From the activation of tetraphosphorus to the chemistry of diphosphorus and beyond

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2013.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references.The niobium-phosphorus triple bond in [P=-Nb(N[Np]Ar)3]- (Np = CH2tBu; Ar = 3,5-Me2C6H3) has produced the first case of P4 activation by a metal-ligand multiple bond. Treatment of P4 with the sodium salt of the niobium phosphide complex in weakly-coordinating solvents led to the formation of the C3-symmetric cyclo-P3 anion, while in THF, it led to the formation of the cyclo-P5 anion [(Ar[Np]N)([eta]4-P5)Nb(N[Np]Ar)2]-. The latter represents a rare example of a substituted pentaphospha-cyclopentadienyl ligand and may be interpreted as the product of trapping an intermediate h5-P5 structure through the migration of one anilide ligand. A search for methods of activating P4 that avoid tedious metal-mediated steps led to the discovery of an incredibly simple procedure involving only commercial reagents. Irradiation of solutions containing P4 and readily available 1,3-dienes produced bicyclic organic diphosphanes in an atom-economical, one-step protocol. Use of 2,3-dimethylbutadiene allowed the isolation of the bicyclic diphosphane P2(C6H10)2 in gram-quantities, but other dienes such as 1,3-butadiene, isoprene, 1,3-pentadiene, and 1,3-cyclohexadiene also provided evidence for incorporation of P2 units via double Diels-Alder reactions. Theoretical investigations provided support for the formation of P2 molecules from photo-excited P4. Investigations into the physical and chemical characteristics of P2(C6H10)2 uncovered an unprecedented stability towards cleavage of the P-P bond relative to other diphosphanes. P2(C6H10)2 exhibits a flexible, yet robust bicyclic framework containing lone pairs disposed at an angle of ca. 45°, and proved to be ideally suited to form multiple bridges between two metal centers. Dinuclear complexes containing tetrahedral, zero-valent group 10 metals bridged by three diphosphane ligands were investigated in detail. These contain D3h-symmetric {M2P6} barrelene cages with metal-metal distances of 4 Å , and exhibited substitution reactions where the cages remain intact. Alternatively, diphosphane P2(C6H10)2 allowed for unprecedented selectivity towards functionalization of a single phosphorus lone pair. Additional functionalization proceeds at a significantly slower rate, thus enabling the selective isolation of various phosphoranes (EP2(C6H10)2 and E2P2(C6H10)2; E = O, S, N-R). Metalation reactions with the bulky diiminodiphosphorane ligand (MesN)2P2(C6H10)2 allowed for multiple metal complexes, showing that such ligands provide an attractive pre-organized binding pocket for transition metals, as well as post-transition metals.by Daniel Tofan.Ph.D

Uptake of one and two molecules of CO2 by the molybdate dianion: a soluble, molecular oxide model system for carbon dioxide fixation

Tetrahedral [MoO4][superscript 2−] readily binds CO[subscript 2] at room temperature to produce a robust monocarbonate complex, [MoO[subscript 3](κ[superscript 2]-CO[subscript 3])][superscript 2−], that does not release CO[subscript 2] even at modestly elevated temperatures (up to 56 °C in solution and 70 °C in the solid state). In the presence of excess carbon dioxide, a second molecule of CO[subscript 2] binds to afford a pseudo-octahedral dioxo dicarbonate complex, [MoO[subscript 2](κ[superscript 2]-CO[subscript 3])[subscript 2][superscript 2−], the first structurally characterized transition-metal dicarbonate complex derived from CO[subscript 2]. The monocarbonate [MoO[subscript 3](κ[superscript 2]-CO[subscript 3])][superscript 2−] reacts with triethylsilane in acetonitrile under an atmosphere of CO[subscript 2] to produce formate (69% isolated yield) together with silylated molybdate (quantitative conversion to [MoO[subscript 3](OSiEt[subscript 3])][superscript −], 50% isolated yield) after 22 hours at 85 °C. This system thus illustrates both the reversible binding of CO[subscript 2] by a simple transition-metal oxoanion and the ability of the latter molecular metal oxide to facilitate chemical CO[subscript 2] reduction.Saudi Basic Industries CorporationSpain. Ministerio de Educación, Cultura y DeporteSpain. Ministerio de Economía y Competitividad (CTQ2012-36966)National Science Foundation (U.S.) (CHE-1111357)National Science Foundation (U.S.) (CHE- 0946721

Facile synthesis of mononuclear early transition-metal complexes of κ3cyclo-tetrametaphosphate ([P4O12]4−) and cyclo-trimetaphosphate ([P3O9]3−)

We herein report the preparation of several mononuclear-metaphosphate complexes using simple techniques and mild conditions with yields ranging from 56% to 78%. Treatment of cyclo-tetrametaphosphate ([TBA]4[P4O12]·5H2O, TBA = tetra-n-butylammonium) with various metal sources including (CH3CN)3Mo(CO)3, (CH3CN)2Mo(CO)2(η3-C3H5)Cl, MoO2Cl2(OSMe2)2, and VOF3, leads to the clean and rapid formation of [TBA]4[(P4O12)Mo(CO)3]·2H2O, [TBA]3[(P4O12)Mo(CO)2(η3-C3H5)], [TBA]3[(P4O12)MoO2Cl] and [TBA]3[(P4O12)VOF2]·Et2O salts in isolated yields of 69, 56, 68, and 56% respectively. NMR spectroscopy, NMR simulations and single crystal X-ray studies reveal that the [P4O12]4− anion behaves as a tridentate ligand wherein one of the metaphosphate groups is not directly bound to the metal. cyclo-Trimetaphosphate-metal complexes were prepared using a similar procedure i.e., treatment of [PPN]3[P3O9]·H2O (PPN = bis(triphenylphosphine)iminium) with the metal sources (CH3CN)2Mo(CO)2(η3-C3H5)Cl, MoO2Cl2(OSMe2)2, MoOCl3, VOF3, WOCl4, and WO2Cl2(CH3CN)2 to produce the corresponding salts, [PPN]2[(P3O9)Mo(CO)2(η3-C3H5)], [PPN]2[(P3O9)MoO2Cl], [PPN]2[(P3O9)MoOCl2], [PPN]2[(P3O9)VOF2]·2CH2Cl2, and [PPN]2[(P3O9)WO2Cl] in isolated yields of 78, 56, 75, 59, and 77% respectively. NMR spectroscopy, NMR simulations and single-crystal X-ray studies indicate that the trianionic ligand [P3O9]3− in these complexes also has κ3 connectivity.Eni S.p.A. (Firm)Eni-MIT Solar Frontiers Center (Program

Synthesis and Characterization of Iron Derivatives Having a Pyridine-Linked Bis(anilide) Pincer Ligand

A pyridine-linked bis(aniline) pincer ligand, [2]H_2 ([2]H_2 = (2,6-NC_5H_3(2-(2,4,6-Me_3C_6H_2)-NHC6H4)2), has been synthesized in two steps. Deprotonation with Me_3SiCH_2Li followed by metalation with FeCl_2 yielded a LiCl adduct of [2]Fe. The complex is freed of LiCl with excess TlPF_6 or by crystallization from toluene/petroleum ether, giving [2]Fe(THF). [2]Fe(THF) reacts with I_2 and O_2 to generate [2]FeI and ([2]Fe)_2O, respectively. The complexes have been characterized by ^1H NMR spectroscopy, elemental analysis, X-ray crystallography, and UV−vis spectroscopy. [2]Fe(THF) has been examined using cyclic voltammetry

Zirconium and Titanium Propylene Polymerization Precatalysts Supported by a Fluxional C_2-Symmetric Bis(anilide)pyridine Ligand

Titanium and zirconium complexes supported by a bis(anilide)pyridine ligand (NNN = pyridine-2,6-bis(N-mesitylanilide)) have been synthesized and crystallographically characterized. C_2-symmetric bis(dimethylamide) complexes were generated from aminolysis of M(NMe_2)_4 with the neutral, diprotonated NNN ligand or by salt metathesis of the dipotassium salt of NNN with M(NMe_2)_2Cl_2. In contrast to the case for previously reported pyridine bis(phenoxide) complexes, the ligand geometry of these complexes appears to be dictated by chelate ring strain rather than metal–ligand π bonding. The crystal structures of the five-coordinate dihalide complexes (NNN)MCl_2 (M = Ti, Zr) display a C_1-symmetric geometry with a stabilizing ipso interaction between the metal and the anilido ligand. Coordination of THF to (NNN)ZrCl_2 generates a six-coordinate C_2-symmetric complex. Facile antipode interconversion of the C_2 complexes, possibly via flat C_(2v) intermediates, has been investigated by variable-temperature ^1H NMR spectroscopy for (NNN)MX_2(THF)_n (M = Ti, Zr; X = NMe_2, Cl) and (NNN)Zr(CH_2Ph)_2. These complexes were tested as propylene polymerization precatalysts, with most complexes giving low to moderate activities (10^2–10^4 g/(mol h)) for the formation of stereoirregular polypropylene

Fluorinated antimony(v) derivatives: strong Lewis acidic properties and application to the complexation of formaldehyde in aqueous solutions

As part of our ongoing studies of water tolerant Lewis acids, we have synthesized and investigated the properties of Sb(C(6)F(5))(3)(O(2)C(6)Cl(4)), a fluorinated stiborane whose Lewis acidity approaches that of B(C(6)F(5))(3). While chloroform solutions of this Lewis acid can be kept open to air or exposed to water for extended periods of time, this new Lewis acid reacts with P(t)Bu(3) and paraformaldehyde to form the corresponding formaldehyde adduct (t)Bu(3)P–CH(2)–O–Sb(C(6)F(5))(3)(O(2)C(6)Cl(4)). To test if this reactivity can also be observed with systems that combine the phosphine and the stiborane within the same molecule, we have also prepared o-C(6)H(4)(PPh(2))(SbAr(2)(O(2)C(6)Cl(4))) (Ar = Ph, C(6)F(5)). These yellow compounds, which possess an intramolecular P→Sb interaction, are remarkably inert to water but do, nonetheless, react with and accomodate formaldehyde into the P/Sb pocket. In the case of the fluorinated derivative o-C(6)H(4)(PPh(2))(Sb(C(6)F(5))(2)(O(2)C(6)Cl(4))), formaldehyde complexation, which occurs in water/dichloromethane biphasic mixtures, is accompanied by a colourimetric turn-off response thus highlighting the potential that this chemistry holds in the domain of molecular sensing

A pathway to diphosphorus from the dissociation of photoexcited tetraphosphorus

We report a computational study of an energetically favorable pathway for the excited-state dissociation of a tetrahedral P[subscript 4] molecule into two P[subscript 2] molecules via the simultaneous breaking of four chemical bonds along a highly symmetric (D[subscript 2d]) reaction pathway. Along this pathway, a degeneracy occurs between the first excited state of P[subscript 4] and the ground state of 2P[subscript 2] at a lower total energy (ca. 4.7 eV) than the initial state, indicating that the initial photoexcitation provides sufficient energy for the dissociation without significant kinetic barriers. We also found that sequential dissociation of the four P–P bonds exhibits larger activation barriers thus making this a less viable dissociation pathway. Our computational investigation uncovers complicated photochemistry in elemental phosphorus, and suggests a likely mechanism for the environmentally friendly inclusion of phosphorus atoms into organic molecules.National Science Foundation (U.S.) (Grant CHE-6923295)National Science Foundation (U.S.) (Grant CHE-1111357