title: Thermodynamic trends in carbon-hydrogen bond activation in nitriles and chloroalkanes at rhodium.
abstract: Several transition-metal systems have been used to establish correlations between metal-carbon and carbon-hydrogen bonds. Here, the [Tp'RhL] fragment, where Tp' = tris(3,5-dimethylpyrazolyl)borate and L = neopentyl isocyanide, is used to investigate C-H bond activation in a series of linear alkylnitriles and chloroalkanes. Using a combination of kinetic techniques, relative free energies can be found for the compounds TpRhL(CH(3))H, Tp'RhL[(CH(2))(n)CN]H (n = 1-5), and Tp'RhL[(CH(2))(m)Cl]H (m = 1, 3, 4, 5). It is found that the CN and Cl substituents dramatically strengthen the M-C bond more than anticipated if in the alpha-position, with the effect on bond strength diminishing substantially as the X group moves further from the metal (i.e, beta, gamma, delta). Examination of M-C vs C-H bond strengths shows that the Tp'RhL(CH(2)X)H compounds (X = phenyl, vinyl, CN, Cl) all show a good correlation, as do the alkyl, aryl, and vinyl derivatives. The compounds in the former group, however, have stronger M-C bonds than expected based on the C-H bond strengths and consequently, their correlation is separate from the other unsubstituted compounds.
authors.affiliation: Department of Chemistry, University of Rochester, Rochester, New York 14627, USA.
authors.forename: Meagan E
authors.initials: ME
authors.lastname: Evans
authors.forename: Ting
authors.initials: T
authors.lastname: Li
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Vetter
authors.forename: Ryan D
authors.initials: RD
authors.lastname: Rieth
authors.forename: William D
authors.initials: WD
authors.lastname: Jones