Duc Le Van

Evidence for an Equilibrium between an N‐heterocyclic Carbene and Its Dimer in Solution

Evidence for the Wanzlick equilibrium between carbene 1 and dibenzotetraazafulvalene (1)(2) at ambient temperature has been found (see scheme). Enetetramines of type (1)(2) can also be cleaved by coordinatively unsaturated transition metal compounds to form dicarbene complexes.

Nachweis des Gleichgewichts zwischen einem N‐heterocyclischen Carben und seinem Dimer in Lösung

Der direkte Nachweis des Wanzlick-Gleichgewichts zwischen dem Carben 1 und dem Dibenzotetraazafulvalen (1)2 bei Raumtemperatur (siehe Schema) wurde erbracht. Entetramine des Typs (1)2 lassen sich aber auch durch koordinativ ungesattigte Ubergangsmetallverbindungen unter Bildung von Dicarbenkomplexen spalten.

Unusual Formation of an Azaphospholene from 1,3,4,5‐Tetramethylimidazol‐2‐ylidene and Di(isopropyl)aminophosphaalkyne

Intramolecular C-H insertion into the methyl group of the amino substituent of 1 is shown by density functional theory calculations to stabilize this intermediate in the formation of the novel 1:1 carbene-phosphaalkyne adduct 2. Compound 2 is formed in near quantitative yield by reaction of 1,3,4,5-tetramethylimidazol-2-ylidene with P≡CNiPr2 .

SYNTHESIS, STRUCTURE AND ISOMERIZATION OF FLUORINE-CONTAINING 1,2-DIHYDRO-1,3-DIPHOSPHETES

Abstract Reaction of perfluoro-2-phosphapropene 1 with phosphaalkynes of the type RC P (2) smoothly yields the formal [2 + 2] cycloaddition products, 1,2-dihydro-1,3-diphosphetes RC=P − − CF 2 − − P ¯ CF 3 (R = Me2N (3a), Et2N (3b), iPr2N (3c), tBu (3d)). Instead of the not isolable aminophosphaalkynes Me2NC P and Et2NC P, the precursors HP C(F)NR2 are successfully used as synthetic equivalents. The results of a single-crystal X-ray analysis of 3a almost exactly agree with the structural data of an ab initio calculation. The elongated sp2 CP distance in 3a (exp. 173.7(2) pm, calc. 171.4 pm) is due to the interaction of the Me2N lone pair with the PC (p p)π bond. Surprisingly, the sterically unshielded derivatives 3a and 3b at 25°C undergo an interesting rearrangement to the thermodynamically more stable 1,2-dihydro-1,2-diphosphetes RC=C(F) − − P(CF 3 ) − − P ¯ F (R = Me2N (6a, Et2N(6b)) via a 1,2-fluorine shift, an electrocyclic ring opening to a 1,4-diphosphabutadiene intermediate and an intramolecular [2 + 2] cycloaddition. This mechanism is supported by high level ab initio calculations.

Reaktive EC(pp)π-systeme XXII. Trifluormethylselenocarbonylfluorid: Darstellung und reaktionen mit 1,3-dienen sowie sekundären aminen

Abstract The red-violet trifluoromethylselenocarbonylfluoride SeC(F)CF 3 ( 1 ) is produced quantitatively by thermal 1,2-elimination of Me 3 SnF from trimethylstannylpentafluoroethylselane Me 3 SnSeC 2 F 5 ( 2 ) at 300°C and 10 −2 torr. 1 is less inert than the related selenocarbonyldifluoride SeCF 2 and shows a strong dienophilicity. The reactions of 1 with 2,3-dimethyl-1,3-butadiene, isoprene, cyclopentadiene, pentamethylcyclopentadiene and 1,3-cyclohexadiene, respectively, afford the corresponding Diels-Alder adducts 3–7 in high yields (70–98%). Compound 1 reacts with secondary amines, such as dimethyl-, diethyl- or di-isopropylamine and pyrrolidine to give trifluoromethyl selenocarbonylamides F 3 CC(Se)NR 2 ( 8–11 ). All the new compounds of this study ( 2–11 ) have been characterized by elemental analysis (C, H, N) and spectroscopic investigations (MS, IR, NMR).

Reaktive EC (pp) π-Systeme: XIII. [2 + 4]-Cycloadditionen mit Selenocarbonyldifluorid als Dienophil☆

Abstract The Diels-Alder adducts 2–6 are prepared in good yields (67–98%) by [2 + 4] cycloaddition of the selenocarbonyldifluoride F2CSe (1) to a 1,3-diene e.g. isoprene, 2,3-dimethyl-1,3-butadiene, cyclopentadiene, pentamethylcyclopentadiene and 1,3-cyclohexadiene. The only by-product, (F2CSe)x, is formed by the polymerization of 1. The new compounds 2–6 are stable at room temperature; they have been characterized by elemental analysis (C, H) and by MS, NMR and IR spectroscopy.

Reaktive EC (p-p)π-systeme: IX. Diels-alder-reaktionen des acyclischen arsaalkens F3CAsCF2☆☆☆

Abstract The Diels-Alder adducts 2–8: are prepared in a one-pot procedure by [2 + 4] cycloaddition of the perfluoro-2-arsapropene F3CAsCF2 (1) to the corresponding 1,3-dienes, producing 1 in situ by thermal (70–80°C) elimination of Me3SnF from trimethylstannylbis(trifluoromethyl)arsane. The extreme reactivity of 1 is demonstrated by its reaction with thiophene. The observed formation of the cis and trans dimers (F3CAsCF2)2 as by-products is due to partial cycloreversion of the Diels-Alder compounds.

NOVEL TETRAPHOSPHABARRELENE AND -SEMIBULLVALENE DERIVATIVES BY REACTIONS OF 2,4,6-TRI-TERT-BUTYL-1,3,5-TRIPHOSPHABENZENE WITH PHOSPHAALKYNES

2,4,6-Tri-tert-butyl-1,3,5-triphosphabenzene 4 reacts with phosphaalkynes P≡C–R [R = tBu (5a), tPen (5b)] at room temperature in a formal [4 + 2] cycloaddition to yield the corresponding 1,3,5,7-tetraphosphabarrelene derivatives 8a and 8b, respectively. The analogous reaction of 4 with the aminophosphaethyne P≡C–N(iPr)2 (9) unexpectedly leads to the 1,3,4,7-tetraphosphasemibullvalene derivative 10 as the only product. The single-crystal X-ray analysis of 10 exhibits a diphosphirane unit with a very long PP distance of 2.274(1) A together with a large extension of the PCP angle in the three-membered ring to 75.3(1)°.

Novel Diphosphetene Derivatives by Reactions of Di(isopropyl)aminophosphaethyne with Chalcogens or Halogens

Abstract The 1λ3σ2,3λ5σ4-diphosphetene derivatives 6a, 6b are formed in quantitative yields by reactions of di(isopropyl)aminophosphaethyne 1a with sulphur and selenium, respectively, at 25°C. 6a is also produced slowly from 1a and CS2. The tert-butylphosphaalkyne P C–tBu (1b), however, does not react with sulphur or selenium, but undergoes a slow reaction with CS2 to give the five-membered heterocycle 3,5-di-tert-butyl-1-thia-2,4-diphosphole as one of the main products. Halogenation of 1a using SO2Cl2, Br2 or I2 as reagents leads to the 1λ3σ2,3λ3σ3-diphosphetenium salts 9a–9c. X-ray diffraction studies of 6a and 6b prove that the easy formation of the four-membered diphospha-heterocycles is obviously governed by electronically delocalized phosphaallyl units within the unsaturated rings.

Novel phosphabicyclo[2.2.2]-octa-2,5-dienes from iPr2N-C P or tBu-C P and a polyfluorinated cyclohexadienone

Abstract The reaction of the phosphaalkyne i Pr 2 N-C  P ( 1 ) with 6-phenyl-3-pentafluorophenoxy-tetrafluorocyclohexa-2,4-dien-1-one ( 2 ) affords the novel [4 + 2] cycloadduct 3 in quantitative yield. The same reaction carried out with t -butylphosphaethyne ( 4 ) only takes place at 60°C giving a mixture of isomers of the Diels-Alder compounds 5a to 5c in the ratio 90:4:6. 5a can be isolated in pure form but - dissolved in chloroform - at 20°C unexpectedly converts into the 1-phospha-tetracyclo[4.2.0.0. 2,8 .0 5,7 ]octane 6 via an intramolecular [2 + 2] cycloaddition reaction.