Activation of Aldehydic Carbon−Hydrogen Bonds under Aerobic Conditions by Masked Rhodium(III) Porphyrin Cation

Abstract

Rh III (ttp)CH 2 CH 2 OH activated the aldehydic carbon-hydrogen bonds of functionalized aryl and enolizable aldehydes to give high yields of Rh(ttp)COR at 50 °C under both anaerobic and aerobic conditions. The Rh(ttp)(C 2 H 4 )OH intermediate was proposed to form via β-hydroxy elimination. The reactions exhibited rate and yield enhancement upon the addition of Ph 3 P, suggesting ligand-promoted β-elimination. The nonlinear free energy relationship of the Hammett plot suggested a multistepwise reaction with the rate-determining step (binding or activation) dependent on the electronic effect of para substituents of aryl aldehydes.Carbon-hydrogen bond activation (CHA) is an important Supporting Information Available: NMR spectra for complexes 4, 7, and 11. This material is available free of charge via the Internet at http://pubs.acs.org. OM070135E

From para‐Benziporphyrin to Rhodium(III) 21‐Carbaporphyrins: Imprinting Rh⋅⋅⋅η2‐CC, Rh⋅⋅⋅η2‐CO, and Rh⋅⋅⋅η2‐CH Coordination Motifs

“…The choiceo fm etal cationi ss trongly motivated by the extensive interest in reactions catalyzedb yr hodium(III)p orphyrins and in particular by their peculiar capability to contribute to processesi nw hich the activation of the single bond is of critical importance, whichi nvolves the formation of the CÀH, CÀC, and C=Ob onds unders ynthetic and catalytic conditions. [22][23][24][25][26][27][28][29][30][31][32][33][34] An impact on organorhodium chemistry,i mposed by the formation of carbametalacycles,c an also be noted. Such structuralm otivesa fford the stabilization of ap eculiar rhodium-carbon bonding situation, outstandingly reflected in the rhodiumo rganometallic chemistry in the surroundings of pincer-typeligands.…”

Mild and Selective C(CO)–C(α) Bond Activation of Ketones with Rhodium(III) Porphyrin β-Hydroxyethyl

“…Though the aldehydic CHA by Rh III (ttp)CH 2 CH 2 OH ( 1a ) was significantly accelerated by added PPh 3 , surprisingly, the addition of PPh 3 reduced the yield of Rh III (ttp)CO i Pr ( 2a ) greatly to about 40% yield, even though Rh III (ttp)CH 2 CH 2 OH ( 1a ) was completely consumed in 15 min (Table , entries 2 and 3). We are unclear of the reason.…”

“…Initially, Rh III (ttp)CH 2 CH 2 OH ( 1a ), prepared from the reductive alkylation of Rh(ttp)Cl ( 1b ) with NaBH 4 /BrCH 2 CH 2 OH, , reacted with diisopropyl ketone under solvent-free conditions under N 2 at 25 °C in 15 min, giving Rh III (ttp)CO i Pr ( 2a ) and acetone in 82% and 39% yields (GC-MS), respectively (eq ). When the reaction was carried out in air, Rh III (ttp)CO i Pr ( 2a ) and acetone were formed in 80% and 40% yields (GC-MS), respectively (eq ).…”

“…Rh III (ttp)CH 2 CH 2 OH (Figure ) has been used as a Rh III (ttp)OH surrogate in the mild aldehydic CHA with aryl and alkyl aldehydes . We now report our findings that Rh III (ttp)CH 2 CH 2 OH can also serve as a Rh III (ttp)OH equivalent to selectively undergo CCA of ketones under mild and aerobic conditions.…”

Alkylation of Rhodium Porphyrin Complexes with Primary Alcohols under Basic Conditions

“…Rhodium porphyrin alkyl complexes, Rh III (por)­R (por = porphyrinato dianion ligand), are convenient and air-stable precursors to rhodium­(II) porphyrin metalloradicals, which display distinct reactivity on C–H and C–C bond activation of various organic substrates under mild reaction conditions. , Rh III (ttp)­R (ttp = 5,10,15,20-tetratolylporphyrinato dianion) has been used as a precatalyst in the catalytic transfer hydrogenation of [2.2]­paracyclophane, , catalytic anaerobic oxidation of ketones, and hydrodebromination of allylic and benzylic bromides with water by hydrolysis or photolysis of the Rh–R bond . Rhodium porphyrin alkyl complexes allow the access of air-sensitive intermediates from benchtop-stable materials for the activation of inert chemical bonds.…”