Understanding the Organometallic Step: SO₂ Insertion into Bi(III)−C(Ph) Bond

Abstract

Heavier main-group element-catalyzed reactions provide an increasingly attractive tool to perform transformations mimicking the behaviors of transition metal catalysts. Recently, Magre and Cornella reported a Bicatalyzed synthesis of aryl sulfonyl fluorides, which involves a fundamental organometallic step of SO 2 insertion into the BiÀ Ph bond. Our theoretical studies reveal that i) the ability of hypervalent coordination of the Bi(III) center allows facile coordination sphere expansion for the SO 2 coordination via one oxygen atom; and ii) the high polarity of the BiÀ Ph bond makes the Ph migration from the Bi(III) center feasible. These features enable the heavier main group element to resemble the transition metal having flexibility for ligand association and dissociation. Furthermore, iii) the available π electron pair of the migrating Ph group stabilizes the SO 2 insertion transition state by maintaining interaction with the Bi(III) center during migration. The insight helps us better understand the heavier main-group catalysis.

Theoretical Study on Bismuth(III) Catalysts for Synthesis of Phenylsulfonyl Fluoride: Reasons of Their Catalysis

“…The next step is the SO 2 insertion into the Bi–Ph bond of (Ph)­Bi­(diAr-SO 2 ). Although this SO 2 insertion has been theoretically investigated without substituents on the diAr-SO 2 ligand, recently, we found several open questions: (i) Does there exist one possibility that this reaction becomes a rate-determining step when some ligand different from diAr-SO 2 is used? (ii) Why is the product of the SO 2 insertion different between transition metal complexes ,, and bismuth complexes? In addition, (iii) are substituent effects large on this insertion reaction like on the transmetalation?…”

“…SO 2 Insertion into the Bi−CH 3 Bond of (CH 3 )Bi(diAr-SO 2 ). Although the SO 2 insertion into the Bi−CH 3 bond has been theoretically investigated recently, 66 we compared here the SO 2 insertion into the Bi−CH 3 bond of (CH 3 )Bi(diAr-SO 2 ) 2E with the rate-determining step of RA; geometry changes are shown in Figure S4B of the Supporting Information. The ΔG° ‡ value (35.0 kcal/mol) for this SO 2 insertion reaction is considerably larger than that of the ratedetermining step by RA (Tables 1 and 3), indicating that the synthesis of alkylsulfonyl fluoride is difficult using the bismuth catalyst.…”

“…Although the SO 2 insertion into the Bi−Ph bond is not a rate-limiting step in this catalytic reaction, as discussed below, we investigated the SO 2 insertion using a bismuth phenyl complex of a diaryl ligand with a CH 2 group (named diAr-CH 2 ) instead of the sulfone (SO 2 ) group in diAr-SO 2 , as shown by (Ph)Bi(diAr-CH 2 ) 2D in Scheme 2, to elucidate the reason why the unique diAr-SO 2 is used for the bismuth catalyst because the participation of the sulfone group in the SO 2 insertion is suggested by the fact showing that the distance between the Bi atom and the O 5 atom of the sulfone group changes in the reaction, as discussed below; we did not investigate the transmetalation and fluorination using the diAr-CH 2 ligand because the Bi−O 5 distance changes little in these reactions. Also, we investigated the SO 2 insertion into a bismuth−methyl (Bi−CH 3 ) bond using a methyl analogue (CH 3 )Bi(diAr-SO 2 ) 2E (Scheme 2) to predict whether alkylsulfonyl fluoride can be synthesized using the bismuth catalyst or not; although this insertion reaction has been theoretically investigated recently, 66 we intended to compare this reaction with the rate-determining step of the catalytic cycle at the same computational level.…”

“…In addition, why is the Bi–OSOPh bond produced by the SO 2 insertion? The SO 2 insertion reaction has been theoretically investigated recently, and a similar insertion reaction of carbon dioxide into the germanium–phenyl bond and those of carbonyl compounds into germanium–aryl and tin–aryl bonds have also been investigated theoretically. , However, no discussion has been presented on the important difference in the product between the transition metal complex and the bismuth complex; in the products of Pd and Au complexes, the S atom of the PhSO 2 group is bound with the metal atom, as observed , and proposed experimentally. In the Bi catalyst, on the other hand, the experimental proposal suggests that the O atom of the PhSO 2 group is bound with the Bi atom .…”