Facile Synthesis of Alkynyl- and Vinylidene-Niobocene Complexes. Unexpected 1-Vinylidene-
详细信息 查看全文
- 作者：Cristina Garcí ; a-Yebra ; Carmen Ló ; pez-Mardomingo ; Mariano Fajardo ; Antonio Antiñ ; olo ; Antonio Otero ; Ana Rodrí ; guez ; Alain Vallat ; Dominique Lucas ; Yves Mugnier ; Jorge Juan Car
- 刊名：Organometallics
- 出版年：2000
- 出版时间：May 1, 2000
- 年：2000
- 卷：19
- 期：9
- 页码：1749 - 1765
- 全文大小：286K
- 年卷期：v.19,no.9(May 1, 2000)
- ISSN：1520-6041
文摘
Treatment of Nb(
5-C5H4SiMe3)2(Cl)(L) (1) with Mg(C
CR)2 in toluene, under appropriate reactionconditions, leads to the alkynyl complexes Nb(5-C5H4SiMe3)2(CCR)(L) (2: L = CO, R = Ph (2a); L= CO, R = SiMe3 (2b); L = CO, R = tBu (2c); L = PMe2Ph, R = Ph (2d); L = P(OEt)3, R = Ph (2e)).The alkynyl-containing niobocene species 2 can be chemically or electrochemically oxidized to givethe corresponding cation-radical alkynyl complexes [Nb(5-C5H4SiMe3)2(CCR)(L)]
+[BPh4]- (3: L =CO, R = Ph (3a); L = CO, R = tBu (3c); L = PMe2Ph, R = Ph (3d)). These complexes, under differentexperimental conditions, give rise to the mononuclear vinylidene d2 niobocene species [Nb(5-C5H4SiMe3)2(=C=CHR)(L)][BPh4] (4: L = CO, R = Ph (4a); L = CO, R = tBu (4c); L = PMe2Ph, R = Ph(4d)) with a hydrogen atom by abstraction from the solvent or, for 3a, the binuclear divinylidene d2niobocene complex [(5-C5H4SiMe3)2(CO)Nb=C=C(Ph)(Ph)C=C=Nb(CO)(5-C5H4SiMe3)2][BPh4]2 (4a')from a competitive ligand-ligand coupling process. Complexes 4 were also prepared by an alternativeprocedure in which the corresponding complexes 2 were reacted with HBF4. Finally, in solution theCO-containing vinylidene mononuclear complexes 4a and 4c undergo an unexpected isomerizationprocess to give the 2-alkyne derivatives [Nb(5-C5H4SiMe3)2(2(C,C)-HCCR)(CO)]+ (5: R = Ph (5a);R = tBu (5c)). The structure of 5a was determined by single-crystal diffractometry. DFT calculationswere carried out on [NbCp2(=C=CHCH3)(L)]+/[NbCp2(HCCCH3)(L)]+ (Cp = 5-C5H5; L = CO, PH3;exo, endo) model systems in order to explain the 1-vinylidene-2-alkyne rearrangement observed.Calculations have shown that in both carbonyl-niobocene and phosphine-niobocene systems the 1-vinylidene and the 2-alkyne complexes are isoenergetic, in marked contrast with the systems previouslyconsidered in theoretical studies. The reaction takes place through an intraligand 1,2-hydrogen shiftmechanism where 2(C,H)-alkyne species are involved. The energy barrier for the isomerization processin the phosphine-containing niobocene systems is almost 10 kcal mol-1 higher than in the analogousprocess for the carbonyl-containing niobocene system. This increase in activation barrier indicatesthat the different experimental behavior between 4a, 4c, and 4d has a kinetic rather than athermodynamic origin. Finally, the interconversion between exo and endo isomers has been studied.
5-C5H4SiMe3)2(Cl)(L) (1) with Mg(CCR)2 in toluene, under appropriate reactionconditions, leads to the alkynyl complexes Nb(5-C5H4SiMe3)2(CCR)(L) (2: L = CO, R = Ph (2a); L= CO, R = SiMe3 (2b); L = CO, R = tBu (2c); L = PMe2Ph, R = Ph (2d); L = P(OEt)3, R = Ph (2e)).The alkynyl-containing niobocene species 2 can be chemically or electrochemically oxidized to givethe corresponding cation-radical alkynyl complexes [Nb(5-C5H4SiMe3)2(CCR)(L)]+[BPh4]- (3: L =CO, R = Ph (3a); L = CO, R = tBu (3c); L = PMe2Ph, R = Ph (3d)). These complexes, under differentexperimental conditions, give rise to the mononuclear vinylidene d2 niobocene species [Nb(5-C5H4SiMe3)2(=C=CHR)(L)][BPh4] (4: L = CO, R = Ph (4a); L = CO, R = tBu (4c); L = PMe2Ph, R = Ph(4d)) with a hydrogen atom by abstraction from the solvent or, for 3a, the binuclear divinylidene d2niobocene complex [(5-C5H4SiMe3)2(CO)Nb=C=C(Ph)(Ph)C=C=Nb(CO)(5-C5H4SiMe3)2][BPh4]2 (4a')from a competitive ligand-ligand coupling process. Complexes 4 were also prepared by an alternativeprocedure in which the corresponding complexes 2 were reacted with HBF4. Finally, in solution theCO-containing vinylidene mononuclear complexes 4a and 4c undergo an unexpected isomerizationprocess to give the 2-alkyne derivatives [Nb(5-C5H4SiMe3)2(2(C,C)-HCCR)(CO)]+ (5: R = Ph (5a);R = tBu (5c)). The structure of 5a was determined by single-crystal diffractometry. DFT calculationswere carried out on [NbCp2(=C=CHCH3)(L)]+/[NbCp2(HCCCH3)(L)]+ (Cp = 5-C5H5; L = CO, PH3;exo, endo) model systems in order to explain the 1-vinylidene-2-alkyne rearrangement observed.Calculations have shown that in both carbonyl-niobocene and phosphine-niobocene systems the 1-vinylidene and the 2-alkyne complexes are isoenergetic, in marked contrast with the systems previouslyconsidered in theoretical studies. The reaction takes place through an intraligand 1,2-hydrogen shiftmechanism where 2(C,H)-alkyne species are involved. The energy barrier for the isomerization processin the phosphine-containing niobocene systems is almost 10 kcal mol-1 higher than in the analogousprocess for the carbonyl-containing niobocene system. This increase in activation barrier indicatesthat the different experimental behavior between 4a, 4c, and 4d has a kinetic rather than athermodynamic origin. Finally, the interconversion between exo and endo isomers has been studied.