A method of preparing a compound having the formula R2 MYR'2-n Hn, where R is an organic group, M is selected from the group consisting of Al, Ga and In, Y is selected from the group consisting of N, P and As, R' is an organic group and n is an integer selected from 0-2; which comprises reacting R2 MR with R'3-m YHm where R, M, Y and R' are as defined above, m is an integer selected from 1-3 and