Bidentate ligands, xanthate structures

This section describes the structural chemistry of 14 molecular structures, 3 of chromium, 8 of molybdenum, and 3 of tungsten. The only binary xanthate structures are those of chromium, all other structures are at least ternary in nature. For the chromium and tungsten structures, conventional monodent-ate and bidentate coordination modes of the xanthate ligand are found. By contrast, a rich, diverse, and fascinating coordination range is observed for the... 

The influence the size of the chelate ring has upon the stereochemistry around the metal atom is clearly shown by complexes of the type [M(bidentate)4]. Bidentate ligands of small normahzed bite form dodecahedral structures, in which each of the BAAB trapezoids is formed from a pair of ligands (Fignre 13). There are nnmerous examples of this structure with three- and fonr-membered chelate rings snch as peroxide, nitrate, acetate, xanthate, and dithiocarbamate... 

A similar structure is observed for the Pd(p-/ -PrPhDta)2PPh3 complex, where a PdS3P core is attained and both uni- and bidentate dithiocumate ligands are found (587). A mechanism involving nucleophilic attack on the OR group of the xanthate ligand by free xanthate ion is proposed (10) for the reaction of M(RXant)2 complexes with tertiary phosphines ... 

Two vanadium(iv) ethylxanthate complexes have been prepared 440 their e.p.r. parameters are practically identical with those of the corresponding diethyldithio-carbamate complexes and on this basis analogous structures were proposed, i.e. a dodecahedral eight-co-ordinate structure with four bidentate ethylxanthate ligands and a distorted tetrahedral structure with four unidentate ligands. Addition of phosphorus(iii) ligands (L) such as trialkylphosphites to solution of the ethyl xanthate... 

Although Mo (II) and W(II) exhibit the most extensive seven-coordinate chemistry yet known (consistent with the application of the effective atomic number rule to these systems), a survey of the substituted metal carbonyl complexes of molybdenum and tungsten reveals no structural data for compounds of the type M(00)3(6-6)2 where 6-6 is a bidentate monoanionic ligand. No tungsten tricarbonyls of this type have been reported to date, but McDonald and co-workers have synthesized and studied the closely related W(CO)2(PPh3) (6-6)2 compounds where 6-6 is a chelating dithiocarbamate (7), xanthate, or dithiophos-phate (8). For molybdenum, the compounds Mo(CO)3(dtc)2(dtc = R2NCS2") (9) are examples of the M(CO)3(6-6)2 type as is Mo(CO)3-[S2P(i-Pr)2]2 (10), which has been well characterized in solution. 

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