SYNTHESIS AND CHARACTERIZATION OF QUADRUPLY BONDED DINUCLEAR MOLYBDENUM(II) COMPLEXES WITH BIS(DIPHENYLPHOSPHINOMETHYL)PHENYLPHOSPHINE AND OXIDATION OF THE TRIPHOSPHINE LIGAND

Reaction of cis-[Mo-2(O2CR)(2)(MeCN)(6)] (BF4)(2) (1) with 2 equiv, of tridentate phosphine, bis(diphenylphospdinomethyl)-phenylphosphine (d pmp), afforded trans-[Mo-2(O2CR)(2)(dpmp)(2)] (BF4)(2) (2a: R = Me; 2b : R = Bu-t; 2c: R = Ph), which were characterized by X-ray crystallogr aphy (2a: monoclinic, P2(1)In, a = 11.329(2), b = 18.439(4), c = 18.10 1(2) Angstrom, beta = 97.81(1)degrees, Z = 2, R = 0.063 and R-W = 0.06 8 for 2186 reflections with I > 3 sigma(I); 2b: monoclinic, P2(1)In, a = 13.29(1), b = 19.979(3), c = 14.265(3) Angstrom, beta = 100.37(3)de grees, Z = 2, R = 0.043 and R-W = 0.049 for 3746 reflections with I>3 sigma(I); 2b: monoclinic, P2(1)In, a = 14.52(1), b = 17.253(4), c = 18 .985(3) Angstrom, beta = 104.34(4)degrees, Z = 2, R = 0.065 and R-W = 0.069 for 2019 reflections with I > 3 sigma(I)). Complexes 2 comprise a quadruply bonded dimolybdenum(II) structure (Mo-Mo = 2.119(3) Angstr om (2a), 2.115(1) Angstrom (2b), and 2.131(4) Angstrom (2c)) bridged b y two carboxylate and two dpmp ligands with a trans geometry. The two dpmp ligands take a head-to-tail arrangement and act as bidentate liga nds with a terminal and the central phosphorus atoms; the remaining te rminal P atom is uncoordinated. Treatment of complexes 2a-c with dioxy gen gave ligand-oxidized dimolybdenum(II) complexes, trans- [Mo-2(O2CR )(2)(dpmp-O)(2)] (BF4)(2) (3a: R = Me; 3b: R = Bu-t; 3c: R = Ph), wher e dpmp-O = Ph2PCH2PPhCH2P(=O)Ph-2. X-ray crystallographic analyses of 3a and 3c demonstrated that the uncoordinated phosphorus atom of dpmp in 2a,c was converted into phosphine oxide in 3a,c and the P = O unit is coordinated to the Mo atom in the axial position via the oxygen ato m (3a: monoclinic, P2(1)In, a = 11.414(4), b = 18.33(1), c = 18.112(7) Angstrom, beta = 97.57(3)degrees, Z = 2, R = 0.052 and R-W = 0.058 fo r 2218 reflections with I > 3 sigma(I); 3c: monoclinic, P2(1)In, a = 1 4.554(8), b = 17.182(3), c = 18.768(2) Angstrom, beta = 104.25(2)degre es, Z = 2, R = 0.058 and R-W = 0.062 for 3888 reflections with I > 3 s igma(I)).