N-O Ligand Supported Stannylenes: Preparation, Crystal, and Molecular Structures

A new series of tin(II) complexes (1, 2, 4, and 5) were successfully synthesized by employing hydroxy functionalized pyridine ligands, specifically 2-hydroxypyridine (hpH), 8-hydroxyquinoline (hqH), and 10-hydroxybenzo[h]quinoline (hbqH) as stabilizing ligands. Complexes [Sn(mu-kappa(ON)-O-2-OC5H4N)(N{SiMe3}(2))](2) (1) and [Sn-4(mu-kappa(ON)-O-2-OC5H4N)(6)(kappa O-1-OC5H4N)(2)] (2) are the first structurally characterized examples of tin(II) oxypyridinato complexes exhibiting {Sn-2(OCN)(2)} heterocyclic cores. As part of our study, H-1 DOSY NMR experiments were undertaken using an external calibration curve (ECC) approach, with temperature-independent normalized diffusion coefficients, to determine the nature of oligomerisation of 2 in solution. An experimentally determined diffusion coefficient (298 K) of 6.87 x 10(-10) m(2) s(-1) corresponds to a hydrodynamic radius of Ca. 4.95 angstrom. This is consistent with the observation of an averaged hydrodynamic radii and equilibria between dimeric [Sn{hp}(2)](2) and tetrameric [Sn{hp}(2)](4) species at 298 K. Testing this hypothesis, H-1 DOSY NMR experiments were undertaken at regular intervals between 298 K-348 K and show a clear change in the calculated hydrodynamic radii form 4.95 angstrom (298 K) to 4.35 angstrom (348 K) consistent with a tetramer reversible arrow dimer equilibria which lies towards the dimeric species at higher temperatures. Using these data, thermodynamic parameters for the equilibrium (Delta H degrees = 70.4 (+/- 9.22) kJ mol(-1), Delta S degrees = 259 (+/- 29.5) J K-1 mol(-1) and Delta G degrees(298) = -6.97 (+/- 12.7) kJ mol(-1)) were calculated. In the course of our studies, the Sn(II) oxo cluster, [Sn-6(m(3)-O)(6)(OR)(4):{Sn-(II)(OR)(2)}(2)] (3) (R = C5H4N) was serendipitously isolated, and its molecular structure was determined by single-crystal X-ray diffraction analysis. However, attempts to characterise the complex by multinuclear NMR spectroscopy were thwarted by solubility issues, and attempts to synthesise 3 on a larger scale were unsuccessful. In contrast to the oligomeric structures observed for 1 and 2, single-crystal X-ray diffraction studies unambiguously establish the monomeric 4-coordinate solid-state structures of [Sn(kappa(ON)-O-2-OC9H6N)(2))] (4) and [Sn(kappa(ON)-O-2-OC13H8N)(2))] (5).

Automated summary

A new series of tin(II) complexes were successfully synthesized by using hydroxy functionalized pyridine ligands. Some of these complexes exhibit oligomerization behavior, with dynamic equilibria between dimeric and tetrameric species at different temperatures.