Coordination chemistry and properties of the trivalent group 13 and divalent group 14 metal triflates with a range of neutral donor ligands

Abstract

Although commonly used within organic chemistry as a leaving group, the main group chemistry of the weakly coordinating anion triflate [SO3CF3]- (OTf) is limited, with a few known coordination complexes incorporating this anion. The work of this thesis is focused on the synthesis of complexes of Group 13 and 14 metal triflates with the coordination of a range of different donor ligands with varying hardness, donor strength and denticity. Each of the novel complexes synthesised here are characterised by IR and NMR spectroscopy (1H, 13C{1H}, 19F{1H}, 31P{1H} and 27Al, 71Ga, 119Sn and 207Pb where applicable) and microanalysis; with structural information being gathered by single crystal X-ray diffraction whenever possible. This began with reaction of the Group 13 metal triflates M(OTf)3 (M = Al, Ga, In) and coordination of the hetroaromatic imine ligands bipy (2,2’-bipyridine), terpy (2,2’;6’,2”-terpyridine) and phen (1,10-phenanthroline). Each ligand was successfully coordinated with terpy producing a set of neutral complexes cis- [M(OTf)3(terpy)], while the bidenate ligands produced cationic complexes [M(OTf)2(bidentate)2][OTf]. The reaction of harder oxygen donor ligands OPR3 (R = Me, Ph), pyNO and dppmO2 were also observed to produce octahedral complexes. The complexes produced from both ligand sets showed displacement of the triflate anion by one or more water ligands, producing di- or tricationic species, with crystal structures showing water ligands becoming involved in H-bonding arrays. This behaviour lead to the formation of a 24-membered pseudomacrocyclic ring with four H-bonded triflate anions bridging four coordinated meridianal water ligands in [In(OTf)2(OPPh3)4][In(OH2)4(OPPh3)2][OTf]4. Following on from previous alkylstibine work in the Reid group, a series of Group 13 metal chloride complexes were synthesised with alkyl-stibine, -arsine and -phosphine ligands. These complexes were reacted with TMSOTf (trimethylsilyl trifluoromethanesulfonate), among other abstraction agents, in an attempt to produce cationic species. The divalent Group 14 metal triflates M(OTf)2 (M = Sn, Pb) were also probed using a range of soft pnictine ligands, following from a previously published report on coordination of these ligands to M(SbF6)2 (M = Sn, Pb). Expanding on this study, harder oxygen donor ligands were including OPR3 (R = Me, Ph), pyNO and dppmO2 exploring the geometry and spectroscopic properties of these complexes. Throughout coordination to the divalent Group 14 metal triflates, a preference for oligomerisation was observed with repeated formation of triflate bridges being observed. Reaction of three equivalents of OPMe3 with Sn(OTf)2 produced a hexameric metallocyclic array containing large solvent voids through the structure. Attempts to produce an analogous species using the structurally related [SO3F]- anion was ultimately unsuccessful however, use of Pb(OTf)2 produced a bridged dimer species [{Pb(OTf)(OPMe3)3}2(μ- OTf)2].

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Identifiers

ORCID for Gill Reid: orcid.org/0000-0001-5349-3468

ORCID for William Levason: orcid.org/0000-0003-3540-0971

ORCID for Philip Bartlett: orcid.org/0000-0002-7300-6900

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