CYCLOPENTADIENONE COMPLEXES OF MOLYBDENUM - SYNTHESIS OF CARBONYL, ACETONITRILE, PHOSPHINE AND PHOSPHIDO-BRIDGED DERIVATIVES

Reaction of [Mo(CO)6] with 2 equivalents of tetraphenylcyclopentadienone (tetracyclone) in refluxing toluene gives [Mo(CO)2(eta4-C4Ph4CO)2] la in ca. 95% yield. With 1 equivalent of tetracyclone in boiling heptane, [{Mo(CO)3(sigma:eta4-C4Ph4CO)}2] 2 is produced as well as la. This dimeric complex has been crystallographically characterised [triclinic, space group P1BAR (no. 2), a = 8.980(3), b = 11.332(4), c = 13.526(5) angstrom;alpha = 77.55(3), beta = 71.94(3), gamma = 81.02(3)-degrees, Z = 2 monomer units]; each molybdenum is in a distorted-octahedral environment, co-ordinated by the eta4-diene ligand, three carbonyl ligands, and the ketonic carbonyl of the other centrosymmetrically related tetracyclone. Another convenient route into the chemistry of tetracyclone molybdenum complexes is provided by [Mo(CO)3(NCMe)(eta4-C4Ph4CO)] 5 which is formed in high yield by treating [Mo(CO)3(NCMe)3] with tetracyclone. One (but only one) of the tetracyclone ligands of complex 1 a can be displaced by chelating phosphines to give [Mo(CO)2(L-L)-(eta4-C4Ph4CO)] (L-L = Ph2PCH2PPh2 or Ph2PCH2CH2PPh2); the stereochemistry and fluxionality of these complexes is briefly discussed. Thermal reaction of la with monodentate phosphines (L = PPh3 or PPh2Me) yields [Mo(CO)3L(eta4-C4Ph4CO)] 7 by a carbonyl redistribution process; the same compounds can be prepared from 5 by displacement of the labile acetonitrile ligand, as can an analogous species with L = PPh2H. Thermolysis of [Mo(CO)3(PPh2H) (eta4-C4Ph4CO)] or thermal reaction of 1 a with PPh2H gives the phosphido-bridged complex [Mo2(CO)3(mu-PPh2)(mu-sigma:eta5-C4Ph4CO)(eta5-C4Ph4COH)] B. The crystal structure of 8 has also been determined [triclinic, space group P1BAR (C(i)1, no. 2), a = 12.806(10), b = 14.173(8), c = 17.958(7) angstrom, alpha = 83.75(4), beta = 86.92(5), gamma = 71.57(5)-degrees, Z = 2] and reveals a formal Mo=Mo double bond [2.923(2) angstrom] bridged by a diphenylphosphido group and a tetracyclone ligand bonded in a sigma:eta5 manner. The other tetracyclone is bonded as an eta5-hydroxytetraphenylcyclopentadienyl ligand, having taken up the proton released by oxidative addition of the P-H bond.