Dedicated to Professor Dieter Seebach on the occasion of his 60th birthday Cyclooligomerization reactions of phosphaalkynes in the coordination sphere of transition metals in which the metal complex fragment is incorporated in the product have played an important role in the development of phosphaalkyne chemistry.[1] Significant examples are the cyclodimerization of tert-butylphosphaacetylene (5a) to give the tricyclic zirconium complex 1, [2] cyclotrimerizations to give the vanadium and hafnium complexes 2[3] and 3, [4] and the formation of the zirconium and hafnium complexes 4[5] by cyclotetramerization. Treatment of 1, 3, and 4 with hexachloroethane leads to detachment of the metal complex fragments and formation of tBu-substituted 1,3,5,7-tetraphosphacubane (cyclodimerization of the residual molecule), [6] 1,3,5-triphosphabenzene (14a), [4] and 1,3,5,7-tetraphosphabarrelene. [5] Reactions of 2 with the same reagent have not yet been investigated. We now report on the chemoselective cyclooligomerization [7] of phosphaalkynes 5 a ± e with the vanadium(v) compounds tBuNVCl 3´D ME (6) [8] (DME 1,2-dimethoxyethane) and tBuNVCl 3 (13) [9] to produce the title compounds in good yields.Reaction of 5 a ± e with 6 in a molar ratio of 4:1 in toluene followed by column chromatography on alumina affords the previously unknown azatetraphosphaquadricyclanes 7 a ± e as yellow solids in yields of 47 ± 76 % (not optimized; Table 1).The elemental analyses and mass spectra (Table 2) indicate that the heteropolycyclic compounds are formed from four molecules of the phosphaalkyne 5 with loss of one molecule of an alkyne RCCR (see Scheme 1) and incorporation of the imide ligand from the vanadium compound 6.As an example the NMR data of 7 a are discussed here (for further spectroscopic data of the compounds 7, see Table 2).[ Table 2. Selected spectroscopic data for the azatetraphosphaquadricyclanes 7.[a]

Eine kleine Variation des Vanadiumreagens hat ein vollkommen anderes Produkt zur Folge: Durch Cyclooligomerisierung reagieren Phosphaalkine 2 mit tBuN=VCl3⋅DME unter Einbau des Imidofragments zu den Azatetraphosphaquadricyclanen 1 (DME=1,2‐Dimethoxyethan), mit dem entsprechenden Lewis‐Basen‐freien Vanadium‐Reagens werden dagegen ohne Einbau dieses Fragments die 1,3,5‐Triphosphabenzole 3 erhalten.

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]).

A small variation in the vanadium reagent leads to a completely different product: The cyclooligomerization of phosphaalkynes 2 with tBuN=VCl ⋅DME (DME=1,2-dimethoxyethane) proceeds with incorporation of the imido fragment to give the azatetraphosphaquadricyclanes 1. In contrast, with the corresponding vanadium compound containing no Lewis base this fragment is not incorporated, and the 1,3,5-triphosphabenzenes 3 are obtained.

Eine kleine Variation des Vanadiumreagens hat ein vollkommen anderes Produkt zur Folge: Durch Cyclooligomerisierung reagieren Phosphaalkine 2 mit tBuN=VCl3⋅DME unter Einbau des Imidofragments zu den Azatetraphosphaquadricyclanen 1 (DME=1,2‐Dimethoxyethan), mit dem entsprechenden Lewis‐Basen‐freien Vanadium‐Reagens werden dagegen ohne Einbau dieses Fragments die 1,3,5‐Triphosphabenzole 3 erhalten.