The molecular interaction and geometrical optimization of Cr$(CO)_5;and;Ni(CO)_3$ units have been studied for phosphinidene complex by means of extended Huckel calculations. The results were compared with those of ab initio calculations and found to be in qualitative agreement. Geometrical optimization of HPCr$(CO)_5;(1);and;HPNi(CO)_3$ (2) gave the values R = 2.36 ${AA}$, ${ heta}$ = $111.5^{circ}$, and ${phi}$ = $45^{circ}$for 1, and R = 2.37 ${AA}$, ${ heta}$= $120^{circ}$, and ${phi}$ = $58^{circ}$for 2. It is found that the low rotational barriers for 1(0.46 kcal $mol^{-1}$) and 2(0.12 kcal $mol^{-1}$) would be accompanied by the free rotation, in spite of the fact that both 1 and 2 adopt staggered conformations.