Asymmetrically Bonded η Ligands. I. Hinging away from Metal of Substituted Allyls: Synthesis of 1-syn-Methyl and -Phenyl Complexes and the Molecular Structures of [(η-1-Ph-C3H4)Pd(tmeda)]BF4, [(η-C5H5)Pd(η-1-Ph-C3H4)] and [(phen)Mo(CO)2(NCS)(η-1-Ph-C3H4)] at 185K

Seven new complexes of (η-1-Me-C₃H₄) and (η-1-Ph-C₃H₄) with symmetric metal ligand backbones have been synthesised and spectroscopically characterised. Crystals of three of them, [(η-1-Ph-C₃H₄)Pd(tmeda)]BF₄ (4), [(η-C₅H₅Pd(η-1-Ph-C₃H₄)] (5), and [(phen)Mo(CO)₂(NCS)(η-1-Ph-C₃H₄)] (8), were suitable for X-ray diffraction studies. 4 is orthorhombic, Pca₁, with four ion pairs in a cell of dimensions a 11.326(4), b 16.048(5), and c 9.950(3) Å. Using 4431 data measured at 185 K, R converged at 0.0311. Crystals of 5 are monoclinic, P2₁/c, with a 14.2255(19), b 5.8203(11), c 13.837(5) Å, and β 91.287(21°) at 185 K, Z = 4. 3064 amplitudes have been used to afford R = 0.0267. For 8 the monoclinic cell is a 15.658(4), b 9.473(3), c 15.666(6) Å, and β 113.95(3)°, P2₁/a, Z = 4. Low temperature (185 K) data were collected, and 3734 used to refine the structure to R = 0.0362. The molecular structures of 4, 5, and 8 all reveal an η-1-syn-Ph-C₃H₄ ligand that is asymmetrically bonded to the metal atom, such that M-C(l) > M-C(3). Analysis of intra- and intermolecular contacts strongly suggests that, at least for 5, the distortion in the metal-allyl bonding is electronic in origin.