Organometallic compounds with interligand resonance

Abstract

R. B. King* Department of Chemistry, University of Georgia, Athens, Georgia 30601 (Received 18 August 1969) Within the last two years compounds of the type (Cs~)2Mo(NO)Y (Y = I, 1 CH3, 1 and cr-CsH52) have been prepared. These compounds pose an interesting structural dilemma since in order to give the molybdenum atom the rare gas configuration indicated by their diamagnetism, one of the Tr-cyclopentadlenyl rings must be bonded to the molybdenum atom thru all five carbon atoms (a pentahapto 3 Iigand) and the other Tr-cyclopentadienyl ring must be bonded to the molybdenum atom thru only three carbon atoms (a trihapto 3 ligand). The recently reported 4 structural determination on the a--cyclopentadlenyl derivative (C5Hs)2Mo(NO)(o--CsHs) was of particular interest since it showed the two polyhapto cyclopentadlenyl rings to be equivalent with three carbon atoms of each ring close enough to the metal atom to engage in the usual type of bonding ( ~'2.3 to 2.4 ~k) but with the remaining two carbon atoms of each ring appreciably further from the metal atom ( '2 .6 )~) but still close enough to engage in bonding oF some type. I would like to point out that these structural .data on this ~-cyclopentadienyl derivative (CsHs)2Mo(NO)(o--CsHs)can be explained if this compound is considered to bearesonance hybrid I (Y= ~-C5FI5) of structures where the two polyhapto cyclopentadienyl rings interchange roles as trlhapto and pentahapto rings. The two carbon atoms of each cyclopentadienyl ring that are -~2.6 ,~ from the metal atom would correspond to the two carbon atoms not bonded to the metal atom in the canonical structure with that ring as the trihapto llgand. This type of interligand resonance is a new phenomenon in organometalllc chemistry.