Vanadium complexes aryls

Top row the three components of the Yandulov-Schrock cycle for catalytic dinitrogen reduction. Left the catalyst with the substrate Nj coordinated to Mo (Ar refers to the aryl substituent drawn in detail for one of the nitrogens). Centre the reductant bis(pentamethylcyclopentadienyl)chromium, CpjCr. Right the proton source 2,6-lutidinium borate. Bottom row vanadium complexes with intermediates of nitrogen reduction activated dinitrogen or diazenido(2—) (46a), imide (46b) and ammonia (46c). 

The asymmetric oxidation of sulphides to chiral sulphoxides with t-butyl hydroperoxide is catalysed very effectively by a titanium complex, produced in situ from a titanium alkoxide and a chiral binaphthol, with enantioselectivities up to 96%342. The Sharpless oxidation of aryl cinnamyl selenides 217 gave a chiral 1-phenyl-2-propen-l-ol (218) via an asymmetric [2,3] sigmatropic shift (Scheme 4)343. For other titanium-catalysed epoxidations, see Section V.D.l on vanadium catalysis. 

The Ji-complexes formed between chromium(O), vanadium(O) or other transition metals, and mono- or poly-fluorobenzene show extreme sensitivity to heat and are explosive [1,2], Hexafluorobenzenenickel(O) exploded at 70°C [3], and presence of two or more fluorine substituents leads to unstable, very explosive chromium(O) complexes [1]. Apparently, the aryl fluorine atoms are quite labile, and on decomposition M—F bonds are formed very exothermically. Laboratory workers should be wary of such behaviour in any haloarenemetal Ji-complex of this type [1]. However, in later work, no indications of explosivity, or indeed of any complex formation, were seen [4]. Individually indexed compounds are ... 

C-M bond addition, for C-C bond formation, 10, 403-491 iridium additions, 10, 456 nickel additions, 10, 463 niobium additions, 10, 427 osmium additions, 10, 445 palladium additions, 10, 468 rhodium additions, 10, 455 ruthenium additions, 10, 444 Sc and Y additions, 10, 405 tantalum additions, 10, 429 titanium additions, 10, 421 vanadium additions, 10, 426 zirconium additions, 10, 424 Carbon-oxygen bond formation via alkyne hydration, 10, 678 for aryl and alkenyl ethers, 10, 650 via cobalt-mediated propargylic etherification, 10, 665 Cu-mediated, with borons, 9, 219 cycloetherification, 10, 673 etherification, 10, 669, 10, 685 via hydro- and alkylative alkoxylation, 10, 683 via inter- andd intramolecular hydroalkoxylation, 10, 672 via metal vinylidenes, 10, 676 via SnI and S Z processes, 10, 684 via transition metal rc-arene complexes, 10, 685 via transition metal-mediated etherification, overview,... 

Cyclopentadienyl-substituted vanadium(III) compound (93) is also allowed to undergo the substitution reaction to give the a-alkyl, a-alkynyl, or a-aryl complexes (94, Scheme 52). 2,132-137 [nbu4][V(C6C15)4], which is prepared... 

Arylimido)vanadium(V) complexes have been prepared from the reaction of VOCl3 with various /wa-substituted aryl isocyanates. The reactivity and structure of some of these have been investigated (78).431 The reactivities of a series of vanadium(V) chalcogens have been reported. The structure of [(Me3Si)2N]2V(Se)[SeSi(SiMe3)3] 432 (79) shows that the V=Se double bond contracts by 8% compared to the single bond in a related dimeric vanadium(IV) structure (vide infra). The... 

Homoleptic alkyl and aryl complexes of vanadium(IV) can in principle be synthesized from VCI4. However their thermal instability of makes them difficult to isolate. In some cases, the use of lithium alkyls and alkyl Grignards leads to reduction from V(IV) to V(III). Interestingly, [V(l-norbornyl)4], prepared from VCI4 and Li(l-norbornyl), is relatively stable up to 100 °C and is only moderately air sensitive [30]. The most air/ thermally stable complex of this class is [V(Mes)4], which was isolated in nearly quantitative yield by air oxidation of Li[V(Mes)4] [31]. 

The title complex is a rare example of a fully characterized homoleptic vanadium aryl (and alkyl) complexes which are fully characterized, and its reactivity has been widely investigated. Some reactions are shown in Scheme 7.7 [43]. 

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