Hi Rick, an alternative way through pattern recognition:
proc iml;
A = rannor( j(6,5) ); /** 5x6 matrix **/
B = rannor( j(5,6) ); /** 6x5 matrix **/
ProdMat = A*B;
Y=ProdMat[do(1, nrow(ProdMat)*ncol(ProdMat), nrow(ProdMat)+1 )]`; /** for a 6*6 matrix, this takes out the 1st, 8th, 15th...36th element which form the diagonal **/
print d3;

Thanks.