Exploring the cellular uptake and localisation of phosphorescent rhenium fac-tricarbonyl metallosurfactants as a function of lipophilicity.

A systematic study of the cellular uptake of emissive complexes as a function of their lipophilicity is presented. Here a series of amphiphilic rhenium fac-tricarbonyl bisimine complexes bearing axial substituted imidazole or thiazole ligands, [Re(bpy)(CO)3(ImCnHm)]+ {n = 1 m = 3 (1+), n = 4 m = 9 (2+), n = 8 m = 17 (3+), n = 12 m = 25 (4+), n = 16 m = 33 (5+), n = 2 m = 3 (6+); bpy = 2,2'-bipyridine, Im = imidazole} and [Re(bpy)(CO)3(L)]+ {L = 1-mesitylimidazole, ImMes (7+), 4,5-dimethylthiazole, dmt (8+) and 4-methyl-5-thiazole-ethanol, mte (9+)} is reported. The X-ray crystal structures of 2+, 8+ and 9+ confirm the geometry and expected distribution of ligands and indicated that the plane of the imidazole/thiazole ring is approximately parallel to the long axis of the bipy ligand. Luminescence studies revealed excellent properties for their use in cell imaging with visible excitation and broad emission profiles. Their uptake in two distinct species has been examined by fluorescence imaging of the diplomonad fish parasite Spironucleus vortens (S. vortens) and rod-shaped yeast Schizosaccharomyces pombe (Schiz. pombe) as a function of their lipophilicity. The uptake of the complexes was highest for the more lipophilic 2+-5+ in both S. vortens and Schiz. pombe in which the long alkyl chain aids in crossing bilipid membranes. However, the increased lipophilicity of longer chains also resulted in greater toxicity. Localisation over the whole cell varied with differing alkyl chain lengths with complex 2+ preferentially locating to the nucleus of S. vortens, 3+ showing enhanced nuclear partitioning in Schiz. pombe, and 4+ for the remaining cell wall bound in the case of S. vortens. Interestingly, complexes of intermediate lipophilicity such as 7+ and 8+ showed reasonable uptake, proved to be non-toxic, and were capable of crossing exterior cell walls and localising in the organelles of the cells.

Ligand-Tuneable, Red-Emitting Iridium(III) Complexes for Efficient Triplet-Triplet Annihilation Upconversion Performance.

A series of substituted 2-phenylquinoxaline ligands have been explored to finely tune the visible emission properties of a corresponding set of cationic, cyclometallated iridium(III) complexes. The electronic and redox properties of the complexes were investigated through experimental (including time-resolved luminescence and transient absorption spectroscopy) and theoretical methods. The complexes display absorption and phosphorescent emissions in the visible region that are attributed to metal to ligand charge-transfer transitions. The different substitution patterns of the ligands induce variations in these parameters. Time-dependent DFT studies support these assignments and show that there is likely to be a strong spin-forbidden contribution to the visible absorption bands at λ=500-600 nm. Calculations also reliably predict the magnitude and trends in triplet emitting wavelengths for the series of complexes. The complexes were assessed as potential sensitisers in triplet-triplet annihilation upconversion experiments by using 9,10-diphenylanthracene as the acceptor; the methylated variants performed especially well with impressive upconversion quantum yields of up to 39.3 %.

Cyclometalated cinchophen ligands on iridium(III): towards water-soluble complexes with visible luminescence.

Eight cationic heteroleptic iridium(III) complexes, [Ir(epqc)2(N^N)](+), were prepared in high yield from a cyclometalated iridium bridged-chloride dimer bearing two ethyl-2-phenylquinoline-4-carboxylate (epqc) ligands. Two X-ray crystallographic studies were undertaken on selected complexes (where the ancillary ligand N^N = 4,4'-dimethyl-2,2'-bipyridine and 4,7-diphenyl-1,10-phenanthroline) each confirming the proposed formulations, showing an octahedral coordination at Ir(III). In general, the complexes are luminescent (620-630 nm) with moderately long lifetimes indicative of phosphorescence. Hydrolysis of the ethyl ester moieties of the epqc ligands gave the analogous cinchophen-based complexes, which were water-soluble and visibly luminescent (568-631 nm). The spectroscopic and redox characterisation of the complexes was complemented by DFT and TD-DFT calculations, supporting the assignment of dominant (3)MLCT to the emissive character.

Using substituted cyclometalated quinoxaline ligands to finely tune the luminescence properties of iridium(III) complexes.

The syntheses of five new heteroleptic iridium complexes [Ir(L(1-4))(2)(Diobpy)]PF(6) (where Diobpy = 4,4'-dioctylamido-2,2'-bipyridine) and [Ir(L(3))(2)(bpy)]PF(6) (where L = para-substituted 2,3-diphenylquinoxaline cyclometalating ligands; bpy = 2,2'-bipyridine) are described. The structures of [Ir(L(3))(2)(Diobpy)]PF(6) and [Ir(L(3))(2)(bpy)]PF(6) show that the complexes each adopt a distorted octahedral geometry with the expected trans-N, cis-C arrangement of the cyclometalated ligands. Electrochemical studies confirmed subtle perturbation of the Ir(III/IV) redox couple as a function of ligand variation. Luminescence studies showed the significant contribution of (3)MLCT to the phosphorescent character with predictable and modestly tunable emission wavelengths between 618 and 636 nm. DFT studies provided approximate qualitative descriptions of the HOMO {located over the Ir(5d) center (11-42%) and the phenylquinoxaline ligand (54-87%)} and LUMO {located over the ancillary bipyridine ligands (ca. 93%)} energy levels of the five complexes, confirming significant MLCT character. TD-DFT calculations indicate that UV-vis absorption and subsequent emission has substantial MLCT character, mixed with LLCT. Predicted absorption and emission wavelengths are in good general agreement with the UV-vis and luminescence experiments.

Enhanced photooxidation sensitizers: the first examples of cyclometalated pyrene complexes of iridium(III).

The iridium(III) cyclometalation of alkylated pyrene-benzimidazole ligands proceeds in an unprecedented manner. The resultant complexes display remarkably enhanced photooxidation capabilities using 1,5-dihydroxynaphthalene as a substrate.

Luminescent rhenium fac-tricarbonyl-containing complexes of androgenic oxo-steroids.

A new route to luminescent derivatives of androgenic steroids containing a ketone group in the 3- or 17-position has been developed. Reaction with the fac-Re(CO)(3)Cl complex of 3,3'-diamino-2,2'-bipyridine (complex 1) afforded a cyclic aminal product with different steroids. The rate of reaction and yield varies according to the conjugation or steric hindrance around the ketone group.

Water-soluble, luminescent iridium(III)-ytterbium(III) complexes using dipyrido[3,2-a:2',3'-c]phenazine derivatives as bridging units.

Amino-substituted dipyrido[3,2-a:2',3'-c]phenazine (L(1)) and dimethyl-dipyrido[3,2-a:2',3'-c]phenazine (L(2)) have been investigated as: (i) chromophores in cyclen-based ligands for lanthanide(III) ions; (II) ancillary co-ligands in cyclometalated iridium(III) complexes; (III) bridging, linker units in covalently linked, water-soluble bimetallic lanthanide(III) iridium(III) hybrid complexes. The dipyrido[3,2-a:2',3'-c]phenazine (dppz) derivatives can act as sensitising chromophores (λ(ex) 400 nm) for Yb(III), resulting in characteristic near-IR emission at 950-1050 nm. The incorporation of dppz-type ligands into cyclometalated Ir(III) complexes of the general type [Ir(epqc)(2)(L(n))](PF(6)) (where epqc = ethylphenylquinoline carboxylate) gave luminescent species with solvent-sensitive emission properties. Steady state and time-resolved luminescence measurements on the water-soluble d-f hybrid species showed that Yb(III) can be sensitised using visible light.

Evaluation of a fluorescent derivative of AMD3100 and its interaction with the CXCR4 chemokine receptor.

AMD3100 is a potent and selective antagonist of the CXCR4 receptor; it has been shown to block the route of entry of HIV into host T-cells. This compound and its analogues have since been found to act as haematopoietic stem cell mobilisation agents and, more recently, as anti-cancer agents. Here, we have examined a fluorescent derivative of AMD3100, L(1), which offered the potential to assess the behaviour of AMD3100 at the cell surface by using optical imaging modalities. The binuclear Zn(II) , Cu(II) and Ni(II) complexes of L(1) have also been investigated as these metals have been previously shown to enhance the binding properties of AMD3100. Furthermore, Zn(II) and Cu(II) are known to enhance and quench, respectively, the fluorescence of similar anthracenyl-based ligands. Whilst L(1) demonstrates an ability to inhibit the binding of the anti-CXCR4 monoclonal antibody 12G5 (IC(50) =0.25-0.9 µM), the incorporation of an anthracenyl moiety resulted in a significantly reduced affinity for CXCR4 compared to AMD3100 (IC(50) =10 nM). We observed no significant increase in fluorescence intensity following incubation with murine pre-B cells overexpressing CXCR4 compared to a control cell line. This limits the usefulness of L(1) as a fluorescent imaging probe. Interestingly, the Zn(II) complex, which carries an overall +4 charge, revealed marginally higher specificity and reduced toxicity in vitro compared to the free ligand, albeit with reduced affinity for CXCR4 (IC(50) =1.8-5 µM). We suggest that the incorporation of an anthracenyl group contributes to the lipophilic character of the free ligand, thereby resulting in transport across the plasma membrane. This effect is seemingly diminished when the ligand is complexed to charged metal ions.

New 2,3-disubstituted-5-hydroxyquinoxaline ligands and their coordination chemistry with cyclometallated iridium(III): syntheses, structures and tunable electronic properties.

A new series of para-substituted 2,3-diphenyl-5-hydroxyquinoxaline ligands (LH(n)) were synthesised and characterised. These ligands were prepared in high yield via a two-step synthetic method. Four novel heteroleptic iridium(III) complexes were correspondingly prepared in high yield giving [Ir(ppy)(2)(L(n))]. Two X-ray crystallographic studies were undertaken on LH(3) and [Ir(ppy)(2)(L(2))] with each confirming the proposed formulations, with the complex showing the O,N-coordination mode of the quinoxalinato ligand. Density functional theoretical calculations were performed, firstly to compare the coordinated quinoxalinato system with the related quinolinato analogue, and secondly to probe the influence of the variation in para-substitution on the ancillary ligand. The calculations suggest that for either the quinoline or quinoxaline systems ligand-centred character appears to dominate the HOMO and LUMOs. Experimental electrochemical and spectroscopic characterisation showed that the subtle variations in absorption and emission wavelengths are probably due to ligand-dominated transitions that are influenced by the electronic nature of the para-substituted phenyl units in coordinated L(n).

The co-ordination chemistry of tris(3,5-dimethylpyrazolyl)methane manganese carbonyl complexes: synthetic, electrochemical and DFT studies.

The tricarbonyl [Mn(CO)(3){HC(pz')(3)}][PF(6)] 1(+)[PF(6)](-) (pz' = 3,5-dimethylpyrazolyl) reacts with a range of P-, N- and C-donor ligands, L, in the presence of trimethylamine oxide to give [Mn(CO)(2)L{HC(pz')(3)}](+) {L = PEt(3)3(+), P(OEt)(3)4(+), P(OCH(2))(3)CEt 5(+), py 6(+), MeCN 7(+), CNBu(t)8(+) and CNXyl 9(+)}. The complex [Mn(CO)(2)(PMe(3)){HC(pz')(3)}](+)2(+) is formed by reaction of 7(+) with PMe(3). Complexes 2(+) and 6(+) were structurally characterised by X-ray diffraction methods. Reaction of 7(+) with half a molar equivalent of 4,4'-bipyridine gives a purple compound assumed to be the bridged dimer [{HC(pz')(3)}Mn(CO)(2)(µ-4,4'-bipy)Mn(CO)(2){HC(pz')(3)}](2+)10(2+). The relative electron donating ability of HC(pz')(3) has been established by comparison with the cyclopentadienyl and tris(pyrazolyl)borate analogues. Cyclic voltammetry shows that each of the complexes undergoes an irreversible oxidation. The correlation between the average carbonyl stretching frequency and the oxidation potential for complexes of P- and C-donor ligands is coincident with the correlation observed for [Mn(CO)(3-m)L(m)(η-C(5)H(5-n)Me(n))]. The data for complexes of N-donor ligands, however, are not coincident due to the presence of a node (and phase change) between the metal and the N-donor in the HOMO of the complex as suggested by preliminary DFT calculations.

Rhodium and iridium complexes of an asymmetric bicyclic NHC bearing secondary pyridyl donors.

A tridentate N^C^N ligand, 1, containing a bicyclic central NHC ring and two flanking pyridyl groups has been coordinated to Rh(I) and Ir(I) to give complexes of the type [M(κ(3)-1)(1,5-COD)]PF(6) (2 M = Rh; 3 M = Ir). In contrast to our earlier study with this ligand, the complexes have been shown to approximate to a trigonal bipyramidal geometry in the solid state and exist as an isomeric mixture in solution as determined by (1)H and (13)C NMR spectroscopy. Electrochemical studies revealed that both complexes undergo a 1-electron oxidation with the potential of the Rh complex 0.1 V less than that of the Ir complex in CH(2)Cl(2). Preliminary DFT studies confirm the lowest energy conformations as those seen in the solid state and show the location and energy of the HOMOs to be identical in 2 and 3. Partial charge analysis shows a greater positive charge on the Ir in 3 compared to the Rh in 2. Some preliminary studies of hydrogenation reactivity have shown the complexes to be efficient for both transfer and direct hydrogenation of prochiral ketones and alkenes at moderate temperatures but without any discernible enantioselectivity.

Purification-free synthesis of a highly efficient ruthenium dye complex for dye-sensitised solar cells (DSSCs).

A novel Ru(II) sensitiser A597 containing the 4,4'-dioctylamido-2,2'-bipyridine ancillary ligand is synthesised without the need for purification steps. It shows an irreversible oxidation at 0.92 V in the cyclic voltammogram and an absorbtion at 539 nm in the UV-vis spectrum corresponding to an (1)MLCT transition. Preliminary DFT calculations reveal that the HOMO is localised on the ruthenium metal centre and the thiocyanate ligands, whereas the LUMO is predominantly on the 4,4'-carboxy-2,2'-bipyridine ligand. The ruthenium complex exhibits a maximum power conversion efficiency (7.25%) compared with the known Z907 (8.32%) in dye-sensitised solar cells.

Cu(I) complexes based on cis, cis-1,3,5-tris(arylideneamino)cyclohexane ligands: synthesis, structure and CO binding.

A new series of sterically bulky, facially coordinating N(3)-donor tach-based ligands (tach; cis,cis-1,3,5-triaminocyclohexane) [2.1; cis,cis-1,3,5-tris(2,4-dimethylbenzylideneamino)cyclohexane, 4.1; cis,cis-1,3,5-tris(pentamethylbenzylideneamino)cyclohexane, 5.1; cis,cis-1,3,5-tris(2,6-dimethoxybenzylideneamino)cyclohexane, 6.1; cis,cis-1,3,5-tris(pentafluorobenzylideneamino)cyclohexane, 7.1; cis,cis-1,3,5-tris(3,5-bis(ditrifluoromethyl)benzylideneamino)cyclohexane, 8.1; cis,cis-1,3,5-tris(2-trifluoromethylbenzylideneamino)cyclohexane, 9.1; cis,cis-1,3,5-tris(2-methoxybenzylideneamino)cyclohexane] have been obtained from the condensation of tach with three equivalents of the appropriate substituted benzaldehyde. Reaction with [Cu(NCCH(3))(4)]PF(6) gives Cu(I) complexes of tach-based ligands {2.2-9.2, eg; 2.2; [Cu(2.1)(NCCH(3))]PF(6)}. Displacement of the acetonitrile ligand by CO was achieved successfully for all the Cu(I) complexes of tach-based ligands and the resulting complexes have been shown to bind carbon monoxide {2.3-9.3, eg; 2.3; [Cu(2.1)(CO)]PF(6)}. The X-ray single crystal structures of 5.1, 8.1, 9.1, 3.2, 7.2, 8.2, 9.2, 3.3, 5.3 and 6.3 have been determined.

Homo- and heterodinuclear complexes of the tetrakis(pyrazolyl)borate ligand.

Monometallic complexes of the tetrakis(pyrazolyl)borate ligand [ML(2){B(pz)(4)}] {M = Rh, Ir; L(2) = eta-cod, eta-nbd, (CO)(2), (CO)(PPh(3))} have two free pyrazolyl rings which can be coordinated to a second ML(2) unit to give the dimeric compounds [L(2)M{mu-B(pz)(4)}ML(2)](+), and to a metal halide to give heterobimetallic species [L(2)M{mu-B(pz)(4)}M'Cl(2)]. (1)H NMR spectroscopy shows that [(eta-cod)Rh{mu-B(pz)(4)}Rh(eta-cod)](+) 1(+), [(eta-nbd)Rh{mu-B(pz)(4)}Rh(eta-nbd)](+) 2(+), [(eta-cod)Ir{mu-B(pz)(4)}Ir(eta-cod)](+) 3(+) and [(CO)(2)Rh{mu-B(pz)(4)}Rh(CO)(2)](+) 4(+) are fluxional at room temperature. Cooling a solution of [(eta-cod)Rh{mu-B(pz)(4)}Rh(eta-cod)](+) 1(+) to -90 degrees C slows the fluxional process, which involves inversion of the two B-(N-N)(2)-M six-membered rings. Attempts to synthesise the asymmetric complexes [(eta-cod)Rh{mu-B(pz)(4)}Rh(eta-nbd)](+) 7(+), [(eta-cod)Rh{mu-B(pz)(4)}Ir(eta-cod)](+) 8(+) and [(eta-cod)Rh{mu-B(pz)(4)}Rh(CO)(2)](+) 9(+) produced a mixture of [L(2)M{mu-B(pz)(4)}ML(2)](+), [L'(2)M'{mu-B(pz)(4)}M'L'(2)](+) and the desired species. The heterobimetallic complexes [L(2)Rh{mu-B(pz)(4)}M'Cl(2)] (M' = Co, L(2) = eta-cod 10; M' = Co, L(2) = eta-nbd 11; M' = Co, L = CO 12; M' = Co, L(2) = (CO)(PPh(3)) 13; M' = Zn, L(2) = eta-cod 14; M' = Zn, L(2) = eta-nbd 15; M' = Pd, L(2) = eta-cod 16) possess square planar Rh(I) linked to square planar Pd(II) or tetrahedral Zn(II) and Co(II) centres. The paramagnetic Co(II) complexes give (1)H NMR spectra with signals shifted over a range of 75 ppm. The UV-Vis spectra of 10-13 show four bands, one MLCT at Rh and three d-d transitions arising from the splitting of the (4)T(1)(P) excited state due to approximate C(2v) symmetry at Co.

Pandemic (H1N1) 2009 influenza vaccine roll-out in NSW.

The roll-out of the pandemic (H1N1) 2009 influenza vaccine in NSW was significantly different to that envisaged for a pandemic vaccination program. Pre-pandemic planning had focused on the urgent roll-out of a vaccine through mass vaccination clinics in a time of high demand due to a virulent influenza virus. Instead the situation was less urgent, with the vaccine available only after the peak of incidence of infections in NSW. Consequently mass vaccination clinics were considered to be a less appropriate method of delivering the vaccine than a primary care focused delivery model. This paper describes the program, some of the controversies considered during its roll-out and factors to be considered in planning for future pandemics.

Luminescent, water-soluble gold nanoparticles functionalised with 3MLCT emitting rhenium complexes.

Rhenium complexes functionalised with thioester-terminated alkyl chains can be attached to gold nanoparticles to yield water-soluble, visibly luminescent Re-GNP hybrid conjugates.

Bonding modes, structures and fluxionality in rhodium and iridium tris(3,5-dimethylpyrazolyl)methane diene complexes.

The structures adopted by a range of hydrotris(3,5-dimethylpyrazolyl)methane complexes [ML(2){HC(pz')(3)}](+) (M = Rh, Ir; L(2) = diene) have been investigated. There is low steric hindrance between ligands in [Rh(eta-nbd){HC(pz')(3)}](+) (nbd = norbornadiene) and [Rh(eta-dmbd){HC(pz')(3)}](+) (dmbd = 2,3-dimethylbuta-1,3-diene) resulting in kappa(3) co-ordination of the pyrazolylmethane. The complexes [M(eta-cod){HC(pz')(3)}](+) (cod = cycloocta-1,5-diene) (M = Rh, Ir) are kappa(2) co-ordinated with the free pyrazolyl ring positioned above and approximately parallel to the square plane about rhodium or iridium. The HC(pz')(3) complexes undergo fast exchange of the co-ordinated and unco-ordinated pyrazolyl rings on the NMR spectroscopic timescale. However, for [Rh(eta-dmbd){HC(pz')(3)}](+), the fluxional process is slowed at low temperatures, so that inequivalent pyrazolyl rings may be observed. A mechanism for the fluxional process is proposed involving dynamic interconversion between isomeric forms in solution. The bonding mode of the HC(pz')(3) ligand can be determined by (13)C NMR spectroscopy. The (13)C chemical shifts (for the sp(3) hybridised carbon of the ligand) show the general pattern, kappa(3) < 71.5 ppm < kappa(2). The electrochemical behaviour of the pyrazolylmethane complexes is related to the degree of structural change, which occurs on electron transfer and is compared with that of the pyrazolylborate analogues.

Copper(I) complexes of cis,cis-1,3,5-tris(mesitylideneamino)cyclohexane ligands: synthesis, structure and substrate selectivity.

The new sterically encumbered facially coordinating N(3)-donor ligand cis,cis-1,3,5-tris(mesitylideneimino)cyclohexane (L1) has been synthesised. Reaction with [Cu(NCCH(3))(4)]PF(6) gives [Cu(L1)NCCH(3)]PF(6) (1), the bound acetonitrile being labile and readily replaced by CO to yield [Cu(L1)CO]PF(6) (2); both 1 and 2 have been structurally characterised. Complexes 1 and 2 do not undergo a substitution reaction with ethylene. This is in contrast to the related bidentate ligand complexes [Cu(L2)NCCH(3)]BF(4) (3) or [Cu(L2)CO]BF(4) (4) (L2= 1,2-bis(mesitylideneamino)cyclohexane) which rapidly form the ethylene complex under the same conditions.

Continuous separation of racemic 3,5-dinitrobenzoyl-amino acids in a centrifugal contact separator with the aid of cinchona-based chiral host compounds.

Resolution through revolution: It is possible to extract 3,5-dinitrobenzoyl-protected amino acids enantioselectively with the aid of a table-top centrifugal contact separator and a catalytic amount of a chiral host compound based on the Cinchona alkaloids. Enantioselectivities of up to 80 % could be reached in a single pass. This allows the development of a process for the continuous separation of racemates.The resolution of racemates is mostly performed by crystallisation of diastereomeric salts. Direct physical separation could be much more efficient, but so far most concepts, with the exception of SMB, have proven to be non-scaleable. Here we report the first scalable process for the resolution of N-protected amino acid derivatives through selective extraction, with the aid of a catalytic amount of a chiral host compound based on Cinchona alkaloids. The method hinges on the use of centrifugal contact separators (CCSs) for fast mixing and separation. Although the highest ee obtained was only 80 %, the concept can be extended through the use of a series of CCSs in countercurrent mode to effect full separation.

Solid state and solution structures of rhodium and iridium poly(pyrazolyl)borate diene complexes.

The structures adopted by a range of poly(pyrazolyl)borate complexes [ML2Tp(x)] [M = Rh, Ir; L2 = diene; Tp(x) = Bp' {dihydrobis(3,5-dimethylpyrazolyl)borate}, Tp' {hydrotris(3,5-dimethylpyrazolyl)borate}, Tp {hydrotris(pyrazolyl)borate}, B(pz)4 {tetrakis(pyrazolyl)borate}] have been investigated. Low steric hindrance between ligands in [Rh(eta-nbd)Tp] (nbd = norbornadiene), [Rh(eta-cod)Tp] (cod = cycloocta-1,5-diene) and [Rh(eta-nbd)Tp'] results in K3 coordination of the pyrazolylborate but [M(eta-cod)Tp'] (M = Rh, Ir) are kappa2 coordinated with the free pyrazolyl ring positioned above and approximately parallel to the square plane about the metal. All but the most sterically hindered Tp(x) complexes undergo fast exchange of the coordinated and uncoordinated pyrazolyl rings on the NMR spectroscopic timescale. For [Rh(eta-cod){B(pz)4}], [Rh(eta-dmbd)Tp'] (dmbd = 2,3-dimethylbuta-1,3-diene) and [Rh(eta-cod)Tp(Ph)] {Tp(Ph) = hydrotris(3-phenylpyrazolyl)borate} the fluxional process is slowed at low temperatures so that inequivalent pyrazolyl rings are observed. The bonding modes of the Tp' ligand (but not of other pyrazolylborate ligands) can be determined by 11B NMR and IR spectroscopy. The 11B chemical shifts (for a series of Tp' complexes) show the general pattern, kappa3 < -7.5 ppm < kappa2 and the nu(BH) stretch kappa3 > 2500 cm(-1) > kappa2. The electrochemical behaviour of the pyrazolylborate complexes is related to the degree of structural change which occurs on electron transfer. One-electron oxidation of complexes with Tp', Tp and B(pz)4 ligands is generally reversible although that of [Ir(etacod)Tp] is only reversible at higher scan rates and that of [Ir(eta-cod){B(pz)4}] is irreversible. Of the complexes with the more sterically hindered Tp(Ph) ligand, only [Rh(eta-nbd)Tp(Ph)] shows any degree of reversible oxidation. The ESR spectra of a range of Rh(II) complexes show coupling to both 14N and 103Rh nuclei in most cases but what appears to be coupling to rhodium and one hydrogen atom, possibly a hydride ligand, for the oxidation product of [Rh(eta-nbd)Tp(Ph)].