QUADRUPLY BONDED DIMOLYBDENUM COMPOUNDS WITH POLYDENTATE PHOSPHINES .2. STRUCTURAL AND SPECTROSCOPIC PROPERTIES OF RAC-MO(4)-MOCL4(PET3)(ETA-3-TETRAPHOS-2) (TETRAPHOS-2 = P(CH2CH2PPH2)3)

The ligand substitution reaction between Mo4-MoCl4(PEt3)4 and the tetraphos-2 ligand, P(CH2CH2PPh2)3, yields the compound rac-Mo4-4MoCl4(PEt3) (eta3-tetraphos-2) that can be assigned as enantiomeric 1,2,5,7/1,2,6,8 type of isomer. This compound displays small torsional angles with an average of 11.7-degrees. Thus the Mo4-Mo bond distance (2.132(3) angstrom) is consequently shorter than those in the previously reported racemic (R,R, and S,S) and meso (R,S and S,R) Mo2X4(tetraphos-1) (tetraphos-1 = Ph2PCH2CH2P(Ph)CH2CH2P(Ph)CH2CH2PPh2, X = Cl, Br) compounds. The crystal structure of rac-Mo4-MoCl4(PEt3)(eta3-tetraphos-2) is fully described. Crystallographic data for this compound are as follows: space group Pna2(1) with a = 16.979(3) angstrom, b = 16.061(3) angstrom, c = 21.280(7) angstrom, V = 5803(4) angstrom3, and Z = 4. The P-31{H-1}NMR spectrum of this complex displays five multiplets corresponding to five magnetically different phosphorus nuclei, and it affords a unique system to study P-31-P-31 Coupling, through the connecting chain between phosphorus nuclei and/or through the metal-metal quadruple bond, in quadruply bonded dinuclear compounds. With use of the structural data for all the compounds with tetraphos-1 and tetraphos-2 ligands, the correlation between Mo4-Mo bond distances and cos 2(chi) has been shown to be an inverse linear function with a correlation coefficient of 0.9672.