Trans-1,4-Bis

Oxidative polymerization of trans-bis-deprotected 79 under Hay coupling conditions [54] yielded, after end-capping with phenylacetylene, the high-melting and readily soluble oligomers 80a-e with the poly (triacetylene) backbone [87,106] (Scheme 8). Poly(triacetylene)s [PTAs,-(C=C-CR=CR-C=C) -] are the third class of linearly conjugated polymers with a non-aromatic allcarbon backbone in the progression which starts with polyacetylene [PA,... 

Many bis-chelate Pd11 complexes possessing a m-arrangcmcnt of the phosphinoalkylsilyl ligands have been synthesized,386-389 but comparatively few /ranx-bis-chelates are known. The kinetic stability of trans-bis-chelates can be greatly enhanced by placing a bulky o-carborane unit in the ligand backbone.390... 

Fig. 7. Selected geometric parameters (A) of the optimized rotational transition-state structure for antilsynA-trans bis(syn),A-trans conversion via the n3-1sTn,V(C3),A-tr

Figure 1.3 Stable intermediates in the enamide hydrogenation by (S,S)-trans-bis(2,3-diphenylphosphino-butane)rhodium, detected by P NMR. The various multiplicities arise from j Rh, P) and J( P, P).

Besides proving the formation of p-chelates [Pd(CH7CH7C(0)Me)(P-P)] at room temperature, the spectra showed the occurrence of chain-transfer by protonolysis with adventitious water to give the p-hydroxo compounds cis/trans [Pd(p-OH)(P-P)]2 as well as the conversion of the latter compounds into cis/trans bis-chelates [Pd(P-P)2] (Chart 7.2) [5f]. Independent experiments with isolated compounds showed that the p-OH and bis-chelate complexes are not dead ends, and can reenter the catalysis cycle to give alternating polyketones. 

Very recently, MacGillivray et al. succeeded in the supramolecular construction of molecular ladders in the solid state using a linear template approach [48]. They designed the cocrystals 1,3-benzenediol (resorcinol) or a derivative with an all-trans-bis(4-pyridyl)butadiene or hexatriene, in which two resorcinol molecules preorganize two polyene molecules through two hydrogen bond interactions, for [2-1-2] photoaddition (Scheme 5). In this design, two polyenes would... 

A. trans-BIS(TETRENNICKEL(II))HEXACYANOCHROMIUM(III) CHLORIDE, [Cr(CN)4 CNNi(tetren) 2]Cl... 

C22H46ClCrNi6Ni2, Chromate(III), trans-bis(tetraethylenepentamine nickel(II))-hexacyano-, chloride, 34 147 C24H4Na20240sio, Osmate(2-), tetra-cosacarbonyltetra(/4-hydrido)deca-, sodium, 34 223... 

Methyltetracyviododecene and bTanfZnPh ) [where bTan = 2,3-trans-bis(ter-butylimido)methy -nornbom-5-ene] block copolymers Zns... 

These compounds have been obtained indirectly by reactions of silylated acetylenes with metal carbonyls or olefin complexes. Thus, trimethylsilylphenylacetylene reacts with rj5-cyclopentadienylcobalt dicarbonyl, cobaltocene, or rjs-cyclopentadienyl-(l,3-cyclooctadiene) cobalt, in refluxing xylene, to give a mixture of cis- and trans-bis-(trimethylsilyl)cyclobutadiene complexes (R = Me, R = Ph) 68, 127, 137) ... 

In the major isomer, the bipyridinium unit is located inside the cavity of the macrocyclic poly ether and the /7Y//7,v-bis(pyridinium)ethylene unit is positioned alongside, as confirmed by the electrochemical analysis. The cyclic voltammo-gram of the catenane shows four monoelectronic processes that, by a comparison with the data obtained for the free cyclophane, can be attributed as follows the first and third processes to the first and second reductions of the bipyridinium unit, and the second and fourth ones to the first and second reductions of the trans-bis (pyridinium)ethylene unit. The comparison with the tetracationic cyclophane also evidences that all these reductions are shifted toward more negative potential values (Fig. 13.33b). 

Fig. 19. Molecular structure of trans-bis(5-phenyltetrazolato)bis(triphenylphos-phine)palladium(II).

When the bis(isopropylamino)iodocyclopropenylium iodide is reacted with platinum black in acetonitrile, the reaction takes a different course, affording mainly the trans-bis[bis(diisopropylamino)cyclopropenylidene] diiodoplatinum complex (equation 277)351. A plausible pathway for this reaction involves two consecutive oxidative additions to platinum leading to the hexacoordinated intermediate Ptlv-complex [ -Pr2N)2C3]Ptf4, followed by reductive elimination of I2 to form the product (cf Section VI. A. 1. a). 

The studies of Wilkinson et al. included IR and H-l NMR spectroscopy of the intermediate species of this catalyst system (7). This led to recognizing tris(triphenylphosphine)rhodium(I) carbonyl hydride (D) as the key stable rhodium complex. The reactive trans-bis-(triphenylphosphine)rhodium(I) carbonyl hydride (E) resulting via the dissociation of this complex... 

An alternative suggestion is based on the helicity of pseudoequatorial P-phenyl rings and explains the reversal of configuration between reactions catalyzed by (R, R)- trans -bis-1,2 (N-dipheny lphos phin-amino)-cyclohexane complexes and (R,R)- rans-bis-l,2(N-methyl-2V-diphenylphosphinamino)cyclohexane complexes (13, 14, 15). 

Method D (equation 37) is neither a convenient nor an effective way to generate 3a. After heating bis[bromo(trimethylsilyl)methyl]mercury for 7 days at 160 °C with cyclohexene and diphenylmercury, 7-trimethylsilylbicyclo[4.1.0]heptane was obtained in a yield of only 9%, accompanied by a trace of the carbene dimers (cis- and trans-bis(trimethylsilyl)ethene) and a large amount of starting material75. 

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