Synthesis and Coordination Chemistry of Iminophosphanes

Iminophosphanes are a new group of 1,3‐P,N‐ligands, readily obtainable from secondary phosphanes and nitrilium ions, having a tunable N‐donor site by means of varying the imine substituents. These ligands give, in high yields, monodentate gold complexes and bidentate rhodium and iridium complexes. Crystal structures are reported for both the ligands and the complexes.     

P−P Condensation and P−N/P−P Bond Metathesis: Facile Synthesis of Cationic Tri‐ and Tetraphosphanes

[L_C^RP((PhP)₂C₂H₄)][OTf] ( 4 a,b [OTf]) and [L_C^iPrP(PPh₂)₂][OTf] ( 5 b [OTf]) were prepared from the reaction of imidazoliumyl‐substituted dipyrazolylphosphane triflate salts [L_C^RP(pyr)₂][OTf] ( 3 a,b [OTf]; a : R=Me, b =iPr; L_C^R=1,3‐dialkyl‐4,5‐dimethylimidazol‐2‐yl; pyr=3,5‐dimethylpyrazol‐1‐yl) with the secondary phosphanes PhP(H)C₂H₄P(H)Ph) and Ph₂PH. A stepwise double P?N/P?P bond metathesis to catena‐tetraphosphane‐2,3‐diium triflate salt [(Ph₂P)₂(L_C^MeP)₂][OTf]₂ ( 7 a [OTf]₂) is observed when reacting 3 a [OTf] with diphosphane P₂Ph₄. The coordination ability of 5 b [OTf] was probed with selected coinage metal salts [Cu(CH₃CN)₄]OTf, AgOTf and AuCl(tht) (tht=tetrahydrothiophene). For AuCl(tht), the helical complex [{(Ph₂PPL_C^iPr)Au}₄][OTf]₄ ( 9 [OTf]₄) was unexpectedly formed as a result of a chloride‐induced P?P bond cleavage. The weakly coordinating triflate anion enables the formation of the expected copper(I) and silver(I) complexes [( 5 b )M(CH₃CN)₃][OTf]₂ (M=Cu, Ag) ( 10 [OTf]₂, 11 [OTf]₂).     

Synthesis of Phosphanes Bearing 2‐Imino‐1,3‐thiazolidine Ligands – X‐Ray Analyses and NMR Spectroscopy

Pseudo‐ephedrine derived 2‐imino‐1,3‐thiazolidine 1 reacts with tris(diethylamino)phosphane by stepwise replacement of the diethylamino group to give the mono‐, bis‐ and tris(imino)phosphanes 2 , 3 and 4 , respectively, of which 4 could be isolated in pure state. The analogous reaction with diethylamino‐diphenylphosphane affords the imino‐diphenylphosphane 5 . The iminophosphanes react with sulfur or selenium to give the corresponding phosphorus(V) compounds. In contrast, the reaction of the iminophosphanes with oxygen is very slow; anhydrous trimethylamine N‐oxide reacts in the melt with the phosphanes to give the oxides 4(O) and 5(O) . The molecular structures of 4(O) (in mixture with 4 ), 4(Se) , 5(S) and 5(Se) were determined by X‐ray analysis. In all cases the ring‐sulfur and the phosphorus atoms are in cis‐positions at the C=N bonds. The analogous solution structures were determined by ¹H, ¹³C, ¹⁵N, ³¹P and ⁷⁷Se NMR spectroscopy. In the case of the compounds 5 , 5(O) , 5(S) and 5(Se) the isotope‐induced chemical shifts ¹δ^14/15N(³¹P) were determined, using INEPT‐HEED experiments.     

P−P Condensation and P−N/P−P Bond Metathesis: Facile Synthesis of Cationic Tri- and Tetraphosphanes

[L_C^RP((PhP)₂C₂H₄)][OTf] ( 4 a,b [OTf]) and [L_C^iPrP(PPh₂)₂][OTf] ( 5 b [OTf]) were prepared from the reaction of imidazoliumyl-substituted dipyrazolylphosphane triflate salts [L_C^RP(pyr)₂][OTf] ( 3 a,b [OTf]; a : R=Me, b =iPr; L_C^R=1,3-dialkyl-4,5-dimethylimidazol-2-yl; pyr=3,5-dimethylpyrazol-1-yl) with the secondary phosphanes PhP(H)C₂H₄P(H)Ph) and Ph₂PH. A stepwise double P−N/P−P bond metathesis to catena-tetraphosphane-2,3-diium triflate salt [(Ph₂P)₂(L_C^MeP)₂][OTf]₂ ( 7 a [OTf]₂) is observed when reacting 3 a [OTf] with diphosphane P₂Ph₄. The coordination ability of 5 b [OTf] was probed with selected coinage metal salts [Cu(CH₃CN)₄]OTf, AgOTf and AuCl(tht) (tht=tetrahydrothiophene). For AuCl(tht), the helical complex [{(Ph₂PPL_C^iPr)Au}₄][OTf]₄ ( 9 [OTf]₄) was unexpectedly formed as a result of a chloride-induced P−P bond cleavage. The weakly coordinating triflate anion enables the formation of the expected copper(I) and silver(I) complexes [( 5 b )M(CH₃CN)₃][OTf]₂ (M=Cu, Ag) ( 10 [OTf]₂, 11 [OTf]₂).     

Pteridines. Part CXIX.

A variety of pyrimidine precursors 12 – 25 were converted into a series of new 7‐hydroxylumazines (=7‐hydroxypteridine‐2,4(1H,3H)‐diones) 26 – 35 which functioned as starting materials for the transformation into the corresponding 7‐chlorolumazines 36 – 45 . Subsequent reaction with hydrazine led to the 7‐hydrazinolumazines 46 – 55 which gave on nitrosation the 7‐azidolumazines 1 and 56 – 64 . These compounds were subjected to short heating in xylene whereby 1 and 56 – 61 showed a new pteridine–purine interconversion in forming a new type of 1,3‐disubstituted or 3‐substituted xanthin‐8‐amine‐derived nitrilium ylides (2,3,6,7‐tetrahydro‐N‐methylidyne‐2,6‐dioxo‐1H‐purin‐8‐aminium ylides) 11 and 65 – 70 . The presence of an additional 6‐alkyl substituent in the 7‐azidolumazines 63 and 64 or of an unsubstituted N(3) position in 62 caused further rearrangement to xanthine‐9‐carbonitriles 71 – 73 . Prolonged heating of 7‐azido‐1,3‐dimethyllumazine ( 1 ) also afforded theophylline‐9‐carbonitrile (=1,2,3,6‐tetrahydro‐1,3‐dimethyl‐2,6‐dioxo‐9H‐purine‐9‐carbonitrile; 5 ). The nitrilium ylide function was established by NMR and UV spectra as well as by elemental analyses. Confirmation of the nitrilium ylide structures was suggested by the result of the heating of 1,3‐dimethyl‐N‐methylidynexanthin‐8‐aminium ylide 11 in EtOH or of 1 in pentan‐1‐ol leading to 8‐aminotheophylline (=8‐amino‐3,7‐dihydro‐1,3‐dimethyl‐1H‐purin‐2,6‐dione; 74 ).     

A Sixteen‐Membered Au8P8 Macrocycle Based on Gold(I) and Diphospha(III)guanidine

The reaction of cyclo ‐P₄Mes₄C(NCy) ( 1 ) with two equivalents of [AuCl(tht)] (tht=tetrahydrothiophene) resulted in the formation of unusual sixteen‐membered Au–P macrocycle 2 . This macrocycle contains diphospha(III)guanidinate as a coordinating ligand, which is formed by P−P bond cleavage of 1 . Macrocycle 2 was characterized by multinuclear NMR spectroscopy, mass spectrometry and X‐ray crystallography.     

Imines in the Titanium Coordination Sphere – Transformation of Imidoyl Chlorides to Nitrilium Ions

In the reaction of TiCl₄ in benzene as solvent with the imidoyl chloride p‐Tolyl(Cl)C=NPh ( 1 ) the abstraction of the chloride substituent is observed, leading to the nitrilium salt [p‐Tolyl–C≡N–Ph]⁺[Ti₂Cl₉]^– ( 2 ) in quantitative yield. The highly electrophilic salt 2 is characterized by IR‐ and NMR spectroscopy. The observed band for the C≡N stretching mode of 2 clearly indicates the formation of a nitrilium ion. Especially a characteristic line broadening of the ¹³C{¹H}‐NMR signals related to carbon atoms next to the nitrogen is observed. By ¹⁵N,¹H‐HMBC NMR experiments it is shown that the nitrogen signal of 2 is significantly shifted to high‐field in relation to nitriles and imines. The molecular structure of 2 was confirmed by single‐crystal X‐ray diffraction. The C≡N bond length and the linearity of the C–C≡N–C unit in 2 confirm the triple bond character of this bond.     

The AZARYPHOS Family of Ligands for Ambifunctional Catalysis: Syntheses and Use in Ruthenium‐Catalyzed anti‐Markovnikov Hydration of Terminal Alkynes

The family of AZARYPHOS (aza–aryl–phosphane) phosphane ligands, containing a phosphine unit and sterically shielded nitrogen lone pairs in the ligand periphery, is introduced as a tool for developing ambifunctional catalysis by the metal center and nitrogen lone pairs in the ligand sphere. General synthetic strategies have been developed to synthesize over 25 examples of structurally diverse (6‐aryl‐2‐pyridyl)phosphanes (ARPYPHOS), (6‐alkyl‐2‐pyridyl)phosphanes (ALPYPHOS), 4,6‐disubsituted 1,3‐diazin‐2‐ylphosphanes or 1,3,5‐triazin‐2‐ylphosphanes, quinazolinylphosphanes, quinolinylphosphanes, and others. The scalable syntheses proceed in a few steps. The incorporation of AZARYPHOS ligands ( L ) into complexes [RuCp( L )₂(MeCN)][PF₆] (Cp=cyclopentadienyl) gives catalysts for the anti‐Markovnikov hydration of terminal alkynes of the highest known activities. Electronic and steric ligand effects modulate the reaction kinetics over a range of two orders of magnitude. These results highlight the importance of using structurally diverse ligand families in the process of developing cooperative ambifunctional catalysis by a metal and its ligand.     

Stereoselective Synthesis and Structure of New Types of Calix[4]resorcinarenes. Complexation of Tetrakis(O,O‐Phosphorus)Bridged‐Calix[4]resorcinarenes with Heavy Metal Atoms

The acid‐catalyzed (with HCl) condensation reactions of resorcinol ( 1 ) with 1‐naphthaldehyde ( 2 ) and isobutyraldehyde ( 3 ) furnished the tetrameric macrocyclic compounds 4 and 6 . Detailed NMR‐investigations of the acetylated tetrameric species 5 surprisingly support a structure not in agreement with the expected all‐cis conformation. The chair conformation (C_2h symmetry) of the acetylated derivative 5 was established through a crystal X‐ray diffraction study. The naphthyl substituents are arranged in trans position above and below the plane made up by the resorcinol units. The reaction of resorcinol 1 with isobutyraldehyde, in accord with expectation, led to the calix[4]resorcinaren ( 6 ). The ¹H NMR spectra of compound 6 and 7 appeared at room temperature as broad signals, indicating a conformation of C_2v symmetry. The reaction of the C‐methyl‐tetrakis‐P‐(chlorodioxaphosphocin)‐calix[4]resorcinarenes ( 8 ) and ( 10 ) with suitable N‐trimethylsilyl organic amines were conducted in tetrahydrofuran suspension, furnishing the P–N‐substituted calix[4]resorcinarenes ( 9 ) and ( 11 ). While in the complexation of C‐methyl‐tetrabromotetrakis‐P‐(dimethylaminodioxaphosphocin)‐calix[4]resorcinarene ( 13 ) with (tht)AuCl (tht = tetrahydrothiophene) the expected, neutral tetra‐substituted complex 15 was formed, the reaction of 13 with moist acetonitrile led to the anionic atomic framework 14 . X‐ray structure determinations of the complexes 14 and 15 show that both possess the cone conformation. In the gold complex 15 , the Au–Cl groups form a loose aggregate, with three Au…Cl contacts of 316–340 pm; one of the groups points towards the centre of the cone. The copper(I) complex 14 displays crystallographic mirror symmetry, with a central Cu₄Cl₅ unit involving tetrahedrally coordinated copper.     

Copper(I) and Gold(I) Complexes with N,N′‐Bis(diphenylphosphino)‐2,6‐diaminopyridine as Ligand: Synthesis and Molecular Structures

Reaction of CuI with 1 or 2 equivalent(s) N,N′‐Bis(diphenylphosphino)‐2,6‐diaminopyridine (BDDP) gives two different complexes, [Cu(I)μ‐(BDDP‐κP,N_py)]₂ ( 1 ) and [Cu(BDDP‐κP,N_py)₂]I ( 2 ), in high yields. The determination of the molecular structure show that both Cu^I atoms are tetrahedrally coordinated, rather than a square‐planar geometry reported for Cr⁰, Ni^II‐BDDP complexes before, which contains a planar tridentate chelate ring system. The introduction of AuCl(tht) (tht = tetrahydrothiophene) into [Cu(BDDP‐κP,N_py)₂]I leads unexpectedly to the formation of a digold complex 2,6‐[(ClAuPh₂P)HN]₂C₅H₃N and dimeric [Cu(I)μ‐(BDDP‐κP,N_py)]₂.     

A Novel N,P,C Cage Complex Formed by Rearrangement of a Tricyclic Phosphirane Complex: On the Importance of Non‐covalent Interactions

The reaction of Li/Cl P‐CPh₃ phosphinidenoid tungsten(0) complex 2 with dimethylcyanamide afforded tricyclic phosphirane complex 4 , an unprecedented rearrangement of which led to the novel N,P,C cage complex 6 . On the basis of DFT calculations, formation and intramolecular [3+2] cycloaddition of the transient nitrilium phosphane ylide complex 3 to a phenyl ring of the triphenylmethyl substituent to give 4 is proposed. Furthermore, theoretical evidence for terminal N‐amidinophosphinidene complex 7 , formed by [2+1] cycloelimination from 4 , is provided, and the role of the electronic structure and non‐covalent interactions of intermediate 7 discussed.     

Ortho‐Trialkylstannyl Arylphosphanes by C–P and C–Sn Bond Formation in Arynes

A novel and efficient approach to ortho‐trialkylstannyl arylphosphanes by the reaction of arynes generated in situ with stannylated phosphanes (R₃Sn? PR₂) is described. Concurrent C? P and C? Sn bond formation occurs with high yields, and stannylated products are easily transformed into valuable ortho‐substituted arylphosphanes. The reaction features high efficiency, good regioselectivity, and excellent practicality.     

Reaction of Pentelidene Complexes with Diazoalkanes: Stabilization of Parent 2,3‐Dipnictabutadienes

The reaction of the phosphinidene complex [Cp*P{W(CO)₅}₂] ( 1 a ) with diphenyldiazomethane leads to [{W(CO)₅}Cp*P=NN{W(CO)₅}=CPh₂] ( 2 ). Compound 2 is a rare example of a phosphadiazadiene ligand (R‐P=N?N=CR′R′′) complex. At temperatures above 0 °C, 2 decomposes into the complex [{W(CO)₅}PCp*{N(H)N=CPh₂)₂] ( 3 ), among other species. The reaction of the pentelidene complexes [Cp*E{W(CO)₅}₂] (E=P, As) with diazomethane (CH₂NN) proceeds differently. For the arsinidene complex ( 1 b ), only the arsaalkene complex 4 b [{W(CO)₅}₂{η^1:2‐(Cp*)As=CH₂}] is formed. The reaction with the phosphinidene complex ( 1 a ) results in three products, the two phosphaalkene complexes [{W(CO)₅}₂{η^1:2‐(R)P=CH₂}] ( 4 a : R=Cp*, 5 : R=H) and the triazaphosphole derivative [{W(CO)₅}P(Cp*)‐CH₂‐N{W(CO)₅}=N‐N(N=CH₂)] ( 6 a ). The phosphaalkene complex ( 4 a ) and the arsaalkene complex ( 4 b ) are not stable at room temperature and decompose to the complexes [{W(CO)₅}₄(CH₂=E?E=CH₂)] ( 7 a : E=P, 7 b : E=As), which are the first examples of complexes with parent 2,3‐diphospha‐1,3‐butadiene and 2,3‐diarsa‐1,3‐butadiene ligands.     

The Synthesis,Characterisation, and Reactivity of Some Polydentate Phosphinoamine Ligands with Benzene‐1,3‐diyl and Pyridine‐2,6‐diyl Backbones

The polydentate phosphinoamines 1,3‐{(Ph₂P)₂N}₂C₆H₄ and 2,6‐{(Ph₂P)₂N}₂C₅H₃N have been prepared in a single step from the reaction of the amines 1,3‐(NH₂)₂C₆H₄ or 2,6‐(NH₂)₂C₅H₃N with Ph₂PCl in presence of Et₃N (1 : 4 : 4 molar ratio) in CH₂Cl₂. Reaction of 1,3‐{(Ph₂P)₂N}₂C₆H₄ or 2,6‐{(Ph₂P)₂N}₂C₅H₃N with elemental sulfur or selenium in CH₂Cl₂ affords the corresponding tetrasulfide or tetraselenide, respectively, in good yield. The complexes [1,3‐{Mo(CO)₄(Ph₂P)₂N}₂(C₆H₄)] and [2,6‐{Mo(CO)₄(Ph₂P)₂N}₂(C₅H₃N)] were prepared from the reaction of these phosphinoamines with [Mo(CO)₄(nbd)] (nbd=norbornadiene) in toluene, and the structure of the latter complex has been determined by single‐crystal X‐ray diffraction analysis.     

Synthesis and Structure of a Hexameric Silver and Tetrameric Gold Aminopyridinates

4‐Methyl‐2‐((trimethylsilyl)amino)pyridine (Ap^TMSH) was synthesized via a salt metathesis reaction. Lithiation of Ap^TMSH with n‐BuLi afforded the transmetallation agent [(Ap^TMS)₂Li₂(OEt₂)₂] ( 1 ) which was structurally characterized. Reaction of 1 with AgCl and [AuCl(tht)] (tht = tetrahydrothiophene) at low temperatures in THF yielded homoleptic aminopyridinates of the heavier group 11 metals, namely [(Ap^TMS)₆Ag₆] ( 2 ) and [(Ap^TMS)₄Au₄] ( 3a and b ) after work‐up in hexane. All compounds were characterized by X‐ray crystal structure analysis. The quality of the structure determination of 3a allows establishing the connectivity only. The lithium complex 1 shows the expected structure from analogous compounds. The hexameric silver compound shows a new structural motif for silver aminopyridinates. The six‐membered ring of silver atoms has a chair conformation. Compounds 3a and b are the first homoleptic gold aminopyridinates and exhibit a rhombic arrangement of the four gold atoms.     

1‐Phosphabicyclo[3.2.1]octane

1‐Phosphabicyclo[3.2.1]octanes 1‐Phosphabicyclo[3.2.1]octane has been obtained by free‐radical cyclization of (2‐vinyl‐4‐pentenyl)‐phosphane in the presence of AIBN. Another approach to 1‐phosphabicyclo[3.2.1]octanes involves free‐radical cyclization of 2‐methyl‐4‐(2‐propenyl)‐phospholane synthesized by the reaction of [2‐(2‐propenyl)‐4‐pentenyl]‐phosphane with KPH₂/[18]crown‐6 in THF. The bicyclic phosphanes are characterized by reactions with CS₂, selenium, sulfur, NO, CH₃I, and HSO₃F, respectively, structural and analytical data as well as ¹H, ¹³C, ³¹P, ⁷⁷Se NMR spectral measurements. The steric crowding of the phosphanes as complex ligands has been estimated from ³¹P–¹H coupling constants according to the Tolman model. The configuration of the methyl substituents as well as the conformation of the six‐membered ring were determined by NMR parameters (coupling constants, noe's) and proved by X‐ray crystal structure analysis.     

Bisaminophosphane – Synthese,Struktur und Reaktivität

Bisaminophosphanes – Synthesis, Structure, and Reactivity Different pathways for the synthesis of bis(alkylamino)phosphanes RP(N(H)R′)₂ are described. t‐BuP(N(H)‐ Dipp)₂ (Dipp = 2,6‐i‐Pr₂–C₆H₃) was structurally characterized by single crystal X‐ray diffraction. The reactivity of the compounds was examplarily investigated using t‐BuP(N(H)t‐Bu)₂. Its reaction with Me₃Al and R₂AlH (R = Me, Et, i‐Bu) in 1 : 1 and 1 : 2 stoichiometrie yield monosubstituted compounds of the type t‐BuP(N(H)t‐Bu)(N(AlR₂)t‐Bu).     

Preparation of Dithienylphospholes by 1,1‐Carboboration

In this study the scope of the 1,1‐carboboration reaction was extended to the preparation of mixed heterole‐based conjugated π‐systems. Two arylbis(alkynyl)phosphane starting materials 2 were synthesized bearing two thiophene isomers at the alkyne units and the bulky tipp‐substituent (tipp=2,4,6‐triisopropylphenyl) at the phosphorous atom. The bis(thienylethynyl)phosphanes 2 were converted into the corresponding 2,5‐thienyl‐substituted 3‐borylphospholes 4 in a double 1,1‐carboboration reaction sequence employing the strongly electrophilic B(C₆F₅)₃ reagent under mild reaction conditions. Subsequent Suzuki–Miyaura type cross‐coupling yielded the corresponding 3‐phenylphospholes 7 in a one‐pot procedure from phosphanes 2 in high yields. Phospholes 7 were converted into the respective phosphole oxides 8 . A photophysical characterization of derivatives 7 and 8 was carried out. The results presented here demonstrate the suitability of the 1,1‐carboboration reaction for the preparation of phosphole‐/thiophene‐based, light‐emitting systems.     

[NiCl2(dppp)]‐Catalyzed Cross‐Coupling of Aryl Halides with Dialkyl Phosphite,Diphenylphosphine Oxide,and Diphenylphosphine

We present a general approach to C? P bond formation through the cross‐coupling of aryl halides with a dialkyl phosphite, diphenylphosphine oxide, and diphenylphosphane by using [NiCl₂(dppp)] as catalyst (dppp=1,3‐bis(diphenylphosphino)propane). This catalyst system displays a broad applicability that is capable of catalyzing the cross‐coupling of aryl bromides, particularly a range of unreactive aryl chlorides, with various types of phosphorus substrates, such as a dialkyl phosphite, diphenylphosphine oxide, and diphenylphosphane. Consequently, the synthesis of valuable phosphonates, phosphine oxides, and phosphanes can be achieved with one catalyst system. Moreover, the reaction proceeds not only at a much lower temperature (100–120 °C) relative to the classic Arbuzov reaction (ca. 160–220 °C), but also without the need of external reductants and supporting ligands. In addition, owing to the relatively mild reaction conditions, a range of labile groups, such as ether, ester, ketone, and cyano groups, are tolerated. Finally, a brief mechanistic study revealed that by using [NiCl₂(dppp)] as a catalyst, the Ni^II center could be readily reduced in situ to Ni⁰ by the phosphorus substrates due to the influence of the dppp ligand, thereby facilitating the oxidative addition of aryl halides to a Ni⁰ center. This step is the key to bringing the reaction into the catalytic cycle.     

A Convenient,Room‐Temperature–Organic Base Protocol for Preparing Chiral 3‐(Enoyl)‐1,3‐oxazolidin‐2‐ones

In this study, we developed a new protocol for the preparation of the chiral 3‐[(E)‐enoyl]‐1,3‐oxazolidin‐2‐ones under the ultimately simple reaction conditions starting with the corresponding enoyl chlorides and 1,3‐oxazolidin‐2‐ones with Et₃N/LiCl at room temperature. The method generally allows efficient preparation of various derivatives regardless of the steric and electronic nature of the substituents on both the enoyl or the oxazolidinone sites. Excellent yields, combined with the simplicity of the experimental procedures, render the present method immediately useful for preparing the target compounds.