Organophosphorus Compounds, Part 146* Imidovanadium(V) Complexes as Reaction Partners for Kinetically Stabilized Phosphaalkynes. Synthesis and Reactivity of 3-Aza-l,2,4,6-tetraphospha-quadricyclanes

Abstract

The Lewis base adducts of imidovanadium(V) compounds 5a,b undergo chemoselective cyclooligomerization reactions with the kinetically stabilized phosphaalkynes 4a-e to furnish the azatetraphosphaquadricyclanes 6a-f with incorporation of the imido fragment. The reac tivity of this novel class of heteropolycyclic compounds has been examined exemplarily for compound 6a. Complexation of one and two phosphorus atoms was achieved by reaction with nonacarbonyldiiron or the tungsten pentacarbonyl-THF complex resulting in the forma tion of the transition metal compounds 17-20. Reactions of 6a with the sulfonyl azides 21ac furnished the Staudinger products 22a-c. The reaction of 6a with two equivalents of tosyl azide gave a surprising result. No double complexation leading to a symmetrical product was achieved, and compound 23 was obtained instead in which the two phosphorus atoms of one diphosphirane ring are functionalized. Oxidative cleavage of a P/P bond in 6a to furnish product 24 is observed in the reaction of 6a with the Lewis base-free imidovanadium(V) species 15a. Intro d u ctio nCage com pounds, som e of which have highly sym m etrical skeletons, have always been of great in terest to chemists. T heir often tedious, m ulti stage syntheses have p resented a challenge to ex p erim ental tech n iq u es and the unusual bonding relationships have gen erated new im pulses for theoretical considerations.Thus, it is n o t surprising that th e construction of phosphoru s-carb o n cage com pounds has devel oped into an im p o rta n t field in th e chem istry of kinetically stabilized phosphaalkynes. In contrast to their all-carbon analogues, how ever, access to the phosp h o ru s-carb o n cage system s has only b e com e possible in th e past ten years w ith the ph o s phaalkynes being indispensable starting com pounds. * Part 145: S. G. Ruf, U. Bergsträsser, M. Regitz, Eur. J. Org. Chem. 2000, 2219. M ajor b reakthroughs in this developm ent in clude the syntheses of the tetrap h o sp h acu b an e 1 [1 ], the tetrap hosphabishom oprism ane 2 [2 ], and the h ex aphosphapentaprism ane 3 [3] (Schem e 1).The cubane 1 was of p articular in terest on account of its high sym m etry and its at first inexplicable spectral properties. A ccordingly, the rem arkably stable cubane 1 has, on th e one hand, b een the subject of num erous th eo retical bonding studies [4 -6 ] and, on the o th er hand, the starting point for m any functionalization reactions at the ph o s phorus atom s [7 -9 ]. A lthough the first syntheses of the phosphaalkyne te tra m ers 1 and 2 w ere based on the therm olysis of the fe/t-butylphosphaalkyne 4a, m any novel synthetic strategies have since been developed for the specific con struction of polycyclic phosphorus-carbon systems. These now provide selective and high-yield access to the cage com pounds 1 and 2. The synthetic p rin ciples em ployed include transition m etal-(-> 1 [10,11]), base-(-»• 2 [12]), and Lewis acid-m ediated processes (-* ■ 3 [3]).

6 Nitrogen, phosphorus, arsenic, antimony and bismuth

“…70 Imidovanadium() complexes also undergo cycloaddition reactions with phosphaalkynes, in this case leading to 3-aza-1,2,4,6tetraphosphaquadricyclanes. 71 The reaction of cobalt atoms with PCBu t using metal vapour synthesis has been shown to give the sandwich compounds [Co(η 5 -1,2,4- 2 ) 2 (py) n ] (M = Zn, n = 2; M = Cd, n = 3). 73 Synthesis of the 1,3-diphospholyl ferrocene analogue [Fe(η 5 -P 2 C 3 Bu t 3 ) 2 ] has been reported, along with photoelectron spectra for a range of 1,3-diand 1,2,4-tri-phospholyl sandwich compounds.…”

Imidovanadium(V) Complexes as Reaction Partners for Kinetically Stabilized Phosphaalkynes: Synthesis of 1,2,4-Azaphosphavanada(V)-cyclobutenes, 1,3,5-Triphosphabenzenes, and 1H-1,2,4-Azadiphospholes

“…[9,20] The trimethylsilylimidovanadium(v) trichloride 9 d or tribromide 14 may also be used for the preparation of 8 a; these species exhibit an identical reaction behavior to 9 a in the presence of an excess of the phosphaalkyne 1 a (4 equiv), but are not synthetically advantageous on account of their more difficult syntheses. [9,20] The trimethylsilylimidovanadium(v) trichloride 9 d or tribromide 14 may also be used for the preparation of 8 a; these species exhibit an identical reaction behavior to 9 a in the presence of an excess of the phosphaalkyne 1 a (4 equiv), but are not synthetically advantageous on account of their more difficult syntheses.…”

“…[9,20] Although the formation of the barrelene 17 can be considered as a known subsequent reaction of 1 a with 8 a, [21] the formation of the azatetraphosphaquadricyclane is most certainly an alternative reaction pathway proceeding with destruction of the catalyst. [9,20] Although the formation of the barrelene 17 can be considered as a known subsequent reaction of 1 a with 8 a, [21] the formation of the azatetraphosphaquadricyclane is most certainly an alternative reaction pathway proceeding with destruction of the catalyst.…”

“…[9,20] Further support of the catalytic trimerization process is provided by the reactions of the metallacylic species 10 a,b with the phophaalkynes 1 b,a. The reaction step with a fourth equivalent of 1 completing the cycle results in liberation of the 1,3,5-triphosphabenzene 8 with renewed formation of the catalyst 10.…”

“…[20] Subsequent reactions of the triphenylmethyl-substituted metallacyclic species 10 g with 1 a were completely suppressed. Although the trimethylsilyl derivative 9 d also reacts with an excess of 1 a (4 equiv) to furnish the trimer 8 a exclusively; reaction of the 1-adamantyl derivative 9 b under comparable conditions affords the N-adamantyl-substituted azatetraphosphaquadricyclane as a by-product.…”