93582-58-2Relevant academic research and scientific papers
New chiral palladacycles from an unprecedented cyclopalladation of cyclobutadiene-bound phenyl groups of cobalt sandwich compounds
Singh, Jatinder,Kumar, Dheeraj,Singh, Nem,Elias, Anil J.
, p. 1044 - 1052 (2014)
Reaction of in situ generated {η5-[MeOC(O)]C 5H4}Co(PPh3)2 with methyl 3-phenyl-2-propynoate followed by diphenylacetylene in refluxing toluene resulted in the formation of the cobalt sandwich compound {η5- [MeOC(O)]C5H4}Co{η4-C4Ph 3[C(O)OMe]} (1), having methyl ester units on both the cyclopentadienyl (Cp) and cyclobutadiene (Cb) rings. Hydrolysis of the ester groups using aqueous KOH resulted in the dicarboxylic acid {η5- C5H4[C(O)OH]}Co{η4-C4Ph 3[C(O)OH]} (2). The dicarboxylic acid 2 was converted to the novel bis(oxazolinyl) derivative [η5-(4-iPr-2-Ox)C5H 4]Co[η4-C4Ph3(4-iPr-2-Ox)] (3; Ox = oxazolinyl) by its reaction with oxalyl chloride, (S)-2-amino-3-methyl-1- butanol, triethylamine, and mesyl chloride. Reaction of the chiral bis(oxazoline) ligand 3 with Pd(OAc)2 in acetic acid at 60 C resulted in the formation of the novel chiral palladacycle 4, resulting from an unprecedented cyclopalladation involving one of the cyclobutadiene-bound phenyl groups. Palladacycle 4 has two trans-oriented oxazolinyl units and one of the phenyl groups of the cyclobutadiene ring bound to the palladium center along with an acetyl group. The reaction of KX (X = Br, I) with 4 in acetone-water medium yielded the bromo- and iodo-derived chiral palladacycles 5a,b. Compounds analogous to 3 having a chiral oxazolinyl unit on the Cb ring and a methyl or acetyl unit on the Cp ring, (η5-RC5H 4)Co(η4-C4Ph3R′) (R′ = oxazolinyl; R = acetyl (8a), methyl (8b)) were also prepared and characterized. Analogous reactions of 8a,b with 1.5 equiv of Pd(OAc)2 in acetic acid at 60 C gave the chiral palladacycles 9a,b. Analysis of these compounds indicated that, in contrast to the monomeric chiral palladacycle obtained from the reaction of 3, compounds 9a,b are molecules with a unique linear tetraacetate-bridged tripalladium core having the two cyclopalladated cobalt sandwich units at the periphery. Structural analysis of 9a indicated that the molecule possesses the same type of seven-membered palladacycle observed in the cases of 4 and 5a,b.
