Mo 2(O)(OCH 2tBu) 4(PMe 3) 4. Preparation and characterization of a partial hydrolysis product of Mo 2(OCH 2tBu) 6

Abstract

Partial hydrolysis of Mo 2(OCH 2 tBu) 6 in the presence of excess trimethylphosphine produced the novel compound Mo 2(PMe 3)( μ-O)( μ-OCH 2 tBu) (OCH 2 tBu) 3 ( 1). The solid-state molecular structure of 1 as determined by single crystal X-ray diffraction revealed an MoMo double bond [2.4931(9) Å] between the metal centers which are in local octahedral and trigonal bi-pyramidal coordination geometries, respectively. The complex possesses an asymmetric oxo bridge [1.996(4) Å and 1.874(4) Å] as well as a bridging alkoxide ligand. Based on the coordination geometries, as well as the metal-metal separation, it is proposed to contain metal centers with formal oxidation states Mo(4+) ( d 2) and Mo(2+) ( d 4). In solution 2 is evidently non-fluxional on the NMR time-scale and maintains a geometry akin to that seen in the solid state. Compound 1 reacted with carbon monoxide (1 equiv.) giving a 1:1 adduct, 2, wherein the d 4-Mo(2+) center is ligated by CO. Thermolysis of 2 does not yield oxidation products, i.e. Me 3PO or CO 2, but does show evidence for the formation of (PMe 3) 4Mo(CO) 2 along with other uncharacterized molybdenum alkoxide products. While 2 may be formally derived from the oxidative cleavage of CO 2 by reaction with Mo 2(OCH 2 tBu) 4(PMe 3) 4, the latter inserts CO 2 into the MoOR bonds, as does Mo 2(O iPr) 4(dmpe) 2, where dmpe = Me 2PCH 2CH 2PMe 2.