Formation of Heterobimetallic Complexes by Addition of d10-Metal Ions to [(Me3P)xM(2-C6F4PPh2)2] (x = 1, 2; M = Ni and Pt): A Synthetic and Computational Study of Metallophilic Interactions.

Treatment of the bis(chelate) complexes trans-[M(κ2-2-C6F4PPh2)2] (trans-1M; M = Ni, Pt) and cis-[Pt(κ2-2-C6F4PPh2)2] (cis-1Pt) with equimolar amounts or excess of PMe3 solution gave complexes of the type [(Me3P)xM(2-C6F4PPh2)2] (x = 2: 2Ma, 2Mb x = 1: 3Ma, 3Mb; M = Ni, Pt). The reactivity of complexes of the type 2M and 3M toward monovalent coinage metal ions (M' = Cu, Ag, Au) was investigated next to the reaction of 1M toward [AuCl(PMe3)]. Four different complex types [(Me3P)2M(µ-2-C6F4PPh2)2M'Cl] (5MM'; M = Ni, Pt; M' = Cu, Ag, Au), [(Me3P)M(κ2-2-C6F4PPh2)(µ-2-C6F4PPh2)M'Cl]x (x = 1: 6MM'; M = Pt; M' = Cu, Au; x = 2: 6PtAg), head-to-tail-[(Me3P)ClM(µ-2-C6F4PPh2)2M'] (7MM'; M = Ni, Pt; M' = Au), and head-to-head-[(Me3P)ClM(µ-2-C6F4PPh2)2M'] (8MM'; M = Ni, Pt; M' = Cu, Ag, Au) were observed. Single-crystal X-ray analyses of complexes 5-8 revealed short metal-metal separations (2.7124(3)-3.3287(7) Å), suggestive of attractive metal-metal interactions. Quantum chemical calculations (atoms in molecules (AIM), electron localization function (ELF), non-covalent interaction (NCI), and natural bond orbital (NBO)) gave theoretical support that the interaction characteristics reach from a pure attractive non-covalent to an electron-shared (covalent) character.

Innovative Molecular Design Strategies in Materials Science Following the Aurophilicity Concept.

The past decade has seen a diverse range of breakthrough inventions that are derived from gold complexes, including the application of aurophilic interactions in the preparation of stimuli-responsive materials. Examples of these gold-based materials include aurophilicity-induced metallogelators, mechanochromic, thermochromic, vapochromic, and solvatochromic luminescent compounds, as well as sensory materials for the detection of metal ions. Sophisticated properties of gold complexes with Au···Au contacts have been explored at the edge of several disciplines including chemistry, crystallography, molecular engineering and advanced materials. As science paves its way to innovation, cross-disciplinary research moves from being a luxury to becoming a necessity. Development of the concept of aurophilicity and its use in designing novel materials is a true example of innovation on a multidisciplinary platform. As miniaturization continues to influence the next generation of technological advancement, using the properties of molecules as chemical tools to enable such developments becomes extremely important. In this Review, recent examples of gold complexes which exhibit a response to external stimuli have been collected and some of their potential applications discussed for selected cases.

Antitumor and Antiangiogenic Properties of Gold(III) Complexes Containing Cycloaurated Triphenylphosphine Sulfide Ligands.

A family of stable anticancer gold(III)-based therapeutic complexes containing cyclometalated triphenylphosphine sulfide ligands have been prepared. The anticancer properties of the newly developed complexes [AuCl2{κ2-2-C6H4P(S)Ph2}] (1), [Au(κ2-S2CNEt2){κ2-2-C6H4P(S)Ph2}]PF6 (2), [AuCl(dppe){κC-2-C6H4P(S)Ph2}]Cl (3), and [Au(dppe){κ2-2-C6H4P(S)Ph2}][PF6]2 (4) were investigated toward five human cancer cell lines [cervical (HeLa), lung (A549), prostate (PC3), fibrosarcoma (HT1080), and breast (MDA-MB-231)]. In vitro cytotoxicity studies revealed that compounds 2-4 displayed potent cell growth inhibition (IC50 values in the range of 0.17-2.50 µM), comparable to, or better than, clinically used cisplatin (0.63-6.35 µM). Preliminary mechanistic studies using HeLa cells indicate that the cytotoxic effects of the compounds involve apoptosis induction through ROS accumulation. Compound 2 also demonstrated significant inhibition of endothelial cell migration and tube formation in the angiogenesis process. Evaluation of the in vivo antitumor activity of compound 2 in nude mice bearing cervical cancer cell (HeLa) xenografts indicated significant tumor growth inhibition (55%) with 1 mg/kg dose (every 3 days) compared with the same dose of cisplatin (28%). These results demonstrate the potential of gold(III) complexes containing cyclometalated triphenylphosphine sulfide ligands as novel metal-based anticancer agents.

Potent and Selective Cytotoxic and Anti-inflammatory Gold(III) Compounds Containing Cyclometalated Phosphine Sulfide Ligands.

Four cycloaurated phosphine sulfide complexes, [Au{κ2 -2-C6 H4 P(S)Ph2 }2 ][AuX2 ] [X=Cl (2), Br (3), I (4)] and [Au{κ2 -2-C6 H4 P(S)Ph2 }2 ]PF6 (5), have been prepared and thoroughly characterized. The compounds were found to be stable under physiological-like conditions and showed excellent cytotoxicity against a broad range of cancer cell lines and remarkable cytotoxicity in 3D tumor spheroids. Mechanistic studies with cervical cancer (HeLa) cells indicated that the cytotoxic effects of the compounds involve the inhibition of thioredoxin reductase and induction of apoptosis through mitochondrial disruption. In vivo experiments in nude mice bearing HeLa xenografts showed that treatment with compounds 4 and 5 resulted in significant inhibition of tumor growth (35.8 and 46.9 %, respectively), better than that of cisplatin (29 %). The newly synthesized gold complexes were also evaluated for their in vitro and in vivo anti-inflammatory activity through the study of lipopolysaccharide (LPS)-activated macrophages and carrageenan-induced hind paw edema in rats, respectively.

Synthesis of Gold(I) Complexes Containing Cinnamide: In Vitro Evaluation of Anticancer Activity in 2D and 3D Spheroidal Models of Melanoma and In Vivo Angiogenesis.

A series of alkynylgold(I) phosphine complexes containing methoxy-substituted cinnamide moieties (3a-3c and 4a-4c) have been synthesized and characterized. All of the synthesized complexes were evaluated for their cytotoxicity against three human cancer cell lines A549 (lung), D24 (melanoma), and HT1080 (fibrosarcoma) and the human embryonic kidney 293 cell line (Hek293T) as a proxy model for noncancer cells. Most of the synthesized compounds showed antiproliferative activity against cancer cell lines at low micromolar concentrations. Among these, complex 3c showed a broad spectrum of anticancer activity with IC50 values in the range of 1.53-6.05 µM against all tested cancer lines. Complex 3c possessed 20 times higher cytotoxicity than the reference drug cisplatin against D24 melanoma cells and showed significant anticancer activity in 3D spheroidal models of melanoma cells. Mechanistic investigations of 3c activity indicate thioredoxin reductase inhibition through steric and hydrogen-bonding interactions, followed by the induction of oxidative stress and a mitochondrial pathway of cell death. Compound 3c also showed significant antiangiogenic properties in a transgenic zebrafish Tg(fli1a:EGFP) in vivo model.

Synthesis, anti-proliferative and apoptosis-inducing studies of palladacycles containing a diphosphine and a Sn,As-based chelate ligand.

Cleavage of the bromide bridges in [Pd2(µ-Br)2{κ2(Sn,As)-2-MeBrSnC6F4AsPh2}2] (1) by diphosphine ligands gave the mono- and dinuclear palladacycles [Pd(L)Br{κ2(Sn,As)-2-MeBrSnC6F4AsPh2}] [L = dppe (2) dppm (3), ortho-dppBz (4)] and [Pd2Br2(para-dppBz){κ2(Sn,As)-2-MeBrSnC6F4AsPh2}2] (5). The interactions of these complexes with DNA (CT-DNA) and proteins (human serum albumin) were studied by UV-Vis and fluorescence spectroscopy, respectively. The results confirmed the interaction of these palladium complexes with CT-DNA through groove binding, and their strong binding affinity to HSA. The anti-proliferative activities of complexes 1-5 were tested against four human cancer cell lines (HeLa, A549, PC-3, and HT1080) and normal keratinocytes (HaCaT). Among the series, the palladium(ii) complex containing the 1,2-bis(diphenylphosphino)benzene ligand (4) showed the highest cytotoxicity against HeLa, PC-3 and HT1080 cells, with IC50 values of 0.25 ± 0.08, 0.85 ± 0.11, and 0.66 ± 0.15 µM, respectively. Interestingly, compound 4 exhibited lower cytotoxic activity toward normal HaCaT cells (IC50 = 4.65 ± 0.16 µM). Additionally, this complex exhibited lower toxicity and better anti-cancer activity than cisplatin. Further mechanistic studies, including Hoechst staining and flow cytometry, confirmed that complex 4 induced G2/M phase cell cycle arrest and apoptotic cell death in HeLa cells.

Gold(i) and gold(iii) phosphine complexes: synthesis, anticancer activities towards 2D and 3D cancer models, and apoptosis inducing properties.

A series of gold(i), gold(iii) and cationic gold(i) complexes of tris(4-methoxyphenyl)phosphine and tris(2,6-dimethoxyphenyl)phosphine were synthesised and fully characterised by spectroscopic methods. The molecular structures of selected complexes were also determined by X-ray diffraction analysis. The prepared complexes [AuX{P(C6H4-4-OMe)3}] [X = Cl (1), Br (2), I (3)], [AuCl3{P(C6H4-4-OMe)3}] (4), [Au{P(C6H4-4-OMe)3}2]PF6 (5), [AuX{P(C6H3-2,6-{OMe}2)3}] [X = Cl (6), Br (7), I (8)], [AuCl3{P(C6H3-2,6-{OMe}2)3}] (9) and [Au{P(C6H3-2,6-{OMe}2)3}2]PF6 (10) were investigated for their anticancer activity against five human tumor cell lines [ovarian (SKOV-3), fibrosarcoma (HT1080), glioblastoma (U87MG), prostate (PC-3), and cervical (HeLa)] as well as against 3D spheroidal models of HeLa cells. The cationic complex 10 was found to exhibit a remarkably broad spectrum of anticancer activity with approximately 30-fold higher toxicity than cisplatin against PC-3 and U87MG cancer cells; this complex also showed the strongest inhibition of spheroid growth in 3D models of HeLa cells. The mechanism of anticancer activity of these gold complexes was found to be strong inhibition of thioredoxin reductase, increased ROS production and subsequent apoptosis induction as evidenced by the sub G1 cell accumulation, DNA fragmentation, and caspase-3 activation.

Synthesis of gold(I) phosphine complexes containing the 2-BrC6F4PPh2 ligand: Evaluation of anticancer activity in 2D and 3D spheroidal models of HeLa cancer cells.

Newly synthesised mononuclear gold complexes containing the 2-BrC6F4PPh2 ligand have been fully characterised and their anticancer activity towards five human tumor [prostate (PC3), glioblastoma (U87MG), cervical (HeLa), fibrosarcoma (HT1080), ovarian (SKOV-3)] and normal human embryonic kidney (Hek-293T) cell lines investigated. Some of the synthesised gold complexes displayed higher cytotoxicity than cisplatin towards PC-3, HeLa and U87MG cells and inhibited the thioredoxin reductase (TrxR) enzyme, which is considered a potential target for new compounds in cancer treatment. The more physiologically relevant tumor spheroid assay demonstrated the superior potency of these gold phosphine complexes in inhibiting the growth of cervical carcinoma cell line HeLa (3D) spheroidal models. The mechanism of cell death was shown to be apoptotic cell death through cell cycle arrest, mitochondrial membrane depolarisation and increased ROS production.

Anti-cancer gold(I) phosphine complexes: Cyclic trimers and tetramers containing the P-Au-P moiety.

We report the application of cationic tri- and tetra-nuclear gold(I) phosphine complexes [Au3(µ-dppen)3]X3 and [Au4(µ-dppa)4]X4 (X=OTf, PF6) [OTf=trifluoromethanesulfonate, dppen=trans-1,2-bis(diphenylphosphino)ethene, dppa=bis(diphenylphosphino)acetylene] for cancer treatment. The results of cytotoxicity tests on four different cancer cells [prostate (DU145), cervical (HeLa), breast (MDAMB-231) and fibro sarcoma (HT1080)] indicate these complexes possess remarkable tumor cell growth inhibitory effects and high selectivity towards cancer cells. The anti-tumor mechanism of the tri- and tetra-nuclear gold(I) complexes has also been investigated.

Tin(IV) Compounds with 2-C6F4PPh2 Substituents and Their Reactivity toward Palladium(0): Formation of Tin-Palladium Complexes via Oxidative Addition.

The tin(IV) compounds MexSn(2-C6F4PPh2)4-x (1, x = 1; 2, x = 2) and ClSn(2-C6F4PPh2)3 (3) were obtained from the reactions of 2-LiC6F4PPh2 with MeSnCl3 (3:1), Me2SnCl2 (2:1), or SnCl4 (3:1), respectively. The reactions of 2-LiC6F4PPh2 with SnCl4 in different stoichiometric ratios (4:1-1:1) gave 3 as the main product. Compound Cl2Sn(2-C6F4PPh2)2 (4) was formed in the transmetalation reaction of 3 and [AuCl(tht)] but could not be isolated. 1 and 2 react with palladium(0) sources {[Pd(PPh3)4] and [Pd(allyl)Cp]} by the oxidative addition of one of their Sn-CAryl bonds to palladium(0) with formation of the heterobimetallic complexes [MeSn(µ-2-C6F4PPh2)2Pd(κC-2-C6F4PPh2)] (5) and [Me2Sn(µ-2-C6F4PPh2)Pd(κ2-2-C6F4PPh2)] (6) featuring Sn-Pd bonds. The reaction of 3 with palladium(0) proceeds via the oxidative addition of the Sn-Cl bond to palladium(0), thus furnishing the complex [Sn(µ-2-C6F4PPh2)3PdCl] (7) featuring a Sn-Pd bond and a pentacoordinate Pd atom. Transmetalation of MexSn(2-C6F4PPh2)4-x (x = 1-3) with [Pd(allyl)Cl]2 gave MexClSn(2-C6F4PPh2)3-x and [Pd(allyl)(µ-2-C6F4PPh2)]2. For x = 1, the compound MeClSn(2-C6F4PPh2)2 (generated in situ) reacted with another 1 equiv of [Pd(allyl)Cl]2 by the oxidative addition of the Sn-Cl bond to palladium(0) and the reductive elimination of allyl chloride, thus leading to [MeSn(µ-2-C6F4PPh2)2PdCl] (8). The reductive elimination of allyl chloride was also observed in the reaction of 3 with [Pd(allyl)Cl]2, giving [Sn(µ-2-C6F4PPh2)3PdCl] (7). All compounds have been characterized by means of multinuclear NMR spectroscopy, elemental analysis, single-crystal X-ray diffraction, and selected compounds by 119Sn Mössbauer spectroscopy. Computational analyses (natural localized molecular orbital calculations) have provided insight into the Sn-Pd bonding of 5-8.

Metallophilic Contacts in 2-C6F4PPh2 Bridged Heterobinuclear Complexes: A Crystallographic and Computational Study.

Treatment of the bis(chelate) complex trans-[Pd(κ(2)-2-C6F4PPh2)2] (7) with PMe3 gave trans-[Pd(κC-2-C6F4PPh2)2(PMe3)2] (13) as a mixture of syn- and anti-isomers. Reaction of 13 with CuCl, AgCl, or [AuCl(tht)] (tht = tetrahydrothiophene) gave the heterobinuclear complexes [(Me3P)2Pd(µ-2-C6F4PPh2)2MCl] [M = Cu (14), Ag (15), Au (16)], from which the corresponding salts [(Me3P)2Pd(µ-2-C6F4PPh2)2M]PF6 [M = Cu (17), Ag (18), Au (19)] could be prepared by abstraction of the chloro ligand with TlPF6; 18, as well as its triflato (20) and trifluoroacetato (21) analogues, were also prepared directly from 13 and the appropriate silver salt. Reaction of 13 with [AuCl(PMe3)] gave the zwitterionic complex [(Me3P)PdCl(µ-2-C6F4PPh2)2Au] (24) in which the 2-C6F4PPh2 ligands are in a head-to-head arrangement. In contrast, the analogous reaction with [AuCl(PPh3)] gave [(Ph3P)PdCl(µ-2-C6F4PPh2)2Au] (25) with a head-to-tail ligand arrangement. Single crystal X-ray diffraction studies of complexes 14-21 show short metal-metal separations [2.7707(11)-2.9423(3) Å] suggestive of attractive noncovalent (dispersion) interactions, a conclusion that is supported by theoretical calculations of the electron localization function and the noncovalent interactions descriptor.

Cyclopalladated complexes containing 2-C6R4PPh2 ligands (R = H, F): one-electron electrochemical reduction leading to metal-carbon σ-bond cleavage via palladium(I).

Three new ortho-metallated palladium complexes, [Pd(O,O'-hfacac)(κ(2)-2-C6F4PPh2)] (), [Pd2(O,O'-hfacac)2(µ-2-C6F4PPh2)2] () and [Pd(O,O'-hfacac)(κC-2-C6F4PPh2)(PPh3)] () (hfacac = hexafluoroacetylacetonate), have been prepared and fully characterised. The electrochemical reductions of complexes , together with those of other cyclopalladated complexes containing 2-C6R4PPh2 ligands (R = H, F) were studied by cyclic, rotating disk and microelectrode voltammetry. Evidence for the one-electron reduction of [PdI(κ(2)-2-C6F4PPh2)(PPh2Fc)] () was obtained from coulometric analysis, although the product is unstable and undergoes further chemical processes. Preparative electro-reduction of [Pd2(µ-Br)2(κ(2)-2-C6F4PPh2)2] () in CH2Cl2 causes reductive cleavage of its Pd-C σ-bonds and formation of the complex [PdBr2{PPh2(2-C6F4H)}2] (); possible mechanisms are discussed.

ortho-Metallated triphenylphosphine chalcogenide complexes of platinum and palladium: synthesis and catalytic activity.

Treatment of [PtI2(COD)] (COD = 1,5-cyclooctadiene) with 2-LiC6H4P(S)Ph2 gives the complex cis-[Pt{κ(2)-2-C6H4P(S)Ph2}2] () containing a pair of ortho-metallated triphenylphosphine sulfide rings. The selenium counterpart, [Pt{κ(2)-2-C6H4P(Se)Ph2}2] (), which exists as cis- and trans-isomers in solution, and the palladium analogues, cis-[Pd{κ(2)-2-C6H4P(X)Ph2}2] [X = S (), Se ()], are obtained by transmetallation of [MCl2(COD)] with the organotin reagent 2-Me3SnC6H4P(X)Ph2 in a 1 : 2 mol ratio. The reaction of [PdCl2(COD)] with 2-Me3SnC6H4P(X)Ph2 in a 1 : 1 mol ratio, and the reaction of with palladium(ii) acetate, give dinuclear, anion-bridged complexes [Pd2(µ-Cl)2{κ(2)-2-C6H4P(X)Ph2}2] [X = S (), Se ()] and [Pd2(µ-OAc)2{κ(2)-2-C6H4P(S)Ph2}2] (), respectively. Complexes and could not be made directly from triphenylphosphine sulfide by standard ortho-palladation procedures. The bridging framework in complexes and is cleaved by tertiary phosphines to give mononuclear derivatives [PdCl{κ(2)-2-C6H4P(X)Ph2}(PR3)] [X = S, R = Ph (); X = Se, R = Ph (); X = Se, R = 4-tolyl ()]. The selenium-containing compounds and decompose slowly in solution giving dinuclear complexes [PdCl(µ2-Se-κ(2)-P,Se-2-SeC6H4PPh2)PdCl(µ-2-C6H4PPh2)(PR3)] [R = Ph (), 4-tolyl ()]. The structure of complex establishes that the bridging 2-C6H4PPh2 group is generated by reduction of the phosphine selenide unit, not by ortho-metallation of the coordinated triphenylphosphine. The chloro-bridges of and are also cleaved by acetylacetonate (acac) and deprotonated Schiff bases forming mononuclear species [Pd{κ(2)-2-C6H4P(X)Ph2}L2] [L2 = acac, X = S (), Se (); L2 = 2-OC6H4CH[double bond, length as m-dash]NC6H4-4-R, X = S, R = OMe (), NO2 (); X = Se, R = OMe (), NO2 ()]. The ability of complexes , and the Schiff base-derivatives to catalyse Heck-Mizoroki and Suzuki-Miyaura C-C bond-forming reactions has also been investigated.

A pyridyl-monoannulated naphthalene diimide motif self-assembles into tuneable nanostructures by means of solvophobic control.

The supramolecular self-assembly of the core-substituted naphthalene diimide bearing pyridyl motifs leads to the formation of a variety of nanostructures with pH and solvent control. The detection of HCl can be monitored by UV/Vis and fluorescence spectroscopy, as well as the naked eye, with a change in colour (blue to red, see figure). The cycle is fully reversed by the addition of triethylamine (TEA).

Synthesis, X-ray structure and electrochemical oxidation of palladium(II) complexes of ferrocenyldiphenylphosphine.

Four new complexes, [PdX(κ(2)-2-C(6)R(4)PPh(2))(PPh(2)Fc)] [X = Br, R = H (1), R = F (2); X = I, R = H (3), R = F (4)], containing ferrocenyldiphenylphosphine (PPh(2)Fc) have been prepared and fully characterised. The X-ray structures of complexes trans-1, cis-2 and cis-4, and that of a decomposition product of 4, [Pd(κ(2)-2-C(6)F(4)PPh(2))(µ-I)(µ-2-C(6)F(4)PPh(2))PdI(PPh(2)Fc)] (5), have been determined. These complexes show a distorted square planar geometry about the metal atom, the bite angles of the chelate ligands being about 69°, as expected. The cis/trans ratio of 1-4 in solution is strongly dependent on solvent. The new complexes and the uncoordinated PPh(2)Fc ligand were electrochemically characterised by cyclic and rotating disk voltammetry, UV-visible spectroelectrochemistry, and bulk electrolysis in dichloromethane and acetonitrile. In both cases, oxidation occurs at both the ferrocene and phosphine centres, but the complexes oxidise at more positive potentials than uncoordinated PPh(2)Fc; subsequently, the metal-phosphorus bond is cleaved, leading to free PPh(2)Fc(+), which undergoes further chemical and electrochemical reactions.

Unprecedented near-infrared (NIR) emission in diplatinum(III) (d7-d7) complexes at room temperature.

The synthesis and single-crystal X-ray structures of the first family of efficient NIR emitters with tunable emission energy based on dihalodiplatinum(III) (5d(7)-5d(7)) complexes of general formulae [Pt(2)(mu-C(6)H(3)-5-R-2-AsPh(2))(4)X(2)] (R = Me or CHMe(2); X = Cl, Br or I), together with that of their diplatinum(II) (5d(8)-5d(8)) precursors ([Pt(2)(mu-C(6)H(3)-5-R-2-AsPh(2))(4)]) and cyano counterparts (X = CN), are reported. The diplatinum(II) complexes with isopropyl groups are isolated initially as a mixture of two species, one being a half-lantern structure containing two bridging and two chelate C(6)H(3)-5-CHMe(2)-2-AsPh(2) ligands (1b) that exists in two crystalline modifications [d(Pt...Pt) = 3.4298(2) A and 4.3843(2) A]; the other is a full-lantern or paddle-wheel structure having four bridging C(6)H(3)-5-CHMe(2)-2-AsPh(2) ligands (2b) [d(Pt...Pt) = 2.94795(12) A]. Complete conversion of the isomers into 2b occurs in hot toluene. The Pt-Pt bond distances in the diplatinum(III) complexes are less than that in 2b and increase in the order X = Cl (3b) [2.6896(2) A] < Br (4b) [2.7526(3) A] < I (5b) [2.7927(7) A] approximately CN (6b) [2.7823(2), 2.7924(2) A for two independent molecules]. Comparison with the corresponding data for our previously reported series of complexes 3a-6a (R = Me) indicates that the Pt-Pt bond lengths obtained from single-crystal X-ray analysis are influenced both by the axial ligand and by intermolecular lattice effects. Like [Pt(2)(mu-pop)(4)](4-) [pop = pyrophosphite, (P(2)O(5)H(2))(2-)], the diplatinum(II) complexes [Pt(2)(mu-C(6)H(3)-5-R-2-AsPh(2))(4)] [R = Me (2a), CHMe(2) (2b)] display intense green phosphorescence, both as solids and in solution, and at room temperature and 77 K, with the emission maxima in the range 501-532 nm. In contrast to the reported dihalodiplatinum(III) complexes [Pt(2)(mu-pop)(4)X(2)](4-) that exhibit red luminescence only at 77 K in a glass or as a solid, complexes 3a-6a and 3b-6b are phosphorescent in the visible to near-infrared region at both room and low temperatures. The electronic spectra and photoemissive behavior are discussed on the basis of time-dependent density functional theory (TDDFT) calculations at the B3YLP level. The photoemissive states for the halide analogues 3a,b-5a,b involve a moderate to extensive mixing of XMMCT character and MC [d sigma-d sigma*] character, whereas the cyano complexes 6a and 6b are thought to involve relatively less mixing of the XMMCT character into the MC [d sigma-d sigma*] state.

Synthesis and interconversions of digold(I), tetragold(I), digold(II), gold(I)-gold(III) and digold(III) complexes of fluorine-substituted aryl carbanions.

Treatment of [AuXL] (X = Br, L = AsPh(3); X = Cl, L = tht) with the lithium or trimethyltin derivatives of the carbanions [2-C6F4PPh2]- and [C6H3-n-F-2-PPh2]- (n = 5, 6) gives digold(I) complexes [Au2(mu-carbanion)2] (carbanion = 2-C6F4PPh2 2, C6H3-5-F-2-PPh2 3, C6H3-6-F-2-PPh2 4) which, like their 2-C6H4PPh2 counterpart, undergo oxidative addition with halogens X2 (X = Cl, Br, I) to give the corresponding, metal-metal bonded digold(II) complexes [Au2X2(mu-carbanion)2] (carbanion = 2-C6F4PPh2, X = Cl 5, Br 8, I 11; carbanion = C6H3-5-F-2-PPh2, X = Cl 6, Br 9, I 12; carbanion = C6H3-6-F-2-PPh2, X = Cl 7, Br 10, I 13). In the case of 2-C6F4PPh2 and C6H3-6-F-2-PPh2, the dihalodigold(II) complexes rearrange on heating to isomeric gold(I)-gold(III) complexes [XAu(I)(mu-P,C-carbanion)(kappa2-P,C-carbanion)Au(III)X] (carbanion = 2-C6F4PPh2, X = Cl 25, Br 26, I 27; carbanion = C6H3-6-F-2-PPh2, X = Cl 28, Br 29, I 30), in which one of the carbanions chelates to the gold(III) atom. This isomerisation is similar to, but occurs more slowly than, that in the corresponding C6H3-6-Me-2-PPh2 system. The Au2X2 complexes 6, 9 and 12, on the other hand, rearrange on heating via C-C coupling to give digold(I) complexes of the corresponding 2,2'-biphenyldiylbis(diphenylphosphine), [Au2X2(2,2'-Ph2P-5-F-C6H3C6H3-5-F-PPh2)] (X = Cl 32, Br 33, I 34), this behaviour resembling that of the 2-C6H4PPh2 and C6H3-5-Me-2-PPh2 systems. Since the C-C coupling probably occurs via undetected gold(I)-gold(III) intermediates, the presence of a 6-fluoro substituent is evidently sufficient to suppress the reductive eliminations, possibly because of an electronic effect that strengthens the gold(III)-aryl bond. Anation of 5 or 8 gives the bis(oxyanion)digold(II) complexes [Au2Y2(mu-2-C6F4PPh2)2] (Y = OAc 14, ONO2 15, OBz 16, O2CCF3 17 and OTf 20), which do not isomerise to the corresponding gold(I)-gold(III) complexes [YAu(mu-2-C6F4PPh2)(kappa2-2-C6F4PPh2)AuY] on heating, though the latter [Y = OAc 35, ONO2 36, OBz 37, O2CCF3 38] can be made by anation of 25-27. Reaction of the bis(benzoato)digold(II) complex 16 with dimethylzinc gives a dimethyl gold(I)-gold(III) complex, [Au(I)(mu-2-C6F4PPh2)2Au(III)(CH3)2] 19, in which both 2-C6F4PPh2 groups are bridging. In contrast, the corresponding reaction of 16 with C6F5Li gives a digold(II) complex [Au(II)2(C6F5)2(mu-2-C6F4PPh2)2] 18, which on heating isomerises to a gold(I)-gold(III) complex, [(C6F5)Au(I)(mu-2-C6F4PPh2)(kappa2-2-C6F4PPh2)Au(III)(C6F5)] 31, analogous to 25-27. The bis(triflato)digold(II) complex 20 is reduced by methanol or cyclohexanol in CH2Cl2 to a tetranuclear gold(I) complex [Au4(mu-2-C6F4PPh2)4] 21 in which the four carbanions bridge a square array of metal atoms, as shown by a single-crystal X-ray diffraction study. The corresponding tetramers [Au4(mu-C6H3-n-F-2-PPh2)4] (n = 5 22, 6 23) are formed as minor by-products in the preparation of dimers 3 and 4; the tetramers do not interconvert readily with, and are not in equilibrium with, the corresponding dimers 2-4. Addition of an excess of chlorine or bromine (X2) to the digold(II) complexes 5 and 8, and to their gold(I)-gold(III) isomers 25 and 26, gives isomeric digold(III) complexes [Au2X4(mu-2-C6F4PPh2)2] (X = Cl 39, Br 40) and [X3Au(mu-2-C6F4PPh2)AuX(kappa2-2-C6F4PPh2)] (X = Cl 41, Br 42), respectively. The structures of the digold(I) complexes 2, 4 and 32, the digold(II) complexes 5-11 and 14-18, the gold(I)-gold(III) complexes 19, 25, 35 and 38, the tetragold(I) complexes 21 and 22, and the digold(III) complexes 41 and 42, have been determined by single-crystal X-ray diffraction. In the digold(II) (5d9-5d9) series, there is a systematic lengthening, and presumably weakening, of the Au-Au distance in the range 2.5012(4)-2.5885(2) A with increasing trans-influence of the axial ligand, in the order X = ONO2 < O2CCF3 < OBz < Cl < Br < I < C6F5. The strength of the Au-Au interaction is probably the main factor that determines whether the digold(II) compounds isomerise to gold(I)-gold(III). The gold-gold separations in the digold(I) and gold(I)-gold(III) complexes are in the range 2.8-3.6 A suggestive of aurophilic interactions, but these are probably absent in the digold(III) compounds (Au...Au separation ca. 5.8 A). Attempted recrystallisation of complex 10 gave a trinuclear gold(II)-gold(II)-gold(I) complex, [Au3Br2(mu-C6H3-6-F-2-PPh2)3] 24, which consists of the expected digold(II) framework in which one of the axial bromide ligands has been replaced by a sigma-carbon bonded (C6H3-6-F-2-PPh2)Au(I)Br fragment.

Electrochemical and chemical oxidation of [Pt2(mu-pyrophosphite)4]4- revisited: characterization of a nitrosyl derivative, [Pt2(mu-pyrophosphite)4(NO)]3-.

Electrochemical studies of the salts [cat](4)[Pt(2)(mu-pop)(4)] (cat(+) = Bu(4)N(+) or PPN(+) [Ph(3)P=N=PPh(3)](+); pop = pyrophosphite, [P(2)O(5)H(2)](2-)) have been carried out in dichloromethane. In agreement with published studies of K(4)[Pt(2)(mu-pop)(4)] in water and [Ph(4)As](4)[Pt(2)(mu-pop)(4)] in acetonitrile, the [Pt(2)(mu-pop)(4)](4-) anion is found to undergo an initial one-electron oxidation under conditions of cyclic voltammetry to a short-lived trianion, [Pt(2)(mu-pop)(4)](3-). However, in the more weakly coordinating solvent dichloromethane, [Pt(2)(mu-pop)(4)](3-) appears to undergo oligomerization instead of solvent-induced disproportionation; thus the overall process remains a one-electron reaction rather than an overall two-electron oxidative addition process, even under long time-scale, bulk electrolysis conditions. Chemical oxidation of [cat](4)[Pt(2)(mu-pop)(4)] with [NO][BF(4)] or AgBF(4) gives mainly a dark, insoluble, ill-defined solid that appears to contain Pt(III) according to X-ray photoelectron spectroscopy (XPS). In the case of [NO][BF(4)], a second reaction product, an orange solid, has been identified as a nitrosyl complex, [cat](3)[Pt(2)(mu-pop)(4)(NO)]. The X-ray structure of the PPN(+) salt shows the anion to consist of the usual lantern-shaped Pt(2)(mu-pop)(4) framework with an unusually large Pt-Pt separation [2.8375(6) A]; one of the platinum atoms carries a bent nitrosyl group [r(N-O) = 1.111(15) A; angle(Pt-N-O) = 118.1(12) degrees] occupying an axial position. The nitrosyl group migrates rapidly on the (31)P NMR time-scale between the metal atoms at room temperature but the motion is slow enough at 183 K that the expected two pairs of inequivalent phosphorus nuclei can be observed. The X-ray photoelectron (XP) spectrum of the nitrosyl-containing anion confirms the presence of two inequivalent platinum atoms whose 4f(7/2) binding energies are in the ranges expected for Pt(II) and Pt(III); an alternative interpretation is that the second platinum atom has a formal oxidation number of +4 and that its binding energy is modified by the strongly sigma-donating NO(-) ligand. Reduction of [Pt(2)(mu-pop)(4)X(2)](4-) (X = Cl, Br, I) in dichloromethane corresponds to a chemically reversible, electrochemically irreversible two-electron process involving loss of halide and formation of [Pt(2)(mu-pop)(4)](4-), as is the case in more strongly coordinating solvents.

ortho-Metallated complexes of platinum(II) and diplatinum(I) containing the carbanions (2-diphenylphosphino)phenyl and (2-diphenylphosphino)-n-tolyl (n = 5, 6).

When the ortho-metallated complexes cis-[Pt(kappa(2)-C6H3-5-R-2-PPh2)2] (R = H 1, Me 2) are either heated in toluene or treated with CO at room temperature, one of the four-membered chelate rings is opened irreversibly to give dinuclear isomers [Pt2(kappa(2)-C6H3-5-R-2-PPh2)2(mu-C6H3-5-R-2-PPh2)2] (R = H 10, Me 11). A single-crystal X-ray diffraction study shows the Pt...Pt separation in 10 to be 3.3875(4) A. By-products of the reactions of 1 and 2 with CO are polymeric isomers (R = H 13, Me 14) in which one of the P-C ligands is believed to bridge adjacent platinum atoms intermolecularly. In contrast to the behaviour of 1 and 2, when cis-[Pt(kappa(2)-C6H3-6-Me-2-PPh2)2] (cis-3) is heated in toluene, the main product is trans-3, and reaction of cis-3 with CO gives a carbonyl complex [Pt(CO)(kappa(1)-C-C6H3-6-Me-2-PPh2)(2-C6H3-6-Me-2-PPh2)] 15, in which one of the carbanions is coordinated only through the carbon. Formation of a dimer analogous to 10 or 11 is sterically hindered by the 6-methyl substituent. Comproportionation of 1 or 2 with [Pt(PPh3)2L] (L = PPh3, C2H4) gives diplatinum(I) complexes [Pt2(mu-C6H3-5-R-2-PPh2)2(PPh3)2] (R = H 16, Me 17). An X-ray diffraction study shows that 17 contains a pair of planar-coordinated metal atoms separated by 2.61762(16) A. There is no evidence for the formation of an analogue containing mu-C6H3-6-Me-2-PPh2. The axial PPh3 ligands of 16 are readily replaced by ButNC giving [Pt2(mu-2-C6H4PPh2)2(CNBut)2] 18, which is protonated by HBF4 to form a mu-hydridodiplatinum(II) salt [Pt2(mu-H)(mu-2-C6H4PPh2)2(CNBut)2]BF4 [21]BF4. The J(PtPt) values in [21]BF4 and 18, 2700 Hz and 4421 Hz, respectively, reflect the weakening of the Pt-Pt interaction caused by protonation. Similarly, 16 and 17 react with the electrophiles iodine and strong acids to give salts of general formula [Pt2(mu-Z)(mu-C6H3-5-R-2-PPh2)2(PPh3)2]Y (Y = Z = I, R = H 19+, Me 20+; Z = H, Y = BF4, PF6, OTf, R = H 22+; Z = H, Y = PF6, R = Me 23+). A single-crystal X-ray diffraction study of [23]PF6 shows that the cation has an approximately A-frame geometry, with a Pt-Pt separation of 2.7888(3) A and a Pt-H bond length of 1.62(1) A, and that the 5-methyl substituents have undergone partial exchange with the 4-hydrogen atoms of the PPh2 groups of the bridging carbanion. The latter observation indicates that the added proton of [23]+ undergoes a reversible reductive elimination-oxidative addition sequence with the Pt-C(aryl) bonds.

Synthesis, structures and reactions of cyclometallated gold complexes containing (2-diphenylarsino-n-methyl)phenyl (n = 5, 6).

Reaction of (C6H3-2-AsPh2-n-Me)Li (n = 5 or 6) with [AuBr(AsPh3)] at -78 degrees C gives the corresponding cyclometallated gold(I) complexes [Au2[(mu-C6H3-n-Me)AsPh2]2] [n = 5, (1); n = 6, (9)]. 1 undergoes oxidative addition with halogens and with dibenzoyl peroxide to give digold(II) complexes [Au2X2[(mu-C6H3-5-Me)AsPh2]2] [X = Cl (2a), Br (2b), I (2c) and O2CPh (3)] containing a metal-metal bond between the 5d9 metal centres. Reaction of 2a with AgO2CMe or of 3 with C6F5Li gives the corresponding digold(II) complexes in which X = O2CMe (4) and C6F5 (6), respectively. The Au-Au distances increase in the order 4 < 2a < 2b < 2c < 6, following the covalent binding tendency of the axial ligand. Like the analogous phosphine complexes, 2a-2c and 6 in solution rearrange to form C-C coupled digold(I) complexes [Au2X2[mu-2,2-Ph2As(5,5-Me2C6H3C6H3)AsPh2]] [X = Cl (5a), X = Br (5b), X = I (5c) and C6F5 (7)] in which the gold atoms are linearly coordinated by As and X. In contrast, the products of oxidative additions to 9 depend markedly on the halogens. Reaction of 9 with chlorine gives the gold(I)-gold(III) complex, [ClAu[mu-2-Ph2As(C6H3-6-Me)]AuCl[(6-MeC6H3)-2-AsPh2]-kappa2As,C] (10), which contains a four-membered chelate ring, Ph2As(C6H3-6-Me), in the coordination sphere of the gold(III) atom. When 10 is heated, the ring is cleaved, the product being the digold(I) complex [ClAu[mu-2-Ph2As(C6H3-6-Me)]Au[AsPh2(2-Cl-3-Me-C6H3)]] (11). Reaction of 9 with bromine at 50 degrees C gives a monobromo digold(I) complex (12), which is similar to 11 except that the 2-position of the substituted aromatic ring bears hydrogen instead halogen. Reaction of 9 with iodine gives a mixture of a free tertiary arsine, (2-I-3-MeC6H3)AsPh2 (13), a digold diiodo compound (14) analogous to 11, and a gold(I)-gold(III) zwitterionic complex [I2Au(III)[(mu-C6H3-2-AsPh2-6-Me)]2Au(I)] (15) in which the bridging units are arranged head-to-head between the metal atoms. The structures of 2a-2c and 4-15 have been determined by single-crystal X-ray diffraction analysis. The different behaviour of 1 and 9 toward halogens mirrors that of their phosphine analogues; the 6-methyl substituent blocks C-C coupling of the aryl residues in the initially formed oxidative addition product. In the case of 9, the greater lability of the Au-As bond in the initial oxidative addition product may account for the more complex behaviour of this system compared with that of its phosphine analogue.