Early lanthanide organometallic hydrides: electronic and steric control ofthe stability

Steric and electronic effects on the stability of early lanthanide, neodymi um and samarium, organometallic hydrides are discussed. The instability of (tmp)(2)SmH (tmp = tetramethylphospholyl) is attributed to electronic facto rs and the low stability of ((BuC5H4)-Bu-t)(2)SmH is related to steric reas ons. The analogous neodymium hydride ((BuC5H4)-Bu-t)(2)NdH, could not be ob tained, whereas the more hindered triethylborohydride was formed. Access te a bisphospholyl bridged heterobimetallic ruthenium-lanthanide hydrides is a lso related to the size of the lanthanide atom. The bimetallic structures a re accessible for lanthanides of ionic radii smaller than 1 Angstrom. The r ole of organometallic hydrides versus alkyls as catalysts for olefin or die ne polymerization is discussed, a first and unique example of hex-1-ene and isoprene copolymerization is presented. (C) 2000 Elsevier Science S.A. All rights reserved.