Ammonium and Potassium Salts of a Hexacoordinate Phosphorus(V) Anion Featuring P-O and P-C Bonds.

Ammonium and potassium salts featuring the chiral mer-[P(C6H4CO2)3]-, mer-[1]-, have been isolated. Specifically, treating phosphorane P(C6H4CO2)2(C6H4CO2H), 2, with N-containing bases [Nbase = PhNMe2, PhNH2, pyridine (py), isoquinoline, (-)-brucine, N( n-C8H17)3] afforded ammonium salts [NbaseH]+- mer-[1]-. Each compound was fully characterized spectroscopically, and four were subjected to X-ray crystallographic analysis. Salts were isolated with the racemic mixture of the mer-[1]- anion except in the case of [(-)-brucineH]-Λ- mer-[1], for which the crystal analyzed was enantiomerically pure. The potassium salt, K- mer-[1], was synthesized by treating 2 with KH. The solid-state structure of K- mer-[1] is a coordination polymer consisting of seven- and eight-coordinate K+ ions that are weakly bound by oxygen of either the racemic anion or the methanol solvent. Preliminary NMR and MS data for the formation of the Brønsted acid, H(DMF) n[1], has also been obtained. An estimate of the basicity of anion mer-[1]- was obtained from IR measurements of the N-H stretching frequency for [( n-C8H17)3NH]- mer-[1]. On the basis of these measurements, anion mer-[1]- was ranked similar to the classical weakly coordinating anion, [ClO4]-, in terms of its coordinating ability.

[HL2][P(1,2-O2C6Cl4)3] (L = THF, DMF): Brønsted acid initiators for the polymerization of n-butyl vinyl ether and p-methoxystyrene.

The development of solid, weighable Brønsted acids featuring the hexacoordinated phosphorous(v) anion [TRISPHAT]- are reported. H(DMF)2[1] and H(THF)2[1] {[1]- = [P(1,2-O2C6Cl4)3]-} were synthesized and fully characterized by 1H, 31P, 13C and 2D-NOESY NMR spectroscopy, X-ray crystallography, mass spectrometry and elemental analysis. Both, H(DMF)2[1] and H(THF)2[1] are found to be suitable initiators for the polymerization of n-butyl vinyl ether and p-methoxystyrene. Optimal polymerization results for these single-component initiators were generally obtained at -50 °C where high molecular weight polymers were isolated in high yield. 1H NMR spectroscopic analysis and dynamic light scattering of solutions of the isolated polymers provide evidence for a branched structure which presumably arises from chain transfer.

Strong Evidence of a Phosphanoxyl Complex: Formation, Bonding, and Reactivity of Ligated Phosphorus Analogues of Nitroxides.

Facile access to [W(CO)5 (Ph2 P-OTEMP)] is used to initiate a study on the generation, properties, and reactions of transient phosphanoxyl complexes [MLn (R2 PO)], the first example of which could be trapped via heterocoupling with the trityl radical. It is also demonstrated that the phosphorus nitroxyl complex acts as radical initiator in the polymerization of styrene. The quest for P-O versus O-N bond homolysis, as well as the initial steps of the polymerization were studied by DFT methods.

Electronic Structure Description of a Doubly Oxidized Bimetallic Cobalt Complex with Proradical Ligands.

The geometric and electronic structure of a doubly oxidized bimetallic Co complex containing two redox-active salen moieties connected via a 1,2-phenylene linker was investigated and compared to an oxidized monomeric analogue. Both complexes, namely, CoL(1) and Co2L(2), are oxidized to the mono- and dications, respectively, with AgSbF6 and characterized by X-ray crystallography for the monomer and by vis-NIR (NIR = near-infrared) spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, superconducting quantum interference device (SQUID) magnetometry, and density functional theory (DFT) calculations for both the monomer and dimer. Both complexes exhibit a water molecule coordinated in the apical position upon oxidation. [CoL(1)-H2O](+) displays a broad NIR band at 8500 cm(-1) (8400 M(-1) cm(-1)), which is consistent with recent reports on oxidized Co salen complexes (Kochem, A. et al., Inorg. Chem., 2012, 51, 10557-10571 and Kurahashi, T. et al., Inorg. Chem., 2013, 52, 3908-3919). DFT calculations predict a triplet ground state with significant ligand and metal contributions to the singularly occupied molecular orbitals. The majority (∼75%) of the total spin density is localized on the metal, highlighting both high-spin Co(III) and Co(II)L(•) character in the electronic ground state. Further oxidation of CoL(1) to the dication affords a low-spin Co(III) phenoxyl radical species. The NIR features for [Co2L(2)-2H2O](2+) at 8600 cm(-1) (17 800 M(-1) cm(-1)) are doubly intense in comparison to [CoL(1)-H2O](+) owing to the description of [Co2L(2)-2H2O](2+) as two non-interacting oxidized Co salen complexes bound via the central phenylene linker. Interestingly, TD-DFT calculations predict two electronic transitions that are 353 cm(-1) apart. The NIR spectrum of the analogous Ni complex, [Ni2L(2)](2+), exhibits two intense transitions (4890 cm(-1)/26 500 M(-1) cm(-1) and 4200 cm(-1)/21 200 M(-1) cm(-1)) due to exciton coupling in the excited state. Only one broad band is observed in the NIR spectrum for [Co2L(2)-2H2O](2+) as a result of the contracted donor and acceptor orbitals and overall CT character.

Class III delocalization and exciton coupling in a bimetallic bis-ligand radical complex.

The geometric and electronic structure of an oxidized bimetallic Ni complex incorporating two redox-active Schiff-base ligands connected via a 1,2-phenylene linker has been investigated and compared to a monomeric analogue. Information from UV/Vis/NIR spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, electrochemistry, and density functional theory (DFT) calculations provides important information on the locus of oxidation for the bimetallic complex. The neutral bimetallic complex is conformationally dynamic at room temperature, which complicates characterization of the oxidized forms. Comparison to an oxidized monomer analogue 1 provides critical insight into the electronic structure of the oxidized bimetallic complex 2. Oxidation of 1 provides [1˙](+), which is characterized as a fully delocalized ligand radical complex; the spectroscopic signature of this derivative includes an intense NIR band at 4500 cm(-1). Oxidation of 2 to the bis-oxidized form affords a bis-ligand radical species [2˙˙](2+). Variable temperature EPR spectroscopy of [2˙˙](2+) shows no evidence of coupling, and the triplet and broken symmetry solutions afforded by theoretical calculations are essentially isoenergetic. [2˙˙](2+) is thus best described as incorporating two non-interacting ligand radicals. Interestingly, the intense NIR intervalence charge transfer band observed for the delocalized ligand-radical [1˙](+) exhibits exciton splitting in [2˙˙](2+), due to coupling of the monomer transition dipoles in the enforced oblique dimer geometry. Evaluating the splitting of the intense intervalence charge transfer band can thus provide significant geometric and electronic information in less rigid bis-ligand radical systems. Addition of excess pyridine to [2˙˙](2+) results in a shift in the oxidation locus from a bis-ligand radical species to the Ni(III) /Ni(III) derivative [2(py)4](2+), demonstrating that the ligand system can incorporate significant bulk in the axial positions.

H(OEt2)2[P(1,2-O2C6Cl4)3]: synthesis, characterization, and application as a single-component initiator for the carbocationic polymerization of olefins.

The development of novel Brønsted acids featuring the hexacoordinate phosphorus(V) anion [TRISPHAT](-) {[1](-)=[P(1,2-O2C6Cl4)3](-)} are reported. The title compound, H(OEt2)2[1], was synthesized from 1,2-(HO)2C6Cl4 (3 equiv) and PCl5 in the presence of diethyl ether. This compound was fully characterized by (1)H, (31)P and (13)C NMR spectroscopy, X-ray crystallography and elemental microanalysis. Dissolution of H(OEt2)2[1] in acetonitrile results in the slow precipitation of crystalline H(OEt2)(NCMe)[1], which was characterized by X-ray diffraction; however, in CD2Cl2 solution the [TRISPHAT](-) anion protonated and ring-opened. The weighable, solid H(OEt2)2[1] was found to be a competent initiator for the polymerization of n-butyl vinyl ether, α-methylstyrene, styrene and isoprene at a variety of temperatures and monomer-to-initiator ratios. At low temperatures, polymers with M(n) >10(5) were obtained for n-butyl vinyl ether and α-methylstyrene whereas slightly lower molecular weights were obtained with styrene and isoprene (10(4) < M(n) <10(5)). The poly(α-methylstyrene) synthesized at -78 °C is syndiotactic-rich (ca. 87% rr) whereas the polystyrene obtained at -50 °C is atactic. The polyisoprene obtained possessed all possible modes of enchainment as well as branched and/or cyclic structures that are often observed in polyisoprene.

Double oxidation localizes spin in a Ni bis-phenoxyl radical complex.

The electronic structure of a doubly oxidized Ni salen complex NiSal(tBu) (Sal(tBu) = N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexane-(1R,2R)-diamine) has been investigated by both experimental and theoretical methods. The doubly oxidized product was probed by resonance Raman spectroscopy, UV-vis-NIR, and EPR to determine the locus of oxidation as well as the spectroscopic signature of the complex. It was determined that double oxidation of NiSal(tBu) affords a bis-ligand radical species in solution via the presence of phenoxyl radical bands at ν(7a) (1504 cm(-1)) and ν(8a) (1579 cm(-1)) in the Raman spectrum, and the loss of the intense NIR transition reported for the mono-radical complex (Angew. Chem., Int. Ed., 2007, 46, 5198). Spectroscopic experiments, complemented by DFT calculations, show that the two radical spins are predominantly localized on the phenolate moieties, in opposition to the extensive delocalization over the ligand framework observed for the mono-radical analogue.