Synthesis and substitution chemistry of some bis(dithiolate) complexes of molybdenum, Mo(S2C6H3R)2(PMePh2)2, R = H, Me

The new bis(dithiolate) complexes Mo(1,2-S 2 -4-R-C 6 H 3 ) 2 (PMePh 2 ) 2 , R = H, Me, are readily synthesized from three different types of starting materials: trans-Mo(N 2 ) 2 (PMePh 2 ) 4 , MoCl 4 (PMePh 2 ) 2 , and MoOCl 2 (PMePh 2 ) 3 . The 31 P NMR spectra of the dithiolate complexes at low temperature are consistent with a cis stereochemistry of the PMePh 2 ligands and isomerism with respect to inversion at sulfur and relative positioning of the methyl groups on the chelating 1,2-S 2 -4-Me-C 6 H 3 ligands. The singlet in the 31 P NMR spectrum at room temperature arises from rapid interconversion of these isomers. Substitution of one or two of the PMePh 2 ligands in the dithiolate complexes proceeds under mild conditions to give the complexes Mo(S 2 C 6 H 4 ) 2 (CO)(PMePh 2 ), Mo(S 2 C 6 H 4 ) 2 (CN-t-Bu)(PMePh 2 ), Mo(S 2 C 6 H 3 Me) 2 (dppe), Mo(S 2 C 6 H 4 ) 2 (depe), Mo(S 2 C 6 H 4 ) 2 (PMePh 2 )(PMe 3 ), Mo(S 2 C 6 H 4 ) 2 (PMePh 2 )(P(OMe) 3 ), and Mo(S 2 C 6 H 4 ) 2 (P(OMe) 3 ) 2 . The 31 P and 13 C NMR spectroscopy of these bis(dithiolate) complexes suggest that they have monodentate ligands cis disposed.A reversible equilibrium exists between Mo(S 2 C 6 H 4 ) 2 (PMePh 2 ) 2 and Mo(S 2 C 6 H 4 ) 2 (CO)(PMePh 2 ) in the presence of carbon monoxide in solution. Isolation of Mo(S 2 C 6 H 4 ) 2 (CO)(PMePh 2 ) is facilitated by use of CH 3 I as a "phosphine sponge" reagent. If the sulfur ligands are viewed as dianions, then this is the first thermally stable carbonyl complex of molybdenum(IV). Keywords: molybdenum, dithiolate, diphenylmethylphosphine, carbonyl, NMR.