Trimetallic N-heterocyclic carbene complexes

Abstract

This thesis describes the coordination chemistry of a range of mono and tridentate N heterocyclic carbenes (NHCs). It contains three distinct areas of chemistry; the synthesis and catalysis of NHC cluster compounds of ruthenium and osmium, the synthesis and reactivity of novel NHC palladium carbonyl clusters and use of the tripodal NHC ligand timtebR (R = tBu or dipp) for the preparation of catalytically active Pd and Cu complexes.

The reactions of Ru3(CO)12 and Os3(CO)12 have been carried out with the NHCs IMes, IPr, ItBu, 6iPr2 and 6oTol, and have led to the formation of a number of compounds. The smaller IMes ligand leads to the formation of Ru(IMes)(CO)4 (2.5) and Ru(IMes)2(CO)3 (2.6) which co crystallised together. The bulkier IPr, ItBu and 6iPr2 ligands generated cluster NHC complexes. For IPr and ItBu, evidence has been observed for abnormal binding of the ligand in the formation of Ru3(abIPr)(CO)11 (2.7) and Os3(abItBu)(CO)11 (2.8), whereas 6iPr2 gave the coordinatively unsaturated cluster complex Ru3(6iPr2)(u-CO)2(CO)8 (2.10). The catalytic activity of Ru3(abNHC)(CO)11, Ru3(u-H)(dabNHC)(CO)9 (NHC = ItBu or IAd, 2.12.4) as well as the unsaturated compound 2.10 have been investigated for the regioselective acylation of pyridine.

The first examples of a range of palladium NHC clusters Pd3(NHC)3(u-CO)3 where NHC = IMes (3.1), IiPr2 (3.2) or InBu2 (3.3) have been synthesised. The addition and ligand substitution reactions of 3.1 have also been investigated, forming Pd3(IMes)3(u-SO2)3 (3.4) upon reaction with SO2.

A series of bisNHC and mixed phosphine/NHC palladium(II) complexes (timtebtBu){PdI2(ICy)}3 (4.1), (timtebtBu){PdI2(PPh3)}3 (4.2) and (timtebdipp){PdI2(PPh3)}3 (4.3) all bearing a tripodal NHC ligand, have been synthesised. The tripodal NHC ligands have also been coordinated to copper(I) centres to give complexes of the form [(timtebR)Cu3(u3-O)]X, where R/X = tBu/PF6 (4.4) and dipp/BF4 (4.5). The Pd and Cu compounds have been studied in a range of catalytic coupling reactions including SuzukiMiyaura and Sonogashira CC coupling reactions as well as Ullmann type CO and CN reactions.

Date of Award	1 Apr 2011
Original language	English
Awarding Institution	University of Bath
Supervisor	Michael Whittlesey (Supervisor)