Exploring Ligand Effects in the Selective Catalytic Dehydrogenative Borylation of Alkynes with Aluminum

The adequate design of ligands is an essential tool for controlling selectivity in catalytic reactions, particularly as the field shifts toward the use of Earth‐abundant metals. Herein, the synthesis and catalytic evaluation of a series of aluminum guanidinato complexes derived from guanidine ligands bearing diverse donor substituents: (iPrHN) 2 CNR (R = 2‐Ph 2 PC 6 H 4 , 2‐MeSC 6 H 4 , 2‐PhSC 6 H 4 , 2‐NCyMeCH 2 C 6 H 4 ) is reported. An interesting correlation is identified between selectivity and the hard–soft donor properties of the substituent. Notably, the complex featuring an additional nitrogen‐based substituent is air‐stable and exhibits high chemoselectivity in the dehydrogenative borylation of alkynes with HBpin, in contrast to the conventional hydroboration pathway. Aromatic and aliphatic alkynes with different substituents have been borylated. This catalyst is also capable of hydroborating and subsequently borylating an aldehyde bearing an alkyne group in a tandem process. The experimental and DFT studies allow to establish bonding situations between the auxiliary group and the metal center ranging from noncovalent interconnections to labile bonds and support a mechanism in which these interactions play a key role in driving this distinct reactivity.