Octylboronate ester

Recently, it was also shown [74] that pentamethylcyclopentadienyl rhodium and iridium complexes with labile dative ligands catalyze the borylation of alkanes at the terminal position under thermal conditions (Scheme 9). It was proposed that Ir(V) and Rh(V) boryl complexes act as intermediates in these reactions. Reaction of Cp IrH4 with HBpin gives Cp Ir(Bpin)(H)3 and Cp Ir(Bpin)2(H)2. Both of the two Ir(V) boryl complexes react with octane to give octylboronate ester [75], though it is still unclear regarding the role... 

The reactions typically proceed at 150°C with n-octane and di-pinacolboronate for 5-24 h, and the amount of catalyst typically is 1-5%. The yields of 1-octylboronate ester are good and the reaction is regioselective in the terminal alkyl position (second equation below, top of p. 418). The proposed mechanism involves oxidative addition of the B-B or B-H bond, followed by a-bond metathesis between the M-B and R-H bonds, which is driven towards formation of the B-R bond by the Lewis-acid property of boron. Note that 16e species (see Scheme p. 418) could also be involved in oxidative addition of the alkane to give an 18e intermediate M(Bpin)2(H)(R) or M(Bpin)(H)2(R) that would provide R-Bpin as well by reductive elimination. Calculations showed, however, that the o-bond metathesis path is preferred by about 10 kcal mol" over this alkane oxidative-addition path. 

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See also in sourсe #XX -- [ ]

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