PCl3 donor or acceptor?

[Benji]

In which reaction does PCl3 act as a donor & in which as an acceptor?

PCl3 + N(CH3)3 -> Cl3PN(CH3)3

PCl3 + BBr3 -> Cl3PBBr3

I think the 2nd is the donor. Am I right?

And second - how do you show on a Lewis structure the donor & acceptor actions? How do you know which electrons jump ship? Thanks!

[ryukolink]

Best way to determine if something acts as a base or acid is to compare pKa values...

Draw out the lewis structures and in the first equation it looks like... wait a minute, hmm...

Br is a better leaving group in the second one so I think the Phosphorous electrons attack the Boron and kick off a (Br)-... the Br comes back and attacks the Boron and kicks down the lone pair electrons on the Boron back to the (P)+...

this appears to rely heavily on pKa values and leaving group rules.