Premium
Reversible Carbon‐Carbon Bond Cleavage of a 3‐Vinyl‐1‐Cyclopropene by Rh(I). Molecular Structures of Two Sterically Crowded 1,2,3,5‐η‐Pentadienediyl Complexes of Rh(III)
Author(s) -
Donovan Bernadette T.,
Egan James W.,
Hughes Russell P.,
Spara Paul P.,
Trujillo Hernando A.,
Rheingold Arnold L.
Publication year - 1990
Publication title -
israel journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.908
H-Index - 54
eISSN - 1869-5868
pISSN - 0021-2148
DOI - 10.1002/ijch.199000037
Subject(s) - chemistry , cyclopropene , isomerization , steric effects , triclinic crystal system , crystal structure , medicinal chemistry , stereochemistry , double bond , ring (chemistry) , deuterium , cyclopentadienyl complex , crystallography , catalysis , polymer chemistry , organic chemistry , physics , quantum mechanics
1,2,3‐Tri‐ tert ‐butyl‐3‐vinyl‐1‐cyclopropene 6a reacts with [RhCl(C 2 H 4 )] 2 to give the dimeric 1,2,3,5‐η‐pentadienediyl complex 7a . The cyclopentadienyl derivative of this complex, 8a , is obtained by reaction of 7a with T1(C 5 H 5 ). Crystal structures of both 7a and 8a were determined: 7a ; orthorhombic, Pbcn, a = 28.136 (4) Å, b = 10.637 (2) Å, c = 12.154 (2) Å, V = 3637.6 (1.2) Å 3 , and Z = 4 : 8a ; triclinic, P 1 ‐bar, a = 9.906 (2) Å, b = 9.736 (2) Å, c = 12.126 (2) Å, α = 76.07 (2)°, β = 78.21 (2)°, γ = 65.34 (2)°, V = 1024.6 (3) Å 3 , and Z = 2. Treatment of 7a with one equivalent of PMe 3 per Rh center results in regeneration of the vinylcyclopropene, demonstrating the reversibility of the ring opening reaction. Deuterium labelling studies show that both the ring opening and closing reactions proceed with retention of configuration at the vinyl olefin. Thus the trans ‐deuterated vinylcyclopropene 6b reacts with [RhCl(C 2 H 4 ) 2 ] 2 to give 7b in which deuterium is located exclusively in the syn position. Treatment of 7b with T1(C 5 H 5 ) yields 8b . Treatment of 7b with one equivalent of PMe 3 per Rh center results in formation of 6b as the sole organic product. Unlike their triphenyl relative 2 , the tri‐Bu complexes 7a , 7b, 8a , and 8b are stereochemically rigid in solution at room temperature, and do not undergo an η 3 → η 1 → η 3 isomerization on the NMR time scale. However, after prolonged heating, syn‐anti site exchange of H and D slowly takes place with 8b .