[beta]-Migratory insertion reactions of ([eta][sup 5]-C[sub 5]R[prime][sub 5])Rh(L)(C[sub 2]H[sub 4])R[sup +]BF[sub 4][sup [minus]] (R[prime] = H, CH[sub 3]; R = H, C[sub 2]H[sub 5]; L = P(OMe)[sub 3], PMe[sub 3]). Comparison of the energetics of hydride versus alkyl migration

Journal Article · Wed Dec 16 00:00:00 EST 1992 · Journal of the American Chemical Society; (United States)

DOI:https://doi.org/10.1021/ja00052a040· OSTI ID:6443975

Brookhart, M; Hauptman, E; Lincoln, D M ^[1]

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1. Univ. of North Carolina, Chapel Hill (United States)

The [beta]-migratory insertion of transition metal olefin hydride complexes is a fundamental transformation of importance in several catalytic processes, including olefin hydrogenations, hydroformylations and isomerizations. Protonation of the rhodium ethylene complexes C[sub 5]R[sub 5](L)Rh(C[sub 2]H[sub 4]), 1a,b and 2a,b (1 R = CH[sub 3], 2 R = H, a L = P(OMe)[sub 3], b L = PMe[sub 3]), with HBF[sub 4][center dot]Me[sub 2]O in CH[sub 2]Cl[sub 2] yields the four corresponding ethylene hydride complexes C[sub 5]R[sub 5](L)Rh(C[sub 2]H[sub 4])H[sup +], 3a,b and 4a,b. NMR techniques were used to measure the rates of migratory insertion for these species. Values for the free energies of activation were found to be 12.2 (3a), 12.1 (3b), 15.0 (4a), and 15.0 (4b) kcal/mol. Eyring plots based on rate constants measured over the [minus]20 to +20[degrees]C range established [Delta]S[sup [double dagger]] = 0 for these migratory insertions. Treatment of 3a,b and 4a,b with excess ethylene gave the ethyl ethylene complexes C[sub 5]R[sub 5](L)RhCH[sub 2]CH[sub 3](C[sub 2]H[sub 4])[sup +], 7a,b and 8a,b, whose structures were established by [sup 1]H and [sup 13]C NMR spectroscopy. These complexes function as ethylene dimerization catalysts; NMR spectroscopic analysis of the catalytic systems shows that 7a,b and 8a,b are the catalyst resting states. The turnover-limiting step is the [beta]-migratory insertion reaction of the ethyl ethylene complexes. The [Delta]G[sup [double dagger]] values for [beta]-migratory insertion calculated from turnover rates were found to be 22.4 (7a), 23.4 (7b), 23.4 (8a), and 24.7 (8b) kcal/mol. The [Delta][Delta]G[sup [double dagger]] values for H versus CH[sub 2]CH[sub 3] migration for these systems thus lie in the range of 8.5-11 kcal/mol, which corresponds to relative migratory aptitudes k[sub H]/k[sub Et] of 10[sup 6]-10[sup 8] at 23[degrees]C. 34 refs., 5 figs., 4 tabs.

• OSTI ID: 6443975
• Journal Information: Journal of the American Chemical Society; (United States), Vol. 114:26; ISSN 0002-7863
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ETHYLENE
CHEMICAL REACTION KINETICS
ORGANOMETALLIC COMPOUNDS
RHODIUM COMPOUNDS
ACTIVATION ENERGY
CATALYSTS
CHEMICAL INDUSTRY
CHEMICAL REACTION YIELD
DIMERIZATION
MIGRATION
NUCLEAR MAGNETIC RESONANCE
PHOTOELECTRON SPECTROSCOPY
THERMODYNAMIC PROPERTIES
ALKENES
CHEMICAL REACTIONS
ELECTRON SPECTROSCOPY
ENERGY
HYDROCARBONS
INDUSTRY
KINETICS
MAGNETIC RESONANCE
ORGANIC COMPOUNDS
PHYSICAL PROPERTIES
POLYMERIZATION
REACTION KINETICS
REFRACTORY METAL COMPOUNDS
RESONANCE
SPECTROSCOPY
TRANSITION ELEMENT COMPOUNDS
YIELDS
400201* - Chemical & Physicochemical Properties