Early lanthanide organometallic hydrides: electronic and steric control of the stability

Steric and electronic effects on the stability of early lanthanide, neodymium and samarium, organometallic hydrides are discussed. The instability of (tmp)2SmH (tmp=tetramethylphospholyl) is attributed to electronic factors and the low stability of (tBuC5H4)2SmH is related to steric reasons. The analogous neodymium hydride (tBuC5H4)2NdH, could not be obtained, whereas the more hindered triethylborohydride was formed. Access to bisphospholyl bridged heterobimetallic ruthenium–lanthanide hydrides is also related to the size of the lanthanide atom. The bimetallic structures are accessible for lanthanides of ionic radii smaller than 1 Å. The role of organometallic hydrides versus alkyls as catalysts for olefin or diene polymerization is discussed, a first and unique example of hex-1-ene and isoprene copolymerization is presented.