[benner]

I am trying to construct the molecular orbital diagram of the complex [PdH3(NHC)]-. I used the fragmentation method where my fragments are PdH3- and NHC. I already have there reducible representation and the atomic orbitals. The atomic orbitals of PdH3- using C2v point group is a1, a1, a1+a2+b1+b2, and b2; and for NHC it is b2, a2 & b2 (with one nodal plane), a1 ( carbene lone pair),a2 & b2(with 2 nodal plane). I don't on how to match this orbitals to form the MO diagram. 

[vex]

I would approach differently. I would start from the MO diagram of [PdH₄]^-, which should be trivial to draw. Then, using what's called the Walsh correlation method, remove a hydride and redraw the MO diagram for [PdH₃]^- in C3v (trigonal pyramidal). At that point you should know which orbitals are oriented towards the open coordination site; place the NHC in the open coordination site and split the orbitals according to the sigma/pi donating/accepting properties of the NHC.

http://en.wikipedia.org/wiki/Walsh_diagram