Chiral Bis(η⁵:η¹-pentafulvene)titanium Complexes

Abstract

The series of bis(pentafulvene)titanium complexes (η⁶-C₅H₄CR₂)₂Ti (CR₂ = C(<i>p</i>-tol)₂ (<b>3</b>), adamantyl\n(<b>4</b>)) and their corresponding bis(benzofulvene) derivatives (η⁶-C₉H₆CR₂)₂Ti (CR₂ = C(<i>p</i>-tol)₂ (<b>7</b>),\nadamantyl (<b>8</b>)) have been synthesized by reaction of TiCl₃·3THF with the pentafulvene ligands (2 equiv)\nand magnesium as reducing agent (1.5 equiv). The bis(fulvene) complexes <b>7</b> and <b>8</b> have been obtained\nas diastereomerically pure compounds. All complexes have been characterized by spectroscopy and by\nsingle-crystal X-ray diffraction. The bonding situation is best described as a π-η⁵:σ-η¹ coordination mode.\nThe bis(fulvene) complex <b>3</b> is approximately <i>C</i>₂ symmetric, whereas <b>7</b> crystallizes as a conglomerate in\nthe monoclinic space group <i>P</i>2₁ and one of the enantiomers was identified as a (<i>S</i>,p<i>S</i>,p<i>R</i>) stereoisomer\nshowing <i>C</i>₁ symmetry. The adamantyl benzofulvene complex <b>8</b> crystallizes in the monoclinic space group\n<i>P</i>2₁/<i>c</i>; both benzofulvene ligands are coordinated as optical antipodes, and a (<i>S</i>,p<i>S</i>,p<i>R</i>)/(<i>R</i>,p<i>R</i>,p<i>S</i>)\nconfiguration is found in the solid state. Reaction of <b>3</b> and <b>7</b> with HCl/Et₂O leads to the corresponding\nbis(cyclopentadienyl)titanium chlorides (η⁵-C₅H₄−CHR₂)₂TiCl₂ (R = <i>p</i>-tol (<b>9</b>)) and the bis(indenyltitanium)\nderivative (η⁵-C₉H₆−CHR₂)₂TiCl₂ (R = <i>p</i>-tol₂ (<b>10</b>)).