The diyne-containing niobocene complexes Nb(η5-C5H4SiMe3)2Cl(η2(C,C)-R1C⋮CR2) (R1 =
C⋮CSiMe3, R2 = SiMe3 (2a); R1 = C⋮CPh, R2 = Ph (2b); R1 = CH2CH2C⋮CH, R2 = H (2c))
were prepared by the reaction of Nb(η5-C5H4SiMe3)2Cl (1) with the diyne reagents, R−C⋮C−C⋮C−R (R = SiMe3 or Ph) and 1,5-hexadiyne. The enyne-containing niobocene complexes
Nb(η5-C5H4SiMe3)2Cl(η2(C,C)-R1C⋮CR2) (R1 = CH2CHCH2, R2 = Ph (3a); R1 = CH2CHC(CH3)2, R2 = Ph (3b); R1 = CH2C(CH3)CH2, R2 = Ph (3c); R1 = C(CH3)CH2, R2 = H
(3d)) were also prepared in the same way, namely by the reaction of 1 with the appropriate
enyne reagents. The paramagnetic niobocene complex Nb(η5-C5H4SiMe3)2(η2(C,C)-R1C⋮CR2)
(R1 = C⋮CSiMe3, R2 = SiMe3 (4a)) was also synthesized from 2a and subsequently oxidized
in the presence of different neutral ligands to give the stable cationic d2 derivatives [Nb(η5-C5H4SiMe3)2(η2(C,C)-R1C⋮CR2)(L)][BPh4] (L = CH3CN (5a); L = tBuNC (5a‘)). Some diyne-
and enyne-containing chloroniobocenes were alkylated by reacting with the appropriate
dialkylmagnesium reagent to give the corresponding alkyl−alkyne compounds Nb(η5-C5H4SiMe3)2(R3)(η2(C,C)-R1C⋮CR2) (R1 = C⋮CSiMe3, R2 = SiMe3, R3 = Me (6a); R1 =
CH2CHCH2, R2 = Ph, R3 = CH2Ph (7a); R1 = CH2CHC(Me)2, R2 = Ph, R3 = Me (7b)).
Furthermore, complex 2b undergoes clean reaction with Co2(CO)8 to give the complex Nb(η5-C5H4SiMe3)2Cl(η2(C,C)-R1C⋮CR2) (R1 = CCPh(Co(CO)3)2, R2 = Ph (8b)) through the
coordination of both Co(CO)3 moieties to the uncoordinated triple bond. Finally, the enyne-containing niobocene complexes 3a and 3b can be hydrogenated at the CC bond using
Pd/C as catalyst to give the alkyne complexes Nb(η5-C5H4SiMe3)2Cl(η2(C,C)-R1C⋮CR2) (R1
= CH2CH2CH3, R2 = Ph (9a); R1 = CH2CH2CH(CH3)2, R2 = Ph (9b)). The structures of 2b
and 3b were determined by single-crystal diffractometry.