The first family of trigonal prismatic M(bidentate)<SUB>2</SUB>(monodentate)2 complexes: synthesis and characterization of halobis(2-amidothiophenolato)triphenylphosphinerhenium(V)

The 1:2 reaction of [Re<SUP>V</SUP>OCl<SUB>3</SUB>(PPh<SUB>3</SUB>)<SUB>2</SUB>] with 2-aminothiophenol (H<SUB>2</SUB>atp) in toluene has afforded red-brown [Re<SUP>V</SUP>(atp)<SUB>2</SUB>(Cl)(PPh<SUB>3</SUB>)]. The corresponding bromo and iodo complexes have been similarly obtained from [Re<SUP>V</SUP>O(OEt)Br<SUB>2</SUB>(PPh<SUB>3</SUB>)<SUB>2</SUB>] and [Re<SUP>V</SUP>O(OEt)I<SUB>2</SUB>(PPh<SUB>3</SUB>)<SUB>2</SUB>], respectively. The X-ray structure of the solvate [Re(atp)<SUB>2</SUB>(Cl)(PPh<SUB>3</SUB>)]&#183;2CH<SUB>2</SUB>Cl<SUB>2</SUB> has revealed trigonal prismatic geometry for the ReS<SUB>2</SUB>N<SUB>2</SUB>ClP coordination sphere in which the two triangular faces are defined by the S, S,P and N, N, Cl triads. The twist angle between them is 8.0&#176;. The [Re(atp)<SUB>2</SUB>(X)(PPh<SUB>3</SUB>)](X=Cl, Br, I) complexes are diamagnetic (Re<SUP>V</SUP>, spin-paired d<SUP>2</SUP>) and in acetonitrile solution these display a quasireversible Re<SUP>VI</SUP>-Re<SUP>V</SUP> response near 0.7 V. Reaction with H<SUB>2</SUB>atp in air converts [Re<SUP>V</SUP>(atp)<SUB>2</SUB>(X)(PPh<SUP>3</SUP>)] to the tris chelate [Re<SUP>VI</SUP>(atp)<SUB>3</SUB>]

Oxygen atom transfer from Re^vO to tertiary diphosphines: spacer length and chemical differentiation of products

The reaction of mer-[ReL(O)Cl3], [L = 2-(p-chlorophenylazo)-1-methylimidazole] with Ph2P(CH2)nPPh2 (abbreviated PnP) affords [ReL(OP1P)Cl3] 2a, [ReL(OP1PO)Cl3] 4 and [ReL(OP2P)Cl3] 2b, [Cl3LRe(OP2PO)ReLCl3] 5, all having mer geometry; unlike 2b which is stable in solution, 2a spontaneously isomerizes to fac-[ReL(P1PO)Cl3] via an associative pathway; the origin of the observed differentiation (2a vs. 2b and 4 vs. 5) is scrutinized in terms of structures and reaction models

Oxygen atom transfer from nitrogenous ReVO reagents to diphosphines and subsequent transformations. Rhenium(III) products and reaction models

The concerned diphosphines are Ph<SUB>2</SUB>P(CH<SUB>2</SUB>)<SUB>n</SUB>PPh<SUB>2</SUB> (1), abbreviated PnP, and the Re<SUP>V</SUP>O reagents are ReOCl<SUB>3</SUB>L (2) and ReOCl<SUB>3</SUB>L' (3), where L and L' are the azopyridine and pyridine-imine ligands p-ClC<SUB>6</SUB>H<SUB>4</SUB>NNC<SUB>5</SUB>H<SUB>4</SUB>N and p-MeC<SUB>6</SUB>H<SUB>4</SUB>NCHC<SUB>5</SUB>H<SUB>4</SUB>N, respectively. One atom transfer from 2 to 1 has afforded Re(OPnP)Cl<SUB>3</SUB>L (4a, n = 1; 4b, n = 2; 4c, n = 3). Of these 4b and 4c are stable, but 4a undergoes spontaneous isomerization to Re(PlPO)Cl3L (5) in solution. Two-atom transfer studied with both 2 and 3 has afforded binuclear LCl<SUB>3</SUB>Re(OPnPO)ReCl<SUB>3</SUB>L (8a, n = 2; 8b, n = 3) and L'Cl<SUB>3</SUB>Re(OPnPO)ReCl<SUB>3</SUB>L' (9a, n = 2; 9b, n = 3) for n = 2, 3 and mononuclear Re(OP1PO)Cl3L (11) and Re(OP1PO)Cl3L' (12) for n = 1. The mixed system L'Cl3Re(OP2PO)ReCl<SUB>3</SUB>L (10) has been prepared from 3 and 4b. The complex Re(PPh<SUB>3</SUB>)Cl<SUB>3</SUB>L (7a) is furnished by the reaction of Re(OPPh3)Cl<SUB>3</SUB>L (6a) or 4b or 11 with PPh<SUB>3</SUB>. The species have been characterized with the help of spectral, electrochemical, and X-ray structural data. All the complexes have mer geometry except 5 and 7a, which have fac geometry. The latter is best suited for concurrent Re-N and Re-P back-bonding. Variable-temperature rate data of the reaction 4a &#8594; 5 are consistent with an intramolecular strongly associative transition state (&#916;S++, -22.6 eu) in which the dangling phosphine function lies close to the metal. Two-atom transfer to P1P is believed to proceed via a transient binuclear intermediate which undergoes cleavage at one end due to steric crowding, affording 11 and 12. Crystal data for the complexes are as follows: 5&#183;1.5 C<SUB>6</SUB>H<SUB>6</SUB>, empirical formula C<SUB>45</SUB>H<SUB>39</SUB>Cl<SUB>4</SUB>N<SUB>3</SUB>OP<SUB>2</SUB>Re, crystal system triclinic, space group P, a = 10.034(2) &#197;, b = 10.737(2) &#197;, c = 20.357(4) &#197;, &#945;= 89.38(3)&#176;, &#946; = 87.79(3)&#176;, &#947;= 80.22(3)&#176;, V = 2159.7(7) A3, Z = 2; 7a&#183;CH<SUB>2</SUB>Cl<SUB>2</SUB>, empirical formula C<SUB>30</SUB>H<SUB>25</SUB>Cl<SUB>6</SUB>N<SUB>3</SUB>PRe, crystal system monoclinic, space group P21/n, a = 11.695(6) &#197;, b = 17.745(7) &#197;, c = 15.459(9) &#197;, &#946; = 100.94(5)&#176;, V = 3150(3) &#197;3, Z = 4; 9a, empirical formula C<SUB>52</SUB>H<SUB>48</SUB>Cl<SUB>6</SUB>N<SUB>4</SUB>O<SUB>2</SUB>P<SUB>2</SUB>Re<SUB>2</SUB>, crystal system monoclinic, space group C2/c, a = 19.769(12)&#197;, b = 12.864(6) &#197;, c = 22.20(2) &#197;, &#946; = 101.76(6)&#176;, V = 5530(6) &#197;3, Z = 4; 11, empirical formula C<SUB>36</SUB>H<SUB>30</SUB>Cl<SUB>4</SUB>N<SUB>3</SUB>O<SUB>2</SUB>P<SUB>2</SUB>Re, crystal system monoclinic, space group I2/a, a = 16.866(6) &#197;, b = 12.583(6) &#197;, c = 34.78(2) &#197;, &#946; = 99.22(4)&#176;, V = 7285(7) &#197;3, Z = 8

Synthesis, structure and redox behaviour of facial [Re^IIIL(PPh₃)Cl₃] and its stereoretentive conversion to [Re^IVL′(PPh₃)Cl₃] via metal promoted aldimine → amide oxidation (L = pyridine-2-aldimine; L′ = pyridine-2-carboxamide)

The reaction of mer-[Re^IIIL(OPPh₃)Cl₃] 2 with PPh₃ in benzene has afforded bluish violet fac-[Re^IIIL(PPh₃)Cl₃] 1, where L is the Schiff base of pyridine-2-carbaldehyde and the substituted aniline p-XC₆H₄NH₂ (X = H, Me, OMe or Cl). Geometrical preferences are rationalized in terms of the electronic nature of the ligands OPPh₃ (σ- and π-donor), PPh₃ (σ-donor and π-acceptor) and L (σ-donor and π-acceptor). The cyclic voltammetric E1/2 values of 1 lie near 0.6 V (Re^IV–Re^III) and –0.6 V (Re^III–Re^II). Electrooxidation of 1 at 1.0 V vs. SCE in wet acetonitrile affords yellow fac-[Re^IVL′(PPh₃)Cl₃] 3 which is also obtainable via oxidation by dilute nitric acid (L′ is a monoanionic pyridine-2-carboxamide). Complex 3 displays Re^IV–Re^III and Re^V–Re^IV couples near –0.2 V and 1.4 V respectively reflecting superior stabilization of the rhenium(IV) state by the amide ligand. The X-ray structures of two representative complexes of type 1 and 3 have revealed the presence of severely distorted and facially configured RePN₂Cl₃ coordination spheres. The average Re–Cl distance is lower by 0.06 Å in 3 due to contraction of the metal radius upon oxidation. The Re–P length is however larger by 0.1 Å in 3 signifying a weakening of Re–P back-bonding

Synthesis of Clinical-Grade [18F]-Fluoroestradiol as a Surrogate PET Biomarker for the Evaluation of Estrogen Receptor-Targeting Therapeutic Drug

16α-[18F]-fluoroestradiol ([18F]FES), a steroid-based positron emission tomography (PET) tracer, has emerged as a dependable tracer for the evaluation and management of estrogen receptor-positive (ER+) breast cancer patients. We have developed a fully automatic, one-pot procedure for the synthesis of [18F]FES using the Eckert & Ziegler (E & Z) radiomodular system. After [18F]fluorination, the intermediate was hydrolyzed with 2.0 M HCl twice and neutralized with sodium bicarbonate. After high-performance liquid chromatography (HPLC) purification, the decay-corrected radiochemical yield and purity of [18F]FES were 40 ± 5.0% (n=12) and >97%, respectively. The product was stable up to 10 h. Total synthesis time including HPLC purification was 80 min. This new, fully automated rapid synthetic procedure provided high and reproducible yields of [18F]FES. Quality control (QC) tests showed that the [18F]FES produced by this method met all specifications for human injection

Synthesis, structure and properties of [Re^VL(O)Cl₃], [Re^VL(NR)Cl₃], [Re^IIIL(OPPh₃)Cl₃], and [Re^IIIL(PPh₃)Cl₃] [L = 2-(arylazo)-1-methylimidazole, R = aryl] †

The reaction of KReO4 with L [2-(arylazo)-1-methylimidazole, with aryl = Ph (L1), C6H4Me-p(L2) or C6H4Cl-p(L3)] in concentrated HCl afforded [ReVL(O)Cl3] 1. Aromatic amines and PPh3 smoothly converted 1 into [ReVL(NR)Cl3] 2 and [ReIIIL(OPPh3)Cl3] 3 respectively. Treatment of 3 with PPh3 yielded [ReIIIL(PPh3)Cl3] 4. Complexes of type 3 and 4 display large paramagnetic shifts of 1H NMR lines which spread over ≈ 60 ppm. Structure determination of [ReL1(O)Cl3] 1a, [ReL2(NC6H4Me-p)Cl3] 2a, [ReL3(OPPh3)Cl3] 3c and [ReL3(PPh3)Cl3] 4c has revealed meridional geometry for all except 4c which is facial. In the latter Re–azo and Re–PPh3 back bonding is maximized. The metal atom is displaced away from the equatorial plane by ≈ 0.3 Å towards the oxo ligand in 1a and the imido ligand in 2a. The imidazole nitrogen is co-ordinated trans to oxo, imido, Ph3PO and chloride ligands in 1a, 2a, 3c and 4c, respectively. The azo N=N distance is lengthened by &#8805; 0.05 Å as a result of direct (3c, 4c) or indirect (1a, 2a) Re–azo back bonding. Azo reduction potential values are consistent with the low-lying nature of the azo(π*) orbital. The metal reduction potentials follow the trends: ReVI–ReV, 1 &#62; 2 (imido better donor than oxo); ReIV–ReIII, 4 &#62; 3 (stabilization of t2 by ReIII–PPh3 back bonding)

Pyridylazole chelation of oxorhenium(V) and imidorhenium(V). Rates and trends of oxygen atom transfer from ReVO to tertiary phosphines

The concerned azoles are 2-(2-pyridyl)benzoxazole (pbo) and 2-(2-pyridyl)benzthiazole (pbt). These react with ReOCl<SUB>3</SUB>(PPh<SUB>3</SUB>)<SUB>2</SUB> in benzene, affording ReVOCl<SUB>3</SUB>(pbo) and ReVOCl<SUB>3</SUB>(pbt), which undergo facile oxygen atom transfer to PPh<SUB>2</SUB>R (R = Ph, Me) in dichloromethane solution, furnishing Re<SUP>III</SUP>(OPPh<SUB>2</SUB>R)Cl<SUB>3</SUB>(pbo) and Re<SUP>III</SUP>(OPPh<SUB>2</SUB>R)Cl<SUB>3</SUB>(pbt). The oxo species react with aniline in toluene solution, yielding the imido complexes ReV(NPh)Cl<SUB>3</SUB>(pbo) and ReV(NPh)Cl<SUB>3</SUB>(pbt). The X-ray structures of pbt, ReOCl<SUB>3</SUB>(pbt), Re(OPPh<SUB>3</SUB>)Cl<SUB>3</SUB>(pbt), and Re(NPh)Cl<SUB>3</SUB>(pbo) are reported. The lattice of pbt consists of stacked dimers. In all the complexes the azole ligand is N,N-chelated and the ReCl<SUB>3</SUB> moiety is meridionally disposed. In ReOCl<SUB>3</SUB>(pbt) the metal-oxo bond length is 1.607(9) &#197;. The second-order rates and the associated activation parameters of the oxygen atom transfer reactions of the ReVO chelates with PPh<SUB>2</SUB>R are reported. The large and negative entropy of activation ( ~-24 eu) is consistent with an associative pathway involving nucleophilic phosphine attack. The rate increases with phosphine basicity (PPh<SUB>2</SUB>Me &gt; PPh<SUB>3</SUB>) and azole heteroatom electronegativity (O(pbo) &gt; S(pbt)). Logarithmic rate constants for ReOCl<SUB>3</SUB>(pbo), ReOCl<SUB>3</SUB>(pbt), and ReOCl<SUB>3</SUB>(pal) are found to correlate linearly with Re<SUP>VI</SUP>O/Re<SUP>V</SUP>O reduction potentials (pal is pyridine-2-(N-p-tolyl)aldimine). The relatively low rate constant of ReOCl<SUB>3</SUB>(pbt) compared to that of ReOCl<SUB>3</SUB>(pal) is consistent with the observed shortness of the metal-oxo bond in the former. Crystal data are as follows: (pbt) empirical formula C<SUB>12</SUB>H<SUB>8</SUB>N<SUB>2</SUB>S, crystal system orthorhombic, space group Pca2<SUB>1</SUB>, a = 13.762(9) &#197;, b = 12.952(8) &#197;, c = 11.077(4) &#197;, V = 1974(2) &#197;<SUP>3</SUP>, Z = 8; (ReOCl<SUB>3</SUB>(pbt)) empirical formula C<SUB>12</SUB>H<SUB>8</SUB>Cl<SUB>3</SUB>N<SUB>2</SUB>OSRe, crystal system monoclinic, space group P21/c, a = 11.174(7) &#197;, b = 16.403(10) &#197;, c = 7.751(2) &#197;, &#946; = 99.35(4)&#176;, V = 1401.8(13) &#197;<SUP>3</SUP>, Z = 4; (Re(NPh)Cl<SUB>3</SUB>(pbo)) empirical formula C<SUB>18</SUB>H<SUB>13</SUB>Cl<SUB>3</SUB>N<SUB>3</SUB>ORe, crystal system monoclinic, space group P2<SUB>1</SUB>/c, a = 9.566(6) &#197;, b = 16.082(8) &#197;, c = 11.841(5) &#197;, &#946; = 94.03(4)&#176;, V = 1817(2) &#197;<SUP>3</SUP>, Z = 4

Chemistry of the rhenium-azopyridine family: an oxo parent and derivatives thereof including a novel oxo-imido dimer

The concerned azo ligands are 2-(phenylazo)pyridine (HL) and 2-((p-chlorophenyl)azo)pyridine (ClL). The reaction of KReO<SUB>4</SUB> with HL in hot concentrated HCl is attended with metal reduction and ligand chlorination affording the oxo complex Re<SUP>V</SUP>OCl<SUB>3</SUB>(ClL), 2, which furnishes Re<SUP>III</SUP>(OPPh<SUB>3</SUB>)Cl<SUB>3</SUB>(ClL), 3, upon treatment with PPh<SUB>3</SUB>. Aromatic amines, ArNH<SUB>2</SUB>, convert 2 to the imido complex Re<SUP>V</SUP>(NAr)Cl<SUB>3</SUB>(ClL), 5, and the unusual oxo-imido dimer (ClL)Cl<SUB>2</SUB>(O)Re<SUP>V</SUP>ORe<SUP>V</SUP>(NAr)Cl<SUB>2</SUB>(ClL), 7. The complex Re<SUP>III</SUP>(OPPh<SUB>3</SUB>)Cl<SUB>3</SUB>(HL), 4, has been generated from Re<SUP>V</SUP>OCl<SUB>3</SUB>(PPh<SUB>3</SUB>)<SUB>2</SUB> and HL. Reaction of 4 with HL has yielded Re<SUP>V</SUP>(NPh)Cl<SUB>3</SUB>(HL), 6, via azo splitting. The complexes have been characterized with the help spectral, magnetic, and X-ray structural data (2, 3, 5c (Ar = pClC<SUB>6</SUB>H<SUB>4</SUB>) and 7·CH<SUB>2</SUB>Cl<SUB>2</SUB> (Ar = pMeC<SUB>6</SUB>H<SUB>4</SUB>)). In 2, 3, and 5c the ReCl<SUB>3</SUB> fragment is meridionally disposed, and in 7 the ReCl<SUB>2</SUB> fragments have a trans configuration. The Re-O(oxo) bond, 1.663(6) &#197;, in 2 and Re-N(imido) bond, 1.719(5) &#197;, in 5c are triple bonds. The corresponding bonds are slightly longer in 7 wherein the (O)Re(1)-O(2)-Re(2)(NAr) bridge is angular (151.0(5)&#176;) and unsymmetrical, the Re(1)-O(2) bond, 1.849(7) &#197;, having a large double-bond character (Re(2)-O(2), 1.954(7) &#197;). In effect, cis-ReVO<SUB>2</SUB> acts as a monodentate oxygen ligand toward ReVNAr in 7. In all cases the pyridine nitrogen binds trans to the oxo, OPPh<SUB>3</SUB>, or NAr donor. Bond length data are consistent with the presence of substantial d(Re)-p(azo) back-bonding. In acetonitrile solution the complexes display electrochemical one-electron metal (Re<SUP>VI</SUP>/Re<SUP>V</SUP> or Re<SUP>IV</SUP>/Re<SUP>III</SUP>) and azo redox. The imido ligand in 5 stabilizes the Re<SUP>VI</SUP> state (E<SUB>1/2</SUB> 1.4 V) better than the oxo ligand in 2 (1.9 V). Parallely it is more difficult to reduce the azo group in 5 (-0.4 V) than in 2 (0.0 V). In 7 the metal (1.0 V) and azo (-0.4 V) couples correspond to the imido and oxo halves, respectively. The significantly higher (by 0.2-0.6 V) metal reduction potentials of the azopyridine compared to pyridine-2-aldimine complexes is ascribed to the superior p-acidity and electron-withdrawing character of the azo function relative to the aldimine function. This also makes the transfer of the Re<SUP>V</SUP>O oxygen function much more facile under azopyridine chelation as in 2. For the same reason, ReOCl<SUB>3</SUB>(PPh<SUB>3</SUB>)<SUB>2</SUB> reacts with HL affording only 4 while it reacts with pyridine-2-aldimines furnishing oxo species. Crystal data for the complexes are as follows: 2, empirical formula C<SUB>11</SUB>H<SUB>8</SUB>Cl<SUB>4</SUB>N<SUB>3</SUB>ORe, crystal system triclinic, space group P&#8593;, &#945; = 7.118(4) &#197;, b = 8.537(4) &#197;, c = 13.231(9) &#197;, &#945; = 79.16(5)&#176;, &#946; = 78.03(5)&#176;, &#947; = 70.96(4)&#176;, V = 737.2(7) &#197;<SUP>3</SUP>, Z = 2; 3, empirical formula C<SUB>29</SUB>H<SUB>23</SUB>Cl<SUB>4</SUB>N<SUB>3</SUB>OPRe, crystal system monoclinic, space group P2<SUB>1</SUB>/n, a = 11.264(2) &#197;, b = 15.221(3) &#197;, c = 17.628(4) &#197;, &#946; = 94.21(3)&#176;, V = 3014(1) &#197;<SUP>3</SUP>, Z = 4; 5c, empirical formula C<SUB>17</SUB>H<SUB>12</SUB>C<SUB>l5</SUB>N<SUB>4</SUB>Re, crystal system triclinic, space group P, a = 9.683(3) &#197;, b = 10.898(3) &#197;, c = 11.522(3) &#197;, &#945; = 63.67(2)&#176;, &#946; = 71.24(2)&#176;, &#947; = 86.79(2)&#176;, V = 1026(1) &#197;<SUP>3</SUP>, Z = 2; 7·CH<SUB>2</SUB>Cl<SUB>2</SUB>, empirical formula C<SUB>30</SUB>H<SUB>25</SUB>Cl<SUB>8</SUB>N<SUB>7</SUB>O<SUB>2</SUB>Re<SUB>2</SUB>, crystal system triclinic, space group P, a = 12.522(6) &#197;, b = 12.857(8) &#197;, c = 13.182(7) &#197;, &#945; = 67.75(4)&#176;, &#946; = 88.30(4)&#176;, &#947; = 82.09(4)&#176;, V = 1945(2) A<SUP>3</SUP>, Z = 2

The first example of a binuclear rhenium(V) oxo-imido system

857-858The reaction of [ReV(O)Cl3(L)] with p-toluidine taken in equimolecular proportion in boiling toluene has afforded the title complex [(L)CI2(O)ReVOReV(NC6H4Me)CI2(L)] (L = 2-(p-chlorophenylazo)pyridine). Structure determination has revealed the presence of an unsymmetri cal oxo bridge (Re-O, 1.849(7) Å and 1.954(7) Å )interlinking ReVO and ReVNAr moieties