Examples of Lewis base nature of sulfur dioxide

I have read that sulfur dioxide acts as both Lewis base (due to presence of lone pair over $$\ce{S}$$ and/or $$\ce{O})$$ and Lewis acid (due to presence of vacant d orbital). I found many examples of $$\ce{SO2}$$ acting as a Lewis acid (towards $$\ce{NMe3},$$ $$\ce{H2O},$$ etc.), but could not find any for its Lewis base behavior. Could someone provide some reactions/equations, please?

You generally want to find a much stronger Lewis acid (typically forming a solvate/adduct) or make a complex with a transition metal: this way either unshared electron pair of oxygen or sulfur can be donated. Canonical examples are given in Shriver & Atkins’ Inorganic Chemistry [1, p. 135]:

To act as a Lewis base, the $$\ce{SO2}$$ molecule can donate either its $$\ce{S}$$ or its $$\ce{O}$$ lone pair to a Lewis acid. When $$\ce{SbF5}$$ is the acid, the $$\ce{O}$$ atom of $$\ce{SO2}$$ acts as the electron pair donor, but when $$\ce{Ru(II)}$$ is the acid, the $$\ce{S}$$ atom acts as the donor … $$(\ce{[RuCl(NH3)4(SO2)]+}).$$

$$\qquad$$

Figure 1. Left: Crystal structure of $$\ce{SbF5 · SO2}$$ (ICSD-67273 [2]). Right: Crystal structure of $$\ce{[RuCl(NH3)4(SO2)]+}$$ (ICSD-26061 [3]). Color code: $$\color{#EEEEEE}{\Large\bullet}~\ce{H}$$; $$\color{#3050F8}{\Large\bullet}~\ce{N}$$; $$\color{#FF0D0D}{\Large\bullet}~\ce{O}$$; $$\color{#90E050}{\Large\bullet}~\ce{F}$$; $$\color{#FFFF30}{\Large\bullet}~\ce{S}$$; $$\color{#1FF01F}{\Large\bullet}~\ce{Cl}$$; $$\color{#248F8F}{\Large\bullet}~\ce{Ru}$$; $$\color{#9E63B5}{\Large\bullet}~\ce{Sb}$$.

Reactions for the synthetic procedures adapted from the corresponding articles [2, 3]:

\begin{align} \ce{SbF5(s) + SO2(l) &->[\pu{-40 °C}] SbF5 · SO2(sln)} \tag{R1} \\ \ce{[Ru^{II}(NH3)4(HSO3)2](aq) + 2 HCl(aq) &->[reflux][15 min] [Ru^{II}(NH3)4(SO2)Cl]Cl(aq) + 2 H2O(l) + SO2(aq)} \tag{R2} \end{align}

References

1. Atkins, P. W. Shriver & Atkins’ Inorganic Chemistry; W.H. Freeman and Co.: New York, 2010. ISBN 978-1-4292-1820-7.
2. Minkwitz, R.; Molsbeck, W.; Preut, H. Kristallstruktur von $$\ce{SbF5 · SO2}$$ / Crystal Structure of $$\ce{SbF5 · SO2}.$$ Zeitschrift für Naturforschung B 1989, 44 (12), 1581–1583. DOI: 10.1515/znb-1989-1218. (Free Access)
3. Vogt, L. H.; Katz, J. L.; Wiberley, S. E. The Crystal and Molecular Structure of Ruthenium-Sulfur Dioxide Coordination Compounds. I. Chlorotetraammine(Sulfur Dioxide)Ruthenium(II) Chloride. Inorg. Chem. 1965, 4 (8), 1157–1163. DOI: 10.1021/ic50030a015.