Triply Bonded Pancake π-Dimers Stabilized by Tetravalent Actinides.

Aromatic π-stacking is a weakly attractive, noncovalent interaction often found in biological macromolecules and synthetic supramolecular chemistry. The weak nondirectional nature of π-stacking can present challenges in the design of materials owing to their weak, nondirectional nature. However, when aromatic π-systems contain an unpaired electron, stronger attraction involving face-to-face π-orbital overlap is possible, resulting in covalent so-called "pancake" bonds. Two-electron, multicenter single pancake bonds are well known, whereas four-electron double pancake bonds are rare. Higher-order pancake bonds have been predicted, but experimental systems are unknown. Here, we show that six-electron triple pancake bonds can be synthesized by a 3-fold reduction of hexaazatrinaphthylene (HAN) and subsequent stacking of the [HAN]3- triradicals. Our analysis reveals a multicenter covalent triple pancake bond consisting of a σ-orbital and two equivalent π-orbitals. An electrostatic stabilizing role is established for the tetravalent thorium and uranium ions in these systems. We also show that the electronic absorption spectrum of the triple pancake bonds closely matches computational predictions, providing experimental verification of these unique interactions. The discovery of conductivity in thin films of triply bonded π-dimers presents new opportunities for the discovery of single-component molecular conductors and other spin-based molecular materials.

A CoII-Hydroxide Complex That Converts Directly to a CoII-Acetamide during Catalytic Nitrile Hydration.

In exploring structural and functional mimics of nitrile hydratases, we report the synthesis of the pseudo-trigonal bipyramidal CoII complexes (K)[CoII(DMF)(LPh)] (1(DMF)), (NMe4)2[CoII(OAc)(LPh)] (1(OAc)), and (NMe4)2[CoII(OH)(LPh)] (1(OH)) (LPh = 2,2',2''-nitrilo-tris-(N-phenylacetamide; DMF = N,N-dimethylformamide; -OAc = acetate)). The complexes were characterized using NMR, FT-IR, ESI-MS, electronic absorption spectroscopy, and X-ray crystallography, showing the LPh ligand to bind in a tetradentate tripodal fashion alongside the respective ancillary donor. One of the complexes, 1(OH), is an unusual structural and functional mimic of the Co active site in Co nitrile hydratases. 1(OH) reacted with acetonitrile to yield the CoII-acetamide complex (NMe4)2[CoII(NHC(O)CH3)(LPh)], 2, which was also thoroughly characterized. In the presence of excess hydroxide, 1(OH) was found to catalyze quantitative conversion of the added hydroxide into acetamide. Despite the differences in Co oxidation state in nitrile hydratases and 1(OH) (CoIII versus CoII, respectively), 1(OH) was nonetheless an effective nitrile hydration catalyst, selectively producing acetamide over multiple turnovers.

Fate of Oxidation States at Actinide Centers in Redox-Active Ligand Systems Governed by Energy Levels of 5 f Orbitals.

We report the formation of a NpIV complex from the complexation of NpVI O2 2+ with the redox-active ligand tBu-pdiop2- =2,6-bis[N-(3,5-di-tert-butyl-2-hydroxyphenyl)iminomethyl]pyridine. To the best of our knowledge, this is the first example of the direct complexation-induced chemical reduction of NpVI O2 2+ to NpIV . In contrast, the complexation of UVI O2 2+ with tBu-pdiop2- did not induce the reduction of UVI O2 2+ , not even after the two-electron electrochemical reduction of [UVI O2 (tBu-pdiop)]. This contrast between the Np and U systems may be ascribed to the decrease of the energy of the 5 f orbitals in Np compared to those in U. The present findings indicate that the redox chemistry between UVI O2 2+ and NpVI O2 2+ should be clearly differentiated in redox-active ligand systems.

Synthesis and Characterization of a Masked Terminal Nickel-Oxide Complex.

In exploring terminal nickel-oxo complexes, postulated to be the active oxidant in natural and non-natural oxidation reactions, we report the synthesis of the pseudo-trigonal bipyramidal NiII complexes (K)[NiII (LPh )(DMF)] (1[DMF]) and (NMe4 )2 [NiII (LPh )(OAc)] (1[OAc]) (LPh =2,2',2''-nitrilo-tris-(N-phenylacetamide); DMF=N,N-dimethylformamide; - OAc=acetate). Both complexes were characterized using NMR, FTIR, ESI-MS, and X-ray crystallography, showing the LPh ligand to bind in a tetradentate fashion, together with an ancillary donor. The reaction of 1[OAc] with peroxyphenyl acetic acid (PPAA) resulted in the formation of [(LPh )NiIII -O-H⋅⋅⋅OAc]2- , 2, that displays many of the characteristics of a terminal Ni=O species. 2 was characterized by UV-Vis, EPR, and XAS spectroscopies and ESI-MS. 2 decayed to yield a NiII -phenolate complex 3 (through aromatic electrophilic substitution) that was characterized by NMR, FTIR, ESI-MS, and X-ray crystallography. 2 was capable of hydroxylation of hydrocarbons and epoxidation of olefins, as well as oxygen atom transfer oxidation of phosphines at exceptional rates. While the oxo-wall remains standing, this complex represents an excellent example of a masked metal-oxide that displays all of the properties expected of the ever elusive terminal M=O beyond the oxo-wall.

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.

Ge-Cu-Complexes Ph(pyO)Ge(µ2-pyO)2CuCl and PhGe(µ2-pyO)4CuCl-Representatives of Cu(I)→Ge(IV) and Cu(II)→Ge(IV) Dative Bond Systems.

Phenylgermaniumpyridine-2-olate PhGe(pyO)3 (compound 1Ge) and CuCl react with the formation of the heteronuclear complex Ph(pyO)Ge(µ2-pyO)2CuCl (2Ge') rather than forming the expected compound PhGe(µ2-pyO)3CuCl (2Ge). Single-point calculations (at the B2T-PLYP level) of the optimized molecular structures confirmed the relative stability of isomer 2Ge' over 2Ge and, for the related silicon congeners, the relative stability of 2Si over 2Si'. Decomposition of a solution of 2Ge' upon access to air provided access to some crystals of the copper(II) compound PhGe(µ2-pyO)4CuCl (3Ge). Compounds 2Ge' and 3Ge were characterized by single-crystal X-ray diffraction analyses, and the Ge-Cu bonds in these compounds were analyzed with the aid of quantum chemical calculations, e.g., Natural Bond Orbital analyses (NBO), Non-Covalent Interactions descriptor (NCI), and topology of the electron density at bond critical point using Quantum Theory of Atoms-In-Molecules (QTAIM) in conjunction with the related silicon compounds PhSi(µ2-pyO)3CuCl (2Si), PhSi(µ2-pyO)4CuCl (3Si), as well as the potential isomers Ph(pyO)Si(µ2-pyO)2CuCl (2Si') and PhGe(µ2-pyO)3CuCl (2Ge). Pronounced Cu→Ge (over Cu→Si) lone pair donation was found for the Cu(I) compounds, whereas in Cu(II) compounds 3Si and 3Ge, this σ-donation is less pronounced and only marginally enhanced in 3Ge over 3Si.

Lewis Acid-Base Adducts of α-Amino Acid-Derived Silaheterocycles and N-Methylimidazole.

In chloroform solution, the reaction of bis(tert-butylamino)dimethylsilane ((tBuNH)2SiMe2) and an α-amino acid (α-amino isobutyric acid, H2Aib; D-phenylglycine, H2Phg; L-valine, H2Val) in the presence of N-methylimidazole (NMI) gave rise to the formation of the pentacoordinate silicon complexes (Aib)SiMe2-NMI, (Phg)SiMe2-NMI and (Val)SiMe2-NMI, respectively. Therein, the amino acid building block was a di-anionic bidentate chelator at the silicon atom. In solution, the complexes were involved in rapid coordination-dissociation equilibria between the pentacoordinate Si complex (e.g., (Aib)SiMe2-NMI) and its constituents NMI and a five-membered silaheterocycle (e.g., (Aib)SiMe2), as shown by 29Si NMR spectroscopy. The energetics of the Lewis acid-base adduct formation and the competing solvation of the NMI molecule by chloroform were assessed with the aid of computational methods. In CDCl3 solution, deuteration of the silaheterocycle NH group proceeded rapidly, with more than 50% conversion within two days. Upon cooling to -44 °C, the chloroform solvates of the adducts (Aib)SiMe2-NMI and (Phg)SiMe2-NMI crystallized from their parent solutions and allowed for their single-crystal X-ray diffraction analyses. In both cases, the Si atom was situated in a distorted trigonal bipyramidal coordination sphere with equatorial Si-C bonds and an equatorial Si-N bond (the one of the silaheterocycle). The axial positions were occupied by a carboxylate O atom of the silaheterocycle and the NMI ligand's donor-N-atom.

P-Ru-Complexes with a Chelate-Bridge-Switch: A Comparison of 2-Picolyl and 2-Pyridyloxy Moieties as Bridging Ligands.

Starting from [Ru(pyO)2(nbd)] 1 and a N,P,N-tridentate ligand (2a: PhP(pic)2, 2b: PhP(pyO)2) (nbd = 2,5-norbornadiene, pic = 2-picolyl = 2-pyridylmethyl, pyO = 2-pyridyloxy = pyridine-2-olate), the compounds [PhP(µ-pic)2(µ-pyO)Ru(κ2-pyO)] (3a) and [PhP(µ-pyO)3Ru(κ2-pyO)] (3b), respectively, were prepared. Reaction of compounds 3 with CO and CNtBu afforded the opening of the Ru(κ2-pyO) chelate motif with the formation of compounds [PhP(µ-pic)2(µ-pyO)Ru(κ-O-pyO)(CO)] (4a), [PhP(µ-pic)2(µ-pyO)2Ru(CNtBu)] (5a), [PhP(µ-pyO)4Ru(CO)] (4b) and [PhP(µ-pyO)4Ru(CNtBu)] (5b). In dichloromethane solution, 4a underwent a reaction with the solvent, i.e., substitution of the dangling pyO ligand by chloride with the formation of [PhP(µ-pic)2(µ-pyO)Ru(Cl)(CO)] (6a). The new complexes 3a, 4a, 5a, 5b and 6a were characterized by single-crystal X-ray diffraction analyses and multi-nuclear (1H, 13C, 31P) NMR spectroscopy. The different coordination behaviors of related pairs of molecules (i.e., pairs of 3, 4 and 5), which depend on the nature of the P-Ru-bridging ligand moieties (µ-pic vs. µ-pyO), were also studied via computational analyses using QTAIM (quantum theory of atoms in molecules) and NBO (natural bond orbital) approaches, as well as the NCI (non-covalent interactions descriptor) for weak intramolecular interactions.

Coordination and Electrochemical Switching on Paddle-Wheel Complexes Containing an As-Ru or a Sb-Ru Axis.

Inspired by the known complex [PhP(µ-PyO)4Ru(CO)] (PyO = 2-pyridyloxy), the family of group 15 paddle-wheel complexes has been expanded to [PhPn(µ-PyO)4Ru(L)] (Pn = P, As, Sb; L = NCMe, CO). Solvent-dependent reversible switching between [PhAs(µ-PyO)4Ru(NCMe)] and [PhAs(µ-PyO)3Ru(κ2-PyO)] was detected. Electrochemical investigations of the [PhPn(µ-PyO)4Ru(L)] complexes showed reversible oxidation of the complexes with L = NCMe and back-formation of the complexes with L = NCMe upon oxidation of the complexes with L = CO in NCMe. In the series of [PhPn(µ-PyO)4Ru(L)] complexes, the Pn→Ru bonding mode is shifted from L-type Pn to X-type upon going from Pn = P and As to Pn = Sb, resulting in a pronounced electron-rich Ru site in the latter case. The easily accessible complex [PhSb(µ-PyO)4RuCl] exhibits reversible electrochemical and coordinative exchange with its reduced analogue [PhSb(µ-PyO)4Ru(NCMe)] under retention of the paddle-wheel motif and Sb-Ru bond properties.

Comparing Metal-Halide and -Oxygen Adducts in Oxidative C/O-H Activation: AuIII-Cl versus AuIII-OH.

High-valent metal-halides have come to prominence as highly effective oxidants. A direct comparison of their efficacy against that of traditional metal-oxygen adducts is needed. [AuIII(Cl)(terpy)](ClO4)2 (1; terpy = 2,2':6',2-terpyridine) readily oxidized substrates bearing O-H and C-H bonds via a hydrogen atom transfer mechanism. A direct comparison with [AuIII(OH)(terpy)](ClO4)2 (2) showed that 1 was a kinetically superior oxidant with respect to 2 for all substrates tested. We ascribe this to the greater thermodynamic driving force imbued by the Cl ligand versus the OH ligand.

Rapid Iron(III)-Fluoride-Mediated Hydrogen Atom Transfer.

We anticipate high-valent metal-fluoride species will be highly effective hydrogen atom transfer (HAT) oxidants because of the magnitude of the H-F bond (in the product) that drives HAT oxidation. We prepared a dimeric FeIII (F)-F-FeIII (F) complex (1) by reacting [FeII (NCCH3 )2 (TPA)](ClO4 )2 (TPA=tris(2-pyridylmethyl)amine) with difluoro(phenyl)-λ3 -iodane (difluoroiodobenzene). 1 was a sluggish oxidant, however, it was readily activated by reaction with Lewis or Brønsted acids to yield a monomeric [FeIII (TPA)(F)(X)]+ complex (2) where X=F/OTf. 1 and 2 were characterized using NMR, EPR, UV/Vis, and FT-IR spectroscopies and mass spectrometry. 2 was a remarkably reactive FeIII reagent for oxidative C-H activation, demonstrating reaction rates for hydrocarbon HAT comparable to the most reactive FeIII and FeIV oxidants.

Ruthenium Complexes of Stibino Derivatives of Carboxylic Amides: Synthesis and Characterization of Bidentate Sb,E, Tridentate Sb,E2, and Tetradentate Sb,E3 (E = N and O) Ligands and Their Reactivity Toward [RuCl2(PPh3)3].

Neutral bi-, tri-, and tetradentate ligands of the type Ph3-xSb(L)x [x = 1 (1), 2 (2), and 3 (3). L = La = phthalimidinyl (1a, 2a, and 3a), Lb = 2-pyridyloxy (1b, 2b, and 3b)] have been synthesized and characterized. Reaction of the Sb,E and Sb,E2 ligands with [RuCl2(PPh3)3] proceeded under anion scrambling with formation of complexes of type [Ph2Sb(µ-L)2Ru(PPh3)(µ-Cl)]2 (5) or [PhSb(µ-L)3RuCl(PPh3)] (8) in addition to various byproducts. Reactions of the Sb,E3 ligands and [RuCl2(PPh3)3] afforded highly diverse product mixtures. Deliberate syntheses of complexes of types 5 and 8 were successful by supplementing the reaction mixture with the required stoichiometric amount of either HLa or HLb and a supporting base. The Sb-Ru bonds, which are bridged by two (type 5) or three (type 8) phthalimidinyl or 2-pyridyloxy ligands, have been investigated using quantum chemical calculations at the DFT level (NBO/NLMO and AIM). Treatment of complexes of type 8 with fluoride ions resulted in the formation of compounds of type [PhFSb(µ-La)3RuL'(PPh3)] (L' = O2 (9a-O2), NCMe (9a-NCMe), or [PhFSb(µ-Lb)2Ru(κ2-Lb)(PPh3)] (10b)). In contrast to other similar bimetallic Sb-TM complexes (TM = transition metal), which may switch the rather dative intermetallic bond from Sb→TM to Sb←TM upon replacing TM bound chloride by Sb-bound fluoride, the character of the Sb→Ru bond is essentially retained upon going from chloro complex 5 or 8 to fluoro complex 9 or 10. Charge discrepancies caused by anion transfer from Ru to Sb are mainly compensated for by charge flow along the ligand backbone. All isolated complexes were characterized with multinuclear NMR spectroscopy, single-crystal X-ray diffraction, elemental analysis, and quantum chemical calculations.

Oxo-Free Hydrocarbon Oxidation by an Iron(III)-Isoporphyrin Complex.

Metal-halides that perform proton coupled electron-transfer (PCET) oxidation are an important new class of high-valent oxidant. In investigating metal-dihalides, we reacted [FeIII(Cl)(T(OMe)PP)] (1, T(OMe)PP = meso-tetra(4-methoxyphenyl)porphyrinyl) with (dichloroiodo)benzene. An FeIII-meso-chloro-isoporphyrin complex [FeIII(Cl)2(T(OMe)PP-Cl)] (2) was obtained. 2 was characterized by electronic absorption, 1H NMR, EPR, and X-ray absorption spectroscopies and mass spectrometry with support from computational analyses. 2 was reacted with a series of hydrocarbon substrates. The measured kinetic data exhibited a nonlinear behavior, whereby the oxidation followed a hydrogen-atom-transfer (HAT) PCET mechanism. The meso-chlorine atom was identified as the HAT agent. In one case, a halogenated product was identified by mass spectrometry. Our findings demonstrate that oxo-free hydrocarbon oxidation with heme systems is possible and show the potential for iron-dihalides in oxidative hydrocarbon halogenation.

Trivalent Antimony as L-, X-, and Z-Type Ligand: The Full Set of Possible Coordination Modes in Pt-Sb Bonds.

In the course of our investigations of the coordination chemistry of trivalent antimony (Sb) compounds, we studied heteronuclear complexes formed in reactions of the compounds RSb(pyS)2 (R = pyS, Ph; pyS- = pyridine-2-thiolate) with [Pt(PPh3)4], i.e., complexes [(R)Sb(µ-pyS)2Pt(PPh3)] (R = pyS, 1; R = Ph, 2). The reaction of 1 with o-chloranil proceeds cleanly with elimination of 2,2'-dipyridyl disulfide and formation of the salt [(PPh3)Pt(µ-pyS)2Sb(µ-pyS)2Pt(PPh3)]+[Sb(C6Cl4O2)2]- (3III), which features the cation 3+. The charge-neutral, unsymmetrically substituted compound [(PPh3)Pt(µ-pyS)2Sb(µ-pyS)2Pt(κS-pyS)] (4) can be accessed by the reaction of 3+ with LipyS. The oxidation of 2 with o-chloranil furnishes the complex [(κ-O,O-C6Cl4O2)PhSb(µ-pyS)2Pt(PPh3)] (5). The oxidation of 1 with PhICl2 afforded the paddlewheel-shaped complex [Sb(µ-pyS)4PtCl] (6). Moreover, compound 6 was obtained by the reaction of Sb(pyS)3 with [PtCl(pyS)(PPh3)]. The polarization of Pt-Sb bonds of compounds 1-6 was investigated by natural localized molecular orbital (NLMO) calculations, which suggest X-type ligand character (covalent Pt-Sb bonds) for 1 and 2, whereas the Sb ligand of 6 reflects Z-type character (dative Pt→Sb bonds). In 3+, 4, and 5, high contributions of the reverse, i.e., L-type (dative Pt←Sb bonds), were observed. In conjunction with the results of NLMO analyses, 121Sb Mössbauer spectroscopy proves that complexes 1-6 represent essentially trivalent Sb complexes with either a free lone pair (LP) at the Sb atom (1, 2, and 6) or LP character involved in L-type Pt←Sb coordination (3+, 4, and 5).

Preparation and Characterisation of a Bis-µ-Hydroxo-NiIII 2 Complex.

Hydroxide-bridged high-valent oxidants have been implicated as the active oxidants in methane monooxygenases and other oxidases that employ bimetallic clusters in their active site. To understand the properties of such species, bis-µ-hydroxo-NiII 2 complex (1) supported by a new dicarboxamidate ligand (N,N'-bis(2,6-dimethyl-phenyl)-2,2-dimethylmalonamide) was prepared. Complex 1 contained a diamond core made up of two NiII ions and two bridging hydroxide ligands. Titration of the 1 e- oxidant (NH4 )2 [CeIV (NO3 )6 ] with 1 at -45 °C showed the formation of the high-valent species 2 and 3, containing NiII NiIII and NiIII 2 diamond cores, respectively, maintaining the bis-µ-hydroxide core. Both complexes were characterised using electron paramagnetic resonance, X-ray absorption, and electronic absorption spectroscopies. Density functional theory computations supported the spectroscopic assignments. Oxidation reactivity studies showed that bis-µ-hydroxide-NiIII 2 3 was capable of oxidizing substrates at -45 °C at rates greater than that of the most reactive bis-µ-oxo-NiIII complexes reported to date.

High-Valent d7 NiIII versus d8 CuIII Oxidants in PCET.

Oxygenases have been postulated to utilize d4 FeIV and d8 CuIII oxidants in proton-coupled electron transfer (PCET) hydrocarbon oxidation. In order to explore the influence the metal ion and d-electron count can hold over the PCET reactivity, two metastable high-valent metal-oxygen adducts, [NiIII(OAc)(L)] (1b) and [CuIII(OAc)(L)] (2b), L = N,N'-(2,6-diisopropylphenyl)-2,6-pyridinedicarboxamidate, were prepared from their low-valent precursors [NiII(OAc)(L)]- (1a) and [CuII(OAc)(L)]- (2a). The complexes 1a/b-2a/b were characterized using nuclear magnetic resonance, Fourier transform infrared, electron paramagnetic resonance, X-ray diffraction, and absorption spectroscopies and mass spectrometry. Both complexes were capable of activating substrates through a concerted PCET mechanism (hydrogen atom transfer, HAT, or concerted proton and electron transfer, CPET). The reactivity of 1b and 2b toward a series of para-substituted 2,6-di-tert-butylphenols (p-X-2,6-DTBP; X = OCH3, C(CH3)3, CH3, H, Br, CN, NO2) was studied, showing similar rates of reaction for both complexes. In the oxidation of xanthene, the d8 CuIII oxidant displayed a small increase in the rate constant compared to that of the d7 NiIII oxidant. The d8 CuIII oxidant was capable of oxidizing a large family of hydrocarbon substrates with bond dissociation enthalpy (BDEC-H) values up to 90 kcal/mol. It was previously observed that exchanging the ancillary anionic donor ligand in such complexes resulted in a 20-fold enhancement in the rate constant, an observation that is further enforced by comparison of 1b and 2b to the literature precedents. In contrast, we observed only minor differences in the rate constants upon comparing 1b to 2b. It was thus concluded that in this case the metal ion has a minor impact, while the ancillary donor ligand yields more kinetic control over HAT/CPET oxidation.

Synthesis and Oxidation of a Paddlewheel-Shaped Rhodium/Antimony Complex Featuring Pyridine-2-Thiolate Ligands.

The paddlewheel-shaped complex [Sb(µ-pyS)4 Rh]2 (1) (pyS- = 2-S-C5 H4 N- ) was synthesized from [Rh(pyS)(cod)]2 (cod=1,5-cyclooctadiene) and Sb(pyS)3 . Upon oxidation with ONMe3 , the complex [(µ-O)Sb(µ-pyS)3 Rh(κ2 -pyS)]2 (2) is formed. Both 1 and 2 form dimers and feature short Rh-Sb bonds and bridging pyS ligands. 121 Sb Mössbauer spectro- scopy and computational studies were employed to elucidate the Rh-Sb bonding in 1 and 2. Both covalent (Rh-Sb, X-type Sb ligand) and dative (Rh→Sb, Z-type; Rh←Sb L-type Sb ligand) interactions have to be considered for the description of their bonding situations.

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.

Preparation and characterization of MnIIMnIII complexes with relevance to class Ib ribonucleotide reductases.

The Mn2 complex [MnII2(TPDP)(O2CPh)2](BPh4) (1, TPDP = 1,3-bis(bis(pyridin-2-ylmethyl)amino)propan-2-ol, Ph =phenyl) was prepared and subsequently characterized via single-crystal X-ray diffraction, X-ray absorption, electronic absorption, and infrared spectroscopies, and mass spectrometry. 1 was prepared in order to explore its properties as a structural and functional mimic of class Ib ribonucleotide reductases (RNRs). 1 reacted with superoxide anion (O2•-) to generate a peroxido-MnIIMnIII complex, 2. The electronic absorption and electron paramagnetic resonance (EPR) spectra of 2 were similar to previously published peroxido-MnIIMnIII species. Furthermore, X-ray near edge absorption structure (XANES) studies indicated the conversion of a MnII2 core in 1 to a MnIIMnIII state in 2. Treatment of 2 with para-toluenesulfonic acid (p-TsOH) resulted in the conversion to a new MnIIMnIII species, 3, rather than causing O-O bond scission, as previously encountered. 3 was characterized using electronic absorption, EPR, and X-ray absorption spectroscopies. Unlike other reported peroxido-MnIIMnIII species, 3 was capable of oxidative O-H activation, mirroring the generation of tyrosyl radical in class Ib RNRs, however without accessing the MnIIIMnIV state.

Aromatic and aliphatic hydrocarbon hydroxylation via a formally NiIVO oxidant.

The reaction of (NMe4)2[NiII(LPh)(OAc)] (1[OAc], LPh = 2,2',2''-nitrilo-tris-(N-phenylacetamide); OAc = acetate) with 3-chloroperoxybenzoic acid (m-CPBA) resulted in the formation of a self-hydroxylated NiIII-phenolate complex, 2, where one of the phenyl groups of LPh underwent hydroxylation. 2 was characterised by UV-Vis, EPR, and XAS spectroscopies and ESI-MS. 2 decayed to yield a previously characterised NiII-phenolate complex, 3. We postulate that self-hydroxylation was mediated by a formally NiIVO oxidant, formed from the reaction of 1[OAc] with m-CPBA, which undergoes electrophilic aromatic substitution to yield 2. This is supported by an analysis of the kinetic and thermodynamic properties of the reaction of 1[OAc] with m-CPBA. Addition of exogenous hydrocarbon substrates intercepted the self-hydroxylation process, producing hydroxylated products, providing further support for the formally NiIVO entity. This study demonstrates that the reaction between NiII salts and m-CPBA can lead to potent metal-based oxidants, in contrast to recent studies demonstrating carboxyl radical is a radical free-chain reaction initiator in NiII/m-CPBA hydrocarbon oxidation catalysis.