Kinetic and Thermodynamic Selectivity of Intermolecular C–H Activation at [Tp′Rh(PMe₃)]. How Does the Ancillary Ligand Affect the Metal–Carbon Bond Strength?

Abstract

Tp'Rh(PMe3)(CH3)H was synthesized as a precursor to produce the coordinatively unsaturated fragment [Tp'Rh(PMe3)], which reacts with benzene, mesitylene, 3,3-dimethyl-1-butene, 2-methoxy-2-methylpropane, 2-butyne, acetone, pentane, cyclopentane, trifluoroethane, fluoromethane, dimethyl ether, and difluoromethane at ambient temperature to give only one product in almost quantitative yield in each case. All of the complexes Tp'Rh(PMe3)(R)H were characterized by NMR spectroscopy, and their halogenated derivatives were fully characterized by NMR spectroscopy, elemental analysis, and X-ray crystallography. The active species [Tp'Rh(PMe3)] was also able to activate the alkynyl C-H bond of terminal alkynes to give activation products of the type Tp'Rh(PMe3)(C≡CR)H (R = t-Bu, SiMe3, hexyl, CF3, Ph, p-MeOC6H4, and p-CF3C6H4). The measured relative rhodium-carbon bond strengths display two linear correlations with the corresponding carbon-hydrogen bond strengths, giving a slope of 1.54 for α-unsubstituted hydrocarbons and a slope of 1.71 for substrates with α-substitution. Similar trends of energy correlations were established by DFT calculated metal-carbon bond strengths for the same groups of substrates.

Bond Formation and Coupling between Germyl and Bridging Germylene Ligands in Dinuclear Palladium(I) Complexes

“…It is well known, that the stability and reactivity of a metal-carbon bond in mononuclear transition-metal complexes varies significantly depending on the auxiliary ligand. [21] In the dinuclear complexes of this study, the two metal centers change their respective coordination bonds in a different but cooperative way, and thus achieve bond formation and activation. Shimada, Tanaka, and co-workers reported nickel(0)-promoted cyclodimerization of 1,2-disilabenzene, which may also involve formation of SiÀSi bonds from the terminal silyl and bridging silylene ligands of a dinickel intermediate.…”

The Effects of Ancillary Ligands on Metal–Carbon Bond Strengths as Determined by C–H Activation

“…Reproduced with permission of the ACS from Jiao et al [14] The )]. Using 5, many hydrocarbon and substituted methyl products could be prepared (Scheme 3) [18].…”

“…The vertical separation of the lines at D C-H ¼ 100 kcal mol À1 is 8.1 kcal mol À1 . Reproduced with permission of the ACS from Jiao et al [18] 82 W.D. Jones as efficient thermal precursors for {Tp 0 Rh[P(OMe) 3 ]}.…”

“…8). These alkynyl hydride products proved to be very stable, as they could be chromatographed in air on the benchtop and the X-ray crystal structures of many of them could be obtained without derivatization [18]. As was done previously, the kinetics of reductive elimination, combined with kinetic competition data, were used to obtain rhodium-carbon bond strengths with [Tp 0 Rh(PMe 3 )] as the metal fragment.…”

“…Reproduced with permission of the ACS from Jiao et al [18] The Effects of Ancillary Ligands on Metal-Carbon Bond Strengths as. .…”