Alkyne complexes reactions with donor ligands

PhS, p-tolS) initially yields the bis(nitrile) complexes [MI2(CO) (NCMe)2(i72-RC2R )]. which dimerize to yield the iodo-bridged complexes [ M(/t-I)I(CO)(NCMe)(T)2-RC2R ) 2].245 The reactions of the diphenylacet-ylene molybdenum complex with donor ligands and alkynes are shown in Scheme 6. 

Tetramethyl- or tetraphenyl- (cyclobutadiene)nickel dihalides undergo reductive ligand substitution with nitrogen donor ligands such as 2,2 -bipyridine or 1,4-diaza-1,3-dienes with the addition of sodium metal237. The 2,2/-bipyridyl ligand is readily displaced and reaction of this complex with a variety of olefins and alkynes leads to cycloaddition reactions with the cyclobutadiene ligand. 

Substitution reactions at Os(CO)4( -alkene) or Os(CO)4 ()] -alkyne) take place through initial dissociation of a ligand. The complexes Os(CO)4(jj -alkyne), where the alkyne is CF3CSCCF3 or HC=CH, compounds are more reactive than Os(CO)5 in substitution and insertion reactions. The acetylene complex is 10 times more reactive than the hexafluoro-2-butyne complex. This is probably due to the ability of the alkyne to act as a four electron donor and stabilize electron-deficient intermediates. The reaction of Os(CO)4( -HC CH) with excess PMes gives a CO insertion product 0s(C0)2(PMe3)2 C(H)=C(H)-C(0) while reaction with the bulkier phosphine PBuj gives a double insertion product, 0s(C0)3(PBu ) C(0)-C(H)=C(H)-C(0) (Scheme 9). ... 

Many complexes containing alkyne ligands are known. Most commonly, these ligands act as two-electron donors, with a n orbital donating an electron pair in a manner analogous to a sidebound alkene. Bridging alkynes may be considered to donate an electron pair to each of two metals (one pair from each of the alkyne s two occupied n orbitals), acting as a two-electron donor to each. Alkyne complexes have been the subject of immense interest in the study of alkyne meth-athesis reactions, to be discussed in Chapter 11.26... 

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