Carbide termination

Linear low-density polyethylene (LLDPE) is produced in the gas phase under low pressure. Catalysts used are either Ziegler type or new generation metallocenes. The Union Carbide process used to produce HDPE could be used to produce the two polymer grades. Terminal olefins (C4-C6) are the usual comonomers to effect branching. 

The 90 electron trigonal prismatic cluster, [Rh C(CO) ], is electron rich and seems to behave as though there is a pair of electrons pointing out of each triangular face. Each metal atom is surrounded by five groups (1 terminal CO, 3 bridging CO s and the interstitial carbide) in an essentially square pyramidal... 

A ligand with great potential for hydroformylation of higher, terminal alkenes is monosulfonated triphenylphosphine, tppms, that was studied by Abatjoglou, also at Union Carbide [12] (section 8.2.6). In this system hydroformylation is carried out in one phase that is worked up afterwards by adding water, which gives two phases to separate catalyst and product. 

Union Carbide Chemicals Co.) in the 1.5 gal. of distilled water resulted in a smaller drop size (which should have had a higher f/ in pure water) and a 23% lowering of terminal velocity. 

In a similar vein, it was shown that molybdenum amido derivatives of the isolobal terminal phosphide and carbide, " and related chalcogenide atoms,could be obtained. Detailed mechanistic studies of the Mo N(R)Ar 3/N2 system involving X-ray, EXAFS, magnetic, Raman, and isotopicaUy labelled NMR spectroscopy showed that the reaction proceeded through an intermediate involving an end-on bound N2 bridging the molybdenum centres (Scheme... 

A new mechanism to interpret alkene formation in Fischer-Tropsch synthesis has been presented 499-501 There is a general agreement that hydrocarbon formation proceeds according to the modified carbene mechanism. Specifically, CO decomposes to form surface carbide and then undergoes hydrogenation to form surface methine (=CH), methylene (=CH2), methyl and, finally, methane. Linear hydrocarbons are formed in a stepwise polymerization of methylene species. When chain growth is terminated by p-hydride elimination [Eq. (3.61)], 1-alkenes may be formed,502 which is also called the alkyl mechanism ... 

Materials L-lactide(LLA)[Aldrich, 99+%], stannous 2-ethyl hexanoate,Sn(Oct)2, catalyst[Sigma, 95%] and the purifying solvents were utilized according to the reported commercial purity. Dihydroxy-terminated PCL ranging in molecular weight from oligomeric compounds[530 and 2000(2K) Daltons] to polymeric species[43,000(43K) and 80,000(80K) Daltons] were obtained from Aldrich and Union Carbide, respectively. 

The structures of 204-207 have been established in the solid state by single crystal X-ray diffraction. Clusters 205 and 206 are based on the Ru6C octahedral skeleton. The [2.2]paracyclophane ligand in 205 coordinates over a triangular metal face, and in 206 one [2.2]paracyclophane adopts a similar face-capping bonding mode and the other coordinates in a terminal mode to an apical Ru atom. The metal polyhedron in 204 is relatively open in comparison to the octahedron having only nine Ru-Ru bonds. A carbide atom occupies the central cavity and interacts with five of the six Ru atoms. 

The first carbidocarbonyl transition metal cluster to be recognized was Fe5C(CO),5 (1), which was isolated in very low yield from the reaction of triiron dodecacarbonyl with methylphenylacetylene and characterized by X-ray diffraction by Dahl and co-workers (2). The molecule (Fig. 1) comprises a square pyramidal Fe5 core with the carbide situated. 08 A below the center of a square face. Each iron atom bears three terminal carbonyls. Improved syntheses of 1 by protonation (5) or oxidation of [Fe6C(CO)l6]2-... 

Fig. 24. TIRu12(C)2(CO)j2, as in its Ph4As+ salt (52). Two Ru6C octahedra are connected via one edge of each to the central thallium atom. The Ru-Ru distances within the octahedron range from 2.813(1) to 2.938(1) A, with the exception of the two Ru-Ru edges bound to thallium (3.098 A mean). The torsional angle at thallium is 35.9°, and is determined by the nonbonded interactions between the carbonyls on the adjacent Ru6C(CO),6 units. There are two bridging and fourteen terminal carbonyls on each Ru6 unit. The carbide carbons lie near the centers of iheir respective Ru6 cages mean Ru-Q t. = 2.05 A.

Fig. 32. Co6C(CO)74,26, as in its (CH 3)4N+ salt (6J). The Co6C core is distorted octahedron. One Co-Co bond [Co(l)-Co(2) = 2.916 A] is longer than the eleven others (mean 2.63 A). The bonds from Co( I) and Co(2) to the carbide carbon are longer (1.93 A average) than those from the other cobalt atoms (1.85 A). There are six edge-bridging and eight terminal carbonyls.

Fig. 42. [Re CO),]1-, 34, as in its Ph4P salt (76). The Re, core comprises a monocapped octahedron of rhenium atoms, with the carbide carbon in the octahedral cavity (mean Re-C = 2.13 0.02 A). The metal-metal bonds fall into several categories. Bonds from the capping atom to the capped face of the octahedron average 2.929 A those on the capped face, 2.9S5 A those between the capped face and the opposite uncapped face alternate longer (3.017 A) and shorter (2.977 A), and those in that uncapped face, average 3.080 A. There are three.terminal carbonyls on each metal atom.

Fig. 43. [Re,C(CO)24p, 35, as in its Et4N+ salt (77). The Re, polyhedron comprises a trans-bicapped octahedron, with the carbide carbon at the center of the octahedral cavity (mean Re-C = 2.12 A). Re- Re bond lengths average 2.993 A within the octahedron and 2.970 A for bonds to the capping atoms. There are three terminal carbonyls per metal atom, and the anion has overall D d symmetry.

---