Cationic M(II)/Co(0) (M = Pd, Pt) metallomacrocycles containing tetrahedral Co2C2 cluster cores formed by self-assembly of cluster-bridged bipyridine (4-C5H4NCO2CH2)2C2Co2(CO)6 and diarsine-chelated complex [Pd(dpab)(H2O)(OTf)[OTf] or [Pt(dpab)(H2O)2][OTf]2

The synthesis, characterization, and some reactions of the tetrahedral Co2C2 cluster-bridged bipyridine (4-C5H4NCO2CH2)(2)C2CO2(CO)(6) (2) and the diarsine-chelated complexes Pd(dpab)Cl-2 (3, dpab = 1,4-bis(diphenylarsino)butane), [Pd(dpab)(H2O)(OTf)][OTf] (4, OTf = SO3CF3) Pt(dpab)Cl-2 (5), and [Pt(dpab)(H2O)(2)] [OTf](2) (6) have been investigated. While the bridged bipyridine 2 could be prepared by reaction of 4-pyridinecarboxylic acid 2-butyne-1,4-diyl ester 1 with Co-2(CO)(8) in 86% yield, the chelated dichloride complexes 3 and 5 were obtained by reaction of K2PdCl4 or (PhCN)(2)PtCl2 with dpab in 90% and 77% yields. Further reactions of 3 and 5 with silver triflate followed by treatment with water afforded the corresponding chelated aqua/triflate complexes 4 and 6 in 92% and 88% yields. More interestingly, 4 and 6 were found to undergo self-assembly with 2 to give two cationic metallomacrocycles {[M(dpab)]-mu-[(4-C5H4NCO2CH2)(2)C2Co2(CO)(6)]}(2)[OTf](4) (7, M = Pd; 8, M = Pt) in 92% and 85% yields. X-ray crystal structures were determined for the Co2C2 cluster-containing metallomacroycles 7 and 8, as well as bipyridine 2 and complexes 4 and 6.