posted on 2006-12-25, 00:00authored bySung Lan Jeon, David M. Loveless, Wayne C. Yount, Stephen L. Craig
The thermodynamics of pyridine coordination in 1,4-phenylene-bridged binuclear palladium and platinum organometallic
complexes [1,4-(MOTf)2-{C6(CH2NR2)4-2,3,5,6}] (11, M = Pd, Pt; R = CH3, C2H5, R2 = −(CH2)5−) are measured
by 1H NMR in DMSO-d6. The coordination of substituted pyridines by bimetallic complexes 11 or 12 in DMSO is
found to proceed via two effectively independent metalligand binding events, and the association constants for
pyridine coordination and rate constants for pyridine exchange are nearly identical to those measured previously
on monometallic analogs. A linear free energy relationship between the association constant for pyridine coordination
and the inductive Hammett constant of the pyridine substituent is observed, and the sensitivity (ρ = −1.7 to −2.1)
in DMSO depends only slightly on metal (Pd vs Pt) and spectator ligand (pincer dialkylamine vs triarylphosphine).
The association constant for a particular pyridine ligand, however, varies by roughly 3 orders of magnitude across
the series of metal complexes. The effective independence of the two coordination sites and the range of available
thermodynamic and kinetic behaviors of the coordination guide the use of these versatile building blocks in
metallosupramolecular applications.