Tertiary Phosphine and Arsine Complexes of Phosphorus Pentafluoride: Synthesis, Properties, and Electronic Structures.

The reaction of PMe3 or PPh3 with PF5 in anhydrous CH2Cl2 or hexane forms the white, moisture-sensitive complexes [PF5(PR3)] (R = Me, Ph). Similar reactions involving the diphosphines o-C6H4(PR2)2 afford the complexes [PF4{o-C6H4(PR2)2}][PF6]. The X-ray structures of [PF5(PR3)] and [PF4{o-C6H4(PMe2)2}][PF6] show pseudo-octahedral fluorophosphorus centers. Multinuclear NMR spectra (1H, 19F{1H}, 31P{1H}) show that in solution in CH2Cl2/CD2Cl2 the structures determined crystallographically are the only species present for [PF5(PMe3)] and [PF4{o-C6H4(PMe2)2}][PF6] but that [PF5(PPh3)] and [PF4{o-C6H4(PPh2)2}][PF6] exhibit reversible dissociation of the phosphine at ambient temperatures, although exchange slows at low temperatures. The complex 19F{1H} and 31P{1H} NMR spectra have been analyzed, including those of the cation [PF4{o-C6H4(PMe2)2}]+, which is a second-order AA'XX'B2M spin system. The unstable [PF5(AsMe3)], which decomposes in a few hours at ambient temperatures, has also been isolated and spectroscopically characterized; neither AsPh3 nor SbEt3 forms similar complexes. The electronic structures of the PF5 complexes have been explored by DFT calculations. The DFT optimized geometries for [PF5(PMe3)], [PF5(PPh3)], and [PF4{o-C6H4(PMe2)2}]+ are in good agreement with their respective crystal structure geometries. DFT calculations on the PF5-L complexes reveal the P-L bond strength falls with L in the order PMe3 > PPh3 > AsMe3, consistent with the experimentally observed stabilities, and in the PF5-L complexes, electron transfer from L to PF5 on forming these complexes also follows the order PMe3 > PPh3 ≈ AsMe3.

Exploring transition metal fluoride chelates - synthesis, properties and prospects towards potential PET probes.

The coordination chemistry of the first row transition metal trifluorides with terpy (2,2':6',2''-terpyridine) and Me3-tacn (1,4,7-trimethyl-1,4,7-triazacyclononane) was explored to identify potential systems for 18F radiolabelling. The complexes [MF3(L)] (M = Cr, Mn, Fe, Co; L = Me3-tacn, terpy) were synthesised and fully characterised by UV-vis and IR spectroscopy, microanalysis, and, for the diamagnetic [CoF3(L)], using 1H, 19F{1H} and 59Co NMR spectroscopy. Single crystal X-ray analyses are reported for [MF3(Me3-tacn)] (M = Mn, Co), [FeF3(terpy)] and [FeF3(BnMe2-tacn)]. Stability tests on [MF3(Me3-tacn)] (M = Cr, Mn, Fe) and [M'F3(terpy)] (M' = Cr, Fe) were performed and Cl/19F halide exchange reactions on [CrCl3(Me3-tacn)] using [Me4N]F in anhydrous MeCN solution, and [FeCl3(Me3-tacn)] using [Me4N]F in anhydrous MeCN or KF in aqueous MeCN solution were also carried out. Halide exchange reactions proved to be successful in forming [FeF3(Me3-tacn)] in aqueous MeCN solution within 30 minutes. Based upon the clean Cl/F exchange and the good stability observed for [FeF3(Me3-tacn)] in a range of competitive media, this was identified as a possible candidate for radiolabelling. 18F/19F isotopic exchange was achieved by addition of [18F]F- in the cyclotron target water to a MeCN solution of the benzyl-substituted analogue, [FeF3(BnMe2-tacn)], at a range of concentrations down to 24 nM with heating to 80 °C for 10 min.; the resulting [Fe18F19F2(BnMe2-tacn)] shows radiochemical purity (RCP) ≥90% after 2 h in a range of formulations, including 10% EtOH/phosphate buffered saline (PBS) and 10% EtOH/human serum albumin (HSA). This is the first reported complex with a transition metal directly bonded to [18F]F-.

Neutral and cationic tungsten(vi) fluoride complexes with tertiary phosphine and arsine coordination.

Reaction of WF6 with AsR3 (R = Me or Et) in anhydrous CH2Cl2 at low temperature forms the neutral seven-coordinate, [WF6(AsR3)] (R = Me, Et), the first arsine complexes of WF6, whilst o-C6H4(EMe2)2 (E = P, As) produces [WF4{o-C6H4(EMe2)2}2][WF7]2. Crystal structures show the latter contain dodecahedral cations, and present the highest oxidation state metal fluoride complexes known (and the highest possible for tungsten) with soft neutral phosphine and arsine coordination.

Rapid Aqueous Late-Stage Radiolabelling of [GaF3 (BnMe2 -tacn)] by 18 F/19 F Isotopic Exchange: Towards New PET Imaging Probes.

A simple and rapid method for 18 F radiolabelling of [GaF3 (BnMe2 -tacn)] by 18 F/19 F isotopic exchange is described. The use of MeCN/H2 O or EtOH/H2 O (75:25) and aqueous [18 F]F- (up to 200 MBq) with heating (80 °C, 10 min) gave 66±4 % 18 F incorporation at a concentration of 268 nm, and 37±5 % 18 F incorporation at even lower concentration (27 nm), without the need for a Lewis acid promoter. A solid-phase extraction method was established to give [Ga18 F19 F2 (BnMe2 -tacn)] in 99 % radiochemical purity in an EtOH/H2 O mixture.

Group 3 metal trihalide complexes with neutral N-donor ligands - exploring their affinity towards fluoride.

Fluorination of [ScCl3(Me3-tacn)] (Me3-tacn = 1,4,7-trimethyl-1,4,7-triazacyclononane) and [ScCl3(BnMe2-tacn)] (BnMe2-tacn = 1,4-dimethyl-7-benzyl-1,4,7-triazacyclononane) by Cl/F exchange with 3 mol. equiv. of anhydrous [NMe4]F in CH3CN solution yields the corresponding [ScF3(R3-tacn)] (R3 = Me3 or BnMe2). These are the first examples of scandium fluoride complexes containing neutral co-ligands. The fluorination occurs stepwise, and using a deficit of [NMe4]F produced [ScF2Cl(Me3-tacn)]. Attempts to fluorinate [YCl3(Me3-tacn)], [YI3(Me3-tacn)], [LaCl3(Me3-tacn)(OH2)] or [MCl3(terpy)] (M = Sc, Y or La; terpy = 2,2':6'2''-terpyridyl) using a similar method were unsuccessful, due to the Cl/F exchange being accompanied by loss of the neutral ligand from the metal centre. Fluorination of [ScCl3(Me3-tacn)] or [ScCl3(terpy)] with Me3SnF was also successful. The products were identified as the very unusual heterobimetallic [Sc(Me3-tacn)F2(µ-F)SnMe3Cl] and [Sc(terpy)F(µ-F)2(SnMe3Cl)2], in which the Me3SnCl formed in the reaction behaves as a weak Lewis acid towards the scandium fluoride complex, linked by Sc-F-Sn bridges. [Sc(terpy)F(µ-F)2(SnMe3Cl)2] decomposes irreversibly in solution but, whilst multinuclear NMR data show that [Sc(Me3-tacn)F2(µ-F)SnMe3Cl] is dissociated into the [ScF3(Me3-tacn)] and Me3SnCl in CH3CN solution, the bimetallic complex reforms upon evaporation of the solvent. The new scandium fluoride complexes and the chloride precursors have been characterised by microanalysis, IR and multinuclear NMR (1H, 19F, 45Sc) spectroscopy as appropriate. X-ray crystal structures provide unambiguous evidence for the identities of [Sc(Me3-tacn)F2(µ-F)SnMe3Cl], [ScF2Cl(Me3-tacn)], [YI3(Me3-tacn)], [{YI2(Me3-tacn)}2(µ-O)], [ScCl3(terpy)], [YCl3(terpy)(OH2)], and [{La(terpy)(OH2)Cl2}2(µ-Cl)2]. Once formed, the [ScF3(R3-tacn)] complexes are stable in water and unaffected by a ten-fold excess of Cl- or MeCO2-, although they are immediately decomposed by excess F-. The potential use of [ScF3(R3-tacn)] type complexes as platforms for 18F PET (positron emission tomography) radiopharmaceuticals is briefly discussed. Attempts to use the Group 3 fluoride "hydrates", MF3·xH2O, as precursors were unsuccessful; no reaction with R3-tacn or terpy occurred either on reflux in CH3CN or under hydrothermal conditions (H2O, 180° C, 15 h). PXRD data showed that these "hydrates" actually contain the anhydrous metal trifluorides with small amounts of surface or interstitial water.

[AlCl3(BnMe2-tacn)] - a new metal chelate scaffold for radiofluorination by Cl/F exchange.

Radiofluorination of a 2.63 µM solution (pH 4, NaOAc buffer) of [AlCl3(BnMe2-tacn)] via treatment with 2.99 mol. equiv. of [19F]KF doped with cyclotron-produced [18F]F- target water, with heating to 80-100 °C for 1 h, gives up to 24% 18F incorporation. SPE purification of the [Al19F218F(BnMe2-tacn)] radio-product gives >99% RCP, with excellent stability (>99% RCP after 3 h).

Hydrothermal synthesis of Group 13 metal trifluoride complexes with neutral N-donor ligands.

The reactions of the hydrated Group 13 fluorides, MF3·3H2O (M = Al, Ga or In) with 2,2':6',2''-terpyridyl, 2,2'-bipyridyl or 1,10-phenanthroline under hydrothermal conditions (180 °C/15 h) produced high yields of the complexes [MF3(terpy)]·3H2O, [MF3(bipy)(OH2)]·2H2O and [MF3(phen)(OH2)]. X-Ray crystal structures of [M'F3(terpy)]·3H2O (M' = Al or Ga), [M'F3(bipy)(OH2)]·2H2O and [GaF3(phen)(OH2)] show that all of them contain distorted octahedral geometries at the metal with mer-trifluoride coordination. Extensive H-bonding (FH-OH) links the molecules. The complexes have been further characterised by microanalysis, IR, (1)H, (19)F{(1)H} and (27)Al NMR spectroscopy. In contrast, reactions of the trifluorides with the acyclic triamine, N,N,N',N',N''-pentamethyldiethylenetriamine, under similar hydrothermal conditions results in cleavage of the triamine and ring-closure to form the 1,1,4-trimethylpiperazinium cation, [⊂Me2N(CH2)2NMe(CH2)2](+), with fluorometallate anions, and confirmed by X-ray analysis of [⊂Me2N(CH2)2NMe(CH2)2]2[Al2F8(OH2)2]·2H2O. The strongly H-bonded [GaF3(terpy)]·3H2O was also obtained by Cl/F exchange from [GaCl3(terpy)] and [NBu4]F or [K(2,2,2-crypt)]F. Crystallisation of a mixture of [NH4][PF6] and [GaF3(terpy)]·3H2O from aqueous solution produced the edge-bridged cationic complex, [{Ga(terpy)F}2(µ-F)2][PF6]2. The synthesis of the more sterically bulky [GaCl3((t)Bu3-terpy)] ((t)Bu3-terpy = 4,4'4''-tris-(t)Bu-2,2':6',2''-terpyridyl) and the crystal structure of [GaCl2((t)Bu3-terpy)][GaCl4], which contains a trigonal bipyramidal cation, are also reported.

Different emissive properties in dithiolate gold(i) complexes as a function of the presence of phenylene spacers.

A family of dinuclear neutral thiolate gold complexes of the type RPh2PAuS(C6H4)nSAuPPh2R (n = 2, 3), RPh2PAuS(C6H4)S(C6H4)SAuPPh2R, RPh2PAuSCH2(C6H4)2CH2SAuPPh2R where R represents a pyridine or a phenylene ring, has been prepared and fully characterized. X-ray crystallographic studies showed the presence of aurophilic interactions for those species bearing two phenylene spacers between the gold metal centers, leading to infinite chains. The complexes are emissive in the solid state. Theoretical calculations together with the photophysical analysis seem to indicate that the main excitations involved in the emissive processes are due to a mixture of ILCT transition involving the thiolate and the conjugated phenylene rings, and LL'CT transitions comprising the thiolate and the pyridine or phenyl from the phosphine fragment which contrast with the typical gold thiolate emission, LMCT from the thiolate fragment to the metal center.