Generation of Organometallic Conjugated Compounds Applicable for Non-linear Optics

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The construction of linear covalently-linked metal clusters has attracted much interest in view of fundamental bonding as well as promising applications as extensive electronic communications and optoelectronic materials. We have already reported synthesis and reaction of a linearly aligned tetranuclear complex, Mo_2Pd_2(pyphos)_4 (1)(pyphos=6-diphenylphosphino-2-prydonate), which was prepared by treating a quadruply bonded dinuclear dimolybdenum (II) complex, Mo_2(pyphos)_4 (2), with Pd_2(dba)_3(C_6H_6) in THF.The most interesting feature is that both Pd(O) atoms of 1 datively interacted with the Mo_2 core and hence the Pd(O) centers, unlike normal monoculear Pd(O) complexes, reacted oxidatively with dichloromethane at room temperature to give a Pd(II) complex, Mo_2PdCl_2(CH_2Cl)_2(pyphos)_4 (3). On monitoring the reaction of equation 1 by UV spectroscopy, the deep orange color (λ_<max>=476 nm) of 1 in dichloromethane turned immediately to greenish brown [the Pd(I) complex, Mo_2Pd_2Cl … More _2(pyphos)_4 (4) was deep green (λ_<max>=642 nm)], and then gradually resulted in the formation of the Pd(II) complex 3. We found that disulfides oxidatively added to both Pd(O) metals of 1 in a 1,4-addition reaction ; 1 reacted with one equivalent of diaryldisulfides in THF at room temperature to give the corresponding Pd(I)-thiolate complexes, Mo_2Pd_2(pyphos)_4(SAr)_2 (5a-f) in modest yields. Multiply-bonded tetranuclear complexes M_2Pd_2Cl_2(pyphos)_4 (6) and dinuclear complexes M_2(pyphos)_4 (7) (a, M=Mo ; b, M=Cr ; pyphos=6-diphenylphosphino-2-pyridonate) are found to exhibit large hyperpolarizability γ of nonlinear optical property by using the picosecond degenerate four-wave mixingg (DFWM) method ; the γ values of 6a (1.5×10^<-30> esu), 6b (5.2×10^<-31> esu), and 7a (6.9×10^<-31> esu) are greater than those (ca.10^<-35>-10^<-33> esu) of transition metal poly(yne) polymers.Recent development of the polymerization chemistry based on well-defined organometallic complexes is remarkable. Coordination polymerization of polar olefinic monomers such as methyl acrylate (MA) and methyl methacrylate (MMA) has been accomplished by using various enolate complexes. In this contribution, we would like to report the first Group 5 metal complex active for MMA polymerization. Moreover, we present our new idea to generate a catalytically active enolate complex from an organometallic complex bearing a polar monomer as a ligand. The coordinated MMA ligands of newly prepared tantalum complexes TaCp^*(η^2-p-MeOC_6H_4-DAD)(η^4supine-MMA)(8) (p-MeOC_6H_4-DAD=1,4-bis(p-methoxyphenyl)-1,4diaza-1,3-butadiene) and TaCp^*(η^2-Cy-DAD)(η^4-supine-MMA)(9) (Cy-DAD=1,4-dicyclohexyl-1,4-diaza-1,3-butadiene) were activated by addition of one equivalent of AlMe_3 to generate active catalysts for polymerization of MMA.The catalyst system of the highest activity was the combination of 9 and one equiv of AlMe_3 at -20℃ ; the polymerization completed within 10 min to give a PMMA with very narrow polydispersity (M_w/M_n=1.10). Less