Abstract
We have prepared quintuply bonded dinuclear complexes M2[μ-κ2-N(Dipp)C(H)N(Dipp)]2 (M = Mo, Cr; Dipp = 2,6-iPr2C6H3) with symmetrical amidinato ligands. Due to their low-coordinate and low-valent properties, these quintuply bonded complexes have been employed to activate many small organic molecules. In this thesis, we tried to prepare the quintuply bonded dinuclear complexes supported by unsymmetrical amidinato ligands, and explored their reactivity with various small organic molecules. The unsymmetrical 2,6-diisopropylphenyl- (Dipp) and 2,6-diethylphenyl- (Dep) substituted amidinato ligand was used to synthesize quadruply bonded dimolybdenum complex [Li(THF)4][Mo2(μ-Cl)Cl2[μ-κ2-N(Dipp)C(H)N(Dep)]2] (1), which was subsequently reduced to the quintuply bonded dimolybdenum complex Mo2[μ-κ2-N(Dipp)C(H)N(Dep)]2 (2). However, the reactivity of 2 toward many small organic molecules is similar to those of our reported symmetrically quintuply bonded dimolybdenum amidinates as before. On the other hand, 2,6-diisopropylphenyl- and 2,6-dimethylphenyl- (Dmp) substituted amidinate was used to prepare the dinuclear complex Cr2(μ-Cl2)[μ-κ2-N(Dipp)C(H)N(Dmp)]2(THF)2 (3), which was subsequently reduced to the quintuply boned dichromium complex Cr2[μ-κ2-N(Dipp)C(H)N(Dmp)]2 (4). Treatment of 4 with p-tolyl azide afforded the complex (μ-p-tolylN)2(p-tolylN)2Cr2[μ-κ2-N(Dipp)C(H)N(Dmp)]2 (5). In addition, treatments of 4 with benzonitrile and acetonitrile produced the complex (μ-κ1C:κ2N-PhCN)2(κ1-PhCN)2Cr2[μ-κ2-N(Dipp)C(H)N(Dmp)]2 (6) and {Cr2[μ-κ2-N(Dipp)C(H)N(Dmp)]2[N(Dipp)C(H)N(Dmp)]2[κ2-NC(CH3)C(CH3)N]}2 (7). Notably, 7 was the only isolable product from the reaction of 4 and acetonitrile, in contrast with the reaction of symmetrical quintuple bonded dichromium complex with acetonitrile, from which two products were isolated. Therefore, complex 4 shows much better selectivity toward acetonitrile. Interestingly, treatment of 4 with phenylacetylene and trimethylsilylacetylene led to the isolation of the [2+2] cycloadduct (μ-η1:η1-C6H5CCH)Cr2[μ-κ2-(NDipp)CH(NDmp)]2 (8) and the inverted sandwich complex [μ-η6:η6-(1,3,5-(SiMe3)3C6H3)]Cr2[κ2-N(Dipp)C(H)N(Dmp)]2 (9), respectively. Complex 9 is a dichromium complex with a tristrimethylsilylbenzene-bridged structure, where tristrimethylsilylbenzene was formed by three molecules of trimethylsilylacetylene via [2+2+2] cycloaddition. It is noteworthy that tristrimethylsilylbenzene of 9 is labile and can be replaced by benzene. Accordingly, we take advantage of this property of 4 to react with other alkynes, and anticipate catalytic reactions to occur.