Simple addition is the link, always reversible, between a donor D (Lewis base) and an acceptor A (Lewis acid) to form an addition compound or adduct (DA). The reverse process is called dissociation.
D + A ⇄ D-A
From the thermodynamic viewpoint the equilibrium depends on the DA bond strength, which can be rationalized by the concept of hard and soft acids and bases.
The F- ion, Lewis base, is added to BF3, a Lewis acid. Observe the change of structure during the addition. The BF3, planar (D3h), switches to pyramidal (C3V) as the F- ion approaches. The final species is tetrahedral (Td)
In reaction must be an accompanying cation must be present, eg Na +, so that complete reaction should be BF3 + NaF & # x21C4; Na [BF4]. The cation an spectator in the process, so often omitted, although influences the choice the reaction medium.
The transition from D3h to C3V eliminates the strong interactions π halogen-boron, which decrease from BF3 to BI 3. Therefore, boron trifluoride is the & aacute; weaker Lewis acid and BI 3 the more strong (and more reactive). Therefore, boron trifluoride is the weakest Lewis acid and BI 3 the strongest (and more reactive) acid.
It is a reaction between a Lewis base, H2O, and a Lewis acid, BF3, a process similar to the addition of fluoride (previous reaction).
The resulting species, the adduct BF3.H2O, is an intermediate in the hydrolysis of BF 3 (see the reaction BF 3 + H 2 O in "additions with elimination").
The addition of a hydride ion to the species BH3 gives the anion BH4-. However, BH3 only exists as a transitional species and the simplest stable boron hydride is diborane B2H6. The addition occurs in two stages and breaks B-H-B bridges.
The accepted mechanism begins with the attack of one H- to a boron atom, generating the intermediate anionic species B2H7- (which can be isolated as a salt). The addition of a second H- on either of the two boron atoms, which are equivalents. The addition of a second H- on the boron breaks the (3c/2e) B-H-B bonds.
IrCl(CO)P2 + CO ⇄ IrCl(CO)2P2
This iridium compound is unsaturated, with 16 electrons in the valence shell, and acts as a Lewis acid. The addition of CO 2e, a Lewis base, yields the 18-electron complex [IrCl(CO)2(PPh3)2] and changes the iridium environment from square-planar to trigonal bipyramid.
This reaction is similar to the previous one. The SO2 coordinates through the sulfur atom generating a Ir-SO2 bond of type η1 (monohapto) pyramidal, in which S has even a pair of electrons shared. The coordination of SO2 changes the Iridium environment from square-planar to trigonal bipyramid.