SYNTHESIS AND ROTATIONAL BARRIER OF TUNGSTEN(II) PORPHYRIN DIMER, [W(TPP)](2) (TPP=TETRAPHENYLPORPHYRIN)

Dimeric tungsten porphyrin, [W(TPP)](2)(TPP = tetraphenylporphyrin dia nion), has been prepared from the reaction between TPPH2 and W(CO)(6) in refluxing decalin and the rotational barrier about the tungsten-tun gsten quadruple bonds examined by variable-temperature H-1 NMR of the beta-pyrrole resonances. The barrier energy obtained by lineshape anal ysis was 11.3 kcal mol(-1). As a measure of relative delta-bond streng th, this result indicates the delta-bond in tungsten porphyrin dimer i s stronger than that of the molybdenum analogue (6.3 kcal mol(-1)) in an isostructural porphyrin system. [W(TPP)](2) has shown reactivities toward p-tolyl azide and hydrogen peroxide to afford N=W(TPP) and W(O) (O-2)(TPP), respectively.