A convenient high yield synthesis of 2,2':6',2'':6'',2''':6''',2'''':6'''',2'''''-sexipyridine and helical transition-metal complexes of substituted sexipyridines

The compoung 2,2':6,2 '':6 '',2''':6''',2 '''':6 '''',2 '''''-sexipyridine (spy) has been synthesised in high yield by the coupling of 6-bromo-2,2':6',2 ''-terpyridine with a nickel(0) reagent, followed by demetallation of the resultant double-helical [Ni-2(spy)(2)](4+) complex with KCN. In order to probe the effects of substitution of spy ypon helication processes, the substituted compounds 4',4 ''''-bis(methylsulfanyl)-2,2':6',2 '':6 '',2''':6''',2 '''':6 '''':6 '''',2 '''''-sexipyridine (msspy), 4',4 ''''-dphyenyl-2,2':6'2 '':6 '',2''',2 '''':6 '''' 2 '''''-sexipyridine (pspy) and 4',4 ''''-bis(4-tert-butylphenyl)-2,2':6',2 '':6 '',2''':6''',2 '''':6,2 '''''-sexipyridine (tbspy) were also prepared and studied. The reaction fo each of these compounds with transition-metal ions capable of adopting an octahedral geometry results in the self-assembly of dinuclear double-helical complexes of the type [M(2)l(2)](4+) [M=iron(II), cobalt(II0, nickel(II), copper(II), zinc(II), cadmium(II) or mercury(II); L=spy, msspy, pspy ro tbspy]; the double-helical topology of the zinc complex of pspy was confirmed by a crystal-structure analysis of the salt [Zn-2(pspy)(2)]-[PF6](4) . 2MeCN . 2H(2)O [space group P4(2)2(1)s, a=16.618(2), c=18.443(1) Angstrom, R=0.0638, R'=0.0735].