Trimethylphosphine adduct of the zirconocene-benzyne complex: synthesis, reactions, and x-ray crystal structure

Abstract

Metal-ligand electron transfer occurs as a fundamental step in redox processes of complexed metal ions, but only in rare cases has it been studied directly. Intramolecular charge separation induced photochemically contributes to the activity of photocatalysts where oxidative and reductive centers result from transfer of charge between localized metal and ligand electronic levels. Ruthenium bipyridine and diimine complexes have been of particular interest in this context5 and recent studies on o-quinone complexes indicate even more facile electron-transfer properties.6 Quinone ligands7 chelated to metal ions as either semiquinone or catecholate form complexes with quinone * electronic levels and metal d-orbitals close in energy yet discrete in the molecular orbital structure of the complex.8 This has permitted studies on parameters which direct charge distribution within the metal-quinone chelate ring.9Air oxidation of Ru(bpy)2(DBCat) yields the Ru"(bpy)2-(DBSq)+ cation with oxidation occuring at the catecholate ligand.10 This charge distribution has been determined from the structural features of the cation11 and from electronic spectroscopic considerations.10 Complexes containing two quinone ligands bonded to ruthenium were prepared by treating Ru2(OAc)4C1 with DBCat.

Synthesis, Structure, and Bonding of a Zirconocene–1,2‐Dehydro‐o‐carborane Complex

“…[14] Meanwhile, the HOMO, despite containing the metal-carbon s-bonding interactions, can also be viewed as having the character of metal(d)-to-p* back-donation commonly used in describing metal-olefin or metal-acetylene bonds. [15] It is not too surprising that the two bonding descriptions discussed above are both responsible for the Zr-h 3 -(o-C 2 B 10 H 10 ) interactions in view of the molecular structure of [Cp 2 Zr(h 2 -benzyne)(PMe 3 )] [7] and the fact that the Lewis structures of metallacyclopropane (or metallacyclopropene) and metal-p complex forms are normally invoked to describe the bonding in metal-olefin or metal-acetylene complexes. [15] In summary, the first example of zirconocene-1,2-dehydro-o-carborane complex has been prepared and structurally characterized, which also exhibits a brand new bonding mode for carboranes.…”

“…[5,6] The first zirconocene-benzyne complex stabilized by PMe 3 was structurally characterized in 1986 (Scheme 1). [7] In sharp contrast, 1,2-dehydro-o-carborane, a three-dimensional relative of benzyne, was suggested as a reactive intermediate for the first time in 1990 by heating a lithium salt of o-bromocarborane. [8] It was recently reported that 1,2-dehydro-o-carborane was also generated from phenyl(o-trimethylsilyl carboranyl)-iodonium acetate in the presence of CsF (Scheme 2).…”

Unique chemical properties of metal-carbon bonds in metal-carboranyl and metal-carboryne complexes

“…Alternatively, one can describe the bonding interaction between the metal center and the two carbon atoms of the η 3 -(o-C 2 B 10 H 10 ) ligand in terms of the metal-carboryne form. DFT calculations suggest that the bonding interactions between the Zr atom and carboryne are best described as a resonance hybrid of both the Zr-C σ and Zr-C π bonding forms, similar to that observed in Cp 2 Zr(η 2 -benzyne) (Chart 2) [65] .…”

New Methods for the Preparation of Multiply Substituted Cyclopentadienes and Related Compounds

“…Treatment of Cp 2 ZrPh 2 with an alkyne affords zirconaindene 4 [16]. Addition of Lewis acid and an aldehyde into the reaction mixture gave substituted indenes in good yields (scheme 4).…”