Synthesis and Crystallographic Characterization of a Reduced Bimetallic Yttrium ansa-Metallocene Hydride Complex, [K(crypt)][(μ-Cp^An)Y(μ-H)]₂ (Cp^An = Me₂Si[C₅H₃(SiMe₃)-3]₂), with a 3.4 Å Yttrium–Yttrium Distance

Abstract

The reduction of a bimetallic yttrium ansa-metallocene hydride was examined to explore the possible formation of Y− Y bonds with 4d 1 Y(II) ions. The precursor [Cp An Y(μ-H)(THF)] 2 (Cp An = Me 2 Si[C 5 H 3 (SiMe 3 )-3] 2 ) was synthesized by hydrogenolysis of the allyl complex Cp An Y(η 3 -C 3 H 5 )(THF), which was prepared from (C 3 H 5 )MgCl and [Cp An Y(μ-Cl)] 2 . Treatment of [Cp An Y(μ-H)(THF)] 2 with excess KC 8 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 An )Y(μ-H)] 2 . The two rings of each Cp An ligand in the reduced anion [(μ-Cp An )Y(μ-H)] 2 1− 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(18crown-6)(THF) 2 ][(μ-Cp An )Dy(μ-H)] 2 , was also synthesized, crystallographically characterized, and studied by variable temperature magnetic susceptibility. The magnetic data are best modeled with the presence of one 4f 9 Dy(III) center and one 4f 9 (5d z 2 ) 1 Dy(II) center with no coupling between them. CASSCF calculations are consistent with magnetic measurements supporting the absence of coupling between the Dy centers.

Intervalence Charge Transfer in Nonbonding, Mixed-Valence, Homobimetallic Ytterbium Complexes

“…Conversely, this result sets a new limit on short-distance nonbonding interactions between lanthanide ions. When paired with recent results on lanthanide–lanthanide bonding, this system highlights both the role of d orbital occupation in forming metal–metal bonds in molecular f -block complexes ,− and the origins of spectroscopic features traditionally described as IVCT transitions.…”

“…In contrast, reduction of lanthanides to mixed 4 f /5 d configurations results in dramatically different properties, such as metal–metal bonding and high magnetic coercivity . Related lanthanide complexes have been reported in recent years, − as well as a related metal–metal bonded trithorium cluster . The abundance of mixed-valence complexes with IVCT transitions outside of the f -block, and the depth of study these compounds have received, contrasts with few examples of mixed-valence lanthanide compounds. − Given the recent reports of mixed-valence and metal–metal bonded lanthanide − and actinide compounds, it is important to build a cohesive understanding of the existing literature and these novel materials.…”

Alkaline earth metals: homometallic bonding

“…The isolation of complexes with homometallic actinide and rare-earth bonding suggests new approaches for the preparation of Ae–Ae bonds for the heavier elements of the group. 58–60 It seems possible that, to access many of these highly reactive species, ligands that impart sufficient solubility to facilitate their preparation in inert alkane solvents, or the use of mechanochemical synthetic methods, will be necessary.…”

“…3) and three-centre one-electron homometallic bonding of the rare-earth element yttrium, which is adjacent to strontium in the Periodic Table, has been described. 60 The homometallic rare-earth element bonds are all calculated to principally comprise contributions from metal d-orbitals, as might be predicted for Ca, Sr, and Ba. 28 In the case of Ra, however, relativistic effects destabilize the 6d-orbital manifold.…”