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The synthesis and characterization of polycarborane-substituted molecules [[Cp*Rh{[E.sub.2][C.sub.2]([B.sub.10][H.sub.10])}].sub.3](tpst) [E = S, Se] are described. Unconventional B[H.sup.[delta]-]-[pyridyl.sup.[delta]+] aromatic hydrogen bonding has enforced the bell-shapes of the molecular units and the Cp* conformations have induced the supramolecular structures.

The interaction of Re-complex with DNA fragment is studied using NMR spectroscopy.The resulting DNA modification makes Re-based complexes effective radiotherapeutic and chemotherapeutic agents.

The preparation of four complexes of the type [Re(guanine)2(X)(CO)3] is presented in order to understand the factors determining orientation of coordinated purine ligands around the [Re(CO)3](super +) core. The results show that guanine ligands can assume both head-to-head and head-to-tail conformation in an octahedral complex around the Re(I) tricarbonyl core.

The chemistry of [(tacn)-N-CO-Re[supIII](CO)[sub2]Br]X (X = Cl or Br), obtained in good yield from the reaction of fac-[(tacn) Re[supI](CO)[sub3]]Br (1, tacn = 1,4,7-triazacyclononane) with X[sub2] in water, is described. The [(tacn)-N-CO-Re[supIII](CO)[sub2]Br]X complex (2 with X = Br[sup-]; 2a with X = BrCl[sub2][sup-]), which we have previously communicated, is characterized by an unusual three-membered ring acyl amide bond. Complex 2 is stable as a solid but is reactive in aqueous solution. Under basic conditions (1 M NaOH), reductive decarbonylation was observed, and the bis-carbonyl complex [(tacn)Re[supI](CO)[sub2]Br] (3) was obtained in quantitative yield. The Br ligand in 3 could be replaced by CN, giving the neutral complex [(tacn) Re[supI](CO)[sub2](CN)] (4). In acidic media (1 M HBr), complex 2 partially converted to the monocarbonyl μ-oxo bridged dinuclear complex ([(tacn)Re°(CO)Br][sub2]O)[sup2+] (5 as [PF[sub6]][sup-] salt). Under mild oxidative conditions the trioxo [(tacn) Re[supVI]°O[sub3]](ReO[sub4][sup-]) (6) was formed almost quantitatively, and small amounts of the uncommon Re[supVI] complex [(tacn) Re[supVI]O[sub2]Br](ReO[sub4][sup-]] (7) were identified. Mechanistic investigations at the density functional level of theory (DFT) showed that the elementary steps in the formation of 2 from 1 and 3 from 2 involved reactions of the complexes with hydroxide. The calculated pathway is strongly exothermic (Ca. -137 kcal/mol), confirming the energetically and kinetically highly favored formation of 3. The X-ray structures of 2a and 3-5 are reported and discussed. [ABSTRACT FROM AUTHOR]

We have prepared four complexes of the type [Re(guanine)2(X)(CO)3] (guanine = 9-methylguanine or 7-methylguanine, X = H2O or Br) in order to understand the factors determining the orientation of coordinated purine ligands around the [Re(CO)3]+ core. The 9-methylguanine ligand (9-MEG) was chosen as the simplest N(9) derivatized guanine, and 7-methylguanine (7-MEG) was chosen because metal binding to N(9) does not impose steric hindrance. Two types of structures have been elucidated by X-ray crystallography, an HH (head-to-head) and HT (head-to-tail) conformer for each of the guanines. All complexes crystallize in monoclinic space groups: [Re(9-MeG)2(H2O)(CO)3]ClO4 (2) in P21n with a = 12.3307(10)Å β = 16.2620(14) Å, c = 13.7171(11) Å. and β = 105.525(9)°, V = 2650.2(4) ų, with the two bases in HT orientation and its conformer Re(9-MeG)2(H2O)(CO)3]Br (3) in P21/c with a = 15.626(13) Å, b = 9.5269(5) Å, c = 15.4078(13) Å, and/β = 76.951(1)°, V = 2234.5(3) ų, and the two bases in an HH orientation. Similarly, [Re(7-MeG)2(H2O)(CO)3]ClO4 (4) crystallizes in P21/c with a = 13.0708(9) Å, b = 15.4082(7) Å, c = 14.316(9) Å, and β = 117.236(7)°, V = 2563.5(3) ų, and exhibits an HT orientation and [ReBr(7-MeG)2(CO)3] (5) in P2/c with a = 17.5117(9) Å, b = 9.8842(7) Å, c = 15.3539(1) Å, and β = 100.824(7)°, V = 2610.3(3) ų, and shows an HH orientation. When crystals of any of these complex pairs are dissolved in D2O, the ¹H NMR spectrum shows a single peak for the H(8) resonance of the respective coordinated purine indicating a rapid equilibrium between HH and HT conformations in solution. DFT calculations simulating the rotation of one ligand around its Re-N bond showed energetic barriers of less than 8.7 kcal/mol. We find no hypochromic effect in the Raman spectrum of 3, which showed base stacking in the solid state. Neither steric interactions nor hydrogen bonding are important in determining the orientation of the ligands in the coordination sphere. [ABSTRACT FROM AUTHOR]

Insights into the interaction of the [Re(H2O)3(CO)3]+ complex (1) with the DNA fragment d(CpGpG) have been obtained by one-(1D) and two-dimensional (2D) NMR spectroscopy. The H8 resonances of the single major [Re(H2O)d(CpGpG)(CO)3] adduct (2) exhibit pH-independent chemical shift changes attributable to metal N7 binding. The structure of this adduct has been characterized by molecular modeling studies based on 1 D and 2D NMR data. In solution, 2 shows the presence of two N7-coordinated guanine moieties in a head-to-head (HH) odentation as evidenced by G2H8/G3H8 cross-peaks in the ¹H-¹H NOESY NMR spectrum. The presence of the 5′-bridging phosphodiester appears to stabilize the HH1 L conformer, as was previously described for related Pt and Rh complexes. [ABSTRACT FROM AUTHOR]

We report the synthesis, characterization, and in vitro biological activities of [Re(η 6 -arene) 2 ] + -terpyridine conjugates and their Cu II complexes. The terpyridine (terpy) chelators were attached to the [Re(η 6 -arene) 2 ] + scaffold via secondary amine linkers allowing for heteroleptic mono- and homoleptic bis-terpyridine-substituted chelators. Complexation with CuCl 2 afforded the respective square pyramidal [Cu(terpy)Cl 2 ] complexes hosted on the [Re(η 6 -arene) 2 ] + scaffold. The chelator conjugates and their respective complexes were found to be remarkably cytotoxic against malignant HT29 and A549 human cancer cell lines in vitro with IC 50 values in the low micromolar range. Mitochondrial respiration disruption was identified as a possible mode of action of these novel drug candidates. Crucially, the [Re(η 6 -arene) 2 ] + hosts delivered water solubility of the otherwise insoluble [Cu(terpy)Cl 2 ] motif. Importantly, the homoleptic [ 99m Tc(η 6 -arene) 2 ] + -terpyridine conjugate is available in a single step, which enables the presented system to be used as a theranostic approach to modern medicinal inorganic chemistry.

Here, we present the light-driven reactions of [Re(η 7 -C 7 H 7 )(η 5 -C 7 H 9 )] + ( 1 + ) with nitriles, phosphines, and isocyanides, which are added to 1 + via a ring slippage of the tropylium cation from η 7 to η 3 , forming [Re(η 3 -C 7 H 7 )(η 5 -C 7 H 9 )(L) 2 ] + (L= acetonitrile 2 + ; 2-phenylacetonitrile 3 + ; 1,3,5-triaza-5-phosphoadamantane (PTA) 4 + ; tert -butyl isocyanide 6 + ; benzyl isocyanide 7 + ) and [Re(η 3 -C 7 H 7 )(η 5 -C 7 H 9 )(L)] + with L = (ethane-1,2-diyl)bis(diphenylphosphane) (dppe) 5 + . To compare the reactivities of rhenium and technetium, we also investigated the synthesis of [ 99 Tc(η 6 -C 10 H 8 ) 2 ] + , its substitution of naphthalene with cyclohepta-1,3,5-triene to obtain [ 99 Tc(η 7 -C 7 H 7 )(η 5 -C 7 H 9 )] + , and its reactivity (or lack thereof) with light.

Thermal treatment of the Re III hydride complex [ReH(η 5 -C 6 H 7 )(η 6 -C 6 H 6 )] + in CH 3 CN results in the formation of [Re(η 6 -C 6 H 6 )(NCCH 3 ) 3 ] + . This semi-solvated complex is remarkably stable under an ambient atmosphere and exhibits a fast CH 3 CN self-exchange, which facilitates substitution reactions. The CH 3 CN ligands are replaced by σ-donating phosphines such as trimethyl phosphine (PMe 3 ), triphenyl phosphine (PPh 3 ), or the bidentate 1,2-bis(diphenylphosphino)ethane (dppe) to afford [Re(η 6 -C 6 H 6 )(NCCH 3 ) 3- x (PR 3 ) x ] + (if R = Me, then x = 2; if R = Ph, then x = 1 or 2) or [Re(η 6 -C 6 H 6 )(dppe)(NCCH 3 )] + , respectively. [Re(η 6 -C 6 H 6 )(NCCH 3 ) 3 ] + also reacts with π-acceptors such as 2,2'-bipyridine (bipy), 1,10-phenanthroline (phen), or CO (1 atm) to give [Re(η 6 -C 6 H 6 )(L)(NCCH 3 )] + (L = bipy or phen) and [Re(η 6 -C 6 H 6 )(CO)(NCCH 3 ) 2 ] + , respectively. The latter does not show any signs of decomposition after being exposed to an ambient atmosphere for multiple days. Additionally, [Re(η 6 -C 6 H 6 )(NCCH 3 ) 3 ] + reacts with π-donors such as the dienes 2,3-dimethyl-1,3-butadiene (DMBD), norbornadiene (NBD), or 1,5-cyclooctadiene (COD) to give [Re(η 6 -C 6 H 6 )(η 4 -diene)(NCCH 3 )] + (diene = DMBD, NBD, and COD). All three complexes are extremely stable and do not decompose during purification by preparative high-performance liquid chromatography (aqueous acidic gradient). In the presence of 18-crown-6, [Re(η 6 -C 6 H 6 )(NCCH 3 ) 3 ] + reacts with lithium cyclopentadienyl to give the sandwich complex [Re(η 5 -C 5 H 5 )(η 6 -C 6 H 6 )]. Loss of the coordinated benzene was observed when treating [Re(η 6 -C 6 H 6 )(NCCH 3 ) 3 ] + with diphenylacetylene (PhC≡CPh), yielding the tetra-coordinated [Re(NCCH 3 )(η 2 -PhC≡CPh) 3 ] + .

Arene substitution reactions in [M(η 6 -arene) 2 ] 0/2+ are well documented for Groups 6 and 8 but are essentially unknown for the manganese triad. Aiming to replace benzene in [Re I (η 6 -C 6 H 6 ) 2 ] + , we altered the hapticity of one coordinated benzene, which we found to be tunable stepwise from an η 6 to an η 3 -allyl coordination mode. Reduction of [Re I (η 6 -C 6 H 6 ) 2 ] + with hydrides gives [Re I (η 5 -C 6 H 7 )(η 6 -C 6 H 6 )]. Subsequent addition of acid yields [Re III H(η 5 -C 6 H 7 )(η 6 -C 6 H 6 )] + , which converts to [Re I (η 4 -C 6 H 8 )(η 6 -C 6 H 6 )NCCH 3 ] + in acetonitrile. Further protonation gives the title complex [Re III (η 3 -C 6 H 9 )(η 6 -C 6 H 6 )(NCCH 3 ) 2 ] 2+ by a rhenium-mediated, intramolecular hydride shift. Herein, we present a full mechanistic elucidation of these transformations based on NMR studies, isolation of reaction intermediates, and their full characterizations. The structural feature {Re III (η 6 -C 6 H 6 )} is unprecedented. Direct arene exchange from [Re I (η 6 -C 6 H 6 ) 2 ] + to [Re I (η 6 -arene)(η 6 -C 6 H 6 )] + was found only under strongly acidic conditions in neat arene. The analogous chemistry of the lighter homologue technetium ( 99 Tc) is distinctly different. Treatment of [Tc I (η 5 -C 6 H 7 )(η 6 -C 6 H 6 )] with acid in acetonitrile yields only mixtures of [Tc I (η 6 -C 6 H 6 ) 2 ] + and [Tc II (NCCH 3 ) 6 ] 2+ .

The oxidation of [Re(η 6 -C 10 H 8 ) 2 ] + with Ag I in acetonitrile yields [Re(NCCH 3 ) 6 ] 2+ . This fully solvated Re II compound was characterized by spectroscopic methods and X-ray structure analyses. We show that [Re(NCCH 3 ) 6 ] 2+ acts as a precursor complex for a variety of substitution reactions. Treatment with monodentate triphenylphosphine (PPh 3 ) and bidentate 1,2-bis(diphenylphosphino)ethane (dppe) yields the complexes [ trans -Re(PPh 3 ) 2 (NCCH 3 ) 4 ] 2+ and [ trans -Re(dppe) 2 (NCCH 3 ) 2 ] + , respectively. [ trans -Re(dppe) 2 (NCCH 3 ) 2 ] + is oxidized under mild conditions by Ag I to its Re II analogue [ trans -Re(dppe) 2 (NCCH 3 ) 2 ] 2+ . Reactions of [Re(NCCH 3 ) 6 ] 2+ with a halide mixture consisting of NaX and AgX (X = Cl, I) result in the formation of the corresponding Re III complexes [ trans -ReX 2 (NCCH 3 ) 4 ] + . [ trans -ReBr 2 (NCCH 3 ) 4 ] + can be obtained directly from [Re(η 6 -C 10 H 8 ) 2 ] + by oxidation with FeBr 3 in acetonitrile. The title compound is thus a convenient starting material for Re II and Re III complexes by simple solvent exchange, which are otherwise difficult to access.

Polycarborane-substituted molecules [Cp*Rh{E 2C 2(B 10H 10)}] 3(tpst) [E = S ( 2a), Se ( 2b)] were synthesized and characterized. 2a and 2b form toluene solvates in the solid state showing infinitely connected [( 2a, b)-(toluene)] infinity helices. The chains of these supramolecules are held together by Cp*-toluene-Cp* pi-stacking interactions of two of the three Cp* ligands of the bell-shaped 2a and 2b molecules. Unconventional BH (delta-)-pyridyl (delta+) aromatic hydrogen bonding enforces the bell-shapes of the molecular units, and the Cp* conformations are expected to induce the supramolecular structures.