| Abstract
| - The hydride isocyanide complexes,Nb(η5-C5H4SiMe3)2(H)(CNR),R = xylyl = 2,6-dimethylphenyl; Cy (cyclohexyl); tBu; as well as thehydride carbonyl complexNb(η5-C5H4SiMe3)2(H)(CO) react with several activated alkynes to afford thecorresponding alkenyl isocyanidecomplexesNb(η5-C5H4SiMe3)2(CNR)(C(R‘)CH(R‘‘)),R = xylyl, R‘ = R‘‘ = CO2Me 1; R=Xylyl, R‘ = R‘‘ = CO2tBu2; R = Xylyl, R‘ = CO2Me, R‘‘ = H3; R = Xylyl, R‘ = CO2Me,R‘‘= Me 4; R = Cy, R‘ = R‘‘ = CO2Me5; R = Cy, R‘ = R‘‘ =CO2tBu 6; R = Cy, R‘= CO2Me,R‘‘ = Me 7; R = tBu, R‘ = R‘‘= CO2Me 8; tBu, R‘= R‘‘ = CO2tBu 9 andalkenyl-carbonylcomplexes,Nb(η5-C5H4SiMe3)2(CO)(C(R‘)CH(R‘‘)),R‘ = R‘‘ = CO2Me 10; R‘ = R‘‘ =CO2tBu11; R‘ = CO2Me, R‘‘ = H 12.The reaction of hydride isocyanide complexes withactivatedalkynes gives cis-insertion resulting in the formation of(E)-alkenyl products. However, thehydride carbonyl derivative undergoes insertion to give, under kineticcontrol, a mixture of(E)- and (Z)-alkenyl isomers. Finally, thetrihydride niobocene complexNb(η5-C5H4SiMe3)2(H)3, reacts with estersRO2CC⋮CCO2R‘ orMeO2CC⋮CH to give the hydride olefinderivatives,Nb(η5-C5H4SiMe3)2(H)[η2-RO2C(H)C(H)CO2R‘],R = R‘ = Me 13; R = R‘ =tBu14; andNb(η5-C5H4SiMe3)2(H)[η2-MeO2C(H)CH2]15, probably as the result of a stereospecific trans-insertion. The different complexes have beencharacterized by spectroscopicmethods. In addition, the structure of 13 and14 were determined by single crystal X-raydiffraction.
- The insertion of activated alkynes intothe Nb−H bond of hydride isocyanide and hydride carbonyl niobocenecomplexes has been studied in detail. Furthermore, the reaction ofa trihydride niobocene complex with activated alkynes has been carriedout yielding the structurally characterized complexesNb(η5-C5H4SiMe3)2(H)[η2-RO2C(H)C(H)CO2R](R = Me ortBu).
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