Transition metal–free ketene formation from carbon monoxide through isolable ketenyl anions

Abstract

The capacity of transition metals to bind and transform carbon monoxide (CO) is critical to its use in many chemical processes as a sustainable, inexpensive C1 building block. By contrast, only few s- and p-block element compounds bind and activate CO, and conversion of CO into useful carbonyl-containing organic compounds in such cases remains elusive. We report that metalated phosphorus ylides provide facile access to ketenyl anions ([RC=C=O] – ) by phosphine displacement with CO. These anions are very stable and storable reagents with a distinctive electronic structure between that of the prototypical ketene (H 2 C=C=O) and that of ethynol (HC≡C–OH). Nonetheless, the ketenyl anions selectively react with a range of electrophiles at the carbon atom, thus offering high-yielding and versatile access to ketenes and related compounds.

Stable Ketenyl Anions via Ligand Exchange at an Anionic Carbon as Powerful Synthons**

“…According to the Pyykkö standard values, [29] the bond lengths of C(1)-C( 2 8) and 1.226(1) Å, respectively. [6] It is notable that the [K(18-C-6)] + cation binds at C(1) in B, whereas in our case it is bound to O(1). This is attributed to the steric hindrance between two flanking Dipp substituents in the diazaphospholidinyl group and [K(18-C-6)] + as our calculations show the modeled [[(CH2)(NDipp)]2P−CCO][K(THF)2] species energetically prefers the C(1)-K(THF)2 isomer rather than the O(1)-K(THF)2 by 1.8 kcal mol -1 (Figure S27).…”

“…[5] During the preparation of this manuscript, Gessner showed an isolable ketenyl anion Ph2P(S)C(K(18-C-6))CO (B) (18-C-6 = 18-crown-6) via an unprecedented phosphine/CO replacement reaction. [6] This breakthrough allowed the isolation of a series of ketene derivatives via facile ketenylations.…”

Stable Ketenyl Anions via Ligand Exchange at an Anionic Carbon as Powerful Synthons

“…According to the Pyykkö standard values, [29] the bond lengths of C(1)-C( 2 8) and 1.226(1) Å, respectively. [6] It is notable that the [K(18-C-6)] + cation binds at C(1) in B, whereas in our case it is bound to O(1). This is attributed to the steric hindrance between two flanking Dipp substituents in the diazaphospholidinyl group and [K(18-C-6)] + as our calculations show the modeled [[(CH2)(NDipp)]2P−CCO][K(THF)2] species energetically prefers the C(1)-K(THF)2 isomer rather than the O(1)-K(THF)2 by 1.8 kcal mol -1 (Figure S27).…”

Stable Ketenyl Anions via Ligand Exchange at an Anionic Carbon as Powerful Synthons**

“…According to the Pyykkö standard values, [34] the bond lengths of C(1)−C(2) (1.248(1) Å) and C(2)−O(1) (1.226(1) Å) lie between the corresponding double and triple bond, whereas the P(1)−C(1) bond length (1.739(1) Å) is found between the corresponding single and double bond. For comparison, the bond lengths of P(1)−C(1), C(1)−C(2) and C(2)−O(1) in B are 1.698(3), 1.178(8) and 1.226(1) Å, respectively [6] . It is notable that the [K(18‐C‐6)] + cation binds at C(1) in B , whereas in our case it is bound to O(1).…”

“…Additionally, the group of Stephan spectroscopically characterized Ph 2 P(S)C(Li(THF) 2 )CO ( A ) at room temperature in a reaction mixture of dilithiomethandiide with CO and N 2 O (Figure 1b). [5] During the preparation of this manuscript, Gessner showed an isolable ketenyl anion Ph 2 P(S)C(K(18‐C‐6))CO ( B ) (18‐C‐6=18‐crown‐6) via an unprecedented phosphine/CO replacement reaction [6] . This breakthrough allowed the isolation of a series of ketene derivatives via facile ketenylations.…”