. On the basis of this hypothesis, the use of pyridinium and 1,2,3-trialkylimidazolium salts was studied in an attempt to limit the formation of such species. It was found, particularly for the 1,2,3-trialkylimidazolium salts, that highly active and selective systems for the telomerization of butadiene with methanol were obtained. Furthermore, a biphasic catalytic system composed of palladium(II) acetate, TPPMS, heptane, and 1-butyl-2,3-dimethylimidazolium bis((trifluoromethyl)sulfonyl)imidate, [BMMI][TF2N], was used. In this case, after the telomerization reaction, the methoxyoctadiene products were recovered by simple decantation and the ionic liquid phase reintroduced to the reactor. In this way the catalyst was recycled four times (to total turnover number of 10 000) with little loss of activity.

We provide a unified overview of methods that currently are widely used to assess the accuracy of prediction algorithms, from raw percentages, quadratic error measures and other distances, and correlation coefficients, and to information theoretic measures such as relative entropy and mutual information. We briefly discuss the advantages and disadvantages of each approach. For classification tasks, we derive new learning algorithms for the design of prediction systems by directly optimising the correlation coefficient. We observe and prove several results relating sensitivity and specificity of optimal systems. While the principles are general, we illustrate the applicability on specific problems such as protein secondary structure and signal peptide prediction.

Over a dozen major degenerative disorders, including myotonic distrophy, Huntington's disease and fragile X syndrome, result from unstable expansions of particular trinucleotides. Remarkably, only some of all the possible triplets, namely CAG/CTG, CGG/CCG and GAA/TTC, have been associated with the known pathological expansions. This raises some basic questions at the DNA level. Why do particular triplets seem to be singled out? What is the mechanism for their expansion and how does it depend on the triplet itself? Could other triplets or longer repeats be involved in other diseases?

The synthesis of new metal complexes containing the keto phosphine ligands R¹2PCH2C(O)R² (R¹ = Ph, R² = Ph, Me, t-Bu, p-C6H4F; R¹ = i-Pr, R² = Ph) is described. Reaction of 1 equiv of (diphenylphosphino)acetophenone (Ph2PCH2C(O)Ph; L) with [Rh(μ-Cl)(C2H4)2]2 gave the dimeric complex [Rh(μ-Cl)(C2H4)(P~O)]2 (1) (P~O = η¹(P) coordinated). With 2 equiv of L, [RhCl(P&arcraise;O)(P~O)] (2) was obtained (P&arcraise;O = η²(P,O)-chelated ligand). Reaction of 2 with TlPF6 afforded the cationic compound [Rh(P&arcraise;O)2][PF6] (3). The X-ray crystal structure determination of 3·H2O shows a distorted-square-planar geometry with the two phosphorus atoms (and oxygen atoms) in cis positions. Treatment of [RhCl(CO)(PPh3)2] with 1 equiv of L gave [RhCl(CO)(P~O)(PPh3)] (5). In the presence of TlPF6 the cationic complex [Rh(CO)(P&arcraise;O)(PPh3)][PF6] (6) was obtained. The X-ray crystal structure determination of 6 shows a slightly distorted square planar geometry with the two phosphorus atoms in trans positions. The reaction of 5 or 6 with 1 equiv of NaOMe produced the phosphino enolate complex [Rh{Ph2PC%@mt;sys@%H%@ub;;-50@%· ·%@ubx@%C%@mx@% (%@mt;sys@%%@ub;;-50@%· ·%@ubx@%%@mx@% O)Ph}(CO)(PPh3)] (7). ³¹P{¹H} NMR shows 7 to dissociate PPh3 in solution, giving a 14-electron species, which proved to be particularly useful for transfer-dehydrogenation reactions. When [Rh(μ-Cl)(COE)2]2 (COE = cyclooctene) was reacted with 4 equiv of L under carbon monoxide, [RhCl(CO)(P~O)2] (8) was isolated. Reaction of 8 with TlPF6 gave [Rh(CO)(P&arcraise;O)(P~O)][PF6] (9), and in the presence of NaOMe the phosphino enolate complex [Rh{Ph2PCH%@mt;sys@%%@ub;;-50@%· ·%@ubx@%%@mx@% C(%@mt;sys@%%@ub;;-50@%· ·%@ubx@%%@mx@% O)Ph}(CO)(P~O)] (10) formed. In an analogous manner, [Rh{Ph2PCH%@mt;sys@%%@ub;;-50@%· ·%@ubx@%%@mx@% C(%@mt;sys@%%@ub;;-50@%· ·%@ubx@%%@mx@% O)Ph}(CO)L¹] (L¹ = P(o-tolyl)3 (11), PPh2(p-tolyl) (12), P(p-C6H4F)3 (13)) were also prepared. In a similar way, L and [RhCl(PPh3)3] gave [RhCl(PPh3)2(P~O)] (14), which was reacted with TlPF6, affording [Rh(P&arcraise;O)(PPh3)2][PF6] (15), analogous to 6. Reacting 14 or 15 with 1 equiv of NaOMe gave the phosphino enolate complex [Rh{Ph2PCH%@mt;sys@%%@ub;;-50@%· ·%@ubx@%%@mx@% C(%@mt;sys@%%@ub;;-50@%· ·%@ubx@%%@mx@% O)Ph}(PPh3)2] (16), analogous to 7. It reacts with PhNCO or Ph2PCl with formation of a Cenolate−C or Oenolate−P bond, respectively. [Rh{Ph2PCH%@mt;sys@%%@ub;;-50@%· ·%@ubx@%%@mx@% C(%@mt;sys@%%@ub;;-50@%· ·%@ubx@%%@mx@% O)Ph}(p-C6H4F)}(PPh3)2] (17) has also been reported. By reacting PPh3, L, and TlPF6 with [Rh(μ-Cl)(NBD)]2 (NBD = norbornadiene) the pentacoordinated complex [Rh(NBD)(P&arcraise;O)(PPh3)][PF6] (20) was obtained. The X-ray crystal structure determination of 20 showed that the coordination geometry around the Rh atom could be described as intermediate between square pyramidal (with the O atom occupying the apical position) and trigonal bipyramidal (with the P atom and the midpoint of one olefinic bond occupying the apical positions). When the diolefin, L, and NaOMe were added in sequence to a suspension of [Rh(μ-Cl)(COE)2]2, [Rh{Ph2PCH%@mt;sys@%%@ub;;-50@%· ·%@ubx@%%@mx@% C(%@mt;sys@%%@ub;;-50@%· ·%@ubx@%%@mx@% O)Ph}(NBD)] (21) and [Rh{Ph2PCH%@mt;sys@%%@ub;;-50@%· ·%@ubx@%%@mx@% C(%@mt;sys@%%@ub;;-50@%· ·%@ubx@%%@mx@% O)Ph}(COD)] (22) were obtained. The related iridium complex [Ir{Ph2PCH%@mt;sys@%%@ub;;-50@%· ·%@ubx@%%@mx@% C(%@mt;sys@%%@ub;;-50@%· ·%@ubx@%%@mx@% O)Ph}(COD)] (26) was obtained in a similar way and reacted with H2 to give [Ir{Ph2PCH%@mt;sys@%%@ub;;-50@%· ·%@ubx@%%@mx@% C(%@mt;sys@%%@ub;;-50@%· ·%@ubx@%%@mx@% O)Ph}H2(COD)] (27). The cationic complex 20 and the phosphino enolate complexes 4, 7, and 16 catalyze the hydrogenation and the isomerization of 1-hexene. The rhodium phosphino enolate carbonyl complexes 7 and 13 are very active catalysts for transfer dehydrogenation of cyclooctane with norbornene under hydrogen pressure (7 MPa) at 60−90 °C. In the presence of 1 equiv of a triarylphosphine, rhodium phosphino enolate complexes not containing carbon monoxide, such as 22, proved to be active catalysts for transfer dehydrogenation at 70 °C, under atmospheric pressure of hydrogen, with turnover numbers up to 240 per mol of rhodium/h.

The synthesis of an unsaturated polymer containing cubane moieties in the backbone has been achieved by acyclic diene metathesis polymerization of 1,4-bis(homoallyl)cubane. The molecular weight as determined by ¹H NMR (6−7 C14H16 repeat units) is Mn = 1100−1300. Copolymerization of 1,4-bis(homoallyl)cubane with 1,5-hexadiene gave a polymer fraction containing an average of 9 C14H16/6 butenylene repeat units. The copolymer is soluble in THF.