Cycloaddition reactions of the kinetically stabilized phosphaalkynes 1 with the imidovanadium(v) trihalides 9 furnish the 1,2,4-azaphosphavanada(v)cyclobutenes 10. The stability of these novel metallacyclic compounds depends solely on the substitutents of the imido unit. Thus, the imidovanadium(v) species 9 with tertiary alkyl groups on the N atom form stable addition products with 1 while in the cases of compounds 9 with a lower degree of substitution at N (primary and secondary alkyl groups) the primarily formed adducts 10 undergo irreversible decomposition to afford the 1H-1,2,4-azadiphospholes 13. Reactions of an excess of the phosphaaalkyne 1 with the vanadium complexes 9 furnish the corresponding triphosphabenzenes 8 in good yields (36-68%). A catalytic reaction course has been demonstrated for the all-tert-butyl system 1a/9a in which the metallacyclic species 10a serves as the catalytically active species. Poisoning of the catalyst leads to a second reaction pathway, which results in formation of the azatetraphosphaquadricyclanes 16. By means of the stepwise use of different phosphaalkynes 1a,b this methodology provides the first access to the differently substituted triphosphabenzenes through cyclotrimerization.
Imidovanadium(V) TrichloridesThe reactions of Me3SiN=VCl3 (1) with MeOH, PhOH, HCl, PyH+Cl~ or LiO'Bu have been studied. The reductive decomposition of 1 by hydrogen chloride in toluene yields HN=VC13 as a labile intermediate which could be isolated only in a small amount. The syntheses of RN=VC13 (R = neopent, "Pr, cyclohex, CPh3, 1-Ad) and [('BuN)2V2Cl4(/i-OC13H9)2] (15) are also described. All compounds obtained are characterized by 5 V NMR spectroscopy, the fluorenolato complex 15 by X-ray diffraction analysis. Einleitung Arylimidovanadium(V)-trichloride sind bekannt und auf folgendem Weg zugänglich [1]: Ergebnisse und Diskussion Halogenid-Ionen (F-, CI" ) spalten die Silicium-Stickstoff-Bindung in 1 unter Bildung des Nitrido-Komplexes [N = VC13]" [10, 11]. Wir haben in Toluol die Reaktion von 1 mit Me thanol, Phenol und Chlorwasserstoff im Mol verhältnis 1 : 1 untersucht und gefunden, daß der nucleophile Angriff von Methanol und Phe nol am Vanadiumatom unter Eliminierung von Chlorwasserstoff erfolgt, während Chlorwasser stoff das Siliciumatom angreift und die Si-N-Bindung spaltet unter Bildung von HN=VC13 (2), siehe Gin. (7), (8), (10).Bei der äquimolaren Umsetzung von 1 mit Chlor wasserstoff entsteht in der Reaktionslösung ein unlöslicher, gelber Niederschlag. Die 51V-NMR-Reaktionskontrolle liefert die Signale von 1 und 2, was zeigt, daß bereits vor dem vollständigen Ab lauf der Reaktion (8) die Zersetzung des Imidovanadium(V)-trichlorids durch Chlorwasserstoff ein setzt (Gl. (11)).
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]).
The reactions of tBuN = VCl2 · DME with LiX (X = NHtBu, NR2, OSiPh3, SR, Alkyl, Cp) have been studied. LiNHtBu and LiCH3 furnish the binuclear diamagnetic tert-butylimido-vanadium( IV) compounds [(μ-NtBu)2V2X4]; in all other cases only the vanadium(V) compounds tBuN=VX3 and tBuN=VCpCl2 formed by disproportionation reactions of vanadium(IV) can be isolated. The syntheses of various mononuclear amido tert-butylimido-vanadium(V) complexes as well as of the binuclear complexes [μ-NtBu)2V2(NtBu)2Cl2] and [(μ-0)V2(NtBu)2Cp2Cl2] are also described. All compounds obtained have been characterized by 51V NMR spectroscopy. tBuN=V(OMe)3 was investigated by X-ray diffraction analysis; the molecular structure has been found to be that of a binuclear vanadium(V) complex with two bridging methoxo ligands.
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