Structure of Polymer-Bound Titanocene Analogues and Reactivity of Their Dinitrogen Complexes

Abstract

ABSTRACT:Various titanocene polymers in which titanium ion of titanocene dichloride (TiCp2 Cl2) was convalently bound to polystyrene [or poly(carboxylic acid)] were synthesized. These polymer-bound titanocene species were found to be active catalysts for the reduction of dinitrogen molecule under mild conditions. When poly[styrene-co-styrylchlorobis(17-cyclopentadienyl)-titanium] and poly[styrene-co-bis(17-cyclopentadienyl) (p-vinylbenzoyloxy)titanium chloride] were cross-linked with divinylbenzene, the NH3 yield was relatively higher than that of the corresponding non-crosslinked homogeneous system. The NH3 yield increased with the percentage of cross-linking in the order 8% > 2% > 1 %- KEY WORDSTitanocene Polymer / Dinitrogen Molecule / Dinitrogen Complex / Reduction / Ammonia / Most of low-valency transition metals are wellknown for their ability to bind molecular nitrogen as end-on or side-on type. 1 -4 The synthesis of polymeric dinitrogen complexes involves the utilization of dinitrogen molecules in air as the nitrogen source of NH 3 and various aminated substances.A dinitrogen complex such as (Cp 2 TiR)iN 2 (R = aryl) is known to be stable due to the delocalization (n-back donation) of the n electrons from the phenyl groups via the Ti atoms to the N 2 ligand. 5 -7 However, these binuclear complexes are catalytically inactive for the reduction of the coordinated dinitrogen molecule. We have studied the chemical behavior of the transition-metal complexes with polymeric ligand and found that the dimerization of metal complexes was inhibited by the polymer chain. 8 This paper is concerned with the syntheses of various polymer-bound titanocene dichlorides and the reduction of the coordinated dinitrogen in the polymer-bound titanocene complexes. EXPERIMENTAL MaterialsPolystyrene was prepared by the radical polymerization of styrene initiated by azobisisobutyronitrile (AIBN). The number-average molecular weight of polystyrene calculated from vapor pressure osmometer was 13500. Bio-Beads SX polystyrene resins cross-linked by 1 %, 2%, and 8% divinylbenzene in the form of white beads (200-400 mesh) from Bio-RAD Laboratories were used without further purification.Commercial grade of titanocene dichloride (TiCp2Cl2), butyllithium (15% hexane solution), anhydrous aluminum trichloride, acetyl chloride, and potassium permanganate were used without further purification. Tetrahydrofuran, carbon disulfide, and isopropyl alcohol were purified in the ordinary way. titanium 793 Preparations of Poly