Synthesis and Crystallographic Characterization of a Reduced Bimetallic Yttrium -Metallocene Hydride Complex, [K(crypt)][(μ-Cp)Y(μ-H)] (Cp = MeSi[CH(SiMe)-3]), with a 3.4 Å Yttrium-Yttrium Distance.

The reduction of a bimetallic yttrium -metallocene hydride was examined to explore the possible formation of Y-Y bonds with 4d Y(II) ions. The precursor [CpY(μ-H)(THF)] (Cp = MeSi[CH(SiMe)-3]) was synthesized by hydrogenolysis of the allyl complex CpY(η-CH)(THF), which was prepared from (CH)MgCl and [CpY(μ-Cl)]. Treatment of [CpY(μ-H)(THF)] with excess KC in the presence of one equivalent of 2.2.2-cryptand (crypt) generates an intensely colored red-brown product crystallographically identified as [K(crypt)][(μ-Cp)Y(μ-H)]. The two rings of each Cp ligand in the reduced anion [(μ-Cp)Y(μ-H)] are attached to two yttrium centers in a "flyover" configuration. The 3.3992(6) and 3.4022(7) Å Y···Y distances between the equivalent metal centers within two crystallographically independent complexes are the shortest Y···Y distances observed to date. Ultraviolet-visible (UV-visible)/near infrared (IR) and electron paramagnetic resonance (EPR) spectroscopy support the presence of Y(II), and theoretical analysis describes the singly occupied molecular orbital (SOMO) as an Y-Y bonding orbital composed of metal 4d orbitals mixed with metallocene ligand orbitals. A dysprosium analogue, [K(18-crown-6)(THF)][(μ-Cp)Dy(μ-H)], was also synthesized, crystallographically characterized, and studied by variable temperature magnetic susceptibility. The magnetic data are best modeled with the presence of one 4f Dy(III) center and one 4f(5d) Dy(II) center with no coupling between them. CASSCF calculations are consistent with magnetic measurements supporting the absence of coupling between the Dy centers.