RATES OF RING-OPENING OF 2,2,4,7,7-PENTAMETHYL-3,6-DITHIAOCTANE TETRACARBONYL TUNGSTEN(0)

Ring displacement from eta(2)-PDOW(CO)(4) (PDO = 2,2,4,7,7-pentamethyl -3,6-dithiaoctane) by L (L = P(O-i-Pr)(3) and P(OEt)(3)) produces a mi xture of cis- and trans- (L)(2)W(CO)(4). Results from kinetics experim ents are consistent with the results observed for the structurally-rel ated eta(2)-DTOW(CO)4 complex (DTO = 2,2,7,7-tetramethyl-3,6-dithiaoct ane). A smaller value for the rate constant (k(1)) for the ring-openin g step of eta(2)-PDOW(CO)(4) reflects the shorter W-S bond distances o bserved in eta(2)-PDOW(CO)4. This observation is consistent with the t rend observed for a series of eta(2)-DTAW(CO)(4) complexes (DTA = Dith iaalkanes) in which the value of k(1) increases with the size of the c helate ring. Since the species eta(2)-PDOW(CO)(4) and eta(2)-DTOW(CO)( 4) are five-membered chelate complexes, differences in their molecular and kinetic parameters are being ascribed to the methyl group in the chelate backbone of eta(2)-PDOW(CO)(4). Our observations confirm earli er findings that small differences in the structure of DTA. greatly af fect the rates of ring-opening in eta(2)-DTAW(CO)(4) complexes.