Ancillary ligand control of the structure, reactivity, and stereochemistry of group 4 aryloxide complexes
Abstract
Reduction of (ArO)2TiCl2 (ArO = substituted phenoxide) by Na/Hg or nBuLi in the presence of unsaturated organic substrates leads to the formation of cyclic organic and organometallic products. The reaction of terminal enynes (6-hepten-1-yne) by this methodology affords trisubstituted benzene rings, the products of cyclotrimerization of the parent enyne. Reaction of internal enynes (R = Me, Ph, Me3Si, PhMe2Si) with reduced titanium centers affords titanacyclopent-2-enes, [Ti(OAr)2{C(R)C(C 3H6)CHCH2}]. The trimethylsilyl derivative will catalytically couple 2,6-dimethylphenylisocyanide to yield a novel bicyclopentenimine. Reduced bis(aryloxy)titanium also promotes the tricyclization of the enyne-derived substrate 1,11-dodecadien-6-yne to afford titanacyclohept-4-ene structures, [Ti(OAr)2-{CH2CH(C3H6)CC(C 3H6)CHCH2}]. The titanacyclic rings form stereoselectively in the cis (meso) conformation. The compounds catalyze the cycloisomerization of 1,11-dodecadien-6-yne. Reduction of the dichlorides in the presence of benzylideneamines affords diazatitanacyclopentates, [Ti(OAr)2{N(R)(CHPh)2N(R)}]. Where ArO = 2,3,5,6-tetraphenylphenoxide, these structures form with the phenyl backbone substituents predominately in the mutually trans conformation. Reduction of Cp(ArO)TiCl 2 by analogous routes in the presence of imines affords diazatitanacyclopentanes with opposite (cis) diastereoselectivity. The compounds [CpTi(OAr){N(R)(CHPh) 2N(R)}] undergo fragmentation and exchange with free imine. Treatment of the compound Zr(BH4)4 with two equivalents ArOH (substituted phenols) affords products with substitution of tetrahydroborate ligands dependent upon ArOH bulk. An exchange reaction may be observed for [(ArO)Zr(BH4)3] (ArO = 2,3,5,6-tetraphenylphenoxide) to yield Zr(BH4)4 and [(ArO)2Zr(BH4 )2]. This reactivity may partially explain non-stoichiometric substitution by sterically unhindered phenols.
Degree
Ph.D.
Advisors
Rothwell, Purdue University.
Subject Area
Chemistry
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