Generation of Spirotricyclic Site-Differentiated Cyclotriphosphazenes: A Solvent-Free Approach to Multidentate N/O Donor Ligand Systems

Cyclotriphosphazene-based ligand systems are valuable materials to model the metal-binding event on the structurally
and electronically related functionalized high molecular weight polyphosphazenes. We here report the facile synthesis
of novel spirotricyclic cyclotriphosphazenes N3P3(MeNC2H4NMe)2L2, N3P3(iPrNC2H4NiPr)2L2, and N3P3(o-O2C12H8)2L2
that enables different substituents to be incorporated into the ligand system. This synthetic approach allows for
control over the solubility and steric requirements of the exocyclic bidentate substituents, as well as the donor type
and denticity of the coordination sites. A mononuclear lanthanum complex ([La(NO3)3{N3P3(pzpy)2(MeNC2H4NMe)2}]
(7)) and a series of dinuclear transition-metal complexes ([{ReCl(CO)3}2{N3P3(pyNH)2(MeNC2H4NMe)2}] (4), [{FeI2}2{N3P3(pyNH)2(MeNC2H4NMe)2}] (5), and [{PdCl2}2{N3P3(pyNH)2(MeNC2H4NMe)2] (6)) have been prepared and
structurally and spectroscopically characterized to explore the metal coordination environments supported by this
class of ligands.