Two iridanonaborane compounds

Two iridanonaborane compounds, 4-carbonyl-5,6:8,9-bis-μH-4-hydrido-4-bis­(tri­methyl­phosphine)-4-irida-arachno-nonaborane(12), [IrH(B₈H₁₂)(C₃H₉P)₂(CO)], (Ia), and 2-carbonyl-2,5:6,9:8,9-tri-μH-4-chloro-2-bis­(tri­methyl­phosphine)-2-irida-nido-nonaborane(11), [Ir(B₈H₁₀Cl)(C₃H₉P)₂(CO)], (II), are described. Compound (II) shows evidence of effective chlorine-substituent migration during its formation.     

Platinum Complexes of a Borane‐Appended Analogue of 1,1′‐Bis(diphenylphosphino)ferrocene: Flexible Borane Coordination Modes and in situ Vinylborane Formation

A bis(phosphine)borane ambiphilic ligand, [Fe(η⁵‐C₅H₄PPh₂)(η⁵‐C₅H₄PtBu{C₆H₄(BPh₂)‐ortho})] (FcPPB), in which the borane occupies a terminal position, was prepared. Reaction of FcPPB with tris(norbornene)platinum(0) provided [Pt(FcPPB)] ( 1 ) in which the arylborane is η³BCC‐coordinated. Subsequent reaction with CO and CNXyl (Xyl=2,6‐dimethylphenyl) afforded [PtL(FcPPB)] {L=CO ( 2 ) and CNXyl ( 3 )} featuring η²BC‐ and η¹B‐arylborane coordination modes, respectively. Reaction of 1 or 2 with H₂ yielded [PtH(μ‐H)(FcPPB)] in which the borane is bound to a hydride ligand on platinum. Addition of PhC₂H to [Pt(FcPPB)] afforded [Pt(C₂Ph)(μ‐H)(FcPPB)] ( 5 ), which rapidly converted to [Pt(FcPPB′)] ( 6 ; FcPPB′=[Fe(η⁵‐C₅H₄PPh₂)(η⁵‐C₅H₄PtBu{C₆H₄(BPh‐CPh=CHPh‐Z)‐ortho}]) in which the newly formed vinylborane is η³BCC‐coordinated. Unlike arylborane complex 1 , vinylborane complex 6 does not react with CO, CNXyl, H₂ or HC₂Ph at room temperature.     

Coulombic Basis for Relative Hydrogen-Bonding Basicities and Conformational Energies of Tertiary Amine Oxides and Phosphine Oxides

The structures, energies, and natural atomic charges of 2-dimethylaminophenol oxide, 2-Me₂N-(O)C₆H₄OH, and 2-dimethylphosphinylphenol, 2-Me₂P(O)C₆H₄OH, in three different conformations were computed at the ab initio MP2/6-31G* level. Computed natural charges indicate distributions of electron density in amine oxides and phosphine oxides that are quite different from what is normally assumed on the basis of the formal charges in the usual representations of these compounds. The charges on nitrogen and phosphorus in these compounds are typically computed to be approximately zero on nitrogen and +2 on phosphorus, and the oxygen is considerably more negative in the phosphine oxide than in the amino oxide. Electronegativity differences thus play a larger role and formal charges a smaller one in determining atomic charges in these compounds than is generally believed. Despite the more negative oxygen in phosphine oxides, amine oxides are computed to be considerably more basic when participating in hydrogen bonding. Calculations treating the computed natural charges on these six conformations as point charges for classical approximations of the coulombic energies support the idea that the quantum mechanically computed relative energies are largely determined by coulombic interactions.     

Tricyclo[4.2.2.22,5] dodecane and Tricyclo [4.2.2.12,5]undecane. Preliminary communication

A synthesis of tricyclo [4.2.2.2^2,5]dodecane ( 19 ), a novel tricyclic C₁₂H₂₀ compound, is described. The key intermediate ketone 13 was prepared either from the C₁₀-photodimer 1 of cyclopentadienone or the C₁₁-cycloaddition products 11 and 12 . 13 was also transformed to tricyclo [4.2.2.1^2,5]undecane ( 8 ).     

α-Amino acetals containing a phosphonate or phosphine oxide group. Synthesis and reactions with resorcinols

New α-amino acetals containing a phosphonate or phosphine oxide group were synthesized by the Kabachnik-Fields reaction in the ternary system amino acetal-paraformaldehyde-dialkyl phosphonate (or dialkylphosphine oxide). Condensation of dialkyl (2,2-dimethoxyethylamino)methylphosphonates with resorcinol and its derivatives in ethanol in the presence of hydrochloric acid, apart from the corresponding 2,2-bis(polyhydroxyphenyl) ethylammonium salts, gave 2,5-bis(polyhydroxyphenyl)-1,4-bis[(dialkoxyphosphoryl)methyl]-piperazines. Dialkyl[(2,2-dimethoxyethylamino)methyl]phosphine oxides (Alk = C₈H₁₇, C₁₀H₂₁) did not react with resorcinol derivatives under similar conditions, and analogous ammonium salts were obtained by heating the reactants in boiling trifluoroacetic acid.     

Structure determination of a bis[4-(di-n-butylamino)phenyl](pyridin-3-yl)borane tetramer highlighting a unique geometric conformation of the core 16-membered ring

The tetramer of bis(4-di-n-butylaminophenyl)(pyridin-3-yl)borane [systematic name: 2λ⁴,4λ⁴,6λ⁴,8λ⁴-tetrabora-1,3,5,7(1,3)-tetrapyridinacyclooctaphane-1¹,3¹,5¹,7¹-tetrakis(ylium)], C₁₃₂H₁₉₂B₄N₁₂, was synthesized unexpectedly and crystallized. Its structure contains an unusual 16-membered ring core made up of four (pyridin-3-yl)borane groups. The ring adopts a conformation with pseudo-S₄ symmetry that is very different from the two other reported examples of this ring system. Density functional theory (DFT) computations indicate that the stability of the three reported ring conformations is dependent on the substituents on the B atoms, and that the pseudo-S₄ geometry observed in the bis(4-dibutylaminophenyl)(pyridin-3-yl)borane tetramer becomes significantly more stable when phenyl or 2,6-dimethylphenyl groups are attached to the boron centers.     

Three-Component Reaction of 4-Methylpyridine with Alkyl Propiolates and Secondary Phosphine Chalcogenides

The reaction between 4-methylpyridine, alkyl propiolates, and secondary phosphine oxides proceeded as N-vinylation-C-phosphorylation with stereo- and regioselective formation of (E)-N-ethenyl-C²- phosphoryl-1,2-dihydropyridines [when using bis(2-phenylethyl)phosphine oxide] or (E)-N-ethenyl-C⁴- phosphoryl-1,4-dihydropyridines (when using diphenylphosphine oxide). The process occurred at 60–62°C within 3 h to give functional dihydropyridines in 40–82% yield. Under similar conditions, bis(2-phenylethyl) phosphine sulfide and selenide reacted with alkyl propiolates preferably by nucleophilic PH-monoaddition at the triple bond.     

A rhodium(III) complex of the linear diborazine H3B·NMe2BH2·NMe2H: an intermediate in the dehydrocoupling of H3B·NMe2H

The solid‐state structure of the rhodium complex (dimethylamine–dimethylaminoborane–borane‐κ²H,H′)dihydridobis(triisopropylphosphane‐κP)rhodium(III) tetrakis[3,5‐bis(trifluoromethyl)phenyl]borate, [RhH₂(C₄H₁₈B₂N₂)(C₉H₂₁P)₂](C₃₂H₁₂BF₂₄), is reported. The complex contains the linear diborazine H₃B·NMe₂BH₂·NMe₂H, a kinetically important intermediate in the transition‐metal‐mediated dehydrocoupling of H₃B·NMe₂H, ultimately affording the dimeric amino‐borane [H₂BNMe₂]₂. The structure of the title complex contains a distorted octahedral Rh^III centre, with mutually trans phosphane ligands and cis hydride ligands. The diborazine is bound through two Rh—H—B σ‐bonds and exhibits a gauche conformation with respect to the B—N—B—N backbone.     

Manganese‐σ‐Borane Complexes from Dihaloboranes

The hydride complex K[(η⁵‐C₅H₅)Mn(CO)₂H] reacted with a range of dihalo(organyl)boranes X₂BR (X = Cl, Br; R = tBu,Mes, Ferrocenyl) to give the corresponding borane complexes[(η⁵‐C₅H₅)Mn(CO)₂(HB(X)R)]., The presence of a hydride in bridging position between manganese and boron was deduced from ¹¹B decoupled ¹H NMR spectra. Additionally, the structure of the tert‐butyl borane complex was confirmed by single‐crystal X‐ray diffraction.     

Magnetochemistry of boron hydride structures. Empirical aspects

The reviews and monographs on magnetochemistry of boron compounds are discussed. The structural peculiarities of borane derivatives relevant to magnetochemical calculations of diamagnetic contributions are are considered. Experimental measurements of diamagnetic susceptibility for deltahedral B₁₀H ₁₀ ^2– and B₁₂H ₁₂ ^2– cluster closo-anions were used to derive the diamagnetic atomic increments of the B atoms (_B) with coordination numbers 5 and 6. The atomic increments _B thus obtained were used to calculate molecular diamagnetic susceptibility _M of borane derivatives. Diamagnetic susceptibility _M was measured and calculated for the series of borane derivatives B_nH _n ^2– and B₁₀H₁₂L₂ (L is a Lewis base)and cobalt(III) derivatives of ortho-carborane(12) [(B₉C₂H₁₁)₂Co_n(B₈C₂H₁₀) _n–1] ^n–. Diamagnetic increments were obtained for |B₁₀H₁₂| fragments and (B₉C₂H₁₁)^2– and (B₈C₂H₁₀)^4– ligands. The increments can be employed for calculating _M for novel compounds. The calculated values of _M coincide with the experimental values within 2%–6%.Original Russian Text Copyright © 2004 by V. V. Volkov and V. N. IkorskiiTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 4, pp. 729–740, July–August 2004.This revised version was published online in April 2005 with a corrected cover date.     

Stability of polyhedral borane anions and carboranes

Polyhedral borane anions and carboranes that can be constructed formally from the interaction of rings and caps will be stable with six interstitial electrons. Interstitial electron count is obtained by summing the number of π electrons of the ring and the electrons of the caps involved in ring cap binding. Thus B₇H₇ ⁻² (D_5h) has 6 interstitial electrons (none from the B₅H₅ ring, two each from the twobh caps and two negative charge),mndo calculations on isoelectronic pyramidal molecules B₆H₆ ⁻⁴ (C_5v), B₅H₅CH⁻³ (C_5v), B₅H₅ ⁻⁴ (C_4v), B₄H₄CH⁻³ (C_4v), B₄H₄ ⁻⁴ (T _d) and B₃H₃CH⁻³ (C_3v) suggests a criterion based on the out-of-plane bendings of the ring B-H bonds to select the best combination of borocycles and BH or CH caps. Three-membered borocycle prefers CH cap, five-membered borocycle prefers BH cap. The preference of four-membered ring for BH or CH cap is not as pronounced. The extra stability of B₁₂H₁₂ ⁻² arises from the geometry of the icosahedron. The relative stabilities ofnido andcloso carboranes follow from these rules.     

Ab initio calculations on icosahedral molecules: I. The implementation of symmetry reduction in calculation exemplified by B12H

The symmetry reduction of icosahedral group has been carried out by means of projective operator method. The irreducible bases and matrices were tabulated for generators C₂, C₃ and C₅ which would be sufficient for the implementation of ab initio or other computations in terms of symmetry-adapted linear combinations of atomic orbitals. As an initial application, the borane dianion B₁₂H^2-₁₂ with I_h symmetry has been calculated with a flexible s, p set, (9s5p/4s) being contracted into [3s2p/2s]. The electron counting rule was then analyzed.     

A 1,3,2‐ox­aza­borolidine dimer derived from (S)‐α,α‐di­phenyl­prolinol

The reaction of (S)‐α,α‐di­phenyl­prolinol with an excess of borane–tetra­hydro­furan complex yields a stable crystalline material with the composition C₃₄H₃₈B₂N₂O₂, which features a borane adduct of a spiro­cyclic structure with two ox­aza­borolidine rings joined by a central tetrahedral B atom. This dimeric ox­aza­borolidine complex, viz. 3,3,3′,3′‐tetra­phenyl‐1,1′‐spiro­bi(3a,4,5,6‐tetra­hydro‐3H‐pyrrolo­[1,2‐c][1,3,2]­ox­azaborole)–7‐borane, is the dominant product under various reaction conditions; its crystal structure is consistent with ¹¹B, ¹H and ¹³C NMR and IR analyses.     

Bifunctionalized allenes. Part XXI. Electrophilic cyclization and addition reactions of 3-(α- or β-hydroxyalkyl)-allenylphosphonates and allenyl phosphine oxides

Abstract

The present paper discusses the electrophilic cyclization and addition reactions of 3-(α- or β-hydroxyalkyl)-allenylphosphonates and phosphine oxides. Treatment of 3-(α- or β-hydroxy-alkyl)-allenylphosphonates with electrophiles takes place with 5-endo-trig cyclization and gives 2-methoxy-2,5-dihydro-1,2-oxaphosphole 2-oxides as a result of the neighboring phosphonate group participation in the electrophilic cyclization. On the other hand, 3-(α- or β-hydroxyalkyl)-alk-(1E)-en-1-yl phosphine oxides were prepared by chemo-, regio-, and stereoselective electrophilic addition to the C²-C³-double bond in the 3-(α- or β-hydroxyalkyl)-alka-1,2-dienyl phosphine oxides and subsequent attack of the external nucleophile (halide anion). The paper proposes a possible mechanism that involves electrophilic cyclization and addition reactions of the phosphorylated (α- or β-hydroxyalkyl)allenes.     

Study of Electron Donor–Acceptor Complex Formation of o-Chloranil With a Series of Phosphine Oxides and Tri- n-butyl Phosphate by the Absorption Spectrometric Method

Electron donor–acceptor (EDA) complex formation of o-chloranil with six different phosphine oxides and tri-n-butyl phosphate (TBP) has been studied in CCl ₄ solution by the UV-VIS absorption spectrophotometric technique. An absorption band due to a charge–transfer (CT) transition is observed in the visible region. Utilizing the CT transition energy, the electron affinity of o-chloranil in solution has been calculated. Degrees of charge transfer, and oscillator and transition dipole strengths have also been calculated for all of the investigated EDA complexes. Except for TBP, other phosphine oxides, viz., tri-n-octyl phosphine oxide, tri-n-butyl phosphine oxide, triphenyl phosphine, octyl(phenyl)-N,N-diisobutylcarbamoylphosphine oxide, octyl(phenyl)-N,N-dicyclohexylcarbamoylmethylphosphine oxide and octyl(phenyl)-N,N-diisopropylcarbamoylmethylphosphine oxide have been shown to form stable 1:1 EDA complexes with o-chloranil. The complex of TBP with o-chloranil decays slowly into a secondary product. Formation constants of the EDA complexes have been determined.     

Selective reduction of allenyl(diphenyl)phosphine oxides to allyl(diphenyl)phosphine oxides

The reduction of allenyl(diphenyl)phosphine oxides with HSiCl₃ or LiAlH₄ selectively afforded the corresponding allyl(diphenyl)phosphine oxides. 3-Methylbut-2-en-1-yl(diphenyl)phosphine oxide reacted with AlCl₃ to give a mixture of 4,4-dimethyl-1-phenyl-1,2,3,4-tetrahydro-λ⁵-phosphinoline 1-oxide and 4,4-dimethyl-1-phenyl-1,4-dihydro-λ⁵-phosphinoline 1-oxide.     

Rh2[(R)-(+)-MTPA]4 as an NMR auxiliary for the enantiodifferentiation of chiral secondary and tertiary phosphine–borane complexes

The direct chiral recognition of secondary and tertiary phosphine–borane complexes is made possible by applying the dirhodium method (NMR in the presence of Rh₂[(R)-(+)-MTPA]₄, Rh¹). Due to the acid lability of the phosphine–borane complexes, it is advisable to use deuterated benzene as solvent rather than deuterated chloroform. The decomposition of the phosphine–borane complexes and the resulting Rh¹–phosphine adducts are also studied.     

Photoinduced and Thermal Single-Electron Transfer to Generate Radicals from Frustrated Lewis Pairs

Archetypal phosphine/borane frustrated Lewis pairs (FLPs) are famed for their ability to activate small molecules. The mechanism is generally believed to involve two-electron processes. However, the detection of radical intermediates indicates that single-electron transfer (SET) generating frustrated radical pairs could also play an important role. These highly reactive radical species typically have significantly higher energy than the FLP, which prompted this investigation into their formation. Herein, we provide evidence that the classical phosphine/borane combinations PMes₃/B(C₆F₅)₃ and PtBu₃/B(C₆F₅)₃ both form an electron donor–acceptor (charge-transfer) complex that undergoes visible-light-induced SET to form the corresponding highly reactive radical-ion pairs. Subsequently, we show that by tuning the properties of the Lewis acid/base pair, the energy required for SET can be reduced to become thermally accessible.     

Thermal conversions of chitosanium dodecahydro-<Emphasis Type="Italic">closo</Emphasis>-dodecaborate

The thermal behavior of chitosanium dodecahydro-closo-dodecaborate, (C₆O₄H₉NH₃)₂B₁₂H₁₂, was studied by thermal analysis, X-ray diffraction, and IR and X-ray photoelectron spectroscopy. As this compound is heated at a rate above 10–20 K/min, it ignites at a temperature of about 300°C. As the compound is heated to 1000°C at a rate below 10 K/min in an inert atmosphere, it yields a mixture of carbon and amorphous boron and/or boron carbides. The presence of a small amount of boron oxide in the product is explained by the formation of a partially oxidized hydroborate anion at the early stages of (C₆O₄H₉NH₃)₂B₁₂H₁₂ decomposition via the interaction between oxygen of the chitosanium cation and the B₁₂H₁₂²⁻ anion. Heating the initial compound in air at a rate below 10 K/min yields carbon and boron oxide as the main products. Molten boron oxide protects boron and/or boron carbides and boron nitride forming in small amounts in the particle bulk from oxidation.     

A “Push–Pull” Stabilized Phosphinidene Supported by a Phosphine-Functionalized β-Diketiminato Ligand

The use of a bis(diphenyl)phosphine functionalized β-diketiminato ligand, [HC{(CH₃)C}₂{(ortho-[P(C₆H₅)₂]₂C₆H₄)N}₂]⁻ (PNac), as a support for germanium(II) and tin(II) chloride and phosphaketene compounds, is described. The conformational flexibility and hemilability of this unique ligand provide a versatile coordination environment that can accommodate the electronic needs of the ligated elements. For example, chloride abstraction from [(PNac)ECl] (E=Ge, Sn) affords the cationic germyliumylidene and stannyliumylidene species [(PNac)E]⁺ in which the pendant phosphine arms associate more strongly with the Lewis acidic main group element centers, providing further electronic stabilization. In a similar fashion, chemical decarbonylation of the germanium phosphaketene [(PNac)Ge(PCO)] with tris(pentafluorophenyl)borane affords a “push–pull” stabilized phosphinidene in which one of the phosphine groups of the ligand backbone associates with the low valent phosphinidene center.