ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Kinetics and mechanism of hydroboration of oct-1-and-4-ene by dimeric dialkylboranes

D. Jaganyi and J. R. Govender

School of Chemistry, Faculty of Science and Agriculture, University of KwaZulu-Natal, Pietermaritzburg, South Africa

E-mail: jaganyi@ukzn.ac.za

Received: 5 May 2006  Revised: 11 August 2006  Accepted: 11 August 2006

Abstract: The kinetics and mechanism of hydroboration of oct-1-and-4-ene with a series of dimeric dialkylboranes was investigated. The kinetic results showed that the hydroboration of terminal olefins proceeds via a three-halves-order mechanism, first-order with respect to the olefin and one-half-order with respect to the dimer. Using dicyclohexylborane, diisopinocamphenylborane, and 3,6-dimethylborepane the observed rate constants for the hydroboration of oct-4-ene were approximately 6 times smaller than those for oct-1-ene. Supporting computations showed that both steric and electronic effects influence the rate of hydroboration of both internal and terminal olefins. A model computational study of the isomerization of oct-4-ene with di(prop-2-yl)borane showed that formation of the terminal hydroborated complex is thermodynamically favored over the internal complex.

Keywords: kinetics - mechanism - hydroboration - octenes - dialkylboranes

Full paper is available at www.springerlink.com.

DOI: 10.2478/s11696-006-0096-7

Chemical Papers 61 (1) 55–60 (2007)