Alkyne ligand

The reactions between alkynes and multinuclear metal carbonyls give various product types, with alkyne coupling and alkyne-CO coupling often being observed, e.g. reaction 23.80, in which the organic ligand in the product is a 6-electron donor (two a- and two w-interactions). Predicting the outcome of such reactions is difficult. 

In solution, w-bonded alkynes of the type in structure 23.46 undergo rotations analogous to those of alkenes. 

The solution H NMR spectrum of K(18-crown-6 PtCl3(t) -MeC=CMe) exhibits a singlet at 3.60 and a pseudo-triplet at 2.11 (/ 32.8 Hz). Assign the signals and explain the origin of the pseudo-triplet . Sketch the pseudotriplet and show where the coupling constant of 32.8 Hz is measured. 

The reactions between alkynes and multinuclear metal carbonyls give various product types, with alkyne coupling and alkyne-CO coupling often being observed, e.g. reaction 

in which the organic ligand in the product is a 6-electron donor (two a- and two 7r-interactions). Predicting the outcome of such reactions is difficult. 

Soluble i-complexed polymers have also been prepared by means of coordination to alkyne groups in a polymer main chain. Both non-conjugated (e.g. alkynylsilox-anes [93]) and conjugated materials have been studied. 

Treatment of n-conjugated poly(phenylenediacetylene) with controlled amounts of Pt(C2H4)(PPh3)2 led to the formation of polymers 4.44 with 20-50% complexa- 

Inorganic Materials (Eds. D.W. Bruce, D. O Hare), John Wiley Sons, Toronto, 1992. 

Okawara, Y. Takemoto, H. Kitaoka, E. Haruki, E. Imoto, Kogyo Kagaku Zas-shi 1962, 65, 685. 

Wilbert, A. Wiesemann, R. Zentel, Macromol. Chem. Phys. 1995, 196, 3771. OrganometalUc Polymers (Eds. C. E. Car-raher, Jr., J. E. Sheats, C. U. Putman, Jr.), Academic Press, New York, 1978, p. 79. Metal-Containing Polymeric Systems (Eds. E. Sheats, C.E. Carraheh, Jr., C.U. Pittman, Jr.), Plenum Press, New York, 1985, p. 1. 

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The alkyne ligand is not displaced by CO or ethene but is substituted by stronger (T-donor ligands like pyridine and 4-picoline, which give the paramagnetic... 

Mercury 7r-complexes with alkene and alkyne ligands 447... 

Another major protocol for the generation of three-membered zirconacycles was initially devised by Erker [47—49] and was extensively developed by Buchwald [36—44] (Erker—Buchwald protocol) (Scheme 1.14). No alkenes or alkynes are used as temporary ligands in this protocol. Unless hydrozirconation is used to generate the initial organyl-zirconocene derivatives, even final alkene or alkyne ligands are not usually derived from the corresponding ji-compounds. Thus, the synthetic values of the two representative protocols are quite different and often complementary to each other. 

When the linear trans-[Pt(PEt3)2Cl2] was used to connect the bis (alkyne) ligand 15a-c, a mixture of different sizes of chiral metallocycles [trans-(PEt3)2Pt(15a-c)] , (rt = 3-8,19-24) was obtained [26], Each of the chiral molecular polygons 19-24 was purified by silica-gel column chromatography and analytically pure 19-24 was obtained in yields (%) of 5,18,16,10,5, and 4, respectively (Figure 4.12). Compounds 19-24 have been characterized by H, and P H NMR spectroscopy,... 

Both pairs of tt electrons in an alkyne ligand are more likely to be involved in (he bunding if it is coordinated to two metal atoms. If acetylene is allowed to react with dicobaltoctucarbonyl, two moles of carbon monoxide are eliminated ... 

Hexafluorobutyne-2 will add to platinum(II) complexes. The insoluble complex PtMe HB(pz)3 reacts with dissolution and the five-coordinate alkyne complexes can be isolated (equation 269).815 The coordination about platinum(II) is essentially trigonal bipyrami-dal. The C C triple bond is lengthened on coordination to 1.292(12) A and the alkyne bend-back angle is 34.4(4)°.816 These complexes have a -bonded alkyne ligand, and show different structural and reaction chemistry than platinum(II) acetylide complexes.817-821... 

Fig. 25. Molecular structure of K[(C5HMe4)2Ti(V-C3CSiMe3)2], 41, showing the tweezers-like interaction with alkyne ligands. (Reprinted with permission from V. Varga et al, J. Organomet. Chem. 1996, 514, 219. Copyright 1996 Elsevier Science SA.)...

Interestingly, above 20°C, compound Sic releases a CO molecule to give [W(CO)(PhC=CPh)2 / s-C2B9H8(CH2C6H4Me-4)Me2 ] (52). In the latter the alkyne ligands probably formally contribute three electrons each to the tungsten valence shell (28). 

Metal activation, and sonochemistry, 1, 314 Metal alkoxides, synthesis, 12, 51 Metal-to-alkyne ligand charge-transfer transitions, rigid-rod transition metal—acetylide polymers,... 

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