The paramagnetic niobocene alkyne complexesNb(
5-C
5H
4SiMe
3)
2(
2(
C,
C)-RC
![](/images/entities/tbd1.gif)
CR')(
2)have been synthesized fromNb(
5-C
5H
4SiMe
3)
2(
2(
C,
C)-RC
![](/images/entities/tbd1.gif)
CR')(Cl)(
1) and subsequentlyoxidized in the presence of different ligands to give stable cationicd
2 derivatives, [Nb(
5-C
5H
4SiMe
3)
2(
2(
C,
C)-RC
![](/images/entities/tbd1.gif)
CR')(L)][BPh
4](L = CH
3CN, R = R' = Ph (
3a); L =CH
3CN, R =R' = CO
2Me (
3b); L =CH
3CN, R = R' = Me (
3c); L =CH
3CN, R = Me, R' = CO
2Me(
3d);L = tBuCN, R = R' = Ph (
4a); L = tBuCN, R = R' =CO
2Me (
4b); L = tBuCN, R = R' =Me(
4c); L = tBuCN, R = Me, R' = CO
2Me(
4d); L = tBuNC, R = R' = Ph (
5a); L =tBuNC, R= R' = CO
2Me (
5b); L = tBuNC, R =R' = Me (
5c); L = THF, R = R' = Me (
6c);L = THF,R = Me, R' = CO
2Me (
6d); L = Py, R= R' = Ph (
7a); L = Py, R = R' = Me(
7c)). Oxidationof the complexNb(
5-C
5H
4SiMe
3)
2(
2(
C,
C)-MeC
![](/images/entities/tbd1.gif)
CCO
2Me)(
2d) under different experimentalconditions gave rise to the divinylidene binuclear d
2niobocene complex[(
5-C
5H
4SiMe
3)
2(CO)Nb=C=C(CH
3)(CH
3)C=C=Nb(CO)(
5-C
5H
4SiMe
3)
2][BPh
4]
2(
8a). A mechanism involvingthe intermediacy of a
![](/images/gifchars/sigma.gif)
-acetylide species is proposed for theformation of this compound.Thus, the divinylidene complex[(
5-C
5H
4SiMe
3)
2(CO)Nb=C=C(Ph)(Ph)C=C=Nb(CO)(
5-C
5H
4SiMe
3)
2][BPh
4]
2(
8c) was easily synthesized by oxidation of thecorresponding Nb(III)alkynyl derivativeNb(
5-C
5H
4SiMe
3)
2(CO)(C
![](/images/entities/tbd1.gif)
CPh)(
13), obtained fromNb(
5-C
5H
4SiMe
3)
2(CO)Cl and Mg(C
![](/images/entities/tbd1.gif)
CPh)
2. Furthermore, theparamagnetic Nb(IV) complexes (
2) undergoclean reactions with alkyl halides to give a mixture of bothalkyl-alkyne and halo-alkynecompounds. The former complexes,Nb(
5-C
5H
4SiMe
3)
2(
2(
C,
C)-RC
![](/images/entities/tbd1.gif)
CR')(R'')(R = R' = Ph,R'' = Me (
9a); R = R' = R'' = Me (
9c); R= H, R' = Ph, R'' = Me (
9e); R = R' = Me, R''=Et (
10c); R = R' = Me, R'' = CH
2Ph(
11c); R = H, R' = Ph, R'' = CH
2Ph(
11e); R = H, R' =Ph, R'' = CH
2CH=CH
2 (
12e)),were also prepared by an alternative procedure in whichthecorresponding chloro derivatives
1 were reacted with theappropriate dialkylmagnesiumreagents. The structure of
11e was determined bysingle-crystal diffractometry.