Acyclic aminocarbenes

Amines react in general more readily than alcohols and aromatic isocyanides are more reactive than ahphatic ones. The ionic diisocyanide complexes react under milder conditions than the neutral monoisocyanide complexes . No reactions with mercaptanes have been reported. Acyclic aminocarbene complexes occur as isomers when R R due to restricted rotation around the C(carbene)—N bond . Dinuclear carbene complexes are formed when the amine complexes [Au(C6F5)NH2(CH2)nNH2] (n = 1 or 2) or the carbene complexes [(C6F5) ,AuC(NHR)NH(CH2)nNH2] (m = 1 or 3) are treated with the isocyanide compound [(C6F5)mAuCNR] (R = Ph or p-tolyl) . ... 

Catalysis with Acyclic Aminocarbene Ligands Alternatives to NHCs with Distinct Steric and Electronic Properties... 

Scheme 16.1 Metalation routes for acyclic aminocarbenes starting from amidinium (Y = NR R ) and related precursors (Y = OR SR, aryl, alkyl, silyl).

Acyclic aminocarbenes have not been used widely as ligands for transition metal catalysts. The amino(aryl)carbene complexes 26 and 27 are rare examples that showed moderate activity in the Suzuki coupling of aryl iodides and bromides with phenylboronic acid (Figure 5.7). ... 

Chromium aminocarbenes [39] are readily available from the reaction of K2Cr(CO)5 with iminium chlorides [40] or amides and trimethylsilyl chloride [41]. Those from formamides (H on carbene carbon) readily underwent photoreaction with a variety of imines to produce /J-lactams, while those having R-groups (e.g.,Me) on the carbene carbon produced little or no /J-lactam products [13]. The dibenzylaminocarbene complex underwent reaction with high diastereoselectivity (Table 4). As previously observed, cyclic, optically active imines produced /J-lactams with high enantioselectivity, while acyclic, optically active imines induced little asymmetry. An intramolecular version produced an unusual anti-Bredt lactam rather than the expected /J-lactam (Eq. 8) [44]. 

Other substituent, which does not participate in the stabilization, can be considered as a spectator substituent (Scheme 3) [34]. This stabilization system is particularly efficient with an amino group which is not only a 71-donating substituent but also a a-electron withdrawing group. This stabilization mode provides a large choice of substituents allowing an easy functionalization of the corresponding stable mono-aminocarbenes. In fact, several types of acyclic and cyclic amino carbenes have been already synthesized [8, 9]. 

The cyclic version of alkylaminocarbenes, the cyclic alkyl aminocarbenes 10c (CAACs), have also been reported [36]. The rigid cyclic structure with very bulky substituents at the nitrogen atom increases the S/T energy gap (45.1 kcal/mol) [37]. Due to this electronic effect as well as to the more resistant substituent pattern, CAACs are much more resistant than the acyclic ones. 

Reaction of aminocarbene complexes with electron-deficient olefins typically involves a formal Q,p2H-insertion of the carbene carbon atom and affords acyclic products. More electrophiUc pyrrol-derived aminocarbene complexes, however, effect cydopropanation [15]. A recently reported example involves the cydopropa-nation of simple alkenes with aminocarbene complexes (Scheme 11.3) [16]. 

The ring-opening aminolysis/recyclization strategy can also be applied to nucleobases. Aminolysis of D-ribose derived chromium carbene 323 by adenine results in the acyclic monodeprotected aminocarbene complex 324. Subsequent... 

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