Preparation of a Copper Ion Complex of Sterically Congested Diphenyldiazomethanes Having a Pyridine Ligand and Characterization of Their Photoproducts

Abstract

To show that persistent high-spin polycarbenes can be realized by utilizing hetero spin systems, two diphenyldiazomethanes having pyridyl groups, i.e., bis{4-(4-pyridyl)-2,6-dimethylphenyl}diazomethane (4,4'-DPy-1-N(2)) and {2,4-di(4-pyridyl)-6-bromophenyl}(2,6-dimethyl-4-tert-butylphenyl)diazomethane (2,4-DPy-1-N(2)), were prepared. Triplet carbenes, 4,4'-DPy-1 and 2,4-DPy-1, generated by photolysis of the corresponding diazomethanes were characterized by spectroscopic means (ESR and UV/vis in matrix at low temperatures and laser flash photolysis in solution at room temperature). The results showed that they were fairly persistent. Magnetic properties of the photoproducts from a 1:1 complex between DPy-1-N(2) and Cu(hfac)(2) (hfac = hexafluoroacetylacetonate) were characterized by ESR and a superconducting quantum interference device (SQUID) magneto/susceptometer. The field dependences of magnetization for the complexes, expressed by using M versus H/T plots, were analyzed in terms of the Brillouin function to be S = 6.80 (F = 0.60) for the 1:1 complex of 4,4'-DPy-1 and Cu(hfac)(2) and S = 3.71 (F = 0.73) for the 1:1 complex of 2,4-DPy-1 and Cu(hfac)(2) at 2.0 K. Thus, it has been demonstrated that a high-spin species is actually generated in the photoproducts and that the complexed carbenes showed significant stability.

Persistent Triplet Carbenes

“…In order to realize persistent high spin polycarbenes, we employed the following three approaches to prepare poly(diazo) compounds: (1) synthesis of dendritic molecules having peripheral diazo groups starting from diazo compounds, 169,232 (2) preparation of a poly(phenylacetylene) bearing a diazo unit using the Rh-complex catalyzed polymerization of diazo compounds bearing a p-ethynyl substituent, 233 and (3) preparation of a polymer chain as a result of complexation of the ligand pyridine introduced on diazo compounds with coordinatively unsaturated metal ions. 234 We also characterized the magnetic properties of photoproducts obtained by photolysis of those poly(diazo) compounds. 235 Although the spin-states observed for those photoproducts were not so high at present, the results suggest that our approach using persistent triplet carbenes will eventually lead us to a persistent high-spin polycarbenes by taking advantage of the stability of our diazo compounds.…”

From Persistent Triplet Carbenes to Persistent High-Spin Polycarbenes

“…57 Both diazo compounds are expected to form a chain as a result of complexation with metal ions (to form -DPy-25-N 2 -M-), and the chain is expected, upon irradiation, to generate a polycarbene chain (-DPy-25-M-) in which the spins on the chain start to interact ferromagnetically. However, there is a potential difference between the two in the connectivity of the ferromagnetic coupling unit with respect to carbene centers (Scheme 19).…”