Dedicated to Professor Heinz A. Staab on the occasion of his 75th birthday
Thermostable homogeneous catalysts have three major advantages: the first is that less reactive substrates, for which the kinetics require high temperatures, can be transformed to products; second, they expand the field of homogeneous catalysis to include more endothermic processes, for which the thermodynamics require high temperatures; the third benefit is facile catalyst separation by distillation of educts and products. A process where such catalysts would definitely show great promise is the C ร H activation of alkanes in homogeneous solution with dehydrogenation to alkenes and hydrogen. [1] However, thermostable homogeneous catalysts for endothermic processes are almost nonexistent [2] and the synthesis of suitable organometallic coordination compounds seemed destined to be abandoned because of complex instability at high temperatures. [3] This trend was reversed with the introduction of tridentate coordination compounds [4] in the form of PCP pincer complexes [MCl(H){C 6 H 3 (CH 2 PtBu 2 ) 2 -2,6}] (1, 2) [5] and their subsequent conversion into [M(H) 2 {C 6 H 3 (CH 2 PtBu 2 ) 2 -2,6}] and [M(H) 4 {C 6 H 3 (CH 2 PtBu 2 ) 2 -2,6}] (M Rh, Ir). [6, 7] The transition metal dihydrides, especially the iridium compounds 3 and 4, are thermally stable up to 200 8C and are reactive to aliphatic and cycloaliphatic CรH bonds. [7] An even higher thermostability can be expected for ยชanthraphosยบ complexes 6 and 7 which are obtained by replacing the benzylic PCP pincer ligands with anthracene-triblock copolymer. Triblock copolymer films were obtained by evaporating a concentrated toluene solution of the copolymer and a hPS standard (M ร
w 2500 g mol ร1 , M ร
w /M ร
n 1.09) in a mass ratio of 1.00/0.40 over 3 d. The films were then annealed at 120 8C for one week. To incorporate Fe 2 O 3 , an excess of FeCl 2 was equilibrated with the nanotubes with PAA-lined cores in deoxygenated THF. The excess FeCl 2 was removed after precipitation of the Fe 2 -impregnated tubes into methanol. The trapped Fe 2 was then treated with NaOH in THF containing 2 % water to form iron(ii) hydroxide or oxide. Fe 2 O 3 was prepared by oxidizing the iron(ii) hydroxide or oxide with hydrogen peroxide.