John D. Protasiewicz

Synthesis and Structural Characterization of New Hindered Aryl Phosphorus Centers (Aryl = 2,6-Dimesitylphenyl)

The new sterically encumbered dichlorophosphine ArPCl2 (Ar = 2,6-dimesitylphenyl = Dmp,1) has been prepared from the corresponding aryliodide, n-butyllithium, and phosphorus trichloride. DmpPCl2 served as a precursor for the phosphinic acid DmpP(O)(OH)H(2), primary phosphine DmpPH2 (3), and diphosphene DmpP = PDmp (4). Compounds 2 and 4 have been crystallographically characterized. The solid state structure of 2 reveals the existence of dimeric phosphinic acids associated by hydrogen bonding in a manner analogous to carboxylic acid dimers. The P‒O distances are 1.508(2) and 1.521(2) A, and the O‒H and O‒H…O distances are 1.06(4) and 1.46(4), consistent with localized hydrogen bonding. The structure of 4 features a trans configuration about the P = P bond and short P = P bond length of 1.985 (2) A. Crystal data for compound 2: a = 9.4552(8) A, b = 11.174(1) A, c = 11.711(1) A, α = 65.775(8) A, β = 75.735(7)°, γ = 69.621(7)°, triclinic, P—1,Z = 2. Crystal data for compound 4: a = 10.940(1) A, b = 22.323(2) ...

Bis(μ-N,N′-η2-N,O-η2-N′,O′-di(o-methoxyphenyl)formamidinato)disilver(I): an interesting coordination geometry for silver(I) and room temperature fluorescence

Abstract Reported here are the synthesis, structural and spectroscopic characterization of the title disilver compound, which provides the first example of room temperature fluorescence from a d10–d10 compound. In addition to confirmation of the dinuclear nature of the compound, X-ray crystallographic analysis reveals an N2O2 (distorted) tetrahedral coordination for each silver(I) center.

Phosphorus as a carbon copy and as a photocopy: New conjugated materials featuring multiply bonded phosphorus*

Phosphaalkenes (RP=CR2) and diphosphenes (RP=PR) are main group analogues of alkenes (R2C=CR2). Molecules featuring such multiply bonded phosphorus functionalities often display structural features and chemical reactivities that mimic their purely organic counterparts, lending credence to the claim that these compounds are “carbon copies”. We have been expanding this analogy to include oligomers and polymers with extended conjugation that directly involve P=C and P=P units. Many of these materials, however, display little or no photoluminescence (PL). This article summarizes our efforts to understand P=C and P=P photobehavior and to produce materials having significant PL that mimic or “photocopy” the PL properties of the phosphorus-free systems. Recent materials based on benzoxaphospholes (BOPs), benzobisoxaphospholes (BBOPs), and higher analogues having significant fluorescence quantum yields are covered.

Synergistic Binding of Both Lewis Acids and Bases to Phosphinidenes

Free phosphinidenes or phosphanylidenes (RP), the heavier analogues of carbenes, remain unisolable owing to their extreme reactivity. Although a significant body of stable transition metal complexes having terminal PR functionalities now exists, simple main group adducts of phosphinidenes are by comparison rare. Phosphanylidene-s-phosphoranes (RP= PR’3) are a fundamental type of base-stabilized adducts of phosphinidenes First recognized in 1961 with the synthesis of CF3P=PMe3, [3] and later studied in more detail, these early derivatives were thermally unstable and not structurally characterized. Derivatives bearing additional phosphorus atoms and lone pairs, such as R2P P=P(X)R’2 are also an important class of such materials, and they have received attention as phosphinidene precursors and transfer reagents. 5] The more recent discovery of thermally stable ArP=PR3, where Ar is a sterically demanding aryl group, allowed for structural identification and more detailed studies. Phosphanylidene-s-phosphoranes can be pictorially represented by various resonance forms (Scheme 1, top)

Triphosphane formation from the terminal zirconium phosphinidene complex [Cp2ZrPDmp(PMe3)] (Dmp=2,6-Mes2C6H3) and crystal structure of DmpP(PPh2)2

Abstract The new terminal phosphinidene complex [Cp2ZrPDmp(PMe3)] (Dmp=2,6-Mes2C6H3; 1) was prepared in 81% yield by the reaction of [Li(Et2O)][P(H)Dmp] with [Cp2Zr(Me)Cl] in the presence of excess PMe3. Compound 1 reacts with Ph2PCl to produce selectively the sterically congested triphosphane DmpP(PPh2)2 (2) and [Cp2ZrCl2] in high yields. The structure of 2 obtained by X-ray diffraction analysis of a single crystal reveals phosphorus–phosphorus bond lengths of 2.251(2) and 2.234(2) A and a PPP bond angle of 105.46(6)°.

Stereocontrolled 1,3-dipolar cycloadditions using Oppolzer's camphor sultam as the chiral auxiliary for carbonyl stabilized azomethine ylides

Abstract Two complementary approaches to substituted pyrrolidines via stereocontrolled 1,3-dipolar cycloaddition reactions of chiral azomethine ylides are described. In one approach, chiral azomethine ylides were generated by thermolysis of aziridine carboxylate sultams and trapped with a variety of dipolarophiles to give good yields of the corresponding cycloadducts. In the second approach, chiral azomethine ylides were generated from glycyl sultams by ‘imine tautomerization’ and trapped with dipolarophiles to give good yields of the corresponding cycloadducts.

Crystal structure of the phosphanylidene-σ4-phosphorane DmpPPMe3 (Dmp=2,6-Mes2C6H3) and reactions with electrophiles

Abstract The stable phosphanylidene-σ4-phosphorane DmpPPMe3 (1, Dmp=2,6-Mes2C6H3) has been examined by single-crystal X-ray diffraction methods. The structure of 1 features a relatively short PP bond length of 2.084(2) A. Reactions of 1 with various electrophiles demonstrate the nucleophilic behavior of the phosphanylidene atom of 1 and also provide access to new organophosphorus compounds. For example, addition of excess BH3 (in the form of either BH3·THF or BH3·SMe2) to 1 leads to formation of a mono-borane adduct DmpP(BH3)PMe3. Reactions of carbon and silicon based electrophiles EX (E=R3C or R3Si; X=halide or OTf−) produce either diphosphanium salts [DmpP(E)PMe3]X or phosphines DmpP(E)X. In some cases equilibrium mixtures of both product types are observed, and the equilibria can be shifted by addition of either X− or PMe3. Compound 1 is also readily protonated by HOTf, HCl and PhOH. As found for the carbon and silicon based electrophiles, the nature of the resulting product depends on the counterion.

Twisting the Phenyls in Aryl Diphosphenes (Ar-P=P-Ar). Significant Impact upon Lowest Energy Excited States

Aryl diphosphenes (Ar-P=P-Ar) possess features that may make them useful in photonic devices, including the possibility for photochemical E-Z isomerization. Development of good models guided by computations is hampered by poor correspondence between predicted and experimental UV/vis absorption spectra. A hypothesis that the phenyl twist angle (i.e., PPCC torsion) accounts for this discrepancy is explored, with positive findings. DFT and TDDFT (B3LYP) were applied to the phenyl-P=P-phenyl (Ph-P=P-Ph) model compound over a range of phenyl twist angles, and to the Ph-P=P-Ph cores of two crystallographically characterized diphosphenes: bis-(2,4,6-tBu(3)C(6)H(2))-diphosphene (Mes*-P=P-Mes*) and bis-(2,6-Mes(2)C(6)H(3))-diphosphene (Dmp-P=P-Dmp). A shallow PES is observed for the model diphosphene: the full range of phenyl twist angles is accessible for under 5 kcal/mol. The Kohn-Sham orbitals (KS-MOs) exhibit stabilization and mixing of the two highest energy frontier orbitals: the n(+) and pi localized primarily on the -P=P- unit. A simple, single-configuration model based upon this symmetry-breaking is shown to be consistent with the major features of the measured UV/vis spectra of several diphosphenes. Detailed evaluation of singlet excitations, transition energies and oscillator strengths with TDDFT showed that the lowest energy transition (S(1) <-- S(0)) does not always correspond to the LUMO <-- HOMO configuration. Coupling between the phenyl rings and central -P=P- destabilizes the pi-pi* dominated state. Hence, the S(1) is always n(+)-pi* in nature, even with a pi-type HOMO. This coupling of the ring and -P=P- pi systems engenders complexity in the UV/vis absorption region, and may be the origin of the variety of photobehaviors observed in diphosphenes.

A role for free phosphinidenes in the reaction of magnesium and sterically encumbered ArPCl2 in solution at room temperature

Abstract The reduction of ArPCl 2 (Ar=2,6-Trip 2 C 6 H 3 , 2,6-Mes 2 C 6 H 3 , 2,6-(2,6-Me 2 C 6 H 3 ) 2 C 6 H 3 , or 2,4,6- t Bu 3 C 6 H 3 ) by various forms of activated magnesium have been examined and compared with previously reported reductions using unactivated magnesium. The current reactions are more rapid and give rise to products that are reminiscent of products obtained by irradiation of phosphanylidene-σ 4 -phosphoranes ArPPMe 3 bearing the same Ar groups. The correlation in product distributions suggests the involvement of phosphinidenes in the reduction of aryldichlorophosphines by activated magnesium.

Long, Directional Interactions in Cofacial Silicon Phthalocyanine Oligomers

Single crystal structures have been determined for the three cofacial, oxygen-bridged, silicon phthalocyanine oligomers, [((CH(3))(3)SiO)(2)(CH(3))SiO](SiPcO)(2-4)[Si(CH(3))(OSi(CH(3))(3))(2)], and for the corresponding monomer. The data for the oligomers give structural parameters for a matching set of three cofacial, oxygen-bridged silicon phthalocyanine oligomers for the first time. The staggering angles between the six adjacent cofacial ring pairs in the three oligomers are not in a random distribution nor in a cluster at the intuitively expected angle of 45° but rather are in two clusters, one at an angle of 15° and the other at an angle of 41°. These two clusters lead to the conclusion that long, directional interactions (LDI) exist between the adjacent ring pairs. An understanding of these interactions is provided by atoms-in-molecules (AIM) and reduced-density-gradient (RDG) studies. A survey of the staggering angles in other single-atom-bridged, cofacial phthalocyanine oligomers provides further evidence for the existence of LDI between cofacial phthalocyanine ring pairs in single-atom-bridged phthalocyanine oligomers.