Discovery and evaluation of highly active imidotitanium ethylene polymerisation catalysts using high throughput catalyst screening.

A family of ca. 50 imidotitanium precatalysts [Ti(NR)(Me(3)[9]aneN(3))Cl(2)](R = alkyl or aryl; Me(3)[9]aneN(3)= 1,4,7-trimethyltriazacyclononane) were prepared in good yields using semi-automated procedures; high-throughput screening techniques identified seven highly active ethylene polymerisation precatalysts with activities in the range ca. 3 400 to 10 000 kg(PE) mol(-1) h(-1) bar(-1).

Studies of a nickel-based single-molecule magnet.

A cyclic complex [Ni(12)(chp)(12)(O(2)CMe)(12)(thf)(6)(H(2)O)(6)] (1) has been synthesised and studied (chp=6-chloro-2-pyridonate). Complex 1 exhibits ferromagnetic exchange between the S=1 centres, giving an S=12 spin ground state. Detailed studies demonstrate that it is a single-molecule magnet with an energy barrier of approximately 10 K for reorientation of magnetisation. Resonant quantum tunnelling is also observed. The field between resonances allows accurate measurement of D, which is 0.067 K. Inelastic neutron scattering studies have allowed exchange parameters to be derived accurately, which was impossible from susceptibility data alone. Three exchange interactions are required: two ferromagnetic nearest neighbour interactions of approximately 11 and 2 cm(-1) and an anti-ferromagnetic next nearest neighbour interaction of -0.9 cm(-1).

Dinuclear and Hexanuclear Iron(III) Oxide Complexes with a Bis(bipyridine) Ligand: A New [Fe(6)(&mgr;(3)-O)(4)](10+) Core.

The use of the bis(bipyridine) ligand L (1,2-bis(2,2'-bipyridyl-6-yl)ethane) has yielded new dinuclear and hexanuclear complexes. The FeCl(3)/NaO(2)CPh/L (4:4:1) reaction system in MeCN gives red-brown [Fe(6)O(4)Cl(4)(O(2)CPh)(4)L(2)][FeCl(4)](2) (1). The same reaction system in a 3:3:1 ratio in MeOH gives orange [Fe(2)(OMe)(2)Cl(2)(O(2)CPh)L][FeCl(4)] (2). Complex 1.2MeCN: monoclinic, P2(1)/a, a = 15.317(2) Å, b = 18.303(3) Å, c = 16.168(3) Å, beta = 108.91(1) degrees, and Z = 2. Complex 2: triclinic, P&onemacr;, a = 14.099(6) Å, b = 18.510(7) Å, c = 7.108(3) Å, alpha = 96.77(2) degrees, beta = 99.45(2) degrees, gamma = 81.16(2) degrees, and Z = 2. The cation of 1 consists of a near-planar [Fe(6)(&mgr;(3)-O)(4)](10+) core that can be described as three edge-fused [Fe(2)O(2)] rhombs to which are attached two additional Fe atoms. The cation of 2 contains a [Fe(2)(&mgr;-OMe)(2)(&mgr;-O(2)CPh)](3+) core. In both cations, the L group acts as a bridging ligand across an Fe(2) unit, with the bpy rings essentially parallel. Variable-temperature solid-state magnetic-susceptibility studies of 1 and 2 in the 2.00-300 K range reveal that for both complexes the data are consistent with an S = 0 cation and S = (5)/(2) [FeCl(4)](-) anions. These conclusions were confirmed by magnetization vs field studies in the 2.00-4.00 K and 10.0-50.0 kG ranges. Fitting of the data for 2 to the appropriate theoretical equation for an equimolar composition of Fe(2) cations and [FeCl(4)](-) anions allowed the exchange interaction in the cation to be determined as J = -10.5 cm(-)(1) (H = -2JS(1)S(2)) with g held at 2.00. The obtained J value is consistent with that predicted by a previously published magnetostructural relationship.