Photocatalytic Carbon–Carbon σ-Bond Anaerobic Oxidation of Ketones with Water by Rhodium(III) Porphyrins

Abstract

Photocatalytic carbon−carbon σ-bond oxidation of unstrained ketones by water using rhodium(III) porphyrin catalyst was accomplished. The catalysis yielded the corresponding one-carbon-less carbonyl compound and H 2 with up to 30 turnovers in both aliphatic and cyclic ketones with α substituents. No carbon loss was observed in aromatic ketone. Mechanistic studies suggest that (Ph 3 P)Rh III (ttp)OH (ttp = tetratolylporphyrinato dianion) is the key intermediate in the carbon−carbon σ-bond anaerobic oxidation.

Regioselective and Room-Temperature Carbon–Carbon Bond Activation of Cyclopropanes by Rhodium(II) Porphyrin

“…On the basis of the above results and earlier reports, 9,15,16 Scheme 5 shows the proposed reaction mechanism for the ring opening of cyclopropyl benzene by Rh II (tmp) (1a) to afford the 1,3-addition product Rh(tmp)CH 2 CH 2 CH 2 Ph (2d). Initially, Rh II (tmp) (1a) cleaves the C-C bond of the cyclopropyl group to afford the benzyl carbon centered stabilized radical 3.…”

“…This result corroborates that H 2 O was not necessary in the CCA of cyclopropanes. As the ketone substrate has been shown to be the H atom donor in our reported photocatalytic C(CO)-C(α) bond activation of ketones, 15 we rationalize the substrate, likely the weak α-C-H bond of cyclopropyl phenyl ketone, is the H atom source.…”

“…Initially, Rh II (tmp) (1a) cleaves the C-C bond of the cyclopropyl group to afford the benzyl carbon centered stabilized radical 3. Then the radical 3 abstracts a hydrogen atom from the substrate 15 or from the weak Rh(tmp)H (1b) bond 9 to generate the 1,3-addition product Rh(tmp)CH 2 CH 2 CH 2 Ph (2d).…”

Alkylation of Rhodium Porphyrin Complexes with Primary Alcohols under Basic Conditions

“…The red residue was purified by column chromatography over silica gel with a solvent mixture of hexane/CH 2 Cl 2 (1/1) as eluent to give Rh III (ttp)Bn (3a) 1d (10.7 mg, 0.013 mmol, 50%). 1 H NMR (CDCl 3 , 400 MHz): δ −3.77 (d, 2 H, 3 J Rh−H = 3.7 Hz), 2.72 (s, 12 H), 2.98 (d, 2 H, J = 7.5 Hz), 5.89 (t, 2 H, J = 7.6 Hz), 6.43 (t, 1 H, J = 7.3 Hz), 7.56 (t, 8 H, J = 6.4 Hz), 8.02 (d, 4 H, J = 7.0 Hz), 8.09 (d, 4 H, J = 6.8 Hz), 8.69 (s, 8 H).…”

“…R f = 0.77 (hexane/CH 2 Cl 2 = 1/1). 1 H NMR (CDCl 3 , 400 MHz): δ −3.75 (d, 2 H, 3 J Rh−H = 3.7 Hz), 0.99 (s, 9 H), 2.73 (s, 12 H), 2.97 (d, 2 H, J = 8.2 Hz), 5.92 (d, 2 H, J = 8.2 Hz), 7.57 (t, 8 H, J = 6.6 Hz), 8.10−8.05 (m, 8 H), 8.68 (s, 8 H).…”