Abstract

The dimeric cyclometallated derivatives of palladium(II) [(L-H)PdCl]₂, 3 (L = 1, Diazepam: 7-chloro-1,3-dihydro-1-methyl-5-phenyl-2H-1,4-benzodiazepin-2-one) and 4 (L = 2, Prazepam: 7-chloro-1-cyclopropylmethyl-1,3-dihydro-5-phenyl-2H-1,4-benzodiazepin-2-one) react with triphenylphosphine to give the complexes (L-H)Pd(PPh₃)Cl, 5(L = Diazepam) and 6 (L = Prazepam). The crystal structure of 6 was determined by X-ray crystallography. The palladium atom is in a square planar arrangement. The deprotonated ligand is bound to the metal through the 4-nitrogen and the ortho-carbon atom of the 5-phenyl substituent. The phosphorous and the chlorine atoms are trans to the nitrogen and the carbon atoms, respectively: Pd---N = 2.085(2), Pd---P=2.263(1), Pd---Cl = 2.377(1), Pd---C = 2.009(3) Å.
The reaction of the dimeric derivatives [(L-H)PdCl]₂ with carbon monoxide was investigated. Under mild conditions (1 atm of CO, room temperature) the unstable (L-H)Pd(CO)Cl derivatives. 7 (L = Diazepam) and 8 (L = Prazepam) are formed, but at high pressure and temperature (60–100 atm of CO, 45–50°C), extrusion of palladium occurs and tetracyclic derivatives having an isoindolo ring condensed on the 1,4-benzodiazepin-2-one system, 9–12, are obtained.

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