Anionic Tantalum Dihydride Complexes: Heterobimetallic Coupling Reactions and Reactivity toward Small-Molecule Activation

Abstract

The anionic dihydride complex [Cp2TaH2](-) was synthesized as a well-defined molecular species by deprotonation of Cp2TaH3 while different solubilizing agents, such as [2.2.2]cryptand and 18-crown-6, were applied to encapsulate the alkali-metal counterion. The ion pairs were characterized by multiple spectroscopic methods as well as X-ray crystallography, revealing varying degrees of interaction between the hydride ligands of the anion and the respective countercation in solution and in the solid state. The [Cp2TaH2](-) complex anion shows slow exchange of the hydride ligands when kept under a D2 atmosphere, but a very fast reaction is observed when [Cp2TaH2](-) is reacted with CO2, from which Cp2TaH(CO) is obtained as the tantalum-containing reaction product, along with inorganic salts. Furthermore, [Cp2TaH2](-) can act as a synthon in heterobimetallic coupling reactions with transition-metal halide complexes. Thus, the heterobimetallic complexes Cp2Ta(μ-H)2Rh(dippp) and Cp2Ta(μ-H)2Ru(H)(CO)(P(i)Pr3)2 were synthesized and characterized by various spectroscopies and via single-crystal X-ray diffraction. The new hydride bridged tantalum-rhodium heterobimetallic complex is cleaved under a CO atmosphere to yield mononuclear species and slowly exchanges protons and hydride ligands when exposed to D2 gas.

Early/Late Heterobimetallic Tantalum/Rhodium Species Assembled Through a Novel Bifunctional NHC‐OH Ligand

“…This complex adds to the short list of well‐defined tantalum/rhodium heterobimetallic species and the surprisingly very limited list of NHC‐based early/late‐TM assemblies …”

“…This complex adds to the short list of well-defined tantalum/ rhodium heterobimetallic species [92][93][94][95][96] and the surprisingly very limited list of NHC-based early/late-TMa ssemblies. [97][98][99] Unfortunately,w hen the alkyl-alkylidene tantalum precursor was used, such clean chemistry was not observed.…”

An Anionic Ruthenium Dihydride [Cp*(iPr2MeP)RuH2]− and Its Conversion to Heterobimetallic Ru(μ-H)2M (M = Ir or Cu) Complexes

“…A particularly successful method involves the reaction of an anionic metal hydride with a halide complex. Since the first report of such a reaction in 1984, between K­[OsH 3 (PMe 2 Ph) 3 ] and Cp 2 ZrXCl (X = Cl or H), this approach has been used to synthesize numerous heterobimetallic complexes particularly from late metal hydride anions. − More recently, this approach has been extended to include early metal polyhydride anions by using [Cp 2 TaH 2 ] − in reactions with late metal halides …”

“…28−45 More recently, this approach has been extended to include early metal polyhydride anions by using [Cp 2 TaH 2 ] − in reactions with late metal halides. 46 This report describes an anionic half-sandwich hydride complex of ruthenium, synthesized from Cp*( i Pr 2 MeP)RuCl complexes were obtained after workup with alumina. The omission of the latter step and crystallization from diethyl ether allowed isolation of 2 rather than the previously described trihydride Cp*( i Pr 2 MeP)RuH 3 (3).…”

Selective Reduction of CO2 to a Tantalum Formate Complex and Release of Methyl Formate from the Tantalum(V) Center

“…The release of the desired C1 products from the coordination sphere of these oxophilic metal cores, however, is often hampered, which represents a major obstacle for the development of closed synthetic cycles or catalytic processes mediated by these nontoxic metals . Yet another difficulty is rooted in the aforementioned high reactivity of early-metal hydrides: namely, the possibility of over-reduction, either via the formation of metal oxo species (and CO) or via the reaction of two hydrides with 1 equiv of CO 2 to afford M–OCH 2 O–M derivatives . Thus, the selective synthesis of early-metal formates via a hydride precursor is commonly considered difficult and has not yet been achieved for tantalum .…”