Syntheses and structures of Ytterbium(II) hydride and hydroxide complexes: Similarities and differences with their calcium analogues

The Yb(II) hydride complex (DIPP-nacnac)YbH center dot THF (3-Yb, DIPP-nacnac = CH{(CMe)(2,6-iPr(2)C(6)H(3)N)}(2)) was prepared by a mild metathesis reaction of (DIPP-nacnac)Yb[N(SiMe3)(2)]center dot THF with PhSiH3. 3-Yb crystallizes as a dimer with bridging hydride ions, and its geometry is similar to that of the analogue calcium hydride complex (3-Ca). 3-Yb is well soluble in benzene and remarkably stable in solution at room temperature. Ligand exchange to the homoleptic Yb(II) complexes takes place at higher temperatures (3-Yb is less stable than the analogue 3-Ca). The soluble hydride complexes 3-Ca and 3-Yb are catalysts for the hydrosilylation of 1,1-diphenylethylene, but differences in the product distributions are observed. Slow hydrolysis of (DIPP-nacnac)Yb[N(SiMe3)(2)]center dot THF gave reduction of water and unidentified Yb(III) complexes. Fast hydrolysis at low temperature, however, resulted in the first Yb(II) hydroxide complex, (DIPP-nacnac)Yb(OH)center dot THF (4-Yb, 20% yield), which is a dimer with bridging hydroxide ions in the solid state. The crystal structure is isomorphous to that of the calcium analogue 4-Ca. 4-Yb is well soluble in benzene and considerably more stable against ligand exchange and formation of homoleptic species than 3-Yb.