Two Types of σ‐Allenyl Complexes from Reactions of Silylenes and Germylenes with Chromium Fischer Alkynyl(alkoxy)carbenes. Issue 36 (27th May 2019)

• Record Type: Journal Article
• Authors: Cabeza, Javier A.; García‐Álvarez, Pablo; Gómez‐Gallego, Mar; González‐Álvarez, Laura; Merinero, Alba D.; Sierra, Miguel A.
• Is Part Of: Chemistry. Volume 25:Issue 36(2019)
• Page Start: 8635
• Page End: 8642
• Publication Date: 2019-05-27
• Subjects: allenyl complexes -- chromium -- Fischer carbenes -- germylenes -- silylenes; Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201901579
• Languages: English
• ISSNs: 0947-6539

Abstract

Abstract: The reactivity of amidinatotetrylenes of the type E( t Bu2 bzm)R 1 (E=Si, Ge; t Bu2 bzm= N, N ′‐bis(tertbutyl)benzamidinate; R 1 =alkyl or aryl) with the chromium Fischer alkynylcarbene complexes [Cr{C(OEt)C2 R 2 }(CO)5 ] (R 2 =Ph; ferrocenyl, Fc) has been studied. At room temperature, two different reaction pathways have been identified: (a) attack of the amidinatotetrylene to the alkynyl C 2 atom (γ‐attack), which leads to σ‐allenyl complexes in which the original Ccarbene atom maintains its attachment to the Cr(CO)5 and OEt groups (compounds 3 E - R 1 - R 2 ), and (b) attack of the amidinatotetrylene to the Ccarbene atom (α‐attack), which ends in σ‐allenyl complexes in which the original Ccarbene atom is not attached to the metal atom and has been inserted into an E−N bond of the amidinatotetrylene forming an E‐C‐N‐C‐N five‐membered ring (compounds 4 E - R 1 - R 2 ). It has been found that compounds 3 E - R 1 - R 2 are thermodynamically less stable than their corresponding 4 E - R 1 - R 2 isomers and that some of the former (E=Ge; R 1 =CH2 SiMe3 ) can be transformed into the latter upon heating. At high temperatures (>70 °C) the reactions involving bulky amidinatotetrylenes (R 1 =Mes, t Bu) end in the carbene‐substitution products [Cr{E( t Bu2 bzm)R 1 }(CO)5 ]. Abstract : Amazing isomerization : Heavier tetrylenes A (E=Si, Ge) can attack the Cγ and Cα atoms of the chromium Fischer alkynylcarbene carbenes B to give the zwitterionic σ‐allenyl derivatives C and D . For E=Ge (but not for E=Si), the γ‐addition can be reversed at 50 °C, enabling the isomerization of CGe into the thermodynamically more stable complex DGe .