Date of Award
Doctor of Philosophy (PhD)
Two types of rearrangement are afforded by the reaction of 1,4-dienes with a catalyst formed from tra ns-d i chIoro- bis(tri-n-butyIphosphine)Ni( I I ) and di isobutyI a I urninum chloride. Type I is exemplified by the rearrangement of I,4-pentadiene to 2-methyI - I,3-butadiene. Type II is exemplified by the rearrangement of 3-methyI - I ,4-pentadiene to I,4-hexadienes. The catalyst is thought to be a nickel hydride or its chemical equivalent.
This study was primarily concerned with the type II rearrangement. Two possible routes for the type I I rearrangement were considered. (I) A 1,2-nickel hydride addition to the terminal unsubstituted double bond of the diene followed by g-elimination of ethylene to form a tt — a I I y I — nieke I( I I)ethyIene complex (fragmentation) which could reform to afford products. (2) A 1,2-nickel hydride addition to the diene followed by cyclization to form a cyclobutyl- car b i ny I n i c ke I ( II ) species which could then rearrange to form products (equation I).
I, I-Dideutero-2-methyI - I ,4-pentadiene was prepared by the pyrolysis of I ,I-dideutero-2-methyI-4-pentenyI acetate . The main precursor of the acetate was 2-methyI-4-pentenoic acid which was prepared by the reaction of a I IyI chloride with diethyImethyI malonate. The resulting diester was hydrolyzed and decarboxyIated by heating it at low pressures. 2-MethyI-4-pentenoic acid was esterified with ethanol and reduced with lithium aluminum deuteride to form 2-methyl- 4-pentenoI - I-D2• The acetate was formed by treating the alcohol, with acetyl chloride.
2,3-DimethyI - I,4-pen tadiene was prepared by codimerizing ethylene and 2-methyI - I,3-butadiene with the nickel catalyst formed from trans-dichlorobis(tri-n-butylphosphi ne)Ni( I I) and di isobutyI a I urninurn chloride.
I, I-Dideutero-2-methyI - I,4-pentadiene when treated with the nickel catalyst resulted in the reappearance of hydrogen at C — I as indicated by the pmr spectrum of recovered di- deutero-2-methyI - I ,4-pentadienes. The pmr spectrum was consistent with the presence of 3,3-dideutero-2-methyI - I,4- pentadiene in recovered unisomerized diene (equation 2).
The rearrangement of 2,3-dimethyI - I,4-pentadiene with the catalyst resulted in the formation of (4E)-4-methyI - I ,4- hexadiene as the only isomeric 1,4-diene product (equation 3) .
The type II rearrangement of I , I-dideutero-2-methyI - I,4- pentadiene and 2,3-dimethyI - I ,4-pentadiene were consistent with the fragmentation route.
Polar solvents increase the rate of conversion of 1,4- dienes to isomeric products.
It was also possible to generate the nickel catalyst by different methods. The thermolysis of trans-chloro(2-al IyI — pheny I ) b i s (tr i ethy I phosph i ne ) N i ( II ) , J_, in tetrachloro- ethylene resulted in the formation of trans-chIo ro(t r i c hIo ro- vinyl)bis(triethy!phosphine)Ni(ll), 2_, and indene as major products. One of the minor products was tra ns-chIoro(2- p rope ny I p he ny I ) b i s (t r i eth y I p hos p h i ne ) N i ( I I ) , 3_. The main product during the thermolysis of J_ in benzene was 3_. Allylbenzene was isomerized to trans-l-phenyI - I-propene and cis-I,4-hexadiene was rearranged to trans-2-methyl-l,3- pentadiene when present during the thermolysis of J_ in benzene. The catalyst formed during the thermolysis of J_ was not a nickel(O) complex since ethyIenebis(triphenyIphos- phine)Ni(O) did not isomerize allylbenzene without the addition of HCI.
Golden, Harry J., "A Study of the Nickel Catalyzed Rearrangement of 1,4-Dienes" (1973). Theses and Dissertations. 3605.