Investigation of Zr−C, Zr−N, and Potential Agostic Interactions in an Organozirconium Complex by Experimental Electron Density Analysis

Abstract

The crystal structure and electron density (ED) distribution of an imine coupling product with an open zirconocene, Zr(2,4-C7H11)[(i-Pr)NCHPhCH2CMeCHCMeCH2] (C7H11 = dimethylpentadienyl), have been derived from accurate synchrotron X-ray diffraction measurements. The molecular structure reveals asymmetric coordination of Zr by the pentadienyl (2,4-C7H11) ligand (〈Zr−C〉 = 2.56(6) Å), the butadiene fragment (〈Zr−C〉 = 2.43(5) Å), and the amide nitrogen atom (Zr−N = 2.0312(5) Å) of the second ligand. The study of the ED and its topological analysis affords new insight into the bonding and electronic structure of the title zirconium complex. The interactions between the metal center and the ligands are represented by a Zr−N bond path and one Zr−C bond path with each of the pentadienyl and butadiene moieties, contrary to the usually depicted global metal−ligand bonding. The butadiene and pentadienyl groups exhibit a polarization of the corresponding π-like ED in the C−Zr directions, indicating that the whole conjugated systems are nonetheless involved. The 4d atomic orbitals of Zr exhibit unusual populations according to ligand field considerations, which reveal a high degree of σ-donation from the conjugated π systems of both ligands. As deduced from numerical integration over the topologically defined atomic basins, the Zr to ligand charge transfer is 1.48 e to the C17NH24 ligand and 0.68 e to dimethylpentadienyl. Topological analysis of a short intramolecular Zr···(C,H) contact provides no indication of the presence of agostic interactions, despite a small Zr−N−C angle of 102.87(4)°. Thus, no bond path and BCP (bond critical point) of the ED are found in the Zr···(C,H) region, which would have provided evidence for such direct interactions, nor is there any evidence for charge accumulation between the Zr and H atoms, or for lengthening of the C−H bond involved in the putative interaction. These characteristics, similar to those in other distorted situations, may be common for other electron-deficient d0 complexes.

Atomic interactions in ethylenebis(1-indenyl)zirconium dichloride as derived by experimental electron density analysis

“…They show a transfer of 2.25 e from the Zr atom to both indenyl ligands and two Cl atoms: 0.93 e are associated with each Cl atom, while 0.19 e are transferred to each indenyl ligand. Pillet et al (2003) have reported a charge transfer of 2.16 e from the Zr atom to ligands in a similar complex -an imine coupling product with zirconocene -which is similar to our result.…”

“…The X-ray experimental deformation electron density has been analyzed in ( 5 -C 5 H 5 )Fe[ 5 -PC 4 H 2 (CH 3 ) 2 ] (Weits et al, 1981), ( 5 -C 5 H 5 ) 2 V (Antipin et al, 1996;Lyssenko et al, 2001) and ( 5 -C 5 H 5 )Ti( 8 -C 8 H 8 ), and ( 5 -C 5 H 5 )M( 5 -C 7 H 7 ) with M = Ti, V, Cr (Lyssenko et al, 2001). Topological features of the experimental electron density in the imine coupling product with open zirconocene were elucidated by Pillet et al (2003) and Coppens et al (2005). Theoretical electron densities of metallocenes M( 5 -C 5 H 5 ) 2 (M = Mg, Ca; Bytheway et al, 1996) Cr, Mn, Fe, Co, Ni;Lyssenko et al, 2003), Cp 2 ZrCl 2 /methylaluminoxane (Belelli et al, 2004), group 5 bent metallocene complexes (Fan & Lin, 1998), and a model complex, which represents interaction of Ti atom with the cyclopentadienyl and cyclohexadienyl ligands (Bader & Matta, 2001), were also studied in a topological analysis.…”

Metal (Ti, Zr, Hf) insertion in the C–H bond of methane: Manifestation of an agostic interaction

“…Two recent comprehensive reviews revisit the phenomenon of agostic interactions [8,9]. On the ground of the available experimental data and theoretical orbital analysis and topological approaches, it has been shown that the b-agostic interaction corresponds actually to a topological bonding [9][10][11][12], whereas there is no general topological evidence for the a-agostic bonding [8,9,[12][13][14]. However, for the MÁ Á ÁHC-a it is now well established that:…”

Determination of the electronic and structural configuration of coordination compounds by synchrotron-radiation techniques

“…The use of synchrotron setups fostered the application of this advanced approach to several metal complexes, even containing very heavy atoms, such as Th [268]. Charge density analysis for instance employed to investigate agostic interaction in metallocenes [269] or chemical bonding of dioxygen metal complexes [270]. More complex molecular architectures, including polynuclear metal clusters and coordination polymers have been also investigated by charge density analysis of synchrotron XRD data; a thorough literature review focusing on synchrotron applications up to 2005 has been provided by Coppens et al [259].…”