Isomerization of the hydridoalkylrhodium complexes formed on oxidative addition of rhodium to alkane C-H bonds. Evidence for the intermediacy of eta/sup 2/-alkane complexes

Journal Article · Tue Nov 11 23:00:00 EST 1986 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00283a032· OSTI ID:7222764

Periana, R A; Bergman, R G

The products of insertion of the coordinatively unsaturated fragment Cp*RhL (Cp* = eta/sup 5/-C/sub 5/Me/sub 5/; L = PMe/sub 3/) into alkane C-H bonds are generated by irradiation of Cp*(L)RhH/sub 2/ or thermal decomposition of Cp*(L)Rh(neopentyl)(H), at temperatures below -30/sup 0/C in alkane solvents. The hydridoalkylrhodium products can be synthesized independently, also at low temperature, from the corresponding haloalkyl complexes by lithiation with t-BuLi followed by protonation. Alternatively, the highly nucleophilic complex Li(Cp*(L)RhH), prepared by deprotonation of Cp*(L)RhH/sub 2/, leads the alkylhydridorhodium complexes upon treatment with alkyl tosylates R-OTs. When Cp*RhL is generated in mixtures of linear alkanes, only the products of insertion into primary C-H bonds are observed, even at -100/sup 0/C. The relative rate constants for the formation of these products correlate directly with the number of secondary C-H bonds in the alkane. This suggests that insertion occurs initially into all the C-H bonds of the alkane, but that even at very low temperatures the secondary insertion products rearrange quickly, and intramolecularly, to the primary products. The authors suggests that this rearrangement occurs through the intermediacy of eta/sup 2/-C-H alkane complexes. Further studies provide support for this idea. The synthetic procedures summarized above can be used to prepare regiospecifically /sup 2/H and /sup 13/C labeled alkyl hydrides at low temperatures. Warming these complexes to temperatures above -80/sup 0/C in aromatic solvent reveals rearrangements which confirms that the alkylhydridorhodium complexes are capable of interconverting with one another intramolecularly at rates competitive with or in some cases faster than they undergo reductive elimination.

• Research Organization: Lawrence Berkeley Lab., CA
• DOE Contract Number: AC03-76SF00098
• OSTI ID: 7222764
• Journal Information: J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 108:23; ISSN JACSA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
ALKANES
CHEMICAL BONDS
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
COMPLEXES
DATA
ELEMENTS
EXPERIMENTAL DATA
HYDROCARBONS
INFORMATION
ISOMERIZATION
ISOTOPE EFFECTS
KINETICS
METALS
NUMERICAL DATA
ORGANIC COMPOUNDS
OXIDATION
PLATINUM METALS
REACTION INTERMEDIATES
REACTION KINETICS
RHODIUM
RHODIUM COMPLEXES
TRANSITION ELEMENT COMPLEXES
TRANSITION ELEMENTS