Assignment of the oxidation states of Zr and Co in a highly reactive heterobimetallic Zr/Co complex using X-ray absorption spectroscopy (XANES)

Abstract

The reduced heterobimetallic complex (THF)Zr(MesNP(i)Pr2)3CoN2 (1) has been examined along with a series of structurally similar reference compounds using X-ray absorption near edge structure (XANES) spectroscopy. Complex 1 has been shown to be highly reactive, often via one-electron pathways that might be expected for a d(1) Zr(III) complex. However, the presence of two strongly interacting metals in complex 1 renders the assignment of oxidation states ambiguous. Both Zr and Co K-edge XANES spectra reveal that the most accurate description of complex 1 is that of a Zr(IV)/Co(-I) zwitterion. Electronic structure calculations support this assignment.

Metal-only Lewis pairs between group 10 metals and Tl(i) or Ag(i): insights into the electronic consequences of Z-type ligand binding

“…Although limited experimental techniques are capable of probing metal–metal dative interactions, X-ray Absorption Near-Edge Spectroscopy (XANES) 71 has begun to find an important use in this regard. 30 , 34 Importantly, its utility lies in its ability to decipher the spectroscopic oxidation states of the metals involved in a given bonding interaction. In order to assess the degree of charge transfer inherent in the formation of a reverse-dative σ-interaction to Tl( i ), Pd K -edge XANES was carried out on the palladium–thallium adduct [TlPd(CNAr Dipp2 ) 2 ]OTf ( 2 , Fig.…”

“… 46 , 47 Similar ambiguities in the electronic structures of MOLPs exist, although considerably less effort has been put toward uncovering satisfactory electronic descriptors for such compounds. 39 Despite the fact that X-ray Absorption Near-Edge Spectroscopy (XANES) holds promise in this regard, 30 , 34 its thus-far limited use in this capacity has not yet led to the development of general principles for properly describing the electronic structures of complexes containing metal–metal dative interactions.…”

A heterobimetallic complex featuring a Ti–Co multiple bond and its application to the reductive coupling of ketones to alkenes

“…The difference in natural charge between the two metal atoms is far smaller for complex 3 (1.04) than for the previously described Zr/Co complex (THF)Zr(MesNP i Pr 2 ) 3 CoN 2 (2.61). 39 …”

“…A recent study using X-ray absorption near edge structure (XANES) spectroscopy showed that the effective oxidation states in the similar complex (THF)Zr(MesNP i Pr 2 ) 3 CoN 2 are Zr IV /Co –I . 39 However, given the polar covalent nature of the metal–metal σ bond, a non-zwitterionic Ti III /Co 0 description may be favored in the case of 3 and further spectroscopic study will be required to determine the effective oxidation states in this molecule.…”

Synthesis of chiral heterobimetallic tris(phosphinoamide) Zr/Co complexes

“…I 2 , RX, CO 2 ) [11,12], and four-electron redox processes (RN 3 ) [13]. The versatile multielectron redox chemistry of (THF)Zr(MesNP i Pr 2 ) 3 CoN 2 is particularly remarkable given that the oxidation states of the two metals were found to be Zr IV and Co -I using XANES (X-ray Absorption Near Edge Structure) spectroscopy [14], so Co is serving as the sole source of electrons in all of the aforementioned multielectron redox processes. While exploring the reactivity and catalytic applications of (THF)Zr(MesNP i Pr 2 ) 3 CoN 2 , we found this complex is an effective catalyst for the hydrosilylation of ketones [15].…”