Ruthenium Half-Sandwich Complexes with Sterically Demanding Cyclopentadienyl Ligands

A chloro-bridged RuIII complex of formula [Cp∧RuCl2]2 (Cp∧ = η5-1-methoxy-2,4-tert-butyl-3-neopentylcyclopentadienyl) (1) was obtained in a single step by reaction of [RuCl3(solv)n] with tert-butylacetylene in methanol. Complex 1 showed polymorphism and crystallized in two distinct forms: an isomer, 1a, with no significant metal−metal interactions (Ru···Ru = 3.684(1) or 3.743(1) Å) and an isomer, 1b, in which the Ru atoms are 2.960(2) Å apart from each other. In solution, a temperature-dependent equilibrium between the two isomers is established. When the reaction of [RuCl3(solv)n] with tert-butylacetylene was carried out in ethanol, the chloro-bridged dimer 2, with an ethoxy instead of a methoxy group attached to the cyclopentadienyl ligand, was formed. Complex 1 was found to be a versatile starting material for the synthesis of mononuclear half-sandwich complexes. With phosphine ligands or norbornadiene (nbd), the 16 e- complexes [Cp∧RuCl(PCy3)] (3), [Cp∧RuCl(PPh3)] (4), and [Cp∧RuCl(PnBu3)] (5), the 17 e- complex [Cp∧RuCl2(PPh3)] (7), and the 18 e- complexes [Cp∧RuX(PPh2RPPh2)] (X = H, Cl; R = CH2, C2H4; 8−11) and [Cp∧RuCl(nbd)] (12) were obtained. Crystallographic analyses show that the Ru−P bond lengths in these complexes are longer than in corresponding pentamethylcyclopentadienyl complexes.