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Reactions at the Boron‐Carbon Double Bond of Methyl(methylidene)boranes

2004; Wiley; Volume: 630; Issue: 4 Linguagem: Inglês

10.1002/zaac.200300396

1521-3749

Peter Paetzold, Ulli Englert, Rudolf Finger, Thomas Schmitz, A. Tapper, Ralf Ziembinski,

Organometallic Complex Synthesis and Catalysis

Abstract The addition of Lewis bases L to the methyl(methylidene)boranes MeB=CA 2 (A = SiMe 3 ) and MeB=CAA′ (A′ = SiMe 2 Cl) gives the adducts MeB(L)=CA 2 ( 1a , b ; L = trimethylpyridine, PMe 3 ) and MeB(L)=CAA′ ( 1c , d ; L = di‐ and trimethylpyridine), respectively. Alcohols and amines HX are added to the BC double bond to give boranes MeB(X)—CHA 2 ( 8a — c ; X = O i Pr, O t Bu, N i Pr 2 ); MeB=CAA′ and HNMe 2 react in the ratio 1:2, yielding MeB(X)—CHA(SiMe 2 X) ( 2d ; X = NMe 2 ). From MeB=CA 2 and BH 3 , the five‐membered ring [—CA 2 —BH—CA 2 —BMe(Hm) 2 BMe—] ( 2e ; 2:1) or the six‐membered ring [—CA 2 —BH(H μ ) 2 BMe—CA 2 —BH(H μ ) 2 BMe—] ( 2f ; 1:1) are formed, both containing double hydrogen bridges; the product 2f crystallizes in the space group P 1¯. The metallocene trihydrides [Cp 2 MH 3 ] add to the BC double bond under formation of a double hydrogen bridge to give [Me(A 2 CH)B(H μ ) 2 MCp 2 ] ( 2g , h ; M = Nb, Ta). MeB=CA 2 can be chloroborated, ‐stannated, and ‐phosphated with E—Cl to yield the boryldisilylmethanes MeB(Cl)—CA 2 —E ( 2i — l ; E = EtClB, t BuClB, Me 2 ClSn, Cl 2 P). The alkyloboration and ‐alumination with E—R leads to the boryldisilylmethanes MeBR—SiA 2 —E ( 2m — o ; E—R = Me 2 B—Me, Et 2 B—Et, Cl 2 Al—Et) and the bromination to MeB(Br)—CA 2 Br. (2+2) Cycloadditions are achieved, when MeB=CA 2 is reacted with unsaturated molecules a=b, yielding four‐membered rings [—BMe—CA 2 —b—a—] [ 4a — d ; a=b = fluorenone, bis(methoxycarbonyl)ethyne (reacting at both of the C=O bonds), phenylisocyanate (reacting at the C=O bond), N ‐isopropylacetoneimine], or with triple bond systems RC≡Z, yielding four‐membered rings [—BMe—CA 2 —Z=CR—] ( 4e — g ; RC≡Z = PhC≡CPh, AC≡CCl, t BuC≡P). With a series of six molecules with an element‐oxygen double bond, a primary (2+2) cycloaddition is followed by a metathetical splitting of the transient four‐membered rings 4h — m . One of the metathesis products is MeB≡O, which is identified as boroxene (MeBO) 3 , the other component is an alkene RR′C=CA 2 [starting from MeB=CA 2 and PhCHO, PhC(Me)O] or an alkene RR′C=CAA′ (starting from MeB=CAA′ and PhCHO, t BuCHO) or the methylidene phosphorane Ph 3 P=CA 2 (starting from MeB=CA 2 and Ph 3 PO) or the dicarbadicobaltatetrahedrane [(CA) 2 {Co(CO) 3 } 2 ] {starting from MeB=CA 2 and [Co 2 (CO) 8 ]}. The (2+3) cyclodaddition of MeB=CA 2 to the azide X 2 PN 3 (X = N i Pr 2 ) as 1, 3‐dipole gives the five‐membered ring [=BMe—CA 2 —N=N—NX=] ( 5a ) and to RN 3 the rings [=BMe—CA=N—NA—NR=] ( 5′b , c ; R = i Bu, A; formed from the cycloadducts 5b , c by migration of A); analogously, [=BMe—CA′=N—NA—NA=] ( 5′d ) is formed from MeB=CAA′ and AN 3 . Finally, the nitrone O—NMe=CHPh and MeB=CA 2 or MeB=CAA′ give the corresponding (2+3) cycloadducts 5e , f , respectively. All of the products were characterized by their 1 H, 11 B, and 13 C NMR spectra.