Allan White

UNEXPECTED PRODUCTS FROM THE REACTION OF TERT-BUTOXYL RADICALS WITH ACETYLENES IN THE PRESENCE OF AN AMINOXYL RADICAL SCAVENGER

The radical trapping technique employing 1,1,3,3-tetramethyl-2,3-dihydro-1H-isoindol-2-yloxyl (1) as a scavenger has been used to study the reaction of tert-butoxyl radicals with phenylacetylene, methyl acetylenecarboxylate and dimethyl acetylenedicarboxylate. With phenylacetylene, an aromatic ketone (5) was formed in which both the tert-butoxy group and the radical trap were bound to the same carbon, whereas the acetylenecarboxylates gave vinylamine and vinyloxyamine products. The mechanism of formation of these unexpected products is discussed. Acetylene and diphenylacetylene did not appear to react with tert-butoxyl radicals.

CCDC 1579934: Experimental Crystal Structure Determination

Related Article: Brian W. Skelton, Allan H. White, Colin L. Raston|2017|CSD Communication|||

The reaction of diphenylphosphine oxide and diphenylphosphine with dialkyl azodicarboxylates

Diphenylphosphine oxide reacts rapidly with azodicarboxylates to give 1 : 1 diphenyl-phosphinoylhydrazine-1,2-dicarboxylate adducts. Structural analysis shows that the diethyl compound crystallises in space group P, a= 12.197(5), b= 9.507(3), c= 8.503(6)A, α= 85.83(5), β= 76.91 (6), γ= 75.61(3)° and the diisopropyl compound crystallises in space group P21/c, a= 21.344(6), b= 9.702(2), c= 10.929(4)A, β= 104.71(3)°. The solid state conformations of the two molecules differ. In the diisopropyl structure the nitrogen protons and phosphorus oxygen atoms lie trans to each other whereas in the diethyl structure they are cis. 1H and 13C NMR spectroscopic studies reveal a high degree of hindered rotation. The mechanism of the reaction is discussed. Unexpectedly, diphenylphosphine and diisopropyl azodicarboxylate react slowly to give a complex mixture of products.

Hypervalent silicon via intramolecular co-ordination in a four-membered ring system: synthesis and structure of SiCl2X[2-C(SiMe3)2C5H4N](X = H or Me); X-ray structures of the former complex and of SiCl2Me(2-CPh2C5H4N)

Reaction of SiCl3X (X = H or Me) with LiR [R = 2-C(SiMe3)2C5H4N] yields the novel hpervalent five-co-ordinate compounds SiRCl2X which show strong Intramolecular Si–N interactions in the four-membered chelate ring [Si–N 2.066(9)A for X = H (X-ray)] which persists in solution; the related compounds, SiR′Cl2X (X = H or Me for R′= 2-CPh2C5H4N) have four-co-ordinate silicon (deduced from the 29Si NMR spectra and, for X = Me, an X-ray structure).