263751-16-2Relevant articles and documents
Synthesis, fluxionality, and propene insertion reactions of zirconium boryldiene complexes with sterically undemanding Cp ligands
Corradi, Marco M.,Jiménez Pindado, Gerardo,Sarsfield, Mark J.,Thornton-Pett, Mark,Bochmann, Manfred
, p. 1150 - 1159 (2008/10/08)
The reduction of CpRZrCl3(dme) (CpR = Cp (a), C5H4SiMe3 (b), C5H4Me (c), Ind (d)) with sodium amalgam in the presence of isoprene, followed by the addition of allylmagnesium chloride, gives the diene complexes CpRZr(η1-allyl)(η4-isoprene) (2a-d). The preparations are conveniently carried out as one-pot reactions. The reaction of 2a-d with B(C6F5)3 in toluene solution at -78°C proceeds quantitatively to give the thermally unstable zwitterionic complexes CpRZr(η3-allyl){η1:η 3-CH2CMeCHCH2B(C6F5) 3} (3a-d), which on warming decompose under C-H activation and propene elimination to give CpRZr(C6F5){η4-CH 2-CMeCHCHB(C6F5)2} (4a-d). The complexes are stabilized by the coordination of one o-F atom of a boryl-C6F5 ring to the metal center. Compounds 4 are fluxional. The rotation of the Zr-C6F5 ligand is influenced by the steric demand of the Cp ligands (ΔG≠ = 43-49 kJ mol-1), while there is little variation in the rotational barriers of the B-C6F5 substituents (ΔG≠ = ca. 47 kJ mol-1). Recrystallization of 4a from diethyl ether affords the 16-electron complex 4a·OEt2, in which fluorine coordination is replaced by an ether ligand. The structure of this complex has been determined; unlike its C5Me5 and C5H3(SiMe3)2 congeners, it shows the boryldiene moiety to occupy a prone (endo) conformation. Propene inserts into the CH2 terminus of the boryldiene ligand under ambient conditions to give the metallacycles CpR-Zr(C6F5){η1:η 3-CH2CH(Me)-CH2C(Me)CHCHB(C6F 5)2} (5a-d), with complete regioselectivity and very high stereoselectivity. The insertion process is reversible; propene extrusion occurs via β-alkyl elimination from the major chair conformation isomer.
