Reversible Carbene Insertion into a Ge−N Bond and Insights into CO and Carbene Substitution Reactions Involving Amidinatogermylenes and Fischer Carbene Complexes. Issue 6 (27th December 2018)

• Record Type: Journal Article
• Authors: Álvarez‐Rodríguez, Lucía; 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 6(2019)
• Page Start: 1588
• Page End: 1594
• Publication Date: 2018-12-27
• Subjects: carbonyl complexes -- Fischer carbenes -- germylenes -- insertion -- ring expansion; Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201805406
• Languages: English
• ISSNs: 0947-6539

Abstract

Abstract: The formation of the five‐membered‐ring germylene complexes [M(CO)5 {Ge( t Bu2 bzamC(OEt)Me) t Bu}] (3M ; M=Cr, W), which occurs readily at room temperature from the germylene Ge( t Bu2 bzam) t Bu (1 t Bu ) and Fischer carbenes [M(CO)5 {C(OEt)Me}] (2M ; M=Cr, W), has been found to be reversible. Upon heating at 60 °C, complexes3M undergo epimerization to an equilibrium mixture of3M and3′M . At that temperature, the chromium epimers (but not the tungsten ones) release CO to end in the mixed germylene–Fischer carbene complexes [Cr(CO)4 {C(OEt)Me}{Ge( t Bu2 bzam) t Bu}] ( cis ‐4Cr and trans ‐4Cr ). The latter decompose at 120 °C to [Cr(CO)5 {Ge( t Bu2 bzam) t Bu}] (6Cr ). Because the formation of cis ‐4Cr and trans ‐4Cr from3Cr or3′Cr requires the presence of free1 t Bu and2Cr in the reaction solutions, the reactions of1 t Bu with2M to give3M (and3′M at 60 °C) should be reversible. This proposal has been proven by germylene‐exchange crossover reactions in which free1 t Bu and [M(CO)5 {Ge( t Bu2 bzamC(OEt)Me)CH2 SiMe3 }] (5′M ; M=Cr, W) were formed when complexes3M were treated at room temperature with the germylene Ge( t Bu2 bzam)CH2 SiMe3 (1tmsm ). A clear differential behavior between N ‐heterocyclic carbenes (NHCs) and amidinatogermylenes (1 t Bu and1tmsm ) in their reactivity against group 6 metal Fischer carbene complexes is demonstrated. The higher electron‐donor capacity of amidinatogermylenes with respect to NHCs and the bias of the former to get involved in ring expansion processes are responsible for this differential behavior. Abstract : Reversible ring expansion : The formation of the five‐membered‐ring germylene complexes3M (M=Cr, W) from germylene1 t Bu and electrophilic Fischer carbenes (2M ) is reversible (see graphic). In fact, complex3Cr leads to the CO substitution products cis ‐4Cr and trans ‐4Cr when it is heated at 60 °C.