H. Videa, M. Á. Fuentes, A. J. Martínez-Martínez. Structure and Bonding, 2026
https://link.springer.com/chapter/10.1007/430_2026_105
Low-valent group 13 fragments can serve as neutral two-electron L-type metalloligands (M) to transition-metal (TM) centers, enabling heterometallic M–TM platforms with bonding and reactivity patterns distinct from classical CO, phosphine, and carbene ligation. This chapter develops a unifying, descriptor-based view of aluminylene Al(I), gallylene Ga(I), and indylene In(I) donors and contrasts them with the limited L-type behavior of Tl(I). We map synthetic gateways to isolable M(I) donors, analyze their σ-donation/π-acceptance profiles, and extract periodic design rules in which the σ-donor strength decreases Al > Ga > In, whereas Tl(I) has not yet been convincingly shown to engage in neutral L-type Tl→TM coordination. Borderline cases that blur L-, X-, and Z-type classifications are also examined to clarify descriptors and guide consistent usage across the series. This contribution links ligand sterics/electronics, ambiphilicity at M(I), and the chosen TM fragment to guide the rational design of M–TM platforms that harness group 13 M(I) donors for small-molecule activation and cooperative catalysis.
