A Tricyclic Hexaphosphane

The reaction of the functionalized cyclo‐tetraphosphane [ClP(μ‐PMes*)]₂ (Mes*=2,4,6‐tri‐tert‐butylphenyl) with different Lewis bases led to the formation of an unprecedented tricyclic hexaphosphane, Mes*P₆Mes*. The formation of this compound was investigated by spectroscopic and theoretical methods, revealing an unusual ring expansion reaction. The title compound was fully characterized by experimental and computational methods.     

Dimers and Trimers of Diphosphenes: A Wealth of Cyclo‐Phosphanes

Various new P‐based ring systems were synthesised by transferring established reaction routes from NP chemistry to the analogous PP compounds. Due to the different electronic situations of phosphorus and nitrogen with respect to s and p character of the lone pair, different reactivity of the phosphorus compounds was observed, especially with regard to the specificity of the reactions and the stability of the products. Whereas Mes*N?PCl (Mes*=2,4,6‐tri‐tert‐butylphenyl) is stable in the solid state and in solution, the formal phosphorus congener Mes*P?PCl is highly reactive and could not be observed. Instead, several formal dimers and trimers of Mes*P?PCl could be isolated, which constitute an intriguing variety of three‐ and four‐membered ring systems.     

Synthesis of a Molecule with Four Different Adjacent Pnictogens

The synthesis of a molecule containing four adjacent different pnictogens was attempted by conversion of a Group 15 allyl analogue anion [Mes*NAsPMes*]^? (Mes*=2,4,6‐tri‐tert‐butylphenyl) with antimony(III) chloride. A suitable precursor is Mes*N(H)AsPMes* ( 1 ) for which several syntheses were investigated. The anions afforded by deprotonation of Mes*N(H)AsPMes* were found to be labile and, therefore, salts could not be isolated. However, the in situ generated anions could be quenched with SbCl₃, yielding Mes*N(SbCl₂)AsPMes* ( 4 ).     

Preparation of 1,3‐diphosphabuta‐1,3‐dienes from sterically encumbered phosphaalkyne and phosphaethenyllithium

Kinetically stabilized 2‐lithio‐1‐(2,4,6‐tri‐t‐butylphenyl)‐1‐phosphapropene was allowed to react with a bulky phosphaalkyne Mes*CP (Mes* = 2,4,6‐t‐Bu₃C₆H₂) followed by quenching with iodomethane or benzyl bromide to give the corresponding 1,3‐diphosphabuta‐1,3‐dienes. The presence of the bulky Mes* group on the 1‐phosphorus atom prevents intramolecular [2+2] cyclization and gave the PC PC skeleton, whereas Mes*CP reacted with half an equivalent of nucleophile to afford the PCPC four‐membered ring compounds. X‐ray crystallography of 4‐benzyl‐1,3‐diphosphabuta‐1,3‐diene confirmed the molecular structure showing conjugation on the 1,3‐diphosphabuta‐1,3‐diene moiety. © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:357–360, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20104     

A Boryl‐Substituted Diphosphene: Synthesis,Structure, and Reaction with n‐Butyllithium To Form a Stabilized Adduct by pπ‐pπ Interaction

A boryl‐substituted diphosphene was synthesized through the nucleophilic borylation of PCl₃ with a borylzinc reagent, followed by a reduction with Mg. A combined analysis of the resulting diboryldiphosphene by single‐crystal X‐ray diffraction, DFT calculations, and UV/Vis spectroscopy revealed a σ‐electron‐donating effect for the boryl substituent that was slightly weaker than that of the 2,4,6‐tri‐tert‐butylphenyl (Mes*) ligand. The reaction of this diboryldiphosphene with ⁿBuLi afforded a boryl‐substituted phosphinophosphide that was, in comparison with the thermally unstable Mes*‐substituted diaryldiphosphene, stabilized by a π‐electron‐accepting effect of the boryl substituent.     

A Boryl‐Substituted Diphosphene: Synthesis,Structure, and Reaction with n‐Butyllithium To Form a Stabilized Adduct by pπ‐pπ Interaction

A boryl‐substituted diphosphene was synthesized through the nucleophilic borylation of PCl₃ with a borylzinc reagent, followed by a reduction with Mg. A combined analysis of the resulting diboryldiphosphene by single‐crystal X‐ray diffraction, DFT calculations, and UV/Vis spectroscopy revealed a σ‐electron‐donating effect for the boryl substituent that was slightly weaker than that of the 2,4,6‐tri‐tert‐butylphenyl (Mes*) ligand. The reaction of this diboryldiphosphene with ⁿBuLi afforded a boryl‐substituted phosphinophosphide that was, in comparison with the thermally unstable Mes*‐substituted diaryldiphosphene, stabilized by a π‐electron‐accepting effect of the boryl substituent.     

Attempt to Synthesize Hindered 2,4,6‐Tri‐Aryloxy‐s‐Triazines: Bis(2,4‐di‐tert‐Butylphenyl) Carbonate – Crystal Structure

Some less hindered 2,4,6‐tri‐aryloxy‐s‐triazines were synthesized through the reaction of the corresponding phenols as a starting materials with cyanogen bromide (BrCN) to obtain the corresponding arylcyanates and then trimerized. Unexpectedly, 2,4‐di‐tert‐butyl‐1‐cyanatobenzene derived from 2,4‐di‐tert‐butylphenol did not trimerize but, indeed, yielded bis(2,4‐di‐tert‐butylphenyl) carbonate. The structures of 2,4,6‐tri‐aryloxy‐s‐triazines and bis(2,4‐di‐tert‐butylphenyl) carbonate were characterized by means of IR, ¹H, and ¹³C NMR spectroscopies. Also the structure of the latter compound was studied by X‐ray crystallography.     

Isolatable Organophosphorus(III)–Tellurium Heterocycles

A new structural arrangement Te₃(RP^III)₃ and the first crystal structures of organophosphorus(III)–tellurium heterocycles are presented. The heterocycles can be stabilized and structurally characterized by the appropriate choice of substituents in Te_m(P^IIIR)_n (m=1: n=2, R=OMes* (Mes*=supermesityl or 2,4,6‐tri‐tert‐butylphenyl); n=3, R=adamantyl (Ad); n=4, R=ferrocene (Fc); m=n=3: R=trityl (Trt), Mesor by the installation of a P^V₂N₂ anchor in RP^III[TeP^V(tBuN)(μ‐NtBu)]₂ (R=Ad, tBu).     

Highly Electron‐Deficient and Air‐Stable Conjugated Thienylboranes

Introduced herein is a series of conjugated thienylboranes, which are inert to air and moisture, and even resist acids and strong bases. X‐ray analyses reveal a coplanar arrangement of the thiophene rings, an arrangement which facilitates p–π conjugation through the boron atoms despite the presence of highly bulky 2,4,6‐tri‐tert‐butylphenyl (Mes*) or 2,4,6‐tris(trifluoromethyl)phenyl (^FMes) groups. Short B???F contacts, which lead to a pseudotrigonal bipyramidal geometry in the ^FMes species, have been further studied by DFT and AIM analysis. In contrast to the Mes* groups, the highly electron‐withdrawing ^FMes groups do not diminish the Lewis acidity of boron toward F^? anions. These compounds can be lithiated or iodinated under electrophilic conditions without decomposition, thus offering a promising route to larger conjugated structures with electron‐acceptor character.     

The Complexed 1,3‐Diphospha‐2‐Arsaallyl Radical and Its Cationic and Anionic Derivatives

Photolysis of [Cp*As{W(CO)₅}₂] ( 1 a ) in the presence of Mes*P?PMes* (Mes*=2,4,6‐tri‐tert‐butylphenyl) leads to the novel 1,3‐diphospha‐2‐arsaallyl radical [(CO)₅W(μ,η²:η¹‐P₂AsMes*₂)W(CO)₄] ( 2 a ). The frontier orbitals of the radical 2 a are indicative of a stable π‐allylic system that is only marginally influenced by the d orbitals of the two tungsten atoms. The SOMO and the corresponding spin density distribution of the radical 2 a show that the unpaired electron is preferentially located at the two equivalent terminal phosphorus atoms, which has been confirmed by EPR spectroscopy. The protonated derivative of 2 a , the complex [(CO)₅W(μ,η²:η¹‐P₂As(H)Mes*₂)W(CO)₄] ( 6 a ) is formed during chromatographic workup, whereas the additional products [Mes*P?PMes*{W(CO)₅}] as the Z‐isomer ( 3 ) and the E‐isomer ( 4 ), and [As₂{W(CO)₅}₃] ( 5 ) are produced as a result of a decomposition reaction of radical 2 a . Reduction of radical 2 a yields the stable anion [(CO)₅W(μ,η²:η¹‐P₂AsMes*₂)W(CO)₄]^? in 7 a , whereas upon oxidation the corresponding cationic complex [(CO)₅W(μ,η²:η¹‐P₂AsMes*₂)W(CO)₄][SbF₆] ( 8 a ) is formed, which is only stable at low temperatures in solution. Compounds 2 a , 7 a , and 8 a represent the hitherto elusive complexed redox congeners of the diphospha‐arsa‐allyl system. The analogous oxidation of the triphosphaallyl radical [(CO)₅W(μ,η²:η¹‐ P₃Mes*₂)W(CO)₄] ( 2 b ) also leads to an allyl cation, which decomposes under CH activation to the phosphine derivative [(CO)₅W{μ,η²:η¹‐P₃(Mes*)(C₅H₂tBu₂C(CH₃)₂CH₂)}W(CO)₄] ( 9 ), in which a CH bond of a methyl group of the Mes* substituent has been activated. All new products have been characterized by NMR spectrometry and IR spectroscopy, and compounds 2 a , 3 , 6 a , 7 a , and 9 by X‐ray diffraction analysis.     

New Aspects of 1,3‐Diphosphacyclobutane‐2,4‐diyls

1,3‐Di(tert‐butyl)‐2,4‐bis[2,4,6‐tri(tert‐butyl)phenyl]‐1,3‐diphosphacyclobutane‐2,4‐diyl was formed from [2,4,6‐tri(tert‐butyl)phenyl]phosphaacetylene and t‐BuLi. In addition, the X‐ray diffraction analysis was carried out, together with theoretical calculations of the structure and NMR data.     

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(C₆F₅)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 .     

Catenation of 1,3‐Diphosphacyclobutane‐2,4‐diyl Units Having 2,4,6‐Tri‐tert‐butylphenyl Protecting Groups and a P‐sec‐Butyl Group in the Ring

Two and three stable 1‐sec‐butyl‐2,4‐bis(2,4,6‐tri‐tert‐butylphenyl)‐1,3‐diphosphacyclobutane‐2,4‐diyl units were catenated to construct multi‐biradical derivatives by utilizing 1,3‐di‐, 1,4‐di‐, and 1,3,5‐trimethylenebenzenes as bridging groups, respectively. UV/Vis spectroscopic and cyclovoltammetric (CV) properties of the multi‐biradicals indicate a non‐conjugative interaction between the concatenated biradical units.     

Coordination Behavior of Sterically Protected Phosphaalkenes on the AuCl Moiety Leading to Catalytic 1,6‐Enyne Cycloisomerization

Mes*‐substituted 2,3‐dimethyl‐1,4‐diphosphabuta‐1,3‐diene, 1,2‐diphenyl‐3,4‐diphosphinidenecyclobutene, 2,2‐bis(methylsulfanyl)‐1‐phosphaethene, and 3,3‐diphenyl‐1,3‐diphosphapropenes (Mes*=2,4,6‐tri‐tert‐butylphenyl) were employed as P ligands of gold(I) complexes. The (E,E)‐2,3‐dimethyl‐1,4‐diphosphabuta‐1,3‐diene functioned as a P2 ligand for digold(I) complex formation with or without intramolecular Au–Au contact, which depends on the conformation of the 1,3‐diphosphabuta‐1,3‐diene. The 1,2‐diphenyl‐3,4‐diphosphinidenecyclobutene, which has a rigid s‐cis P?C? C?P skeleton, afforded the corresponding digold(I) complexes with a slight distortion of the planar diphosphinidenecyclobutene framework and intramolecular Au–Au contact. In the case of the 2,2‐bis(methylsulfanyl)‐1‐phosphaethene, only the phosphorus atom coordinated to gold, and the sulfur atom showed almost no intra‐ or intermolecular coordination to gold. On the other hand, the 1,3‐diphosphapropenes behaved as nonequivalent P2 ligands to afford the corresponding mono‐ and digold(I) complexes. Some phosphaalkene–gold(I) complexes showed catalytic activity for 1,6‐enyne cycloisomerization without cocatalysts such as silver hexafluoroantimonate.     

2,4,6‐Tri‐tert‐butylphenyl and 2,4‐di‐tert‐butyl‐6‐methylphenyl groups: Look similar,react differently

The crystal structures of molecules with two phosphaalkene groups have been determined. Differences in the stabilization of the PC π‐bond by the 2,4,6‐tri‐tert‐butylphenyl and 2,4‐di‐tert‐butyl‐6‐methylphenyl groups were observed. It has been found that lithium supermesityl(trimethylsilyl)phosphide could be a very efficient base to remove a proton from acetonitrile.© 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:662–666, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10083     

Imino‐Bridged Bisphosphaalkenes (2,4‐Diphospha‐3‐azapentadienes)

Deprotonation of aminophosphaalkenes (RMe₂Si)₂C?PN(H)(R′) (R=Me, iPr; R′=tBu, 1‐adamantyl (1‐Ada), 2,4,6‐tBu₃C₆H₂ (Mes*)) followed by reactions of the corresponding Li salts Li[(RMe₂Si)₂C?P(M)(R′)] with one equivalent of the corresponding P‐chlorophosphaalkenes (RMe₂Si)₂C?PCl provides bisphosphaalkenes (2,4‐diphospha‐3‐azapentadienes) [(RMe₂Si)₂C?P]₂NR′. The thermally unstable tert‐butyliminobisphosphaalkene [(Me₃Si)₂C?P]₂NtBu ( 4 a ) undergoes isomerisation reactions by Me₃Si‐group migration that lead to mixtures of four‐membered heterocyles, but in the presence of an excess amount of (Me₃Si)₂C?PCl, 4 a furnishes an azatriphosphabicyclohexene C₃(SiMe₃)₅P₃NtBu ( 5 ) that gave red single crystals. Compound 5 contains a diphosphirane ring condensed with an azatriphospholene system that exhibits an endocylic P?C double bond and an exocyclic ylidic P⁽⁺⁾? C^(?)(SiMe₃)₂ unit. Using the bulkier iPrMe₂Si substituents at three‐coordinated carbon leads to slightly enhanced thermal stability of 2,4‐diphospha‐3‐azapentadienes [(iPrMe₂Si)₂C?P]₂NR′ (R′=tBu: 4 b ; R′=1‐Ada: 8 ). According to a low‐temperature crystal‐structure determination, 8 adopts a non‐planar structure with two distinctly differently oriented P?C sites, but ³¹P NMR spectra in solution exhibit singlet signals. ³¹P NMR spectra also reveal that bulky Mes* groups (Mes*=2,4,6‐tBu₃C₆H₂) at the central imino function lead to mixtures of symmetric and unsymmetric rotamers, thus implying hindered rotation around the P? N bonds in persistent compounds [(RMe₂Si)₂C?P]₂NMes* ( 11 a , 11 b ). DFT calculations for the parent molecule [(H₃Si)₂C?P]₂NCH₃ suggest that the non‐planar distortion of compound 8 will have steric grounds.     

Synthesis of Peripherally Nitrated,Aminated, and Arylaminated Subporphyrins

2‐Nitro‐5,10,15‐tri(4‐tert‐butylphenyl)subporphyrin 2 was prepared by the nitration of 5,10,15‐tri(4‐tert‐ butylphenyl)subporphyrin 1a with five equivalents of Cu(NO₃)₂ ? 5 H₂O in a mixed EtOAc/Ac₂O solution and was reduced into 2‐amino‐5,10,15‐tri(4‐tert‐butylphenyl)subporphyrin 3 . Bromination of 5,10,15‐triphenylsubporphyrin 1b with 1.5 equivalents of N‐bromosuccinimide (NBS) gave 2‐bromo‐5,10,15‐triphenylsubporphyrin, which was converted into various 2‐arylamino‐5,10,15‐triphenylsubporphyrins ( 4a , 4b , 4c , 4d ) and 2‐benzamido‐5,10,15‐triphenylsubporphyrin 5 through Pd‐catalyzed cross‐coupling reactions. These molecules constitute the first examples of mono‐β‐substituted subporphyrins. These subporphyrins exhibit significantly perturbed optical and electrochemical properties, which reflect a large influence of the peripherally attached substituents on the electronic networks of subporphyrins.     

Ring‐opening Polymerization of L‐Lactide by an Anionic Cobalt(II) Aryloxide

The reaction of anhydrous CoCl₂ with NaOAr (ArO=2,4,6‐tri‐tert‐butylphenoxo) in THF at room temperature in 1:3 molar ratio afforded anionic cobalt aryloxide [Na(THF)₆][Co(OAr)₃] ( 1 ). The definite structure of this complex was characterized by X‐ray single crystal diffraction. It was found that this anionic aryloxo cobalt(II) complex could effectively initiate the ring‐opening polymerization of L‐lactide both in solution and in bulk, leading to high molecular weight poly(L‐lactide).     

Selective [3+1] Fragmentations of P4 by “P” Transfer from a Lewis Acid Stabilized [RP4]− Butterfly Anion

Two [3+1] fragmentations of the Lewis acid stabilized bicyclo[1.1.0]tetraphosphabutanide Li[Mes*P₄⋅ BPh₃] (Mes*=2,4,6‐tBu₃C₆H₂) are reported. The reactions proceed by extrusion of a P₁ fragment, induced by either an imidazolium salt or phenylisocyanate, with release of the transient triphosphirene Mes*P₃, which was isolated as a dimer and trapped by 1,3‐cyclohexadiene as a Diels–Alder adduct. DFT quantum chemical computations were used to delineate the reaction mechanisms. These unprecedented pathways grant access to both P₁‐ and P₃‐containing organophosphorus compounds in two simple steps from white phosphorus.     

Intramolecular C?H Activation through Gold(I)‐Catalyzed Reaction of Iodoalkynes

The cycloisomerization reaction of 1‐(iodoethynyl)‐2‐(1‐methoxyalkyl)arenes and related 2‐alkyl‐substituted derivatives gives the corresponding 3‐iodo‐1‐substituted‐1H‐indene under the catalytic influence of IPrAuNTf₂ [IPr=1,3‐bis(2,6‐diisopropyl)phenylimidazol‐2‐ylidene; NTf₂=bis(trifluoromethanesulfonyl)imidate]. The reaction takes place in 1,2‐dichloroethane at 80 °C, and the addition of ttbp (2,4,6‐tri‐tert‐butylpyrimidine) is beneficial to accomplish this new transformation in high yield. The overall reaction implies initial assembly of an intermediate gold vinylidene upon alkyne activation by gold(I) and a 1,2‐iodine‐shift. Deuterium labeling and crossover experiments, the magnitude of the recorded kinetic primary isotopic effect, and the results obtained from the reaction of selected stereochemical probes strongly provide support for concerted insertion of the benzylic C H bond into gold vinylidene as the step responsible for the formation of the new carbon–carbon bond.