The nature of M–B and B–N bonding in iminoboryl complexes of rhodium and iridium cis,mer-[(L)3(Br)2M(B[tbnd]NSiMe3)] (L = PMe3, CO): Dispersion corrected DFT study

Abstract

Dispersion corrected quantum-chemical calculations of iminoboryl complexes cis,mer-[(L)3(Br)2M(BNSiMe3)] (M = Rh, Ir; L = PMe3, CO) were studied with and without dispersion interactions using density functionals BP86, BLYP, PBE, PW91 and TPSS. The calculations of the 11B NMR chemical shifts were carried out at DFT-D3(BJ)/BP86/TZ2P/ZORA with scalar and spin orbit relativistic level of theory in solvent C6D6. The calculated geometrical parameters of the rhodium iminoboryl complex cis,mer-[(Me3P)3(Br)2Rh(BNSiMe3)] (Braunschweig et al., J. Am. Chem. Soc. 130 (2008) 7974–7983) are in good agreement with the available experimental values. The calculated M−B and B–N bond distances, Mayer bond orders and Pauling bond orders suggest that the M–B bond has more than single bond character and B–N bond has less than triple bond character. The calculated bond dissociation energies (BDEs) of the M−B bonds follow the order BLYP < BP86 < TPSS < PBE < PW91. The absolute value of orbital interactions is significantly larger than the electrostatic interactions. The 11B NMR shielding is larger for carbonyl complexes cis,mer-[(CO)3Br2M(BNSiMe3)] than the phosphine complexes cis,mer-[(PMe3)3Br2M(BNSiMe3)]. On going from rhodium to iridium in the complexes cis,mer-[(L)3(Br)2M(BNSiMe3)] (L = PMe3, CO), the 11B NMR chemical shift decreases. The calculation of 11B chemical shifts by means of the ZORA relativistic scalar yields reliable results.