A new family of flexible scorpionate ligands based on 2-mercaptopyridine

A new family of flexible scorpionate ligands based on 2-mercaptopyridine is reported. The tris- and bis-substituted ligands, K[HB(mp)(3)] (1) and Na[H(2)B(mp)(2)] (2) (mp = 2-mercaptopyridine) have been prepared and fully characterised. The structural characterisation of 1 reveals an unprecedented mu(3)-kappa(3)-SS'H-eta(1)eta(1)eta(2)-kappa(2)-S''C-eta(1)eta(1)-kappa(1)-S'-eta(1) coordination mode. The coordination of both 1 and 2 to copper(I) complexes containing triphenylphosphine and tricyclohexylphosphine co-ligands is investigated suggesting kappa(3)-SSS coordination modes for [Cu{HB(mp)(3)}(PR(3))] {where R = Ph (3); R = Cy, (4)} and kappa(3)-SSH coordination modes for [Cu{H(2)B(mp)(2)}(PR(3))] {where R = Ph (5); R = Cy (6)} the latter confirmed by structural characterisation of 5. A structural comparison with the sulfur based scorpionates, HB(mt)(3) and H(2)B(mt)(2) (mt = methyl-2-mercaptoimidazole) is made in terms of the degree of tautomerisation of the heterocyclic rings.