Cationic gold(I) complexes have recently emerged as effective catalysts for the functionalization of C-C multiple bonds. 1 With few exceptions, mechanisms involving outersphere attack of a nucleophile on a transient cationic gold π-complex have been invoked for these transformations. 1 However, although gold π-complexes have been known for over 40 years, examples of the cationic, two-coordinate gold(I) π-complexes germane to π-activation catalysis are exceedingly rare and monomeric gold(I) π-alkene complexes are unknown. [2][3][4][5] Echvarren 6 and Bertrand 7 have reported the X-ray crystal structures cationic, two coordinate gold π-arene complexes. Sadighi 8 and Bertrand 7 have reported monomeric, cationic gold(I) π-alkyne complexes, but high-resolution X-ray analysis has not been reported. 9 Toste has reported the X-ray crystal structures of multimeric, cationic, two-coordinate gold(I) π-alkyne and π-alkene complexes; however, no evidence supports the integrity of the gold(I) π-alkene bond in solution. 10 Here we report the syntheses, X-ray crystal structures, and solution behavior of monomeric, cationic, two-coordinate gold π-alkene complexes.Treatment of a methylene chloride suspension of (IPr)AuCl [IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidine] and AgSbF 6 (1:1) with isobutylene at room temperature for 20 min led to isolation of [(IPr)Au(η 2 -H 2 C=CMe 2 )] + SbF 6 − (1a) in 98% yield as an air-and thermally-stable white solid that was characterized by NMR, MALDI-MS, combustion analysis, and X-ray crystallography (see below). Complexation of isobutylene to gold in solution was established by NMR, in particular by the large difference in the 13 C NMR shifts of the olefinic carbon atoms of bound [δ155.2 (s), 88.2 (t)] and free [δ142.4 (s), 110.5 (t)] isobutylene. The 1 J C=C coupling constant of the isobutylene ligand of the 13 C-isotopomer (IPr)Au(η 2 -H 2 13 C=CMe 2 ) (1a-13 C 1 ) ( 1 J C=C = 66 Hz) was diminished only slightly relative to free isobutylene ( 1 J C=C = 71 Hz), pointing to minimal deviation of the bound isobutylene from ideal sp 2 hydbridization. 11In addition to 1a, gold π-alkene complexes [(IPr)Au(η 2 -alkene)] + SbF 6 − [alkene = norbornene (1b), 2-methyl-2-butene (1c), methylenecyclohexane (1d), 2,3-dimethyl-2-butene (1e), cis-2-butene (1f), 1-hexene (1g), and 4-methylstyrene (1h)] were isolated in >80% yield and were fully characterized (Chart 1).Slow diffusion of hexane into a CH 2 Cl 2 solution of 1a at 4 °C gave colorless crystals of 1a·2CH 2 Cl 2 suitable for X-ray analysis ( Figure 1, Table 1). Complex 1a adopts a slightly distorted linear conformation with a C (carbene) -Au-alkene (centroid) angle of 172 °. The C=C bond of the isobutylene is rotated 52 degrees out of the carbene N-C-N plane, which positions E-mail: rwidenho@chem.duke.edu. Supporting Information Available: Experimental procedures, spectroscopic data, and X-ray crystallographic data. This material is available free of charge via the Internet at http://pubs.acs.org. one isobutylene methyl group near the car...

A number of cationic gold pi-alkene complexes of the form {[P(t-Bu)(2)o-biphenyl]Au(pi-alkene)}(+)SbF(6)(-) were isolated and three were analyzed by X-ray crystallography.

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A photosensitive caged copper complex has been prepared from a tetradentate ligand (H2cage) composed of two pyridyl-amide arms connected by a photoreactive nitrophenyl group. H2cage binds Cu2+ in aqueous solution with a stability constant (log beta) of 10.8, which corresponds to a KD of 16 pM at pH 7.4. The neutral Cu2+ complex, [Cu(OH2)(cage)], crystallizes as a distorted trigonal bipyramid coordinated by two amide and two pyridyl N atoms, with a water molecule bound in the trigonal plane. Photolysis with 350 nm UV light cleaves the ligand backbone to release photoproducts with significantly diminished affinity for Cu2+, thereby uncaging the metal ion. When coordinated as the caged complex, copper has diminished reactivity to produce hydroxyl radicals from Fenton-like reaction mixtures containing hydrogen peroxide and ascorbic acid. Postphotolysis, uncaged copper promotes hydroxyl radical formation under the same conditions. The strategy of caging copper is promising for applications where light could be used to trigger release of copper as a pro-oxidant to increase oxidative stress or as a tool to release copper intracellularly to study mechanisms of copper trafficking.

Summary: The cationic gold π-allene complex {[P(t-Bu) 2 obiphenyl ]Au[η 2 -H 2 CdCdC(CH 3 ) 2 ]} þ SbF 6 -was isolated in 98% yield from reaction of 3-methyl-1,2-butadiene with a mixture of [P(t-Bu) 2 o-biphenyl]AuCl and AgSbF 6 and was characterized by X-ray crystallography and variable-temperature NMR spectroscopy. These studies revealed preferential binding of gold to the less substituted CdC bond of the allene in both the solid state and solution and also revealed fluxional behavior consistent with π-face exchange of the allene ligand via an η 1 -C2 allene intermediate or transition state.Over the past 10 years considerable progress has been made in the utilization of soluble gold complexes, in particular cationic gold(I) complexes, as catalysts for the electrophilic activation of C-C multiple bonds. 1 Allenes have played a central role in the development of this chemistry, not only as substrates but also as intermediates and products. 1 Although it is widely assumed that gold π-allene complexes are generated as reactive intermediates in these transformations, no well-defined gold π-allene complex has been documented. 2 As such, information regarding the structure and behavior of gold π-allene complexes is limited to that provided by recent computational studies 3,4 or gleaned from related transition metal π-allene complexes [5][6][7][8][9][10] and gold π-complexes. 11,12 Here we report the synthesis, X-ray crystal structure, and fluxional behavior of a cationic, two-coordinate gold(I) π-allene complex.Reaction of 3-methyl-1,2-butadiene with a mixture of [P(t-Bu) 2 o-bipheny]AuCl (1) and AgSbF 6 (1:1) employing a procedure similar to that used for the synthesis of cationic gold(I) π-alkene complexes 12 (excess allene, room temperature, ∼12 h) led to formation of black suspensions that contained only traces of*To whom correspondence should be addressed. E-mail: rwidenho@ chem.duke.edu.(

Since clinically approved immunosuppressive drugs (e.g., cyclosporin A, FK506) possess dose-dependent biphasic effects that cause undesirable side effects on bone structure, including osteopenia, osteoporosis, and increased incidence of bone fractures, considerable effort has been devoted to the identification of immunosuppressive drugs that promote bone formation in a dose-dependent manner. Herein, we report the stereoselective synthesis of subglutinols A and B and present initial biological data showing the significant potential of subglutinol A as an immunosuppressive drug with dose-dependent osteogenic activity. We also show that activating protein 1 (AP-1) family transcription factors could be one of the key regulators for the anabolic activity of subglutinol A. Such drugs with dose-dependent osteogenic activity might help reduce bone-associated side effects and be clinically useful for bone tissue transplantation.

A novel platinum(II) photocaged complex called [Pt(cage)] has been prepared and characterized by X-ray crystallography. The complex contains a photolabile nitrophenyl group incorporated into the backbone of a tetradentate ligand that contains two pyridyl and two amide nitrogen donor sites. The intact complex is unreactive toward ligand-exchange reactions until activation with UV light cleaves the ligand backbone, releasing a Pt II complex that more readily exchanges

A fluorescent sensor prochelator, FlamB (fluorescein hydrizido 2-imidophenylboronic ester), has been developed that selectively probes for copper under conditions of oxidative stress. High levels of hydrogen peroxide trigger release of a boronic ester masking group from the prochelator to unveil a metal chelator, FlamS (fluorescein hydrizido 2-imidophenol), that provides a modest fluorescence increase in response to Cu2+ but not other metal ions. X-ray crystal structures of FlamB, FlamS, and Cu-bound FlamS are all reported. The fluorescence turn-on results from opening of a fluorescein spirolactam ring upon Cu2+ binding to FlamS in aqueous solution. Oxidation of the aryl boronic ester of FlamB to the metal-binding phenol of FlamS proceeds in organic solvents. However, in aqueous solution a competing mechanism occurs due to hydrolytic instability of the masked prochelator. Hydrolysis of FlamB leads to formation of fluorescein hydrazide, which interacts with copper or H2O2 to produce fluorescein and a significant fluorescence increase.