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(CbR 4 )] [ 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 = CF 3 SO 3 – ). The heterotrimetallic barrel 1 exhibited selective 1:1 interaction with a N, N ′-dimethyl-1,4,5,8-naphthalenetetracarboxylic diimide guest, as revealed by 1 H NMR analysis. The self-assembly of donor L with two other Ru(II)-based 180° acceptors [( p -cymene) 2 Ru 2 (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 ( 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.