Synthesis of 2H-1,2-Azaphosphole Complexes by [3 + 2] Cycloaddition of Nitrilium Phosphane−Ylide Complexes with Various Alkynes:  Studies of the C-Substituent and Metal Effects on the Reaction Course

Abstract

Thermal ring opening of [2-(bis(trimethylsilyl)methyl)-3-phenyl-2H-azaphosphirene-κP]pentacarbonylchromium(0), -molybdenum(0), or -tungsten(0) (1a−c) in the presence of three different alkynes, phenylacetylene, ethyl acetylenecarboxylate (EAC), and dimethyl acetylenedicarboxylate (DMAD) (i−iii), was investigated, using toluene (a) and benzonitrile (b) as solvents, whereby special emphasis was to determine the dependence of the [2 + 1]/[3 + 2] cycloaddition product ratio and the regioselectivity on the electronic properties of the acetylenes and the transiently formed nitrilium phosphane−ylide complexes. It is shown that the stability of the latter clearly depends on the donor abilities of the C-substituent of the C,N,P 1,3-dipole system. In toluene 1H-phosphirene complexes 11a−c are obtained exclusively (ia), whereas when EAC (iia) and DMAD (iiia) were employed as trapping reagents, the metal-dependent formation of either a mixture of 1H-phosphirene and 2H-1,2-azaphosphole complexes (M = Cr, W; iia, 12a,c and 13a,c; iiia, 4a,c and 5c) or a mixture of 1H-phosphirene and a diphosphene complex was observed (M = Mo; iia, 12b and 14; iiia, 4b and 14). Reaction iia yielded 13a,c regioselectively. Exclusively in the case of DMAD (iiia,b), but for all 2H-azaphosphirene complexes 1a−c, the further unidentified byproduct 15 was detected spectroscopically. In benzonitrile the reactions of complexes 1a−c led generally to decreased yields of 1H-phosphirene complexes 11a−c (ib) but not to 2H-1,2-azaphosphole complex formation in the case of ib. In the case of the reactions iib and iiib, significantly changed 1H-phosphirene/2H-1,2-azaphosphole complex ratios are observed in favor of the latter (complexes 13a,c and 5c). Although the regioisomeric complexes 13a,c were formed predominantly, evidence was obtained spectroscopically, at least, for the other regioisomeric tungsten complex 18a. The dependence of the 1H-phosphirene/2H-1,2-azaphosphole complex ratios on the arylnitrile concentration and the electronic influence of the para aryl substituent was demonstrated by an 31P NMR spectroscopic study (iv) for the 2H-azaphosphirene complexes 1c and 16a,b. Further three-component reactions with 2H-azaphosphirene complexes, different nitriles, and DMAD (v), EAC (vi−viii), and phenylacetylene (ix) are reported. Thus, thermolysis of complex 1c in acetonitrile or tert-butyl cyanide and with DMAD led to 5-alkyl-substituted 2H-1,2-azaphosphole complexes 17c,d (v), and with acetonitrile and EAC the 2H-1,2-azaphosphole complex 13d was obtained (vi). Thermolysis of 2H-azaphosphirene complexes 1a−c in toluene with EAC as trapping reagent and dimethyl cyanamide (vii) or 1-piperidinonitrile (viii) selectively furnished 2H-1,2-azaphosphole complexes 13e−h and 18b−e, the former being the preferred regioisomers. Using the 2H-azaphosphirene complex 1c, dimethyl cyanamide or 1-piperidinonitrile, and phenylacetylene (ix), the last as solvent and trapping reagent, gave complicated product mixtures. These consist each of three different types of main p...

Diphosphanylketenimines: New Reagents for the Synthesis of Unique Phosphorus Heterocycles

“…These findings are in accord with a HOMO–LUMO interaction between 3 and the alkyne, the first acting as 1,3‐dipole. In fact, the reactivity of these alkynes toward the ketenimine 3 correlates well with their LUMO energy, which is higher in PhCCH and PhCCPh than in the activated alkynes MeO 2 CCCH and MeO 2 CCCCO 2 Me 11…”

An unconventional route to [(Me3Si)2HCPCl2W(CO)5] and its conversion to the structurally characterized P-chalcogenides (Me3Si)2HCP(X)Cl2 [X = S, Se]

“…So far, the only ring cleavage reactions of 2H-azaphosphirene complex 1 in which no π-system was involved (at one stage or another) were reactions with triethylammonium chloride, giving complex 3, 3 or water, thus yielding complex 4 4 via reaction of the transiently formed phosphinidene complex 2; the pathway of the latter reaction was not elucidated (Scheme 2).…”

The synthesis of 1,2-azaphospholes, 1,2-azaphosphorines and 1,2-azaphosphepines

“…Furthermore, the reaction of complex 56 with 2-(triphenyl- 5 -phosphanyl)acetonitrile led to the formation of 1,2-azaphosphole 59 (Scheme 18). 33,[48][49][50]…”

“…Also, reaction of complex 56 with ethyl propiolate and different nitriles in pentane gave 1,2-azaphospholes 65 in high yield (Scheme 20). 49,50,52,54…”