Oligophosphine ligands. XXVI. Halogenomolybdenum complexes containing oligo(tertiary) phosphine ligands: synthesis, electrochemistry, and molecular structures

Abstract

The reaction of MoCl 3(OC 4H 8) 3 with MeP(CH 2-CH 2- CH 2PMe 2) 2 in THF gare the unsolvated complex MoCl 3[MeP(CH 2CH 2CH 2PMe 2) 2] (2) as well as its addition compound 2·0.75OC 4H 8, which are analogues of the previously reported MoCl 3[PhP- (CH 2CH 2CH 2PPh 2) 2] ( 1). Sodium amalgam reduction of 2·0.75OC 4H 8 in the presence of PMe 3 or PMe 2Ph, in THF under nitrogen atmosphere, yielded the Mo(II) derivatives MoCl 2[MeP(CH 2CH 2CH 2- PMe 2) 2](PMe 3) (3) and MoCl 2[MeP(CH 2CH 2CH 2- PMe 2) 2](PMe 2Ph) (4). The electrochemical investigation of complexes 1 and 2 (performed on THF solutions of the addition compounds 1·CH 2Cl 2 and 2·0.75OC 4H 8 by cyclic voltammetry) demonstrated that the reduction products 2 − and 3 − undergo rapid replacement of chloride by solvent and phosphine donor molecules. Whereas 2 − and its Cl −/PMe 3 substitution product were not reduced further at potentials > ca. −2.50 V ( versus Ag/AgNO 3, 0.1 M, in CH 3CN), the voltammogram of 1 revealed a further reduction step occurring at −2.40 V in the presence of added PPh 2Me. This is consistent with the finding that 1, but not 2, is easily reduced to low valent molybdenum complexes by chemical reductants, such as sodium amalgam. X-ray crystallography established a meridional-octahedral arrangement of the ligands for complexes 1 and 2, and a trans- octahedral coordination geometry for compounds 3 and 4. Relevant crystallographic data are: 1·CH 2Cl 2: orthorhombic Pbca, a=1677.5(9), b= 3167(1), c=1457.9(9) pm, Z=8, R=0.119, R w= 0.116 (1790 data). 2·0.75OC 4H 8: tetragonal I 4 , a=1733.5(4), c=1589.7(5) pm, Z=8, R=0.050, R w=O.041 (1689 data). 3·0.50CH 3OH: orthorhombic Pca2 1, a=1491.1(12), b=1168.0(7), c= 1434.1 (9), Z=4, R=0.071, R w=0.072 (1380 data). 4: monoclinic P 1 , a=1375.7(4), b=1892(1), c= 2074(1) pm, α=86.86(5), β=88.06(4), γ=84.81°, Z=8, R=0.085, R w=0.073 (9284 data).