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Cited by 16 publications
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Readily Available Onio‐Substituted Methyleneiminium Salts: Single Precursors for a Variety of Aminocarbenes
Due to their strong s-donor properties, N-heterocycliccarbenes (NHCs) have found numerous applications as ligands for transition-metal catalysts.[1] More recently, it has been found that acyclic diaminocarbenes A (see Scheme 1) [2] or even amino aryl carbenes B[3] also behave as strong-sdonor weak-p-acceptor ligands and therefore could be considered as alternative ligands for catalysts; [4,5] to date, A is the most basic carbene ligand known.[4c] However, the range of acyclic amino carbenes (AAC) known is far surpassed by that of their NHCs counterparts. Obstacles to extending the range of available AACs reside in their supposed inherent instability, [6] but also in the lack of a general and convenient synthetic route for their preparation. We have recently reported that substitution reactions occur at the carbene center of the phosphonio-substituted carbene D, thus giving rise to new stable carbenes. [7] However, the synthesis of D requires several steps, which includes the preparation of a stannyl phosphane; a very fragile carbene intermediate C; [8] and most importantly, is limited to (methyl)di(tert-butyl)-phosphane as a leaving group. Indeed, to assure the stability of carbene C, bulky groups at phosphorus are required, and the addition of an organic group to the phosphane to form a quaternary P center is limited to methylation. (Methyl)di(tertbutyl)phosphane is 1) very basic, therefore not the perfect leaving group; 2) bulky, thus preventing the substitution reaction with sterically hindered nucleophiles; 3) features acidic methyl protons, which often react with the nucleophile (base) to afford undesirable products.Herein, we report an easy entry to amino(phosphonio)-carbenes by using simple phosphanes and readily available reagents, and the subsequent substitution reactions at the carbene center.As one of the most common synthetic routes to stable carbenes is based on the deprotonation of the corresponding iminium salt, [1] phosphonio iminium salts 3 were the obvious precursors to amino(phosphonio)carbenes. Based on the elegant work by Weiss and co-workers, we predicted that dications such as 3 should be accessible and stable as compounds that feature bis(onio)substituted sp 3 -and even sp 2 -carbon atoms have been isolated.[9] Indeed, we have found that Alders dimer 1 [2,10] cleanly reacts at room temperature with the basic tricyclohexylphosphane, but also with very simple phosphanes such as triphenylphosphane, thus leading to the formation of the desired dications 3 a,b in 94 and 93 % yield, respectively (Scheme 2). Although 3 a,b are water sensitive, giving back diisopropylamide when exposed to moisture, they are highly thermally stable (m.p.: 3 a: 217 8C; 3 b: 172 8C). Importantly, although the trifluoromethane sulfonate salts 3 a,b are barely soluble in most classical organic solvents, they are soluble in acetonitrile; thus, their purification is quite easy and large quantities can be prepared in a one-pot reaction from the amide (it is not necessary to isolate Alders dimer 1). However, in this re...
Readily Available Onio‐Substituted Methyleneiminium Salts: Single Precursors for a Variety of Aminocarbenes
Due to their strong s-donor properties, N-heterocycliccarbenes (NHCs) have found numerous applications as ligands for transition-metal catalysts.[1] More recently, it has been found that acyclic diaminocarbenes A (see Scheme 1) [2] or even amino aryl carbenes B[3] also behave as strong-sdonor weak-p-acceptor ligands and therefore could be considered as alternative ligands for catalysts; [4,5] to date, A is the most basic carbene ligand known.[4c] However, the range of acyclic amino carbenes (AAC) known is far surpassed by that of their NHCs counterparts. Obstacles to extending the range of available AACs reside in their supposed inherent instability, [6] but also in the lack of a general and convenient synthetic route for their preparation. We have recently reported that substitution reactions occur at the carbene center of the phosphonio-substituted carbene D, thus giving rise to new stable carbenes. [7] However, the synthesis of D requires several steps, which includes the preparation of a stannyl phosphane; a very fragile carbene intermediate C; [8] and most importantly, is limited to (methyl)di(tert-butyl)-phosphane as a leaving group. Indeed, to assure the stability of carbene C, bulky groups at phosphorus are required, and the addition of an organic group to the phosphane to form a quaternary P center is limited to methylation. (Methyl)di(tertbutyl)phosphane is 1) very basic, therefore not the perfect leaving group; 2) bulky, thus preventing the substitution reaction with sterically hindered nucleophiles; 3) features acidic methyl protons, which often react with the nucleophile (base) to afford undesirable products.Herein, we report an easy entry to amino(phosphonio)-carbenes by using simple phosphanes and readily available reagents, and the subsequent substitution reactions at the carbene center.As one of the most common synthetic routes to stable carbenes is based on the deprotonation of the corresponding iminium salt, [1] phosphonio iminium salts 3 were the obvious precursors to amino(phosphonio)carbenes. Based on the elegant work by Weiss and co-workers, we predicted that dications such as 3 should be accessible and stable as compounds that feature bis(onio)substituted sp 3 -and even sp 2 -carbon atoms have been isolated.[9] Indeed, we have found that Alders dimer 1 [2,10] cleanly reacts at room temperature with the basic tricyclohexylphosphane, but also with very simple phosphanes such as triphenylphosphane, thus leading to the formation of the desired dications 3 a,b in 94 and 93 % yield, respectively (Scheme 2). Although 3 a,b are water sensitive, giving back diisopropylamide when exposed to moisture, they are highly thermally stable (m.p.: 3 a: 217 8C; 3 b: 172 8C). Importantly, although the trifluoromethane sulfonate salts 3 a,b are barely soluble in most classical organic solvents, they are soluble in acetonitrile; thus, their purification is quite easy and large quantities can be prepared in a one-pot reaction from the amide (it is not necessary to isolate Alders dimer 1). However, in this re...
Struktur, Stereoelektronik und Synthesepotenzial von 1,2‐Bisonio‐1,2‐bis(dialkylamino)ethenen
Mithilfe der selbstaktivierenden silylassistierten Polyoniosubstitution (SASAPOS) konnten erste Vertreter von 1,2‐Bisonio‐1,2‐bis(dialkylamino)ethenen synthetisiert und strukturell charakterisiert werden (siehe Bild; DMAP=4‐Dimethylaminopyridin). Dabei wurden – je nach Art der eingeführten Onioliganden – zwei grundlegende Strukturtypen gefunden, die sich hinsichtlich ihrer internen stereoelektronischen Stabilisierung unterscheiden.
Due to their strong s-donor properties, N-heterocycliccarbenes (NHCs) have found numerous applications as ligands for transition-metal catalysts.[1] More recently, it has been found that acyclic diaminocarbenes A (see Scheme 1) [2] or even amino aryl carbenes B[3] also behave as strong-sdonor weak-p-acceptor ligands and therefore could be considered as alternative ligands for catalysts; [4,5] to date, A is the most basic carbene ligand known.[4c] However, the range of acyclic amino carbenes (AAC) known is far surpassed by that of their NHCs counterparts. Obstacles to extending the range of available AACs reside in their supposed inherent instability, [6] but also in the lack of a general and convenient synthetic route for their preparation. We have recently reported that substitution reactions occur at the carbene center of the phosphonio-substituted carbene D, thus giving rise to new stable carbenes. [7] However, the synthesis of D requires several steps, which includes the preparation of a stannyl phosphane; a very fragile carbene intermediate C; [8] and most importantly, is limited to (methyl)di(tert-butyl)-phosphane as a leaving group. Indeed, to assure the stability of carbene C, bulky groups at phosphorus are required, and the addition of an organic group to the phosphane to form a quaternary P center is limited to methylation. (Methyl)di(tertbutyl)phosphane is 1) very basic, therefore not the perfect leaving group; 2) bulky, thus preventing the substitution reaction with sterically hindered nucleophiles; 3) features acidic methyl protons, which often react with the nucleophile (base) to afford undesirable products.Herein, we report an easy entry to amino(phosphonio)-carbenes by using simple phosphanes and readily available reagents, and the subsequent substitution reactions at the carbene center.As one of the most common synthetic routes to stable carbenes is based on the deprotonation of the corresponding iminium salt, [1] phosphonio iminium salts 3 were the obvious precursors to amino(phosphonio)carbenes. Based on the elegant work by Weiss and co-workers, we predicted that dications such as 3 should be accessible and stable as compounds that feature bis(onio)substituted sp 3 -and even sp 2 -carbon atoms have been isolated.[9] Indeed, we have found that Alders dimer 1 [2,10] cleanly reacts at room temperature with the basic tricyclohexylphosphane, but also with very simple phosphanes such as triphenylphosphane, thus leading to the formation of the desired dications 3 a,b in 94 and 93 % yield, respectively (Scheme 2). Although 3 a,b are water sensitive, giving back diisopropylamide when exposed to moisture, they are highly thermally stable (m.p.: 3 a: 217 8C; 3 b: 172 8C). Importantly, although the trifluoromethane sulfonate salts 3 a,b are barely soluble in most classical organic solvents, they are soluble in acetonitrile; thus, their purification is quite easy and large quantities can be prepared in a one-pot reaction from the amide (it is not necessary to isolate Alders dimer 1). However, in this re...
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