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

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° acceptor [ cis-(dppf)Pd(OTf)2] (A1; dppf = (diphenylphosphino)ferrocene and OTf = CF3SO3-). The heterotrimetallic barrel 1 exhibited selective 1:1 interaction with a N, N'-dimethyl-1,4,5,8-naphthalenetetracarboxylic diimide guest, as revealed by 1H NMR analysis. The self-assembly of donor L with two other Ru(II)-based 180° acceptors [( p-cymene)2Ru2(OO∩OO)(OTf)2] [OO∩OO = 6,11-dioxido-5,12-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 cyclopentadienyl moiety out-out (2a) or out-in (2b) 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.