Competition between Intra and Intermolecular Triel Bonds. Complexes between Naphthalene Derivatives and Neutral or Anionic Lewis Bases

• Main Authors: Wiktor Zierkiewicz, Mariusz Michalczyk, Steve Scheiner
• Format: Article
• Language: English
• Published: MDPI AG 2020-02-01
• Series: Molecules
• Subjects: triel bond; intramolecular triel bond; mp2; mep; π-hole
• Online Access: https://www.mdpi.com/1420-3049/25/3/635

<b>: </b>A TrF₂ group (Tr = B, Al, Ga, In, Tl) is placed on one of the &#945; positions of naphthalene, and its ability to engage in a triel bond (TrB) with a weak (NCH) and strong (NC^&#8722;) nucleophile is assessed by ab initio calculations. As a competitor, an NH₂ group is placed on the neighboring C^&#945;, from which point it forms an intramolecular TrB with the TrF₂ group. The latter internal TrB reduces the intensity of the &#960;-hole on the Tr atom, decreasing its ability to engage in a second external TrB. The intermolecular TrB is weakened by a factor of about two for the smaller Tr atoms but is less severe for the larger Tl. The external TrB can be quite strong nonetheless; it varies from a minimum of 8 kcal/mol for the weak NCH base, up to as much as 70 kcal/mol for CN^&#8722;. Likewise, the appearance of an external TrB to a strong base like CN^&#8722; lessens the ability of the Tr to engage in an internal TrB, to the point where such an intramolecular TrB becomes questionable.