NEW PHOSPHINE-CONTAINING CYCLOPENTADIENYLMOLYBDENUM(IV) COMPLEXES WITH AN 18-ELECTRON AND A 16-ELECTRON COUNT - X-RAY STRUCTURE OF CPMOCL3(PME2PH)2 AND CP-ASTERISK-MOCL3L (L = PME3, PMEPH2)

Molybdenum(IV) complexes of the general formula CPMoCl3Ln (Cp = eta5-C5H5; n = 1, 2) and Cp*MoCl3L (Cp* = eta5-C5Me5) have been synthesized by addition of L to CPMOCl3 and by reduction of Cp*MoCl4 with amalgamated Na in the presence of L. For the Cp system, although both mono- and bis-L adducts can be obtained when L = PMe3 and PMe2Ph, only the monoadduct has been observed when the bulkier PMePh2 ligand is used. For the Cp* system only mono-adducts were obtained (L = PMe3, PMe2Ph, PMePh2), and no tendency of these to add additional L was observed. All 16-electron mono-adducts show paramagnetically shifted H-1-NMR spectra in accord with the observed spin triplet ground state. A variable-temperature study on CP*MoCl3(PMe3) and the analogous tribromide complex indicates the rapid equilibration between two isomeric species, each one showing paramagnetically shifted proton resonances. The crystal structure of three of these complexes has been determined. CpMoCl3(PMe2Ph)2: triclinic, P1BAR, a = 10.807(2) angstrom, b = 11.621(2) angstrom, c = 11.644(2) angstrom, a = 89.72(1)-degrees, beta = 70.61(1)-degrees, gamma = 83.15(1)-degrees, V = 1368.6(4) angstrom3, Z = 2, d(calcd) = 1.494 g.cm-3. CP*MoCl3(PMe3): orthorhombic, P2(1)2(1)2(1), a = 8.178(2) angstrom, b = 13.186(3) angstrom, c = 15.206(3) angstrom, V = 1764.1(7) angstrom3, Z = 4, d(calcd) = 1.557 g.cm-3. CP*MoCl3(PMePh2): monoclinic, P2(1)/a, a = 16.062(2) angstrom, b = 15.335(2) angstrom, c = 19.914(3) angstrom, beta = 103.90(1)-degrees, V = 4761(2) angstrom3, Z = 8, d(calcd) = 1.50 g-cm-3. The two Cp* compounds adopt a pseudo-square pyramidal geometry with the Cp* ring in the apical position, whereas the CPMoCl3(PMe2Ph) complex has a pseudooctahedral geometry with a mer,trans relative arrangement of the ligands.