DFT studies on heterobimetallic complexes of Ru with Zn, Ga and In

Abstract

Density Functional Theory (DFT) was used to study a series of heterobimetallic complexes of ruthenium with zinc, gallium and indium. In this thesis, Chapter 1 presents an introductory discussion on the fundamental computational approaches and Chapter 2 describes a literature survey of transition metal complexes featuring Zn, Ga and In moieties. Chapters 3, 4 and 5 look at the mechanisms of the reactions of the Ru-H species 67, [Ru(IPr)2(CO)(H)]+, with ZnEt2, InMe3 and GaMe3, respectively, as well as the reactivities of the resultant heterobimetallic complexes with small molecules. Bonding analyses of the heterobimetallic complexes are also reported. In Chapter 3, the formation of [Ru(IPr)2(CO)ZnEt]+, 68, is modelled and shown to involve Et transfer from Zn to Ru followed by the reductive elimination of ethane. 68 is shown to be a Ru(0)-Zn(II) species. H2 activation at 68 occurs homolytically to produce [Ru(IPr)2(CO)(n2‒H2)(H)2(ZnEt)]+, 69. Mechanisms for H2 loss from 69 to give [Ru(IPr)2(CO)(H)2(ZnEt)]+, 70, and H/H exchange in 69 and 70 were also characterised. Chapter 4 presents the computed mechanism for the formation of 71, [Ru(IPr)2(CO)(Me)InMe]+. As with the Ru-Zn chemistry, this involves alkyl transfer along with a reductive elimination step. A second alkyl group then transfers to Ru to give 71 which is characterised as a Ru(II)-In(I) species. H2 activation at 71 occurs via a -CAM mechanism which releases methane to form [Ru(IPr)2(CO)(n2‒H2)(H)(InMe)]+, 72. A computed mechanism for the reaction of 71 with CO shows that addition of the first CO to Ru transfers the Me group back to In with a low energy barrier to give a Ru-indyl species which can then be trapped by the addition of the second CO to give 74, [Ru(IPr)2(CO)3(InMe2)]+. In Chapter 5, reaction of 68 with GaMe3 to give 77, [Ru(IPr)(CO)(GaMe2IPr)]+, is modelled. In this process, instead of transferring a second Me from Ga to Ru, an IPr ligand transfers from Ru to Ga to give the 77 which is shown to be a Ru(0)-Ga(III) species. Discrepancies between the stability of 77 and the Ga congener of 71 were found but could not be resolved. Chapter 6 focuses on two new Cu complexes, [(6-Mes)Cu(HBR3)] (R = Et and C6F5), that are characterised as Cu-borate complexes. Modelling the isolated species in the gas phase shows that the geometry of the {CuHBR3} unit is sensitive to the functional choice and dispersion correction, with M06 and ɷB97xD giving the best overall results. Calculations in the extended solid state using periodic DFT showed the geometries are still sensitive to the functional choice but now dispersion is well balanced by the inter-molecular interactions. The PBE functional gives the best overall results.