Metalloradical-Catalyzed Aliphatic Carbon−Carbon Activation of Cyclooctane

Abstract

The aliphatic carbon-carbon activation of c-octane was achieved via the addition of Rh(ttp)H to give Rh(ttp)(n-octyl) in good yield under mild reaction conditions. The aliphatic carbon-carbon activation was Rh(II)(ttp)-catalyzed and was very sensitive to porphyrin sterics.

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

“…3As Rh(tmp)H is known to contain a small amount of Rh II (tmp) in equilibrium in solution, 16 we therefore propose the reaction mechanism operates with a Rh II (tmp)-catalyzed 1,3-addition of Rh(tmp)H into the C-C bond of cyclopropane, analogous to the Rh II (ttp)-catalyzed 1,2-addition of Rh(ttp)H into the C-C bond of cyclooctane (Scheme 3). 9 The relationship between substrate and the reaction rate as well as the product yield also validates this proposal. The attack of Rh II (tmp) to cyclopropane generates a Rh(tmp) propyl carbon centered radical.…”

“…Previously, we have reported the Rh II (ttp)-catalyzed 1,2-addition of Rh(ttp)H to the C-C bond of cyclooctane to afford the ring-opening product of Rh(ttp)(n-octyl) (Scheme 3). 9 Therefore, as part of our longterm interest, we now report the regioselective room-temperature CCA of cyclopropanes by the metalloradical Rh II (tmp) to afford linear ring-opening products through 1,3-addition under neutral conditions.…”

Carbon–Carbon Bond Activation by Group 9 Metal Complexes

“…Rh II 2 (ttp) 2 51 at 120 o C yielded 73 % of Rh III (ttp)( n ‐octyl) 52 (Scheme ). [40a] Rh II (ttp) metalloradical, generated in situ from the thermolysis of Rh II 2 (ttp) 2 51 , attacks the cyclooctane carbon to open up the ring and gives a Rh III (ttp)(CH 2 ) 7 CH 2 radical intermediate. This intermediate then rapidly picks up a hydrogen atom from Rh III (ttp)H 50 to afford the Rh III (ttp)( n ‐octyl) product 52 and regenerate the Rh II (ttp) metalloradical.…”

“…This transformation is estimated to be exothermic by 9.4 kcal/mol based on the BDEs (BDEs of C–C = 79.6 kcal/mol, Rh–H = 60 kcal/mol, Rh–C = 50 kcal/mol and C–H = 99 kcal/mol), which roughly agrees with the computed value of 14.7 kcal/mol. [40b] On the other hand, it is important to employ Rh II 2 (ttp) 2 in catalytic amount in conjunction with stoichiometric amount of Rh III (ttp)H to kinetically suppress the termolecular C–H activation of cyclooctane …”

Direct activation of relatively unstrained carbon–carbon bonds in homogeneous systems

“…47 Similar chemistry was developed by the group previously in the context of C–C activation using stoichiometric rhodium phorphyrin complexes. 48,49 In this transformation, PCP is catalytically converted to 4,4′-dimethyl-bibenzyl 113 under two possible conditions (eqn (29)). Rh III (ttp)I (ttp = tetratolylporphyrinato dianion) in the presence of KOH (1 equiv.)…”