Coordination-Driven Self-Assembly of Heterotrimetallic Barrel and Bimetallic Cages Using a Cobalt Sandwich-Based Tetratopic Donor

Abstract

Three-dimensional molecular architectures self-assembled with tripodal and tetratopic donors are valuable because of their encapsulation properties. Here, we present Co(I)-Fe(II)-Pd(II) heterotrimetallic trifacial barrel 1, which was self-assembled using a newly synthesized tetratopic donor [CpCo(CbR4)] [L; Cp = cyclopentadienyl, Cb = cyclobudiene, and R = 4-(4-pyridylphenyl)] and a 90 degrees acceptor [cis-(dppf)-Pd(OTf)(2)] (Al; dppf = (diphenylphosphino)ferrocene and OTf = CF3 SO3-). The heterotrimetallic barrel 1 exhibited selective 1:1 interaction with a N,N'-dimethyl-1,4,5,8-naphthalenetetracarboxylic diimide guest, as revealed by H-1 NMR analysis. The self-assembly of donor L with two other Ru(II)-based 180 degrees acceptors [(p-cymene)(2)Ru-2 (OO boolean AND OO)(OTf2] [OO boolean AND OO = 6,11-dioxido-S,12-naphthacenedione (A2) and oxalate (A3)] resulted in tetragonal-prismatic cages. Self-assembly using the longer acceptor A2 provided rare isomers of a tetragonal-prismatic cage by varying the orientation of the cydopentadienyl moiety out-out (2(a)) or out-in (2(b)) of the cavity, whereas self-assembly using the shorter acceptor A3 selectively resulted in the tetragonal-prismatic cage 3. The three-dimensional molecular architectures 1-3 were characterized by combined spectroscopic and elemental analyses. The structures of molecular barrel 1 and prismatic cage 3 were elucidated by single-crystal X-ray analysis.