Synthesis And Catalytic Reactivity Of Ruthenium And Rhodium N-Alkyl Substituted N-Heterocyclic Carbene Complexes

Abstract

This thesis describes the synthesis and stoichiometric/catalytic reactivity of Ru and Rh N-alkyl substituted N-heterocyclic carbene complexes. In an effort to make new Ru(NHC)x (x = 1-4) complexes, a range of Ru halide precursors, including Ru(DMSO)4Cl2 and Ru(PPh3)3Cl2, were combined with N-alkyl substituted carbenes. Treatment of Ru(PPh3)3Cl2 with IiPr2Me2 or ItBu resulted in C-H activation of the NHCs to form Ru(IiPr2Me2)2(IiPr2Me2’)Cl and Ru(ItBu’)(PPh3)2Cl respectively. C-H activation also took place with Ru(DMSO)4Cl2 and IEt2Me2 to give Ru(IEt2Me2’)(DMSO)3Cl. This underwent substitution with 13CO to afford the tricarbonyl complex Ru(IEt2Me2’)(CO)3Cl, and with PPh3 to give the bis-phosphine species Ru(IEt2Me2’)(PPh3)2Cl. Attempts to generate Ru(IEt2Me2’)(PPh3)2Cl by an alternative reaction of IEt2Me2 with Ru(PPh3)3Cl2 proved successful with two equiv. of carbene, although with four equiv. of NHC, the dichloride complex Ru(IEt2Me2)4Cl2 was produced. Upon turning to Ru(PPh3)3HCl, our group observed that the non-metallated tetrakiscarbene species [Ru(NHC)4H]+ are formed instead where alkyl = Me, Et and iPr. The reactivity of these species towards a range of amine boranes were investigated. [Ru(IMe4)4H]+ was able to catalyse the dehydrogenation of H3B.NMe2H to form the dimeric species [H2B-NMe2]2 and also catalytically hydrogenate a series of organic substrates such as ketones, nitriles, alkynes and alkenes at 323 K.Treatment of Rh(PPh3)4H with the six-membered ring NHCs 6-Me and 6-Et afforded the rhodium mono-carbene hydride complexes Rh(6-NHC)(PPh3)2H, in each case as a mixture of cis- and trans-phosphine isomers. Treatment of Rh(PPh3)3(CO)H with 6-Et did not afford a hydride complex but instead gave the CO bridged dimer Rh(PPh3)2(CO)2Rh(PPh3)(6-Et). Reaction of Rh(6-Me)(PPh3)2H with Et3N.3HF gave only the trans-isomer of the bifluoride complex Rh(6-Me)(PPh3)2(FHF), whereas the 6-Et hydride precursor gave Rh(6-Et)(PPh3)2(FHF) as a mixture of cis- and trans-phosphine isomers. 19F NMR Magnetization transfer and chemical exchange experiments revealed intra- and intermolecular F exchange in both of these bifluoride compounds. Treatment of 6-Rh(NHC)(PPh3)2H (NHC= 6-Me, 6-Et, 6-iPr) with CF3CF=CF2 gave the corresponding fluoride complexes Rh(6-NHC)(PPh3)2F. The 6-iPr derivative reacted slowly with H2 to partially reform Rh(6-iPr)(PPh3)2H, but rapidly with CO to give Rh(6-iPr)(PPh3)(CO)F and Rh(PPh3)2(CO)F, and also with Me3SiCF3 to form Rh(6-iPr)(PPh3)2(CF3).

Date of Award	16 Oct 2014
Original language	English
Awarding Institution	University of Bath
Supervisor	Michael Whittlesey (Supervisor)