Non-covalent interactions in σ-alkane complexes of Rh in solid state microenvironments based on [BAr F 4 ] and [S-BAr F 4 ] anions M. Arif Sajjad and Stuart A. Macgregor Heriot-Watt University, UK s-alkane complexes obtained by solid-state molecular organometallic chemistry (SMOM) are important models of key intermediates in C-H activation reactions. These s-complexes can also act as heterogeneous catalysts for alkene isomerisation under solid/gas or solid/liquid conditions, processes where a parent alkane is replaced by another alkene or alkane. 1 It has been suggested that the stability and reactivity of these s-complexes are linked with the non-covalent interactions present between the microenvironment of anions and the cationic Rh centre. 2 For instance, both [Rh(Cy 2 P(CH 2 ) 2 PCy 2 )(NBA)][S-BAr F 4 ], [1-NBA][S-BAr F 4 ] (NBA = norbornane, S-BAr F 4 = [B(3,5-(SF 5 ) 2 C 6 H 3 ) 4 ] and the [BAr F 4 ] - analogue, [Rh(Cy 2 P(CH 2 ) 2 PCy 2 )(NBA)][BAr F 4 ], [1-NBA][BAr F 4 ] , (BAr F 4 = [B(3,5-(CF 3 ) 2 C 6 H 3 ) 4 ], feature an octahedral array of anions around a central Rh cation (see Figure 1), but differences in their properties were attributed to the greater non-covalent C-HLF-C interactions in the former. 3,4 Thus, to design robust, stable and reactive s-alkane complexes, proper understanding of intermolecular interactions between the cation and its surrounding anions is crucial.
Figure 1. Octahedral arrangement of [BAr F 4 ]
2 η 2 -NBA)] + cation in [1-
- and [S-BAr F
4 ] - anions around the [Rh(Cy
2 P(CH 2 ) 2 PCy 2 )(η
NBA][1-BAr F 4 ] and [1-NBA][S-BAr F 4 ] . In this work, we employ computational modelling to identify the nature and strength of intermolecular interactions in [1-NBA][1-BAr F 4 ] and [1-NBA][S-BAr F 4 ] . 5 The solid-state geometries have been optimised by periodic DFT calculations by relaxing only H and F atoms. All the cation-anion (1-NBA + - BAr F 4 - or S-BAr F 4 - ) pairs with respect to their arrangement in the octahedron have been considered i.e., top, bottom and equatorial anions. Bonding analyses of ion-pairs are based on quantum theory of atoms in molecules (QTAIM) and independent gradient model based on Hirshfeld partition (IGMH) approaches. References 1. A. S. Weller, F. M. Chadwick and A. I. McKay, in Adv. Organomet. Chem. Eds: P. J. Pérez, Academic Press, 2016, vol. 66, pp. 223-276. 2. A. J. Bukvic, A. L. Burnage, G. J. Tizzard, A. J. Martínez-Martínez, A. I. McKay, N. H. Rees, B. E. Tegner, T. Krämer, H. Fish, M. R. Warren, S. J. Coles, S. A. Macgregor and A. S. Weller, J. Am. Chem. Soc. , 2021, 143 , 5106-5120. 3. L. R. Doyle, E. A. Thompson, A. L. Burnage, A. C. Whitwood, H. T. Jenkins, S. A. Macgregor and A. S. Weller, Dalton Trans. , 2022, 51 , 3661-3665. 4. S. D. Pike, F. M. Chadwick, N. H. Rees, M. P. Scott, A. S. Weller, T. Krämer and S. A. Macgregor, J. Am. Chem. Soc., 2015, 137, 820–833. 5. A. G. Algarra, A. L. Burnage, M. Iannuzzi, T. Krämer, S. A. Macgregor, R. E. M. Pirie, B. Tegner and A. S. Weller, in 21st Century Challenges in Chemical Crystallography II: Structural Correlations and Data Interpretation Eds: D. MichaelP. Mingos and P. R. Raithby, Springer International Publishing, Cham, 2020, pp. 183-228.
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