Tetrakis[bis(trimethylsilyl)ethyne]diiron

Abstract

expected in view of the electronic properties of the reaction partners.[51 Conjugation of the exocyclic double bond may be achieved by treatment with bases or, more quickly, under acid catalysis. The 6H-1,2-oxazines 5 are thereby obtained in good yields.Since 3 can be easily substituted at C-1 by deprotonation and subsequent reaction with electrophiles,[61 it is also possible to synthesize 1,2-oxazine derivatives containing two substituents in the 6-position. Whereas the addition of 2 to I-al kylated methoxyallenes affords only moderate yields (e.g., 309'0 yield of I-methyl-1-methoxyallene and 2a), the sterically encumbered hydroxylated allenes 6 and 7 give the functionalized heterocycles 8 and 9, respectively, with reasonable efficiency. A moderate diastereoselectivity (60 : 40) was found in the cycloaddition of 2a to 7 to give 9. The products 8 and 9 can also be transformed into the conjugated systems 5 by treatment with base. Na2C03 Me0 t Bu " + 2a Me0 R' R' = C(OH)Me2 8 , 49% 6 7 R' = CH(0H)Me. 56%(60 : 40) Me0 L R .

Koordinativ ungesättigte Dieisenkomplexe: Synthese und Kristallstrukturen von [Fe2(CO)4(μ-H)(μ-PtBu2)(μ-Ph2PCH2PPh2)] und [Fe2(CO)4(μ-CH2)(μ-H)(μ-PtBu2)(μ-Ph2PCH2PPh2)]

“…Bei ho È herer sterischer Beanspruchung wie z. B. in [Fe 2 (l-C 2 R 2 ) 2 (C 2 R 2 ) 2 ] (R = SiMe 3 ), d(Fe±Fe) = 2.465(1) A Ê [16], wird ebenso eine Aufweitung der Fe±Fe-Doppelbindung beobachtet. Da als strukturelles Pendant zu 3 bisher nur der analoge Dirutheniumkomplex 7 b bekannt ist, erscheint ein Vergleich zwischen beiden Verbindungen sinnvoll.…”

Synthesis, Structure, and Reactivity of Niobium and Tantalum Alkyne Complexes

“…Complex 2, Co 2 (CO) 6 (RCCR), is used as a reagent in the Pauson−Khand reaction, which generates cyclopentenones from an alkyne, an alkene, and CO. 8,9 In complex 3, alkyne moieties are coordinated to the iron center as both bridging and terminal ligands. 10 Each of the late-transition-metal (groups 8−10) examples discussed above (1−3) was synthesized by the direct addition of an alkyne to an electron-rich, low-or zerovalent (i.e., Pt II , Co 0 , Fe 0 ) metal center. Similarly, some of the first examples 11−14 of early-transition-metal (group 4 or 5) alkyne complexes employed a comparable synthetic methodology, as shown in Scheme 2; adding 1 equiv of alkyne to formally Ti II metallocenes affords alkyne complexes such as 4 and 5.…”

“…In both cases, the ligand binds “side-on” to the metal center through the C–C multiple bond. Complex 2 , Co 2 (CO) 6 (RCCR), is used as a reagent in the Pauson–Khand reaction, which generates cyclopentenones from an alkyne, an alkene, and CO. , In complex 3 , alkyne moieties are coordinated to the iron center as both bridging and terminal ligands …”