Pyramidal Phosphorus Research Articles

Bending Ferrocenes with Low Coordinated Bridging Units: The Investigation of Carbenes and Their Analogues with a Ferrocenophane Backbone

[3]ferrocenophanes with X–E–X ansa moieties containing a low coordinated center E stabilized by adjacent donor units X were studied by density functional theory methods. The cyclopentadienyl (Cp) rings favor an eclipsed position in most cases and exhibit a shortened C(1)–C(1′) distance compared to parent ferrocene. In case of bridges with the second row elements, the tilt of the Cp rings is more significant than that in case of third row elements; however, the estimated strain does not exceed 6 kcal/mol. The ansa unit has similar structural characteristics to the X–E–X-fragment in a six-membered saturated ring, with bond angles larger than that in the well-known heterocycles featuring five-membered cyclic systems. For compounds with X = PMe and E = C, Si, Ge, the non-planar coordination of the phosphorus atoms yields two symmetric minimum structures that are distinguished by trans and cis alignment of the PMe groups and are connected by a low-energy asymmetric transition structure with one planarized and one highly pyramidal phosphorus. In case of the analogous species with E = P+, this asymmetric structure was located as the sole minimum. A detailed analysis of the Kohn–Sham orbitals and the analysis of the electron density show that the electronic system of the ferrocene fragment is not mixing considerably with that of the low coordinated center of the ansa unit.

P-Ge/Sn π Interactions Versus Arene···Ge/Sn Contacts for the Stabilization of Diphosphatetrylenes, (R2P)2E (E = Ge, Sn).

The diphosphatetrylenes {(Dipp)(R')P}2E [R' = Mes, E = Ge (1Ge), Sn (1Sn); R' = CH(SiMe3)2, E = Sn (2Sn)] have been isolated and characterized by multinuclear and variable temperature NMR spectroscopy and X-ray crystallography [Dipp = 2,6-iPr2C6H3, Mes = 2,4,6-Me3C6H2]. All three compounds crystallize as discrete monomers with two pyramidal phosphorus centers. However, variable-temperature 31P{1H} NMR spectroscopy indicates that both 1Ge and 2Sn are subject to dynamic exchange between this form and a form containing one planar and one pyramidal phosphorus center in solution. In contrast, 1Sn retains two pyramidal phosphorus centers in solution and exhibits no evidence for exchange with a form containing a planar phosphorus center. The related compound [{(Me3Si)2CH}2P]2Sn (3Sn) was isolated in very low yield and was shown by X-ray crystallography to possess one planar and one pyramidal phosphorus center in the solid state. DFT calculations reveal that the conformations of 1Ge, 1Sn, and 2Sn observed in the solid state are significantly stabilized by the delocalization of electron density from the aromatic rings into the vacant p-orbital at the tetrel center. Thus, for diphosphatetrylenes possessing aromatic substituents at phosphorus, stabilization may be achieved by two competing mechanisms: (i) planarization of one phosphorus center and consequent delocalization of the phosphorus lone pair into the vacant tetrel p-orbital or (ii) pyramidalization of both phosphorus centers and delocalization of aromatic π-electron density into the tetrel p-orbital. For 3Sn, which lacks aromatic groups, only the former stabilization mechanism is possible.

Is the Inversion of Phosphorus Trihalides (PF3, PCl3, PBr3, and PI3) a Diradical Process?

This work explores possible reaction paths for the inversion of a series of trigonal pyramidal phosphorus trihalides, PF3, PCl3, PBr3, and PI3, and it especially addresses the question of whether and when the bonding of the lowest-energy species along the inversion paths should be described as a hyper-open-shell diradical. The various paths for inversion are calculated using a single-reference method within the framework of Kohn-Sham density functional theory and also with multireference wave function methods. Our calculated results using both kinds of methods show that, for all the halogens studied (F, Cl, Br, and I), the lowest-energy singlet path for the inversion occurs by the formation of a C2 v transition structure rather than a D3 h transition structure. This geometrical preference agrees with what has been inferred previously based on closed-shell singlet calculations. But in the present study, we examined not only closed-shell singlet transition states but also open-shell singlet states and triplet states for calculating stationary points and inversion paths, and for some of the phosphorus trihalides, we found that paths involving open-shell configurations are lower in energy than those restricted to closed-shell configurations. We analyzed the changes along the paths in terms of hybridization and orientation of the frontier orbitals and in terms of locally avoided crossings, and the extent of the diradical character was quantified by calculating the effective number of unpaired electrons. Even for the singlet inversion path that goes via a D3 h structure, the barrier for PF3, PCl3, and PBr3 is higher for a closed-shell singlet spin state than for the open-shell singlet configuration. Furthermore, the energy of the triplet D3 h structure is below even that of the open-shell D3 h singlet for PCl3, PBr3, and PI3. This necessitates rethinking the role of open-shell states in nominally closed-shell processes.

Influence of P-Bonded Bulky Substituents on Electronic Interactions in Ferrocenyl-Substituted Phospholes.

2,5-Diferrocenyl-1-Ar-1H-phospholes 3 a-e (Ar=phenyl (a), ferrocenyl (b), mesityl (c), 2,4,6-triphenylphenyl (d), and 2,4,6-tri-tert-butylphenyl (e)) have been prepared by reactions of ArPH2 (1 a-e) with 1,4-diferrocenyl butadiyne. Compounds 3 b-e have been structurally characterized by single-crystal XRD analysis. Application of the sterically demanding 2,4,6-tri-tert-butylphenyl group led to an increased flattening of the pyramidal phosphorus environment. The ferrocenyl units could be oxidized separately, with redox separations of 265 (3 b), 295 (3 c), 340 (3 d), and 315 mV (3 e) in [NnBu4 ][B(C6 F5 )4]; these values indicate substantial thermodynamic stability of the mixed-valence radical cations. Monocationic [3 b](+)-[3 e](+) show intervalence charge-transfer absorptions between 4650 and 5050 cm(-1) of moderate intensity and half-height bandwidth. Compounds 3 c-e with bulky, electron-rich substituents reveal a significant increase in electronic interactions compared with less demanding groups in 3 a and 3 b.

Why edge inversion? Theoretical characterization of the bonding in the transition states for inversion in F n NH(3−n) and FnPH(3−n) (n = 0–3)

As first noted by Dixon et al. (J Am Chem Soc 108:2461–2462, 1986), heavily fluorinated pyramidal phosphorus compounds, e.g., F n PH(3−n) with n > 1, invert through a T-shaped transition state (edge inversion) rather than the D3h-like transition states (vertex inversion) found in the corresponding nitrogen compounds and less fluorinated phosphorus compounds. Subsequent studies by Dixon and coworkers established that this is a general phenomenon and has important chemical consequences. But what is the reason for the change in the structure of the transition state? Recent theoretical investigations have resulted in the discovery of a new type of chemical bond, the recoupled pair bond. In particular, it was found that recoupled pair bond dyads account for the hypervalency of the elements beyond the first row. In this paper, we show that recoupled pair bond dyads also account for the existence of the edge inversion pathway in heavily fluorinated phosphorus compounds and likely account for the presence of the lower energy inversion pathways in pyramidal compounds of other elements beyond the first row.

Dual Supermesityl Stabilization: 1-Alkyl-1H-[1,2,4]triphospholes, with Among the Most Planar and Least Sterically Hindered σ3,λ3-Phosphorus Atoms, and Novel C2P3S4 Folded Heterocycles

1-Methyl-3,5-bis(2,4,6-tri-tert-butylphenyl)-1H-[1,2,4]triphosphole (6) and 1-benzyl-3,5-bis(2,4,6-tri-tert-butylphenyl)-1H-[1,2,4]triphosphole (7) were synthesized and isolated with among the most planar and least sterically hindered σ3,λ3-phosphorus atoms, which are an indication of the aromaticity of this heterocycle. The sums of the bond angles at the σ3,λ3-phosphorus atoms in 6 and 7 are close to 360°. σ3,λ3-Phosphorus atoms in 6 and 7 have substantial deshielded chemical shifts at 151.86 and 161.71 ppm in the 31P NMR spectra. The parental trimethylphosphine and tribenzylphosphine with pyramidal phosphorus atoms have chemicals shifts at −62.0 and −10.4 ppm. There are large P−P coupling constants: 1JPP = 549.7 Hz for 6 and 553.3 Hz for 7. This is further evidence of a significant delocalization of the electron density in these polyphosphorus heterocycles. Compound 7 reacts with sulfur to afford 3-benzyl-2,4-bis(2,4,6-tri-tert-butylphenyl)-6,7-dithia-1,3λ5,5-triphosphabicyclo[3.1.1]hepta-2,3-diene 1,5-disulfide (8), which is the first example of a C2P3S4 folded heterocycle. The formation of 8 involves an unusual 1,3-benzyl shift with oxidation of all λ3-phosphorus atoms to λ5-phosphorus atoms.

1H-Phosphepine-benzene phosphine valence tautomerizations: Impacts of substituents at ab initio and DFT levels

The main goal of this work is to find a more stable seven-membered ring 1H-phosphepine connected to its bicyclic benzene phosphine valence tautomer after passing through a nonplanar transition state. This challenge is met by probing the impacts of substituents (X = H, F, Cl, Br, CN, Me, CF3, NH2, and OMe) on the umbrella inversions of 1H-phosphepines, as well as their effects on two series of equilibria consisting of 2-X-benzene phosphines ⇌ 3-X-1H-phosphepines (series A) and 3-X-benzene phosphines ⇌ 4-X-1H-phosphepines (series B), all in the more stable endo form of pyramidal phosphorus atom. Among 17 tautomerization systems, scrutinized at B3LYP/6-311G∗ level, only the 3-methoxybenzene phosphine ⇌ 4-methoxy-1H-phosphepine system shows equilibrium shift to the right. In contrast to the tautomerizations, umbrella inversions of 1H-phosphepines are not much sensitive to the effects of substituents placed around their carbon skeletons. The magnetic (NICS) and structural criteria indicate partial aromaticity of 1H-phosphepines and high anti-aromaticity for their planar inversion transition states. Some justifications based on NBO data and calculated ΔEHOMO–LUMO are presented. Various inconsistencies occur between the ab initio and DFT data, making the equilibrium constants (Keqs) sensitive to the methods of calculation along the substituents effects.

The α-Iminophospholide Ligands

The reaction of phospholide ions with imidoyl chlorides in the presence of tBuOK gives the alpha-iminophospholides that are isolated as their trimethylstannyl derivatives. These derivatives in turn react with metal chlorides to give complexes of the title ligands. A DFT study shows that substantial electronic delocalization takes place between the imino group and the phospholyl ring in these anions. The X-ray crystal structure of one stannylphosphole shows a highly pyramidal phosphorus atom (sum of angles = ca. 280 degrees ). A tetrameric copper complex has also been structurally characterized.

PM3 STUDY OF PHOSPHINES AND PHOSPHINE CHALCOGENIDES. CONFORMATIONAL AND CONFIGURATIONAL PROPERTIES OF TRI-O-TOLYL PHOSPHINE AND ITS CHALCOGENIDES

An investigation employing the PM3 semiempirical self-consistent field molecular orbital method to calculate structure optimization and pyramidal phosphorus atom inversion barriers for phosphines and phosphine chalcogenides 1–16 has been undertaken. The calculated structural parameters (for 1–12) and inversion barriers (for 13–16) are in good agreement with experimental results. The conformational interconversion pathways for tri-o-tolylphohphine (9), tri-o-tolylphosphine oxide (10), tri-o-tolylphosphine sulfide (11) and tri-o-tolylphosphine selenide (12) were investigated in detail. For compounds 9–12, four rotamers are possible with respect to the position of the methyl groups. In the most stable geometry of 9, two of the methyl groups are close to the phosphorus lone pair. In 10, the methyl groups assume the paddle conformation, having all methyl groups close to the oxygen atom. In 11, the most stable rotamer is similar to that in 9. In the most stable rotamer of 12, all methyl groups are far from the selenium atom.

Quantumchemical Investigation of Unsaturated Sixmembered Heterocycles: I. Steric and Electronic Structures of 1,2-dihydro-1,2-azaphosphorin

By quantumchemical calculations of 1,2-dihydro-1,2-azaphosphorin by semiempirical and abinitio calculations we discovered that in gas phase it has twist form with planar nitrogen and pyramidal phosphorus atoms, the latter with a pseudoaxial substituent. The N-H and P-H bonds occupy anticlinal positions.

The sulphur 2p photoabsorption spectrum of NSF 3

Abstract The high resolution sulphur 2p photoabsorption spectrum of gaseous NSF3 has been measured using synchrotron radiation. Assignment of the pre-edge spectral features was accomplished with the aid of ab initio GSCF3 configuration interaction calculations. Similar to the isoelectronic OPF3 and other pyramidal phosphorus compounds there exist two states which are best described as LS coupled because of a very large core–valence electron exchange. The post-edge features, corresponding to outer well p and d shape resonances, were assigned with the aid of Xα calculations.

1,3-Distanna-2-phospha-[3]ferrocenophanes - Synthesis, Reactivity and NMR Spectroscopic Properties

1,1,3,3-Tetramethyl-2-organo(R)-1,3-distanna-2-phospha-[3]ferrocenophanes [R = Me (2a), tBu (2b), C6H11 (2c), Ph (2d)] and one arsa-analogue 2d(As) were obtained from the reaction of 1,1′-bis(chlorodimethylstannyl)ferrocene 1 with either bis(trimethylsilyl)methylphosphane or the dilithio derivatives, Li2PR and Li2AsPh, respectively. All compounds 2 react with chalcogens (oxygen, sulfur, selenium) by cleavage of the Sn-P bonds and formation of the known 1,3-distanna-2-chalcogena-[3]ferrocenophanes. In contrast, 2d traps pentacarbonylmetal fragments [M(CO)5] to give the stable phosphane complexes [M = Cr (4d), Mo (5d), W (6d)]. The 1,1′-bis(diorganophosphanostannyl)ferrocenes [R = tBu (3b), Ph (3d)] were prepared for comparison of NMR data. The ferrocenophanes 2 are fluxional with respect to fast movement of the cyclopentadienyl rings which induces inversion at the pyramidal phosphorus atom. This dynamic process is slow in the cases of 2d(As) and of the pentacarbonyl complexes 4d - 6d. All new compounds were characterised by 1H, 13C, 31P and 119Sn NMR spectroscopy. Various 2D heteronuclear shift correlations (e.g. 31P/1H and 119Sn/1H ) were carried out for the compounds 2 and also for non-cyclic derivatives such as bis(trimethylstannyl)phenvlphosphane and -arsane in order to determine absolute signs of coupling constants [e.g. 1J(119Sn,31P) > 0 and 2J(119Sn,117Sn) < 0]. The NMR data suggest that the molecular frameworks of the ferrocenophanes 2 are not particularly strained.

Structural Characterization and Coordination Behavior of 1,2-Diphosphino and 1,2-Diarsino-Diborane(4) Compounds

Reaction of either LiPPh2 or LiAsMes2 with the diborane(4) compound (Me2N) BrBBBr(NMe2) affords the compounds (Me2N)(Ph2P)BB(PPh2)(NMe2), 1, and (Me2N) (Mes2As)BB(AsMes2)(NMe2)·0.5 PhMe, 2·0.5 PhMe (Mes = 2,4,6-Me3C6H2-). Both 1 and 2 feature normal B–B single bond lengths; however, the empty boron p-orbitals display strong π-interactions with the dimethylamino substituents. The B–P and B–As distances and the pyramidal phosphorus and arsenic geometries are consistent with single bonding. Furthermore, the stereochemical activity of the phosphorus and arsenic lone pairs is demonstrated by the ready formation of the complex cis-[Cr(CO)4(Me2N)(Ph2P)BB(PPh2) (NMe2)]·C6H6, 3·C6H6, by treatment of 1 with [Cr(CO)4(2,5-norbornadiene)]. Compounds 1–3 were characterized by X-ray crystallography, 11B and 31P NMR spectroscopy, and by IR spectroscopy in the case of 3.

2-YIidvl-1,3,2-oxathiaphosphole und -oxaselenaphosphole / 2-Ylidyl-1,3,2-oxathiaphospholes and -oxaselenaphospholes

Ylidyl thioxophosphines or selenoxophosphines and phenacyl halides undergo addition in a 1:1 ratio and yield in the presence of triethylamine the title compounds. The molecular structure of an ylidyl oxathiaphosphole demonstrates a strong interaction between the ylid substituent and the heterocycle, making the exocyclic PC-bond unusually short and the endocyclic PO- and PS-bonds considerably longer than normal for a pyramidal phosphorus atom. The ylidyl chalcogenoxophosphines are oxidized by sulfur or selenium at the phosphorus atom and protonated at the ylidic carbon atom. No Wittig-type reaction is observed.

Stereochemistry of the P–C bond formation in an oxazaphospholidine borane complex

The reaction of the 3,4-dimethyl-2,5-diphenyl-1,3,2-oxazaphospholidine borane complex 1 with organometallic reagents involves a stereoselective P–O bond cleavage; the X-ray structures of the starting complex 1 and of the aminophosphine boranes 2a,b, reveal a stereochemistry of the P–C bond formation with a retention of the configuration which is explained by a nucleophilic attack on the less hindered side-face of the pyramidal phosphorus atom.

Preparation and Crystal Structures of Th5Fe19P12 and ThFe4P2

The new compounds Th5Fe19P12 and ThFe4P2 were prepared by reaction of the elemental components in a tin flux and their crystal structures were determined from single-crystal X-ray data. Th5Fe19P12 crystallizes with a new monoclinic structure type: C2/m, a = 2920.3(3), b = 379.18(3), c = 931.48(8) pm, β = 103.36(1)°, Z = 2, R = 0.031. ThFe4P2 is isotypic with SmNi4P2: P nnm, a = 1448.9(2), b = 1074.7(2), c = 376.98(4) pm, Z = 6, R = 0.030. Both compounds belong to the large family of structures with a metal : nonmetal ratio of exactly or nearly 2:1. In these phosphides all phosphorus atoms have nine metal neighbors: six are forming a trigonal prism with three additional neighbors capping the rectangular faces of the prism. In both structures the thorium atoms have trigonal prismatic or octahedral phosphorus coordination. Most iron atoms have the usual tetrahedral phosphorus environment. In addition, the structure of Th5Fe19P12 has iron atoms in rectangular and distorted square pyramidal phosphorus coordination, while the structure of ThFe4P2 contains iron atoms with only two or three phosphorus neighbors.

Nouveau type structural dans la chimie des phosphures : Le compose ternaire Ni 20Zr 6P 13. Preparation, structure et proprietes

Abstract Two new compounds Ni 12 Zr 2 P 7 and Ni 20 Zr 6 P 13 were synthesized in the NiZrP system by reacting the constituent elements. Ni 12 Zr 2 P 7 is of the Fe 12 Zr 2 P 7 -type while Ni 20 Zr 6 P 13 appears as a new structural type in the chemistry of transition metal phosphides. Its unit cell is hexagonal with space group P6 and contains one formula unit. The X-ray structure was studied from three-dimensional single-crystal counter data and was refined down to R = 0.040 for 221 independent reflections. The structure of Ni 20 Zr 6 P 13 can be described as built up by two groups of three phosphorus trigonal prisms occupied by the zirconium atoms. In each group, the |ZrP 6 | prisms are linked together by common edges in order to generate triangular phosphorus sites occupied by nickel atoms. In addition, nickel atoms are also in tetrahedral and square-planar pyramidal phosphorus sites. A comparative study with the Fe 2 P- and Co 4 Hf 2 P 3 -type structures having the same metal/non metal ratio as in Ni 12 Zr 2 P 7 and Ni 20 Zr 6 P 13 is also discussed. A nearly temperature independent paramagetism and a metallic conduction deducted from magnetic and electrical measurements exhibit the metallic behavior for these new compounds.

On the nature of the “free electron pair” on phosphorus in aromatic phosphorus compounds: The photoelectron spectrum of 2-phosphanaphthalene

The electronic structure of the 2-phosphanaphthalene system has been studied by photoelectron spectroscopy. The assignment of bands in the PE spectra of 2-phosphanaphthalene and 3-methyl-2-phosphanaphthalene has been performed with the aid of two useful generalisations, one pertaining to the energies of the the π ionizations, and the other to the phosphorus n ionization, as well as by calculations using the extended CNDO/S method. The n ionization of the 2-phosphanaphthalenes can be observed as a well separated single band. From the breadth of this n band the “lone pair” is seen to have considerable bonding character resulting from orbital mixing with other σ-orbitals of the molecule. This appears to be the first evidence of appreciable delocalization of ldlone pair” phosphorus electrons in aromatic molecules, which, judging from the breadth of the bands, is almost as large as with pyramidal phosphorus atoms.

Square pyramidal phosphorus. X-Ray analysis of the 1,3,2-dioxaphospholans from hexafluoroacetone and phosphetans

X-Ray crystal structure determinations of two 1,3,2-dioxaphospholans formed from hexafluoroacetone and 1-p-bromophenylphosphetans reveal square pyraamidal geometry about phosphorus.