The C−H Activation of Methane by Laser-Ablated Zirconium Atoms:  CH₂ZrH₂, the Simplest Carbene Hydride Complex, Agostic Bonding, and (CH₃)₂ZrH₂

Abstract

Reaction of laser-ablated Zr with CH(4) ((13)CH(4), CD(4), and CH(2)D(2)) in excess neon during condensation at 5 K forms CH(2)=ZrH(2), the simplest alkylidene hydride complex, which is identified by infrared absorptions at 1581.0, 1546.2, 757.0, and 634.5 cm(-)(1). Density functional theory electronic structure calculations using a large basis set with polarization functions predict a C(1) symmetry structure with agostic C-H- - -Zr bonding and distance of 2.300 A. Identification of the agostic CH(2)=ZrH(2) methylidene complex is confirmed by an excellent match of calculated and observed isotopic frequencies particularly for the four unique CHD=ZrHD isotopic modifications. The analogous reactions in excess argon give two persistent photoreversible matrix configurations for CH(2)=ZrH(2). Finally, methane activation by CH(2)=ZrH(2) gives the new (CH(3))(2)ZrH(2) molecule.

Agostic Structure of Titanium Methylidene Hydride (CH2=TiH2): A Theoretical Investigation for the Elusive Intramolecular Interaction

“…The present results reconfirm the fact that the polarization functions are essential to reproduce the agostic interaction. 7,11 The agostic distortion is also associated with the shorter C=Ti bond as shown in Table 1. The carbon-titanium bond lengths are 1.811 and 1.840 Å in the B3LYP C 1 and C s (no agostic distortion) structures from computations with and without the polarization functions.…”

“…[6][7][8] The matrix IR spectra of the Group 4 metal methylidene hydrides, which are studied most among the recently introduced complexes, reveal that the two M-H bonds are different, showing two sets of M-H and M-D stretching absorptions between the MH2 and MD2 bands in the half deuterated isotopomer spectra. [6][7][8] The following theoretical studies have reproduced the distorted C 1 structure of the methylidene hydride (CH2=MH2) with two different M-H bonds. 3,4 In this study, the agostic interaction of titanium methylidene hydride (CH2=TiH2) has been examined at various levels of theory as a subsequent study of the previous report for the Zr analogue.…”

“…7,11 Evidently the polarization functions reshape the C-H bond orbital to effectively overlap with σ*(Ti-H4), which carries a strong Ti d-character, and the effective overlap is expected to overcome the structural strain due to the distortion of the CH2 group from the ethylene-like C s structure. This overlap between the C-H bonding and Ti-H4 anti-bonding orbitals shortens the C=Ti bond and elongates the C-H and Ti-H bonds.…”

Agostic Interaction of the Smallest Zirconium Methylidene Hydride: Reproduction of the Distorted Structure Experimentally Observed in Matrix Infrared Spectra

“…6 Furthermore, electronic structure calculations show that CH2=ZrH2 has a highly distorted C1 structure, where the methylene group is considerably distorted, and the Zr atom is located at the apex of the trigonal pyramid structure. 2,3,6 The 8 possible isotopomers with C1 symmetry shown in Scheme 1 are grouped into four sets (1-2, 3-5, 4-6, and 7-8), the two configurations in each set having essentially the same hydrogen stretching frequencies. 6 Calculations with the planar C 2V symmetry constraint generate two imaginary frequencies (the ZrH 2 wagging and CH 2 rocking modes).…”

“…2,3,6 The 8 possible isotopomers with C1 symmetry shown in Scheme 1 are grouped into four sets (1-2, 3-5, 4-6, and 7-8), the two configurations in each set having essentially the same hydrogen stretching frequencies. 6 Calculations with the planar C 2V symmetry constraint generate two imaginary frequencies (the ZrH 2 wagging and CH 2 rocking modes).In this study we have carried out a theoretical investigation at various levels in an effort to properly understand the details of the agostic interactions, which often play an important role for the structures of high oxidation-state transition-metal complexes. Density functional theory (DFT) calculations were carried out using the Gaussian 03 package, 7 the B3LYP density functional, 6-311++G(3df,3pd) basis sets for C, H, and SDD pseudopotential and basis for Zr (28 electron core).…”