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Jonas C Peters

Publications and source records attributed to Jonas C Peters.

At least 19 recordsLinked to original sources
PubMed2006

Unexpected photoisomerization of a pincer-type amido ligand leads to facial coordination at Pt(IV).

The divalent complex (BQA)PtMe undergoes oxidative addition with MeI to afford the octahedral complex cis-(mer-BQA)PtMe2I {(BQA)- = bis(8-quinolinyl)amide}. When this molecule is irradiated with visible light, it isomerizes to (fac-BQA)PtMe2I, where the BQA ligand adopts an unexpected facial coordination mode. The amide nitrogen in this molecule is sp3 hybridized and can be easily quarternized with HBF4, resulting in [H(fac-BQA)PtMe2I][BF4], with only minor perturbation to the coordination sphere.

Journal Article↗
PubMed2006

Characterization of the terminal iron(IV) imides [[PhBP(t)(Bu)2(pz')]Fe(IV)NAd]+.

New hybrid bis(phosphine)(pyrazole)borate tripodal ligands ([PhBPtBu2(pz')]-) are reported that support pseudotetrahedral iron in the oxidation states +1, +2, +3, and +4. The higher oxidation states are stabilized by a terminal FeNR linkage. Of particular interest is the generation and thorough characterization of an S = 1 FeIVNR+ imide cation using this new ligand system. The latter species can be observed electrochemically and spectroscopically, and its solid-state crystal structure is reported.

Borates↗
PubMed2006

Mid- to high-valent imido and nitrido complexes of iron.

This short review summarizes recent advances in the synthesis and reactivity of iron imides and nitrides. Both monometallic and multimetallic assemblies featuring these moieties are discussed. Recent synthetic approaches have led to the availability of new mid- to high-valent iron imides and nitrides, allowing us to begin assembling models to describe the factors influencing their relative stabilities and reactivity patterns.

Imides↗
PubMed2005

Structural snapshots of a flexible Cu2P2 core that accommodates the oxidation states Cu(I)Cu(I), Cu1.5Cu1.5, and Cu(II)Cu(II).

The phosphido-bridged dicopper(I) complex {(PPP)Cu}2 has been synthesized and structurally characterized ([PPP]- = bis(2-di-iso-propylphosphinophenyl)phosphide). Cyclic voltammetry of {(PPP)Cu}2 in THF shows fully reversible oxidations at -1.02 V (Cu1.5Cu1.5/CuICuI) and -0.423 V (CuIICuII/Cu1.5Cu1.5). Chemical oxidation of {(PPP)Cu}2 by one electron yields the class III mixed-valence species [{(PPP)Cu}2]+ (EPR, UV-vis). Structural data establish an unexpectedly large change (0.538 A) in the Cu...Cu distance upon oxidation state. Oxidation of {(PPP)Cu}2 by two electrons yields the dication [{(PPP)Cu}2]2+, an antiferromagnetically coupled dicopper(II) complex. Maintenance of a pseudotetrahedral geometry that is midway between a square plane and an ideal tetrahedron at the copper centers, along with a high degree of flexibility at the phosphide hinges, allows for efficient access to CuICuI, Cu1.5Cu1.5, and CuIICuII redox states without the need for ligand exchange, substitution, or redistribution processes.

Journal Article↗
PubMed2005

High-spin and low-spin iron(II) complexes with facially-coordinated borohydride ligands.

Rare examples of monometallic high-spin and low-spin L3Fe(H3BH) complexes have been characterized, where the two L3 ligands are [TpPh2] and [PhBP3] ([TpPh2] = [HB(3,5-Ph2pz)3]- and [PhBP3] = [PhB(CH2PPh2)3]-). The structures are reported wherein the borohydride ligand is facially coordinated to the iron center in each complex. Density functional methods have been employed to explain the bonding in these unusual iron(II) centers. Despite the differences in spin states, short Fe-B distances are observed in both complexes and there is significant theoretical evidence to support a substantial bonding interaction between the iron and boron nuclei. In light of this interaction, we suggest that these complexes can be described as (L3)Fe(eta4-H3BH) complexes.

Borohydrides↗
PubMed2005

Heterolytic H2 activation mediated by low-coordinate L3Fe-(mu-N)-FeL3 complexes to generate Fe(mu-NH)(mu-H)Fe species.

The diiron mu-nitride complexes, {L3FeII(mu-N)FeIIL3}- and L3FeIII(mu-N)FeIIL3, heterolytically activate hydrogen (1 atm) at ambient temperature in solution (L3 = [PhB(CH2PPh2)3]-). These transformations lead to structurally unique {L3FeII(mu-NH)(mu-H)FeIIL3}- and L3FeIII(mu-NH)(mu-H)FeIIL3 products. X-ray data establish a marked reduction in the Fe-Fe distance upon H2 uptake, and spectroscopic data establish both FeIIFeII species to be diamagnetic, whereas the FeIIIFeII species, L3FeIII(mu-N)FeIIL3 and L3FeIII(mu-NH)(mu-H)FeIIL3, populate doublet ground states with thermally accessible higher spin states.

Crystallography, X-Ray↗
PubMed2005

Spin-state tuning at pseudotetrahedral d(7) ions: examining the structural and magnetic phenomena of four-coordinate [BP3]CoII-X systems.

Electronic structure, spin-state, and geometrical relationships for a series of pseudotetrahedral Co(II) aryloxide, siloxide, arylthiolate, and silylthiolate complexes supported by the tris(phosphino)borate [BP(3)] ligands [PhBP(3)] and [PhBP(i)()(Pr)(3)] ([PhB(CH(2)PPh(2))(3)](-) and [PhB(CH(2)P(i)()Pr(2))(3)](-), respectively) are described. Standard (1)H NMR, optical, electrochemical, and solution magnetic data, in addition to low-temperature EPR and variable temperature SQUID magnetization data, are presented for the new cobalt(II) complexes [PhBP(3)]CoOSiPh(3) (2), [PhBP(3)]CoO(4-(t)()Bu-Ph) (3), [PhBP(3)]CoO(C(6)F(5)) (4), [PhBP(3)]CoSPh (5), [PhBP(3)]CoS(2,6-Me(2)-Ph) (6), [PhBP(3)]CoS(2,4,6-(i)()Pr(3)-Ph) (7), [PhBP(3)]CoS(2,4,6-(t)()Bu(3)-Ph) (8), [PhBP(3)]CoSSiPh(3) (9), [PhBP(3)]CoOSi(4-NMe(2)-Ph)(3) (10), [PhBP(3)]CoOSi(4-CF(3)-Ph)(3) (11), [PhBP(3)]CoOCPh(3) (12), [PhBP(i)()(Pr)(3)]CoOSiPh(3) (14), and [PhBP(i)()(Pr)(3)]CoSSiPh(3) (15). The low-temperature solid-state crystal structures of 2, 3, 5-10, 12, and 15 are also described. These pseudotetrahedral cobalt(II) complexes are classified as featuring one of two limiting distortions, either umbrella or off-axis. Magnetic and spectroscopic data demonstrate that both S = (1)/(2) and S = (3)/(2) ground-state electronic configurations are accessible for the umbrella distorted structure type, depending on the nature of the X-type ligand, its denticity (eta(1) versus eta(3)), and the tripodal phosphine ligand employed. Off-axis distorted complexes populate an S = (1)/(2) ground-state exclusively. For those four-coordinate complexes that populate S = (1)/(2) ground states, X-ray data show two Co-P bond distances that are invariably shorter than a third Co-P bond. The pseudotetrahedral siloxides 2, 10, and 11 are exceptional in that they display gradual spin crossover in the solid state. The diamagnetic cobalt(III) complex {[PhBP(3)]CoOSiPh(3)}{BAr(4)} ({16}{BAr(4)}) (Ar = Ph or 3,5-(CF(3))(2)-C(6)H(3)) has also been prepared and structurally characterized. Accompanying electronic structure calculations (DFT) for complexes 2, 6, and {16}(+) support the notion of a close electronic structure relationship between these four-coordinate systems and octahedral, sandwich, and half-sandwich coordination complexes.

Journal Article↗
PubMed2005

Synthetic control of excited-state properties in cyclometalated Ir(III) complexes using ancillary ligands.

The synthesis and photophysical characterization of a series of (N,C(2')-(2-para-tolylpyridyl))2 Ir(LL') [(tpy)2 Ir(LL')] (LL' = 2,4-pentanedionato (acac), bis(pyrazolyl)borate ligands and their analogues, diphosphine chelates and tert-butylisocyanide (CN-t-Bu)) are reported. A smaller series of [(dfppy)2 Ir(LL')] (dfppy = N,C(2')-2-(4',6'-difluorophenyl)pyridyl) complexes were also examined along with two previously reported compounds, (ppy)2 Ir(CN)2- and (ppy)2 Ir(NCS)2- (ppy = N,C(2')-2-phenylpyridyl). The (tpy)2 Ir(PPh2CH2)2 BPh2 and [(tpy)2 Ir(CN-t-Bu)2](CF3SO3) complexes have been structurally characterized by X-ray crystallography. The Ir-C(aryl) bond lengths in (tpy)2 Ir(CN-t-Bu)2+ (2.047(5) and 2.072(5) A) and (tpy)2 Ir(PPh2CH2)2 BPh2 (2.047(9) and 2.057(9) A) are longer than their counterparts in (tpy)2 Ir(acac) (1.982(6) and 1.985(7) A). Density functional theory calculations carried out on (ppy)2 Ir(CN-Me)2+ show that the highest occupied molecular orbital (HOMO) consists of a mixture of phenyl-pi and Ir-d orbitals, while the lowest unoccupied molecular orbital is localized primarily on the pyridyl-pi orbitals. Electrochemical analysis of the (tpy)2 Ir(LL') complexes shows that the reduction potentials are largely unaffected by variation in the ancillary ligand, whereas the oxidation potentials vary over a much wider range (as much as 400 mV between two different LL' ligands). Spectroscopic analysis of the cyclometalated Ir complexes reveals that the lowest energy excited state (T1) is a triplet ligand-centered state (3LC) on the cyclometalating ligand admixed with 1MLCT (MLCT = metal-to-ligand charge-transfer) character. The different ancillary ligands alter the 1MLCT state energy mainly by changing the HOMO energy. Destabilization of the 1MLCT state results in less 1MLCT character mixed into the T1 state, which in turn leads to an increase in the emission energy. The increase in emission energy leads to a linear decrease in ln(k(nr)) (k(nr) = nonradiative decay rate). Decreased 1MLCT character in the T1 state also increases the Huang-Rhys factors in the emission spectra, decreases the extinction coefficient of the T1 transition, and consequently decreases the radiative decay rates (k(r)). Overall, the luminescence quantum yields decline with increasing emission energies. A linear dependence of the radiative decay rate (k(r)) or extinction coefficient (epsilon) on (1/deltaE)2 has been demonstrated, where deltaE is the energy difference between the 1MLCT and 3LC transitions. A value of 200 cm(-1) for the spin-orbital coupling matrix element 3LC absolute value(H(SO)) 1MLCT of the (tpy)2 Ir(LL') complexes can be deduced from this linear relationship. The (fppy)2 Ir(LL') complexes with corresponding ancillary ligands display similar trends in excited-state properties.

Journal Article↗
PubMed2005

A highly emissive Cu2N2 diamond core complex supported by a [PNP]- ligand.

A Cu2N2 diamond core structure, {(PNP)CuI}2 (2), supported by a [PNP]- ligand (1) ([PNP]- = bis(2-(diisobutylphosphino)phenyl)amide) has been prepared. 2 is highly emissive at ambient temperature in both the solid and solution states and is characterized by a relatively long-lived excited state (tau > 10 mus) and an unusually high quantum yield (phi > 0.65). These observations are consistent with a low degree of structural reorganization between the ground state of 2 and its excited state *2, and also with a high degree of steric protection of the two copper centers of 2 afforded by the bulky [PNP]- ligand. An estimate for the excited-state reduction potential of *2 (ca. -3.2 V vs Fc+/Fc), and the availability of two well-separated and reversible ground-state redox processes, suggests that bimetallic copper systems of these types may be interesting candidates to consider for photochemically driving multielectron redox transformations.

Journal Article↗
PubMed2005

Ground-state singlet L3Fe-(mu-N)-FeL3 and L3Fe(NR) complexes featuring pseudotetrahedral Fe(II) centers.

Pseudotetrahedral iron(II) coordination complexes that contain bridged nitride and terminal imide linkages, and exhibit singlet ground-state electronic configurations, are described. Sodium amalgam reduction of the ferromagnetically coupled dimer, {[PhBP(3)]Fe(mu-1,3-N(3))}(2) (2) ([PhBP(3)] = [PhB(CH(2)PPh(2))(3)](-)), yields the diamagnetic bridging nitride species [{[PhBP(3)]Fe}(2)(mu-N)][Na(THF)(5)] (3). The Fe-N-Fe linkage featured in the anion of 3 exhibits an unusually bent angle of approximately 135 degrees , and the short Fe-N bond distances (Fe-N(av) approximately equal to 1.70 A) suggest substantial Fe-N multiple bond character. The diamagnetic imide complex {[PhBP(3)]Fe(II)(triple bond)N(1-Ad)}{(n)()Bu(4)N} (4) has been prepared by sodium amalgam reduction of its low-spin iron(III) precursor, [PhBP(3)]Fe(III)(triple bond)N(1-Ad) (5). Complexes 4 and 5 have been structurally characterized, and their respective electronic structures are discussed in the context of a supporting DFT calculation. Diamagnetic 4 provides a bona fide example of a pseudotetrahedral iron(II) center in a low-spin ground-state configuration. Comparative optical data strongly suggest that dinuclear 3 is best described as containing two high-spin iron(II) centers that are strongly antiferromagnetically coupled to give rise to a singlet ground-state at room temperature.

Journal Article↗
PubMed2004

Synthetic, structural, and mechanistic aspects of an amine activation process mediated at a zwitterionic Pd(II) center.

A zwitterionic palladium complex [[Ph(2)BP(2)]Pd(THF)(2)][OTf] (1) (where [Ph(2)BP(2)] = [Ph(2)B(CH(2)PPh(2))(2)](-)) reacts with trialkylamines to activate a C-H bond adjacent to the amine N atom, thereby producing iminium adduct complexes [Ph(2)BP(2)]Pd(N,C:eta(2)-NR(2)CHR'). In all cases examined the amine activation process is selective for the secondary C-H bond position adjacent to the N atom. These palladacycles undergo facile beta-hydride elimination/olefin reinsertion processes as evident from deuterium scrambling studies and chemical trap studies. The kinetics of the amine activation process was explored, and beta-hydride elimination appears to be the rate-limiting step. A large kinetic deuterium isotope effect for the amine activation process is evident. The reaction profile in less polar solvents such as benzene and toluene is different at room temperature and leads to dimeric [[Ph(2)BP(2)]Pd](2) (4) as the dominant palladium product. Low-temperature toluene-d(8) experiments proceed more cleanly, and intermediates assigned as [Ph(2)BP(2)]Pd(NEt(3))(OTf) and the iminium hydride species [[Ph(2)BP(2)]Pd(H)(Et(2)N=CHCH(3))][OTf] are directly observed. The complex (Ph(2)SiP(2))Pd(OTf)(2) (14) was also studied for amine activation and generates dimeric [(Ph(2)SiP(2))Pd](2)[OTf](2) (16) as the dominant palladium product. These collective data are discussed with respect to the mechanism of the amine activation and, in particular, the influence that solvent polarity and charge have on the overall reaction profile.

Journal Article↗
PubMed2004

Considering Fe(II/IV) redox processes as mechanistically relevant to the catalytic hydrogenation of olefins by [PhBP iPr 3]Fe-H x species.

Several coordinatively unsaturated pseudotetrahedral iron(II) precursors, [PhBP(iPr)(3)]Fe-R ([PhBP(iPr)(3)] = [PhB(CH(2)P(i)Pr(2))(3)](-); R = Me (2), R = CH(2)Ph (3), R = CH(2)CMe(3) (4)) have been prepared from [PhBP(iPr)(3)]FeCl (1) that serve as precatalysts for the room-temperature hydrogenation of unsaturated hydrocarbons (e.g., ethylene, styrene, 2-pentyne) under atmospheric H(2) pressure. The solid-state crystal structures of 2 and 3 are presented. To gain mechanistic insight into the nature of these hydrogenation reactions, a number of [PhBP(iPr)(3)]-supported iron hydrides were prepared and studied. Room-temperature hydrogenation of alkyls 2-4 in the presence of a trapping phosphine ligand affords the iron(IV) trihydride species [PhBP(iPr)(3)]Fe(H)(3)(PR(3)) (PR(3) = PMe(3) (5); PR(3) = PEt(3) (6); PR(3) = PMePh(2) (7)). These spectroscopically well-defined trihydrides undergo hydrogen loss to varying degrees in solution, and for the case of 7, this process leads to the structurally identified Fe(II) hydride product [PhBP(iPr)(3)]Fe(H)(PMePh(2)) (9). Attempts to prepare 9 by addition of LiEt(3)BH to 1 instead lead to the Fe(I) reduction product [PhBP(iPr)(3)]Fe(PMePh(2)) (10). The independent preparations of the Fe(II) monohydride complex [PhBP(iPr)(3)]Fe(II)(H)(PMe(3)) (11) and the Fe(I) phosphine adduct [PhBP(iPr)(3)]Fe(PMe(3)) (8) are described. The solid-state crystal structures of trihydride 5, monohydride 11, and 8 are compared and demonstrate relatively little structural reorganization with respect to the P(3)Fe-P' core motif as a function of the iron center's formal oxidation state. Although paramagnetic 11 (S = 1) is quantitatively converted to the diamagnetic trihydride 5 under H(2), the Fe(I) complex 8 (S = (3)/(2)) is inert toward atmospheric H(2). Complex 10 is likewise inert toward H(2). Trihydrides 5 and 6 also serve as hydrogenation precatalysts, albeit at slower rates than that for the benzyl complex 3 because of a rate-contributing phosphine dependence. That these hydrogenations appear to proceed via well-defined olefin insertion steps into an Fe-H linkage is indicated by the reaction between trihydride 5 and ethylene, which cleanly produces the ethyl complex [PhBP(iPr)(3)]Fe(CH(2)CH(3)) (13) and an equivalent of ethane. Mechanistic issues concerning the overall reaction are described.

Journal Article↗
PubMed2004

The coordination chemistry of "[BP3]NiX" platforms: targeting low-valent nickel sources as promising candidates to L3Ni=E and L3Ni(triple bond)E linkages.

A series of divalent, monovalent, and zerovalent nickel complexes supported by the electron-releasing, monoanionic tris(phosphino)borate ligands [PhBP3] and [PhBPiPr3] ([PhBP3] = [PhB(CH2PPh2)3]-, [PhBPiPr3] = [PhB(CH2PiPr2)3]-) have been synthesized to explore fundamental aspects of their coordination chemistry. The pseudotetrahedral, divalent halide complexes [PhBP3]NiCl (1), [PhBP3]NiI (2), and [PhBPiPr3]NiCl (3) were prepared by the metalation of [PhBP3]Tl or [PhBPiPr3]Tl with (Ph3P)2NiCl2, NiI2, and (DME)NiCl2 (DME = 1,2-dimethoxyethane), respectively. Complex 1 is a versatile precursor to a series of complexes accessible via substitution reactions including [PhBP3]Ni(N3) (4), [PhBP3]Ni(OSiPh3) (5), [PhBP3]Ni(O-p-tBu-Ph) (6), and [PhBP3]Ni(S-p-tBu-Ph) (7). Complexes 2-5 and 7 have been characterized by X-ray diffraction (XRD) and are pseudotetrahedral monomers in the solid state. Complex 1 reacts readily with oxygen to form the four-electron-oxidation product, [[PhB(CH2POPh2)2(CH2PPh2)]NiCl] (8A or 8B), which features a solid-state structure that is dependent on its method of crystallization. Chemical reduction of 1 using Na/Hg or other potential 1-electron reductants generates a product that arises from partial ligand degradation, [PhBP3]Ni(eta2-CH2PPh2) (9). The more sterically hindered chloride 3 reacts with Li(dbabh) (Hdbabh = 2,3:5,6-dibenzo-7-azabicyclo[2.2.1]hepta-2,5-diene) to provide the three-coordinate complex [kappa2-PhBPiPr3]Ni(dbabh) (11), also characterized by XRD. Chemical reduction of complex 1 in the presence of L-type donors produces the tetrahedral Ni(I) complexes [PhBP3]Ni(PPh3) (12) and [PhBP3]Ni(CNtBu) (13). Reduction of 3 following the addition of PMe3 or tert-butyl isocyanide affords the Ni(I) complexes [PhBPiPr3]Ni(PMe3) (14) and [PhBPiPr3]Ni(CNtBu) (15), respectively. The reactivity of these [PhBP3]NiIL and [PhBPiPr3]NiIL complexes with respect to oxidative group transfer reactions from organic azides and diazoalkanes is discussed. The zerovalent nitrosyl complex [PhBP3]Ni(NO) (16) is prepared by the reaction of 1 with excess NO or by treating 12 with stoichiometric NO. The anionic Ni(0) complexes [[kappa2-PhBP3]Ni(CO)2][nBu4N] (17) and [[kappa2-PhBPiPr3]Ni(CO)2][ASN] (18) (ASN = 5-azoniaspiro[4.4]nonane) have been prepared by reacting [PhBP3]Tl or [PhBPiPr3]Tl with (Ph3P)2Ni(CO)2 in the presence of R4NBr. The photolysis of 17 appears to generate a new species consistent with a zerovalent monocarbonyl complex which we tentatively assign as [[PhBP3]Ni(CO)][nBu4N], although complete characterization of this complex has been difficult. Finally, theoretical DFT calculations are presented for the hypothetical low spin complexes [PhBP3]Ni(NtBu), [PhBPiPr3]Ni(NtBu), [PhBPiPr3]Ni(NMe), and [PhBPiPr3]Ni(N) to consider what role electronic structure factors might play with respect to the relative stability of these species.

Journal Article↗
PubMed2004

A tetrahedrally coordinated L3Fe-Nx platform that accommodates terminal nitride (Fe(IV)N) and dinitrogen (Fe(I)-N2-Fe(I)) ligands.

A tetrahedrally coordinated L3Fe-Nx platform that accommodates both terminal nitride (L3FeIVN) and dinitrogen (L3FeI-N2-FeIL3) functionalities is described. The diamagnetic L3FeIVN species featured has been characterized in solution under ambient conditions by multinuclear NMR (1H, 31P, and 15N) and infrared spectroscopy. The electronic structure of the title complex has also been explored using DFT. The terminal nitride complex oxidatively couples to generate the previously reported L3FeI-N2-FeIL3 species. This reaction constitutes a six-electron transformation mediated by two iron centers. Reductive protonation of the nitride complex releases NH3 as a significant reaction product.

Journal Article↗
PubMed2004

Hydrogenolysis of [PhBP3]Fe[triple bond]N-p-tolyl: probing the reactivity of an iron imide with H2.

This paper describes the reductive hydrogenolysis of a low-spin (S = 1/2) iron(III) imide. Pseudotetrahedral [PhBP3]FeIIIN-p-tolyl is reduced by hydrogen at ambient temperature and pressure in benzene solution. The reduction appears to proceed in a stepwise fashion. An intermediate S = 2 iron(II) anilide, [PhBP3]Fe(N(H)-p-tolyl), is observed and has been independently generated and structurally characterized. Prolonged hydrogenolysis in benzene results in the complete hydrogenolysis of the Fe-N linkage to release H2N-p-tolyl. The major iron-containing product formed from this step is the diamagnetic cyclohexadienyl complex, [PhBP3]Fe(eta5-cyclohexadienyl), which has also been independently prepared and structurally characterized. Evidence is presented to suggest that the final [PhBP3]Fe(eta5-cyclohexadienyl) product is formed via benzene insertion into a reactive [PhBP3]FeII-H intermediate.

Journal Article↗