Mo2(O)(OCH2tBu)4(PMe3)4. Preparation and characterization of a partial hydrolysis product of Mo2(OCH2tBu)6

Abstract Partial hydrolysis of Mo 2 (OCH 2 t Bu) 6 in the presence of excess trimethylphosphine produced the novel compound Mo 2 (PMe 3 )( μ -O)( μ -OCH 2 t Bu) (OCH 2 t Bu) 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) A] 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) A and 1.874(4) A] 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 3 PO or CO 2 , but does show evidence for the formation of (PMe 3 ) 4 Mo(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 t Bu) 4 (PMe 3 ) 4 , the latter inserts CO 2 into the MoOR bonds, as does Mo 2 (O i Pr) 4 (dmpe) 2 , where dmpe = Me 2 PCH 2 CH 2 PMe 2 .