¹¹B NMR of Transition Metal Boron Compounds

Abstract

A large number of boron transition metal compounds has been prepared and investigated in the last decade. In order to keep the discussion within reasonable limits we restrict ourselves to those compounds which are derived from simple boranes, while metalloboranes derived from higher boron hydrides and from carboranes will be excluded. Although there are some reviews on the compounds under consideration [70/28; 74/72; 75/62] none of them is specially dedicated to the subject of ¹¹ B NMR. We have attempted to divide the compounds into four different classes: (i) the coordination number of boron is 3 and it is thought that a boron-metal σ-bond is formed (Table LIV); (ii) the coordination number of boron is 4, due to adduct formation between a borane and a transition metal complex acting as a Lewis base and a coordinative boron-metal σ-bond is formed (Table LV); (iii): the substituents at the boron atom act primarily as ligands but it is assumed from spectroscopic and structural information that the boron atoms of these boranes also interact with the transition metal atom (complexes from noncyclic and cyclic boranes are known, Table LVIa, b); (iv) the distance between the boron atom and the transition metal atom is too large for a direct interaction to be likely to take place; however, in some cases spectroscopic evidence indicates indirect metal-boron interactions (Table LVII). The δ¹¹ B-data of boron-metal compounds where the metal is a main group element (e.g., Sn, Pb) have already been discussed (see Section 4.10).