Volker Plack

The Reaction of Triphenylmethyl-substituted Primary and Secondary Phosphines with Phosgene

The nature of the products from the reaction of TrtPH2 (1) with an equimolar amount of phosgene strongly depends on the solvent. The initial intermediate 2 was isolated from toluene, but lost CO in dichloromethane, and HCl in diethyl ether, yielding TrtP(H)Cl (3), and (TrtPCO)2 (4 b), respectively. TrtP(H)Cl (3) was found to be a halophosphine of amazing stability. Treatment of 3 with excess phosgene led to partial substitution of the P-bonded proton for C(:O)Cl with formation of 5, which did not eliminate CO to give TrtPCl2. Substitution of chlorine in TrtP(H)Cl (3) for fluorine or bromine furnished the halophosphines, 6 and 7. Minute quantities of the diphosphene 8 were formed upon treatment of 3 with NEt3 or DBU. The course of the reaction between the secondary phosphines Trt(R)PH and phosgene depends on the group R. If R was t-Bu, formation of a mixture of Trt(t-Bu)PCl (10), and t-BuPCl2 (resulting from partial cleavage of the P–C-bond) was observed. Although in the case of R = Ph, the intermediate 12 could be isolated, at elevated temperature HCl was eliminated from 12, giving Trt(Ph)PCl (13). The diphosphine (TrtPH)2 (14) is inert towards HCl-free phosgene. In the presence of HCl the P–P-bond in 14 was cleaved, and upon chlorination of the resulting TrtPH2 (1) by phosgene, TrtP(H)Cl (3) was obtained as the only phosphorus-containing product. Reaktionen von Triphenylmethyl-substituierten Primaren und Sekundaren Phosphinen mit Phosgen Der Reaktionsverlauf der Umsetzung von TrtPH2 (1) mit Phosgen zeigte sich erheblich vom verwendeten Losungsmittel gepragt. Das primare Reaktionsprodukt TrtP(H)C(:O)Cl (2) wurde bei der entsprechenden Umsetzung in Toluol als masig stabile Verbindung erhalten. In Dichlormethan wandelte sich dieses Intermediat unter Decarbonylierung zu TrtP(H)Cl (3), in Diethylether unter Abspaltung von Chlorwasserstoff zu (TrtPCO)2 (4 b) um. 3 reagierte mit uberschussigem Phosgen zu TrtP(Cl)C(:O)Cl (5), wobei eine unter CO-Eliminierung verlaufende Zersetzung von 5 in TrtPCl2 nicht beobachtet wurde. Nach Standardmethode gelang aus 3 die Darstellung von TrtP(H)F (6) und die NMR-spektroskopische Charakterisierung von TrtP(H)Br (7). Der Einsatz von organischen Basen zur HCl-Eliminierung fuhrte bei 3 nur in Spuren zu TrtP=PTrt (8). Die Umsetzung von Trt(R)PH mit Phosgen resultierte bei R = Ph in der Bildung von Trt(Ph)PC(:O)Cl (12), bei R = t-Bu in einem Produktgemisch, bestehend aus Trt(t-Bu)PCl (10) und t-BuPCl2. 12 war bei Raumtemperatur stabil und setzte sich erst bei 60 °C zum erwarteten Chlorphosphin Trt(Ph)PCl (13) um. Gegenuber HCl-freiem Phosgen waren die PH-Bindungen in (TrtPH)2 (14) inert. Bei Anwesenheit von katalytischen HCl-Mengen fuhrte diese Umsetzung dagegen unter Spaltung der PP-Bindung zur Bildung von 3 als einzigem phosphorhaltigen Produkt.

Selective P–C-Bond Cleavage in P(III)-Triphenylmethyl Compounds

The phosphorus-carbon bond in various P-triphenylmethyl-substituted phosphorus compounds of simple as well as more complex structure can be cleaved selectively by treatment with Lewis acids, halogens (or halogen transfer agents), and hydrogen halides. The course of the reaction can be followed easily by NMR spectroscopy, in certain cases this P–C-bond cleavage can be used as a synthetic principle for phosphorus difluorohalides, F2PHal (Hal = Cl, Br, F). In the presence of the appropiate structural elements, cleavage of P–P-bonds or rearrangements are observed.

Unusual Stability despite a P-bonded Proton: Phospha and Diphospha Ureas with the TrtP(H)-Moiety

As the first diphospha-urea with P-bonded protons, [TrtP(H)]2C=O (3) was found to be of amazing stability, which is thought to be due to the presence of the triphenylmethyl groups. Unlike known cyclic or non-cyclic analogues, 3 showed next to no tendency to eliminate carbon monoxide. 3 was obtained by reaction of the dimeric phospha-isocyanate (TrtPCO)2 (1) with LiAlH4, in which the intermediary phosphaalkene 2 was observed. Caused by its two asymmetric phosphorus atoms, 3 appeared as a mixture of two isomers, meso-3 and rac-3 (ratio: 20 : 1). Theoretical considerations, and the analysis of the proton-coupled 31P NMR spectrum (spin system: AA′XX′), allowed the assignment of the signals to the two isomers. The action of anhydrous hydrogen chloride on 3 led to the cleavage of one P–C(:O)-bond, and formation of an equimolar mixture of TrtPH2 (5) and TrtP(H)C(:O)Cl (6). Cleavage of a P–C(:O)-bond in 3 was also observed in its reaction with tetramethylguanidine (TMG) or ammonia. As proved by 31P NMR spectroscopy in the case of TMG, the reaction proceeded via the phosphaalkene intermediate 8. Acting as nucleophiles, TMG and ammonia substituted TrtP(H) in 3, and the P,N-ureas 9 and 10, with TrtPH2 (5) as a side product, were obtained. Ungewohnliche Stabilitat trotz eines Protons am Phosphor: Phospha- und Diphosphaharnstoffe mit der TrtP(H)-Gruppe Als erster Phospha-Harnstoff mit P-gebundenen Protonen ist [TrtP(H)]2C=O (3) von erstaunlicher Stabilitat, die auf die Anwesenheit der Triphenylmethyl-Gruppen zuruckzufuhren ist. Anders als bereits bekannte offenkettige oder cyclische Analoga zeigt 3 kaum Neigung zur Eliminierung von Kohlenmonoxid. 3 wurde durch die uber das Phosphaalken-Intermediat 2 verlaufende Umsetzung des dimeren Phospha-Isocyanats (TrtPCO)2 (1) mit LiAlH4 erhalten. Aufgrund seiner beiden asymmetrischen Phosphoratome liegt 3 als Gemisch der Isomere meso-3 und rac-3 (Verhaltnis: 20 : 1) vor. Modellbetrachtungen und die Analyse des protonengekoppelten 31P NMR Spektrums (Spinsystem: AA′XX′) erlaubten die Zuordnung der Signale zu den beiden Isomeren. Einwirkung von Chlorwasserstoff auf 3 fuhrte unter Spaltung einer P–C(:O)-Bindung zur Bildung eines aquimolaren Gemisches von TrtPH2 (5) und TrtP(H)C(:O)Cl (6). Die Spaltung einer P–C(:O)-Bindung in 3 wurde auch bei dessen Umsetzung mit Tetramethylguanidin (TMG) oder Ammoniak beobachtet, wobei im ersteren Fall nachweislich die Phosphaalken-Zwischenstufe 8 durchlaufen wurde (31P NMR Evidenz). Beide Basen agierten als Nucleophile, wodurch, unter Substitution von TrtP(H) in 3, die P,N-Harnstoffe 9 bzw. 10 und jeweils TrtPH2 (5) als Nebenprodukt erhalten wurden.

Synthesis of Stable N,N,N,N-Tetramethylguanidine-Substituted σ4(P)- and σ3(P)-Organophosphorus Compounds with N-Protonated P–N Bonds - The First σ3-Phosphorus-Substituted Ammonium Salts

The dependence of the protolytic decomposition rate of phosphorus amides on the substituents at phosphorus is decribed. On treatment with HCl, the N′,N′,N′′,N′′-tetramethylguanidine(= TMG)-substituted σ4(P) compounds 5 and 9 formed salts that were protonated at the imino nitrogen atoms and were completely stable in the solid state, and surprisingly stable in solution. Even with a large excess of HCl, only the imino nitrogen atom underwent protonation, with formation of HCl2– as a counter anion, without cleavage of the P–N bond. The basicity of the imino nitrogen atom also protected σ3(P) species from electrophilic attack, and the ionic compounds 12, 14, and 20c were formed, providing examples of the first stable σ3(P) amides with one or two protonated P–N bonds. Such unusual stability is associated with steric protection by the Ph3C (= trityl) group and charge delocalization over the TMG-moiety. In contrast, MeP(TMG)2 was unstable towards HCl, whereas treatment with HSbF6 led to the phosphonium salt 24, where protonation had occurred at phosphorus. The same result was obtained when triphenylmethylphosphonous dichloride 1 was allowed to react with 3 equivalents of HTMG, forming the stable phosphonium salt 19, soluble in water, which was converted to the bicationic species 20c upon treatment with HCl. – The basicity of the tritylated phosphorus compounds was found to increase in the order 5 < 2 < 19 < 13 HTMG < 21; the basic centre is the phosphorus atom in 21 and the imino nitrogen atom in all other compounds. The fluorinating agent Et3N · 3 HF caused rapid conversion of compound 6to 25, the nucleophilic attack of fluoride ion at phosphorus could not be prevented by the stabilizing effects mentioned. – All compounds were investigated by 1H- and 31P-NMR spectroscopy. The crystal structures of compounds 5, Ph3CP(=O)-(H)TMG, and 6, [5 · 2 HCl], were determined; 6 is protonated at the imino nitrogen, leading to a longer P–N bond [5: 161.6(2), 6: 168.7(2) pm], and the counterion is HCl2–. In the structure of 20c, [Ph3CP(TMG)2] · 3 HCl, the cation is protonated at both imino N atoms and the counterions are Cl– and HCl2– (one of each).

The reaction of triphenylmethylhalophosphines with tetrachloro-orthobenzoquinone: Oxidation—isomerization—dehydrohalogenation

Treatment of solutions of the halophosphines TrtP(H)F (Trt = trityl, Ph3C) 1a and TrtP(H)Cl 1b with equimolar amounts of TOB (tetrachloro-orthobenzoquinone) led to the formation of mixtures of products. They contained the phosphoranes 2a and 2b, which were formed by oxidation with TOB and are in equilibrium with the phosphines 3a and 3b. Moreover, the trityl phosphonite 4, which was formed by dehydrohalogenation of 2a, 2b and 3a, 3b, was observed in both mixtures. The dehydrohalogenation was found to be reversible in the case of HF. The pure compounds 4 and 5 were obtained from the reaction of TrtPCl2 with tetrachlorocatechol 4 and by the oxidation of 1a and 1b with two equivalents of TOB. Because of its importance in this reaction sequence, an X-ray crystal structure determination was carried out on 4. The P–O bond lengths of 168.4(2) and 167.7(2) pm are probably to be attributed to a bond-lengthening effect of the chlorine atoms of the quinone. As a comparison with analogous systems reveals, the phosphorane 5 is an example of a σ5λ5(P) species in which the phosphorus atom exhibits square-pyramidal coordination.

Triphenylmethyl fluoride as a fluorinating agent in phosphorus–halogen chemistry

Abstract Triphenylmethyl fluoride 1 will effect chlorine–fluorine exchange in certain phosphorus chlorides. Exchange of chlorine for fluorine was observed only in σ 3 λ 3 (P)- and σ 5 λ 5 (P)-compounds, while phosphorus oxychloride as an example of a σ 4 λ 5 (P)-compound was unreactive towards 1 .

The reaction of secondary phosphines and di-1-adamantylphosphine oxide with trifluoroacetic anhydride and hexafluoroacetone

Abstract While the secondary phosphines (1-Ad) 2 PH (1) (l-Ad = adamantyl) and Trt(Ph)PH (2) (Trt = triphenylmethyl) reacted readily with trifluoroacetic anhydride (TFAA) to give the trifluoroacetylphosphines 7 and 8 . (1-Ad) 2 P(:O)H (6) could not be converted into the corresponding trifluoroacetylphosphine oxide 10 by treatment with TFAA. Compound 10 was observed by 19 F and 31 P NMR spectroscopy in the reaction of (1-Ad) 2 PC(:O)CF 3 (7) with (H 2 N) 2 C(:O) · H 2 O 2 . Two pathways were observed for the reaction of 1 with excess hexa-fluoroacetone (HFA), starting from the primary HFA adduct (1-Ad) 2 PC(CF 3 ) 2 OH (13) . Oxidation of 13 led to the tertiary phosphine oxide 14 which was also available from (1-Ad) 2 P(:O)H (6) and HFA. Isomerization of 13 gave (1-Ad) 2 POCH(CF 3 ) 2 (15) whose oxidation with excess HFA furnished the phosphorane 16 . Hydrolysis of 16 led to the phosphinic ester 17 . As is known for Ph 2 PH (3) , Ph(C 6 F 5 )PH (4) reacted with HFA to give the α-hydroxyphosphine 19 . No reaction was observed when Trt(Ph)PH (2) and (C 6 F 5 ) 2 PH (5) were treated with HFA.

Organophosphorverbindungen mit tertiären Alkylsubstituenten, II*: Synthese und Charakterisierung triphenylmethylsubstituierter λ4P(V)-Verbindungen; Kristallstruktur von Triphenylmethyl-Phosphonsäuredifluorid / Organophosphorus Compounds with Tertiary Alkyl Substituents, II*: Synthesis and Characterization of Triphenylmethyl-Substituted λ4P(V) Compounds; Crystal Structure of Triphenylmethylphosphonic Difluoride

The synthesis of the triphenylmethyl-phosphonic and -phosphonothioic dihalides Ph3CP(:X)Y2 (X = O, S; Y = F, Cl) is described. The NMR parameters of these compounds are discussed and compared to these of other phosphonic and thiophosphonic dihalides. Single crystal X-ray analysis was used to confirm the structure of Ph3CP(:O)F2 2 [C2/c, a = 1599.6(4), b = 1096.3(3), c = 1863.1(7) pm, ß = 109.11(2)°, T = 178 K, R = 0.034]. The geometry at the phosphorus atom is approximately tetrahedral. The bonds between phosphorus and fluorine are extremely short [P— F 153.1(1) and 153.3(1) pm]. Bond distances and angles for this compound are compared to those of methylphosphonic difluoride which were obtained from microwave spectra.

Tris-N-(N′,N′,N″,N″-tetramethylguanidyl)phosphine Oxide – Synthesis and Reaction with Acids

The phosphoryl compound (O:)P(TMG)3 (TMG = N’,N’,N”,N”-tetramethylguanidyl) (6) was synthesized during attempts to obtain the potentially very basic (but still unknown) compound P(TMG)3 (1). Its reaction with HCl resulted in the triply protonated species 7. The crystal structure of compound 7 was determined; it crystallizes as a bis-dichloromethane solvate. Each protonated nitrogen forms a hydrogen bond to one chloride. A series of protonation experiments was conducted in order to test the behaviour of 6 towards weak acids.

CLEAVAGE AND FORMATION OF P-C BONDS DURING AN UNUSUAL KINNEAR-PERREN REACTION

Treatment of triphenylmethyldichlorophosphine 1 with aluminium trichloride in the presence of tert-buty1 chloride leads, after hydrolysis, with high selectivity to di-tert-butylphosphinic chloride 5. The reaction is suggested to proceed via a chlorophosphinidene intermediate which is trapped by the alkyl chloride.