Issue 1, 1993

Cyclopentadienone complexes of molybdenum: synthesis of carbonyl, acetonitrile, phosphine and phosphido-bridged derivatives

Abstract

Reaction of [Mo(CO)6] with 2 equivalents of tetraphenylcyclopentadienone (tetracyclone) in refluxing toluene gives [Mo(CO)24-C4Ph4CO)2]1a in ca. 95% yield. With 1 equivalent of tetracyclone in boiling heptane, [{Mo(CO)3(σ:η4-C4Ph4CO)}2]2 is produced as well as 1a. This dimeric complex has been crystallographically characterised [triclinic, space group P[1 with combining macron](no. 2), a= 8.980(3), b= 11.332(4), c= 13.526(5)Å; α= 77.55(3), β= 71.94(3), γ= 81.02(3)°, Z= 2 monomer units]; each molybdenum is in a distorted-octahedral environment, co-ordinated by the η4-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)(η4-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 1a can be displaced by chelating phosphines to give [Mo(CO)2(L–L)(η4C4Ph4CO)](L–L = Ph2PCH2PPh2 or Ph2PCH2CH2PPh2); the stereochemistry and fluxionality of these complexes is briefly discussed. Thermal reaction of 1a with monodentate phosphines (L = PPh3 or PPh2Me) yields [Mo(CO)3L(η4-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)(η4-C4Ph4CO)] or thermal reaction of 1a with PPh2 H gives the phosphido-bridged complex [Mo2(CO)3(µ-PPh2)(µ-σ:η5-C4Ph4COH)]8. The crystal structure of 8 has also been determined [triclinic, space group P[> with combining macron](Ci1 no. 2), a= 12.806(10), b= 14.173(8), c= 17.958(7)Å, α= 83.75(4), β= 86.92(5), γ= 71.57(5)°, Z= 2] and reveals a formal Mo[double bond, length half m-dash]Mo double bond [2.923(2)Å] bridged by a diphenylphosphido group and a tetracyclone ligand bonded in a σ:η5 manner. The other tetracyclone is bonded as an η5-hydroxytetraphenylcyclopentadienyl ligand, having taken up the proton released by oxidative addition of the P–H bond.

Article information

Article type
Paper

J. Chem. Soc., Dalton Trans., 1993, 91-100

Cyclopentadienone complexes of molybdenum: synthesis of carbonyl, acetonitrile, phosphine and phosphido-bridged derivatives

H. Adams, N. A. Bailey, P. D. Hempstead, M. J. Morris, S. Riley, R. L. Beddoes and E. S. Cook, J. Chem. Soc., Dalton Trans., 1993, 91 DOI: 10.1039/DT9930000091

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