Olefin Coordination Compounds of Rhodium. III. The Mechanism of

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Olefin Coordination Compounds of Rhodium. 111. The Mechanism of Olefin Isomerization Richard Cramer Contribution No. 1123 f r o m the Central Research Department, Experimental Station, E. I. du Pont de Nemours and Company, Wilmington,Delaware. Received December 18, 1965

Abstract: A mechanism is proposed for the isomerization of linear butenes with a soluble rhodium catalyst. It is a modification of addition and elimination of rhodium hydride at the olefin bond and involves an intermediate (formulated as a rhodium(II1) hydride with coordinated olefin) which exchanges with free olefin faster than with solvent proton. The mechanism is based principally upon deuterium transfer which accompanies isomerization of deuterated olefin or in deuterated solvent.

M

igration of unsaturation in terminal olefins is catalyzed by compounds of many transition metals including titanium, chromium,* iroq2I3molybden~m,~~ rhodium,5 i r i d i ~ m , ~ " ?nickel,2 ~,' p a l l a d i ~ m , ~ and " . ~ p l a t i n ~ m . ~ ~ , ~Two , ~ ' , ~isomeriza,~ tion mechanisms have been favored: (a) addition and elimination of a kinetically long-lived metal hydride4dJas7(eq 1) and (b) rearrangement through a

mH 4- RCH,CH=CH,

-

[RCH2CHCHJ]'-

I

m RCH=CHCH3

4- m H ( 1 )

RCH=CHCH,

(2)

I m (1) (a) C. S. Marvel and J. R. Rogers, J . Polj"u?r Sci., 49, 335 (1961); (b) G . D . Cooper and H. L. Finkbeiner, J . Org. Chem., 27, 1493 (1962); (c) F. H. C. Edgecombe, Tetruhedrorr Letters, 1161 (1962); H. Bestian and I