STEPWISE SYNTHETIC STRATEGY FOR THE PREPARATION OF TRINUCLEAR COMPLEXES OF BIS(TERPYRIDYL) BRIDGING LIGANDS CONTAINING AZA-CROWN MACROCYCLIC SPACER GROUPS
Kl. Bushell et al., STEPWISE SYNTHETIC STRATEGY FOR THE PREPARATION OF TRINUCLEAR COMPLEXES OF BIS(TERPYRIDYL) BRIDGING LIGANDS CONTAINING AZA-CROWN MACROCYCLIC SPACER GROUPS, Journal of the Chemical Society. Dalton transactions (Print), (20), 1998, pp. 3397-3403
A synthetic strategy has been devised for the preparation of the monon
uclear complex [Ru(tpy)(L-2)][PF6](2) (where L-2 is a bridging ligand
containing two chelating 2,2' :6',2 ''-terpyridyl fragments attached v
ia tolyl spacers to the N atoms of a 1,10-diaza-18-crown-6 macrocycle)
, which avoids the separation of a statistical mixture of mono- and di
-nuclear complexes which would arise from normal synthetic methods. Re
action of 1,10-diaza-18-crown-6 with one equivalent of 4'-[4-(bromomet
hyl)phenyl]terpyridine afforded L-1, in which there is one terpyridyl
group pendant from the macrocycle, and the second NH site of the macro
cycle is not alkylated. Reaction of L-1 with [Ru(tpy)Cl-3] gave mononu
clear [Ru(tpy)(L-1)][PF6](2). Subsequent reaction of this with a secon
d equivalent of 4'-[4-(bromomethyl)phenyl]terpyridine resulted in atta
chment of the second (vacant) terpyridyl chelating site by alkylation
of the remaining secondary amine group in the macrocycle to give [Ru(t
py)(L-2)][PF6](2). Assembly of two of these mononuclear 'complex ligan
ds' around first-row transition-metal dications M2+ (M = Fe or Ni) aff
orded in high yield the linear trinuclear Ru-M-Ru complexes [{(tpy)Ru(
L-2)}(2)M][PF6](6). in which the two terminal {Ru(tpy)(2)}(2+) and the
central {M(tpy)(2)}(2+) fragments are separated by diaza-18-crown-6 u
nits. Electrospray mass spectrometry proved a very useful characterisa
tional tool in all cases, showing a variety of charged species arising
from both loss of anions and protonation of the basic amine sites in
the aza-crown macrocycles: for [{(tpy)Ru(L-2)}(2)Fe][PF6](6) for examp
le intact complex cations were observed with charges of up to +9 (from
loss of all six anions, and triple protonation). The mononuclear comp
lexes [Ru(tpy)(HL1)][ClO4](2)[PF6]. 2MeCN . Et2O . H2O and [Ru(tpy)(L-
2)][PF6](2). 0.7 HPF6. 0.3Et(2)O . MeCN . 1.5H(2)O were crystallograph
ically characterised. Electrochemical and electronic spectroscopic stu
dies show that the {Ru(tpy)(2)}(2+) and {M(tpy)(2)}(2+) components of
the trinuclear complexes are essentially electronically isolated.