Microwave Spectra and Theoretical Calculations for Two Structural Isomers of Methylmanganese Pentacarbonyl

Abstract

The first microwave rotational spectra for two structural isomers of methylmanganese pentacarbonyl were measured in the 4–9 GHz range using a pulsed-beam Fourier transform microwave spectrometer. The spectra for the two isomers, a symmetric-top structure and an asymmetric-top acyl isomeric structure, were fit to obtain rotational and centrifugal distortion constants and 55Mn quadrupole coupling parameters. The rotational constants, the manganese (55Mn) nuclear quadrupole coupling constant, the centrifugal distortion constants, and the spin–rotation constant were determined for the symmetric CH3Mn­(CO)5 and have the following values: A = B = 793.153(3) MHz, D J = 0.00040(4) MHz, D JK = 0.0018(2) MHz, C cc = 0.183(6) MHz, and eQqcc= −87.4(3) MHz. Rotational constants and 55Mn quadruple coupling constants were determined for the isomeric acyl-CH3C­(O)­Mn­(CO)4 and have the following values: A = 839.96(4) MHz, B = 774.20(7) MHz, C = 625.63(1) MHz, and 1.5 eQqaa= 44.9(47) MHz and 0.25­(eQqbb – eQqcc) = 11.9(12) MHz. The measured rotational constants from the isomeric acyl-CH3C­(O)­Mn­(CO)4 were compared with various theoretical computations. The calculated rotational constants for the dihapto-acyl and the agostic-acyl structures are reasonably close to the experimental values. We note that the calculated dihapto-acyl structure most closely matches the experimental data, as the calculation for the dihapto structure using the B3LYP functional with the aug-cc-pVDZ basis set closely reproduced the experimental values for A, B, and C.

Corrections and Additions to “Microwave Spectra and Theoretical Calculations for Two Structural Isomers of Methylmanganese Pentacarbonyl”

“…In the original paper on methylmanganese pentacarbonyl, good agreement was obtained between the experimental rotational constants and the calculated values for dihapto acyl-CH 3 C­(O)­Mn­(CO) 4 , but agreement between experimental and calculated quadrupole parameters was poor. Calculated χ aa were negative whereas the previous experimental values were positive.…”

“…Calculated χ aa were negative whereas the previous experimental values were positive. This note provides corrections and some additions to the earlier paper . Subsequent to the initial study, many calculations were carried out using different methods and basis sets and the calculated quadrupole coupling parameters between these different calculations were reasonably consistent.…”

Generating High-Precision Force Fields for Molecular Dynamics Simulations to Study Chemical Reaction Mechanisms Using Molecular Configuration Transformer

“…Figure 5a illustrates a simple example, wherein Mn(CO) 5 CH 3 reacts with carbon monoxide, resulting in the migration of a methyl group to a carbonyl moiety, producing Mn(CO) 5 (COCH 3 ). This reaction is also commonly referred to as carbonyl insertion 95 and consists of two steps. 96 Here, we focused on the process of methyl group migration (Figure 5b).…”