ORGANOMETALLIC NITROSYL CHEMISTRY .47. CYCLOPENTADIENYL(ETA(4)-TRANS-DIENE)NITROSYLMOLYBDENUM COMPLEXES AND THEIR REACTIVITIES TOWARD ACETYLENES AND PROTONIC ACIDS

{Reduction of [Cp*Mo(NO)I2]2 [CP* = eta-5-C5Me5] by sodium amalgam in THF at -30-degrees-C in the presence of an isomeric mixture of (E)- and (Z)-1,3-pentadiene affords two isolable isomers of Cp*Mo(NO)(eta-4-trans-1,3-pentadiene), one yellow (1A) and one red (1B). The most significant feature of the solid-state molecular structure of 1A is the fact that the transoidal (E)-1,3-pentadiene ligand is coordinated to the molybdenum with its methyl substituent pointing away from the cyclopentadienyl ring. The spectroscopic properties of 1B are consistent with it possessing a similar orientation of its (Z)-1,3-diene methyl substituent. This observation establishes that even though the Cp*Mo(NO) fragment in 1A and 1B exerts the electronic influence to bind the diene ligands in a twisted, transoidal fashion, steric interactions determine which face of the diene ligand can best accommodate this electronic requirement. Cyclic voltammetry studies have been carried out on two representative diene-containing compounds, namely CpMo(NO)(eta-4-trans-2,5-dimethyl-2,4-hexadiene) and CpMo(NO)(eta-4-cis-2,3-dimethylbutadiene) (Cp = eta-5-C5H5), in order to establish the redox properties of these types of complexes. The cyclic voltammograms indicate that both diene complexes are reasonably stable with respect to addition of electrons, since no reduction behavior is observed to the limit of the CH2Cl2 solvent (ca. -2 V). On the other hand, each of the complexes is quite readily oxidized and each exhibits three irreversible oxidations before the solvent limit of ca. +2 V. These redox properties are in accord with the results of Fenske-Hall molecular orbital calculations previously performed on the CpMo(NO)(eta-4-butadiene) model systems. Consistently, CpMo(NO)(eta-4-trans-2,5-dimethyl-2,4-hexadiene) does not undergo concomitant reduction when treated with acetylenes but rather effects a coupling between the diene ligand and the alkyne to produce a eta-4 (eta-3, eta-1) ligand in which the eta-3-allyl portion of the ligand is oriented endo with respect to the cyclopentadienyl ring. Thus, when the alkyne employed is 1-phenylpropyne, the resulting complex is CpMo(NO)[eta-4-C(Me)2CHCHC(Me)2C(Me)C(Ph)] (2), whose molecular structure has been established by specialized NMR spectroscopic techniques and by single-crystal X-ray crystallography. The reaction between CpMo(NO)(eta-4-trans-2,5-dimethyl-2,4-hexadiene) and 1,7-octadiyne affords two major isomers of a similar organometallic product. Finally, the isolable products of the reactions between CpMo(NO)(eta-4-trans-diene) and HX (diene = 2,5-dimethyl-2,4-hexadiene