The synthesis of the (qa-cyclooctatetraene)(q4-l,3-and -1,Zdiphosphacyc1obutadiene)titanium complexes 3a-c and 4a, b by cyclodimerization of the phosphaalkynes 2a-c [a: R = tBu, b: R = adamantyl (ad), and c: R = (iPr)(Me,Si)N] in the coordination sphere of the (qa-cyc1ooctatetraene)titanium complex 1 is described. The molecular structures of 3a-c and 4a, b were determined by spectroscopic methods (31P, 'H, and 13C NMR). In the case of 3a and 4a, X-ray analyses were carried out. The increased reactivity of 4a compared to 3a was utilized to separate 3 a from 4a. Displacement of the 1,2-diphosphete (isolated as its cyclodimer 5) from 3b was achieved by reaction with hexachlorethane.Recently, we reported on a high-yield synthesis of an (qscyclooctatetraene)(q4-1 ,3,5,7-tetraphosphabarrelene)-zirconium derivative by cyclotetramerization of the phosphaalkyne 2a in the coordination sphere of bis(cyc1ooctate-traene)zirconium [']. Since this behavior of 2a differs considerably from that found in the reaction of zirconocene derivatives with 2a, which leads to the formation of (1,3-diphosphabicyclo[ 1.1 .0]butanediyl)zirconocene[2], we studied the reactivity of phosphaalkynes toward other bis(cyclooctatetraene) complexes of the group-4 metals. The results obtained by the use of bis(cyc1ooctatetraene)titanium (1) are presented in this paper.It is well documented that the reactivity of phosphaalkynes 2 toward transition metal complexes is similar to that of alkynes. This indicates that reactions of both types of compounds are characterized by a side-on coordination to the metalL3]. Differences exist in the products, since in cycloaddition reactions of alkynes at a late transition metal center benzene derivatives or cyclooctatetraenes are formed ~atalytically [~], whereas with phosphaalkynes q4-l ,3-diphosphacyclobutadiene complexes are the most typical products The reaction of bis(cyc1ooctatetraene)titanium (1) with the phosphaalkynes 2a-c proceeds slowly. After heating for few days at 80-85 "C replacement of the q4-bonded cyclooctatetraene of 1 by two equivalents of 2a or 2b was complete. In contrast to the zirconium analog of 1, which reacts with 2a by cyclotetramerization ['], the reaction of 1 with 2a or 2b affords in a clean [2 + 21 cycloaddition q4-bonded diphosphacyclobutadiene (diphosphete) in more than 60% yield. However, these cycloadditions are not regioselective as observed with appropriate late metal c~mplexes [~,~], since (Us-cyc1ooctatetraene)titanium complexes of 1,3-diphosphete (3a, b) and 1,2-diphosphete (4a, b) were obtained in nearly equal amounts. This is the first time that a 1,2-diphosphete formation was observed by a [2 + 21 cycloaddition of two molecules of a phosphaalkyne in the coordination sphere of a transition metal complex.The phosphaalkyne 2c is much less reactive than 2a and b. The titanium complex 3c was formed regioselectively as Chem.
High-yield methods for the preparation of (PMe3)3RhC1 (2) and [(R3P)2RhC1]2 [R = Me (3a); iPr (3b), and cyclohexyl (3c)I are described. The dimeric nature of 3b in the solid state has been established by an X-ray analysis.Die dimeren [Bis(trialkylphosphan)rhodiumchloride] 3 mit Alkyl=Methyl (3a) ['l, Isopropyl (3b)
Die Chemie der Phosphaalkine (RC-P) hat wesentliche Impulse durch die Verwendung von Ubergangsmetalltemplaten in Cyclooligomerisierungen erhalten [']. Wichtige Stationen auf diesem sich noch immer sturmisch entwickelnden Gebiet ist die Cyclodimerisierung von tert-Butylphosphaacetylen 5 zu den y4-1,3-Diphosphacyclobutadienkomplexen von Cobalt['] und Rhodium, 1 [jl, die unerwartete Bildung der tricyclischen Zirconium-und Hafniumkomplexe 2 aus 5[41 sowie die Cyclotrimerisierung von 5 zum 1,3,5-Triphospha-Dewar-Benzolkomplex 3 niit Vanadium als Zentralatom[s]. 1 2 M = Co, Rh M=Zr,Hf 3 Von diesen Metallkomplexen mit heterocyclischen Liganden haben sich bisher nur die Zirconium-und Hafniumverbindungen 2 als ergiebige Quellen zur Synthese neuartiger Phosphaheterocyclen e r~i e s e n [~~. 'I, wobei besonders die Synthese des symmetrischen Tetraphosphacubans aus 2 bemerkenswert ist[']. Wir berichten hier erstmals uber die erfolgreiche Cyclotetramerisierung des Phosphaalkins 5 am Bis(cyc1ooctatetraen)-Zirconiumkomplex 4 zum y4-1 ,3,5,7-Tetraphosphabarrelen-Zirco-niumkomplex6, aus dem mit Hilfe von Hexachlorethan das 1,3,5,7-Tetraphosphabarrelenderivat 7 als neues, cyclisches Tetramer des Phosphaalkins 5 freigesetzt werden kann (Schema 1). 4 6 Schema 1. a: Toluol. 2 d. 70 C. -cot; b: Pentan. 12 h. -78 -20"C, -C,CI,, -[(cotJZrCI,]. TS 2 116 c) VCH Verlugsgrsellsrhafl mbH. 0-69451 Weinhetin, 1995
A surprisingly straightforward cyclotetramerization of tBuC ≡ P in the coordination sphere of an η8‐cyclooctatertraene–zirconium complex yields 1,3,5,7‐tetraphosphabarrelen 1. The bicyclic compound is initially bound to the Zr atom through two PC bonds, but can easily be liberated from the complex by reaction with hexachloroethane.
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