When CpMo(NO)(eta-4-trans-butadiene) (Cp = eta-5-C5H5) is treated with acetone, a ligand-coupling reaction occurs to form two complexes having the composition CpMo(NO)(eta-4-CH2CHCHCH2CMe2O), one in which the allyl portion of the coupled ligand is endo (1A) and one in which the allyl is exo (1B) with respect to the Cp ligand. Complete structural assignment of 1A and 1B has been effected by using NMR spectroscopic methods. Similar treatment of Cp*Mo(NO)(eta-4-trans-butadiene) (Cp* = eta-5-C5Me5) affords a single organometallic product, 2, which is the Cp* analogue of 1A. The coupling reaction between CpMo(NO)(eta-4-trans-2,5-dimethyl-2,4-hexadiene) and acetone is fairly rapid, the initial products being the endo-allyl (3A) and exo-allyl (3B) complexes. The endo isomer, however, converts quickly and irreversibly to the exo-allyl isomer. If the latter reaction is left for 15 h at ambient conditions, then 3B and [CpMo(NO)]3(mu-2-eta-2-eta-1-O-CMe2)3, which is isolable as a THF solvate (4), are the only organometallic species present in the final reaction mixture. All new complexes isolated during this work have been fully characterized by conventional methods, and crystal structure analyses have been performed on 2, 3B, and 4. Crystals of Cp*Mo(NO)(eta-4-endo-CH2CHCHCH2CMe2O) (2) are orthorhombic, P2(1)2(1)2(1), with a = 9.2465 (15) angstrom, b = 13.496 (2) angstrom, c = 14.290 (3) angstrom, and Z = 4; the structure was solved by conventional heavy-atom methods and was refined by full-matrix least-squares procedures to R = 0.030 and R(w) = 0.034 for 1454 absorption-corrected reflections with I greater-than-or-equal-to 3-sigma(I). Crystals of Cp(NO)Mo[eta-4-C(Me)2CHCHC(Me)2C(Me)2O] (3B) are triclinic P1BAR, with a = 9.381 (4) angstrom, b = 14.085 (6) angstrom, c = 14.563 (7) angstrom, alpha = 117.36 (3)-degrees, beta = 100.91 (4)-degrees, gamma = 96.37 (4)-degrees, and Z = 4; R = 0.073 and R(w) = 0.077 for 2577 reflections. Crystals of [CpMo(NO)]3(mu-2-eta-2-eta-1-OCMe2)3.THF (4) are monoclinic, P2(1)/c, with a = 14.726 (3) angstrom, b = 11.097 (4) angstrom, c = 19.369 (2) angstrom, beta = 98.479 (11)-degrees, and Z = 4; R = 0.040 and R(w) = 0.066 for 3963 reflections. Complexes 2 and 3B are monomeric and possess four-legged piano-stool molecular structures in the solid state. The allyl portions of the coupled ligands in these compounds are bonded somewhat asymmetrically (particularly in 2) to the molybdenum centers, being oriented endo with respect to the Cp ligand in 2 and exo in 3B. In contrast, the structure of 4 consists of three four-legged piano stool monomeric units connected by Mo-acetone-Mo linkages, the angles around the O-bound carbon of the bridging acetone group being quite distorted. The trimer 4 persists in the presence of excess acetone, but it can be broken with 1,3-(diphenylphosphino)propane (dppp) to form CpMo(NO)(dppp).
